JP2015232522A - Optical fiber sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber sensor device that can measure properties such as a refractive index and density of a material with high sensitivity.SOLUTION: An optical fiber sensor device 1 includes an optical fiber 2 that includes a light transmission part 4 and a hetero core part 3 having a core 5a with diameter smaller than that of the light transmission part 4, and gold nanoparticles 10 that are adhered to the outer peripheral surface of a clad 6a of the hetero core part 3. When light is transmitted through the optical fiber 2, the degree of absorption of light at a predetermined wavelength in the hetero core part 3 changes according to the refractive index of a material around the hetero core part 3.

Description

  The present invention relates to a sensor device configured using an optical fiber.

  As a sensor device for measuring the refractive index or concentration of a liquid, a sensor device configured using an optical fiber is conventionally known.

  For example, Patent Document 1 discloses a metal film obtained by laminating a gold film on a chromium film on the outer peripheral surface of a clad of a hetero-core part (a part having a different core diameter from other parts) formed in a part of an optical fiber, The applicant of the present application has proposed an ethanol sensor having a structure in which an alternating laminated film whose refractive index changes by contraction or expansion due to ethanol is mounted.

  This ethanol sensor generates surface plasmon resonance (SPR) on the outer peripheral surface of the clad of the hetero-core portion of the optical fiber on which the metal film is mounted, so that the refractive index of the alternately laminated film according to the ethanol concentration around the hetero-core portion The transmission intensity of the light is changed in accordance with the change of.

  For example, Non-Patent Document 1 describes a sensor having a structure in which gold nanoparticles are fixed to the outer peripheral surface of a core exposed by removing a clad at an end of an optical fiber. In Non-Patent Document 1, by generating a phenomenon called localized surface plasmon resonance by the gold nanoparticles on the outer peripheral surface of the core, the wavelength at which the light absorption by the exposed portion of the core of the optical fiber has a peak value is It is described that it varies depending on the refractive index of the material around the core of the exposed portion.

JP 2010-223817 A

Optimization of gold-nanoparticle-based optical fiber surface plasmon resonance (SPR) -based sensors / M.H.Tu, T.Sun, K.T.V.Grattan / Sensors and Actuators B 164 (2012) 43-53

  In recent years, a sensor capable of measuring the refractive index, concentration, etc. of a substance such as a liquid accurately and with high sensitivity is desired. For example, in the automobile industry and the like, an inexpensive sensor that can accurately and highly sensitively measure the mixing ratio of gasoline and alcohol in a mixed fuel of gasoline and alcohol such as ethanol is desired.

  However, the sensor as described in Patent Document 1 or Non-Patent Document 1 is insufficient for measuring characteristics such as refractive index and concentration of a substance such as a liquid with high sensitivity.

  The present invention has been made in view of such a background, and an object of the present invention is to provide an optical fiber sensor device capable of measuring characteristics such as a refractive index and a concentration of a substance with high sensitivity.

  It is another object of the present invention to provide a method capable of easily manufacturing such an optical fiber sensor device.

  It is another object of the present invention to provide a measurement system that can realize characteristics such as refractive index and concentration of a substance with an inexpensive system configuration.

  In order to achieve the above object, an optical fiber sensor device of the present invention includes an optical transmission unit having a core and a clad, and a heterocore unit having a core and a clad respectively connected to the core and the clad of the optical transmission unit. The optical fiber having a core having a smaller diameter than the core of the optical transmission unit, and gold nanoparticles fixed to the outer peripheral surface of the cladding of the hetero core unit, and passing through the optical transmission unit and the hetero core unit When the light is transmitted through the optical fiber, the degree of absorption of light of a predetermined wavelength in the hetero core portion is configured to change according to the refractive index of the material around the hetero core portion. (First invention).

  Here, in the optical fiber sensor device having a structure in which gold nanoparticles are fixed to the outer peripheral surface of the clad of the hetero core part through various experiments and examinations of the inventor of the present application, the optical fiber sensor device enters the clad of the hetero core part from the optical transmission part. Due to the localized surface plasmon resonance excited by light acting on the gold nanoparticles on the outer peripheral surface of the cladding, the degree of absorption of light of a predetermined wavelength in the heterocore portion (and thus a predetermined amount in the optical fiber). The degree of attenuation of the transmission intensity of light having a wavelength) is significantly more sensitive to changes in the refractive index around the cladding of the hetero-core portion than the conventional sensor devices as seen in Patent Documents 1 and 2 above. It turned out to be something.

  Therefore, the optical fiber sensor device of the present invention is configured as described above. As a result, according to the optical fiber sensor device of the present invention, it is possible to measure properties such as the refractive index and concentration of a substance with high sensitivity.

  Supplementally, when the material around the heterocore portion is, for example, a mixed material of two or more types of materials, the refractive index of the mixed material generally changes according to the concentration of the composition material constituting the mixed material. For this reason, the degree of light absorption in the heterocore portion can vary depending on the concentration of the substance around the heterocore portion. Therefore, the optical fiber sensor device of the present invention can be used not only as a refractive index of a substance but also as an apparatus capable of measuring other characteristics such as a concentration of a substance affecting the refractive index with high sensitivity.

  In the first invention, in the case where light is transmitted through the optical fiber in a state where the refractive index of the material around the cladding of the hetero core portion to which the gold nanoparticles are fixed is maintained at a constant refractive index. The degree of attenuation of light transmission intensity is defined as X, the gold nanoparticles are not fixed to the outer peripheral surface of the cladding of the hetero core portion, and the refractive index of the substance around the hetero core portion is the constant refraction When the transmission degree of light transmitted through the optical fiber is defined as X0 when the transmission rate is maintained at a rate, the gold nanoparticle has a ratio of X to X0 of 1. It is preferably fixed to the outer peripheral surface of the cladding of the hetero-core portion at a density of / 100 or less (second invention).

  According to various experiments and examinations by the inventors of the present application, the ratio of X to X0 increases as the density of gold nanoparticles (the number of gold nanoparticles per unit area) fixed to the outer peripheral surface of the cladding of the hetero core portion increases. Tend to decrease. The state in which the ratio is 1/100 or less is a state in which the density of the gold nanoparticles fixed to the outer peripheral surface of the cladding of the heterocore portion is high.

  In such a state, the inventor of the present application shows that the degree of light absorption in the heterocore portion is significantly sensitive to changes in the refractive index of the substance around the heterocore portion at wavelengths in the near infrared region. It became clear by various experiment, examination.

  Therefore, the optical fiber sensor device of the second invention is configured as described above. According to this optical fiber sensor device, by measuring the attenuation degree of the transmission intensity of light in the near-infrared region in the optical fiber, the characteristics such as the refractive index of the material around the heterocore portion are measured with high sensitivity. It becomes possible.

  Here, near-infrared light has a smaller attenuation of transmission intensity per unit distance of the optical fiber than light in the visible light region. Further, light in the near infrared region can be detected by an inexpensive light receiving element such as a photodiode that is generally used.

  For this reason, by using the optical fiber sensor device of the second invention, it is possible to construct an inexpensive measurement system for measuring characteristics such as the refractive index of the substance around the heterocore portion. In addition, even in an environment where the required length of the optical fiber becomes long, it is possible to construct a measurement system that can measure characteristics such as the refractive index of the substance around the heterocore portion with high sensitivity.

  In addition, the measurement system of the present invention includes the optical fiber sensor device of the first invention, a light source that enters the optical fiber at least including light of a predetermined wavelength, and the intensity of light of the predetermined wavelength that is emitted from the optical fiber. And detecting a characteristic of a substance existing around the cladding of the hetero-core portion based on the output of the photodetector (third invention).

  Alternatively, the measurement system of the present invention includes the optical fiber sensor device of the second invention, a light source that enters light including at least light in the near infrared region, and a near infrared outside line region that is emitted from the optical fiber. And a light detector for detecting the intensity of light having a predetermined wavelength, and measuring the characteristics of a substance existing around the cladding of the heterocore portion based on the output of the light detector (fourth feature) invention).

  According to the measurement system of the third or fourth aspect of the present invention, the characteristics such as the refractive index of the substance around the heterocore portion can be measured with high sensitivity using the output of the photodetector. And since the said photodetector may be what can detect the intensity | strength of the light of the said predetermined wavelength, generally inexpensive inexpensive light receiving elements, such as a photodiode, can be used. For this reason, the measurement system can be configured at low cost.

  Further, particularly in the measurement system of the fourth invention, since the attenuation degree of the light in the near-infrared wavelength per unit length of the optical fiber is relatively smaller than the light in the visible light wavelength, the light source and the photodetector Even in an environment where the required length of the optical fiber between the two is long, characteristics such as the refractive index of the material around the heterocore portion can be measured with high sensitivity.

  The measurement system of the third invention or the fourth invention is suitable when the substance is a mixed fuel of gasoline and alcohol, and is a system for measuring a mixing ratio of gasoline and alcohol in the mixed fuel (first 5 invention).

  Here, the refractive index of the mixed fuel increases with an increase in gasoline concentration (decrease in alcohol concentration) in the mixed fuel. Therefore, according to the fifth aspect, the mixing ratio of gasoline and alcohol in the mixed fuel can be measured with high sensitivity based on the output of the photodetector.

  Further, the method of manufacturing the optical fiber sensor device of the present invention includes an optical transmission unit having a core and a clad, and a hetero core unit having a core and a clad respectively connected to the core and the clad of the optical transmission unit. An optical fiber sensor device manufacturing method comprising: an optical fiber having a core having a smaller diameter than a core of the optical transmission unit; and gold nanoparticles fixed to an outer peripheral surface of a clad of the hetero core unit, wherein the gold nanoparticle X represents the degree of attenuation of the transmission intensity of light when the light is transmitted through the optical fiber in a state where the refractive index of the material around the cladding of the hetero-core portion to which is fixed is maintained at a constant refractive index. And the gold nanoparticles are not fixed to the outer peripheral surface of the cladding of the hetero core portion, and the refractive index of the substance around the hetero core portion is set to the constant refractive index. In a state where the transmission intensity of the light is transmitted in the state where the optical fiber is held, X0 is defined as the degree of attenuation of the transmission intensity of the light until the ratio of X to X0 is saturated. By immersing the hetero core portion of the fiber in a suspension of gold nanoparticles, the gold nanoparticles are fixed to the outer peripheral surface of the clad of the hetero core portion (the sixth invention).

  Here, according to various experiments and examinations of the inventors of the present application, when the heterocore portion of the optical fiber is immersed in a suspension of gold nanoparticles until the ratio of X to X0 is saturated. The gold nanoparticles can be fixed to the outer peripheral surface of the cladding of the hetero-core portion at a density such that the ratio is 1/100 or less.

  Therefore, according to the manufacturing method of the sixth invention, the optical fiber sensor device of the second invention can be easily manufactured.

The figure which shows the structure of the optical fiber sensor apparatus of one Embodiment of this invention. The figure which shows the structure of the measurement system of one Embodiment of this invention. (A), (b) is a graph which shows the measurement data of the verification test 1 using the optical fiber sensor apparatus of embodiment. (A), (b) is a graph which shows the measurement data of the verification test 2 using the optical fiber sensor apparatus of embodiment. (A), (b) is a graph which shows the measurement data of the verification test 3 using the optical fiber sensor apparatus of embodiment. The figure which shows the structure of other embodiment of the measurement system of this invention.

  An embodiment of the present invention will be described below with reference to FIGS.

  As shown in FIG. 1, the optical fiber sensor device 1 of the present embodiment includes optical fibers 2b and 2b constituting optical transmission units 4 and 4 at both ends in the axial direction of an optical fiber 2a constituting a hetero core portion 3 having a predetermined length. Are connected to each other, and a plurality of gold nanoparticles 10 fixed to the outer peripheral surface of the hetero-core portion 3.

  Each optical fiber 2b constituting the optical transmission unit 4 is formed of a multimode optical fiber, and includes a core 5b having a constant diameter (for example, 50 μm) and a cladding 6b on the outer periphery thereof.

  The optical fiber 2a constituting the hetero-core part 3 is constituted by a single mode optical fiber, and has a core 5a having a constant diameter (for example, 3 μm) smaller than the core 5b of the optical transmission part 4 and a cladding 6a on the outer periphery thereof.

  The optical fibers 2b and 2b constituting the optical transmission parts 4 and 4 are coaxially joined to both axial ends of the optical fiber 2a constituting the heterocore part 3 by fusion or the like. Thereby, the core 5a and the clad 6a of the hetero core part 3 are connected to the core 5b and the clad 6b of each optical transmission part 4, respectively.

  In the present embodiment, the diameter of the core 5a of the heterocore portion 3 is constant, but the diameter of the core 5a may not be constant. For example, the diameter of the core 5a may be formed so as to gradually change at the portions near both ends of the hetero core portion 3 (the diameter gradually decreases as the distance from the optical transmission portion 4 increases).

  The gold nanoparticles 10 are fixed to the outer peripheral surface of the cladding 6 a of the heterocore portion 3. This fixing is performed by the following method, for example.

  First, an amino group is introduced into the outer peripheral surface of the heterocore portion 3 by subjecting the outer peripheral surface of the heterocore portion 3 of the optical fiber 2 to surface treatment using a silane coupling agent.

  Next, the heterocore portion 3 is immersed in a suspension (colloid) containing gold nanoparticles 10 having a particle size of 5 nm to 100 nm. As a result, a plurality of gold nanoparticles 10 having a particle size of 5 nm to 100 nm are fixed to the outer peripheral surface of the clad 6 a of the heterocore portion 3.

  In this case, the longer the time during which the hetero core portion 3 is immersed in the suspension, the more gold nanoparticles 10 are fixed to the outer peripheral surface of the clad 6 a of the hetero core portion 3. Therefore, by appropriately adjusting the time for immersing the hetero core part 3 in the suspension, the density of the gold nanoparticles 10 fixed to the outer peripheral surface of the cladding 6a of the hetero core part 3 (the gold nano particles 10 per unit area) (Number) can be adjusted.

  The suspension is prepared, for example, by reducing chloroauric acid using a reducing agent such as citric acid, L-ascorbic acid, tannic acid, sodium borohydride, or lithium aluminum hydride. In addition, the particle size of the gold nanoparticle 10 in the suspension, and thus the particle size of the gold nanoparticle 10 to be fixed to the outer peripheral surface of the clad 6a of the heterocore portion 3 may not be uniform.

  The optical fiber sensor device 1 of the present embodiment is configured as described above.

  Next, an example of a measurement system using the optical fiber sensor device 1 of the present embodiment will be described with reference to FIG.

  The measurement system 20 shown in FIG. 2 includes a light source 21 that outputs light incident on the optical fiber 2 including the heterocore unit 3 and a photodetector 22 that receives light emitted from the optical fiber 2.

  The light source 21 is connected to one end of the optical transmission units 4 and 4 of the optical fiber 2. As the light source 21, for example, a white light source or a multi-wavelength light source that outputs white light as multi-wavelength light, or a laser light source that outputs laser light having a predetermined wavelength is used.

  The photodetector 22 is connected to the other end on the other side of the optical transmission units 4 and 4 of the optical fiber 2. As the photodetector 22, for example, a spectrum analyzer (spectrometer) or a light receiving element that generates an output corresponding to the light receiving intensity of light having a predetermined wavelength or a wavelength in the vicinity thereof is used.

  In the illustrated measurement system 20, the photodetector 22 is connected to a computer 23 such as a personal computer. Then, the measurement data of the photodetector 22 can be taken into the computer 23 to perform data analysis or the like.

  In addition, both end portions in the axial center direction of the hetero core portion 3 at the intermediate portion of the optical fiber 2 are attached to the jig 24. By moving the jig 24, the heterocore part 3 can be immersed in the liquid to be measured or moved into the gas to be measured.

  The measurement by the measurement system 20 is performed as follows. That is, the hetero core part 3 of the optical fiber sensor device 1 is arranged so that the substance to be measured exists around it. For example, when the substance to be measured is a liquid, the heterocore part 3 is immersed in the liquid. Further, when the substance to be measured is a gas, the hetero core 3 is disposed in the atmosphere of the gas.

  In this state, light is incident on one end of the optical fiber 2 from the light source 21.

  Light incident on one end of the optical fiber 2 enters the hetero core section 3 through the core 5b of the light transmission section 4 on the light source 21 side, passes through the hetero core section 3, and then transmits light on the photodetector 22 side. The light is emitted from the other end of the optical fiber 2 through the core 5 b of the portion 4. The light emitted from the other end of the optical fiber 2 is received by the photodetector 22, and the intensity, spectrum distribution (wavelength distribution), and the like of the emitted light are measured by the photodetector 22.

  Here, a part of the light that enters the hetero-core unit 3 from the core 5b of the optical transmission unit 4 on the light source 21 side enters the cladding 6a of the hetero-core unit 3, and the cladding 6a is used as an optical transmission unit on the photodetector 22 side. Propagate toward 4.

  Of the light that has entered the clad 6a of the heterocore portion 3, light that is totally reflected by the outer peripheral surface of the clad 6a acts as near-field light on the gold nanoparticles 10 on the outer peripheral surface (interface) of the clad 6a. Thus, localized surface plasmon resonance (hereinafter referred to as LSPR) is excited on the outer peripheral surface of the cladding 6a. The excitation of the LSPR absorbs energy of light having a predetermined wavelength passing through the heterocore portion 3 and a wavelength in the vicinity thereof.

  In this case, the degree of absorption of light of a predetermined wavelength caused by LSPR, and hence the degree of attenuation of the transmission intensity of light of the predetermined wavelength in the optical fiber 2, depends on the refractive index of the material around the heterocore portion 3. . In addition, when the material around the hetero-core part 3 is, for example, a mixed material of a plurality of materials, the refractive index of the mixed material generally varies depending on the content ratio of the material composing the mixed material.

  For this reason, the degree of attenuation of the transmission intensity of light of a predetermined wavelength in the optical fiber 2 (ratio of the intensity of the emitted light to the intensity of the incident light of the optical fiber 2) is such as the refractive index or the concentration of the substance around the hetero core portion 3. It depends on the characteristics. And in the optical fiber sensor apparatus 1 of the structure of this embodiment, the sensitivity of the change of the attenuation degree of the transmission intensity of the light according to the refractive index of the substance around the hetero core part 3 becomes high.

  Therefore, the optical fiber sensor device 1 can be used as a sensor for measuring characteristics such as a refractive index of a substance around the hetero core 3.

  Below, the verification test regarding the characteristic of the optical fiber sensor apparatus 1 is demonstrated.

[Verification test 1]
In producing the optical fiber sensor device 1, in order to fix the gold nanoparticles 10 to the outer peripheral surface of the clad 6a of the hetero core part 3, the time for immersing the hetero core part 3 in the suspension containing the gold nanoparticles 10 is different. A plurality of optical fiber sensor devices 1 were prepared.

  And about each optical fiber sensor apparatus 1 from which the said immersion time differs, in the state which has arrange | positioned the hetero core part 3 in the air as gas which has a fixed refractive index, the said measurement system 20 of the emitted light of the optical fiber 2 is carried out. The spectrum (wavelength distribution) was measured. The measurement results are shown in the graphs of FIGS. 3 (a) and 3 (b). In this case, a white light source was used as the light source 21 of the measurement system 20 and a spectrum analyzer (spectrometer) was used as the photodetector 22.

  FIG. 3A is a graph showing the relationship between the wavelength of light and the relative attenuation degree of the light transmission intensity of the optical fiber 2 for the optical fiber sensor device 1 with different immersion times, and FIG. These are graphs showing the relationship between the relative attenuation degree of the transmission intensity of light at a predetermined wavelength (540 nm) and the immersion time.

  Here, the relative attenuation degree is a relative attenuation degree based on the attenuation degree of light transmission intensity in a state where gold nanoparticles are not fixed to the outer peripheral surface of the clad 6 a of the heterocore portion 3.

  More specifically, the attenuation degree of the light transmission intensity (ratio of the intensity of the emitted light to the intensity of the incident light of the optical fiber 2) in a state where the gold nanoparticles are not fixed to the outer peripheral surface of the clad 6a of the hetero core portion 3 is set. X0, where X is the degree of attenuation of the transmission intensity of light in the optical fiber sensor device 1 in a state where the gold nanoparticles are fixed to the outer peripheral surface of the clad 6a of the hetero-core portion 3, the degree of relative attenuation is X / X0. .

  In the description of the present embodiment, the degree of relative attenuation is expressed in decibels. In this case, 10 · log (X / X0) represents the relative attenuation degree expressed by the ratio of X / X0 in decibels.

  As shown in FIG. 3 (a), the magnitude (absolute value) of the relative attenuation degree is around the predetermined wavelength (wavelength of 540 nm) for any of the optical fiber sensor devices 1 with different immersion times. At the peak value.

  Further, as shown in FIG. 3 (b), the magnitude of the relative attenuation at a wavelength of 540 nm where the magnitude (absolute value) of the relative attenuation becomes a peak value basically corresponds to the immersion time. The longer it gets, the bigger it becomes. This is because the longer the immersion time, the higher the density (number per unit area) of the gold nanoparticles 10 fixed to the outer peripheral surface of the clad 6b of the heterocore portion 3, and thus a predetermined wavelength (here, This is probably because the degree of absorption of light at a wavelength of 540 nm increases.

  However, the magnitude of the relative attenuation is saturated when the immersion time exceeds approximately 15 minutes. This is presumably because when the immersion time exceeds approximately 15 minutes, the fixation of the gold nanoparticles 10 to the outer peripheral surface of the cladding 6b of the hetero-core portion 3 is saturated. In this saturation state, the degree of relative attenuation is about −20 dB (X / X0 = 1/100). Therefore, the state in which the relative attenuation degree (X / X0) is 1/100 or less is a state in which the relative attenuation degree is saturated (in other words, the gold nanoparticles 10 on the outer peripheral surface of the clad 6a of the heterocore portion 3). It can be considered that the fixation is saturated. Hereinafter, the state in which the relative attenuation degree is saturated in this way may be referred to as a fixed saturation state of the gold nanoparticles 10.

[Verification test 2]
Next, the immersion time is defined as a time until the relative attenuation degree reaches a relative attenuation degree (≈−17 dB) of about 80% of the relative attenuation degree (≈−20 dB) in the fixed saturation state of the gold nanoparticles 10. An optical fiber sensor device 1 was manufactured. Then, in the state where the hetero core portion 3 of the optical fiber sensor device 1 is immersed in a mixed fuel of gasoline and ethanol (a state in which a substance around the hetero core portion 3 is used as a mixed fuel), the optical fiber 2 is obtained by the measurement system 20. The spectrum (wavelength distribution) of the emitted light was measured.

  In this case, the measurement was performed by changing the mixing ratio of gasoline and ethanol (and consequently the gasoline concentration and ethanol concentration) in the mixed fuel to a plurality of values. The measurement results are shown in the graphs of FIGS. 4 (a) and 4 (b). In this case, a white light source was used as the light source 21 and a spectrum analyzer (spectrometer) was used as the light detector 22.

  FIG. 4A is a graph showing the relationship between the wavelength of light and the relative attenuation degree of the light transmission intensity of the optical fiber 2 in the measurement for each mixed fuel with different mixing ratios, and FIG. These are graphs showing the relationship between the relative attenuation degree of the transmission intensity of light at a predetermined wavelength (545 nm) and the gasoline concentration corresponding to the mixing ratio.

  As shown in FIG. 4 (a), the magnitude (absolute value) of the relative attenuation degree is a peak value in the vicinity of a predetermined wavelength (wavelength of 545 nm) for any of the mixed fuels having different mixing ratios. It becomes.

  Further, as shown in FIG. 4B, the magnitude of the relative attenuation at a wavelength of 545 nm at which the magnitude (absolute value) of the relative attenuation is almost the peak value is higher as the gasoline concentration of the mixed fuel becomes higher. (In other words, the lower the ethanol concentration of the mixed fuel), the larger.

  Here, the refractive index of the mixed fuel of gasoline and ethanol increases as the concentration of gasoline increases. Therefore, the higher the gasoline concentration of the mixed fuel around the heterocore part 3 is, the greater the degree of relative attenuation of the light transmission intensity is. The larger the refractive index of the mixed fuel around the heterocore part 3 is, the more the light transmission is transmitted. This corresponds to an increase in the degree of relative attenuation of the intensity.

  In this case, when the gasoline concentration of the mixed fuel changes from 0% to 100%, the relative attenuation degree changes by about 11 dB. That is, the relative attenuation degree (X / X0) of the transmission intensity of light in the optical fiber 2 changes 10 times or more between the case where the gasoline concentration of the mixed fuel is 0% and the case where it is 100%.

  Therefore, it can be seen that the mixing ratio (or gasoline concentration or ethanol concentration) of the mixed fuel of gasoline and ethanol can be measured with high sensitivity using the optical fiber sensor device 1 produced in the verification test 2. For this reason, the optical fiber sensor device 1 produced in the verification test 2 can be used as a sensor for detecting the mixing ratio (or gasoline concentration or ethanol concentration) of the mixed fuel.

  As described above, when the optical fiber sensor device 1 is used as a sensor for detecting the mixing ratio of the mixed fuel, for example, operation control (control of the fuel injection amount, etc.) of the internal combustion engine that can be operated by the mixed fuel is performed. This can be performed according to the detected value of the mixing ratio of the mixed fuel.

  Further, in this case, the relative attenuation degree of light having a wavelength near 545 nm changes with high sensitivity according to the mixing ratio of the mixed fuel, so that the photodetector 22 that detects the intensity of the emitted light from the optical fiber 2. May not be a spectroscope such as a spectrum analyzer, but may be a generally popular light receiving element such as a photodiode capable of detecting light having a constant wavelength near 545 nm. Therefore, the measurement system 20 can be configured at a low cost.

[Verification test 3]
Next, an optical fiber sensor device 1 was produced in which the heterocore portion 3 was immersed in the suspension until the gold nanoparticles 10 were in a fixed saturation state (until the relative attenuation degree X / X0 was saturated). Then, in the same manner as in the verification test 2, the hetero core portion 3 of the optical fiber sensor device 1 is immersed in a mixed fuel of gasoline and ethanol, and the measurement system 20 causes the output light of the optical fiber 2 to be emitted. The spectrum (wavelength distribution) was measured.

  In this case, the measurement was performed by changing the mixing ratio of gasoline and ethanol (and consequently the gasoline concentration and ethanol concentration) in the mixed fuel to a plurality of values. The measurement results are shown in the graphs of FIGS. 5 (a) and 5 (b). In this case, a white light source was used as the light source 21 of the measurement system 20 and a spectrum analyzer (spectrometer) was used as the photodetector 22.

  FIG. 5 (a) is a graph showing the relationship between the wavelength of light and the relative attenuation degree of the light transmission intensity of the optical fiber 2 in the measurement for each mixed fuel with different mixing ratios, and FIG. 5 (b). These are graphs showing the relationship between the relative attenuation degree of the transmission intensity of light at three types of predetermined wavelengths (415 nm, 580 nm, 900 nm) and the gasoline concentration corresponding to the mixing ratio.

  As shown in FIG. 5 (a), the magnitude (absolute value) of the relative attenuation level is approximately 415 nm, 580 nm, and 900 nm of three predetermined wavelengths for any of the mixed fuels with different mixing ratios. It becomes a peak value in the vicinity.

  In this case, in the optical fiber sensor device 1 manufactured in the verification test 3, the gold nanoparticles 10 are fixed at a higher density on the outer peripheral surface of the cladding 6a of the heterocore portion 3 than in the optical fiber sensor device 1 manufactured in the verification test 2. Therefore, a strong electric field is generated between the gold nanoparticles 10 that are close to each other during light transmission. Due to this, the spectral characteristic (wavelength distribution characteristic) of the relative attenuation degree of the transmission intensity of light in the optical fiber sensor device 1 manufactured in the verification test 3 is the optical fiber sensor device 1 manufactured in the verification test 2. It is considered that the difference is relatively large.

  Further, in the optical fiber sensor device 1 manufactured in the verification test 3, as shown in FIG. 5B, the wavelength of 415 nm at which the magnitude (absolute value) of the degree of relative attenuation is substantially the peak value, or 580 nm. The magnitude of the relative attenuation degree at the wavelength or 900 nm is basically as the gasoline concentration of the mixed fuel becomes higher (in other words, as the ethanol concentration of the mixed fuel becomes lower or the refractive index of the mixed fuel). The larger the rate), the larger.

  Here, as can be seen by comparing FIG. 5A and FIG. 4A relating to the verification test 2, the fixation of the gold nanoparticle 10 to the heterocore portion 3 does not reach the fixed saturation state. In the optical fiber sensor device 1 (the optical fiber sensor device 1 produced in the verification test 2), the sensitivity of the relative attenuation degree with respect to the mixing ratio of the mixed fuel is relatively high at a wavelength near 580 nm. In the optical fiber sensor device 1 (the optical fiber sensor device 1 manufactured in the verification test 3) in a fixed saturation state, the sensitivity of the change in the relative attenuation degree with respect to the mixture ratio of the mixed fuel is relatively high at a wavelength near 580 nm. It will be low.

  On the other hand, in the optical fiber sensor device 1 (the optical fiber sensor device 1 produced in the verification test 2) in which the gold nanoparticles 10 are not fixed to the hetero core portion 3 in the fixed saturation state, the wavelength is in the near infrared region. At a certain wavelength of 900 nm, the sensitivity of the change in the relative attenuation degree with respect to the mixing ratio of the mixed fuel is low, whereas the optical fiber sensor device 1 in which the gold nanoparticles 10 are in a saturated saturation state (produced in the verification test 3). In the optical fiber sensor device 1), at a wavelength near 900 nm, the sensitivity of the change in the relative attenuation degree with respect to the mixing ratio of the mixed fuel becomes high.

  Specifically, in the optical fiber sensor device 1 manufactured in the verification test 3, the magnitude of the relative attenuation at a wavelength near 900 nm is about 11 dB when the gasoline concentration of the mixed fuel is changed from 0% to 100%. Change. That is, the degree of attenuation (X / X0) of the near-infrared light transmission intensity in the optical fiber 2 changes 10 times or more when the gasoline concentration of the mixed fuel is 0% and when it is 100%.

  Therefore, it can be seen that the mixing ratio (or gasoline concentration or ethanol concentration) of the mixed fuel of gasoline and ethanol can be measured with high sensitivity using the optical fiber sensor device 1 produced in the verification test 3. For this reason, the optical fiber sensor device 1 produced in the verification test 3 can be used as a sensor for detecting the mixing ratio (or gasoline concentration or ethanol concentration) of the mixed fuel.

  In this case, in particular, the light for detecting the intensity of the emitted light from the optical fiber 2 because the relative attenuation level changes with high sensitivity according to the mixing ratio of the mixed fuel with respect to light having a wavelength in the near infrared region. The detector 22 may not be a spectroscope such as a spectrum analyzer, and a light receiving element capable of detecting light of a constant wavelength in the near infrared region can be used. Such light receiving elements are generally widely used. Therefore, the measurement system 20 can be configured at a low cost.

  Further, since light having a wavelength in the near infrared region is less likely to be attenuated in the optical transmission unit 4 of the optical fiber 2 than light having a wavelength lower than that (for example, 415 nm, 580 nm, etc.), the optical transmission unit The light attenuation per unit length at 4 is small. For this reason, even in the measurement system 20 in which the required length of the optical fiber 2 is relatively long, it is possible to measure the mixing ratio of the mixed fuel or the refractive index of the substance around the heterocore portion 3 with high sensitivity. it can.

  As described above, according to the optical fiber sensor device 1 of the present embodiment, when light is transmitted through the optical fiber 2 by fixing the gold nanoparticles 10 to the outer peripheral surface of the cladding 6a of the hetero-core portion 3. In addition, the relative attenuation degree of the transmission intensity of light at a predetermined wavelength changes with high sensitivity in accordance with the refractive index of the substance around the hetero core portion 3. For this reason, the refractive index of the substance, or the characteristics such as the concentration that defines the refractive index, is highly sensitive based on the output of the photodetector 22 that detects the intensity of light having a predetermined wavelength emitted from the optical fiber 2. Can be measured.

  In addition, since the measurement system 20 can be configured using the relatively inexpensive photodetector 22 that can detect the intensity of light of a predetermined wavelength, the measurement system 20 can be configured at low cost.

  In particular, when the gold nanoparticles 10 are fixed to the outer peripheral surface of the clad 6a of the hetero-core part 3 to the fixed saturation state, the relative attenuation degree of the light transmission intensity at the near-infrared wavelength is the hetero-core part. 3 changes with high sensitivity according to the refractive index of the surrounding material.

  For this reason, not only can the measurement system 20 capable of measuring the refractive index of the substance around the hetero-core portion 3 or the characteristics such as the concentration defining the refractive index with high sensitivity be constructed at low cost, but also the required length of the optical fiber 2 Can be appropriately measured without using the high-power light source 21 or the like, even if the refractive index or the concentration of the material around the hetero-core portion 3 is relatively long.

  In the embodiment described above, a mixed fuel of gasoline and ethanol is exemplified as an example of a substance to be measured. However, a mixed ratio of a mixed fuel of gasoline and alcohol other than ethanol (such as methanol) (or gasoline concentration, Alternatively, the alcohol concentration can be measured with high sensitivity by the measurement system 20 using the optical fiber sensor device 1 of the embodiment.

  Moreover, in the said embodiment, although the measurement system 20 which transmits light from the one end of the optical fiber 2 which equips the intermediate | middle part with the hetero core part 3 was illustrated, for example, even if it comprises a measurement system as shown in FIG. Good.

  In the measurement system 30 shown in FIG. 6, the optical fiber 2 b constituting the optical transmission unit 4 is connected to one end of the optical fiber 2 a constituting the heterocore unit 3 of the optical fiber sensor device 1, while the light constituting the heterocore unit 3 is connected. A reflecting mirror 7 is attached to the other end of the fiber 2a. The optical fiber 2 b constituting the optical transmission unit 4 is connected to the light source 21 and the photodetector 22 via the coupler 25.

  In the measurement system 30 configured in this way, light incident on the optical fiber 2b from the light source 21 via the coupler 25 enters the heterocore portion 3 from the optical fiber 2b, and then is reflected by the reflecting mirror 7 and is reflected by the optical fiber. Return to 2b. This return light is received by the photodetector 22 via the coupler 25.

  Also in such a measurement system 30, the intensity of light of a predetermined wavelength received by the photodetector 22 changes with high sensitivity according to the refractive index of the substance around the heterocore portion 3. For this reason, the refractive index of the substance around the hetero core portion 3 or the concentration defining the substance can be measured with high sensitivity based on the intensity of light of a predetermined wavelength received by the photodetector 22.

  DESCRIPTION OF SYMBOLS 1 ... Optical fiber sensor apparatus, 2, 2a, 2b ... Optical fiber, 3 ... Hetero core part, 4 ... Optical transmission part, 5a, 5b ... Core, 6a, 6b ... Cladding, 10 ... Gold nanoparticle, 20 ... Measurement system, 21: Light source, 22: Photo detector.

Claims (6)

An optical transmission unit having a core and a clad; and a heterocore unit having a core and a clad respectively connected to the core and the clad of the optical transmission unit, wherein the heterocore unit has a smaller core than the core of the optical transmission unit Optical fiber,
Comprising gold nanoparticles fixed to the outer peripheral surface of the cladding of the hetero-core portion,
When light is transmitted through the optical fiber via the optical transmission unit and the hetero core unit, the degree of absorption of light of a predetermined wavelength in the hetero core unit is the refraction of the material around the hetero core unit. An optical fiber sensor device configured to change according to a rate. The optical fiber sensor device according to claim 1,
Attenuation of light transmission intensity when light is transmitted through the optical fiber in a state where the refractive index of the material around the cladding of the hetero-core portion to which the gold nanoparticles are fixed is maintained at a constant refractive index. The degree is defined as X, the gold nanoparticles are not fixed to the outer peripheral surface of the cladding of the heterocore portion, and the refractive index of the substance around the heterocore portion is maintained at the constant refractive index. When the degree of attenuation of the transmission intensity of light when the light is transmitted through the optical fiber is defined as X0, the gold nanoparticles have a density such that the ratio of X to X0 is 1/100 or less. The optical fiber sensor device is fixed to the outer peripheral surface of the clad of the hetero core portion.   The optical fiber sensor device according to claim 1, a light source that makes light including at least light of a predetermined wavelength incident on the optical fiber, and a photodetector that detects the intensity of light of the predetermined wavelength emitted from the optical fiber. A measurement system for measuring characteristics of a substance existing around the cladding of the hetero-core portion based on the output of the photodetector.   The optical fiber sensor device according to claim 2, a light source that enters light including at least light in the near infrared region into the optical fiber, and light that detects intensity of light having a predetermined wavelength in the near infrared region that is emitted from the optical fiber. A measurement system characterized by measuring a property of a substance existing around the cladding of the hetero-core portion based on an output of the photodetector.   5. The measurement system according to claim 3, wherein the substance is a mixed fuel of gasoline and alcohol, and a mixing ratio of gasoline and alcohol in the mixed fuel is measured. An optical transmission unit having a core and a clad, and a hetero core unit having a core and a clad respectively connected to the core and the clad of the optical transmission unit, wherein the hetero core unit has a smaller core than the core of the optical transmission unit A manufacturing method of an optical fiber sensor device comprising a fiber and gold nanoparticles fixed to the outer peripheral surface of the cladding of the hetero core part,
Attenuation of light transmission intensity when light is transmitted through the optical fiber in a state where the refractive index of the material around the cladding of the hetero-core portion to which the gold nanoparticles are fixed is maintained at a constant refractive index. The degree is defined as X, the gold nanoparticles are not fixed to the outer peripheral surface of the cladding of the heterocore portion, and the refractive index of the substance around the heterocore portion is maintained at the constant refractive index. When the degree of attenuation of the transmission intensity of light when transmitting light through the optical fiber is defined as X0, the hetero-core portion of the optical fiber until the ratio of X to X0 is saturated. A method of manufacturing an optical fiber sensor device, wherein the gold nanoparticles are fixed to the outer peripheral surface of the clad of the hetero-core portion by immersing in a suspension of gold nanoparticles.