GB2466783A

GB2466783A - Optical transmission link with intrusion detection

Info

Publication number: GB2466783A
Application number: GB9204635A
Authority: GB
Inventors: Pierre Gaillard; Jean-Pierre Bonicel
Original assignee: Alcatel Cable SA
Current assignee: Nexans France SAS
Priority date: 1991-03-06
Filing date: 1992-03-04
Publication date: 2010-07-14
Anticipated expiration: 2012-03-04
Also published as: ES2102286B1; IT1269224B; ITTO920124A1; DE4206802A1; GB9204635D0; FR2739459A1; ES2102286A1; GB2466783B; FR2739459B1; ITTO920124A0

Abstract

An optical transmission link with intrusion detection is provided with optical fibres for data transmission and means for the detection of intrusion comprising at least one terminal means 2 for transmitting/receiving a monitoring signal sent along monitoring fibres 4, mounted in a grooved inner casing 10 surrounding transmission fibres 3, and which are looped at both ends of the cable. Grooves 11 may be connected to one or more sources of pressurized gas and the pressure in the grooves monitored to detect intrusion.

Description

OPTICAL TRANSMISSION LINK WITH INTRUSION

DETECTION

The present invention concerns optical transmission links with intrusion detection, for protection of transmitted confidential data.

It is necessary, in order to prevent data transmitted over a link from being intercepted in some way, to detect any attempt at intrusion on this link. In the case of an optical fibre transmission link, a known method to detect intrusion uses the superposition on the optical data signal of an optical monitoring signal with a different wavelength and a clearly defined level and by monitoring the level of this monitoring signal. Any attenuation of this signal below a given threshold can signify an attempted intrusion which then may cause the transmission of data over the link to be stopped.

This known intrusion detection method requires complicated terminal equipment for superposing this other signal on the data signal at one end for each fibre, and a further terminal for separating this other signal from the data signal at the other end and measuring its level.

This known method has the disadvantage that the detection is relatively late, in the sense that the intrusion is not detected until there has effectively already been actual access to the fibres of the optical transmission link.

An object of the present invention is to overcome these disadvantages by detecting at attempted intrusion before the transmitted optical data is intercepted, even if this is only for a brief moment, by implementing distinctly simpler means than the terminal equipment of the known method.

According to the present invention, there is provided an optical transmission link with intrusion detection having optical transmission fibres defining the data link to be protected against intrusion, and intrusion detection means including optical transmitting/receiving terminal means to detect intrusion of an optical monitoring signal transmitted through the link, wherein the intrusion detection means comprise optical monitoring fibres mounted in a first grooved inner casing surrounding the data transmission fibres, the inner casing surrounded in turn by a protective outer casing to form a cable assembly, the monitoring fibres being looped together at both ends of the cable and including transmitting/receiving means.

Preferably, some monitoring fibres are directly looped together at a first end of the cable and are connected to the transmitting/receiving terminal means at the second end of the cable and the remaining monitoring fibres are directly linked together at the second end of the cable and are connected to further transmitting! receiving terminal means at the first end.

The data transmission fibres may be mounted in grooves of a central rod, surrounded by the grooved inner casing.

The grooves of the central rod and inner casing may be helicoid in opposite senses.

The central grooved rod may be cylindrical and mounted on a reinforced central carrier.

The cable may be free from any metallic elements.

The grooves of the inner casing may in operation of the transmission link be placed under fluid pressure and be coupled by pressure detecting means, associated with the optical detection means, to detect intrusion of the cable.

The features and advantages of the present invention may be more readily understood from a study of the detailed description of the attached figure drawing.

In this single figure, it can be seen that the optical transmission link with intrusion detection is formed by an optical cable 1, shown in section, and terminal means 2 for the detection and monitoring of intrusion comprising at least one transmitter/receiver means.

The cable 1 comprises optical fibres 3 defining the optical transmission link to be protected against intrusion. These fibres 3 are located in the inner part of the cable 1 and are referred to as data transmission fibres in the following. The cable 1 further comprises optical fibres 4 connected to transmitter/receiver means to detect intrusion of the optical data link. These optical fibres 4 are situated in the outer part of the cable 1 to surround the data transmission fibres 3 and are referred to as monitoring fibres in the following.

The data transmission fibres 3 are mounted in S-shaped or SZ-shaped grooves (single or double helical grooves) formed on a central rod 5 having a cylindrical outer surface. The rod 5 is mounted on a central carrier 6. Preferably, the grooves 7 are filled with sealing material, such as sealing gel or a material which swells in the presence of water.

The rod 5 and the carrier 6 are both non-metallic and are made of a polymer or preferably, in the case of the carrier 6, of a fibre reinforced polymer. The reinforcement fibres may be made of polyamide (aramide fibres). The central rod 5 and/or the carrier 6 may be a thermosetting or an (un)cross-linked thermoplastic.

Belt or tape means 8 capable of being reinforced with fibres, protects the date transmission fibres 3 and ensures that they are retained in the grooves 7 of the central rod 5. An inner casing 10 with Z-shaped or SZ-shaped grooves surrounds the rod 5 and the belt means 8 to protect the transmission fibres 3. Monitoring fibres 4 are mounted in grooves 11 which are preferably also filled with sealing materiel. Further belt means 12, capable of being reinforced with fibres, protects the monitoring fibres 4 and retains them in the grooves 11.

An outer casing 15 is provided to surround the inner casing 10 to protect the monitoring fibres 4 and to complete the cable assembly 1.

The grooves 7 and 11 of the rod 5 and the inner casing 10 are wound in opposite senses and would intersect but for their radial separation.

The grooved inner casing 10 and the outer casing 15 may be made of polyethylene resin. The outer casing 15 may be fire resistant.

The data transmission fibres 3 and the monitoring fibres 4 may be of any known type. Preferably, the fibres 3 are themselves resistant to intrusion further to being mounted in the said casing to delay any possible intrusion.

The optical monitoring fibres 4 are looped together by way of at least one transmitter/receiver means 2 at each of the two ends of the cable. This ensures that a monitoring signal is transmitted to each end of the cable on some fibres in one direction and for the remaining fibres in the other direction to enable a monitoring signal to be received at each end of the cable. A single transmitter/receiver means 2 has been shown for simplicity and is shown coupled to two fibres 4, to transmit a monitoring signal, and coupled to two other fibres 4 to receive end detect a monitoring signal.

The receiving means of each transmitter/receiver has an attenuation detector which is arranged to cause all transmission along the data transmission fibres 3 to stop as soon as unusual attenuation is detected.

While it is preferable for a relatively long optical link to utilise at least one transmitter/receiver means to loop the monitoring fibre 4 at each of the two ends of the cable, for a relatively short link some fibres may be coupled directly together at one end of the cable and looped through a transmitter receiver means at the opposite end and for the remaining fibres to be coupled directly together at the other end of the cable and to be looped through the transmitter/receiver means at the one end.

Furthermore, independent of the means to detect attenuation of the optical signals in the monitoring fibres 4, additional means may be provided to detect intrusion by monitoring the variation in pressure in the cable when it is placed under pressure by an inert gas or more preferably by dry air or nitrogen. The grooves 11 of the inner casing 10 may be pressurised and their ends connected to one or more sources of pressurised gas and to one or more pressure detectors (not shown in the Figure). Preferably, one detector may be provided for some of the grooves at one end of the cable and another detector for the other grooves at the other end of the cable. Detection of an abnormal pressure variation in one of the grooves 11 may be interpreted as an attempted intrusion which then may cause all data transmission over the link to stop.

Therefore, the cable 1 enables in both cases any attempted intrusion to be detected before the data transmission fibres 3 are affected. Furthermore, owing to the absence of any metallic parts, the cable 1 is rendered undetectable by known cable detection means which in itself constitutes a protective measure against possible intrusion.

To locate an attempted intrusion in the link, transmitting/receiving terminal means 2 may consist of or be associated with, a ref lectometer. This transmits calibrated pulses, gauged for amplitude and width, at one end of the monitoring fibres 4 and receives at the same end the reflected diffusion signal.

In an alternative embodiment to the present invention, optical data transmission fibres 3 may be mounted inside a plastic tube forming the grooved inner casing 10 rather than on the grooved central rod 5.

Claims

Claims: 1. An optical transmission link with intrusion detection, having data optical transmission fibres defining the data link to be protected against an intrusion, and intrusion detection means including optical transmitting/receiving terminal means to detect intrusion of an optical monitoring signal transmitted through the link, wherein the intrusion detection means comprise optical monitoring fibres mounted in a first grooved inner casing surrounding the data transmission fibres, the inner casing surrounded in turn by a protective outer casing to form an assembly of the cable, the monitoring fibres being looped together at both ends of the cable and including at least one transmitting/receiving means.
2. An optical transmission link as claimed in claim 1, wherein some monitoring fibres are directly looped together at a first end of the cable and are connected to the transmitting/receiving terminal means at the second end of the cable and the remaining monitoring fibres are directly looped together at the second end of the cable and are connected to further transmitting/receiving terminal means at the first end.
3. An optical transmission link as claimed in claims 1 or 2, wherein the data transmission fibres are mounted in grooves on a central rod, surrounded by the grooved inner casing.
4. An optical transmission link as claimed in claim 3, wherein grooves of the central rod and the inner casing are helicoid.
5. An optical transmission link as claimed in claims 3 or 4, wherein the central grooved rod is cylindrical and is mounted on a central carrier.
6. An optical transmission link according to any one of claims 3 to 5, wherein the grooves of the central rod and of the inner casing are filled with sealing material.
7. An optical transmission link as claimed in any one of claims 3 to 6, wherein the data transmission fibres and/or the monitoring fibres are retained in their respective grooves by belt or tape means.
8. An optical transmission link as claimed in claim 7, wherein the belt or tape means and/or the central carrier comprise non-metallic reinforcing elements.
9. An optical transmission link as claimed in claim or claim 6, 7 or 8 as appended to claim 5, wherein the central rod and/or central carrier is made of a polymer material.
10. An optical transmission link as claimed in claim 5 or claims 6, 7 or 8 as appended to claim 5, wherein the central rod and/or central carrier is non-metallic.
11. An optical transmission link as claimed in any one of claims 3 to 10, wherein at least the outer casing is fire resistant.
12. An optical transmission link as claimed in any one of claims 1 to 11, wherein the grooves of the inner casing are, in operation of the transmission link, placed under fluid pressure and are coupled to pressure detecting means associated with the optical detection means to detect intrusion of the cable.
13. An optical transmission link as claimed in any preceding claim, wherein the transmitting/receiving means comprise or are associated with reflectometers to locate the intrusion of the cable.
14. An optical transmission link substantially as hereinbefore described with reference to the accompanying drawing. *1'Amendments to the claims have been filed as follows 1. An optical transmission link with intrusion detection, having data optical transmission fibres defining the data link to be protected against an intrusion, and intrusion detection means including optical transmitting/receiving terminal means to detect intrusion of an optical monitoring signal transmitted through the link, wherein the intrusion detection means comprise optical monitoring fibres mounted in the grooves of a grooved inner casing surrounding the data transmission fibres, the inner casing surrounded in turn by a protective outer casing to form an assembly of the cable, the monitoring fibres being looped together at both ends of the cable and including at least one transmitting/receiving means.2. An optical transmission link as claimed in claim 1, wherein some monitoring fibres are directly looped together at a first end of the cable and are connected to the transmitting/receiving terminal means at the second end of the cable and the remaining monitoring fibres are directly looped together at the second end of the cable and are connected to further transmitting/receiving terminal means at the first end.3. An optical transmission link as claimed in claim 1 or 2, wherein the data transmission fibres are mounted in grooves in a central rod, surrounded by the grooved inner casing.4. An optical transmission link as claimed in claim 3, wherein grooves of the central rod and the inner casing are helicoid.5. An optical transmission link as claimed in claim 3 or 4, wherein the central grooved rod is cylindrical and is mounted on a central carrier.6. An optical transmission link according to any one of claims;3to 5, wherein the grooves of the central rod and of the inner casing are filled with sealing material. Ct7. An optical transmission link as claimed In any one of claims 3 to 6, wherein the data transmission fibres and/or the monitoring fibres are retained In their respective grooves by belt or tape means.8. An optical transmission link as claimed in claim 7, wherein the belt or tape means and/or the central carrier comprise non-metallic reinforcing elements.9. An optical transmission link as claimed in claim or claim 6, 7 or 8 as appended to claim 5, wherein the central rod and/or central carrier is made of a polymer material.10. An optical transmission link as claimed in claim 5 or any one of claims 6, 7 or 8 as appended to claim 5, wherein the central rod and/or central carrier is non-metallic.11. An optical transmission link as claimed in any one of claims 3 to 10, wherein at least the outer casing is fire resistant.12. An optical transmission link as claimed in any one of claims 1 to 11, wherein the grooves of the Inner casing are, in operation of the transmission link, placed under fluid pressure and are coupled to pressure detecting means associated with the optical detection means to detect intrusion of the cable.13. An optical transmission link as claimed in any preceding claim, wherein the transmitting/receiving means comprise or are associated with a reflectometer to locate the intrusion of the cable.14. An optical transmission link substantially as hereInbefore described with reference to the accompanying drawing.