Development of Electro-Absorption Modulator Driver ICs for 25G/40G Transmission

As Internet traffic increases, large communication capacity is required in optical communication systems. For the client side of DWDM *1 (dense wavelength division multiplexing) systems, the baud rate of current optical communication is mainly 10 Gbit/s, which has already been used in 10G Ethernet. However, these systems will be insufficient for the accelerated traffic increase expected in the next few years. Therefore, a 100G Ethernet system using the LAN-WDM (1) technique has been standardized by the IEEE (Institute of Electrical and Electronics Engineers). In this standard, 4-lane wavelength division multiplex with 800 GHz spacing from 1296 to 1309 nm is employed. In addition, as part of the OTN (optical transport network) standardization, OTU4 (optical-channel transport unit 4; 112 Gbit/s), which is more compatible with 100G Ethernet, was proposed in ITU-T (International Telecommunication Union Telecommunication Standardization Sector. The baud rate of the 100G Ethernet system and OTU4 are 25 Gbit/s and 28 Gbit/s, respectively. On the other hand, STM-256, a well-known standard of ITUT, has a baud rate of 39.8 Gbit/s. In addition, demand is increasing for OTU3 (43.0 Gbit/s), a new standard compliant with 40G Ethernet. In the latest system, low power dissipation is essential. More particularly, CFP (centum gigabit form factor pluggable)*2 (2) a widely-used MSA (MultiSource Agreement) transceiver, requires to have low power consumption and fit in a small outline package for optical transmitter modules. We have already developed an optical transmitter module and a driver IC for high-speed optical communication systems up to 10 Gbit/s. As for 40G and 25G transmitters, electro-absorption modulators integrated with DFB laser (EA-DFB*3) are suitable for high-optical transmitter sources. In this paper, we outline newly developed EA modulator driver ICs for both 25G and 40G transmission. These ICs have low power dissipation and high-speed drivability, and are fabricated by an in-house InP D-HBT process (ft/fmax = 150/250 GHz). To minimize power dissipation for each bit rate, the circuit topology was optimized. These ICs have a built-in optical transmitter module to provide the best performance. This paper describes an overview of EA modulator driver ICs and their evaluation results. The performances of the optical transmitter modules, compliant with SDH, OTN and 100G Ethernet standards, are also reported.