Efficient and Tunable Strip-to-Slot Fundamental Mode Coupling

TL;DR

This paper introduces a highly efficient, tunable wire-to-slot waveguide coupler in SOI, achieving 99% coupling efficiency both theoretically and experimentally, with applications in resonators and thermal stability.

Contribution

It presents a novel mode transformer-based coupler with near-perfect efficiency and demonstrates its practical application in ring resonators with improved thermal stability.

Findings

Achieved 99% coupling efficiency in experiments.

Demonstrated excitation of slot modes in ring resonators.

Showed nearly athermal behavior in PMMA-filled slot rings.

Abstract

We present a novel photonic wire-to-slot waveguide coupler in SOI. The phase matching between a wire and slot mode is achieved using a mode transformer. The architecture consists of a balanced 50/50 power splitter and a tunable phase matched taper combiner forming a slot waveguide. We show a theoretical wire-to-slot coupling efficiency of 99 % is achievable and experimentally, we demonstrate a coupling efficiency of 99 % in the 1550 nm band. Based on the coupling scheme, we also show excitation of a slot mode in a slotted ring resonator and verified the excitation through the thermo-optic response of the rings. We show a nearly athermal behaviour of a PMMA filled slot ring with a thermo-optic response of 12.8 pm/C compare to 43.5 pm/C for an air clad slot waveguide.