This letter describes our DFB-LD module for use in WDM optical access networks. We realized an isolator-free DFB-LD module with a thermo-electric cooler in aim of stabilizing the emission wavelength for WDM systems. Silicon waferboard technology was employed to achieve simple assembly and small size of the module. This small size contributed to low TEC power. Our fabricated module demonstrated low-noise and stable emission wavelength characteristics under 156 Mbit/s pseudo random modulation.

Laser module fabricated with silicon platform technology is very attractive for low-cost modules. The technology enables passive optical alignment of an LD to an optical fiber. Our marker design for passive alignment allows positioning accuracy within 1 µm of LD. However, coupling efficiency is a key issue because that by conventional butt coupling scheme is low with about 10 dB coupling loss. We investigated optical coupling characteristics in various types of coupling scheme: conventional flat end fibers, cone fibers, integrated GRIN rod lenses on the platform and the coupling with new-type LDs integrated with spot size transformer. Improvement of coupling efficiency with 3 dB and 7.5 dB compared to flat-end fiber is achieved by using the cone fiber and the GRIN rod lens, respectively, although 1-dB coupling tolerances for alignment deteriorated with these schemes. We obtained high efficient coupling with 3.5 dB coupling loss and wide alignment tolerance of 2.3 µm simultaneously with a new-type LD integrated with spot size transformer owing to its expanded spot size characteristics.

A transmission data format for high-speed optical parallel interconnections is proposed and a 4-channel transmitter and receiver link module operating at up to 1.2 Gb/s per channel is demonstrated. The data format features "Group Multiplexing and Coding." In this scheme, input several tens channels are multiplexed and coded in group into reduced channels, resulting in burst-mode compatible, skew-free transmission, and low power-consumption of a link module. Experiments with fabricated modules comfirm that our data coding in multichannel optical transmission is promising for use in high-speed interconnections in information and switching systems.