Uniform emission, constant wavevector silicon grating surface emitter for beam steering with ultra-sharp instantaneous field-of-view.

Kuanping Shang,Guangyao Liu,S.J B Yoo,Xian Xiao,Yu Zhang,Chuan Qin,Shaoqi Feng

doi:10.1364/oe.25.019655

Abstract

We report on uniform emission intensity profile, uniform propagation constant silicon gratings for beam steering application with ultra-sharp instantaneous field-of-view (IFOV). To achieve uniform emission intensity across relatively long emission length, we designed a custom grating with varying Si3N4 width and duty cycle while maintaining a uniform propagation constant for relatively narrow divergence emission pattern. We designed and fabricated the custom Si3N4/Si grating with the varying Si3N4 width/duty cycle together with the reference Si3N4/Si grating with a constant 50:50 duty cycle. The custom grating demonstrated the beam steering angle value of 6.6° by sweeping wavelength between 1530 nm and 1575 nm with the emission length over 1 mm. The measured IFOV based on the 3-dB beamwidth values of the far field patterns for the TE polarization are 0.10° and 0.75° for the custom grating and for the reference grating, respectively. The custom grating also indicates mode-selective behavior due to the perturbation of propagation constant for input modes other than TE polarization. The measured TE-mode to TM-mode suppression ratio for the custom grating is approximately 8.2 dB peak-to-peak measured at far field.

Highlights

Optical phased arrays (OPAs) are attracting strong interest in numerous optical beam-steering applications [1,2,3,4], such as free-space optical interconnect, sensing, data communication [5], and light detection and ranging (LIDAR) [6]
We report on uniform emission intensity profile, uniform propagation constant silicon gratings for beam steering application with ultra-sharp instantaneous field-of-view (IFOV)
The measured IFOV based on the 3-dB beamwidth values of the far field patterns for the TE polarization are 0.10° and 0.75° for the custom grating and for the reference grating, respectively

Summary

Introduction

Optical phased arrays (OPAs) are attracting strong interest in numerous optical beam-steering applications [1,2,3,4], such as free-space optical interconnect, sensing, data communication [5], and light detection and ranging (LIDAR) [6]. We propose the uniform emission intensity profile and constant wavevector silicon gratings with integration of silicon nitride (Si3N4) as the low index material overlay for ultra-sharp IFOV surface emission grating application. Pure silicon nitride-based gratings [13, 14] can achieve low emission rate with small IFOV They require additional low-loss coupling solutions to integrate with silicon photonics. The mode with uniform propagation constant forms a clear far field pattern with narrow beamwidth, while the other modes scatter as background without introducing additional side lobes This property of the custom grating serves as a mode selection mechanism, which is useful to filter emissions from undesired polarization rotations due to perturbations in the waveguide

Design

Fabrication and near fieldcharacterization

Experimental setup and results for far field measurement

Conclusion