Optical Rf Signal Processing Method

The performance of microwave resource, especially the millimeter-wave source, such as phase noise, frequency stability, tunability, has great effect on the performance of the radar, electronic warfare and communication microwave system and so on. However, the technological level of solid state millimeter-wave resource couldn't generate millimeter-wave above 40 GHz with splendid performance, while optical generation of microwave or millimeter-wave can be an effective means to generatemicrowave/millimeter-wave since it does not rely on the complicated semiconductor technological. Therefore, optical generation of millimeter-wave with its unique merits can have more potential and more significant value in application.Firstly, a review of many experiments about optical generation of microwave/millimeter-wave at home and abroad was given and the Optoel-Elctronic Oscillator (OEO) is chosen to generate microwave/millimeter-wave. Among so many schemes of generate millimeter-wave, the optoelectronic oscillator have evident superiority to generate microwave with ultra-low phase noise, stability, tunability. The author then introduces the construction and theory of optoelectronic oscillator, including the oscillation threshold, linearization of the electro-optic modulator's response function, oscillation frequency and amplitude, spectrum and noise-to-signal ratio. The experiment of single-loop OEO is performed with different fiber length and center frequency filter, generating microwave signal with high performance at 225MHz, 600MHz and 4.1GHz frequency respectively. Thereinto, we achieve phase noise of-100dBc/Hz at 1kHz, -122 dBc/Hz at 10 kHz and side-mode suppression better than 81 dB from a 4.1 GHz oscillation frequency with 900m-length fiber. Then the relation between the oscillation loop gain and spurious oscillation and that between the space length and mode jump are discussed in detail. Also then the characteristic of phase noise, stability and tunability are investigated.Lastly the theory of dual-loop optoelectronic oscillator is represented in the paper. And then the oscillation is simulated, and an experiment about the dual-loop optoelectronic oscillator is carried out to study the effect of the power proportion and length of dual-loop on phase noise and side mode suppression. The author achieves the result with the same phase noise as the single-loop OEO in the experiment of dual-loop OEO with short loop of 305m-length and long loop of 907m-length. More importantly, it is found that the side-mode suppression achieves above 95dB, more 10 dB better than the single-loop OEO.