JP5219166B2 - Wavelength detection type fiber sensor system - Google Patents

Description

  The present invention relates to a wavelength detection type fiber sensor system including a wavelength change type optical sensor for measuring physical quantities such as temperature, strain, vibration, and acceleration.

Optical fibers are widely used mainly for communication, but extensive research has been conducted in the measurement field, and various optical fiber sensors have been put into practical use.
Among them, the wavelength detection type optical fiber sensor (FBG sensor) using fiber Bragg grating (FBG) is excellent in electromagnetic noise resistance and does not generate a spark like an electric system, so there is a risk of ignition and explosion. It has the characteristics common to optical fiber sensors that are suitable for instrumentation of chemical plants and petroleum plants, etc. In addition, a plurality of optical fiber sensors are installed in one optical fiber by wavelength division multiplexing (WDM) technology. It has an excellent feature that a spatial distribution measurement system can be realized by arranging.

As a conventional example of a wavelength detection type fiber sensor, there is known a strain sensor that utilizes the fact that the reflection center wavelength of the FBG sensor changes with strain applied to the FBG sensor (Conventional example 1; Non-patent document 1, Non-patent document). Reference 2).
In Conventional Example 1, a sensor is configured by drawing FBG on an optical fiber. Light is incident on the FBG from a light source, and the reflected light length reflected at a predetermined wavelength is measured by the detecting means. In the detection means, the reflection spectrum of the FBG is detected, and a measured value is obtained based on the detected wavelength.

Alan D. kersy, Mihael A. Davis, Heather j. Patric, Michel LeBlanc, K. P. Koo, C. G. Askins, M. A. Putnam, and E. Joseph Friebele, “Fiber Bragg Sensors,” Journal of Lightwave Technology, Vol. 15, No. 8 1997 W.W.Morey, G.Meltz, and W.H.Glenn, “Fiber optic Bragg grating sensors,” SPIE Vol.1169, pp.98-106,1989

In Conventional Example 1, even if the reflection spectrum of the FBG sensor is narrow, the full width at half maximum is about 100 pm, so that wavelength measurement reproducibility is about 5 pm. Since the FBG sensor has a variable wavelength change width of about 2 nm, the dynamic range is 800 (4 nm / 5 pm), which is narrower than the dynamic range of the electric sensor, and there is a limit to improvement in measurement accuracy.
And even if the full width at half maximum of the reflection spectrum of the FBG sensor is narrow, it is about 100 pm, so the measurement resolution of the distortion is about 130 nstrain / Hz. In other words, the measurement resolution is 5 pm per sampling, and about 1000 samplings can be performed per second, so the measurement resolution per second is 5 pm / 1000 ^1/2 = 0.16 pm. . On the other hand, since the relationship between strain and wavelength is about 1.2 pm / μstrain, the strain measurement resolution per second is (0.16 pm / 1.2 pm) = 0.133 μstrain / Hz = 130 nstrain / Hz. Therefore, when measuring with high resolution, it is desirable to use a sensor element having a spectrum with a small full width at half maximum.

  When trying to reduce the full width at half maximum with the FBG sensor of Conventional Example 1, it is conceivable to increase the grating length. For example, the length of the normal grating length is approximately 5 mm to 10 mm, but it is conceivable to extend the grating length to 20 mm and 30 mm. As described above, when the grating length is increased, not only does the sensor element itself become large, but also the long sensor element does not have a completely uniform strain distribution. A problem occurs. Therefore, the method of increasing the grating length is not practical.

  An object of the present invention is to provide a wavelength detection type fiber sensor system capable of improving measurement accuracy even when there is an environmental change such as a temperature change or a strain change.

The wavelength detection type fiber sensor system of the present invention includes a light source, a wavelength change type optical sensor on which light emitted from the light source is incident and installed in a measurement target, and an output output from the wavelength change type optical sensor. A wavelength detection type fiber sensor system comprising a wavelength detection means for detecting light, wherein the wavelength change type optical sensor constitutes a Fabry-Perot etalon and is a sensor element for measuring a pair of band reflection filters arranged close to each other And a band reflection filter having a reflection wavelength band narrower than a wavelength band including one line spectrum in the transmission spectrum band of the measurement sensor element, and the measurement sensor element and the band reflection filter are the same stress is placed on the same plane of the same members as such of the wavelength detection means, enter the output light from the sensor element And a first port through which light emitted from the measurement sensor element is incident, and a first port for calculating a wavelength corresponding to a physical quantity detected by each sensor element based on the input signal. A third port for emitting the light incident from the first port to the band reflection filter and receiving the reflected light reflected by the band reflection filter, and the wavelength detection means for the light incident on the third port And a circulator having a second port for emitting light.

In the present invention having this configuration, since the sensor element for measurement is configured by a Fabry-Perot etalon, the full width at half maximum of the transmission spectrum of the sensor is narrower than that of a conventional single FBG, and the measurement resolution can be improved.
Moreover, in the present invention, the reflection wavelength region of the band reflection filter is configured to include the transmission spectrum of one line of the measurement sensor element made of a Fabry-Perot etalon. Only one line transmission spectrum of the sensor element for measurement composed of a Fabry-Perot etalon is obtained. Thereby, the utilization efficiency of the wavelength region to be used can be improved.
In addition, the measurement sensor element and the band reflection filter are arranged on the same plane so that the same stress is applied. Even if the distortion of the part to be measured changes and the transmission spectrum of the pair of measurement sensor elements shifts to the short wavelength side or the long wavelength side, the reflection spectrum of the band reflection filter shifts to the shifted transmission spectrum by the same amount. Thus, the transmission spectrum can be completely separated. Therefore, even if the distortion of the part to be measured changes, the measurement accuracy can be improved.
Furthermore, since it has an arithmetic circuit that calculates the wavelength corresponding to the physical quantity detected by each sensor element based on the input signal and the output light from the sensor element, the signal output from the plurality of sensor elements On the basis of this, accurate measurement can be performed by calculating accurately with an arithmetic circuit.
Then, a first port through which light emitted from the sensor element for measurement enters, and a first port through which light incident from the first port is emitted to the band reflection filter and reflected light reflected by the band reflection filter is incident. Since the circulator having the three ports and the second port for emitting the light incident on the third port to the wavelength detecting means is provided, the signal is transmitted only in one direction by the circulator. Can be prevented from malfunctioning.

The wavelength detection type fiber sensor system of the present invention includes a light source, a wavelength change type optical sensor on which light emitted from the light source is incident and installed in a measurement target, and an output output from the wavelength change type optical sensor. A wavelength detection type fiber sensor system comprising a wavelength detection means for detecting light, wherein the wavelength change type optical sensor constitutes a Fabry-Perot etalon and is a sensor element for measuring a pair of band reflection filters arranged close to each other A band reflection filter having a reflection wavelength band narrower than a wavelength band including one line spectrum in the transmission spectrum band of the measurement sensor element, and the measurement sensor element and the band reflection filter have the same stress. a plurality of sensor heads having the same member which is arranged such that such said band reflection filter pairs and band reflection fill Are each composed of a fiber Bragg grating, and the sensor element is connected in series with a plurality of pairs each having a different center wavelength, and the wavelength detection means inputs output light from the sensor element and multi-channel demultiplexing A calculation circuit that calculates a wavelength corresponding to a physical quantity detected by each sensor element based on a signal demultiplexed by the device; a first port through which light emitted from the measurement sensor element is incident; A third port that emits light incident from the first port to the band reflection filter and incident reflected light reflected by the band reflection filter, and light incident on the third port has the wavelength. A circulator having a second port that emits to the detection means, and the circulator includes a plurality of the measurement sensor elements and the band. A third port of the upstream circulator is connected to the first port of the downstream circulator via the band reflection filter and the measurement sensor element, The second port of the most downstream circulator is connected to the wavelength detection means.
In the present invention of this configuration, the sensor element for measurement is configured by a Fabry-Perot etalon, as in the above-described invention, so that the full width at half maximum of the transmission spectrum of the sensor is narrower than that of a conventional single FBG, and the measurement resolution is improved. I can plan.
In addition, since the band reflection filter pair and the band reflection filter are each composed of a fiber Bragg grating, the cost of the filter can be suppressed, and the reflection band of the band reflection filter can be dynamically changed. Therefore, the measurement range of physical quantities can be expanded.
And the measurement range can be expanded by using a plurality of circulators.

The Fabry-Perot etalon preferably has a configuration in which the reflection wavelength band BW is narrower than twice the free spectrum range FSR so that only one transmission line spectrum is generated in the reflection wavelength band.

In the present invention having this configuration, only one transmission line spectrum is generated, so that a measurement error during wavelength calculation can be avoided.

The fiber Bragg grating pair constituting the band reflection filter pair has the same wavelength spectrum characteristics, the same physical length, and the relationship between the effective length Le and the grating pitch Λ of the fiber Bragg grating pair is Lg = A configuration in which the wavelength of the transmission line spectrum is made to coincide with the reflection center wavelength of the fiber Bragg grating so as to satisfy mΛ-2Le (m is a natural number and Lg is the length of the portion where the grating between the fiber Bragg grating pair is not drawn) is preferable. .
In the present invention having this configuration, the physical quantity measurement range of the sensor element composed of the FBG pair can be widened.

The reflection center wavelength of the fiber Bragg grating constituting the band reflection filter is matched with the wavelength of the transmission line spectrum of the Fabry-Perot etalon, and the reflection band of the fiber Bragg grating includes the transmission line spectrum of the Fabry-Perot etalon. And the structure narrower than the free spectrum range is preferable.
In the present invention of this configuration, the physical quantity measurement range is expanded to prevent the measurement range from being lowered due to the deviation of the center wavelength of the band reflection filter and the transmission spectrum of the Fabry-Perot etalon due to disturbance factors such as temperature. it can.

It is preferable that the measurement sensor element and the band reflection filter are arranged close to each other so as to satisfy the same temperature condition.
In the present invention having this configuration, even if the transmission spectrum of the pair of measurement sensor elements shifts to the short wavelength side or the long wavelength side due to a change in temperature, the reflected spectrum of the band reflection filter is equal to the shifted transmission spectrum. The transmission spectrum can be completely separated. Therefore, even if the temperature of the part to be measured changes, the measurement accuracy can be improved.

It is preferable that the measurement sensor element and the band reflection filter are bonded and fixed to the same member with an adhesive.
In the present invention having this configuration, the measurement sensor element and the band reflection filter are bonded and fixed to the base in a state where they are arranged close to each other. Can be accommodated by structure.

It is preferable that a part other than the fiber Bragg grating of the measurement sensor element and a part other than the band reflection filter are bonded and fixed to the same member with an adhesive.
In the present invention having this configuration, the physical quantity measurement range can be expanded.

It is preferable that a tube which is the same member is inserted through the measurement sensor element and the band reflection filter, and both ends of the tube, the measurement sensor element and the band reflection filter are bonded and fixed with an adhesive.
In the present invention having this configuration, since important portions of the measurement sensor element and the band reflection filter can be covered with the tube, even if a force is applied from the outside, these filters and the like can be prevented from being damaged.

The wavelength detection unit preferably includes a light spectrum pattern recognition circuit that receives a signal based on light transmitted from the sensor element and recognizes a detection wavelength from the sensor element from a signal pattern stored in advance.
In the present invention having this configuration, the detection wavelength is recognized from the signal pattern stored in advance, so that measurement can be easily performed.

The same members each comprise a silicon substrate having an under-cladding and over-cladding consisting of silicon dioxide, the Fabry-Perot etalon, said respective surrounded by the under-cladding and said over cladding, these undercladding and overcladding A first optical waveguide formed from a first core made of silicon dioxide doped with impurities for higher refractive index and having the same reflection wavelength band drawn close to the first optical waveguide. is composed of a waveguide Bragg grating and the second optical waveguide Bragg grating, the band reflection filter, the enclosed respectively under cladding and the overcladding, for the high refractive index than those of the undercladding and overcladding Impurity doped silicon dioxide It is preferably composed of an optical waveguide Bragg grating in the second optical waveguide formed from a second core and materials.
In the present invention having this configuration, the sensor can be mass-produced.

1 is a schematic configuration diagram of a wavelength detection fiber sensor system according to a first embodiment of the present invention. The schematic block diagram of the principal part of 1st Embodiment. The schematic block diagram which shows the principal part of the example from which 1st Embodiment differs. The schematic block diagram which shows the principal part of the example from which 1st Embodiment differs. The figure which shows the spectrum of the sensor element of the principal part of 1st Embodiment. The figure which shows the spectrum of the sensor element of the principal part of 1st Embodiment. The figure which shows the relationship between the emission spectrum of the broadband light source in 1st Embodiment, the incident spectrum to a 3rd Bragg grating (band reflection filter), the incident spectrum of an array waveguide grating, and the transmission spectrum of an array waveguide grating. The graph which shows the example of an actual measurement of the transmission spectrum of a sensor element. The schematic block diagram of the wavelength detection type fiber sensor system concerning 2nd Embodiment of this invention. The figure which shows the relationship of the emission spectrum of the broadband light source in 2nd Embodiment, the incident spectrum to a 3rd Bragg grating, the emission spectrum from an optical circulator, and the incident spectrum to a sweeping Fabry-Perot interference filter. Output pulse signal of transmitter, sawtooth output voltage of digital-to-analog converter driven by counting counter for counting the pulse signal, binary signal waveform, and swept Fabry-Perot interference driven by sawtooth output voltage It is a figure which shows the transmittance | permeability spectrum for every wavelength corresponding to this sawtooth-like output voltage of a filter in time series. The schematic block diagram of the wavelength detection type fiber sensor system concerning 3rd Embodiment of this invention. The figure which shows the relationship between the emission spectrum of the variable wavelength laser in 3rd Embodiment, the incident spectrum to a 3rd Bragg grating, the emission spectrum from a sensor element, and the incident spectrum to a photodiode. The figure which shows the modification of this invention and corresponds to FIG.

Embodiments of the present invention will be described with reference to the drawings.
1 to 8 show a first embodiment of the present invention.
FIG. 1 is a schematic configuration diagram of a wavelength detection type fiber sensor system according to the first embodiment.
In FIG. 1, a wavelength detection type fiber sensor system measures physical quantities such as temperature, strain, acceleration, vibration, etc., and a broadband light source 10 and an optical fiber F through which light incident from the broadband light source 10 passes. And a wavelength change type optical sensor 2 provided in the optical fiber F, and a wavelength detection means 3 for detecting the output light output from the wavelength change type optical sensor 2.
The broadband light source 10 has the same structure as that of the conventional example, and makes light incident on the optical fiber F over a predetermined wavelength region.

The wavelength change type optical sensor 2 includes a plurality of sensor elements 21 to 2n, a circulator 6 provided in each of the sensor elements 21 to 2n, and an ad filter 7 connected to the circulator 6. The add filter 7 may be used for general purposes in optical communication. For example, an add drop filter (model 100 GHz ROADM or 200 GHz ROADM) manufactured by Optoplex can be applied, and a signal transmitted from the circulator 6 is converted into a wavelength. This is a configuration for sending to the detection means 3.
Here, among the 21~2n plurality of sensor elements, the sensor element 21 is arranged on the broadband light source 10 side, the sensor element 22 toward the sensor element 21 to the wavelength detection means 3 side, the sensor element 23, the sensor element 24 ... ... sensor element 2n-1 and sensor element 2n are arranged. These sensor elements 21 to 2n are different from each other in the wavelength variation regions of the center wavelengths λ1 to λn to be detected.

The outline of the main part of the first embodiment is shown in FIG. 2A is a schematic diagram showing a plane, and FIG. 2B is a schematic diagram showing the side surfaces of the sensor elements 21 to 2n.
In FIG. 2, each of the sensor elements 21 to 2n includes a measurement sensor element 2A including first and second Bragg gratings, and a transmission line spectrum of the measurement sensor element 2A, and the first and second Bragg gratings. A third band reflection filter 2B having a wavelength band narrower than the reflection wavelength band as a reflection wavelength region, a base 2C in which the measurement sensor element 2A and the band reflection filter 2B are arranged on a plane, and the base 2C A sensor head including an adhesive layer 2D formed by adhering the measurement sensor element 2A and the band reflection filter 2B is provided. The base 2C is fixed to an installation object (not shown).

  The adhesive layer 2D has a thickness that is thicker than the thickness of the measurement sensor element 2A and the band reflection filter 2B, and the size on the plane is slightly smaller than the size of the base 2C. The material constituting the adhesive layer 2D is appropriately set. In the first embodiment, the structure of the sensor elements 21 to 2n is not limited to that shown in FIG. 2. For example, as shown in FIGS. 3A and 3B, the adhesive 2D is sensed. For example, the optical fiber F may be provided only in the optical fiber F excluding the FBG, and further, as shown in FIG. 4, an air hole made of, for example, a metal having an inner diameter slightly larger than the outer diameter of the optical fiber F is formed. Alternatively, an example in which the optical fiber F having the first and second FBGs and the optical fiber F having the FBG as the band reflection filter are inserted into the pipe 2P and both ends are fixed by the adhesive 2D may be used. In FIG. 4, reference numeral 2H is a hole for communicating the inside and outside of the pipe.

As described above, the measurement sensor element 2A has a pair of fiber Bragg gratings FBG, and the pair of fiber Bragg gratings FBG has a distance d required for forming a Fabry-Perot etalon at the center thereof, for example, They are formed with a gap of 100 μm.
The fiber Bragg grating FBG formed on both sides has a role of a mirror in the reflection wavelength band, and the lattice spacing of the FBG is 534.1144 when the reflection center wavelength is 1550 nm and the effective refractive index of the fiber core is 1.451, for example. nm.
The band reflection filter 2B is a fiber Bragg grating FBG formed on the optical fiber F, and this FBG is close to the center where the distance d of the measuring sensor element 2A is formed. In addition, the formation method of this FBG to the optical fiber F is the same as the past.

  The measuring sensor element 2A and the band reflection filter 2B are fixed to the base 2C so that the same temperature and the same stress are applied. Specifically, the smaller the distance between the center position of the measurement sensor element 2A (intermediate position of the distance d) and the center position of the band reflection filter 2B, the better. For example, an optical fiber having a diameter of 200 μm, coated with plastic on a quartz optical fiber on which a fiber Bragg grating is drawn, is used for the sensor element 2A and the band reflection filter 2B, respectively, and these optical fibers F are in contact with a plastic coating portion. The method to do can be adopted. Then, the measurement sensor element 2A and the band reflection filter are provided via the adhesive layer 2D so that the same stress is applied to the measurement sensor element 2A and the band reflection filter 2B due to distortion of the base 2C fixed to the measurement target. 2B is firmly fixed to the base 2C.

The measurement sensor element 2 </ b> A and the band reflection filter 2 </ b> B are connected to a circulator 6, and the circulator 6 has a first port 61, a second port 62, and a third port 63. The light emitted from the broadband light source 10 passes through the measurement sensor element 2A and enters the first port 61 of the circulator 6, and the light incident from the first port 61 is transmitted from the third port 63 to the band reflection filter 2B. The light reflected by the band reflection filter 2B is sent from the third port 63 to the wavelength detection means 3 through the second port 62. In FIG. 2, the add filter 7 is not shown. In addition, light in a wavelength region other than the reflection band of the band reflection filter enters the next sensor element after passing through the filter. For example, the sensor element 21 is incident on the sensor element 22, and the sensor element 22 is incident on the sensor element 23 via the optical fiber F.

FIG. 5 shows a schematic diagram of the spectrum transmitted from the sensor elements 21 to 2n. FIG. 5A shows the relationship between the wavelength and the wavelength of the light transmitted through the measurement sensor element 2A. Since the measurement sensor element 2A having the pair of fiber Bragg gratings FBG constitutes a Fabry-Perot etalon, the transmission spectrum transmitted through the measurement sensor element 2A has one line spectrum as shown in FIG. Will be included.
That is, the relationship between the bandwidth BW of the FBG constituting the Fabry-Perot etalon represented by Equation (4-4) described later and the free spectral range FSR of the Fabry-Perot etalon represented by Equation (6-5) is expressed by Equation (7). In order to equalize the reflection center wavelength of the FBG represented by the formula (4-3) and the peak wavelength of the Fabry-Perot etalon represented by the formula (6-4), the formula (8-1), that is, If the design parameters are set so that (8-2) holds, only one line spectrum appears at the center of the transmission band of the Fabry-Perot etalon.

  FIG. 5B shows the reflectance spectrum of the band reflection filter 2B. The reflectance spectrum from the band reflection filter 2B has a peak in a predetermined wavelength region. In the present embodiment, as shown in FIGS. 5A and 5B, the wavelength reflected by the band reflection filter 2B is matched with the wavelength band including the transmission spectrum including one line spectrum of the measurement sensor element 2A. To do. Therefore, in the present embodiment in which the measurement sensor element 2A and the band reflection filter 2B are connected in series, the spectrum of light reflected by the band reflection filter 2B through the measurement sensor element 2A is shown in FIG. As shown, it is detected as a single transmission spectrum. That is, if the band reflection filter 2B is a fiber Bragg grating and satisfies the following formulas (7) and (8-2), the spectrum of light reflected from the Bragg grating is one transmission spectrum. It becomes.

  Here, when a change in temperature or stress occurs in the measurement sensor element 2A, the measurement sensor element 2A itself expands or contracts, or the refractive index of the core portion of the fiber Bragg grating FBG constituting the measurement sensor element 2A. Changes, and the wavelength of the transmission spectrum transmitted by the measurement sensor element 2A changes. For example, as shown in FIG. 6A, the wavelength of the transmission spectrum is shifted to the longer wavelength side compared to FIG. 5A when no temperature change or stress change occurs. In the present embodiment, the measurement sensor element 2A and the band reflection filter 2B are fixed to the base 2C so that the same temperature and the same stress are applied, and the optical fiber F and the Bragg grating FBG constituting them are made of the same material. If so, the measurement sensor element 2A and the band reflection filter 2B are the same even if the temperature or stress change occurs in the measurement sensor element 2A and the wavelength of the transmission line spectrum of the measurement sensor element 2A changes. Since the conditions are temperature and stress, the spectrum reflected by the band reflection filter 2B is shifted in the same manner as the transmission line spectrum of the measurement sensor element 2A. For example, as shown in FIG. 6 (A), in the case where the transmission spectrum includes one line spectrum of the measuring sensor element 2A and the transmission spectrum is displaced to the long wavelength side, as shown in FIG. 6 (B), the band reflection filter The spectrum reflected by 2B shifts in the same way as the transmission spectrum. Therefore, in the present embodiment in which the measurement sensor element 2A and the band reflection filter 2B are connected in series, the spectrum of the light reflected by the band reflection filter 2B through the measurement sensor element 2A is shown in FIG. Even if the transmission spectrum of the measuring sensor element 2A shifts, the center wavelength of the line spectrum can be detected.

The above can be explained using mathematical formulas described later.
When the temperature T or strain ε of the center wavelength of the Fabry-Perot etalon represented by the formula (6-4) changes, the change Δλ _{e of the} center wavelength caused by the change is obtained from the formula (9). Similarly, the Fabry-Perot etalon The change Δλ _be of the center wavelength of the FBG that constitutes is obtained from Expression (10-1), and Expression (10-2) can be obtained by considering Expression (8-1). This means that the line spectrum is always located at the center of the transmission band of the etalon even if the temperature or strain changes.
Similarly, if the band reflection filter 2B is used as an optical fiber Bragg grating so as to satisfy the equations (7) and (8-2), the spectrum of light reflected from the fiber Bragg grating FBG will change with temperature and strain. Regardless of the line spectrum, it is always one line spectrum, and its wavelength matches the transmission wavelength of the fiber Fabry-Perot etalon.

In FIG. 1, the wavelength detection means 3 receives the output light from the sensor elements 21 to 2n and demultiplexes each wavelength band based on the AWG 31 as an array waveguide grating and the signal demultiplexed by the AWG 31. And an arithmetic circuit 32 that calculates the wavelengths detected by the sensor elements 21 to 2n.
The arrayed waveguide grating 31 includes a plurality of channels CH1 to CHn corresponding to the wavelength of output light to be demultiplexed.

The arithmetic circuit 32 is output from the photodiodes 3F1 to 3Fn arranged to face the respective channels CH1 to CHn, preamplifiers 3A1 to 3An connected to these photodiodes 3F1 to 3Fn, and preamplifiers 3A1 to 3An, respectively. And an arithmetic processing unit 32C that calculates based on the signal.
The arithmetic processing unit 32C receives analog signals output from the preamplifiers 3A1 to 3An, and a ratio operation using the digital signals output from these analog to digital conversion circuits 3B1 to 3Bn as input signals. The units 3C1 to 3Cm and the CPU 30 that calculates based on signals from these ratio calculation units 3C1 to 3Cm are configured.
The ratio calculation unit 3C1 receives signals from the analog-digital conversion circuit 3B1 and the analog-digital conversion circuit 3B2, and the ratio calculation unit 3C2 receives signals from the analog-digital conversion circuit 3B3 and the analog-digital conversion circuit 3B4. The ratio calculation unit 3Cm receives signals from the analog / digital conversion circuit 3Bn-1 and the analog / digital conversion circuit 3Bn.
Here, the ratio calculation performed for each of the sensor elements 21 to 2n is actually represented by W represented by Expression (1), which is a logarithm of the ratio. A method for calculating the output W of the sensor element is disclosed in Japanese Patent No. 3760649.

In the above mathematical formula (1), I ₁ and I ₂ are photocurrents generated by adjacent photodiodes 3F1 to 3Fn, for example, photodiodes 3F1 and 3F2, and S ₁ (λ) and S ₂ (λ). Indicates the product of the transmittance at each wavelength of the channels CH1 and CH2 of the AWG 31 that supplies light to each of these photodiodes and the light transmittance of the sensor at that wavelength, and φ (λ) is the wavelength-dependent intensity distribution of the light source 10 Δλ is the bandwidth of the wavelength of light incident on the photodiode. The center wavelength of one sensor is designed to shift with the physical quantity to be measured between the center wavelengths of the two channels of the arrayed waveguide grating used to detect the wavelength of the sensor.
If the wavelength of the light from the sensor is within a predetermined range, log (I ₁ / I ₂ ) is substantially constant for each wavelength of the irradiation light, and the light wavelength at that time is expressed by Equation (2). It is.

In this embodiment, the wavelength measurement principle based on the formulas (1) and (2) described above is applied to a predetermined wavelength range (a range of, for example, 3 nm or less between two adjacent channels of the AWG 31). This AWG31 is described in detail in a paper “Takahashi, et.al,“ Wavelength Multiplexer Based on SiO ₂ -Ta ₂ O ₅ Arrayed-Waveguide Grating, ”Journal of Lightwave Technology Vol.12, No.6, 1994”. ing.
Output light wavelength ranges are assigned to the sensor elements 21 to 2n so as not to overlap each other (for example, the sensor element 21 has 1500 to 1503 nm, the sensor element 22 has 1512 to 1515 nm, and the sensor element 23 has 1524 to By inputting the output light from these sensor elements 21 to 2n to the AWG 31, the center wavelengths of the plurality of sensor elements are separated and output to a plurality of channels of the AWG for each sensor.
By applying light from two adjacent channels of the AWG 31 to the photodiodes 3F1 to 3Fn, the mathematical formulas (1) and (2) described above are applied to the wavelength measurement ranges of the above-described sensors. In addition, the wavelength of each sensor is measured with high resolution.

  Output light from the sensor elements 21 to 2n of the light emitted from the broadband light source 10 (λ1 to λn of the center wavelength of the line spectrum in the transmission band) is input to the AWG 31. The photocurrents of the photodiodes 3F1, 3F2 (3F3, 3F4,... 3Fn-1, 3Fn) of the two adjacent channels CH1, CH2 (CH3, CH4,. The wavelength corresponding to the physical quantity such as the temperature at the position of each sensor element 21 to 2n can be obtained with high resolution by inputting the output to 3 Cm and inputting the output to the CPU 30 and performing the calculation of the formula (2). It can be detected.

FIG. 7 is a diagram showing the relationship between the outgoing light of the broadband light source 10, the incident light of the AWG 31, and the transmission spectrum of the AWG 31.
In FIG. 7A, when light is emitted from the broadband light source 10, this light passes through the measurement sensor element 2 </ b> A of the sensor element 21. The spectrum of the transmitted light is shown in FIG. The light that has passed through the measurement sensor element 2 </ b> A is incident on the first port 61 of the circulator 6. Thereafter, the light transmitted from the third port 63 of the circulator 6 to the band reflection filter 2B and reflected by the band reflection filter 2B returns to the third port 63 again, and then the AWG 31 of the wavelength detection means 3 from the second port 62. Sent to. FIG. 7C shows a spectrum of light emitted from the second port 62.

On the other hand, FIG. 7D shows an incident spectrum of the light irradiated from the broadband light source 10 to the band reflection filter 2B in the sensor element 22. FIG. 7E shows a spectrum of light emitted from the sensor element 22 through the circulator 6.
The above steps are performed for the sensor element 21, the sensor element 22, the sensor element 23,..., The sensor element 2n-1, and the sensor element 2n, and the line spectrums of signals as sensors of these sensor elements 21 to 2n are shown in FIG. 1 is added by the add filter 7 shown in FIG. The light incident on the AWG 31 is shown in FIG.

  In the AWG 31, the sensor element 21, the sensor element 22, the sensor element 23,..., The sensor element 2n-1 and the sensor element 2n correspond to the light transmitted from the sensor element 2n toward the AWG 31, respectively. , Channel CH4,..., Channel CHn-1 and channel CHn output a transmission spectrum. In the present embodiment, as described above, the wavelength of each corresponding sensor element is measured by calculating the ratio of the amount of light emitted from adjacent channels CH1 and CH2 (CH2 and CH3,... CHn-1 and CHn).

The operation of the wavelength detection means 3 in this embodiment is described in Japanese Patent No. 3760649, “Compact and fast wavelength detection method of FBG multiple sensor for plant control (Proceedings of the 32nd Optical Wave Sensing Technology Research Group, pp161- 168, December 2003), "Y.Sano and T.Yoshino," Fast Optical Wavelength Interrogator Employing Arrayed Waveguide Grating for Distributed Fiber Bragg Grating Sensors, ". Journal of Lightwave Technology Vol.21, pp.132-139 , January 2003., “Y.Sano and T. Yoshino,” “Effect of Light Source Spectral Modulation on Wavelength Interrogation in Fiber Bragg Grating Sensors and Its Reduction,” IEEE Sensors Journal, Vol.3, pp.44-49, According to the technology described in February 2003.

   Here, in the present embodiment, the fact that the full width at half maximum of the transmission spectrum of light output from the sensor elements 21 to 2n can be made smaller than the full width at half maximum of the conventional reflection spectrum will be described using mathematical expressions. The reflectance R of the FBG is obtained by solving a mode coupling equation, and can be expressed by the following equation (3).

However, if the average value of the refractive index-modulated effective refractive index generated by the FBG grating drawing is equal to the effective refractive index of the core where the FBG is not drawn, the following equation (4-1) (4-3) is complete. The bandwidth BW indicated by the difference between the wavelength on the long wavelength side and the wavelength on the short wavelength side where the reflectance becomes zero only when viewed from the wavelength giving the peak of the FBG can be obtained from Expression (4-4). Note that in equation (4-1) Equation (4-4) from, n _e is the effective refractive index of the FBG, [Delta] n _e is the amplitude of the refractive index modulation of the FBG, lambda is the grating pitch, lambda is the wavelength, lambda _B is reflection center wavelength of the FBG, _{L b} is the physical length of the FBG.

  On the other hand, since the transmittance T of the sensor elements 21 to 2n constitutes a Fabry-Perot interferometer, both FBGs have the same characteristics and dimensions. 5). The transmittance T of the sensor element is described in the paper “Yuri O. Barmenkov, et.al,“ Effective length of short Fabry-Perot cavity formed by uniform fiber Bragg gratings, ”Optics Express, Vol. 14, No. 14, pp.6394- 6399 ”.

However, Lg is the actual length of the portion not drawn lattice of adjacent FBG, L _e is a effective length caused by the phase delay with respect to the incident light of the reflected light FBG, equation (6 -1). Further, the maximum value Rmax of the reflectance R of the FBG can be obtained from Expression (6-2). Therefore, the effective length L _e is obtained from Expression (6-3). Further, the wavelength λ that gives the maximum value of the transmittance T can be obtained from Equation (6-4), where m is a natural number. Using this equation (6-4), the free spectral range FSR can be obtained from equation (6-5).

The transmission spectrum T of the sensor elements 21 to 2n having the Fabry-Perot configuration can be obtained by appropriately setting parameters and calculating using the formula (5).
For example, 2.08000Mm the length L _b of the FBG, 0.0006 refractive index variation Δn of FBG, the grating pitch Λ 537nm, 90.000μm the actual length L _g of the portion not drawn grid between FBG, FBG When the effective refractive index n _e and 1.4493, reflection wavelength band of the Fabry-Perot configured sensor element is 850Pm, full width at half maximum of the transmission spectrum in the band is 10pm, the center wavelength is 1556.476Nm.
The relationship between the bandwidth BW of the FBG constituting the Fabry-Perot etalon represented by Equation (4-4) and the free spectral range FSR of the Fabry-Perot etalon represented by Equation (6-5) is represented by Equation (7). The reflection center wavelength λ _{B of the} FBG represented by Expression (4-3) and the Fabry-Perot etalon peak wavelength Lg represented by Expression (6-4) are equal to each other, that is, Expression (8-2) ).

If the design parameters are set so that Equation (7) and Equation (8-2) hold simultaneously, only one line spectrum appears at the center of the transmission band of the Fabry-Perot etalon. Furthermore, even if the transmission spectrum of the sensor element shifts, the center wavelength of the line spectrum can be detected.
The reason for this will be described below using mathematical expressions. When the temperature T or strain ε of the center wavelength of the Fabry-Perot etalon represented by the formula (6-4) changes, the change Δλ _{e of the} center wavelength caused by the change is obtained by the formula (9).

Similarly, the change Δλ _be of the center wavelength of the FBG constituting the Fabry-Perot etalon can _be obtained by Expression (10-1).
Here, considering the equation (8-1), the equation (10-2) can be obtained.

  From the above, it can be shown by a theoretical formula that the full width at half maximum of the transmission spectrum of light transmitted from the sensor elements 21 to 2n can be made smaller than the full width at half maximum of the conventional reflection spectrum. Moreover, it means that the center wavelength of the line spectrum is always located at the center wavelength of the transmission band of the etalon even if the temperature or strain further changes.

Therefore, in the first embodiment, the following operational effects can be achieved.
(1) The wavelength change type optical sensor 2 includes a measurement sensor element 2A composed of a pair of fiber Bragg gratings FBG arranged close to each other constituting a Fabry-Perot etalon, and is in the reflection band of the measurement sensor element 2A. And a band reflection filter 2B having a wavelength band including the central wavelength of the transmission line spectrum as a reflection wavelength. Since the pair of measurement sensor elements 2A constitutes a Fabry-Perot etalon, the full width at half maximum of the transmission spectrum of light transmitted from the measurement sensor element can be made narrower than the full width at half maximum of the conventional reflection spectrum. The measurement resolution can be improved by making the full width at half maximum narrower than the conventional FBG. The full width at half maximum of the actually manufactured sensor element of this embodiment is several pm, which is more than 10 times narrower than that of the conventional FBG. For this reason, for example, the center wavelength is measured a plurality of times every predetermined time under a certain strain. However, when the data of the center wavelength was recorded, it was possible to easily increase the sensitivity, that is, the measurement resolution by about 5 times compared with the conventional sensor element. FIG. 8 shows an actual measurement example of the transmission spectrum of the sensor element 2A. As shown in FIG. 8, it can be seen that the wavelength around 1546 nm has higher transmittance than the wavelength regions before and after that, and as a result, the sensitivity of the sensor element is high.
Moreover, since the band reflection filter 2B has a wavelength band including the center wavelength of the transmission line spectrum in the reflection band of the measurement sensor element 2A as a reflection wavelength, a pair of measurement sensor elements due to temperature and strain Since the shift amount of the transmission spectrum of 2A and the shift amount of the reflection spectrum of the band reflection filter 2B are the same, one transmission line spectrum can be separated and detected. Therefore, wavelength measurement accuracy can be maintained regardless of temperature change, strain change, and the like.

(2) The measuring sensor element 2A and the band reflection filter 2B are arranged close to each other so as to be in the same temperature condition. When the temperature changes in the part to be measured, the transmission spectrum of the pair of measurement sensor elements 2A is shifted to the short wavelength side or the long wavelength side. In this embodiment, the measurement sensor element is shifted to the shifted transmission spectrum. The amount of shift of the reflection spectrum of the band reflection filter 2B under the same temperature condition as 2A is the same, and the transmission spectrum can be detected reliably. Therefore, the utilization efficiency of the wavelength region to be used is not narrowed due to the temperature change of the part to be measured, and the utilization efficiency of the wavelength region can be improved.

(3) The measuring sensor element 2A and the band reflection filter 2B were fixed to the base 2C so that the same stress was applied. When the distortion of the part to be measured changes, stress is transmitted to the measurement sensor element 2A and the band reflection filter 2B through the base 2C, and the transmission spectrum of the pair of measurement sensor elements 2A becomes shorter or longer. Will shift. In the present embodiment, the transmission spectrum can be reliably detected by making the shifted transmission spectrum have the same wavelength shift amount of the reflection spectrum of the band reflection filter 2B under the same stress as the measurement sensor element 2A. Therefore, the utilization efficiency of the wavelength region to be used is not narrowed due to the temperature change of the part to be measured, and the utilization efficiency of the wavelength region can be improved.

(4) Since the sensor element for measurement 2A and the band reflection filter 2B are bonded and fixed to the base 2C in a state where they are arranged close to each other, the transmission spectrum can be reliably obtained even if there is a change in temperature or strain in the measured part. Can be detected. For this reason, even if there is a change in the temperature and distortion of the part to be measured, the utilization efficiency of the wavelength region to be used is not narrowed, and the utilization efficiency of the wavelength region can be improved.

(5) Since the sensor elements 21 to 2n have different change wavelength regions of the sensing wavelengths λ1 to λn, respectively, it is possible to accurately measure the physical quantity change of the measured part.
(6) The wavelength detection means 3 includes an AWG 31 that is an arrayed waveguide grating that demultiplexes the output light from the sensor elements 21 to 2n for each wavelength region of each channel, and each signal based on the signal demultiplexed by the AWG 31. And an arithmetic circuit 32 that calculates the wavelengths detected by the sensor elements 21 to 2n. Since the wavelength range to be demultiplexed for each channel of the AWG 31 can be narrowed, a large number of channels can be secured. As a result, physical quantities of a large number of sensors can be measured.

Next, a second embodiment of the present invention will be described with reference to FIGS.
One component of the second embodiment is a swept Fabry-Perot interference filter 41. Papers “Alan D. kersy, Mihael A. Davis, Heather j. Patric, Michel LeBlanc, KP Koo, C. G. Askins, MA Putnam, and E. Joseph Friebele,“ Fiber Bragg Sensors, ”Journal of Lightwave Technology, Vol. 15, No. 8 1997 ”describes a method of performing wavelength detection from an FBG sensor using a Fabry-Perot interference filter. The feature of this embodiment is“ from an FBG pair constituting a Fabry-Perot etalon ”. There is no description in the above-mentioned paper of “a method for obtaining the center wavelength of a sensor element using a sweeping Fabry-Perot interference filter for a sensor”.
The second embodiment is different from the first embodiment in the configuration of the wavelength detection means, and the other configurations are the same as those in the first embodiment.
FIG. 9 is a schematic configuration diagram of a wavelength detection type fiber sensor system according to the second embodiment.
9, the wavelength detection fiber sensor system includes a broadband light source 10, an optical fiber F through which light emitted from the broadband light source 10 passes, a wavelength change optical sensor 2 provided in the optical fiber F, This is a configuration provided with wavelength detection means 4 for detecting output light output from the wavelength change type optical sensor 2.

The wavelength detection means 4 includes a swept Fabry-Perot interference filter 41 that receives light transmitted from the sensor elements 21 to 2n, and a photodiode 4F that is disposed to face the output CH of the swept Fabry-Perot interference filter 41. The preamplifier 4A connected to the photodiode 4F, the binarization circuit 4B for converting the analog signal output from the preamplifier 4A into a binary signal, and the optical spectrum pattern recognition circuit for receiving this time-series binary signal 42, a piezo element PZT for driving the swept Fabry-Perot interference filter 41, a count counter 43 for receiving the pulse signal from the transmitter 44 to drive the piezo element PZT, and counting the number of pulses, and the count counter 43 Digital-to-analog converter 45 that outputs the analog voltage corresponding to the count value. Configured to include a.
The optical spectrum pattern recognition circuit 42 receives the pulse signal from the transmitter 44 and the binary signal from the binarization circuit 4B. The binary signal is a time series signal, and its timing is defined by a pulse signal from the transmitter 44.

FIG. 10 is a diagram showing the relationship between the emission light spectrum of the broadband light source and the incident light spectrum to the sweeping Fabry-Perot interference filter in the second embodiment.
When the spectrum of light shown in FIG. 10A is incident from the broadband light source 10, this light passes through the sensor element 21, the sensor element 22, the sensor element 23,..., The sensor element 2n-1, and the sensor element 2n. Then, the light enters the sweep type Fabry-Perot interference filter 41. The light incident on the sweep type Fabry-Perot interference filter 41 is light emitted from the sensor elements 21 to 2n, and has a spectrum similar to that in FIG. 7F as shown in FIG.
2B shows the spectrum of the light that has passed through the measurement sensor 2A of the sensor element 21, and FIG. 3C shows the spectrum of the band reflection filter 2B that has passed through the measurement sensor 2A of the sensor element 21 through the circulator 6. The spectrum of the light reflected by the FBG and incident on the add filter 7 through the circulator 6, (D) shows the light that has passed through the measurement sensor 2 </ b> A of the sensor element 22 and reflected by the FBG of the band reflection filter 2 </ b> B through the circulator 6. (E) shows the spectrum of light incident on the add filter 7 via the circulator 6, and the light passing through the measurement sensor 2 </ b> A of the sensor element 22 passes through the circulator 6 and is reflected by the FBG of the band reflection filter 2 </ b> B and passes through the circulator 6 to the add filter 7. It is a spectrum of incident light.
FIG. 11 shows the output pulse signal of the transmitter 44 in (A), the sawtooth output voltage (B) of the digital-to-analog converter 45 driven by the counter 43 that counts the pulse signal, and the binary signal waveform (D). The transmission spectrum (C1), (C2),... (CN) for each wavelength corresponding to the sawtooth output voltage of the swept Fabry-Perot interference filter 41 driven by the sawtooth output voltage. This is schematically shown in time series. For example, when the center wavelength of the swept Fabry-Perot interference filter is swept from the short wavelength to the long wavelength in steps of 0.1 pm, if the sweep start wavelength is 1550.000 nm, (C1) is 1550.0000 nm, (C2 ) Is 1550.001 nm, and (C3) is 1550.0002 nm.

That is, in the optical spectrum pattern recognition circuit 42, when the light transmitted from the sensor elements 21 to 2n is input to the sweep-type Fabry-Perot interference filter 41, the sawtooth output of the digital / analog converter 45 input to the piezo element PZT. Since the voltage and the pass center wavelength of the swept Fabry-Perot interference filter 41 are linked by the transmitter 44, the center wavelengths of the sensor elements 21 to 2n can be found by observing the sawtooth output voltage.
For example, when the center wavelength of the swept Fabry-Perot interference filter 41 changes from a short wavelength to a long wavelength, the binary signal waveform becomes “0,0,0... 0,1,0,0,0,0 The wavelength that is “1” by the signal waveform pattern that is “is determined from the sawtooth output voltage shown in FIG. This determined wavelength is the center wavelength of the sensor elements 21 to 2n.
On the other hand, a signal waveform pattern such as “0,... 0,0,0,1,1,1,1,0,0,0” has a center wavelength of the sensor elements 21 to 2n. It is determined that it is not. That is, when “1” is equal to or less than the predetermined number of times, it is determined as the signal spectrum from the sensor elements 21 to 2n, and the wavelength giving “1” is determined as the center wavelength of the sensor elements 21 to 2n. When the predetermined number of times is 1, the wavelength is specifically determined. When the predetermined number N is 2 or more, for example, 3, the average value of these three wavelengths is set as the measurement wavelength.
The optical spectrum pattern recognition circuit 42 extracts a pattern in which several 0s exist on both sides of 1 and determines a wavelength corresponding to 1 based on the sawtooth output voltage. This can be realized by using a microcomputer. Further, when the count value of the count counter 45 is the highest count value of the counter, the transmission band of the sweep type Fabry-Perot interference filter 41 is set to the longest wavelength side (short wavelength side) by the piezo element PZT, and the next counter The count counter is initialized by the input pulse signal to 45, and the transmission band of the swept Fabry-Perot interference filter 41 is set to the shortest wavelength side (long wavelength side) by the piezo element PZT.

In the second embodiment, in addition to the same effects as (1) to (5) of the first embodiment, the following operational effects can be achieved.
(7) The wavelength detection means 4 is disposed opposite to the sweep type Fabry-Perot interference filter 41 for inputting the light transmitted from the sensor elements 21 to 2n and the output channel CH of the sweep type Fabry-Perot interference filter 41. Optical spectrum pattern recognition for receiving a photodiode 4F, a preamplifier 4A connected to the photodiode 4F, a binarization circuit 4B output from the preamplifier 4A, and a binary signal output from the binarization circuit 4B A circuit 42, a piezo element PZT for driving the sweep-type Fabry-Perot interference filter 41, a count counter 43 for counting the number of pulses from the transmitter 44, and a saw for driving the piezo element PZT upon receiving the output of the counter A wave voltage generating digital-analog converter 45 is provided. The optical spectrum pattern recognition circuit 42 receives the output pulse signal of the transmitter 44 and the binary signal, and recognizes the center wavelength from each of the sensor elements 21 to 2n from the signal pattern stored in advance. The center wavelength of the spectrum of each sensor element 21 to 2n is extracted by data processing of a signal such as “0,0,0,... 0,0,1,0,0,0,. Compared with the first embodiment in which the measurement range is determined by the AWG 31, the measurement range can be greatly increased. However, since there is no sweep in the first embodiment, the sweep time is unnecessary, and the system is characterized by having a higher speed response than the second embodiment.

Next, a third embodiment of the present invention will be described with reference to FIGS.
The third embodiment is different from the first embodiment in the configuration of the light source and the light detection means, and the other configurations are the same as those in the first embodiment.
FIG. 12 is a schematic configuration diagram of a wavelength detection fiber sensor system according to the third embodiment.
In the figure, a wavelength detection type fiber sensor system includes a variable wavelength laser 11 as a light source, an optical fiber F through which light incident from the variable wavelength laser 11 passes, and a wavelength change type light provided in the optical fiber F. The sensor 2 and the wavelength detection means 5 for detecting the output light output from the wavelength change type optical sensor 2 are provided.

The wavelength detection means 5 includes a photodiode 5F that inputs light transmitted from the sensor elements 21 to 2n, a preamplifier 5A connected to the photodiode 5F, and an analog signal output from the preamplifier 5A as a digital binary signal. A binarization circuit 5B for converting the signal to the optical spectrum, an optical spectrum pattern recognition circuit 52 for receiving a digital signal output from the binarization circuit 5B, and a pulse signal to the optical spectrum pattern recognition circuit 52 and the variable wavelength laser 11 And a transmitter 54 for sending.
The variable wavelength laser 11 has a count counter (not shown) inside and emits laser light corresponding to the number of input pulses. When the count counter is the maximum count value of the counter, The oscillation wavelength is set to be the longest wavelength in the variable range, and when the next pulse is input, the counter count value returns to zero, and the emitted wavelength becomes the shortest wavelength in the variable range. The variable wavelength laser 11 further shifts its oscillation wavelength to the longer wavelength side by one pulse when a pulse is further input. Similarly to the case of the variable wavelength laser, a count counter (not shown) is built in the optical spectrum pattern recognition circuit 52, and the count value corresponds to the laser oscillation wavelength. As a result, the binary signal corresponding to the laser oscillation wavelength is processed by the optical spectrum pattern recognition circuit 52 to determine the wavelength of each sensor element.
That is, the optical spectrum pattern recognition circuit 52 receives the pulse signal from the transmitter 54 and the signal from the binarization circuit 5B, so that the detection wavelength from each of the sensor elements 21 to 2n is determined from the signal pattern recorded in advance. Determine.

  FIG. 13 is a diagram showing the relationship between the emission spectrum of the variable wavelength laser and the emission spectrum from the sensor element in the third embodiment. As shown in FIG. 13A, when light having a wavelength that changes sequentially from the variable wavelength laser 11, that is, wavelength swept light, enters the optical fiber F, this light is sensor element 21, sensor element 22, sensor element 23. ,... Passes through the sensor element 2n-1 and the sensor element 2n. At this time, the spectrum transmitted from the sensor elements 21 to 2n is as shown in FIG. Hereinafter, the meanings of the signals in FIGS. 13B, 13C, 13D, and 13E are the same as the signals in FIGS. 10B, 10C, 10D, and 10E of the second embodiment, respectively. The meaning is the same.

The optical spectrum pattern recognition circuit 52 operates as follows, for example. The emitted light from the sensor elements 21 to 2n is “0,..., 0, 0, 0 when the laser center wavelength is changed from a short wavelength to a long wavelength by the photodiode 5F and the binarization circuit 5B via the preamplifier 5A. , 1, 0, 0, 0, 0,..., The wavelength corresponding to “1” is determined as the center wavelength from the sensor element.
In contrast, for example, "0, ... 0,1,1,1,1,1,1,1,1,1,0,0,0,0, ..." It is determined that the data pattern is not the center wavelength of the sensor elements 21 to 2n. That is, it is determined that the signal spectrum from the sensor elements 21 to 2n is “1” equal to or less than a certain number of times. When the predetermined number of times is 1, the wavelength is specifically determined. When the predetermined number N is 2 or more, for example, 5, the average value of these five wavelengths is set as the measurement wavelength. The optical spectrum pattern recognition circuit 52 can be realized by using a commonly used microcomputer. In order to change an analog signal into a digital signal, a binarization circuit is used in the second and third embodiments, but a multi-bit analog-digital converter is used instead of this binarization circuit. For example, a more accurate spectral pattern can be recognized.

Therefore, in 3rd Embodiment, there can exist the same effect as (1)-(5) of the said embodiment other than the same effect.
(8) The wavelength detection means 5 uses a photodiode 5F that receives light transmitted from the sensor elements 21 to 2n, a preamplifier 5A connected to the photodiode 5F, and an analog signal output from the preamplifier 5A as a binary value. A binarizing circuit 5B for converting to the optical spectrum pattern recognizing circuit 52 for receiving a digital signal output from the binarizing circuit 5B, and a count counter for serial pulse input / parallel output. An optical spectrum pattern recognition circuit 52 having a laser oscillation wavelength calculation unit corresponding to the above, and a variable wavelength laser 11 that has a built-in serial pulse input or parallel output counter and outputs light of a wavelength corresponding to the count value; And an optical spectrum pattern recognition circuit 52 that transmits the pulse signal from the transmitter 54 and the binarization circuit. Since the signal received from the path 5B is received and the detection signals from the sensor elements 21 to 2n are recognized from the pre-recorded signal patterns, the spectrum of the sensor elements 21 to 2n is the same as in the second embodiment. The center wavelength is extracted by signal processing the data series of “0, ... 0,0,0,1,0,0,0,0, ...”, so the measurement range is wide. The effect of becoming can be produced.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.
For example, in the above-described embodiment, the pair of measurement sensor elements 2A and the band reflection filter 2B are configured by FBG sensors. However, in the present invention, as shown in FIG. 14, the measurement sensor element 2A and the band reflection filter 2B are combined. The optical waveguide may be configured by a WBG sensor in which a fiber Bragg grating is drawn.
14A and 14B are diagrams corresponding to FIG. 2, in which FIG. 14A is a schematic diagram illustrating a plane, and FIG. 14B is a schematic diagram illustrating side surfaces of sensor elements 21 to 2n.

In FIG. 14, each of the sensor elements 21 to 2n includes a substrate 20C, a clad 20E provided on the substrate 20C, and a measurement sensor element 20A and a band reflection filter 20B provided on the clad 20E. .
The substrate 20C is formed in a plate shape from silicon or the like, and the back surface thereof is fixed to a measured part (not shown). The substrate 20C includes an underclad 20WUC and an overclad 20WOC, which are formed by depositing silicon dioxide (SiO ₂ ).
The measurement sensor element 20A is a WBG sensor configured by drawing a pair of wave guide Bragg grating WBGs with, for example, ultraviolet rays on an optical waveguide composed of an underclad 20WUC and a core 20WCO sandwiched between the overclad 20WOC. is there. Core 20WCO is the undercladding 20WUC formed of SiO ₂ as described above, the overcladding 20WOC as compared to germanium-doped SiO ₂ refractive index is formed from is fabricated to be higher than both the cladding. The optical waveguide is connected to the end of the optical fiber F via an adhesive portion 20D.

The pair of wave guides, Braggs, and gratings WBG constitutes a Fabry-Perot etalon, and a plurality of diffraction gratings are formed on both sides at a distance d required to construct the Fabry-Perot etalon at the center. Yes. Each diffraction grating formed on each side has a role of a mirror.
The band reflection filter 20B is a WBG sensor in which a wave guide, Bragg, and grating WBG are formed on the optical waveguide 20W, and the wavelength band including the peak of the transmission spectrum of the measurement sensor element 20A is used as the reflection wavelength, as in the above embodiment. Have. The embodiment using this optical waveguide is characterized in that the sensor element can be configured without using an adhesive. It is composed of an optical planar circuit technique based on a technique such as so-called sputtering or etching. When adhesives are used, problems remain in long-term reliability. However, this method is known as an element manufacturing technology that has a proven record of stability in devices in the field of optical communication, such as the aforementioned arrayed waveguide grating. That is, the wave guide Bragg grating that senses strain or temperature changes is formed by an optical planar circuit technology on a silicon substrate without using an adhesive, and thus has a feature that a sensor element having excellent stability can be realized. Note that although an adhesive is used for connection with the fiber F in FIG. 14, even if some instability remains in this portion, there is a possibility of affecting the connection loss between the optical path and the optical fiber. The adhesive does not adversely affect the stability of the sensor element 20A because it does not affect the filtering characteristics of the grating WBG.
When this sensor element for measurement is used for a temperature sensor, for example, it is obvious that if the temperature of the wave guide Bragg grating WBG changes, the reflected wavelength of the WBG changes, so that it can be used as a temperature sensor. Of course, it is obvious that a casing may be added to appropriately transmit the temperature of the case as the temperature sensing portion to the WBG. Similarly, with respect to strain, if the WBG is distorted, the reflection wavelength of the WBG changes, so that the strain sensor can be used.
The sensor element 2n may be configured such that the add filter 7 is omitted and the output signal from the circulator 6 is directly returned to the optical fiber F. In the above description, the embodiment for determining the center wavelength of the sensor element has been described. However, for example, since the center wavelength of the swept Fabry-Perot interference filter or the center wavelength of the emission spectrum of the variable wavelength laser changes with time, the wavelength at which the received light amount of the photodiode 4F or 5F shows a peak is detected as the wavelength to be measured. It may be a method to do.

Further, in each of the above-described embodiments, the light source is assumed to be constantly lit, but it is obvious that the light source may be lit only when measurement is desired to extend the substantial life of the light source.
In any of the embodiments, in the sensor element 2n, the add filter 7 may be omitted, and the output signal from the circulator 6 may be directly returned to the optical fiber F.

  The present invention relates to a health monitoring field for detecting and repairing, for example, deterioration of seismic performance before an earthquake occurs in a building structure such as a power plant including buildings, iron bridges, tunnels, and nuclear power plants, or ships, aircrafts, etc. In the preventive maintenance field, which constantly measures the strain of large structures such as rockets and predicts in advance that the strain will exceed a certain level and the structure suddenly breaks down, as well as chemical plants, oil refineries, etc. It can be used in the field of plant instrumentation for measuring the temperature of various parts of a plant where there is a possibility of explosion.

DESCRIPTION OF SYMBOLS 10 ... Broadband light source, 11 ... Variable wavelength laser (light source), 2 ... Wavelength change type optical sensor, 2A, 20A ... Sensor element for measurement, 2B, 20B ... Band reflection filter, 2C ... Base, 2D ... Adhesive layer, 3, 4, 5 ... Wavelength detection means, 21-2n ... Sensor element, 31 ... Array waveguide grating (AWG), 32 ... Arithmetic circuit, 42, 52 ... Center wavelength detection circuit, FBG ... Fiber Bragg grating, WBG ... Wave guide Bragg Grating

Claims (12)

A light source, a wavelength change type optical sensor that is incident on the light emitted from the light source and installed in a measurement target, and a wavelength detection unit that detects output light output from the wavelength change type optical sensor A wavelength detection type fiber sensor system,
The wavelength-variable optical sensor includes a measurement sensor element of a band reflection filter pair that constitutes a Fabry-Perot etalon and is arranged close to each other, and a wavelength that includes one line spectrum in the transmission spectrum band of the measurement sensor element A band reflection filter having a reflection wavelength band narrower than the band, and the sensor element for measurement and the band reflection filter are arranged on the same plane of the same member so that the same stress is applied,
The wavelength detection means includes an arithmetic circuit that inputs the output light from the sensor element and calculates a wavelength corresponding to a physical quantity detected by each sensor element based on the input signal.
A first port through which light emitted from the sensor element for measurement enters, and light incident from the first port is emitted to the band reflection filter and reflected light reflected by the band reflection filter is incident. A wavelength detection type fiber sensor system comprising: a circulator having a third port and a second port for emitting light incident on the third port to the wavelength detection means. A light source, a wavelength change type optical sensor that is incident on the light emitted from the light source and installed in a measurement target, and a wavelength detection unit that detects output light output from the wavelength change type optical sensor A wavelength detection type fiber sensor system,
The wavelength-variable optical sensor includes a measurement sensor element of a band reflection filter pair that constitutes a Fabry-Perot etalon and is arranged close to each other, and a wavelength that includes one line spectrum in the transmission spectrum band of the measurement sensor element A plurality of sensor heads having a band reflection filter having a reflection wavelength band narrower than the band, and the same member disposed so that the same stress is applied to the measurement sensor element and the band reflection filter;
The band reflection filter pair and the band reflection filter are each composed of a fiber Bragg grating,
In the sensor element, a plurality of pairs each having a different central wavelength are connected in series,
The wavelength detection means has an arithmetic circuit that inputs the output light from the sensor element and calculates a wavelength corresponding to a physical quantity detected by each sensor element based on a signal demultiplexed by the multi-channel demultiplexing device. And
A first port through which light emitted from the sensor element for measurement enters, and light incident from the first port is emitted to the band reflection filter and reflected light reflected by the band reflection filter is incident. A circulator having a third port and a second port for emitting the light incident on the third port to the wavelength detection means;
A plurality of the circulators are connected in series via the measurement sensor element and the band reflection filter, and the third port of the upstream circulator is connected to the first port of the downstream circulator. A wavelength detection type fiber sensor system, which is connected via a filter and the measurement sensor element, and the second port of the circulator on the most downstream side is connected to the wavelength detection means. In the wavelength detection type fiber sensor system according to claim 1,
Each of the band reflection filter pair and the band reflection filter includes a fiber Bragg grating. In the wavelength detection type fiber sensor system according to claim 2 or 3,
The Fabry-Perot etalon is configured such that the reflection wavelength band BW is narrower than twice the free spectrum range FSR so that only one transmission line spectrum is generated in the reflection wavelength band. Detection type fiber sensor system. In the wavelength detection type fiber sensor system according to claim 4,
The fiber Bragg grating pair constituting the band reflection filter pair has the same wavelength spectrum characteristics, the same physical length, and the relationship between the effective length Le and the grating pitch Λ of the fiber Bragg grating pair is Lg = The wavelength of the transmission line spectrum is matched with the reflection center wavelength of the fiber Bragg grating so as to satisfy mΛ-2Le (m is a natural number, Lg is the length of the portion where the grating between the fiber Bragg grating pair is not drawn). Wavelength detection type optical fiber sensor system. In the wavelength detection type fiber sensor system according to claim 5,
The reflection center wavelength of the fiber Bragg grating constituting the band reflection filter is matched with the wavelength of the transmission line spectrum of the Fabry-Perot etalon, and the reflection band of the fiber Bragg grating includes the transmission line spectrum of the Fabry-Perot etalon. A wavelength detection type optical fiber sensor system characterized by being narrower than the free spectrum range. In the wavelength detection type fiber sensor system according to any one of claims 1 to 6,
The wavelength detection type fiber sensor system, wherein the measurement sensor element and the band reflection filter are arranged close to each other so as to satisfy a condition of the same temperature. In the wavelength detection type fiber sensor system according to any one of claims 2 to 7,
The wavelength detecting fiber sensor system, wherein the measurement sensor element and the band reflection filter are bonded and fixed to the same member with an adhesive. In the wavelength detection type fiber sensor system according to claim 8,
The wavelength detection type fiber sensor system, wherein a part other than the fiber Bragg grating of the measurement sensor element and a part other than the band reflection filter are bonded and fixed to the same member with an adhesive. In the wavelength detection type fiber sensor system according to any one of claims 7 to 9,
A pipe which is the same member is inserted through the measurement sensor element and the band reflection filter, and both ends of the pipe are bonded and fixed to the measurement sensor element and the band reflection filter with an adhesive. Wavelength detection type fiber sensor system. In the wavelength detection type fiber sensor system according to any one of claims 2 to 9,
The wavelength detection means includes an optical spectrum pattern recognition circuit that receives a signal based on light transmitted from the sensor element and recognizes a detection wavelength from the sensor element from a signal pattern stored in advance. Wavelength detection type fiber sensor system. In the wavelength detection type fiber sensor system according to any one of claims 1 to 7 ,
The same member includes a silicon substrate having an under clad and an over clad each made of silicon dioxide,
The Fabry-Perot etalon, the enclosed respectively under clad and said over cladding, the first core having impurities doped silicon dioxide as a material for the high refractive index than those of the undercladding and overcladding The first optical waveguide to be formed is composed of a first optical waveguide Bragg grating and a second optical waveguide Bragg grating having the same reflection wavelength band drawn close to each other,
The band reflection filter, formed from the respective enclosed under cladding and the overcladding, a second core impurity for the high refractive index than those of the undercladding and overcladding has a doped silicon dioxide and material A wavelength detection type fiber sensor system, wherein the second optical waveguide is composed of an optical waveguide Bragg grating.

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