Photonic generation of phase-coded chirp microwave waveform by an improved frequency-sweeping optoelectronic oscillator

Abstract

Generation of phase-coded chirped microwave waveforms by an improved frequency-sweeping optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. In the proposed system, an upgraded frequency-sweeping OEO has function to generate not only a linearly chirped microwave waveform (LCMW) but also to output an optical sideband and the latter is then modulated in phase by a binary phase-coded electrical signal. By beating the phase modulated signal and a portion of the frequency-sweeping laser light at a high-speed photodetector, a phase-coded chirped microwave waveform is generated. In order to realize large time-bandwidth product (TBWP), the key significance of the improved frequency-sweeping OEO is that a near-zero-dispersion single-mode-fiber (SMF) introduced into the loop which can not only avoid the limitation of high frequency oscillation caused by dispersion, but also construct long OEO delay loop to realize large time duration. Finally, phase-coded chirped microwave waveform with a bandwidth of 6 GHz and a TBWP of 130,392 is experimentally demonstrated.