Improvements in index alignment method for laser-fiber array packaging

An “index alignment” method, based on the registration of fiducial marks, was previously developed for passive alignment of a laser array to a corresponding fiber array. This method has recently been improved and used to fabricate laser-fiber array transmitter modules for single-mode operation at 1300 nm. An improved computer-controlled alignment-stage system with machine-vision features has been installed in order to render the alignment procedure faster, more precise, and more reliable; this system was particularly effective in quick achievement of the difficult but necessary angular alignment of the components. Special “self-registration” component-fabrication techniques were also developed to avoid mask-registration errors associated with the fabrication of the laser chip and the fiber carrier. Measures were also taken to improve the accuracy of alignment of the etch mask to the silicon crystallographic axes during fiber-carrier fabrication, and to improve the etch-stop indication process. Test results showed that for single-mode operation at 1300 nm, coupling efficiencies greater than 8% could be achieved, approaching the 9% coupling efficiency observed with active alignment. Tests of a completed module at 1 Gb/s showed values of RIN low enough to permit operation at distances of about 1 km