Temperature-dependence of 780 nm VCSEL polarization output power and efficiency with and without optical feedback

Temperature-dependence of 780 nm VCSEL polarization output power and efficiency with and without optical feedback | 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 Temperature-dependence of 780 nm VCSEL polarization output power and efficiency with and without optical feedback SALAM NAZHAN This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9511706/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract This study presents an experimental investigation of the effects of temperature on the light-current (L-I) characteristics of the polarisation-resolved output of a 780 nm vertical-cavity surface-emitting laser (VCSEL), both in free-running operation and with optical feedback (OF). The results show that as temperature increases from low to room temperature, the linearity of the polarisation behaviour with OF is enhanced, and the polarization extinction ratio (ER) reaches a maximum. ER collapses for both low and high temperatures. The lasing mode (dominant mode) is more efficient but more sensitive to temperature. Linearity and ER between the two modes increase depending on the OF polarisation degree. OF plays a larger role at and near room temperature than at any other temperature. 90° OF yields exceptionally high ER (> 100) with enhancement of polarization, and 45° OF significantly improves ER, with clear separation between the two modes. Knowledge of polarisation mode selection in such devices is valuable for applications in optical communications and polarisation-sensitive imaging. VCSEL Temperature effect optical feedback L-I curve polarization threshold current Figures Figure 1 Figure 3 Figure 5 Figure 6 Introduction Vertical-cavity surface-emitting laser (VCSEL) is a semiconductor laser with unique features, including a low threshold current, high efficiency, a narrow, low-divergence beam, and circular emission, which make these devices favoured for a wide range of applications. Industrial and scientific applications, including sensing, imaging, scanning, small, low-power atomic sensors, magnetometers, and gyroscopes, require high-reliability and stable output power despite temperature changes and fluctuations [ 1 – 3 ]. VCSEL achieved a side-mode suppression ratio of more than 40 dB over a temperature range of 25°C ~ 85°C, maintaining stable single-mode emission at 794.8 nm. Output power, polarisation purity, and side-mode suppression ratio of a VCSEL are crucial factors to consider, particularly with respect to current and temperature. Such parameters are important when evaluating a laser's performance, as they significantly affect the quality of the laser's output. The temperature-dependent factors that contribute to the VCSEL characteristics are Auger recombination, optical loss and gain, carrier leakage and threshold current as reported in [ 4 , 5 ]. The temperature effects of the dynamics of VCSELs have been widely studied in the literature [ 6 , 7 ]. The dynamics of a 980 nm VCSEL showed wavelength stability over a wide temperature range. The VCSEL cavity is nearly cylindrically symmetric, offering no strong intrinsic polarization‑selective mechanism. Therefore, polarisation instabilities are widely observed in the output power of such devices. As temperature varies, the gain spectrum, cavity resonance, birefringence, and carrier‑related effects fluctuate, often leading to abrupt polarisation switching (PS), mode hopping, or elliptically polarised transient states. These states may occur with injection current and temperature because the polarization‑mode differential gain and losses change [8{Choquette, 2002 #60]}. Temperature studies and investigations into laser performance and dynamics contribute to the formation of VCSEL cavities for efficient operation. These studies concluded that laser performance fluctuations are mainly due to variations in cavity gain, with other factors remaining relatively constant. On the other hand, VCSELs are highly sensitive to optical feedback (OF) [ 9 – 12 ]. Laser operation at a low temperature allows an increase in the mode gain of the active region and a decrease in the accumulation of free electrons, which leads to a reduction in the threshold current and an upsurge in the slope efficiency, thereby increasing the power and electro-optical conversion efficiency [ 13 ]. OF occurs when a portion of the emitted light is reflected into the VCSEL cavity. This can happen intentionally, e.g. via external mirrors or unintentionally from nearby surfaces [ 14 ]. VCSELs often establish two orthogonal polarisation modes, horizontal (Hor) and vertical (Ver). OF can enhance one mode while suppressing the other, depending on the OF strength and polarisation angle [ 15 , 16 ]. This can be useful for the application of polarisation switching or laser output stabilisation [ 9 , 17 ]. Additionally, the polarisation of light in a VCSEL subjected to isotropic OF can be regularly switched between two orthogonal polarisation states as the injection current increases. This enables the polarisation L-I characteristics channelled [ 18 ]. OF reduces the threshold current and spectral linewidth, improving coherence, which makes VCSELs more energy-efficient and suitable for high-resolution sensing and communication [ 19 ]. Furthermore, this technique induced chaotic dynamics in the VCSEL, which is essential for secure communication applications [ 20 ]. One important laser characteristic is the light output power as a function of injected current (L-I curve). This can be used to identify several substantial parameters, including threshold current, differential responsivity, and internal and external quantum efficiency. The L-I curve can show linear fluctuation, or sudden jumps (polarization switching) or stability (polarization bi-stability) due to a change in internal cavity gain, particularly leading to polarisation mode hopping. Generally, higher temperatures increase threshold current, resulting in decreased slope efficiency, which requires thermal control. Testing the L-I curve ensures that VCSELs meet the requirements for different applications in terms of high performance and reliability. In addition, control of polarisation is useful in optical communication systems, polarisation-sensitive imaging, laser stabilisation, and polarisation mode selection, where polarisation purity or switching control is critical. This work offers valuable insights into the L-I properties of 780 nm VCSELs, in terms of temperature sensitivity and operational stability, which are essential components in temperature-sensitive applications, such as optical communication systems, enabling high performance across a wide range of temperatures. It also contributes to the design and optimisation of VCSEL structures. Experimental setup Figure 1 shows the experimental setup, including the following: light source (VCSEL), Lens (L) to focus the output of the VCSEL. The collimated beam passes through a half-wave plate (HWP) to rotate the polarization of the beam to the desired angle before entering a 50/50 non-polarizing beam splitter (BS). The BS splits the beam into a reflected beam and a transmitted beam. The reflected beam goes to the mirror (M) through a polarizer (P) to select the OF states, and the transmitted beam travels to the measurement section. The transmitted beam passes through a Wollaston prism (WP), which divides the beam into vertical (Ver) and horizontal (Hor) beams. A beam splitter (BS) is used to direct the beam into the detector (D) and to a fibre coupler (FC), passing through an optical isolator (IS) and lenses. Part of the beam is directed to the camera (CCD) through a filter (F). Output instruments feed different analysis devices: Computer (Com) and Optical Spectrum Analyzer (OSA). The output of the detectors is recorded by an analogue IO-card (Labview PCI-6036E, 16-bit). The angle of the HWP is adjusted such that the emission of the polarization components along the principal axes of the VCSEL is turned to the horizontal and vertical, i.e. the principal axes of the beam splitter cube and the analysing Wollaston prism. We will refer to these as Hor and Ver in the following. Results 1. Temperature effect on the L-I curve at free running In the free-running operation of the VCSEL, Fig. 2 illustrates the relationship between injection current and output power for two polarisation states: Hor mode (black line) and Ver mode (red line), under free-running conditions at different temperatures of 10.5°C, 15°C, 20°C, 30°C, and 40°C, presented in Fig. 2 (a-e) respectively. At 10.5°C. The polarisation component begins to lase around 2 mA. The horizontal (Hor) mode remains dominant across the entire bias-current range, whereas the output power of the orthogonal polarisation component remains low, despite increasing gradually with current. From 4.3 to 5 mA, the power in the Hor polarization drops significantly, whereas the power in the Ver increases, but the Hor polarization stays dominant. At around 5 mA, there is a very abrupt switch to a strong dominance of the Hor again. The kinks and abrupt switches in the L-I curve indicate instabilities and mode competition. Indeed, observations with a CCD camera and the OSA indicate the excitation of multiple high-order modes. As higher‑order transverse modes turn on, abrupt transitions occur in the output power and modal behaviour, which exactly reflects the behaviour of L-I curve discontinuities, indicating mode competition [ 21 ]. Theoretical analysis of multimode VCSELs demonstrates competition among transverse modes with different polarisations, leading to complex dynamics, including polarisation switching, mode competition, chaos, and additional bifurcations [ 22 ]. At 15°C, a similar behaviour is observed, but threshold and switching points are shifted by about 0.2 mA to higher currents, as one can expect from heating a semiconductor laser. At a temperature of 20°C, the Hor mode starts lasing around 2.5 mA, reaching a maximum power of 4 (V) at 5 mA, while the Ver mode gradually increases after 4 mA reaches just above 0.5 (V) at 6 mA. At a temperature of 30°C, horizontal and vertical behaviour are similar to that at 20°C, but the dominant mode starts lasing around 2.8 mA, increasing by 0.3 mA compared with the previous case. This indicates an increase in threshold current with increasing temperature. Nevertheless, at 40°C, the Hor mode output power is significantly reduced, with a peak just below 2 (V) at 5 mA, and the lasing threshold increases to ~ 3.4 mA. The Ver mode still gradually improves, reaching just above 0.5 V at 6 mA. The Hor mode demonstrates strong temperature dependence, with high output power at low temperatures, 10.5°C to 30°C, compared to the high temperature of 40°C, where a noticeable drop occurs at 40°C. Ver mode remains relatively stable across temperatures, but with low output power. Figure 1 (f) shows a comparison of efficiency for the two modes, Hor, the dominant mode, and Ver, the suppressed mode, as a function of temperature. The results indicate that efficiency drops as temperature increases, as follows: efficiencies of ~ 1.1 V/mA, 1.0 V/mA, 0.8 V/mA, and 0.8 V/mA at temperatures of 10.5°C, 15°C, 20°C and 30°C, respectively, then drops to ~ 0.4 V/mA at 40°C. Implies that the Hor mode (dominant mode) is more efficient but more sensitive to the temperature. Hor mode is most efficient at 10.5°C and 15°C, suggesting that these are the optimal operating temperatures for the lasing mode. Ver orientation consistently yields low efficiency across all temperatures. This reinforces the need for temperature control to maintain high performance in Hor mode. Extinction ratio calculations at free running We defined the extinction ratio (ER) as: \(\:\text{E}\text{R}=\left(\frac{{P}_{\text{Hor}\text{.}}}{{P}_{\text{Ver.}}}\right)\) . Figure 3 shows the ER vs. injection current for polarization mode of VCSEL under four conditions of temperature: 10.5°C (black), 20°C (red), 30°C (blue), 40°C (green). At low temperature (10.5°C ), very low ER is measured from 1–2.2 mA with almost no polarization preference. VCSEL emits around 2.2 mA with a high ER peak observed around 2.5 mA (~ 20 ), then falls back toward 0 for higher currents. Near threshold, the gain‑cavity alignment favours one polarization over a current range. This produces a stable single polarization region (mid‑current plateau). When the current increases, heating causes cavity detuning, reducing polarization preference and collapsing ER. At room temperature (20°C), the threshold point shifts forward to ~ 2.4 mA and the ER rises gradually to ~ 20–25 between 2.5–4 mA, then drops beyond ~ 4 mA again. The gain‑cavity alignment favours one polarization over a wider current range. This produces a stable region of single polarisation. When the injection current rises, it causes heating of the cavity, leading to detuning and collapse of ER. Elevating the temperature to 30°C yields the low ER at low current, indicating that both modes are nearly equal. After ~ 3 mA, ER rapidly rises with a very high peak (~ 80 ) compared with all curves, then an abrupt collapse happens after 4.5 mA. Once more, the threshold current shifts forward to ~ 2.9 mA. At 30°C, the VCSEL achieves optimal birefringence/gain alignment, yielding a pure-polarisation output over a small current range. At a high temperature of 40°C and a low current, the ER is low and noisy, with a peak > 40 at ~ 4.2 mA, then falls quickly afterwards, beyond 4.5 mA. As temperatures increase, the thermal redshift moves the cavity and gain curves apart, thereby increasing mode competition and polarisation fluctuations. The VCSEL temporarily stabilises a single polarisation mode (peak). But once the injection current increases further, excess heating of the cavity may lead to PS and reduce ER. The fact that the polarization extinction ratios below threshold are inconsistent is possibly due to the fact that temperature changes induce some strain in the mount, and the principal axis of the polarization changes slightly. This is exacerbated by the low signal-to-noise ratio in that regime and the extreme sensitivity to offset corrections (most apparent for the 30 o curve). 2. Effect of optical feedback on the L-I curve We study here the effect of weak polarised feedback, which may be caused by spurious reflections in an optical setup. Feedback at 90° means feedback on the Hor component, feedback at 0° refers to feedback on the Ver component, The behaviour of the Hor and Ver polarisation modes under OF of 0°, 45° and 90° of the polarisation angles operated at different temperature degrees is examined to provide an analysis of the OF effect on the L-I curve dynamics of the two polarization components depending on temperature. Figure 4 (a-d) shows the result of the polarisation resolved output power at a temperature of 10.5°C (a), 20°C (b), 30°C (c) and 40°C (d), Hor, and Ver, in solid lines and dashed lines, respectively, under conditions of Free-running, no feedback (black lines) and OF at 0° (green lines), 45° (blue lines), 90° (red lines). A threshold reduction can be found for applying feedback at 90° (Fig. 6 ). For other OF settings, no discernible reduction of threshold is found. At a temperature of 10.5°C and for the condition of free-running, Hor and Ver modes show a baseline behaviour of the laser without feedback, including a downward (upward) peak after a sharp decrease (increasing) around 5 mA, then going up (down) afterwards, respectively. Under the OF of 0°, Hor and Ver show a slight decrease (increase), respectively, in output power compared to the free-running status, especially at higher currents, but Ver mode remains lower than Hor mode. This suggests that at 0° of OF, Ver polarisation is enhanced, whereas the natural mode is reinforced. At 90°, Hor shows a strong increase in output power, whereas Ver mode is suppressed relative to the free-running and 0° OF counterparts. At 45 ° of OF, where the two modes gain similarity in OF power, the power level of the two modes is just between 0° and 90°. As a result, at 90°, the ASOOF favours the Hor polarisation mode, thereby enhancing the dominant mode and suppressing the Ver mode. At 20°C, similar dynamics were observed under free-running conditions, 0° OF, and 90° OF. Still, the peak and dip disappeared from the L-I curve, and strong fluctuations were observed for both polarisations at 0° OF near the low-current region. When the temperature increased to 30°C and 40°C, as shown in Figs. 4 (c) and (d), respectively, the overall output power of the system degraded, and the threshold current increased noticeably from 2.9 mA to 3.6 mA under free-running conditions at a temperature of 40°C. Similar trends were observed with OF, but with lower threshold-current values, as shown in Fig. 3 (a). Extinction ratio measurements with OF Extinction ratio measurements with OF ER measurement under different temperatures and OF display in Fig. 5 . A physics‑based explanation and comparative analysis of the ER of VCSEL polarization modes under OF at 0°, 45°, and 90° polarization angles at temperatures of 10°C (a), 20°C (b), 30°C (c), and 40°C (d) presented at (a-d), respectively. For 10°C (Feg. 5(a)) at free‑running, ER rises gradually to ~ 15–20 between 2.5–3.5 mA, indicating that moderate dominance of one polarization, no strong peaks, which means weak anisotropy at low temperature. Under 0° of OF, no noticeable threshold reduction happened over the free‑running and 45 °, but there is a reduction compared to 90 °. Otherwise, for low and high current, the ER nearly overlaps the free case, indicating that OF slightly enhances one polarization but does not significantly lock polarization at this temperature. While at 45°, a higher ER than 0° occurs, especially around ~ 2.2–4.5 mA. Because OF is split, leading to competition between the two modes. One mode becomes temporarily dominant, resulting in a moderate rise in ER. At 90° OF, the highest ER is observed (up to 35 ), and a broad region of enhanced ER is also observed, with small spikes. Attributed to injecting feedback into the orthogonal polarization forces a stronger separation between the orthogonal modes. At 20°C, as in Fig. 5 (b), the VCSEL illustrates a maximum ER and more stable polarization, particularly at 90° and 45° of OF between ~ 2.4–4.7 mA, peaks ~ 70 and > 100, respectively. For 0° OF, polarizations behaviours become noisy and unstable compared with the others, which leads to polarization jitter, modal instability and ER much worse than free‑running. This can be explained by the fact that reinforcing the suppressed polarisation leads to increased mode competition between the two modes. At room temperature, VCSEL shows the best polarisation stability, especially at 90 °, exceeding all other cases. Polarization stability gets more enhanced at 20°C, and OF plays a larger role compared to all cases. 90° OF yields exceptionally high ER (> 100), and 45° OF significantly improves ER, with clear separation between the two modes. Whereas at 0° OF, where the suppressed mode is enhanced, unstable behaviours occur due to mode competition. Thus, polarization‑selective OF at 90° is the most effective method for achieving a high ER and strong polarization locking in VCSELs, particularly near room temperature. The ER at 10°C and 40°C shows weaker polarisation stability than that at 20°C and 30°C. This can be attributed to low thermal birefringence and nonoptimal cavity gain alignment. Whiles, ER at 20°C and 30°C illustrate stronger levels. At 90 °, injecting feedback into the orthogonal polarization enhances the separation between the modes, with one dominant polarization at the expense of the other. This obviously gives 90° feedback the strongest polarization control. Figure 6 demonstrated the effects of temperature on the threshold current of the dominant polarization mode and, overall, on system performance in the free-running state and under OF application. The measured values of the threshold currents for a temperature range of 10.5°C to 40°C are plotted in Fig. 6 (a). As the temperature increases, the threshold current rises; the threshold value is lower at low temperatures. The threshold values are lower with OF than in free-running mode. The output power and efficiency decrease as the temperature increases from 10.5°C to 40°C, as shown in Fig. 6 (b). This is because increased temperature can affect the resonance alignment and gain of the laser cavity. Conclusion Over a temperature range of 10.5°C to 40°C, this experimental investigation analysed the influence of temperature on key parameters, namely threshold current, output power and efficiency, for the polarisation modes of a 780 nm VCSEL. The polarisation-dependent output performance of a VCSEL was evaluated using the L-I curve as a function of temperature, with and without the OF. The dominant mode (Hor mode) was significantly more efficient than the vertical mode; its threshold current and efficiency decreased as temperature increased. The Ver mode (suppressed mode) remained stable but inefficient across all temperatures. The dominant mode was highly efficient at lower temperatures but suffered a drop of more than 50% in efficiency at higher temperatures, reaching 40 °c. Additionally, the VCSEL was sensitive to the reflected light (OF), with the Hor mode’s linearity and efficiency enhanced with OF at 90° and losing those advantages at 0°. In contrast to the Hor polarisation mode, the Ver mode grew at 0°, leading to mode competition. High ER, more than 100, was achieved with 90 ° OF at room temperature. Polarization‑selective OF at 90° is the most effective method for achieving a high ER and strong polarization locking in VCSELs, particularly near room temperature. Temperature is a key factor in a laser’s performance and output power quality, which plays a role particularly with OF, in the laser properties. Declarations Ethics declarations The Author confirms that proper consideration has been given to any ethical issues raised Conflicts of interest The author declares no conflict of interest Funding Declaration There is no fund for the manuscript Author Contribution Salam Nazhan wrote the whole manuscript Acknowledgement The authors would like to thank Prof. Thorsten Ackemann of the University of Strathclyde /Glasgow, UK, for their invaluable discussions and for providing access to the laboratory facilities where the experimental results were obtained Data Availability declaration Data available on a reasonable request References P. Zhou et al. , "Application of VCSEL in bio-sensing atomic magnetometers," Biosensors , vol. 12, no. 12, p. 1098, 2022. G. Pan, M. Xun, X. Zhou, Y. Sun, Y. Dong, and D. Wu, "Harnessing the capabilities of VCSELs: unlocking the potential for advanced integrated photonic devices and systems," Light: Science & Applications , vol. 13, no. 1, p. 229, 2024. Y. Wang, Y. Zhang, C. Li, J. Li, X. Wei, and L. Chen, "Stable Single-Mode 795 nm Vertical-Cavity Surface-Emitting Laser for Quantum Sensing," Materials , vol. 17, no. 19, p. 4872, 2024. R. Michalzik, "VCSEL fundamentals," in VCSELs: fundamentals, technology and applications of vertical-cavity surface-emitting lasers : Springer, 2012, pp. 19–75. S. Mogg, N. Chitica, U. Christiansson, R. Schatz, P. Sundgren, C. Asplund, and M. Hammar, "Temperature sensitivity of the threshold current of long-wavelength InGaAs-GaAs VCSELs with large gain-cavity detuning," IEEE Journal of Quantum Electronics , vol. 40, no. 5, pp. 453–462, 2004. W. Miao et al. , "Gain spectrum engineering for temperature-insensitive 980 nm VCSEL performance using heterogeneous quantum wells," Results in Optics , p. 100912, 2025. G. Larisch, P. Moser, J. A. Lott, and D. Bimberg, "Impact of photon lifetime on the temperature stability of 50 Gb/s 980 nm VCSELs," IEEE Photonics Technology Letters , vol. 28, no. 21, pp. 2327–2330, 2016. T. Ackemann and M. Sondermann, "Polarization dynamics in vertical-cavity surface emitting lasers," arXiv preprint arXiv:2507.08672 , 2025. H. Lu, O. Alkhazragi, H. Lin, T. K. Ng, and B. S. Ooi, "Shaping the light of VCSELs through cavity geometry design," Light: Science & Applications , vol. 14, no. 1, p. 344, 2025. H. U. Rehman, W. Bi, F. Wang, and Y. Liu, "Performance Optimization of (InxGa1-xN QWs/GaN LQB) Structures for Vertical-Cavity Surface-Emitting Lasers," Journal of Luminescence , p. 121512, 2025. Z. Tang, C. Li, F. Zhao, J. Liu, A. Ren, H. Xu, and J. Wu, "Vertical-cavity surface-emitting laser linewidth narrowing enabled by internal-cavity engineering," IEEE Journal of Quantum Electronics , vol. 60, no. 2, pp. 1–8, 2024. R. Xu, K. Shibata, H. Akiyama, J. Zhang, L. Ying, and B. Zhang, "Low threshold lasing of GaN-based vertical-cavity surface-emitting lasers with thin InGaN/GaN quantum well active region," Optics & Laser Technology , vol. 182, p. 112117, 2025. S. Wu et al. , "Study of temperature effects on the design of active region for 808 nm high-power semiconductor laser," Crystals , vol. 13, no. 1, p. 85, 2023. S. Yurish, Advances in Optics: Reviews, Vol. 5 . IFSA Publishing, 2021. Y. Hong, P. S. Spencer, and K. A. Shore, "Suppression of polarization switching in vertical-cavity surface-emitting lasers by use of optical feedback," Optics Letters , vol. 29, no. 18, pp. 2151–2153, 2004/09/15 2004, doi: 10.1364/OL.29.002151 . S. Nazhan and T. Ackemann, "Below-threshold polarization behaviors of a VCSEL under external optical feedback," Journal of Optics , pp. 1–7, 2025. S. Nazhan, Z. Ghassemlooy, and K. Busawon, "Harmonic distortion dependent on optical feedback, temperature and injection current in a vertical cavity surface emitting laser," Journal of Physics D: Applied Physics , vol. 49, no. 14, p. 145107, 2016. P. Besnard, M. Chares, G. Stephan, and F. Robert, "Switching between polarized modes of a vertical-cavity surface-emitting laser by isotropic optical feedback," Journal of the Optical Society of America B , vol. 16, no. 7, pp. 1059–1063, 1999. H. Kazemi, I. N. Osahon, N. Ledentsov, I. Titkov, and H. Haas, "Achieving 70 Gb/s Over A VCSEL-Based Optical Wireless Link Using A Multi-Mode Fiber-Coupled Receiver," Journal of Lightwave Technology , 2025. S. Nazhan, Z. Ghassemlooy, K. Busawon, and A. Gholami, "Variable-polarization optical feedback induced high-quality polarization-resolved chaos synchronization in VCSEL," in 2015 Science and Information Conference (SAI) , 2015: IEEE, pp. 1052–1055. C. Chang-Hasnain, M. Orenstein, A. Von Lehmen, L. Florez, J. Harbison, and N. Stoffel, "Transverse mode characteristics of vertical cavity surface‐emitting lasers," Applied physics letters , vol. 57, no. 3, pp. 218–220, 1990. Y. G. Sanvert, J. Mercadier, S. Bittner, A. Valle, and M. Sciamanna, "Polarization and transverse-mode nonlinear dynamics in a multimode VCSEL," Optics Letters , vol. 50, no. 24, pp. 7645–7648, 2025. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 06 May, 2026 Editor assigned by journal 05 May, 2026 Submission checks completed at journal 05 May, 2026 First submitted to journal 23 Apr, 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-9511706","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":635553591,"identity":"b3bd0362-7e3b-40e9-a9a8-0a4213a1bac5","order_by":0,"name":"SALAM NAZHAN","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5UlEQVRIiWNgGAWjYFAC5gYwZcDAwPiAgeEAMVoY4VqYDUjWwiZBlBb59oONn24w3LE3Zz97rJqn5o4cPwPzw0c38GgxOJPYLJ3D8IzZsicv7TbPsWfGkg1sxsY5+LQwJDYAtRxmMziQY3abh+1w4oYDPGzS+LTI9z9s/g3UwmNw/o1ZMc8/IrQw3EhsA9kiYXAjx4yZt40ILQY3HrZZA7UYGNx4Yyw5t++wsWQzAb/I9ycfvg3UYm9wPsfww5tvh+X42ZsfPsbrMBBg/AehmXhAJDMh5Shaf5CiehSMglEwCkYMAAAJyE26WWGn5AAAAABJRU5ErkJggg==","orcid":"","institution":"University of Diyala","correspondingAuthor":true,"prefix":"","firstName":"SALAM","middleName":"","lastName":"NAZHAN","suffix":""}],"badges":[],"createdAt":"2026-04-24 03:09:50","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9511706/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9511706/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109331854,"identity":"7ac0ee88-0d6e-4aa7-a827-78eca3b74ae4","added_by":"auto","created_at":"2026-05-15 16:10:35","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":31229,"visible":true,"origin":"","legend":"\u003cp\u003eOptical experimental setup\u003c/p\u003e","description":"","filename":"groupimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9511706/v1/3107358aead1a4835f0fb227.jpeg"},{"id":109331855,"identity":"e6dc2a56-7eaa-41d9-ab4a-a031fee22830","added_by":"auto","created_at":"2026-05-15 16:10:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":68734,"visible":true,"origin":"","legend":"\u003cp\u003eER measurements of polarization mode of free-running VCSEL vs. injection current under four conditions of temperatures: 10.5 °C (black), 20 °C (red), 30 °C (blue), 40 °C (green).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9511706/v1/a25adaf63aeae7921906812e.png"},{"id":109331857,"identity":"440ec82f-dea5-45c4-b9d6-f983fe651aa1","added_by":"auto","created_at":"2026-05-15 16:10:35","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":66322,"visible":true,"origin":"","legend":"\u003cp\u003eER measurements of polarization mode vs. injection current under four conditions of temperatures: 10.5 °C (a), 20 °C (b), 30 °C (c), 40 °C (d), at free running (black) and at polarization angles OF of 0 ° (green), 45 ° (blue), 90 ° (red).\u003c/p\u003e","description":"","filename":"groupimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9511706/v1/c31e2027ee5217482943690b.jpeg"},{"id":109405760,"identity":"f55b697c-782e-4bde-aab1-87ed4aa1797e","added_by":"auto","created_at":"2026-05-17 13:20:05","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":27709,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Threshold current changes at different temperatures of the dominant mode in the case of free running and optical feedback at 90 °, (b) efficiency of total power of VCSEL at free running and OF versus temperature\u003c/p\u003e","description":"","filename":"groupimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9511706/v1/40b8d95262c25c9c588736de.jpeg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Temperature-dependence of 780 nm VCSEL polarization output power and efficiency with and without optical feedback","fulltext":[{"header":"Introduction","content":"\u003cp\u003eVertical-cavity surface-emitting laser (VCSEL) is a semiconductor laser with unique features, including a low threshold current, high efficiency, a narrow, low-divergence beam, and circular emission, which make these devices favoured for a wide range of applications. Industrial and scientific applications, including sensing, imaging, scanning, small, low-power atomic sensors, magnetometers, and gyroscopes, require high-reliability and stable output power despite temperature changes and fluctuations [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. VCSEL achieved a side-mode suppression ratio of more than 40 dB over a temperature range of 25\u0026deg;C\u0026thinsp;~\u0026thinsp;85\u0026deg;C, maintaining stable single-mode emission at 794.8 nm. Output power, polarisation purity, and side-mode suppression ratio of a VCSEL are crucial factors to consider, particularly with respect to current and temperature. Such parameters are important when evaluating a laser's performance, as they significantly affect the quality of the laser's output.\u003c/p\u003e \u003cp\u003eThe temperature-dependent factors that contribute to the VCSEL characteristics are Auger recombination, optical loss and gain, carrier leakage and threshold current as reported in [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The temperature effects of the dynamics of VCSELs have been widely studied in the literature [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The dynamics of a 980 nm VCSEL showed wavelength stability over a wide temperature range. The VCSEL cavity is nearly cylindrically symmetric, offering no strong intrinsic polarization‑selective mechanism. Therefore, polarisation instabilities are widely observed in the output power of such devices. As temperature varies, the gain spectrum, cavity resonance, birefringence, and carrier‑related effects fluctuate, often leading to abrupt polarisation switching (PS), mode hopping, or elliptically polarised transient states. These states may occur with injection current and temperature because the polarization‑mode differential gain and losses change [8{Choquette, 2002 #60]}. Temperature studies and investigations into laser performance and dynamics contribute to the formation of VCSEL cavities for efficient operation. These studies concluded that laser performance fluctuations are mainly due to variations in cavity gain, with other factors remaining relatively constant.\u003c/p\u003e \u003cp\u003eOn the other hand, VCSELs are highly sensitive to optical feedback (OF) [\u003cspan additionalcitationids=\"CR10 CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Laser operation at a low temperature allows an increase in the mode gain of the active region and a decrease in the accumulation of free electrons, which leads to a reduction in the threshold current and an upsurge in the slope efficiency, thereby increasing the power and electro-optical conversion efficiency [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. OF occurs when a portion of the emitted light is reflected into the VCSEL cavity. This can happen intentionally, e.g. via external mirrors or unintentionally from nearby surfaces [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. VCSELs often establish two orthogonal polarisation modes, horizontal (Hor) and vertical (Ver). OF can enhance one mode while suppressing the other, depending on the OF strength and polarisation angle [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. This can be useful for the application of polarisation switching or laser output stabilisation [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Additionally, the polarisation of light in a VCSEL subjected to isotropic OF can be regularly switched between two orthogonal polarisation states as the injection current increases. This enables the polarisation L-I characteristics channelled [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. OF reduces the threshold current and spectral linewidth, improving coherence, which makes VCSELs more energy-efficient and suitable for high-resolution sensing and communication [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Furthermore, this technique induced chaotic dynamics in the VCSEL, which is essential for secure communication applications [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. One important laser characteristic is the light output power as a function of injected current (L-I curve). This can be used to identify several substantial parameters, including threshold current, differential responsivity, and internal and external quantum efficiency. The L-I curve can show linear fluctuation, or sudden jumps (polarization switching) or stability (polarization bi-stability) due to a change in internal cavity gain, particularly leading to polarisation mode hopping.\u003c/p\u003e \u003cp\u003eGenerally, higher temperatures increase threshold current, resulting in decreased slope efficiency, which requires thermal control. Testing the L-I curve ensures that VCSELs meet the requirements for different applications in terms of high performance and reliability. In addition, control of polarisation is useful in optical communication systems, polarisation-sensitive imaging, laser stabilisation, and polarisation mode selection, where polarisation purity or switching control is critical. This work offers valuable insights into the L-I properties of 780 nm VCSELs, in terms of temperature sensitivity and operational stability, which are essential components in temperature-sensitive applications, such as optical communication systems, enabling high performance across a wide range of temperatures. It also contributes to the design and optimisation of VCSEL structures.\u003c/p\u003e"},{"header":"Experimental setup","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the experimental setup, including the following: light source (VCSEL), Lens (L) to focus the output of the VCSEL. The collimated beam passes through a half-wave plate (HWP) to rotate the polarization of the beam to the desired angle before entering a 50/50 non-polarizing beam splitter (BS). The BS splits the beam into a reflected beam and a transmitted beam. The reflected beam goes to the mirror (M) through a polarizer (P) to select the OF states, and the transmitted beam travels to the measurement section. The transmitted beam passes through a Wollaston prism (WP), which divides the beam into vertical (Ver) and horizontal (Hor) beams. A beam splitter (BS) is used to direct the beam into the detector (D) and to a fibre coupler (FC), passing through an optical isolator (IS) and lenses. Part of the beam is directed to the camera (CCD) through a filter (F).\u003c/p\u003e \u003cp\u003eOutput instruments feed different analysis devices: Computer (Com) and Optical Spectrum Analyzer (OSA). The output of the detectors is recorded by an analogue IO-card (Labview PCI-6036E, 16-bit). The angle of the HWP is adjusted such that the emission of the polarization components along the principal axes of the VCSEL is turned to the horizontal and vertical, i.e. the principal axes of the beam splitter cube and the analysing Wollaston prism. We will refer to these as Hor and Ver in the following.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results","content":" \u003cp\u003e \u003cb\u003e1. Temperature effect on the L-I curve at free running\u003c/b\u003e \u003c/p\u003e \u003cp\u003eIn the free-running operation of the VCSEL, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the relationship between injection current and output power for two polarisation states: Hor mode (black line) and Ver mode (red line), under free-running conditions at different temperatures of 10.5\u0026deg;C, 15\u0026deg;C, 20\u0026deg;C, 30\u0026deg;C, and 40\u0026deg;C, presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a-e) respectively. At 10.5\u0026deg;C. The polarisation component begins to lase around 2 mA. The horizontal (Hor) mode remains dominant across the entire bias-current range, whereas the output power of the orthogonal polarisation component remains low, despite increasing gradually with current. From 4.3 to 5 mA, the power in the Hor polarization drops significantly, whereas the power in the Ver increases, but the Hor polarization stays dominant. At around 5 mA, there is a very abrupt switch to a strong dominance of the Hor again. The kinks and abrupt switches in the L-I curve indicate instabilities and mode competition. Indeed, observations with a CCD camera and the OSA indicate the excitation of multiple high-order modes. As higher‑order transverse modes turn on, abrupt transitions occur in the output power and modal behaviour, which exactly reflects the behaviour of L-I curve discontinuities, indicating mode competition [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Theoretical analysis of multimode VCSELs demonstrates competition among transverse modes with different polarisations, leading to complex dynamics, including polarisation switching, mode competition, chaos, and additional bifurcations [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAt 15\u0026deg;C, a similar behaviour is observed, but threshold and switching points are shifted by about 0.2 mA to higher currents, as one can expect from heating a semiconductor laser. At a temperature of 20\u0026deg;C, the Hor mode starts lasing around 2.5 mA, reaching a maximum power of 4 (V) at 5 mA, while the Ver mode gradually increases after 4 mA reaches just above 0.5 (V) at 6 mA. At a temperature of 30\u0026deg;C, horizontal and vertical behaviour are similar to that at 20\u0026deg;C, but the dominant mode starts lasing around 2.8 mA, increasing by 0.3 mA compared with the previous case. This indicates an increase in threshold current with increasing temperature. Nevertheless, at 40\u0026deg;C, the Hor mode output power is significantly reduced, with a peak just below 2 (V) at 5 mA, and the lasing threshold increases to ~\u0026thinsp;3.4 mA. The Ver mode still gradually improves, reaching just above 0.5 V at 6 mA.\u003c/p\u003e \u003cp\u003eThe Hor mode demonstrates strong temperature dependence, with high output power at low temperatures, 10.5\u0026deg;C to 30\u0026deg;C, compared to the high temperature of 40\u0026deg;C, where a noticeable drop occurs at 40\u0026deg;C. Ver mode remains relatively stable across temperatures, but with low output power. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (f) shows a comparison of efficiency for the two modes, Hor, the dominant mode, and Ver, the suppressed mode, as a function of temperature. The results indicate that efficiency drops as temperature increases, as follows: efficiencies of ~\u0026thinsp;1.1 V/mA, 1.0 V/mA, 0.8 V/mA, and 0.8 V/mA at temperatures of 10.5\u0026deg;C, 15\u0026deg;C, 20\u0026deg;C and 30\u0026deg;C, respectively, then drops to ~\u0026thinsp;0.4 V/mA at 40\u0026deg;C. Implies that the Hor mode (dominant mode) is more efficient but more sensitive to the temperature. Hor mode is most efficient at 10.5\u0026deg;C and 15\u0026deg;C, suggesting that these are the optimal operating temperatures for the lasing mode. Ver orientation consistently yields low efficiency across all temperatures. This reinforces the need for temperature control to maintain high performance in Hor mode.\u003c/p\u003e\n\u003ch3\u003eExtinction ratio calculations at free running\u003c/h3\u003e\n\u003cp\u003eWe defined the extinction ratio (ER) as: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{E}\\text{R}=\\left(\\frac{{P}_{\\text{Hor}\\text{.}}}{{P}_{\\text{Ver.}}}\\right)\\)\u003c/span\u003e\u003c/span\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the ER vs. injection current for polarization mode of VCSEL under four conditions of temperature: 10.5\u0026deg;C (black), 20\u0026deg;C (red), 30\u0026deg;C (blue), 40\u0026deg;C (green). At low temperature (10.5\u0026deg;C ), very low ER is measured from 1\u0026ndash;2.2 mA with almost no polarization preference. VCSEL emits around 2.2 mA with a high ER peak observed around 2.5 mA (~\u0026thinsp;20 ), then falls back toward 0 for higher currents. Near threshold, the gain‑cavity alignment favours one polarization over a current range. This produces a stable single polarization region (mid‑current plateau). When the current increases, heating causes cavity detuning, reducing polarization preference and collapsing ER.\u003c/p\u003e \u003cp\u003eAt room temperature (20\u0026deg;C), the threshold point shifts forward to ~\u0026thinsp;2.4 mA and the ER rises gradually to ~\u0026thinsp;20\u0026ndash;25 between 2.5\u0026ndash;4 mA, then drops beyond ~\u0026thinsp;4 mA again. The gain‑cavity alignment favours one polarization over a wider current range. This produces a stable region of single polarisation. When the injection current rises, it causes heating of the cavity, leading to detuning and collapse of ER. Elevating the temperature to 30\u0026deg;C yields the low ER at low current, indicating that both modes are nearly equal. After ~\u0026thinsp;3 mA, ER rapidly rises with a very high peak (~\u0026thinsp;80 ) compared with all curves, then an abrupt collapse happens after 4.5 mA. Once more, the threshold current shifts forward to ~\u0026thinsp;2.9 mA. At 30\u0026deg;C, the VCSEL achieves optimal birefringence/gain alignment, yielding a pure-polarisation output over a small current range. At a high temperature of 40\u0026deg;C and a low current, the ER is low and noisy, with a peak\u0026thinsp;\u0026gt;\u0026thinsp;40 at ~\u0026thinsp;4.2 mA, then falls quickly afterwards, beyond 4.5 mA. As temperatures increase, the thermal redshift moves the cavity and gain curves apart, thereby increasing mode competition and polarisation fluctuations.\u003c/p\u003e \u003cp\u003e The VCSEL temporarily stabilises a single polarisation mode (peak). But once the injection current increases further, excess heating of the cavity may lead to PS and reduce ER. The fact that the polarization extinction ratios below threshold are inconsistent is possibly due to the fact that temperature changes induce some strain in the mount, and the principal axis of the polarization changes slightly. This is exacerbated by the low signal-to-noise ratio in that regime and the extreme sensitivity to offset corrections (most apparent for the 30\u003csup\u003eo\u003c/sup\u003e curve).\u003c/p\u003e \u003cp\u003e \u003cb\u003e2. Effect of optical feedback on the L-I curve\u003c/b\u003e \u003c/p\u003e\u003cp\u003eWe study here the effect of weak polarised feedback, which may be caused by spurious reflections in an optical setup. Feedback at 90\u0026deg; means feedback on the Hor component, feedback at 0\u0026deg; refers to feedback on the Ver component, The behaviour of the Hor and Ver polarisation modes under OF of 0\u0026deg;, 45\u0026deg; and 90\u0026deg; of the polarisation angles operated at different temperature degrees is examined to provide an analysis of the OF effect on the L-I curve dynamics of the two polarization components depending on temperature. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a-d) shows the result of the polarisation resolved output power at a temperature of 10.5\u0026deg;C (a), 20\u0026deg;C (b), 30\u0026deg;C (c) and 40\u0026deg;C (d), Hor, and Ver, in solid lines and dashed lines, respectively, under conditions of Free-running, no feedback (black lines) and OF at 0\u0026deg; (green lines), 45\u0026deg; (blue lines), 90\u0026deg; (red lines).\u003c/p\u003e \u003cp\u003eA threshold reduction can be found for applying feedback at 90\u0026deg; (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). For other OF settings, no discernible reduction of threshold is found. At a temperature of 10.5\u0026deg;C and for the condition of free-running, Hor and Ver modes show a baseline behaviour of the laser without feedback, including a downward (upward) peak after a sharp decrease (increasing) around 5 mA, then going up (down) afterwards, respectively. Under the OF of 0\u0026deg;, Hor and Ver show a slight decrease (increase), respectively, in output power compared to the free-running status, especially at higher currents, but Ver mode remains lower than Hor mode. This suggests that at 0\u0026deg; of OF, Ver polarisation is enhanced, whereas the natural mode is reinforced. At 90\u0026deg;, Hor shows a strong increase in output power, whereas Ver mode is suppressed relative to the free-running and 0\u0026deg; OF counterparts. At 45 \u0026deg; of OF, where the two modes gain similarity in OF power, the power level of the two modes is just between 0\u0026deg; and 90\u0026deg;. As a result, at 90\u0026deg;, the ASOOF favours the Hor polarisation mode, thereby enhancing the dominant mode and suppressing the Ver mode.\u003c/p\u003e \u003cp\u003eAt 20\u0026deg;C, similar dynamics were observed under free-running conditions, 0\u0026deg; OF, and 90\u0026deg; OF. Still, the peak and dip disappeared from the L-I curve, and strong fluctuations were observed for both polarisations at 0\u0026deg; OF near the low-current region. When the temperature increased to 30\u0026deg;C and 40\u0026deg;C, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c) and (d), respectively, the overall output power of the system degraded, and the threshold current increased noticeably from 2.9 mA to 3.6 mA under free-running conditions at a temperature of 40\u0026deg;C. Similar trends were observed with OF, but with lower threshold-current values, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a).\u003c/p\u003e\n\u003ch3\u003eExtinction ratio measurements with OF\u003c/h3\u003e\n\u003cdiv class=\"Heading\"\u003eExtinction ratio measurements with OF\u003c/div\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eER measurement under different temperatures and OF display in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. A physics‑based explanation and comparative analysis of the ER of VCSEL polarization modes under OF at 0\u0026deg;, 45\u0026deg;, and 90\u0026deg; polarization angles at temperatures of 10\u0026deg;C (a), 20\u0026deg;C (b), 30\u0026deg;C (c), and 40\u0026deg;C (d) presented at (a-d), respectively. For 10\u0026deg;C (Feg. 5(a)) at free‑running, ER rises gradually to ~\u0026thinsp;15\u0026ndash;20 between 2.5\u0026ndash;3.5 mA, indicating that moderate dominance of one polarization, no strong peaks, which means weak anisotropy at low temperature. Under 0\u0026deg; of OF, no noticeable threshold reduction happened over the free‑running and 45 \u0026deg;, but there is a reduction compared to 90 \u0026deg;. Otherwise, for low and high current, the ER nearly overlaps the free case, indicating that OF slightly enhances one polarization but does not significantly lock polarization at this temperature. While at 45\u0026deg;, a higher ER than 0\u0026deg; occurs, especially around ~\u0026thinsp;2.2\u0026ndash;4.5 mA. Because OF is split, leading to competition between the two modes. One mode becomes temporarily dominant, resulting in a moderate rise in ER. At 90\u0026deg; OF, the highest ER is observed (up to 35 ), and a broad region of enhanced ER is also observed, with small spikes. Attributed to injecting feedback into the orthogonal polarization forces a stronger separation between the orthogonal modes.\u003c/p\u003e \u003cp\u003eAt 20\u0026deg;C, as in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e (b), the VCSEL illustrates a maximum ER and more stable polarization, particularly at 90\u0026deg; and 45\u0026deg; of OF between ~\u0026thinsp;2.4\u0026ndash;4.7 mA, peaks\u0026thinsp;~\u0026thinsp;70 and \u0026gt;\u0026thinsp;100, respectively. For 0\u0026deg; OF, polarizations behaviours become noisy and unstable compared with the others, which leads to polarization jitter, modal instability and ER much worse than free‑running. This can be explained by the fact that reinforcing the suppressed polarisation leads to increased mode competition between the two modes. At room temperature, VCSEL shows the best polarisation stability, especially at 90 \u0026deg;, exceeding all other cases. Polarization stability gets more enhanced at 20\u0026deg;C, and OF plays a larger role compared to all cases. 90\u0026deg; OF yields exceptionally high ER (\u0026gt;\u0026thinsp;100), and 45\u0026deg; OF significantly improves ER, with clear separation between the two modes. Whereas at 0\u0026deg; OF, where the suppressed mode is enhanced, unstable behaviours occur due to mode competition. Thus, polarization‑selective OF at 90\u0026deg; is the most effective method for achieving a high ER and strong polarization locking in VCSELs, particularly near room temperature.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe ER at 10\u0026deg;C and 40\u0026deg;C shows weaker polarisation stability than that at 20\u0026deg;C and 30\u0026deg;C. This can be attributed to low thermal birefringence and nonoptimal cavity gain alignment. Whiles, ER at 20\u0026deg;C and 30\u0026deg;C illustrate stronger levels. At 90 \u0026deg;, injecting feedback into the orthogonal polarization enhances the separation between the modes, with one dominant polarization at the expense of the other. This obviously gives 90\u0026deg; feedback the strongest polarization control. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e demonstrated the effects of temperature on the threshold current of the dominant polarization mode and, overall, on system performance in the free-running state and under OF application. The measured values of the threshold currents for a temperature range of 10.5\u0026deg;C to 40\u0026deg;C are plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (a).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs the temperature increases, the threshold current rises; the threshold value is lower at low temperatures. The threshold values are lower with OF than in free-running mode. The output power and efficiency decrease as the temperature increases from 10.5\u0026deg;C to 40\u0026deg;C, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (b). This is because increased temperature can affect the resonance alignment and gain of the laser cavity.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eOver a temperature range of 10.5\u0026deg;C to 40\u0026deg;C, this experimental investigation analysed the influence of temperature on key parameters, namely threshold current, output power and efficiency, for the polarisation modes of a 780 nm VCSEL. The polarisation-dependent output performance of a VCSEL was evaluated using the L-I curve as a function of temperature, with and without the OF. The dominant mode (Hor mode) was significantly more efficient than the vertical mode; its threshold current and efficiency decreased as temperature increased. The Ver mode (suppressed mode) remained stable but inefficient across all temperatures. The dominant mode was highly efficient at lower temperatures but suffered a drop of more than 50% in efficiency at higher temperatures, reaching 40 \u0026deg;c.\u003c/p\u003e \u003cp\u003eAdditionally, the VCSEL was sensitive to the reflected light (OF), with the Hor mode\u0026rsquo;s linearity and efficiency enhanced with OF at 90\u0026deg; and losing those advantages at 0\u0026deg;. In contrast to the Hor polarisation mode, the Ver mode grew at 0\u0026deg;, leading to mode competition. High ER, more than 100, was achieved with 90 \u0026deg; OF at room temperature. Polarization‑selective OF at 90\u0026deg; is the most effective method for achieving a high ER and strong polarization locking in VCSELs, particularly near room temperature. Temperature is a key factor in a laser\u0026rsquo;s performance and output power quality, which plays a role particularly with OF, in the laser properties.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eEthics declarations\u003c/h2\u003e \u003cp\u003eThe Author confirms that proper consideration has been given to any ethical issues raised\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eConflicts of interest\u003c/h2\u003e \u003cp\u003eThe author declares no conflict of interest\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding Declaration\u003c/h2\u003e \u003cp\u003eThere is no fund for the manuscript\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eSalam Nazhan wrote the whole manuscript\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors would like to thank Prof. Thorsten Ackemann of the University of Strathclyde /Glasgow, UK, for their invaluable discussions and for providing access to the laboratory facilities where the experimental results were obtained\u003c/p\u003e\u003ch2\u003eData Availability declaration\u003c/h2\u003e\u003cp\u003eData available on a reasonable request\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eP. Zhou \u003cem\u003eet al.\u003c/em\u003e, \"Application of VCSEL in bio-sensing atomic magnetometers,\" \u003cem\u003eBiosensors\u003c/em\u003e, vol. 12, no. 12, p. 1098, 2022.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eG. Pan, M. Xun, X. Zhou, Y. Sun, Y. Dong, and D. Wu, \"Harnessing the capabilities of VCSELs: unlocking the potential for advanced integrated photonic devices and systems,\" \u003cem\u003eLight: Science \u0026amp; Applications\u003c/em\u003e, vol. 13, no. 1, p. 229, 2024.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eY. Wang, Y. Zhang, C. Li, J. Li, X. Wei, and L. Chen, \"Stable Single-Mode 795 nm Vertical-Cavity Surface-Emitting Laser for Quantum Sensing,\" \u003cem\u003eMaterials\u003c/em\u003e, vol. 17, no. 19, p. 4872, 2024.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eR. Michalzik, \"VCSEL fundamentals,\" in \u003cem\u003eVCSELs: fundamentals, technology and applications of vertical-cavity surface-emitting lasers\u003c/em\u003e: Springer, 2012, pp. 19\u0026ndash;75.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eS. Mogg, N. Chitica, U. Christiansson, R. Schatz, P. Sundgren, C. Asplund, and M. Hammar, \"Temperature sensitivity of the threshold current of long-wavelength InGaAs-GaAs VCSELs with large gain-cavity detuning,\" \u003cem\u003eIEEE Journal of Quantum Electronics\u003c/em\u003e, vol. 40, no. 5, pp. 453\u0026ndash;462, 2004.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eW. Miao \u003cem\u003eet al.\u003c/em\u003e, \"Gain spectrum engineering for temperature-insensitive 980 nm VCSEL performance using heterogeneous quantum wells,\" \u003cem\u003eResults in Optics\u003c/em\u003e, p. 100912, 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eG. Larisch, P. Moser, J. A. Lott, and D. Bimberg, \"Impact of photon lifetime on the temperature stability of 50 Gb/s 980 nm VCSELs,\" \u003cem\u003eIEEE Photonics Technology Letters\u003c/em\u003e, vol. 28, no. 21, pp. 2327\u0026ndash;2330, 2016.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eT. Ackemann and M. Sondermann, \"Polarization dynamics in vertical-cavity surface emitting lasers,\" \u003cem\u003earXiv preprint arXiv:2507.08672\u003c/em\u003e, 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eH. Lu, O. Alkhazragi, H. Lin, T. K. Ng, and B. S. Ooi, \"Shaping the light of VCSELs through cavity geometry design,\" \u003cem\u003eLight: Science \u0026amp; Applications\u003c/em\u003e, vol. 14, no. 1, p. 344, 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eH. U. Rehman, W. Bi, F. Wang, and Y. Liu, \"Performance Optimization of (InxGa1-xN QWs/GaN LQB) Structures for Vertical-Cavity Surface-Emitting Lasers,\" \u003cem\u003eJournal of Luminescence\u003c/em\u003e, p. 121512, 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZ. Tang, C. Li, F. Zhao, J. Liu, A. Ren, H. Xu, and J. Wu, \"Vertical-cavity surface-emitting laser linewidth narrowing enabled by internal-cavity engineering,\" \u003cem\u003eIEEE Journal of Quantum Electronics\u003c/em\u003e, vol. 60, no. 2, pp. 1\u0026ndash;8, 2024.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eR. Xu, K. Shibata, H. Akiyama, J. Zhang, L. Ying, and B. Zhang, \"Low threshold lasing of GaN-based vertical-cavity surface-emitting lasers with thin InGaN/GaN quantum well active region,\" \u003cem\u003eOptics \u0026amp; Laser Technology\u003c/em\u003e, vol. 182, p. 112117, 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eS. Wu \u003cem\u003eet al.\u003c/em\u003e, \"Study of temperature effects on the design of active region for 808 nm high-power semiconductor laser,\" \u003cem\u003eCrystals\u003c/em\u003e, vol. 13, no. 1, p. 85, 2023.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eS. Yurish, \u003cem\u003eAdvances in Optics: Reviews, Vol. 5\u003c/em\u003e. IFSA Publishing, 2021.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eY. Hong, P. S. Spencer, and K. A. Shore, \"Suppression of polarization switching in vertical-cavity surface-emitting lasers by use of optical feedback,\" \u003cem\u003eOptics Letters\u003c/em\u003e, vol. 29, no. 18, pp. 2151\u0026ndash;2153, 2004/09/15 2004, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1364/OL.29.002151\u003c/span\u003e\u003cspan address=\"10.1364/OL.29.002151\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eS. Nazhan and T. Ackemann, \"Below-threshold polarization behaviors of a VCSEL under external optical feedback,\" \u003cem\u003eJournal of Optics\u003c/em\u003e, pp. 1\u0026ndash;7, 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eS. Nazhan, Z. Ghassemlooy, and K. Busawon, \"Harmonic distortion dependent on optical feedback, temperature and injection current in a vertical cavity surface emitting laser,\" \u003cem\u003eJournal of Physics D: Applied Physics\u003c/em\u003e, vol. 49, no. 14, p. 145107, 2016.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eP. Besnard, M. Chares, G. Stephan, and F. Robert, \"Switching between polarized modes of a vertical-cavity surface-emitting laser by isotropic optical feedback,\" \u003cem\u003eJournal of the Optical Society of America B\u003c/em\u003e, vol. 16, no. 7, pp. 1059\u0026ndash;1063, 1999.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eH. Kazemi, I. N. Osahon, N. Ledentsov, I. Titkov, and H. Haas, \"Achieving 70 Gb/s Over A VCSEL-Based Optical Wireless Link Using A Multi-Mode Fiber-Coupled Receiver,\" \u003cem\u003eJournal of Lightwave Technology\u003c/em\u003e, 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eS. Nazhan, Z. Ghassemlooy, K. Busawon, and A. Gholami, \"Variable-polarization optical feedback induced high-quality polarization-resolved chaos synchronization in VCSEL,\" in \u003cem\u003e2015 Science and Information Conference (SAI)\u003c/em\u003e, 2015: IEEE, pp. 1052\u0026ndash;1055.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eC. Chang-Hasnain, M. Orenstein, A. Von Lehmen, L. Florez, J. Harbison, and N. Stoffel, \"Transverse mode characteristics of vertical cavity surface‐emitting lasers,\" \u003cem\u003eApplied physics letters\u003c/em\u003e, vol. 57, no. 3, pp. 218\u0026ndash;220, 1990.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eY. G. Sanvert, J. Mercadier, S. Bittner, A. Valle, and M. Sciamanna, \"Polarization and transverse-mode nonlinear dynamics in a multimode VCSEL,\" \u003cem\u003eOptics Letters\u003c/em\u003e, vol. 50, no. 24, pp. 7645\u0026ndash;7648, 2025.\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":false,"isWithdrawnOrRetracted":false,"journal":{"display":false,"email":"","identity":"journal-of-russian-laser-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Journal of Russian Laser Research","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"VoR Journals","inReviewEnabled":false,"inReviewRevisionsEnabled":false},"keywords":"VCSEL, Temperature effect, optical feedback, L-I curve, polarization, threshold current","lastPublishedDoi":"10.21203/rs.3.rs-9511706/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9511706/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study presents an experimental investigation of the effects of temperature on the light-current (L-I) characteristics of the polarisation-resolved output of a 780 nm vertical-cavity surface-emitting laser (VCSEL), both in free-running operation and with optical feedback (OF). The results show that as temperature increases from low to room temperature, the linearity of the polarisation behaviour with OF is enhanced, and the polarization extinction ratio (ER) reaches a maximum. ER collapses for both low and high temperatures. The lasing mode (dominant mode) is more efficient but more sensitive to temperature. Linearity and ER between the two modes increase depending on the OF polarisation degree. OF plays a larger role at and near room temperature than at any other temperature. 90\u0026deg; OF yields exceptionally high ER (\u0026gt;\u0026thinsp;100) with enhancement of polarization, and 45\u0026deg; OF significantly improves ER, with clear separation between the two modes. Knowledge of polarisation mode selection in such devices is valuable for applications in optical communications and polarisation-sensitive imaging.\u003c/p\u003e","manuscriptTitle":"Temperature-dependence of 780 nm VCSEL polarization output power and efficiency with and without optical feedback","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-15 16:10:28","doi":"10.21203/rs.3.rs-9511706/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-05-06T13:35:42+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-05-05T23:12:39+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-05-05T23:12:15+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Russian Laser Research","date":"2026-04-24T02:55:48+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":false,"email":"","identity":"journal-of-russian-laser-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Journal of Russian Laser Research","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"VoR Journals","inReviewEnabled":false,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d110c6b2-9712-4fbd-93ab-0d3e1941d709","owner":[],"postedDate":"May 15th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewersInvited","content":"1","date":"2026-05-06T13:35:42+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-05-05T23:12:39+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-05-05T23:12:15+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-15T16:10:28+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-15 16:10:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9511706","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9511706","identity":"rs-9511706","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}