A LOCAL AREA NETWORK SYSTEM USING LIGHT

Field of the Invention

The present invention relates to an improved data transmission system as part of a local area network. In particular, the system enables a flexible network to be more easily installed and managed.

Background to the Invention

With the advent of locally connected arrays of computers, usually within an organisation, has arisen the need for lower cost, secure Local Area Networks(LANs). The LANs allow individual computers within an organisation to communicate with one another, to access and use shared software, and also, when desired use a communal conduit to transmit and receive information to and from computers outside the LAN.

When devising the means by which information is communicated within the LAN, a number of considerations must be borne in mind. Firstly, the means of transmission should not corrupt the data being transmitted. Secondly, security must be maintained, both in terms of ensuring that information does not accidentally reach the wrong recipient but also so that an outside party cannot gain access to the LAN without permission. The transmission means should also be fast and relatively inexpensive.

A number of means are known in the art to transmit data. For example, physical means such as Unshielded Twisted Pair(UTP) cables or fibre cables can be used. Alternatively, wireless means using radio or infrared radiation are also well established. For each of these means, there are advantages and disadvantages relative to one of the other means. For example, when installing UTP cables, the labour costs are high.

Also, although transmission rates of the order of a Gigabit are possible with UTP cables this is relatively slow for current and expected future usage. Further, the location of any data outlet is restricted to those areas in the region of an already located cable. Using UTP cables however, security is high and necessitates anybody trying to gain unauthorised access to the LAN establishing a physical connection into the cable network to allow the data using the cable to be intercepted.

Fibre cables have similar characteristics to UTP cables but are more expensive to install although transmission rates are faster.

Wireless transmission systems using radio waves are significantly less expensive to install than cable systems as less hardware is required. Moreover, the flexibility in respect of where computers can be stationed is high. However, the speed of transmission of information is lower than for cables. Of greater seriousness however is that the use of radio waves raises security concerns due to the ready transmissibility of the waves through building materials leading to susceptibility of the waves to interception. Even where good encryption means are used there remains the risk of an outside party being able to decipher encrypted information. The use of microwave infrared radiation instead of radio waves overcomes most of the security problems of wireless transfer because of the restricted range of the infrared radiation. However, this feature of infrared and microwave radiation makes its usage difficult to employ as signal degradation and loss can be high.

It is therefore an object of the present invention to address the issues and problems with the above known transmission systems

Summary of the Invention

According to a first aspect of the invention there is provided a ceiling tile, the ceiling tile comprising;

two opposed planar surfaces, separated by connecting walls, the surfaces and the walls defining a volume within the ceiling tile,

one of said planar surfaces defining an aperture through which a light beam can pass,

the ceiling tile including a wave guide along which light is transmitted, the walls of the wave guide being reflective to light to prevent its escape from the guide,

light diversion means to divert light entering through the aperture into the wave guide or divert light from the wave guide through the aperture.

The ceiling tile thus provides for relatively cheap installation of a means for transmitting information across a LAN. Moreover, the tiles can be retrofit to replace conventional ceiling tiles already in position.

The wave guide advantageously comprises a cavity defined by reflective walls to transmit light. Alternatively, the wave guide comprises a solid medium, transparent to the wavelength of the light utilised.

The wavelength of the light is preferably from 10 ^"4 - 10 ^"9 m.

Preferably, the light diversion means comprises one or more elements selected from a prism, lens, mirror or the like. A beam emitted by a computer can be refocused where required.

The ceiling tile advantageously includes linkage means to ensure correct alignment with a neighbouring tile to enable a network of wave guides within the ceiling being formed.

According to a second aspect of the invention there is provided a system for transmitting and receiving information between two locations using light of wavelength from 10 ^" — 10 ^" m, comprising a computer having emission means to transmit a focused light beam; a network of ceiling tiles, the ceiling tiles being in accordance with the first aspect of the invention, a computer having light receiving means to receive light transmitted from a ceiling tile.

The light emission means is preferably a laser or a light emitting diode(LED).

Detailed Description Of The Invention

The invention is now described with reference to Figure 1 which illustrates the functioning of the system. In the particular embodiment shown, the path of information transmitted to and from a user's computer lies partially within a wave guide located within or integral with a ceiling tile. The ceiling tiles referred to particularly in this invention are those used as part of a suspended ceiling. Such ceilings are well known and are used in large numbers of offices, especially more modern offices and those located, for example, in high rise buildings or specially designated industrial areas.

The ceiling is formed by location of ceiling tiles within an already constructed steel framework. During construction of the suspended ceiling, particular care is normally taken to ensure that the surfaces of the ceiling tiles lie in a plane. This type of ceiling offers the advantage to the user of hiding pipes, ducting etc. and also of improving the acoustic quality of the office space.

The present invention utilises the features of a suspended ceiling to form an information transmission system. It should be understood by the reader that the system described can also be incorporated into office flooring through the use of flooring tiles having the corresponding features.

As can be seen from Figure 1, by providing reflective surfaces within the internal volume of a ceiling tile, these surfaces can function as wave guides for electromagnetic radiation. Wavelengths particularly contemplated for use in the current invention are from 10 ^"4 - 10 ^" m, that is from far infrared to hard ultra- violet, hi the following, these will be designated generically as light waves.

Ceiling tiles as described above typically are of dimension 0.6m by 0.6m or 0.6m by 0.9m. The internal volume of the ceiling tile, in accordance with the invention includes a wave guide to define a path for light emitted by a user's computer. In order to be effective the depth of the wave guide is from about 8.10 ^" - 1.10 ^" m, but the depth used depends very much on the wavelength of the light used within a system. The depth of the ceiling tile used is to some extent therefore governed by the depth of the wave guide and the amount of support required by the wave guide.

As possible wave guides, a cavity having reflective internal surfaces can be envisaged. Alternatively, a solid, light-conducting medium can be included within the internal volume of the ceiling tile.

Li order to transmit information into the ceiling tile, a light source needs to be included in a first computer. The light source, in order to minimise energy requirements and also provide security emits a directed and quite tightly focused beam. Laser emission systems or LEDs are particularly effective.

The light beam emitted from the computer is directed towards an aperture defined in the surface of the ceiling tile. Once through the aperture the light beam is

diverted along the wave guide by one or more diversion means selected from a prism, lens, or a mirror.

The diversion means can be so configured such that, should it be necessary, the beam received from the first user's computer is focused.

When the beam emitted by the first user reaches its destination, a corresponding diversion means, installed for a second user, diverts the beam out of the wave guide and the ceiling tile to that second user. In order to increase security the beam's spread on leaving the ceiling tile is minimised.

The system is illustrated in Figure 1. The computer 10 of a first user includes light transmission and receiving means which can respectively transmit a focused beam and receive a beam 11, which beam carries information. In some embodiments the transmission and receiving means can be incorporated into a single unit. On leaving the computer 10 the beam is directed to an aperture 12 defined in a surface of a ceiling tile 13. Alternatively, a floor tile 14 can be used employing the same principles.

Once through the aperture 12, the light beam is diverted and, if desired, focused by diversion means(not illustrated) such as a prism. The light beam is diverted into a waveguide 15 within the internal volume of the ceiling tile 13. The light beam is reflected randomly within the wave guide 15 until it encounters the diversion means 16, above the user of the computer 17 to which the information carried in the light is to be transmitted. The light beam is diverted out of the ceiling tile 18, through the aperture 19 to the computer 17 where it is picked up and the information suitably decoded.

In order to enhance transmission of data within the cavity then technology presently employed in the technical area of Free Space Optics can be employed. In such aspects of the invention a number of transmitter/receivers can be included within the tiles, perhaps set around lcm apart within the tile, each

transmitter/receiver including a laser light source together with one or more lenses to focus incoming signals. Switching of data direction can be by means of Micro- Electro-Mechanical Systems.

In the embodiment shown above, a traditional Ethernet (BUS)-type network is envisaged in which an identifier is attached to each transmission signal to identify the intended recipient. The result of this is that each user's computer in the LAN receives the signal, but only the recipient to whom the identifier relates actually accepts the signal and decodes it. Apart from being wasteful of energy, this method is susceptible to misuse as computers could be reconfigured to accept signals not intended for the recipient, without the other users in the LAN being aware thereof.

An alternative to the above is to allocate each user in the LAN a wavelength or a bandwidth for their signals. In this alternative each of the stations is capable of transmitting data within a number of bandwidths within the overall capability of the system and the bandwidth (or bandwidths for multiple recipients) used to carry a signal is selected to suite the recipient.

Where desired each tile can include a multiplicity of apertures to allow laser light to enter and exit the tiles. Such an arrangement facilitates positioning of a computer or workstation beneath a tile, by providing a number of positions for the computer.

The system as devised therefore, provides a secure local environment for the transmission and receipt of confidential information. The system can moreover be installed as part of an office when built or retrofit by substitution of conventional tiles for those according to the invention. The latter aspect also enables ceiling tiles to be re-arranged according to different office usage. An office manager is therefore provided with greater flexibility of usage of available space.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention.