JP2014130071A - Optical sensing system, optical sensing method, and interrogator based on light zero method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve "temperature compensation" and "measuring range enlargement" in a same one reflection spectral shift optical sensor such as a BOF or an FBG.SOLUTION: An optical sensing system includes an optical processing part having a light emission part for outputting reference light and a light receiving part for receiving reflected light from an optical sensor part, the optical sensor part for shifting a reflection spectrum according to a physical amount to be measured, and a signal processing part for outputting a processing signal based on the reflection spectrum. The signal processing part outputs a control signal for subjecting the optical processing part to negative feedback control so that a specific parameter in the processing signal is constant, and a measuring signal corresponding to the physical amount based on the processing signal.

Description

  The present invention relates to a technique for optically measuring a physical quantity using a sensor such as FBG or etalon.

The inventors have proposed a simultaneous multi-point optical sensing system for temperature, pressure, and vibration that supports BOF (BPF on fiber end) as a sensor for several years and supports it with a DWPR (Dual Wavelength Push-pull Ratiometric Reflectometry) interrogator. ing. A sensing system for conventional FBG (Fiber Bragg Grating) is also proposed. (See Patent Documents 1 and 2.)
These are time-domain reflection measurement systems based on the PN code correlation method, and are attracting attention as new methods with many features compared to the spectral-domain measurement methods that have been the mainstream. There are many points that need to be improved for widespread use.
The present invention proposes a technique that solves several problems common to conventional sensors such as FBG and etalon, and also realizes new functions based on ideas beyond conventional common knowledge of optical fiber measurement. Is.

PCT / JP2009 / 64582 Japanese Patent No. 4308868

Reflection spectrum shift type optical sensors such as BOF and FBG are sensitive to temperature as well as pressure and strain, so that there is a problem that both are included in the obtained measurement signal and cannot be distinguished.
Further, the linearity of the optical sensor is sufficient within a certain range centering on a predetermined operating point, but sufficient linearity cannot be obtained if it is out of the above range. There is a problem that the predetermined operating point shifts depending on the environmental temperature. Therefore, when performing vibration measurement with fast movement (measured with a mechanism that changes the pressure on the BOF and the strain on the FBG due to vibration), the operating point as a vibration sensor shifts when the temperature changes. Therefore, there is a problem that accurate measurement cannot be performed. In order to solve such a problem, appropriate temperature compensation is required.
However, the temperature compensation usually employs a method in which two sensors having the same characteristics are prepared, the temperature conditions are the same, and the difference between both measured outputs is obtained when vibration is applied to only one of them. Such a temperature compensation method is very troublesome and expensive.
In the case of temperature measurement, the spectral shift measurement range of the reflection sensor is limited by the bandwidth of the multilayer BPF (Band Pass Filter) if it is BOF, and limited by the slope area width of the filter for wavelength analysis if it is FBG. I can't.
Therefore, an object of the present invention is to realize "temperature compensation" and "expansion of measurement range" in a reflection spectrum shift type optical sensor such as BOF or FBG with one same sensor.

In claim 1 according to the present invention,
A light processing unit including a light emitting unit that outputs reference light and a light receiving unit that receives reflected light from the optical sensor unit, the optical sensor unit that shifts a reflection spectrum according to a physical quantity to be measured, and the reflection spectrum In an optical sensing system comprising a signal processing unit that outputs a processing signal based on
The signal processing unit
A control signal for performing negative feedback control of the optical processing unit and a measurement signal corresponding to the physical quantity are output based on the processing signal so that a specific parameter in the processing signal is constant. It is characterized by that.
In claim 2,
The light emitting unit of the light processing unit is
Configured to output two reference beams of different wavelengths,
The optical sensor unit is
The band-pass type is configured such that the reflection level with respect to the two reference lights is complementarily shifted according to the applied physical quantity,
The signal processing unit
A ratio logarithm of reflectance corresponding to the two reference lights sandwiching the center wavelength of the reflection spectrum in the standard state of the sensor unit is output as the measurement signal, and
A signal for moving the wavelengths of the two reference lights of the light processing unit in parallel so that the direct current component of the specific logarithm is always zero is output as the control signal.
In claim 3,
The light receiving unit of the light processing unit is
When the reflected light from the optical sensor section is introduced into the inclined filter, the transmitted light and the reflected light whose levels are shifted in a complementary manner are given an optical path difference to be merged and received, and the levels of both lights are separated and detected in the time domain. Configured,
The gradient filter is
The spectral wavelength position is controlled by the control signal,
The signal processing unit
While obtaining the specific logarithm of the both lights in the time domain and outputting as the measurement signal,
A signal for controlling the characteristics of the gradient filter is output as the control signal so that the direct current component of the specific logarithm is always zero.

In claim 4,
The signal processing unit
Extracting the direct current component from the logarithm of the reflectance of the two wavelengths to obtain a measurement signal corresponding to a slow changing physical quantity,
An AC component is extracted from the specific logarithm of the reflectance of the two wavelengths and is configured to output as a measurement signal corresponding to a fast changing physical quantity,
The slow change physical quantity applied to the optical sensor unit and the fast change physical quantity can be separated and measured.

In the optical sensing method according to claim 5,
A light processing unit including a light emitting unit for outputting reference light and a light receiving unit for receiving reflected light;
A reference light emitted from the light emitting unit is supplied via an optical fiber, and a light sensor unit that changes a reflection spectrum returned to the optical fiber in accordance with a given physical quantity;
An optical sensing method using an optical sensing system comprising:
A control signal for controlling the change in the reflection spectrum is generated and output to the optical processing unit, so that a specific parameter included in the reflection spectrum is controlled to be always zero, and the control signal is signal-processed. By doing so, a measurement signal corresponding to the physical quantity is output.

The interrogator according to claim 6 is:
An interrogator used in the optical sensing system according to claim 1,
A light processing unit including a light emitting unit for outputting reference light and a light receiving unit for receiving reflected light from the optical sensor unit; and a signal processing unit for outputting a processing signal based on a reflection spectrum obtained from the light processing unit; With
The signal processing unit
A control signal for performing negative feedback control of the optical processing unit so that a specific parameter in the processing signal is constant, and a measurement signal corresponding to the physical quantity based on the processing signal are output. It is characterized by that.
In claim 7,
The light emitting unit of the light processing unit is
Configured to output two reference beams of different wavelengths,
The signal processing unit
A ratio logarithm of reflectance corresponding to the two reference lights sandwiching the center wavelength of the reflection spectrum in the standard state of the sensor unit is output as the measurement signal, and
A signal for moving the wavelengths of the two reference lights of the light processing unit in parallel so that the direct current component of the specific logarithm is always zero is output as the control signal.
In claim 8,
The light receiving unit of the light processing unit is
The reflected light from the optical sensor unit is configured to receive and merge by receiving an optical path difference between the transmitted light and the reflected light when introduced into the inclined filter, and separately detect the levels of both lights in the time domain,
The gradient filter is
The spectral wavelength position is controlled by the control signal,
The signal processing unit
While obtaining the specific logarithm of the both lights in the time domain and outputting as the measurement signal,
A signal for controlling the characteristics of the gradient filter is output as the control signal so that the direct current component of the specific logarithm is always zero.

In claim 9,
The signal processing unit
Extracting the direct current component from the logarithm of the reflectance of the two wavelengths to obtain a measurement signal corresponding to a slow changing physical quantity,
An AC component is extracted from the specific logarithm of the reflectance of the two wavelengths and is configured to output as a measurement signal corresponding to a fast changing physical quantity,
It is characterized in that it is possible to measure a physical quantity with a slow change and a physical quantity with a fast change applied to the optical sensor unit separately.

In the present invention, as described above, the signal processing unit always inputs the control signal to the optical processing unit, so that the DC component included in the relative logarithm ζ of the two-wavelength reflectance is always maintained at zero. To be controlled.
By performing signal processing on the control signal in this state, it is possible to obtain a signal including temperature information, which is a slowly changing physical quantity. A signal including vibration information, which is a physical quantity that changes quickly, can be obtained from the AC component included in the specific logarithm ζ of the two-wavelength reflectance.

<Concept>
The basic concept of the present invention will be described below.
Temperature, pressure, etc. are DC physical quantities that change gradually over time (this is called DC physical quantity), but changes in acceleration, strain, etc. due to vibration change compared to temperature, pressure, etc. Is a fast alternating physical quantity (this is called an alternating physical quantity).
By separating the DC component and the AC component from the measurement output, the DC physical quantity and the AC physical quantity can be separated.
The direct current component can be obtained by time averaging the measured output. In terms of electrical circuits, the DC component is a low-pass filtered output and the AC component is a high-pass filtered output, both of which can be obtained by simple signal processing.
The DC component corresponds to a DC physical quantity, that is, a DC physical quantity that changes gradually with time, such as temperature and pressure. The AC component corresponds to an AC physical quantity, that is, an AC physical quantity that changes more rapidly than temperature, pressure, or the like, such as a change in acceleration or strain due to vibration.
From the above, it is possible to measure both DC physical quantities and AC physical quantities with the same optical sensor, but in reality, the temperature change of the environment is not very small, and as described above, the operating point shifts due to the temperature change. Therefore, there is a problem in practical use because it exceeds the range where a certain degree of linearity can be obtained.

<Conventional electrical null method>
As a technique that can solve such a problem of the shift of the operating point, there is an idea of an electric zero method used in a moving electromagnetic coil type servo seismometer.
The seismometer detects vibration information from the capacitance change due to vibration, and negatively feeds it back to the moving electromagnetic coil to compensate for the shift of the operating point, so that the coil is always stationary, and the coil drive current in this state The value is taken out as a vibration measurement output. The biggest reason why this method is used is that the dynamic range is dramatically expanded.
However, even if such an electrical zero method is applied to a measurement system using an optical sensor, the optical sensor unit and the interrogator are only connected by an optical fiber, and the optical sensor unit is electrically connected to the optical sensor unit. You cannot give control.

<Optical Zero Method of the Present Invention>
Therefore, in the present invention (for example, the invention according to claim 2), in the measurement system using two wavelengths as reference light, the DC component of the measurement signal is negatively fed back to the means for controlling the wavelengths of the two reference lights.
In the case of a measurement system that detects the amount of shift in the reflected light spectrum using an inclined filter, the direct current component of the measurement signal is negatively fed back to the means for controlling the wavelength of the inclined filter for wavelength analysis, thereby the direct current component. Is always kept at zero. Such a system according to the present invention is referred to as an “optical zero method” with respect to the electric zero method.
In addition, by making a DC component of the measurement signal correspond to a DC physical quantity and making the AC component of the measurement signal correspond to an AC physical quantity, a single optical sensor is used to temporally measure temperature, pressure, and the like. It is possible to simultaneously measure both a DC physical quantity that changes gradually and an AC physical quantity that changes more rapidly than temperature, pressure, and the like, such as changes in acceleration and strain due to vibration.
Since the temperature change is generally gentle, the wavelength of the reference light and the spectral wavelength axis of the filter can be easily controlled by a Peltier element or the like in the laser module or the filter module. At this time, only the interrogator requires power, and no power is required up to the optical sensor.
In other words, in the case of a measurement system that uses two wavelengths as reference light depending on the operating temperature, the measurement system uses a method that negatively controls the two reference light wavelengths and detects the shift amount of the reflected light spectrum using a gradient filter. In this way, the DC component is always kept at zero by negative feedback control of the wavelength of the gradient filter for wavelength analysis.

In the following, techniques necessary for realizing the present invention will be described.
(1) Technology using two wavelengths As shown in FIG.
In order to detect the shift of the spectral characteristics of the MEMS etalon, the relative logarithm ζ of the reflectances r1 and r2 at the two wavelengths λ1 and λ2 sandwiching the wavelength (hereinafter simply referred to as “bottom wavelength”) λ0 of the spectral characteristics is set. Direct observation amount. This is represented by ζ as in the above equation. Since ζ uniquely corresponds to the spectral shift, it is possible to measure either one or both of the vibration displacement and the temperature.
The aim of using two wavelengths is to increase resistance to disturbances other than the shift of spectral characteristics by ratio calculation processing, as in the case of BOF. In other words, the reflectances r1 and r2 are affected by a wavelength-independent factor due to the bending loss of the optical fiber used, the power supply of the interrogator and fluctuations in the ambient temperature. Since it is canceled, robust measurement is possible.
The reason why the “specific logarithm ζ” of both the reflectances is taken into account is that the specific logarithm ζ becomes zero when they are equal and changes to ± symmetrically with respect to the left and right spectral shifts. This is a very important requirement when considering the “optical zero method” of the present invention.

(2) Technology for compensating for the amount of change The wavelength shift of the light source is controlled to shift in the direction opposite to the direction of the spectrum shift, thereby compensating for the spectrum shift.
(3) Technology to separate and extract multiple physical quantities BOF, etalon, FBG, etc. are sensitive not only to temperature but also to pressure and strain, so the physical quantity given to the sensor unit cannot be unified to any one In some cases, it is not possible to distinguish what the observed spectral shift is due to. However, if attention is paid to the difference in temporal movement of physical quantities, they may be discriminated.
When vibration and temperature are applied to the sensor unit, the specific logarithm ζ of the two-wavelength reflectance, which is a direct observation amount, appears as shown in FIG. 7A, for example.
At this time, the direct and static variation such as temperature and the alternating and dynamic variation such as vibration can be separated by the following signal processing.
First, only the direct current component is extracted by temporally averaging the specific logarithm ζ of the two-wavelength reflectivity, which is a direct observation amount.
Next, the AC component is extracted by subtracting the extracted DC component from the specific logarithm ζ of the two-wavelength reflectivity, which is a direct observation amount.

The DC component obtained by the above signal processing can include temperature information, and the AC component can include vibration information.
In FIG.
(A) is an instantaneous value of the two-wavelength reflectance ratio ζ. On the direct current temperature line with slow movement, fast vibration alternating current vibration information is superimposed.
(B) is obtained by extracting only the DC component by temporally averaging ζ.
(C) is obtained by subtracting a DC component from the instantaneous value, and is an AC component corresponding to vibration information.
In the present invention, by appropriately combining such signal processing, even when a plurality of physical quantities are mixed in the physical quantities given to the sensor unit, it may be possible to separate the physical quantities.

According to the present invention, the following effects can be obtained.
(1) The temperature measurement range is greatly expanded.
(2) Easy to use because it can compensate for a wide temperature range.
(3) Since the sensor part can be a single fiber, construction and maintenance are easy.
(4) Since it can be applied to conventional BOF / FBG / etalon, etc., its application range is wide.
(5) Since the conventional DWPR can be used almost as it is, the application is easy.
(6) When BOF / FBG is used for the sensor unit, the wavelength can be controlled by controlling the temperature of the light source, so that the control can be easily performed.
(7) The accuracy can be kept constant over a wide measurement area.
(8) No electrical / mechanical actuation mechanism is required.
(9) It is convenient because a single optical sensor can simultaneously measure a DC physical quantity such as temperature and an AC physical quantity such as vibration.
(10) High reliability due to simple principle.
(11) Construction and maintenance are easy because no complicated mechanism is required.
As described above, the optical sensing system according to the present invention is an epoch-making technique that can be said to be a servo system in the optical region, that is, “optical zero method”.

It is a block diagram of the basic composition of the present invention. It is a block diagram at the time of using BOF and an etalon for a sensor part. It is a block diagram at the time of using FBG for a sensor part. It is explanatory drawing at the time of using BOF and an etalon for a sensor part. It is explanatory drawing at the time of using FBG for a sensor part. It is explanatory drawing of the technique using 2 wavelengths in this invention. It is explanatory drawing of the technique isolate | separated into the some physical quantity in this invention. It is explanatory drawing of the wavelength control technique of the light source used for this invention. It is explanatory drawing of the technique which compensates the spectrum shift in this invention.

In FIG. 1 showing the basic configuration of the present invention,
Reference numeral 1 denotes an optical sensing system according to the present invention.
An optical processing unit 2 includes a light emitting unit 21 that outputs reference light and a light receiving unit 22 that receives reflected light.
Reference numeral 3 denotes an optical sensor unit to which the reference light emitted from the light emitting unit 21 is supplied via the optical fiber 5 and changes the reflection spectrum returned to the optical fiber 5 in accordance with a given physical quantity.
4 obtains a processing signal based on the reflection spectrum of the reflected light obtained in the light processing unit 2, and performs negative feedback control on the light processing unit 2 so that a specific parameter in the processing signal is constant. A signal processing unit configured to output a control signal and a measurement signal corresponding to the physical quantity based on the processing signal.
The signal processing unit 4 includes a control unit 41 that generates the control signal, and a processing unit 42 that performs signal processing on the processing signal and outputs the measurement signal including information on the physical quantity.
The optical processing unit 2 and the signal processing unit 4 constitute an interrogator 10.

In the optical sensing system 1 configured as described above,
Reference light having a predetermined wavelength corresponding to the characteristics of the optical sensor unit 3 is supplied from the light emitting unit 21 of the optical processing unit 2 to the optical sensor unit 3 through the optical fiber 5.
As will be described later, the light emitting unit 21 emits two reference lights having different wavelengths (reference light having two wavelengths) or broadband reference light according to the form of the optical sensor unit 3.

The optical sensor unit 3 may have a configuration in which a plurality of optical sensor units 3 are connected to the optical fiber 5 through optical branching and coupling means such as an optical coupler, if necessary.
The optical sensor unit 3 is provided with physical quantities such as temperature, vibration, and pressure as physical quantities to be measured. The optical sensor unit 3 shifts the spectrum of reflected light according to the given physical quantities. The reflected light given the change is returned to the optical fiber 5.
For example, the light emitting unit 21 of the light processing unit 2 emits reference light modulated by a predetermined random code (PN code), and the light receiving unit 21 of the light processing unit 2 emits the light sensor unit 3. A reflection response light from the optical sensor unit 3 is received by cross-correlation processing with the PN code, and a PNCR system configured to output as a processing signal is adopted. it can.

In the signal processing unit 4, the control signal generation unit 41 generates a control signal for changing the wavelength of the reference light or changing the characteristics of the gradient filter in the light receiving unit 22 based on the processing signal. And output to the light processing unit 2.
In the case of a measurement system in which the optical sensor unit 3 uses two wavelengths as reference light, the DC component of the control signal is negatively fed back to the means for controlling the wavelengths of the two reference lights.
In the case of a measurement system in which the optical sensor unit 3 detects the shift amount of the reflected light spectrum using a tilt filter, the DC component of the control signal is negatively fed back to the means for controlling the wavelength of the wavelength analysis tilt filter. By doing so, the direct current component is controlled to be always kept at zero.

  In addition, the DC component of the control amount is made to correspond to a DC physical quantity, the AC component is made to correspond to an AC physical quantity, a physical quantity that changes gradually in time, such as temperature and pressure, and acceleration and distortion caused by vibration. It is possible to simultaneously measure both physical quantities that change more rapidly than temperature, pressure, etc., such as changes.

FIG. 2 is a block diagram of an optical sensing system 1A using BOF and / or etalon in the optical sensor unit, and FIG.
This optical sensing system 1A includes an optical processing unit 2A, an optical sensor unit 3A, and a signal processing unit 4A.
The light processing unit 2A includes a light emitting unit 21A that outputs two reference lights having different wavelengths to the optical fiber 5A via the circulator 51A, and a light receiving unit 22A that receives the reflected light extracted by the circulator 51A. Yes.
The light emitting unit 21A is configured to output two reference lights having different wavelengths λ1 and λ2.
The optical sensor unit 3A is a band-pass sensor configured such that the level of the reflection spectrum with respect to the two reference lights λ1 and λ2 is complementarily shifted according to a physical quantity.
The circulator 51A is configured so that light from the light emitting portion 21A passes through the optical fiber 5A, and reflected light from the optical fiber 5A passes through the light receiving portion 22A.

The light receiving unit 22A is composed of one light receiving element that receives reflected light with respect to the two reference lights λ1 and λ2, and is configured to obtain respective reflectances γ1 and γ2.
The signal processing unit 4A sets a specific logarithm ζ of the reflectances γ1 and γ2 corresponding to the two reference lights λ1 and λ2 across the center wavelength λ0 of the reflection spectrum in the standard state of the optical sensor unit 3A, for example, The signal is processed by the measurement signal separation means 42 using the filtering means and output as a measurement signal, and the specific logarithm ζ is processed by the control signal generating means 41 using the low-pass filtering means, for example, to obtain the direct current component. And a control signal λCNT for shifting the wavelengths of the two reference lights of the light processing unit 2A in parallel so that the DC component thereof is always zero.

In the first embodiment, the wavelength of the light emitting element is controlled by the control signal so that the spectral shift in the optical sensor unit is compensated.
Control of the wavelength of the light emitting element can be realized by controlling the temperature in the module including the light emitting element. For this purpose, the light emitting unit 22A is provided with temperature control means for controlling the temperature in the module including the light emitting element based on the control signal.
The graph showing the relationship between temperature and wavelength shown in Fig. 8 is an experimental calculation of the relationship between the TEC (Thermo-Electric Control) temperature and output wavelength of two DFB LDs used as light sources in the DWPR interrogator. is there. The nominal output wavelength of each LDM is 1,540.56 nm and 1,542.94 nm, respectively.
According to FIG. 8, the wavelength temperature gradients of both LDMs are approximately equal to 75.5 and 77.2 pm / ° C. Therefore, if the settable temperature range is ± 30 ° C., the LD wavelength can be controlled with a width of about 2.3 nm. .
On the other hand, since the spectral shift due to the temperatures of BOF and FBG is both about 10 pm / ° C., it is practically sufficient that the temperature can be measured in the range of ± 230 ° C. with the above-mentioned wavelength variable width.

In the above configuration, as shown in FIG. 4B, when the spectrum of the reflected light from the optical sensor unit 3A is shifted from, for example, a solid line state to a broken line state by the given physical quantity, two wavelengths λ1 , Λ2, and the reflectances r1 and r2 increase and decrease (for example, when the reflectance r1 at one wavelength λ1 increases, the reflectance r2 at the other wavelength λ2 decreases) and change complementarily. Then, the ratio logarithm ζ (two-wavelength reflectance ratio) of the reflectances r1 and r2 at two wavelengths λ1 and λ2 sandwiching the bottom wavelength λ0 of the spectral characteristics is obtained.
By inputting the direct current component of the specific logarithm ζ to the light emitting unit 21 as a control signal, the wavelength of the reference light of two wavelengths is changed, and as shown in FIG. Is controlled so that the direct current component of the two-wavelength reflectance ratio ζ is always zero.
Such control can be said to be control for negative feedback control of the light processing unit 2A so that a specific parameter of the processing signal obtained by the light receiving unit 22A is constant.
Since the specific logarithm ζ uniquely corresponds to a spectral shift, a physical quantity that gradually changes with time such as temperature and pressure, and a change in temperature and pressure such as acceleration and distortion due to vibration. It is possible to simultaneously measure both physical quantities that change more rapidly than pressure.

In the signal processing unit 4A, the control signal generating unit 41 performs low-pass filtering processing and averaging processing of a two-wavelength reflectance ratio to extract the DC component, and the measurement signal separating unit 42 performs high-pass filtering. The AC component is extracted by processing or subtracting the DC component from the two-wavelength reflectance ratio.
The DC component is made to correspond to a DC physical quantity, the AC component is made to correspond to an AC physical quantity, a physical quantity that changes gradually over time, such as temperature and pressure, and a change in acceleration and strain due to vibration. Both physical quantities that change more rapidly than temperature, pressure, etc. can be measured simultaneously.

FIG. 3 is a block diagram of an optical sensing system 1B using FBG for the optical sensor unit, and FIG.
The optical sensing system 1B includes an optical processing unit 2B, an optical sensor unit 3B, and a signal processing unit 4B.
The light processing unit 2B receives two reference lights having different wavelengths to the optical fiber 5B via the first circulator 51B and the reflected light extracted by the first circulator 51B. A light receiving unit 22B is provided.
The optical sensor unit 3B is configured so that the reference light emitted from the light emitting unit 21B is supplied via the optical fiber 5B, and the reflection spectrum returned to the optical fiber 5B is changed according to a given physical quantity. This is a light reflection type sensor such as an FBG.

For example, an SLD (Super Luminescent Diode) having a broadband emission spectrum is used for the light emitting unit 21B.
The light receiving unit 22B
A second circulator 23B, a gradient filter 24B, a dummy fiber 25B (see FIG. 5A) coupler 26B, and a light receiving element are provided.
The filter module including the gradient filter 24B is provided with temperature control means for controlling the temperature of the gradient filter 24B based on the control signal.
The reflected light from the optical sensor unit 3B is taken out by the first circulator 51B and further introduced into the inclined filter 24B by the second circulator 23B, and the reflected light from the inclined filter 24B is reflected by the second circulator. 23B is introduced to the dummy fiber 25B side.

The coupler 26B is configured to combine the light transmitted through the inclined filter 24B and the reflected light having an optical path difference given by the dummy fiber 25B, and introduce it to the light receiving element. Since the transmitted light and the reflected light are given a time difference by the dummy fiber 25B, the light receiving element can separately detect the levels of both lights in the time domain.
The spectral wavelength position of the inclined filter 24B is controlled by controlling the temperature of the filter module including the inclined filter 24B by the control signal.

The signal processing unit 4B obtains a specific logarithm ζ of both the lights separated and detected in the time domain and outputs it as a processing signal,
A low-pass filter that outputs the DC component as the control signal in order to control the temperature of the filter module including the gradient filter 24B of the light receiving unit 22B so that the DC component of the specific logarithm ζ is always zero. A wave portion 41B is provided.
Depending on the physical quantity applied to the optical sensor unit 3B, for example, when the peak wavelength λ0 of the spectrum of the reflected light is shifted toward the shorter wavelength as shown in FIG. 5B, the transmission characteristic indicated by the solid line and the broken line The level of transmitted light of the inclined filter 24B increases and the level of reflected light decreases (the change in level is referred to as “complementary level shift”).
The temperature of the filter module is controlled by the control signal, and the operating point of the gradient filter 24B is shifted on the wavelength axis of FIG. 5B so that the direct current component of the specific logarithm ζ is always zero. To control. (See FIG. 5C.)
Such control can be said to be control for negative feedback control of the light processing unit 2B so that a specific parameter of the processing signal obtained by the light receiving unit 22B is constant.

A predetermined initial value is set in the low-pass filtering unit 41B. The DC component is output as a measurement signal corresponding to the DC physical quantity.
In addition, a high-pass filtering unit 42B that outputs an AC component of the specific logarithm ζ as a measurement signal corresponding to the AC physical quantity is provided.
The light receiving element is a single light receiving element, and the transmitted light and the reflected light are collectively received by a coupler. However, since a time difference is given, the levels of both lights can be separately detected in the time domain.

In the optical sensing method using the optical sensing system according to the present invention,
As shown in FIG.
When the spectrum of the observed two-wavelength reflectance ratio ζ is shifted on the wavelength axis due to the physical quantity given to the optical sensor unit, the reflectance at the two wavelengths is equal, in other words, the two-wavelength reflectance. By automatically controlling the wavelength of the light source with a control signal so that the DC component of the ratio ζ is always 0 (dB), the DC operating point is fixed at the optimum point. The control signal at this time includes physical quantity information given to the optical sensor unit.
Therefore, it is possible to reproduce the physical quantity given to the optical sensor unit by processing the control signal.
When the physical quantity includes a plurality of different elements, as in the case described above, information on the physical quantity that changes slowly is obtained from the direct current component of the two-wavelength reflectance ratio, and the alternating current of the two-wavelength reflectance ratio is obtained. It is possible to obtain information on physical quantities that change quickly from the components.
Thus, by generating a control signal that compensates for the shift in the spectrum of the reflected wave in the optical sensor unit, the optical sensor unit can be operated at an optimum point. In addition, by processing the control signal, information on the physical quantity added to the optical sensor unit can be obtained.

1, 1A, 1B Optical sensing system 10 Interrogator 2, 2A, 2B Light processing unit 21, 21A, 21B Light emitting unit 22, 22A, 22B Light receiving unit 24B Tilting filter 25B Dummy fiber 3, 3A, 3B Optical sensor unit 4, 4A, 4B Signal processing unit 41, 41A, 41B Control unit 42, 42A, 42B Processing unit 5, 5A, 5B Optical fiber

Claims (9)

A light processing unit including a light emitting unit that outputs reference light and a light receiving unit that receives reflected light from the optical sensor unit, the optical sensor unit that shifts a reflection spectrum according to a physical quantity to be measured, and the reflection spectrum In an optical sensing system comprising a signal processing unit that outputs a processing signal based on
The signal processing unit
A control signal for performing negative feedback control of the optical processing unit and a measurement signal corresponding to the physical quantity are output based on the processing signal so that a specific parameter in the processing signal is constant. An optical sensing system based on the optical null method. The light emitting unit of the light processing unit is
Configured to output two reference beams of different wavelengths,
The optical sensor unit is
The band-pass type is configured such that the reflection level with respect to the two reference lights is complementarily shifted according to the applied physical quantity,
The signal processing unit
A ratio logarithm of reflectance corresponding to the two reference lights sandwiching the center wavelength of the reflection spectrum in the standard state of the sensor unit is output as the measurement signal, and
2. The optical zero according to claim 1, wherein a signal that moves the wavelengths of the two reference lights of the optical processing unit in parallel so that the direct current component of the specific logarithm is always zero is output as the control signal. Optical sensing system based on the position method. The light receiving unit of the light processing unit is
When the reflected light from the optical sensor section is introduced into the inclined filter, the transmitted light and the reflected light whose levels are shifted in a complementary manner are given an optical path difference to be merged and received, and the levels of both lights are separated and detected in the time domain. Configured,
The gradient filter is
The spectral wavelength position is controlled by the control signal,
The signal processing unit
While obtaining the specific logarithm of the both lights in the time domain and outputting as the measurement signal,
2. The optical null method according to claim 1, wherein a signal for controlling the characteristics of the gradient filter is output as the control signal so that the direct current component of the logarithm is always zero. Optical sensing system. The signal processing unit
Extracting the direct current component from the logarithm of the reflectance of the two wavelengths to obtain a measurement signal corresponding to a slow changing physical quantity,
An AC component is extracted from the specific logarithm of the reflectance of the two wavelengths and is configured to output as a measurement signal corresponding to a fast changing physical quantity,
4. The optical null method according to claim 2, wherein a slow-change physical quantity and a fast-change physical quantity applied to the optical sensor unit can be separated and measured. 5. Optical sensing system. A light processing unit including a light emitting unit for outputting reference light and a light receiving unit for receiving reflected light;
A reference light emitted from the light emitting unit is supplied via an optical fiber, and a light sensor unit that changes a reflection spectrum returned to the optical fiber in accordance with a given physical quantity;
An optical sensing method using an optical sensing system comprising:
A control signal for controlling the change in the reflection spectrum is generated and output to the optical processing unit, so that a specific parameter included in the reflection spectrum is controlled to be always zero, and the control signal is signal-processed. And outputting as a measurement signal corresponding to the physical quantity. An interrogator used in the optical sensing system according to claim 1,
A light processing unit including a light emitting unit for outputting reference light and a light receiving unit for receiving reflected light from the optical sensor unit; and a signal processing unit for outputting a processing signal based on a reflection spectrum obtained from the light processing unit; With
The signal processing unit
A control signal for performing negative feedback control of the optical processing unit so that a specific parameter in the processing signal is constant, and a measurement signal corresponding to the physical quantity based on the processing signal are output. Interrogator characterized by that. The light emitting unit of the light processing unit is
Configured to output two reference beams of different wavelengths,
The signal processing unit
A ratio logarithm of reflectance corresponding to the two reference lights sandwiching the center wavelength of the reflection spectrum in the standard state of the sensor unit is output as the measurement signal, and
7. The interrogator according to claim 6, wherein a signal that moves the wavelengths of the two reference lights of the light processing unit in parallel so that the DC component of the logarithm is always zero is output as the control signal. The light receiving unit of the light processing unit is
The reflected light from the optical sensor unit is configured to receive and merge by receiving an optical path difference between the transmitted light and the reflected light when introduced into the inclined filter, and separately detect the levels of both lights in the time domain,
The gradient filter is
The spectral wavelength position is controlled by the control signal,
The signal processing unit
While obtaining the specific logarithm of the both lights in the time domain and outputting as the measurement signal,
7. The interrogator according to claim 6, wherein a signal for controlling the characteristics of the gradient filter is output as the control signal so that the DC component of the specific logarithm is always zero. The signal processing unit
Extracting the direct current component from the logarithm of the reflectance of the two wavelengths to obtain a measurement signal corresponding to a slow changing physical quantity,
An AC component is extracted from the specific logarithm of the reflectance of the two wavelengths and is configured to output as a measurement signal corresponding to a fast changing physical quantity,
9. The interrogator according to claim 7, wherein a physical quantity that changes slowly and a physical quantity that changes quickly can be measured separately.

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