GB2240681A

GB2240681A - Communicator

Info

Publication number: GB2240681A
Application number: GB9001548A
Authority: GB
Inventors: Jonathan Stewart Leggatt; David John Mccartney; David William Smith
Original assignee: British Telecommunications PLC
Current assignee: British Telecommunications PLC
Priority date: 1990-01-23
Filing date: 1990-01-23
Publication date: 1991-08-07
Also published as: GB9001548D0

Abstract

A communicator (2) for communicating control data has a screen retroreflector (8) for reflecting electromagnetic radiation, for example infra-red radiation, back towards the source of the radiation. A liquid crystal cell (8) impresses an amplitude modulation signal on the electromagnetic radiation impinging on the communicator. A receiver in the vicinity of the source receives the modulated signal. The communicator has a reduced power consumption because it has no need for an electromagnetic radiation source. <IMAGE>

Description

COMMUNICATOR This invention relates to communicators and in particular, but not exclusively, to communicators used in controlling remote equipment.

Hand-held communicators are well known in the domestic environment for their use in controlling such equipment as televisions and sound reproduction equipment. They operate by modulating a battery powered source of electromagnetic radiation in the communicator, generally infra-red optical radiation, with control data. The radiation is directed towards a receiver incorporated in the remotely located equipment. A disadvantage of such communicators is that the power requirement of the source of radiation can lead to frequent battery changes or recharges.

In other communications systems the power requirement of a source in the communicator may not be a disadvantage, for example in the case of an electric mains powered computer terminal with an infra-red optical free-space link to a computer. However, such provision of electromagnetic radiation sources in each terminal of a multiterminal computer network requires the provision of a number of sources.

According to the present invention a communicator includes a retroreflecting means for reflecting at least a portion of electromagnetic radiation incident upon it back towards the source of the radiation and a modulation means for impressing a modulation signal on the electromagnetic radiation impinging on the communicator.

Battery power may be required for powering the modulation means but this can be chosen to be a mechanical, hand-operated means or to be an electrically driven means having low power consumption and so provide long battery life. Alternatively electrical power may be provided by solar cells incorporated onto the communicator. In multicommunication systems a single source of radiation can be used to provide the electromagnetic radiation for all the communication links from a central equipment to the many terminals.

According to a further aspect of the present invention a communications systems comprises at least one communicator according to the first aspect of the present invention, a source of electromagnetic, radiation separate from the communicator, and a receiver located in the vicinity of the source of radiation for receiving any retroreflected radiation from the communicator.

The retroreflector may be a triple mirror screen or corner cube screen for example or an array of such screens or other type of retroreflector. Preferably, the retroreflecting means comprises a fine pitch retroreflective sheet, an example of which is high gain sheeting #7610 manufactured by 3M Inc, as it is cheaper than the screen retroreflectors. PCT patent application W088/03659 describes the use of fine pitch retroreflective sheet with an overlaid array of optical lenses to provide an enhanced degree of accuracy in the retroreflective direction over the sheet used alone. The invention is not limited to the particular type of retroreflector employed.

The modulating means may comprise, for example, means to alter the reflectivity of the retroreflector, to vary the amount of radiation entering or exiting the communicator via the retroreflecting means, or to modulate some other characteristic of the radiation, for example the phase or frequency of the radiation including electro-optic and magneto-optic modulators.

Preferably the modulating means is of a type which can be positioned in front of the retroreflector, conveniently a shutter, either a mechanical shutter or an electrically controlled shutter such as a liquid crystal cell, for ease of construction.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which Figure 1 is a schematic, part sectional side view of a communicator according to the invention; and Figure 2 is a schematic diagram of a transmission system according to the present invention.

In Figure 1 a communicator 2 comprises a housing 4 having at one end a recess in which is located at its base a retroreflective sheet 6 adjacent the top face of which is a liquid crystal cell 8, constituting the modulation means, and a recess cover plate 10. The communicator 2 is designed for use with infra-red electromagnetic radiation in that the cover plate 10 is transparent to infra-red radiation and the retroreflector is operable at these wavelengths. The cell 8 is switchable via electrical control wires 12 by control means (not shown) between two states of different transmissivity to infra-red radiation.

Infra-red light from a relatively distant source (not shown) reaching the retroreflective sheet 6 will be reflected back towards the source. The accuracy of the return direction will depend on the particular retroreflector used and the distance of the communicator from the source. Modulation of the transmissivity of the cell 8 results in the impressing of a modulation signal on the infra-red radiation impinging on the communicator and returned towards the source.

Referring now to Figure 2 a communications system according to the present invention comprises the communicator 2 of Figure 1, and a piece of equipment 20 to be controlled by the user of the communicator 2 for example a television. The equipment 20 includes a wide angle infra-red source 22 and a receiver 24.

Infra-red radiation impinging on the communicator 2 will be modulated and reflected back towards the source 22 as described above in relation to Figure 1. The receiver 24 is located sufficiently close to the source to detect the reflected, modulated radiation.

The diverging source 22 allows the communicator to be used in a range of positions in front of the equipment. The use of a retroreflector provides a reflection of the radiation back to the source for a range of orientations of the communicator 2 relative to the equipment 20.

The invention is also applicable to multi-communicator systems where several communicators may wish to send modulated signals to a control system via for example a source/receiver combination positioned separately from the equipment to be controlled, for example in the ceiling of a room.

A communicator according to the present invention may also be used as a remote sensor by providing that the modulation means is responsive to the output of sensor in the communicator, for example temperature, sound, pressure or vibration, which information can then be accessed remotely by interrogating the communicator in a manner described above.

The communicator may also be used as an identifier by being configured to return an identity signal as the modulated signal, for example as a motor vehicle identifier for interrogation by roadside equipment.

Claims

1. A communicator including a retroreflecting means for reflecting at least a portion of electromagnetic radiation incident upon it back towards the source of the radiation and a modulation means for impressing a modulation signal on the electromagnetic radiation impinging on the communicator.

2. A communicator as claimed in claim 1 in which the modulating means comprises a liquid crystal cell.

3. A communicator as claimed in claim 2 in which the liquid crystal cell is capable of modulating the intensity of electromagnetic radiation incident upon it.

4. A communicator as claimed in claim 3 in which the liquid crystal cell is capable of modulating the phase of electromagnetic radiation incident upon it.

5. A communications system comprising at least one communicator each as claimed in any of the preceding claims, a source of electromagnetic radiation separate from the communicator and a receiver located in the vicinity of the source for receiving any retroreflected radiation from the communicator.

6. A communication as claimed in any preceding claim including a sensor means for controlling the modulation means to impress a modulation signal representative of a sensed parameter.