Frequency-Doubling Brillouin Optoelectronic Oscillator With Variable Optical Attenuator

A novel frequency-doubling Brillouin optoelectronic oscillator (OEO) based on a variable optical attenuator (VOA) has been proposed and experimentally demonstrated in the letter. Specifically, a Brillouin fiber laser (BFL) is integrated into an OEO to create the Brillouin OEO, and a VOA is connected to the end of the BFL to enable frequency selection through switching the BFL between half- and fully-open cavities. When the VOA loss is relatively low, for instance of 0.2 dB, the BFL cavity is equivalent to a half-open cavity, and a 10.434 GHz RF signal equal to single Brillouin frequency shift is generated. Whereas the VOA loss is increased (for example 20 dB), the BFL cavity becomes equivalent to a fully-open cavity, and a 20.869 GHz RF signal equal to double Brillouin frequency shifts is obtained. At an offset frequency of 10 kHz, the phase noises of the fundamental and frequency-doubling microwave signals are −98.123 dBc/Hz and −96.519 dBc/Hz, respectively. Moreover, the Brillouin gain spectral width is only a few tens of MHz, and the attained RF signal has high spectral purity. Overall, the frequency-doubling Brillouin OEO proposed has broad application prospects in areas such as radar systems and measurement.