# 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.

## Key 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.

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Source: https://tomesphere.com/paper/1705.01698