Intrusion warning apparatus using an optical fiber

Intrusion warning apparatus using an optical fiber

1 is a block diagram of an intrusion alarm device using an optical fiber according to an embodiment of the present invention;

FIG. 2 is a view showing in detail an end portion of the auxiliary optical fiber of FIG. 1 and a photodiode array of a light receiving unit installed corresponding thereto;

FIG. 3 is a cross-sectional view taken along line AA of FIG. 2 .

Explanation of the symbols for the main parts of the drawing

110, 150: optical fiber 120: light source generator

121: laser diode 122: laser diode driver

123: laser diode stabilization circuit unit

130: reflection mirror 140: light branching part

160: optical isolator 170: spatial filter

180: light receiving unit 181: photodiode

190: amplification unit 200: low-pass filter unit

210: full-wave rectification unit 220: comparison unit

230: alarm unit 240: shielding unit

<background-art><p>The present invention relates to a monitoring system for preventing intrusion, and more particularly, by installing an optical fiber underground or installing a fence, etc. The present invention relates to an intrusion warning device using an optical fiber to prevent intrusion from the outside by detecting and issuing an alarm.</p><p>In general, the conventional intruder monitoring system mainly uses a system using an ultrasonic sensor or an infrared sensor, but there is a disadvantage that the monitoring area is narrow when using the ultrasonic sensor, and when using the infrared sensor, the monitoring area is higher than that of the ultrasonic sensor Although this is widened, the monitoring range is also limited, and in both cases, when the weather conditions deteriorate, such as heavy rain or heavy snow, false alarms due to interference in the signal transmission path, or the sensor is installed in a state exposed to the outside, intruders can detect the sensor device. There was a disadvantage that the crime prevention function was lost if it was recognized in advance.</p><p>In order to compensate for the shortcomings of such a monitoring system using an ultrasonic sensor or an infrared sensor, an intruder using an optical fiber is used as a sensor, and the optical fiber is used to detect and alert the phase change of the input light according to the vibration or pressure of the optical fiber. An alarm device has been proposed by the applicant of the present invention.</p><p>However, according to the proposed conventional chip particle warning device using optical fiber, the range of the monitoring area can be adjusted as needed, and the security can be improved by burying the optical fiber in the basement of the area to be monitored or disguising it in a fence, etc. , it has many advantages such as preventing false alarms caused by bad weather such as heavy rain or heavy snow. Since the optical fiber must be installed separately, or the optical fiber must be installed in the form of a loop to integrate the transmitter and receiver to produce a single device, the length of the optical fiber is Problems such as doubling the need were found.</p></background-art><tech><p>Therefore, the present invention was created to realize all the advantages of the intruder warning device using the conventional optical fiber as described above and to solve the problems. An object of the present invention is to provide an intrusion alarm device using an optical fiber that improves the sensor installation and signal processing efficiency by allowing the receiver to be installed at the same location, and doubles the reception sensitivity.</p></tech>

<p>In order to achieve the above object, an intrusion alarm device using an optical fiber according to the present invention includes an optical fiber as an optical path medium having a certain length and installed at the boundary of the monitoring area; a light source means for generating a coherent optical signal and injecting it into the optical fiber through one end of the optical fiber; reflection means for reflecting light transmitted forward through the optical fiber and emitted through the other end of the optical fiber in a reverse direction of the transmission direction; an optical branching means for branching a traveling direction of the reflected backward optical signal; an auxiliary optical fiber as a path medium for transmitting the branched reverse optical signal; light receiving means for receiving the optical signal emitted through the end of the auxiliary optical fiber and converting it into an electrical signal; amplifying means for amplifying the converted electrical signal; filtering means for removing a noise signal from among the amplified electrical signals; rectifying means for rectifying the filtered electrical signal; a comparing means for comparing the rectified signal with the variable reference signal; and an alarm means for issuing an alarm according to the comparison result through the comparison means.</p><p>In addition, an optical isolator is installed in the optical fiber portion between the light source means and the optical branching means to reliably block the reverse optical signal from being transmitted in the reverse direction to the light source means, and the optical fiber in contact with the light source means A shielding means made of a copper tube or the like is installed on the one end of the, the end of the auxiliary optical fiber in contact with the light receiving means, and the part of the optical fiber installed inside the building and/or outside the monitoring area. The signal due to external stress or vibration is not transmitted to the optical fiber, and a spatial filter is installed between the optical receiving means and the end of the auxiliary optical fiber to increase the signal-to-noise ratio of the optical signal received by the optical receiving means. let it be</p><p>In addition, the optical branching means is configured of an optical coupler or a beam splitter so that the forward optical signal transmitted into the optical fiber proceeds as it is, and the backward transmitted optical signal is branched and transmitted toward the auxiliary optical fiber. , The reflecting means is characterized in that it is composed of a high reflectance optical fiber reflecting mirror or a general mirror installed so that the reflecting surface is in contact with the other end face of the optical fiber.</p><p>The present invention configured as described above recognizes an intruder by changing the speckle of an optical signal received when an intruder breaks in by burying the optical fiber underground or installing it in a fence, and coherent light is transmitted inside the optical fiber. Wavelength components (i.e., modes) constituting light interfere with each other while proceeding in the this will appear Accordingly, when a pressure is applied to the optical fiber from the outside, the positions of the bright and dark portions are changed to cause a change in the speckle pattern, and intrusion from the outside can be detected based on the change.</p><p>Hereinafter, an intrusion alarm device using an optical fiber according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.</p><p>1 is a block diagram of an intrusion warning device using an optical fiber according to an embodiment of the present invention. An optical fiber 110 having a predetermined length and being buried or installed at the boundary of the corresponding monitoring area to serve as an optical path medium and sensor. ); a light source generating unit 120 for generating a coherent optical signal and injecting the generated light through one end 111 of the optical fiber 110; In order to reflect an optical signal transmitted forward through the optical fiber 110 and emitted through the other end 112 of the optical fiber 110 in the reverse direction of the transmission direction, that is, toward one end 111 of the optical fiber 110 . , a high reflection optical fiber mirror 130 as a reflection means installed so that the reflection surface is in contact with the exit surface of the other end 112 of the optical fiber 110; The optical signal incident through one end 111 of the optical fiber 110 and transmitted forward into the optical fiber 100 proceeds as it is, and the optical signal reflected by the optical fiber mirror 130 and transmitted in the reverse direction is an auxiliary optical fiber. an optical splitter 140 configured as an optical coupler or a beam splitter in order to be transmitted to the (150) side; an auxiliary optical fiber 150 serving as a path medium and/or a sensor for transmitting a reverse optical signal branched by the optical branching unit 140; an optical isolator 160 installed on the optical fiber 110 between the light source generator 120 and the optical branch 140 to block the reverse optical signal from proceeding; a spatial filter 170 filtering the optical signal emitted through the end part 151 of the auxiliary optical fiber 150; a light receiving unit 180 for receiving an optical signal emitted through the end portion 151 of the auxiliary optical fiber 150 and passing through the spatial filter 170 and converting it into an electrical signal; an amplifying unit 190 amplifying the electrical signal converted by the light receiving unit 180; a low-pass filter unit 200 for removing a noise signal by passing only a signal having a frequency component or less among the electrical signals amplified by the amplifying unit 190; a full-wave rectifying unit 210 for rectifying the electrical signal filtered by the low-pass filter unit 200 to obtain only a positive (+) signal; a comparator 220 for comparing the signal rectified by the full-wave rectifying unit 210 with the variable reference signal Vref; an alarm unit 230 for issuing an alarm according to the comparison result through the comparison unit 220; and the one end 111 portion of the optical fiber 110 in contact with the light source generator 120 , the end 151 portion of the auxiliary optical fiber 150 in contact with the light receiving unit 180 , and inside and outside the building / or a shielding unit 240 made of a copper tube or the like to surround and shield a portion of the optical fiber 140 installed in a non-monitoring area.</p><p>The light source generator 120 includes a laser diode 121 , a laser diode (LD) driver 122 that drives the laser diode 121 to generate coherent light, and the laser diode 121 . is composed of a laser diode (LD) stabilization circuit unit 123 for maintaining a stable operation of the LD, and the light receiving unit 180 is composed of one or more photodiodes (PD) 181 receiving a laser light signal.</p><p>Next, the operation of the present invention will be described.</p><p>First, coherent light from the laser diode 121 driven by the LD driver 122 is incident through one end 111 of the optical fiber 110 . The light incident on the optical fiber 110 is forwardly transmitted through the optical isolator 160 and the optical coupler 140 sequentially through the optical fiber 110 serving as a sensor, and the forward transmitted light is the optical fiber. When the reflection surface of the high reflectance optical fiber mirror 130 at the end section of 110 is met, most of the light there is reflected in the opposite direction to the incident direction. The reflected light travels in the reverse direction through the optical fiber 110 again, reaches the optical coupler 140 , and is branched and transmitted to the auxiliary optical fiber 150 by the optical coupler 140 . The optical signal reaching the end 151 of the auxiliary optical fiber 150 is emitted, passes through the spatial filter unit 170 , and is then received and detected by the photodiode 181 of the light receiving unit 180 .</p><p>FIG. 2 is a view showing a terminal portion of the auxiliary optical fiber 150 and an array of photodiodes 181 of the light receiving unit 180 installed corresponding thereto. A cross-section AA of the terminal portion of the auxiliary optical fiber 150 is shown in FIG. As shown in FIG. 3 , it can be seen that the speckle pattern 10 made of light and dark appears due to light interference, and the speckle pattern 10 is the photo of the light receiving unit 180 . It is detected by diode 181 .</p><p>The number of the speckles depends on the number of advanced light modes, and the intensity of light at each point of the optical fiber is different depending on the phase of the mode to form the speckle pattern 10 . At this time, when the phase shift (Φ) of the light passing through the optical fibers 110 and 150 is expressed by a formula, Φ=Lβ, where L is the length of the optical fiber and β is the propagation constant of the mode.</p><p>The propagation constant β of the mode is different depending on the size of the optical fiber and the refractive indices of the core and the clad. If an external stress is applied to the optical fibers 110 and 150 that has a slight effect on the cross-sectional size and refractive index of the optical fibers, the phase change occurs by affecting the path length of each mode in the optical fibers 110 and 150 . That is, when an external stress is applied to the optical fibers 110 and 150 , a speckle pattern change occurs. As shown in FIG. 2 , between the end of the auxiliary optical fiber 150 and the photodiode 181 array of the light receiver 180 . If the spatial filter 170 is put in the , the movement of the speckle pattern 10 can be accurately measured through the photodiode 181 . If the size of the spatial filter 170 is equal to the size of one speckle, the current of the photodiode 181 changes according to the movement of the speckle, but the size of the spatial filter 170 is increased to increase the signal-to-noise ratio. needs to be made reasonably large.</p><p>The optical signal received by the photodiode 181 of the light receiving unit 180 is converted into an electric signal through a preamplifier (not shown), amplified by the amplifying unit 190, and has a cutoff frequency of several KHz. After the noise components are removed while passing through the low-pass filter unit 200 , it is input to the full-wave rectification unit 210 to obtain a positive (+) signal. </p><p>In the comparator 220 , when the output signal of the full-wave rectifier 210 comes in as a signal of a level greater than the reference signal set by the resistor R3 , the comparator 220 informs the alarm unit 230 that an event has occurred, and the alarm unit 230 ) from the signal sent from the comparison unit 220 distinguishes and displays whether the currently generated event is an event caused by an intruder or an event caused by other (wind, animal, etc.). </p><p>In addition, the LD stabilization circuit unit 123 monitors the output from the laser diode 121 so that light of a certain wavelength and size is always output from the laser diode 121 . The optical isolator 160 prevents the light reflected from the mirror 130 and transmitted in the reverse direction from being fed back to the laser diode 121 . The shielding part 240 using an external protective material such as a copper tube that can wrap the optical fiber 110 and the auxiliary optical fiber 150 is a part of the optical fiber 110 in contact with the laser diode 121 , and the light receiving part 180 . ), the part of the auxiliary optical fiber 150 in contact with the photodiode 181, and the parts located inside the building or not in the monitoring area are blocked so that the signal due to external pressure or vibration is not transmitted to the optical fibers 110 and 150 .</p><p>The optical fiber 110 is buried underground or installed in a fence where an intruder is to be monitored at a depth of several cm to several tens of cm depending on the conditions of the monitoring area. When the optical fiber 110 is reflected by the inner wall of the optical fiber 110, the phase of the propagating or straight light is changed, and the speckle pattern 10 is changed. Accordingly, the photodiode 181 of the light receiving unit 180 is The amount of received light is changed, and the changed light received signal is processed into an appropriate electrical signal through the amplifying unit 190, the low-pass filter unit 200, and the full-wave rectifying unit 210 sequentially, and then the comparison A reference signal (V) that is variably set according to the environment and situation through the unit 220_ref), and the alarm unit 230 determines whether there is an intruder based on the comparison result and gives an alarm.</p><p>The present invention, which is constructed and operated as described above, can be used in various ways for security and military purposes as well as protection of general homes or industrial facilities. It can be considered a valid invention.</p>

<p>As described above in detail, the intrusion warning device using the optical fiber according to the present invention can be used in various ways for protection of general homes and industrial facilities and for security and military purposes, like the intruder warning device using the existing optical fiber, and the standard in the comparison section By variably defining the signal, it is possible not only to determine the intrusion target or type, but also to install the optical transmitter and the receiver integrally at the same location without installing the optical fiber in the form of a loop in the boundary area on a straight line. Thus, the sensor installation and signal processing efficiency are improved, and the received optical signal is reused, thereby doubling the reception sensitivity.</p>