차량용 FMCW라이다의 위상변환 광소자 제작에 관한 연구 = A Study on the Fabrication of Phase Shift Optical Device for Automotive Frequency Modulated Continuous Wavelength Lidar

다국어 초록 (Multilingual Abstract)

This paper presents the design and fabrication of a planar lightwave circuit (PLC) based phase-shifting optical device for automotive frequency-modulated continuous-wave (FMCW) LiDAR systems. The proposed phase shifter is implemented as a Mach Zehnder interferometer (MZI) type optical waveguide circuit driven by a 1550-nm narrow-linewidth laser source, in order to achieve a compact and mechanically stable optical front-end. The PLC chip is designed with three input ports and four output ports, and is combined with a 1×2 asymmetric tap splitter that separates the transmit path and the local-oscillator (LO) reference path. During fabrication, process parameters such as the core refractive index, waveguide cross-section, and directional coupler spacing are optimized to reduce insertion loss and to improve channel-to-channel uniformity. The phase characteristics of the fabricated module are evaluated using a measurement setup consisting of a tunable laser source, polarization controller, optical power meters, and an oscilloscope operated in XY-mode to obtain Lissajous figures, confirming that the phase difference between the in-phase and quadrature ports is maintained close to the target 90° over the measured samples.
When the proposed phase-shifter module is integrated into an FMCW LiDAR testbed, stable interference between the reference signal and the signal reflected from external objects is achieved, enabling qualitative reconstruction of target distance and shape.
These results demonstrate the applicability of the PLC-based phase shifter as a key integrated optical component for automotive FMCW LiDAR.