Silicon Nitride (Si3N4) (De-)Multiplexers for 1-μm CWDM Optical Interconnects

Stanley S Cheung,Michael R T Tan

doi:10.1109/jlt.2019.2956382

Abstract

We discuss the design and demonstration of 4-channel coarse wavelength-division (de-)multiplexers based on cascaded Mach-Zehnder interferometer (MZI) lattice filters and arrayed waveguide gratings (AWG) on a 150 nm silicon nitride (Si 3 N 4 ) platform. The 1 × 4 (de-)multiplexers are designed for a channel separation of 25 nm and operate within 990-1065 nm for bottom emitting vertical cavity surface emitting lasers (VCSEL)-based optical links. For Si 3 N 4 Gaussian AWGs, we demonstrate crosstalk <; -35 dB at the peak transmission band with insertion loss <; 0.5 dB. Measurements were performed over many dies, and pass-band standard deviations for channel 1-4 are 0.49, 0.66, 0.42, and 0.37 nm, respectively. Results for flat-top AWGs indicate crosstalk <; -20 dB, with insertion loss <; 3 dB for the best devices. Flat-top cascaded 2 nd order and 3 rd order MZI lattice filters show a minimum of crosstalk <; -15 dB and <; -20 dB, respectively. The pass-band temperature shift was determined to be 14.5 pm/°C, which is lower than reported values for silicon. The device footprint of the Gaussian and flat-top AWGs are both ~670 × 200 μm. The device footprint of the flat-top cascaded 2 nd order and 3 rd order lattice filters are 1160 × 470 μm and 1570 × 470 μm, respectively. We believe the Si3N4 platform has potential for its use in CWDM and possibly DWDM transceiver/optical-modules for data/computer communication in high temperature environments up to 80 °C.

Highlights

T HERE continues to be an increased demand for high bandwidth density optical interconnects for future mega data centers, long-haul communications, and peta/exa-scale high performance computing (HPC)
We demonstrate 4-channel CWDMmultiplexers based on Si3N4 arrayed waveguide gratings (AWG) and Mach–Zehnder interferometer (MZI) lattice filters for 990–1065 nm optical engines
There are a number of material platforms that are transparent at CWDM wavelengths of 990–1065 nm such as InP, GaAs, ZnS, SiO2, CaF2, MgF2, TiO2, BaF2, BaTiO3, ITO, etc., there are considerable trade-offs between insertion loss, crosstalk, phase errors, footprint size, process tolerance, cost, and manufacturability

Summary

INTRODUCTION

T HERE continues to be an increased demand for high bandwidth density optical interconnects for future mega data centers, long-haul communications, and peta/exa-scale high performance computing (HPC). Current and generation computing architectures all employ low-latency optical links that come in the form of parallel optical modules, active optical cables or QSFP (Quad Small Form-factor Pluggable) transceivers and it is believed that optical interconnects are still one of the key technologies that can continue to address the bandwidth, energy, and cost challenge required in the future Based on these challenges, the 3 main desired requirements for the (de-)multiplexing filters within an optical interconnect module should be: 1) lowering the optical losses such that there is minimal impact on the optical power budget, 2) the pass-band wavelengths are tolerant enough to accommodate high temperature operation (80 °C) such that electrical thermal tuning is not required, 3) the material platform is robust enough to yield devices with repeatable performance such that post fabrication trimming is avoided [6]–[8]. CHEUNG AND TAN: SILICON NITRIDE (Si3N4) (DE-)MULTIPLEXERS FOR 1-μm CWDM OPTICAL INTERCONNECTS

SILICON NITRIDE PLATFORM

CWDM MZI LATTICE FILTERS

Findings

CONCLUSION