Performance enhancement of an optically-injected-semiconductor-laser-based optoelectronic oscillator by subharmonic microwave modulation

An approach to enhancing the performance of an optically-injected-semiconductor-laser-based optoelectronic oscillator (OEO) is proposed by subharmonic microwave modulation. A free-running OEO is first established based on period-one dynamics of an optically injected semiconductor laser. The oscillation frequency can be tuned in the range of 8.87 to 18.41 GHz by controlling the injection strength, but the output signal suffers from strong side modes and poor frequency stability. To address these problems, subharmonic microwave modulation is applied to the injected semiconductor laser. In the experiment, microwave modulation with 1/2, 1/4, and 1/6 subharmonics is demonstrated. The side-mode suppression ratio is improved by over 40 dB, while the phase noise at a 1 kHz offset is reduced by about 18 dB. Furthermore, the frequency drift over a period of 20 min, which characterizes the long-term stability, is reduced from 8.7 kHz to less than 1 Hz, indicating a significant reduction of over three orders.