Optical fiber connectors and coupling components

BACKGROUND OF THE INVENTION

1. Technical Field

0001This invention relates to connectors for physically and optically connecting optical fibers to one another, and to coupling components each forming a part of such a connector or for coupling an optical fiber to another device.

2. Background Art

0002A known type of optical fiber connectors is termed expanded beam connectors, examples of which are described in European Patent Application Publication No. 100,921 and U.S. Patent No. 4,183,618. In such connectors the light beam emitted from a fiber end is expanded and collimated by a lens and directed at a component which receives the collimated, larger diameter beam and focusses it onto the end of another fiber. Because the beam is of relatively large diameter where it is transferred from one component to another, the task of alignment is reduced as compared to aligning the tiny light- conductive cores of two fibers. Thus, the optical loss in the connector may be reduced. However, even if the expanded beam principle is adopted, it is still important, for reduction of light loss in the connector, that the two components, namely the transmitting and receiving components, be accurately aligned so that the maximum possible amount of light emitted by one fiber end is focussed onto the other fiber end. The task of such alignment may be regarded as having two interrelated aspects, namely the need to gain parallelism of the axes of the transmitting and receiving components and the need to gain coincidence of the axes (i.e. the reduction to zero of the distance between the parallel axes). The former may be regarded as concerning control of the tilt of the axes and the latter may be regarded as concerning the lateral positioning of the axes.

0003The term parallel, or parallelism, has a dictionary definition of "continuously equidistant" and the distance is a finite value other than zero. As used herein in relation to axes it is intended to cover also the case in which the distance is zero.

0004U.S. Patent No. 4,421,383 describes an optical fiber connector for optically coupling two optical fibers together. The connector comprises two similar coupling components. One of said coupling components may be regarded as a device to which the other component couples an optical fiber. The device includes a cylindrical alignment surface and a forward piano surFace. The coupling component includes lens means including a lens having forward and rearward surfaces and a circumferential surface extending between the forward and rearward surfaces. The forward surface of the lens has a convex portion, for refracting radiation, and an annular piano portion radially outwardly of the convex portion. The plane of the piano portion is perpendicular to a datum axis. The lens means has a cylindrical outer surface coaxial with the datum axis. There are means for securing an optical fiber to the lens with the end of the fiber in contact with the rearward surface of the lens. Light emitted from the fiber is transmitted by the convex surface portion in a collimated beam of a width greater than the width of the fiber and with the axis of the collimated beam parallel to said datum axis. There is a sleeve member disposed about the cylindrical outer surface of the lens means.

0005The connector described in 4,421,383 has the disadvantage that the sleeve member, termed therein a union, has to perform many roles. It has to assist in the gaining of parallelism of the axes of the transmitting and receiving components. This it does by virtue of its elasticity and the line contacts between its lips and the rings on the lens means, i.e. the connectors as therein termed. The elasticity of the union draws the piano faces of the lens means into contact with one another. The sleeve member, i.e. the union, is solely responsible for the other aspect of alignment, i.e. the lateral positioning of the axes. The elasticity of the union and the line contacts of the lips and rings are disadvantageous to the accurate lateral positioning of the axes relative to one another. The sleeve member in U.S. 4,421,383 also has to perform the task of physically coupling the two conductors and hence may be subjected to tensile stress. Evidently, the connector described in U.S. 4,421,383 has disadvantages in that the axes of the two halves of the connector are not fixedly located laterally and hence signal loss may occur when the axes are laterally displaced as may occur when the union flexes. Also, the parallelism of the axes may be destroyed upon flexing of the union, which would allow the piano forward faces of the lens means to move out of parallelism.

Disclosure of the Invention

0006The present invention is defined in the claims and overcomes the disadvantages of the prior art by providing the sleeve member with first and second coaxial cylindrical surfaces. The first cylindrical surface of the sleeve member is an internal surface arranged to engage the cylindrical outer surface of the lens means. The axial length of the region of contact of the cylindrical outer surface of the lens means and the first cylindrical surface of the sleeve member is short. The cooperation of the sleeve member with the lens means locates said datum axis laterally within said sleeve member and the shortness of the axial length of contact of the surfaces allows small freedom of the datum axis to tilt relative to the sleeve member. Thus, the sleeve member does not influence the critically important parallelism of the axes, because the lens means can tilt, relative to the sleeve member, to achieve the optimum angular orientation (i.e. tilt) of the datum axis.

0007In a coupling embodying the present invention, parts of the optical aspect of the coupling are given some freedom for movement relative to those parts which perform the physical coupling of the conductors. In this way the optical parts can, by mutual cooperation between themselves, gain some of the alignment characteristics without constraint imposed by the rugged physical coupling parts, which constraint could adversely affect the gaining of those alignment characteristics. Because of the partial independence of the lenses to gain some aspects of alignment independently of the physical coupling components, tolerances in the manufacture of the physical coupling may be relaxed, with resultant economies in manufacturing costs.

0008This is achieved by letting the physical coupling parts participate in the location of the axes of the lenses laterally of the axes, but giving the lenses freedom to tilt relative to the physical coupling parts. Also, the lenses cooperate with one another so that parallelism of the axes of the lenses is gained by this cooperation relatively independently of the physical coupling components. Parallelism of the axes of the lenses is achieved by providing lenses each of which has forward and rearward surfaces and a circumferential surface extending between the forward and rearward surfaces. The forward surface includes a convex surface portion and radially outwardly thereof an annular piano surface portion the plane of which constitutes a datum plane. Spacer means, preferably in the form of three hard spheres having identical diameters, are placed between the annular piano surfaces of the two lenses and the lenses are resiliently biased towards one another. This achieves parallelism of the datum planes and parallelism of the datum axes, as herein defined. This parallelism can be achieved because the lenses have a small freedom to tilt relative to the physical coupling parts.

0009The term "datum axis" as herein used is defined as a) in the case of the convex surface being aspheric, the aspheric axis, b) in the case of the convex surface being spheric and the rearward surface having a piano operative portion, the line passing through the center of curvature of the spheric surface and perpendicular to the plane of the piano portion of the rearward surface, or c) in the case of the convex surface being spheric and the rearward surface having a curved operative portion, the line passing through the centers of curvature of the spheric surface portion of the forward surface and of the curved operative portion of the rearward surface.

0010In one embodiment of the present invention in the form of a connector, the lateral positioning of the datum axes, so that they are coincident, is achieved in a simple and effective manner by coaxial cooperating surfaces. The lens, or a ring member provided around the lens, has a cylindrical surface coaxial with the datum axis of the lens. This cylindrical surface cooperates with a cylindrical internal surface on a sleeve member which is part of the physical coupling. The sleeve member has an external cylindrical surface which is coaxial with its cylindrical internal surface. The two external cylindrical surfaces, one on each of the two sleeve members, cooperate with internal cylindrical surfaces of a single intermediary member. The two internal cylindrical surfaces of the intermediary member are coaxial with one another. Thus, the axes of the cylindrical internal surfaces of the two sleeve members are coaxial in a complete coupling.

0011The cylindrical region of contact between the cylindrical surface of the lens, or the ring member around the lens, and the cylindrical internal surface of the sleeve member locates the lens, or lens and ring member, relative to the sleeve member laterally of the datum axis, by virtue of the contact. However, the axial extent of the cylindrical region of contact is short so as to allow the lens, or lens and ring member, to tilt by a small amount within the sleeve member, i.e, the datum axis has small freedom to tilt relative to the axes of the cylindrical surface of the sleeve member. In this way, an effective lateral location with freedom to tilt is achieved in a simple and effective manner.

0012The physical coupling is completed by two collar nuts, one cooperating with each of the sleeve members, and both threadedly engaged with the intermediary member. In this way, the two coupling components, including lens, sleeve member and collar nut, associated with the ends of conductors to be joined, are identical and can be joined by the intermediary member. This avoids problems encountered when non-identical, e.g. male and female, components are used, such as occur when it happens that two male or two female components have to be connected.

0013The resilient bias of the two lenses towards one another is achieved in a simple, convenient and economical manner by resilient O-rings acting between the sleeve member and the lens of each coupling component.

0014The association of a ring member with the lens has advantages in that the required cylindrical surface is more economically formable as part of a molding process forming the ring member, than it is to form it on the lens itself.

0015Conveniently, the spacer means in the form of hard spheres, between the annular piano surfaces of the lenses, are carried in a cage. In order to avoid adverse influence by the cage on the alignment of the lenses, the cage is formed from thin flexible plastic material as a continuous annulus with lobes carrying the spheres. The construction is such that while the spheres are constrained against movement relative to one another radially and circumferentially of the axis, the forces the cage exerts on the lenses through the spheres are negligible.

0016For best performance of the connector, the end of a fiber has to be accurately positioned relative to the convex surface of the lens. This accurate positioning, having been determined using test apparatus, is maintained by transparent cement having a refractive index corresponding to that of the lens.

Brief Description of the Drawings

0017A preferred embodiment of the present invention will now be described, by way of example, with reference being made to the accompanying drawings in which: <ul id="ul0001" list-style="none"><li>Fig. 1 is an elevational view, partially broken away for the sake of understanding, of an optical fiber connector embodying the present invention;</li><li>Fig. 2 is a view similar to Fig. 1, but with parts of the connector spaced away from one another prior to effecting the connection of the optical fibers;</li><li>Fig. 3 is a perspective view of spacer means included in the connector illustrated in Figs. 1 and 2;</li><li>Fig. 4 is a partial section taken on line 4-4 in Fig. 2 showing keys and keyways; and</li><li>Fig. 5 is an enlarged section of a portion of the connector illustrated in Fig. 1.</li></ul>

Best Mode of Carrying out the Invention

0018The embodiment of the invention now to be described is a connector for coupling two optical fibers to one another. It comprises two similar coupling components and an intermediary member. For the purposes of understanding the invention in its broadest form, one of the coupling components may be regarded as a device to which an optical fiber is to be connected by the other coupling component.

0019Illustrated in Fig. 1 of the drawings is a connector 11 optically coupling two optic fiber conductors 13a, 13b. Each conductor 13a, 13b, comprises an optic fiber 15a, 15b surrounded by a buffer 17a, 17b in turn surrounded by a sheath 19a, 19b, in known manner. End portions of the fibers 15a, 15b are bared for connection.

0020The connector 11 comprises two identical coupling components 21a, 21b and an intermediary member 23. As the coupling components are identical a description of one will suffice.

0021The coupling component 21a includes lens means including a lens 25 formed of a refractive material, in the present embodiment, glass, and having a rearward surface, which is substantially piano in at least an operative central region 27, and a forward surface 29. The forward surface 29 has a convex surface portion 31 which in the present embodiment is spheric. In other embodiments the portion 31- is aspheric. Radially outwardly of the portion 31 a piano annular portion 33 to which the rearward piano surface region 27 is substantially parallel. The term "radially outwardly" is intended to describe distance from the axis and not relative positions along the axis. The plane of the piano annular portion 33 is termed the datum plane. A datum axis 34 in the present embodiment, in accordance with the definition given above, is the line passing through the center of curvature of the spheric surface and perpendicular to the plane of the piano central region 27 of the rearward surface. The datum axis and datum plane are perpendicular. A circumferential surface 35 extends between the forward and rearward surfaces and, in the present embodiment, is of generally circular cylindrical shape having an axis approximately coaxial with the datum axis 34. Abutting the rearward piano surface region 27 of the lens 25 is a tubular element 37 formed, in the present embodiment, of glass transparent to ultraviolet light, and having an axial bore 39 in which is disposed a bared end portion of the fiber 15a. For the purpose of illustration, the bore 39 is shown with a diameter much greater than that of the fiber. This is not the case in reality. For example, the bore may have a 0.017 cm diameter and the fiber may have a 0.012 cm diameter. The end of the fiber is in contact with the lens. The end portion of the fiber, the tubular element 37 and the lens are bonded together by cement 40 having a refractive index matching that of the glass of the lens. The location of the end of the fiber relative to the convex surface portion 31 is such that light emitted from the fiber end is transmitted from the convex surface portion in a collimated beam having a diameter larger than that of the fiber and having its axis parallel to the datum axis. The technique for achieving this important condition involves moving the location of the end of the fiber, in contact with the lens, until a test apparatus shows that light emitted by the fiber end is transmitted by the convex surface portion as a collimated beam with the axis of the beam parallel to the datum axis. When this condition is achieved, ultraviolet light is applied to the uncured cement around the fiber end, the cement being of a type curable by ultraviolet light.

0022The forward surface of the lens has an antireflection coating.

0023The lens means also includes ring member 41 which is fixedly disposed around the circumferential surface of the lens and is secured to the lens so that relative movement of the ring member and the lens is prevented. The ring member is formed of plastics material and is molded in situ onto the lens. The ring member 41 has an outer surface 43 of circular cylindrical shape, the orientation of the axis of which is coaxial with the datum axis. Thus, whatever may be the shape of the circumferential surface 35 of the lens, the ring member 41 provides a surface, the surface 43, for the lens means which is cylindrical and coaxial with the datum axis.

0024The lens means, consisting of the lens 25 and the ring member 41, is disposed radially within a sleeve-like end portion 45 of a tubular member 47. The portion 45 has a circular cylindrical inner surface 49 which is in mating surface to surface engagement with the surface 43 of the ring member over a cylindrical region of short axial length. Movement of the ring member 41 out of the end portion 45 of the tubular member (to the right as seen in Fig. 1), is prevented by inwardly directed resiliently mounted teeth 51 on the tubular member.

0025The end portion 45 of the tubular member 47 has a circular cylindrical external surface 53 coaxial with its inner surface 49.

0026End portion 55 of the tubular member 47 remote from its end portion 45, is formed to allow physical connection between the tubular member 47 and the sheath 19a or 19b of the conductor. In the present embodiment the physical connection is achieved by mastic 57, but it may also be achieved in other ways, for example, by a resilient or split collar compressible or deformable by a nut threadedly engaged with the tubular member.

0027The tubular member 47 has a forwardly facing annular recess 59 the bottom of which is formed by a forwardly facing annular shoulder 61. Disposed in the recess 59 is an O-ring 63 of resilient material. A rearwardly facing annular surface 65 on the ring member 41 faces the 0-ring 63.

0028Each coupling component 21 a, 21 b also includes a collar nut 67 having a forwardly facing annular surface 69 engageable with a rearwardly facing annular surface 71 on the tubular member 47. The collar nut 67 has internal threads 73.

0029The two coupling components 21a, 21b are physically connected by the intermediary member 23 which has inner cylindrical surfaces 75 for mating telescopic engagement with the external surfaces 53 of the tubular members 47. The intermediary member 23 also has external threads 77 for cooperation with the internal threads 73 of the collar nuts 67.

0030The coupling components 21a, 21b can be drawn towards one another by rotation of the collar nuts 67 relative to the intermediary member 23 when the threads 73 and 77 are engaged with one another.

0031The outer surface 43 of the ring member 41 has a keyway 79 and the inner surface 49 of the tubular member47 has a key 83 extending into the keyway 79, see Fig. 4. The external surface 53 ofthe tubular member 47 has a keyway 85 and the inner surface 75 of the intermediary member 23 has a key 89 extending into the keyway 85. The keys and keyways are axially extensive allowing relative axial movement of the ring member, tubular member and intermediary member, but are so formed as to prevent relative rotational movement about the datum axis, of the ring member, tubular member and intermediary member. Thus, the angular orientation of the fibers relative to one another is controlled once they have been cemented to their respective lens members.

0032The piano annular portions 33 of the forward surfaces of the lenses are held apart in parallel, spaced relationship (i.e., the datum planes are held parallel) by spacer means including three spheres 91 of incompressible material, in the present example, steel, having substantially identical diameters. The spheres 91 are retained in a cage 93 formed of thin flexible plastic material, and are in mutually spaced disposition about the datum axis. In the present embodiment they are at 120° to one another. The cage 93 includes a continuous annulus 96 and three lobes 95 extending radially inwards from, and integral with, the annulus. The external diameter of the annulus is such that the cage fits with minimal play within one of the cylindrical surfaces 75 of the intermediary member 23. The cage is located axially within the intermediary member 23 by abutting against an annular rib 94. The cage resists movement of the spheres radially relative to the datum axis and circumferentially about the datum axis. However, the cage imposes minimal opposition to movement of the spheres axially, with respect to the remainder of the coupling, out of their positions when the cage is unflexed. The minimization of the axially directed forces applied by the cage on the spheres minimizes any influence the cage might have on one orthe other (or both assymmetrically) of the lens means.

0033As described above, appropriate rotation of the collar nuts 67 draws the lens means towards one another. The approach of the lens means towards one another is terminated when the forward surfaces of the lenses contact all spheres. Further rotation of the collar nuts causes compression of the O-rings 63. Compression of the O-rings is limited by engagement of annular shoulders 97 on the tubular member 47 with end surfaces 99 of the intermediary member. Any further rotation of the collar nuts 67 after engagement of the shoulders 97 with the surfaces 99 serves to put the threads 73 and 77 under stress thereby locking the collar nuts 67 with the intermediary member 23 so that the connector does not unintentionally come apart.

0034The intermediary member 23 is, for the purpose of illustration, shown with an enlarged central portion 101. This central portion may take any convenient form such as a flange for mounting on a panel or for connection to flanges of other similar connectors. Also, it may be provided with a tool- engaging surface, such as a hexagonal surface for cooperation with a wrench, for example, for holding the intermediary member against rotation as the collar nuts 67 are tightened onto it.

0035It is stated above that the axial extent of the cylindrical region of contact of the outer surface 43 of the ring member 41 with the inner surface 49 of the tubular member is short. As an example, the aforesaid axial extent may be 0.050 to 0.075 cm in an embodiment in which the thickness of each lens is 0.5 cm, and the diameter of the cylindrical outer surface 43 of the ring member is 1 cm. The axial extent of the region of contact is short in order to minimize any influence which the tubular member might exert, through such contact, which might tend to destroy parallelism of the datum axes. The region of contact, with small axial extent, might be likened to a gimbal. Thus, the short axial extent of the region of contact allows small freedom of the datum axis to tilt relative to the sleeve member. The region of contact is, however, fully adequate for the lateral positioning of the datum axis to be determined by the tubular member.

0036The use of the steel spheres 91, often termed micro-spheres, to maintain the parallelism of the datum planes, with the lens means being resiliently biased towards one another by the compressed O-rings 63, has advantages because they are readily available with high accuracy of diameter at economical price.

0037The intermediary member and tubular members are molded from rigid plastics material.

0038The ring member 41 allows the creation of a desired cylindrical surface coaxial with the datum axis by molding techniques and does not require the creation on the lens of a circumferential surface which both is accurately cylindrical and has an axis coaxial with the datum axis.

0039It will have been realized that parallelism of the datum planes is achieved by the spheres 91, the piano annular surface portions 33 and the resilient O-rings 63. Coincidence of the parallel datum axes is achieved by making the circular cylindrical surfaces 43, 49, 53, 75 coaxial.

0040In the embodiment described above, the cage 93 for the spheres 91 is an element separate from the intermediary member. However, the cage may be molded integrally with the intermediary member 23 and in such case the rib 94 would be omitted.

0041The invention has been described above in an embodiment which is a connector for optically coupling two optic fibers. A coupling component in accordance with the present invention may be used for optically coupling an optic fiber to another device, such as a terminal device, as well as to another fiber. In such an embodiment of the present invention in which a single coupling component, such as is described above, is used for coupling a fiber to another device, the coupling component would be physically connectible to the other device which would have a piano surface corresponding in function to the piano annular surface 33. Spacer means, such as spheres 91 and cage 93, would be interposed between the piano annular surface 33 of the coupling component and the corresponding piano surface of the device. The device would have a cylindrical surface, coaxial with a datum axis of the device, for direct or indirect cooperation with a cylindrical surface on the coupling component, such as surface 53. Preferably, the light source or receiver of the device would be mounted in the device in a manner similar to that in which the lens 25 and its ring member 41 is mounted in the tubular member as described above.

0042In the embodiment particularly described above with reference to the drawings, the two coupling components are both male and there is an intermediary member which is female at both ends. In another connector embodying the present invention, one coupling component may be male and the other may be female. In this case there need be no intermediary member. In order to achieve the necessary coaxial relationship of the two components in the assembled condition, the tubular member of the female would have a circular cylindrical internal surface, coaxial with the datum axis, which would extend forwardly and mate with the circular cylindrical external surface of the tubular member of the male component.

0043In the embodiments specifically described above, there are surfaces which are described as cylindrical internal surfaces. Those skilled in the art of molding plastic parts will readily recognize that the forming of such surfaces may be difficult. They will recognize that the effect of such surfaces may be created by a plurality of flat surfaces, tangential to the cylindrical surface desired. Accordingly, reference in the preceding description and ensuing claims to cylindrical surfaces is to be understood as including slightly conical (draft) surfaces, interrupted cylindrical surfaces and theoretical cylindrical surfaces defined by a plurality of other, e.g. flat, surfaces tangential to the theoretical cylindrical surface.

Industrial Applicability

0044The present invention finds application in connecting optical fibers to one another for transmission of optical signals from one to the other with low loss, and also for connecting an optical fiber to another device such as a transmitter or receiver for transmitting or receiving an optical signal into or from an optical fiber.