THE OPTO -FIBER SENSORY SYSTEM IS USED FOR INTRUSION DETECTION MONITORED AREAS AND TO PREVENT DAMAGE Next year OPTOKON will be launching a completely unique system on the market, comprising a multipurpose surveillance system using standard telecommunication optical fiber as a distributed sensor. The system is suitable to be integrated into a master system for border surveillance of objects or areas for monitoring pipeline networks, and tracking and measuring other sources of mechanical vibration. Using this solution can, for example, when used in existing telecommunication optical paths follow railway traffic and detect faults in train brakes. Similarly, traffic on roads, runways etc can also be evaluated. Fig. 1: Perimeter Protection Supervision pipeline - failure, damage,... Localization of protective fencing Protecting buildings against undue distortions of space
Tracking Rail Traffic Fig. 1: Examples of use of the system The proposed monitoring system consists of the following basic elements as shown in Fig. 2 central supervisory node - C, local database for measured data - DB, measuring unit - M. The central supervisory node is the central monitoring system, which is used for the resulting evaluation, presentation of the current state of the surveillance system and to react according to the seriousness of the situation. The local database is used to store the measured data and the expected large number generated is needed to provide good network connectivity to other elements of the system. Fig. 2: Architecture of the monitoring system A key element of the system is measuring unit M, which generates test signals, receives responses from the optical system, processes and evaluates. An additional, but necessary element of the client application enables to control the measurement nodes not only from the center but also from the terminal branches of the local operator so that the operator can check the status of the measuring units, or be alerted to the problems of measuring units, and both locally and remotely, can perform some basic maintenance. Examples for use in the monitoring of pipelines is shown in Fig. 3.
Fig. 3: Designing applications for pipeline monitoring system The monitoring system is designed so that further node connection options are available. Given the importance of surveillance, these are designed in three ways, namely: wired connection to the Internet mobile ground connection mobile satellite connection Our technology utilizes a reflectometric method of measurement and the entire measuring system is placed on only one side of the optical fiber, as depicted in Fig. 4. Fig. 4: Basic structure of the reflectometric method measuring system
In both the laboratories at the Technical University in Brno and at OPTOKON this has been designed and tested with OTDR phase coherent detection, which as the most important component of this system, is a highly stable laser. The continuous optical signal (CW - continual wave) of the DFB laser with extremely narrow spectral line passes through the first optical isolator coupler (coupler). Part of the CW signal passes further to the direct branch, and the remainder is used for coherent detection (feature local oscillator). The optical signal enters straight to the block of an acousto- optic modulator (AOM). The AOM is managed by a special module (driver) and is controlled by a pulse generator that generates electrical pulses. The AOM modulates the CW signal and produces very narrow optical pulses with a shifted frequency control radio frequency pulse generator. The pulse signal is run through an EDF (Erbium Doped Fiber Amplifier) amplifier that operates as a booster and also to the test fiber (FUT - fiber under test), which forms the sensor. This is a standard telecommunication fiber type G.652.D in this case, 64 km long. The backscattered Rayleigh signal type scatters the return of any portion of the fiber at the beginning. This signal also passes through the optical circulator to a second coupler where it is merged with the signal from the second branch (local oscillator). The combined optical signal is then applied to the optical- electrical (O / E) converter. Fig. 5: The typical backscattered signal prior to demodulation and frequency shift AOM. The electrical signal from the O / E converter is amplified; the process response for the amplifier can be seen in Fig. 5, blue waveform. Subsequently, the signal is converted to baseband and then recorded into an acquisition card (DAQ - data acquisition card). To select the correct repetition rate, it is necessary to calculate the appropriate time constant τ, which is given by [1]:
2 s τ = [Hz], (1) c n where s is the total fiber length, and cn is the speed of light in optical fiber (m / s). After this the condition for a pulse repetition rate [1] can be calculated: f 1 [Hz]. (2) τ For a fiber length of 64 km there is the constant τ = 64 microseconds, and frequency f = 1562.5 Hz. Another important parameter is the pulse width, which determines the spatial resolution. In this case, the applied pulse width Tp = 1 microsecond. The spatial resolution is determined by [1]: 8 6 ct p 2 10 1 10 z = = = 100 m. (3) 2 2 In our system, we use an acquisition card with a sampling rate of 30 MS / s. One sample corresponds to the length of the fiber: 8 c 2 10 l = = = 6,666 m, (4) 6 F 30 10 s where l is the corresponding fiber length and Fs is the sampling frequency. We used 15 samples per section of 100 m. In addition to the above parameters, it is important to correctly set many other parameters. For coherent reception, the ratio of the first and second coupler must be optimally selected. The power level of the laser and EDFA amplifiers must also be appropriately selected to avoid the creation of non-linear phenomena, notably Brillouin scattering, which is undesirable for the system. Furthermore, the isolation between the output ports of the couplers and the circulator must be maximized. Our system ensures sufficient sensitivity to distances exceeding 60 km in the vibration frequency tuning range from 100 Hz to 1 khz. After recording, the processed DAQ card signal guarantees locating the position of the vibrations with a spatial resolution of 100 m, as shown in Fig. 6
Fig. 6: Detailed view of space-time responses in the presence of vibrations at a distance of 61 km from the beginning of the fibers Further processing can be done when highlighting the occurrence of vibrations in the vicinity of the fibers, as shown in Fig. 7 Fig. 7: Highlighting the occurrence of mechanical vibrations near the fibers for signal processing. We can conclude that this solution fully developed by the MPO Technical University in Brno and OPTOKON, a.s. is designed for vibration monitoring of events in a long optical fiber up to a distance of 100 km. Know-how solutions to this system are the intellectual property of the company.
A threat can be localized over the entire length of laid and secured optic telecommunication cable, without the need for any adjustment. The benefits include the ability to configure the system so that the alarm is only activated for selected events. The selected system detects a large range of activities, movement of vehicles, aircraft and intruders. A huge benefit is that it is a very flexible system that can be connected directly to the customer s previously installed monitoring equipment. Vít Novotný 1, Radko Krkoš 2, Radim Šifta 3, Petr Münster 4, Jiří Štefl 5, František John 6, Pavel Pospíchal 7, Zdeněk Malý 8 1,2,3,4 Department of Telecommunications, Faculty of Electrical Engineering and Communication, Brno University of Technology, Technická 12, 616 00 Brno, CZ 5,6,7,8 OPTOKON, a.s., Červený Kříž 250, 586 01 JIHLAVA, Czech Republic, www.optokon.com