Transmitter Optical Subassembly Using a Polarization Beam Combiner for 100 Gbit/s Ethernet over 40-km Transmission

A transmitter optical subassembly (TOSA) has been developed for a 100-Gbit/s Ethernet system for a long optical transmission distance over a 40-km single-mode fiber (SMF). To obtain a high optical output power and a high dynamic extinction ratio, the TOSA consists of two two-channel distributed feedback laser diode array chips integrated with electro-absorption modulators (EADFB laser array chips) with a 2 × 1 multimode interference (MMI) optical coupler and a polarization beam combiner for wavelength multiplexing. The TOSA is 8.7 mm × 28.7 mm × 6.5 mm including an LC-type receptacle. The TOSA has a twin collimator path for two EADFB laser array chips. The wavelength multiplexer consists of a mirror, a half-wavelength plate, and a polarization beam combiner. The TOSA could improve the optical output power by around 2 dB compared with a TOSA with a four-channel EADFB laser array chip and a 4 × 1 MMI optical coupler. An optical modulation amplitude of over 0.5 dBm and a mask margin exceeding 21% were obtained for each lane when all lanes were operated simultaneously with an EA modulator driving voltage of 1.5 V at a bit rate of 25.78125 Gbit/s, which fully satisfies the 100GBASE-ER4 specifications. We demonstrated error-free operation for an SMF transmission of over 40 km. Moreover, we confirmed that the TOSA was capable of error-free SMF transmission over 60 km with a power penalty of less than 1.4 dB.

I. Introduction

Telecommunication traffic has continued to increase greatly and will continue to do so. To deal with this phenomenon, 100-Gbit/s Ethernet (100 GbE), which is an optical communications technology, was standardized as IEEE 802.3ba [1] in 2010. It specifies two kinds of long transmission reach over single-mode fiber (SMF), namely 100 GBASE-LR4 for a 10 km reach and 100 GBASE-ER4 for a 40 km reach. These 100 GbE specifications employ a system with a multi-lane approach that uses four 25.78125 Gbit/s per lane with local area network wavelength division multiplexing (LAN-WDM), which is assigned a wavelength channel spacing of 800 GHz in the 1.3-μm wavelength band. For a 100 GbE transceiver, a centum form-factor pluggable (CFP) transceiver was defined in the CFP multi-source agreement (MSA) [2]. To realize the more compact 100 GbE transceiver defined in CFP2 or CFP4, we must further miniaturize and integrate optical components such as the transmitter optical sub-assembly (TOSA) for the transmitter section and the receiver optical sub-assembly (ROSA) for the receiver section.