Photonic Generation and Transmission of Linearly Chirped Microwave Pulses With High TBWP by Self-Heterodyne Technique

This paper shows the generation of linearly chirped microwave pulses employing the photonic self-heterodyne technique, leading to ultrawideband signals with time-bandwidth products up to 74 000. By using low-frequency electronics to drive a distributed feedback laser diode, optical chirping is generated predominantly by thermal effect. Combining laser chirping, delay-optimized self-heterodyning, and saturated optical amplification yields to linearly chirped pulses with 2-25.2-GHz wide spectrum and better than ±3 dB flatness. A simple theoretical model showing the tradeoff between maximum attainable bandwidth and time-bandwidth product was developed and experimentally verified. Undistorted transmission along >40 km standard single-mode optical fiber is also shown.