Researchers: Youmin Wang, Xiaosheng Zhang, Kyungmok Kwon
Funding Agency: Texas Instruments, DARPA
Optical beam steering device is a key enabling technology for light detection and ranging (LiDAR), free-space optical communication, and augmented reality/virtual reality. Most of the current beam scanners employ mechanical scanning units such as motors, which are bulky, slow and often unreliable. Solid-state beam scanners with integrated scanning elements have received increasing interests. In particular, the optical phased array (OPA) provides non-mechanical scanning in a compact form factor. More importantly, it enables sophisticated beamforming such as simultaneous scanning, pointing, and tracking of multiple objects.
OPAs with various types of phase modulators have been demonstrated, most notably with liquid crystal, silicon photonics, and MEMS technologies. Large-scale OPA has been realized with liquid crystal spatial light modulators, albeit with slow response time. Silicon photonics OPA typically relies on thermal phase tuning, which results in high power consumption. In this project, we report on a fine-pitch 2D MEMS OPA with fast response time. A 160×160-element grating-based OPA with a 3.2×3.1 mm2 aperture is designed and fabricated to achieve a 6.6°x4.4° scanning angle. The OPA can operate in a broad wavelength band of 1200 – 1700 nm. The response time of the MEMS device is measured to be 5.7 μs and the actuation voltage is 10 V.
Figure 1: Schematic of the MEMS OPA device
The schematic of our OPA device is shown in Figure 1. It consists of a 2D array of sub-wavelength gratings. When free-space input light is diffracted by the gratings, the optical phase distribution of the output light over the array area can be controlled by relative displacements between the gratings. To achieve high fill factor while minimizing the crosstalk between adjacent gratings, we employ MEMS comb-drive actuators underneath the gratings. The photo and scanning electron micrographs (SEMs) of the fabricated OPA device are shown in Figure 2.
Figure 2: Photo and SEMs of the OPA device and grating-based phase shifter.
More details can be found in our paper “2D broadband beamsteering with large-scale MEMS optical phased array” published in Optica in 2019.