CN110706435A - Optical fiber perimeter intrusion alarm system based on 3 x 3 coupler - Google Patents
Optical fiber perimeter intrusion alarm system based on 3 x 3 coupler Download PDFInfo
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- CN110706435A CN110706435A CN201910861620.7A CN201910861620A CN110706435A CN 110706435 A CN110706435 A CN 110706435A CN 201910861620 A CN201910861620 A CN 201910861620A CN 110706435 A CN110706435 A CN 110706435A
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- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/02—Mechanical actuation
- G08B13/12—Mechanical actuation by the breaking or disturbance of stretched cords or wires
- G08B13/122—Mechanical actuation by the breaking or disturbance of stretched cords or wires for a perimeter fence
- G08B13/124—Mechanical actuation by the breaking or disturbance of stretched cords or wires for a perimeter fence with the breaking or disturbance being optically detected, e.g. optical fibers in the perimeter fence
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- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/22—Electrical actuation
- G08B13/24—Electrical actuation by interference with electromagnetic field distribution
- G08B13/2491—Intrusion detection systems, i.e. where the body of an intruder causes the interference with the electromagnetic field
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/548—Phase or frequency modulation
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Abstract
The invention discloses an optical fiber perimeter intrusion alarm system based on a 3 x 3 coupler, which comprises an annular sensing optical cable, a DFB laser source and the 3 x 3 coupler which are arranged on the perimeter, the laser output of the DFB laser source is connected to one input of a coupler through an isolator, one path of light source input in the coupler is uniformly divided into three paths of outputs with the phase difference of 120 degrees, two paths of outputs of the coupler are connected to two ends of the sensing optical cable, the optical paths of the two paths of outputs passing through in the transmission process are equal to meet the interference condition, and then coupling the two outputs to generate interference to form interference optical signals, wherein one of the two outputs is directly fused with an optical fiber delay ring and then connected with a sensing optical cable, and the other two input ends of the laser coupler are used as interference optical signal coupling output ports and are connected with an alarm monitoring host through a photoelectric detector.
Description
Technical Field
The invention relates to the technical field of photoelectricity, in particular to an optical fiber perimeter intrusion alarm system based on a 3 x 3 coupler.
Background
The periphery alarm system is wide and complex in the face of an invading object, is influenced by factors such as external environment, climate and the like, and has higher requirements on the system performance in application.
The electric perimeter monitoring system in the market at present needs outdoor power supply equipment in practical application, is easily interfered by an electromagnetic field, and the application occasion and the stability of the system are influenced. The optical fiber perimeter intrusion alarm system based on light wave interference uses a light passive device in a sensor part, makes up for the defects of an electrical sensing system, and has the advantages of electromagnetic interference resistance, corrosion resistance, low cost, high sensitivity, low false alarm rate and the like. However, due to the birefringence effect of the single-mode fiber, two orthogonal linear polarization modes exist in the light wave transmission process, and after the external temperature, stress and the like change, the propagation modes of the two modes are not the same any more, polarization errors exist in the two modes, and the light wave coupling shows that the light intensity amplitude changes randomly, so that the stability and the measurement accuracy of the interference system are influenced. Obviously, the condition that the optical fiber perimeter system works in high and low temperature environments cannot be met, in the field use process, the problems that the signal envelope is small, the report is missed, the sensitivity of the sensor is obviously reduced when the sensor continuously works for a long time in an outdoor low-temperature or high-temperature environment compared with that of the sensor working at normal temperature and the like occur in feedback, and the detection performance and the stability of the sensor are influenced. (because two orthogonal linear polarization modes exist in the single-mode fiber, after the external temperature, stress and the like change, the propagation modes of the two modes are not the same any more, polarization errors exist in the two modes, and the light wave coupling shows that the light intensity amplitude changes randomly, so that the stability and the measurement precision of an interference system are influenced.
There are three common methods currently used to address the effects of "polarization fading" present in optical fibers: (1) the polarization controller is used for real-time adjustment to keep the polarization states of coherent light consistent, but the algorithm of the polarization adjustment controller is complex, and for an optical fiber with the distance of several kilometers, the reliability of the sensor is limited due to the birefringence of the optical fiber and the birefringence caused by the external environment; (2) the method can reduce the influence of polarization fading on signals, and can simultaneously cause the contrast of interference signals to be reduced, so that the detection sensitivity of a system is reduced, and the phenomenon of missing report is easy to occur; (3) the polarization state of light wave transmission is stabilized by adopting the full polarization maintaining optical fiber and utilizing the special structure of the polarization maintaining optical fiber, but the price of the polarization maintaining optical fiber is very expensive, so that the production cost is increased sharply.
Disclosure of Invention
The invention aims to provide an optical fiber perimeter intrusion alarm system based on a 3 x 3 coupler, which reduces the influence of polarization fading on the system performance by utilizing the internal coupling light wave interference of the 3 x 3 coupler and has the characteristics of simple structure and high sensitivity.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a3 x 3 coupler-based optical fiber perimeter intrusion alarm system comprises an annular sensing optical cable arranged on the perimeter, a DFB laser source and a coupler, wherein the coupler is a 3 x 3 coupler, the laser output of the DFB laser source is connected to an input of the 3 x 3 coupler through an isolator, one path of light source input in the 3 x 3 coupler is uniformly divided into three paths of outputs with the phase difference of 120 degrees, two paths of outputs of the 3 x 3 coupler are connected to two ends of the sensing optical cable, so that the optical paths of the two paths of outputs passing through in the transmission process are equal to meet the interference condition, and then coupling the two outputs to generate interference to form interference optical signals in the 3 x 3 coupler, wherein one of the two outputs is directly fused with an optical fiber delay ring and then connected with a sensing optical cable, and the other two input ends of the 3 x 3 coupler are used as interference optical signal coupling output ports and are connected with an alarm monitoring host through a photoelectric detector.
The scheme is further as follows: the DFB laser source is a 1310nm narrow-linewidth laser source, and the power is 1 mW.
The scheme is further as follows: the sensing optical cable and the optical fiber delay ring optical fiber both adopt single-mode optical fibers.
The scheme is further as follows: the 3X 3 coupler and the optical fiber delay ring are placed in a shockproof box with shock-absorbing materials arranged on four walls.
The scheme is further as follows: the sensing optical cable is fixed on the fence arranged on the circumference spacing pile in a wave shape.
The scheme is further as follows: the fiber length of the fiber delay loop is determined by equation 1,
Wherein:
n1is the refractive index of the optical fiber delay ring;
n2is the refractive index of the sensing optical cable;
c is the propagation speed of light in vacuum;
L2is the sensing cable length;
f is the modulation and demodulation frequency that the signal processing circuit can realize.
The advantages of the invention include:
1. after the used multiplied 3 coupler is used for modulation, the phase difference between output light of each port is 120 degrees, the influence of polarization fading on a system is reduced, and the missing report and the false report of the system are reduced.
2. The used light source is a narrow linewidth DFB laser, the coherence of the light source is enhanced compared with an SLED bandwidth light source, and the perimeter effective distance which can be monitored is improved. Meanwhile, the narrow-linewidth light source is more sensitive to interference phase change, and the detection sensitivity of the light source to vibration signals is greatly improved.
3. The vibration optical cable is of an annular loop structure, so that the contact area with the external environment is increased, and the detection sensitivity is favorably improved.
4. The classification and identification of the intrusion signals can be realized according to the difference of the extracted characteristics of the waveform envelope, the amplitude, the energy and the like of the vibration signals.
5. The invention has higher environmental adaptability and simple structure, only uses one optical coupling device in the sensing optical path, saves the production cost and is easy to implement; due to the design of the annular loop, the detection sensitivity of the system is improved; the intrusion signals can be classified, distinguished and alarmed according to different characteristics of the intrusion signals.
The invention is described in detail below with reference to the figures and examples.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a schematic view of a perimeter fence according to the present invention;
fig. 3 is a schematic diagram of the knock, climb and buried walking intrusion signals detected by the present invention.
Detailed Description
As an optical fiber perimeter intrusion alarm based on a coupler, an optical path structure of an SFP light source +2 x 2 optical module coupler is tried, and as the phase difference of optical paths at two output ends of the coupler is 180 degrees, polarization fading has a large influence on a system, so that the system generates false alarm and missing report. In the field use process, the problems of missing report caused by small signal envelope in feedback, obvious reduction of the sensitivity of the optical fiber sensor when the optical fiber sensor continuously works for a long time in an outdoor low-temperature or high-temperature environment compared with the sensitivity when the optical fiber sensor works at normal temperature and the like occur. However, through multiple experiments, the 3 × 3 coupler is used, the phase difference between output light of each port is 120 degrees, so that the phase noise generated by random drift of the light source frequency can be reduced, the influence of polarization fading on the system is reduced, and the missing report and the false report of the system are reduced.
For this purpose, the optical fiber perimeter intrusion alarm system based on the 3 × 3 coupler of the present embodiment is a Sagnac interferometric optical fiber alarm system, as shown in fig. 1, the optical fiber perimeter intrusion alarm system includes an annular sensing optical cable 1, a laser source 2 and a coupler 3, which are arranged on the perimeter, and as shown in fig. 2, the sensing optical cable 1 is fixed on a fence 5 arranged on an annular perimeter spacing pile 4 in a wave-shaped arrangement. The laser source is a 1310nm narrow-line-width laser source, the power is 1mW, and the effective monitoring distance of the perimeter of the defense area is increased by using the DFB laser source. Meanwhile, the narrow-linewidth light source is more sensitive to interference phase change, and the detection sensitivity of the light source to vibration signals is greatly improved. The coupler is a 3 × 3 coupler, the 3 × 3 coupler is a standard device, the energy of a light source is uniformly divided into 1:1:1 and 120-degree phase difference output, the laser output of the DFB laser source is connected with one input end in1 of the 3 × 3 coupler through an isolator 6, one path of light source input in the 3 × 3 coupler is uniformly divided into three paths of outputs with 120-degree phase difference, two paths of outputs out1 and out 3 of the 3 × 3 coupler can also be out1 and out2 or out2 and out 3 are connected to two ends of the sensing optical cable 1, so that the optical paths of the two paths of outputs passing through in the propagation process are equal to meet interference conditions, and further coupling and interference are generated in the 3 × 3 coupler to form interference optical signals, one path of the two paths of outputs is directly fused (in series) with an optical fiber delay ring 7 and then is connected with the other two input ends of the sensing optical cable 1, 3 × 3 coupler, the input end in2 and the input end in3 are used as interference light signal coupling output ports and are connected with an alarm monitoring host 9 through a photoelectric detector 8.
Wherein: the sensing optical cable and the optical fiber delay ring optical fiber both adopt single-mode optical fibers. And the 3X 3 coupler and the optical fiber delay ring are placed in a shockproof box with sponge shock-absorbing materials arranged on four walls.
In the examples: when the fence is disturbed, the generated vibration signal is applied to the sensing optical cable, the propagation path of the clockwise and anticlockwise optical signals propagated in the sensing optical cable is changed, so that the phase of the formed interference light is changed, the phase change information of the sensor is converted into the detected light intensity signal through the photoelectric detector, and the safety monitoring of the perimeter area can be realized.
Since the coupling phase shift of the 3 x 3 coupler is
The jones matrix expression for an ideal 3 × 3 coupler is:
after light emitted by the light source passes through the x 3 coupler, the optical signal intensities of the OUT1 and OUT2 ports are:
two paths of interference light intensity generated when two optical signals of the OUT1 port and the OUT2 port return to the coupler again through the sensing optical cable are as follows:
in the formula (I), the compound is shown in the specification,
the phase difference of the generated forward and backward light signals. When disturbance exists outside, the interference light intensity is modulated when the disturbance acts on the sensing optical cable, and the interference light intensity changes along with the modulation, so that the safety early warning of the outside intrusion behavior can be realized by monitoring the interference light intensity. The phase difference is formed by 3 x 3 couplersThe method reduces the influence of the noise fluctuation and the polarization fading of the light source on the system performance, and simultaneously improves the response range of the system, thereby realizing high-sensitivity detection with large signal dynamic range without any modulation device.
Generally, the optical fiber delay loop in the optical path has the function of prolonging the propagation time of optical waves and reducing the eigenfrequency of the system, thereby reducing the modulation and demodulation difficulty of sensing signals. In addition, the optical fiber delay loop in the sensing system designed in this embodiment also has the effect of improving the detection sensitivity. In the experimental process, the signal noise detected when the length of the optical fiber delay loop is too long is found to be too large, and the demodulation difficulty of the system is increased. When the frequency is too low, the frequency is insensitive to external vibration signals, and the detection performance of the system is influenced. Therefore, the time delay ring is selected to be of a proper length, and the time delay ring plays an important role in reducing signal noise and improving sensing precision. Therefore, the fiber length of the fiber delay loop according to this embodiment is determined by equation 1,
Wherein:
n1is the refractive index of the optical fiber delay ring;
n2is the refractive index of the sensing optical cable;
c is the propagation speed of light in vacuum;
L2is the sensing cable length;
f is the modulation and demodulation frequency that the signal processing circuit can realize.
Because the optical fiber delay ring and the sensing optical cable adopt the same single-mode optical fiber, the refractive index n of the optical fiber delay ring1And the refractive index n of the sensing alarm optical fiber21.4662 for each single mode fiber, the propagation speed c of light in vacuum is 3X 108m/s, the modulation and demodulation frequency f that can be realized by the signal processing circuit of the embodiment is 10 KHz.
The test results for this example are shown in fig. 3, where the sensor cables were fixed to the fences, and the fences were individually tested. Meanwhile, the optical cable is laid under the carpet for walk test. The result shows that the system can quickly respond to the external intrusion action within 2 seconds.
Claims (6)
1. A3 x 3 coupler-based optical fiber perimeter intrusion alarm system comprises an annular sensing optical cable arranged on the perimeter, a DFB laser source and a coupler, wherein the coupler is a 3 x 3 coupler, the laser output of the DFB laser source is connected to an input of the 3 x 3 coupler through an isolator, one path of light source input in the 3 x 3 coupler is uniformly divided into three paths of outputs with the phase difference of 120 degrees, two paths of outputs of the 3 x 3 coupler are connected to two ends of the sensing optical cable, so that the optical paths of the two paths of outputs passing through in the transmission process are equal to meet the interference condition, and then coupling the two outputs to generate interference to form interference optical signals in the 3 x 3 coupler, wherein one of the two outputs is directly fused with an optical fiber delay ring and then connected with a sensing optical cable, and the other two input ends of the 3 x 3 coupler are used as interference optical signal coupling output ports and are connected with an alarm monitoring host through a photoelectric detector.
2. The fiber perimeter intrusion alarm system of claim 1, wherein the DFB laser source is a 1310nm narrow linewidth laser source with 1mW power.
3. The optical fiber perimeter intrusion alarm system of claim 1, wherein the sensing optical cable and the optical fiber delay loop optical fiber are single mode optical fibers.
4. The fiber perimeter intrusion alarm system of claim 1, wherein the 3 x 3 couplers and the fiber delay rings are placed in a shock-proof box with four walls provided with shock-absorbing material.
5. The fiber perimeter intrusion alarm system of claim 1, wherein the sensing cables are fixed in a wave shape to rails provided on the perimeter spacer piles.
6. The fiber perimeter intrusion alarm system of claim 1, wherein the fiber length of the fiber delay loop is determined by equation 1,
Wherein:
n1is the refractive index of the optical fiber delay ring;
n2is the refractive index of the sensing optical cable;
c is the propagation speed of light in vacuum;
L2is the sensing cable length;
f is the modulation and demodulation frequency that the signal processing circuit can realize.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111489514A (en) * | 2020-03-19 | 2020-08-04 | 天津大学 | Long-distance perimeter security positioning and monitoring device and method thereof |
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