Linear frequency-modulated waveform generation based on a tunable optoelectronic oscillator

A photonic linear frequency-modulated (LFM) microwave waveform generator is proposed and demonstrated using a tunable optoelectronic oscillator (OEO) based on an optically injected semiconductor laser. Frequency tunability of the OEO is achieved by controlling optical injection strength. When the sweep period of output frequency matches with the cavity round-trip time, signal quality of generated LFM waveform is significantly improved by the high Q optoelectronic oscillation. In the experiment, LFM signal with a sweep range as large as 7 GHz, a tuning rate reaching 0.18 GHz/ns, and a time-bandwidth product (TBWP) up to 2804.2 is generated. A frequency comb contrast of 47 dB is also observed in the spectrum. Compared with other approaches, the proposed LFM waveform generator shows superiorities of large bandwidth, fast sweeping rate and high spectral purity.