# AWG-Based Spectral Multiplexing for Unambiguous Range-Extended FMCW LiDAR

## TL;DR

This paper introduces a new FMCW LiDAR system using AWG-based spectral multiplexing to extend measurable range and avoid distance ambiguity.

## Contribution

The novel use of AWG-based spectral multiplexing and a channel-pair-based decoding algorithm enables unambiguous range extension in FMCW LiDAR.

## Key findings

- The system extends the measurable range to about five times that of conventional FMCW LiDAR.
- High measurement accuracy and 3D distance map reconstruction were experimentally validated.
- Distance ambiguity is resolved using a channel-pair-based decoding algorithm.

## Abstract

Frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) based on coherent ranging is a technology capable of high-resolution distance measurement while remaining robust against ambient light interference. However, extending the measurable range remains challenging due to (i) the coherence length limitation of the laser and (ii) distance ambiguity caused by frequency ambiguity in coherent detection. To overcome these limitations, we propose an unambiguous range-extended FMCW LiDAR enabled by arrayed waveguide grating (AWG)-based spectral multiplexing. By spectrally demultiplexing the reference arm into four wavelength channels with sequentially designed optical path delays, multiple independent interference signals are obtained simultaneously without increasing the number of photodetectors or optical couplers. A channel-pair-based distance decoding algorithm is further introduced to resolve distance ambiguity by classifying detection outcomes across adjacent channels and selectively applying predefined operations. The proposed FMCW LiDAR system effectively extends the measurable range to approximately five times that of a conventional FMCW LiDAR. Experimental results demonstrate high measurement accuracy and successful reconstruction of three-dimensional distance maps, validating the system’s potential for extended-range FMCW LiDAR applications.