A tunable stabilized optoelectronic oscillator (OEO) based on stimulated Brillouin scattering (SBS) is proposed to solve the low stability problem of microwave signals output by the OEO. An OEO is affected by the characteristics of devices in the structure and the external environment, and the frequency and intensity of its output microwave signals have a certain degree of fluctuations, which influences its subsequent application. Therefore, it is important to improve the stability of microwave signals output by OEOs for improvement in OEO performance. For the OEO based on electric filters to achieve oscillation frequency selection, researchers have improved the frequency stability of output signals by effectively controlling devices such as intensity modulators and optical fibers or electric filters. However, the inclusion of an electrical filter in the structure limits the tunability and integrability of the OEO to some degree. Researchers have introduced the SBS effect into the OEO loop instead of the electrical filter to achieve the oscillation frequency selection so that the tunable range of OEO can be increased. However, the OEO structure usually confronts the problems of laser wavelength drift and DC bias drift, which affect the stability of the microwave signal output by OEO. Therefore, this study proposes a simple-structured OEO that can output a more stable microwave signal and achieve more integrated devices.

A single light source is used to provide an optical carrier and pump light, and the phase modulator (PM) is used to modulate the phase of the optical carrier. It is worth mentioning that the RF signal initially loaded onto the PM comes from the white noise at the photodetector (PD), which is amplified by an electrical amplifier (EA) and fed back to the RF port of the PM to realize the phase modulation of the optical carrier. The Brillouin gain spectrum and Brillouin loss spectrum generated by the SBS effect of pump light in the dispersion-shifted fiber (DSF) break the amplitude balance of the phase modulation sidebands of the optical carrier, and the light wave is photoelectrically converted by the PD to obtain a microwave signal. Then, the microwave signal is fed back to the PM, and through continuous positive feedback, the OEO finally outputs a stable oscillating microwave signal. For higher stability of microwave signals, a tunable stabilized OEO based on SBS is designed. the SBS effect is used instead of an electrical filter to achieve frequency selection, and a single light source is used to provide the optical carrier and pump light, which simplifies the device structure. No other bias regulating devices are introduced into the structure to avoid the effect of DC bias drift, which makes the microwave signal output by the OEO more stable. The use of DSF as the SBS effect medium in the structure reduces the influence of the phase changes in the phase modulation sidebands of the optical carrier caused by the fiber dispersion effect.

A tunable OEO based on SBS is designed to raise the stability of its output microwave signal. The frequency of microwave signal output by the OEO with a laser wavelength of 1553 nm is 10.48 GHz (Fig. 6(a)), and the measured phase noise is -94 dBc/Hz@10 kHz. Through adjustment to the laser output wavelength, the OEO outputs a microwave signal tunable in the range of 10.13 GHz to 10.65 GHz (Fig. 6(b)), i.e., a tuning range of 520 MHz. At the resolution of 1 MHz, the frequency and intensity stability of the microwave signal output by the OEO is measured within 20 min. In addition, there is no drift in frequency (Fig. 7(a)), and the intensity fluctuation is 1.15 dB (Fig. 7(b)). Under the same conditions, when the optical carrier and pump light are provided by two independent light sources, the microwave signal output by the OEO has a frequency fluctuation of 82 MHz (Fig. 9(a)) and an intensity fluctuation of 1.69 dB (Fig. 9(b)). The experimental results show that compared with the OEO that uses two independent light sources to provide the optical carrier and pump light, the single-source OEO has a simple structure, and the intensity stability of its output microwave signal is improved by 0.54 dB, with its frequency measured without fluctuations at 1 MHz resolution.

In this paper, a tunable OEO based on SBS is proposed, which has the advantages of high frequency, high stability, low phase noise, and tunable output frequency. The output microwave signal frequency is tuned from 10.13 GHz to 10.65 GHz, i.e., a tuning range of 520 MHz, by changing the output wavelength of the tunable laser. The phase noise is measured at 10.48 GHz to be -94 dBc/Hz@10 kHz, and the output microwave signal reports no frequency drift in 20 min and a maximum power drift of 1.15 dB. The experimental results show that compared with the dual-source OEO, the single-source OEO has a simple structure and can output a more stable microwave signal. It is a better choice for obtaining a microwave signal with high frequency, low phase noise, and high stability.