FR2541466A1 - Optical coupler for fibre=optic circuit - Google Patents

Abstract

The coupler is used between an optical fibre light conductor and at least two optical elements which are fitted into respective reception chambers (16) in the transparent coupling block (10). The block incorporates at least two optical surfaces (20,22) lying in the optical path between each of the reception chambers (16) and the output end of the optical fibre light conductor. Pref. the transparent block (10) is made of injection moulded plastics, with at least one of the optical surfaces (20,22) providing total internal reflection of the incident light. Pref. the optical surfaces (20,22) are defined by an ellipse function or a parabolic function and they may be provided as the base of a respective recess (24,26) formed in the block (10).

Description

 Fiber optic couplers are typically used to apply modulated light from an emitting source to an optical fiber and to apply backward fiber light to a sensing element. Such couplers can also be used for multiplexing or demultiplexing a module light transported or to be transported by an optical fiber. On this subject, one can usefully refer to the French patent application filed today by the applicant under the title "Bidirectional coupler for optical fiber".

 Such couplers are likely to be used in large numbers, and it is therefore desirable that the production of a coupler can be obtained in large series at reduced cost with a minimum of production steps and a reliable structure. These couplers must also be able to operate in environments with variable temperatures and in the presence of other effects which may affect the optical properties or the alignment of the coupler by causing negative effects on the coupling function.

 It is necessary to ensure high positional precision for the installation of coupler elements in order to obtain low losses in the coupling of light between the ends of the fibers and the emitters and detectors. Injection molding techniques can be used for this purpose, but these are often made complex by the need to perform lateral actions in the creation of all the pockets of a coupler mold. A coupler which can avoid lateral action molds is therefore desirable.

 Optical properties allowing the concentration of light, the separation of the beams or the correction of spherical aberrations and coma are also desired in the coupler with a view to minimizing losses or obtaining flexibility in use.

 According to the invention, a coupler is proposed in which an optical coupling is produced between the end of an optical fiber and the respective detectors and transmitters by means of one or more focusing surfaces, or concentration of light. High positional precision and good alignment are ensured by molding the coupler in the form of a single piece of plastic material in which the end of the fiber and the emitters and detectors are precisely placed using formed cavities. by molding. The focusing surfaces which guide the radiation between the end and the emitters and detectors are also molded in the form of pockets in the body of the coupler. In a single injection molding operation, all the delicate constituents of the body of the coupler, which ensures the reproduction at reduced cost, precise and repeatable, of the coupler.

 In a first preferred embodiment of the invention, the focusing surfaces of the coupler are reflective and use the principle of total internal reflection in the absence of reflective coatings. These surfaces can be aspherical or spherical depending on whether one wishes to correct spherical aberrations and coma or obtain a certain flexibility in the positioning of the focusing surfaces.

Molds of either shape are about the same cost. It is possible to eliminate the lateral action molds by placing all the constituting cavities on mutually opposite sides of the cutter body. The focusing surfaces are segmented when it is desirable to completely isolate the radiation paths connecting the end of the fiber and the emitters and detectors. When using reflective surfaces, the coupler is not sensitive to variations in the refractive index and dimensions that can be attributed to temperature or other effects, as well as to variations in length d 'wave.

 In: - another preferred embodiment, the coupler contains a groove which ends in a beam separation surface. The groove is intended to receive and position an optical fiber so that its end is close to the beam separation surface. A first radiation path leads from the end to a cavity intended for an emitter or a detector by reflection at the level of the beam separation surface. The other path leads through the beam separation surface, to a transmitter or detector cavity by total internal reflection on a focusing surface produced.

by molding. In the coupler mold according to this embodiment, lateral actions are avoided.

 In another embodiment of the invention, a focusing surface is reflective while a second focusing surface acts by refraction.

The following description, designed to illustrate the invention, aims to give a better understanding of its characteristics and advantages; it is based on the accompanying drawings, among which
- Figure 1 is a cross-sectional view of a coupler according to the invention comprising ellipsoSdales surfaces of total internal reflection;
- Figure 2 is a cross-sectional view of a coupler, different from that of Figure 1, using ellipsoidal surfaces of total internal reflection and produced using a mold requiring no lateral action;
- Figure 3 is a cross-sectional view of a coupler, different from that of Figure 1, using paraboloidal surfaces of total internal reflection and produced using a mold requiring no lateral action;
- Figure 4 is a front view of the reflecting surfaces of Figures lj 2 or 3;
- Figure 5 is a front view of another form of the reflective surfaces of Figures 1, 2 or 3;
FIGS. 6A and 6B are respectively a cross-section view and a top view of a coupler according to a second preferred embodiment of the invention, comprising a beam separation surface and a focusing and focusing surface. total internal reflection which are used to perform the coupling function; ;
- Figure 7 is a cross-sectional view of a coupler according to another embodiment of the invention, comprising a focusing surface acting by refraction and a focusing surface with total internal reflection which serve to produce the coupling function;
- Figure 8 is a front view of another focusing surface intended to be used with one or more of the couplers of the invention;
- Figure 9 is a front view of another focusing surface intended to be used with one or more of the couplers of the invention; and
- Figures 13k and LOB are respectively a front view and a sectional view of another coupler having a focusing surface acting by refraction and a focusing surface with total internal reflection according to the invention.

 The invention provides a fiber optic coupler in which at least two optical surfaces, which can act by reflection or by refraction, define materially distinct light paths between the end of an optical fiber and active elements such as a transmitter. or a detector. Reflection or refraction surfaces of the coupler are typically produced in the form of interfaces between the air and the plastic forming the body of the coupler.

 According to the first embodiment of the invention, represented in FIG. 1, a coupler body 10 has a fixing orifice 12 intended to receive an optical fiber and a connector so as to position the end of the fiber at the level d an interface 14 with the molded plastic of the body 10. The body 10 has cavities 16 and 13 dimensioned so as to receive and precisely align emitters or detectors, preferably one of each, in a typical application. The type of transmitter or detector used in the invention includes a central emission or detection location. The optical path between the center of the cavities 16 and 18 and the end of the optical fiber is produced at the interface 14 by means of respective ellipsoidal surfaces 20 and 22. These surfaces are presented at an angle equal to or greater than the critical angle so as to produce a total internal reflection, which avoids the need for reflective coatings. The ellipsoidal surfaces 20 and 22 are molded in the body 10 or they appear respectively as the ends of cavities 24 and 26. These aspherical surfaces eliminate spherical aberrations. In the case of the ellipsordal surface 20, its shape is dimensioned so that a first focal point of the ellipsold is at the location of a point 28 centered inside the cavity 16 at the point where light is applied by the emitter or is received by the detector which is there inserted. The other focal point of the ellipsoidal surface 20 coincides with the location of the end of the optical fiber at the interface 14. A light path 30 is therefore defined between them. The ellipsoidal surface 22 is dimensioned so that a focal point of the ellipsoid is located at a point 32, having the same characteristics with respect to the cavity 18 as point 28 with respect to the cavity 16. The other focal point of the ellipsoid of the surface 22 is at the point where the fiber ends, at the interface 14, which defines an optical path 34 between the point 32 and the interface 14. When looking at the surfaces from the front optics 20 and 22 from the interface 14, they are generally in the form of respective segments 36 and 38, as shown in FIG. 4. The position of the innermost end 40 of the cavity 24 can be varied so to act on the position of the dividing line 42 between the segments 36 and 38, which has the effect of adjusting the percentage of radiation respectively transported by paths 30 and 34. In a typical application, this percentage is 50% for each journey.

 The cavities 24 and 26 can be rotated on the axis of the orifice 12 to 90 on either side when it is desired to eliminate the displacement of the light between the points 28 and 32 in order to reduce the transmission between these points of the stray radiation. It is possible to segment the surface 20 or 22 or these two surfaces, in order to achieve isolation from crosstalk between the radiation applied or received at the level of the cavities 16 and 18 as a result of the reflection on the interface 14. A similar segmentation is illustrated in FIG. 5, which is a front view of surfaces 20 and 22 from the interface 14. As can be seen from this point, surface 22 occupies the left 46 and right 48 parts of the field of vision of FIG. 5, while the surface 20 is formed of a narrow strip oriented from top to bottom in FIG. 5 and forming a central part 50.

 The material of the coupler body 10 is typically a transparent plastic material moldable by injection, such as "Lexan" registered trademark of the company General Electric. In general, transparent plastics of the acrylic or palycarbonate type have been found to be particularly useful. Injection molding techniques for producing surfaces inside a body 10 are well known. Several companies, having the capacity to mold objectives in plastic material or other optical forms, can be used to produce these couplers.

 Another embodiment of a plastic coupler body 60 is shown in Figure 2. The coupler body 60 has a connector 62 for fixing an optical fiber and a connector so that the end of the fiber is centered at an interface 64. Respective optical paths 66 and 68 are defined between the center of the interface 14, at the end of the fiber, and the center of the respective emitting or detecting cavity 70 and 72. The paths 66 and 68 are limited by ellipsoidal surfaces with total internal reflection 74, 76 and 78. The ellipsoids of the surfaces 74, 76 and 78 have a common focus at a point 80, while the other focus of the surface 74 is found at the end of the fiber, on the interface 64. The surfaces 76 and 78 have their other foci at the respective points 82 and 84, respectively centered inside the cavities 70 and 72, where light can be applied or received by means of transmitters or detectors insert are in these cavities. The surfaces 76 and 78 are located halfway between point 80 and points 82 and 84 respectively.

 The mold associated with the body 60 does not require any lateral action) since all the cavities are mella, es in the upper or lower faces mutually opposite. This offers an important advantage in reducing the cost and increasing the precision of the injection molding of these couplers.

 The innermost end in the cavity forming the surface 76, at a point 86, defines the percentage of radiation sharing between the paths 66 and 68, as is typically shown in the front view in Figure 4.

 It is also possible to carry out a segmentation of the reflecting surfaces along the line shown in FIG. 5, or according to other desired lines.

 Since each of the optical paths 66 and 68 has reflections on two oppositely oriented ellipsoidal surfaces, it is possible to correct the coma and spherical aberrations of the focusing function of the reflecting surfaces on each path.

 A third embodiment using focusing surfaces with total internal reflection in the optical paths connecting an end of optical fiber and emitter and cavities.

detector is illustrated in Figure 3. As indicated, a coupler body 90 has a fixing 92 for mounting an optical fiber by its protective cable and its connector on the body 90 so as to position the end of the fiber at the center of an interface 94 with the plastic material of the coupler body 90.

A first and a second cavity-96 and 9 & are formed inside the body 90 on either side of the fixing 92 to house transmitters or dsetectors, as desired. The optical paths 100 and 102 leading to the cavities 96 and 98 are produced by paraboloids 104 and 105 respectively, total internal reflection of collimation, terminal surfaces 105, 105 and surfaces 108 and 110 with total internal reflection of focusing.

Due to the focusing function of the parabolodal reflectors 108 and 110, their positioning is not crucial and it is possible to place them at any distance from the interface 94 with the end of the fiber, as desired. It is also possible, as discussed above in relation to FIGS. 4 and 5, to adjust the separation of the field of vision obtained from the interface 94 using the surfaces 104 and 106.

 The mold of the body 90 also does not require lateral actions. The molding of a coupler according to the embodiment of FIG. 3 can therefore be carried out in a highly efficient manner.

The couplers of Figures 1 to 3 are not sensitive to variations in the refractive index, dimensions and wavelengths by the fact that they are entirely made using reflective surfaces.

 Figures 6A and 6B illustrate one. second general embodiment of the invention in which a beam separation surface is used to direct the radiation between one end of optical fiber and the position of the emitter or detector cavities. A cutter body 120 is shown in section in FIG. 6A, while FIG. 6B shows an upper surface 122. The coupler body 120 comprises a channel 124 in which a single optical fiber is conventionally bonded so that its end is placed in the vicinity of a beam separation surface 126 carrying a dielectric coating. A first cavity 128 is centered directly in the vicinity of the surface 126 and opens onto the surface 122, so as to position an emitter (or a detector) so that the radiation can be applied to the end of the fiber, or received from it, by reflection on the surface 126. The part of the radiation which crosses the surface 126, due to the beam separation function which is assigned to it given by the dielectric coating, forms an optical path 130 which has total internal reflections on a focusing surface 132, which redirects the path 130 towards the center of a cavity 134 dest inee to wear a detector (or transmitter) element.

 It is possible to injection mold the coupler of FIGS. 6A and 6B without lateral actions on the mold. The end of the fiber can be coupled to the surface 126 by means of a refractive index adaptation substance or without such a substance, as desired. The embodiment of FIGS. 6A and 6B ensures a particularly effective coupling with a transmitter placed inside the cavity 128, as well as with the cavity 134, which is typically used with a detector.

 The cavity 128, as well as the cavity 134, includes notches 126 which ensure precise positioning of the housing of the transmitter, or of the detector.

 FIG. 7 illustrates a third general embodiment of the invention. As shown, a coupler body 140 has a connector 142 which receives an optical fiber 144 inside a connector so as to position the end of the fiber 144 against an interface 146 with the body 140. A first optical path 148 is established between the end of the fiber 144 and a detector or emitter assembly 152, placed inside a cavity 154, via a surface 150 with total internal reflection. A second optical path 156 leads from the end of the fiber 144 to an emitter or detector assembly 160, placed inside a second cavity 162 of the coupler 140, via a refractive surface 158.

 In the representation of FIG. 7, the detectors and emitters shown are of the focusing type using lenses 164 to form an image on a semiconductor detector element or to direct the light coming from a semiconductor emitter element. It will be understood that it is possible to use, there or elsewhere in the invention, as desired, other forms of detectors and transmitters.

 The surfaces 150 and 158, considered from the end of the fiber 144, can have the character as described above in relation to FIGS. 4 and 5. It is also possible to envisage that the surfaces 150 and 158 are segmented , as illustrated in FIG. 8, - the sections 170 corresponding to one of the surfaces 150 and 158, while the opposite sections 172 correspond to the other of the surfaces 150 and 158. Likewise, on the FIG. 9, the segments 174 and 176 illustrate a layout for the surfaces 150 and 158, or else extensions of these suitable for the production of the indicated segments. These segmented reflection and refraction surfaces prove useful in avoiding reflections in the opposite cavity from the interface 146 and, therefore, in reducing crosstalk.

 In FIGS. 10k and lOB, another form of the embodiment of FIG. 7 is shown, where the functions of reflection and refraction are distributed between concentric surfaces 180 and 182 inside a coupler body 184 .

FIG. 10B illustrates the part of the coupler containing the reflection and refraction surfaces 182 and 180 associated respectively with the reflection and refraction paths between a fiber end 186 and respective cavities 188 and 190 intended for transmitters or detectors. Figure 10.4 is a substantially front view of these surfaces.

 The shape illustrated in FIGS. 10k and lOB also prevents crosstalk between the emitter and detector elements which may result from reflections at the interface with the fiber optics.

 I1 can be used at the ends of the fibers an index matching substance as another means to prevent crosstalk in all the embodiments described above.

 The reflecting surfaces 150 and 182 of the respective figures 7 and 10A, lOB are typically ellipsoidal, as has been indicated above, two focal points being respectively chosen so as to be at the end of the fiber and at the optical center of the detector or transmitter cavity. The refractive surfaces 158 and 180 are typically Cartesian ovoids, to eliminate spherical aberrations if this is desirable.

 The description given above is that of an optical fiber coupler using one or more focusing surfaces with total internal reflection with or without refraction surfaces, the coupler being easily moldable using injection molding techniques. so as to allow precise optical alignment of the ends of the fibers with the centers of the emitter and detector elements.

 Of course, those skilled in the art will be able to imagine, from the couplers, the description of which has just been given by way of illustration and in no way limitative, various other variants and modifications which do not go beyond the scope of invention.

Claims (16)

1. Optical coupler, characterized in that it comprises  a coupler body (10; 60, 90; 120; '140; 184) formed of an optical transmission substance;  first and second optical surfaces (20, 22; 76, 78; 104, 106, 108, 110; 126, 132; 150, 158; 180, 182) physically separated inside said body;  said body having means (12; 62; 92; 124; 142; 185) for receiving an optical fiber in a first position;  said body having at least first and second means (16, 18; 70, 72; 96, 98; 128, 134; 154, 162; 188, 190) for positioning and fixing first and second emitting elements or detectors;  said first and second physically separated optical surfaces being placed inside said body so as to establish optical paths (30, 34; 66, 68; 100, 102; 130; 148, 156) between said first position and said first and second respective positioning means. 2. Coupler according to claim 1, characterized in that said body is formed of a moldable plastic. 3. Coupler according to claim 1, characterized in that at least one (20, 22; 76, 78; 104, -106, 108, 110; 132; 150; 182) of said first and second optical surfaces establishes a optical path by total internal reflection. 4. Coupler according to claim 1, characterized in that at least one (126) of said first and second optical surfaces establishes an optical path by beam separation. 5. Coupler according to claim 1, characterized in that at least one (158; 180) of said first and second optical surfaces establishes an optical path by refraction. 6. Coupler according to claim 1, characterized in that said coupler body is formed from an acrylic plastic material or polycarbonate. 7. Coupler according to claim 1, characterized in that said first and second slightly separate material optical surfaces (20; 22; 76, 78; 104> 106, 108> 110) establish the first and second optical paths by total internal reflection at inside said coupler body. 8. Coupler according to claim 7, characterized in that said first and second optical surfaces (20, 22; 76, 78) are ellipsoidal. 9. Coupler according to claim 8, characterized in that it further comprises a third ellipsoSdåle surface (74) with total internal reflection having a first focal point in common with the focal points of eIpsoSesdes said first and second optical surfaces (76, 78j and a second focal point placed at the expected end (64) of the optical fiber in said first position, the second focal points of said first and second ellipsoidal optical surfaces being placed at the level of said first and second positibnment means. 10. Coupler according to claim 7, characterized in that said first and second optical surfaces (104, 106, 108, 110) are parabolic.  ll. Coupler according to claim 1, characterized in that one (132) of said first and second optical surfaces is with total internal reflection and the second (126) of said optical surfaces is beam separation. 12. Coupler according to claim 11, characterized in that said means intended for receiving an optical fiber further comprises means for positioning the end of said optical fiber in the vicinity of said optical beam-splitting surface. 13. Coupler according to claim 12, characterized in that the first (128) of said positioning means is placed so as to position a detector or emitter element in the vicinity of said separation surface. beam. 14. Coupler according to claim 13 characterized in that said second optical surface is placed on the path of the radiation transmitted through said optical beam-splitting surface destined for the second (134) of said positioning means or coming from this second positioning means. 15. Coupler according to claim 1, characterized in that said first optical surface (150; 182) is a total internal reflection surface and said second optical surface (158; 180) is a refraction surface. 16. Coupler according to claim 1, 7 or 11, characterized in that said body has recesses making it possible to place said first and second materially separated optical surfaces, said means for receiving optical fiber and said first and second means for positioning on mutually opposite surfaces of the body, so that the body can be molded using a mold without side actions. 17. Coupler according to claim 1, characterized in that said first and second materially separated optical surfaces are segmented so as to avoid crosstalk between said first and second positioning means.