GB2141258A - Electro-optical line of sight communications apparatus - Google Patents

Abstract

A directable optical transmitter 62 formed by an optical fibre is moveable by means of a piezoelectric bending assembly. A receiver 64 receives a light beam transmitted by the transmitter and provides a feedback signal via a wide beam transmitter 74 and receiver 76 to control the direction of the transmitter in dependence upon the accuracy of aim at the receiver. The bending assembly is controlled by a microprocessor, first in a raster pattern search mode. When a signal is first received the raster is stopped and the x, y co-ordinates stored. Bending then takes place one step at a time in an optimising mode and continues until the received signal is a maximum. If the signal should then drop below this level the beam is directed on the stored co-ordinates and the optimising routine is repeated. <IMAGE>

Description

SPECIFICATION Electro-optical line of sight communications apparatus Field of the invention The present invention relates to communication apparatus and more particularly to electro-optical line-of-sight communication apparatus.

Background ofthe invention Various types of electro-optical line-of-sight communication apparatus are known for providing electro-optical communication. A major difficulty associated with such apparatus is maintaining the precise alignment of the communicating elements. Minute direction changes in the communicating elements, which may result from external forces as well as limitations in the rigidity of the communicating themselves and their mounting, elements may easily cause an interruption in communications. Reestablishment of the correct position and relative alignment of the communicating elements is time consuming and expensive and can result in considerable down time of the communications link.As a result electro-optical line-of-sight communications either employ relatively wide transmission beams and thus are operative only over short distances or require heavy, rigid and expensive structural support elements.

Summary ofthe invention The present invention seeks to provide electrooptical line-of-sight communication apparatus in which the above mentioned disadvantages of known apparatus are mitigated.

There is thus provided in accordance with an embodiment of the present invention an electrooptical line-of-sight communications apparatus comprising a directable optical transmitter including an optical fibre having a first end for receiving light from a light source modulated in accordance with an electrical signal and a second end; piezoelectric bending means, the second end of the optical fibre being associated with the piezoelectric bending means for selectable positioning of the second end; an electro-optical receiver for receiving an optical beam transmitted by the optical transmitter and for providing an electrical output signal and transmitter position control means for controlling the position of the directable optical transmitter in response to control signals derived from the electro-optical receiver and indicative of the accuracy of the aim of the directable optical transmitter.

Further in accordance with an embodiment of the invention, the piezoelectric bender elements mounted in series perpendicularly to each other so as to provide selectable scanning in two dimensions.

By use of the present invention it is possible to provide a relatively narrow light beam for line of sight communications. The relative narrowness of the beam concentrates the light energy and enables greater distances to be covered with a beam of given energy.

In accordance with a preferred embodiment of the invention there is provided electro-optical line-ofsight communication apparatus including a directable transmitter of the type described hereinabove, a relatively wide beam receiver and a wide beam control signal transmitter. The wide beam receiver and control signal transmitter are useful for establishing and maintaining correct aligment of the communications beam.

The transmitter position control means may comprise means for operating said directable optical transmitter in a raster scan for establishment of line-of-sight communication. The scan may be interrupted in response to the control signals indicating receipt of the optical beam by the electro-optical receiver.

The position control means may operate for subsequent scanning of a region adjacent a direction indicated by the received control signals at interruption of the scanning.

Brief description of the drawings The invention will be more fully understood and appreciated from the following detailed description taken in conjunction with the drawings in which: Figure 7 is an illustration of part of an electrooptical line-of-sight communication apparatus in accordance with the invention and employing a directable transmitter including a single piezoelectric bender element; Figure 2 is an illustration of a directable transmitter including a pair of perpendicularly oriented piezoelectric bender elements which is useful in the electro-optical line-of-sight communication apparatus of the present invention; Figure 3 is an illustration of a transceiver for electro-optical line-of-sight communication; Figure 4 is an illustration of a pair of the transceivers of Figure 3 arranged for electro-optical line-ofsight communication;; Figure 5 is a block diagram of circuitry for one-way communication employing the apparatus of Figures 1-4.

Figure 6 is a block diagram of circuitry for two-way communication employing the apparatus of Figures 1-4; Figure 7 is a block diagram of positioning circuitry useful in the apparatus of Figures 5 and 6; and Figure 8 is a flow chart illustrating operations of the circuitry of Figures 6 and 7 for establishing and maintaining an optical line-of-sight communications link.

Detailed description of the invention Referring now to Figure 1 there is seen part of a line-of-sight communication apparatus constructed and operative in accordance with an embodiment of the present invention. The line-of-sight communication apparatus comprises a transmitter 10, which will be described hereinbelow and a remote receiver 12, located along a direct line-of-sight from transmitter 10.

Transmitter 10 comprises a housing 14which is securely mounted at a selected location by means of mounting apparatus 16, which is outside of the scope of the present disclosure. Mounted onto the housing is a piezoelectric bending assembly 18, which in the illustrated embodiment comprises a single piezoelectric bender element such as a model G - 1278 manufactured by Gulton Industries of New Jersey, U.S.A.

An optical fibre end 20 is mounted on the outward facing end 22 of assembly 18 and defines the outer end of an optical fibre 24 which communicates at its other end with a source of modulated radiation bearing information to be transmitted. This source, which is not illustrated herein, may be any conventional source of optical radiation and will be referred to hereinafter for convenience as a "light source".

A relatively small range of bending movement of the piezoelectric bending assembly produces with the aid of focussing means formed by for example a lens 26, a significant range of direction changes of a beam. The range of bending movement of the piezoelectric bending assembly 18 is typically between 102 and 103 microns and the range of beam directions is between 20 and 100 milliradians.

The operation of the device described in Figure 1 may be understood to be as follows: The housing 14 is mounted by conventional techniques facing the remote receiver within the range of beam directions of the transmitter. The fine adjustment is accomplished through operation of the piezoelectric bending assembly 18, by application of predetermined voltage to the bender element causing it to assume a predetermined bent orientation. The position thus attained by the optical fibre end 20 results in the provision of a beam having the desired direction for communicating with the receiver.

Reference is now made to Figure 2 which illustrates an alternative embodiment of transmitter 30 wherein the piezoelectric bending assembly 31 comprises a pair of bender elements 32 and 34 arranged at right angles to each other. The bender elements 32 and 34 are arranged in series, that is, bender element 34 is mounted on the outer end of bender element 32, such that the combined displacements of bender elements 32 and 34 in perpendicular planes are determinative of the position of the outer end 36 of bender element 34. An optical fibre end 40 is mounted on the outer end 36.The connection of the optical fibre and the operation of the transmitter 30 is essentially similar to that described in connection with Figure 1 except that the bending assembly 31 has two separate sets of leads corresponding to two bender elements 32 and 34 and permitting independent control of the bending displacement of each bender element in perpendicular planes.

It is appreciated that the bender elements 32 and 34 need not necessarily be located in perpendicular planes, although this arrangement is preferred.

Reference is now made to Figure 3 which illustrates a transceiver for use in electro-optical line-ofsight communication in accordance with the present invention. The transceiver comprises a housing 50 containing a directable transmitter 52 of the type described hereinabove, a wide beam control signal transmitter 54 and a wide field of view receiver 56.

Preferably the range of the directable beam provided by transmitter 52 is of the same order of magnitude and generally corresponds to the range of the control signal transmitter beam and the field of view of the detector 56.

Referring now additionally to Figure 4 it is seen that when a pair of such transceivers are employed for eiectro-optical line-of-sight communication therebetween, they are initially arranged such that their respective wide beams and wide ranges encompass each other so as to enable precise aiming of the directional transmitters to take place automatically.

It is appreciated that one-way communication may be accomplished by devices similar to the transceivers described hereinabove but wherein the receiver need not include a directable transmitter and the transmitter need not include a wide beam control signal transmitter.

The operation of the apparatus illustrated in Figures 3 and 4 will be described hereinafter in detail in connection with a description or circuitry associated therewith.

Reference is now made to Figure 5 which is a block diagram illustration of circuitry for one-way line-ofsight communication in accordance with the present invention.

In the circuitry of Figure 5, information to be transmitted is received at an input terminal 60 in the form of an output of a light source modulated in accordance with an electrical signal and is fed via an optical fibre to a directable transmitter 62 such as the transmitter described in connection with Figures 1 and 2. It is appreciated that information in any form may be transmitted by the apparatus of Figure 5.

Where the information is not in the form of modulated light signals, suitable electronic circuitry (not shown) is provided for converting the information into modulated light signals. It is to be understood that all of the communication apparatus described in the present invention is suitable for the transmission of information originally received in any form which can be electronically converted into modulated light signals.

The directable transmitter 62 transmits information in a directed beam of radiation to a remote electro-optical receiver 64. The output of receiver 64 is supplied to an output terminal 68 for transfer to utilization circuitry such as a display or recorder and is also supplied to power level detection circuitry 70 which typically comprises a AID converter and provides an output indicating the relative power level of the received signal. The output of circuitry 70 is supplied to coding circuitry 72 which provides a coded signal indicating received signal power. The coded output of circuitry 72 is supplied to a wide beam control signal transmitter 74 which transmits an optical beam bearing the coded control signal as an indication of the received signal power in a wide beam relative to that transmitted by the directable transmitter 62.

The wide beam output of transmitter 74 is detected by a wide field of view receiver 76 associated with directable transmitter 62, notwithstanding relatively small alignment errors between the two remote units, due to the wide range and field of view of the transmitter 72 and receiver 76. The output of receiver 76 is supplied as a control signal to transmitter position control circuitry 78 which determines the beam direction of the output of transmit ter62.

A preferred embodiment of the transmitter position control circuitry is illustrated in Figure 7 and comprises a microprocessor 81, such as a MC 68000 which is coupled via respective data and address busses to a pair of latches 83 and 85. The outputs of latches 83 and 85 are supplied via respective D/A converters 87 and 89 to the respective X and Y control leads of a directable transmitter such as the transmitter illustrated in figure 2. Control signals from the wide field of view receiver 76 are received by the microprocessor 81 and indicate the directional location at which a received signal with at least a minimum power level was received by the remote receiver.

The operation of the position control circuitry described hereinabove in connection with Figure 7 will now continue to be described with reference to Figure 8 which is a flow chart illustrating operation of the circuitry.

Microprocessor 81 is programmed to initially function in accordance with two nested do loops illustrated at block 91 and which produce a raster scan by the directable transmitter. The raster scan is a stepwise scan and at each step, the microprocessor inquires whether the received signal power P indicated by the control signals from receiver 76 is greater than zero. If P is not greater than zero, the raster scan continues to the next step. (Block 93) Once the received signal power P is indicated to be greater than zero the raster scan is terminated and the directable transmitter is aimed in a direction having x, y co-ordinates corresponding to the coordinates xO, y0 at which the received signal power P = P0 which is greater than zero (Block 93).

From the direction indicated by co-ordinates xO, yO, the direction of the directable transmitter is sequentially shifted slightly to the sides of this direction and at each step the received signal power P1 is checked to see if it exceeds PO If so, the transmitter is shifted to the new location at which the received signal power is P1, having co-ordinates x1, y1 and the slight shift sequence is repeated. This procedure is continued (Blocks 95 and 97) until none of the slight shifts produce a higher received signal power.

Provided that the received signal power remains above zero (Block 99), once all of the four indicated slight shifts have been carried out, the microprocesor enters a wait mode and periodically rechecks the received signal power. Should it fall below P,, less a predetermined amount A P, the transmitter is redirected to co-ordinates xO, y0 and the slight changes begin again. (Block 101) Transmission of information by the directable transmitter continues throughout the tracking mode operation of the position control circuitry, (blocks 93 - 101) and terminates only when the received signal power falls to zero.

Reference is now made to Figure 6 which is a block diagram illustration of apparatus for two-way lineof-sight communication in accordance with the present invention. The apparatus comprises a pair of remote transceivers 80 and 82 which may be of identical construction. For the sake of conciseness only one transceiver will be described in detail, it being noted that corresponding elements of both transceivers are denoted by the same reference numerals.

Each transceiver comprises a directable transmitter 84, preferably of the type illustrated in Figure 2, a wide field of view receiver 86 and a control signal transmitter 88 which provides a relatively wide beam output. Transmitter 84 receives data to be transmitted from an input terminal 90 via an optical fibre and transmits a narrow beam to a remote receiver 86 in the opposite transceiver. The output from receiver 86 is supplied to a filter 94, such as a frequency filter which distinguishes between received data and control signals. The data output of filter 94 is supplied to an output terminal 96 for transfer to utilization apparatus such as a display or recorder and is also supplied to a received signal power detector 98, which typically comprises an analog to digital converter.

The output of detector 98, which indicates the degree to which the narrow beam of transmitter 84 is aligned with the receiver 92, is supplied to coding circuitry 100 which provides a coded signal indicating received signal power. The coded output of circuitry 100 is supplied to the wide beam control transmitter 88 which transmits an indication of the received signal power in a wide beam to the other transceiver.

The control output of filter 94 is supplied to position control circuitry 104 whose output is supplied to the control leads of the piezoelectric bending assembly (Figures 1 and 2) of transmitter 84 for governing the precise aiming of the narrow transmitter beam. Position control circuitry 104 may be identical to that illustrated in Figure 7 and its operation may be similar in all relevant respects to that described hereinabove in connection with Figure 8.

It will be appreciated by persons skilled in the art that the invention is not limited to what has been particularly shown and described hereinabove.

Rather the scope of the present invention is defined only by the claims which follow.

Claims (15)

1. Electro-optical line-of-sight communications apparatus comprising a directable optical transmitter including an optical fibre having a first end for receiving light from a light source modulated in accordance with an electrical signal and a second end; piezoelectric bending means, the second end of the optical fibre being associated with the piezoelectric bending means for selectable positioning of the second end; an electro-optical receiver for receiving an optical beam transmitted by the optical transmitter and for providing an electrical output signal and transmitter position control means for controlling the position of the directable optical transmitter in response to control signals derived from the electrooptical receiver and indicative of the accuracy of the aim of the directable optical transmitter.

2. Apparatus as claimed in claim 1 and further including focussing means for focussing the optical beam transmitted by the directable optical transmitter.

3. Apparatus according to claim 1 and wherein said piezoelectric bending means comprises a single piezoelectric bender element movable in a single dimension.

4. Apparatus according to claim 1 and wherein said piezoelectric bending means comprises first and second piezoelectric bender elements each having an inner and outer end, said second bender element being mounted on the outer end ofsaid first bender element.

5. Apparatus according to claim 4 and wherein said first and second bender elements are arranged for motion in respective perpendicular planes.

6. Apparatus according to claim 1 and also comprising a relatively wide beam control signal transmitter for transmitting the control signals derived from the electro-optical receiver and indicative of the accuracy of the aim of the directable optical transmitter.

7. Apparatus according to claim 6 and also comprising a relatively wide field of view receiver for receiving the control signals transmitted by the control signal transmitter.

8. Apparatus according to claim 1 and wherein said transmitter position control means comprises means for operating said directable optical transmitter in a raster scan for establishment of line-of-sight communication.

9. Apparatus according to claim 8 and wherein said transmitter position control means comprises means for interrupting the scan in response to the control signals indicating receipt of the optical beam by the electro-optical receiver.

10. Apparatus according to claim 9 and wherein the transmitter position control means comprises means for operating the directable optical transmitter for subsequent scanning of a region adjacent a direction indicated by the received control signals at interruption of the scanning.

11. Apparatus according to claim 10 and wherein said control signal indicates received signal power at the electro-optical receiver.

12. A transmitter for an electro-optical line-ofsight communications apparatus the transmitter comprising a directable optical transmitter including an optical fibre having a first end for receiving light from a light source modulated in accordance with an electrical signal, and a second end; piezoelectric bending means, the second end of the optical fibre being associated with the piezoelectric bending means for selectable positioning of the second end and transmitter position control means for controlling the position of the directable optical transmitter in response to a control signal indicative of the accuracy of aim of the directable optical transmitter.

13. A receiver for an electro-optical line of sight communications apparatus the receiver comprising an electro-optical receiver for providing an electrical output signal in response to a received optical signal and means for providing an electrical control signal indicative of the accuracy of aim of the received optical signal on the electro-optical receiver.

14. A receiver as claimed in claim 13 and further including an electro-optical transmitter for transmitting the electrical control signal in the form of an optical beam.

15. Electro-optical line-of-sight communication apparatus substantially as herein described with reference to and as illustrated in Figures 1 and 5 or Figures 2 and 5 or Figures 2 and 6 of the drawings.