A Broadband Algorithm for Adiabatic Mode Evolution and its Application on Polarization Splitter-Rotator on LNOI Platform

TL;DR

This paper introduces a new analytical algorithm for adiabatic mode evolution waveguides that shortens device length and reduces computational resources, demonstrated by a broadband polarization splitter-rotator on LNOI with high efficiency.

Contribution

A novel analytical design algorithm for adiabatic waveguides that shortens device length and simplifies computations, applied to a broadband polarization splitter-rotator on LNOI.

Findings

PSR length reduced by 3.5 times

Insertion loss of 0.8 dB over 76 nm bandwidth

Polarization extinction ratio of 12.2 dB

Abstract

Adiabatic mode evolution waveguides (AMEWs) are widely utilized in integrated photonics, including tapered waveguides, edge couplers, mode converters, splitters, etc. An analytical theory and a novel AMEW design algorithm are developed to create shortcuts to adiabaticity (STA). This new algorithm is effective in shortening the total length of the AMEW while maintaining the desired wavelength range. Moreover, this analytical algorithm requires much fewer computing resources than traditional numerical algorithms. With the new algorithm, we demonstrate a broadband and highly efficient polarization splitter-rotator (PSR) on a lithium-niobate-on-insulator (LNOI) platform with an LN thickness of 500 nm. According to our simulation, the length of the PSR is shortened by 3.5 times compared to the linear design. The fabricated PSR, with a total length of 2 mm, exhibits an insertion loss (IL) of 0.8 dB and a polarization extinction ratio (ER) of 12.2 dB over a wavelength range exceeding 76 nm.