Compact low-noise photonic-terahertz synthesizer

Compact low-noise photonic-terahertz synthesizer | 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 Research Article Compact low-noise photonic-terahertz synthesizer Chenye Qin, Jiankang Li, Yingying Ji, Kunpeng Jia, Yuancheng Cai, and 12 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9251646/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract High-performance terahertz (THz) sources are increasingly important for next-generation communication, sensing and precision metrology systems. However, existing approaches often rely on complex system architectures, making it difficult to simultaneously achieve low noise and deployable implementations. Here we demonstrate a compact photonic THz source based on a packaged, self-injection-locked Kerr microcomb using a fiber Fabry–Pérot resonator. The device supports stable soliton operation at a repetition rate of ~ 20 GHz while preserving coherence at THz carrier frequencies. Using a soliton-crystal-derived carrier at 319 GHz, we realize 5 m free-space THz wireless communication with 16- and 64-QAM modulation at symbol rates up to 15 GBd, achieving bit-error rates well below the soft-decision forward-error-correction threshold under turnkey operation. Beyond single-carrier transmission, the microcomb also generates multiple mutually coherent THz carriers near 300 GHz with consistent noise performance. These results establish a compact and low-noise platform for coherent THz synthesis that supports both high-speed communication and parallel multi-channel operation, offering a scalable route toward high-capacity THz systems while reducing device bandwidth requirements and overall system complexity. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Terahertz (THz) technology is widely recognized as a key enabler for next-generation wireless communication [ 1 – 3 ], high-resolution sensing [ 4 , 5 ], and precision metrology [ 6 , 7 ], owing to its large spectral bandwidth, high carrier frequencies, and enhanced spatial and temporal resolution. In particular, the THz regime offers unique opportunities for ultra-high-capacity data transmission, low-latency, and strong interference resilience [ 8 – 10 ]. Conventional THz synthesis relies mainly on electronic frequency multiplication or photonic heterodyne approaches. Electronic schemes suffer from rapid phase-noise accumulation during multiplication, which limits spectral purity at high carrier frequencies [ 11 , 12 ]. Photonic approaches can transfer the stability of optical references to the THz domain and achieve excellent noise performance, for example through dual Brillouin lasers [ 13 – 15 ], Pound–Drever–Hall locking scheme [ 16 ], and electro-optic frequency division [ 17 , 18 ]. However, these systems typically rely on ultrastable cavities, high-bandwidth feedback electronics, and carefully isolated environments, resulting in large system size and high complexity that hinder practical deployment. Kerr microresonator frequency combs provide a highly integrated platform for optical frequency synthesis [ 12 , 19 – 23 ]. Benefiting from advanced fabrication, large free spectral ranges, and efficient parametric nonlinear interactions, Kerr microcombs generate mutually coherent optical lines [ 24 – 27 ]. Through photomixing or photodetection, these comb lines enable direct access to high-frequency beat notes while transferring the phase stability of the pump laser to the THz domain [ 28 , 29 ]. In addition, the comb structure offers the potential to generate multiple mutually coherent carriers from a single device, providing a natural basis for multi-channel THz synthesis and parallel signal processing. Despite these advantages, low-noise soliton in existing microresonator comb platforms is often accompanied by increased system complexity, while relatively high quantum noise floors further constrain their phase-noise performance. These limitations continue to hinder the development of integrated photonic THz sources. In this work, we demonstrate a packaged, self-injection-locked Kerr microcomb based on a fiber Fabry–Pérot resonator (FFPR) that addresses these limitations. The system supports stable soliton generation at a repetition rate of ~ 20 GHz while maintaining strong coherence at THz carrier frequencies. Benefiting from the packaged self-injection-locking architecture, the microcomb operates in a compact and robust configuration without relying on bulky ultrastable references or complex feedback infrastructure, providing a practical route toward low-phase-noise THz generation. Using a soliton-crystal-derived carrier at 319 GHz, we demonstrate free-space THz wireless communication over a 5 m link, achieving 16-QAM and 64-QAM transmission at symbol rates up to 15 GBd with bit-error rates well below the 20% soft-decision forward-error-correction (SD-FEC) threshold and stable turnkey operation. Beyond single-carrier transmission, we further explore the capability of the platform for multi-channel THz synthesis. By exploiting a single-soliton microcomb, multiple THz carriers can be generated near the 300 GHz band, exhibiting ultra-narrow beat-note linewidths and nearly identical noise performance. These results indicate that the number of available frequency channels can be increased without sacrificing coherence, enabling a scalable and parallel channel architecture. Together, our results establish a practical route toward low-noise, multi-channel THz synthesis using a packaged Kerr microcomb source and provide a promising foundation for future parallel THz communication [ 30 – 32 ] and sensing systems [ 33 ]. Results In this work, we employ a ~ 5 mm-long few-mode fiber with dielectric coatings exceeding 99.95% reflectivity on both ends to form the Kerr microresonator, providing a compact and high-Q platform for nonlinear photonics. The high reflectivity ensures strong light confinement, which is essential for achieving the intensity thresholds required for parametric frequency comb generation. A commercial distributed-feedback (DFB) laser, operated without an optical isolator, is used to achieve self-injection locking, in which a portion of the light transmitted from the FFPR is fed back into the DFB chip. This self-feedback mechanism not only stabilizes the laser frequency but also significantly narrows the pump linewidth [ 34 , 35 ], creating favorable conditions for low-noise comb generation. The configuration allows the system to access multiple operational regimes, including continuous-wave, modulation-instability, and single-soliton states, as the pump frequency is tuned across a cavity resonance. A conceptual schematic of the setup is illustrated in Fig. 1 a, with a photograph of the packaged FFPR device shown in the lower-left inset. To characterize the FFPR, the transmission spectrum is recorded by scanning a tunable semiconductor laser (CTL 1550, Toptica). The measured resonance linewidth of 825.6 kHz corresponds to an exceptionally high quality factor of Q = 3.36×10 8 (Fig. 1 b). Such a high Q not only reduces the intrinsic linewidth of the DFB pump but also enhances the resonator’s ability to sustain low-noise Kerr combs over extended periods. Importantly, the free spectral ranges (FSR) of the FFPR can be directly tuned via the cavity length, enabling flexible frequency spacing and compatibility with integrated packaging. For practical deployment in butterfly-packaged devices, a cavity length of less than 1 cm is preferred, striking a balance between tunability, footprint, and mechanical stability. The linewidth of the self-injection-locked DFB laser is characterized using a self-coherent detection scheme [ 36 – 38 ], where one arm of the laser output is frequency-shifted by 40 MHz using an acousto-optic modulator, while the other arm is delayed by 1 km of single-mode fiber to provide a long interferometric baseline. The single-sideband (SSB) frequency noise power spectral density (PSD) is then extracted from the SSB phase noise PSD, revealing a compressed pump linewidth as narrow as 0.386 Hz (Fig. 1 c). This remarkable linewidth reduction demonstrates the effectiveness of self-injection locking in suppressing both intrinsic and technical frequency fluctuations. By finely tuning the DFB drive current (Thorlabs TED200C), stable single-soliton states are obtained, as shown in Fig. 1 d. After spectral filtering, optical amplification, and photodetection, a soliton repetition rate of 20.293 GHz is observed with a carrier-to-noise ratio exceeding 90 dB (inset). Phase-noise characterization further confirms the excellent stability of the system. The measured SSB phase noise reaches − 95.4 dBc/Hz, − 129 dBc/Hz, and − 141.2 dBc/Hz at offset frequencies of 1 kHz, 10 kHz, and 100 kHz, respectively, and approaches − 160 dBc/Hz at high offset frequencies (Fig. 1 e). Notably, the phase-noise floor approaches the quantum-limited shot-noise level. This low noise floor is enabled by the high Q factor and large mode-field diameter [ 11 , 39 ] of the FFPR, which effectively reduces the quantum noise limit during photodetection. These results highlight the FFPR-based microcomb as a robust, compact, and low-noise source capable of supporting high-fidelity THz generation and downstream microwave photonic applications, providing a practical foundation for multi-line coherent THz synthesis in integrated platforms. To investigate the noise performance of self-injection-locked Kerr microcomb devices in high-frequency THz generation, we implemented the experimental configuration shown in Fig. 2 a. Two independent FFPR modules with identical architecture but slightly different repetition rates, 20.293 GHz (comb1) and 19.959 GHz (comb2), were employed. Both devices were stably operated in selected soliton crystal states, providing coherent multi-line spectra with controllable (FSRs). The outputs of the two microcombs were combined and routed through a programmable optical wave shaper for precise spectral line selection prior to amplification. After amplification by an erbium-doped fiber amplifier (EDFA), the filtered optical tones were converted into THz signals using a uni-traveling-carrier photodiode (UTC-PD, IOD-PMJ-13001). The generated THz signals were subsequently amplified using a low-noise THz amplifier (H-LNA 250–350 GHz) providing 25 dB of gain. To facilitate high-resolution analysis, the THz signals are directly downconverted to an intermediate frequency (IF) using a zero-bias diode (ZBD, WR3.4ZBD) operating over 220–330 GHz with a typical responsivity of 1700 V/W, followed by electrical amplification and spectral analysis with a high-performance electrical spectrum analyzer (ESA, FSW-50). In this scheme, two low-noise THz signals generated from optical frequency combs are simultaneously incident on a single UTC-PD, where they are heterodyned to produce an IF signal. The instantaneous phase of the IF signal corresponds to the phase difference between the two THz signals. In such a direct-beating measurement, the IF phase-noise spectrum equals the sum of the individual THz phase-noise spectra when the two sources are uncorrelated, resulting in a 3 dB increase for equal-performance sources. This enables direct extraction of the phase noise of a single THz source from the measured IF signal. Compared with harmonic mixing, this approach avoids excess noise from high-order multiplication and preserves the intrinsic noise of optically generated THz signals, similar to fundamental-frequency mixing [ 11 ], while reducing system complexity by removing the need for additional multipliers and photomixers. As a result, this heterodyne downconversion scheme enables direct characterization of the intrinsic noise of optically synthesized THz signals, effectively bypassing the additional noise and instability associated with electronic multiplication chains [ 26 ]. Finally, the results are recorded via a high-performance spectrum analyzer (FSW-50). In this configuration, comb1 was fixed in a 5-FSR soliton crystal state, yielding a tooth spacing of 101.465 GHz (Fig. 2 b). Two spectral lines at 1547.398 nm and 1549.845 nm were selected, corresponding to a frequency spacing of 304.395 GHz, which defines the reference THz tone for downconversion. Comb2 was systematically tuned to generate 2-FSR, 8-FSR, and 16-FSR soliton crystal states [ 40 , 41 ], with their corresponding optical spectra shown in Fig. 2 c from top to bottom. In each case, two spectral lines separated by approximately 319.36 GHz were selected to generate the THz signals. The filtered spectra of both combs are displayed in Fig. 2 d, with the shaded region marking the two fixed wavelengths of comb1. As a result, a fixed downconverted IF signal at 14.965 GHz was obtained in all cases, enabling a direct comparison of the noise characteristics associated with different soliton configurations. Despite the distinct soliton crystal states used in comb2, the measured RF linewidths were consistently limited by the resolution bandwidth of the spectrum analyzer to 100 Hz (Fig. 2 e), indicating preserved coherence at THz carrier frequencies. We further reveal nearly identical noise performance across all soliton states. The dashed curve in Fig. 2 f represents the system noise floor measured in the absence of optical input. The measured phase noise exhibits values of − 63 dBc/Hz, − 70 dBc/Hz, and − 75 dBc/Hz at 1 kHz offset for the 40 GHz, 160 GHz, and 320 GHz cases, respectively. At 10 kHz offset, the phase noise converges to − 93 dBc/Hz, − 94 dBc/Hz, and − 93 dBc/Hz. At high offset frequencies (10 MHz), the corresponding noise floors are − 110 dBc/Hz, − 117 dBc/Hz, and − 119 dBc/Hz, respectively. Notably, both the 160 GHz and 320 GHz cases reach the system noise floor. A clear trend can be observed: the phase noise remains nearly identical at low offset frequencies, while it gradually improves with increasing carrier frequency at higher offsets. The similarity at low offset frequencies indicates that the phase noise is dominated by thermal noise and common technical fluctuations, which are comparable across all three cases. In contrast, at higher offset frequencies, the overall noise level decreases from the 40 GHz case to the 160 GHz case and reaches its lowest value in the 320 GHz case. This behavior arises from the different dominant noise mechanisms across offset frequencies. At low offsets, thermal noise dominates, leading to similar performance across all cases. At high offsets, however, the phase noise becomes increasingly influenced by amplified spontaneous emission (ASE) from the EDFA and shot-noise-related contributions during photodetection [ 42 , 43 ]. Since the EDFA-amplified seed comb power involved in the beating process increases from the 40 GHz case to the 320 GHz case, the corresponding high-frequency THz beat notes exhibit progressively improved signal-to-noise characteristics, resulting in lower overall phase noise at larger carrier spacings. Building on the demonstrated low-noise THz generation enabled by the FFPR-based Kerr microcomb, we further evaluate the feasibility of the proposed architecture for THz wireless communication. For simplicity, we demonstrate a single-wavelength, single-polarization coherent communication architecture, with wavelength and polarization multiplexing left as straightforward extensions once single-channel performance is verified [ 44 , 45 ]. The experimental configuration is illustrated in Fig. 3 a. An optical tone at 1551.660 nm was modulated using an IQ modulator (IQM) to encode an ultra-wideband complex baseband signal, while a second optical tone at 1549.105 nm served as the optical carrier reference. After recombination and optical amplification, the two tones were injected into a UTC-PD, generating a 319 GHz THz signal through heterodyne photomixing. The output THz power as a function of the input optical power into the UTC-PD is shown in Fig. 3 b, reaching a maximum of approximately − 7 dBm at 319 GHz. The generated THz signal was then transmitted over a 5 m free-space wireless link. THz horn antennas and dielectric lenses were employed at both transmitter and receiver sides to mitigate beam divergence and compensate free-space propagation loss at this frequency [ 46 ]. At the receiver, an integrated THz mixing module with an embedded ×9 multiplier chain was used to downconvert the received THz signal to an IF. A radio-frequency (RF) local oscillator (LO) operating near 33.7 GHz was first multiplied to generate an unmodulated THz tone around 303.3 GHz, which was subsequently mixed with the incoming 319 GHz signal to produce an IF signal near 15.7 GHz. The downconverted IF signal was then amplified by an electrical amplifier (EA) and captured by a real-time digital storage oscilloscope (DSO) for offline digital signal processing. We systematically evaluated the wireless transmission performance under multiple symbol rates and modulation formats. Specifically, symbol rates of 5 GBd, 10 GBd, and 15 GBd were tested using both 16-QAM and 64-QAM modulation schemes. The corresponding constellation diagrams and eye diagrams, recorded under a launched optical power of 14 dBm into the UTC-PD, are presented in Fig. 3 c. Clear constellation patterns were observed across all tested cases, confirming the suitability of the low-noise Kerr-comb-derived THz carrier for multi-gigabaud coherent modulation. For practical deployment, THz sources are expected not only to be compact and integrated, but also to operate in a turnkey manner with high reproducibility, enabling direct access to stable low-noise states after each restart. Achieving such behavior remains non-trivial for Kerr microcombs, where soliton formation is often sensitive to operating conditions and requires careful tuning. To assess the stability and robustness of the communication link under repeated turnkey operation, four consecutive on–off cycles were performed. After each restart, the signal-to-noise ratio (SNR) and bit-error rate (BER) of the demodulated signals were remeasured for all symbol-rate cases. The spectral evolution over a 600 s on–off sequence is shown in Fig. 4 a, demonstrating highly reproducible operation. The corresponding SNR and BER results are summarized in Fig. 4 b and Fig. 4 c. For 16-QAM modulation at 5 GBd, all four measurements exhibited error-free performance within the measurement resolution (BER = 0), with SNR values ranging from 19.69 dB to 20.01 dB. At 10 GBd, the BER remained on the order of 10⁻ 5 (9.53×10⁻ 6 ~1.26×10⁻ 5 ), while the SNR was consistently maintained between 18.40 dB and 18.51 dB. When increasing the symbol rate to 15 GBd, clear constellations were still obtained, with BER values ranging from 3.70×10⁻ 5 to 7.41×10⁻ 5 and corresponding SNRs of 17.43 ~ 17.53 dB. For 64-QAM modulation, at 5 GBd, BER values between 4.54×10 − 4 and 8.39×10 − 4 were measured, with SNRs in the range of 19.93 ~ 20.08 dB. At 10 GBd, the BER increased to the ~ 2×10⁻ 3 level (1.95×10⁻ 3 ~2.18×10⁻ 3 ), while the SNR remained stable between 18.17 dB and 18.31 dB. At 15 GBd, BERs ranging from 4.48×10⁻ 3 to 5.09×10⁻ 3 were obtained, corresponding to SNRs of 16.11 ~ 16.50 dB. All measured BERs for both modulation formats remained well below the 20%-overhead SD-FEC threshold [ 47 ]. Across all symbol rates and modulation formats, consistent SNR and BER performance was maintained over repeated turnkey operations, highlighting the excellent stability and robustness of the THz generation and proposed THz wireless transmission system. While the above results validate the performance of a single Kerr-comb-derived THz carrier for wireless transmission, future systems seek to exploit the large THz bandwidth. Single-carrier operation imposes stringent bandwidth requirements on THz hardware, whereas parallel multi-carrier can distribute data across frequency channels to relax device constraints and increase aggregate throughput. Generating multiple coherent THz carriers within practical bandwidths, however, remains challenging, particularly for Kerr microcombs with large repetition rates (> 100 GHz). In this context, a moderate repetition rate enabled by the FFPR provides a suitable channel spacing for bandwidth-efficient multi-channel synthesis, as it provides the minimum achievable frequency spacing determined by the comb repetition rate while maintaining spectral continuity [ 48 ]. To evaluate this capability, we investigate the spectral properties of the generated parallel THz multi-carrier, as shown in Fig. 5 . The conceptual schematic in Fig. 5 a illustrates the generation principle of multi-carrier THz tones. A single-soliton microcomb produces a series of equally spaced optical lines, which give rise to a set of THz tones upon photomixing, with their spacing determined by the comb repetition rate. To characterize these THz tones, a low-noise THz reference derived from a soliton crystal with a comparable THz frequency spacing is used to downconvert the THz comb into a set of IF signals, each corresponding to the frequency difference between the reference and individual THz tones. This heterodyne-based downconversion scheme avoids the inaccuracies associated with purely electronic frequency-multiplication chains at high carrier frequencies. Experimentally, a soliton-crystal state with an effective spacing of 319.344 GHz was employed to generate a low-noise THz reference, while a single-soliton state with a repetition rate of 20.293 GHz was used to produce the multi-carrier THz tones. As a result, five IF signals were observed, corresponding to the beat notes between the reference and the 14th, 15th, 16th, 17th, and 18th harmonics of the single-soliton repetition rate, respectively, as shown in Fig. 5 b. This number is limited by the bandwidth of the UTC-PD and the ESA, while the underlying optical comb supports a much broader spectral span and can in principle generate a larger number of THz carriers. One additional beat note at 55.59 GHz exceeded the bandwidth of the ESA and could not be directly measured. The five detected beat notes exhibit carrier-to-noise ratios of 63 dB, 68 dB, 60 dB, 66 dB, and 51 dB, respectively. When measured with a resolution bandwidth of 100 Hz, all tones display narrow linewidths and high coherence, with well-defined spectral peaks and negligible linewidth broadening. The consistent spectral purity across all detected tones further confirms the strong mutual coherence and stability of the generated multi-carrier THz signals. These observations provide direct evidence that multi-carrier THz tones generated from a single-soliton microcomb simultaneously supports multi-line operation with high coherence and low noise. Such capability enables efficient utilization of the limited bandwidth of existing THz hardware while preserving the intrinsic advantages of optical frequency comb–based synthesis. Importantly, the demonstrated platform provides a viable pathway toward parallel THz architectures, where multiple coherent carriers can be simultaneously exploited to increase aggregate data throughput without relying on excessively high modulation bandwidth on a single channel. In this context, microcombs with moderate repetition rates are particularly advantageous, as they offer sufficiently dense spectral spacing to support multi-carrier operation while maintaining compatibility with the bandwidth constraints of practical THz modulators and detectors. This balance between spectral density and device bandwidth represents a key advantage over conventional high-repetition-rate Kerr combs, and highlights the potential of the proposed approach for scalable, high-capacity THz communication systems. In conclusion, we have demonstrated a compact and low-noise Kerr microcomb platform based on a self-injection-locked FFPR, enabling coherent synthesis from the microwave to the THz domain. Using a moderate-FSR microcomb, we generated a 319 GHz carrier and demonstrated high-order modulated THz wireless communication, supporting 64-QAM modulation at symbol rates up to 15 GBd. The system achieved BERs well below the 20% SD-FEC threshold while maintaining stable performance under repeated turnkey operation. In addition, multiple mutually coherent THz carriers were generated near the 300 GHz band and their coherence was experimentally verified. By combining low phase noise with dense spectral spacing, the demonstrated architecture supports multi-channel THz operation within the limited bandwidth of practical hardware, while relaxing bandwidth and linearity constraints on individual modulators and detectors. This integrated and scalable platform therefore provides a robust foundation for next-generation THz systems. Looking ahead, increasing the Q factor [ 49 – 51 ] of the FFPR can significantly reduce pump power requirements and improve nonlinear conversion efficiency, potentially enabling amplifier-free operation in photonic frequency synthesis applications. The use of fibers with larger mode volume [ 39 , 52 ] can further lower the quantum noise limit, providing additional improvements in phase-noise performance. In addition, more compact and self-stabilized microcomb devices will facilitate deployment across diverse system platforms by significantly reducing system complexity and improving overall energy efficiency. These advantages will become even more prominent as comb-enabled multi-carrier architectures are adopted in THz wireless communication systems, enabling scalable high-capacity transmission based on parallel THz carrier synthesis [ 53 ]. Beyond high-capacity wireless links, the proposed approach may also enable advanced architectures for multi-channel sensing, coherent radar, precision spectroscopy, and reconfigurable THz signal generation, paving the way toward fully integrated photonic THz systems. Declarations Competing interests Authors declare that they have no competing interests. Data and materials availability All data are available in the main text. Author Contribution C.Q., K.J., Y.C., M.Z. and Z.X. conceived the original idea and designed the experiment. C.Q., Y.J., W.L. and K.J. prepared the FFPRs sample, designed and packaged the Kerr comb module. C.Q., Y.J., and J.L., performed the measurement and conducted the data analysis. C.Q., K.J., Y.C., X.C., H.Y., Z.L. and Y.Z. participated in the manuscript writing. Z.Z., C.S., B.J., W.L and X.Y. provided valuable feedback and comments. Z.X., M.Z., X.Y. and S.Z. supervised the whole work. All authors contributed to the manuscript preparation. Acknowledgements: This work was supported by the National Key R&D Program of China (2023YFB2805700), the National Natural Science Foundation of China (62288101, 62293523, 62571564, 62271135, 62293520, 12304421, 12341403, 92463304, 92463308, 623B2047), Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (JYB2025XDXM106), the Zhangjiang Laboratory (ZJSP21A001), the Guangdong Major Project of Basic and Applied Basic Research (2020B0301030009), the Natural Science Foundation of Jiangsu Province (BK20230770, BK20232033), the Key project of Basic Research Program of Jiangsu Province (BK20253015), and the Major Project of Scientific and Technological Innovation 2030 (2023ZD0301500). 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Pfeiffer, H. Guo, W. Weng, J. Liu, and T. J. Kippenberg, "Dynamics of soliton crystals in optical microresonators," Nat. Phys. 15, 1071–1077 (2019). D. C. Cole, E. S. Lamb, P. Del’Haye, S. A. Diddams, and S. B. Papp, "Soliton crystals in Kerr resonators," Nat. Photonics 11, 671–676 (2017). M. Erkintalo, "Got the quantum jitters," Nat. Phys. (2021). J. Wang, H. Shi, G. Steinmeyer, Y. Cai, S. Wang, W. Chen, C. Gu, J. Fan, and M. Hu, "CW-Seeded Parametric Combs with Quantum-Limited Phase Noise," Laser Photonics Rev. 18, (2024). J. Zhang, M. Zhu, B. Hua, M. Lei, Y. Cai, Y. Zou, W. Tong, J. Ding, L. Tian, L. Ma, J. Xiao, Y. Huang, J. Yu, and X. You, "Real-Time Demonstration of 100 GbE THz-Wireless and Fiber Seamless Integration Networks," J. Light. Technol. 41, 1129–1138 (2023). J. Ding, L. Zhang, J. Liu, W. Li, Y. Wang, K. Wang, L. Zhao, W. Zhou, J. Zhang, M. Zhu, and J. Yu, "THz-over-fiber transmission with a net rate of 5.12 Tbps in an 80 channel WDM system," Opt. Lett. 47, 3103 (2022). 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Yang, X. Yi, B. Shen, H. Wang, and K. Vahala, "Bridging ultrahigh-Q devices and photonic circuits," Nat. Photonics 2018 125 12, 297–302 (2018). A. Ø. Svela, F. Copie, G. N. Ghalanos, J. M. Silver, L. Del Bino, M. T. M. Woodley, N. Moroney, P. Del’Haye, and S. Zhang, "Sub-milliwatt-level microresonator solitons with extended access range using an auxiliary laser," Opt. Vol. 6, Issue 2, pp. 206–212 6, 206–212 (2019). L. Yao, P. Liu, H.-J. Chen, Q. Gong, Q.-F. Yang, and Y.-F. Xiao, "Soliton microwave oscillators using oversized billion Q optical microresonators," Optica 9, 561 (2022). Y. Geng, H. Zhou, X. Han, W. Cui, Q. Zhang, B. Liu, G. Deng, Q. Zhou, and K. Qiu, "Coherent optical communications using coherence-cloned Kerr soliton microcombs," Nat. Commun. 13, 1–8 (2022). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 13 Apr, 2026 Reviewers agreed at journal 12 Apr, 2026 Reviewers agreed at journal 03 Apr, 2026 Reviewers invited by journal 03 Apr, 2026 Editor assigned by journal 31 Mar, 2026 Submission checks completed at journal 31 Mar, 2026 First submitted to journal 28 Mar, 2026 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. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9251646","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":617383483,"identity":"96983d7c-e40c-4c92-a882-aced60d7d29c","order_by":0,"name":"Chenye Qin","email":"","orcid":"","institution":"Nanjing University","correspondingAuthor":false,"prefix":"","firstName":"Chenye","middleName":"","lastName":"Qin","suffix":""},{"id":617383488,"identity":"82827464-1551-4831-a413-6f9a4ecfda50","order_by":1,"name":"Jiankang Li","email":"","orcid":"","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"Jiankang","middleName":"","lastName":"Li","suffix":""},{"id":617383489,"identity":"18459cde-fca8-4892-8245-c72160484ce6","order_by":2,"name":"Yingying Ji","email":"","orcid":"","institution":"Nanjing University","correspondingAuthor":false,"prefix":"","firstName":"Yingying","middleName":"","lastName":"Ji","suffix":""},{"id":617383490,"identity":"5d6e63a8-81c7-4140-8010-7e362c2d3655","order_by":3,"name":"Kunpeng Jia","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8UlEQVRIiWNgGAWjYBACxmYGZiiT+QCDBIg+QLwWtgTitIBMh9I8BhCakBbmdubHxrw77siZ86/59sCyjUGO70YC4+cCvA5jM07mPfPM2HLG2+0Gkm0MxpI3EpilZ+DVwmB8mLftcOKGG2e3SQC1ABkJbMw8eLWwfwZpqd9w48wzkJZ6IrTwAB3WdjjB4HwPG0hLggERWooN57Y9M9xwg81MQuKchOHMMw+bpfFpMew/vlnibdsdeYPzh59JS5TZyPMdTz74Ga+WBjB1gIFBIoGBWQIcmYwNeDQwMMgzwLTwH2Bg/IBX7SgYBaNgFIxUAAA2A0wGJGkpfQAAAABJRU5ErkJggg==","orcid":"","institution":"Nanjing University","correspondingAuthor":true,"prefix":"","firstName":"Kunpeng","middleName":"","lastName":"Jia","suffix":""},{"id":617383491,"identity":"010cb4c8-7a2c-4351-91fa-6251403bb609","order_by":4,"name":"Yuancheng Cai","email":"","orcid":"","institution":"Purple Mountain 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Zhang","email":"","orcid":"","institution":"Nanjing University","correspondingAuthor":false,"prefix":"","firstName":"Yuzhe","middleName":"","lastName":"Zhang","suffix":""},{"id":617383502,"identity":"31be3cd0-74c8-4faf-ba96-3fe00579711f","order_by":9,"name":"Zexing Zhao","email":"","orcid":"","institution":"Nanjing University","correspondingAuthor":false,"prefix":"","firstName":"Zexing","middleName":"","lastName":"Zhao","suffix":""},{"id":617383503,"identity":"c5653027-8b2b-4640-a7ba-2bc1134f9bea","order_by":10,"name":"Chong Sheng","email":"","orcid":"","institution":"Nanjing University","correspondingAuthor":false,"prefix":"","firstName":"Chong","middleName":"","lastName":"Sheng","suffix":""},{"id":617383504,"identity":"a058b694-7dae-439d-8b02-2357e1fca217","order_by":11,"name":"Biaobing Jin","email":"","orcid":"","institution":"Nanjing University","correspondingAuthor":false,"prefix":"","firstName":"Biaobing","middleName":"","lastName":"Jin","suffix":""},{"id":617383505,"identity":"9a7ee44c-8351-4bba-9e5a-798e727c9114","order_by":12,"name":"Wei Liang","email":"","orcid":"","institution":"Suzhou Institute of Nano-tech and Nano-bionics","correspondingAuthor":false,"prefix":"","firstName":"Wei","middleName":"","lastName":"Liang","suffix":""},{"id":617383506,"identity":"2b2912b8-4aa9-413b-a4af-8293e63d8c76","order_by":13,"name":"Xiaohu You","email":"","orcid":"","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"Xiaohu","middleName":"","lastName":"You","suffix":""},{"id":617383507,"identity":"b1adb211-1f02-4b41-9546-b216ecbd5450","order_by":14,"name":"Shi-ning Zhu","email":"","orcid":"","institution":"Nanjing University","correspondingAuthor":false,"prefix":"","firstName":"Shi-ning","middleName":"","lastName":"Zhu","suffix":""},{"id":617383508,"identity":"5f51e21c-93cb-4c07-902a-5f904bd565f3","order_by":15,"name":"Min Zhu","email":"","orcid":"","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"Min","middleName":"","lastName":"Zhu","suffix":""},{"id":617383509,"identity":"69dd425c-5b20-44a3-b94d-c734cf50b3d1","order_by":16,"name":"Zhenda Xie","email":"","orcid":"","institution":"Nanjing University","correspondingAuthor":false,"prefix":"","firstName":"Zhenda","middleName":"","lastName":"Xie","suffix":""}],"badges":[],"createdAt":"2026-03-28 09:54:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9251646/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9251646/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106602070,"identity":"cd2263ed-963b-49ea-a80a-a60cf4abe5ed","added_by":"auto","created_at":"2026-04-10 10:28:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":744856,"visible":true,"origin":"","legend":"\u003cp\u003eCharacterizations of compact self-injection locked microcomb. \u003cstrong\u003ea.\u003c/strong\u003e Concept of self-injection locked Kerr comb generation based on fiber Fabry–Perot resonator (FFPR). A portion of transmitted light is fed back into the FFPR, causing the self-injection locking effect. The lower-left inset shows a photograph of the FFPR, with the pink region indicating the high-reflectivity dielectric-coated area. The FFPR has a length of ~5 mm. The lower-right inset shows the packaged device, with overall dimensions of 3.4 cm×1.7 cm×0.9 cm. \u003cstrong\u003eb.\u003c/strong\u003e Transmission spectrum of the resonant mode. According to the measurements, the Q-factor is 3.36×10\u003csup\u003e8\u003c/sup\u003e.\u003cstrong\u003e c.\u003c/strong\u003e The frequency noise spectral density of the DFB laser in self-injection-locked states.\u003cstrong\u003e d.\u003c/strong\u003e The optical spectra of generated single soliton. The inset is the RF spectrum of the soliton repetition rate. \u003cstrong\u003ee.\u003c/strong\u003e Single-sideband (SSB) phase noise spectrum of the 20.293 GHz soliton repetition rate.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9251646/v1/24ee0277b22751b284b1af56.png"},{"id":106602073,"identity":"5b5d1dd3-f339-4815-a54e-fbac1ca7317e","added_by":"auto","created_at":"2026-04-10 10:28:09","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":314906,"visible":true,"origin":"","legend":"\u003cp\u003eGeneration and characterizations of THz beat-notes based on FFPR comb. \u003cstrong\u003ea.\u003c/strong\u003eThe setup of dual-THz comb beat-note measurements. \u003cstrong\u003eb.\u003c/strong\u003e The optical spectrum of comb1 with repetition rate of 101.465 GHz. The dashed lines represent the fixed filtered wavelength. c. The optical spectrum of comb1 with 2-FSR, 8-FSR, and 16-FSR (from top to bottom).\u003cstrong\u003e d\u0026amp;e.\u003c/strong\u003e Corresponding filtered wavelengths and beat-note with frequency spacings of 319.36 GHz and 304.395 GHz. f. Phase noise measurements\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9251646/v1/1a218f6a214104d79f94057b.png"},{"id":106728741,"identity":"626faf00-4c95-48b6-9744-e23d52fcf845","added_by":"auto","created_at":"2026-04-12 18:44:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1541356,"visible":true,"origin":"","legend":"\u003cp\u003eTHz wireless communication enabled by a Kerr comb. \u003cstrong\u003ea.\u003c/strong\u003e Experimental setup of the THz wireless communication link based on a Kerr comb with a 319 GHz repetition rate. The transmission is established over a 5 m THz free-space link. At the receiver, an integrated THz mixing receiver with an embedded ×9 multiplier chain was used to downconvert the modulated THz signal to an IF. \u003cstrong\u003eb.\u003c/strong\u003e Measured output THz power on the UTC-PD with the corresponding input optical power.\u003cstrong\u003ec.\u003c/strong\u003e Constellation diagrams and eye diagrams for 16-QAM and 64-QAM modulation at baud rates of 5 GBd, 10 GBd, and 15 GBd, with a fixed launched optical power of 14 dBm into the UTC-PD.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9251646/v1/b300019d930b7a8f73dba849.png"},{"id":106726551,"identity":"930a899a-e071-4f7e-ad66-0f725970e58d","added_by":"auto","created_at":"2026-04-12 18:36:30","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":169723,"visible":true,"origin":"","legend":"\u003cp\u003eTHz communication results during four consecutive on–off switching cycles. \u003cstrong\u003ea. \u003c/strong\u003eWavelength evolution in 600 s. \u003cstrong\u003eb\u0026amp;c\u003c/strong\u003e. Measured SNR and BER of demodulated signal across recovered soliton states for two different modulation formats under 5 GBd, 10 GBd and 15 GBd baud rates.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-9251646/v1/9b1862b9b1d381df27e09a8a.png"},{"id":106602079,"identity":"7b3d80b9-fbcf-41f6-8533-e9b030560fec","added_by":"auto","created_at":"2026-04-10 10:28:18","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":417157,"visible":true,"origin":"","legend":"\u003cp\u003eMulti-carrier THz tones generation and coherence characterization. \u003cstrong\u003ea.\u003c/strong\u003e Conceptual schematic of multi-carrier THz generation based on a single-soliton microcomb. In the optical domain, comb lines with frequency spacings of FSR × \u003cem\u003en\u003c/em\u003e, FSR × (\u003cem\u003en\u003c/em\u003e+1), FSR × (\u003cem\u003en\u003c/em\u003e+2), … are selected and converted via photomixing to generate a set of THz tones (\u003cem\u003eT₁\u003c/em\u003e, \u003cem\u003eT₂\u003c/em\u003e, \u003cem\u003eT₃\u003c/em\u003e, …). As a result, a series of equally spaced THz carriers with spacing of 20.293 GHz is obtained in the THz domain. To characterize their spectral properties, a reference THz signal generated from a soliton crystal with a comparable THz frequency spacing is introduced for heterodyne downconversion. \u003cstrong\u003eb.\u003c/strong\u003e Measured RF spectra of the downconverted signals. From left to right, the detected beat notes correspond to THz carriers at 284.10 GHz, 304.40 GHz, 324.69 GHz, 344.98 GHz, and 365.27 GHz mixed with the reference THz signal. The spectra are recorded with resolution bandwidths (RBW) of 1 kHz (top row) and 100 Hz (bottom row), respectively.\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9251646/v1/0c36bea55114bf66970bd644.jpeg"},{"id":106959917,"identity":"b16a5aa4-a08a-499c-8652-c10f85249861","added_by":"auto","created_at":"2026-04-15 09:17:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3694279,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9251646/v1/a6c69293-537b-4246-995c-cf23fbf1fab7.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Compact low-noise photonic-terahertz synthesizer","fulltext":[{"header":"Introduction","content":"\u003cp\u003eTerahertz (THz) technology is widely recognized as a key enabler for next-generation wireless communication [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], high-resolution sensing [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], and precision metrology [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], owing to its large spectral bandwidth, high carrier frequencies, and enhanced spatial and temporal resolution. In particular, the THz regime offers unique opportunities for ultra-high-capacity data transmission, low-latency, and strong interference resilience [\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Conventional THz synthesis relies mainly on electronic frequency multiplication or photonic heterodyne approaches. Electronic schemes suffer from rapid phase-noise accumulation during multiplication, which limits spectral purity at high carrier frequencies [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Photonic approaches can transfer the stability of optical references to the THz domain and achieve excellent noise performance, for example through dual Brillouin lasers [\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], Pound\u0026ndash;Drever\u0026ndash;Hall locking scheme [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], and electro-optic frequency division [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. However, these systems typically rely on ultrastable cavities, high-bandwidth feedback electronics, and carefully isolated environments, resulting in large system size and high complexity that hinder practical deployment.\u003c/p\u003e \u003cp\u003eKerr microresonator frequency combs provide a highly integrated platform for optical frequency synthesis [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan additionalcitationids=\"CR20 CR21 CR22\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Benefiting from advanced fabrication, large free spectral ranges, and efficient parametric nonlinear interactions, Kerr microcombs generate mutually coherent optical lines [\u003cspan additionalcitationids=\"CR25 CR26\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Through photomixing or photodetection, these comb lines enable direct access to high-frequency beat notes while transferring the phase stability of the pump laser to the THz domain [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. In addition, the comb structure offers the potential to generate multiple mutually coherent carriers from a single device, providing a natural basis for multi-channel THz synthesis and parallel signal processing.\u003c/p\u003e \u003cp\u003eDespite these advantages, low-noise soliton in existing microresonator comb platforms is often accompanied by increased system complexity, while relatively high quantum noise floors further constrain their phase-noise performance. These limitations continue to hinder the development of integrated photonic THz sources.\u003c/p\u003e \u003cp\u003eIn this work, we demonstrate a packaged, self-injection-locked Kerr microcomb based on a fiber Fabry\u0026ndash;P\u0026eacute;rot resonator (FFPR) that addresses these limitations. The system supports stable soliton generation at a repetition rate of ~\u0026thinsp;20 GHz while maintaining strong coherence at THz carrier frequencies. Benefiting from the packaged self-injection-locking architecture, the microcomb operates in a compact and robust configuration without relying on bulky ultrastable references or complex feedback infrastructure, providing a practical route toward low-phase-noise THz generation. Using a soliton-crystal-derived carrier at 319 GHz, we demonstrate free-space THz wireless communication over a 5 m link, achieving 16-QAM and 64-QAM transmission at symbol rates up to 15 GBd with bit-error rates well below the 20% soft-decision forward-error-correction (SD-FEC) threshold and stable turnkey operation.\u003c/p\u003e \u003cp\u003eBeyond single-carrier transmission, we further explore the capability of the platform for multi-channel THz synthesis. By exploiting a single-soliton microcomb, multiple THz carriers can be generated near the 300 GHz band, exhibiting ultra-narrow beat-note linewidths and nearly identical noise performance. These results indicate that the number of available frequency channels can be increased without sacrificing coherence, enabling a scalable and parallel channel architecture. Together, our results establish a practical route toward low-noise, multi-channel THz synthesis using a packaged Kerr microcomb source and provide a promising foundation for future parallel THz communication [\u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] and sensing systems [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eIn this work, we employ a\u0026thinsp;~\u0026thinsp;5 mm-long few-mode fiber with dielectric coatings exceeding 99.95% reflectivity on both ends to form the Kerr microresonator, providing a compact and high-Q platform for nonlinear photonics. The high reflectivity ensures strong light confinement, which is essential for achieving the intensity thresholds required for parametric frequency comb generation. A commercial distributed-feedback (DFB) laser, operated without an optical isolator, is used to achieve self-injection locking, in which a portion of the light transmitted from the FFPR is fed back into the DFB chip. This self-feedback mechanism not only stabilizes the laser frequency but also significantly narrows the pump linewidth [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], creating favorable conditions for low-noise comb generation. The configuration allows the system to access multiple operational regimes, including continuous-wave, modulation-instability, and single-soliton states, as the pump frequency is tuned across a cavity resonance. A conceptual schematic of the setup is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, with a photograph of the packaged FFPR device shown in the lower-left inset.\u003c/p\u003e \u003cp\u003eTo characterize the FFPR, the transmission spectrum is recorded by scanning a tunable semiconductor laser (CTL 1550, Toptica). The measured resonance linewidth of 825.6 kHz corresponds to an exceptionally high quality factor of Q\u0026thinsp;=\u0026thinsp;3.36\u0026times;10\u003csup\u003e8\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Such a high Q not only reduces the intrinsic linewidth of the DFB pump but also enhances the resonator\u0026rsquo;s ability to sustain low-noise Kerr combs over extended periods. Importantly, the free spectral ranges (FSR) of the FFPR can be directly tuned via the cavity length, enabling flexible frequency spacing and compatibility with integrated packaging. For practical deployment in butterfly-packaged devices, a cavity length of less than 1 cm is preferred, striking a balance between tunability, footprint, and mechanical stability.\u003c/p\u003e \u003cp\u003eThe linewidth of the self-injection-locked DFB laser is characterized using a self-coherent detection scheme [\u003cspan additionalcitationids=\"CR37\" citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e], where one arm of the laser output is frequency-shifted by 40 MHz using an acousto-optic modulator, while the other arm is delayed by 1 km of single-mode fiber to provide a long interferometric baseline. The single-sideband (SSB) frequency noise power spectral density (PSD) is then extracted from the SSB phase noise PSD, revealing a compressed pump linewidth as narrow as 0.386 Hz (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). This remarkable linewidth reduction demonstrates the effectiveness of self-injection locking in suppressing both intrinsic and technical frequency fluctuations.\u003c/p\u003e \u003cp\u003eBy finely tuning the DFB drive current (Thorlabs TED200C), stable single-soliton states are obtained, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed. After spectral filtering, optical amplification, and photodetection, a soliton repetition rate of 20.293 GHz is observed with a carrier-to-noise ratio exceeding 90 dB (inset). Phase-noise characterization further confirms the excellent stability of the system. The measured SSB phase noise reaches \u0026minus;\u0026thinsp;95.4 dBc/Hz, \u0026minus;\u0026thinsp;129 dBc/Hz, and \u0026minus;\u0026thinsp;141.2 dBc/Hz at offset frequencies of 1 kHz, 10 kHz, and 100 kHz, respectively, and approaches \u0026minus;\u0026thinsp;160 dBc/Hz at high offset frequencies (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee). Notably, the phase-noise floor approaches the quantum-limited shot-noise level. This low noise floor is enabled by the high Q factor and large mode-field diameter [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] of the FFPR, which effectively reduces the quantum noise limit during photodetection. These results highlight the FFPR-based microcomb as a robust, compact, and low-noise source capable of supporting high-fidelity THz generation and downstream microwave photonic applications, providing a practical foundation for multi-line coherent THz synthesis in integrated platforms.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo investigate the noise performance of self-injection-locked Kerr microcomb devices in high-frequency THz generation, we implemented the experimental configuration shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. Two independent FFPR modules with identical architecture but slightly different repetition rates, 20.293 GHz (comb1) and 19.959 GHz (comb2), were employed. Both devices were stably operated in selected soliton crystal states, providing coherent multi-line spectra with controllable (FSRs). The outputs of the two microcombs were combined and routed through a programmable optical wave shaper for precise spectral line selection prior to amplification. After amplification by an erbium-doped fiber amplifier (EDFA), the filtered optical tones were converted into THz signals using a uni-traveling-carrier photodiode (UTC-PD, IOD-PMJ-13001). The generated THz signals were subsequently amplified using a low-noise THz amplifier (H-LNA 250\u0026ndash;350 GHz) providing 25 dB of gain. To facilitate high-resolution analysis, the THz signals are directly downconverted to an intermediate frequency (IF) using a zero-bias diode (ZBD, WR3.4ZBD) operating over 220\u0026ndash;330 GHz with a typical responsivity of 1700 V/W, followed by electrical amplification and spectral analysis with a high-performance electrical spectrum analyzer (ESA, FSW-50). In this scheme, two low-noise THz signals generated from optical frequency combs are simultaneously incident on a single UTC-PD, where they are heterodyned to produce an IF signal. The instantaneous phase of the IF signal corresponds to the phase difference between the two THz signals. In such a direct-beating measurement, the IF phase-noise spectrum equals the sum of the individual THz phase-noise spectra when the two sources are uncorrelated, resulting in a 3 dB increase for equal-performance sources. This enables direct extraction of the phase noise of a single THz source from the measured IF signal. Compared with harmonic mixing, this approach avoids excess noise from high-order multiplication and preserves the intrinsic noise of optically generated THz signals, similar to fundamental-frequency mixing [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], while reducing system complexity by removing the need for additional multipliers and photomixers. As a result, this heterodyne downconversion scheme enables direct characterization of the intrinsic noise of optically synthesized THz signals, effectively bypassing the additional noise and instability associated with electronic multiplication chains [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Finally, the results are recorded via a high-performance spectrum analyzer (FSW-50).\u003c/p\u003e \u003cp\u003eIn this configuration, comb1 was fixed in a 5-FSR soliton crystal state, yielding a tooth spacing of 101.465 GHz (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). Two spectral lines at 1547.398 nm and 1549.845 nm were selected, corresponding to a frequency spacing of 304.395 GHz, which defines the reference THz tone for downconversion. Comb2 was systematically tuned to generate 2-FSR, 8-FSR, and 16-FSR soliton crystal states [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e], with their corresponding optical spectra shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec from top to bottom. In each case, two spectral lines separated by approximately 319.36 GHz were selected to generate the THz signals. The filtered spectra of both combs are displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, with the shaded region marking the two fixed wavelengths of comb1. As a result, a fixed downconverted IF signal at 14.965 GHz was obtained in all cases, enabling a direct comparison of the noise characteristics associated with different soliton configurations. Despite the distinct soliton crystal states used in comb2, the measured RF linewidths were consistently limited by the resolution bandwidth of the spectrum analyzer to 100 Hz (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee), indicating preserved coherence at THz carrier frequencies.\u003c/p\u003e \u003cp\u003eWe further reveal nearly identical noise performance across all soliton states. The dashed curve in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef represents the system noise floor measured in the absence of optical input. The measured phase noise exhibits values of \u0026minus;\u0026thinsp;63 dBc/Hz, \u0026minus;\u0026thinsp;70 dBc/Hz, and \u0026minus;\u0026thinsp;75 dBc/Hz at 1 kHz offset for the 40 GHz, 160 GHz, and 320 GHz cases, respectively. At 10 kHz offset, the phase noise converges to \u0026minus;\u0026thinsp;93 dBc/Hz, \u0026minus;\u0026thinsp;94 dBc/Hz, and \u0026minus;\u0026thinsp;93 dBc/Hz. At high offset frequencies (10 MHz), the corresponding noise floors are \u0026minus;\u0026thinsp;110 dBc/Hz, \u0026minus;\u0026thinsp;117 dBc/Hz, and \u0026minus;\u0026thinsp;119 dBc/Hz, respectively. Notably, both the 160 GHz and 320 GHz cases reach the system noise floor. A clear trend can be observed: the phase noise remains nearly identical at low offset frequencies, while it gradually improves with increasing carrier frequency at higher offsets. The similarity at low offset frequencies indicates that the phase noise is dominated by thermal noise and common technical fluctuations, which are comparable across all three cases. In contrast, at higher offset frequencies, the overall noise level decreases from the 40 GHz case to the 160 GHz case and reaches its lowest value in the 320 GHz case.\u003c/p\u003e \u003cp\u003eThis behavior arises from the different dominant noise mechanisms across offset frequencies. At low offsets, thermal noise dominates, leading to similar performance across all cases. At high offsets, however, the phase noise becomes increasingly influenced by amplified spontaneous emission (ASE) from the EDFA and shot-noise-related contributions during photodetection [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Since the EDFA-amplified seed comb power involved in the beating process increases from the 40 GHz case to the 320 GHz case, the corresponding high-frequency THz beat notes exhibit progressively improved signal-to-noise characteristics, resulting in lower overall phase noise at larger carrier spacings.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBuilding on the demonstrated low-noise THz generation enabled by the FFPR-based Kerr microcomb, we further evaluate the feasibility of the proposed architecture for THz wireless communication. For simplicity, we demonstrate a single-wavelength, single-polarization coherent communication architecture, with wavelength and polarization multiplexing left as straightforward extensions once single-channel performance is verified [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. The experimental configuration is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. An optical tone at 1551.660 nm was modulated using an IQ modulator (IQM) to encode an ultra-wideband complex baseband signal, while a second optical tone at 1549.105 nm served as the optical carrier reference. After recombination and optical amplification, the two tones were injected into a UTC-PD, generating a 319 GHz THz signal through heterodyne photomixing.\u003c/p\u003e \u003cp\u003eThe output THz power as a function of the input optical power into the UTC-PD is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, reaching a maximum of approximately \u0026minus;\u0026thinsp;7 dBm at 319 GHz. The generated THz signal was then transmitted over a 5 m free-space wireless link. THz horn antennas and dielectric lenses were employed at both transmitter and receiver sides to mitigate beam divergence and compensate free-space propagation loss at this frequency [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAt the receiver, an integrated THz mixing module with an embedded \u0026times;9 multiplier chain was used to downconvert the received THz signal to an IF. A radio-frequency (RF) local oscillator (LO) operating near 33.7 GHz was first multiplied to generate an unmodulated THz tone around 303.3 GHz, which was subsequently mixed with the incoming 319 GHz signal to produce an IF signal near 15.7 GHz. The downconverted IF signal was then amplified by an electrical amplifier (EA) and captured by a real-time digital storage oscilloscope (DSO) for offline digital signal processing.\u003c/p\u003e \u003cp\u003eWe systematically evaluated the wireless transmission performance under multiple symbol rates and modulation formats. Specifically, symbol rates of 5 GBd, 10 GBd, and 15 GBd were tested using both 16-QAM and 64-QAM modulation schemes. The corresponding constellation diagrams and eye diagrams, recorded under a launched optical power of 14 dBm into the UTC-PD, are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec. Clear constellation patterns were observed across all tested cases, confirming the suitability of the low-noise Kerr-comb-derived THz carrier for multi-gigabaud coherent modulation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor practical deployment, THz sources are expected not only to be compact and integrated, but also to operate in a turnkey manner with high reproducibility, enabling direct access to stable low-noise states after each restart. Achieving such behavior remains non-trivial for Kerr microcombs, where soliton formation is often sensitive to operating conditions and requires careful tuning.\u003c/p\u003e \u003cp\u003eTo assess the stability and robustness of the communication link under repeated turnkey operation, four consecutive on\u0026ndash;off cycles were performed. After each restart, the signal-to-noise ratio (SNR) and bit-error rate (BER) of the demodulated signals were remeasured for all symbol-rate cases. The spectral evolution over a 600 s on\u0026ndash;off sequence is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, demonstrating highly reproducible operation.\u003c/p\u003e \u003cp\u003eThe corresponding SNR and BER results are summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec. For 16-QAM modulation at 5 GBd, all four measurements exhibited error-free performance within the measurement resolution (BER\u0026thinsp;=\u0026thinsp;0), with SNR values ranging from 19.69 dB to 20.01 dB. At 10 GBd, the BER remained on the order of 10⁻\u003csup\u003e5\u003c/sup\u003e (9.53\u0026times;10⁻\u003csup\u003e6\u003c/sup\u003e~1.26\u0026times;10⁻\u003csup\u003e5\u003c/sup\u003e), while the SNR was consistently maintained between 18.40 dB and 18.51 dB. When increasing the symbol rate to 15 GBd, clear constellations were still obtained, with BER values ranging from 3.70\u0026times;10⁻\u003csup\u003e5\u003c/sup\u003e to 7.41\u0026times;10⁻\u003csup\u003e5\u003c/sup\u003e and corresponding SNRs of 17.43\u0026thinsp;~\u0026thinsp;17.53 dB.\u003c/p\u003e \u003cp\u003eFor 64-QAM modulation, at 5 GBd, BER values between 4.54\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e and 8.39\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e were measured, with SNRs in the range of 19.93\u0026thinsp;~\u0026thinsp;20.08 dB. At 10 GBd, the BER increased to the ~\u0026thinsp;2\u0026times;10⁻\u003csup\u003e3\u003c/sup\u003e level (1.95\u0026times;10⁻\u003csup\u003e3\u003c/sup\u003e~2.18\u0026times;10⁻\u003csup\u003e3\u003c/sup\u003e), while the SNR remained stable between 18.17 dB and 18.31 dB. At 15 GBd, BERs ranging from 4.48\u0026times;10⁻\u003csup\u003e3\u003c/sup\u003e to 5.09\u0026times;10⁻\u003csup\u003e3\u003c/sup\u003e were obtained, corresponding to SNRs of 16.11\u0026thinsp;~\u0026thinsp;16.50 dB. All measured BERs for both modulation formats remained well below the 20%-overhead SD-FEC threshold [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAcross all symbol rates and modulation formats, consistent SNR and BER performance was maintained over repeated turnkey operations, highlighting the excellent stability and robustness of the THz generation and proposed THz wireless transmission system.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWhile the above results validate the performance of a single Kerr-comb-derived THz carrier for wireless transmission, future systems seek to exploit the large THz bandwidth. Single-carrier operation imposes stringent bandwidth requirements on THz hardware, whereas parallel multi-carrier can distribute data across frequency channels to relax device constraints and increase aggregate throughput. Generating multiple coherent THz carriers within practical bandwidths, however, remains challenging, particularly for Kerr microcombs with large repetition rates (\u0026gt;\u0026thinsp;100 GHz). In this context, a moderate repetition rate enabled by the FFPR provides a suitable channel spacing for bandwidth-efficient multi-channel synthesis, as it provides the minimum achievable frequency spacing determined by the comb repetition rate while maintaining spectral continuity [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. To evaluate this capability, we investigate the spectral properties of the generated parallel THz multi-carrier, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe conceptual schematic in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea illustrates the generation principle of multi-carrier THz tones. A single-soliton microcomb produces a series of equally spaced optical lines, which give rise to a set of THz tones upon photomixing, with their spacing determined by the comb repetition rate. To characterize these THz tones, a low-noise THz reference derived from a soliton crystal with a comparable THz frequency spacing is used to downconvert the THz comb into a set of IF signals, each corresponding to the frequency difference between the reference and individual THz tones. This heterodyne-based downconversion scheme avoids the inaccuracies associated with purely electronic frequency-multiplication chains at high carrier frequencies.\u003c/p\u003e \u003cp\u003eExperimentally, a soliton-crystal state with an effective spacing of 319.344 GHz was employed to generate a low-noise THz reference, while a single-soliton state with a repetition rate of 20.293 GHz was used to produce the multi-carrier THz tones. As a result, five IF signals were observed, corresponding to the beat notes between the reference and the 14th, 15th, 16th, 17th, and 18th harmonics of the single-soliton repetition rate, respectively, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb. This number is limited by the bandwidth of the UTC-PD and the ESA, while the underlying optical comb supports a much broader spectral span and can in principle generate a larger number of THz carriers. One additional beat note at 55.59 GHz exceeded the bandwidth of the ESA and could not be directly measured. The five detected beat notes exhibit carrier-to-noise ratios of 63 dB, 68 dB, 60 dB, 66 dB, and 51 dB, respectively. When measured with a resolution bandwidth of 100 Hz, all tones display narrow linewidths and high coherence, with well-defined spectral peaks and negligible linewidth broadening. The consistent spectral purity across all detected tones further confirms the strong mutual coherence and stability of the generated multi-carrier THz signals.\u003c/p\u003e \u003cp\u003eThese observations provide direct evidence that multi-carrier THz tones generated from a single-soliton microcomb simultaneously supports multi-line operation with high coherence and low noise. Such capability enables efficient utilization of the limited bandwidth of existing THz hardware while preserving the intrinsic advantages of optical frequency comb\u0026ndash;based synthesis. Importantly, the demonstrated platform provides a viable pathway toward parallel THz architectures, where multiple coherent carriers can be simultaneously exploited to increase aggregate data throughput without relying on excessively high modulation bandwidth on a single channel. In this context, microcombs with moderate repetition rates are particularly advantageous, as they offer sufficiently dense spectral spacing to support multi-carrier operation while maintaining compatibility with the bandwidth constraints of practical THz modulators and detectors. This balance between spectral density and device bandwidth represents a key advantage over conventional high-repetition-rate Kerr combs, and highlights the potential of the proposed approach for scalable, high-capacity THz communication systems.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn conclusion, we have demonstrated a compact and low-noise Kerr microcomb platform based on a self-injection-locked FFPR, enabling coherent synthesis from the microwave to the THz domain. Using a moderate-FSR microcomb, we generated a 319 GHz carrier and demonstrated high-order modulated THz wireless communication, supporting 64-QAM modulation at symbol rates up to 15 GBd. The system achieved BERs well below the 20% SD-FEC threshold while maintaining stable performance under repeated turnkey operation. In addition, multiple mutually coherent THz carriers were generated near the 300 GHz band and their coherence was experimentally verified. By combining low phase noise with dense spectral spacing, the demonstrated architecture supports multi-channel THz operation within the limited bandwidth of practical hardware, while relaxing bandwidth and linearity constraints on individual modulators and detectors. This integrated and scalable platform therefore provides a robust foundation for next-generation THz systems.\u003c/p\u003e \u003cp\u003eLooking ahead, increasing the Q factor [\u003cspan additionalcitationids=\"CR50\" citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] of the FFPR can significantly reduce pump power requirements and improve nonlinear conversion efficiency, potentially enabling amplifier-free operation in photonic frequency synthesis applications. The use of fibers with larger mode volume [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e] can further lower the quantum noise limit, providing additional improvements in phase-noise performance. In addition, more compact and self-stabilized microcomb devices will facilitate deployment across diverse system platforms by significantly reducing system complexity and improving overall energy efficiency. These advantages will become even more prominent as comb-enabled multi-carrier architectures are adopted in THz wireless communication systems, enabling scalable high-capacity transmission based on parallel THz carrier synthesis [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. Beyond high-capacity wireless links, the proposed approach may also enable advanced architectures for multi-channel sensing, coherent radar, precision spectroscopy, and reconfigurable THz signal generation, paving the way toward fully integrated photonic THz systems.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eAuthors declare that they have no competing interests.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eData and materials availability\u003c/h2\u003e \u003cp\u003eAll data are available in the main text.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eC.Q., K.J., Y.C., M.Z. and Z.X. conceived the original idea and designed the experiment. C.Q., Y.J., W.L. and K.J. prepared the FFPRs sample, designed and packaged the Kerr comb module. C.Q., Y.J., and J.L., performed the measurement and conducted the data analysis. C.Q., K.J., Y.C., X.C., H.Y., Z.L. and Y.Z. participated in the manuscript writing. Z.Z., C.S., B.J., W.L and X.Y. provided valuable feedback and comments. Z.X., M.Z., X.Y. and S.Z. supervised the whole work. All authors contributed to the manuscript preparation.\u003c/p\u003e\u003ch2\u003eAcknowledgements:\u003c/h2\u003e \u003cp\u003eThis work was supported by the National Key R\u0026amp;D Program of China (2023YFB2805700), the National Natural Science Foundation of China (62288101, 62293523, 62571564, 62271135, 62293520, 12304421, 12341403, 92463304, 92463308, 623B2047), Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (JYB2025XDXM106), the Zhangjiang Laboratory (ZJSP21A001), the Guangdong Major Project of Basic and Applied Basic Research (2020B0301030009), the Natural Science Foundation of Jiangsu Province (BK20230770, BK20232033), the Key project of Basic Research Program of Jiangsu Province (BK20253015), and the Major Project of Scientific and Technological Innovation 2030 (2023ZD0301500).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data supporting the results in this study are available within the paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eT. 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Commun. 13, 1\u0026ndash;8 (2022).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"photonix-synergy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [PhotoniX Synergy](https://link.springer.com/journal/44519)","snPcode":"44519","submissionUrl":"https://submission.springernature.com/new-submission/44519/3","title":"PhotoniX Synergy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-9251646/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9251646/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHigh-performance terahertz (THz) sources are increasingly important for next-generation communication, sensing and precision metrology systems. However, existing approaches often rely on complex system architectures, making it difficult to simultaneously achieve low noise and deployable implementations. Here we demonstrate a compact photonic THz source based on a packaged, self-injection-locked Kerr microcomb using a fiber Fabry\u0026ndash;P\u0026eacute;rot resonator. The device supports stable soliton operation at a repetition rate of ~\u0026thinsp;20 GHz while preserving coherence at THz carrier frequencies. Using a soliton-crystal-derived carrier at 319 GHz, we realize 5 m free-space THz wireless communication with 16- and 64-QAM modulation at symbol rates up to 15 GBd, achieving bit-error rates well below the soft-decision forward-error-correction threshold under turnkey operation. Beyond single-carrier transmission, the microcomb also generates multiple mutually coherent THz carriers near 300 GHz with consistent noise performance. These results establish a compact and low-noise platform for coherent THz synthesis that supports both high-speed communication and parallel multi-channel operation, offering a scalable route toward high-capacity THz systems while reducing device bandwidth requirements and overall system complexity.\u003c/p\u003e","manuscriptTitle":"Compact low-noise photonic-terahertz synthesizer","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-10 10:27:04","doi":"10.21203/rs.3.rs-9251646/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-04-13T05:52:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"56060118094256769833648335399501439564","date":"2026-04-12T11:52:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"197703488745977691783557410702354895813","date":"2026-04-04T03:24:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-03T13:28:36+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-31T07:41:41+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-31T05:20:27+00:00","index":"","fulltext":""},{"type":"submitted","content":"PhotoniX Synergy","date":"2026-03-28T09:39:55+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"photonix-synergy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [PhotoniX Synergy](https://link.springer.com/journal/44519)","snPcode":"44519","submissionUrl":"https://submission.springernature.com/new-submission/44519/3","title":"PhotoniX Synergy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"32552b92-74e0-47ce-9dee-32769a2bfadd","owner":[],"postedDate":"April 10th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-10T10:27:05+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-10 10:27:04","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9251646","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9251646","identity":"rs-9251646","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}