Narrow-linewidth microwave generation by an optoelectronic oscillator with a directly modulated microsquare laser

A simple dual-loop optoelectronic oscillator using a 16 μm side length AlGaInAs/InP directly modulated microsquare laser is proposed and investigated without an external modulator. High-performance first harmonics are realized, with 3 dB linewidth, less than 200 Hz, and a frequency-tunable range from 2 to 8 GHz. Meanwhile, a side-mode suppression ratio of 60 dB is obtained for the microwave by the dual-loop structure. Within the whole tuning range, the measured single-sideband phase noises of the first harmonics are about -110  dBc/Hz at 10 kHz frequency offset. Furthermore, the second and third harmonics with frequency-tunable ranges from 4 to 16 GHz and 6 to 24 GHz are achieved as well.