INPUT-OUTPUT FIBER CONFIGURATION IN A LASER PACKAGE DESIGN - OPTIMIZATION FOR LOWER STRESSES

Mechanically and thermally induced stresses in the input/output (I/O) fiber of a laser package design are evaluated for different configurat ions of this fiber. It is found that if the fiber exhibits bending def ormations, mechanical stresses can be minimized if a proper end offset is applied and thermal stresses can be reduced if the fiber is mechan ically prestressed. It is found also that if the optical device can be rotated by a small angle around the transverse axis, this rotation ca n be used effectively to minimize the stresses in both categories. It is shown that the smallest fiber span can be obtained if one makes the end planes of the device perpendicular to the package axis, i.e., by making the fiber straight. Clearly in this case the fiber should be ma de short enough to avoid buckling under the compressive action of ther mally induced stresses. Such a configuration is the most feasible beca use it results in the shortest fiber span (length) and in minimal opti cal losses. Such a configuration should be employed in all cases when rotation of the optical device is possible, when the fiber ends can be easily aligned, and if the support structures are strong enough to wi thstand the higher thermally induced forces from the compressed fiber. Thermal stresses can be brought down by the use of low-expansion mate rials such as Kovar or Invar for the package enclosure. It should be p ointed out that although the results of this analysis provide designer s with a useful theoretical guide for optimizing the I/O fiber configu ration, the final configuration can be selected only after the allowab le stress and the achievable alignment (in the case of straight fiber) are evaluated experimentally.