Ultra-compact low-loss broadband waveguide taper in silicon-on-insulator

TL;DR

This paper introduces a compact, broadband, and fabrication-tolerant silicon-on-insulator waveguide taper that maintains high efficiency across multiple telecom bands, significantly reducing device footprint.

Contribution

It presents a novel, CMOS-compatible taper design with broad bandwidth and high fabrication tolerance, outperforming traditional adiabatic tapers and focusing gratings in size and robustness.

Findings

Broadband operation over 600 nm in O, C, and L-bands.

Tolerance to fabrication variations with <0.4 dB transmission change.

Device footprint is 20 times smaller than adiabatic tapers.

Abstract

A novel design of large bandwidth, fabrication tolerant, CMOS-compatible compact tapers (15 um) have been proposed and experimentally demonstrated in silicon-on-insulator. The proposed taper along with linear grating couplers for spot-size conversion exhibits no degradation in the coupling efficiency compared to a standard focusing grating in 1550 nm band. A single taper design has a broadband operation over 600 nm that can be used in O, C and L-band. The proposed compact taper is highly tolerant to fabrication variations; 80 nm change in the taper width and 200 nm in end waveguide width varies the taper transmission by <0.4 dB. The footprint of the device i.e. taper along with the linear gratings is ~ 250 {\mu}m2; this is 20X smaller than the adiabatic taper and 2X smaller than the focusing grating coupler.