A Linear Chirped Microwave Waveform Generator with a Large Time-Bandwidth Product Based on Optical Heterodyne Detection

Abstract

We demonstrated a linearly chirped microwave waveform (LCMW) generator with an ultra-large time-bandwidth product (TBWP) based on optical heterodyne detection. A linear frequency chirped optical pulse from a distributed feedback laser diode (DFB-LD) and a stable optical carrier from a reference laser are optical-heterodyne beaten at a photodetector (PD) with broad bandwidth. Thanks to the cavity changing caused by the electrically induced refractive index changing in the active section of the DFB-LD, the frequency chirped optical pulse is achieved by adjusting the injection current into the DFB-LD active section. Then, an LCMW is generated from the PD. Experimental results show that the generated LCFM has a bandwidth of 20 GHz and a temporal duration of 4.5 ms, corresponding to a calculated TBWP of 9×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> . The pulse compression ratio is measured to be 8.49×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> , which is close to the calculated TBWP.