Compact and Broadband Edge Coupler Based on Multi-Stage Silicon Nitride Tapers

Bishal Bhandari,Chul-Soon Im,Min-Cheol Oh,Sung-Moon Kim,Sang-Shin Lee,Kyeong-Pyo Lee

doi:10.1109/jphot.2020.3036498

Bishal Bhandari, Chul-Soon Im + Show 4 more

Open Access

https://doi.org/10.1109/jphot.2020.3036498

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Abstract

We have proposed and experimentally realized an ultra-compact and broadband silicon nitride edge-coupler that enables high coupling efficiency. The proposed coupler was realized by concatenating short tapers in four stages, whose angles were designed to minimize the footprint while preserving the coupling efficiency. The constituting taper segments were designed by carefully sectioning a long adiabatic taper while adapting to an appropriate taper angle for each segment. The designed coupler exhibited an extremely short footprint of 76 μm. A coupling efficiency of 92% was experimentally attained at 1550 nm wavelength when coupled to a single-mode fiber having a mode field diameter of ∼4 μm. Further, an efficiency of over 90% throughout the C and L bands was observed. A 3-dB bandwidth of 965 nm, spanning λ = 1015–1980 nm, was achieved in the simulation. Additionally, the fabricated device exhibited an enhanced cleaving tolerance by virtue of its elongated tip, along with relaxed alignment tolerances ranging up to 3.5 μm. The proposed design was also found to comply with the waveguides having widths between 1 μm and 4 μm without affecting the overall footprint and efficiency. This work is anticipated to provide a promising foundation for the development of compact photonic devices.

Highlights

With the growing prominence of high-speed and compact devices, photonic integrated circuits (PICs) have garnered considerable interest owing to their large-capacity transmission and fabrication compatibility with the existing complementary metal-oxide-semiconductor (CMOS) technology
A substantially miniaturized edge coupler was successfully demonstrated by cascading a series of taper segments with meticulously determined taper angles, which were obtained by segmenting a long adiabatic taper
The coupling efficiency of the proposed coupler was as high as 92% and 88% for the transverse electric (TE) and transverse magnetic (TM) modes at 1550-nm wavelength, respectively

Summary

Introduction

With the growing prominence of high-speed and compact devices, photonic integrated circuits (PICs) have garnered considerable interest owing to their large-capacity transmission and fabrication compatibility with the existing complementary metal-oxide-semiconductor (CMOS) technology. To achieve a miniaturized coupler, a fiber-to-waveguide coupler, where two tapers with different thicknesses were appended to each other, was demonstrated to provide a coupling loss of 0.58 dB for an overall taper length of 151 μm [17]. It incorporated multiple Si3N4 thicknesses, which might lead to increased complexity and additional cost for the fabrication process. A fiber-to-waveguide edge coupler based on a low-index platform should be developed from the perspective of optimizing the reproducibility, design complexity, taper length, taper angle, and coupling efficiency [9]–[17].

Design of the Proposed Multi-Stage Tapered Coupler

Fabrication and Characterization of the Proposed Coupler

Findings

Conclusion