A circular-sided square microcavity laser etched a central hole has achieved chaos operation with a bandwidth of 20.8 GHz without external optical feedback or injection, in which the intensity probability distribution of a chaotic signal with a two-peak pattern was observed. Based on the self-chaotic microlaser, physical random numbers at 400 Gb/s were generated by extracting the four least significant bits without other complex post-processing methods. The solitary chaos laser and minimal post-processing have predicted a simpler and low-cost on-chip random number generator in the future.

通过建立包含朗之万噪声源的三模速率方程模型，模拟研究了回音壁模式微腔激光器的噪声特性和线宽特性，特别是注入电流热效应引起的跳模及其对光功率和实现窄线宽的影响。回音壁微腔激光器单模工作时，在大偏置电流下可由低频处的频率噪声得到百kHz以下的激光器线宽；在微腔双模激射状态下，由于模式竞争作用，微腔激光器的相对强度噪声和频率噪声在低频处都有明显的升高，使得激光器的线宽展宽。此外，还采用快速傅里叶变换的方法由时域信号计算获得激光模式光谱线型，由此得到的激光模式线宽与通过频率噪声谱获得的线宽基本一致。

针对双波长激光器间距精细调谐的需求，基于正方形微腔的模场分布，设计了中心及四个角区电流注入窗口的正方形微腔激光器。利用有限元法对提出的结构进行分析，发现改变腔体折射率分布差，可以调控基横模和一阶横模的波长间距。基于半导体平面加工工艺成功制备了边长为30 μm的非均匀注入正方形微腔激光器。当注入电流从42 mA增加到53 mA时，该激光器的波长间隔从0.18 nm减小到0.1 nm，强度比小于4 dB。除此之外，继续增加电流，由于双模间隔的进一步减小，出现了明显的单周期振荡现象。

We report a 1.65 µm square-Fabry–Pérot (FP) coupled cavity semiconductor laser for methane gas detection. The laser output optical power can reach 7.4 mW with the side mode suppression ratio about 40 dB. The wavelength tuning range is 2 nm by adjusting the FP cavity injection current, covering the methane absorption line at 1653.72 nm. The lasing wavelength can also be tuned by adjusting the square microcavity injection current or temperature, respectively. Methane gas detection is successfully demonstrated utilizing this laser.

We propose and demonstrate the generation of wideband chaos based on a dual-mode microsquare semiconductor laser with optical feedback. By adjusting the dual-mode intensity ratio and the feedback strength, wideband chaos covering more than 50 GHz in the RF spectrum is achieved. The standard and effective bandwidths of the chaotic signal are 31.3 GHz and 30.7 GHz with the flatness of 8.3 dB and 6.1 dB, respectively.

Hybrid octagonal-ring microlasers are investigated for realizing a stable output from a silicon waveguide based on a two-dimensional simulation. The inner radius of the ring is optimized to achieve single-mode and low-threshold operation. Using the divinylsiloxane-benzocyclobutene (DVS-BCB) bonding technique, a hybrid AlGaInAs/Si octagonal-ring microlaser vertically coupled to a silicon waveguide is fabricated with a side length of 21.6 μm and an inner radius of 15 μm. A single transverse-mode operation is achieved with a threshold current density of 0.8 kA/cm2 and a side-mode suppression ratio above 30 dB, and a stable output from the lower silicon waveguide is obtained.