A 36 × 240 Gbps hybrid mode/wavelength division multiplexing transmitter using lithium niobate on insulator

A 36 × 240 Gbps hybrid mode/wavelength division multiplexing transmitter using lithium niobate on insulator | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article A 36 × 240 Gbps hybrid mode/wavelength division multiplexing transmitter using lithium niobate on insulator Weike Zhao, Mingyu Zhu, Weihan Wang, Ruitao Ma, Aoyun Gao, Chun Gao, and 8 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8061035/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In the era of big data and artificial intelligence, the explosive growth of data capacity has driven unprecedented demands for high-capacity and high-speed optical communication systems. The traditional single-mode and single-wavelength transmission technologies can no longer meet the requirements of massive data transmission, thereby continuously driving the industry to explore more efficient multiplexing schemes. Here, a hybrid 6-mode × 6-wavelength division multiplexing transmitter based on lithium niobate-on-insulator (LNOI) is proposed as a groundbreaking solution for next-generation optical communication. The transmitter innovatively combines six different waveguide modes (TE 0 ~ TE 5 modes) with six wavelengths spaced 3.2 nm apart, enabling the dense multiplexing of 36 independent channels within a compact optical bandwidth and achieving a capacity of 36 × 240 Gbps. The 3.2 nm channel spacing (approximately 400 GHz at 1550 nm) complies with the ITU-T grid standards, ensuring compatibility with existing optical network infrastructures. Meanwhile, the mode division multiplexing component utilizes multi-mode waveguides to fully leverage the spatial degrees of freedom in optical transmission, thereby significantly enhancing the spectral efficiency of the system compared to traditional single-mode solutions. This hybrid mode/wavelength division multiplexing architecture exhibits excellent applicability in next-generation data center interconnections and long-haul optical transmission networks. Physical sciences/Optics and photonics/Optical materials and structures/Microresonators Physical sciences/Optics and photonics/Applied optics/Integrated optics Physical sciences/Optics and photonics/Applied optics/Fibre optics and optical communications lithium niobate transmitter wavelength division multiplexing mode division multiplexing modulator Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1 Introduction Fueled by artificial intelligence, big data, and cloud computing, data traffic in the information age grows with an annual increase of ~ 25% 1 . Such a dramatic surge has pushed optical interconnects beyond their traditional role in long-haul backbone networks, enabling their widespread adoption in short-reach links and intra-chip applications 2 – 4 . Core components such as lasers 5 – 7 , modulators 3 , 8 – 10 , routers 2 , 11 , and detectors 12 – 15 are essential in optical transmission systems. To meet the demands of these components for high speed, low power consumption, compact size, and low cost, integrated photonics platforms—particularly silicon photonics—have gained significant attention. By heterogeneously integrating direct bandgap III-V materials and narrow bandgap germanium, silicon photonics enables monolithic integration of passive and active components, thus meeting various demands 16 – 18 . However, in the specific context of electro-optic modulation, silicon photonics suffers from notable drawbacks, including excessive waveguide propagation loss, unwanted nonlinear responses, and a constrained electro-optic (E-O) modulation bandwidth. These limitations stem inherently from the carrier dispersion effect—an underlying operating principle of silicon modulators 4 , 19 . Lithium niobate has drawn extensive interest ever since its synthesis in the 1960s, all attributed to its remarkable properties: a large electro-optic coefficient (~γ 33 = 33 pm/V), excellent nonlinearity coefficient, low waveguide loss (Intrinsic loss: 0.2 dB/m) 20 , and a wide transparency window (0.4-5 µm) 21,22 . Recently, the newly developed lithium niobate on insulator (LNOI) has renewed research focus. Benefiting from its sub-wavelength waveguide size and CMOS-compatible processes, LNOI has shown great potential in key fields like E-O modulation 23 – 25 , microwave photonics 20 , 26 , as well as nonlinear optics involving both second-order 27 and third-order effects 28 . Mach-Zehnder modulators (MZMs) on LNOI can achieve E-O bandwidths exceeding 110 GHz with half-wave voltage-length product (V π ·L) < 2–3 V·cm 4 . When combined with advanced modulation formats such as dual-polarization, pulse amplitude modulation (PAM) and IQ modulation, single-wavelength data rates beyond 1.96 Tb/s are attainable 29 . In practical applications, though, the single-channel rate remains limited to approximately 100 Gbaud. This limitation mainly stems from the constraints of high-frequency responses in radio frequency (RF) amplifiers, RF transmission lines, and photodetectors. To address this issue, multiplexing techniques—including wavelength division multiplexing (WDM) and mode division multiplexing (MDM)—are under active investigation. The challenge, however, lies in the anisotropic crystal structure and weak optical confinement of LNOI: these properties make designing traditional wavelength manipulation devices (e.g., arrayed waveguide gratings (AWGs) and microring resonators) significantly difficult, particularly when it comes to achieving precise phase control and a large free spectral range (FSR). Several innovative solutions have been proposed recently. Yi et al. introduced an AWG design based on a 45° rotated crystal orientation to mitigate phase errors caused by waveguide path differences. The demonstrated 8-channel AWG features an insertion loss range from 2.4 dB to 4.8 dB, and a crosstalk of ~ -22.8 dB 30 . He et al. developed an x-cut LNOI optical filter via a multimode waveguide grating (MWG) and a mode multiplexer—eliminating bent waveguides, with an insertion loss of -0.15 dB and sidelobe suppression ratio > 26 dB 31 . They later extended this to an 8-channel dense wavelength multiplexer (flat spectral responses) and a compact 4-channel dense wavelength division multiplexing (DWDM) transmitter (1.6 nm channel spacing) supporting 4×100 Gbps high-speed transmission 32 , 33 . On the other hand, mode hybridness induced by the anisotropy of LNOI waveguides is a core challenge in mode manipulation. To address this issue, early high-order mode multiplexers based on LNOI mostly adopt the directional coupler scheme to avoid the use of tapered waveguides 34 . However, this scheme suffers from low conversion efficiency, narrow operating bandwidth, and small fabrication tolerance, which limit the performance of the devices. Aiming at this bottleneck, the mode multiplexers designed along the Z-propagating LNOI waveguides are proposed to suppress mode hybridness fundamentally 35 – 37 . These devices support up to eight modes with less than 0.1 dB per-mode loss and below − 18 dB crosstalk, enabling a gross transmission rate of 8×60 Gbps using MDM. Despite these advances, current research remains largely focused on manipulating a single dimension of photons. Achieving simultaneous multi-dimensional multiplexing in LNOI waveguides—combining wavelength and mode—would further boost transmission capacity 38 . In this paper, we present a hybrid 6-mode × 6-wavelength division multiplexing transmitter designed to further expand the capacity limitations of optical networks. This innovative transmitter seamlessly integrates six distinct waveguide modes (e.g., TE 0 , TE 1 , TE 2 , TE 3 , TE 4 , and TE 5 modes) with six precisely spaced wavelengths, enabling the dense multiplexing of 36 independent channels within a compact optical bandwidth. The channel spacing is meticulously designed to be 3.2 nm, corresponding to approximately 400 GHz at the C-band, and adheres to the ITU-T grid standards. By leveraging MDM, the transmitter achieves highly efficient utilization of spatial resources, significantly boosting spectral efficiency and enabling terabit-scale data transmission over a single optical waveguide. Experimentally, the cascaded Fabry-Perot (F-P) cavity-based wavelength multiplexers exhibit box-like response characteristics with a 3-dB bandwidth of 1.8 nm, low crosstalk of -22 dB, and minimal insertion loss ranging from 0.15 dB to 0.83 dB. The mode (de)multiplexer, designed along the Z-propagating axis, demonstrates equally impressive performance with low crosstalk of -14 dB and insertion loss between 0.05 dB and 0.3 dB. Furthermore, the 3-dB E-O bandwidth of the employed MZM exceeds 67 GHz, and we have successfully demonstrated the transmission of 120 GBaud on-off keying (OOK) and 4-level pulse-amplitude modulation (PAM4) signals. The hybrid multiplexing transmitter proposed in this work achieves an overall system capacity of 8.64 Tbps, offering robust technical support for high-speed optical interconnection networks. 2 Results Device design and experimental approach As illustrated in Fig. 1 (a) and (b), the proposed hybrid 6-mode × 6-wavelength division multiplexing transmitter integrates six 6-channel WDM transmitters with a single 6-channel mode multiplexer. Each 6-channel WDM transmitter is composed of six cascaded optical filters featuring flat-top spectral responses and six Mach-Zehnder modulators (MZMs) configured to operate along the Y-propagating direction. The modulated optical signals output from the six WDM transmitters are respectively connected to distinct multiplexing ports of the 6-channel MDM, ultimately forming the hybrid transmitter. Notably, the 6-channel mode multiplexer consists of five cascaded adiabatic directional couplers (ADCs, i.e., ADC #1 to ADC #5), which are dedicated to handling the TE₁, TE₂, TE₃, TE₄, and TE₅ modes, respectively. These five ADCs are aligned along the Z-propagating axis, a design choice intended to suppress mode hybridness and ensure stable mode transmission. The device was fabricated on a 400-nm x-cut LNOI wafer with a 3-µm silica buffer layer and a 525-µm-thick Si handle substrate (see “method”, fabrication). The LNOI wafer has an extraordinary refractive index ( n e ) of ~ 2.138 along the crystal z-axis and an ordinary refractive index ( n o ) of ~ 2.211 along the crystal x-axis and y-axis at 1550 nm wavelength. Figure 1 (c) and (d) present the cross-section of the Z-propagating and Y-propagating LNOI photonic waveguide, featuring an etching depth of h r =200 nm, a slab thickness of h s =200 nm, a sidewall angle of 60° (determined by the fabrication process), and an air cladding. The top width of the LNOI waveguide is denoted as W 1 . Z-propagating mode multiplexer Figure 2 (a) and (b) present the calculated effective mode indices ( N eff ) for Y-propagating and Z-propagating LNOI photonic waveguides under different W 1 at 1550 nm wavelength, respectively. Due to the anisotropic nature of the LNOI material, these two waveguides exhibit distinct mode properties. For the Y-propagating LNOI waveguide, TE modes predominantly experience an extraordinary refractive index ( n e ), while TM modes experience an ordinary refractive index ( n o ) with n o > n e . Due to the flat structure characteristics of LNOI waveguides, the TE and TM modes have nearly identical N eff , leading to the formation of hybrid mode regions as shown in Fig. 2 (a). Specifically, there is an obvious hybridness region between TM 0 and TE 1 modes around W 1 = 1.3 µm, and another hybridness region between TM 0 and TE 3 modes around W 1 = 3.3 µm. These mode hybridness regions pose significant challenges for on-chip mode manipulation. In contrast, in the Z-propagating LNOI waveguide, both TE and TM modes experience n o index, resulting in TE modes having much larger N eff values compared to TM modes. Consequently, the mode hybridness is greatly suppressed as shown in Fig. 2 (b). Our mode multiplexer is designed along the Z-propagating axis of the LNOI waveguide to suppress mode hybridness, and adopts a structure of ADC to enable broadband and large fabrication-tolerance on-chip mode manipulation. The design rules and critical parameters for Z-propagating ADCs targeting TE 1 , TE 2 , TE 3 , TE 4 , and TE 5 modes, respectively, have been detailed in our previous work 35 . Figures 2 (c)-(h) illustrate the simulated transmission characteristics of the designed ADCs for these modes. All five modes feature an insertion loss of less than 0.1 dB and crosstalk below − 20 dB across the wavelength range of 1500–1560 nm. The corresponding simulated light propagation is shown in Figs. 2 (i)-(m), higher-order TE 1 -TE 5 modes convert to the fundamental TE 0 mode adiabatically. The transmission spectra of the fabricated mode multiplexer were measured by connecting a pair of mode multiplexers back-to-back, as illustrated in Fig. 3 (a). Figure 3 (b)-(g) presents the measured spectra of the 6-channel mode multiplexer normalized with the transmission of a straight waveguide fabricated on the same chip. It is observed that the mode (de)multiplexer pair achieves mode crosstalk below − 14 dB and insertion losses ranging from approximately 0.05 dB to 0.3 dB for all six modes within the wavelength range of 1520–1560 nm. Flat-top wavelength multiplexer Figure 4 (a) shows the detailed illustration of a flat-top optical wavelength filter, which consists of a cascaded F-P cavity and a mode (de)multiplexer based on an ADC. The cascaded F-P cavity with asymmetric teeth converts the launched TE 0 mode into the TE 1 mode when the wavelength is matched with the Bragg condition; then, the reflected TE 1 mode is delivered into the drop port as the TE 0 mode passing through the mode (de)multiplexer. The mode (de)multiplexer is designed according to the method proposed in our previous work 39 . The coupled F-P cavity is formed with three cascaded mirrors based on asymmetric multimode waveguide gratings (AMWGs). We designed the coupled F-P cavity according to the requirement of realizing a 6-channel wavelength multiplexer with a channel spacing of 400 GHz. The structural parameters are chosen as L c = 440 nm, δ = 850 nm, Λ = 440 nm, η = 0.5, W = 2000 nm, b = 10, N 1 = N 3 = 60, and N 2 = 90. The core widths w a and w b for the input/output ends of the adiabatic couplers are selected as ( w a1 , w b1 ) = (1000, 600) nm and ( w a2 , w b2 ) = (2000, 200) nm, respectively. In this case, the core waveguide width w a increases from 1000 nm to 2000 nm, while the core width w b decreases from 600 nm to 200 nm. The taper lengths are chosen as ( L 01 , L 12 , L 23 ) = (50, 100, 50) µm, while the gap widths ( w g1 , w g2 , w g3 ) are chosen as (2.25, 0.25, 1.25) µm. The simulated optical transmission spectrum is shown in Fig. 4 (b). It can be seen that the designed flat-top optical filter has a large FSR of ~ 20 nm, a low insertion loss 20 dB, verifying that the coupled F-P cavity enables a large FSR and box-like optical transmission. It helps break the FSR and spectral efficiency limitations. Figure 4 (c) shows the measured optical transmission spectra at the drop and through ports of the fabricated flat-top optical filters, indicating an insertion loss of ~ 0.1–0.45 dB, an ER of ~ 20 dB, a 3-dB bandwidth of ~ 1.8 nm, and an FSR of ~ 20 nm. The 6-channel wavelength multiplexer is designed by cascading six flat-top optical filters in series, as illustrated in Fig. 4 (d). The operating wavelengths of these filters increase linearly from bottom to top, achieved by carefully optimizing the cavity length L c . For the six channels with a channel spacing of 400 GHz, the corresponding cavity lengths are set to L c = 440, 505, 570, 635, 700, and 765 nm, respectively. The remaining parameters of these six filters are identical. The simulated transmission spectra of the multiplexer are shown in Fig. 4 (e), indicating the 6-channel dense wavelength multiplexer has a channel spacing of 400 GHz, an insertion loss of ~ 0.05–0.3 dB, a crosstalk between adjacent channels of − 25 dB, and a crosstalk between non-adjacent channels of − 35 dB. Experimental results, presented in Fig. 4 (f), show the measured optical transmission spectra of the 6-channel wavelength multiplexer without any calibration. These measurements reveal a channel spacing of 400 GHz, an insertion loss between 0.15 dB and 0.75 dB, a crosstalk between adjacent channels of approximately − 20 dB, and a crosstalk between non-adjacent channels of approximately − 30 dB. The channel spacing of the F-P cavity-based wavelength multiplexer can be further decreased to 200 GHz, thus achieving higher spectral efficiency (Supplementary Material S1). Hybrid multiplexing transmitter Figure 5 (a) illustrates the optical microscopic image of the fabricated hybrid multiplexing transmitter. Scanning electron microscopic images of the key components—the asymmetric multimode waveguide gratings, grating coupler, and mode multiplexer—are presented in Figs. 5 (b)–(d). Figures 5 (e)–(j) display the measured drop optical transmission spectra for each TE mode (TE 0 to TE 5 ) in the 6 × 6 channel hybrid multiplexing transmitter without calibration. Each spectrum corresponds to six wavelength channels, exhibiting a channel spacing of 400 GHz, insertion losses in the range of 0.3–1.07 dB, adjacent channel crosstalk below − 20 dB, and non-adjacent channel crosstalk below − 30 dB. The statistical distribution of center wavelengths for each wavelength channel is further illustrated in Figs. 5 (k)–(p) for TE 0 , TE 1 , TE 2 , TE 3 , TE 4, and TE 5 modes, respectively. The results indicate that the six wavelength channels across all six modes maintain good consistency in channel spacing. Additionally, the center wavelength drift caused by fabrication errors is less than 0.2 nm for all six mode channels, confirming the high fabrication precision of the device. Figure 6 (a) presents a schematic illustration of the MZM. The structural parameters have been optimized as follows: W wg = 1.5 µm, L MMI = 35.2 µm, W MMI = 7.5 µm, h = 600 nm, W s = 18 µm, We = 60 µm, g p =150 µm, L = 4500 µm, and W g = 6.5 µm, to achieve group velocity and 50-Ω impedance matching 35 , 40 , 41 . The simulation results of the MZM can be found in the supplementary material S2. The static V π of the MZM was measured using a 1-kHz triangular voltage sweep method, as shown in Fig. 6 (b) (See “method”, Half-wave voltage measurement). The measured results, depicted in Fig. 6 (c), indicate that the V π for the 4.5 mm MZM is 4.58 V, with a corresponding V π ·L of 2.06 V·cm. For the compact six-channel WDM transmitter, the modulation crosstalk between different MZMs was measured with the experimental setup in Fig. 6 (d) (See “method”, E-O response measurement). Figure 6 (e) demonstrates the modulation strength when light was injected into CH3 and RF signals were applied to CH1–CH6, showing that the modulation strength for RF applied to CH3 was at least 22 dB higher than that from CH1, CH2, CH4, CH5, and CH6. Figures 6 (f)–(k) show all the measured bandwidths of the small-signal EO response (S 21 ) for all 36 transmission channels of the fabricated transmitter, indicating that the 3-dB bandwidth of all 36 MZMs exceeds 67 GHz. It is important to note that the currently measured bandwidth is limited by the experimental setup The experimental setup for characterizing high-speed transmission eye diagrams of the transmitter is illustrated in Fig. 7 (a) (See “method”, High-speed transmission characterization). Figure 7 (b)-(g) shows the measured well-open eye diagrams of OOK and PAM4 signals for all 36 channels across TE 0 -TE 5 modes and six different wavelengths at the rates of 120 GBaud, respectively. These results indicate that the hybrid multiplexing transmitter achieves a total data capacity of 8.64 Tbps, showcasing its high-speed modulation capabilities. It should be noted that the high transmission rates achieved across all channels are enabled by the low insertion loss and flat-top spectral response of the wavelength multiplexer designed in this work. The effect of flat-top spectral response on high-speed signal transmission can be found in the supplementary material S3. Table 1 provides a comprehensive summary of the key performance parameters of multiplexing transmitters reported in recent studies. State-of-the-art implementations leverage diverse material platforms, such as silicon-on-insulator (SOI), indium phosphide (InP), lead zirconate titanate (PZT), and LNOI. Notably, the newly developed LNOI-based transmitter exhibits the highest single-channel data rate of 240 Gbps (our work), which is attributed to its excellent electro-optical modulation properties. Our proposed solution addresses the challenges associated with mode and wavelength manipulation in LNOI platforms: it increases the number of multiplexed channels to an unprecedented 36, thereby achieving a total transmission capacity of 8.64 Tbps. Table 1 Summary of key parameters and performance metrics for photonic multiplexing transmitters Reference Material Channel number Multiplexing type Bitrate per channel Total Capacity 42 SOI 4 WDM 56 Gbps 224 Gbps 43 SOI 4 WDM 112 Gbps 448 Gbps 44 SOI 2 MDM 25 Gbps 50 Gbps 45 SOI 6 WDM + MDM 25 Gbps 150 Gbps 46 SOI 20 WDM + MDM + PDM 50 Gbps 1 Tbps 47 InP 17 WDM 25 Gbps 425 Gbps 48 InP 8 WDM 50 Gbps 400 Gbps 49 PZT 40 WDM 40 Gbps 1.6 Tbps 9 LNOI 4 WDM 100 Gbps 400 Gbps 50 LNOI 2 WDM 200 Gbps 400 Gbps 51 LNOI 4 WDM 100 Gbps 400 Gbps 35 LNOI 8 MDM 60 Gbps 480 Gbps 52 LNOI 8 WDM + MDM + PDM 120 Gbps 0.96 Tbps This work LNOI 36 WDM + MDM 240 Gbps 8.64 Tbps 3 Conclusion In summary, this research presents a state-of-the-art hybrid mode/wavelength division multiplexing transmitter based on the LNOI platform, which achieves a high communication capacity of 36 × 240 Gbps. Its core innovation lies in the integration of MDM and WDM. Specifically, it leverages the Z-propagating LNOI waveguide to suppress mode hybridness, thereby facilitating on-chip mode manipulation, while adopting cascaded FP cavities for flop-top WDM implementation. For the MDM functionality, the proposed scheme supports six transverse electric modes (TE 0 -TE 5 ). Through meticulous optimization along the Z-propagating direction, the mode multiplexer ultimately achieves an insertion loss of < 0.1 dB and an inter-mode crosstalk of < − 15 dB. In terms of WDM, the cascaded F-P cavity design enables a wavelength multiplexer with a large FSR and a channel spacing of 3.2 nm. The incorporation of widened waveguides and higher-order F-P cavities further guarantees channel flatness and spacing uniformity—two key prerequisites for maintaining high data transmission rate across all optical channels. Notably, this wavelength multiplexer exhibits a box-like frequency response, characterized by a 3-dB bandwidth of 1.8 nm, a channel crosstalk of < − 22 dB, and a per-channel additional loss ranging from 0.15 to 0.83 dB. Additionally, the integrated electro-optic MZM delivers exceptional performance: its 3-dB bandwidth exceeds 67 GHz, and its Vπ·L is 2.06 V·cm, enabling support for both 120 Gbaud OOK and PAM4 signals. Experimental results verify that the transmitter achieves a total information transfer rate of 8.64 Tbps, thus demonstrating its high-data-rate capabilities. Looking ahead, potential optimizations include leveraging higher-order modes and reducing WDM channel spacing to 1.6 nm, which could further increase channel count. The exploration of slow-light modulators 53 and compact microcavity-type modulators 54 holds promise for enhancing modulation efficiency and reducing chip size. Compared to previous 45°-tilted array waveguide gratings, the cascaded F-P cavity design offers greater flexibility and compactness, integrating filtering and modulation functions seamlessly. The vision for the future involves the heterogeneous integration of frequency-comb-based multi-wavelength light sources and III-V photodetectors, aiming for monolithic integration of all components. Our results demonstrate a novel, promising method to boost optical communication capacity, applicable to data-intensive scenarios like long-haul backbone networks and short-reach optical interconnects. Methods Fabrication The device was fabricated on a 400-nm x-cut LNOI wafer with a 3-µm silica buffer layer and a 525-µm-thick Si handle substrate. The device was first patterned by electron-beam lithography, and then the pattern was transferred onto the LN layer by Ar + plasma dry etch, which gives the waveguide a sidewall angle θ of 60°. Next, a step of UV lithography was used to form electrode patterns, and a layer of 10/500-nm Ti/Au electrodes was deposited by electron-beam evaporation and lift-off process. Half-wave voltage measurement Light emitted from a tunable laser (TL) operating at 1550 nm wavelength was directed through a fiber polarization controller (PC) and coupled into the I 1 port via a single-mode fiber (SMF). The light output from CH1 was received by another SMF and detected by a photonic detector (PD), with the signal then transmitted to an oscilloscope (OSC) for analysis. Concurrently, a function generator generated a 1-kHz triangular signal that was applied to the MZM connected to the I 1 port. The trigger signal associated with this process was also directed to the oscilloscope for reference. E-O response measurement The radio frequency (RF) signal from the signal light component analyzer (LCA) was applied to the electrode of MZM via a 67-GHz RF probe and terminated with another RF probe connected to a 50-Ω terminator after passing through the modulation region. The modulated light was coupled out of the chip through a grating coupler and subsequently collected and relayed back to the LCA. Crosstalk between two channels was evaluated by measuring the modulation strength when light was transmitted through one channel while an RF signal from the LCA was applied to the other. High-speed transmission characterization An arbitrary waveform generator (AWG) was used to convert the electrical signal generated by a clock source into OOK or PAM4 signals. These OOK or PAM4 signals, combined with static voltage via a bias-tee, were applied to the fabricated device. The resulting modulated optical signal was detected and subsequently fed into an electrical sampling oscilloscope for analysis. Declarations Funding This work was supported by the Zhejiang Provincial Natural Science Foundation of China (LDT23F04012F05, LD22F040004) and the National Natural Science Foundation of China (62375238, U23B2047, 62321166651, 62205292). Data availability statements Authors can confirm that all relevant data are included in the paper and/-or its supplementary information files. Disclosures The authors declare no competing interests. Acknowledgments We would like to thank West Lake University and Zhejiang University for providing access to their micro- and nano-fabrication platforms, which facilitated the identification of collaborators for this work. Author contributions: M.Z. and W.W. performed the experiments. M.Z., R.M., A.G, Z.W. carried out data analysis and simulations. F.H., J.G., D.L, W.Z and A.G. provided experimental supports. 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Ultra-compact lithium niobate microcavity electro-optic modulator beyond 110 GHz. Chip 2022; 1: 100029. Additional Declarations There is no conflict of interest Supplementary Files SupplementaryInformationzhu1028.docx A 36 × 200 Gbps hybrid mode/wavelength division multiplexing transmitter using lithium niobate on insulator Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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1","display":"","copyAsset":false,"role":"figure","size":642848,"visible":true,"origin":"","legend":"\u003cp\u003eConcept of the hybrid mode/wavelength division multiplexing transmitter. (a) Three-dimensional schematic of the transmitter, (b) detailed design of the transmitter, (c) the cross-section of the Z-propagating LNOI photonic waveguide, (d) the cross-section of the Y-propagating LNOI photonic waveguide.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8061035/v1/2b30067feb29625f31bf4e3b.png"},{"id":96914443,"identity":"7e6b4f23-34fd-4404-a68f-c52d28a7c69a","added_by":"auto","created_at":"2025-11-27 14:05:55","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":258294,"visible":true,"origin":"","legend":"\u003cp\u003eDesign of the 6-channel mode multiplexer. Dispersion curves for (a) Y-propagating LNOI waveguide and (b) Z-propagating LNOI waveguide, (c) Schematic illustration of 6-channel mode multiplexer. Calculated transmissions of the designed ADCs for the (d) TE\u003csub\u003e1\u003c/sub\u003e, (e) TE\u003csub\u003e2\u003c/sub\u003e, (f) TE\u003csub\u003e3\u003c/sub\u003e, (g) TE\u003csub\u003e4\u003c/sub\u003e, and (h) TE\u003csub\u003e5\u003c/sub\u003e modes. Simulated light propagations of the designed ADCs for the (i) TE\u003csub\u003e1\u003c/sub\u003e, (j) TE\u003csub\u003e2\u003c/sub\u003e, (k) TE\u003csub\u003e3\u003c/sub\u003e, (l) TE\u003csub\u003e4\u003c/sub\u003e, and (m) TE\u003csub\u003e5\u003c/sub\u003e modes.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8061035/v1/be182dfa961f7741a2846ff9.png"},{"id":96914199,"identity":"d7241368-edea-41ee-b0f2-8e0efe88dbe0","added_by":"auto","created_at":"2025-11-27 14:05:34","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":285502,"visible":true,"origin":"","legend":"\u003cp\u003eMeasured transmissions of the 6-channel mode multiplexer. (a) Optical microscopic image of the 6-channel mode multiplexer. The measured transmissions of the 6-channel mode multiplexer for (b) TE\u003csub\u003e0\u003c/sub\u003e, (c) TE\u003csub\u003e1\u003c/sub\u003e, (d) TE\u003csub\u003e2\u003c/sub\u003e, (e) TE\u003csub\u003e3\u003c/sub\u003e, (f) TE\u003csub\u003e4\u003c/sub\u003e, (g) TE\u003csub\u003e5\u003c/sub\u003e mode channels.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8061035/v1/08556faee3e7c00c6ea15788.png"},{"id":96913967,"identity":"54f605f4-f553-4a15-a7b2-6676154c97bf","added_by":"auto","created_at":"2025-11-27 14:04:54","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":220529,"visible":true,"origin":"","legend":"\u003cp\u003eSimulated and\u003cstrong\u003e \u003c/strong\u003emeasured results of the flat-top optical filter. (a) The present schematic diagram of the flat-top optical filter; (b) simulated optical transmission spectrum of the coupled F-P cavity with structural parameters of δ = 850 nm, \u003cem\u003eΛ \u003c/em\u003e= 440 nm, duty cycle \u003cem\u003eη \u003c/em\u003e= 0.5, \u003cem\u003ew \u003c/em\u003e= 2000 nm, b = 10, \u003cem\u003eN\u003c/em\u003e\u003csub\u003e1 \u003c/sub\u003e= \u003cem\u003eN\u003c/em\u003e\u003csub\u003e3 \u003c/sub\u003e= 60, and \u003cem\u003eN\u003c/em\u003e\u003csub\u003e2 \u003c/sub\u003e= 90; (c) Measured results of the fabricated flat-top optical filter. Simulated light propagation in the designed flat-top optical filter (d) at the through wavelength λ = 1570 nm, (e) at the resonant wavelength λ = 1537 nm, and (f) at the nonresonant wavelength λ = 1525 nm. Simulated and\u003cstrong\u003e \u003c/strong\u003emeasured results of the 6-channel wavelength multiplexer. (g) Schematic illustration of the 6-channel wavelength multiplexer, which consists of six cascading flat-top optical filters; (h) simulated optical transmission of the designed 6-channel wavelength multiplexer, (i) measured optical transmission of the fabricated 6-channel \u0026nbsp;wavelength multiplexer.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8061035/v1/c9b773df571d8d1940522c4c.png"},{"id":96913976,"identity":"e744aaaf-7a16-44b8-ba4c-8edaa8d8bfcf","added_by":"auto","created_at":"2025-11-27 14:04:55","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":266232,"visible":true,"origin":"","legend":"\u003cp\u003eMeasurement results of the hybrid 6-mode × 6-wavelength division multiplexer transmitter. (a) Optical microscopic image of the transmitter. (b). Scanning electron microscopic images of the (c) MWG, (d) grating coupler, (e) the mode (de)multiplexer. The measured results of the hybrid multiplexing transmitter for the (f) TE\u003csub\u003e0\u003c/sub\u003e, (g) TE\u003csub\u003e1\u003c/sub\u003e, (h) TE\u003csub\u003e2\u003c/sub\u003e, (i) TE\u003csub\u003e3\u003c/sub\u003e, (j) TE\u003csub\u003e4\u003c/sub\u003e, and (k) TE\u003csub\u003e5\u003c/sub\u003e modes. The center wavelength of the hybrid multiplexing transmitter for the (l) TE\u003csub\u003e0\u003c/sub\u003e, (m) TE\u003csub\u003e1\u003c/sub\u003e, (n) TE\u003csub\u003e2\u003c/sub\u003e, (o) TE\u003csub\u003e3\u003c/sub\u003e, (p) TE\u003csub\u003e4\u003c/sub\u003e, and (q) TE\u003csub\u003e5\u003c/sub\u003e modes.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8061035/v1/7d83e137274b94eef7f59e72.png"},{"id":96913954,"identity":"231c2314-663b-4eb4-b46d-8d00f493db5b","added_by":"auto","created_at":"2025-11-27 14:04:54","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":102622,"visible":true,"origin":"","legend":"\u003cp\u003eMeasurement results of the MZM. (a) Schematic diagram of the MZM. (b) The experimental setup for half-wave voltage measurement, (c) Measured optical transmission as a function of driving voltage. (d) Experimental setup for characterizing modulation crosstalk between different wavelength channels. (e) The measured modulation crosstalk strength when light was sent into CH3, but the RF signal was applied to CH1–CH6. Normalized measurement EO S\u003csub\u003e21\u003c/sub\u003e for the (f) TE\u003csub\u003e0\u003c/sub\u003e, (g) TE\u003csub\u003e1\u003c/sub\u003e, (h) TE\u003csub\u003e2\u003c/sub\u003e, (i) TE\u003csub\u003e3\u003c/sub\u003e, (j) TE\u003csub\u003e4\u003c/sub\u003e, (k) TE\u003csub\u003e5\u003c/sub\u003e mode channels.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8061035/v1/b0154fef63931c563c7f3aa5.png"},{"id":96913974,"identity":"39c1c2c7-bc65-4102-897b-9311d50e3b75","added_by":"auto","created_at":"2025-11-27 14:04:55","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":494012,"visible":true,"origin":"","legend":"\u003cp\u003eHigh-speed transmission experiment. (a) Schematic of the experimental setup, EDFA: Er-doped fiber amplifier, ESO: electrical sampling oscilloscope, AWG: arbitrary waveform generator.; Measured eye diagrams of six wavelengths for the (b) TE\u003csub\u003e0\u003c/sub\u003e, (c) TE\u003csub\u003e1\u003c/sub\u003e, (d) TE\u003csub\u003e2\u003c/sub\u003e, (e) TE\u003csub\u003e3\u003c/sub\u003e, (f) TE\u003csub\u003e4\u003c/sub\u003e, (g) TE\u003csub\u003e5 \u003c/sub\u003emode channels.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8061035/v1/56dd26d115ec41d59d934427.png"},{"id":97137620,"identity":"3632b310-162b-49cf-afb6-6715bab379a1","added_by":"auto","created_at":"2025-12-01 09:58:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3028723,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8061035/v1/27aca85e-f011-4283-84e8-972e626b870f.pdf"},{"id":96736774,"identity":"f5992e26-440e-4a4b-82c9-fb0f801486c2","added_by":"auto","created_at":"2025-11-25 14:30:16","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1086637,"visible":true,"origin":"","legend":"A 36 \u0026#x00D7; 200 Gbps hybrid mode/wavelength division multiplexing transmitter using lithium niobate on insulator","description":"","filename":"SupplementaryInformationzhu1028.docx","url":"https://assets-eu.researchsquare.com/files/rs-8061035/v1/b71cfd52de9b1d29d4c353f6.docx"}],"financialInterests":"There is no conflict of interest","formattedTitle":"A 36 × 240 Gbps hybrid mode/wavelength division multiplexing transmitter using lithium niobate on insulator","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eFueled by artificial intelligence, big data, and cloud computing, data traffic in the information age grows with an annual increase of ~\u0026thinsp;25%\u003csup\u003e1\u003c/sup\u003e. Such a dramatic surge has pushed optical interconnects beyond their traditional role in long-haul backbone networks, enabling their widespread adoption in short-reach links and intra-chip applications\u003csup\u003e\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Core components such as lasers\u003csup\u003e\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e, modulators\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e, routers\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, and detectors\u003csup\u003e\u003cspan additionalcitationids=\"CR13 CR14\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e are essential in optical transmission systems. To meet the demands of these components for high speed, low power consumption, compact size, and low cost, integrated photonics platforms\u0026mdash;particularly silicon photonics\u0026mdash;have gained significant attention. By heterogeneously integrating direct bandgap III-V materials and narrow bandgap germanium, silicon photonics enables monolithic integration of passive and active components, thus meeting various demands\u003csup\u003e\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. However, in the specific context of electro-optic modulation, silicon photonics suffers from notable drawbacks, including excessive waveguide propagation loss, unwanted nonlinear responses, and a constrained electro-optic (E-O) modulation bandwidth. These limitations stem inherently from the carrier dispersion effect\u0026mdash;an underlying operating principle of silicon modulators\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eLithium niobate has drawn extensive interest ever since its synthesis in the 1960s, all attributed to its remarkable properties: a large electro-optic coefficient (~γ\u003csub\u003e33\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;33 pm/V), excellent nonlinearity coefficient, low waveguide loss (Intrinsic loss: 0.2 dB/m)\u003csup\u003e20\u003c/sup\u003e, and a wide transparency window (0.4-5 \u0026micro;m)\u003csup\u003e21,22\u003c/sup\u003e. Recently, the newly developed lithium niobate on insulator (LNOI) has renewed research focus. Benefiting from its sub-wavelength waveguide size and CMOS-compatible processes, LNOI has shown great potential in key fields like E-O modulation\u003csup\u003e\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e, microwave photonics\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e, as well as nonlinear optics involving both second-order\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e and third-order effects\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Mach-Zehnder modulators (MZMs) on LNOI can achieve E-O bandwidths exceeding 110 GHz with half-wave voltage-length product (V\u003csub\u003eπ\u003c/sub\u003e\u0026middot;L)\u0026thinsp;\u0026lt;\u0026thinsp;2\u0026ndash;3 V\u0026middot;cm\u003csup\u003e4\u003c/sup\u003e. When combined with advanced modulation formats such as dual-polarization, pulse amplitude modulation (PAM) and IQ modulation, single-wavelength data rates beyond 1.96 Tb/s are attainable\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. In practical applications, though, the single-channel rate remains limited to approximately 100 Gbaud. This limitation mainly stems from the constraints of high-frequency responses in radio frequency (RF) amplifiers, RF transmission lines, and photodetectors. To address this issue, multiplexing techniques\u0026mdash;including wavelength division multiplexing (WDM) and mode division multiplexing (MDM)\u0026mdash;are under active investigation. The challenge, however, lies in the anisotropic crystal structure and weak optical confinement of LNOI: these properties make designing traditional wavelength manipulation devices (e.g., arrayed waveguide gratings (AWGs) and microring resonators) significantly difficult, particularly when it comes to achieving precise phase control and a large free spectral range (FSR). Several innovative solutions have been proposed recently. Yi et al. introduced an AWG design based on a 45\u0026deg; rotated crystal orientation to mitigate phase errors caused by waveguide path differences. The demonstrated 8-channel AWG features an insertion loss range from 2.4 dB to 4.8 dB, and a crosstalk of ~ -22.8 dB\u003csup\u003e30\u003c/sup\u003e. He et al. developed an x-cut LNOI optical filter via a multimode waveguide grating (MWG) and a mode multiplexer\u0026mdash;eliminating bent waveguides, with an insertion loss of -0.15 dB and sidelobe suppression ratio\u0026thinsp;\u0026gt;\u0026thinsp;26 dB\u003csup\u003e31\u003c/sup\u003e. They later extended this to an 8-channel dense wavelength multiplexer (flat spectral responses) and a compact 4-channel dense wavelength division multiplexing (DWDM) transmitter (1.6 nm channel spacing) supporting 4\u0026times;100 Gbps high-speed transmission\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. On the other hand, mode hybridness induced by the anisotropy of LNOI waveguides is a core challenge in mode manipulation. To address this issue, early high-order mode multiplexers based on LNOI mostly adopt the directional coupler scheme to avoid the use of tapered waveguides\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. However, this scheme suffers from low conversion efficiency, narrow operating bandwidth, and small fabrication tolerance, which limit the performance of the devices. Aiming at this bottleneck, the mode multiplexers designed along the Z-propagating LNOI waveguides are proposed to suppress mode hybridness fundamentally\u003csup\u003e\u003cspan additionalcitationids=\"CR36\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. These devices support up to eight modes with less than 0.1 dB per-mode loss and below \u0026minus;\u0026thinsp;18 dB crosstalk, enabling a gross transmission rate of 8\u0026times;60 Gbps using MDM. Despite these advances, current research remains largely focused on manipulating a single dimension of photons. Achieving simultaneous multi-dimensional multiplexing in LNOI waveguides\u0026mdash;combining wavelength and mode\u0026mdash;would further boost transmission capacity\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eIn this paper, we present a hybrid 6-mode \u0026times; 6-wavelength division multiplexing transmitter designed to further expand the capacity limitations of optical networks. This innovative transmitter seamlessly integrates six distinct waveguide modes (e.g., TE\u003csub\u003e0\u003c/sub\u003e, TE\u003csub\u003e1\u003c/sub\u003e, TE\u003csub\u003e2\u003c/sub\u003e, TE\u003csub\u003e3\u003c/sub\u003e, TE\u003csub\u003e4\u003c/sub\u003e, and TE\u003csub\u003e5\u003c/sub\u003e modes) with six precisely spaced wavelengths, enabling the dense multiplexing of 36 independent channels within a compact optical bandwidth. The channel spacing is meticulously designed to be 3.2 nm, corresponding to approximately 400 GHz at the C-band, and adheres to the ITU-T grid standards. By leveraging MDM, the transmitter achieves highly efficient utilization of spatial resources, significantly boosting spectral efficiency and enabling terabit-scale data transmission over a single optical waveguide. Experimentally, the cascaded Fabry-Perot (F-P) cavity-based wavelength multiplexers exhibit box-like response characteristics with a 3-dB bandwidth of 1.8 nm, low crosstalk of -22 dB, and minimal insertion loss ranging from 0.15 dB to 0.83 dB. The mode (de)multiplexer, designed along the Z-propagating axis, demonstrates equally impressive performance with low crosstalk of -14 dB and insertion loss between 0.05 dB and 0.3 dB. Furthermore, the 3-dB E-O bandwidth of the employed MZM exceeds 67 GHz, and we have successfully demonstrated the transmission of 120 GBaud on-off keying (OOK) and 4-level pulse-amplitude modulation (PAM4) signals. The hybrid multiplexing transmitter proposed in this work achieves an overall system capacity of 8.64 Tbps, offering robust technical support for high-speed optical interconnection networks.\u003c/p\u003e"},{"header":"2 Results","content":"\u003cp\u003e\u003cb\u003eDevice design and experimental approach\u003c/b\u003e\u003c/p\u003e\u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a) and (b), the proposed hybrid 6-mode \u0026times; 6-wavelength division multiplexing transmitter integrates six 6-channel WDM transmitters with a single 6-channel mode multiplexer. Each 6-channel WDM transmitter is composed of six cascaded optical filters featuring flat-top spectral responses and six Mach-Zehnder modulators (MZMs) configured to operate along the Y-propagating direction. The modulated optical signals output from the six WDM transmitters are respectively connected to distinct multiplexing ports of the 6-channel MDM, ultimately forming the hybrid transmitter. Notably, the 6-channel mode multiplexer consists of five cascaded adiabatic directional couplers (ADCs, i.e., ADC #1 to ADC #5), which are dedicated to handling the TE₁, TE₂, TE₃, TE₄, and TE₅ modes, respectively. These five ADCs are aligned along the Z-propagating axis, a design choice intended to suppress mode hybridness and ensure stable mode transmission.\u003c/p\u003e\u003cp\u003eThe device was fabricated on a 400-nm x-cut LNOI wafer with a 3-\u0026micro;m silica buffer layer and a 525-\u0026micro;m-thick Si handle substrate (see \u0026ldquo;method\u0026rdquo;, fabrication). The LNOI wafer has an extraordinary refractive index (\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e) of ~\u0026thinsp;2.138 along the crystal z-axis and an ordinary refractive index (\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003eo\u003c/em\u003e\u003c/sub\u003e) of ~\u0026thinsp;2.211 along the crystal x-axis and y-axis at 1550 nm wavelength. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c) and (d) present the cross-section of the Z-propagating and Y-propagating LNOI photonic waveguide, featuring an etching depth of \u003cem\u003eh\u003c/em\u003e\u003csub\u003e\u003cem\u003er\u003c/em\u003e\u003c/sub\u003e=200 nm, a slab thickness of \u003cem\u003eh\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e=200 nm, a sidewall angle of 60\u0026deg; (determined by the fabrication process), and an air cladding. The top width of the LNOI waveguide is denoted as \u003cem\u003eW\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eZ-propagating mode multiplexer\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a) and (b) present the calculated effective mode indices (\u003cem\u003eN\u003c/em\u003e\u003csub\u003e\u003cem\u003eeff\u003c/em\u003e\u003c/sub\u003e) for Y-propagating and Z-propagating LNOI photonic waveguides under different \u003cem\u003eW\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e at 1550 nm wavelength, respectively. Due to the anisotropic nature of the LNOI material, these two waveguides exhibit distinct mode properties. For the Y-propagating LNOI waveguide, TE modes predominantly experience an extraordinary refractive index (\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e), while TM modes experience an ordinary refractive index (\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003eo\u003c/em\u003e\u003c/sub\u003e) with \u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003eo\u003c/em\u003e\u003c/sub\u003e \u0026gt;\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e. Due to the flat structure characteristics of LNOI waveguides, the TE and TM modes have nearly identical \u003cem\u003eN\u003c/em\u003e\u003csub\u003e\u003cem\u003eeff\u003c/em\u003e\u003c/sub\u003e, leading to the formation of hybrid mode regions as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a). Specifically, there is an obvious hybridness region between TM\u003csub\u003e0\u003c/sub\u003e and TE\u003csub\u003e1\u003c/sub\u003e modes around \u003cem\u003eW\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1.3 \u0026micro;m, and another hybridness region between TM\u003csub\u003e0\u003c/sub\u003e and TE\u003csub\u003e3\u003c/sub\u003e modes around \u003cem\u003eW\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;3.3 \u0026micro;m. These mode hybridness regions pose significant challenges for on-chip mode manipulation. In contrast, in the Z-propagating LNOI waveguide, both TE and TM modes experience \u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003eo\u003c/em\u003e\u003c/sub\u003e index, resulting in TE modes having much larger \u003cem\u003eN\u003c/em\u003e\u003csub\u003e\u003cem\u003eeff\u003c/em\u003e\u003c/sub\u003e values compared to TM modes. Consequently, the mode hybridness is greatly suppressed as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b). Our mode multiplexer is designed along the Z-propagating axis of the LNOI waveguide to suppress mode hybridness, and adopts a structure of ADC to enable broadband and large fabrication-tolerance on-chip mode manipulation. The design rules and critical parameters for Z-propagating ADCs targeting TE\u003csub\u003e1\u003c/sub\u003e, TE\u003csub\u003e2\u003c/sub\u003e, TE\u003csub\u003e3\u003c/sub\u003e, TE\u003csub\u003e4\u003c/sub\u003e, and TE\u003csub\u003e5\u003c/sub\u003e modes, respectively, have been detailed in our previous work\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. Figures\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c)-(h) illustrate the simulated transmission characteristics of the designed ADCs for these modes. All five modes feature an insertion loss of less than 0.1 dB and crosstalk below \u0026minus;\u0026thinsp;20 dB across the wavelength range of 1500\u0026ndash;1560 nm. The corresponding simulated light propagation is shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(i)-(m), higher-order TE\u003csub\u003e1\u003c/sub\u003e-TE\u003csub\u003e5\u003c/sub\u003e modes convert to the fundamental TE\u003csub\u003e0\u003c/sub\u003e mode adiabatically.\u003c/p\u003e\u003cp\u003eThe transmission spectra of the fabricated mode multiplexer were measured by connecting a pair of mode multiplexers back-to-back, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a). Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b)-(g) presents the measured spectra of the 6-channel mode multiplexer normalized with the transmission of a straight waveguide fabricated on the same chip. It is observed that the mode (de)multiplexer pair achieves mode crosstalk below \u0026minus;\u0026thinsp;14 dB and insertion losses ranging from approximately 0.05 dB to 0.3 dB for all six modes within the wavelength range of 1520\u0026ndash;1560 nm.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eFlat-top wavelength multiplexer\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a) shows the detailed illustration of a flat-top optical wavelength filter, which consists of a cascaded F-P cavity and a mode (de)multiplexer based on an ADC. The cascaded F-P cavity with asymmetric teeth converts the launched TE\u003csub\u003e0\u003c/sub\u003e mode into the TE\u003csub\u003e1\u003c/sub\u003e mode when the wavelength is matched with the Bragg condition; then, the reflected TE\u003csub\u003e1\u003c/sub\u003e mode is delivered into the drop port as the TE\u003csub\u003e0\u003c/sub\u003e mode passing through the mode (de)multiplexer. The mode (de)multiplexer is designed according to the method proposed in our previous work\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. The coupled F-P cavity is formed with three cascaded mirrors based on asymmetric multimode waveguide gratings (AMWGs). We designed the coupled F-P cavity according to the requirement of realizing a 6-channel wavelength multiplexer with a channel spacing of 400 GHz. The structural parameters are chosen as \u003cem\u003eL\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e= 440 nm, \u003cem\u003eδ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;850 nm, \u003cem\u003eΛ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;440 nm, \u003cem\u003eη\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.5, \u003cem\u003eW\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2000 nm, \u003cem\u003eb\u003c/em\u003e\u0026thinsp;=\u0026thinsp;10, \u003cem\u003eN\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eN\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;60, and \u003cem\u003eN\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;90. The core widths \u003cem\u003ew\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e and \u003cem\u003ew\u003c/em\u003e\u003csub\u003eb\u003c/sub\u003e for the input/output ends of the adiabatic couplers are selected as (\u003cem\u003ew\u003c/em\u003e\u003csub\u003ea1\u003c/sub\u003e, \u003cem\u003ew\u003c/em\u003e\u003csub\u003eb1\u003c/sub\u003e) = (1000, 600) nm and (\u003cem\u003ew\u003c/em\u003e\u003csub\u003ea2\u003c/sub\u003e, \u003cem\u003ew\u003c/em\u003e\u003csub\u003eb2\u003c/sub\u003e) = (2000, 200) nm, respectively. In this case, the core waveguide width \u003cem\u003ew\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e increases from 1000 nm to 2000 nm, while the core width \u003cem\u003ew\u003c/em\u003e\u003csub\u003eb\u003c/sub\u003e decreases from 600 nm to 200 nm. The taper lengths are chosen as (\u003cem\u003eL\u003c/em\u003e\u003csub\u003e01\u003c/sub\u003e, \u003cem\u003eL\u003c/em\u003e\u003csub\u003e12\u003c/sub\u003e, \u003cem\u003eL\u003c/em\u003e\u003csub\u003e23\u003c/sub\u003e) = (50, 100, 50) \u0026micro;m, while the gap widths (\u003cem\u003ew\u003c/em\u003e\u003csub\u003eg1\u003c/sub\u003e, \u003cem\u003ew\u003c/em\u003e\u003csub\u003eg2\u003c/sub\u003e, \u003cem\u003ew\u003c/em\u003e\u003csub\u003eg3\u003c/sub\u003e) are chosen as (2.25, 0.25, 1.25) \u0026micro;m. The simulated optical transmission spectrum is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b). It can be seen that the designed flat-top optical filter has a large FSR of ~\u0026thinsp;20 nm, a low insertion loss\u0026thinsp;\u0026lt;\u0026thinsp;0.1\u0026ndash;0.4 dB, a 3-dB bandwidth of 1.5 nm, and an ER of \u0026gt;\u0026thinsp;20 dB, verifying that the coupled F-P cavity enables a large FSR and box-like optical transmission. It helps break the FSR and spectral efficiency limitations. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c) shows the measured optical transmission spectra at the drop and through ports of the fabricated flat-top optical filters, indicating an insertion loss of ~\u0026thinsp;0.1\u0026ndash;0.45 dB, an ER of ~\u0026thinsp;20 dB, a 3-dB bandwidth of ~\u0026thinsp;1.8 nm, and an FSR of ~\u0026thinsp;20 nm.\u003c/p\u003e\u003cp\u003eThe 6-channel wavelength multiplexer is designed by cascading six flat-top optical filters in series, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(d). The operating wavelengths of these filters increase linearly from bottom to top, achieved by carefully optimizing the cavity length \u003cem\u003eL\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e. For the six channels with a channel spacing of 400 GHz, the corresponding cavity lengths are set to \u003cem\u003eL\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e = 440, 505, 570, 635, 700, and 765 nm, respectively. The remaining parameters of these six filters are identical. The simulated transmission spectra of the multiplexer are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(e), indicating the 6-channel dense wavelength multiplexer has a channel spacing of 400 GHz, an insertion loss of ~\u0026thinsp;0.05\u0026ndash;0.3 dB, a crosstalk between adjacent channels of \u0026minus;\u0026thinsp;25 dB, and a crosstalk between non-adjacent channels of \u0026minus;\u0026thinsp;35 dB. Experimental results, presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(f), show the measured optical transmission spectra of the 6-channel wavelength multiplexer without any calibration. These measurements reveal a channel spacing of 400 GHz, an insertion loss between 0.15 dB and 0.75 dB, a crosstalk between adjacent channels of approximately \u0026minus;\u0026thinsp;20 dB, and a crosstalk between non-adjacent channels of approximately \u0026minus;\u0026thinsp;30 dB. The channel spacing of the F-P cavity-based wavelength multiplexer can be further decreased to 200 GHz, thus achieving higher spectral efficiency (Supplementary Material S1).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eHybrid multiplexing transmitter\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a) illustrates the optical microscopic image of the fabricated hybrid multiplexing transmitter. Scanning electron microscopic images of the key components\u0026mdash;the asymmetric multimode waveguide gratings, grating coupler, and mode multiplexer\u0026mdash;are presented in Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b)\u0026ndash;(d). Figures\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(e)\u0026ndash;(j) display the measured drop optical transmission spectra for each TE mode (TE\u003csub\u003e0\u003c/sub\u003e to TE\u003csub\u003e5\u003c/sub\u003e) in the 6 \u0026times; 6 channel hybrid multiplexing transmitter without calibration. Each spectrum corresponds to six wavelength channels, exhibiting a channel spacing of 400 GHz, insertion losses in the range of 0.3\u0026ndash;1.07 dB, adjacent channel crosstalk below \u0026minus;\u0026thinsp;20 dB, and non-adjacent channel crosstalk below \u0026minus;\u0026thinsp;30 dB. The statistical distribution of center wavelengths for each wavelength channel is further illustrated in Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(k)\u0026ndash;(p) for TE\u003csub\u003e0\u003c/sub\u003e, TE\u003csub\u003e1\u003c/sub\u003e, TE\u003csub\u003e2\u003c/sub\u003e, TE\u003csub\u003e3\u003c/sub\u003e, TE\u003csub\u003e4,\u003c/sub\u003e and TE\u003csub\u003e5\u003c/sub\u003e modes, respectively. The results indicate that the six wavelength channels across all six modes maintain good consistency in channel spacing. Additionally, the center wavelength drift caused by fabrication errors is less than 0.2 nm for all six mode channels, confirming the high fabrication precision of the device.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a) presents a schematic illustration of the MZM. The structural parameters have been optimized as follows: \u003cem\u003eW\u003c/em\u003e\u003csub\u003ewg\u003c/sub\u003e = 1.5 \u0026micro;m, \u003cem\u003eL\u003c/em\u003e\u003csub\u003eMMI\u003c/sub\u003e = 35.2 \u0026micro;m, \u003cem\u003eW\u003c/em\u003e\u003csub\u003eMMI\u003c/sub\u003e = 7.5 \u0026micro;m, \u003cem\u003eh\u003c/em\u003e\u0026thinsp;=\u0026thinsp;600 nm, \u003cem\u003eW\u003c/em\u003e\u003csub\u003es\u003c/sub\u003e = 18 \u0026micro;m, We =\u0026thinsp;60 \u0026micro;m, \u003cem\u003eg\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e =150 \u0026micro;m, \u003cem\u003eL\u003c/em\u003e\u0026thinsp;=\u0026thinsp;4500 \u0026micro;m, and \u003cem\u003eW\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e = 6.5 \u0026micro;m, to achieve group velocity and 50-Ω impedance matching\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e,\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. The simulation results of the MZM can be found in the supplementary material S2. The static V\u003csub\u003eπ\u003c/sub\u003e of the MZM was measured using a 1-kHz triangular voltage sweep method, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b) (See \u0026ldquo;method\u0026rdquo;, Half-wave voltage measurement). The measured results, depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(c), indicate that the V\u003csub\u003eπ\u003c/sub\u003e for the 4.5 mm MZM is 4.58 V, with a corresponding V\u003csub\u003eπ\u003c/sub\u003e\u0026middot;L of 2.06 V\u0026middot;cm. For the compact six-channel WDM transmitter, the modulation crosstalk between different MZMs was measured with the experimental setup in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(d) (See \u0026ldquo;method\u0026rdquo;, E-O response measurement). Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(e) demonstrates the modulation strength when light was injected into CH3 and RF signals were applied to CH1\u0026ndash;CH6, showing that the modulation strength for RF applied to CH3 was at least 22 dB higher than that from CH1, CH2, CH4, CH5, and CH6. Figures\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(f)\u0026ndash;(k) show all the measured bandwidths of the small-signal EO response (S\u003csub\u003e21\u003c/sub\u003e) for all 36 transmission channels of the fabricated transmitter, indicating that the 3-dB bandwidth of all 36 MZMs exceeds 67 GHz. It is important to note that the currently measured bandwidth is limited by the experimental setup\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe experimental setup for characterizing high-speed transmission eye diagrams of the transmitter is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a) (See \u0026ldquo;method\u0026rdquo;, High-speed transmission characterization). Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b)-(g) shows the measured well-open eye diagrams of OOK and PAM4 signals for all 36 channels across TE\u003csub\u003e0\u003c/sub\u003e-TE\u003csub\u003e5\u003c/sub\u003e modes and six different wavelengths at the rates of 120 GBaud, respectively. These results indicate that the hybrid multiplexing transmitter achieves a total data capacity of 8.64 Tbps, showcasing its high-speed modulation capabilities. It should be noted that the high transmission rates achieved across all channels are enabled by the low insertion loss and flat-top spectral response of the wavelength multiplexer designed in this work. The effect of flat-top spectral response on high-speed signal transmission can be found in the supplementary material S3.\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e provides a comprehensive summary of the key performance parameters of multiplexing transmitters reported in recent studies. State-of-the-art implementations leverage diverse material platforms, such as silicon-on-insulator (SOI), indium phosphide (InP), lead zirconate titanate (PZT), and LNOI. Notably, the newly developed LNOI-based transmitter exhibits the highest single-channel data rate of 240 Gbps (our work), which is attributed to its excellent electro-optical modulation properties. Our proposed solution addresses the challenges associated with mode and wavelength manipulation in LNOI platforms: it increases the number of multiplexed channels to an unprecedented 36, thereby achieving a total transmission capacity of 8.64 Tbps.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSummary of key parameters and performance metrics for photonic multiplexing transmitters\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eReference\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMaterial\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eChannel number\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMultiplexing type\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eBitrate per channel\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eTotal Capacity\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e42\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSOI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e56 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e224 Gbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSOI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e112 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e448 Gbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e44\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSOI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e25 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e50 Gbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSOI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u0026thinsp;+\u0026thinsp;MDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e25 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e150 Gbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSOI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u0026thinsp;+\u0026thinsp;MDM\u0026thinsp;+\u0026thinsp;PDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e50 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1 Tbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e47\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eInP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e25 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e425 Gbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e48\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eInP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e50 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e400 Gbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePZT\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e40 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.6 Tbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLNOI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e100 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e400 Gbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLNOI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e200 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e400 Gbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLNOI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e100 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e400 Gbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLNOI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e60 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e480 Gbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLNOI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u0026thinsp;+\u0026thinsp;MDM\u0026thinsp;+\u0026thinsp;PDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e120 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.96 Tbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eThis work\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLNOI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWDM\u0026thinsp;+\u0026thinsp;MDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e240 Gbps\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e8.64 Tbps\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"3 Conclusion","content":"\u003cp\u003eIn summary, this research presents a state-of-the-art hybrid mode/wavelength division multiplexing transmitter based on the LNOI platform, which achieves a high communication capacity of 36 × 240 Gbps. Its core innovation lies in the integration of MDM and WDM. Specifically, it leverages the Z-propagating LNOI waveguide to suppress mode hybridness, thereby facilitating on-chip mode manipulation, while adopting cascaded FP cavities for flop-top WDM implementation. For the MDM functionality, the proposed scheme supports six transverse electric modes (TE\u003csub\u003e0\u003c/sub\u003e-TE\u003csub\u003e5\u003c/sub\u003e). Through meticulous optimization along the Z-propagating direction, the mode multiplexer ultimately achieves an insertion loss of \u0026lt; 0.1 dB and an inter-mode crosstalk of \u0026lt; − 15 dB. In terms of WDM, the cascaded F-P cavity design enables a wavelength multiplexer with a large FSR and a channel spacing of 3.2 nm. The incorporation of widened waveguides and higher-order F-P cavities further guarantees channel flatness and spacing uniformity—two key prerequisites for maintaining high data transmission rate across all optical channels. Notably, this wavelength multiplexer exhibits a box-like frequency response, characterized by a 3-dB bandwidth of 1.8 nm, a channel crosstalk of \u0026lt; − 22 dB, and a per-channel additional loss ranging from 0.15 to 0.83 dB. Additionally, the integrated electro-optic MZM delivers exceptional performance: its 3-dB bandwidth exceeds 67 GHz, and its Vπ·L is 2.06 V·cm, enabling support for both 120 Gbaud OOK and PAM4 signals. Experimental results verify that the transmitter achieves a total information transfer rate of 8.64 Tbps, thus demonstrating its high-data-rate capabilities.\u003c/p\u003e\u003cp\u003eLooking ahead, potential optimizations include leveraging higher-order modes and reducing WDM channel spacing to 1.6 nm, which could further increase channel count. The exploration of slow-light modulators\u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e and compact microcavity-type modulators\u003csup\u003e\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e holds promise for enhancing modulation efficiency and reducing chip size. Compared to previous 45°-tilted array waveguide gratings, the cascaded F-P cavity design offers greater flexibility and compactness, integrating filtering and modulation functions seamlessly. The vision for the future involves the heterogeneous integration of frequency-comb-based multi-wavelength light sources and III-V photodetectors, aiming for monolithic integration of all components. Our results demonstrate a novel, promising method to boost optical communication capacity, applicable to data-intensive scenarios like long-haul backbone networks and short-reach optical interconnects.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eFabrication\u003c/strong\u003e\u003c/p\u003e\u003cp\u003eThe device was fabricated on a 400-nm x-cut LNOI wafer with a 3-µm silica buffer layer and a 525-µm-thick Si handle substrate. The device was first patterned by electron-beam lithography, and then the pattern was transferred onto the LN layer by Ar\u003csup\u003e+\u003c/sup\u003e plasma dry etch, which gives the waveguide a sidewall angle \u003cem\u003eθ\u003c/em\u003e of 60°. Next, a step of UV lithography was used to form electrode patterns, and a layer of 10/500-nm Ti/Au electrodes was deposited by electron-beam evaporation and lift-off process.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eHalf-wave voltage measurement\u003c/strong\u003e\u003c/p\u003e\u003cp\u003eLight emitted from a tunable laser (TL) operating at 1550 nm wavelength was directed through a fiber polarization controller (PC) and coupled into the I\u003csub\u003e1\u003c/sub\u003e port via a single-mode fiber (SMF). The light output from CH1 was received by another SMF and detected by a photonic detector (PD), with the signal then transmitted to an oscilloscope (OSC) for analysis. Concurrently, a function generator generated a 1-kHz triangular signal that was applied to the MZM connected to the I\u003csub\u003e1\u003c/sub\u003e port. The trigger signal associated with this process was also directed to the oscilloscope for reference.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eE-O response measurement\u003c/strong\u003e\u003c/p\u003e\u003cp\u003eThe radio frequency (RF) signal from the signal light component analyzer (LCA) was applied to the electrode of MZM via a 67-GHz RF probe and terminated with another RF probe connected to a 50-Ω terminator after passing through the modulation region. The modulated light was coupled out of the chip through a grating coupler and subsequently collected and relayed back to the LCA. Crosstalk between two channels was evaluated by measuring the modulation strength when light was transmitted through one channel while an RF signal from the LCA was applied to the other.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eHigh-speed transmission characterization\u003c/strong\u003e\u003c/p\u003e\u003cp\u003eAn arbitrary waveform generator (AWG) was used to convert the electrical signal generated by a clock source into OOK or PAM4 signals. These OOK or PAM4 signals, combined with static voltage via a bias-tee, were applied to the fabricated device. The resulting modulated optical signal was detected and subsequently fed into an electrical sampling oscilloscope for analysis.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThis work was supported by the Zhejiang Provincial Natural Science Foundation of China (LDT23F04012F05, LD22F040004)\u0026nbsp;and the National Natural Science Foundation of China (62375238,\u0026nbsp;U23B2047, 62321166651, 62205292).\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003eData availability statements\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eAuthors can confirm that all relevant data are included in the paper and/-or its supplementary information files.\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003eDisclosures\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe authors declare no\u0026nbsp;competing interests.\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eWe would like to thank West Lake University and Zhejiang University for providing access to their micro- and nano-fabrication platforms, which facilitated the identification of collaborators for this work.\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003eAuthor contributions:\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eM.Z. and W.W. performed the experiments. M.Z., R.M., A.G, Z.W. carried out data analysis and simulations. F.H., J.G., D.L, W.Z and A.G. provided experimental supports. M.Z. wrote the manuscript with the assistance of W.Z. and Z.Y., with the input from all co-authors. Z.Y., H.L., W.Z. and D.D supervised the project.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eCorcoran B, Mitchell A, Morandotti R, Oxenl\u0026oslash;we LK, Moss DJ. Optical microcombs for ultrahigh-bandwidth communications. \u003cem\u003eNat Photon\u003c/em\u003e 2025; 19: 451\u0026ndash;462.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAsadi Y. 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The traditional single-mode and single-wavelength transmission technologies can no longer meet the requirements of massive data transmission, thereby continuously driving the industry to explore more efficient multiplexing schemes. Here, a hybrid 6-mode \u0026times; 6-wavelength division multiplexing transmitter based on lithium niobate-on-insulator (LNOI) is proposed as a groundbreaking solution for next-generation optical communication. The transmitter innovatively combines six different waveguide modes (TE\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;~\u0026thinsp;TE\u003csub\u003e5\u003c/sub\u003e modes) with six wavelengths spaced 3.2 nm apart, enabling the dense multiplexing of 36 independent channels within a compact optical bandwidth and achieving a capacity of 36 \u0026times; 240 Gbps. The 3.2 nm channel spacing (approximately 400 GHz at 1550 nm) complies with the ITU-T grid standards, ensuring compatibility with existing optical network infrastructures. Meanwhile, the mode division multiplexing component utilizes multi-mode waveguides to fully leverage the spatial degrees of freedom in optical transmission, thereby significantly enhancing the spectral efficiency of the system compared to traditional single-mode solutions. This hybrid mode/wavelength division multiplexing architecture exhibits excellent applicability in next-generation data center interconnections and long-haul optical transmission networks.\u003c/p\u003e","manuscriptTitle":"A 36 × 240 Gbps hybrid mode/wavelength division multiplexing transmitter using lithium niobate on insulator","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-25 14:30:11","doi":"10.21203/rs.3.rs-8061035/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ded463db-2e37-45b1-9963-fdf850d3c9eb","owner":[],"postedDate":"November 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":57645498,"name":"Physical sciences/Optics and photonics/Optical materials and structures/Microresonators"},{"id":57645499,"name":"Physical sciences/Optics and photonics/Applied optics/Integrated optics"},{"id":57645500,"name":"Physical sciences/Optics and photonics/Applied optics/Fibre optics and optical communications"}],"tags":[],"updatedAt":"2025-11-28T06:51:23+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-25 14:30:11","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8061035","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8061035","identity":"rs-8061035","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}