Spectrum-sparse broadband chaotic signal generation based on an optical frequency shift loop

Spectrum-sparse chaotic signals offer both a large detection bandwidth and low spectral occupancy. However, existing photonic schemes have difficulty in reconfiguring their sparsity characteristics. A microwave photonic scheme based on an optical frequency shift loop (OFSL) is proposed to generate a broadband chaotic signal with sparse spectrum. Feeding a narrowband chaotic seed signal into the OFSL generates the spectrum-sparse broadband chaotic signal, whose sparsity depends on the ratio of the seed's bandwidth to the frequency shift. A mathematical model is developed, demonstrating the principle of broadband chaotic signal generation based on the OFSL. Experimental results present autocorrelation and time-frequency characteristics of chaotic signals with sparse factors from 5% to 25%, covering a range from 0 to 8 GHz. Reconstructed phase spaces verify that the chaotic attractor structure is unchanged in the OFSL.