HIGH OPTICAL COUPLING SCHEME IN LD MODULES WITH SILICON PLATFORM TECHNOLOGY

Laser module fabricated with silicon platform technology is very attra ctive for low-cost modules. The technology enables passive optical ali gnment of an LD to an optical fiber. Our marker design for passive ali gnment allows positioning accuracy within +/- 1 mu m of LD. However, c oupling efficiency is a key issue because that by conventional butt co upling scheme is low with about 10 dB coupling loss. We investigated o ptical coupling characteristics in various types of coupling scheme: c onventional flat end fibers, cone fibers, integrated GRIN rod lenses o n 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 an d the GRIN rod lens, respectively, although I-dB coupling tolerances f or alignment deteriorated with these schemes. We obtained high efficie nt coupling with 3.5 dB coupling loss and wide alignment tolerance of +/- 2.3 mu m simultaneously with a new-type LD integrated with spot si ze transformer owing to its expanded spot size characteristics.