EP1282947A2 - Systeme de signalisation - Google Patents

Systeme de signalisation

Info

Publication number
EP1282947A2
EP1282947A2 EP00948094A EP00948094A EP1282947A2 EP 1282947 A2 EP1282947 A2 EP 1282947A2 EP 00948094 A EP00948094 A EP 00948094A EP 00948094 A EP00948094 A EP 00948094A EP 1282947 A2 EP1282947 A2 EP 1282947A2
Authority
EP
European Patent Office
Prior art keywords
signalling
elements
array
signalling device
optical
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP00948094A
Other languages
German (de)
English (en)
Inventor
Alan Edward Green
Euan Morrison
Michael Reynolds
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Quantumbeam Ltd
Original Assignee
Quantumbeam Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB9916080.6A external-priority patent/GB9916080D0/en
Priority claimed from GBGB9916422.0A external-priority patent/GB9916422D0/en
Application filed by Quantumbeam Ltd filed Critical Quantumbeam Ltd
Publication of EP1282947A2 publication Critical patent/EP1282947A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2587—Arrangements specific to fibre transmission using a single light source for multiple stations
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/112—Line-of-sight transmission over an extended range
    • H04B10/1123—Bidirectional transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/112—Line-of-sight transmission over an extended range
    • H04B10/1123—Bidirectional transmission
    • H04B10/1125—Bidirectional transmission using a single common optical path
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/114—Indoor or close-range type systems
    • H04B10/1149—Arrangements for indoor wireless networking of information

Definitions

  • the present invention relates to a signalling system.
  • One aspect of the invention relates to an optical free space signalling method and apparatus.
  • This point to multipoint data transmission system employs pixelated reflector/modulator arrays and a telecentric optical lens systems. The system operates by assigning each user of the system a unique pixel in the array. Each pixel in the array is matched to a unique angular position in the field of view of the telecentric optical lens system.
  • the present invention aims to alleviate the problems described above by providing at least one additional optical element to increase the apparent packing density of the communication pixels.
  • the present invention provides a communication system which employs a plurality of arrays of communication elements which are optically combined to increase their effective packing density (i.e. to increase the effective area covered by the communication elements compared to the gaps between the elements).
  • the plurality of arrays are arranged so that the packing density is increased to 100% to provide maximum coverage .
  • the present invention provides an optical communication system having an array of optical communication elements and a micro lens array positioned in front of the array of elements to increase the apparent packing density of the elements.
  • the present invention provides an optical communication system having two or more telecentric optical systems which are offset in angle from each other and which include a respective array of communication elements .
  • Figure 1 is a schematic diagram of a video broadcast system for supplying video signals for a plurality of television channels, to a plurality of remote users;
  • Figure 2 is a schematic block diagram of a local distribution node and a user terminal which forms part of the video broadcast system shown in Figure 1 ;
  • Figure 3 is a schematic diagram of a retroreflector array and lens system employed in the local distribution node shown in Figure 2;
  • Figure 4 is a schematic diagram of an optically combined pixelated retroreflector array which forms part of the system shown in Figure 3 ;
  • Figure 5 is a schematic diagram of a data distribution system
  • Figure 6 is a schematic diagram of a local distribution node and a user terminal which forms part of the data distribution system shown in Figure 5 ;
  • Figure 7 is a schematic diagram of an emitter and detector array and lens system employed in the local distribution node shown in Figure 6 ;
  • Figure 8 is a schematic diagram of a data distribution system for supplying data to a plurality of users
  • Figure 9 is a schematic diagram of an array of emitters and detectors which forms part of one of the user terminals in the system shown in Figure 8;
  • Figure 10 is a schematic diagram of an alternative form of local distribution node and user terminal which can be used in the data distribution system shown in Figure 1;
  • Figure 11 is a schematic diagram of an alternative form of local distribution node and user terminal which can be employed in the data distribution system shown in Figure l;
  • Figure 12 is schematic diagram of an alternative form of local distribution node and user terminal which can be employed in the data distribution system shown in Figure i;
  • Figure 13 is a schematic diagram of an alternative form of local distribution node and user terminal which can be employed in the data distribution system shown in Figure i ;
  • Figure 14 is a schematic diagram of an alternative form of an optically combined pixelated communications cell array which may be used in any of the above embodiments;
  • Figure 15 is a schematic diagram of an alternative form of an optically combined pixelated communication cell array which may be used in any of the embodiments described above;
  • Figure 16 is a schematic block diagram of a retroflector array and lens system which may be employed in the local distribution node shown in Figure 2 and which includes a micro lens array for increasing the apparent packing density of the communication cells;
  • Figure 17 is a schematic block diagram of two telecentric optical systems and modulator arrays which are offset at an angle from each other.
  • Figure 1 schematically illustrates a video broadcast system for supplying video signals, for a plurality of television channels, to a plurality of remote users.
  • the system comprises a central distribution system 1 which transmits optical video signals to a plurality of local distribution nodes 3 via a bundle of optical fibres 5.
  • the local distribution nodes 3 are arranged to receive the optical video signals transmitted from the central distribution system 1 and to transmit relevant parts of the video signals to respective user terminals 7 (which are spatially fixed relative to the local distribution node 3) as optical signals through free space, i.e. not as optical signals along an optical fibre path.
  • each user terminal 7 informs the appropriate local distribution node 3 which channel or channels it wishes to receive (by transmitting an appropriate request) and, in response, the local distribution node 3 transmits the appropriate video data, to the respective user terminals 7.
  • Each local distribution node 3 does not, however, broadcast the video data to the respective user terminals 7. Instead, each local distribution node 3 is arranged (i) to receive an optical beam transmitted from each of the user terminals 7 which are in its locality, (ii) to modulate the received beams with the appropriate video data for the desired channel or channels, and (iii) to reflect the modulated beams back to the respective user terminals 7.
  • each of the local distribution nodes 3 can also transmit optical data, such as status reports, back to the central distribution system 1 via the respective optical fibre bundle 5, so that the central distribution system 1 can monitor the status of the distribution network.
  • Figure 2 schematically illustrates in more detail the main components of one of the local distribution nodes 3 and one of the user terminals 7 of the system shown in Figure 1.
  • the local distribution node 3 comprises a communications control unit 11 which (i) receives the optical signals transmitted along the optical fibre bundle 5 from the central distribution system 1; (ii) regenerates the video data from the received optical signals; (iii) receives messages 12 transmitted from the user terminals 7 and takes appropriate action in response thereto; and (iv) converts the appropriate video data into data 14 for modulating the respective light beams 15 received from the user terminals 7.
  • the communications control unit 11 will encode the video data with error correction coding and coding to reduce the effects of inter-symbol- interference and other kinds of well known sources of interference such as from the sun and other light sources.
  • the local distribution node 3 also comprises a retro- reflector and modem unit 13, which is arranged to receive the optical beams 15 from the user terminals 7 which are within its field of view, to modulate the respective light beams with the appropriate modulation data 14 and to reflect the modulated beams back to the respective user terminals 7.
  • the retro-reflector and modem unit 13 retrieves the message 12 and sends it to the communications control unit 11 where it is processed and the appropriate action is taken.
  • the retro-reflector and modem unit 13 has a horizontal field of view which is greater than +/- 50° and a vertical field of view of approximately +/- 5°.
  • Figure 2 also shows the main components of one of the user terminals 7.
  • the user terminal 7 comprises a laser diode 17 for outputting a laser beam 19 of coherent light.
  • the user terminals 7 are designed so that they can communicate with the local distribution node 3 within a range of 150 metres with a link availability of 99.9 per cent.
  • the laser diode 17 is a 50 mW laser diode which outputs a laser beam having a wavelength of 850 nm.
  • This output laser beam 19 is passed through a collimator 21 which reduces the angle of divergence of the laser beam 19.
  • the resulting laser beam 23 is passed through a beam splitter 25 to an optical beam expander 27, which increases the diameter of the laser beam for transmittal to the retro-reflector and modem unit 13 located in the local distribution node 3.
  • the optical beam expander 27 is used because a large diameter laser beam has a smaller divergence than a small diameter laser beam. Additionally, increasing the diameter of the laser beam also has the advantage of spreading the power of the laser beam over a larger area. Therefore, it is possible to use a higher powered laser diode 17 whilst still meeting eye-safety requirements.
  • Using the optical beam expander 27 has the further advantage that it provides a fairly large collecting aperture for the reflected laser beam and it concentrates the reflected laser beam into a smaller diameter beam.
  • the smaller diameter reflected beam is then split from the path of the originally transmitted laser beam by the beam splitter 25 and focused onto a photo-diode 29 by a lens 31. Since the operating wavelength of the laser diode 17 is 850nm, a silicon avalanche photo-diode (APD) can be used, which is generally more sensitive than other commercially available photo detectors, because of the low noise multiplication which can be achieved with these devices.
  • the electrical signals output by the photo- diode 29, which will vary in dependence upon the modulation data 14, are then amplified by the amplifier 33 and filtered by the filter 35.
  • the filtered signals are then supplied to a clock recovery and data retrieval unit 37 which regenerates the clock and the video data using standard data processing techniques.
  • the retrieved video data 38 is then passed to the user unit 39, which, in this embodiment, comprises a television receiver in which the video data is displayed to the user on a CRT (not shown) .
  • the user unit 39 can receive an input from the user, for example indicating the selection of a desired television channel, via a remote control unit (not shown). In response, the user unit 39 generates an appropriate message 12 for transmittal to the local distribution node 3. This message 12 is output to a laser control unit 41 which controls the laser diode 17 so as to cause the laser beam 19 output from the laser diode 17 to be modulated with the message 12.
  • a laser control unit 41 which controls the laser diode 17 so as to cause the laser beam 19 output from the laser diode 17 to be modulated with the message 12.
  • different modulation techniques should be employed. For example, if the amplitude of the laser beam 15 is modulated by the local distribution node 3, then the laser control unit 41 should modulate, for example, the phase of the transmitted laser beam.
  • the laser control unit 41 could apply a small signal modulation to the laser beam 19 to create a low-bandwidth control channel between the user terminal 7 and the local distribution node 3. This is possible provided the detector in the local distribution node 3 can detect the small variation in the amplitude of the received laser beam. Furthermore, such a small signal amplitude modulation of the laser beam would not affect a binary "on” and "off” type modulation which could be employed by the retro-reflector and modem unit 13.
  • FIG 3 schematically illustrates the retro-reflector and modem unit 13 which forms part of the local distribution node 3 shown in Figure 2.
  • the retro-reflector and modem unit 13 comprises a wide angle telecentric lens system 51, two arrays of modulators and detectors 53a and 53b and a beamsplitter 54 for dividing beams from the telecentric lens system 51 between the modulator/detector arrays 53a and 53b.
  • the telecentric lens system 51 comprises lens elements 61 and 55 and a stop member 57, having a central aperture 59.
  • the size of the aperture 59 is a design choice and depends upon the particular requirements of the installation.
  • the structure and function of a telecentric lens system is described in the applicants earlier International application WO 98/35328, the content of which is incorporated herein by reference.
  • each of the modulator/detector arrays 53a and 53b comprises 100 columns and 10 rows of modulator/detector cells. As shown in Figure 3, these arrays are located at the back focal plane 62a and 62b of the lens system 51. The cells of these arrays are spatially staggered from each other so that the cells in array 53b are optically located in the spaces between the cells of array 53a. This is schematically illustrated in Figure 4, which shows the optically combined modulator/detector arrays 53a and 53b. As shown, the cells c 2 ij of the array 53b are positioned so that the are optically located between the cells c 1 ⁇ of the array 53a.
  • each modulator/detector cell c ij comprises a modulator m i:j and a detector d ⁇ j located adjacent the corresponding modulator.
  • the size 71 of the cells c ⁇ is between 50 and 200 ⁇ m, with the spacing (centre to centre) 72 between the cells being slightly smaller than the cell size 71.
  • the telecentric lens 51 is designed so that the spot size of a focused laser beam from one of the user terminals 7 corresponds with the size 71 of one of the modulator/detector cells c ij , as illustrated by the shaded circle 73 shown in Figure 4, which covers the modulator/detector cell c l lQ l .
  • the way in which the laser beams from the user terminals 7 are aligned with the retro-reflector and the way in which the system initially assigns the modulator/detector cells to the respective user terminals is described in WO 98/35328 and will not be described again here.
  • each of the detectors d ij comprises a photo-diode which is connected to an associated amplifier, filter and clock recovery and data retrieval unit similar to those employed in the user terminal 7 shown in Figure 2 , which operate to detect any modulation of the corresponding laser beam and to regenerate any messages 12 which are transmitted from the corresponding user terminal 7. All the recovered messages 12 are then transmitted back to the communications control unit 11 where they are processed and appropriate actions are taken.
  • QCSE Quantum Confined Stark Effect
  • SEEDs Self Electro-optic Effect Devices
  • FIG. 5 schematically shows a data distribution system which employs a point to multipoint signalling system.
  • the data distribution system is similar to the video data distribution system shown in Figure 1, except that data is passed in only one direction, from the central distribution system 1 to the user terminals 7.
  • Such a data distribution system can be employed to distribute information relating to, for example, the prices of shares which are bought and sold on a stock market.
  • the individual user terminals 7 would comprise a display unit for displaying the new prices of the stocks to the traders so that they can be kept up-to-date with changes in the share prices.
  • such a one-way data distribution system could be used in railway stations, airports and the like for informing passengers of arrivals and departures etc.
  • the local distribution node 3 used in this embodiment is similar to the local distribution node of the system shown in Figure 1. The only difference is that the cells in the arrays do not include detectors d ii r for receiving communications transmitted from the user terminals 7. Similarly, the user terminals 7 are similar to those of the first embodiment except that there is no need for the optical beam expander in front of the beam splitter nor a laser control circuit for modulating the laser diode for transmitting messages to the local distribution nodes . The remaining components of this embodiment are the same and will not, therefore, be described again.
  • FIG. 6 schematically illustrates in more detail the main components of one of the local distribution nodes 3 and one of the user terminals 7 of such an embodiment.
  • the local distribution node 3 comprises a communications control unit 11 which (i) receives the optical signals transmitted along the optical fibre 5 from the central distribution system 1; (ii) regenerates the video data from the received optical signals; (iii) receives messages 12 transmitted from the user terminals 7 and takes appropriate action in response thereto; and (iv) converts the appropriate video data into data 14 for transmission from the emitter elements of the emitter/detector array and lens system 80.
  • a communications control unit 11 which (i) receives the optical signals transmitted along the optical fibre 5 from the central distribution system 1; (ii) regenerates the video data from the received optical signals; (iii) receives messages 12 transmitted from the user terminals 7 and takes appropriate action in response thereto; and (iv) converts the appropriate video data into data 14 for transmission from the emitter elements of the emitter/detector array and lens system 80.
  • the emitter/detector array and lens system 80 which is arranged (i) to receive the optical beams 15 from the user terminals 7 which are within its field of view and to transmit the received messages 12 to the communications control unit 11 where they are processed and the appropriate action taken; and (ii) to transmit the respective video data 14, via optical beams 15, to the respective user terminals 7.
  • the user terminal 7 is identical to that of Figure 2.
  • FIG 7 schematically illustrates the emitter and the detector array and lens system 80 which forms part of the local distribution node 3 shown in Figure 6.
  • the emitter and detector array and lens system 80 comprises a lens system 89, two arrays of emitters/detectors 90a, 90b and a beam splitter 54 located between the arrays 90 and the lens system 89.
  • the lens system 89 comprises a wide angled lens 55 and a convex lens 87 which operate to provide a wide field of view for the emitter and detector array and lens system 80.
  • the lens system 89 is not telecentric.
  • Each of the emitter/detector arrays 90a and 90b comprise a regular array of communication cells similar to the cells formed in the modulator/detector arrays of the first embodiment, except with the modulators replaced by light emitters.
  • the emitters are formed from vertical cavity surface emitting lasers (hereinafter referred to as VCSELs ) .
  • VCSELs vertical cavity surface emitting lasers
  • the VCSEL array is preferred because the array can be manufactured from a single semiconductor wafer, without having to cut the wafer. This allows a higher number of the emitter elements per unit area than would be the case with an array made from traditional laser diodes.
  • VCSEL arrays manufactured and sold by CSEM SA (Badenerstrasse 569, 8048 Zurich, Switzerland), operate in a power range of between 1 and 30 mW and output a laser beam having a wavelength the same as conventional laser diodes.
  • the cells of the arrays 90a and 90b are spatially arranged so that, through the operation of the beam splitter 54, the cells of the arrays are interleaved with each other like the cells shown in Figure 4.
  • the VCSEL emitters e ⁇ j in the emitter arrays 90a, 90b are selectively addressable and the data 14 from the communications control unit includes respective data for each VCSEL emitter e ⁇ j .
  • the data for each VCSEL emitter may be the same or it may be different, depending on the application.
  • the light output by each emitter e ⁇ j in the arrays 90a, 90b is a diverging beam, the divergence being primarily caused by diffraction at the emitting aperture of the laser.
  • the lens system 89 collects the diverging beam from each emitter and forms it into a collected beam.
  • each emitter in each array maps to a particular angle in space and can therefore communicate with a respective user terminal 7.
  • the local distribution nodes 3 are substantially the same as the local distribution node shown in Figure 7, except that the lens system is telecentric, like the lens system shown in Figure 3, and the arrays are just emitter rays.
  • telecentric lenses are used since this allows the collection efficiency (of light from the emitter arrays 90) of the lens to be constant across the emitter arrays. Therefore, provided that all the emitter elements are the same, the intensity of the light output from the local distribution node will be the same for each emitter. In contrast, with a non-telecentric lens, the intensity of the light output from the local distribution node will be greater for light emitted by emitters in the centre of the array than for those at the edge.
  • the use of a telecentric lens also avoids the various cosine fall-off factors which are well known in conventional lenses .
  • the user terminals include arrays of detector cells similar to the arrays of emitter cells located in the local distribution nodes 3.
  • Figure 9 schematically illustrates the lens system and detector array 100 which forms part of a user terminal 7 and which replaces the lens 31 and photo diode 29 of Figure 6.
  • the lens system 101 comprises a wide angle lens 103 and a convex lens 105, and operates to focus light received from different local distribution nodes 3 (represented by light rays 106 and 107) onto a beamsplitter 109 which divides the beams between the two detector arrays 108a and 108b.
  • the detector cells in the two detector arrays 108a and 108b are spatially arranged so that they are interleaved with each other, like the cells shown in Figure 4.
  • the packing density of the detector arrays can be increased over the packing density obtainable through a single array.
  • one of the advantages of this embodiment is that if one of the laser beams (106 or 107) from one of the local distribution nodes 3 is blocked, then the user terminal 7 will still receive the data from the other beam.
  • Another advantage of this embodiment is that since both sides of the free space communications link use wide angled lenses, their fields of view are relatively large. Therefore, successful communications can still be carried out even if the user terminal 7 moves relative to the local distribution node 3, provided both remain within the other's field of view.
  • Another advantage of this embodiment is that if the user terminals 7 do move relative to the local distribution nodes 3 , then they can determine either when they are about to move out of the field of view of one of the local distribution nodes 3 or when one of the local distribution nodes 3 is about to move out of their field of view. This is possible because as the user terminals 7 move, the laser beams from the local distribution nodes 3 move over the respective detector array 108a, 108b and the user terminals 7 can detect this by sampling the signals from the detector cells in their arrays.
  • the user terminal 7 may be configured so as to warn the user that connection to the central distribution system 1 is about to be lost.
  • either side of the communication link can track the movement of the other side within its field of view by tracking the focussed laser beam from the other side as it moves over its emitter/detector arrays. This information can then be used to control the emitter and detector cell which is used in the communications link.
  • each side of the communications link would use a wide angled telecentric lens such as the one shown in Figure 3, for the reasons mentioned above.
  • emitter and detector arrays may be provided in the local distribution nodes 3 and retroreflector and modulator arrays may be provided in each of the user terminals 7.
  • a retroreflector and modem unit may be provided in each of the local distribution nodes 3 and emitter and detector arrays may be provided in each of the user terminals 7.
  • retroreflector and modem units may be provided in both the local distribution nodes 3 and the user terminal 7.
  • the local distribution node or the user terminal must also include a laser diode for illuminating the light reflectors of one of the retroreflectors .
  • this laser diode is provided in the local distribution node 3.
  • light from the laser diode 111 is expanded and collimated by the lens 112 and used to illuminate the modulator array 113 via a polarising beamsplitter 114.
  • Each element of the modulator array reflects or absorbs a part of the incident light in accordance with the electric bias applied to that element (which depends on the input modulation data 14).
  • the reflected light then passes through the beamsplitter and a ⁇ /4 wave plate 119 (for changing the polarisation of the reflected light from linear to circular) and lens 115 towards the user terminal 7.
  • the beam received at the user terminal is focussed by a lens 116 onto a retro-reflector array (including both modulators and detectors) 117 where the received light is both detected (to recover the modulation data 14) and modulated with data 12 and reflected back towards the local distribution node 3.
  • the "handedness" of the polarised light is inverted and therefore, when the reflected light passes again through the ⁇ /4 wave plate 119, the linear polarisation of the received light is rotated by 90° relative to the transmitted light. Therefore, the reflected light is reflected by the polarising beamsplitter 114 towards the photodiode array 118, where the modulation data 12 is recovered.
  • the techniques described above which are used to increase the effective packing density of the retro-reflectors may also be employed in this embodiment at one or at both ends of the communications link.
  • two arrays of optical communication elements (such a light emitters, light reflectors and light detectors) were optically combined using beamsplitters in order to increase the packing density of the optical elements.
  • the packing density of the optical elements can be effectively increased using other techniques.
  • an array of microlenses may be placed in front of the array of optical elements.
  • the microlens array would be arranged so that the centres of the microlens have the same grid spacing as that of the elements in the optical element array, so that each microlens acts as an optical system for an individual optical element.
  • each of the microlenses 137 is located adjacent a modulator pixel 53-1, which, in this embodiment, are spaced apart along the array 53 by regular intervals 53-2. As shown, each of the microlenses 137 acts to form a magnified image of the associated modulator pixel, so that, when viewed from the exit pupil of the telecentric optical system 51, the array appears to have a 100% packing density.
  • the numerical aperture of the beam at the modulator pixel will be larger than without the lens by a factor equal to the linear magnification afforded by the microlens.
  • the linear magnification required to achieve a 100% packing density is 1.167, and hence the numerical aperture at the pixel is increased by this factor.
  • this is a relatively small increase in numerical aperture and in most cases is well within acceptable limits for the modulator pixel.
  • FIG. 17 Another way of increasing the packing density of a single array of optical communication elements is to use two or more separate optical systems and arrays of communication elements.
  • a system is schematically illustrated in Figure 17.
  • the system includes two telecentric optical systems 120a and 120b and two arrays 125a and 125b of optical communication elements.
  • This embodiment makes use of the fact that a beam 127 incident upon the transmitter or receiver is typically significantly larger than the telecentric stop of the telecentric lens. Therefore, the beam can be received by more than one telecentric system. Therefore, by pointing the two telecentric lens systems in slightly different directions, as shown in Figure 17, the mapping between direction within the field of view and position on the arrays 125a and 125b, for the two arrays will be different.
  • the communications elements in the two arrays 125a and 125b can be arranged to intermesh in a similar manner to the embodiments which employ beamsplitters.
  • this technique can achieve a 100% packing density without the additional optical loss associated with beamsplitters, but at the cost of additional telecentric optical systems .
  • an array of QCSE modulators were used in the retro- reflecting end of the communication link. These QCSE modulators either absorb or reflect incident light.
  • QCSE modulators either absorb or reflect incident light.
  • other types of reflectors and modulators can be used.
  • a plane mirror may be used as the reflector and a transmissive modulator (such as a liquid crystal) may be provided between the lens and the mirror.
  • beamsplitters may be used to temporarily separate the path of the incoming beam from the path of the reflected beam and, in this case, the modulator may be provided in the path of the reflected beam so that only the reflected light is modulated.
  • such an embodiment is not preferred since it requires additional optical components to split the forward and return paths and then to re-combine the paths after modulation has been effected.
  • the array of emitters or detectors or modulators are located substantially at the back focal plane of the telecentric lens.
  • the telecentric lens can be adapted to have a back focal plane which is curved or partially curved.
  • the array of emitters or detectors or modulators should also be curved or partially curved to match the back focal plane of the telecentric lens.
  • the light generated by each of the emitters is modulated with the data to be transmitted to the other end of the communication link.
  • the easiest way to modulate the light from the VCSEL emitters is to switch the emitters on and off to thereby amplitude modulate the light emitted from them.
  • other modulation techniques such as frequency or phase modulation may be used.
  • other types of light emitters such as laser diodes and light emitting diodes may be used.
  • An array of emitters could also be formed by a bundle of optical fibres, closely packed into a regular array with a laser diode coupled to the other end of each fibre.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Computing Systems (AREA)
  • Optical Communication System (AREA)
  • Optical Couplings Of Light Guides (AREA)

Abstract

L'invention concerne un système de signalisation dans lequel on utilise au moins une matrice d'éléments de communication en même temps qu'un élément optique supplémentaire, afin d'accroître, dans le(s) groupe(s), la densité apparente de tassement des éléments. Dans un mode de réalisation on obtient cet accroissement en utilisant un ensemble de microlentilles adaptées au(x) matrice(s) d'éléments de communication. Dans un autre mode de réalisation, on a combiné optiquement deux matrices avec un diviseur de faisceaux. Dans un troisième mode de réalisation, on utilise deux systèmes optiques décalés l'un de l'autre en formant entre eux un angle, de façon à créer une cartographie différente entre une position dans la matrice et une position dans le champ de vision.
EP00948094A 1999-07-08 2000-07-10 Systeme de signalisation Withdrawn EP1282947A2 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
GB9916080 1999-07-08
GBGB9916080.6A GB9916080D0 (en) 1999-07-08 1999-07-08 Increased packing density
GBGB9916422.0A GB9916422D0 (en) 1999-07-13 1999-07-13 Optical cellular communication
GB9916422 1999-07-13
PCT/GB2000/002668 WO2001005069A2 (fr) 1999-07-08 2000-07-10 Systeme de signalisation

Publications (1)

Publication Number Publication Date
EP1282947A2 true EP1282947A2 (fr) 2003-02-12

Family

ID=26315747

Family Applications (1)

Application Number Title Priority Date Filing Date
EP00948094A Withdrawn EP1282947A2 (fr) 1999-07-08 2000-07-10 Systeme de signalisation

Country Status (5)

Country Link
EP (1) EP1282947A2 (fr)
JP (1) JP2003523108A (fr)
AU (1) AU6166800A (fr)
CA (1) CA2378410A1 (fr)
WO (1) WO2001005069A2 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6522437B2 (en) * 2001-02-15 2003-02-18 Harris Corporation Agile multi-beam free-space optical communication apparatus
US7106973B2 (en) * 2002-08-13 2006-09-12 Lightpointe Communications, Inc. Apparatus and method for use in free-space optical communication comprising optically aligned components integrated on circuit boards
US7120363B2 (en) 2002-12-20 2006-10-10 Lightpointe Communications, Inc. Method and apparatus for maintaining optical alignment for free-space optical communication

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2186457A (en) * 1984-10-18 1987-08-12 Gec Avionics Optical communications
CA2279934A1 (fr) * 1997-02-11 1998-08-13 Scientific Generics Limited Systeme de signalisation

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO0105069A3 *

Also Published As

Publication number Publication date
AU6166800A (en) 2001-01-30
WO2001005069A2 (fr) 2001-01-18
WO2001005069A3 (fr) 2002-11-14
JP2003523108A (ja) 2003-07-29
CA2378410A1 (fr) 2001-01-18

Similar Documents

Publication Publication Date Title
EP0960492B1 (fr) Systeme de signalisation
US20010043381A1 (en) Optical free space signalling system
US4775971A (en) Optical communication system
US20030147652A1 (en) Optical free space signalling system
AU2452800A (en) Optical free space signalling system
US20030058506A1 (en) Optical free space signalling system
KR20080041371A (ko) 가시광 통신을 위한 휴대용 무선 단말기
CA2378722A1 (fr) Systeme de signalisation
WO2002005459A2 (fr) Systeme de signalisation optique a espace libre
US20030002124A1 (en) Optical free space signalling system
EP1282947A2 (fr) Systeme de signalisation
AU763790B2 (en) Signalling system
US11218219B2 (en) Bidirectional optical wireless transmission system
WO2002056507A2 (fr) Infrastructure de communications optiques redondante en espace libre et equipements connexes
US11804904B1 (en) Systems and methods for optical wireless communication
TW390070B (en) Signalling system

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 20020207

AK Designated contracting states

Designated state(s): AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 20050201