Scalable switched slab coupler based optical phased array on silicon nitride

TL;DR

This paper presents a scalable silicon nitride optical phased array using a multi-input star coupler, achieving improved beam steering with reduced footprint and optical loss, suitable for FMCW LiDAR applications.

Contribution

It introduces a multi-input star coupler design for optical phased arrays, enhancing scalability and efficiency over previous single-input approaches.

Findings

Fabricated a silicon nitride phased array with 0.36° x 0.175° beam waist.

Achieved a field of view of 15° x 2.8° with initial design.

Improved design with 0.24° x 0.16° beam waist and 15° x 11.2° FOV.

Abstract

A two-dimensional optical-phased array is demonstrated by using a multiple-input star coupler, compatible with FMCW LiDAR. Previous approach using a single-input design achieves two-dimensional beam-steering by relying on a tunable laser source, taking advantage of grating coupler radiation angle wavelength dependance and variation of the waveguide refractive index. While implementing a convenient way to distribute power in a single step, star coupler architecture is inefficient in terms of employed waveguide length and thus, optical loss and footprint. Multi-input approach partially alleviates this by condensing several single-input devices into one, permitting to reduce the footprint proportionally to the employed number of inputs. We fabricated in silicon nitride technology a proof of concept steerer with beam waist 0.36 deg x 0.175 deg addressing a field of view of 15 deg x 2.8 deg. A new design iteration is also reported with and 0.24 deg x 0.16 deg beam waist and 15 deg x 11.2 deg field of view. Implications of this optical-phased array chips from a LiDAR system perspective are also presented.