Method of fixing an optical fibre in a laser package

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Abstract
In order to couple the light emitted from a semiconductor laser into the core of an optical fibre, the simplest option is to use a butt coupling. In this case the core of the optical fibre is the same size as the emitting area of the laser and the NA of the fibre is greater than or equal to the divergence of the emitted beam. However where this is not the case and the core and laser emitting are not matched it is necessary to use a lens system. This lens system then focuses the divergent light into the fibre core. Though discrete lenses are sometimes used, often this lens is fabricated on the end of the fibre. When the lens is on the end of the fibre it must be fixed in place in front of the emitting laser using a method which will hold the fibre in position relative to the laser during the lifetime of the laser. This reliability requirement is particularly critical in the case of lasers with a highly elliptical output beams. In this case the tolerances for the displacement of a lensed fibre relative to the laser are extremely tight and a movement of less than 0.5 microns in the vertical direction can cause a drop in coupled power of greater than 10%. In this paper existing techniques of fixing the fibre relative to the laser are outlined and contrasted to an improved method. FEA analysis is used in the improved method. The improved method is described with salient features such as the fixing of the fibre to a rigid support member and the laser welding process used to fix the rigid support member in front of the laser is explained in detail. Reliability information is also presented demonstrating the capability of this technique in the fixing of an optical fibre relative to a laser device.

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