Fabrication-tolerant and CMOS-compatible polarization splitter and rotator based on a compact bent-tapered directional coupler

Humaira Zafar,Kenneth L Kennedy,Dalaver Hussain Anjum,Mauro Fernandes Pereira

doi:10.1063/5.0030638

Abstract

In this paper, we demonstrate a broadband, low-loss, compact, and fabrication-tolerant polarization splitter and rotator (PSR) on a silicon-on-insulator platform. The PSR is based on an asymmetric directional coupler (ADC), which is covered with SiO2 from the top to make it compatible with the standard metal back end of line (BEOL) process. Conventional ADC-based PSRs suffer from stringent fabrication requirements and relatively low bandwidth, while the proposed bent-tapered design is highly insensitive to the fabrication errors (＞70 nm tolerance on the coupling gap) with an enlarged bandwidth and a compact footprint of 53 µm × 7 µm. It yields a polarization conversion loss less than 0.7 dB, a transverse electric (TE) insertion loss better than 0.3 dB, an ultra-low crosstalk with the TE extinction better than 30 dB, and the transverse magnetic extinction better than 25 dB, over a 200 nm wavelength range (1.5 µm–1.7 µm), in both ports. At the 1.55 µm wavelength, the calculated ultra-low polarization conversion loss and TE insertion loss are 0.27 dB and 0.08 dB, respectively.

Highlights

Controlling the polarization of light as it propagates and different modes get coupled is a subject of perennial interest in optics and photonics,1–3 notably within the context of silicon photonics.4Silicon photonics has shown great potential as it promises compact footprint and low-energy high-bandwidth technology to integrate optical circuits on a silicon chip, driven by its compatibility with complementary metal-oxide semiconductor (CMOS) processes.5 A compact and dense integration of silicon photonics devices is achieved due to a large refractive index contrast, but the performance of the devices is strongly dependent on the polarization state of the input light
We present a novel polarization splitter and rotator (PSR) based on a bent and tapered asymmetric directional coupler (ADC), making it compact and insensitive to fabrication errors
Once the phase matching is achieved at a certain position along the tapered curvature, the converted power is maintained as the phase matching is no longer satisfied for the rest of the bent taper, relaxing the fabrication error sensitivity of PSR and making it insensitive to the length of the ADC

Summary

Introduction

Controlling the polarization of light as it propagates and different modes get coupled is a subject of perennial interest in optics and photonics,1–3 notably within the context of silicon photonics.4Silicon photonics has shown great potential as it promises compact footprint and low-energy high-bandwidth technology to integrate optical circuits on a silicon chip, driven by its compatibility with complementary metal-oxide semiconductor (CMOS) processes.5 A compact and dense integration of silicon photonics devices is achieved due to a large refractive index contrast, but the performance of the devices is strongly dependent on the polarization state of the input light. The strip waveguide and the slab section of the ridge waveguide are designed as tapers to ensure a broadband and fabrication-friendly PSR operation.

Results

Conclusion