JPH05107119A - Detecting device of temperature distribution - Google Patents

Abstract

PURPOSE:To conduct highly-precise measurement of a temperature distribution by controlling the relationship between an oscillation wavelength of a laser and a cut wavelength of a filter to be prescribed and by eliminating thereby an error due to a change in the oscillation wavelength of the laser. CONSTITUTION:A reflected light signal from the terminal 8b of an optical fiber 4 for measurement, which is contained in two Raman scattering lights outputted from a branching filter 15, is detected by a storage-computation control circuit 22. An oscillation temperature control signal is generated on the basis of the ratio between the two Raman scattering lights, an ambient temperature of a laser light source 12 generating a light signal is controlled by a thermal drive circuit 13 on the basis of the oscillation temperature control signal, and thereby the wavelength of the light signal is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature distribution detecting device using backscattered light in an optical fiber.

[0002]

2. Description of the Related Art In a sensor utilizing the backscattered light of an optical fiber, the scattered light in the optical fiber is excited by a laser pulse incident on the optical fiber, and the scattered light is scattered into the spectrum, intensity, polarization, etc. of the excited scattered light. Including location temperature information,
The one-dimensional distribution of the temperature along the optical fiber is measured by detecting the backscattered light propagating to the incident side of the excitation laser pulse which is the rear in the optical fiber as a time series signal.

In this case, scattered light generated when a laser pulse is incident on the optical fiber includes Rayleigh scattered light due to density fluctuation, Brillouin scattered light due to propagation fluctuation, and Raman scattered light due to vibrational rotation of molecules.

Of these, the Brillouin scattered light and the Raman scattered light are inelastic scattered light, and have different spectra from the excitation light. The temperature information is contained in all three scattered lights, but Raman scattered light has the highest sensitivity to temperature, and its intensity changes depending on the temperature.

When the temperature is measured using Raman scattered light, the Stokes Raman scattered light whose wavelength shifts to the longer wavelength side than the excitation light and the anti-Stokes Raman scattered light whose wavelength shifts to the shorter wavelength side are filtered by a filter. It is selected and the temperature distribution is calculated from the value based on the ratio of the two scattered lights. Further, even if the ratio is not used, it is necessary to select one of the scattered lights with a filter.

In this case, a dielectric multi-layer film filter, a metal film filter, or the like is used as the filter, and the scattered light deviated by the Raman shift wavelength of several tens nm determined by the fiber material from the spectrum of the excitation light is steep. It must be selected according to the filter characteristics.

Therefore, the relative positional relationship between the cut wavelength of the filter and the oscillation wavelength of the pump laser must be stable with respect to changes in ambient temperature. If the relationship between the two changes, the apparent temperature change causes a zero point change or a span error.

In order to industrially produce such a sensor, the oscillation wavelength of the laser with respect to the above-described filter is compensated so that it does not vary from laser to laser, and it is always relative to the cut wavelength of the filter. The positional relationship must be constant.

[0009]

However, in the above-mentioned conventional temperature distribution detecting device, since the ratio of the anti-Stokes Raman scattered light and the Stokes Raman scattered light is essentially a function of temperature, a change in the detected signal is caused. Since it is not possible to determine whether the value is due to the temperature or the oscillation wavelength of the laser, the laser oscillation wavelength and the filter cut wavelength are not controlled, and accurate temperature distribution cannot be measured. There was a problem.

In view of the above circumstances, the present invention makes it possible to control the relationship between the laser oscillation wavelength and the cut wavelength of the filter to be constant, thereby eliminating errors caused by fluctuations in the oscillation wavelength of the laser and achieving high accuracy. An object of the present invention is to provide a temperature distribution detecting device capable of measuring temperature distribution.

[0011]

In order to achieve the above-mentioned object, the temperature distribution detecting device according to the present invention makes an optical signal incident on the incident end of a measuring optical fiber, and the optical signal is measured by a demultiplexer. The backward Raman scattered light generated when traveling through the optical fiber for use is sorted into two Raman scattered lights, anti-Stokes Raman scattered light and Stokes Raman scattered light,
The arrival time of the two Raman scattered lights at the entrance end,
In a temperature distribution detecting device that measures a temperature distribution along the measurement optical fiber based on a calculation result with the intensity, in the measurement optical fiber included in the two Raman scattered lights output from the demultiplexer, An end face reflected light detection unit that detects a reflected light signal from the end face, and an oscillation temperature control signal generation unit that generates an oscillation temperature control signal based on the ratio of two Raman scattered lights detected by the end face reflected light detection unit. ,
And a temperature control unit for controlling the ambient temperature of the laser light source that generates the optical signal based on the oscillation temperature control signal output from the oscillation temperature control signal generation unit to control the wavelength of the optical signal. It has a feature.

[0012]

In the above construction, the reflected light signal from the end face of the optical fiber for measurement contained in the two Raman scattered lights outputted from the demultiplexer is detected by the end face reflected light detecting section, and the oscillation temperature control signal is generated. Section generates an oscillation temperature control signal based on a ratio of the two Raman scattered lights detected by the end surface reflected light detection section, and the temperature control section converts the oscillation temperature control signal obtained by the oscillation temperature control signal generation section into an oscillation temperature control signal. Based on this, the ambient temperature of the laser light source that generates the optical signal is controlled to control the wavelength of the optical signal.

[0013]

1 is a block diagram showing an embodiment of a temperature distribution detecting device according to the present invention.

The temperature distribution detecting apparatus shown in this figure comprises a laser light source section 2, a directional coupler 3, an optical fiber 4, a light receiving section 5, a processing section 6 and a display 7, and a laser. The laser pulse light is emitted from the light source unit 2 and is guided into the optical fiber 4 through the directional coupler 3, and the backscattered light of the laser pulse light is extracted through the directional coupler 3 and extracted. Is guided to the light receiving section 5 and separated into anti-Stokes Raman scattered light and Stokes Raman scattered light to generate two electric signals corresponding to the temperature distribution of the measurement target portion 9 in which the optical fiber 4 is installed. This is processed by the processing unit 6 and displayed on the display 7, and the Fresnel reflection signal when the laser pulse light reaches the terminal end 8b of the optical fiber 4 is received via the directional coupler 3. Guide to Part 5 Controlling a bench-Stokes Raman scattering light, the temperature of the laser light source 12 constituting the laser light source unit 2 as these ratios is constant at Stokes Raman scattering light and the separating processing unit 6.

The laser light source unit 2 generates a drive pulse signal when a trigger signal is output from the processing unit 6, and a pulse signal when the drive pulse signal is output from the pulse generation circuit 10. When a drive circuit 11 for generating, a drive signal is output from the drive circuit 11, a laser light source 12 for generating laser pulse light, and an oscillation temperature control signal is output from the processing unit 6,
A thermal drive circuit 13 that controls the temperature of the laser light source 12 based on the oscillation temperature control signal and adjusts the wavelength of the laser pulse light emitted from the laser light source 12 is supplied from the processing unit 6. When the pulse signal is supplied from the processing unit 6 while controlling the temperature of the laser light source 12 based on the control signal, the laser light source 12 generates a laser pulse light having a wavelength specified by the oscillation temperature control signal. Then, this is supplied to the directional coupler 3.

The directional coupler 3 takes in the laser pulse light emitted from the laser light source 12 of the laser light source unit 2 and makes it enter from one end (entrance / emission end) 8a of the optical fiber 4 and from this one end 8a. The emitted backscattered light or Fresnel reflected light is extracted and supplied to the light receiving unit 5.

In this case, when the laser pulse light is incident from the one end 8a of the optical fiber 4, the Stokes Raman scattered light or the anti-Stokes Raman scattered light is returned from each part in the optical fiber 4 by the laser pulse light, and this is the above-mentioned. The laser pulse light is emitted from one end 8a of the optical fiber 4, and when the laser pulse light reaches the end portion 8b of the optical fiber 4, the end portion 8b is Fresnel-reflected and emitted from the one end 8a of the optical fiber 4. The Stokes Raman scattered light, anti-Stokes Raman scattered light, and Fresnel reflected light are extracted by the directional coupler 3 and supplied to the light receiving unit 6.

The light receiving section 6 converts the scattered light and the reflected light supplied from the directional coupler 3 into Stokes Raman scattered light components,
A demultiplexer 15 for separating the anti-Stokes Raman scattered light component, a detector 16 configured by an avalenche photodiode or the like for converting the Stokes Raman scattered light component output from the demultiplexer 15 into an electric signal, Amplifier 17 that amplifies the electrical signal output from detector 16
A detector 18 configured by an avalenche photodiode or the like for converting the anti-Stokes Raman scattered light component output from the demultiplexer 15 into an electric signal, and an amplifier for amplifying the electric signal output from the detector 18. 19
And the scattered light and the reflected light supplied from the directional coupler 3 are separated into a Stokes Raman scattered light component and an anti-Stokes Raman scattered light component, each of which is converted into an electric signal and processed. Supply to part 6.

The processing unit 6 outputs the Stokes Raman scattered light component signal output from the amplifier 17 of the light receiving unit 5 at high speed.
An A / D converter 20 for A / D conversion, an A / D converter 21 for A / D converting the anti-Stokes Raman scattered light component signal output from the amplifier 19 of the light receiving unit 5 at a high speed, which are set in advance. The process of generating a trigger signal at a predetermined cycle and supplying the trigger signal to the laser light source unit 2 and the A / D
A process of measuring the temperature distribution at the place where the optical fiber 4 is installed based on the Stokes Raman scattered light component signal and the anti-Stokes Raman scattered light component signal output from the converters 20 and 21, and the processing result is displayed on the display. 7, the laser light source 1 based on the Stokes Raman scattered light component signal and the anti-Stokes Raman scattered light component signal by Fresnel reflection among the Stokes Raman scattered light component signal and the anti-Stokes Raman scattered light component signal.
A storage arithmetic control circuit 22 for performing a process of determining the wavelength of the laser pulsed light emitted from the laser light source 2, a process of generating an oscillation temperature control signal based on the process result, and a process of supplying the oscillation temperature control signal to the laser light source unit 2 and the like. It has and.

Then, a trigger signal is generated at a preset predetermined period and is supplied to the laser light source unit 2, or the Stokes Raman scattered light component signal output from each of the amplifiers 17 and 19 Based on the Stokes Raman scattered light component signal, the temperature distribution of the measurement target portion 9 in which the optical fiber 4 is installed, the measurement result is supplied to the display 7, the Stokes Raman scattered light component signal, Among the anti-Stokes Raman scattered light component signals, the wavelength of the laser pulse light emitted from the laser light source 12 is determined based on the Stokes Raman scattered light component signal due to Fresnel reflection and the anti-Stokes Raman scattered light component signal, and this processing is performed. An oscillation temperature control signal is generated based on the result and is supplied to the laser light source unit 2.

The display 7 is composed of a CRT or the like, and when a measurement result or the like is output from the processing section 6, the display 7 is loaded and displayed on the screen.

Next, the operation of this embodiment will be described with reference to the block diagram shown in FIG.

First, if the memory arithmetic control circuit 22 of the processing unit 6 generates a trigger signal at a preset cycle and supplies the trigger signal to the laser light source unit 2, the pulse generation circuit 10 of the laser light source unit 2 generates the trigger signal. A pulse signal is generated and supplied to the drive circuit 11, and laser pulse light is emitted from the laser light source 12 controlled by this drive circuit 11, and this is emitted to the one end 8a of the optical fiber 4 via the directional coupler 3. It is incident.

When the laser pulse light is incident from the one end 8a of the optical fiber 4, a part of the laser pulse light is reflected by the one end 8a of the optical fiber 4 as shown in FIG. The Stokes Raman scattered light and the anti-Stokes Raman scattered light are returned from each part in the optical fiber 4 by the pulsed light and emitted from the one end 8a of the optical fiber 4, and then the laser pulsed light is terminated by the end portion 8b of the optical fiber 4. When it reaches, the light is reflected by the end portion 18 and is emitted from one end 8a of the optical fiber 4. The Stokes Raman scattered light, anti-Stokes Raman scattered light, and Fresnel reflected light are extracted by the directional coupler 3. And is supplied to the light receiving unit 5.

In parallel with this operation, the reflected light obtained by the demultiplexer 15 of the light receiving section 5 from the directional coupler 3 at the one end 8a of the optical fiber 4 and the reflected light in the optical fiber. The backscattered light obtained by the scattering operation and the Fresnel reflected light obtained by the reflection action at the end portion 8b of the optical fiber are separated into a Stokes Raman scattered light component and an anti-Stokes Raman scattered light component, and each detector 16 and 18, the electric signals are converted into electric signals, and the electric signals are amplified by the amplifiers 17 and 18 and are supplied to the A / D converters 20 and 21 of the processing unit 6, respectively.
After being D / D converted, it is supplied to the storage operation control circuit 22.

The storage operation control circuit 22 takes in the Stokes Raman scattered light component signal and the anti-Stokes Raman scattered light component signal output from the A / D converters 20 and 21, and these are subject to synchronous addition processing. It is stored as data.

Hereinafter, the Stokes Raman scattered light component signal and the anti-Stokes Raman scattered light component signal included in the backscattered light from the optical fiber 4 by repeating the above-described operation at a preset cycle are described. Are synchronously added to create temperature distribution data of the place where the optical fiber is installed.

In parallel with this operation, the background for the Stokes Raman scattered light component signal and the anti-Stokes Raman scattered light component signal output from the A / D converters 20 and 21 by the storage operation control circuit 22. Of Stokes Raman scattered light component signal corresponding to the Fresnel reflected light generated at the end portion 8b of the optical fiber 4 based on the representative value obtained from the amplitude value obtained by subtracting or the value near the peak value, and the anti-Stokes Raman scattered light The component signals are extracted, and it is determined whether or not these ratios have a preset value (for example, "1").

In this case, as shown in FIG. 3, the relative positional relationship between the wavelength of the laser pulse light emitted from the laser light source 12 and the high cut filter characteristic and the low cut filter characteristic of the demultiplexer 15 is preset. Within the range, as shown in FIG. 4, the A / D converters 20, 2 are
Of the Stokes Raman scattered light component signal and the anti-Stokes Raman scattered light component signal output from 1, the Stokes Raman scattered light component signal during Fresnel reflection generated at the end portion 8b of the optical fiber 4 and the anti-Stokes Raman scattered light If the ratio to the component signal is "1", which is a preset value, the storage arithmetic control circuit holds the value of the oscillation temperature control signal currently being output as it is.

At this time, each of the A / D converters 2
Of the Stokes Raman scattered light component signal and the anti-Stokes Raman scattered light component signal output from 0 and 21, the Stokes Raman scattered light component signal during Fresnel reflection generated at the terminal portion 8 of the optical fiber 4 and the anti-Stokes Raman If the ratio to the scattered light component signal is shifted to the "+" side from the preset "1", the value of the oscillation temperature control signal currently being output is shifted to "-" and the laser The wavelength of the laser pulse light emitted from the light source 12 is shortened, and the Stokes Raman scattered light component signal is
The ratio with the anti-Stokes Raman scattered light component signal is "-"
If it is shifted to the side, the value of the oscillation temperature control signal currently being output is shifted to "+" to lengthen the wavelength of the laser pulse light emitted from the laser light source 12.

In this case, if a longitudinal mode multi-pulse semiconductor laser capable of obtaining a large output is used as the laser light source 12, as shown in FIG. 5, if the ambient temperature rises by "10 ° C.", the oscillation wavelength becomes about "2 nm". "Increase and ambient temperature is" 1
When the temperature is lowered by 0 ° C., the oscillation wavelength is reduced by about 2 nm.

Below, the relative positions of the wavelength of the laser pulse light emitted from the laser light source 12 by repeating the above-described operation at a preset cycle and the high cut filter characteristic and low cut filter characteristic of the demultiplexer 15. While maintaining the relationship constant, the Stokes Raman scattered light component signal and the anti-Stokes Raman scattered light component signal included in the backscattered light from the optical fiber 4 are synchronously added, and the optical fiber is installed. The temperature distribution data of the place where it exists is created and displayed on the display unit 7.

As described above, in this embodiment, the ratio of the Stokes Raman scattered light component signal during the Fresnel reflection generated at the end portion 8b of the optical fiber 4 and the anti-Stokes Raman scattered light component signal is preset. The wavelength of the laser pulse light emitted from the laser light source 12 is adjusted by controlling the ambient temperature of the laser light source 12 so that it becomes a value (for example, "1"). The relationship with the cut wavelength can be controlled to be constant, and by doing so, it is possible to eliminate errors caused by fluctuations in the oscillation wavelength of the laser and perform highly accurate temperature distribution measurement.

Further, in the above-described embodiment, the laser light source 12 emits light based on the Fresnel reflected light generated at the end portion 8b of the optical fiber 4, that is, the pulse signal having the intensity higher than the Raman scattered light generated by the transmission loss. Since the relative positional relationship between the wavelength of the laser pulse light and the filter characteristic of the demultiplexer 15 is detected,
A large Stokes Raman scattered light component signal and an anti-Stokes Raman scattered light component signal can be obtained, which can improve detection accuracy.

[0035]

As described above, according to the present invention, the relationship between the laser oscillation wavelength and the cut wavelength of the filter can be controlled to be constant, thereby eliminating the error caused by the fluctuation of the laser oscillation wavelength. Therefore, highly accurate temperature distribution measurement can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a temperature distribution detection device according to the present invention.

FIG. 2 is a schematic diagram showing an example of an optical signal returned from one end of the optical fiber shown in FIG.

FIG. 3 is a schematic diagram showing the relationship between the wavelength of Fresnel reflected light returned from the end of the optical fiber shown in FIG. 1 and the filter characteristic of a demultiplexer.

FIG. 4 is a schematic diagram showing the relationship between the wavelength of Fresnel reflected light returned from the terminal end of the optical fiber shown in FIG. 1 and the filter characteristic of the demultiplexer.

5 is a schematic diagram showing a relationship between a wavelength of laser pulse light emitted from the laser light source shown in FIG. 1 and an ambient temperature.

[Explanation of symbols]

4 optical fiber (optical fiber for measurement) 8a input / output end (incident end) 12 laser light source 13 thermal drive circuit (temperature control unit) 15 demultiplexer 22 memory operation control circuit (end face reflection light detection unit, oscillation temperature control signal generation) Part)

Claims (1)

[Claims] 1. An anti-Stokes Raman scattered light, which is a backward Raman scattered light generated when an optical signal is incident on an incident end of a measuring optical fiber and the optical signal travels in the measuring optical fiber by a demultiplexer. And Stokes Raman scattered light, and the temperature along the measuring optical fiber is selected based on the calculation result of the arrival time of the two Raman scattered lights at the incident end and the intensity thereof. In a temperature distribution detecting device for measuring distribution, an end face reflected light detection part for detecting a reflected light signal from the end face of the measuring optical fiber contained in the two Raman scattered lights output from the demultiplexer, and this end face An oscillation temperature control signal generation unit that generates an oscillation temperature control signal based on the ratio of the two Raman scattered lights detected by the reflected light detection unit, and an output from this oscillation temperature control signal generation unit. A temperature distribution detecting device, comprising: a temperature control unit that controls the ambient temperature of a laser light source that generates the optical signal based on an oscillation temperature control signal to control the wavelength of the optical signal.