Photonics

The increasing power consumption and intensified thermal coupling in next-generation high-speed optical interconnect modules present severe thermal management challenges. To address these issues, we propose a high-precision lumped-parameter thermal modeling method for optical interconnect modules. Building upon the constructed lumped-parameter thermal model (LPTM), a real-time transient temperature prediction framework utilizing a hybrid convolutional neural network and long short-term memory (CNN-LSTM) architecture is developed. The LPTM achieves high-precision modeling while reducing computational complexity. Compared with the simulation results from COMSOL Multiphysics 6.3, the proposed LPTM model exhibits an average mean absolute error (MAE) of only 0.52 $°\mathrm{C}$ and an average root mean square error (RMSE) of only 0.69 $°\mathrm{C}$ for the transient temperatures of key components. Furthermore, the CNN-LSTM neural network, trained on the dataset generated by the LPTM, achieves an MAE of 0.34 $°\mathrm{C}$ and an RMSE of 0.78 $°\mathrm{C}$ on an independent transient temperature testset generated by COMSOL Multiphysics. The proposed methodology successfully achieves both high-precision modeling and real-time, accurate transient temperature prediction, providing a solid theoretical foundation for thermal management in next-generation optical interconnect systems.

We demonstrate an all-fiber polarization-maintaining (PM) single-cavity dual-comb fiber laser based on intracavity polarization multiplexing. Two pulse trains share a common cavity section while two partially non-common branches provide independent gain, spectral filtering, and cavity-length control. The repetition rates are approximately 37.281 and 37.270 MHz, giving a repetition-rate difference of about 11 kHz. With radio-frequency (RF)-referenced repetition-rate stabilization, the 1 h standard deviations of $f_{\mathrm{rep}1}$, $f_{\mathrm{rep}2}$, and $\Delta f_{\mathrm{rep}}$, measured with a 1 s gate time, are 290, 178, and 342 $\mathsf{\mu }$Hz, respectively, corresponding to fluctuation-suppression factors of $6.3\times {10}^5$, $1.2\times {10}^6$, and $4.4\times {10}^5$ relative to free-running operation. Stable dual-comb operation is also obtained at discrete, fiber-length-customized working points near 4, 11, and 43 kHz. Autocorrelation measurements give pulse durations of 30.02 and 36.39 ps for the two outputs. A free-space ranging demonstration at $\Delta f_{\mathrm{rep}}=4$ kHz yields a precision of 96.3 $\mathsf{\mu }$m at a 250 $\mathsf{\mu }$s update time, which improves to 2.7 $\mathsf{\mu }$m after averaging 400 points (100 ms). The proposed architecture combines all-fiber PM propagation, branch-level controllability, and RF-referenced repetition-rate stabilization in one single-cavity platform.

Visible light communication (VLC) is inherently a broadcast medium, since any receiver inside the illuminated volume can capture the transmitted signal. Physical layer security exploits the asymmetry between the legitimate and eavesdropping channels, yet lighting design pursues a uniform illumination that suppresses exactly this asymmetry. This paper quantifies the resulting trade-off for three luminaire layouts, namely four symmetric clusters, a single central cluster and a distributed grid, in a 5 m × 5 m × 3 m room, under an amplitude-constrained Gaussian wiretap model and a lower bound on the secrecy capacity. Unlike most prior studies, the channel model includes diffuse multipath reflections, obtained from an interreflection matrix truncated at the third order. Three schemes are compared, namely common SISO broadcasting, spatially confined data transmission (SCDT) and SCDT with artificial noise (SCDT-AN). Uniform illumination yields the lowest secrecy under SISO, whereas SCDT and SCDT-AN create the required asymmetry through the transmission itself. At the best receiver location with a 20° half-power semi-angle and reflections included, the average secrecy rate of the four-cluster layout rises from 2.10 to 5.36 and 5.68 bit per channel use. It is found that although reflections reduce the SISO rate at every position, SCDT can overcome the residual reflected lights with a nearly unchanged rate, and SCDT-AN further improves it.