Abstract:
The present invention relates to an optical fiber collimator with applications including optical fiber communication systems. An embodiment of the present invention includes a housing, optical fiber, and a lens system having at least one lens. The embodiment does not require the fiber ferrule employed in a conventional optical fiber collimator.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention generally relates to optical fiber technology. Particularly, this invention relates to an improved collimator for an optical fiber.  
         BACKGROUND OF THE INVENTION  
         [0002]    Optical fiber technology is widely applied in the field of communications, including telecommunication, data communication, cable television, and fiber-to-home applications. Other representative applications of optical fiber technology include illumination and imaging. One of the key components in optical fiber technology is the optical fiber collimator. In many applications, the optical fiber collimator optically couples an optical fiber to an optical component. Representative optical components that couple through optical fiber collimators to optical fibers include optical attenuator, optical switches, photodetector, light sources, acousto optic devices, and electro optic devices. One skilled in the art understands that the optical fiber collimator has other applications. Optical fiber systems, in particular, optical fiber communication systems, employ a large quantity of optical fiber collimators. Most of the optical fibers employed in an optical fiber system are terminated with optical fiber collimators.  
           [0003]    There are numerous prior art optical fiber collimator designs. Until recently, the most important design goal for passive optical components employed in an optical fiber communication system was optimal optical transmission performance. The laser signal sources employed in the optical fiber communication system were costly compared to the passive components employed in the system. These passive components included optical fiber collimators. By optimizing the transmission performance of passive optical components in an optical communication system, the lowest power and therefore the least expensive laser signal source could be employed in the system. FIGS. 1 through 5 illustrate a selection of representative prior art optical fiber collimator designs. Many of these prior art designs are optimized for optical transmission performance.  
           [0004]    [0004]FIG. 1 shows a prior art optical fiber collimator design. Referring to FIG. 1, optical fiber  107  attaches to fiber ferrule  1 . Fiber ferrule  1  provides support for optical fiber  107 . In the fabrication process of this optical fiber collimator, optical fiber  107  is inserted into fiber ferrule  1  and secured to fiber ferrule  1  with an adhesive. Then the end of optical fiber  107  and the end of fiber ferrule  1  are polished to form optical fiber termination  108 . To reduce reflection and to improve optical transmission performance, the surface of optical fiber termination  108  is polished so that it is at an angle other than zero degrees to the surface that is perpendicular to the axis of the fiber ferrule, which is essentially the same as the optical axis of optical fiber  107  at optical fiber termination  108 . Collimating lens  109  is placed at a distance from fiber termination  108 . Similar to the surface at optical fiber termination  108 , the surface of collimating lens  109  that is facing optical fiber termination  108  is polished so that it is at an angle other than zero degrees to the surface that is perpendicular to the optical axis of collimating lens  109 . This angle is introduced to the collimating lens design to reduce reflection and to match the corresponding angle of optical fiber  107  at optical fiber termination  108 . During the alignment phase in the fabrication process, the optical axis of optical fiber  107  at optical fiber termination  108  and the optical axis of collimating lens  109  are aligned. Then the relative distance between optical fiber termination  108  and collimating lens  109  is adjusted, and collimating lens  109  is rotated about its optical axis for optimal optical transmission performance. Typically, fiber ferrule  1  and collimating lens  109  are attached to a base plate through support structures in this design after the alignment phase is completed. Other parameters that may be adjusted during the alignment phase include the relative offset and the angle between the optical axes. The design shown in FIG. 1 allows for the adjustment of numerous parameters in the alignment process to achieve optimal optical transmission performance. These parameters, including relative distances and orientations in various directions, represent the degrees of freedom in alignment. Nevertheless, the alignment process in the fabrication of this design is labor intensive and costly because many parameters in this design require adjustment.  
           [0005]    [0005]FIG. 2 shows another prior art optical fiber collimator design. It is an improvement to the one shown in FIG. 1. Referring to FIG. 2, housing  101  is introduced in this design as a support member for fiber ferrule  1  and collimating lens  109 . Optical fiber  107  attaches to fiber ferrule  1 . Fiber ferrule  1  and collimating lens  109  attach to housing  101 . Housing  101  limits the parameters that can be adjusted during the alignment process of this design to two. These parameters are the relative distance and the angular orientation between optical fiber termination  108  and collimating lens  109 . The labor cost for aligning this design is thus reduced compared to the design depicted in FIG. 1.  
           [0006]    The prior art design shown in FIG. 3 is a variation of the prior art design shown in FIG. 1. Referring to FIG. 3, optical fiber  107  attaches to fiber ferrule  1 . Fiber ferrule  1  attaches to collimating lens  109  with a transparent adhesive  2 . The alignment labor cost for this design is expected to be approximately the same as that of FIG. 1.  
           [0007]    [0007]FIG. 4 shows another prior art design. It is a variation of the design shown in FIG. 2. Compared to the design shown in FIG. 2, the design shown in FIG. 4 has an additional second housing  4 . Referring to FIG. 4, optical fiber  107  attaches to fiber ferrule  1  and collimating lens  109  attaches to second housing  4 . Fiber ferrule  1  and second housing  4  attaches to first housing  3 . The addition of second housing  4  allows for the adjustment of the relative offset between the optical axes of optical fiber  107  at optical fiber termination  108  and collimating lens  109  during the alignment process in the fabrication of this design to achieve the desirable optical transmission performance.  
           [0008]    [0008]FIG. 5 shows yet another prior art design. There are no fiber ferrule and no housing in this design. Specially designed lens  6  and optical fiber  107  are mechanically attached with a heat-shrinkable tube  5 . The fabrication cost for this design is low compared to the designs shown in FIGS. 1 through 4. Nevertheless, the yield for obtaining high performance optical fiber collimators using this design is low compared to designs shown in FIGS. 1 through 4 because the optical alignment between lens  6  and optical fiber  107  is subjugate to the process of applying heat-shrinkable tube  5  to mechanically attach lens  6  to optical fiber  107 . Consistently controlling this process to optical precision is difficult. Further, external mechanical forces can easily perturb the optical alignment of the finished product that uses this design because heat-shrinkable tube  5  is not rigid. Additionally, for this collimator to achieve high optical transmission performance, optical fiber  107  and the portion of lens  6  that is in heat-shrinkable tube  5  must have similar diameters and the light-collecting surface of lens  6  must be large compared to the cross-sectional surface of optical fiber  107 . These design constraints on the size and the shape of lens  6  increase the cost of this optical fiber collimator.  
           [0009]    With the advent of low cost laser signal sources for optical fiber systems, there is an incentive to reduce manufacturing costs associated with the passive components employed in optical fiber systems. Passive optical components, including optical fiber collimators, become commodities. Low cost replaces optimal optical transmission performance as the primary design goal for optical fiber collimators in many optical communication applications. It is therefore one of the objectives of this invention to provide an optical fiber collimator and a method for fabricating this optical fiber collimator to reduce manufacturing cost.  
         SUMMARY OF THE INVENTION  
         [0010]    According to this invention, an optical fiber collimator design with improved cost performance can be achieved through reducing parts count and improving the fabrication process. Optical transmission performance is achieved by providing a mechanism that allows for the adjustment of the relative distance between the collimating lens and the optical fiber termination, and the adjustment of other applicable parameters.  
           [0011]    An embodiment of this invention includes a housing that has a first channel and a second channel. The first channel is coupled to the second channel. An optical fiber extends into the housing through the first channel. The optical fiber terminates in the housing. A collimating lens locates in the second channel of the housing. The collimating lens may be partially or totally in the second channel. The optical fiber is optically coupled to the collimating lens.  
           [0012]    A method for fabricating an embodiment of the invention includes the following steps. Installing an end portion of the optical fiber and the collimating lens in the housing. Align the collimating lens and the end portion of the optical fiber in the housing. Attach the end portion of the optical fiber and the collimating lens if they are not attached to the housing during installation. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0013]    A better understanding of the invention may be gained from the consideration of the following detailed descriptions taken in conjunction with the accompanying drawings in which:  
         [0014]    [0014]FIG. 1 shows the configuration of a conventional optical fiber collimator.  
         [0015]    [0015]FIG. 2 shows the configuration of an improved optical fiber collimator, which allows for the adjustments of the relative distance between the collimating lens and the optical fiber end portion to achieve optimal optical transmission performance.  
         [0016]    [0016]FIG. 3 shows the configuration of another improved optical fiber collimator, which allows the adjustment of the relative position between the collimating lens and the optical fiber end portion, and the angle between the optical axis of the collimating lens and the optical axis of the optical fiber end portion to achieve optimal optical transmission performance.  
         [0017]    [0017]FIG. 4 shows the configuration of another improved optical fiber collimator. It allows for the adjustment of the relative distance between the collimating lens and the optical fiber end portion, and the offset between the optical axis of the collimating lens and the optical fiber end portion to achieve optimal optical transmission performance.  
         [0018]    [0018]FIG. 5 shows the configuration of another conventional optical fiber collimator.  
         [0019]    [0019]FIG. 6 shows the configuration of an embodiment of the present invention.  
         [0020]    [0020]FIG. 7 is a sectional view of a representative housing of the embodiment shown in FIG. 6.  
         [0021]    [0021]FIG. 8 shows the configuration of an alternative embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    In the description that follows, like parts are indicated throughout the specification and drawings with the same reference numerals. The present invention is not limited to the specific embodiments illustrated herein.  
         [0023]    [0023]FIG. 6 shows the configuration of an embodiment of this invention and FIG. 7 shows a sectional view of a representative housing of this embodiment. Referring to FIG. 7, housing  101  has a first channel  102  and a second channel  103 . First channel  102  and second channel  103  are generally tubular-shaped and share a common axis. Because first channel  102  and second channel  103  may have different diameters, there is optional transition region  104  between first channel  102  and second channel  103 . Entrance to first channel  105  and entrance to second channel  106  are tapered. Housing  101  provides structural support to the embodiment.  
         [0024]    Referring to FIGS. 6 and 7, the end portion of optical fiber  107  is located in first channel  102  of housing  101 . The inner diameter of first channel  102  is larger than the outer diameter of optical fiber  107 . Therefore, optical fiber  107  may slide inside first channel  102 . At the end of optical fiber  107  is optical fiber termination  108 . There are numerous methods to form optical fiber termination  108 . A typical method is to cleave optical fiber  107 . The surface at optical fiber termination  108  is at an angle to the plane that is perpendicular to the optical axis of the end option of optical fiber  107 . Ones skilled in the art readily understand that by keeping this angle to be positive and small, typically between one degree and ten degrees, will help to reduce transmission loss and reflection of the embodiment. When the end portion of optical fiber  107  is installed in first channel  102  as shown in FIG. 6, the optical axis of the end portion of optical fiber  107  is the same as the axis of first channel  102 . To further reduce transmission loss and reflection, optical fiber termination  108  has an optional anti-reflection coating. The fiber ferrule  1  in the prior arts shown in FIG. 1 through  4  is eliminated in this invention.  
         [0025]    Referring to FIGS. 6, the cross section of collimating lens  109  on the plane that is perpendicular to the optical axis of collimating lens  109  has the shape of a circle. The diameter of this circle is the diameter of the body of collimating lens  109 . At least a portion of collimating lens  109  is located in second channel  103 . The inner diameter of second channel  103  is larger than the outer diameter of the body of collimating lens  109 . Therefore collimating lens  109  may slide inside second channel  103 . Collimating lens  109  employed in this embodiment is a spherical drum lens. The surface of collimating lens  109  has an optional anti-reflection coating to maximize optical transmission and minimize reflection.  
         [0026]    The fabrication process of an embodiment of the present invention includes the following tasks and one skilled in the art readily understands that it is not necessary to execute these tasks in the following sequence to successfully fabricate the embodiment:  
         [0027]    Install collimating lens  109  in second channel  103  of housing  101 ;  
         [0028]    Attach collimating lens  109  to housing  101 , preferably with a securing means such as an adhesive;  
         [0029]    Insert optical fiber  107  into first channel  102  of housing  101  through entrance to first channel  105 ;  
         [0030]    Align the embodiment by adjusting the position of optical fiber termination  108  in housing  101  by sliding optical fiber  107  in first channel  102  to achieve desirable optical transmission characteristics; and  
         [0031]    Attach the end portion of optical fiber  107  to housing  101 , preferably with a securing means such as an adhesive.  
         [0032]    Further, one skilled in the art understands that:  
         [0033]    The task of installing the end portion of optical fiber  107  into housing  101  and the task of installing collimating lens into housing  101  should be completed before the task of aligning collimating lens  109  and the end portion of optical fiber  107  in housing  101 ;  
         [0034]    The task of installing the end portion of optical fiber  107  into housing  101  should be completed before the task of attaching the end portion of optical fiber  107  to housing  101 ;  
         [0035]    The task of installing collimating lens  109  into housing  101  should be completed before the task of attaching collimating lens  109  to housing  101 ; and  
         [0036]    The task of aligning collimating lens  109  and the end portion of optical fiber  107  in housing  101  should be completed before both the tasks of attaching the end portion of optical fiber  107  to housing  101  and the task of task of attaching collimating lens  109  to housing  101  are completed.  
         [0037]    When compared to some of the prior art designs, the embodiment shown in FIG. 6 has fewer parameters in adjustment available for alignment to achieve high optical transmission performance. Although this embodiment has fewer parameters available for alignment, empirical results show that the optical transmission performance of the embodiment and those of the prior arts that have numerous alignment parameters are comparable. An example of a prior art that have numerous alignment parameters is shown in FIG. 4. Because this embodiment has fewer parts and fewer parameters available for alignment, the total manufacturing cost, including material cost, tooling cost, inventory cost, and labor cost is reduced compared to the optical fiber collimator shown in FIG. 4.  
         [0038]    [0038]FIG. 8 illustrates an alternative embodiment of this invention. A gradient index (GRIN) lens is employed as collimating lens  109  in this embodiment instead of the drum lens shown in FIG. 6. The entrance to the second channel is not tapered. Housing  101  has relatively uniform wall thickness and optional transition region  104  has a different design.  
         [0039]    There are numerous variations to the embodiments discussed above which will be trivial to the one skilled in the art. Examples of these variations include but not limited to:  
         [0040]    The cross section of the channel along the axis of first channel  102  is not circular, common alternatives include polygon-shaped, star-shaped, or irregular-shaped;  
         [0041]    The cross section of the channel along the axis of first channel  102  is not uniform, common alternatives include tapered or irregular;  
         [0042]    The cross section of the channel along the axis of second channel  103  is not circular, common alternatives include polygon-shaped, star-shaped, or irregular-shaped;  
         [0043]    The cross section of the channel along the axis of second channel  103  is not uniform, common alternatives include tapered or irregular;  
         [0044]    The entrance to first channel  105  may be tapered or not tapered;  
         [0045]    The entrance to second channel  106  may be tapered or not tapered;  
         [0046]    Other types of lens such as aspheric lens or asymmetrical lens may be employed as a collimating lens;  
         [0047]    The single collimating lens is replaced by a collimating lens system that includes at least one lens;  
         [0048]    The collimating lens system has its own supporting structure;  
         [0049]    The cross section of collimating lens  109  on the plane that is perpendicular the optical axis of collimating lens  109  has a shape other than that of a circle;  
         [0050]    The collimating lens has shapes other than the rod shape illustrated, such as a Boolean composite comprised of a hemisphere and a right cone connected and aligned at their planer surfaces;  
         [0051]    The alignment of the embodiment include adjusting other than the distance between optical fiber termination  108  and collimating lens, such as the relative angular orientation about their optical axes; and  
         [0052]    Optical fiber  107  or collimating lens  109  is attached to housing  101  through mechanical methods.  
         [0053]    Although the embodiment of the invention has been illustrated and that the form has been described, it is readily apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the invention.