This invention relates to laser diode assemblies and, more particularly, to the alignment of the output coupling optical fiber with the laser diode source through a sealed housing.
The alignment of an output optical fiber with a laser diode housed in a sealable or hermetically sealed enclosure is a difficult problem. One approach disclosed in U.S. Pat. No. 4,119,363 involves first accurately locating the diode within the enclosure adjacent to an oversized opening. Next, the fiber is threaded through a flanged tube having a conical constriction which centers the fiber within the tube followed by soldering the fiber within the tube, advantageously using a solder preform. Finally, the flanged tube is positioned at the oversized opening in the enclosure, aligned to the diode and the flange soldered to the enclosure. Obviously, the need for two soldering operations increases the expense of fabrication. And while this approach may be satisfactory for aligning a single optical fiber to a laser diode, it is not applicable to the alignment of a plurality of optical fibers.
An approach that is more applicable to the alignment of multiple optical fibers is shown in U.S. Pat. No. 6,061,374. In this approach the ends of the plurality of optical fibers are positioned in respective V-grooves of an alignment block which is accurately positioned within the enclosure with respect to a multiple emitter laser diode. The other ends of the fibers are gathered into a cylindrical bundle and brought out through a circular hole in the enclosure which may be conventionally sealed.
An alternative approach to the alignment of multiple optical fibers is depicted in FIG. 1 in which the parallel fibers are mounted in an elongated assembly external to the enclosure. The fiber optic assembly is then clamped to the enclosure using an O-ring seal. Sufficient clamping force must be applied to compress the O-ring by approximately 20% to provide an adequate degree of sealing.
It is to be appreciated that the accurate alignment to the laser diode of either a single fiber optic or an assembly of parallel fibers requires the use of a manipulative mechanism sometimes referred to as an ultra-precision translation stage that is capable of locating the parts to be assembled with sub micron accuracy. Illustrative ultra-precision translation stages are available from Newport, Inc., Irvine, Calif. An ultra-precision translation stage operates most accurately when the parts to be moved do not xe2x80x9cloadxe2x80x9d the translation mechanism. On the other hand the compression of an O-ring sufficiently to make an effective seal requires the application of force that may load the translational mechanism enough to affect the accuracy with which it moves the parts to be aligned.
In accordance with an illustrative embodiment of the invention, a fiber optic clamp assembly is provided which permits precise alignment of a fiber bundle with a laser diode mounted in a sealable enclosure. Using an ultra-precision translation stage such alignment is achievable with a sub-micron degree of accuracy. The precise alignment is facilitated by removing from the ultra-precision translation stage any load occasioned by the need to compress the enclosure seal. When the fiber bundle is fully aligned with the laser diode of the enclosure, the ultra-precision translation stage is locked and the clamp assembly made up to the laser diode enclosure. In accordance with an aspect of the illustrative embodiment, the enclosure seal comprises a flexible seal having an O-ring cross-section and a compression collar slidably mounted in the clamp assembly and which is kept out of contact with the O-ring while the translation stage is being moved to align the parts. Once the translation stage is locked, the compression collar is made up to compress the O-ring against the enclosure to effect the sealing of the clamp assembly to the enclosure without disturbing the alignment of fiber optic bundle with the laser diode.