Light detection and ranging (lidar) is widely accepted as an indispensable sensor for autonomous vehicles. There are two fundamental challenges in a lidar system: optical beam steering technique and ranging method. Optical phased array (OPA) is considered as one of the most promising beam steering schemes due to its solid state, compact size, and high reliability. As for ranging method, time-of-flight and frequency-modulate continuous-wave (FMCW) are commonly utilized in numerous research. However, they are impractical to commercial OPA lidar due to either requiring excessive optical power or the poor stability, high complexity, and high insertion loss of the FMCW source. As a result, the development of OPA lidars is significantly hindered by the lack of a feasible ranging method. In this paper, we present a phase-modulated continuous-wave (PhMCW) ranging method with excellent ranging accuracy and precision. Ranging error as low as 0.1 cm and precision on the order of 3.5 cm are achieved. In addition, theoretical and experimental study on simultaneous velocity measurement is carried out and velocity error as low as 0.15 cm/s is obtained. Finally, we develop a proof-of-concept OPA-PhMCW lidar and obtain a point cloud with excellent fidelity. Our work paves a novel approach to solid-state, cost-effective and high-performance OPA lidars.

Phase-modulated continuous-wave coherent ranging method for optical phased array lidar.

We present the wafer-level characterization of a 256-channel optical phased array operating at 1550 nm, allowing the sequential testing of different OPA circuits without any packaging steps. Using this, we establish that due to random fabrication variations, nominally identical circuits must be individually calibrated. With this constraint in mind, we present methods that significantly reduce the time needed to calibrate each OPA circuit. In particular, we show that for an OPA of this scale, a genetic optimization algorithm is already >3x faster than a simple hill climbing algorithm. Furthermore, we describe how the phase modulators within the OPA may be individually characterized 'in-situ' and how this information can be used to configure the OPA to emit at any arbitrary angle following a single, initial calibration step.

Wafer-level calibration of large-scale integrated optical phased arrays.

Light detection and ranging (LiDAR) is a widely utilized technology for extracting information from the outside world in fields such as automotive, robotics, and aerospace. Optical phased array (OPA) is a promising solution for LiDAR technology, although its application is limited by loss and alias-free steering range. In this paper, we propose a dual-layer antenna that achieves a peak directionality of over 92%, thereby mitigating antenna loss and enhancing power efficiency. Based on this antenna, we design and fabricate a 256-channel non-uniform OPA that achieves 150° alias-free steering. 

Wide field of view optical phased array with a high-directionality antenna.

We demonstrate an optical phased-array equipped with a 3D-printed facet-attached element for shaping and deflection of the emitted beam. The beam shaper combines freeform refractive surfaces with total-internal-reflection mirrors and is in-situ printed to edge-emitting waveguide facets using high-resolution multi-photon lithography, thereby ensuring precise alignment with respect to on-chip waveguide structures. In a proof-of-concept experiment, we achieve a grating-lobe free steering range of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>±</mml:mo> </mml:mrow> <mml:mspace width="thinmathspace" /> <mml:msup> <mml:mn>30</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> and a full-width-half-maximum beam divergence of approximately <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msup> <mml:mn>2</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> . The concept opens an attractive alternative to currently used grating structures and is applicable to a wide range of integration platforms.

3D-printed facet-attached optical elements for beam shaping in optical phased arrays

Optical phased array has become a potentially critical component for beam scanner benefiting from its advantages in cost, mass production, integration, stability and scanning rate. However, the practicalization of OPA still has some great challenges, such as complex circuit control and the need for pre-calibrated phase. In this paper, we propose two passive OPA chips based on silicon nitride delay lines, which can achieve two-dimensional scanning only by wavelength tuning. The two passive OPA chips have different delay line lengths between 128 channels, achieving 2D scanning efficiency of 0.44°/nm×0.07°/nm and 0.87°/nm×0.07°/nm. The beam quality of both passive OPA chips is excellent, with a side lobe level of about 12 dB, without any degradation compared to the OPA chip without the delay line. The delay length of the proposed passive OPA chip can be further increased to obtain denser 2D scans, thereby improving the practicality of the OPA chip. 

Two-dimensional beam scanning of passive optical phased array based on silicon nitride delay line

Silicon based optoelectronic integrated optical phased array is attractive owing to large-dense integration, large scanning range and CMOS compatibility. In this paper, we design and fabricate a SiN-on-SOI two-dimensional optical phased array chip. We demonstrate a two-dimensional scanning range of 96°×14.4° and 690 mW peak power of the main lobe. Additionally, we set up the time of flight (ToF) and frequency-modulated continuous-wave (FMCW) ranging systems by using this optical phased array chip, and achieve the objects detection at the range of 20 m in the ToF system and 109 m in the FMCW system, respectively.

Two-dimensional multi-layered SiN-on-SOI optical phased array with wide-scanning and long-distance ranging.

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Two-dimensional multi-layered SiN-on-SOI optical phased array with wide-scanning and long-distance ranging.