JP2010271254A - Optical fiber temperature measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber temperature measuring instrument that includes an extremely compact temperature sensor and is high in measuring accuracy, covering a high-temperature range of 500-600°C. <P>SOLUTION: A light is entered into the temperature sensor (1) including a facing tapered fiber pair (11), a non-tapered section (12), a reflector (13), and a protective means to prevent the surface of the tapered fiber pair from being brought into contact with a gas and liquid in surroundings, so that the reflected light is received. The light reflected on the temperature sensor (1) undergoes periodic intensity modulation, so that the phase of a period is shifted by temperature. Thus, the phase is measured to detect the temperature. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to an optical fiber temperature measuring device that measures temperature using an optical fiber, and more specifically to an optical fiber temperature measuring device that can measure even in a high temperature range of 500 to 600 ° C.

  Various types of optical fiber temperature sensors have been developed because they are excellent in explosion-proof and electromagnetic noise resistance, and are easy to remotely and multi-point monitor.

  Patent Documents 1, 2, and 3 and Non-Patent Documents 1 and 2 disclose temperature sensors using optical fibers.

Patent Document 1 discloses a temperature sensor that utilizes the fluorescence decay characteristics of a fluorescent material loaded at the end of a fiber.

Patent Document 2 describes a method of utilizing the temperature dependence of Raman scattered light intensity for temperature measurement.

Patent Document 3 discloses a temperature sensor that uses microbend loss caused by coating agents having different thermal expansion coefficients arranged along the axial direction of an optical fiber.

Non-Patent Document 1 describes a sensor that utilizes the temperature dependence of a periodic refractive index profile (FBG) formed in a fiber.

Non-Patent Document 2 describes a temperature sensor that utilizes the fact that transmitted light of a fiber having two tapered portions and a very long non-tapered portion between them has a periodic spectrum.
JP-T 62-501448 JP 07-167717 A Japanese Patent Laid-Open No. 08-015054 "PR Forman et. Al., Rev. Sci. Instrum. 61 (10), 2970-2972 (1990)" "KQ Kieu et. Al., IEEE Photon. Lett., 18 (21), 2239-2241 (2006)" `` RJ Black et.al., IEE Proceeings-J, 138 (5), 355-364 (1991)

However, the fluorescent temperature sensor disclosed in Patent Literature 1, the Raman scattering temperature sensor disclosed in Patent Literature 2, the macrobend temperature sensor disclosed in Patent Literature 3, and the non-patent literature 1. All of the FBG type temperature sensors are difficult to measure temperatures of 500 ° C. or higher.

Non-Patent Document 2 describes a sensor that measures the temperature from the phase change of the period using the fact that light transmitted through two tapered fibers is subjected to periodic intensity modulation. Non-Patent Document 2 does not describe a measurable temperature range, but describes a problem that the measurement accuracy is low because the phase change is as small as about 10 pm / ° C. Moreover, in order to measure the transmitted light, two fibers are required for light input and output, and the outer diameter is 10 μm or less and the length is 10 mm or more between the opposing tapered portions. Since the fiber portion is present, the sensor fiber must be fixed to some base material, which causes a problem that the temperature sensor portion is complicated and large.

The present invention has been made in view of the above, and an object thereof is to provide an optical fiber temperature measuring device having an extremely small temperature sensor section, high measurement accuracy, and capable of measuring even in a high temperature range of 500 to 600 ° C. Is to provide.

For this reason, the present invention includes an opposing tapered fiber pair, a non-tapered portion connected to one side of the tapered fiber pair, a reflector that reflects measurement light at the end face of the non-tapered portion, and a surface of the tapered fiber pair. A temperature sensor unit having a protection means for preventing contact with surrounding gas and liquid, a light generation unit for generating measurement light to be supplied to the temperature sensor unit, and a periodic intensity change at the temperature sensor unit. A light measurement means for measuring the reflected light spectrum, a light guide means for guiding the measurement light to the temperature sensor unit, and a reflected light returning from the temperature sensor part to the light measurement means, and a reflection subjected to a periodic intensity change A measurement unit including an arithmetic processing unit that detects a phase of an optical spectrum and calculates a temperature from the phase, and a transmission optical fiber that performs optical transmission between the temperature sensor unit and the measurement unit. To.

  According to the present invention, it is possible to realize an optical fiber temperature measuring device that includes an extremely small temperature sensor unit, has high measurement accuracy, and can measure even in a high temperature range of 500 to 600 ° C.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an optical fiber temperature measuring instrument that is Embodiment 1 of the present invention, and FIG. 2 is an enlarged sectional view of a temperature sensor unit 1. The arrow in FIG. 1 shows how light travels. In FIG. 2A, the protective means (15, 16) for preventing the surface of the tapered fiber pair 11 from coming into contact with the surrounding gas or liquid is omitted for easy viewing of the drawing. FIG. 2B shows a configuration covered with the coating layer 15 as a protection means, and FIG. 2C shows a configuration in which the temperature sensor unit 1 is enclosed in the hollow container 16.

The first embodiment includes a temperature sensor unit 1, a measurement unit 3, and a transmission optical fiber 6.

The temperature sensor unit 1 includes a tapered fiber pair 11, a non-tapered part 12 connected to one side thereof, a reflector 13 that reflects measurement light at the end face of the non-tapered part 12, and a gas surrounding the surface of the tapered fiber pair 11. The coating layer 15 for preventing contact with the liquid or the hollow container 16 is provided. The tapered fiber pair 11 has a fiber outer diameter that gradually decreases toward the waist portion 14, and a core diameter that decreases in proportion to the outer diameter. The outer diameter of the waist part 14 which is the thinnest part of the tapered fiber pair 11 is about 30 to 50 μm, and has rigidity that does not bend due to the weight of the non-tapered part 12. The length of the non-taper part 12 is about 1 to 5 mm. The reflector 13 is composed of, for example, a dielectric multilayer film or a metal film.

The measuring unit 3 guides the light generated from the broadband light source 31, the spectroscopic measuring device 33 that measures the spectrum of the light reflected from the temperature sensor unit 1, and the broadband light source 31 to the transmission optical fiber 6, and the temperature sensor unit 1 includes an optical circulator 7 that guides the light returning from 1 to the spectroscopic measuring instrument 33, and an arithmetic processing circuit 34 that detects a phase from a periodic change of the spectrum and converts it into a temperature.

  As the broadband light source 31, a light source having a wide spectral width such as an ASE light source, SLD (Super Luminescent Diode), or LED is used.

As the spectroscopic measuring instrument 33, a device such as a monochromator or a wavelength tunable filter that splits light and measures the relationship between light intensity and wavelength, for example, an optical spectrum analyzer, a combination of a wavelength tunable filter and a photodetector, or the like is used.

The transmission optical fiber 6 is a single mode optical fiber that performs optical transmission between the temperature sensor unit 1 and the measurement unit 3, and may be the same type or different type of optical fiber used for the temperature sensor unit 1.

The reflected light spectrum returning from the temperature sensor unit 1 according to the first embodiment is periodically intensity-modulated by the action of the temperature sensor unit 1. Since the phase of this cycle changes depending on the temperature, the phase is detected from the spectrum measured by the spectroscopic measuring instrument 33 and converted into temperature by the arithmetic processing circuit 34 to measure the temperature.

Hereinafter, the operation of the temperature sensor unit 1 of the first embodiment will be described in detail.

FIG. 3 shows an example in which a broadband light source is incident on the temperature sensor unit 1 of the first embodiment and a reflected light spectrum is measured, and a spectrum example of light transmitted through a similar tapered fiber pair 11. The spectrum of the reflected light shows a clear periodic change close to a sine function. On the other hand, in the transmitted light spectrum, although a slight change in the amount of light is observed with respect to the wavelength, a clear periodic spectrum cannot be observed. The generation of such a periodic spectrum is a requirement for functioning as a temperature sensor. In the temperature sensor unit 1 of the first embodiment, this phenomenon appears specifically in the reflected light.

FIG. 4 shows an example in which the temperature change of the periodic spectrum obtained by the temperature sensor unit 1 of the first embodiment is measured. It can be seen that the spectrum shifts to the longer wavelength side as the temperature rises. The amount of shift is as large as about 100 pm / ° C. Therefore, if this phase shift amount is detected by the spectroscopic measuring instrument 33 and converted into temperature by the arithmetic processing circuit 34, a highly accurate temperature measuring instrument is obtained.

The reason why such a periodic spectrum appears may be interference and coupling between the cladding mode and the core mode. As shown in FIG. 5, in the waist portion 14 of 50 μm or less in which the periodic spectrum can be observed remarkably, the MFD (mode field diameter) widens more than the cladding diameter because the core diameter is small, and between the core mode and the cladding mode. Interference and coupling can occur. Also, the reason why the phase shifts to the longer wavelength side as the temperature rises is considered to be because the optical path length in the fiber changes due to the temperature change of the fiber refractive index.

The magnitude of the amplitude depends on the diameter of the waist portion 14 and increases as the diameter of the waist portion 14 decreases. However, if the diameter of the waist portion 14 is 30 μm or less, the rigidity of the waist portion 14 is small and easily bent, and therefore, about 30 to 50 μm is practical.

The period strongly depends on the length of the non-tapered portion 11. FIG. 6 shows an example in which the spectrum is measured by changing the length of the non-tapered portion 11. The shorter the non-tapered portion 11, the longer the period and the regular change. On the other hand, when the non-tapered portion 11 becomes longer, the cycle becomes shorter and irregularly changes. The reason why the cycle becomes shorter as the non-tapered portion 11 is longer is considered to be because interference and coupling with higher-order cladding modes occur. The irregular period is considered to be due to interference and coupling with a plurality of cladding modes. For use as the temperature sensor of the first embodiment, 5 mm or less that provides a regular period is suitable.

In the waist portion 14 of the temperature sensor unit 1 according to the first embodiment, the core mode also has a large MFD, and light oozes out of the fiber. Therefore, it is easy to be influenced by the surrounding atmosphere, and the amount of reflected light changes due to, for example, liquid adhesion to the temperature sensor unit 1 or humidity change. In order to solve this problem, it is effective to protect the temperature sensor unit 1 with a material capable of blocking the surrounding liquid and gas and confining light in the fiber. FIG. 2B shows a structure in which a coating layer 15 made of a material capable of blocking liquid and gas is provided on the outer periphery of the temperature sensor unit 1. As the coating material, metals such as gold, platinum, nickel, and stainless steel, or inorganic materials such as MgF2 and CaF2 having a lower refractive index than clad glass can be used. When an insulating material such as MgF2 or CaF2 is coated, the temperature sensor unit 1 is not affected by the electromagnetic field, so that there is an advantage that the temperature can be measured in a high frequency environment or in a strong electromagnetic field. FIG. 2C shows a structure in which the temperature sensor unit 1 is enclosed in a hollow container 16 made of a material capable of blocking liquid and gas. In this case, since light is confined in the fiber by the gas enclosed in the hollow container 16, the material of the hollow container may be any material as long as it can shut off liquid and gas. For example, metal, glass, ceramics, etc. are used. it can.

  As described above, the light incident on the temperature sensor unit 1 according to the first embodiment is reflected by periodic intensity modulation. Further, the phase of the periodic spectrum is greatly shifted to the long wavelength side as the temperature rises. Therefore, the temperature can be measured by detecting this phase change by the spectroscope 33 and converting it to a temperature by the arithmetic processing circuit 34. Further, since the phase shift is as large as about 100 pm / ° C., temperature measurement with high accuracy is possible.

  The temperature sensor unit 1 includes a quartz optical fiber and a reflector 13, a coating layer 15, or a hollow container 16. For the reflector 13, for example, a dielectric multilayer film can be used. The reflector 13, the coating layer 15, and the hollow container 16 can be made of an inorganic material that can withstand a high temperature of 600 ° C., and become an optical fiber temperature measuring device capable of measuring a temperature higher than 500 ° C.

  In addition to having excellent radiation resistance, these inorganic materials can be measured using light in the 1.5 μm band, which is not easily affected by defects caused by radiation. It becomes a temperature measuring instrument that can be used in a radiation environment such as measurement.

Since reflected light is measured, light can be input and output with a single optical fiber, and a compact temperature sensor head can be obtained. Since the temperature sensor unit 1 is small, the response to the temperature is fast and the temperature of a narrow part can be measured. Since the tapered fiber pair 11 has rigidity that does not bend due to the weight of the non-tapered fiber portion, it can be used as a sensor without fixing both ends to the base material, and a small sensor head is obtained.

If the reflector 13 is made of a dielectric multilayer film, the coating layer 15, or the hollow container 16 is made of an insulating inorganic material such as glass or ceramics, the temperature sensor unit 1 can be composed entirely of a non-conductive material. But it becomes a temperature measuring instrument that can be used.

It is also possible to produce the tapered fiber pair 11 by fusion splicing with different types of fibers. In this case, a spectrum having a larger amplitude than the connection of the same fiber may be obtained.

  FIG. 7 shows the configuration of the second embodiment. In this configuration, the light source is a tunable laser 41, and the reflected light intensity returned from the temperature sensor unit 1 is measured by the light receiver 43.

  Light whose wavelength is continuously changed by the wavelength tunable laser 41 enters the transmission optical fiber 6 through the optical circulator 7. The intensity of the reflected light that has undergone the intensity change by the temperature sensor unit 1 is continuously measured by the light receiver 43, the phase is detected from the periodic change in the light intensity by the arithmetic processing circuit 44, and the temperature is calculated from the phase. The configuration of the second embodiment has an advantage that a light source having a flat light intensity with respect to the wavelength can be used.

  Although the invention has been described with reference to specific embodiments, various modifications may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. Such changes and modifications are also within the technical scope of the present invention.

It is a figure which shows schematic structure of the optical fiber temperature measuring device which is Example 1 of this invention. It is an expanded cutaway view of a temperature sensor part. It is a figure which shows the spectrum of the light which permeate | transmitted the temperature sensor part and the reflected light. It is a figure which shows the temperature change of the periodic spectrum obtained in a temperature sensor part. It is a figure which shows the relationship between a fiber outer diameter and MFD. It is a figure which shows the relationship between the length of a non-taper part, and a period spectrum. It is a figure which shows Example 2 of this invention.

1: Temperature sensor unit 3, 4: Measuring unit 6: Transmission optical fiber 7: Optical circulator 11: Tapered fiber pair 12: Non-tapered unit
13: Reflector 14: Waist part 15: Coating layer 16: Hollow container 31: Broadband light source 41: Wavelength variable laser 33, 43: Optical measuring means 34, 44: Arithmetic processing circuit

Claims (9)

An opposing tapered fiber pair (11), a non-tapered portion (12) connected to one side of the tapered fiber pair (11), and a reflector (13) that reflects measurement light at the end face of the non-tapered portion (12) And a temperature sensor unit (1) having protective means (15, 16) for preventing the surfaces of the tapered fiber pair (11) from coming into contact with the surrounding gas and liquid, and supplying the temperature sensor unit (1) Light generating means (31, 41) for generating measurement light to be measured, light measuring means (33, 43) for measuring a reflected light spectrum subjected to periodic intensity modulation in the temperature sensor section (1), and the temperature Light guide means (7) for guiding the measurement light to the sensor section (1) and guiding reflected light returning from the temperature sensor section (1) to the light measurement means (33, 43), and reflection subjected to periodic intensity modulation Detects the phase of the optical spectrum and calculates the temperature from the phase A measurement unit (3, 4) having arithmetic processing means (34, 44) for performing transmission, and an optical fiber for transmission that performs optical transmission between the temperature sensor unit (1) and the measurement unit (3, 4). And 6) an optical fiber temperature measuring device. The outer diameter of the waist part (14) which is the thinnest part of the taper fiber pair (11) is in the range of 30 to 50 μm, and the length of the non-taper part (12) is 5 mm or less. The optical fiber temperature measuring device according to claim 1.   2. The optical fiber temperature measuring device according to claim 1, wherein the tapered fiber pair (11) is made of different kinds of fibers. The optical fiber temperature measuring device according to claim 1, wherein the reflector (13) is a dielectric multilayer film.   2. An optical fiber temperature measuring device according to claim 1, wherein said protective means is a metal coating layer (15).   2. The optical fiber temperature measuring device according to claim 1, wherein the protective means is a coating layer (15) made of ceramics having a lower refractive index than the clad layer of the tapered fiber pair (11).   2. An optical fiber temperature measuring device according to claim 1, wherein said protective means is a hollow container (16).   The optical fiber temperature measuring device according to claim 1, wherein the light generating means (31) is a broadband light source, and the light measuring means (33) is a spectroscopic measuring instrument. The optical fiber temperature measuring device according to claim 1, wherein the light generating means (41) is a tunable laser, and the light measuring means (43) is a light receiver.

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