Abstract
A scheme for photonic generation of linearly chirped microwave waveforms (LCMWs) with a large time-bandwidth product (TBWP) is proposed and demonstrated based on an optically injected semiconductor laser. In the proposed system, the optically injected semiconductor laser is operated in period-one (P1) oscillation state. After optical-to-electrical conversion, a microwave signal can be generated with its frequency determined by the injection strength. By properly controlling the injection strength, an LCMW with a large TBWP can be generated. The proposed system has a simple and compact structure. Besides, the center frequency, bandwidth, as well as the temporal duration of the generated LCMWs can be easily adjusted. An experiment is carried out. LCMWs with TBWPs as large as 1.2x105 (bandwidth 12 GHz; temporal duration 10 μs) are successfully generated. The flexibility for tuning the center frequency, bandwidth and temporal duration is also demonstrated.
Highlights
Chirped microwave waveforms (LCMWs) have wide applications in modern radar systems, where Linearly chirped microwave waveforms (LCMWs) with a large time-bandwidth product (TBWP) are highly desired to simultaneously achieve a large detection range and a high range resolution [1, 2]
Among all the schemes for photonic LCMW generation, one method is based on space-to-time mapping (STM) or frequency-to-time mapping (FTM) [5,6,7,8,9,10]
Microwave waveform generation scheme based on FTM usually contains an optical spectral shaper and a dispersive element [8,9,10]
Summary
Chirped microwave waveforms (LCMWs) have wide applications in modern radar systems, where LCMWs with a large time-bandwidth product (TBWP) are highly desired to simultaneously achieve a large detection range and a high range resolution [1, 2]. The third method for photonic LCMW generation is based on heterodyning of a linearly chirped optical pulse with a continuous wave (CW) light or another linearly chirped optical pulse with different chirp rate [15,16,17] In these systems, a short optical pulse from a mode-locked laser is sent to a dispersive element, a quadratic phase profile would be imposed on the optical pulse. The dispersive element can be a dispersion compensation fiber, a single-mode fiber or a linearly chirped FBG For this method, the small time aperture (usually several or tens of nanoseconds) is the major problem that limits the TBWP of the generated LCMW. The feasibility of tuning the central frequency, bandwidth and temporal duration is verified
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