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1. WO2002025339 - OPTICAL FIBER COUPLER ASSEMBLY

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[ EN ]

OPTICAL FIBER COUPLER ASSEMBLY

This application claims the benefit of U.S.
Provisional Application No. 60,235,381, entitled LASER FIBER COUPLER ASSEMBLY and filed September 25, 2000.

Background

This application relates to techniques and
mechanisms for mechanical mounting a fiber coupler module to a platform.
Certain optical transmitters and transceivers use a semiconductor laser as a light source to produce a light beam and an optic fiber to receive the light beam and transport it to a desired destination. Some coupling optics may be implemented between the laser and the fiber to facilitate the coupling of the light beam into the fiber. Various mechanical devices may be used to hold or mount the light source, the coupling optics, and the fiber to their respective positions with respect to one another so that proper optical alignment can be
established and maintained.

Summary

The systems and techniques of this application are in part based on the recognition that it may be desirable to integrate the light source, the coupling optics, and the fiber together in a single, compact module so that an optical transmitter or transceiver can be directly and conveniently coupled to a fiber system without extensive assembling steps and optical alignment. Examples of such integrated compact modules are provided to simplify the manufacturing, assembling, and optical alignment and to reduce the overall cost of such modules.
In one embodiment, elongated engagement members are used mount a fiber coupler module to a support platform so that a light source on the platform and the fiber coupler module are optically aligned.

Brief Description of the Drawings

FIG. 1 shows one embodiment of an optical fiber coupler assembly which includes a support platform, a light source, and a fiber coupler module.
FIG. 2 shows a three-dimensional view of the fiber coupler module and its respective engagement mechanism for engaging to the support platform.

FIG. 3 shows a three-dimensional view of the support platform an its respective engagement mechanism for engaging to the fiber coupler module.
FIG. 4 shows the fiber coupler module and the support platform in engagement to each other.

Detailed Description

FIG. 1 shows an exemplary optical fiber coupler assembly 100 according to one embodiment. The entire assembly is built on a base 102 and is enclosed in a housing 101. A support module 103 is formed over the base 102 and may be a single piece formed of a rigid material or two separated pieces that are fixed to the base 102. The support module 103 may include a first part 105 to mount a light source 110 (e.g., diode laser or LED) , and a second part which includes a support platform 104 to mount a fiber coupler module 120 so that the light source 110 and the fiber coupler module 120 are optically aligned with each other to couple the light from the laser 110 into the fiber coupler module 120. A fiber 130 is coupled to the fiber coupler module 120 to receive and transport the light from the laser 110 to a destination outside the assembly 100.
The fiber coupler module 120 may include a coupler housing 120A which has two openings 120B and 120C at opposite ends along the optical path of the assembly 100. The exterior of the coupler housing 120A may be
cylindrical with some portion flattened for engaging to other components. The opening 120B is used to receive light from the laser 110 and the opening 120C is used to receive the fiber 130 into which the received light from the laser 110 is coupled. The coupler housing 120A may be designed to engage coupling optics and a fiber fitting unit 122 along the optical path of the light from the laser 110. The coupling optics may include, for example, a collimating lens 121A that modifies the divergent beam from the laser 110 to be collimated and a focusing lens 121C that focuses the collimated beam into the receiving terminal of the fiber 130. An optical isolator 121B may also be included to reduce adverse optical feedback to the laser 110 due to optical reflections at various surfaces in the optical path.
In one implementation, the coupler housing 120A may be designed to engage to the coupling optics 121 and the fiber fitting unit 122 without separate mounting devices. For example, a cylindrical through channel may be formed to connect the openings 120B and 120C. The coupling optics and the fiber fitting unit 122, when properly shaped, can be inserted into the cylindrical through channel and fixed at their proper positions relative to each other according to the optical parameters of the coupling optics so that the light from the laser 110 can be coupled into the fiber 130. One way for fixing the optical elements in the optics 121 and the fiber fitting unit 122 uses one or more set screws on the through holes 121A1, 121B1, 121C1, and 122A formed on the side wall of the coupler housing 120A. Alternatively, the optical elements 121A, 121B, 121C, and the fiber fitting unit 122 may be affixed at their respective positions by adhering them to the inner wall of the cylindrical through channel with a proper epoxy.
A special engagement mechanism may be implemented in the assembly 100 for mounting the fiber coupler module 120 onto the platform 104. This mechanism includes parts on both the fiber coupler module 120 and the platform 104 to fix the position and orientation of the fiber coupler module 120 on the platform 104 with respect to the laser 110.
FIG. 2 shows two horizontal engaging bands 210 and 220 formed on the cylindrical exterior of the fiber coupler module 120 as one part of the engagement
mechanism. The bands 210 and 220 may be formed of a metal, an alloy, or other suitable materials so that the bands 210 and 220 are substantially rigid but can be slightly deformed to produce a resilient force. Each horizontal band 210 or 220 includes a first elongated part, 210A or 220A, for engaging the band onto the fiber coupler module 120 and a second elongated part, 210B or 220B, for engaging the fiber coupler module 120 to the platform 104. The first and second parts, 210A and 219B, or 220A and 220B, in generally form an angle with respect to each other. This angle may be 90 degrees or an acute angle. A portion 230 of the cylindrical exterior of the fiber coupler module 120 may be flat for attaching the first parts 210A and 220A of the horizontal bands 210 and 220. The first parts of the two bands 210 and 220 may be fixed to the flat portion 230 of the fiber coupler module 120 at two different locations that are substantially along the cylindrical axis of the fiber coupler module 120. One way to attach the first parts 210A and 220A to the fiber coupler module 120 is laser welding.
FIG. 3 shows another part of the engagement
mechanism implemented on the platform 104. The platform 104 includes a top flat surface 104D to interface with flat portion 230 with the horizontal bands 210 and 220 of the fiber coupler module 120 and a bottom opposing surface 104C to be placed on the base 102. Three
vertical bands 310, 320, and 330 are formed on two opposite side surfaces 104A and 104B of the platform 104. The opposite side surfaces 104A and 104B are
substantially along the optic axis of the fiber coupler module 120 when the fiber coupler module 120 is set to a proper position relative to the platform 104. Two vertical bands 310 and 320 are engaged to two different locations 310A and 320A on the side surface 104A and the vertical band 330 is engaged to the opposite side surface 104B at a location 330A between 310A and 320A.
The opposite side surfaces 104A and 104B on the platform 104 may be parallel to each other or form a small acute angle towards each other so that the planes defined by the side surfaces 104A and 104B intercept each other on the side of the top supporting surface 104D. However configured, prior to engaging the vertical bands 310, 320, and 330 to the exterior of the fiber coupler module 120, the fiber coupler module 120 should be in contact with the vertical bands 310, 320, and 330 without causing substantial deformation so that the pressure at each contact area is small.
FIGS. 3 and 4 illustrate the configuration where the vertical bands 310, 320, and 330 are slightly slanted with respect to the vertical direction at essentially the same angle as that between the side surfaces 104A and 104B. This angle is designed so that, when the fiber coupler module 120 is placed above the top supporting surface 104D between the vertical bands 310, 320 and the vertical band 330, each of the vertical bands 310, 320, and 330 is slightly deflected to touch the exterior surface of the fiber coupler module 120 and is slightly bent to apply a pressure on the1 fiber coupler module 120. This three-point contact configuration can secure a proper initial position of the fiber coupler module 120 to couple the light from the laser 110 into the fiber 130.
Two additional support structures 340 and 350 may also be respectively formed on the side surfaces 104A and standoff portion, 342 or 352, above the top flat surface 104D of the platform 104 to contact and support a horizontal band, 220 or 210, respectively, when the fiber coupler module 120 is placed in a nominally aligned position over the platform 104. The support structures 340 and 350 are displaced from each other respectively along the side surfaces 104A and 104B by about the same spacing between the horizontal bands 210 and 220 on the fiber coupler module 120.
In assembly, the fiber coupler module 120 is first placed between the vertical bands 330, and 310, 320 so that the fiber coupler module 120 is suspended over the top supporting surface 104D by the two horizontal bands 210 and 220 that are respectively rest on the standoff portions 352 and 342 of the support structures 340 and 350. The upper portions of the vertical bands 310, 320, and 330 are slightly deflected to touch the exterior surface of the fiber coupler module 120. Similarly, the parts 210B and 220B of the horizontal bands 210 and 220 are also slightly deflected to exert a force against the fiber coupler module 120 so that the parts 210A and 220A on the flat portion 220 of the exterior of the module 120 are suspended above the top surface 104D with a small gap- Next, the position and orientation of the fiber coupler module 120 are adjusted to maximize the output from the fiber 130. Finally, the contacts of the vertical bands 310, 320, and 330 with the exterior of the fiber coupler module 120, and the contacts of the horizontal bands 210 and 220 with the platform 104 are fixed by, e.g., laser welding or epoxy, at the position where the optical coupling is at or near the maximum. All six degrees of freedom of the fiber coupler module 120 are now fixed with respect to the platform 140.
FIG. 4 illustrates a view along the lines AA' in FIG. 1 after the fiber coupler module 120 is placed above the platform 104. The vertical band 320 is shown to touch one side of the module 120 at a location 410. The vertical band 330 is shown to touch on the other side of the module 120 at another location 410. These locations 410 and 420 are fixed by welding or applying epoxy.
Locations 420 and 440 are also fixed so horizontal bands 210 and 220 are fixed to the platform 104 without contacting the top surface 104D.
The following describes one exemplary flow in assembling such a system. First, the fiber coupler module 120 is assembled. The optical elements for the coupling optics 121, such as the lenses 121A, 121C, and the isolator 121B, are inserted and secured, in their respective positions in the fiber coupler module 120 by using either a suitable epoxy or using the set screws

121A1, 121C1, and 121B1. Also, the fiber 130 is attached to the fiber fitting unit 122. The buffer on one distal end of the fiber 130 is removed. A portion of the fiber end is also metalized for soldering to the fiber fitting unit 122 which is formed of a metal. A suitable epoxy is dispensed in the fitting hole of the fiber fitting unit

122 to affix the fiber therein. The epoxy is then heated and cured. The receiving facet of the fiber in the fitting unit 122 is then polished. Next, the fiber fitting unit 122 is attached to the fiber coupler module 120 by, e.g., using a suitable epoxy. The fiber coupler mount 120 is then degassed by, e.g., baking at a high temperature, and hermetically sealed. Then, the fiber coupler mount 120 is mounted to the platform 104 and adjusted to optimize the optical coupling efficiency. Finally, the contact points of the bands are fixed to complete the assembly.
A number of advantages can be achieved by the above design. For example, the design is simple partially due to elimination of conventional optical mounts within the module housing 120A for placing the optical elements. This can reduce the cost of components. Also, the assembly process is simple due to the design and hence can reduce the time for alignment and assembly. This increases the throughput of the production and the further reduces the cost of each device.

Only a few examples are described. However, other modifications and enhancements may be made without departing from the following claims .