Design of Optically Path Length Matched, Three-Dimensional Photonic Circuits Comprising Uniquely Routed Waveguides

TL;DR

This paper presents a novel method for designing 3D photonic circuits with path length matching and unique routing, enabling their use in interferometry, and demonstrates fabrication and verification of such circuits.

Contribution

It introduces a new design approach for physically path length matched, uniquely routed 3D photonic circuits suitable for interferometric applications.

Findings

Circuits were fabricated using femtosecond laser direct-write.

Optical path length matching within 45 micrometers was achieved.

The circuits are suitable for interferometric measurements.

Abstract

A method for designing physically path length matched, three-dimensional photonic circuits is described. We focus specifically on the case where all the waveguides are uniquely routed from the input to output; a problem which has not been addressed to date and allows for the waveguides to be used in interferometric measurements. Circuit elements were fabricated via the femtosecond laser direct-write technique. We demonstrate via interferometric methods that the fabricated circuits were indeed optically path length matched to within 45 um which is within the coherence length required for many applications.