Autonomous driving technology has put forward higher requirements for sensors, including light detection and ranging. An optical phased array is a viable solution and numerous efforts have been made in this area. For its outstanding optical properties such as linear electro-optic effect and low optical loss, lithium niobate exhibits great potential and unique advantages in solid-state light-emitting arrays. Here we propose and experimentally demonstrate an end-fire optical phased array on thin film lithium niobate for passive beam steering. Furthermore, based on this work, we propose a three-line optical phased array to achieve a larger beam steering range. Our results provide a solution for the integrated optical phased array on thin-film lithium niobate which shows potential in sensing and imaging with reduced size and power.

Fig. 1 Schematic of the end-fire OPA on TFLN. Inset (i) shows the wavelength scan period of the input laser. Inset (ii) is the far-field intensity profile of the OPA with a phase difference of 2kπ.

The scheme is shown in Fig. 1. Four cascaded Y branches are used as beam splitters to distribute the input laser into 16 waveguides. The waveguide array then takes a U-turn to form a delay line array and an optical path difference is introduced in adjacent emitting elements. For an input laser with a fixed wavelength, the far-field intensity profile of the OPA is shown as the inset (ii), which is a multiple-slit interference modulated by single-slit diffraction. While with a scanning laser input (as shown in inset (i)), the phase difference induced by the optical path difference changes due to the dispersion of the waveguide, thus the main beam is steered. By tuning the input laser from 1532 nm to 1560 nm, we achieve a steering range of 15°, with a beam divergence angle of 1.6°, and the wavelength tuning efficiency is -0.536°/nm. It is worth noting that the steering range we obtained is limited to the wavelength tuning range. To achieve a larger field of view, we propose a three-line OPA design, where the emitting waveguide in the upper (lower) OPA unit is tilted 10°(-10°). The simulated steering range then reaches ±49.6°.

Fig. 2 Experimental setup and the performance of OPA. (a) Experimental setup for the far-field imaging test. (b) Beam Steering of OPA by passive tuning scheme. (c)Far-field interference pattern of the OPA with input wavelength at 1545 nm.

Fig. 3 The three-line OPA design and simulation results. (a) schematic of three-line OPA. (b) Normalized far-field intensity profile of the -10° tilted OPA with different linear phase differences. (c) Three-line OPA output beam steering range. (d) Beam steering angles for different sets of emitter arrays, respectively. (e) Beam width varies with different steering angles.

Fig. 2 shows the experimental setup and OPA performance, and Fig. 3 shows the three-line OPA design and simulation results.

Our result provides a solution for low-loss beam steering with the TFLN platform, and the three-line OPA design would help achieve OPA with a large Field of View, which has potential application in autonomous driving and far-field imaging.

This work is published in“Jiangwei Wu, Zhaokang Liang, Xueyi Wang, Zhiwei Wei, Hao Li, Yuping Chen and Xianfeng Chen, End-fire optical phased array for passive beam steering on thin-film lithium niobate, Optics Letters, 49(18), 5087-5090 (2024)”。

Link：https://doi.org/10.1364/OL.536761