Frequency-modulated continuous-wave (FMCW) lasers are the key components in FMCW LiDAR systems. In this paper, we develop and implement a rapid linearization algorithm to adaptively pre-distort the injection current, we manage to reduce the residual nonlinearity of the triangular-waveform modulated frequency down to $5.4 \times 10^{-9}$ and $4.1 \times 10^{-9}$ for down- and up-ramp frequency sweeping, respectively. The relative residual nonlinearity for down- and up-ramp frequency sweeping are 0.0020% and 0.0017%, respectively. We use this FMCW laser source with high linearity to implement a LiDAR system. We showcase three-dimensional imaging with the depth contrast and the measurement of the distance and velocity, simultaneously, of a moving object.

Ultrafast linear frequency modulated continuous-wave (FMCW) lasers are a special category of CW lasers. The linear FMCW laser is the light source for many sensing applications, especially for light detection and ranging (LiDAR). However, systems for the generation of high quality linear FMCW light are limited and diverse in terms of technical approaches and mechanisms. Due to a lack of characterization methods for linear FMCW lasers, it is difficult to compare and judge the generation systems in the same category. We propose a novel scheme for measuring the mapping relationship between instantaneous frequency and time of a FMCW laser based on a modified coherent optical spectrum analyzer (COSA) and digital signal processing (DSP) method. Our method has the potential to measure the instantaneous frequency of a FMCW laser at an unlimited sweep rate. In this paper, we demonstrate how to use this new method to precisely measure a FMCW laser at a large fast sweep rate of 5000 THz/s by both simulation and experiments. We find experimentally that the uncertainty of this method is less than 100 kHz and can be improved further if a frequency feedback servo system is introduced to stabilize the local CW laser.

A multicarrier light source based on a recirculating frequency shift loop (RFSL) driven by a parity–time (PT)-symmetric optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The impact of the side-mode suppression ratio (SMSR) of the radio frequency (RF) signal on the multicarrier is studied for the first time, to our knowledge. The RFSL driven by PT-symmetric OEO significantly optimizes the phase noise and flatness of the multicarrier, facilitating the system miniaturization. In the experiment, a 10.019 GHz RF signal with a SMSR of 42 dB is generated with −98.63dBc/Hz measured phase noise at 10 kHz offset frequency (actual phase noise should be lower than −122.87dBc/Hz). Up to 120 subcarriers with 2.32 dB flatness are obtained successfully, covering the overall bandwidth of approximately 1.2 THz.