Optical package with improved fiber alignment fixture

#The present invention relates to an optical package with an improved fiber alignment fixture and, more particularly, to a two-piece fiber ferrule which provides simplified axial alignment of the fiber to the active optical device and allows visible inspection of the stability of the fiber axial alignment fixation.

#An important factor in the reliability of optical transmission systems is the stability of the various components--transmitters, repeaters, and receivers. The packages housing these components have been the subject of much study, especially the aspect of attaching and aligning the optical fiber to the active component (laser, LED, photodiode, etc.) contained in the package. The stability of these alignments over long periods of time is one of the most important components of the overall system reliability.

#This is especially true for laser-based transmitters designed for high frequency, single mode transmission systems, where relatively small lateral movements between the laser and the fiber can result in large coupling losses. For example, a lateral motion of 2 .mu.m can result in a 1 dB coupling loss. Since many of these single mode transmitters are destined for use in remote locations (undersea, for example), the need to maintain precise and accurate alignment is critical.

#Referring now to the drawings, where like numerals represent like parts in several views:

#FIG. 1 illustrates a cross-sectional view of an exemplary laser package formed in accordance with the present invention;

#FIG. 2 illustrates an exemplary laser subassembly which may be used in conjunction with the package of FIG. 1;

#FIG. 1 shows a completed package 10 with a laser 12 mounted on a stud 14 and an optical fiber 16 feeding through a ferrule 18 and aligned with laser 12. The package can be considered as comprising two separate subassemblies; a laser subassembly 20 and a fiber subassembly 22. The focus of this invention is primarily related to the axial alignment of these two subassemblies, since the alignment of the two is often critical to the reliability of the final package.

#FIG. 2 illustrates in detail a portion of an exemplary laser subassembly 20. As shown, laser 12 is attached to a mount 24 which is part of stud 14. Since the output from a laser is a divergent beam with a divergent angle in the range of, for example, 10.degree. to 50.degree., a lens 26 is placed in an opening in a platform 28 using a retaining spring 29, where lens 26 is used to collimate the beam into a more desirable parallel form. Lens 26 is positioned in the z-direction (indicated in the figure) until the required spacing between laser 12 and lens 26 is achieved. In most cases, this spacing should be in the range of 10-20 .mu.m. Active alignment is then performed to position the axis of lens 26 relative to the output from laser 12. In one active alignment procedure, a video system is used where the optical axis of the lens is first aligned with a fiduciary on a video screen. Laser 12 is then activated, and the emission through lens 26 is viewed on the screen at a relatively far distance (>150 mm). The position of platform 28 is then adjusted until the emission aligns with the fiducial marking. Once alignment is achieved, platform 28 is attached to mount section 24 of stud 14. In order to achieve high reliability and insure that the relative positions of laser 12 and lens 26 remain constant, a series of laser welds are used to attach platform 28 to mount 24. Three such laser welds are illustrated at points A, B and C in FIG. 2. A similar set of welds is used to attach the opposite side of platform 28 to mount 24 (now shown).

#Referring back to FIG. 1, the remainder of laser subassembly 20 will be described. A first graded-index (GRIN) lens 32 is positioned in front of lens 26 and is used to focus the output from laser 12 to a small spot size. First GRIN lens 32 is held in a first retainer 34 which mates with the housing surrounding laser 12 (shown in FIG. 1). A second GRIN lens 36 is positioned at the rear of laser 12, and is used to focus the output from the rear face of laser 12, where this light output is used to monitor the operation of laser 12. A second retainer 38 is used to hold GRIN lens 36 in place.