KR20000022321A - Optical sensor system utilizing bragg grating sensors - Google Patents

Abstract

PURPOSE: An optical sensor system is provided for the optical fiber sensing system using the fiber Bragg grating, which is measured the time division measurement machine, and for a number of a sensor element between 50 and 400 of FBG sensor without additional filter and complicated rate measurement device. CONSTITUTION: The system has a plurality of reflect Bragg gating. Each gating includes the function of sensor element, and has the only position and the only wavelength ingredient reflecting incident light. An optical system for detecting perturbations indicative of the performance of the piece of equipment being monitored is disclosed. The optical system comprises sensors (12), each of which uses Bragg gratings (12A - 12N), induced therein and wherein the Bragg gratings (12A - 12N) are arranged into a preselected distribution and each Bragg grating returns, when subjected to incident light, a narrowbeam signal (22, 24, 26) identified by a predetermined wavelength. The optical system utilizes at least one interferometer (56) whose operation is interlinked with optical multiplexing techniques, such as differentiate across multiplying and time division multiplexing.

Description

Optical Sensor System Using Bragg Grating Sensor

Sensor systems are known to monitor acoustic emissions or changes in electric or magnetic fields generated by or appearing from equipment, materials, structures and structural components under test. Monitoring of the system is used as an analytical method for evaluating the performance of the monitored device. The sensor system typically utilizes a number of sensors required to install complex mechanical components such as transmissions. Optical fiber sensors responsive to optical multiplexing techniques are commonly used in that they provide a means of using a relatively large number of sensors installed in a structure. Sensor systems for multipoint sensing applications are described in Optics Lett 14, p. 823, 1989, entitled "Generation of Bragg Gratings in Optical Fibers by Transverse Holographic Methods," entitled G. Meltz, w.w. Morey, and W.H. The fiber Bragg grating (FBG) sensor disclosed in Glenn's technical paper is used, which is incorporated herein by reference. The popularity of FBG sensors has been improving over the years due to their inherent characteristics and wavelength coding operation. A safety system using Bragg gratings is disclosed in US Pat. No. 5,351,324, filed on September 27, 1994, which is incorporated herein by reference.

The FBG sensor is particularly suitable for similar distribution sensing, in which a large number of Bragg gratings can be derived or recorded in the length of the fiber, and Proc. OFS, 90, p. 285, Sydeney, Australia, Dec. W.w. under the term "Distributed Fiber Grating Sensor" published in 1990. This is because they are interlocked by wavelength division multiplexing or time division multiplexing in the manner described in detail in Morey's technical paper, which is also referred to herein. FBG sensors have the most suitable utilization in the area of improved mixture analysis or "smart structure" analysis because they can be embedded in the material to provide a real-time assessment of the load induced stresses therein. The current use of FBG sensors for sensing the utilization of selected equipment, such as machinery, is described in detail in connection with the prior art device 10 of FIG.

The device 10 utilizes a Bragg grating sensor 12 consisting of a plurality of reflective Bragg gratings 12A, 12B, 12C ... 12N, which grating functions as a sensing element of the sensor 10, each of which is SPIE vol, 1586, paper # 22, Boston, Sept. Introduced in 1991, W.W. The "multiplexed fiber Bragg grating sensor" by Morey, J. R. Dunphy and G. Meltz is interrogated by the wavelength division multiplexing technique disclosed in the technical paper. Sensor 12 is referred to herein as an FBG sensor. A plurality of reflective Bragg gratings 12A, 12B, 12C ... 12N are guided or recorded in the sensor 12 in a manner known in the art, and each grating serving as a sensing element is the equipment that the device 10 monitors. It has a unique position along a portion of and has a unique wavelength component that reflects incident light in the manner disclosed in detail in US Pat. No. 5,351,324. Each FBG sensor 12 is located on the equipment to be monitored or in a device of molding not shown.

The circuit arrangement 10 of FIG. 1 uses a broadband source 14 which serves as a light source for providing the input light indicated by the directional arrow 16, the input light being the Y-axis and the input light indicated as I (current). It is defined as the input spectrum 18 shown as having the X axis indicated as λ representing the wavelength of (16). The input light 16 is applied to the coupler 20 and propagates as incident light intercepting each of the sensing elements 12A, 12B, 12C .... 12N, each of which senses the incident light in turn and is directed. Shown by arrows 22, 24, 26 ... 28, respectively. The reflected lights 22, 24, 26 ... 28 are shown in FIG. 1 as having respective spectra 22A, 24A, 26A ... 28A, the spectra being reflected Bragg gratings 12A, 12B, 12C. Waveforms having the central wavelength components lambda ₁ , lambda ₂ , lambda ₃ , ... lambda _N respectively corresponding to the wavelengths of light reflected by .12N).

Broadband source 14 is known in the art as a type selected from the group having an edge emitting LED (ELED), a superluminescent diode, a superluminescent fiber source and a fiber Erbium source. The broadband source 14 has a typical operating wavelength of about 1.3 micrometers (μm) and a bandwidth of about 50 nanometers (nm). In the case of this broadband source 14, the plurality of Bragg gratings 12A, 12B, 12C ... 12N are physically spaced apart from each other by a predetermined distance X (not shown) along the sensor 12, each of which is It has unique wavelength components spaced apart from one nanometer to one nanometer or more. The incident light selected from the Bragg gratings 12A, 12B, 12C ... 12N has its own wavelength component of each Bragg grating, and the distance X is the sensor element 12A, 12B, 12C ... 12N used. And the total distance to the monitored equipment or material that the sensor 12 should cover. When selecting a broadband source 14 having an operating wavelength of 1.3 μm, a bandwidth of 50 nm, and a sensor 12 having Bragg gratings separated from each other by a wavelength component of 1 nm, fifty, fifty reflective Bragg gratings have wavelength separation (1 nm). As the device of FIG. 1 determined by the bandwidth divided by 50 nm.

Each of the plurality of Bragg gratings 12A, 12B, 12C ... 12N receives the incident light 16 and returns the narrowbeam wavelength component, all within the bandwidth of the broadband source 14. In particular, as shown in FIG. 1, the incident light 16 causes the Bragg gratings 12A, 12B, 12C ... 12N to reflect light 22, 24 having response characteristics 22A, 24A, 26A ... 28A, respectively. , 26 ... 28). Referring to Fig. 1, the response characteristics 22A, 24A, 26A, ... 28A represent the positions of wavelengths λ ₁ , λ ₂ , λ ₃ , ... λ _N , respectively, all of which operate the broadband source 14. Λ or less indicating a wavelength. In operation, as described in detail, the measurement induction (i.e., acoustic induction) perturbation of each particular grating, such as Bragg gratings 12A, 12B, 12C ... 12N, in the sensor 12 is caused by a particular element. Change the returned wavelength. For example, the Bragg grating 12A, which operates in particular as a sensing element of the sensor 12, changes the inherent wavelength lambda ₁ component of the Bragg grating 12A reflecting the incident light 16 when subjected to acoustic force perturbation. The reflected light 22 is changed in proportion to the intrinsic wavelength λ ₁ , and the reflected light 22 has a changed wavelength component that is proportional to and represents the perturbation sensed by the sensing element 12A. The modified wavelength component outputs the coupler 20 on the signal path 30 by monitoring the wavelength shift detected by the wavelength shift decoder 32 associated with each Bragg grating 12A, 12B, 12C ... 12N. Is detected. This wavelength shift represents the magnitude of the perturbation that sensor 12 receives.

The prior art shown in FIG. 1, which detects the wavelength at each Bragg grating 12A, 12B, 12C ... 2N, is a channel by signal for the wavelength of the Bragg grating return signal 22,24, 26 ... 28. Based on channel-by-channel determination, described in detail with reference to FIG.

As shown in FIG. 2, the wavelength moving decoder 32 receives a signal through the signal path 30 having a signal having wavelength components lambda ₁ -λ _N respectively associated with the Bragg gratings 12A .... 12N. Split Multiplexer (WDM) splitter (demux) 32A. The wavelength division multiplexer 32A applies the wavelength components λ ₁ -λ _N to the respective wavelength components λ ₁ , λ ₂ , λ ₃ ... provided on the terminals 36A, 36B, 36C ... 36N, respectively. Separated by λ _N , the terminals are connected to optical filters 38A, 38B, 38C ... 38N, respectively. Optical filters 38A, 38B, 38C ... 38N are at their bends and λ ₁ -λ _N A characteristic response 42 having a cutoff frequency λ _j corresponding to an element j contained in the band defined by < RTI ID ₌ 0.0 > is < / RTI > The element j is the pulse waveform 44 defined by the Y axis representing the width T and the X axis representing the wavelength λ having the maximum value defined by the operating wavelength λ of the broadband source 14. The optical filters 38A, 38B, 38C ... 38N require a set of filter characteristics to match the Bragg wavelength range of the sensing elements 12A, 12B, 12C ... 12N, which matching is relatively difficult and practical. Expensive to Furthermore, due to known exceptions such as bending loss (sensor bending), source variation (power variation), as shown in FIG. 3 to compensate for possible variations in the optical power level at the output of the broadband source 14 of FIG. It needs to be realized.

3 is Photonic Technol referred to herein. Lett., 4, p. Although the wavelength division multiplexer (WDM) splitter of FIG. 2 is disclosed showing the ratiometric method disclosed in detail in the technical literature of SM Melle, K. Liu and RM Measures published in 516-518, 1992, the optical filter 38A ... 38N). The multiplexer 32A has a plurality of outputs of [lambda] ₁ , [lambda] ₂ , [lambda] ₃ ... [lambda] _N , each of which has an additional element coupled thereto. For example, λ ₁ is the terminal 36A identified as having the optical coupler 46A and the wavelength λ ₁ flowing therefrom, the detector 48 coupled to the output of the coupler 46A and the output λ of the terminal 36A. A detector 50 for receiving ₁ ). The detector 48 generates an output signal of I ₁ ^ref , the detector 50 generates an output of I, and the outputs of these detectors are connected to the ratio actuating device 52. When the ratio actuating device 52 is operated, an output signal defined as quantity I ₁ / (I ₁ ^ref ) is generated, which does not have the drawback shown in FIG. 2, but is a disadvantage due to additional factors. You have no choice but to have Therefore, there is a need for a means different from the circuit arrangement of FIGS. 2 and 3 so that the optical sensor system can be realized without the drawbacks and disadvantages as described in FIGS.

The present invention relates to a sensor system, and more particularly to a sensor system using a Bragg grating sensing element for the measurement of a weak time-varying measurement system, such as acoustic pressure, vibration and magnetic field.

1 is a schematic diagram of a device of the prior art,

2 and 3 are schematic diagrams relating to the prior art device of FIG. 1 for the detection of perturbation associated with the monitored equipment;

4 is a schematic diagram of one embodiment of the present invention;

5, 6 and 7 (including FIGS. 7A and 7B) illustrate various embodiments of the sensor of the present invention in connection with acoustic radiation detection;

8 (A), 8 (B), 8 (C) and 8 (D) each show a sensor for measuring perturbation using magnetic field or field detection techniques,

9 shows another embodiment of the invention similar to the embodiment of FIG. 4;

10 is a view showing another embodiment of the present invention;

11 is a schematic diagram of another embodiment of the present invention similar to the embodiment of FIG.

Thus, the present invention uses a sensor with a fiber Bragg grating that functions as a sensing element to monitor a portion of the device but without adding a filter mechanism and without using a relatively complex rate measurement device. It is a first object to provide an optical sensor system capable of providing a plurality of sensor elements,

Another object of the present invention is to provide an optical fiber sensing system using a fiber Bragg grating that is used to measure acoustic pressure vibration and time varying measuring systems such as electromagnetic fields.

The present invention relates to an optical system using a fiber Bragg grating that monitors and measures the perturbation that a piece of equipment receives.

The system includes an optical sensor, a light source, an unbalanced interferometer, means for generating a modulated signal, a phase modulator and a demodulator. The sensor is located along the piece of equipment and has a plurality of reflective Bragg gratings derived from the sensor, each of which serves as a sensor element. Each grating has a unique location along the portion of the device and has a unique wavelength component that reflects incident light. Each unique wavelength component of the sensor changes when subjected to perturbation. The light source provides input light to the sensor at all wavelength components of the Bragg grating to reflect incident light from each of the gratings. An unbalanced interferometer receives reflected incident light from each of the gratings, has first and second arms, and generates an interferometer signal for each of the wavelength components of the incident light reflected by each of the Bragg gratings. The phase modulator receives the modulated signal and is located in one of the arms of the unbalanced interferometer. The phase modulator modulates each interferometer signal and generates an output signal indicative of the amount of each of the intrinsic wavelength components of the changed reflected incident light upon receiving and modulating the modulated interferometer signal.

The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments with reference to the accompanying drawings. Like reference numerals designate the same or corresponding parts throughout the drawings.

Before describing the drawings, it is pointed out that the optical sensor system of the present invention detects perturbations indicative of the performance of the monitored equipment. The optical sensing system includes one or more optical fibers having Bragg gratings fitted therein arranged in a preselected distribution, each Bragg grating functioning as a sensing element and identified by a predetermined wavelength when excited by incident light. The narrowband signal is returned. Perturbations occurring in the monitored system are detected by an unbalanced interferometer that cooperates with optical response devices interlocked by multiplexing techniques, including differential-cross-multiply (sine / cosine function) and time division techniques. do.

An embodiment of the present invention is shown in FIG. 4, which includes the elements described above for the prior art device 10 of FIGS. 1,2 and 3, but in addition each Bragg grating 12A, 12B, 12C ... 12N. Inherent wavelength components λ ₁ , λ ₂ , λ ₃ . and an optical coupler 54 for receiving reflected light 22, 24, 26 ... 28, each comprising λ _N. The optical coupler 54 is at the input of an unbalanced interferometer 56 with arms 58 and 60, one of the arms, for example arm 58, having a phase modulator 62, the other being a compensation or delay. With a coil 64 acting as a coil, the length of the optical path difference (described) between the two arms 58, 60 is about (1) centimeters. The unbalanced interferometer 56 has a coupler 66 at its output end.

The unbalanced interferometer 56 is of the Mac Zehnder type, each of the Bragg gratings 12A, 12B, 12C ... 12N contained in the returned incident light 22, 24, 26 ... 28, respectively. Each wavelength component λ ₁ . Generate an interferometer signal for λ _N. However, other interferometer configurations, such as the Michelson interferometer configuration, can be used instead of the Macgender configuration. The unbalanced interferometer 56 has an optical path difference, or OPD, between the arms 58 and 60. The optical path difference OPD is equal to nd, where d is the length unbalance between the arms 58 and 60 and n is the effective propagation index of the core 64. The unbalanced interferometer 56 is of the type described in more detail in US Pat. No. 5,227,857, registered July 13, 1993, which is incorporated herein by reference. Operation of devices such as an unbalanced interferometer 56 that also produces an interferometer signal is described in Electronics Letters, 28, p. 236-238, 1992, published in AD Kersey, TA Berkoff and wwMorey, in detail. The form of the generated interferometer signal is as shown in Equation (1) below.

(One)

I (λ _j ) = A _j [1 + kcos [Ψ _j (λ _j ) + Φ]]

Where Ψ _j (λ _j ) is 2πnd / λ _j , A _j is the system loss depending on the input intensity and profile of the incident light 16, and the lattice reflectivity at λ _j ; λ _j is the Bragg grating 12A ... 12N Is the wavelength of the return light from the j-th grating sensor (sensor signal) included as, and Φ is the random bias phase offset. All interferometer signals generated by the unbalanced interferometer 56 pass through the output coupler 66 and onto the wavelength division multiplexer (WDM) splitter 32A as previously described with reference to FIGS. 1,2,3. See Proc. OFC'92, p. 123, (OSA), 1992 "Spectrometer on a Chip: Monolithic WDM Components" is disclosed in the technical paper by JBD Soole et al. The wavelength division multiplexing performed by the wavelength division multiplexer 32A is applied to the Bragg gratings 12A, 12B, 12C ... 12N (λ ₁ , λ ₂ ,) of the sensor 12 located on the equipment monitored by the apparatus of FIG. 4. It is desirable to match in the nominal wavelength response to the range of center wavelengths of [lambda] ₃ ... [lambda] _N ).

The wavelength spacing between Bragg gratings 12A, 12B, 12C ... 12N depends on the dynamic range needed to account for the possible residual quasi-static strain and temperature shift at the point where the Bragg grating is located. Facilities that allow for effective large wavelength ranges for one or more of the sensors of FIG. 4 are important when static strain sensing is involved in the sensing system of the present invention. The wavelength range takes into account the wavelength spacing between the intrinsic wavelengths of each of the Bragg gratings 12A, 12B, 12C ... 12N, each of which serves as a sensing element for the entire sensor 12. Typically, the Bragg wavelength travels approximately 1 nm per 1,000 microstrain meters in the environment of broadband source 14 with an operating wavelength of 1,3 μm. For example, when the Bragg grating 12A having an intrinsic light component having a wavelength of 1.3 μm is received by the Bragg grating 12A having a unique wavelength component of λ ₁ and receives a strain of 1,000 micro strains, the Bragg grating 12A has a wavelength. Reflects incident light having a wavelength changed by 1 nm in proportion to λ ₁ , and its component of reflected light is present in the returned optical signal 22.

When utilizing the sensing system of the present invention for measuring acoustic radiation vibration sensing, the sensor 12, in particular Bragg gratings 12A, 12B, 12C ... 12N, can be designed to weakly couple static strain, A dense spacing of Bragg grating wavelengths in the grating, i. Another factor influencing the wavelength spacing between the Bragg gratings 12A, 12B, 12C ... 12N is temperature. The Bragg wavelength of a typical fiber grating varies with temperature at a rate of 10 ⁵ to 1 part per degree Celsius. 100 ° C. in the FBG sensor 12 where 1.3 nm spacing between Bragg gratings 12A, 12B, 12C ... 12N is allowed when operating with a broadband source 14 having an operating wavelength of 1,3 μm. The large temperature difference is allowed by using a wide wavelength gap between the Bragg gratings by causing a temperature change of. The sensitivity of the wavelengths of conventional unbalanced interferometers, such as unbalanced interferometer 56, results in different interference phase shifts for each wavelength component at the output of wavelength division multiplexer 32A.

In one embodiment of measuring acoustic radiation without considering the advantages of the present invention, each received processed by acoustically induced modulation at Bragg wavelengths of the respective Bragg gratings 12A, 12B, 12C ... 12N. Modulation in the phase shift of the interferometer output signal generated by the unbalanced interferometer 56 for the wavelength component is derived. This phase modulation component is represented by the following formula (2).

(2)

Where Δε _j is the acoustically induced dynamic strain received by the jth grating and ζ is the normalized strain versus wavelength isosceles response of the associated Bragg grating.

In order to monitor and accommodate the unwanted phase shift of the signal represented by equation (2), the signal generated by the interferometer 56 is placed on one arm such as the arm 58 of the unbalanced interferometer 56. Demodulated using a phase modulator 62 such as a latcher, the phase modulator 62 receives a modulated signal generated by a modulation generator 68. Demodulation techniques used in the interferometer of the apparatus of FIG. 4 are described in IEEE J, Ouantum Electron., QE-18, p. A. Dandridge, A.B., entitled "Homodyne Demodulation Technology for Optical Fiber Sensors Using Phase-Generated Carriers," published in 1647, 1982. Tveten and T.G. Differential cross-multiplication (sign / cosine) method disclosed in Giallorenzei's technical paper, Electron. Lett., 18, p. 1081, 1982, entitled "Pseudo Heterodyne Detection Technique for Optical Interferometers," under D.A. Jackson, A.D. Synthetic heterodyne detection technique and known phase tracking circuit disclosed in the technical papers of Kersey and M. Corke.

Figure 4 shows a differential cross-multiply (DCM) demodulator consisting of a wavelength division multiplexer (WDM) 32A and detectors 70A, 70B ... 70N, each detector comprising its sine and cosine components, its output signal. Is passed to the sine-cosine processor 72 via signal paths 74A, 74B ... 74N, respectively. Sine-cosine processor 72 receives the modulated signal generated by modulation generator 68 via signal path 76, and detectors 70A, 70B ... 70N are of the type disclosed in US Pat. No. 5,227,857. The sine-cosine detector 72 is of the type disclosed in the US patent for signal processor 55.

The interference demodulator of FIG. 4, consisting of an unbalanced interferometer 56, a wavelength division multiplexer 32A, detectors 70A, 70B ... 70N, and a processor 72, has a typical range of approximately 1-10 μrad / Hz in the acoustic range. With a phase resolution, small vibrations of Bragg wavelengths can be detected. In the practice of the present invention, it can be expected that acoustically induced movement at the Bragg wavelength of the sensor elements 12A, 12B, 12C ... 12N as small as ¹⁰ to 1 part can be detected.

FIG. 5 is a cross-sectional view of an acoustic sensor having a preselected Bragg grating 84 as a fiber Bragg grating (FBG) acoustic sensor having an optical fiber 82 for directing light, or embedded or embedded therein. The Bragg gratings 84 correspond to Bragg gratings 12A, 12B, 12C ... 12N, each of which functions as the sensing elements disclosed in FIGS. 9-11 and 1 and 4 described below.

The FBG sensor 80 directly responds to the acoustic system and is located directly in an acoustic medium such as air or liquid, and its sensitivity is directly determined by the strain optical coefficient of the fiber. The strain-optical coefficients of such optical fibers are known and are disclosed in Chapter 10 under the text “optical fiber sensor” published in E. UDD Editor, Wiley, 1992, which is incorporated herein by reference. The FBG acoustic sensor 80 has an elastomeric material, i.e., a fiber coating 86 that improves the sensing sensitivity of the sensor 80, since the material has a high Young module and a low bulk module (high compressibility). The above-mentioned elastomeric material increases the improvement of the free field response of the FBG sensor 80 by 30 dB or more, and the sensing sensitivity of the sensor is in the range of about 100 db for 1 μPa / Hz. It becomes The sensor 80 is suitably located in some equipment filled with oil as found in the power distribution equipment. Direct coupling provided by the sensor 80 of the acoustic signal through the medium of the fiber coating 86 provides a point-by-point map of acoustic radiation within the equipment to be monitored. Another sensor that responds to acoustic radiation or vibration is described with reference to FIG. 6.

FIG. 6 shows a diaphragm sensor 88 with an optical fiber 82 having Bragg gratings 84 secured to the flexible diaphragm 90 by suitable means not shown and introduced therein, such as adhesive. The response of the diaphragm sensor 88 is determined by the deflection response of the diaphragm element 90 and is not determined by the fiber coating properties such as the elastomeric material 86 of FIG. The diaphragm sensor 88 has improved sensing sensitivity compared to the sensor 88 of FIG. 5, but is not pressure compensated to prevent the quasi-static pressure induced in the wavelength component of the Bragg grating 84. The diaphragm sensor is expected to have a sensing sensitivity close to 80db for 1 μPa / Hz.

Another embodiment of a sensor that responds to acoustic radiation is described with reference to FIG.

7 (A) and 7 (B) show accelerometer type sensors 93, where FIG. 7 (A) shows light in flexible material layer 96 loaded with rigid baring layer 98 serving as mass M. FIG. An accelerometer sensor 93 comprising a fiber 82 is shown, wherein the material 96 is made of any form of soft flexible material such as plastic or rubber, while the rigid layer 98 is made of metal, glass or ceramic. Same as any rigid material.

As can be seen in FIG. 7B, the optical fiber 82 has a Bragg grating 84 guided therein, on a structure 100 that is subjected to perturbation 102 produced by acoustic radiation, typically. Flexible material 96 is located. The perturbation 102 is an out-of-plane vibration with respect to the structure 100. The accelerometer sensor 93 is located on a structure 100 that constitutes a transmission casing, the sensor The frequency response and responsiveness of 93 depend on the stiffness of the rigid material 98 and the mass M. If desired, the fiber 82 which carries the induced Bragg grating 84 together with it is directly enclosed in any material, which is in particular a plastic, glass-fiber, or synthetically evaluated component. Materials are suitable. Sensors that respond to time-varying vibrations or electrical and / or magnetic field disturbances are described with reference to FIG. 8.

8 (A), (B), (C) and (D) each show a sensor used to respond to perturbations other than perturbation due to acoustic radiation. All of the sensors in FIG. 8 can be used to monitor equipment by detecting a physical system, such as an electromagnetic field. The sensors of FIGS. 8 (A) and 8 (B) respond to the magnetic distortion effect while the sensors of FIGS. 8 (C) and (D) respond to the electric distortion effect.

8 (A) shows a sensor 103 responsive to a magnetic distortion effect, with an optical fiber 82 having a Bragg grating 84 introduced therein. The optical fiber 82 is located between two devices 104 and 106 that effectively form a composite bar, and the devices 104 and 106 are made of a magnetic material such as Imbar, Monel metal, Nichrome, Nickel, metallic glass or Stiic metal. All of these are known materials, and stretch and contract in proportion to the strength of the applied magnetic field 107 to match the perturbation that the material 94 receives. The magnetic distortion effect that the sensor 93 responds to is nonlinear, but such nonlinearity is compensated by the embodiment of FIG. 8 (B).

FIG. 8B shows a sensor 108 that responds to the magnetic distortion effect in a similar manner as described with respect to the sensor 103, which is a local permanent magnet located near the Bragg grating 84. And a bias system. The magnet 110 compensates for the nonlinearity of the magnetic distortion effect imposed on the sensor 108, in particular the magnet 110 interacts with time-varying changes, such as changes generated by alternating current, in the Bragg grating 84 This leads to an incidental vibration in the strain, and the incidental vibration leads to the Bragg grating wavelength of the grating 84. Sensing sensitivity in the range of 1 milli-Gauss / Hz is expected to be achieved, which makes the sensor 108 particularly suitable for the use of vehicle detection / counting traffic pattern monitoring, all of which are popular in so-called smart highway systems. Became. Another embodiment used in the practice of the present invention is described with reference to FIG. 8 (C).

8 (C) shows a sensor 114 having an optical fiber 82 having a Bragg grating 84 introduced therein, the optical fiber 82 having a barium titanate to form a ceramic plate. Located between layers 116 and 118 of the same material, the ceramic plate contracts when the voltage shown by the directional arrow 120 applied across its parallel plate is contracted, and the voltage is dependent on the perturbation the material 94 receives. Will be suitably and represent the physical vibration of the material. Another further embodiment related to the practice of the present invention is described with reference to FIG. 8 (D).

FIG. 8D shows a sensor 122 having piezoelectric properties, the sensor 122 having a Bragg grating 84 introduced therebetween located between piezoelectric materials 124 and 126, such as known piezoelectric ceramics. An optical fiber 82 is provided, which transmits a voltage upon deformation or, conversely, causes a change in shape when a voltage is applied to it, which is shown by the directional arrow 128. The sensors of FIGS. 5-7 as well as all the embodiments of FIG. 8 are used in the apparatus of FIG. 4 and the apparatus of FIG. 9 already discussed.

9 is similar to Figure 4 which wavelength division multiplexing technology as well, and used as the broadband source 14 having an operating wavelength λ also Figure 9 is a more broadband operating wavelength of λ ¹ having a typical value of 1.55μm Has a circle 130, which is a second light source for providing incident light as shown by the directional arrow 132. The broadband source 130 may be of the same type as the broadband source 14. It has a bandwidth of 50 nm covering all wavelengths reflecting light from the Bragg gratings 12A, 12B, 12C ... 12N in the same manner as described with respect to broadband source 14 in FIG.

The apparatus of FIG. 9 also has a demodulator consisting of a second unbalanced interferometer 56 ', a wavelength division multiplexer (WDM) 32A' and a detector 70A ', 70B' .... 70N '. Cosine processor 72 '. All of the above elements of FIG. 9, shown prime, operate in the same manner as the elements of FIG. 4 without priming. The second unbalanced interferometer 56 'is connected to the signal path 30 via the signal path 134, and the second unbalanced interferometer 56' is modulated signal generator 68 via the signal path 136. ) And its phase modulator 62 '. Similarly, the sine / cosine processor 72 'is connected to a modulation signal generator 68 via signal path 76'.

In operation, the apparatus of FIG. 9 selects an operating wavelength lambda 'of 1.3 mu m for the broadband source 14, and selects the broadband source 130 as having an operating wavelength lambda' of 1.55 mu m. Similarly, the first unbalanced interferometer 56 and the wavelength division multiplexer 32A are selected to have an operating frequency to correspond to the broadband source 14 of 1.3 μm with respect to the wavelength λ, and also the second unbalanced interferometer 56 'and the wavelength. The division multiplexer 32A 'is selected to have an operating wavelength of 1.55 mu m so as to correspond to the wavelength [lambda]' of the broadband source 30. In addition, the plurality of Bragg gratings 12A, 12B, 12C ... 12N are spaced apart from each other by a normal distance X as described in FIG. 4, and are selected to have a spacing of wavelength components of 1 nm so that the apparatus of FIG. Bragg grating sensing elements 12A, 12B, 12C ... 12N can be accommodated. In selecting this operating wavelength and Bragg grating number, the apparatus of FIG. 9 operates similarly to FIG. 4 so that the sine / cosine processor 72 has a reflected incident light signal 22 having a carrier frequency of 1.3 μm of the broadband source 14. .28 provides an output signal on the signal paths 78A..78N representing the respective amounts of wavelength components contained in the respective signals, which are subject to Bragg lattice 12A, 12B, 12C ... 12N when perturbed. ) wavelength of λ ₁ .... are changed in proportion to λ _N. Similarly, the sine / cosine processor 72 'is a signal path 78A' representing the amount of each wavelength component contained in each of the reflected incident light signals 22 .... 28 having a carrier frequency of 1.55 m of the broadband source 130. .... 78N ') output signal, which is changed in proportion to the wavelength λ ₁ ' .... λ _N 'of Bragg gratings 12A, 12B, 12C ... 12N when perturbed . Although both circuits of FIGS. 4 and 9 can accommodate multiple sensors, the ability to accommodate additional sensors is provided by the time division multiplexing technique described below in connection with FIG. 10.

The apparatus of FIG. 10 comprises reflective Bragg grating elements, indicated by the first and second plurality of reference numerals 12 and 12 ', which are separated from each other by a fiber delay device 138 to be formed in two arrangements. Each of the arrays has the same Bragg grating having unique wavelength components that are matched with one another. For example, the first arrays 12A, 12B, 12C ... 12N included in the sensor 12 have their own wavelength component λ ₁ reflecting the incident light of the Bragg grating 12A 'of the sensor 12'. And a Bragg grating 12A having a unique wavelength component λ ₁ so as to reflect incident light corresponding thereto. If more than one sensor 12, 12 ′ is used, an additional fiber delay device 138 is interposed between each FBG sensor having a Bragg grating arrangement therein. Also, the Bragg gratings 12A, 12B, 12C ... 12N and 12A ', 12B', 12C '... 12N' are separated by a predetermined interval X as described in FIG. Preferably spaced apart.

The apparatus of FIG. 10 further includes a pulse driver 140 for generating a pulse coupled to the coupler 20 through a gating device 142 and having incident pulses having a pulse characteristic 146 having a predetermined pulse interval τ. That is, it is shown as an arrow to indicate the pulse 144. The gating device 142 permits passage of the output of the broadband source 14 on the optical coupler 20 during the presence of the pulse 144. The pulse 144 passes through the signal path 148 through a gating circuit ( 150). In addition, the circuit arrangement of FIG. 10 receives sine and cosine signals from detectors 70A, 70B .... 70N, responds to pulse 144, and is represented by a plurality of grouped signal paths 152A .... 152N. And a gating circuit 150 for providing sine and cosine signals as output signals.

Bragg gratings 12A, 12B, 12C ... 12N and (12A ', 12B', 12C '... 12N') are introduced or recorded in their respective FBG sensors 12, 12 '. It has a nominal reflection coefficient of 2%. A portion of the incident light 16 is reflected from each Bragg grating by the above arrangement, while the remaining strong signals forming the incident light 16 are further Bragg grating series, i.e., Bragg gratings 12A, 12B, 12C. .12N) and (12A ', 12B', 12C '... 12N'). Several (ie 5 to 8) Bragg grating series are interlocked by having a wavelength reflection coefficient of a few percent Bragg gratings 12A... 12N '. In the case of interrogation of more than 10 Bragg grating series (12... 12 '), a reflection coefficient of less than 2% ensures low crosstalk between sensors, such as sensors 12, 12'.

In operation, referring to FIG. 10, the output of broadband source 14 is pulsed as pulse 144 with an interval of [tau]. The pulse 144 generates a return signal from the sensors 12, 12 'at each output of the wavelength division multiplexer 32A. Each of these outputs has a series of pulses generated from the corresponding Bragg grating in each grating series 12, 12 'in the array. These series of pulses appear at the outputs of the detectors 70A, 70B... 70N and the wavelength components λ ₁ ,... ₂ ... Corresponding to the Bragg gratings 12A. λ _{N. When} the width of the pulse 144 is selected to be less than or equal to the optical round trip propagation between the Bragg grating series and the matching grating sensor elements 12, 12 ′, the detectors 70A, 70B. Pulses generated at the output of 70N are time separated and connected to a gating circuit 150 responsive to the pulse 144. For example, when the Bragg gratings 12A and 12A 'are selected to have their own wavelength component lambda ₁ to reflect incident light (pulse 144), the pulses appearing at the output lambda ₁ of the wavelength division multiplexer 32A are represents λ ₁ and is separated in time. The time division multiplexed pulses at the outputs of the detectors 70A, 70B ... 70N are applied to the gating circuit 150 via signal paths 74A ... 74N, respectively. The output of the gating circuit 150 is relayed to the sine / cosine processor 72 so that the processor performs time division multiplexing to be supported by the device of FIG. 10 as compared to the device of FIGS. 4 and 9. A slight fold improvement can be obtained. For example, comparing FIG. 4 and FIG. 10, since the broadband source 14 having a bandwidth of 50 nm and an operating wavelength lambda of 1.3 μm is used, four In case of folding, a split multiplex (TDM) improvement is performed, and thus, a total of 200 sensor elements may be used as compared to the 50 sensor elements of FIG. 4. Four fold enhancements consider the need to monitor the active and idle states of the multiplexed signal. The number of the sensor elements is doubled by the circuit arrangement of FIG.

The circuit arrangement of FIG. 11 operates similar to the circuit arrangement of FIG. 10 with a prime number and also operates similarly to the elements of the prime not shown in FIGS. 1, 4, 9 and 10 previously described. The prime element is selected to have an operating wavelength to correspond to the broadband wavelength 130 operating wavelength [lambda] in the manner already described with reference to FIG. If the operating wavelength is selected for the first and second interferometers 56, 56 'and for the first and second wavelength division multiplexers 32A, 32A', respectively, the circuit arrangement of FIG. 11 is similar to that of FIG. Sine / cosine processor 72 outputs an output signal 154A ... that represents the amount changed with respect to wavelength [lambda] when each of the unique wavelength components of Bragg grating 12A ... 12N 'is perturbed. .154N), and similarly the sine / cosine processor 72 'has an output indicating the amount of change in relation to the wavelength [lambda]' when each of the unique wavelength components of the Bragg grating 12A ... 12N 'is perturbed. Generate signals 154A '.... 154N'.

The practice of the present invention provides various embodiments in which at least 400 sensors can be used, which is not a practical limitation. The practice of the present invention also provides a variety of sensors used to detect acoustic radiation field disturbances or magnetic field disturbances. The practice of the present invention also discloses using multiple sensors to monitor the performance of selected equipment parts using FBG sensors, which can be realized without using any complex filtering method and any ratio measuring method described in the background. have.

Although the present invention has been described by some embodiments so far, the present invention is not limited thereto and various modifications and changes can be made by those skilled in the art without departing from the spirit and scope of the appended claims.

Claims (17)

A system that detects the perturbation that some equipment receives. (a) an optical sensor disposed along the equipment, the optical sensor having a plurality of reflective Bragg gratings introduced therein, each grating acting as a sensor element, and having a unique position and incident light along the equipment An optical sensor having a unique wavelength component which reflects, and adapted to be changed when each unique wavelength component of the sensor element is perturbed; (b) a light source providing input light to the sensor to cover all of the wavelength components to reflect incident light from each grating; (c) an unbalance that receives the reflected incident light from each grating and has first and second arms, and generates an interferometer signal for each wavelength component of the incident light reflected by the respective Bragg gratings; interferometer; (d) means for generating a modulated signal; (e) a phase modulator that receives the modulated signal and is located on one arm of the unbalanced interferometer, and modulates each of the interferometer signals; And and (f) a demodulator for receiving each of the modulated interferometer signals and generating an output signal indicative of an amount that changes when each unique wavelength component of the reflected incident light is perturbed. The perturbation detection system of claim 1, wherein the unique wavelength components of the plurality of gratings are separated from each other by a wavelength of about 1 nm. The perturbation detection system of claim 1, wherein the sensor is selected from the group consisting of a free field sensor, a diaphragm sensor, an accelerometer type, a magnetic distortion type, an electrical distortion type, and a piezoelectric type. 2. The light source of claim 1, wherein the light source comprises a first broadband source of a type selected from the group consisting of an edge emitting LED (ELED), a superluminescent diode, a superluminescent fiber source and a fiber erbium source. Perturbation Detection System. The light source of claim 1, wherein the light source includes a second broadband source of a type selected from the group consisting of an edge emitting LED (ELED), a superluminescent diode, a superluminescent fiber source, and a fiber erbium source. The second wideband source has operating wavelengths of 1.3 μm and 1.55 μm, respectively, and the first and second wideband sources each have a bandwidth of about 50 nm. The method of claim 1, wherein the demodulator, (a) means for receiving the modulated interferometer signal and dividing it into a signal representing the intrinsic wavelength component; (b) detection means for generating corresponding sine and cosine signals in response to each of the divided inherent wavelength components; And and (c) signal processor means responsive to said modulated signal and generating said demodulator output signal in response to said sine and cosine signals. The method of claim 1, wherein the demodulator, (a) means for generating pulses applied to the sensor with the input light at predetermined pulse intervals; (b) means for receiving and dividing each of said modulated interferometer signals into a signal representing said intrinsic wavelength component; (c) detection means for generating corresponding sine and cosine signals in response to the divided inherent wavelength components; (d) gating means for receiving the corresponding sine and cosine signals and responsive to the pulse to provide the sine and cosine signals as outputs thereof; And and (e) signal processor means responsive to said modulation signal and generating said demodulator output signal in response to output sine and cosine signals of said gating means. 8. The perturbation detection system of claim 7, wherein the plurality of reflective Bragg gratings are separated in two arrangements by a fiber delay device, each having a Bragg grating having unique wavelength components that match each other. A system that detects the perturbation that some equipment receives. (a) an optical sensor disposed along the equipment, the optical sensor having a plurality of reflective Bragg gratings introduced therein, each grating acting as a sensor element, and having a unique position and incident light along the equipment An optical sensor having a unique wavelength component which reflects, and adapted to be changed when each unique wavelength component of the sensor element is perturbed; (b) a first light source for providing incident light to the sensor at a first operating wavelength [lambda] having a bandwidth covering all wavelength components to reflect incident light from each of the gratings; (c) a second light source providing incident light to the sensor at a second operating wavelength [lambda] 'having a bandwidth covering all wavelength components to reflect incident light from each of the gratings; (d) each wavelength of the incident light having an operating wavelength corresponding to the wavelength [lambda], receiving reflected incident light from each of the Bragg gratings, having first and second arms, and reflected by the respective Bragg gratings A first unbalanced interferometer for generating an interferometer signal for the component; (e) having an operating wavelength corresponding to the wavelength λ ', receiving reflected incident light from each of the Bragg gratings, having a first and second arms, and an angle of the incident light reflected by the respective Bragg gratings A second unbalanced interferometer for generating an interferometer signal for the wavelength component; (f) means for generating a modulated signal; (g) a first phase modulator for receiving said modulated signal, located in one arm of said arms of said first unbalanced interferometer, and modulating each of said interferometer signals of said first unbalanced interferometer; (h) a second phase modulator for receiving said modulated signal, located in one arm of said arms of said second unbalanced interferometer, and modulating each of said interferometer signals of said first unbalanced interferometer; (i) receiving the respective modulated interferometer signals from the first unbalanced interferometer and generating an output signal indicative of an amount that changes in proportion to the wavelength [lambda] when each of the intrinsic wavelength components of the reflected incident light is perturbed A first modulator; And (j) an output signal that receives the respective modulated interferometer signals from the second unbalanced interferometer and indicates an amount of change in proportion to the wavelength lambda 'when each induction wavelength component of the reflected incident light is subjected to the perturbation Perturbation detection system comprising a second modulator for generating a. 10. The perturbation detection system of claim 9, wherein the intrinsic wavelength components of the plurality of Bragg interferometers are separated from each other by a wavelength of about 1 nm. 10. The perturbation detection system of claim 9, wherein the sensor is selected from the group consisting of a free field sensor, a diaphragm sensor, an accelerometer sensor, a magnetic distortion type, an electrical distortion type, and a piezoelectric type. 10. The method of claim 9, wherein each of the first and second light sources is of a type selected from the group consisting of an edge detection LED (ELED), a superluminescent diode, a superluminescent fiber source, and a fiber erbium source. And the second wideband source has an operating wavelength of about 1.3 μm and 1.55 μm, respectively, and the first and second wideband sources have a bandwidth of about 50 nm. The method of claim 9, wherein the first modulator, (a) first means for receiving each modulated interferometer signal from the first unbalanced interferometer and dividing it into a signal representing the intrinsic wavelength component of the Bragg grating; (b) first detecting means for generating a corresponding sine and cosine signal in response to each of the divided intrinsic wavelength components of the first means; and (c) a first signal processor responsive to said modulated signal and further generating a first modulated output signal in response to the sine and cosine signals of said first detection means. The method of claim 9, wherein the second modulator, (a) second means for receiving each modulated interferometer signal from the second unbalanced interferometer and dividing it into a signal representing the intrinsic wavelength component of the Bragg grating; (b) second detection means for generating a corresponding sine and cosine signal in response to each of the divided intrinsic wavelength components of the second means. And a second signal processor responsive to said modulated signal and generating a second modulated output signal in response to the sine and cosine signals of said second detecting means. 10. The method of claim 9, The first demodulator, (a) means for generating pulses applied to the sensor with predetermined light intervals and input light of the first and second light sources; (b) first means for receiving each of the modulated interferometer signals of said first unbalanced interferometer and dividing it into signals representing said intrinsic wavelength component; (c) first detecting means for generating corresponding sine and cosine signals in response to the divided inherent wavelength components; (d) first gating means for receiving the corresponding sine and cosine signals and responsive to the pulse to provide the sine and cosine signals as outputs thereof; And (e) a first signal processor means responsive to said modulated signal and generating said demodulator output signal in response to output sine and cosine signals of said gating means. (a) means for generating pulses applied to the sensor with predetermined light intervals and input light of the first and second light sources; (b) second means for receiving each of the modulated interferometer signals of said second unbalanced interferometer and dividing it into signals representing said intrinsic wavelength component; (c) second detecting means for generating corresponding sine and cosine signals in response to the divided inherent wavelength components; (d) second gating means for receiving the corresponding sine and cosine signals and responsive to the pulse to provide the sine and cosine signals as outputs thereof; And (e) a second signal processor means responsive to said modulation signal and generating said demodulator output signal in response to output sine and cosine signals of said gating means. 10. The perturbation detection system of claim 9, wherein the plurality of reflective Bragg gratings are separated into two arrays by a fiber delay device, each having a Bragg grating having a unique wavelength component that matches each other.