JP2011007767A - Optical fiber sensor device and sensing method using optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly durable, inexpensive optical fiber sensor device with an extremely small sensor head, which can measure temperature, humidity, types of liquid-steam, density, and so on with an identical sensor head or with a plurality of sensor heads at the same time.SOLUTION: Light is allowed into a sensor section 1 including a pair of opposed tapered fibers 11, a non-tapered section 12, and a reflector 13 to receive reflected light. The reflected light becomes a cyclical spectrum as a result of intermode interference and coupling, and a phase and an amplitude of the spectrum change due to the temperature and an refractive index of an ambient substance. Since a reflected light quantity also changes along with a change of the spectrum, a change of the light quantity is detected to measure a desired physical quantity.

Description

  The present invention relates to a sensor device and a sensing method using an optical fiber that measures temperature, humidity, type of liquid / vapor, concentration and the like using an optical fiber.

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

  Patent Document 1 discloses a temperature sensor using FBG.

  Patent Document 2 discloses a humidity sensor in which a substance that changes color depending on humidity is applied to the tip of a fiber.

  Patent Document 3 discloses a humidity sensor in which a part of the cladding is a moisture sensitive layer.

  Patent Document 4 discloses a liquid sensor using a swelling material.

  Patent Document 5 discloses a sensor that measures the concentration of an organic solvent in water using the swelling and shrinkage of a chitosan composite membrane.

  Patent Document 6 discloses a sensor that measures the liquid concentration using surface plasmons of a hetero-core fiber provided with a metal film.

Japanese Patent Laid-Open No. 08-101078 Japanese Patent Laid-Open No. 06-11448 Japanese Patent Laid-Open No. 05-60689 JP 2001-50855 A JP-A-5-19123 JP2005-010025

  However, the temperature sensor using FBG disclosed in Patent Document 1 is expensive, and the sensors disclosed in Patent Documents 2 to 5 have a complicated structure because they use a special moisture-sensitive material and swelling agent. There are also problems in size and durability, and the sensor disclosed in Patent Document 6 also has a problem that it is expensive and the sensor head is large. Also, with these sensor devices, it is difficult to measure the temperature, humidity, liquid / vapor concentration, etc. with the same sensor head, or to simultaneously measure using a plurality of sensor heads.

  The present invention has been made in view of the above, and as its purpose, temperature, humidity, type of liquid / vapor, concentration, etc. can be measured with the same sensor head, and simultaneous measurement with a plurality of sensor heads is possible. An object of the present invention is to provide an optical fiber sensor device and a sensing method using an optical fiber, which have a very small sensor head, high durability, and low cost.

  Therefore, an optical fiber sensor device according to the present invention includes a pair of opposed tapered fibers, a non-tapered portion connected to one side of the tapered fiber pair, and a sensor unit including a reflector that reflects measurement light at an end surface of the non-tapered portion. , A light emitting means for generating measurement light to be supplied to the sensor unit, a light receiving means for receiving reflected light subjected to an intensity change at the sensor unit, guiding the measurement light to the sensor unit, and reflecting the reflected light from the sensor unit A light guide means that leads to the light receiving means, a measuring section that includes an arithmetic processing circuit that converts the output of the light receiving means into physical quantities to be detected such as temperature, humidity, type of liquid / vapor, concentration, the sensor section, and the And a transmission optical fiber that performs optical transmission between the measurement units.

  In addition, the sensing method using the optical fiber of the present invention includes an opposing tapered fiber pair, a non-tapered portion connected to one side of the tapered fiber pair, and a reflector that reflects measurement light at the end face of the non-tapered portion. Measuring light is introduced into the sensor unit using a transmission optical fiber, and in the tapered fiber pair, a part of the measuring light is leaked from the core to the cladding side, and at least in the non-tapered part, the leaked light is leaked. Is reflected in the clad mode and reflected by the reflector, and the change in the reflected light of the sensor unit is detected through the transmission optical fiber, thereby changing the refractive index of the surrounding environment of the non-tapered part, or Further, it is characterized in that a change in refractive index of the non-tapered portion itself depending on temperature is detected.

  The present invention enables measurement with the same sensor head such as temperature, humidity, type of liquid / vapor, concentration, etc., and simultaneous measurement with multiple sensor heads, and is extremely compact, highly durable, and inexpensive. A fiber sensor device and a sensing method can be realized.

It is a figure which shows schematic structure of the optical fiber sensor apparatus which is Example 1 of this invention. It is an expanded cutaway view of a sensor part. It is a figure which shows the spectrum of the light which permeate | transmitted the sensor part and the reflected light. 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 the relationship between a fiber outer diameter and MFD. It is a figure which shows the temperature change of the periodic spectrum obtained by a sensor part. It is a figure which shows the structure which protects a sensor part from ambient atmosphere in the case of temperature measurement. It is the example which measured the relationship between the temperature of the sensor part protected with the hollow container, and the amount of reflected light. It is an example of the measurement of the reflection spectrum obtained when a sensor part is immersed in various liquids. It is the example which measured the change of the reflected light amount when a sensor part was immersed in various liquids. It is an example in which the change in the reflection spectrum accompanying the process of evaporation of acetone is measured. It is an example in which the relationship between the process in which acetone evaporates and the change in the amount of light is measured. It is the example which measured the change of the reflected light amount accompanying a humidity change. It is the example which measured the relationship between a propanol density | concentration and a light quantity change. It is an example of the temperature change of the reflected light spectrum measured with the 1300 nm band ASE light source. It is a figure which shows the spectrum of a 1300 nm band ASE light source. It is an example of the temperature change of the reflected light intensity measured by 1300nm band ASE light source and 1313nmLD. It is a figure which shows schematic structure of the optical fiber sensor apparatus which is Example 2 of this invention.

  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 sensor device that is Embodiment 1 of the present invention, and FIG. 2 is an enlarged sectional view of the sensor unit 1. The arrow in FIG. 1 shows how light travels.

  The first embodiment includes a sensor unit 1, a measurement unit 2, and a transmission optical fiber 3.

  The sensor unit 1 includes a tapered fiber pair 11, a non-tapered part 12 connected to one side thereof, and a reflector 13 that reflects measurement light at the end face of the non-tapered part 12. 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 non-tapered portion 12 is not coated and the glass surface of the clad 102 is exposed, or when the coating is applied, the non-tapered portion 12 does not completely impede the penetration of light propagating through the clad 12, that is, the coating The thickness is such that it is affected by the change in the refractive index of the object to be measured outside of. For example, when the glass surface of the clad 102 is exposed, the clad 102 can be brought into contact with an ambient atmosphere or a liquid serving as an object to be measured. As a result, the outer peripheral side region of the clad 102 has a refractive index peculiar to the substance in contact therewith. When the refractive index of the ambient atmosphere or the liquid is lower than that of the cladding, the outer peripheral side region of the cladding 102 is naturally in a lower refractive index state than that of the cladding 12. In this case, the non-tapered portion 12 has a structure capable of propagating at least part of the measurement light leaking from the core 101 to the clad 102 side as a clad mode without being emitted to the outside. Even when the refractive index of the ambient atmosphere or liquid is higher than that of the clad 102, if the length of the non-tapered portion 12 is short, at least a part of the leaked light is not emitted to the outside and becomes a clad mode. Can propagate.

  For example, when the glass surface of the clad 102 is coated with a material having a higher refractive index than that of the clad 102, it is preferable to reduce the film thickness (specifically, the wavelength of the measurement light or less). This is because, by thinning the high refractive index coating layer, leakage light is not confined in the high refractive index coating layer and can propagate as a clad mode. In addition, when the coating layer is thinned, light permeation to the vicinity of the boundary with the ambient atmosphere or the liquid becomes strong, which has an advantage of increasing the sensitivity of the sensor. That is, by forming a coating layer that is a highly refractive material on the clad 102, light is leached out of the clad 102 and totally reflected at the boundary with the object to be measured on the outer periphery of the coating layer. By being strongly influenced by the change in the refractive index, and further reducing the film thickness of the coating layer, the total reflected light can be positively returned to the clad 102 side so that the influence can be detected with high sensitivity. To do. As a result, the outer peripheral side region of the clad 102 can be substantially in a lower refractive index state than the clad 102. This is because the leaked light is totally reflected and returns to the cladding 102 side at the boundary between the ambient atmosphere and the liquid in contact with the outer periphery of the coating, and can propagate as a cladding mode without being emitted to the outside. This is particularly suitable when detecting vapor characteristics.

  The outer diameter of the waist part 14 which is the narrowest part of the taper fiber pair 11 is set to 70 μm or less, preferably about 30 to 50 μm. Further, the tapered fiber pair 11 has a rigidity that does not bend due to the weight (self-weight) of the non-tapered portion 12. As described above, as a reason for securing the rigidity by setting it to 30 μm or more, in principle, the sensor unit 1 is configured such that the non-tapered portion 12 side becomes a free end so as not to erroneously detect an external biasing force. This is because it is held in a cantilever state. That is, when the both-end holding state is established, if the holding member side expands or contracts due to a temperature change or is deformed due to some factor, stress acts on the sensor unit 1 and the amount of reflected light changes due to the deformation. The reason why the outer shape of the waist portion 14 is 70 μm or less, preferably 50 μm or less will be described later.

  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 2 includes a light source 21 that generates measurement light, an optical branching coupler 22 that guides the measurement light to the transmission optical fiber 3, and guides reflected light that has undergone an intensity change at the sensor unit 1 to the light receiver 24, and a sensor unit A light receiver 24 that measures the amount of reflected light from 1 and an arithmetic processing circuit 25 that converts the output of the light receiver 24 into physical quantities to be detected such as temperature, humidity, type of liquid / vapor, concentration, and the like. Although not shown in FIG. 1, when the light intensity of the light source 21 fluctuates, it is possible to monitor the light intensity of the light source 21 and correct the reflected light intensity returning from the sensor unit 1. .

  The transmission optical fiber 3 is a single mode optical fiber that performs optical transmission between the sensor unit 1 and the measurement unit 2, and may be the same type or different type of optical fiber used in the sensor unit 1.

  Hereinafter, the sensor unit 1 of the present embodiment will be described in detail.

  FIG. 3 shows an example in which a broadband light source is incident on the sensor unit 1 of the first embodiment and a reflected light spectrum is measured, and a spectrum measurement example of light transmitted through the same tapered fiber pair 11 is shown. 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. That is, the sensor unit 11 of the first embodiment has a function of converting the reflected light into a periodic spectrum.

  The periodic stability of the reflection spectrum strongly depends on the length of the non-tapered portion 12. FIG. 4 shows an example in which the spectrum is measured by changing the length of the non-tapered portion 12. The shorter the non-tapered portion 12 is, the longer the cycle is, and regular changes occur at 15 mm or less. On the other hand, when the non-tapered portion 12 becomes longer, the cycle becomes shorter, and when the non-tapered portion 12 becomes longer than 20 mm, it changes irregularly. Therefore, a length of less than 20 mm that changes regularly is suitable for use as a sensor. Particularly, it is preferably 15 mm or less, more preferably 5 mm or less with a long cycle.

  The reason why such a periodic spectrum appears is that, in the tapered fiber pair 11, part of the measurement light leaks from the core 101 to the cladding 102 side, and this leaked light propagates as a cladding mode in the non-tapered portion 12. As a result, the periodic spectrum is detected as a part of the reflected light. Specifically, interference and coupling between the clad modes or between the clad mode and the core mode can be considered.

  The magnitude of the amplitude of the reflection spectrum depends on the diameter of the waist portion 14 and increases as the diameter of the waist portion 14 decreases. As described above, when the diameter of the waist portion 14 is 30 μm or less, the rigidity is reduced, so that loss due to bending at the waist portion 14 is likely to occur, and mounting as a sensor head becomes complicated. Or Accordingly, the diameter of the waist portion 14 is suitably about 30 μm or more.

  As shown in FIG. 5, it is preferable that the waist portion 14 is 70 μm or less because the MFD (mode field diameter) starts to widen and the amplitude of the reflection spectrum starts to spread. This is considered that leakage light from the core 101 to the clad 102 is generated, and light propagation in the clad mode is started in the non-tapered portion 12. The MFD (mode field diameter) means the diameter of the spread of the electric field distribution in the propagation mode (light path).

  Furthermore, when the waist part 14 is 50 μm or less, the MFD spreads more rapidly than the cladding diameter, and it is considered that interference and coupling between the core mode and the cladding mode are more likely to occur. Accordingly, it is more suitable to obtain the periodic spectrum by setting the waist portion 14 to 50 μm or less.

  Note that the longer the length of the non-tapered portion 12, the shorter the cycle is considered 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.

  Hereinafter, the periodic spectrum of the reflected light returning from the sensor unit 1 of the first embodiment changes due to temperature, immersion in liquid, exposure to vapor, etc., and by measuring the change in the reflected light intensity associated therewith, the temperature, humidity, Explain that the type and concentration of liquid / vapor can be detected.

  First, the temperature change of the periodic spectrum will be described. The example which measured the temperature change of the periodic spectrum is shown in FIG. The sensor part 1 used was prepared by fusion splicing of single mode optical fibers having core diameters different from 8.5 μm and 6 μm, respectively, the outer diameter of the waist part 14 was 38 μm, and the length of the non-tapered part was 3.8 mm. is there. It can be seen that the spectrum shifts to the longer wavelength side as the temperature rises. It can also be seen that the amount of reflected light changes monotonously when focusing on a specific wavelength. For example, when focusing on the wavelength of 1500 nm, the amount of reflected light monotonously increases as the temperature rises. On the other hand, at a wavelength of 1550 nm, the amount of reflected light monotonously decreases with increasing temperature. Regardless of which wavelength is incident on the sensor unit 1, a monotonous change in the amount of reflected light can be obtained with respect to the temperature. Therefore, the temperature can be detected by measuring the amount of reflected light.

  The reason why the phase of the periodic spectrum 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. As described above, in order to detect the change in the refractive index of the fiber based on the change in temperature by the interference / coupling of light, a state where no external force acts on the optical fiber due to the change in temperature, that is, the non-tapered part 12 side in the sensor part 1 is the free end. It is important to keep it in a state where it can be freely expanded and contracted in the axial direction.

  However, as will be described later, when the glass surface of the clad 102 is exposed at the waist portion 14 and the non-tapered portion 12 in the sensor portion 1 of this embodiment, light tends to ooze out of the fiber. The influence of the change in the refractive index of the surrounding material in contact with the outer surface of the clad 102 is also affected. That is, when the refractive index of the surrounding material in contact with the clad 102 fluctuates due to a temperature change, the clad mode changes and the spectrum is affected. For example, the amount of reflected light changes due to adhesion of liquid to the temperature sensor unit 1, change in humidity (water vapor amount), or the like. In order to solve this problem and measure the temperature change without being influenced by the surrounding material, it is possible to block liquid and gas from the waist portion 14 to the non-tapered portion 12 of the sensor unit 1 and to transmit light into the fiber. It is effective to cover with a material that can be confined. For example, FIG. 7A shows a cutaway view of 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. The thickness of the coating layer in this case needs to be a thickness that does not allow light propagating through the clad 102 to ooze out of the coating layer. 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. 7B shows a cut-away view of 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 the refractive index of the gas sealed in the hollow container 16 is significantly lower than the refractive index of the cladding, the light can be easily confined in the fiber. Therefore, since the material of the hollow container 16 is not related to the refractive index, any material can be used as long as it can block liquid and gas. For example, metal, glass, ceramics, etc. can be used.

  FIG. 8 shows an example in which the sensor unit 1 is sealed in the hollow container 16 and the relationship between the temperature and the amount of reflected light is measured. A glass thin tube was used for the hollow container 16, and the sensor unit 1 was sealed using a heat-resistant adhesive. It is clear that a monotonous change is obtained in the range from room temperature to 220 ° C, and that the temperature rise and fall are equivalent, no hysteresis is seen, and accurate temperature measurement is not affected by the ambient atmosphere. .

  Next, changes due to immersion in a liquid will be described. FIG. 9 is a measurement example of a reflection spectrum obtained when the sensor unit 1 is immersed in a liquid of water, acetone, ethanol, and propanol. In FIG. 9, the spectrum measured in air is drawn with a thicker solid line. It can be seen that the spectrum measured by immersing in a liquid greatly changes from the spectrum measured in air. The change is correlated with the refractive index of the liquid. For example, when attention is focused on the short wavelength side from the peak of the spectrum, the spectrum is shifted to the short wavelength side in descending order of the refractive index.

  The reason why the spectrum changes in correlation with the refractive index of the immersed liquid is considered as follows. Since the diameter of the tapered fiber pair 11 is narrowed toward the waist portion 14, a part of the light propagating through the core 101 leaks into the clad 102. When this leaked light (clad mode) propagates from the waist part 14 to the non-tapered part 12, there is no coating of the clad 102, so that a part of the light soaks into these liquids. As a result, it is considered that the interference and coupling between modes are changed due to the influence of the refractive index of the liquid. That is, the difference in refractive index between the clad 102 and the liquid affects the change in spectrum.

  FIG. 10 shows a change in the amount of reflected light obtained when the sensor unit 1 is immersed in the order of water, acetone, ethanol, and propanol using a broadband light source having a center wavelength of 1538 nm, which is indicated as the measurement center wavelength in FIG. The example of the time change which measured was shown. As expected from the spectrum of FIG. 9, the amount of light decreased when immersed in water compared to the amount of light measured in air, and the amount of light increased according to the refractive index of the liquid when immersed in acetone, ethanol, and propanol. . As is apparent from this result, the sensor device of the first embodiment is used as a liquid discrimination sensor for discriminating liquids having different refractive indexes, a water leak, a liquid leak sensor, or a process monitor such as liquid alteration or mixing. Available.

  Next, changes due to exposure to steam will be described. FIG. 11 shows an example in which the change in the reflection spectrum is measured as the acetone in the beaker evaporates. The sensor unit 1 used is the same as that used in the immersion in the liquid. It can be seen that the spectrum continuously changes from a state where the acetone vapor concentration is highest where the acetone liquid is present in the beaker to a state where the acetone vapor disappears from the beaker. This change is considered to be due to the influence of the refractive index of the vapor in contact with the clad 102 since the clad 102 is not covered when the clad mode propagates through the non-tapered portion 12.

  FIG. 12 shows a time change in which the relationship between the process of evaporating acetone in a beaker and the change in the amount of light is measured using a broadband light source having a center wavelength of 1538 nm, which is indicated as the measurement center wavelength in FIG. An example of The amount of light is constant up to more than 3 minutes when the acetone liquid is present in the beaker, but when there is no acetone liquid in the beaker and only vapor is present, the amount of light increases as the acetone vapor concentration decreases. When the steam runs out, the light intensity becomes constant again. As is clear from this result, the optical fiber sensor device of the first embodiment senses not only liquid but also vapor, so it can be used as a sensor for monitoring distillation processes and gas phase reaction processes of organic solvents and petroleums. it can.

  As another example of the change due to the exposure to vapor, the change due to humidity will be described. The sensor unit 1 used is the same as that used for immersion in the liquid and measurement of acetone vapor. FIG. 13 shows an example in which a change in the amount of reflected light due to a change in humidity is measured. The temperature was constant at 70 ° C. A monotonous light amount change is obtained with respect to the humidity change, and it is clear that the optical fiber sensor device of the first embodiment can be used as a humidity sensor.

  Next, changes due to liquid concentration will be described. FIG. 14 shows an example in which the relationship between the propanol concentration and the change in the amount of light when propanol is diluted with water is measured. The sensor unit 1 used is the same as that used for immersion in the liquid, measurement of acetone vapor, and humidity measurement. The change in the amount of light corresponding to the propanol concentration is obtained, and it is clear that the optical fiber sensor device of the first embodiment can be used as a liquid concentration sensor.

  In the optical fiber sensor device of the first embodiment, a broadband light source or a laser can be used as the light source 21. Hereinafter, the difference between the case where a broadband light source is used and the case where a laser is used will be described using temperature measurement as an example.

  FIG. 15 shows an example in which the light of a 1300 nm band ASE light source, which is one type of broadband light source, is incident on the sensor unit 1 and the temperature change of the reflected light spectrum is measured. As shown in FIG. 16, the spectrum of the incident light is unimodal and has a peak wavelength of 1303 nm. Although the reflection spectrum is expected to have a shape obtained by multiplying the incident spectrum by a sine function, the spectrum change having the expected shape is actually obtained.

  In FIG. 15, the area of the spectrum corresponds to the amount of light. From FIG. 15, it can be seen that the amount of light in the entire spectrum changes with temperature as the spectrum shape changes. It can be seen that the amount of reflected light decreases monotonously from 50 ° C. to 250 ° C., becomes minimum between 250 ° C. and 300 ° C., and increases at higher temperatures. Therefore, when this light source is used, it is understood that the temperature can be measured up to about 250 ° C. by measuring the amount of reflected light.

  An advantage of using the light source 21 as a broadband light source is that accurate measurement with less noise is possible. In the example of temperature measurement, it was possible to measure with an accuracy of a standard deviation of 0.4 ° C. with respect to the reference temperature. The main reason that the measurement can be performed with high accuracy is considered that the light emitted from the broadband light source is incoherent light having non-uniform phases, and therefore noise due to interference is extremely small. In the optical fiber sensor device of the present invention, since reflected light is detected, noise due to interference is likely to occur, and it is very effective to use the light source 21 as a broadband light source as a preventive measure.

  In FIG. 15, when attention is focused on light having a wavelength of 1313 nm, the light intensity decreases monotonously from 50 ° C. to 300 ° C. Therefore, if a laser beam having a wavelength of 1313 nm is used, temperature measurement up to at least 300 ° C. is considered possible.

FIG. 17 shows an example in which a temperature change in reflected light intensity from the sensor unit 1 is continuously measured using a 1300 nm band ASE light source and a semiconductor laser (LD) having a wavelength of 1313 nm. As expected, a monotonous change in light intensity with increasing temperature was obtained up to about 250 ° C. for the 1300 nm band ASE light source and up to about 350 ° C. for the 1313 nm semiconductor laser. Since these curves can be approximated by a polynomial within the monotonous change range, a temperature sensor device capable of measuring up to 250 ° C. and 350 ° C., respectively, by converting the output of the light receiver 24 into a temperature by the arithmetic processing circuit 25 using an approximate expression. Obviously you can do that.
When the 1300 nm band ASE light source is used, the light intensity change is about 5.5 dB, and the change amount is small compared to the change of 12 dB obtained when the 1313 nm LD is used. There is an advantage that it can be measured. On the other hand, when the 1313 nm LD is used, there is an advantage that the measurement can be performed up to a high temperature of 350 ° C. in addition to the light intensity change as large as 12 dB. However, since it is coherent light, it is affected by noise due to interference, and the temperature measurement accuracy is inferior to that of a broadband light source with a standard deviation of ± 3 ° C. with respect to the reference temperature. Also, from these results, if light near 1310 nm is extracted from the ASE light source by a bandpass filter and used as the light source, a large change in light intensity can be obtained, measurement up to a high temperature is possible, and noise caused by interference can be obtained. It is thought that it is possible to measure with little high accuracy.

  In the configuration of the first embodiment, it has been described that the temperature, the humidity, the type of liquid / vapor, the concentration, and the like can be measured. However, in the configuration of the first embodiment, when measuring a physical quantity other than the temperature, a light amount change due to temperature fluctuation is superimposed. Correct measurement is not possible. Example 2 shows a configuration in which a physical quantity other than temperature can be correctly measured even when there is a temperature change.

  FIG. 18 is a schematic configuration diagram of the optical fiber sensor device according to the second embodiment of the present invention.

  Example 2 is a sensor unit 1-1 for measuring temperature, a sensor unit 1-2 for measuring a physical quantity other than temperature, a measuring unit 2, sensor units 1-1, 1-2, and measurement. It comprises transmission fibers 3-1 and 3-2 that perform transmission between the units 2. The sensor unit 1-1 for temperature measurement is covered with a coating layer 15 made of metal, ceramics or the like so as not to be affected by surrounding substances, or is enclosed in a hollow container 16. On the other hand, the clad glass of the non-tapered part in the sensor part 1-2 can come into contact with surrounding substances in a state where it is not coated. The measurement unit 2 includes a light source 21, optical branching couplers 22-1 to 22-3, light receivers 24-1 and 24-2, and an arithmetic processing circuit 25.

  Hereinafter, the operation of the second embodiment will be described with reference to FIG. The measurement light emitted from the light source 21 is branched by the optical branching coupler 22-1, and is incident on the optical branching couplers 22-2 and 22-3. Light emitted from the optical branching couplers 22-2 and 22-3 passes through transmission optical fibers 3-1 and 3-2, and a sensor unit 1-1 for temperature measurement, a sensor for measuring a physical quantity other than temperature. After entering the section 1-2, it is reflected by the reflector 13. The reflected light from the sensor unit 1-1 and the sensor unit 1-2 is modulated into a periodic spectrum, and has a light intensity corresponding to changes in temperature and measurement target physical quantity. The reflected light again passes through the transmission optical fibers 3-1 and 3-2 and enters the optical couplers 22-2 and 22-3. The amount of light is measured by the light receivers 24-1 and 24-2, and the arithmetic processing circuit The light quantity data is sent to 25. A relational expression between the temperature of the sensor unit 1-1 and the amount of reflected light and a relational expression between the temperature of the sensor unit 1-2 and a physical quantity change to be measured and the amount of reflected light are input to the arithmetic processing circuit 25 in advance. Then, the superimposition of the light amount change due to the temperature change generated in the sensor unit 1-2 is corrected based on the temperature measured by the sensor unit 1-1. In this way, the physical quantity change to be measured can be accurately measured by the sensor unit 1-2 without being affected by the temperature.

  The configuration of the second embodiment has an effect of generating not only the temperature correction function of the sensor unit 1-2 but also a new sensor function. Hereinafter, a case where the sensor unit 1-2 is a humidity sensor will be described.

  In FIG. 18, the relational expression between the temperature of the sensor unit 1-1 and the amount of reflected light and the relational expression of the temperature, humidity and change in the amount of reflected light of the sensor unit 1-2 are input in advance to the arithmetic processing unit 25, If this temperature correction is performed, naturally, an accurate humidity sensor is obtained. Further, when moisture adheres to the sensor unit 1-2, as already shown in FIG. Condensation can be detected by measuring the temperature at which this change occurs with the sensor unit 1-1. Further, if the adhering water freezes to become ice, the sensor unit 1-2 can detect the freezing because it causes a sudden light quantity change again at a lower temperature. In other words, by adopting the configuration of the second embodiment, it becomes an unprecedented sensor capable of detecting not only humidity but also dew condensation and freezing.

  Although FIG. 18 shows a configuration including two sensor units 1-1 and 1-2, a configuration including more sensor heads is naturally possible. In this case, the optical fiber sensor device is capable of simultaneous monitoring of temperature, humidity, liquid / vapor concentration, etc., or simultaneous monitoring at a plurality of locations.

  As described above, in the optical fiber sensor device of the present embodiment, the reflected light returning from the sensor unit 1 is modulated into a periodic spectrum, and this periodic spectrum changes depending on temperature, humidity, type of liquid / vapor, concentration, and the like. To do. Since the intensity of the reflected light changes with this spectrum change, the output of the light receiver 24 is converted into a physical quantity to be detected such as temperature, humidity, type of liquid / vapor, concentration, etc. by the arithmetic processing circuit 25. Can be measured.

  Since the same sensor unit 1 can detect temperature, humidity, liquid / vapor type, concentration, etc., if data to be converted into these physical quantities is input to the arithmetic processing circuit 25, the temperature, humidity, The type and concentration of liquid and vapor can be measured.

  Since the taper fiber pair 11 can be manufactured using a commercially available optical fiber and a fusion splicer, and the measurement is also a light amount measurement using a commercially available photodetector, an inexpensive optical fiber sensor device is obtained.

  The sensor unit 1 has a simple structure including only an optical fiber and a reflector 13, and only one optical fiber may be input / output for measuring reflected light, and an extremely small optical fiber sensor head can be obtained. Since the temperature sensor unit 1 is small, the response is quick and a narrow portion can be measured.

  Since the sensor unit 1 can be composed of only an optical fiber and a reflector 13, the reflector 13 is made of a material such as quartz in the case of a dielectric multilayer film, and gold or platinum in the case of a metal film. If such a metal having excellent corrosion resistance is used, it can be composed only of a material having very high chemical and thermal stability together with quartz, which is a fiber material, and a sensor head having excellent durability can be obtained.

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

  If the reflector 13 is a dielectric multilayer film, the sensor unit 1 can be entirely made of a non-conductive material, so that the sensor can be used even in a high frequency environment.

  If the temperature of the sensor unit 1-2 is measured by the configuration in which the sensor unit 1-1 measures temperature and the sensor unit 1-2 measures other physical quantities, accurate measurement without being affected by temperature can be performed. it can.

  By configuring the sensor unit 1-1 to measure temperature and the sensor unit 1-2 to measure humidity, it becomes an unprecedented sensor that can detect not only humidity but also dew condensation and freezing.

  By adopting a configuration including a plurality of sensor heads, an optical fiber sensor device capable of simultaneous monitoring of temperature, humidity, type of liquid / vapor, concentration, etc., or simultaneous monitoring at a plurality of locations is provided.

  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.

  The present invention can be used in various sensing applications for measuring temperature, humidity, type of liquid / vapor, concentration, and the like.

1, 1-1, 1-2: Sensor unit 2: Measuring unit 3, 3-1, 3-2: Transmission optical fiber 11: Tapered fiber pair 12: Non-tapered unit
13: Reflector 14: Waist part 15: Coating layer 16: Hollow container 21: Light sources 22, 22-1 to 22-3: Optical branching couplers 24, 24-1, 24-2: Light receiver 25: Arithmetic processing circuit 101 : Core 102: Clad

Claims (28)

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) The sensor unit (1),
Light emitting means (21) for generating measurement light to be supplied to the sensor section (1), light receiving means (24) for receiving reflected light whose intensity has been changed by the sensor section (1), and measuring light for the sensor section (1), light guide means (22) for guiding the reflected light from the sensor section (1) to the light receiving means (24), and arithmetic processing for converting the output of the light receiving means (24) into a physical quantity to be detected A measuring section (2) comprising a circuit (25);
A transmission optical fiber (3) that performs optical transmission between the sensor unit (1) and the measurement unit (2);
An optical fiber sensor device comprising:   The optical fiber sensor device according to claim 1, wherein at least the non-tapered portion (12) propagates the measurement light of the light emitting means (21) in a clad mode.   The optical fiber sensor device according to claim 1 or 2, wherein at least an outer peripheral region of the clad in the non-tapered portion (12) is in a lower refractive index state than a refractive index of the clad.   4. The optical fiber sensor device according to claim 3, wherein at least an outer peripheral surface of the clad in the non-tapered portion (12) is exposed so as to be in contact with an ambient atmosphere.   The optical fiber sensor device according to claim 3, wherein at least the outer peripheral surface of the clad in the non-tapered portion (12) is covered with a material having a refractive index higher than that of the clad.   The optical fiber according to any one of claims 1 to 5, wherein the tapered fiber pair (11) leaks measurement light of the light emitting means (21) from the core to the cladding at all times during measurement. Sensor device.   The optical fiber sensor device according to any one of claims 1 to 6, wherein an outer diameter of the waist portion (14) which is the thinnest portion of the tapered fiber pair (11) is 70 µm or less.   The optical fiber sensor device according to claim 7, wherein an outer diameter of the waist (14) which is the thinnest portion of the tapered fiber pair (11) is 50 µm or less.   The optical fiber sensor device according to any one of claims 1 to 8, wherein an outer diameter of a waist part (14) which is the thinnest part of the tapered fiber pair (11) is 30 µm or more.   The optical fiber sensor device according to any one of claims 1 to 9, wherein the length of the non-tapered fiber portion (12) is less than 20 mm.   11. The optical fiber sensor device according to claim 1, wherein the sensor unit (1) is held such that the non-tapered fiber unit (12) side is a free end.   12. The optical fiber sensor device according to claim 1, wherein the reflector (13) is a dielectric multilayer film.   The optical fiber sensor device according to any one of claims 1 to 12, wherein the tapered fiber pair (11) is made of different kinds of fibers.   14. The optical fiber sensor device according to claim 1, wherein the sensor section (1) is covered with a metal.   The optical fiber sensor device according to any one of claims 1 to 14, wherein the sensor section (1) is enclosed in a hollow container.   The optical fiber sensor device according to any one of claims 1 to 15, wherein the light emitting means (21) is a broadband light source. The optical fiber sensor device according to any one of claims 1 to 16, wherein the light emitting means (21) is light obtained by cutting out a part of a wavelength band from a broadband light source.   18. The optical fiber sensor device according to claim 1, wherein the light emitting means (21) is a semiconductor laser.   The relationship between the amount of reflected light and the type of liquid when the sensor unit (1) is immersed in the liquid is input to the arithmetic processing circuit (25), and the type of the immersed liquid is determined. The optical fiber sensor device according to any one of claims 1 to 18.   A steep change in the amount of reflected light when the sensor section (1) is immersed in a liquid is detected by an arithmetic processing circuit (25) to detect water leakage or liquid leakage. The optical fiber sensor device according to any one of 1 to 19.   The relationship between the vapor concentration and the change in the amount of reflected light when the sensor unit (1) is exposed to vapor is input to the arithmetic processing circuit (25), and the vapor concentration is measured. Item 21. The optical fiber sensor device according to any one of Items 1 to 20. The humidity of the said sensor part (1) and the relationship of a reflected light amount change are input into the said arithmetic processing circuit (25), and humidity was measured, The any one of Claim 1 thru | or 21 characterized by the above-mentioned. Optical fiber sensor device.   23. The liquid concentration is measured by inputting the relationship between the liquid concentration of the sensor section (1) and the change in the amount of reflected light into the arithmetic processing circuit (25). An optical fiber sensor device according to claim 1.   Among the relationships between the temperature, humidity, type of immersed liquid, immersed liquid concentration, vapor concentration, etc., and reflected light amount change of the sensor unit (1), a plurality of relationships are input to the arithmetic processing circuit (25). The optical fiber sensor device according to any one of claims 1 to 23, wherein a plurality of physical quantities are measured by a single sensor unit (1).   At least one sensor unit (1-1) for measuring temperature, a plurality of sensor units (1-2) for measuring physical quantities other than temperature, and temperature characteristic data of the plurality of sensor units (1-2) The arithmetic processing circuit (25) inputted in advance is provided, and the amount corresponding to the temperature change of the reflected light amount returned from the plurality of sensor units (1-2) is corrected. The optical fiber sensor apparatus in any one of thru | or 24.   Data on the relationship between the temperature of the sensor unit (1-1) and the amount of reflected light, the relationship between the humidity of the sensor unit (1-2) and the amount of reflected light, the drastic change in the amount of reflected light accompanying water droplet adhesion and freezing of attached water The optical fiber sensor device according to any one of claims 1 to 25, wherein the optical fiber sensor device is inputted to the arithmetic processing circuit (25) to measure temperature, humidity, dew point, and freezing.   27. A plurality of sensor units (1) are provided to simultaneously monitor temperature, humidity, type of liquid / vapor, concentration, etc., or simultaneously monitor a plurality of locations. An optical fiber sensor device according to any one of the above. 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) The measurement light is introduced into the sensor unit (1) using the transmission optical fiber (3),
In the tapered fiber pair (11), a part of the measurement light is leaked from the core to the cladding side,
At least in the non-tapered portion (12), the leakage light propagates in the clad mode and is reflected by the reflector (13).
By detecting the change in the reflected light of the sensor unit (1) through the transmission optical fiber (3), the refractive index change in the surrounding environment of the non-tapered portion (12) or the temperature dependent A sensing method using an optical fiber, characterized by detecting a change in refractive index of the non-tapered portion (12) itself.

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