All-optical microwave oscillator using cross-gain modulation of semiconductor optical amplifier and cascaded stimulated Brillouin scattering effects in optical fiber

Abstract

In this paper, an all-optical microwave oscillator is proposed and experimentally demonstrated. Via cascaded stimulated Brillouin scattering effects, the second-order Stokes wave can be obtained. A microwave envelope can be generated by beating the continuous wave and the second-order Stokes wave. The functions of microwave envelope detection and feedback modulation are implemented by using cross-gain modulation of a semiconductor optical amplifier, further, the Vernier effect is used to improve the microwave signal. The second Brillouin-selective sideband amplification is employed to enhance oscillation frequency. In this reported scheme, the electrical microwave devices such as high-Q electrical bandpass filter and electro-optic modulator are not required in the microwave oscillation feedback loop. This all-optical microwave oscillator can shake off the electronic block. Meanwhile, the frequency of the generated microwave signal is twice the Stokes frequency shift of the stimulated Brillouin scattering. Furthermore, it can also result in phase noise reduction that only one laser source is used here. Finally, coupled cavities are used to suppress the harmonic presentation. The experimental results show that the all-optical microwave oscillator can generate a single-mode-microwave-oscillation signal with a frequency of 21.66 GHz. The phase noise value at 10 kHz frequency offset is −90 dBc/Hz.