End-fire optical phased array with a wide beam-steering for near-visible infrared applications

Recent emerging applications in LiDAR, free-space data link, projection, and imaging increase the demand for high performance optical phased array (OPA) [1] – [3] . The radiating elements considered for most applications are mainly diffractive elements such as gratings or photonic crystal waveguides. It has been shown recently that edge-emitting waveguide arrays, also known as end-fire, facilitate subwavelength spacing in IR range, which results in a large beam steering [4] , [5] . For several applications such as data centers, sensing, and spectroscopy, the near-visible infrared OPAs are in high demand. We demonstrated an end-fire-based OPA at a wavelength of 852nm. The OPA is fabricated on a PECVD SiN-on-insulator platform offered by imec available through BioPIX300 technology. The waveguide is designed for the first fundamental mode with a cross-section of 550×300nm 2 . As shown in Fig. 1(a) , the optical input is divided into eight branches using a tree of optically optimized Y-splitters (insertion loss < 0.03dB). After each splitting level, four thermo-optical phase shifters are connected electrically in parallel. Phase shifting is enabled by a TiN heater on top of the waveguide with a length of L=90μm. The effect of thermal coupling length [6] , [7] is considered after the first, second, and third splitter 4L, 2L, and L, respectively. This configuration provides a simple three-level resolution for beam steering resolution, all with the same applied voltage. To reduce the thermal crosstalk, adjacent channels are not active at the same time. Even- and odd channels are separated in an active mode, each responsible for left and right beam steering. The channels finally end at two microns before the chip's edge with a center-to-center spacing of 800nm.