Abstract:
An expanded beam (EB) optical connector. In some embodiments, the EB optical connector includes: a rigid, hollow, straight contact tube having a centerline axis; and a collimator assembly having an optical axis and comprising an optical fiber and a collimating lens, wherein the centerline axis of the contact tube is at least substantially aligned with the optical axis such that collimated light produced by the lens from light exiting the fiber travels though the contact tube and the loss of light caused by misalignment of the axes is not more than 2 dB.

Description:
TECHNICAL FIELD 
     This disclosure relates to an expanded beam optical connector and a method of making an expanded beam optical connector. 
     BACKGROUND 
     Connectors that are used to align two optical fibers are commonly referred to as optical connectors. The vast majority optical connectors are of the “physical contact (PC)” type, and are referred to as PC optical connectors. In a PC optical connector that is used to connect to fibers the two fibers are physically touching under pressure. For single mode fibers, the glass optical core of the fiber has to be aligned extremely accurately to ensure a low loss connection. The core of the fiber is generally between 6 and 100 microns, with 9-10 micron core fiber being almost universally used for telecommunications. This small core means that a scratch or dust on a fiber will cause the light to be greatly attenuated and for the communication link to be lost. 
     Another type of optical connector is the “expanded beam (EB)” optical connector. An EB optical connector eliminates (or reduces) the effect of dust contamination or scratches by using a pair of lenses  101 ,  102  to focus the light between the two fibers  104 , 105 , as illustrated in  FIG. 1 . Expanded beam connectors commonly use ball lenses in a metal block with steel alignment pins to ensure the light is focused back into the fiber without significant loss. These implementations rely on the accuracy of the machining of this block, the pins, the lens and the fiber ferrule in order to provide a reasonably low optical insertion loss. 
     What is desired is an improved EB optical connector. 
     SUMMARY 
     This disclosure describes embodiments of an improved EB optical connector and methods for making the same. 
     In some embodiments, the improved EB optical connector comprises: a rigid, hollow, straight contact tube having a centerline axis; and a collimator assembly having an optical axis and comprising an optical fiber and a collimating lens, wherein the centerline axis of the contact tube is at least substantially aligned with the optical axis such that collimated light produced by the lens from light exiting the fiber travels though the contact tube and the loss of light caused by misalignment of the axes is not more than about 2 dB. In some embodiments, the lens is positioned between an end of the contact tube and an end of the optical fiber. In some embodiments, the loss of light caused by misalignment of the axes is not more than 1.5 dB. In some embodiments, the loss of light caused by misalignment of the axes is not more than 1.2 dB. 
     In other embodiments, the EB optical conectro comprises a rigid, hollow contact tube holder; a rigid, hollow contact tube having a first end attached to a first end portion of the contact tube holder; and a collimator assembly comprising a lens, an optical fiber and a lens holder, wherein at least a portion of the lens and at least a portion of optical fiber are housed in the lens holder, at least a portion of the lens holder is positioned in a cavity formed by a second end portion of the contact tube holder, the lens holder is adhesively fastened to the contact tube holder, and an optical axis of the collimator is aligned with an axis of the contact tube. In some embodiments, the contact tube is integrally attached to the contact tube holder. 
     In some embodiments, the contact tube is integrally attached to the contact tube holder (e.g., the contact tube and contact tube holder are machined from a single object). 
     The above and other aspects and embodiments are described below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments. 
         FIG. 1  illustrates components of a typical EB optical connector. 
         FIG. 2  is a drawing illustrating an improved EB optical connector according to some embodiments. 
         FIG. 3  is an exploded view of the improved EB optical connector. 
         FIG. 4  is a cross-sectional view of the improved EP optical connector. 
         FIG. 5-13  illustrates various steps in a process of making the improved EP optical connector. 
         FIG. 14  illustrates the improved EB connector mating with female EB connector. 
         FIG. 15  illustrates a lead-in component of the female EB connector. 
         FIG. 16  illustrates an alignment between an optical axis of a collimator assembly and an axis of a contact tube. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  is a drawing illustrating an improved EB optical connector  200  (or “EB connector  200 ” for short) according to some embodiments. As shown in  FIG. 2 , EB connector  200  includes: (1) a protective rigid sleeve  202  that protects, among other things, a portion of an optical fiber  201 , (2) a rigid, hollow contact tube holder  203 , and (3) a rigid, hollow contact tube  204 . Contact tube holder  203  may be generally cylindrical in shape, hollow, and open at both its distal  393  and proximal  394  ends. In some embodiments, contact tube  204  has a length between 0.5 millimeters (mm) and 100 mm. In some embodiments, the length is between 5 and 25 mm. In other embodiments, the length is around 12 mm. In some embodiments, the inner diameter (ID) of contact tube  204  is about 0.8 mm and the outer diameter (OD) of contact tube  204  is about 1.25 mm. In other embodiments, the ID of contact tube  204  ranges between 0.1 mm and 10 mm, and the OD of contact tube  204  ranges between 0.15 mm and 15 mm. 
       FIG. 3  is an exploded view of EB connector  200 . As shown in  FIG. 3 , EB connector  200  may further include: a rigid sleeve (a.k.a, ferrule)  302  that serves to, among other things, protect an exposed glass strand  301  of fiber cable  201 , a lens holder  303 , and a lens  304 .  FIG. 4  is a cross-sectional view of the improved EP optical connector. As shown in  FIG. 4 , lens  304  is positioned between proximal end  390  of contact tube  204  and distal end  490  of strand  301 . As further shown, proximal end  480  of lens and distal end of ferrule  302  may be angled with respect to the transverse axis of the connector. As further shown, because lens need not be positioned within contact tube  204 , the width of lens  304  may be greater than the internal width of contact tube  204 . For instance the OD of lens  304  may be about 1.8 millimeters and the ID of contact tube  204  is less than 1.8 mm (e.g., as mentioned above, the ID of contact tube  204  may be about 0.8 mm, in some embodiments). 
     While contact tube  204  and contact tube holder  203  are shown as two separate pieces, in some embodiments contact tube  204  is integrally attached to contact tube holder  203 . For example, in some embodiments contact tube  204  and contact tube holder  203  are machined from a single, unitary object 
     In the embodiment shown, lens holder  303  is a tube (e.g., a glass tube) open at both ends, and lens  304  is generally cylindrical in shape and having a diameter (or width) in the range of 0.5 millimeters to 2.0 millimeters. In some embodiments, lens  304  is a gradient-index (GRIN) lens (e.g., a GRIN cylindrical lens). In other embodiments, lens  304  may be a ball lens (e.g., a 3 mm ball lens). 
     Referring now to  FIGS. 5-13 , a process of making EB connector  200  will be described. The process may begin by inserting glass strand  301  into ferrule  302  as pictured in  FIGS. 5 and 6 . Strand  301  and ferrule  302  may be polished to provide a smooth surface and may also be optically coated with an antireflective coating. Additionally, the strand  301 , ferrule  302 , and lens  304  may be polished at an angle to reduce reflections. For example, proximal end of lens  304  may be angled with respect to the optical axis at least 8 degrees. 
     The next steps may include inserting distal end  701  of ferrule  302  into end  702  of lens holder  303  and inserting proximal end  480  of lens  304  into the other end  703  of lens holder  303 , as pictured in  FIGS. 7-10 . The resulting assembly  1000  is referred to as a “collimator assembly  1000 .” 
       FIG. 11  is a cross-sectional view of the collimator assembly  1000 . As illustrated in  FIG. 11 , at least a portion of lens  304  and at least a portion of ferrule  302  are housed in the cavity of lens holder  303 . As also shown, there is a free space  1101  between the distal end of ferrule  302  and proximal end  480  of lens  304 . The distance between the distal end of ferrule  302  and proximal end  480  of lens  304  may be about 0.01 mm to 0.2 mm or in some embodiments from 0 to 10 mm.  FIG. 11  also illustrates the optical axis  1102  of collimator assembly  1000  (i.e.,  FIG. 11  illustrates the path that light exiting fiber strand  301  and passing through lens  304  will follow if unimpeded). 
     The next steps include: (a) inserting proximal end  390  of contact tube  204  into the distal end  393  of contact tube holder  203  and fastening contact tube  204  within contact tube holder  203 ; and (b) inserting collimator assembly  1000  into contact tube holder  203  such that distal end  1302  of lens  304  is positioned within a cavity  1301  (see  FIG. 12  and  FIG. 13 ) formed by contact tube holder  203  and fastening collimator assembly  1000  within contact tube holder  203 . 
     In some embodiments, contact tube  204  is fastened within contact tube holder  203  merely by press fitting tube  204  into the distal open end of contact tube holder  203 . As further shown, contact tube may be fastened such that its proximal end is located with a cavity defined by contact tube holder  203  and its distal end is positioned beyond the distal end of contact tube holder  203 . 
     In some embodiments, collimator assembly  1000  is fastened within contact tube holder  203  by injecting an epoxy adhesive or other adhesive into the cavity formed contact tube holder  203  in which collimator  1000  is placed. To facilitate the injection of this adhesive, holes  1201  (see  FIG. 12 ) may be formed in a wall of contact tube holder  203  that defines the cavity in which collimator  1000  is placed. In some embodiments, the adhesive used to fasten collimator  1000  within holder is a low shrinkage epoxy. Additionally, the epoxy may cure at room temperature or by exposure to ultraviolet light. 
     After fastening contact tube  204  within contact tube holder  203  and inserting collimator  1000  into contact tube holder  203 , but before fastening collimator  1000  within holder, there is a step of aligning the optical axis  1102  of collimator  1000  with an axis  1602  (see  FIG. 16 ) of contact tube  204  (e.g., the centerline or longitudinal axis). This is illustrated in  FIG. 16 , which shows both the optical axis  1102  of collimator  1000  and the centerline axis  1602  of contact tube  204 . In the example shown in  FIG. 16 , it can be seen that axis  1102  is not perfectly aligned with axis  1602  (i.e., the axis are parallel—there is not angular offset—but the axis  1102 ,  1602  are laterally offset by a small distance). In some embodiments, the alignment process includes adjusting the position of collimator  1000  within contact tube holder  203  until a light beam exiting lens  304  in the direction of contact tube  204  will pass through and exit contact tube  204  substantially unattentuated, that is, experiencing not more than a loss of about 2 dB (more preferably, in some embodiments, the insertion loss of the optical signal is less than about 1.5 dB, and in other embodiments a loss of not more than 1.2 dB may be achieved). A loss of not more than about 2 dB may be achieved by ensuring that the optical axis of collimator  1000  is substantially laterally and axially aligned with axis of  1602  of contact tube  204 . 
     After the collimator  1000  is aligned with contact tube  104 , an adhesive may be used to fasten collimator  1000  within contact tube holder  203  in the satisfactorily aligned position, as discussed above. Thus, once alignment is achieved, collimator  1000  should not be repositioned (or repositioned only very slightly). Accordingly, in some embodiments, a very low shrinkage and high strength adhesive is used to fasten collimator  1000  to contact tube holder  203  to help ensure that collimator  1000  will not move out of the aligned position. 
       FIG. 14  illustrates the improved EB connector  200  mating with an improved female EB connector  1400 . 
     In the example shown, EB connector  1400  is similar to EB connector  200 . That is like, EB connector  200 , EB connector  1400  includes a collimator assembly  1401  that is aligned with a contact tube  1404  and that includes a lens holder  1453  housing a lens  1409  and a fiber  1491 . In some embodiments, collimator assembly  1401  may be identical to collimator assembly  1000 . Unlinke EB connector  200 , however, EB connector  1400  may include a cover tube  1402  for receiving contact tube  204  and an alignment sleeve  1473  (e.g., a split tube) for aligning contact tube  204  with the corresponding tube  1404  such that the centerline axis of each is aligned. Cover  1402  and alignment sleeve  1473  surround contact tube  1404 . 
       FIG. 15  is a further cross-sectional view of a portion of contact  1400 , which figure further illustrates cover tube  1402  and alignment sleeve  1473  according to some embodiments. As shown in  FIG. 15 , cover tube  1402  may include a rim extending radially inward from the distal end of alignment sleeve  1402  defining a frustoconical lead-in  1502 . As also shown, alignment sleeve  1473  is in the form of a split tube. 
     An advantage of EB connectors  200 ,  1400  is that the collimating lens ( 304 ,  1409 ) is protected from contamination because no portion of the lens is exposed. 
     EB connector  200  may be used in combination with a fiber optic jack, such as the fiber optic jack described in U.S. Patent Application Publication No. US 2010/0202730 (“the &#39;730 publication”), which is incorporated by reference herein in its entirety. For example, EB connector  200  can be used in combination with the fiber optic jack  100  disclosed in the &#39;730 publication just as fiber optic connectors  202 / 204  described in the &#39;730 publication are used with the fiber optic jack. 
     While various embodiments of the present disclosure have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context. 
     Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.