30-km Error-Free Transmission of Directly Modulated DFB Laser Array Transmitter Optical Sub-Assembly for 100-Gb Application

We fabricated the first compact 100-gigabit Ethernet (100GbE) transmitter optical sub-assembly (TOSA) using a directly modulated DFB laser (DML) array monolithically integrated with an optical multiplexer. Specially designed InGaAlAs/InGaAlAs multiple quantum wells make it possible to obtain a large gain in the 1295-1310-nm wavelength range and to operate at a high temperature of 55 °C. The four-channel DML array chip is only 2.0 mm × 2.4 mm in size, and the fabricated TOSA is only 7.2 mm(W ) × 14.3 mm(L) × 6.5 mm(H), which fits a CFP2 or smaller 100-GbE transceiver. For all the lanes, the 3-dB bandwidths of the TOSA exceeded 17 GHz, and it could operate at 25.8 Gb/s. With 25.8-Gb/s × four-channel simultaneous operation, error-free transmissions over a 30-km single-mode fiber were demonstrated for all the lanes.

I. Introduction

Data center traffic is increasing greatly in response to the growth of cloud computing, and the Ethernet data rate is rising rapidly to handle this increase. 100-gigabit Ethernet (100GbE) was standardized in 2010 [1], and 100GBASE-LR4 was standardized for 10-km reach applications. 100GBASE-LR4 employs a multilane interface with a data rate of . The wavelength band is 1.3 μm and the lane spacing is 800 GHz which corresponds to the LAN-WDM grid. As for the low power consumption and low cost light sources of 100GBASE-LR4, directly modulated DFB lasers (DMLs) are promising candidates and some DMLs operating at 25.8 Gb/s have been studied [2]–[6] . 100GBASE-ER4 was standardized for use with a reach of over 10 km (e.g., 40 km). And an electroabsorption modulator integrated with a DFB laser (EADFB laser) is a promising light source for 100GBASE-ER4 [7]–[11]. However, the EADFB laser is a little expensive and has fairly high power consumption. Therefore, the DML is also expected to provide low power consumption and low cost light source for applications where the reach exceeds 10 km and is less than 40 km (e.g., 30 km).