Stability Characteristics of Photonic Microwave Generated by Semiconductor Lasers Subject to Optical Injection and Optical Feedback
Lyu-Chih Lin1*, Ssu-Hsin Liu1, Fan-Yi Lin1
1Institute of Photonics Technologies, National Tsing Hua University, Hsinchu, Taiwan
* presenting author:Lyu-Chih Lin,
The stability of the period-one (P1) nonlinear dynamics generated by a semiconductor laser subject to optical injection (OI) and optical feedback (OF) is experimentally quantified and investigated. The P1 dynamic oscillates at broadly tunable frequency for photonic microwave generation, but the stability of the P1 dynamic causes by the intrinsic spontaneous emission noise and extrinsic environmental fluctuation such as injected current variations and temperature fluctuation. To characterize and quantify the stability, the P1 linewidth and linewidth reduction ratio (LRR) are first experimentally compared through the OI and OF systems. Both two characteristics are observed to vary with the OI and OF operating conditions. Because of the spontaneous emission noise in the OI system, the detuning-insensitive point is not the same as the minimal-linewidth point. As a result, the P1 with the lowest linewidth is not the most stable microwave with higher LRR. In the OF system, the P1 linewidth and LRR vary periodically with the P1 frequency when the external cavity length increases. Furthermore, more stable P1 nonlinear dynamics occurring under high feedback strength or long external cavity length strongly depends on whether the P1 frequency locks one of the external cavity modes. In this study, we experimentally analyzed the linewidth of the two optical signals constituting the P1 oscillation and compared the linewidths of the P1 nonlinear dynamics generated by the OI and OF systems. The OF system is shown to have a narrower linewidth of 209 kHz and a better linewidth reduction ratio of 98% within a broader operational region, compared to 4.685 MHz and 82.3% in the OI system.

Keywords: Semiconductor lasers, Laser stabilization, Linewidth, Photonic microwave, Laser dynamics