Nonlinearity correction-free FMCW LiDAR based on monolithically integrated sideband injection locking: Breaking coherence length limit

Abstract

The frequency-sweep nonlinearity of the light source in frequency-modulated continuous-wave (FMCW) LiDAR degrades the signal-to-noise ratio, thereby affecting the ranging accuracy and effective detection range of the LiDAR. Meanwhile, the maximum detection range of FMCW LiDAR is restricted by the coherence length of the light source. The inherent frequency modulation nonlinearity of a linear frequency-modulated (LFM) laser has to be corrected by complex predistortion compensation circuits or digital post-processing algorithms, which increases hardware cost and system integration difficulty. In addition, the ultra-narrow linewidth required for long-distance detection also raises the fabrication difficulty of LiDAR light sources. To solve the above-mentioned problems, this paper proposes an innovative FMCW LiDAR scheme without nonlinearity correction. Based on monolithically integrated sideband injection-locking technology, low-distortion LFM laser output can be realized without additional correction systems. Experimental results show that the proposed scheme achieves a frequency modulation nonlinearity of approximately 0.025% and a relative ranging error of less than 0.6%. Clear scanning imaging of the target is obtained. Moreover, the proposed scheme overcomes the light source's coherence length limitation, achieving a detection range exceeding seven times its intrinsic coherence length.