Widely-tunable, narrow-linewidth III-V/silicon hybrid external-cavity laser for coherent communication.

Hang Guan,Tal Galfsky,Michael Hochberg,Michael Caverley,Tam N Huynh,Saeed Fathololoumi,Yangjin Ma,Thomas Baehr-Jones,Yang Liu,Alexandre Horth,Ruizhi Shi,Jose Roman,Ari Novack,Keren Bergman

doi:10.1364/oe.26.007920

Abstract

We demonstrate a III-V/silicon hybrid external cavity laser with a tuning range larger than 60 nm at the C-band on a silicon-on-insulator platform. A III-V semiconductor gain chip is hybridized into the silicon chip by edge-coupling the silicon chip through a Si3N4 spot size converter. The demonstrated packaging method requires only passive alignment and is thus suitable for high-volume production. The laser has a largest output power of 11 mW with a maximum wall-plug efficiency of 4.2%, tunability of 60 nm (more than covering the C-band), and a side-mode suppression ratio of 55 dB (>46 dB across the C-band). The lowest measured linewidth is 37 kHz (<80 kHz across the C-band), which is the narrowest linewidth using a silicon-based external cavity. In addition, we successfully demonstrate all silicon-photonics-based transmission of 34 Gbaud (272 Gb/s) dual-polarization 16-QAM using our integrated laser and silicon photonic coherent transceiver. The results show no additional penalty compared to commercially available narrow linewidth tunable lasers. To the best of our knowledge, this is the first experimental demonstration of a complete silicon photonic based coherent link. This is also the first experimental demonstration of >250 Gb/s coherent optical transmission using a silicon micro-ring-based tunable laser.

Highlights

Silicon photonics (SiPh) devices have gained significant market traction in metro, data center interconnect, and intra-data center applications, and are widely viewed as a key technology for next-generation networks which will require high data rates, high density, energy efficiency, and low cost [1,2,3,4,5,6,7]
2.2 Spot-size converter Due to the large mode mismatch between reflective semiconductor optical amplifier (RSOA) waveguide and silicon waveguide, we introduce an optical spot-size converter on the silicon photonics chip to reduce the coupling loss between the chips
From 3D FDTD simulations shown in Fig. 3, we find that a 0.5 μm vertical misalignment (y-axis) increases the mode mismatch by 1.2 dB; the coupler is more resilient in the horizontal direction (x-axis) given the asymmetric mode shape, the same 0.5 μm misalignment would result in a 0.5 dB increase in insertion loss

Summary

Introduction

Silicon photonics (SiPh) devices have gained significant market traction in metro, data center interconnect, and intra-data center applications, and are widely viewed as a key technology for next-generation networks which will require high data rates, high density, energy efficiency, and low cost [1,2,3,4,5,6,7] This kind of technology can be used to address a wide range of applications from short-reach interconnects [8,9,10] to long-haul communications [11,12,13,14,15]. Practical silicon-based light sources are still missing, despite the progress in germanium lasers [16,17], as both silicon and germanium are indirect-band semiconductors and inefficient at light generation. To the best of our knowledge, this is the first experimental demonstration of a complete silicon photonic based coherent link

Laser structure

Findings

Discussion

Conclusion