Bound state in the continuum enabled ultralong silicon ridge waveguide grating antennas for integrated LiDAR applications

As a novel method for solid-state light detection and ranging (LiDAR), optical phased arrays (OPAs) cater to the growing market requirement for mass-produced chip-scale beam steering devices. Waveguide grating antennas (WGAs) with low loss, high efficiency and large emitting aperture are strongly desirable to achieve low beam divergence and high resolution for OPAs. In this paper, we report two kinds of silicon ridge-waveguide-based WGAs with ultra-sharp instantaneous field-of-view (IFOV) for LiDAR applications. The ridge-concave WGA (RCC-WGA) and ridge-convex WGA (RCV-WGA) are designed on account of both sides of ridge area have relatively weak mode field distribution. Lateral quasi-bound state in the continuum (L-BIC) is utilized to further suppress side scattering and improve the emission efficiency. The RCC-WGAs and RCV-WGAs are fabricated on silicon-on-insulator (SOI) platform with 220 nm device layer and foundry compatible etching depths. The measured losses are as low as 2.64 and 2.40 dB/mm at 1550 nm wavelength. The antenna length can up to 6 mm, with theoretical beam divergences of 0.0195° and 0.0175° at the wavelength of 1550 nm, while the experimental results are 0.0251° and 0.0237°, respectively. The proposed low-beam-divergence WGAs are promising in high resolution solid-state LiDAR applications.