A large-scale microelectromechanical-systems-based silicon photonics LiDAR

Abstract

Three-dimensional (3D) imaging sensors allow machines to perceive, map and interact with the surrounding world¹. The size of light detection and ranging (LiDAR) devices is often limited by mechanical scanners. Focal plane array-based 3D sensors are promising candidates for solid-state LiDARs because they allow electronic scanning without mechanical moving parts. However, their resolutions have been limited to 512 pixels or smaller². In this paper, we report on a 16,384-pixel LiDAR with a wide field of view (FoV, 70° × 70°), a fine addressing resolution (0.6° × 0.6°), a narrow beam divergence (0.050° × 0.049°) and a random-access beam addressing with sub-MHz operation speed. The 128 × 128-element focal plane switch array (FPSA) of grating antennas and microelectromechanical systems (MEMS)-actuated optical switches are monolithically integrated on a 10 × 11-mm² silicon photonic chip, where a 128 × 96 subarray is wire bonded and tested in experiments. 3D imaging with a distance resolution of 1.7 cm is achieved with frequency-modulated continuous-wave (FMCW) ranging in monostatic configuration. The FPSA can be mass-produced in complementary metal-oxide-semiconductor (CMOS) foundries, which will allow ubiquitous 3D sensors for use in autonomous cars, drones, robots and smartphones.

Fig. 1. Architecture and working principle of the FPSA.

a, Perspective-view schematic of the 2D FPSA with the lens and output beam. Light is coupled onto the FPSA chip by means of one of the input ports and then routed to the selected grating antenna by turning on the corresponding row-selection and column-selection switches. The lens converts the emitted light to a collimated beam. b, Schematic of a 1D FPSA beam scanner demonstrating the working principle. c, Top-view schematic of the 2D FPSA design. d, Schematics of the MEMS optical switches and grating antennas in the ON and OFF states. In the ON state, the tip of the polysilicon coupler waveguide (green) is pulled down close to the bus waveguides (yellow) to couple light to the grating antenna.

Fig. 2. Microscopic images of the fabricated FPSA device.

a–c, Microscopic images showing the FPSA chip (a), the grating antennas with column-selection switches (b) and the row-selection switch (c). d–f, Scanning electron micrographs of the FPSA chip (d), the column-selection switches (e) and the grating antennas (f). Scale bars: a, 2 mm; b and c, 40 μm; d, 100 μm; e, 20 μm; f, 4 μm.

Fig. 3. Characterization of the FPSA beam scanner.

a, Beam-steering pattern projected on a paper screen showing a 70° × 70° FoV. b, A scanned ‘Cal’ logo pattern with 475 distinct output beam directions projected on a paper screen. c, Zoomed-in beam-steering pattern captured at the focal plane of a Fourier lens. d, Beam profile measured at 0.71 m away from the FPSA beam scanner. e, f, Dynamic responses of the row-selection switch (average of 22 measurements of optical power measured at the drop port) (e) and the column-selection switch (average of 32 measurements of optical power measured at the through port) (f) in the FPSA. The red curves show the applied voltage waveform and the blue curves show the measured optical power.

Fig. 4. 3D imaging results.

a, Schematic of the FMCW LiDAR with the FPSA beam scanner. b, Representative FMCW LiDAR spectrum with a target at 0.84 m. c, d, Point clouds and camera images of the targets composed of three letters in the same plane (c) and in different planes (d) at about 0.8 m. e, f, Representative FMCW LiDAR spectra with targets at 5.5 m (e) and 10.8 m (f). g, h, Point clouds and camera images of targets at about 5.2 m (g) and 10 m (h). The point clouds are colour-coded by the z-coordinate values.

Extended Data Fig. 1. Comparison of integrated FPSAs in the literature and this work.

1D and 2D arrays are indicated by dots and squares, respectively, and this work is indicated by a star.

Extended Data Fig. 2. Confocal microscopic images of the fabricated FPSA device.

a, Confocal microscopic image showing the grating antennas with column-selection switches. b, Confocal microscopic image showing the row-selection switch.

Extended Data Fig. 3. FDTD simulation results of the grating antenna.

The emission angle and efficiency as a function of the grating period are simulated for a focusing-curved grating antenna of 10 μm × 5 μm in size. The green-shaded region shows the grating periods selected for the FPSA grating antenna design.

Extended Data Fig. 4. Measured beam profiles of 13 pixels across the FPSA.

The beam profiles are measured at 0.71 m away from the FPSA beam scanner.

Extended Data Fig. 5. Histograms of measured free-space output power of the FPSA beam scanner.

The output power is measured from 128 pixels in row 22 (a) and 128 pixels in row 62 (b). The bars at −27 dB represent pixels with no output power measured.

Extended Data Fig. 6. Schematics of the optical characterization setups.

a, Schematic of the setup for capturing the beam-steering pattern in the 70° × 70° FoV. b, Schematic of the setup for capturing the zoomed-in beam-steering pattern. c, Schematic of the setup for measuring the beam profiles.

Extended Data Fig. 7. Optical and electrical control setup of the FMCW LiDAR with the FPSA beam scanner for 3D imaging.

The LiDAR is operated in a monostatic configuration, in which the same grating antenna on the FPSA is used to transmit the FMCW light and receive the returned signal from the target.