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Lil’ S/ll/ag. (inf-7 ( United States Patent [19] [11] Patent Number: 4,569,569 Stewart [45] Date of Patent: Feb. 11, 1986 [54] OPTICAL COUPLING DEVICES FOREIGN PATENT DOCUMENTS [75] Invent” gilglig‘d‘l' Stewart’ Fmweu’ 0012274 6/1980 European Pat. Off. . [73] Assignee: Plessey Overseas Limited, Ilford, 2441860 6/1980 France -‘ 0016593 10/1980 European Pat. Off. . England [21] Appl. No.: 363,661 [22] Filed Mar 31 1982 . . ................... .. . , References Cited U.S. PATENT DOCUMENTS 4,111,524 4,185,885 4,208,094 4,239,330 4,245,889 9/1978 1/1980 6/1980 12/1980 1/1981 Primary Examiner-William L; Sikes Assistant Examiner__Robm E. wise . Field of Search ................ .. 350/96.18, 96.19, 102, 350/292, 293, 294, 299 [56] 8/1979 United Kingdom . 2097550 11/1982 United Kingdom . cg ............................... .sgiiyggnlng'Gglszligi/ig . 2/1978 United Kingdom . 2091899 8/1982 United Kingdom . , [58] 1500257 2014751 Tomlinson, III . Chown et a1. ................. .. 350/9618 Tomlinson, III et a1. . Ashkin et al. . Hoffman ........................... .. 350/ 102 . __ Ammey' Age“ “Fm” [57] . . Fle‘t' Ja°°bs°“’ c°hn 8‘ Pm" ABSTRACT A coupler for an optical ?bre system includes a retrore flector which because of its properties allows consider able relaxation in the positioning of the ?bre in relation to the retroreflector. The principle may be used to pro vide switches or couplers. 9 Claims, 9 Drawing Figures OUT US. Patent Feb. 11, 1986 :‘ Sheet 1 of2 2 /2 g 4,569,569 /2 7 /6 7 \ I \4 € ‘ F/cj. PRIOR FIG 2 ART ' \ - - PRIOR ART /5 2 7P05/7'l0/V 20 Hal 7 POS/T/O/V l9 US. Patent Feb. 11,1986 Sheet20f2 4,569,569 1 4,569,569 2 being offset from 90° such that light of the wavelength OPTICAL COUPLING DEVICES reflectable by the dichroic mirror is re?ected back to a different position from other wavelengths of light. Thus The present invention relates to optical devices and a wavelength seperator and or optical switching cou more particularly to optical couplers, switches wave 5 pler maybe produced. length combiners etc. wherein light is modi?ed in direc The optical ?bres maybe held accurately in position tion or form. In particular the invention is concerned by mounting them in V shaped grooves etched in silicon with light transmitted along optical ?bres. ‘ blocks or by other known accurate mounting means. Many known optical ?bre couplers, switches, wave length combiners, etc. use expanded beam techniques. Optical lens means is preferably used between the optical ?bre or optical ?bre combination and the retro re?ector to focus the light beam out of and into the These techniques use a small lens or mirror to manipu late a beam of light much larger than the ?bre to optical ?bres. achieve this function, the light being ultimately rei The present invention also provides an optical ?bre connection device comprising means for holding the optical ?bre or ?bres in a ?xed relationship with respect to the retrore?ector, said means being detachable for disconnection. maged down onto the original, or another ?bre (or of course a source or detector.) The basic device of this type, from which others are derived, may be regarded as being a device that re?ects the light emerging from a ?bre back into itself. Types of device using this princi ple are shown in the FIGS. 1 and 2. Although these expanded beam devices may allow the relaxing of tolerances in some respects compared to the equivalent “?bre-only" device the tolerancing on the crucial ?bre transverse positioning is not improved. However, according to the present invention, by replacing the mirror with a retrore?ector such as a comer cube a device can be made in which the image Embodiments of the present invention will now be described, by way of example with reference to the 20 accompanying drawings in which: FIGS. 1 and 2 show known optical ?bre connection devices. FIG. 3 shows a ?rst optical connection device in accordance with the present invention employing a 25 corner cube prism as retrore?ector, FIG. 4 shows a second optical connection device in accordance with the present invention employing a concave and convex mirror retrore?ector arrangement, FIG. 5 shows a Frisnel bi-prism arrangement which will “track” the object as it is moved in any sideways direction. Axial tolerances are not improved but these are less critical in any case. According to the present invention there is therefore when used in conjunction with the arrangement of FIG. 3 or FIG. 4 will provide two tracking images, provided an optical ?bre connection device comprising a retrore?ector, means for holding a ?rst optical ?bre in a ?rst position in front of the retore?ector such that FIG. 6 shows a third optical connection device simi lar to FIG. 3 but including a dichroic mirror surface re?ected by the retrore?ector along a de?ned path so as 35 within the comer cube prism offset from one face of the prism, to be received at the plane of the ?rst optical ?bre at a FIG. 7 shows a switching coupler using a corner cube de?ned second position with respect to said ?rst posi light emitted from said ?rst optical ?bre is received and tion said device being such that within the working angle of said retrore?ector the ?rst position maybe varied whilst maintaining the relative distance between said ?rst and second positions. In a ?rst preferred embodiment the retrore?ector is retro prism with one “off-90°” face, FIG. 9 shows a connector emboding the corner cube retro prism as shown in FIG. 3. Referring now to the drawings it maybe seen that in the arrangement of FIG. 1 or FIG. 2 the vertical or formed by a comer cube prism and in a second pre ferred embodiment the retrore?ector is formed by a concave mirror and convex mirror arrangement. horizontal displacement of the end of the optical ?bre 1 The present invention also provides an optical switching coupler comprising a retrore?ector, means for holding a rotatable optical ?bre combination in position in front of and within the working angle of said retrore?ector, said optical ?bre combination compris ing a ?rst optical ?bre capable of emitting light to be re?ected by said retrore?ector and one or more further _ FIG. 8 shows the rotatable optical ?bre combination 40 device used to secure the optical ?bres in position in the arrangement of FIG. 7, and from its position will cause problems because the re ?ected beam will not return to that spot. Thus the posi 50 tioning of the ?bre is critical. As illustrated in FIG. 1, light beam or ray 12 is emit ted and received by optical ?ber 1. The emitted ray is transmitted through lens 2 toward a planar re?ective optical ?bres displaced a ?xed distance apart from said ?rst optical ?bre in a ?xed relationship, in which the surface 14. The lens illustrated in FIG. 1 is a complex position and the further optical ?bres are arranged symetrically and concentrically around ?rst optical ?bre 1 as it is moved from position 19 to any position 20 as in FIG. 3. Hence, the present invention is less suscep tible to the crucial transverse positioning of prior art devices. Thus any beam emitted by the ?bre will return to the same ?bre providing that the corner cube prism lens including a convex and a concave lens combina retrore?ector is modi?ed by alteration of one or more 55 tion. In FIG. 2, optical ?bre 1 emits ray 12 towards a re?ection angles to displace the re?ected beam by an concave re?ective surface 16 and also the ?bre receives ray 12. amount equal to said ?xed distance when said re?ected beam reaches said optical ?bre combination. In the arrangement of FIG. 3 or 4 however the Preferably the ?rst optical ?bre is held in a central retore?ector used causes the re?ected beam to track the ?bre. The retrore?ector used may in a preferred em bodiment be a corner ~cube prism with one face offset from 90° with respect to its adjoining face by a small angle. The optical ?bre combination is preferably rotat able around the central optical ?bre. 65 18 or concave and convex mirror arrangements 3,4 are accurate because the illustrated optical systems utilize a ‘ In a further embodiment a dichroic mirror surface degenerate self-conjugated retrore?ector, i.e., retore maybe positioned within the corner cube prism, its face ?ectors which return the light beam back to its source. 3 4,569,569 The comer cube prism 18 is shown for simplicity as an angle in two dimensions only but will of course com prise mirrors in three dimensions. The mirrors 3,4 shown in FIG. 4 are concentric. In practice however M2, mirror 4, may be planar, with some loss of performance. Central obstruction will gen erally be minimal. As illustrated in FIG. 4, emitted ray 21 is re?ected twice by M1, mirror 3, and once by M2, mirror 4, and is returned to optical ?bre 1. Other alternative forms of retore?ector may be used for example, a length of graded index rod with a plane 4 merely restricts the number of arrangements of 3 signs achieved by any one cube to 6 of the possible 8. The angular de?ection of any one beam (of the six possible as above) is a sum of 3 vectors in angular space (ie. on a diagram of 0,, vs 6y) orientated at 120° intervals and each of a magnitude related to the angle of one of the roofs according to: de?ection = 2 2/3 80 with the angle 0 de?ned as before. The factor \fgarises because the roof prism is tilted away from the normal. Useful devices may be made from these (any of The six possible spots are obtained by adding the 3 FIGS. 1-4 in some cases) using extra components. For example the use of a Fresnel bi-prism, 23 FIG. 5, close 5 vectors with any combination of signs, except for two as indicated above. This gives the six output beam direc to the mirror (M1) or lens will give two “tracking” tions needed to make the 6-way splitter. If one of the images either side of the input ?bre at spacings deter roofs is exactly 90° (max. interfacial angle) there will of mined by the prism angle. If other ?bres are placed at course be only 4 spots, but two will be bright the two these points a splitter is obtained. The relative positions dim. If two faces are perfect right angles there will be of these ?bres may easily be accurately controlled us mirror at the end. ing, for example, precision etched silicon V-grooves. Variations of this using a dispersive prism or a diffrac tion grating to achieve wavelength separated images are obvious. A similar effect could be achieved in FIG. 3 by using slightly tilted dichroic mirrors one behind the other as one face of the comer cube (FIG. 6). FIG. 6 illustrates a mirror surface 22 and a dichroic mirror 24 and another mirror surface 26. As illustrated in the just two output spots (equally bright.) All spots appear in diametrically opposite pairs, and it is, unfortunately, not possible to obtain 6 in a single row, the nearest being 4 in a row with two out of line. To produce a connector as shown in FIG. 7 a retro prism with a slightly tilted face is used. This re?ects the beam back to two de?ned points close to the original source and hence if a receiving ?bres are mounted at ?gure, dichroic mirror 24 is offset slightly from a plane normal to the surface 22, i.e., the angle between mirror 22 and mirror 24 is different than the angle between mirror 22 and mirror 26. Therefore, the offset angle is the difference between 90° and the actual angle of any those points in accurate ?xed relationships to the emit ting ?bre the light will transfer. The illustrated retrore?ector is a non-degenerate conjugate retrore?ector because the device has a conju mirror. As illustrated, ray 28 is re?ected off of mirror 22. Dichroic mirror 24 re?ects a selected spectral band, i.e., wavelength, as ray 30. The balance of ray 28 is mined distance apart. When a pair of ?bres, separated by this distance, is placed at or near the conjugate plane, light is directed from one ?bre to the other ?bre irre spective of the location of the pair- relative to the optical gate focal plane for which conjugate pairs (e. g., B) of all randomly selected foci (e.g., A) are a ?xed predeter transmitted by mirror 24 and re?ected by mirror 26 as, ray 32. Hence, wavelength sepearation is achieved as axis of the coupling assembly. described earlier. A grating might also be used here and 40 A switching coupler as shown in FIG. 8 may be a split face, with different parts tilted differently, could produced by using the arrangement of FIG. 7, the replace the bi-prism. A particularly simple way to produce a splitter is to use a corner cube with off-90° interfacial angles. This switching action being performed by rotation of the prism about the system axis A-—A1. By this means any two of several output ?bres may be selected. The spe ci?c advantage of this form of switch lies again in terms of insensitivity to both angular and spatial movement of can be arranged to produce 2, 4 or 6 spots; according to 45 the description below. The division of power is mode along diameters in the far ?eld, and is thus made unse the retroprism or similar moving part (see FIGS. 2, 3 lective. etc.) The following is a description of the mode of opera The key advantage of these techniques is the relaxing tion of an ‘imperfect’ corner cube. of ?bre positioning tolerances and a switch coupler A corner cube maybe regarded as constructed of incorporating the corner cube prism arrangement is three mutually perpendicular roof prisms, each of which returns a ray de?ected at an angle of i2 80 shown in FIG. 9. By using an imperfect (oneface “off 90°) comer cube prism of course an optical switch cou where 89 is the angle by which the roof angle differs pler can be constructed using the principles described from 90°, and the sign depends upon the direction in 55 above. which the ray appears (viewed from the front) to cross the roof apex. In the complete cube all rays of interest As illustrated in FIG. 9, a ?bre bundle 48 is held by block 52. Bundle 48 includes a plurality of ?bres, at least are re?ected from each face once and therefore cross one of which is an emitting ?bre and at least another is the line of each roof apex (a re?ection of this in the a receiving ?bre as discussed in relation to FIG. 3 opposite face is equally counted.) The negligible pro 60 above. Emitted rays 49 and received rays 51 clearly portion of rays striking the vertex of the cube is ignored. illustrate bundle 48’s dual components. Block 52 is se If the directions across each apex are labelled consis cured within cylinder 50 as is the illustrated complex tently (ie. in a similar way) it can easily be shown that lens 53, lens 2 and corner cube prism 18. Additionally, the signs of the angular tilts always alternate. Rays may lenses 53, 2 and retrore?ector 18 are retained by sup therefore cross the 3 roofs with any combination of 65 ports 54, 56 and 58, respectively, as is shown in FIG. 9. signs except all +ve or all -—ve. Since the individual What I claim is: i roof angles may each be +ve or —ve (ie.> or <90“), 1. An optical coupling device for optically coupling this does not restrict the combinations achieved, but an emitting ?rst optical ?bre and a receiving second 5 4,569,569 optical ?bre comprising: an imperfect, non-degenerate 6 5. An optical coupling device as claimed in claim 1 wherein said means for holding said ?rst and second conjugate retrore?ector; means for holding said retro~ re?ector; means for holding said ?rst optical ?bre at a optical ?bres is detachable for disconnection. ?rst arbitrary position, in close proximity to an optical 6. An optical switching coupler comprising: conjugate focal plane of said retrore?ector, and for 5 an optical ?bre combination including a ?rst optical holding said second optical ?bre at a de?ned second ?bre capable of emitting light and a plurality of position laterally displaced with respect to said ?rst second optical ?bres displaced a ?xed distance position, both said ?rst and second positions being in apart from said ?rst optical ?bre in a ?xed relation front of the retrore?ector and within the working angle ship; thereof such that light emitted from said ?rst optical means for rotatably holding said optical ?bre combi ?bre is received and re?ected by the retrore?ector so as to be received by said second optical ?bre at the plane of the ?rst optical ?bre. nation; an imperfect corner cube prism having at least one off-90° interfacial angle, said angle displacing the 2. An optical coupling device as claimed in claim 1 in which the imperfect retrore?ector is formed by a com 15 bination of lens means and an imperfect corner cube re?ector, said re?ector being imperfect in that at least re?ected beam by an amount equal to said ?xed distance when said re?ected beam reaches said optical ?bre combination; and means for holding said imperfect cube prism such that said optical ?bre combination is in front of and one face thereof is offset off-90° relative to an adjoining face. within the working angle of said comer cube 3. An optical coupling device as claimed in claim 2 in 20 prism. which a dichroic mirror surface is positioned within the 7. An optical switching coupler as claimed in claim 6 corner cube re?ector, the re?ecting surface of said in which the ?rst optical ?bre is held in a central posi mirror being offset from 90“ relative to said adjoining tion and said second optical ?bres are arranged symmet face such that light of the wavelength re?ectable by the rically and concentrically around said ?rst optical ?bre. dichroic mirror is re?ected back to a different position 25 8. An optical switching coupler as claimed in claim 6 from other wavelengths of light, thus forming a wave in which said interfacial angle is small as compared with length separator. 90". 4. An optical coupling device as claimed in claim 1 in 9. An optical switching coupler as claimed in claim 6 which said ?rst and second optical ?bres are held accu in which the optical ?bre combination is rotatable rately in position by mounting the ?bres in grooves 30 etched in silicon blocks. around the central optical ?bre. # 35 45 55 65 i i i t