Low-loss, high-index-contrast Si_3N_4/SiO_2 optical waveguides for optical delay lines in microwave photonics signal processing

Leimeng Zhuang,David Marpaung,Chris Roeloffzen,Maurizio Burla,Willem Beeker,Arne Leinse

doi:10.1364/oe.19.023162

Abstract

We report the design and characterization of Si₃N₄/SiO₂ optical waveguides which are specifically developed for optical delay lines in microwave photonics (MWP) signal processing applications. The waveguide structure consists of a stack of two Si₃N₄ stripes and SiO₂ as an intermediate layer. Characterization of the waveguide propagation loss was performed in race track-shaped optical ring resonators (ORRs) with a free-spectral range of 20 GHz and a bending radius varied from 50 μm to 125 μm. A waveguide propagation loss as low as 0.095 dB/cm was measured in the ORRs with bend radii ≥ 70 μm. Using the waveguide technology two types of RF-modulated optical sideband filters with high sideband suppression and small transition band consisting of an Mach-Zehnder interferometer and ORRs are also demonstrated. These results demonstrate the potential of the waveguide technology to be applied to construct compact on-chip MWP signal processors.

Highlights

Microwave photonics (MWP) signal processing techniques have gained a lot of attention in the last few years [1,2,3,4]
Narrowband RF filtering and beamforming for large-size phased array antennas may require optical delay path lengths of tens of centimeter or more. This will result in a low link-gain of the MWP signal processor if there is a significant waveguide propagation loss
We have reported the design and characterization of Si3N4/SiO2 optical waveguides which are developed for optical delay lines in MWP signal processing applications

Summary

Introduction

Microwave photonics (MWP) signal processing techniques have gained a lot of attention in the last few years [1,2,3,4]. Narrowband RF filtering and beamforming for large-size phased array antennas may require optical delay path lengths of tens of centimeter or more This will result in a low link-gain of the MWP signal processor if there is a significant waveguide propagation loss. Low propagation loss in the figure of sub 1 dB/m have been reported in [17,19] but this has been shown in optical waveguides with very low refractive index contrast (

Waveguide geometry

ORR device layout

Waveguide propagation loss characterization

Characterization of optical sideband filter

Conclusion