Air-trench splitters for ultra-compact ring resonators in low refractive index contrast waveguides

Nazli Rahmanian,Yongbin Lin,Seunghyun Kim,Gregory P Nordin

doi:10.1364/oe.16.000456

Abstract

We demonstrate air-trench splitters in low index contrast perfluorocyclobutyl (PFCB) waveguides. Splitters are fabricated by etching 800 nm wide high aspect ratio (18:1) trenches. The measured optical loss is 0.4 dB/splitter. The reflection/transmission splitting ratio is 0.859/0.141, which closely matches two-dimensional finite difference time domain (2DFDTD) simulation results. Air-trench splitters and bends are used to demonstrate an ultra-compact ring resonator (RR) with a size reduction of 1,700 compared to a RR based on traditional curved waveguides in the same material system. A comparison between the RR's measured and analytically calculated performance shows close agreement when splitter and bend losses are taken into account.

Highlights

Low index contrast (LIC) waveguide materialssuch as silica and various polymers offer low propagation and fiber coupling losses in addition to well-developed fabrication processes [1,2,3,4,5,6,7]
We demonstrate air-trench splitters in low index contrast perfluorocyclobutyl (PFCB) waveguides
An ultra-compact ring resonator is demonstrated based on air-trench splitters and bends, which reduces RR size by 1,700 compared to a comparable RR realized with traditional curved waveguides

Summary

Introduction

Low index contrast (LIC) waveguide materials (core/clad refractive index difference ≤1.5%). We recently demonstrated that compact bends can be realized in low refractive index, low index contrast (LILIC) materials using air trenches based on adjusting the bend angle to insure that all of the angular spectrum components of the waveguide mode undergo total internal reflection (TIR) [14,15,16]. Using this approach we achieved a measured bend efficiency of 97.2% for TE polarization (electric field in the plane of the substrate) and 96.2% for TM polarization (electric field out of the plane) [16].

Fabrication

Experimental measurement

Air-trench splitters

Ring resonator

Discussion

Conclusion