GB2139034A - Communications exchange - Google Patents

Abstract

A communications exchange comprising a plurality of wide beam optical transmitting units having overlapping transmission beams and at least one directable receiving unit, said receiving unit including apparatus for selectably orienting an end of an optical fiber. <IMAGE>

Description

SPECIFICATION Communications exchange The present invention relates to communications exchanges and to optical fiber communication.

Attention is directed to my divisional application No.

8324605.

Various types of optical switching apparatus are known in the patent literature. Switching employing directable light beams has been proposed in U.S.

Patents 3,985,975 and 4,065,644 using holograms and Cry tubes for directing the light beam.

The present invention seeks to provide a communications exchange or switching exchange for telephone or other communications apparatus which is simple and which is easy to construct, economical and modular in the sense that it can be accommodated changeably to the growing needs of a customer.

As viewed from one aspect, the invention provides a communications exchange comprising a plurality of wide beam optical transmitting units having overlapping transmission beams and at least one directable receiving unit, said receiving unit including apparatus for selectably orienting an end of an optical fiber.

As viewed from a further aspect, the invention provides a communications exchange comprising; a first plurality of electromagnetic radiation transmitting units each of which provides a beam of information bearing electromagnetic radiation; at least one electromagnetic radiation receiving unit arranged in radiation receiving relationship with said first plurality; means for selectably directing said at least one receiving unit to a desired one of said first plurality of transmitting units; said directing means comprising at least one device for selectably orienting an end of an information bearing optical fiber.

It is a particular feature of the present invention that substantially no cross talk is encountered since the intersection of electromagnetic radiation produces substantially no interference.

The present invention will be more fully understood and appreciated from the following detailed descripton taken in conjunction with the drawings in which: Figure 1 illustrates a one-dimensional optical fiber end positioning device constructed and operative for use in an embodiment of the present invention; Figures2 and 3 illustrate respective two- and three-dimensional counterparts of the device illustrated in Figure 1; Figure 4 is a schematic illustration of a directable transmitter; Figure 5 is a schematic illustration of a transmitter constructed and operative for use in an alternative embodiment of the invention; Figure 6 is a schematic illustration of a portion of a communications exchange constructed and operative in accordance with an embodiment of the present invention;; Figure 7 is a schematic illustration of transmitter and receiver arrays useful in the exchange of Figure 6; Figure 8 shows alternative arrangements of transmitter and receiver arrays useful in the exchange of Figure 6; Figure 9 is a schematic illustration of a switching exchange comprising a pair of facing arrays each having interspersed receivers and transmitters; Figure 10 is a schematic illustration of a switching exchange comprising an array of interspersed receivers and transmitters and a reflecting element; Figure 11 is a block diagram illustration of transmission and receiving apparatus associated with a single subscriber in the exchange of Figure 6; Figure 12 illustrates, in block diagram form, apparatus for calibrating the transmission apparatus illustrated in Figure 11;; Figure 13 is a schematic illustration of a switching exchange useful for cable television and similar transmissions; Figure 14 is a block diagram illustration of apparatus for high accuracy feedback control of a directional transmitter; Figures 15 and 16 are pictorial illustrations of arrangements of optical fibers associated with piezoelectric bender assemblies fpr use in with the present invention.

The preferred embodiment of the invention will now be described with reference to Figures 1 - 16 which illustrate a variety of constructions thereof suitable for different applications.

Referring now to Figure 1 there is seen apparatus for positioning an optical fiber end constructed and operative in accordance with a preferred embodiment of the present invention and comprising a generally elongate piezoelectric bender element 20 which is mounted at a first end thereof onto a base 22. The piezoelectric bender element 20 may be of conventional construction and manufacture such as a G-1278 Lead Zinconate-TitanateThin Sheet piezoceramic manufactured by Gulton Industries of Metuchen, New Jersey, U.S.A. Leads 24 associated with the piezoelectric bender element may be connected to any suitable source of electrical voltage for controlling the position of the free end 26 of the bender element.

In accordance with the present invention, the free end 28 of an optical fiber 18 is attached as by glueing, clamping or by another suitable means onto the free end 26 of the bender element 20 or adjacent thereto for motion together therewith. Figure 1 illustrates bender element 20 in a straight orientation at rest when the bender element is de-energized and curved to one side when a voltage of a first polarity is applied to leads 24 by means of a selectable voltage source 16. It may be appreciated that normally the bender element may also be bent in an opposite direction by applicaton of a voltage of an opposite polarity to leads 24. Furthermore any desired position intermediate the two extreme bent positions may be realized by the application of a suitable voltage to the leads 24.

It is a particular feature of the present invention that piezoelectric bender elements 20 of the type employed herein display a generally linear and repeatable position in response to voltage inputs within part of their operative range. The positionvoltage characteristics can be calibrated and an open loop control may thus be employed. Relatively complex control circuitry employing microprocessor technology may be employed to take into account the hysteresis behaviour of the position voltage curve of the bender elements. Conventional technol ogy is available for this purpose.

Referring now to Figure 2, there is seen apparatus for positioning an optical fiber end along two dimensions. The apparatus comprises the apparatus of Figure 1 to which is attached atthe free end of bender element 20 a second bender element 30 which is oriented such that its plane of bending lies perpendicular to the plane of bending of bender element 20. In the illustration, the apparatus of Figure 1 is shown rotated 90 degrees from the illustration of Figure 1 and bender element 30 is attached to the free end of bender element 20 by means of a mounting element 32 formed of metal or any other suitable material. Bender element 30 is provided with leads 34 which are coupled to position control circuitry (not shown). The free end 28 of the optical fiber is mounted on the free end of bender element 30.

Figure 3 shows apparatus for positioning an optical fiber end along three dimensions and com prises the apparatus of Figure 2 to which is attached by means of a second mounting element 36 a third bender element 38 at the free end of second bender element 30. Leads 40 are associated with the third bender element 38 and are coupled to position control circuitry (not shown). In practice third bender element 38 is oriented such that its bending plane is perpendicular to the bending planes of bender elements 20 and 30 and serves to position the free end 28 of the optical fiber which is attached to its free end for focussing purposes. Bender elements 20 and 30 may be moved through their position ranges to provide a scanning function.

It is appreciated that the bender elements forming a multi-element bender assembly need not necessarily be arranged in perpendicular planes. Instead it may be sufficient that their directions of motion have respective perpendicular components.

Figure 4 shows a simplified version of a transmitter useful in the present invention and comprising a selectable position modulatable light source 42 which is substantially similar to those illustrated in Figures 1,2 and 3. The free end 28 of the optical fiber provides a beam of electromagnetic radiation 44 which impinges on a lens 46 which focusses the beam at a location which is selected to correspond to a receiver 48. The position of the optical fiber end 28 determines the location of the impinging focused beam.

Reference is now made to Figure 5 which illustrates a transmitter substantially similar two that illustrated in Figures 1,2 and 3 with the difference being that here the lens 50 is mounted on the free end of the bender element 52 in front of the end of the fiberoptic conduit 54 and thus moves together with the free end of the bender element. Beam directing is achieved by changing the direction of the free end of the bender element. A rod lens may be used instead of the lens 50.

Alternatively, the elements described in Figures 4 and 5 may be utilized as directable radiation detec tors.

Reference is now made to Figure 6 which illus trates a portion of a communications exchange constructed and operative in accordance with an embodiment of the present invention. The exchange is suitable for use in telephone, telegraph, radio or any other mode of communication in which informa tion can be transmitted via electromagnetic radia tion.

The apparatus of Figure 6 comprises an array of transmitters 150 disposed in spaced facing relation ship to an array of receivers 152. Each subscriber, indicated by reference numeral 154, is intercon nected with a single transmitter 150 and a single receiver 152 via circuitry 156, an exemplaryembodi ment of which will be described hereinafter in detail.

In the illustrated embodiment, three subscribers U, V and W are shown connected to respective transmitters and receivers. Two way communication between subscribers U and W is illustrated, with a radiated beam of electromagnetic radiation being beamed by the transmitter of subscriber U so as to impinge on the receiver of subscriber Wand a radiated beam of electromagnetic radiation being beamed by the transmitter of Subscriber W to impinge on the receiver of subscriber U.

It is appreciated that there may be cases in which each subscriber may be associated with more than one transmitter and more than one receiver, as in conference call facilities, for example.

Any suitable form of electromagnetic radiation may be employed. In accordance with a preferred embodiment of the invention infra-red radiation is preferred.

Referring now to Figure 7 there is seen, in schematic illustration, an array arrangement for a communications exchange constructed and operative in accordance with a preferred embodiment of the invention. There is provided a first array 160 of transmitters 162, disposed in selectable radiation communicaton relationship with a second array 164 of receivers 166. As seen in the illustrated example, arrays 160 and 164 are generally flat arrays disposed in spaced facing orientation such that a beam of radiation provided by any one of the transmitters 162 may selectively impinge on any individual one of the receivers 166 forthe establishment of communication therebetween.

Each transmitter 162 is associated with a given subscriber and coupled thereto by apparatus providing a modulated radiation beam containing information to be communicated. This modulation may take any suitable form depending on the communication requirements of the system. Each transmitter 162 may be constructed similarly to the directable transmitter described in Figure 4, and the optical fiber may be coupled to a light emitting diode or laser diode.

Since modulation of light beams for communications applications is widely known in the literature it will not be described here, and reference will only be made here to the employment of such modulated light information transmission. A general description of light communication is provided in: Optical Communication Research and Technology; Fiber Optics, by T.G. Giallorenzi, Proc. of the IEEE, Vol. 66.

No. 7, July, 1978, p.744.

The receiving elements may typically comprise photo detectors each of which is coupled via suitable amplification means to a given subscriber.

Figure 8 illustrates an alternative form of arrangement of transmitters and receivers employing a reflecting element for communication. Here arrays 170 and 172, comprising transmitters 174 and receivers 176 respectively, are disposed in adjacent angled relationship facing a reflecting element 178 and arranged so that beams of radiation from any of the transmitters 174 can selectably impinge on any of the receivers 176.

According to an alternative embodiment of the invention illustrated in Figure 9 first and second arrays 180 and 182 are provided in respective facing arrangement. Each of the trays comprises an interspersed arrangement of transmitters and receivers 184 and 186. It is appreciated that the transmitters and receivers 184 and 186 on the same array cannot communicate. Nevertheless, such a construction would be suitable for use with a submarine cable, where such local communication would not be required.

Figure 10 shows an alternative embodiment of the invention in which a single array 192 is arranged facing a reflecting element 194. Array 192 comprises an interspersed arrangement of transmitters 196 and receivers 198. It is appreciated that in this arrangement any of the transmitters 196 can communicate with any of the receivers 198.

Reference is now made to Figure 11 which illustrates transmission and receiving apparatus associated with a single subscriber in the exchange of Figure 6. A subscriber, 236 which may represent any desired type of communications terminal is coupled to transmitter and receiver circuits, 240 ands 242 respectively. Transmitter circuit 240 comprises a line receiver 244 which separates the dialing information (in the case of a telephone link) or alternatively the address instructions from the voice or data information. The dialing information passes to a dialing information decoder 246 while the voice or data information passes to a modulator 248.

The voice or data information causes the modulator 248 to operate a source of radiation, for example a LED with a selectable modulation representative of the voice or data signal received thereby. This radiation is transmitted along an optical fiber link 250 and from an end thereof through a lens 252 which beams the radiation at a desired receiver.

The dialing or address instructions are employed to determine the angular orientation of the radiaton beam, typically by suitable energization of a piezoelectric bender element, as shown in Figure 2.

The dialing decoder 246 employs a conventional microprocessor 254, such as an Intel 8080 and memories 256 for decoding received address or dialling inputs into X and Y position co-ordinates.

Decoder 246 provides X and Y position outputs along a data bus to first and second latches 257 and 258, each of which is coupled to a respective Digital to Analog converter 260 and 262. Digital to Analog converter 260 is coupled to the electrodes of a piezoelectric bender element 261 arranged to bend along an X-axis and converter 262 is coupled to the electrodes of a piezoelectric bender element 263 arranged to bend along a Y-axis.

The receiver circuit 242 comprises a wide field of a view detector 264 which is arranged to receive an incident beam of light from a transmitter and which provides an output to an amplifier 266. Amplifier 266 provides an output to a call detector 268 which may be of conventional construction and which interfaces with the dialing information decoder 246 for producing dialing or address information of the basis of information given by the incoming beam.

Amplifier 266 also provides an output to a demodulator 270 which provides a decoded voice or data output to a line transmitter 272 which also receives an address or dialing input from call detector 268 and which is coupled to the subscriber terminal.

Signalling can be accomplished using a common electrical bus shared among all of the subscribers and a time ordered usage of this bus by subscribers.

An alternative control arrangement may be utilized using a central processor unit shared among several subscribers.

According to a preferred embodiment of the invention, a switching exchange may be constructed having a 10,000 subscriber capacity and comprising transmitter and receiver arrays arranged in a 100x 100 grid. In such an example, each array would have to be of area 1 m2, each transmitter and receiver being separated by 10 mm from each adjacent transmitter and receiver in their respective arrays.

Assuming that the arrays are arranged in facing relationship as shown schematically in Figure 7, the separation between the arrays would be approximately 5 meters.

If a transmitter of the general type illustrated in Figure 2 were employed, the diameter of the fiber optic core would be 5 microns and the focal length of the lens 5 mm. The diameter of the spot of radiation impinging on the opposite array would be 8 mm.

The f number of the lens would be between 1 and 2.

The field of motion of the free end of the fiber optic would be 1 xl mm.

The preferred piezoelectirc bender element is catalog number G-1278 manufactured by Gulton Industries Inc., of New Jersey and is made of Zirconate Titanate. It has a piezoelectric constant as follows: d31=-270 x 10 -12m/v. The thickness of the piezoelectric bender element is selected to be 0.125 mm and its length is selected to be 25mm. Its voltage requirement is 50 volts for producing a 1 mm movement. The light source is preferably a LED and the detector is P.I.N. Silicon.

Figure 12 illustrates calibration apparatus for a beam directing system such as that employed for directing the transmitter beams in acordance with dialing or address information. A plurality of detectors 210 are arranged facing a transmitter 212. The detectors 210 may conveniently be arranged in a grid 200 and are individually connected to a selector circuit 214. The selector is coupled to an analog to digital converter 216 whic in turn is coupled to a microprocessor 218, which may be of conventional construction and interfaces with one or more EPROM memories 220. The microprocessor 218 provides direction signals to the transmitter 212 and selection signals to selector 214.

Calibration is effected as follows: A beam is transmitted in sequence to the individual detectors 210 disposed on grid 200, which defines the detection surface. The signal received by each detector will be maximized by adjustment of the beam direction. The instructions producing the best direction for each detector are written on the EPROM and this data may be used to interpolate for any other detectors intermediately positioned between detectors 210. The microprocessor 218 may be employed as microprocessor 154 (Figure 11) Reference is now made to Figure 13 which illustrates anothertype of switching exchange. Here, as opposed to the configurations described hereinabove, a plurality of transmitters 222 provides a wide beam that impinges on substantially all of the receivers 224 arranged in a facing grid 226.Each receiver 224 is coupled to a subscriber and is selectably directable so as to receive the radiation from only a single transmitter 222 at any given time.

It is noted that this type of exchange is particularly useful in cable television systems.

It may be appreciated that the switching exchange operates by providing to each selectably directable receiver 224 control inputs which cause it to aim its detector at a desired single transmitter, thus coupling a subscriber associated with that receiver to the information channel associated with that transmitter. In a cable television system, each television receiver receives a broadcast channel by controlling the directable receiver 224. The optical fiber that emerges from receiver 224 may be extended towards the television receiver and carry T.V. channel information directly to the receiver.

Reference is now made to Figure 14 which is a block diagram illustration of apparatus for high accuracy feedback control of a directional transmitter. The transmitter 280 which may be a transmitter of the type illustrated in any of Figures 1,2 and 3, receives a signal input from a data source 282 and from a control signal source 284. A detector 286 receives the combined data and control signals which may be differentiated from each other by conventional frequency filters or equivalenttechni- ques. The data outputs frorn detector 286 are supplied to a data destination 288 and the control outputs from detector 286 are supplied to a control signal utilization circuit 290. A microprocessor control 292 senses the received control signal at circuit 290 and aims the transmitter accordingly.

Figure 15 illustrates an arrangement of a pair of optical fibers 293 and 294 arranged on the free end of bender element 296. Preferably one of the optical fibers is a data carrying fiber while the other carries control information for assisting in accurate aiming.

Figure 16 shows a plurality of optical fibers arranged on the free end of bender element 298. A center fiber 300 carries data while the remaining fibers 302 carry control signals for providing a very high level of aiming accuracy.

Bending assemblies having a plurality of optical fibers associated therewith and including both data and control information carrying fibers may be incorporated in any of the switching exchanges illustrated in Figures.

It will be appreciated by persons skilled in the art that the invention is not limited to the particular examples illustrated and discussed herein. Rather, the scope of the present invention is defined only by the claims which follow.

Claims (7)

1. A communications exchange comprising a plurality of wide beam optical transmitting units having overlapping transmission beams and at least one directable receiving unit, said receiving unit including apparatus for selectably orienting an end of an optical fiber.

2. A communications exchange comprising: a first plurality of electromagnetic radiation transmitting units each of which provides a beam of information bearing electromagnetic radiation; at least one electromagnetic radiation receiving unit arranged in radiation receiving relationship with said first plurality; means for selectably directing said at least one receiving unit to a desired one of said first plurality oftransmitting units, said directing means comprising at least one device for selectably orienting an end of an information bearing optical fiber.

3. A communications exchange according to claim 2 and wherein said means for selectably directing comprises means for selectably orienting an end of an information bearing optical fiber.

4. A communications exchange according to either of claims 2 and 3 and wherein said at least one electromagnetic radiation receiving unit comprises a plurality of receiving units.

5. A communications exchange according to claim 2 and wherein said selectably orienting device comprises apparatus for selectably positioning an optical fiber end comprising: a bender assembly including at least two series connected piezoelectric bender elements arranged for bending motion in different directions, said bender assembly having a free end thereof arranged for association with at least one optical fiber end and a mounting end thereof located at a reference at a reference position.

6. A communciations exchange according to claim 1 and also comprising a plurality of optical fibers arranged to be oriented by said at least one selectably orienting device, said plurality of optical fibers including at least one position control adapted to carry position control signals for closed loop servo control of the orientation of said at least one selectably orienting device.

7. A communications exchange according to any of claims 2 - 5 and also comprising a plurality of optical fibers arranged to be oriented by said means for selectably directing, said plurality of optical fibers including at least one position control fiber adapted to carry position control signals for closed loop servo control of the selectably directing means of said at least one selectably orienting device.