Broadening Gain Margin of an Optoelectronic Oscillator for Stable Single-Mode Oscillation

The gain margin of an optoelectronic oscillator (OEO) is the range of gain (RoG) over which stable single-mode oscillation is maintained without being switched to oscillations in multi-mode. A large RoG indicates a stable single-mode oscillation against gain variations due to environmental perturbations. For an OEO incorporating an electrical bandpass filter (EBPF) and an electrical amplifier (EA), we propose to increase the RoG by reducing the bandwidth of the EBPF and by reducing the saturation output power of the EA. The proposed scheme is studied by numerical simulations and is verified by an experiment. The simulation results based on the extended microwave-photonic iterative nonlinear gain (eMING) model show that reducing the bandwidth of the EBPF from 1 GHz to 20 MHz, the RoG is increased by 5.5 dB. Additionally, lowering the saturation output power of the EA from 16 dBm to 3 dBm, the RoG is increased by 9 dB. The simulation results are then verified by an experiment. Experimental results demonstrate a 3.6 dB improvement in RoG by reducing the bandwidth of the EBPF from 1 GHz to 20 MHz. Similarly, the RoG shows a 2.6 dB improvement by lowering the saturation output power of the EA from 16 dBm to 3 dBm. This work provides an effective solution to maximize the stable single-mode operation range of an OEO without complicating the system architecture.