Multi-Band FMCW Signal Generator with a Tunable Sweep-Frequency Bandwidth and Inter-Band Interval

In this work, we experimentally demonstrate a scheme for generating a multi-band FMCW signal with a tunable sweep bandwidth and inter-band interval. For such a scheme, an original FMCW signal is first acquired by directly current-modulating a master distributed feedback semiconductor laser (DFB-SCL) using a pre-distorted triangular waveform. Then, the original FMCW signal is injected into a slave DFB-SCL, in which a multi-band FMCW signal is generated via the four-wave mixing (FWM) effect. The experiment results show that, under appropriate injection parameters, a tri-band FMCW signal can be obtained, which is composed of a regenerated original FMCW signal (named as main band) and two newly generated FMCW signals originating from idler waves (named as upper band and lower band, respectively). Under the optical injection with negative frequency detuning, the sweep-frequency bandwidth for upper band is the same as that of the original FMCW signal, and the sweep-frequency bandwidth for lower band is twice that of the original FMCW signal. Meanwhile, the interval between the central frequencies of two adjacent bands depends on the frequency detuning between two DFB-SCLs operating at free-running. By adjusting the sweep-frequency bandwidth of the original FMCW signal and the temperature of the slave DFB-SCL, the sweep-frequency bandwidth of each band and the interval between two adjacent bands of the generated FMCW signal can be tuned. For demonstration of a proof of concept, we inspect the case that the original FMCW signal with a sweep-frequency bandwidth varied within 3 GHz~7 GHz and the frequency detuning varied within 44 GHz~59 GHz. The corresponding results demonstrate that each band with the different sweep-frequency bandwidth possesses high linearity of R2 > 0.990 under the frequency detuning fixing at 59 GHz. Such a scheme offers a simplified architecture for generating multi-band FMCW signals with a tunable sweep-frequency bandwidth and inter-band interval.