KR100678685B1 - Invader detection system utilizing single mode optical fiber - Google Patents

Abstract

An invader detection method using a single mode optical fiber is provided to remove noise caused due to mode interference and to secure reliability by outputting an invader alarm signal only when an invader exists by amplifying signal components by a mode combination detector. An invader detection method using a single mode optical fiber(2) is composed of a semiconductor laser(1) outputting a laser beam; a transmitting side single mode optical fiber buried in the soil to transmit the laser beam to an inner core of an optical fiber cable; a mode combination detector(5) for separating the other end of the single mode optical fiber and one end of a receiving side single mode optical fiber by a predetermined gap and disposing the shafts of cores facing each other of the optical fibers on the same axis; a light receiving element(6) changing an optical signal received through the other end of the receiving side single mode optical fiber into an electric signal; a receiver(7) amplifying the electric signal transmitted from the light receiving element to the desirable electric output level; and a signal processor(8) separating only an invader detection signal(9) by removing noise from the electric signal received through the receiver and outputting the invader detection signal by extracting only signal components changed by the invader.

Description

Intruder Detection System Using Single Mode Fiber {Invader Detection System Utilizing Single Mode Optical Fiber}

1 is a block diagram of an intruder detection apparatus according to the present invention.

Figure 2 is a block diagram of the optical fiber mode coupling ratio sensor according to the present invention.

3 is a block diagram of a transmission end optical fiber terminal according to the present invention.

Figure 4 is a configuration diagram of the receiving end optical fiber starting end according to the present invention.

<Description of Symbols for Main Parts of Drawings>

1 semiconductor laser 2 single mode optical fiber

2a: fiber optic cable 2b: core

3: soil in which fiber is buried underground 4: intruder

5: mode coupling rate detector 6: light receiving element

7 receiver 8 signal processor

9: intruder detection signal 10: optical mode

The present invention embeds a single mode optical fiber sensor in the ground by sensing the optical fiber mode coupling rate sensing method to detect an intrusion by detecting an impact applied to the optical fiber when the intruder penetrates through the ground where the single mode optical fiber is embedded. The present invention relates to an intruder monitoring apparatus using a single mode optical fiber.

The conventional optical fiber sensor is a signal generated by the impact or vibration generated when an intruder shakes the wire fence installed by the sensor by installing a multi mode fiber cable used as a sensor on a wire fence on the ground. After amplifying, the noise band component was filtered and rectified and converted into a pulse form. These methods can be broadly classified into two methods. The first method is light intensity change detection. In this method, the optical fiber is bent by external shocks or vibrations such as intruders and other modes, which have different propagation paths propagated in a core having a diameter of 50 μm or more. When a deformation occurs, a change occurs in a degree of loss of propagated optical power, and the change is detected by an average current by photoelectric conversion in a light receiving element connected to an optical fiber terminal to detect shock or vibration. This method is useful when installed on the ground, but it is difficult to apply due to its low sensitivity when buried underground. The second method is the speckle method. In this method, several optical beams with different propagation paths propagating in a core having a diameter of 50 μm or more of a multimode optical fiber used as a sensor can be shaken by an external shock or vibration such as an intruder. In this case, a change occurs in the paths of these modes, and a change in the speckle pattern, which is a two-dimensional pattern generated by mutual interference due to coherence characteristics, in which the wavelength of the laser light is constant between the modes. Will happen. The speckle pattern is a method of detecting shock or vibration by detecting a change in the average current when the photoelectric conversion is performed in the light receiving element connected to the optical fiber terminal.

However, this method has high sensitivity, but due to the coherence characteristic of light, it has a high probability of malfunction, such as generating a similar signal by natural phenomena such as wind in response to small changes or by other factors than intruders. There was this.

As a result, the light intensity change detection method using a multi-mode optical fiber cable according to the prior art has a disadvantage in that it is useful when installed on the ground, but it is difficult to apply due to its low sensitivity when buried underground. An intruder monitoring system using the AH has a high sensitivity but has a high probability of malfunctioning by generating a similar signal by other factors than the intruder.

SUMMARY OF THE INVENTION The present invention has been invented to solve the above problems, and its object is to provide a single mode without using a multimode optical fiber cable which is likely to malfunction in response to small changes due to the coherence characteristics of the light. mode) To provide an intruder detection device using a single mode optical fiber that can improve the sensitivity while using the optical fiber.

Another object of the present invention is to embed a single-mode optical fiber sensor in the ground to detect a single-mode optical fiber that can recognize the intrusion by detecting the impact applied to the optical fiber sensor when the intruder penetrates through the ground where the single-mode optical fiber sensor is buried It is to provide an intruder detection device using.

The present invention for achieving the above object is a semiconductor laser for outputting a laser light on one side, a transmission side single-mode optical fiber is transmitted to the inner core of the optical fiber cable, and the other end of the transmission side single-mode optical fiber A mode coupling rate detector configured by arranging the axes of cores facing each other so that the end sides of the receiving side single mode optical fibers facing each other are aligned on the same line, and the receiving side single mode optical fibers of the other side coupling mode detector A light receiving element for converting an optical signal received at an end of the light signal into an electrical signal, a soil in which the single mode optical fiber is embedded in the ground, a receiver capable of amplifying the electric signal received from the light receiving element to a required electrical output, and Remove noise component from electrical signal received from receiver and detect intruder And a signal processor for separating only, extracts only the signal component is changed by an intruder in the signal processor will be characterized by the intruder detection device using a single-mode fiber to trigger the intruder detection signal.

According to the present invention, when a single mode optical fiber passes through a buried ground, a single mode optical propagation path propagated in the sensor optical fiber core is changed and this change is amplified by the mode coupling rate detector, and then only the signal component generated by the intruder in the signal processor is amplified. Extract and generate an intruder detection signal.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth. Note that the same reference numerals are used for the same parts in the drawings of the present invention.

1 is a configuration diagram of an intruder detection apparatus according to the present invention, Figure 2 is a configuration diagram of an optical fiber mode coupling rate sensor according to the present invention. 3 is a configuration diagram of the transmission end optical fiber terminal according to the present invention, and FIG. 4 is a configuration diagram of the reception side optical fiber start end according to the present invention.

1 to 4, an intruder detecting apparatus using a single mode optical fiber includes a semiconductor laser 1 that outputs laser light to one side, and the laser light is an inner core of the optical fiber cable 2a ( 2b) of the transmitting side single mode optical fiber 2, the mode coupling rate sensor 5 which has a shaft of the core 2b of the single mode optical fiber 2 spaced by a specific distance, and the mode coupling rate sensor 5 A light receiving element 6 for converting the optical signal received at the end of the other receiving side single mode optical fiber 2 into an electrical signal, the soil 3 embedding the single mode optical fiber, and the light receiving element 6 A receiver 7 capable of amplifying the received electrical signal to a required electrical output, a signal processor 8 for removing noise components from the electrical signal received from the receiver 7 and separating only an intruder detection signal; In the signal processor 8, the intruder ( By extracting only the signal component changed by 4) it is configured to issue the intruder detection signal (9).
The mode coupling ratio sensor 5 is formed by connecting the ends of the transmitting side single mode optical fiber 2 and the receiving side single mode optical fiber 2 facing each other by a specific distance d by a commonly used connecting means. The axes of the cores 2a and 2b of 2) are arranged to coincide on the same line. That is, a block having a precisely processed V-groove, an optical fiber sleeve precisely matching the outer diameter of the optical fiber 2, or an optical fiber connector including a combination of two optical fiber connectors and one connector adapter The cores 2a and 2b of each single-mode optical fiber 2 are spaced apart from each other by the distance d between the transmitting side single-mode optical fiber 2 and the receiving single-mode optical fiber 2 facing each other by a specific distance d. ) Axis is arranged to match exactly on the same line.

In the present invention, the laser light output from the semiconductor laser 1 is transmitted to the light receiving element 6 for converting the optical signal into an electrical signal while passing through the core 2b of the single mode optical fiber 2. At this time, as shown in FIG. 2, when the single-mode optical fiber 2 is embedded in the Mediterranean, the soil 3 is pressed by the intruder 4, and when the optical fiber 2 is pressed, the core 2b of the optical fiber cable 2a is pressed. The propagation path inside is changed. This amount of change is amplified while passing through the mode coupling rate sensor 5 with two axes of the optical fiber core 2b separated by a specific distance, and then converted into an electrical signal in the light receiving element 6. The photoelectrically converted electrical signal is amplified to the extent that the receiver 7 can process the signal, and then extracts only the signal component changed by the intruder 4 in the signal processor 8 to issue the intruder detection signal 9. .

In general, in the case of a single mode optical fiber (2), unlike in the case of a multimode optical fiber, since there is only one optical path propagated in the ground, even if there is an external impact by an intruder or the like, the optical fiber (2) has a small degree of warp, so transmission loss At least, even if it is directly photoelectrically changed by the light receiving element 6, its electrical output is insignificant.

However, if the mode coupling rate detector 5 according to the present invention is placed in the middle of an optical propagation path, one optical mode 10 propagating along the core 2b of the optical fiber 2 is received through the mode coupling rate detector 5. When recombined to the core 2b of the optical fiber cable 2a, a large amount of light loss is generated, and the change in the amount of light loss is converted in the light receiving element 6 into an electrical output. The electrical signal thus obtained includes a high frequency white noise generated by the optical mode propagation path and a low frequency signal generated by the intruder 4 together. Therefore, in order to extract only the signal components from the electrical signal, the signal processor 8 extracts only the signal components changed by the intruder of the low frequency components using a low pass filter.
Referring to the operation principle of the mode coupling ratio sensor 5, the instantaneous direction and the amount of change in the amount of light traveling through the inside of the optical fiber 2 cores 2a and 2b due to external impacts are determined by When the angles of the axes are the same, the longer the separation distance between the cross sections of the optical fiber jumped by a certain distance, the farther the traveling light waves move away from the central axis of the optical fiber. It is possible to detect the amount of change in light amount due to the propagation angle of the light wave more sensitively, so that the amount of change in light amount is amplified in spite of some loss of light amount due to the separation d of the axis of the optical fiber 2 cores 2a and 2b. As a result, the signal component is enlarged as compared to the remaining white noise, which improves the signal-to-noise ratio, thereby reducing the unnecessary noise component. And you get a.
When the intruder (4) stepped on the soil (3) buried in the ground, the optical fiber (2) is pressed or stimulated due to the surrounding vibration The propagation path in the core 2b of the optical fiber 2a is changed by the shape change of the optical fiber 2. The mode coupling ratio in which the amount of change is formed by placing two optical fiber 2 cores, that is, a transmission side optical fiber 2 core 2b axis and a receiving optical fiber 2 core 2a axis by a specific distance d. The optical fiber 2 core 2a caused by the intruder has an effect of amplifying the amount of change in the optical power despite some optical power loss due to the separation of the axis of the optical fiber 2 cores 2a and 2b while passing through the detector 5. , 2b) it is possible to efficiently detect the amount of change of the light waves traveling in the interior.

As shown in Fig. 2, one side shows the transmitting optical fiber 2 which is the semiconductor laser 1 side, and the optical fiber cable 2a is a cladding portion of a single mode optical fiber used as a sensor, and has a central core ( 2b) is the core portion of a single mode optical fiber used as a sensor. An arrow line in the core 2b of the optical fiber 2 shows the optical mode 13 propagated. And a mode coupling ratio sensor 5 showing the air gap d between the transmitting optical fiber 2 and the receiving optical fiber 2. One side shows the transmission side optical fiber 2 which is the semiconductor laser side, and the other side shows the reception side optical fiber 2 which is the light receiving element side.

The optical fiber has a cross-sectional size of about 125 μm, and an inner core of about 8-12 μm is suitable. The distance d of the mode coupling rate detector 5 between the transmitting optical fiber 2 and the receiving optical fiber 2 is 5-150 μm.

In the above configuration, the optical mode 10 propagated along the optical fiber 10 is recombined into the opposite optical fiber 2 via the mode coupling rate detector 5, which is an interval spaced apart by a predetermined distance from both single-mode optical fiber cores 2b axes. Will be.
Specifically, light propagates in the core 2b of the transmitting optical fiber 2 and propagates into the core 2a of the receiving optical fiber 2, between the cores 2a and 2b of the both single mode optical fibers 2. A part of the optical mode 10 leaks out through the space generated by the distance d, and the optical mode 10 which is not leaked propagates inside the core 2a of the receiving optical fiber 2 and is recombined. Can be.
Therefore, the optical mode 10 propagated along the transmitting side optical fiber 2 is not completely recombined due to the presence of this gap, and much loss occurs when recombining to the opposite optical fiber 2. This change in loss over time is different in normal and invaders. In other words, a relatively high frequency component is usually generated in a normal state, and a relatively low frequency component is generated when an intruder 4 is present.

The optical fiber sensor of the optical fiber mode coupling rate sensing method according to the present invention extracts only the low frequency components by the intruder from this loss amount to generate the intruder detection signal 9.

Meanwhile, referring to FIG. 3, a longitudinal cross-sectional view of the optical fiber 2 close to the semiconductor laser 1 side is shown. The optical fiber cable 2a of the single-mode optical fiber 2 has a cladding portion. The center of the cross section of the single mode optical fiber 2 represents the core 2b portion, and the upper portion of the core 2b represents the cross section at the end of the optical mode 10 propagated along the core.

Fig. 4 shows a cross section of the starting point of the optical fiber 2 close to the light-receiving element 6 side, which is the receiving side, and of the cross section of the single mode optical fiber 2, the optical fiber cable 2a shows a cladding portion, The center of the cross section of the mode optical fiber 2 represents a portion of the core 2b, and the lower portion of the core 2b represents an optical mode 13 exiting the end of the optical fiber 2 and thus the interval of the mode coupling rate detector 5. It shows the cross section of the projected optical mode 10 when it reenters the core 2b of the opposite optical fiber 2 after it has passed.

In the above configuration, the optical mode 10 propagated along the optical fiber 2 is spaced apart from the mode coupling rate detector 5 with two single mode optical fiber cores 2b axes spaced by a predetermined distance to the opposite optical fiber 2. When recombination, there is a large difference in the amount of loss depending on the position of the optical mode 10. The change in the amount of loss decreases the average optical power which is a direct current component as compared to the case where there is no gap, but the alternating current component photoelectrically converted by the change of the optical mode 10 by the intruder 4 becomes large inversely and thus invades the intruder 4. The signal component is amplified. Since the signal components caused by the intruder are relatively low frequency components, the optical fiber sensor of the optical fiber mode coupling rate detection method according to the present invention extracts only the low frequency components caused by the double intruder to issue the intruder detection signal 9.

In the intruder detection apparatus using the single mode optical fiber of the present invention, the optical fiber sensor is usually the end of the other optical fiber spaced at a certain distance from the optical fiber end vertically cut one optical mode running through the core of the single mode optical fiber While the average optical power that is combined changes slightly rapidly when recombined, the change rate is relatively slow and greatly changes when the intruder passes the buried position, so the low frequency signal component generated by the intruder is extracted. By using this as a detection signal to issue an alarm signal.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but it will be apparent to those skilled in the art that various modifications are possible without departing from the scope of the present invention.

As described above, the present invention eliminates noise components caused by interference between modes generated when a conventional multimode is used using a single mode optical fiber as a sensor, and is generated by an intruder using a mode coupling rate detector. By amplifying the signal component so that it can be issued as an intruder alarm signal only when an intruder is present, the user can obtain reliability and can reduce the probability of malfunction of the optical fiber sensor.

Claims (3)

A semiconductor laser that outputs laser light to one side, a transmitting side single mode optical fiber configured to be transmitted to the inner core of the optical fiber cable and embedded in soil, and a receiving side facing the other end of the transmitting side single mode optical fiber A mode coupling rate detector configured by arranging the axes of cores facing each other so that the ends of the single mode optical fibers are separated from each other by a specific distance, and arranged at the ends of the single mode optical fibers on the other receiving side of the mode coupling rate detector. A light receiving element for converting an optical signal into an electrical signal, a receiver capable of amplifying the electric signal received from the light receiving element to a required electrical output, and removing noise components from the electric signal received from the receiver and detecting an intruder A signal processor that separates only the signal, and the signal processor An intruder detection apparatus using a single mode optical fiber, characterized in that configured to issue an intruder detection signal by extracting only the signal component changed by the. The method of claim 1, The distance (d) of the mode coupling rate detector (5) is 5-150μm, intruder detection apparatus using a single mode optical fiber. The method of claim 2, The optical fiber has a cross-sectional size of about 125μm, the inner core is about 8-12μm, intruder detection apparatus using a single mode optical fiber.

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