BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to optical systems and, more particularly, to reducing contamination in optical devices. 
   2. Description of the Related Art 
   Many optical devices include mirrors, lenses, and other optic components that are used to process light. These optical components are often very sensitive to contamination. The presence of contaminants on the optic components may decrease the performance of an optical device. For example, the presence of contaminants may lead to an increase in a device&#39;s insertion loss. Insertion loss is total optical power loss caused by the insertion of an optical device into a system. The cleanliness of the optics may also affect signal to noise ratio and return loss. 
   One example of contamination occurs in high power optical systems. In these systems, dirt on the surface of an optical component may act as a tiny lens that locally focuses a light beam until the intensity burns a hole in the surface of that component (or a coating on that component), increasing the insertion loss of that component. 
   In order to reduce the possibility of contamination, great care is usually taken when handling optic components. Optical components are typically enclosed within sealed packages to prevent environmental contaminants such as dirt and water from coming into contact with the enclosed optical components. However, various processes used during the assembly process of optical devices may themselves create contaminants. For example, soldering, epoxy bonding, and laser welding may each produce contaminants through outgassing, smoking, and/or splashing (e.g., of flux). This contamination results in what is commonly referred to as “fogging” on the optics. Like other forms of contamination, this fogging may cause insertion loss or otherwise reduce performance. 
   SUMMARY 
   Various embodiments of methods and systems for reducing the amount of contamination that enters an optical device are disclosed. In one embodiment, an optical device includes a housing and a first sleeve that encloses a portion of an optical fiber. The first sleeve is received by a receiving portion of the housing. A flexible seal contacts a portion of the surface of the first sleeve and contacts the surface of the receiving portion of the housing. 
   In some embodiments, the flexible seal may be made from one or more materials such as plastics, rubber, polymers, glass, composites (e.g., fiberglass), and low-density open cell foams. The flexible seal may be positioned at or near a pivot point (which the first sleeve will be pivoted about during an process that aligns the end of the optical fiber with an optical component within the housing) of the first sleeve. The outer surface of the first sleeve may include a visual or physical indication, such as an indentation or an extrusion along all or part of a cross-sectional portion of the first sleeve, which constrains the placement of the flexible seal and/or identifies where the flexible seal should be positioned. The first sleeve may be part of a collimator assembly in some embodiments. 
   One embodiment of a method of assembling an optical device may include placing a flexible seal on a sleeve, inserting the sleeve into a receiving portion of a housing so that the flexible seal contacts a surface of the receiving portion of the housing, and affixing (e.g., soldering, welding, and/or epoxying) the sleeve to the housing. The sleeve encloses a portion of the optical fiber. The flexible seal inhibits contaminants generated during the affixing process from reaching an interior portion of the optical device. 
   Another embodiment of a method of assembling an optical device may involve placing a flexible seal into a receiving portion of a housing, inserting a sleeve into the receiving portion of the housing so that the flexible seal contacts a surface of the sleeve, where the sleeve encloses a portion of an optical fiber, and affixing the sleeve to the housing. Affixing the sleeve to the housing generates contaminants, and the flexible seal inhibits contamination of interior of the optical device by the contaminants. 
   In one embodiment, an optical device may include means for housing an optical component (e.g., a housing as shown in  FIGS. 1 and 2 ) and means for enclosing a portion of an optical fiber (e.g., a sleeve that is part of a collimator assembly like the one shown in FIGS.  1  and  2 ). A receiving portion of the means for housing the optical component receives the means for enclosing the portion of the optical fiber. In some embodiments, the means for enclosing the portion of the optical fiber may include means for collimating light (e.g., a collimator lens like the ones shown in  FIG. 2 ) output from the end of the optical fiber. The optical device also includes means for inhibiting contamination (e.g., a flexible seal like the one shown in FIGS.  1  and  2 ). The means for inhibiting contamination are coupled between the means for housing the optical component and the means for enclosing the portion of the optical fiber. The means for inhibiting contamination are flexible. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention can be obtained when the following detailed description is considered in conjunction with the following drawings, in which: 
       FIG. 1  shows an embodiment of an optical device that includes a flexible seal. 
       FIG. 2  shows a cutaway side view of one embodiment of an optical device that includes a flexible seal. 
       FIG. 3  shows a cutaway side view of another embodiment of an optical device that includes a flexible seal. 
       FIG. 4  shows a cutaway side view of yet another embodiment of an optical device that includes a flexible seal. 
       FIG. 5  shows one embodiment of a method of assembling an optical device. 
       FIG. 6  shows another embodiment of a method of assembling an optical device. 
   


   While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. Note, the headings are for organizational purposes only and are not meant to be used to limit or interpret the description or claims. Furthermore, note that the word “may” is used throughout this application in a permissive sense (i.e., having the potential to, being able to), not a mandatory sense (i.e., must). The term “include” and derivations thereof mean “including, but not limited to.” The term “connected” means “directly or indirectly connected,” and the term “coupled” means “directly or indirectly coupled.” 
   DETAILED DESCRIPTION OF EMBODIMENTS 
     FIG. 1  shows one embodiment of an optical device  150 . Optical device  150  includes housing  100  and one or more passive optical components  10 . Exemplary passive optical components include lenses, glass crystals, gratings, mirrors, etc. such as those used in passive devices like collimators, isolators, couplers, multiplexers, filters, power splitters, etc. In this embodiment, the housing  100  houses a passive optical component  10 . Optical device  150  also includes two collimator assemblies  15 A and  15 B, which are attached to housing  100  at joints  20 A and  20 B (e.g., solder, weld, or epoxy joints) respectively. For simplicity, components with like reference numerals are collectively referred to by that reference numeral alone (e.g., collimator assemblies  15 A and  15 B are collectively referred to as collimator assemblies  15 ). 
   In this embodiment, a collimator assembly  15 A introduces one end of an optical fiber  25 A into housing  100 . Collimator assembly  15 A includes a collimating lens (not shown) that is configured to collimate an optical signal output from the end of optical fiber  25 A and to provide the collimated signal to passive optical component  10 . Each end of housing  100  receives one of the collimator assemblies  15 . 
   Passive optical component  10  processes the collimated optical signal and outputs a processed optical signal. A second collimator assembly  15 B may receive the processed optical signal output from passive optical component  10  and convey it to the end of a second optical fiber  25 B. A second lens (not shown) inside second collimator assembly  15 B may refocus the optical signal from passive optical component  10  into the end of optical fiber  25 B. 
   Contaminants inside the housing may settle on the collimator lenses, the ends of the optical fibers  25 , and/or the passive optical component  10 . These contaminants may cause component damage to one or more of these components inside the housing, increasing the insertion loss of these components. 
   In this embodiment, passive optical component  10  is packaged in a tubular structure  100 . Collimator assembly  15 A includes sleeve  35 A, which encloses a portion of optical fiber  25 , and a collimating lens. The outer sleeve  35 A of collimator assembly  15 A may be made from a metal, plastic, or glass material. Housing  100  may be made of a metal material in some embodiments. The collimator assemblies  15 A and  15 B are partially inserted into the housing  100  and attached to the housing at joints  20 A and  20 B respectively. The collimator assemblies  15  may be attached by solder joints in some embodiments. In alternative embodiments, the collimator assemblies  15  may be attached by other means (e.g., welding, glass bonding, brazing, and/or epoxying). In order to reduce the amount of contaminants that enter optical path  30  (e.g., as a result of the process(es) used to attach collimator assemblies  15 A and  15 B to housing  100 ), a flexible seal  17 A is placed between the outer surface of collimator assembly  15 A and the inner surface of housing  100 . A similar flexible seal  17 B is placed between the outer surface of collimator assembly  15 B and the inner surface of housing  100 . Flexible seals  17  have some flexibility so that they may be placed between the a collimator assembly and an optical component housing during device assembly and so that they allow alignment of optical devices. Note that while housing  100  and sleeves  35  shown in this embodiment are both cylindrical structures, structures of different shapes may be used for the housing, the sleeves, or both in other embodiments. Generally, the shape of flexible seal  17  is such that flexible seal  17  contacts a surface of sleeve  35  and a surface of housing  100  in a way that forms a barrier against contaminants. For example, if both the housing and the sleeve are cylindrical, flexible seal  17  may be shaped as a circular ring. 
   Each flexible seal  17  forms a barrier against contaminants. For example, contaminants generated when sleeve  35 A is soldered, welded and/or epoxied to housing  100  may be inhibited from entering optical path  30  by flexible seal  17 A. While the barrier formed by each flexible seal  17  reduces the amount of contaminants that enter optical path  30 , the flexible seals may not prevent all contaminants from entering (i.e., the barrier may not be hermetic) in some embodiments. In many embodiments, flexible seals  17  may not physically attach sleeves  35  to housing  100  (although in some embodiments, each flexible seal  17  may create a friction attachment between a sleeve and the housing that makes it more difficult to remove the sleeve from the housing once the sleeve and flexible seal have both been inserted into the housing). 
   It is noted that in other embodiments, a flexible seal  17  may be placed contacting other surfaces (e.g., the end surfaces) or either the housing or the sleeve instead of contacting the respective inner and/or outer surfaces of the housing and the sleeve (as shown in FIG.  1 ). In yet other embodiments, a flexible seal  17  may contact the end surfaces of both the housing and the sleeve in addition to contacting the respective inner and/or outer surfaces of the housing and the sleeve. 
   A flexible seal  17  may be made from materials such as plastics, rubbers, low-density open cell foams, metal foils, composites (e.g., fiberglass), glass, and/or polymers. The particular type and combination of materials used in a given embodiment may depend on factors such as the amount of heat the flexible seal  17  may be exposed to, the type of contaminant(s) the flexible seal  17  may be exposed to, the environment in which optical device  150  may be operated in, the intended lifetime of the optical device  150 , and so on. For example, a flexible seal  17  may need to withstand certain temperatures during assembly and/or operation of optical device  150 . Different materials may be better suited to operating under certain conditions than others, and thus materials may be selected based on the particular operating and/or assembly conditions expected for a given embodiment. In some embodiments, the material(s) included in the flexible seal  17  may be selected based on how much those materials outgas at the temperatures that the flexible seal  17  is expected to be exposed to during the assembly and lifetime of the optical device  150 . 
   The temperatures that flexible seal  17  is exposed to during device assembly due to processes such as soldering, welding (e.g., laser welding, TIG (Tungsten Intert Gas) welding, or MIG (Metal Inert Gas) welding), or heating to cure epoxy may depend on the placement of flexible seal  17  relative to the area of the sleeve and/or housing that will be exposed to heat. Generally, the temperature of the flexible seal  17  may depend on the distance between the flexible seal  17  and the point (e.g., a joint  20 ) at which the heat is applied. As the distance between a flexible seal  17  and a heat source increases, the temperature of the flexible seal  17  decreases. Many materials outgas more at increased temperatures. Thus, if outgassing of flexible seal  17  is a concern, the amount of potential outgassing may be reduced by increasing the distance between the flexible seal  17  and the point(s) (e.g., joints  20 ) at which heat will be applied to the device  150  during assembly. 
     FIG. 2  shows a cutaway side view of one embodiment of optical device  150 . This cutaway view shows the placement of an inner ferrule  94  and a collimator lens  80  (e.g., a Gradient Index (GRIN) lens) within each sleeve  35 . As shown, each fiber  25  may be attached to the inner ferrule by a material such as epoxy  90  in some embodiments. Each ferrule  94  may be attached to a sleeve  35  by epoxy, solder, glass, etc. 
   Exemplary pivot points  50 A and  50 B for sleeves  35 A and  35 B are shown. Each sleeve  35  may be rotated about its respective pivot point  50  during device assembly so that an end of a fiber  25  and lenses  80 A and  80 B are aligned with an optical component  10  inside housing  100 . For example, such an alignment process may be performed after sleeve  35 A and seal  17 A are inserted into housing  100  and before sleeve  35 A is affixed to housing  100 . In some embodiments, a flexible seal  17  may limit adjustment of a sleeve  35  about its pivot point  50 . Potential restrictions on sleeve adjustment caused by a flexible seal  17  may be reduced by placing flexible seal  17  closer to a pivot point  50  around which a sleeve  35  is rotated during alignment. 
   In the embodiment shown in  FIG. 2 , each flexible seal  17  is a gasket with a frusto-conical surface. Note that in other embodiments, a flexible seal may be an o-ring with a circular, square, or other cross-section. In general, any type and/or shape of flexible seal  17  that, when placed between sleeve  35  and housing  100 , reduces the amount of contaminants that enter an optical path within housing  100  may be used. 
   In some embodiments, flexible seal  17  may be attached to a sleeve  35  before sleeve  35  is inserted into housing  100 . In many embodiments, each sleeve  35  may include an indication identifying a point at which a flexible seal  17  should be placed and/or constraining the movement and/or placement of the flexible seal. Such an indication may extend around a portion (or all) of the circumference of the sleeve at the location where the flexible seal  17  should be placed. For example, in the embodiment shown in  FIG. 2 , each of the collimator assembly sleeves  35  includes a groove  70  that indicates the position at which the flexible seal  17  should be placed. A person or machine attaching the flexible seal  17  to the sleeve  35  may roll, slide, or otherwise move the flexible seal  17  across the sleeve  35  until the flexible seal  17  is positioned within the groove  70 . In another embodiment, an indication may include a circumferential line marked (e.g., drawn, etched, or painted) around the sleeve  35  at a point at which the flexible seal  17  should be located. Such a line may assist a human assembler or a machine assembler using machine vision to properly place the flexible seal  17  at the desired location on a sleeve  35 . In yet another embodiment, the indication may include one or more raised portions (e.g., ridges) on the sleeve that indicate the position at which the flexible seal should be placed (e.g., two ridges may surround the portion of the sleeve on which the flexible seal should be placed). In some embodiments, the raised portion(s) may constrain the placement and/or movement of the flexible seal by making it physically difficult to place the flexible seal at a location on and/or beyond the raised portion. The desired location of the flexible seal may be a location on top of or next to the indication. 
   In some embodiments, flexible seal  17  may be inserted into housing  100  before sleeve  35  is inserted (e.g., the sleeve  35  may be inserted through the flexible seal  17  after the flexible seal  17  is already positioned within the housing  100 ). For example, flexible seal  17  may be a plastic sleeve or ring that is placed within housing  100  before sleeve  35  is inserted into the housing. In some of these embodiments, one or more physical and/or visual guides on housing  100  (e.g., on an inner surface of housing  100 ) may indicate where the flexible seal  17  should be placed within the housing  100 . Guides on sleeve  35  may indicate where sleeve  35  should be positioned with respect to the flexible seal  17 . These guides on housing  100  and/or sleeve  35  may include visual markings, physical indentations (e.g., grooves), and/or physical extrusions (e.g., ridges). 
     FIG. 3  shows a partial view of another embodiment of an optical device  150  that includes a flexible seal  17 . In this embodiment, a receiving portion of housing  100  receives sleeve  35 A. Sleeve  35 A is part of a collimator assembly that may include a lens  80 A, ferrule  94 A, and a portion of fiber  25 A in this embodiment. In one embodiment, optical device  150  may be a fiber-coupling device that couples fiber  25 A to another fiber (not shown). In some embodiments, optical device  150  may contain additional optical components, as shown in  FIGS. 1-2  and  4 . 
     FIG. 4  shows an example of another embodiment of an optical device  150  in which a flexible seal  17  may be used to reduce the amount of contaminants that enter the optical device. In this embodiment, optical device  150  may contain one or more active optical components  10 A. Exemplary active optical components  10 A include laser diodes, photosensors, transmitters, receivers, modulators, attenuators, switches, amplifier pumps, semiconductor optical amplifiers, etc. and any associated optics (e.g., optics to allow efficient light coupling). Note that active and passive optical components may be integrated into the same housing. For example, a passive device (e.g., a collimator lens) may process a light signal output from an active device (e.g., a laser diode) for transmission in an optical fiber. 
   In this embodiment, active component  10 A&#39;s housing  100  is not cylindrical in shape (e.g., active component  10 A may be housed in a box). In this embodiment, a cylindrical receiving portion  100 A of housing  100  receives sleeve  35 . Note that while the receiving portion  100 A is cylindrical in this embodiment, other embodiments may have differently shaped receiving portions. Additionally, in many embodiments, a receiving portion of a housing may be the same shape as the rest of the housing (e.g., as shown in FIGS.  1 - 3 ). A flexible seal  17  may be placed between sleeve  35  and the receiving portion of the housing  100  in order to reduce contamination. In some embodiments, the receiving portion  100 A of the housing may be produced as a separate component that is eventually attached to the rest of housing  100  at some point during device assembly. In such embodiments, sleeve  35  and flexible seal  17  may be inserted into the receiving portion  100 A (e.g., a ferrule) of the housing  100  before or after the receiving portion of the housing is attached to the rest of the housing. Flexible seal  17  may reduce the amount of contaminants that enter an interior portion of the housing  100 . 
   In the embodiments shown in  FIGS. 1-3 , each sleeve  35  is part of a collimator assembly  15 . Note that in some embodiments like the one shown in  FIG. 4 , a sleeve  35  may not be part of a collimator assembly  15 . Instead, the sleeve  35  may part of a connecting device used to introduce an optical fiber  25  into a housing  100 . Sleeve  35  may contain other passive components (in addition to or instead of a collimator lens) in some embodiments. 
     FIG. 5  is a flowchart of one embodiment of a method of assembling an optical device. In this embodiment, a flexible seal is moved onto a sleeve (e.g., a sleeve around a collimator assembly or a ferrule used to introduce an optical fiber into a component housing), as shown at  301 . Moving the flexible seal may involve rolling, sliding, or otherwise moving the flexible seal from one end of the sleeve to a desired location along the sleeve. In some embodiments, the desired location of the flexible seal may be identified by an indication (e.g., a visual and/or physical marking) on the outer surface of the sleeve. 
   At  303 , the sleeve is inserted into a receiving portion of a housing for an optical component so that the flexible seal contacts a surface of the receiving portion of the housing. In some embodiments, the receiving portion of the housing may be a ferrule that is attached to the remainder of the housing at some time after the sleeve in inserted into the receiving portion. In other embodiments, the receiving portion may already be integrated with the housing when the sleeve is inserted. At  305 , the sleeve is affixed to the housing (e.g., by soldering, welding, and/or epoxying). Affixing the sleeve to the housing may generate contaminants, and the flexible seal reduces the amount of contaminants that enter an optical path within the housing. 
     FIG. 6  is a flowchart of another embodiment of a method of assembling an optical device. At  401 , a flexible seal is inserted into a receiving portion of the housing for an optical component. In some embodiments, visual and/or physical indications may show the location at which the flexible seal should be placed within the receiving portion. At  405 , a sleeve is inserted into the receiving portion of the housing so that the flexible seal contacts a surface of the sleeve and a surface of the receiving portion of the housing. The sleeve is affixed to the housing at  405 . The process(es) used to affix the sleeve to the housing may generate contaminants. The flexible seal may reduce the amount of contaminants that enter an optical path within the housing. 
   Note that the embodiments shown in  FIGS. 3 and 4  are merely exemplary and that other embodiments of assembly methods may also be used. 
   Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.
Various embodiments of methods and systems for reducing the amount of contamination that enters the optical path of an optical device are disclosed. In one embodiment, an optical device includes a housing containing at least one optical component (active, passive, or both) that is configured to process an optical signal. The optical device also includes a first sleeve that encloses a portion of an optical fiber, an optical path configured to convey the optical signal between the optical component(s) and the end of the optical fiber. A flexible seal contacts a portion of the surface of the first sleeve and contacts the surface of a portion of the housing through which the first sleeve passes.