Low spurious optoelectronic oscillator achieved by frequency conversion filtering without deteriorating phase noise

In order to obtain microwave signals with low spurs and low phase noise, we studied the residual phase noise of the frequency-conversion filtering oscillator and methods to improve its phase noise performance. We first analyze the influence of the dispersion of the intermediate frequency (IF) filter on the residual phase noise in the frequency conversion filtering process. Then, we use an electro-optic modulator to achieve up-conversion in the frequency conversion filtering and extend the intra-cavity delay with an optical fiber after the modulator. This allows the optoelectronic oscillator (OEO) to improve the phase noise performance while having a good suppression of spurs. The spurs suppression ratio of the proposed OEO is 80 dB with a fiber of about 1.6 km in the cavity. The phase noise of the proposed OEO is -130 dBc/Hz at 10 kHz offset from 10 GHz, which is 10 dB lower than our previous work.