- ~24~7 OPTICAL FIBER CONNECTOR WITH SPHERICAL LENSES
In one kind of optical fiber connector, aligned cavities are formed in opposite faces of a light-transmissive member, the cavities having tapered surfaces and terminating at inner ends defined by surfaces of revolution. Clptical fibers are biased into the cavities with their end corners engaging the tapered cavity surfaces which aligns the fibers with the axes of the cavities. An optical fluid occupies the space between the end of each fiber and the adjacent cavity end surface so that fluid lenses are formed and the two fibers are coupled.
There remains a difficulty, however, in preventing contamination of the connector when the optical fibers are removed. It is not permissible to allow any foreign matter to enter the lens cavities because this will seriously degrade the efficiency of the light transmission. Nevertheless, in these connectors, there are openings through which the lens cavities are exposed upon removal of the optical fibers, so there i8 a danger of foreign matter finding its way into the lens cavities.
In another connector, spherical lenses are positioned adjacent the ends of the optical-fibers, permitting light to be transmitted from one fiber to the adjacent spherical lens, from one spherical lens to the other, and from the second spherical lens to the second fiber. The light travels in a quasi collimated beam between the spherical lenses. This connector, however, requires an elaborate screw adjustment to properly align the connector sections and accomplish reasonably efficient coupling. This greatly adds to the expense of ~/
manufacture, making the connector impractical for mass production, and there is no complete assurance that the adjustment will not be lost during the use of the connector in service. Moreover, in this connector, the optical fiber is bonded in place within the connector so that the fiber cannot be removed and replaced.
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~2463~;7 The present invention overcomes the difficulties of the prior art noted above with an efficient optical connector that can be mated and unmated limitless times in service without danger of lessening the efficiency of light transmission. When needed, optical fibers readily are removed and replaced, not being bonded into the system.
The optical connector of this invention includes a receptacle which receives two plug assemblies, each of which carries the end of one of the two optical fibers being interconnected. The plug assemblies include tubular members having inner ends that extend i Ito the receptacle. Within each of the tubular members is an inwardly tapering surface complementarily engaged by the exterior surface of a light-transmissive me:nber of predetermined index of refraction. This effectively aligns the tubular members and the light-transmissive members. Precisely at the axes of the tubular members are blind cavities having tapered entrances and curved inner ends, with the optical fibers being biased into the cavities so that their end corners engage and are centered by the tapered surfaces. An optical fluid occupies the inner portions of the cavities beyond the end faces of the optical fibers forming fluid lenses.
Aligned with each of the cavities is a frustoconical recess receiving a spherical lens, which may be glass. The spherical lenses engage and are centered by the frustoconical surfaces of the recesses, and are spaced from the inner recess walls. An optical cement secures them in place. The light-transmissive members are of molded plastic as a result of which they can be very accurately dimensioned, with unvaryingly high performance being obtained from all of a production run of these items. The distance between the fiber end and the spherical lens and the shape of the fluid cavity is a critical dimension that can be controlled with precision, yet varied by a simple change in the mold to permit the connector to accommodate optical fibers of different characteristics.
Accordingly, light from one fiber passes through the cavity, through the light-transmissive member to the spherical lens where it travels through the space between the two spherical lenses, enterin~ the other spherical lens, to be i2~63~'7 transmitted through the other light-transmissive member and into the second optical fiber. Rather than using imaging quality as the critereon for optical design, maxirnum mode volume coupling of the fibers is achieved using the spherical lenses.
The connector is separated simply by disconnecting the plugs at the receptacle, leaving exposed only the spherical lenses. The cavities remain buried within the plug assemblies when the connector is mated and unmated, with no access for contamination. If necessary, however, the optical fiber may be removed by sliding it out of the cavity for replacement by another optical fiber.
Good results are obtained when the optical fluid in the cavity that receives the fiber has the same index of refraction as that of the light-transmissive member in which it is formed. In that event, the cavity end wall does not affect the path of the light and the only lenses are the spheres. In this arrangement, the manufacturing tolerances in molding the cavity in the light-transmissive member is not critical, other than assuring that the fiber is centered and its end is the correct distance from the sphere. Any minute chips of the material of the light-transmissive member scraped off the wall of the cavity by the fiber end, and present in the inner end of the cavity, will not adversely affect the light path.
Fig. 1 is a perspective view of an optical fiber connector embodying the invention;
Fig. 2 is a longitudinal, sectional view taken along line 2-2 of Fig. l;
Fig. 3 is an enlarged, fragmentary, longitudinal, sectional view of the central portion of the connector;
Fig. 4 is a longitudinal sectional view of another embodiment of the invention; and Fig. 5 is an enlarged, fragmentary, longitudinal, sectional view of the central portion of the connector of Fig. 4.
The connector 10 is used to interconnect optical fibers 11 and 12 at the axes of protective cables 13 and 14. At the center of the connector 10 is a tubular receptacle shell 15 having a straight cylindrical bore 16 terminating at an internal radial shoulder 17 at one end, and an enlargement to an internally threaded section 18 at the other end. One plug 19 of the connector includes an elongated sleeve 20 received within the right-hand end of the receptacle shell 15, as the device i9 illustrated. This end of the sleeve 20 includes an enlarged forward end portion 21 defining an external radial shoulder 22 that engages the shoulder 17 of the receptacle shell 15. The enlarged portion 21 of the sleeve 20 is internally threaded and meshes with the externally threaded rearward end of a tubular member 23. The remainder of the external surface of the tubular member 23 is cylindrical and substantially complementarily received in the bore 16 of the receptacle shell 15. The rearward end edge 24 of the tubular member 23 bears against an internal radial shoulder 25 at the end of the internal thread in the forward end portion 21 of the sleeve 20. An annular groove in the external surface of the tubular member 23 receives an O-ring 26 tn form a seal with respect to the bore 16 of the receptacle shell 15.
The radial inner end wall 27 of the tubular member 23 butts against the radial inner end wall 28 of a tubular member 29, which is identical to the tubular member 23 and forms a part of the second plug 30. Thus, the tubulsr mernber 29 has a cylindrical part complementarily received in the receptacle shell 15, an annular groove to receive an O-ring 31, and a rearward end 32 that is externally threaded. The two tubular members 23 and 29 are axially aligned by the inner wall 16 of the receptacle shell 15.
The second plug 30 of the connector includes elongated sleeve 33 which has an enlarged forward end 34 that is externally threaded and meshes with the threads of the internally threaded end 1~ of the receptacle shell 15. An hexagonal exterior section 35 facilitates holding the sleeve 33 stationary as the receptacle shell is rotated to make the connection. Internally, the end 34 of the sleeve 33 has a threaded forward entrance which meshes with the externally - ~2~636,7 threaded rearward end part 32 of the tubular member 29. The rearward end edge 36 of the member 29 bears against an internal radial shoulder 37 at the inner end of the threaded entrance to the forward end 34 of the sleeve 33. As a result, when the end ~4 of the sleeve 33 is tightened into the end of the receptacle shell 15, the shoulder 22 of the sleeve 20 is caused to bear against the shoulder 17 of the receptacle shell, and the ends 27 and 28 of the tubular members 23 and 29, respectively, are forced together. This holds the elements 15, 20, 23, 29 and 33 as a single assembly when the connector is mated.
The bore of the tubular member 23 includes a frustoconical portion 41 that tapers forwardly at a shallow angle from the rearward end 24 of the member 23.
The frustoconical portion 41 terminates at a straight cylindrical bore 42 at the forward end of the member 23. The other tubular member 29 has a similar forwardly tapering frustoconical section 43 and a stralght cylindrical bore 44 at its forward end.
Within the tubuiar member 23 i9 a transparent member 45 having a predetermined index of refraction, preferably molded of plastic, such as poly-methylpentene. The member 45 has a frustoconical exterior surface 46 that tapers toward the forward end of the member 45 and complementarily engages the frustoconical surface 41 of the member 23. This positions the radial forward end 47 of the member 45 within the bore of the tubular member 23, recessed with respect to the forward end 27 of the latter member. A blind cavity extends into the rearward end of the member 45 and is defined by a rearward, inwardly tapering frustoconical surFace 48 that connects to an inner~ smaller similarly tapering surface 49. The latter surface terminates at an arcuate inner end 50 which is defined by a surface of revolution.
A recess is formed in the forward end of the light-transmissive member 45, including an inwardly tapering frustoconical surface 51 terminating at a flat radial inner end wall 52 which is closely spaced from the inner end 50 of the cavity. The member 45 is molded so that the frustoconical surFace 51 is accurately aligned with the tapered surface 49 of the cavity. Within the recess in the forward end 47 of the member 45 is a spherical lens 53, which may be of glass. The lens 53 engages and is centered by the frustoconical surface 51 of the cavity, just clearing the inner end wall 52. This locates the spherical lens 53 within the bore of the tubular member 23, spaced from the forward end 27 of the member 23. An epoxy resin 54, having light transmissibility in the infrared region and a selected index of refraction, provides an optical cement that secures the lens 53 in its recess in the light-transmissive member 45.
Another light-transmissive member 55, identical to member 45, fits within the tubular mernber 29. In its rearward end is a cavity with an outer frustoconical surface 56 and an inner portion 57, including a curved inner end surface 58. In the forward end of the light-transmissive member 55 is a recess with a frustoconical wall 59 receiving a spherical lens 60 which is spaced from the inner radial end wall 61 of the recess and held in place by an additional quantity of optical cement 54. The exterior surface 62 of the light-transmissive member 55 is forwardly tapered and complementarily engages the surface 43 of the tubular member 29. As a result, the spherical lenses 53 and 6D are closely spaced apart and aligned with the optical axis of the system.
The light-transmissive members 45 and 55 are molded so that there is an exact predetermined distance between the end of the fiber and adjacent spherical lens, whieh is important for efficient light transmission. The tapered walls of the cavities control the locations of the fiber ends as the tapered surfaces of the recesses govern the positions of the spherical lenses. Being made of molded plastic, the light-transmissive members can be made to hold these dimensions very accurately throughout a production run. It is irnportant that the spherical lenses 53 and 60 be spaced from the inner walls 52 and 61 of the recesses so that the spherical lenses can be aligned and positioned by the frustoconical recess walls. This spacing also is a factor in obtaining efficient light transmission, advantageously being within the range of 25 to 75 microns, with the optical cement 54 occupying the space between the spherical lens and the inner recess wall.
~2D~63~7 Each of the plugs includes a front shell 63, axially slidabJe within a rearward shell 64, which has a radial shoulder 65 at its forward end, and internal threads at its rearward end 66. There is also a rearward plug member 67 which includes a hollow forward portion 68 that receives the rearward end of the forward plug shell 63. The forward portion 6~ of the rearward plug member 67 is externally threaded and meshes with the threads of the rearward shell 64.
Within the rearward snell 64 is a cornpression spring 69, one end of which bears against the end edge surface 70 of the forward end portion 68 of the member 67, and the other end of which engages the rearward shoulder of an annular enlargement 71 on the front plug shell 63. This biases the latter member forwardly toward the interior of the receptacle. The front plug shell 63 includes a frustoconical surface 72 at its forward end which is complernentary to and pressed against the tapered cavity surface 48 of the light-transmissive member 45 by the compresslon spring 69. This produces an axial force on the member 45 which urges its tapered surface 46 against the surface 41 of the tubular member, assuring axial alignment of the members 45 and 23.
At the other end of the connector, to the left as illustrated, the forward end 72 of the front plug shell 63 is urged against the tapered surface 56 of the light-transmissive member 55 in a manner similar to that for the front plug shell 63.
The optical fibers 11 and 12 extend through the plugs and into the cavities in the light-transmissive mernbers 45 and 55. The fibers are clamped and held at the rearward ends of the plug members 67, which are segmented to resemble collets. Tapered surfaces 73 at the rearward end of each member 67 at its segmented portion are engaged by complementary tapered surfaces 74 on a nut 75 which meshes with external threads on the reduced diameter rearward portion 76 of the men ber 67. Accordingly, tightening of the nut 75 onto the member 67 reacting through the tapered surfaces 73 and 74, closes the segmented collet end about the optical fiber to grip it. An O-ring 77 circumscribes the nut 75 to form a seal in the plug sleeve which receives it.
L63Çi7 The plugs are closed off at their rearward ends by back shell nuts 79 which engage the rearward threaded end of the receptacle sleeve 20 in one instance and sleeve 33 in the other. The back shell nut 79 includes a radial end wall 80 that engages the rearward end 81 of the nut 75 and is provided with a central opening to allow the fiber to enter. A key 82 fits in a keyway 83 in the end of the sleeve 20 to assure that the cable 14 will not become twisted as the back shell nut is tightened onto the sleeve 20. A sirnilar keyway 8~ in the sleeve 33 prevents twisting of the cable 13.~
When the plugs are assembled into the receptacles, the plug shells 63 are pressed rearwardly by their engagement with the tapered surfaces 4B and 56 of the transparent members 45 and 55, exposing the ends of the optical fibers 11 and 12 and causing these fiber ends to be pressed into the cavities. The corners of the fiber ends bear against the tapered cavity walls 49 and 57, which center the fibers within the cavities. The surplus in the length of each fib0r is accommodated in an accumulation chamber 85 in the forward plug shell 63.
As a result of this construction, the ends of the fibers 11 and 12 and the spherical lenses 53 and 60 are precisely aligned along a common axis, which is the optical axis of the system. The cavities 49 and 57 may contain optical fluid 86 of different index of refraction from that of the light-transmissive members 45 and 55, and form fluid lenses at the surfaces 50 and 58, which are made as surfaces of revolution, in conjuction with these members.
On the other hand, the optical fluid 86 may have the same index of refraction as that of the light-transmissive members 45 and 55. In this event there is no refraction at the cavity surfaces 50 and 58, the only lenses being the spheres 53 and 60. Therefore, so long as the cavities accurately center the fibers 11 and 12 and position their ends appropriate distances from the spherical lenses, the contour of their inner end surfaces 50 and 58 is not critical and efficient light coupling will be obtained. This makes the tolerancPs in molding the cavities less severe so that manufacturing the connector is easier.
L63~7 The connector is separable without withdrawing the fibers from their cavities, thus avoiding contamination of those areas. By loosening the plug sleeve 33 from the central receptacle shell 15, the entire left-hand assembly may be removed from the receptacle, leaving exposed only the small spherical lenses 53 and 6D, rather than the fiber end or the fluid lens cavity. Therefore, the connector may be mated and unmated limitless times with no degredation of its performance.
In the embodiment of Figs. 4 and 5, the optical fiber connector includes a tubular receptacle 87 receiving identical plug assemblies 88 in its opposite ends.
Each of the plug assemblies includes a sleeve 89, the forward end of which is threaded into a tubular member 90. The latter member includes a rearward flange 91 bearing against an end of the receptacle 87. A nut 92 threads onto each end of the receptacle, and includes an interior shoulder 93 that engages the flange 91 of the tubular member 90 to hold the latter in engagement with the receptacle end.
A keyway 95 is included in the forward end of each of the tubular members 90 to receive a key 96 extending radially inwardly from the internal wall 97 of the receptacle ~7. The positions of the keys and keyways may be varied to control the mating of the connector. This is particularly important where a number of optical fiber connectors are mounted side-by-side, and assurances must be made that a plug will mate only with a receptacle that is intended to receive it.
Within each tubular member is a plastic light-transmissive member 99 which, as in the previously described embodiment, includes an exterior frusto-conical surface 100 complementarily engaging an interior surface 101 of the tubular member. The taper is toward the forward end so that forces exerted on the light-transmissive member 99 tend to keep it in place, firmly engaged with the frustoconical surface lûl of the tubular member 90. This, in turn, assures that the light-transmissive member 99 is properly located and accurately aligned with the optical axis of the connector.
~gL63~7 In the embodiment oF Figs. 4 and 5~ the forward end 103 of the sleeve 89 bears against the rearward end 104 of the light-transmissive member 99 when the sleeve is threaded into the tubular member 90. This produces the forces on the light-transmissive member 99 that urge it into the opening in the tubular member 90.
As before, the light-transmissive member has a frustoconical recess 105 which receives a transparent sphere 106 that forms a spherical lens. This sphere is held in the recess by means of optical cement 54, and i5 positioned so that it does not engagej but instead is spaced, a predetermined distance from the inner radial wall 107 of the reces~ 105.
The front plug shell 10B has a frustoconical surface 109 bearing against the similar surface 110 in the rearward end of the light-transmissive member 99, being biased against this surface by a compression spring 111. The optical fiber 112 is biased axially into its cavity 113, as in the previously described embodiment, where the optical fluid 86 may have an index of refraction either the same as that of the member 99, or different to form a fluid lens.
The optical connector shown in Figs. 4 and 5 is readily disconnected from either end by loosening the nut 92, which frees the plug 88 from the receptacle 87. Only the spherical lenses 106 are exposed when the connector is separated~
as the optical fiber ends remain in their lens cavities.