Gennum debuts integrated ROSA line for 10GbE

Gennum Corp. has announced fully integrated receive optical subassemblies (ROSAs), which it will demonstrate at the Optical Fibers in Communications conference later this month.

With the Lightcharger technology it acquired from SiGe Semiconductor in 2004, Gennum was able to utilize the patents surrounding its Rchip (receiver on a chip) technology, which combines a photodiode, transimpedance amplifier and passives on a stacked die.

The company will debut a range of short- and long-wave ROSAs for 10GbE and Sonet applications spanning data center to ultra-longhaul distances. Imran Sherazi, director of marketing for optical products at Gennum, predicted the long-wave GN 3050 for 1,310nm applications may prove the most popular since it is intended for metro-area Ethernet links up to 10km.

Rchip was optimized to reflect Gennum's experience in manufacturing surface-mount hybrids and special video chips. The methodology reduces wirebonding between devices in the ROSA, and shows high sensitivity and gain stability as well as consistency across devices manufactured in a single lot. One advantage of the Rchip design is that it can use traditional wafer fab step-and-repeat lithography to integrate passive devices.

In contrast to ROSAs with three inductors in the AC path, Gennum's Rchip has no inductors in the AC path, allowing stable gain of approximately 20k?. This can eliminate post-amplification in designs using the new SFP+ optical form factor, Sherazi said. The ROSA device uses only seven wirebonds, and no external RF capacitors.

Long-wave ROSAs use flip-chipped PIN diodes, with wafer-level test performed after PIN integration. The short-wave ROSA is wafer-tested after TIAs are integrated with decoupling capacitors.

Four ROSAs will be shown at the optical conference: