Generation of Linearly Chirped Microwave Waveform With an Increased Time-Bandwidth Product Based on a Tunable Optoelectronic Oscillator and a Recirculating Phase Modulation Loop

Photonic generation of a linearly chirped microwave waveform with an increased time-bandwidth product (TBWP) based on a frequency-tunable optoelectronic oscillator (OEO) and a recirculating phase modulation loop (RPML) is proposed and experimentally demonstrated, for the first time to the best of our knowledge. In the proposed system, a continuous-wave (CW) light wave is divided into two parts: one is sent to the tunable OEO to generate a frequency-tunable microwave signal and the other is intensity-modulated by a switching signal at an intensity modulator to form a chirp-free optical pulse, which are then sent to the RPML, in which the chirp-free pulse is phase modulated by a parabolic waveform to generate a linearly chirped optical waveform. The recirculation of the linearly chirped optical waveform inside the loop would lead to the waveform to experience multiple phase modulations, thus multiplying its chirp rate. By beating the chirped waveform and an optical sideband from the OEO at a high-speed photodetector (PD), a linearly chirped microwave waveform is obtained. The key significance of the approach is that the chirp rate is significantly increased, leading to a significantly increased TBWP. In addition, the approach allows the generation of a linearly chirped frequency-tunable microwave waveform without using a separate microwave source. The technique is experimentally verified. The generation of a linearly chirped microwave waveform with an increased TBWP by 16 times is demonstrated.