Input/output fiber configuration in a laser package design

The mechanical and thermally induced stresses are evaluated for different configurations of the input/output (I/O) fibers in a laser package design. We show that, if the fibers experience bending deformations, the mechanical stresses can be minimized by applying a proper ends off-set and that the thermal stresses can be reduced, if necessary, by the mechanical prestressing of the fibers. We show also that if the optical device can be rotated by a small angle around the transverse axis, this rotation can be effectively used for minimizing the stresses. We found that the smallest fiber span can be achieved by making the end planes of the optical device perpendicular to the package´s axis. In this case the I/O fibers become straight, and should be made short enough to avoid buckling under the action of the thermally induced compressive stresses. We suggest that such a configuration is employed, when the appropriate rotation of the optical device is possible, the fiber ends can be easily aligned, and the support structures are sufficiently strong to withstand a relatively high thermally induced force from the compressed fiber. This force can be brought down, if necessary, by application of low expansion materials for the package enclosure (such as, say, Kovar or Invar). Although the results of our analysis enable a designer to evaluate the mechanical behavior of the I/O fiber of different configurations, the final selection of the I/O fiber configuration can be made only after the allowable stresses and the achievable alignment (in the case of straight fiber) are determined experimentally