Low bend loss waveguides enable compact, efficient 3D photonic chips

TL;DR

This paper introduces a new fabrication method for low bend loss femtosecond-laser written waveguides, enabling compact 3D photonic chips with high efficiency and minimal bend losses, suitable for complex integrated photonic devices.

Contribution

A novel two-step thermal annealing process that produces low bend loss, single-mode waveguides with sharp bends for 3D photonic chip integration.

Findings

Waveguides with 16.6 mm bend radius and 80% throughput

First demonstration of a low bend loss 3D pupil-remapper

Process enables compact, complex photonic chips with many waveguides

Abstract

We present a novel method to fabricate low bend loss femtosecond-laser written waveguides that exploits the differential thermal stabilities of laser induced refractive index modifications. The technique consists of a two-step process; the first involves fabricating large multimode waveguides, while the second step consists of a thermal post-annealing process, which erases the outer ring of the refractive index profile, enabling single mode operation in the C-band. By using this procedure we report waveguides with sharp bends (down to 16.6 mm radius) and high (80%) normalized throughputs. This procedure was used to fabricate an efficient 3D, photonic device known as a pupil-remapper with negligible bend losses for the first time. The process will also allow for complex chips, based on 10's - 100's of waveguides to be realized in a compact foot print with short fabrication times.