WO2008155769A2 - System and method based on waveguides for the protection of sites - Google Patents

System and method based on waveguides for the protection of sites Download PDF

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Publication number
WO2008155769A2
WO2008155769A2 PCT/IL2008/000835 IL2008000835W WO2008155769A2 WO 2008155769 A2 WO2008155769 A2 WO 2008155769A2 IL 2008000835 W IL2008000835 W IL 2008000835W WO 2008155769 A2 WO2008155769 A2 WO 2008155769A2
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WO
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Prior art keywords
light
waveguide
system
sensors
workstation
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PCT/IL2008/000835
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French (fr)
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WO2008155769A3 (en )
Inventor
Gil Pogozelits
Moti Margalit
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Rafael Advanced Defence Systems Ltd.
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    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00Burglar, theft or intruder alarms
    • G08B13/18Actuation by interference with heat, light or radiation of shorter wavelength; Actuation by intruding sources of heat, light or radiation of shorter wavelength
    • G08B13/181Actuation by interference with heat, light or radiation of shorter wavelength; Actuation by intruding sources of heat, light or radiation of shorter wavelength using active radiation detection systems
    • G08B13/183Actuation by interference with heat, light or radiation of shorter wavelength; Actuation by intruding sources of heat, light or radiation of shorter wavelength using active radiation detection systems by interruption of a radiation beam or barrier
    • G08B13/186Actuation by interference with heat, light or radiation of shorter wavelength; Actuation by intruding sources of heat, light or radiation of shorter wavelength using active radiation detection systems by interruption of a radiation beam or barrier using light guides, e.g. optical fibres

Abstract

A system for monitoring an area comprising at least one waveguide such as an optical fiber having at least one Bragg grating sensor integrated in the waveguide; a plurality of light sources adapted to emit light into both ends of said waveguide; and at least one detector adjusted to detect light at each end of the waveguide,. The Bragg grating sensors may enable sensing at least one type of physical stimuli such as strain or temperature changes by changing at least one feature of the light they reflect, wherein the light sources and detectors may be adapted to be set selectively into operation according to the light detected by the detectors.

Description

SYSTEM AND METHOD BASED ON WAVEGUIDES FOR THE PROTECTION OF

SITES

CROSSREFERENCETORELATEDAPPLICATION [0001] This application claims the benefit of U.S. Provisional Patent Application 60/929,272, filed June 20, 2007, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] In general, the present invention relates to the field of protection and surveillance over premises, objects or both. More specifically, the present invention relates to sensors based on waveguides having Bragg gratings utilized for the detection of unauthorized intrusion into premises or the detection of damages to the objects, the sites, or both.

BACKGROUND OF THE INVENTION

[0003] Optical fibers can be used as detectors by using the optical-mechanical features of the fiber. Changes in the mechanical and/or optical conditions of parts of an optical fiber such as stress applied on the fiber (e.g. bending), temperature changes and the like can cause changes in the light beam transmitted through the fiber (e.g. dispersion, aberrations and the like). Accordingly, mechanical changes can be identified and detect by measuring parameters and features of the light exiting of the fiber while knowing the mode pattern, frequency and wavelength band of the light beam entering the fiber.

[0004] There are several fiber based detection techniques known in the art such as interferometry, amplitude modulation and frequency or wavelength modulation, for example. [0005] Bragg Waveguide Grating is a method for integrating Bragg diffraction filters into an optical fiber, where each set of filters may be used as a sensor, enabling to sense movement, pressure, tension and/or temperature changes and the like, referred to hereinafter as "mechanical changes". [0006] A patent application number US2004/0237648A1 and a patent number US69550S5, which are incorporated herein by reference in its entirety, disclose an acceleration sensor that uses a fiber with Bragg grating. Other sensors that involve fibers with Bragg grating, such as provided by patents number US6923048 and US68888125, which are incorporated herein by reference in its entirety, may be used for sensing changes in temperature and strain.

BRIEF DESCRIPTION OF THE DRAWINGS [0007] The subject matter regarded as the invention will become more clearly understood in light of the ensuing description of embodiments herein, given by way of example and for purposes of illustrative discussion of the present invention only, with reference to the accompanying drawings, wherein

Figure IA is a schematic illustration of a lengthwise sectional view of a waveguide having Bragg gratings at a plurality of locations, according to an embodiment of the invention;

Figure IB is a schematic illustration of wavelengths reflected in the waveguide due to the

Bragg gratings, according to an embodiment of the invention;

Figure 2 is a schematic block-diagram of a waveguide based damage and intrusion detection system laid out in an area that is to be monitored, according to an embodiment of the invention;

Figure 3 is another schematic diagram of the waveguide based damage and intrusion detection system, according to an embodiment of the invention;

Figure 4 is a schematic diagram of the waveguide based damage and intrusion detection system laid out in the area, wherein communication between workstations is interrupted, according to an embodiment of the invention;

Figure 5 is a schematic diagram of the waveguide based damage and intrusion detection system laid out in the area, wherein communication between the workstations is interrupted at other locations, according to an embodiment of the invention;

Figure 6 is a block diagram of a flowchart of a method of monitoring the area using sensors based on Bragg grating, according to an embodiment of the invention;

Figure 7 depicts a graph of amplitude as a function of time of light reflected from a sensor implemented by Bragg grating, said graph representing a knock on a surface, according to an embodiment of the invention;

Figure 8 depicts a graph of power as a function of normalized frequency representing the knock, according to an embodiment of the invention; Figure 9 depicts a graph of signal amplitude as a function of time of light reflected from the sensor implemented by Bragg grating, said graph representing a series of knocks on the surface, according to an embodiment of the invention;

Figure 10 depicts a graph of power as a function of normalized frequency, said graph representing the series of knocks, according to an embodiment of the invention;

Figure 11 depicts a graph of signal amplitude as a function of time of light reflected from the sensor implemented by Bragg grating, said graph representing a person's gait and noise, according to an embodiment of the invention;

Figure 12 depicts a graph of signal amplitude as a function of time of light reflected from the sensor implemented by Bragg grating, said graph representing the opening of a door, a person's gait and the closing of the door, according to an embodiment of the invention;

Figure 13 depicts a graph of signal amplitude as a function of time, said graph representing the opening of the door of Figure 12, according to an embodiment of the invention;

Figure 14 depicts a graph of signal power as a function of normalized frequency, said graph representing the opening of the door of Figure 12, according to an embodiment of the invention; and

Figure 15 is a graph depicting stress as a function of time as measured by three sensors implemented by Bragg gratings in a waveguide, according to an embodiment of the invention. [0008] The drawings together with the description make apparent to those skilled in the art how the invention may be embodied in practice.

SUMMARY OF THE INVENTION

[0009] The present invention, in some embodiments thereof, provides a system and a method for monitoring an area using one or more waveguides (such as optical fibers) having at least one Bragg grating sensor integrated in said at least one waveguide.

[0010] Bragg grating sensors are integrated in the waveguide and located at predefined locations along the waveguide. Each sensor enables reflecting light in a specific wavelength narrow band peaking at a specific wavelength value. Therefore, detecting the reflected wavelength (corresponding to the frequency of the light) may enable sensing that area of the waveguide. [0011] According to some embodiments of the invention, the sensors may enable sensing at least one type of physical stimuli (such as temperature changes and/or strain applied upon said area in the waveguide where the sensor is located) by changing at least one feature of the light they reflect. [0012] According to some embodiments of the invention, the system may comprise: at least one waveguide; a plurality of light sources adapted to emit light into both ends of said waveguide; and at least one detector adjusted to detect light at each end of said waveguide. The light sources and detectors may be adapted to be set selectively into operation according to the light detected at said detectors. [0013] According to some embodiments of the invention, the waveguides of the system may be optical fibers, wherein each said Bragg grating sensor is made of a set of filtering surfaces enabling to reflect light of a narrow predefined wavelength band with a predefined wavelength peak. [0014] According to some embodiments of the invention, each Bragg grating sensor may be adapted to alter the intensity of light in said waveguide as a result of physical stimuli applied upon the waveguide where said sensor is located.

[0015] According to some embodiments of the invention, each waveguide may comprise a multiplicity of Bragg grating sensors located in different locations along each said waveguide, where each said sensor enables reflecting a different wavelength, thereby enabling to identify the sensor by detecting the reflected wavelength of each sensor.

[0016] According to some embodiments of the invention, the system may further comprise a plurality of workstations each comprising a power source, at least one light source and an interrogation module comprising at least one detector. Each said workstation may be connected to at least one of the waveguides of said system and where said light source enables emitting a predefined light beam into one end of said waveguide and said detector enables detecting light outputted from that end of the waveguide that is connected to said workstation. [0017] According to some embodiments of the invention, the detector may enable detecting at least one of: the wavelength of the outputted light or the intensity of outputted light. [0018] According to some embodiments of the invention, the light source is a laser enabling to input coherent light within a predefined wavelength band range. [0019] According to some embodiments of the invention, once light emission into one end of the waveguide arriving from the light source of a first workstation of the system is interrupted light can be emitted from the light source of a second workstation into the other end of said waveguide. [0020] According to some embodiments of the invention, The workstation may further comprise an optical expansion unit enabling to receive light from the light source of said workstation and optically route the light to a multiplicity of waveguides. [0021] According to some embodiments of the invention, the interrogation module may further comprise a processor and at least one database, where said processor enables receiving data from the detector and from said database and identifying a physical stimuli according to predefined rules.

[0022] According to some embodiments of the invention, the processor may enable receiving detected values from the detector and retrieving corresponding threshold values from the database and comparing said corresponding values, wherein an exceeding in at least one of the threshold values may be defined as an emergency.

[0023] According to some embodiments of the invention, the interrogation module may further comprise a notification unit enabling to receive data from said processor and notify at least one user regarding an identified stimuli. [0024] According to some embodiments of the invention, the notification unit may enable transmitting alarming messages to at least one of: predefined user's terminal or a predefined surveillance service center.

[0025] According to some embodiments of the invention, each workstation may further comprise an application operatively associated with said processor, light source and said detector, wherein said application comprises commands enabling running calculations, decisions and other aspects of the processing operations that enable identifying an emergency. The processor may be embedded in hardware of a computerized system such as a Processing card and the like. DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION [0026] The present invention, in some embodiments thereof, provides a system and method enabling the monitoring and surveillance of premises, objects, sites and the like using sensors that are based on Bragg gratings incorporated in waveguides such as optical fibers. [0027] For example, a core having at some locations of the waveguide an index of refraction, which is modulated in a substantially periodical manner, may implement the Bragg grating. Bragg gratings having such a periodic structure may give rise to interference effects, which may cause reflecting specific frequency components of light striking the Bragg grating. [0028] The wavelengths and/or intensity amplitudes of the reflected light depend on the structure of the Bragg grating. Therefore, changing the structure, such as, e.g., the period of the modulation, the index of refraction and the like, may alter the reflected light's intensity as a function of the wavelengths of the light striking the Bragg grating.

[0029] The mechanical structure of the sensor's Bragg grating is adapted to be coupled to a specific target stimuli, e.g., a weight, which may change the structure of the Bragg grating as a result of physical stimuli, thereby enabling implementing various types of sensors.

[0030] For example, an acceleration sensor, which may enable sensing of, e.g., a person's gait near said sensor, may be implemented by attaching a weight to a Bragg grating. [0031] A temperature sensor may be implemented by attaching thermally expanding material to the Bragg. Therefore, in some embodiments of the invention, a fiber comprising sensors based on Bragg gratings may be used for monitoring premises, sites, objects and the like as such sensors may enable detecting, for example, intruders into premises; the activities of tools for breaking through doors, walls and the like; damage to objects such as, e.g., water leakage from pipelines, and the like. [0032] The premises may be any area and/or structure that can be monitored using the fibers such as, for example, fences and borders, facilities and buildings and the like.

[0033] According to some embodiments of the invention, a first light source and a second light source may be adapted to selectively emit light into the both ends of the waveguide. Each source may emit light of a predefined and known wavelength band. The fibers may be adapted to optimally guide light of the predefined bands of the light sources. [0034] A module, which may be a computerized workstation, for instance, may determine the type of physical stimulus (e.g. acceleration, weight, strain, temperature and the like) detected at each sensor based on the wavelength(s) and/or intensity of the light reflected back to the detectors.

[0035] According to some embodiments of the invention, only said first light source may emit light into the waveguide's first end as long as all sensors in the waveguide reflect at least some of the light emitted from said first light source. If one or more sensors do not reflect light for a predetermined time, the second light source may start to emit light into the second end of the waveguide. Emitting light into the waveguide from both ends enables the system to delimit the location(s) of interruption(s) in the waveguide, as will be outlined in detail below. In some embodiments, the first light source may stop emitting light when the second light source is actuated.

[0036] It is to be understood that an embodiment is an example or implementation of the inventions. The various appearances of "one embodiment," "an embodiment" or "some embodiments" do not necessarily all refer to the same embodiments. [0037] Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination.

[0038] Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment. [0039] Reference in the specification to "one embodiment", "an embodiment", "some embodiments" or "other embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiments, but not necessarily all embodiments, of the inventions.

[0040] It is to be understood that the phraseology and terminology employed herein is not to be construed as limiting and are for descriptive purpose only. [0041] The principles and uses of the teachings of the present invention may be better understood with reference to the accompanying description, figures and examples.

[0042] It is to be understood that the details set forth herein do not construe a limitation to an application of the invention.

[0043] Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in embodiments other than the ones outlined in the description below. [0044] It is to be understood that the terras "including", "comprising", "consisting" and grammatical variants thereof do not preclude the addition of one or more components, features, steps, or integers or groups thereof and that the terms are to be construed as specifying components, features, steps or integers. [0045] The phrase "consisting essentially of", and grammatical variants thereof, when used herein is not to be construed as excluding additional components, steps, features, integers or groups thereof but rather that the additional features, integers, steps, components or groups thereof do not materially alter the basic and novel characteristics of the claimed composition, device or method. [0046] If the specification or claims refer to "an additional" element, that does not preclude there being more than one of the additional element.

[0047] It is to be understood that where the claims or specification refer to "a" or "an" element, such reference is not be construed that there is only one of that element. [0048] It is to be understood that where the specification states that a component, feature, structure, or characteristic "may", "might", "can" or "could" be included, that particular component, feature, structure, or characteristic is not required to be included. [0049] Where applicable, although state diagrams, flow diagrams or both may be used to describe embodiments, the invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described.

[0050] Methods of the present invention may be implemented by performing or completing manually, automatically, or a combination thereof, selected steps or tasks. [0051] The term "method" refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the art to which the invention belongs. [0052] The descriptions, examples, methods and materials presented in the claims and the specification are not to be construed as limiting but rather as illustrative only. [0053] Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined. [0054] The present invention can be implemented in the testing or practice with methods and materials equivalent or similar to those described herein.

[0055] Unless specifically stated otherwise, as apparent from the following discussions, it is to be understood that utilizing terms such as "computing", "processing", "determining", "calculating," or the like, refer to the action or processes or both of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such transmission, information storage or display devices.

[0056] Reference is now made to Figure IA, which schematically illustrates a lengthwise sectional view of a waveguide 110, which is an optical fiber having Bragg grating sections at a plurality of locations, serving as sensors 111, 112 and 113, according to some embodiments of the invention. [0057] According to some embodiments of the invention, as illustrated in figure IA, waveguide 110, when waveguide 110 is an optical fiber, may comprise a cladding 150 and a core 160, where the index of refraction of the core 160 is higher than the index of refraction of the cladding 150, thereby enabling guiding a light beam of a specific wavelength " λO" or a specific narrow wavelength band through the core 160, as known in the art. In addition, waveguide 110 may be an optical fiber that includes one or more sensors based on Bragg grating, such as sensors 111, 112 or 113 or any combination thereof, e.g., as known in the art. [0058] Sensors 111, 112 or 113 or any combination thereof may be adapted to receive a certain input wavelength/wavelength band "λO" and reflect different wavelengths, where each sensor 111, 112 and 113, for example, reflects a different wavelength λl, λ2 and λ3, respectively. For example, each sensor 111, 112 and 113 may serve as a filter reflecting wavelengths: λl=1530nm, λ2=1532nm, and λ3=1534nm, respectively (where nm refers to nanometers). [0059] As known in the art, the Bragg grating is created by placing a set of rounded surfaces (having the core's 160 diameter) each having an index of refraction, which is different from the index of refraction of the core 160 and the cladding 150. The wavelength reflected by each Bragg grating depends upon the distance between each two surfaces of the grating "Λ", where: λ = 2πΛ [0060] Further reference is made to Figure IB, which schematically illustrates a graph 175 illustrating the relation between wavelengths reflected in waveguide 110 due to the Bragg gratings and the amplitude "P", according to some embodiments of the invention. Each Bragg grating sensor 111, 112 and 113 enables receiving the input wavelength or wavelength band and reflecting a single wavelength or a narrower band: λl, λ2 and λ3. As illustrated in figure IB, each grating or sensor may create an amplitude-peak "P" that can be normalized to only output a narrow band of wavelengths around the main wavelength.

[0061] When a mechanical or physical stimulus is applied on the fiber waveguide 110 (e.g. physical strain), each grating of each sensor 111, 112 and 113 may response by a change its output wavelength. For example if one of the sensors 111 has an output reflection wavelength λl=1530nm a pressure applied upon sensor 111 may cause a diversion in the peak wavelength λl '=1540nm or widening of the width of the rang of wavelength band. [0062] To identify a detected change in reflected light as an intrusion or an emergency situation, the diversion may be required to exceed a predefined threshold value, so as to avoid false alarms.

[0063] In case sensors 111, 112 and 113 do not sense physical stimuli exceeding a certain threshold value, said sensors 111, 112 and 113 may be adapted to substantially reflect wavelengths λl, λ2 and λ3 at a predefined intensity of II, 12 and 13, respectively (which may be either equal or different from one another). In case sensors 111, 112 or 113 or any combination thereof are subject to physical stimuli, the sensors 111, 112 and/or 113 may reflect light at shifted wavelengths, as outlined and illustrated hereinafter for exemplary purposes only with reference to Figures 7-14.

[0064] As already mentioned above, a waveguide, such as waveguide 110, may include a plurality of sensors, such as sensors 111, 112 and 113, set up in a series. According to some embodiments of the invention, each sensor or set of sensors may be positioned in a predefined location of the monitored area 400. A physical stimulus applied to one or more of said sensors may have substantially no influence on the pattern of the light reflected from the other sensors that are not subject to a physical stimulus. For example, applying stress to sensor 112 may change the intensity of the light reflected from sensor 112, whereas the intensity of the light reflected from sensors 111 and 113 may remain substantially unaffected. [0065] Reference is now made to Figure 2, which provides a block-diagram of system 100 for monitoring and surveillance over an area 400, where system 100 may be positioned in at least one of area's 400 locations, according to some embodiments of the invention. [0066] According to the embodiments illustrated in Fig. 2, system 100 may comprise: • at least two fibers waveguides 110, each waveguide 110 having at least one sensor

(e.g. where the first waveguide 110 comprises sensors 111, 112 and 113 and the second waveguide 110 comprises sensors 121, 122 and 123); and • one or more workstations 130. [0067] According to some embodiments of the invention, each workstation 130 may be operatively associated with at least one of the waveguides 110. Each workstation 130 may be adapted to emit at least one of the light sources into the corresponding end of at least one of the waveguides 110. Additionally, at least some of the workstations 130 may enable detecting features of the light outputted by the fibers (at the other end of the fiber) such as wavelength and light intensity, modes shapes and the like. For this, the workstation 130 is required to include optical and perhaps digital equipment enabling to measure and detect those features as well as optical means such as at least one laser enabling to input coherent or non-coherent source light into the waveguides 110.

[0068] The input light emitted into each waveguide 110 fiber may travel through the waveguide 110 while each of the Bragg grating sensors 111, 112 and 113 or 121, 122 and 123 reflects its own specific wavelength back to the emitting workstation 130. If one of the sensors 111, 112 and 113 or 121, 122 and 123 is disturbed it may reflect a different wavelength or may not reflect back any light (e.g. in case the fiber is bent to a point where no light can travel through the fiber waveguide 110) the workstation 130 may enable measure the diversion from normal threshold values of predefined parameters (such as reflected wavelength values and intensities) and decide whether the diversion is regarded as an emergency.

[0069] For example, the fibers waveguides 110 may be deployed along borders or on the floor of area 400, depending on the requirements and structure of system 100. [0070] According to some embodiments of the invention, workstation 130 may enable saving the measured data and transmitting it. [0071] The data representing the reflected light may be transmitted via signal 162 to a module 170, which may be a hardware unit comprising a transceiver (not shown). [0072] According to some embodiments of the invention, data representing the reflected light may be sent via a signal 161, 162 and/or 163 to workstation 130. Workstation 130 may be adapted to execute an application that, inter alia, may determine whether light detected at detector 135 exceeds a certain threshold and/or whether the detected light corresponds to a physical stimulus that requires notifying the user.

[0073] Reference is now made to figure 3, which schematically illustrates system 100, according to some embodiments of the invention. According to these embodiments, at least one of the workstations 130 may comprise:

• a power supply 131; • at least one light source 132;

• an optical expansion unit 133;

• an interrogation module 134; and

• at least one database 201.

[0074] All components of workstation 130 may be operatively associated with one another. For instance, power source 131 may be operatively associated with light sources 132 and optical expansion unit 133 and the like.

[0075] According to some embodiments of the invention, optical expansion unit 133 may enable receiving light from light source 132 and optically route the light to a multiplicity of waveguides 110. [0076] According to some embodiments of the invention, interrogation module 134 may comprise: one or more detectors 135, a processor 136 and a notification unit 138. [0077] According to some embodiments of the invention, interrogation module 134 may be operatively associated with an application 139 (e.g. a software application 139), where processor 136 is embedded in a computerized system (E.g. a PC or any other hardware enabling to digitally process data) .Application 139 may comprise commands enable running the calculations and other aspects of the processing operations.

[0078] According to some embodiments of the invention, module 170 may be adapted to execute application 139 that, inter alia, may determine whether output light (arriving from the sensors) detected by detector 135 exceeds the predefined threshold values and/or corresponds to a physical stimulus that requires notifying the user about said stimulus. [0079] According to some embodiments of the invention, processor 136 may enable receiving data from detector 135 and retrieving data from database 201and identifying an emergency situation according to predefined rules and/or algorithms. For example, processor 136 may receive measured values (e.g. wavelength values arriving from the sensor that were detected by detector 135) from detector 135 and compare them with corresponding threshold values which are predefined and stored in database 201.

[0080] According to some embodiments of the invention, notification unit 138 may enable receiving data from processor 136 and transmitting alarming messages (e.g. text messages) to at least one predefined user's terminal (e.g. the user's mobile phone) and or displaying an alarming message on the screen of a surveillance service center and or operate a vocal alarm.

[0081] It is to be understood that module 170 may be any type of software and/or hardware that enables processing data. Accordingly, module 170 may be, for example, a server. [0082] It is to be understood that the number of sensors in each waveguide indicated throughout the specification is for exemplary purposes only, as the number of sensors in each waveguide may vary. For example, in some embodiments of the invention, one waveguide 110 may have fifteen sensors based on Bragg grating and the other waveguide 110 may have two sensors based on Bragg grating.

[0083] It is further to be understood that the number of light sources, modules 170 and workstations 130 operatively associated and adapted to waveguides 110 is not limited to the number of light sources, modules 170 and workstations 130 specified throughout the specification.

[0084] For example, in some embodiments, system 100 may include four workstations, of which three may be operatively associated to four waveguides and one to two waveguides. In some other embodiments of the invention, both ends of a waveguide may be adjusted to a single light source adapted to selectively emit light into both ends of said waveguide. Additional or alternative configurations may be possible.

[0085] According to some embodiments of the invention, workstations 130 may be adapted to detect intensity and wavelength of outputted light, which may be reflected from a sensor such as, e.g., sensor 111. Furthermore, workstation 130 may be adapted to detect and determine the type of physical stimuli applied at each sensor based on the intensity and wavelength of the light reflected from each sensor. [0086] Additionally, processor 136 may further determine whether the detected light corresponds to a physical stimulus requiring notification of a user of system 100. For example, if the detected light exceeds the predetermined threshold value, application 139 may, for example, search in database 201 for a dataset whose data matches with the data representing the detected light. In the event that a match is found, application 139 may notify a user of system 100 about the type of the physical stimulus by, for example, displaying a suitable message on display 138. [0087] According to some embodiments of the invention, any workstation in system 100 may be configured similarly to workstation 130. [0088] According to some embodiments of the invention, the notification unit 138 may enable notifying a user or a service center regarding an identifies alarming situation in which at least one of the sensors 11, 112, 113 etc. exceeds one of the predefined threshold values. The notification may be carried out through any means known in the art such as through a display screen embedded in the workstation 130, SMS messages sent to a predefined authority, siren and the like. [0089] According to some embodiments of the invention, workstation 130 may generate light and emit a first and a second portion of the generated light into waveguides 110. The first portion and the second portion of the light, hereinafter referred to as LightAi, out and Lights, out, as illustrated in figures 2-5, may comprise of a plurality of wavelengths that may be generated, e.g., as known the art. For example, a plurality of wavelengths may be generated by light source 132, as in Dense Wavelength Division Multiplexing (DWDM). According to some other embodiments of the invention, light source 132 may be adapted to tune the wavelength of LightAi, out and/or LightAi, out, e.g., as known in the art, using, for example, a distributed feedback (DFB) laser. [0090] According to some embodiments of the invention, at least some light of LightAi, out and/or LightAi, out may be reflected by the sensors in waveguide 110. The reflected light may be detected by detector 135 and may then be converted into data representing said reflected light by performing, for example, analog-to-digital (A/D) conversion, e.g., as known in the art. The data representing the reflected light may be stored in storage device 201. [0091] According to some embodiments of the invention, database 201 may store a plurality threshold values and other related data, such as, for instance, patterns of light (e.g. normalized 2D functions representing the pattern of the cross sectional faces of light beams) and a corresponding physical stimulus such as, for example, a human gait, the closing of a door, and the like.

[0092] According to some embodiments of the invention, application 139 may include an algorithm enabling to determine the location where the physical stimulus occurred based on information about the locations of the sensors from which the light has been reflected. During the installation of said sensors, the frequency of the light reflected from each sensor may be mapped with the location of each sensor. Consequently, each sensor may be located by, e.g., application 139.

[0093] Reference is now made to Figure 4; which schematically illustrates system 100 laid out in area 400, wherein communication between workstations 130 may be interrupted (indicated by a broken line), according to an embodiment of the invention;

[0094] According to some embodiments of the invention, only one light source such as, e.g., light source 132 may emit light into at least one of waveguides 110, as long as all sensors 111,

112 and 113 and/or 121, 122 and 123 of waveguides 110 reflect light back to workstation 130 and/or as long as workstation 130 detects the light emitted from workstation 130 during a predetermined time-interval. Due to an interruption in at least one of waveguides 110, one of the workstations 130 may not detect the light emitted by light source 132 into waveguide 110. In addition, due to an interruption in waveguide 110, not all sensors may reflect light back to workstation 130. Accordingly, an interruption in waveguide 110 may be detected by, e.g., workstation 130.

[0095] According to some other embodiments of the invention, the light source 132 of a second workstation 130 may be set into operation after light source 132 of a first workstation 130 does not emit light into waveguide 110 due to, for example, a power failure in power supply 131. Similarly, workstation 130 may be set into operation after the light source of said workstation 130 does not emit light into waveguide 110. Accordingly, workstation 130 may be used as a backup for workstation 130 and vice versa. For these purposes, at least some of workstations 130 of system 100 may be operatively associated, enabling to communicated through any communication means, including by sensing whether light arrives from inlets of the waveguides 110. [0096] For example, according to some embodiments of the invention, an application such as application 139 may be adapted to determine whether all sensors are suitably connected to workstation 130 by checking whether all sensors of waveguide 110 reflect light or not. Application 139 may, for example, compare the number of detected signals with the number of sensors in waveguide 110. If the number of signals detected from waveguide 110 matches the number of sensors stored in storage device 201, then application 139 may determine that all of the sensors in waveguides 110 may be suitably connected to workstation 130. Other methods for determining whether all sensors are suitably connected to workstation 130 may be used. [0097] For example, according to some embodiments of the invention, application 139 may determine whether detector 135 detects all wavelengths within a certain predetermined time- interval. [0098] For example, if sensors 111, 112 and 113 are suitably connected to workstation 130, detector 135 should detect light having substantially wavelengths λll5 λχ2 and λ^. In case detector 135 does not detect, for example, light having wavelength λ χ2 during the predetermined time-interval, application 139 may determine that a first waveguide 110 is interrupted from sensor 111 onwards. Similarly, in case application 139 determines that, for example, light having wavelength λ22 is not reflected within a certain time-interval, application 139 may, as a result, determine that second waveguide 110 is interrupted from sensor 121 onwards. [0099] It is to be understood that applications in other computing modules may determine which sensors reflect light back to workstation 130 and which do not. For example, workstation 130 may send to module 170 data representing the light detected at detector 135. The application of module 170 may determine, based on said data, which sensors reflect light back to workstation 130 and which do not.

[00100] By emitting light into a waveguide from one end only, it may be indeterminable by, e.g., application 139, whether waveguides 110 are being interrupted at a single location, or whether an entire portion of one of the waveguides 110 is being interrupted. It may, for example, be possible that waveguide 110 is being interrupted between sensor 111 and sensor 113, or between sensor 111 and workstation 130. Similarly, it may be possible that another waveguide 110 is being interrupted between sensor 121 and 123, or between sensor 121 and another workstation 130. The larger the portion of waveguide 110 that is being interrupted between workstation 130, the higher the risk of, e.g., intrusion into area 400 remaining undetected. It is therefore necessary to delimit, as much as possible, the location of interruptions in waveguides 110. In order to delimit the location(s) of interruption(s) in at least one of the waveguides 110, a light source, which may be included in workstation 130, may start to emit light into waveguide 110 upon detection of an interruption in waveguide 110. Emitting light into waveguide 110 from the other end of said waveguide 110, may enable, e.g., application 139, to determine which sensors reflect light back to the detector 135 of workstation 130 and which do(es) not.

[00101] According to some embodiments of the invention, light source 132 may not emit light into the first end of waveguide 110, while light is emitted into waveguide 110 from the second end, in order to avoid interference between the light emitted into the first and second ends. [00102] According to some embodiments of the invention, information about the sensors that do no reflect light back to workstation 130 may be sent to module 170 via signal 163. [00103] Furthermore, information about the sensors that do not reflect light back to workstation 130 may also be sent to module 170. Therefore, according to the example of Figure 4, an application in module 170 may determine that the first waveguide 110 is being interrupted between sensor 111 and 112, and that the second waveguide 110 is being interrupted between sensor 121 and sensor 122, as well as between sensor 122 and sensor 123.

[00104] According to some other embodiments of the invention, workstation 130 may send to data representing information about the sensors that do not reflect light to the other workstation 130 workstation 130 via signal 161. Application 139 may then determine the location(s) of interruption(s) in one of the waveguides 110. [00105] According to some alternative embodiments of the invention, workstation 130 may send to the second workstation 130 data representing information about the sensors that do not reflect light to the first workstation 130 via signal 161. The application in the second workstation 130 may then determine the location(s) of interruption(s) in waveguide 110. [00106] Reference is now made to Figure 5, which schematically illustrates system 100 laid out in area 400, wherein communication between workstations 130 is interrupted at other locations, according to an embodiment of the invention;

[00107] According to some embodiments of the invention, waveguide 110 may be interrupted between the second workstation 130 and sensor 113. The interruption between the light source of workstation 130 and sensor 113 may remain undetected in the event light is emitted only from light source 132. In order to avoid a situation in which an interruption between the light source and sensor 113 remains undetected, the light source of workstation 130 may replace light source 132 in emitting light into waveguide 110 at predetermined instances. For example, light source

132 and the light source of workstation 130 may emit, alternately every 2 seconds, light into waveguide 110.

[00108] Is to be understood that the terms "interruption", "disruption", "disturbance" and variations thereof relate to any condition that may disrupt communication between workstations

130. Such a condition may be hardware and/or software related.

[00109] Reference is now made to Figure 6, which is a flowchart of a method of monitoring area 400 using sensors based on Bragg grating, according to an embodiment of the invention.

[00110] As indicated by box 1510, the method may include, for example, the step of emitting light into a waveguide. For example, light source 132 may emit light into waveguide 110.

[00111] As indicated by box 1520, the method may include, for example, the step of determining whether a physical stimulus is detected. For example, application 139 may determine whether a physical stimulus is detected according to the threshold value of the light reflected from a sensor such as, e.g., sensor 111. [00112] As indicated by box 1525, in case no physical stimulus has been detected, the method may include, for example, the step of continuing to emit light into a waveguide such as, e.g., waveguide 110.

[00113] As indicated by box 1530, the method may include, if a physical stimulus has been detected, the step of classifying the detected physical stimulus. This may be accomplished, for example, by application 139, which may compare between datasets stored in storage device 201 and the data representing the reflected light, i.e., the physical stimulus.

[00114] As indicated by box 1535, the method may include, for example, the step of notifying the user about the physical stimulus. For example, application 139 may display a suitable message on display 138, trigger an alarm in case an intrusion was detected, and the like. [00115] As indicated by box 1540, the method may include, for example, the step of checking whether all sensors reflect light. For example, application 139 may determine whether all sensors reflect light back to workstation 130.

[00116] In case all sensors reflect light back to, e.g., workstation 130, the method may include continuing emitting light as indicated by box 1510. [00117] As indicated by box 1560, in case not all sensors reflect light back to, e.g., workstation 130, meaning if at least one of the sensors is identified as failing to reflect a predefined threshold of light intensity an emitting of light from the other end of the waveguide is carried out to verify whether a physical stimuli is actually applied upon the sensor.

[00118] the method may include, for example, the step of emitting light into the waveguide from the other end. For example, if one of sensors 111, 112 and 113 does not reflect light back to workstation 130, the light source of the other second workstation 130 may start to emit light into the second end of the waveguide 110.

[00119] According to some embodiments of the invention, light source 132 may stop emitting light as soon as a second light source 132 of a second workstation 130 is actuated.

[00120] As indicated by box 1570, the method may include, for example, the step of determining which sensors do not reflect light back to detector 135 and to the detector of workstation 130.

[00121] Figure 7 depicts a graph 70 of amplitude as a function of time of light reflected from a sensor implemented by Bragg grating, said graph 70 representing a knock on a surface, according to an embodiment of the invention. [00122] Figure 8 depicts a graph 80 of power as a function of normalized frequency representing the knock, according to an embodiment of the invention.

[00123] Figure 9 depicts a graph 90 of signal amplitude as a function of time of light reflected from the sensor implemented by Bragg grating, said graph 90 representing a series of knocks on the surface, according to an embodiment of the invention. [00124] Figure 10 depicts a graph 91 of power as a function of normalized frequency, said graph 91 representing the series of knocks, according to an embodiment of the invention.

[00125] Figure 11 depicts a graph 92 of signal amplitude as a function of time of light reflected from the sensor implemented by Bragg gratings, said graph 92 representing a person's gait and noise, according to an embodiment of the invention. [00126] Figure 12 depicts a graph 93 of signal amplitude as a function of time of light reflected from the sensor implemented by Bragg gratings, said graph 93 representing the opening of a door, a person's gait and the closing of the door, according to an embodiment of the invention.

[00127] Figure 13 depicts a graph 94 of signal amplitude as a function of time, said graph 94 representing the opening of the door of Figure 7, according to an embodiment of the invention. [00128] Figure 14 depicts a graph 95 of signal power as a function of normalized frequency, said graph 95 representing the opening of the door of Figure 13, according to an embodiment of the invention.

[00129] Reference is now made to Figure 15, which schematically illustrates a graph 96 depicting stress as a function of time as measured by three corresponding sensors implemented by Bragg gratings in a waveguide 110, according to an embodiment of the invention. The graph 96 shows the stress curves 51, 52 and 53 of three different sensors 111, 112 and 113 located at three different locations in area 400, where only the second sensor 112 corresponding to curve 52 senses a stress applied to it. [00130] It is to be understood that some embodiments of the invention may be implemented, for example, using a machine-readable medium or article that may store an instruction or a set of instructions that, if executed by a machine, cause the machine to perform a method or operations or both in accordance with embodiments of the invention. Such a machine may include, for example, any suitable processing platform, computing platform, computing device, processing device, computing system, processing system, computer, processor, or the like, and may be implemented using any suitable combination of hardware or software or both. The machine- readable medium or article may include but is not limited to any suitable type of memory unit, memory device, memory article, memory medium, storage article, storage device, storage medium or storage unit such as, for example, memory, removable or non-removable media, erasable or non-erasable media, writeable or re-writeable media, digital or analog media, an optical disk, a hard disk, a floppy disk, a Compact Disk Recordable (CD-R), a Compact Disk Read Only Memory (CD-ROM), a Compact Disk Rewriteable (CD-RW), magnetic media, various types of Digital Versatile Disks (DVDs), a tape, a cassette, or the like. The instructions may include any suitable type of code, for example, an executable code, a compiled code, a dynamic code, a static code, interpreted code, a source code or the like, and may be implemented using any suitable high-level, low-level, object-oriented, visual, compiled or interpreted programming language. Such a compiled or interpreted programming language may be, for example, C, C++, Java, Pascal, MATLAB, BASIC, Cobol, Fortran, assembly language, machine code and the like. [00131] While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the embodiments. Those skilled in the art will envision other possible variations, modifications, and programs that are also within the scope of the invention. Accordingly, the scope of the invention should not be limited by what has thus far been described, but by the appended claims and their legal equivalents. Therefore, it is to be understood that alternatives, modifications, and variations of the present invention are to be construed as being within the scope and spirit of the appended claims.

Claims

What is claimed is:
1. A system for monitoring an area, said system comprising at least one waveguide having at least one Bragg grating sensor integrated in said at least one waveguide, wherein said sensors enable sensing at least one type of physical stimuli by changing at least one feature of the light they reflect, said system comprising: said at least one waveguide; a plurality of light sources adapted to emit light into both ends of said waveguide; and at least one detector adjusted to detect light at each end of said waveguide, wherein said light sources and detectors are adapted to be set selectively into operation according to the light detected at said detectors.
2. The system of claim 1 wherein said at least one waveguide is an optical fiber, wherein each said Bragg grating sensor is made of a set of filtering surfaces enabling to reflect light of a narrow predefined wavelength band with a predefined wavelength peak.
3. The system of claim 2 wherein said at least one Bragg grating sensor is adapted to alter the intensity of light in said waveguide as a result of physical stimuli applied upon the waveguide where said sensor is located.
4. The system of claim 2 wherein each waveguide comprises a multiplicity of Bragg grating sensors located in different locations along each said waveguide, wherein each said sensor enables reflecting a different wavelength, thereby enabling to identify the sensor by detecting the reflected wavelength of each sensor.
5. The system of claim 2 further comprising a plurality of workstations each comprising a power source, at least one light source and an interrogation module comprising at least one detector, wherein each said workstation is connected to at least one of the waveguides of said system and wherein said light source enables emitting a predefined light beam into one end of said waveguide and said detector enables detecting light outputted from that end of the waveguide that is connected to said workstation.
6. The system of claim 5 wherein said detector enables detecting at least one of: the wavelength of the outputted light or the intensity of outputted light.
7. The system of claim 6 wherein said light source is a laser enabling to input coherent light within a predefined wavelength band range.
8. The system of claim 5 wherein once light emission into one end of the waveguide arriving from the light source of a first workstation of the system is interrupted light is emitted from the light source of a second workstation into the other end of said waveguide.
9. The system of claim 5 wherein said workstation further comprises an optical expansion unit enabling to receive light from the light source of said workstation and optically route the light to a multiplicity of waveguides.
10. The system of claim 5, wherein said interrogation module further comprises a processor and at least one database, wherein said processor enables receiving data from the detector and from said database and identifying a physical stimuli according to predefined rules.
11. The system 10 wherein said processor enables receiving detected values from the detector and retrieving corresponding threshold values from the database and comparing said corresponding values, wherein an exceeding in at least one of the threshold values is defined as an emergency.
12. The system of claim 10, wherein said interrogation module further comprises a notification unit enabling to receive data from said processor and notify at least one user regarding an identified stimuli.
13. The system of claim 12, wherein said notification unit enables transmitting alarming messages to at least one of: predefined user's terminal or a predefined surveillance service center.
14. The system of claim 10, wherein said workstation further comprises an application operatively associated with said processor, light source and said detector, wherein said application comprises commands enabling running calculations, decisions and other aspects of the processing operations that enable identifying an emergency, wherein said processor is embedded in hardware of a computerized system.
15. A method for monitoring a predefined area and identifying a physical stimuli applied on at least one waveguide using a system comprising at least one waveguide having a plurality of Bragg grating sensors enabling to reflect light upon receiving it and a plurality of light sources and detectors, said method comprising: emitting input light into said at least one waveguide; detecting physical stimuli applied on at least one of the sensors; and checking whether all sensors reflect light; and emitting light from another end of said waveguide; wherein said emitting of light from another end of the waveguide is carried out once at least one of the sensors is identified as failing to reflect a predefined threshold of light intensity.
16. The method of claim 15 wherein said waveguide is an optical fiber, and wherein said emitting of light is carried out by said light source and said detector carries out said checking of the reflected light from1 the sensors.
17. The method of claim 15 , wherein once light is emitted from the other end of the waveguide the reflection of the sensors is checked and if at least one of said sensors fail to reflect light an identification of the physical stimuli type is carried out.
18. The method of claim 17 further comprising notifying at least one of: a user's terminal or a predefined service center regarding identified stimuli, once said physical stimuli type is identified.
19. The method of claim 17, wherein said identification of the physical stimuli type is carried out by identifying which of the sensors does fail to reflect light.
20. The method of claim 19, wherein each Bragg grating sensor reflects a different wavelength thereby enables identifying the sensor by identifying the wavelength of the reflected light.
PCT/IL2008/000835 2007-06-20 2008-06-19 System and method based on waveguides for the protection of sites WO2008155769A3 (en)

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