We have developed a multiple quantum well (MQW) electroabsorption (EA) modulator for wavelength-division multiplexing (WDM) switching systems. The fabricated MQW EA gate has low polarization and wavelength-dependent loss and high extinction ratio within the wavelength range of 1545 to 1560 nm. And by using this gate ultra-high-speed switching is achieved for WDM signals. Moreover, we optimize the EA gate for the full gain-band of an erbium-doped fiber amplifier (EDFA)(1535 to 1560 nm). This EA gate provides low polarization-dependent loss, higher extinction ratio, and high saturation input power in the wider wavelength range. These MQW EA gates will play an important role in future WDM switching systems.

A dual-core spot size converter (DC-SSC) is integrated with a lateral grating assisted lateral co-directional coupler (LGLC) tunable laser by using no additional complicated fabrication processes. The excess loss due to the DC-SSC is only 0.5 dB, and narrow full width half maximums (FWHMs) of vertical and horizontal far-field patterns (FFPs) produced by the laser are about 25° and 20°. This integration causes no degradations of the performance of the LGLC laser; in other words, it maintains good lasing characteristics, namely, wide tuning range of over 68 nm and SMSR of over 35 dB in the C-band under a 50 semi-cooled condition.

A 50-Gb/s optical transmitter, consisting of a 25-Gb/s-class lens-integrated DFB-LD (with -3-dB bandwidth of 20GHz) and a LD-driver chip based on 0.18-µm SiGe BiCMOS technology for inter and intra-rack transmissions, was developed and tested. The DFB-LD and LD driver chip are flip-chip mounted on an alumina ceramic package. To suppress inter-symbol interference due to a shortage of the DFB-LD bandwidth and signal reflection between the DFB-LD and the package, the LD driver includes a two-tap pre-emphasis circuit and a high-speed termination circuit. Operating at a data rate of 50Gb/s, the optical transmitter enhances LD bandwidth and demonstrated an eye opening with jitter margin of 0.23UI. Power efficiency of the optical transmitter at a data rate of 50Gb/s is 16.2mW/Gb/s.