Mitsubishi Electric develops an uncooled direct-modulated 10-Gbit/sec DFB laser

15 December 2003 Tokyo Lightwave--Mitsubishi Electric Corporation has developed a direct-modulated 10-Gbit/sec distributed feedback laser diode (DFB-LD) that will be used for optical telecommunications. This DFB has cleared the OC-192 mask criterion related to communication transmission quality and will satisfactorily transmit at 10 Gbits/sec in conditions up to, and including, 120°C without a cooling element.

Adopting this uncooled DFB laser enables the installation of a large capacity data communication network at low cost, with optical transmission capable of high speeds up to 10 Gbits/sec. Furthermore, its low electric power consumption makes it ideal for an internet-type network such as the metro-network, which combines high speed initiation fiber to the home and intranet LAN with backbone lines.

The optical transmitters with smaller size and lower power consumption will meet the strong demand of increasing internet-traffic, and the uncooled 10-Gbit/sec direct-modulated DFB-LDs are the key devices for current and next generation optical transmitters such as XENPAK and XFP. Mitsubishi Electric has already released the uncooled DFB-LDs for 85°C operation, in which an InGaAsP active layer is adopted. Meeting the request for the smaller size transmitters with smaller size that can operate without a cooling element at higher temperatures was the obvious next step.

Device features
By applying an AlGaInAs active layer instead of a conventional InGaAsP active layer material, electrons in the active layer are confined. The efficiency of the light emission does not degrade at high temperatures, which allows the clear eye-opening for 10-Gbit/sec telecommunications applications even at 120°C.

To obtain high-speed operation, the strong interaction of photons with electrons and holes in the active layer through a grating process with high optical reflectivity is necessary. For this purpose, using the deep grating close to the active layer is effective. Mitsubishi Electric developed new crystal growth techniques for burying the deep grating grooves flat by a semiconductor layer of only 100-nm thickness. An AlGaInAs active layer is successively formed on the previous semiconductor layer on the grating with no crystal defect. These techniques enable both high-speed operation and high reliability at high temperature.