JP2015031594A - Multichannel fbg sensor monitor system and multichannel fbg sensor monitor method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multichannel FBG sensor monitor system and a multichannel FBG sensor monitor method capable of measuring physical quantities at a plurality of places.SOLUTION: The present invention connects, to each output port of an optical coupler 14, an FBG line to which a plurality of FBGs are connected in line; outputs, to each output port of the optical coupler 14, measurement light inputted from an input port; shifts the timing for input, to the optical coupler 14, of the reflected light of the measurement light reflected by any FBG of the FBG line 30 by using an optical delay device 18 inserted between the output ports of the optical coupler 14 and the FBG line 30; and separates, for each wavelength, the reflected light returned to the optical coupler 14 by an AWG 15, and receives the separated light by a PD 16.

Description

  The present invention relates to a multi-channel FBG sensor monitor system and method for measuring physical quantities using FBG lines in which a plurality of Bragg gratings (hereinafter referred to as FBG (Fiber Bragg Grating)) are connected in series.

  There has been proposed an FBG sensor monitor system in which one or more FBGs are formed in an optical fiber into which measurement light is incident, and a physical quantity such as temperature and strain at the position of each FBG is measured by measuring a reflection wavelength from each FBG. . In the FBG sensor monitor system, the reflected light from each FBG is incident on an arrayed waveguide grating (AWG), and the light intensity of each wavelength separated by the AWG is detected using a light receiver. Thereby, the reflection wavelength of FBG is measured.

In the invention of Patent Document 1, wavelength measurement is performed using a quadratic function using a wavelength range in which the wavelength sensitivity of each light receiver is substantially linear. This makes it possible to measure the reflected wavelength of the FBG with higher accuracy than the wavelength channel spacing of the AWG.
The invention of Patent Document 2 uses the light intensity of the adjacent wavelength channel to determine whether the reflected wavelength is shifted to the long wavelength side or the short wavelength side. As a result, the invention of Patent Document 2 makes it possible to accurately measure the reflected wavelength of the FBG even when the reflected wavelength of the FBG is near the center wavelength of the wavelength channel of the AWG.

JP 2000-180270 A JP 2008-151574 A

  In recent years, aircraft using CFRP (Carbon-Fiber-Reinforced Plastic) as airframe members have been operated. CFRP has characteristics of high strength and light weight compared to metal, but when an impact is applied, the surface may be intact even if the surface is intact, and there is a risk that this crack will grow and reduce the strength of the aircraft. is there. Therefore, research is underway to measure what is called dynamic strain (dynamic physical quantity) such as strain at the time of applying an impact by using FBG as a strain sensor on the CFRP surface. Since the airframe surface area is vast, several tens of FBGs are required to detect an impact without any loss. FBGs can be connected in a column to one FBG line while shifting the reflection wavelength, but the number is about 10.

  It is required to measure physical quantities at a plurality of locations almost simultaneously using a plurality of FBG lines. However, since the inventions of Patent Documents 1 and 2 are configured on the premise of measuring one FBG line, the number of locations that can be measured simultaneously is about 10 at most.

  Accordingly, an object of the present invention is to provide a multi-channel FBG sensor monitor system and a multi-channel FBG sensor monitor method in which measurement points are dramatically improved.

The multi-channel FBG sensor monitor system of the present invention is
Light that can be connected to each output port in which FBG lines in which a plurality of FBGs (Fiber Bragg Gratings) are connected in series are arranged in parallel and that branches the measurement light input from the input port to each output port and outputs the light A coupler (14);
A light source (12) that emits measurement light including a reflection wavelength of at least one of the FBGs included in the FBG line;
Reflected light that is connected between the output port of the optical coupler and the FBG line and reflected by any FBG of the FBG line after measurement light from the light source is output from each output port of the optical coupler. An optical delay unit (18) for inputting to the optical coupler at different timings;
A spectroscope (15) for separating reflected light delayed by the optical delay device for each predetermined wavelength;
A light receiver (16) for detecting the light intensity of the reflected light separated by the spectroscope for each wavelength;
Is provided.

The multi-channel FBG sensor monitor system of the present invention is
In a state where FBG lines in which a plurality of FBGs are connected in series are connected to each output port of the optical coupler (14), measurement light including at least one of the reflection wavelengths of the FBGs provided in the FBG lines is input to the optical coupler. An optical output procedure for inputting to the port, branching the measurement light input to the optical coupler, and outputting the measurement light toward the FBG line;
Using the optical delay device (18) connected between the output port of the optical coupler and the FBG line, the FBG of any one of the FBG lines is output after the measurement light is output from each output port of the optical coupler. An optical delay procedure for inputting the reflected light reflected by the optical coupler to the optical coupler at different timings;
A light receiving procedure for separating the reflected light after being delayed by the optical delay unit for each predetermined wavelength, and detecting the light intensity of the separated reflected light for each wavelength;
In order.

  According to the present invention, it is possible to provide a multi-channel FBG sensor monitoring method capable of simultaneously measuring physical quantities at a plurality of locations.

1 shows an example of a multi-channel FBG sensor monitor system according to a first embodiment of the present invention. It is an example of the measurement light which concerns on this embodiment, (a) shows the measurement light Pm output from each input / output port 142 of the optical coupler 14, (b) is connected to the input / output port 142 # 1. The measurement light Pm # 1 output from the optical delay device 18 to the FBG line 30 is shown, and (c) shows the measurement light Pm output from the optical delay device 18 connected to the input / output port 142 # 2 to the FBG line 30. (D) shows the measurement light Pm # k output to the FBG line 30 from the optical delay device 18 connected to the input / output port 142 # k. It is an example of the reflected light which concerns on this embodiment, (a) shows the measurement light Pm output from each input / output port 142 of the optical coupler 14, (b) is the reflection input into input / output port 142 # 1. (C) shows the reflected light Pr # 2 input to the input / output port 142 # 2, and (d) shows the reflected light Pr # k input to the input / output port 142 # k. , (E) shows the reflected light Pr # 1... Pr # k output from the input / output port 141. FIG. An example of the reflection level of the reflected light output from the spectroscope 15 is shown. An example of the reflected light level per one wavelength channel received by the light receiver 16 is shown. It shows an example of the reflected light level of ch1~ch48 at time _{t 3.} Is an example of a spectrum of the reflected light, (a) shows measurement light pulse width w _p which is emitted from the white light source 12, (b) the measurement of the reflected light Pr # k input to the spectroscope 15 The spectrum of the reflected light from the FBG 31 connected to the position closest to the input / output end of the light Pm # k is shown. (C) shows the measurement light Pm # of the reflected light Pr # k input to the spectrometer 15. The spectrum of the reflected light from the FBG 31 connected to the second closest position to the input / output terminal of k is shown, and (d) shows the measurement light Pm # k of the reflected light Pr # k input to the spectrometer 15. 2 shows the spectrum of the reflected light from the FBG 31 connected to the position farthest from the input / output terminal, and (e) shows the spectrum of the reflected light Pr # k input to the spectrometer 15. It is an example of the sum total spectrum of a reflected light level, (a) shows the reflected light level of reflected light Pr # k, (b) shows the reflected light level of reflected light Pr # k + 1. An example of a total spectrum of reflected light levels input to the spectroscope 15 when the optical coupler 14 has eight branches is shown.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(First embodiment)
FIG. 1 shows an example of a multi-channel FBG sensor monitor system according to this embodiment. The multi-channel FBG sensor monitoring system according to the present embodiment includes a pulse signal source 11, a white light source 12, an optical circulator 13, an optical coupler 14, a spectroscope 15, a light receiver 16, an optical delay device 18, A signal processing unit 17 is provided.

  In the optical coupler 14, the optical circulator 13 is connected to the input / output port 141, and the optical delay device 18 is connected to the input / output port 142. An FBG line 30 is connected to each optical delay unit 18. In the FBG line 30, a plurality of FBGs 31 are connected in series to an optical fiber.

The multi-channel FBG sensor monitoring method according to this embodiment includes an optical output procedure, an optical delay procedure, and a light receiving procedure in order.
In the optical output procedure, the measurement light is input to the input / output port 141 of the optical coupler 14, and the measurement light input to the optical coupler 14 is branched to each input / output port 142 and output to the FBG line 30.
In the optical delay procedure, the measurement light is output from each input / output port 142 of the optical coupler 14 using the optical delay device 18 connected between the input / output port 142 of the optical coupler 14 and the FBG line 30. The reflected light reflected by any one of the FBGs 31 is input to the optical coupler 14 at different timings.
In the light receiving procedure, the delayed delayed light 18 is separated for each predetermined wavelength by the optical delay unit 18, and the light intensity of the separated reflected light is detected for each wavelength.

  The white light source 12 outputs pulsed light according to the pulse signal from the pulse signal source 11 to the optical circulator 13 as measurement light. The white light source 12 includes, for example, an SLD (Super Luminescent Diode) or an ASE (Amplified Spontaneous Emission) light source. The optical circulator 13 outputs measurement light to the optical coupler 14. The optical coupler 14 branches the input measurement light and outputs it to each input / output port 142. As a result, the measurement light is input to each optical delay device 18. The optical delayer 18 delays the measurement light for a predetermined time.

  The measurement light that has passed through the optical delay device 18 is input to the FBG line 30 and reflected by each FBG 31. The reflected light passes through the optical delay device 18 and is input to the input / output port 142 of the optical coupler 14. The optical coupler 14 combines the reflected lights input from the input / output ports 142 and outputs the combined light from the input / output ports 141. The optical circulator 13 outputs the reflected light output from the input / output port 141 of the optical coupler 14 to the spectrometer 15. The spectroscope 15 demultiplexes the reflected light for each wavelength and outputs it to the light receiver 16. The light receiver 16 detects the reflected light level that is the light intensity of the reflected light for each wavelength. For example, the reflected light level of each wavelength channel is detected using a 48ch PD (Photodiode).

  The signal processor 17 calculates the reflected wavelength of the FBG 31 using the reflected light level of each wavelength detected by the light receiver 16. Thereby, the multi-channel FBG sensor monitor system according to the present embodiment can measure a physical quantity using the FBG line 30.

  FIG. 2 shows an example of measurement light according to the present embodiment. 2A shows the measurement light Pm output from each input / output port 142 of the optical coupler 14, and FIG. 2B shows the FBG line 30 from the optical delay device 18 connected to the input / output port 142 # 1. FIG. 2C shows the measurement light Pm # 2 output to the FBG line 30 from the optical delay unit 18 connected to the input / output port 142 # 2. 2 (d) shows the measurement light Pm # k output to the FBG line 30 from the optical delay device 18 connected to the input / output port 142 # k. As shown in FIG. 2B to FIG. 2D, the input timing from the optical delay device 18 to the FBG line 30 is shifted for each FBG line 30.

  FIG. 3 shows an example of reflected light according to the present embodiment. 3A shows the measurement light Pm output from each input / output port 142 of the optical coupler 14, and FIG. 3B shows the reflected light Pr # 1 input to the input / output port 142 # 1. 3 (c) shows the reflected light Pr # 2 input to the input / output port 142 # 2, and FIG. 3 (d) shows the reflected light Pr # k input to the input / output port 142 # k. e) shows the reflected light Pr # 1... Pr # k output from the input / output port 141. As shown in FIG. 3E, the reflected lights Pr # 1... Pr # k have different timings so that pulses do not overlap.

FIG. 4 shows an example of the reflected light level of each wavelength detected by the light receiver 16. 4A shows the wavelength channel ch1, FIG. 4B shows the wavelength channel ch2, and FIG. 4C shows the wavelength channel ch48. Reflected light Pr # 1 is detected at time _{t 1,} the reflected light Pr # 2 are detected in the time _{t 2, the} reflected light Pr # k is detected ... time _{t k.}

The operation of the signal processor 17 will be described with reference to the reflected light level shown in FIG. The reflected light level shown in FIG. 5 is, for example, the reflected light level of wavelength channel ch2 of reflected light Pr # 3 shown in FIG. The signal processor 17 samples the analog signal from the light receiver 16. The sampling period at this time is, for example, 0.02 μs (= 1/50 MHz). The reflected light level per channel is like a trapezoid with a widening end. Therefore, the signal processing unit 17 discards the sampling point p _d flared portion indicated by a white circle, to employ a sampling point p _u substantially planar portions indicated by black circles put between them.

The signal processor 17 stores the sampling point _pu in association with information such as time that can identify the input / output port 142 and the wavelength channel of the light receiver 16. At this time, the storage unit 23 may store the reflected light level after averaging the plurality of sampling points _pu . The signal processor 17 calculates the reflection wavelength of each FBG 31 provided in the FBG line 30 using the stored reflected light level of each wavelength channel.

The signal processor 17 reads the reflected light level of each wavelength channel stored in association with the common FBG line 30. For example, it reads the reflected light level of ch1~ch48 at time _{t 3} when shown in Fig. 6 shows an example of the reflected light level of ch1~ch48 at time _{t 3.} When 10 FBGs 31 are connected to one FBG line 30 and the reflection wavelength of each FBG 31 is within the light receiving range of the light receiver 16, there are 10 wavelength channels that are maximum in the wavelength channel of 48ch. . If the wavelength of each maximum wavelength channel is used, the reflection wavelength of each FBG 31 provided in each FBG line 30 can be measured.

In the present embodiment, a wavelength channel in which the maximum value of the detected light intensity of the reflected light is obtained is detected, and the light intensity of the FBG 31 is determined using the maximum value and the light intensity of at least two wavelength channels adjacent to the wavelength channel. Calculate the reflection wavelength. For example, there is a maximum wavelength channel in the wavelength channel chp3 corresponding to the wavelength λ _P , the reflected light level is y ₀ , and the reflected light levels of the adjacent channels ch (p3-1) and ch (p3 + 1) are When y ₋₁ and y ₊₁ , respectively, and the wavelength interval of the wavelength channel is w _c , the reflection wavelength λ _FBG can be obtained using the following equation.

Similar to the wavelength channel chp3, the reflection wavelength λ _FBG of each of the ten _FBGs 31 is obtained. Thereby, the reflection wavelength λ _FBG of each FBG 31 provided in one FBG line 30 can be obtained. In the present embodiment, two adjacent wavelength channels are used. However, the reflection wavelength λ _FBG may be obtained using two or more wavelength channels in which a maximum wavelength channel exists.

By performing processing similar to that at time t ₃ at each time, the reflection wavelengths λ _FBG of all the FBGs 31 provided in each FBG line 30 can be obtained.

  When an optical switch is used as the optical component, only a part of the reflected light may reach the spectrometer 15 depending on the polarization characteristics of the optical switch. Since the invention according to the present embodiment uses the optical coupler 14 without using the optical switch, it can be hardly affected by the polarization dependence. Therefore, the invention according to this embodiment provides a multi-channel FBG sensor monitor system and a multi-channel FBG sensor monitor method that are not easily affected by polarization dependence and that can simultaneously measure physical quantities at a plurality of locations. be able to.

(Second Embodiment)
In the present embodiment, the relationship between the maximum fiber length of the connectable FBG line 30, the pulse width of the measurement light, and the measurement time will be described.
The pulse width of the measurement light is w _p , the light propagation distance from the white light source 12 to the optical delay device 18 is A ₁ , the light propagation distance from the optical delay device 18 to the spectroscope 15 is A ₂ , kth (k is an arbitrary value) positive number.) the length of the input and output ports 142 # k are connected to the optical delay 18 and _{L k} of. Further, regarding the FBG line 30 connected to the input / output port 142 # k, the light propagation distance from the input / output end of the FBG 31 connected to the position closest to the input / output end of the measurement light Pm # k is defined as MIN _k , The light propagation distance from the input / output end of the FBG 31 connected to the position farthest from the input / output end of the measurement light is defined as MAX _k .

FIG. 7 is an explanatory diagram illustrating an example of a spectrum of reflected light. FIG. 7A shows measurement light having a pulse width w _p emitted from the white light source 12. FIG. 7B shows the spectrum of the reflected light from the FBG 31 connected to the position closest to the input / output end of the measurement light Pm # k among the reflected light Pr # k input to the spectrometer 15. FIG. 7C shows the spectrum of the reflected light from the FBG 31 connected to the second closest position to the input / output end of the measurement light Pm # k among the reflected light Pr # k input to the spectrometer 15. Show. FIG. 7D shows the spectrum of the reflected light from the FBG 31 connected to the position farthest from the input / output end of the measurement light Pm # k among the reflected light Pr # k input to the spectrometer 15. FIG. 7E shows the spectrum of the reflected light Pr # k input to the spectrometer 15.

The k-th total spectrum from all the FBGs 31 connected to the k-th input / output port 142 is stepped as shown in FIG. In the time domain B, the spectrum of the reflected light from the FBG can enter the spectroscope at the same time.
In order to measure the spectrum of reflected light from all the FBGs 31 connected to the kth input / output port 142 for T seconds,
(Equation 1)
B> T Formula (1)
Need to be.

を満たす必要がある。ここで、ｎは光ファイバの屈折率、ｃは光速である。 Therefore,

It is necessary to satisfy. Here, n is the refractive index of the optical fiber, and c is the speed of light.

となる。 Organize

It becomes.

となる。 From this equation, it can be seen that MAX _k has an upper limit when the pulse width w _p and the measurement time T are determined. This upper limit, that is, the maximum fiber length of the connectable FBG line 30 is _defined as E (E> MAX _k ). If the FBG 31 can be connected immediately after the optical port, MIN _k = 0,

It becomes.

を満たす必要がある。 FIG. 8 shows an example of the total spectrum of reflected light levels. FIG. 8A shows the reflected light level of the reflected light Pr # k, and FIG. 8B shows the reflected light level of the reflected light Pr # k + 1. In order to measure each separately on the time axis,

It is necessary to satisfy.

となる。 Organizing this formula,

It becomes.

となる。 Also, the difference in time for the two summed spectra to reach the spectrometer is

It becomes.

の関係が導出せる。 From Formula (4) and Formula (6),

The relationship can be derived.

If the pulse width w _p is 1 μs and the measurement time T is 0.4 μs,
E <60 [m]
L _{k + 1} −L _k > 100 [m]
It becomes. However, the refractive index n of the optical fiber was 1.5, and the speed of light c was 3 × 10 ⁸ [m / s].

For example, L _{k + 1} −L _k = 110 [m] is set so that there is a margin of 10%. In this case, the lengths of the optical delay devices 18 connected to the input / output port 142 of the optical coupler 14 having the branch number N of 8 are L ₁ = 0 m, L ₂ = 110 m, L ₃ = 220 m, and L ₄ = 330 m. , L ₅ = 440 m, L ₆ = 550 m, L ₇ = 660 m, and L ₈ = 770 m. In this case, as shown in FIG. 9, the reflected light is input to the spectrometer 15 every 1.1 μs.

  The present invention can be applied to the information communication industry.

11: Pulse signal source 12: White light source 13: Optical circulator 14: Optical coupler 15: Spectroscope 16: Light receiver 17: Signal processor 18: Optical delay device 30: FBG line 31: FBG
141: First input / output port 142: Second input / output port

Claims (2)

Light that can be connected to each output port in which FBG lines in which a plurality of FBGs (Fiber Bragg Gratings) are connected in series are arranged in parallel and that branches the measurement light input from the input port to each output port and outputs the light A coupler (14);
A light source (12) that emits measurement light including a reflection wavelength of at least one of the FBGs included in the FBG line;
Reflected light that is connected between the output port of the optical coupler and the FBG line and reflected by any FBG of the FBG line after measurement light from the light source is output from each output port of the optical coupler. An optical delay unit (18) for inputting to the optical coupler at different timings;
A spectroscope (15) for separating reflected light delayed by the optical delay device for each predetermined wavelength;
A light receiver (16) for detecting the light intensity of the reflected light separated by the spectroscope for each wavelength;
A multi-channel FBG sensor monitor system comprising: In a state where FBG lines in which a plurality of FBGs are connected in series are connected to each output port of the optical coupler (14), measurement light including at least one of the reflection wavelengths of the FBGs provided in the FBG lines is input to the optical coupler. An optical output procedure for inputting to the port, branching the measurement light input to the optical coupler, and outputting the measurement light toward the FBG line;
Using the optical delay device (18) connected between the output port of the optical coupler and the FBG line, the FBG of any one of the FBG lines is output after the measurement light is output from each output port of the optical coupler. An optical delay procedure for inputting the reflected light reflected by the optical coupler to the optical coupler at different timings;
A light receiving procedure for separating the reflected light after being delayed by the optical delay unit for each predetermined wavelength, and detecting the light intensity of the separated reflected light for each wavelength;
A multi-channel FBG sensor monitoring method comprising:

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