Optical Circuit Switching Using REC-DFB Laser Array

The ongoing growth of data traffic from existing and new latency-sensitive applications poses a challenge to the data center network. Wavelength-routed optical circuit switching promises high bandwidth, low power and latency networking for data centers, but requires a wideband wavelength tunable source capable of nanosecond-scale hitless wavelength switching at every node. A tunable source based on DFB laser arrays is a potential candidate due to the high-speed dynamic property and high single-longitudinal-mode (SLM) stability of the DFB laser. However, the large-scale integration of the DFB laser and the high precision control of the lasing wavelength are still problems. In this work, we proposed and fabricated a monolithic integrated 16-channel DFB laser array with high SLM stability and 100-GHz channel spacing by using the reconstruction-equivalent-chirp (REC) technique. The maximum output power of each channel was above 6 mW. Based on the custom-designed fast switching drive board with a field-programmable gate array (FPGA), the switch-ON and OFF time between any pair of channel combinations were measured at less than 10 ns. Dynamic switching wavelengths remained stable and resided within the receiver bandwidth. Wavelength switching experiments for modulated light signals were done by driving the external modulator, achieving bit error performance at 1 × 10⁻⁹ for 10 Gb/s NRZ data.

I. Introduction

The massive growth of data traffic from existing and new latency-sensitive applications such as video, the Internet of Things, big-data analytics, and cloud computing put enormous pressure on the current data centers (DCs) [1], [2], [3], [4], [5]. This growth has led to renewed interest in optical switches for DCs. As compared with the electrical packet switches (EPS) in the current DC networks, first, it eliminates power-consuming optical-electrical-optical (OEO) conversions at the switch nodes, which significantly improves energy and cost-efficiency [6]. Second, by being transparent to the modulation format, it can support much higher throughput than today's switches and at much lower latency due to the lack of buffering or packet inspection overhead. Moreover, wavelength division multiplexing (WDM) technology can be employed to boost the optical network capacity at a superior power-per-unit bandwidth performance [7]. Finally, it does not use electronics for switching, thus sidestepping the electrical switches scaling wall [8]. Based on the aforementioned features, optical switching has the potential to be a future-proof solution for DC networks with deterministic low latency and high bandwidth.