Design and manufacturability issues of a co-packaged DFB/MZ module

Abstract
10 Gb/s data transmission over 80 km of standard fiber, or 2.5 Gb/s over 1000 km, can best be accomplished with an external Mach-Zehnder modulator and a high power DFB laser operating CW. Co-packaging those devices, and including dense WDM wavelength locking plus variable optical attenuation, provides an extremely compact, cost-effective, yet highly sophisticated module. Co-packaging discrete DFB and InP MZ chips has also paved the way for introducing cost-reducing integrated DFB/MZ devices with minimal impact at the system level. Nortel has been manufacturing, and using in its state-of-the-art transmission systems, evolving versions of these modules since 1995. We describe the optics train which couples laser light into the MZ chip. Because of the extreme alignment sensitivity, the design must provide both high coupling efficiency and stability. Because production volumes of these modules were initially low, with costs dominated by the laser and modulator chips themselves, the design is based on skilled manual alignment techniques. As volumes have increased the design has had to adapt to manufacturability issues such as operator training, quality, and productivity limits.