Permanent Low Loss Coupling of Single Mode Fiber Arrays to Waveguides

Over the past few years, a wide range of guided wave devices have been demonstrated in LiNbO3 and glass. The next step in the development of guided wave technology is to integrate several devices on a single substrate and to use the integrated device in a practical application. To this end, there is a clear need to further explore methods for permanently bonding large linear arrays of single mode fibers to waveguides. The principal challenge is to develop a technique that can maintain the required submicron accuracy over distances on the order of several millimeters. In reference 1, we reported on the attachment of V-grooved silicon chip arrays (with two fibers per array) to waveguides in LiNbO3. Here, we report on the extension of this technique to larger arrays. Specifically, we have permanently bonded arrays of six and twelve fibers to both ends of straight waveguides in lithium niobate. In both cases, low excess loss (average 0.3dB per interface) was measured. These are the largest arrays and the lowest excess losses reported in the literature. The six element structure (fiber-waveguide-fiber) was subjected to environmental testing with favorable results.