Alarm system for an optical network

Abstract

A method is provided for detecting intrusion into optical fibers of a Passive Optical Network (PON) of the type which includes a multiplexing system at the head end for separating a data signal output at the head end to the plurality of fibers for supply to user end terminals and a data transmission system at each of the user end terminals for entering onto the fiber data as an optical signal. The method includes providing a monitor system having a transmitter at the head end and a monitor signal analysis system for analyzing changes in the optical monitor signal after transmission along the fiber for detecting an intrusion event. A monitor signal analysis system is provided at one or more user end terminals for detection and conversion of data from the analysis into a digital signal which is then transmitted from the user end terminals back to the head end using the data transmission system through the PON system or separately from the PON system.

Claims

1. A method for detecting intrusion into an optical network wherein the optical network comprises: a plurality of fibers each having a first end at a head end of the network and a second user end; the second user end of at least two of said plurality of fibers being connected to respective ones of a plurality of user end terminals; a splitter/combiner system for separating a data signal output at said head end to said plurality of fibers for supply data signals to said plurality of user end terminals; a data transmission system at each of said plurality of user end terminals for transmitting data as an optical signal along a respective one of said plurality of the fibers to said head end; the method comprising: transmitting a monitor signal from the head end on at least two of said plurality of fibers; at said second user end of each respective fiber on which the monitoring signal is transmitted, detecting changes in the monitor signal after transmission along said respective one of said fibers, which changes are indicative of vibration, motion, or handling of said respective one of said fibers indicative of an attempt to intrude into said respective one of said fibers; at said second user end of said respective one of said fibers, generating from said detected changes, change data signals containing data related to the changes; encoding the change data signals to form encoded change data signals which are transmitted from said second user end of each respective one of said fibers back to the head end; and at the head end, carrying out an analysis of the encoded change data signals from all of said respective fibers to detect said vibration, motion, or handling of each of said respective fibers indicative of an attempt to intrude into said respective fiber; whereby said analysis can distinguish on which one of said fibers the changes indicative of an attempt to intrude have occurred.

2. The method according to claim 1 wherein the encoded change data signals are transmitted to the head end using the data transmission system.

3. The method according to claim 1 wherein the supply data signals and the monitor signals are time division split as TDM signals onto said fibers so that said TDM signals are received by a single photodetector/ADC at the second end of said fibers.

4. The method according to claim 3 wherein said TDM signals are combined at the second end of said fibers.

5. The method according to claim 3 wherein said TDM signals are combined at the head end.

6. The method according to claim 1 wherein the monitor signal is an out of band monitor wavelength of the supply data signals.

7. The method according to claim 1 wherein the monitor signal is a portion of the supply data signal.

8. The method according to claim 1 wherein the monitor signal is an unused wavelength of the supply data signals and is split with the supply data signals using WDM.

9. The method according to claim 1 wherein there is provided an insensitive lead-in fiber leading to the splitter/combiner system.

10. The method according to claim 1 wherein the fibers are located in an approved hardened conveyance so as to meet federal approval for alarmed carrier PDS.

11. The method according to claim 1 wherein connection between the head end and the user end terminals is provided solely by fiber.

12. The method according to claim 1 wherein connection between the head end and the user end terminals is provided by hybrid fiber/electrical.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) One embodiment of the invention will now be described in conjunction with the accompanying drawings in which:

(2) FIG. 1 is a schematic illustration of the system according to the present invention.

DETAILED DESCRIPTION

(3) Data signals from a data source 3, such as a PON Optical Line Terminal (OLT) are supplied on an optical fiber 4. A monitor controller 1 provides control signals on a line 1A to a laser optical source 1B to generate monitor signals on a fiber 1C.

(4) The data signal on the fiber 4 and the monitor signal on the optical connection 1C are multiplexed onto the single fiber 4 by an optical interface 5.

(5) The system includes a junction box 20 including a 1?N optical splitter 6, which is typically, but not necessarily a 1?16 splitter, which acts to connect the monitor and data signals to multiple outputs. Each output from the splitter 6 is supplied respectively to a patch panel 8.

(6) The output from the distribution box 20 is supplied to cables 10A, 10B for transmission to user end terminals at remote locations. Thus fiber 10 of the cable carries combined monitor and data signals to a remote location such as a user drop box or monitoring interface 16. Thus fiber 11 carries combined monitor and data signals to remote location such as a user drop box or interface 15. The cables 10 and 11 are shown as examples of a series of such cables from the separate output ports.

(7) At each user's drop box 15, 16 is a connector 12 for delivering data to an optical network terminals (ONT) 21 which supplies a plurality of lines 22A to individual user equipment UE. The user drop boxes 15 and 16 are conventional and allow end user to access secure network with equipment such as a computer via ONT 21.

(8) In some more complex systems there can be provided a secondary distribution box similar to the distribution box 20, also known as a Zone Box for further distributing the data and/or monitoring to further locations 15, 16 etc

(9) The PON Optical Line Terminal (OLT) 3 is sending out data for the end users over fiber 4. The signals are split by splitter 6 for feeding the ultimate end users.

(10) Additional implementations can include substituting additional layers of distribution by additional distribution boxes 20 for many more end users 15, 16. For example, patch panel 8 might feed cables to individual floors of a building. On those floors are the additional distribution boxes such as distribution boxes 20 for supplying the users in offices.

(11) The PON transmitter 3 is connected to the lead-in fiber 4, which is preferably insensitive, leading to the distribution box 20. The PON signal and the monitor signal on the cables 10, 11 are located in an armored fiber or cable 10A so as to meet federal approval for armored cable PDS. Alternatively, the PON and monitoring fibers can be located in other approved hardened carrier conveyances such as EMT or conduit.

(12) As described above, the PON signal and the protection signal can be the same signal, or can be separate signals that are multiplexed using WDM so that Secure PON (SPON) exists on a single fiber.

(13) In one implementation as described above, the multiplexing is performed by wavelength and can use as the source at the alarm unit 1 an out of band laser unused wavelength of the PON transmitter for monitoring, coupled in through the WDM.

(14) In another implementation as described above a portion of the PON data signal is used as the monitor source and analyzed for intrusion, thereby precluding the need for controller 1A, optical source 1B or interface 5.

(15) As shown at 13, each of the ONTs of the end users includes a receiver or optical interface for the transmitted monitoring signal which acts to extract the monitor signal and to transfer it to a signal analysis and detection device 13A which acts to detect changes in the monitor signal after transmission along said respective fiber, which changes are indicative of vibration, motion, or handling of said respective fiber indicative of an attempt to intrude into said respective fiber. The device 13A can include an A/D converter for conversion of the signal to a digital signal. The receiver is arranged to transfer the digital signal through an interface 13B to the ONT along a data connector 13C for encoding as a digital data signal for transmission back along the same fiber 12. Thus the system 13A acts as an input to the ONT for data to be multiplexed with data from the user terminals and transmitted back along the fiber as data.

(16) The optical interface comprises an inline device such as an optical coupler or WDM. Alternatively the interface can comprise or an external device such as a clip on tap-coupler for extracting a portion of the monitor or data signal for intrusion analysis.

(17) Multiple fiber runs can be secured by daisy chaining the runs onto a single monitoring port at one of the ONTs thus reducing the number of ports required to monitor a given number of fiber runs so that only OLT or port 15D reports to the system 1.

(18) The signal processing system in FIG. 1 is at the OLT. A single computer or other analysis system 1 may be used to monitor multiple monitor interfaces 16.

(19) Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.