Experimental investigation of the injection-locked optoelectronic oscillator with analog modulated RF signal injection

This paper experimentally investigates the injection-locking behaviour of a single-loop optoelectronic oscillator (OEO) subjected to analog-modulated radio-frequency (RF) signals. When an under-driven OEO is injection-locked to a monotone amplitude-modulated (AM) signal, the output exhibits a reduced modulation index, indicating signal distortion. Under small, nonzero frequency detuning, the OEO demonstrates AM-to-phase-modulation (PM) conversion. When injected with a monotone frequency-modulated (FM) signal, the OEO produces an amplified FM output with controllable distortion, depending on the modulating frequency and locking-range ratio. The influence of the modulation index of the injected AM and FM signals on the locking range is also experimentally investigated. Furthermore, both AM and FM signal injection significantly improve the phase noise performance of the injection-locked OEO at low offset frequencies compared with its free-running operation. These findings highlight the potential of injection-locked OEOs for analog modulation conversion, RF signal amplification, and low-noise microwave signal generation.