Single-mode fiber packaging for semiconductor optical devices

The authors describe an approach which increases package assembly alignment tolerances substantially while demonstrating coupling efficiencies as high as 40%. This has been accomplished by utilizing a spherical lens to couple from the device into single-mode fiber. The ball lens is mounted directly on the chip carrier for maximum thermal and mechanical stability and is aligned mechanically rather than actively. The single-mode fiber alignment is done actively, and the fiber is positioned so as to compensate for misalignments of the ball lens. Coupling to the single-mode fiber was done directly and by using a second lens affixed to the end of the fiber. In addition to relaxed alignment tolerances, this coupling scheme has other advantages. The working distance between the ball lens and single-mode fiber is typically ≈2-4 mm. This allows for easy insertion of microoptical components such as optical isolators or filters into the package. The scheme also lends itself to a flexible, modular approach to packaging. The dual-lens coupling technique has been used to package optical amplifiers. A fiber-to-fiber gain as large as 10 dB has been demonstrated using this coupling technique