Photonic Generation of Frequency-Modulated Interrupted Continuous Waveforms

A frequency-modulated interrupted continuous waveform (FMICW) generator with an ultra-large bandwidth based on optical heterodyne detection is proposed and experimentally demonstrated. The FMICW generator is implemented through the heterodyne detection of a stable optical carrier and a gate-function-modulated frequency-chirped optical pulse. A stable sub-kHz optical fiber laser operates the optical carrier. The optical pulse is generated from a three-electrode distributed Bragg reflector (DBR) laser diode (LD), which is gate-function modulated by a current source via the passive phase control section. By beating the optical carrier and the optical pulse at a photodetector (PD), an FMICW is generated. The bandwidth of the FMICW is over 20 GHz, and the temporal duration is around 200 <inline-formula> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula>. The compression ratio is obtained as large as <inline-formula> <tex-math notation="LaTeX">$3.78\times 10 ^{6}$ </tex-math></inline-formula>. Thanks to the tunability of the gate-function-modulated frequency-chirped optical pulse, the generated FMICW is fully tunable in terms of gate-function period and duty ratio.