Wide field-of-view biaxial FMCW LiDAR with high-speed detection utilizing a photoreceiver based on static unitary detector technique

Frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) has been used in a wide range of applications due to its ability to simultaneously acquire highly accurate distance and velocity information in real-time, as well as its immunity to sunlight and signals from surrounding LiDARs. Most FMCW LiDARs have been implemented as uniaxial structures composed of fiber-based devices that, while easily acquiring the beat signal between the local oscillator and the reflected signal, struggle to improve the signal-to-noise ratio (SNR) and the field-of-view (FoV) due to structural limitations. On the other hand, the LiDAR based on a biaxial structure, in which the optical paths of the transmitter and receiver are separated, can enhance both the FoV and the SNR by using a large active area photodiode and receiving the reflected signals with relatively low attenuation. However, the detection of high-speed beat frequency is limited for a typical large-area photodiode due to the influence of high junction capacitance. In this paper, we newly proposed the FMCW LiDAR system of a biaxial structure with a photoreceiver based on the static unitary detector (STUD) technique which can simultaneously improve the SNR, the detection speed, and the FoV. The STUD photoreceiver is designed to operate the multiple small-area photodiodes as a single large-area photodetector, enabling high-speed detection with a large active area, thus it can achieve both beat frequency detection of high-speed and a wide FoV at the same time. Furthermore, the biaxial structure is advantageous for the acquisition of high SNR signals as the reflected signal only passes through the receiving lens and then impinges on the active area. Moreover, we obtained various distance information and spectral resolution characteristics using a linearized optical swept source that employed an optical phase-locked loop (OPLL) to minimize the nonlinearity in the optical frequency sweep range.