DISCONNECTABLE COLLIMATION ASSEMBLY

Abstract: The present invention relates to a disconnectable collim­ ation assembly designed to transmit a light beam toward a device to be connected. The assembly comprises a base hav­ ing a plane of reference strictly parallel to a plane of reference of the device to be connected, a sleeve mounted in the base ­ and supporting a centering device holding a bar-lens, the lens being adjusted so that its optical axis will be in a pred­ etermined position relative to the plane of reference.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a dismountable collimation assembly. Description of the Prior Art It is often necessary to break an optical line in order to insert systems for switching, tapping, injecting or attenuating signals. The direct use of the light emanating from an optical fiber presents difficulties. In particular, the resulting beams diverge and the insertion of a system is obtained at the cost of high losses and of mechanical precision. For example, the act of longitudinally separating two fibers with a diameter of 50/125 µ by a distance of 7 µ results in a loss of 0.5 dB as well as an angular misalignment of 1.5 degrees. To separate the ends of the fibers in a efficient fashion, it is sufficient to collimate the beams by using two lenses of the plano-convex type, the ends of the fibers being placed at the respective focal point of each lens. Under these conditions, the front face of the lenses can be separated by about 30 mm. With the use of lenses of the glass bar type, the insertion loss is then 1.5 db for fibers of 50/125 µ . This type of system tolerates an axial misalignment on the order of 0.1 mm and allows a lower tolerance optical coupling. But the system none the less remains sensitive with respect to angular misalignment. Due to this sensitivity of the angular alignment, known devices are non-disconnectable, one-piece optical components permanently inserted in the system and which require factory adjustment for the fiber-lens coupling. Furthermore the manufacturers of optical equipment generally provide their components equipped with a certain length of optical fiber (commonly called a "pig-tail" in the art), which prevents the users from easily creating their own collimation assembly. There also exists a disconnectable optical component but they are always integrated in the body of a specific optical device. It would be desirable to provide a disconnectable collimation assembly which did not have the above disadvantages. SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a dismountable collimation assembly designed to transmit a light beam toward a further device to be optically coupled thereto, the beam being transmitted by means of a plug having a tip, the assembly comprising: a base having a plane of reference which, in use, is intended to be strictly parallel to a plane of reference of said further device; a sleeve mounted in the base and designed to receive said tip; means for positioning the plug and its tip in the sleeve; and characterized by: a centering device placed within the sleeve, in alignment with the tip and held by the sleeve and optical collimation means disposed within said centering device, said optical collimation means being initially adjustable within the sleeve so that the optical axis of the collimating means can be placed in a predetermined orientation relative to the plane of reference of the base. In order to remedy the above drawbacks, the invention thus proposes a dismountable collimation assembly which can be separate from any equipment and which performs the collimation function itself. It can be designed so as to receive standard optical plugs having optical fibers with diameters ranging from 50/125 µ to 100/140 µ . This collimation assembly is based on the principle of the predetermined orientating of the optical axis of the optical collimation means relative to a reference surface. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 and 2 are sectional views of the front and side of a collimation assembly according to the invention. Figures 3 and 4 are views of a sleeve for a collimation assembly according to the invention. Figure 5 and 6 are views of elements of the assembly according to this invention. Figures 7 and 8 represent a particular element of the collimation assembly. Figures 9 and 10 represent various lenses that can be used by this invention. Figure 11 is a diagram of an optimization bench for a collimation assembly according to this invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS To precisely align two elements, an arrangement of the precision bore and shaft type could be used. However, providing a precision bore of small diameter is expensive. As mentioned above, the coupling between two optical fiber ends is relatively tolerant of to radial and axial misalignments, thereby permiting the use of an alignment bore of low precision and of short length. In contrast, since the coupling between optical fiber ends is very sensitive to angular misalignment, large size, mutually parallel, contact surfaces can be used which are easy to produce. In this case, in order to obtain good coupling, each constituent optical axis must be strictly perpendicular to such contact surfaces and the fiber-lens interface must be optimized. The positioning of the lens is optimized directly within the mechanical part of the assembly by means of a micromanipulation tool. In so doing the influence of imprecisions in the mechanical assembly on the fiber-lens coupling are minimized. A collimation assembly according to the invention is represented in Figures 1 and 2. Figure 1 is a section along axis A-A and Figure 2 along axis B-B. The collimation assembly includes a mechanical part and optical collimation means. The mechanical part assures the alignment of the optical fiber plug and the optical collimation means, and also allows positioning and fixation on the equipment to be fitted therewith. The mechanical assembly comprises a sleeve 1 mounted in a base 2, a centering device 3 fitted in sleeve 1, a spring 4 serving to press the tip 5 of an optical plug into the bottom of its lodging, and preferably a stop washer 6. The assembly also comprises means of fixation of the sleeve 1 into the base 2, for example a set-screw 7 screwed directly into the sleeve, and with a head received in a recess 8 in the base. The centering device 3 is introduced via the front of the sleeve and held by force fitting. The spring is fitted in a groove 9 milled in the full thickness of the sleeve. The dimensions of the groove and its form assure the retention of the spring without letting it fall inside the sleeve. With the centering device and the spring installed, the sleeve is engaged in the bore of the base. The screw 7 assures the assembly of the unit, and its head can be encapsulated to prevent any subsequent disassembly. The bore in the sleeve has a cross-sectional shape formed by the junction of a circular part and a V-shaped part. This bore permits the reception and positioning of a plug whose tip 5 has a cross-section of identical form. The positioning V is carefully machined. The sleeve has a cutaway 10 portion opposite two holes 11. The Cutaway portion 10 and holes 11 permit access to parts on opposite sides of the centering device 3 when the latter is in place. They allow for passage of a lens micromanipulation tool. Centering device 3 permits holding the optical collimation means, in this case a bar lens 12, in its position of optimum adjustment by gluing. It has a tubular shape and the diameter of its bore is such that it permits orienting the lens by means of the micromanipulation tool. An adhesive joint 13 integrates the lens 12 with the centering device 3. Base 2 provides protection for the collimation unit, its mounting on the device 30 to be connected can be achieved, for example, by the use of screws 14 with the mounting of an optical plug being by means of a thread located on its rear part. It also has internal orientation error-prevention keys defined by longitudinal cavities 15, 16 and 17 to facilitate the placement of the plug. Cavity 17 also serves to accommodate spring 4. Base 2, in particular, has a accurately machined reference surface 18 intended come in contact with a reference surface of the device to be connected. A slot 19 receives a gasket 20. It can be advantageous to equip the collimation assembly with a washer 6 to serve as a stop for the lens 12. This washer will serve to diminish the force applied to adhesive joint 13 by the spring which generally is used with an optical plug. Washer 6 has one face machined so as to follow the convex face of the lens 12. It is integrated with the assembly by a peripheral adhesive joint 21. To assure a good mounting of washer 6, a small groove 22 is machined in the front part of the bore in the sleeve to serve as a point of attachment for peripheral joint 21. Sleeve 1 is represented by itself in Figures 3 and 4 which are respectively front and side views. Figure 3 is a sectional view along axis D-D and Figure 4 a sectional view along axis C-C. These figures permit a better understanding of the configuration of the sleeve. There can be seen the groove 9, the cutaway portion 10, two holes 11 and the groove 22. A threaded hole 23 permits the mounting of the sleeve in the base by means of a set-screw. The V surface 24 for receiving the plug extends from the rear of the sleeve to a shoulder 25 of the cutaway portion 10. There is also seen a cutout 26 made in the wall of the sleeve extending approximately to the axis of the sleeve, which will serve for passage of a micromanipulation tool. Figures 5 and 6 represent sleeve 1 equipped with the centering device 3 which is force-fitted against the shoulder 25. Figure 5 is a section along axis F-F and Figure 6 is a section along the axis E-E passing through the middle of the centering device. When the centering device is installed in the sleeve, a flared hole 27 is formed, common to the sleeve and the centering device, for the injection of adhesive. Figures 7 and 8 are front and side views of the base 2. Figure 8 is a sectional view along axis G-G. There is shown the slot 19, the receptacle 8 for the screw fixing the sleeve on the base, the reference face 18 and the cavities 15, 16 and 17. The four holes 31 are for the passage of the screws mounting the base on the device to be connected. The thread 32 of the rear part of the base permits screwing in the optical plug to be connected. A peripheral slot 33 permits the installation of a toric gasket between the base and the optical plug. Glass lenses have the advantage of good resistance to the wear resulting from the contact of the plug tip. They can, however, be replaced by plastic lenses. In this case it is preferable to reinforce their resistance to wear as shown in Figures 9 and 10. In Figure 9, wear protection is provided by an axial cavity 35 in lens 12. In Figure 10, the protection is provided by the interposition of a metal washer 36 between the tip and the lens. Length "a" represents the focal length. The device is assembled as follow. The sleeve 1, equipped with the centering device 3 and the spring 4, is introduced into the base 2. The lens 12 is then introduced and followed by the operation of optimisation, in which the optical axis of the collimation assembly is made strictly perpendicular to the reference face 18. This operation is carried out with an optimization bench. Figure 11 is a schematic view of an optimization bench for a collimation assembly according to this invention. It comprises a coherent laser 40 generating a light beam 41 toward the convex face of a bar lens 42. The laser can be a 10 mW laser generating a signal of 630 nm. Lens 42 focuses the light beam on the end of an optical fiber 43 which is 300 m in length and has a diameter of 50/125 µ . This fiber length permits the extinction of the cladding modes. The other end of the fiber is molded very precisely inside a standard plug which will be mounted in the base 2 of the future optical component. The base is attached to a micromanipulation device 44 by four screws fitting in the holes 31. The device is placed on a rigid bench 45 on which are placed, facing one another, device 44 and a screen 46 at a distance of about 1200 mm. The first stage in the optimization operation is the establishment of a target on the screen. For this a lens is glued with no special precautions in the centering device. An optical point of poor quality is obtained, which can serve to determine the point of the target to be aimed at in order to align the lenses and the standard plug as precisely as possible. The procedure as as follows. The optical component is rotated about itself, 90° at a time. Each time, the contour of the light spot on screen 46 is traced very precisely. Then the center of the circle which circumscribes the four circles traced previously is determined geometrically. Around this center a circle is traced, with a diameter equal to that of the light spot. This circle constitutes the target to be aimed at by micromanipulating the lens in front of the standard plug. When, in the course of a manipulation, the target circle is made to coincide with the light spot, the optical axis of the collimation assembly will be considered to he perpendicular to the plane of reference of the base. The lens will then be glued in its centering device. The glue is introduced through hole 27. Preferably, the glue is one which hardens under ultra-violet radiation directed toward hole 27 or through the front face of the lens. The micromanipulation of the lens is done in all possible directions. The standard plug has a tip without a spring and hence is nonretractable. The holes 11 in te sleeve permit the passage of manipulation rods. Cutaway 10 and the cutout 26 permit the introduction of a small V surface held by the micromanipulation arm. After gluing the lens, and the stop washer 6 can be installed and glued in turn. Since the device to be connected with the assembly will have an equivalent structure (reference surface parallel to plane 18 and optical axis strictly perpendicular to this reference surface), optical losses will be reduced to a minimum. All optical components constructed in this manner will be capable of being aligned with each other with the least possible insertion loss in the transmission of a light signal. The molding of fibers in diameters of 50/125 µ and 100/140 µ is now done with a precision of less then ± 3 µ of the theoretical reference dimensions, which makes for small variations from the lens-reference fiber coupling to the lens-utilization fiber coupling. The invention is not limited to the type of plug described above, but can be adapted to other plugs with modification of the forms of the base or the sleeve to assure guidance of the plugs. This type of disconnectable optical component can be used on any optical device inserted in an optical fiber line, for example on couplers, attenuators, switches, and any type of sensor.

Claims: A dismountable collimation assembly designed to transmit a light beam toward a further device to be optically coupled thereto, the beam being transmitted by means of a plug having a tip (5) , the assembly comprising: a base (2) having a plane of reference which, in use, is intended to be strictly parallel to a plane of reference of said further device; a sleeve (1) mounted in the base (2) and designed to receive said tip (5); means for positioning the plug and its tip (5) in the sleeve (1); and characterized by: a centering device (3) placed within the sleeve, in alignment with the tip (5) and held by the sleeve (1) and optical collimation means disposed within said centering device, said optical collimation means (12) being initially adjustable within the sleeve so that the optical axis of the collimating means (12) can be placed in a predetermined orientation relative to the plane of reference of the base. A collimation assembly according to claim 1, characterized in that the optical collimation means comprises a bar lens (12). A collimation assembly according to claim 2, characterized in that the means for positioning the said plug comprises orientation error-prevention keys engaging in cavities (15,16,17) in said base (2). A collimation assembly according to claim 2, characterized in that the means for positioning the said tip in said sleeve are assured by the plug and the internal surface of the sleeve having complementary V shapes (24) which are pressed together by means of a spring (4) lodged in said assembly and acting on said plug tip. A collimation assembly according to claim 4, characterized in that the centering device is held in said sleeve by force fit. A collimation assembly according to claim 5, characterized in that the optical collimating means is glued in the centering device. A collimation assembly according to claim 6, characterized in that a hole (27) is pierced through the sleeve and the centering device for the introduction of glue. A collimation assembly according to claim 1, characterized in that the sleeve has a portion cut away (10) and holes (11) to enable the introduction of a tool for micromanipulation of the optical collimation means. A collimation assembly according to claim 1, characterized in that the sleeve is fixed to the base by a screw (7). A collimation assembly according to claim 1, characterized in that it also comprises a washer (6) fixed into the end of the sleeve and serving as a stop for the optical collimation means.

Inventors: DESMURS, ROLAND, MALINGE, JEAN-LOUIS, POUYEZ, PHILIPPE
Applicants: SOCAPEX S.A.
Application year: 1986
Main classification: G02B6
IPC codes: G02B6, G02B7