Fiber optic based security system

[0001] The present invention relates to a compact and practical security system using fiber optics.

[0002] Security systems are well known in the art, and come in a variety of configurations. In a basic configuration, a security system includes a sensor and a warning system so that when the sensor is triggered, the warning system is activated.

[0003] One of the drawbacks with conventional security systems is that they are well adapted to protect for instance the inside of a building, such as a house, factory, warehouse, etc. Such systems include infra-red detectors, motion sensors, contact switches, etc., connected to a central location. When one or more of the sensors is triggered, an alarm, either visual or audible or both, is activated in order to give the proper authorities the time to respond appropriately.

[0004] At times, objects to be protected are located outside a building. This is the case of trailers, snowmobiles, bicycles, for example, and other items which can be located outside of a building. In order to protect those items, either a sometimes prohibitively expensive perimeter security system must be installed, or motion sensors can be used. The disadvantage of motion sensors is that they are triggered not only by potential thieves, but also by animals, thereby giving off false alarms.

[0005] It is an object of the present invention to provide an optical fibre based security system which provides an inexpensive alternative to existing security systems. In accordance with the invention, this object is achieved with a fibre optic based security system, comprising:

• • [0006] a length of optical fibre having two opposite ends;
  • [0007] a light emitter optically coupled to one of the opposite ends of said fibre for injecting light therein;
  • [0008] a light detector optically coupled to the other of said opposite ends of the fibre for detecting a level of light transmitted by said fibre;
  • [0009] threshold means connected to said light detector for determining if the level of light transmitted by the fibre is below a predetermined threshold level;
  • [0010] a power source for powering said system; and
  • [0011] an alarm operatively associated with said threshold means, said alarm being triggered when said level of light transmitted by said fibre falls below the threshold level.

[0018] Stated generally, the present invention uses light propagating in a loop of optical fibre as a means to protect an article from theft. The fibre is looped around the article in a manner that the article cannot be removed without breaking the fibre, such as shown in FIG. 5. At one end of the loop, a light source emits light into the fibre, and at the other end a photoreceptor receives the light after its travel in the fibre. The photoreceptor is also linked to an alarm system, or threshold means, which is activated if the light received is lower than a pre-defined threshold. Consequently, should somebody attempt to steal the object that is to be protected by cutting the optical fibre, or by tampering with it resulting in a decrease in the intensity of light transmitted, the alarm system is immediately activated. Advantageously, all the components of the invention with the exception of the fibre loop, are conveniently included in a single casing.

[0019] Referring to FIG. 1, there is shown a schematic representation of the system 10 according to a preferred embodiment of the present invention. The system 10 first includes a fiber loop 24, defining an input branch and an output branch. The input branch is connected to a light emitter 25, for example a LED, which is operatively connected to appropriate electronics. The output branch is connected to a light detector 27. In this manner, if the integrity of the fiber loop is compromised, the light level received at the light detector 27 will be lowered. A logic detector system 18 to detect tampering of the fiber loop 24 is provided, and is connected both to the detector 27 and either an audible alarm 22 or a visual alarm 20 or both. The alarm 20, 22 is activated if the light level at the detector is lower than a predetermined threshold. Preferably, the logic system 18 is connected to green LED 21, which indicate if the system is activated or not. The system 10 is preferably powered by an ordinary power outlet 26 to which is connected an AC/DC converter. A battery or set of batteries may be provided as a backup power source. An ON/OFF switch 12 is also provided.

[0020] Alternatively, the light can be emitted according to a predetermined or random pattern. If the light received at the detector is different in pattern or amplitude, then the alarm will be different.

[0021] In a preferred embodiment of the invention, the optical fibre is made of plastic or glass. Furthermore, a LED 21 may further be provided for indicating proper functioning of the system and power of the system.

[0022] Referring to FIGS. 2 and 5, there is shown a preferred embodiment of the fiber optic loop 24. The loop 24 is wrapped around a portion 101, 111 of an article to be protected. The article in question may advantageously be stored outdoors, such as for example a bicycle, a motorcycle, camping equipment, a lawnmower, etc. In a preferred embodiment of the invention, the two branches of the fibre 24 are preferably connected to a connector 38, from which they emerge bundled together and protected by a sleeve 40. The length of the branches is preferably long enough to span the distance from the object to be protected and a neighbouring residence or other power source. The branches are again separated so that they may be connected to the emitter 25 and detector 27.

[0023] Referring to FIG. 4, there is shown how the components of the alarm system according to the present invention may advantageously be installed in a casing 31. Such an embodiment makes the system 10 very convenient to install, carry or sell. Preferably, the casing 42 is round shaped, and is provided with an inner cavity 30 in which the fiber loop 24 may be stored when the system is not in use.

[0024] Referring to FIG. 3, there is shown another embodiment of the invention where the fiber loop 24 is hidden into the link 43 of a padlock 44. In this manner, cutting the padlock would also cut the fiber optic loop, therefore activating the alarm. In such an embodiment, the padlock 44 is also provided with a connector 38 for connecting the balance of the optical fibre thereto.

[0025] It should also be understood that the electronics and optical components of the present invention can be advantageously embodied in integrated circuits, and other electronic components, but that the invention is not limited thereto.

[0026] Although the present invention has been described by way of a preferred embodiment thereof, it should be understood that modifications within the scope of the invention are contemplated by the present application.