IE55298B1 - A space-divided optical switch assembly - Google Patents

Abstract

1. A device for an optical spatial switching being accesses of a first group (GA) of N first distinct optical elements (fa) and a second group (GP) of P second distinct optical elements (fp), characterized in that it comprises : - an optical selection assembly (10) constituted by a stack of N rigid, flat optical plates (1) interposed and each maintained in a fixed position face to the access of one of the N first optical elements (fa) which are mounted according to the pitch of the optical plates (1) in their stack in a network which is transverse to these plates, each optical plate (1) in the assembly (10) comprising P distinct waveguides (g), first ends of which are coupled in common to the access of the first optical element which faces it and to which this optical plate is associated, second aligned ends of the P distinct waveguides (g) emerging on one of the edges, each optical plate being associated to an opaque tape (5, 7) presenting at least one perforation (I) and being movable in front of the second ends of the P waveguides of this optical plate, and all the optical plates (1) in this assembly having the second ends of their waveguides with their N tapes associated to the same side of the optical selection assembly (10), - an optical distribution assembly (20) constituted by a stack of P optical distribution plates (21) in which the plates (21) are mounted transversely to the optical plates (1) of the optical selection assembly (10) and at the same pitch as that between the second ends of the waveguides of each of the optical plates (1) of the optical selection assembly (10), and each one incorporating N individual waveguides (h) having their first ends coupled in common to the access of said second optical element (fp) to which the respective plate (21) is associated, whereas second aligned ends emerge on one of the edges of the plate, the first ends of the guides (h) of the different plates (21) being disposed at the same side of the stack and being coupled to the accesses of the second optical elements (fp), the second ends of the waveguides of the different plates (21) emerging at a common side of the stack and being arranged in N rows perpendicularly to the planes of the plates (21) of the distribution assembly, these second ends facing on each row second ends of the P waveguides respectively of one of said plates of the selection assembly (10) and being separated from said plate by the associated tape (5, 7). [EP0131131A1]

Description

ί» The present invention relates to optical transmission. It relates more particularly to a space-divided optical switch assembly which selectively couples accesses to a first group of N distinct first optical elements, with accesses to a second group of P distinct optical elements. This switching assembly is particularly suitable for transmitting P programmes to N subscribers and thus constitutes an optical programme broadcaster.

Generally speaking, an optical system for broadcasting P programmes to N subscribers requires N distinct fibers for transmitting each of the P programmes to each of the N subscribers, making a total of P times N fibers. These fibers are regrouped into N groups of P fibers each, ie. one group of fibers per subscriber, with each subscriber being able to select a desired one of the P available programmes.

Optical switching means enable each subscriber to select one out of P programmes.

A mechanical optical switch is described in U.S. patent number 4 304 460, in which the desired coupling is obtained by deflecting a beam of light. This device includes collimator (or focusing) means constituted by a lens, and deflection means’ constituted by a rotating mirror.

In common with other light-deflecting opto-mechanical switching devices in general, this switching device is bulky in comparison with the very small size of the optical fibers used, and is difficult to implement if light losses are to be minimized.

Another form of mechanical optical switching device capable of selecting a desired optical fiber is described in an article entitled "La commutation optique dans Les reseaux locaux de videocommunication" (Optical switching in local videocommunication networks) by L. Jeunhomme and published in the Thomson-CSF Technical Journal vol 14, No 3, September 1982, pages 767 to 785. This solution consists in equipping the end of each subscriber fiber with a microlens, and in placing a fiber-carrying barrel opposite each of said ends, the barrel being constituted by a cylinder having peripheral grooves receiving the ends of the P programme fibers, which are likewise fitted with microlenses. Selection is by rotating the barrel by means of a micromotor so as to bring the desired programme opposite to the subscriber fiber. In .the context of broadcasting by optical fiber (as particularly envisaged by the present invention), this would require one switching device per subscriber, and again the total bulk of the system would be prohibitive in comparison with the compactness of the optical fibers themselves.

Preferred embodiments of the present invention provide a space-divided switching assembly, in particular for broadcasting programmes to a plurality of subscribers, in which the switching assembly is particularly compact and uses modular components of simple structure.

The present invention provides a space divided optical switch assembly between accesses to a first group of N distinct first optical elements and to a second group of P distinct second optical elements, the switch assembly comprising an optical selector assembly associated with an optical distribution assembly: the optical selector assembly being constituted by a stack of N distinct optical plates each of which is associated with a corresponding one of the first optical elements, each optical plate being flat and rigid and being held fixed facing the access to the said corresponding one of the N first optical elements, which optical elements are disposed at the pitch of the optical plates in their stack in a network which is transverse to the stack; each optical plate in the assembly including P distinct waveguides which have respective first ends coupled in common and facing the access of the said corresponding first optical element, and which have respective second ends emerging in a line along one of the sides of the optical plate, each optical plate further including a tape which is opaque to light, which is disposed in front of the said emerging second ends to prevent the passage of light therethrough, which includes at least one light-passing hole, and which is movable to place the said at 4 least one hole opposite a selected one of the said second ends to permit the passage of light therethrough; the opaque tapes of the N optical plates being located on the same face of the stack of optical plates; 5 the optical distribution assembly being constituted by a stack of P distinct optical distribution plates in which the distribution plates are mounted transversely to the optical plates of the optical selector assembly and at the same pitch as that between the second ends of the 10 waveguides of each of the optical plates of the optical selector assembly, and each one incorporating N individual waveguides having their first ends coupled in common to the access of said second optical element to which the respective distribution plate is associated, whereas 15 second aligned ends emerge on one of the sides of said plate, the first ends of the guides of the different distribution plates being disposed at the same side of the stack and being coupled to the accesses of the second optical elements, the second ends of the waveguides of 20 the different distribution plates emerging at a common side of the stack and being arranged in H rows perpendicularly to the planes of the plates of the distribution assembly, said second ends facing on each row second ends of the P waveguides respectively of one of said optical 25 plates of the selector assembly and being separated from 5 said plate by the associated tape.

Embodiments of the invention are described by way of example with reference to the accompanying drawings, in which: 5 Figure 1 is a diagram of a single opto-mechanical switching device as employed in the present invention; Figure 2 is a diagram of a particularly advantageous variant of the Figure 1 switching device; Figure 3 is a diagram of a space-divided optical 10 switch assembly in accordance with the invention, in particular for optically broadcasting P programmes to N subscribers, and making use of switching devices of the kinds shown in Figures 1 or 2; Figure 4 is a cross section through a concrete implementation of the space-divided optical switch assembly shown in Figure 3; Figure 5 is a view of the Figure 4 switch assembly which is partially in section on a line V-V; Figure 6 is a further view of the Figure 4 switch assembly which is partially in section on a line VI-VI; Figure 7 is a diagram of the disposition of position markers in the opto-mechanical switch devices of the assembly shown in Figures 3 to 6; and Figure 8 is a diagram of a single optical distributor plate as used in the optical switch assembly of Figures 3 to 6.

Figure 1 is a diagram of one example of an Qptg-mtchenical switch device as used in the invention for selectively coupling an access to a first optical element, eg. a subscriber fiber fa, with an access to a single second optical element chosen from a plurality of P distinct optical elements. In the example shown, there are four second optical elements (P=4) and they are constituted by second optical fibers _fd1 to fd4. The accesses to the second optical fibers are disposed at a regular pitch £ along the same line.

The opto-mech'anical switch device is disposed between the access to the fiber fa_ and the accesses to the second fibers fdl to fd4. The device includes a rigid, flat, rectangular optical plate 1 and a flexible tape 5 which is opaque to the light used and which is disposed between the optical plate 1 and the accesses to the fibers fdl to fd4. The optical plate constitutes a collector and includes as many light guides £1 to £2 as there are second optical fibers fdl to fd4. These light guides £1 to £4 spread out from a point on a first edge 2 of the optical plate 1 where they have respective first ends commoned together and facing an access to the fiber fa, to a plurality of points along a second edge 3 of the optical plate 1 where they have respective second ends aligned along said second edge at a regular pitch chosen to be equal to the pitch £ of the accesses to the second optical fibers which are disposed opposite respective second ends of the light guides. 7 The tape 5 is interposed between the second ends of the guides jjl to £4 in the plate 1 and the accesses to the second optical fibers fdl to fd4, and is free to move in translation as symbolized by an arrow 6. The tape has a hole _l which is suitably sized and located for the tape to have P different positions in each of which it couples second end of respective waveguide £ in the optical plate to the corresponding second optical fiber fd.

The maximum necessary amplitude of tape movement past the accesses to the second optical fibers .fd and the second ends of the waveguides £ is equal to the maximum distance between two accesses to the second fibers or between two second ends of the waveguides, ie. to (P - 1)r = 3r in the present case.

From the diagrammatic representation of Figure 1, it will be readily understood that there may be a number P of second optical fibers fci along the line other than four. In such cases the plate 1 will include the same number P of waveguides as there are second optical fibers.

In a variant of the Figure 1 device, the second optical fibers fd are not regularly spaced along the line. The corresponding second second ends of the waveguides are spaced in a matching configuration along the edge 3, and the tape 5 is driven in translation by various steps to match the differing spaces between adjacent accesses to the second optical fibers.

Figure 2 is a diagram of another variant of the device shown in Figure 1. In this variant, items which are identical to corresponding items in Figure 1 have been given the same reference, while altered items have been given new references.

In Figure 2, the tape 7 is moved past the accesses to the second optical fibers fri and the second ends of the waveguides £ in the plate 1 as symbolized by an arrow 8. The tape has as many holes J/Ι to J.4 as there are waveguides £1 to £4 or second optical fibers fdl to fd4. Each of the holes J/I to .14 is analogous to the preceding single hole JL. They are aligned and at a regular pitch x, which is equal to the regular pitch £ of the accesses to the second optical fibers along the line less a difference £ which is small compared with r. 8 In a variant/ the pitch of the holes _L1 to _14 can be equal to the pitch r_ plus a small difference £.

Under such conditions/ the tape 7 is driven in small steps equal to the difference £. In comparison to the Figure 1 embodiment/ the reduced amplitude of tape displacement in this embodiment enables the tape to be positioned more accurately and has increased switching speed.

In a variant of the Figure 2 embodiment/ the accesses to the second optical fibers fd are aligned but no longer at a regular pitch along the line. The second ends of the waveguides are disposed along the facing edge 3 in positions which correspond to the positions of the accesses to the various second optical fibers, and the tape 7 has holes which are likewise aligned and which are spaced at distances apart which match the distances between successive accesses to the second optical fibers, plus or minus a small difference £.

To ensure that the optical fiber fa. can be coupled to only one of the accesses to the second optical fibers at a time in each of the P positions of the tape 7 (driven in regular steps £), the pitch £ and the spacing between the accesses to the second optical fibers fd are chosen, for example, in such a manner that the access spacing is greater than (P - 1)p.

In both of the embodiments shown, the optical plate 1 may be obtained as an integrated structure by using ion diffusion to make the waveguides £ in a plate of glass. This method of making waveguides is described in the article "Planar multimode devices for fiber optics" by G.L. Tangonan et al. presented at the Optical Communication Conference, Amsterdam, September 17 to 19, 1979, and in the article "Fast fabrication method for thick and highly multimode optical waveguides" by G.H. Chartier et al. published in Electronics Letters, vol. 13 No 25 December 8th, 1977 pages 21.5-1 to 21.5-7.

The optical plate 1 can also be obtained by setting individual waveguide-constituting optical fibers in silica-impregnated epoxy resin or in glass having a melting point of about 500°C and a low coefficient of thermal expansion so as to minimize stress during cooling. In such implementations, an 5 9 additional "common" waveguide of larger cross section than the individual waveguides £ may be coupled directly to the first ends of the individual waveguides £ bunched together in a hexagonal bundle, with the common waveguide constituting a single common first end for the waveguides £ at the edge of the plate 1.

In both methods of obtaining the plate 1, the waveguides £ are chosen to be of small numerical aperture so as to minimize coupling losses. Given the small but non-negligible tape gap between the second ends of the waveguides £ and the facing accesses to the second optical fibers fd# it is preferable for at least the second ends of the waveguides £ and also the accesses to the second optical fibers to be individually fitted with microlenses to improve the quality of the coupling provided thereby. 20 In addition to the advantage of rigidity due to the flat shape of the optical plate 1, the optical switch device has the advantage of having only the tape 5 or 7.as a moving part, while the accesses to the fibers fa_ and fd are fixed as is the optical plate 1, thereby enabling the ends of the waveguides £ to be initially positioned very accurately relative both to the first optical fiber _fa and to the accesses to the second optical fibers fd_.

Furthermore, this device is an easily reproducible modular item which facilitates making an optical selector assembly by merely stacking such modules. Such an optical selector provides a space-divided optical switch which is useable, in particular, as an optical programme broadcaster which is highly compact.

Figure 3 is a diagrammatic representation of such a space-divided optical switch assembly between a first group GA of N distinct first optical elements fa and access to a group GP of P distinct second optical elements ^g. The optical elements fa, and jfg as shown are optical fibers. This space divided optical switch assembly comprises N opto-mechanical switch devices each comprising a fixed optical plate with a moving tape as shown in Figure 1 or Figure 2. In this switch assembly, the individual optical plates and their associated tapes are given the references 1 and 7 as used for Figure 2, with each tape being individually driven as symbolized by the corresponding arrow 8. 10 The N opto-mechanical switch devices constitute an optical selector assembly 10.

The space-divided optical switch assembly illustrated is described below in the context of its application to optically broadcasting P programmes to N subscribers. The programmes are transmitted from P programme optical fibers fg_ and they are transmitted to N subscriber optical fibers fa, each of which is selectively connectable to receive any one of the P programmes. This space divided optical switch assembly is referred to hereinafter as an optical broadcaster. The description is given, by way of example, for the case where there are 16 programmes and 32 subscribers, ie. P = 16 and N = 32.

The optical broadcaster comprises a first stack of 16 identical programme distribution plates 21. Each programme distribution plate 21 serves to distribute one of the 16 programmes to any of the 32 subscribers. The 16 optical programme distribution plates 21 constitute an optical distribution assembly 20.

Each of the plates 21 includes 32 distinct optical waveguides hi to j£2 referred to as programme distribution guides. The 32 guides in each plate 21 have first accesses coupled in common to an access of one of the programme fibers fp attributed to the plate in question, and have second or "programme output” accesses exiting along an edge of the plate where they are disposed in line at a regular pitch Jt.

The output accesses from the waveguides hi to h32 for all P programs in the stack of 16 distribution plates are disposed on the same face of the stack. These 16 times 32 output accesses thus define 32 rows of 16 accesses each, leading to 16 different programmes. Along each row the output accesses are at a pitch £ and constitute 16 accesses to 16 second optical elements for a single opto-mechanical switch device of the kind shown in Figure 2 (or in a variant of the kind shown in Figure 1). The plates 21 in the optical distribution assembly are therefore stacked at the pitch £.

The opto-mechanical switch devices on the switch assembly (each device comprising an optical plate 1 and a 11 tape 7) are attributed to respective ones of the fibers fa^ in the group GA, and are disposed in a second stack in which the individual devices of the second stack are at right angles to the distribution plates 21 of the first stack, ie. parallel to the 32 rows of output accesses defined by the first stack. In each of the opto-mechanical switch devices, the optical plate 1 includes 16 individual waveguides £l to £I6. These 16 waveguides £1 to £16 have their first ends commoned and disposed facing one of the subscriber fibers fa. In the stack of optical plates 1, the commoned 32 first ends of the waveguides (one for each of the 32 optical plates) are disposed on the same side of the stack facing a corresponding one of the subscriber optical fibers fa_ attributed to the optomechanical switch device in question. The 16 waveguides in each optical plate 1 have their second ends aligned at the pitch r_ and disposed facing respective ones of the 16 programme output accesses of one of the 32 rows provided by the optical distribution assembly.

The tape 7 associated with each optical plate is thus disposed between the 16 second ends of the waveguides £1 to £16 of the corresponding optical plate 1 and the 16 output accesses of the the 16 programmes along one of the 32 rows of output accesses in the optical distribution assembly 20. The tapes 7 are individually driven in translation as symbolized by an arrow 8.

This optical broadcaster in which the distribution assembly and the stack of optical plates 1 are fixed and in which the tapes are individually driven serves to broadcast the desired one out of P possible programmes to each subscriber, with it being quite possible for one particular programme to be received by a plurality of distinct subscriber optical fibers fa_.

In the example illustrated in Figure 3, the P second optical elements coupled to the P distribution plates are respective optical fibers as mentioned above. In a variant, they could be programme-emitting light sources, each source being constituted by a laser diode, for example, or more advantageously by a plurality of laser diodes all emitting the 12 same programme, which configuration has the advantages of greater reliability and of reducing mode noise by superpositioning different modes from the laser diodes.

Figures 4, 5 and 6 show a concrete example of the optical broadcaster shown in diagrammatic form in Figure 3, and items which are identical with those shown in Figure 3 have the same references.

The stack of 16 programme distribution plates 21 constituting the optical distribution assembly 20 is disposed between two plates or grids 23 and 24 for positioning the plates 21. These grids 23 and 24 have ribs (25 on the grid 23 ad 26 on the grid 24) which face one another and which receive the opposite edges of the various plates 21 through which access is provided to the internal light guides which are not shown in these three figures.

The ribs 25 are of rectangular section and receive those edges of the plates 21 that provide accesses for coupling to the programme optical fibers _fg. The grid 23 has a common window or a plurality of individual windows (not shown) into which the guide accesses for coupling to the programme optical fibers fjs appear. The grid also has resilient tongues 27 disposed on the bottoms of the grooves between the ribs 25 for play-free positioning the individual distribution plates 21 in the final optical broadcaster.

The ribs 26 receive those edges of the plates 21 that provide accesses for coupling the other ends of their internal waveguides to the second ends of the waveguides £ in the optomechanical switch devices. Each rib 26 has a chamfered edge to accurately position this edges of each of the plates 21 and to accurately position the spacing from one accesses to the next in the stack. The slots between the ribs 26 are open over the entire length of the plates 21. The stack of plates 21 between the grids 23 and 24 is held between two side blocks 28 and 29 which are held together by screws such as 30. The edges of the grid 24 are engaged and mounted in suitable internal recesses formed in facing sides of the blocks 28 and 29, with a rubber gasket 31 being placed between the bottom of each recess and 13 the face of the grid 24 which engages it. The outside edge of the block 28 at the same end as the grid 24 has a chamfered surface 28'.

The optical selector assembly 10 is made of a stack of 32 optical plates 1 held between positioning plates or grids 13 and 14/ in an analogous manner to the stack of plates 21/ and which can be seen in Figure 4 and more particularly in Figure 6. The grid 14 has ribs 16 which delimit slots which are open over the entire length of the plates 1 and which receive those edges of the optical plates 1 which have the second ends of the waveguides £ for positioning opposite to the various programme output accesses in one of the 32 rows of the distribution assembly 20. These ribs 16 likewise have chamfered to accurate position and hold the plates 1. In the final broadcaster,, the grids 14 and 24 are placed face to face leaving a small gap in between to pass the tape 7.

The grid 13 has ribs 15 of rectangular section like the the ribs of the grid 23. The ribs 15 delimit slots having bottoms fitted with rubber tongues 17 for receiving those edges of the optical plates 1 which have the first ends to be coupled in common to the subscriber fibers fa. The grid 13 also includes fiber carriers 12 disposed on the opposite side to the ribs 15 and arranged in a line at the pitch of the plates 1 in the grid 13. The fiber carriers 12 are disposed opposite and very close to the first ends to be coupled in common of the various optical plates 1.

This stack of optical plates 1 and associated subscriber fibers _fa fixed to the grid 13 is held held by two side blocks 41 and 42 by means of screws such as a screw 73.

With reference to Figures 4 to 6, it can be seen that the blocks 41 and 42 are parts of a frame 40 of generally rectangular section in which they constitute two opposite sides. The outside edges of these side blocks have respective recesses 43 and 44 which constitute housings of the means for guiding and driving the tapes 7, which means are described further on. The side recesses 43 and 44 are interconnected by an additional recess 45 formed in one of the other two faces 14 of the frame. The recess 45 serves not only to house the tapes 7, but also the grid 13 whose ribs point into the frame through a window (no reference) made in the bottom of the recess 45.

In each optical plate 1, the means for positioning, guiding, and driving the tape 7 in front of the plate are constituted by a set of four pulleys 46 to 49, with the pulley 46 being fixed to a drive gear wheel 50. The gear wheel 50 is in turn coupled to a motor gear wheel 51 on the shaft of a motor 52.

The sets of pulleys for the various optical plates 1 are positioned in the recesses 43, 44, and 45 substantially at the corners of the frame 40, with each pulley wheel being mounted to rotate freely about a respective shaft 46', 47', 48', and 49'. The drive gear wheels 50 of the various optical plates 1 associated with respective pulleys 46 are likewise free to rotate about the shaft 46', which shaft thus has alternating gear wheels 50 and pulleys 46. Each tape 7 thus forms an endless loop disposed over a respective set of pulleys 46 to 49. To facilitate coupling between each of the subscriber fibers ^a and the waveguides of the corresponding optical plates 1, the tapes 7 are slightly offset as they pass round the optical plate and the fibers fa. are offset in the opposite direction so as to pass through the gaps between adjacent fibers fa, (Figure 6).

To reduce overall bulk, the motor gear wheels 51 and the motors 52 attributed to successive optical plates 1 in the stack are disposed alternately at two different angles corresponding to the chamfered face 28' of the block 28 and to the chamfered face 41' of the block 41. Two side plates 53 and 54 are fixed to the blocks and support the two rows of motors.

The distribution assembly 20 and the optical selector assembly 10 to which the fiber-carriers 12 for the subscriber fibers fa are fixed are disposed orthogonally to one another and are held by sets of screws such as 56 connecting the blocks 28 and 29 and the frame 40. The resulting optical broadcaster is also fitted with cover plates, not shown. Individual screws such as 35 for the distribution plates 21 and individual screws 15 55 for the optical plates 1 enable each of these elements to be finally adjusted in position along its respective slot and thus relative to the other .elements, thereby enabling final accurate positioning of the accesses of the optical plates 1 opposite to the corresponding accesses of the plates 21.

To complete the description of an optical broadcaster, Figure 4 shows an optical coupler 60 mounted on the other end of one of the subscriber fibers fa_. This coupler 60 which is a type known per se not only provides continuity of transmission towards the subscriber of the selected programme, but also transmits programme selection signals from the subscriber to the corresponding motor. For example, it may comprise a semitransparent mirror mounted between a focusing lens and a collimator lens. This programme selection control signal from the subscriber is transmitted from the coupler 60 over a link 61, and after detection in a corresponding motor control circuit (not shown) is applied to the corresponding motor 52. Links 62 are draw to represent individual motor power supply leads.

It will be observed that, in order to avoid positioning the tapes incorrectly in response to programme selection signals from the various subscribers, means may be provided (not shown) for detecting the position of each tape and for supplying a binary code representative of the position of each tape, thereby enabling a comparison to be made with the programme selection made by the corresponding subscriber and causing the tape to be driven until it occupies a position in which the programme desired by the subscriber has been effectively selected.

Such detection means could include, for example, five plates (where 2^ < P=16 < 2^) which are identical to the distribution plates 21 and which are incorporated with the plates 21 in the distribution assembly 20, said additional plates being powered by continuous light signals, and said tapes 7 having additional holes (33 additional holes per tape in this case) and as many additional waveguides in each optical plate as there are additional plates. 16 The five additional plates in the distribution assembly are added at one end of the stack of 16 distribution plates 21 and each has the first accesses of its 32 waveguides coupled in common to the access of an optical element Ca fiber or a source) for receiving a continuous light signal therefrom while the second accesses of the 32 light guides, ie the additional output accesses, define 32 rows of five accesses each disposed at a regular pitch £.

The five additional waveguides in each optical plate are disposed at one end of the plate which is made to be Long enough to incorporating these five additional waveguides. First ends of the additional waveguides are disposed opposite respective ones of the five additional output accesses on one of the 32 rows and their other ends (which may leave the plate via its face opposite to the corresponding Subscriber fiber) are coupled to respective photodiodes connected to the control circuit for the motor driving the corresponding tape.

The 33 additional holes in each tape are disposed in such a manner that each of the 16 different possible positions of the tape in which the corresponding subscriber fiber fa_ is coupled to a selected programme access gives rise to a specific different five-bit code which can be detected at the outputs of the additional waveguides of the optical plate with which the tape is associated.

Figure 7 shows how the additional holes are arranged in the tape 7 relative to the additional output accesses referenced si to s5 and relative to the additional waveguides referenced vl to v5. The holes are in five successive groups H1 to H5, with the first group M1 comprising one hole, and with the four following groups H2 to H5 comprising 8 holes each. All the holes in a given group are intended to be°placed opposite the same additional output access in different positions of the tape out of the 16 possible coupling positions thereof. Thus the five groups of holes correspond to respective ones of the five additional output accesses. The second group of holes M2, ie. the group immediately after the first group M1, the holes are disposed at the tape drive pitch £ with the first hole of 17 the second group being (£-¾) from the sole hole of the first group. The holes in the third group M3 are in two bunches of four holes each, with the holes in each bunch being at pitch £, with the first holes of each of the two bunches being 8£ apart 5 and with the first hole of the third group being (jr-4£) from the first hole of the second group. The holes in the fourth group H4 are in four bunches of two holes each which are at a distance £ apart within the bunch, with the first- holes of successive bunches being 4£ apart, and with the first hole of 10 the fourth group being (r-2£) from the first hole of the third group. The holes in the fifth group are regularly spaced at a pitch 2£ and the first hole of the fifth group is (£-£) from the first hole of the fourth group.

Figure 8 shows an example of a distribution plate 21 for 15 one of the programmes and as used in the embodiment shown in Figures 3 to 6.

The plate 21 has the 32 individual waveguides h.1 to h32 indicated in Figure 3, with their ends coupled in common at one edge of the plate coupled to the progamme fiber _f£ to which the 20 plate is attributed and having the other ends of the waveguides along the opposite edge at the pitch of the optical plates 1 in the broadcaster. The common coupling of the ends of the waveguides hi to h32 to the access to the programme fiber f£ is provided by a common auxiliary guide j_, of short length but of 25 larger cross section than the individual guides hi to h32.

The distribution plate also includes a peripheral frame 38, eg. made of an aluminium based alloy.

The distribution plate may be made as an integrated structure like an optical plate 1, with the peripheral frame 30 being placed on and glued to the plate of glass in which the guides _h and their common coupling length j_ are created. The plate 21 could also be obtained like the optical plates 1 by embedding individual optical fibers _h and in a casting.

The ends of the fibers h_ and j_ adjacent to the frame are 35 prepositioned by being glued to the frame. The other ends of the fibers h^ for coupling to the fiber j_ are bunched together in conventional manner into a multi-layer compact hexagonal 18 bundle placed opposite to the end of the fiber j_. The edges of the resulting plate with the ends of the fibers are subsequently rectified and polished.

Claims (2)

1. 9 1/ A space divided optical switch assembly between accesses to a first group of N distinct first optical elements and to a second group of P distinct second optical elements/ the switch l-> assembly comprising an optical selector assembly associated with an optical distribution assembly: the optical selector assembly being constituted by a stack of N distinct optical plates each of which is associated with a corresponding one of the first optical elements, each 10 optical plate being flat and rigid and being held fixed facing the access to the said corresponding one of the N first optical elements, which optical elements are disposed at the pitch of the optical plates in their stack in a network which is transverse to the stack; 15 each optical plate in the assembly including P distinct waveguides which have respective first ends coupled in common and facing the access of the said corresponding first optical element, and which have respective second ends emerging in a line along one of the sides of the optical plate, each optical plate 20 further including a tape which is opaque to light, which is disposed in front of the said emerging second ends to prevent the passage of light therethrough, which includes at least one light-passing hole, and which is movable to place the said at least one hole opposite a selected one of the said second ends 25 to permit the passage of light therethrough; the opaque tapes of the N optical plates being located on the same face of the stack of optical plates; the optical distribution assembly being constituted by a stack of P distinct optical distribution plates in which the 30 distribution plates are mounted transversely to the optical plates of the optical selector assembly and at the same pitch as that between the second ends of the waveguides of each of the optical plates of the optical selector assembly, and each one incorporating N individual Viaveguid.es having their 35 first ends coupled in common to the access of said second optical element to which the respective distribution plate is associated, whereas second aligned ends emerge on one of the sides of said plate, the first ends of the guides of the of the different distribution plates being disposed at the same side of the stack and being coupled to the accesses of the second optical elements, the second ends of the waveguides of the different distribution plates emerging at a common side of the stack and being arranged in N rows perpendicularly to the planes of the plates of the distribution assembly, said second ends facing on each row second ends of the P waveguides respectively of one of said optical plates of the selector assembly and being separated from said plate by the associated tape. 21. space divided optical switch assembly according to claim 1, further including: first mechanical means for holding and positioning the said plates in their stack, said first mechanical means canprising a pair of grids each having ribs that face the ribs on the other grid,· said plates being mounted between the ribs, and the first mechanical means further including side blocks on which are mounted said qrids; second mechanical means for holding and positioning the said optical plates in their stack, said second mechanical means comprising a pair of grids each having ribs that face the ribs on the other grid, said optical plates being mounted between the ribs, and the second mechanical means further including side blocks; third mechanical means for holding the accesses to said first optical elements relative to the stack of optical plates said third mechanical means being constituted by one of the grids of said second mechanical means which grid is further fitted with individual supports for said first elements; and fourth mechanical means for holding and positioning the said tapes relative to the said stack of optical plates, said fourth mechanical means including a set of peripheral pulleys for each tape and individual drive means for driving each tape as mounted on said pulleys independently of the other 21 tapes, said drive means being mounted on one of said side blocks of said second mechanical means. 3/ A space divided optical switch assembly according to claim 2, wherein said side blocks of said second mechanical means include recesses for receiving the set of pulleys and the individual tape drive means. 4/ A space divided optical switch assembly according to any one of claims 1 to 3, wherein the said tape includes P holes which are disposed in line and which are at the same spacing as the spacing between the second ends of the P waveguides in each optical plate plus or minus a difference £ which is small in comparison to the said spacing between the said second ends, said difference £ being the step size of tape displacement. 5/ A space divided optical switch assembly according to any one of claims 1 to 4, wherein each distribution plate has a peripheral strengthening frame. ό/ A space divided optical switch assembly according to any one of claims 1 to 5, wherein each of the distribution plates further includes an additional "common coupling" wave guide providing coupling between the access to the corresponding second optical element and the N first mentioned waveguides of said plate. 7/ A space divided optical switch assembly according to any one of claims 5 and 6, wherein each plate is made of silica-impregnated epoxy resin with the plate's waveguides being embedded in the resin. 8/ A space divided optical switch assembly according to any one of claims 5 and 6, wherein each plate is made of glass with the plate's waveguides being embedded in the glass. 9/ A space divided optical switch assembly according to any one of claims 1 to 5, wherein each distribution plate is made of a plate of glass in which the plate's waveguides are formed by ion diffusion into the glass. 10/ A space divided optical switch assembly according to claim 1f substantially as herein described, with reference to and as illustrated in the accompanying drawings. Dated thiB the 30th day of May, 1984. BY Ml 27 diy F. R. KELLY & CO. r EXECUTIVE.

2. 7 C®ydeRD*dT^Ballebridge, Dublin 4. AGENTS FOR THE APPLICANTS.