Low-Loss, Low-Crosstalk, and Large-Scale Optical Switch Based on Silicon Photonics

Keijiro Suzuki,Satoshi Suda,Shu Namiki,Kazuhiro Ikeda,Hiroyuki Matsuura,Hitoshi Kawashima,Ryotaro Konoike

doi:10.1109/jlt.2019.2934768

Abstract

We review the research progress of strictly nonblocking optical switches based on silicon photonics. We have developed a switch chip fabrication process based on a complementary metal-oxide-semiconductor pilot line and optical and electrical packaging technologies. We demonstrated all-paths transmission and switching of up to 32 input ports × 32 output ports with an average fiber-to-fiber insertion loss of 10.8 dB. Furthermore, we demonstrated an operating bandwidth wider than 100 nm for −30 dB crosstalk with double-Mach–Zehnder element switches in an 8 × 8 switch. For polarization-insensitive operation, we adopted a polarization diversity scheme and fabricated an 8 × 8 switch with fiber-based polarization-beam-splitters and two switch chips. The 8 × 8 switch exhibited a polarization-dependent loss of less than 0.5 dB. Moreover, an on-chip polarization diversity 8 × 8 switch integrated with polarization splitter rotators and two switch matrices on a single chip demonstrated a differential group delay less than 1 ps. Based on current technologies, we discuss the prospects for further port count expansion and remaining challenges for commercial deployment.

Highlights

D ATACENTER-RELATED traffic is growing, especially within data centers, with traffic forecast to grow at a rate of 25% per year until 2021 [3]
Among the integrated waveguide-based optical switches, we focus on the complementary metal-oxide-semiconductor (CMOS)-compatible silicon photonics switch, because the CMOS-compatible silicon photonics platform provides high density and uniform integration, and potentially low cost owing to its mass producibility
We review the current performance of CMOSbased silicon photonics path-independent insertion-loss (PILOSS) switches and discuss the remaining challenges for their practical application [20]

Summary

INTRODUCTION

D ATACENTER-RELATED traffic is growing, especially within data centers, with traffic forecast to grow at a rate of 25% per year until 2021 [3]. The switching capacity requirements for the switch ASICs to handle the massive data flow is outpacing Moore’s law This switching capacity expansion is accompanied by increased power consumption that is approaching the thermal limit (∼300 W) of practical integrated electronic circuit cooling technology [5]. Free-space optical switches can provide several hundred switching ports with a fiber-to-fiber insertion loss of only a few dB, and are commercially available. Silica planar lightwave circuit (PLC) based switches are commercially available and can provide up to 32 ports switching with an insertion loss of 6.6 dB. As for micro electro mechanical system (MEMS) based silicon switches, they possess a switching speed of ∼μs and the maximum port count of 240 Their electrical packaging is challenging, and transmissions of all paths have not been demonstrated yet. SUZUKI et al.: LOW-LOSS, LOW-CROSSTALK, AND LARGE-SCALE OPTICAL SWITCH BASED ON SILICON PHOTONICS. The wavelength dependence can be relaxed by exchanging the output port of the element MZ switch, resulting in the bandwidth expansion to 14.2 nm [6]

WAVELENGTH INSENSITIVITY

POLARIZATION INSENSITIVITY

Findings

DISCUSSION

CONCLUSION