Improvements in Index alignment method for laser-fiber array packaging

Abstract

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 singlemode operation at 1300nm. 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, so that the fiducial marks were automatically keyed to the positions of the laser ridges and V grooves, respectively. 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.These techniques permitted an estimated accuracy and wafer-scale uniformity of ≈ ±0. 5μm of the fiber carrier V-groove widths. In addition, the essential elements of a practical technique for separation of a large-array laser-fiber module into a multiplicity of small-array submodules was demonstrated; in this way the cost of the alignment procedure could be amortized over a large number of transmitter modules. Several connectorized laser-fiber array modules were fabricated with the improved alignment apparatus and components. Test results showed that for single-mode operation at 1300 nm, coupling efficiencies greater than 8% could be achieved for a laser-fiber spacing of about 35 μm. Such values closely approach the 9% coupling efficiency observed at this spacing with active alignment. Tests of the completed module at 1 Gb/s showed values of RIN low enough to permit operation at distances of about 1 km.