JPH10319253A - Optical fiber sensor and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce an optical fiber sensor simply by using two pieces of inexpensive ordinary optical fibers without using a costly bundled optical fiber relating to an improvement of the optical fiber sensors formed by utilizing a change in fluorescence which occurs when a fluorescent material comes into contact with ions and molecules and to provide the optical fiber sensor which has high response sensitivity exceeding that of the sensor of a type to utilize the bundled optical fiber, is easy to use on site and may be easily constituted as a sensor array. SOLUTION: This optical fiber sensor is constituted by integrating two pieces of optical fiber terminals 2 from which clad layers 1 are removed by heating and fusing, then sharpening the front end thereof and forming a water absorptive gel layer 4 on the surface of the sharpened terminal part 3. After the fluorescent material is fixed into the light absorptive gel layer 4, exciting light is made incident from the one optical fiber terminal 5 toward the water absorptive gel layer 4 to generate the fluorescence. The generated fluorescence is detected through another optical fiber 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention
Optical fiber sensor for measuring ON and molecular concentrations. In particular, the present invention relates to an improvement in an optical fiber sensor utilizing a change in fluorescence generated when a fluorescent substance comes into contact with ions or molecules.

[0002]

2. Description of the Related Art As an optical fiber sensor using a change in fluorescence, (A) an evanescent wave type and (B) a bundled optical fiber (thousands of thin optical fibers assembled in a bundle) have been studied. It has been. In the method (A), after removing the optical fiber cladding layer, a fluorescent substance is fixed on the side surface of the core, the fluorescent substance is excited using an evanescent wave oozing out of the optical fiber core, and the generated fluorescence is transmitted to the optical fiber. Through a photodetector (eg,
Z. M. Hale et al., Sensors and Acut
uators, B17, p. 233, 1994, etc.). In the method (B), a fluorescent substance is fixed to the end portion of the bundle optical fiber, and the optical fiber bundle at the other end portion is fixed by two.
And irradiate the excitation light toward the fluorescent substance from one of the divided terminals, and place a photodetector on the other divided terminal to detect the generated fluorescence via a bundled optical fiber. (Eg G. Ollellana et al., An
al. Chem. , 67, p. 2231, 1955, etc.).

[0003]

However, in the method (A), not only the (1) process of fixing the fluorescent substance on the core surface requires time but also it is difficult to make the fixing uniform.
(2) the intensity of the sensor portion on which the fluorescent substance is fixed is extremely weak, making it difficult to use in the field; (3) the sensor response sensitivity to ions and molecules is not sufficient; (4) it is difficult to assemble as a sensor array; There was a problem called. The method (B) is (1) expensive because a bundled optical fiber is used, (2) the fixing of the fluorescent substance at the terminal is complicated, and (3) the sensor response sensitivity to ions and molecules is not sufficient. (4) There is a problem that it is difficult to configure a multi-channel sensor array.

Accordingly, the present invention has been made to solve the drawbacks of the optical fiber sensor utilizing the change in fluorescence, particularly, the above-mentioned method (B), and uses an inexpensive ordinary optical fiber without using an expensive bundle optical fiber. To provide an optical fiber sensor that can be easily manufactured using only two optical fibers, has higher response sensitivity than a sensor using a bundled optical fiber, is easy to use in the field, and is easy to configure as a sensor array. With the goal.

[0005]

An optical fiber sensor according to claim 1 will be described with reference to FIG. The two optical fiber ends 2 from which the cladding layer 1 has been removed are heated and melted to be integrated and sharpened, and a water-absorbing gel layer 4 is formed on the sharpened end 3 surface.
The fluorescent substance is fixed inside the gel layer. Next, excitation light is incident from the other end 5 of the optical fiber to generate fluorescence in the water-absorbing gel layer 4 of the sharpened terminal portion 3, and the generated fluorescence is detected through the other optical fiber 6. .

The optical fiber sensor according to a second aspect is characterized in that the sharpening angle of the sharpening terminal portion 3 is in a range of 15 degrees to 50 degrees.

According to a third aspect of the present invention, the raw material optical fiber used for fabricating the sensor is made of POF containing PMMA as a main component, and the water-absorbing gel layer 4 has a hydrolyzed PMMA layer on the surface of the sharpened terminal 3. It is characterized by forming.

According to a fourth aspect of the present invention, there is provided a method for manufacturing an optical fiber sensor.
4. A method of forming a PMMA hydrolysis layer according to claim 3, wherein the sharpened terminal surface is brought into contact with concentrated sulfuric acid to form PMMA.
It is characterized by causing a hydrolysis reaction of.

The optical fiber sensor according to the present invention is characterized in that, as the fluorescent substance fixed in the water-absorbing gel layer 4, one to three kinds of fluorescent dyes exhibiting a fluorescent change when contacted with ions or molecules are used. .

In the optical fiber sensor according to the present invention, a silica glass core / plastic clad optical fiber (PCF) is used as a raw material optical fiber, and a water absorbing crosslinked polymer layer is formed as the water absorbing surface gel layer 4. Features.

According to a seventh aspect of the present invention, there is provided a method of manufacturing an optical fiber sensor.
As a method for forming the water-absorbent crosslinked polymer layer according to claim 6, the glass surface of the optical fiber sharpened end portion (3) according to claim 6 is treated with a silane coupling agent, and then the water-absorbent polymer is formed. Alternatively, a dye solution obtained by mixing a fluorescent dye with a photopolymerizable liquid containing an oligomer, a monomer, a photosensitizer, a photocrosslinking agent, or the like is applied to the surface of the sharpened terminal portion (3), or the terminal portion is coated with the dye solution. In this state, visible light or ultraviolet light is incident from the other end (5) of the optical fiber in a state of being immersed in the water-absorbent polymer to form a water-absorbing crosslinked polymer layer.

[0012]

Next, embodiments of the present invention will be described in detail. POF with core material of PMMA (core diameter 1m
The method of manufacturing a sharpened terminal using m) will be described with reference to FIG. 1. Prepare two optical fiber terminals 2 from which the clad layer 1 has been removed (A). After fixing these two fibers, the ends are heated and crimped to integrate the two optical fiber terminals. After confirming that the crimped portion has been fused, this portion is further heated and stretched to be sharpened (B). The time required to make this integrated and sharpened terminal is about 2 minutes, and can be reduced to 1 minute with skill. Then immersing the sharpening terminal unit 3 in concentrated sulfuric acid, to form a PMMA hydrolyzed layer by washing with water _{(-CH 3 COOCH 3 → -CH 3} C
OOH). This sharpened terminal is further immersed in an aqueous solution of caustic soda to ion dissociate the carboxyl group (−
CH ₃ COOH → -COO ⁻ ), and the water-absorbing gel layer can be swollen even in neutral water. For measurement of ions in water, measurement in this swollen state is desirable. A rhodamine B dye is immobilized on the water-absorbing gel layer 4, and the other end of the optical fiber 5 is fixed.
FIG. 2 shows the state when fluorescence is generated in the water-absorbing gel layer 4 when excitation light is incident from FIG. Here, the lower side is the excitation light side 5,
The upper side is the detection side 6. Bright part, ie excitation light side 5
It turns out that fluorescence mainly occurs in This fluorescence is detected through the upper detection side optical fiber 6. From the above results, it is possible to easily produce a terminal in which both terminals are integrated and sharpened by heating and stretching two POF (for excitation light source and light collection detection) terminals together, and the surface of the sharpened terminal absorbs water. 2. A fluorescent gel layer is formed on which a fluorescent dye is fixed.
It can be seen that the optical fiber sensor can be easily realized.

The above

In the optical fiber sensor described above, the fluorescence generated in the water-absorbing gel layer 4 on the surface of the sharpened terminal portion 4 is detected through the optical fiber 6 on the detection side. Table 1 shows how the fluorescence intensity differs when the tip is sharp (sharpened) or flat (trapezoidal).
Shown in Here, three sharpened terminals (sharpened length 3 mm) made of POF having a core diameter of 1 mm are prepared, and the trapezoidal terminals whose ends are cut by 2 mm, the trapezoidal terminals cut by 1 mm, and the sharpened terminals that are not cut are concentrated sulfuric acid. Immersion treatment, 1N
-A swollen water-absorbent gel layer was formed by immersion in an aqueous solution of sodium hydroxide. Rhodamine B was immobilized on the gel layer. The fluorescence intensity is in the order of 0 mm> 1 mm> 2 mm,
It can be seen that, as the terminal is sharpened, the detection fluorescence sensitivity is improved, and that the effect of sharpening the integrated terminal in the optical fiber sensor according to claim 1 clearly appears.

The above

The optical fiber sensor described above (core diameter 1 mm
When the length of the sharpened terminal section 3, that is, the sharpened angle is changed in the POF, how the fluorescence detection intensity detected through the detection-side optical fiber 6 changes will be described.
Table 2 shows the differences. From the results in Table 2, it can be seen that the fluorescence detection sensitivity is maximized when the sharpening angle is around 36 degrees, and that the effect of specifying the sharpening angle in the optical fiber sensor according to claim 2 clearly appears. .

The above

In the optical fiber sensor described above, the sharpened terminal on which the water-absorbing surface gel layer is formed is a fluorescent dye / organic solvent solution, a fluorescent dye / aqueous solution, a fluorescent dye / organic solvent /
The dye can be fixed to the gel layer by immersion in an aqueous solution. The binding form of the dye to the gel layer depends on the molecular structure and functional group of the dye, including hydrogen bonding, ionic bonding,
It is classified into chemical bond, acid / alkali interaction, etc. Figure 3 shows the change in the fluorescence spectrum when the optical fiber sensor with the sodium fluorescein dye immobilized on the gel layer was immersed in a pH buffer. Wavelength 53
It can be seen that the fluorescence (F) of sodium fluorescein having a peak near 0 nm decreases as the pH changes from an alkali of pH 9.0 to an acid of pH 3.3, and has a clear pH response, that is, it can be sufficiently used as a pH sensor.
On the other hand, when the fluorescein sodium dye was directly fixed to the sharpened terminal without forming a gel layer, no clear pH response was exhibited (FIG. 4). From the above results, it can be seen that when a water-absorbing gel layer is formed on the sharpened terminal and a fluorescent dye is fixed thereon, the response of the sensor to hydrogen ion concentration (pH) is dramatically improved. 2. The ion responsiveness is low even when a dye is directly immobilized on the dye.
It can be seen that the effect of forming the water-absorbing gel layer clearly appears in the described optical fiber sensor.

The above

In the optical fiber sensor described above, if one kind of fluorescent dye is fixed instead of one kind of fluorescent dye in the water-absorbing gel layer, the concentrations of plural kinds of ions and molecules can be measured simultaneously. become. Figure 5 shows the response to pH and ethanol concentration of an optical fiber sensor in which two types of dyes, fluorescein and rhodamine B, were mixed and immobilized in a water-absorbing gel layer. Fluorescein fluorescence (5
30 nm) selectively responds to pH, and the fluorescence of rhodamine B (595 nm) responds selectively to ethanol concentration. From the above results, it can be seen that when two types of dyes are immobilized on the water-absorbent gel layer, different types of ions and molecules can be measured simultaneously, and the effect of claim 5 is clearly exhibited. This effect is not limited to the fixation of the two dyes. 400nm to 900n
If dyes with different fluorescence wavelengths are selected in the wavelength range of m, it is possible to mix and fix three types of dyes.

A method for manufacturing a sharpened terminal using a PCF (core diameter: 200 μm) using silica glass as a core material will be described with reference to FIG. 1. Prepare two PCF terminals 2 from which the clad layer 1 has been removed (A). After temporarily fixing the two fibers, the distal end is heated with a carbon dioxide gas laser, and is stretched and sharpened when the distal ends of the fibers are fused and integrated (B). The time required to make this integrated and sharpened terminal is less than one minute. Next, the surface of the sharpened end portion 3 was immersed in [γ- (methacryloxy) propyltrimethoxysilane solution to perform a silane coupling agent treatment. While immersing the sharpened terminal in aminofluorescein / photopolymerizable solution, an argon laser (488 nm) was incident from the other end of the optical fiber to form a water-absorbing gel film on the surface of the sharpened terminal. The time required for gel film formation was within one minute. Fluorescence spectrum change (peak wavelength 545 n) when this optical fiber sensor is immersed in a pH buffer solution.
m)

When the measurement was performed in the same manner as described, FIG.
Similar results were obtained. Here, a solution containing hydroxyethyl methacrylate, ethylene glycol dimethacrylate, and benzoin ethyl ether was used as the polymerizable solution. The above is one embodiment (example) of the present invention.
However, the present invention is not limited to the above embodiment. The water-absorbing gel film 4 according to claim 6, wherein polyvinyl alcohol and its derivative, polyvinyl alcohol and its derivative, polyvinyl acetate hydrolyzate, polyacrylamide and its derivative, polyacrylic acid and polymethyl acrylate hydrolyzate, A crosslinked polymer composition containing polymethacrylic acid and polymethyl methacrylate hydrolyzate, hydroxyethyl methacrylate and its derivatives, hydroxypropyl cellulose, polyethylene oxide and its derivatives can be used. The method of crosslinking is not limited to photopolymerization. From the above results, two PCFs
(Excitation light source, for light detection) The terminal can be easily formed by heating and stretching the terminals together, and both terminals can be easily integrated and sharpened. A water-absorbing gel layer is formed on the sharpened terminal surface and the fluorescence is formed there. It can be seen that the optical fiber sensor according to claim 6 in which a dye is fixed can be easily realized. In addition, a water-absorbing gel layer can be easily formed on the surface of the sharpened terminal 3 by a photopolymerization method,
It can be seen that the method of manufacturing the optical fiber sensor according to claim 7 is sufficiently effective.

[0013]

Embodiment 1 POF using PMMA as a core material
(Mitsubishi Rayon SH-4001, core diameter 1mm) 2 pieces (length 1m) are prepared. The two optical fiber terminals from which the cladding layer was removed using dioxane were fixed with adhesive tape, heated with an electric heater, and the two fiber terminals were integrated by crimping using tweezers. This was stretched while further heating, and it was integrated and sharpened. The thinned (sharpened) length was 3 mm. Next, the tips of these sensors were immersed in concentrated sulfuric acid, washed with water, and then immersed in a 1N aqueous solution of sodium hydroxide for 5 minutes. This sharpened terminal is called Rhodamine B /
Rhodamine B dye was immobilized in the gel layer by immersion in an ethanol solution. The optical fiber sensor manufactured in this way is immersed in a 0.1 mM KCl aqueous solution, and argon laser light (48
8 nm), and the fluorescence generated at the sharpened terminal is transmitted through the other optical fiber to a multi-channel photodetector (PM).
A-11, manufactured by Hamamatsu Photonics) and measured the fluorescence spectrum. Table 3 shows how the fluorescence intensity detected through the detection-side optical fiber 6 changes when the concentrated sulfuric acid immersion time is changed at room temperature (when the thickness of the water-absorbing gel layer is changed). Show. Here, whether or not the hydrolysis was uniform was determined by the degree of surface whitening. The thickness of the hydrolyzed layer was measured by observing the cross section with a metallographic microscope. From the results in Table 3, it can be seen that there is an optimum time for the concentrated sulfuric acid treatment, that is, there is an optimal thickness of the hydrolysis layer, and the sharpened terminal (PMM)
A) It can be seen that a water-absorbing gel layer (hydrolyzing layer) can be easily formed on the surface, and is sufficiently effective as the optical fiber sensor manufacturing method according to claim 4.

[0014]

Example 2 A pH sensor was manufactured by immersing the sharpened terminal (sulfuric acid treatment time: 20 seconds) prepared in Example 1 in an aqueous solution of sodium fluorescein. A high brightness blue light emitting diode (LED, 470
nm, Nichia Chemical, 1995)
The fluorescein sodium in the water-absorbent gel film 4 is excited to generate fluorescence, and the generated fluorescence is filtered at the other end of the optical fiber (Wratten No. 1).
2, Eastman Kodak) and a silicon photodiode (S2387-66R, Hamamatsu Photonics)
Was detected. The pH response was measured by computer using this system. Figure 5 shows the results. It can be seen that it has sensor characteristics that can be used sufficiently for monitoring acid rain for measuring the acidity of rivers and lakes.

[0015]

Embodiment 3 Using the pH sensor manufactured in Embodiment 2, a blue light emitting diode, a filter, and a photodiode, a pH measuring circuit was manufactured in which all parts were solidified. Figure 6 shows the configuration. When the pH response characteristics were measured in combination with a notebook computer, results similar to those in Fig. 5 were obtained. If this sensor system is used as a device, an optical fiber sensor system that can be used in the field for measuring acidity of rivers and lakes and monitoring acid rain can be constructed.

[0015]

According to the first aspect of the present invention, the efficiency of fluorescence generation and the efficiency of fluorescence detection at the terminal are greatly improved by integrating and sharpening the two optical fiber terminals. In addition, since the sensor structure is simple and robust, it is easy to use in the field and can be easily configured as a multi-channel sensor array. Also, by forming a highly water-absorbing gel layer on the sharpened terminal surface and fixing a fluorescent substance on the gel layer,
The response sensitivity to the molecule (the amount of change in fluorescence) is dramatically improved. Responsiveness to ionic molecules is low even if the dye is immobilized directly on the sharpened terminal surface. If a sensor array is constructed using multiple types of dyes with different responsiveness to ions / molecules, simultaneous measurement of multiple ionic molecules and pattern recognition identification of multiple components are possible. Simultaneously, recognition and distribution can be measured if multiple types of dyes are mixed and fixed on one sensor and multi-channeled. The optical fiber sensor of the present invention is suitable for these purposes.

According to the second aspect of the present invention, by optimizing the degree (angle) of sharpening, the fluorescence in the water-absorbing gel layer 4 can be generated most effectively, and can be detected most efficiently. By optimizing the sharpening angle, a sensor that is easy to manufacture and easy to handle can be realized.

According to the third aspect of the present invention, P is used as a sensor material.
The use of OF eliminates the need for special tools and equipment for integrated and sharpening, and the use of ordinary electric heaters, cutters and tweezers makes it possible to manufacture sharpened terminals and shorten the processing time. Further, the formation of the water-absorbing gel layer 4 (PMMA hydrolysis layer) on the surface of the sharpened terminal 3 is facilitated.

According to the fourth aspect of the present invention, the PMMA hydrolysis layer can be uniformly formed in a short time (30 seconds or less) by the concentrated sulfuric acid contact treatment, and a simple and reproducible optical fiber can be manufactured.

According to the fifth aspect of the present invention, since a fluorescent dye is used as the fluorescent substance, it is possible to design and manufacture a sensor according to the purpose and application. This is because the properties and characteristics of many fluorescent dyes have been compiled into a database and can be used for designing and manufacturing. By fixing multiple dyes with different responsiveness, simultaneous measurement of multiple ions / molecules or pattern recognition identification of multiple components becomes possible.

According to the sixth aspect of the present invention, the silica glass core is used in place of the plastic core, so that the transmission loss can be greatly reduced, and the field of use such as application to a sensor for remote monitoring and a sensor for wide area distribution measurement is expanded. . Further, the POF has a large transmission loss of 300 to 400 nm and 700 to 900 nm.
The wavelength region of nm can be used, and the range of choice of fluorescent materials that can be used as sensing materials is expanded.

According to the seventh aspect of the present invention, by treating with a silane coupling agent, a chemical bond can be formed between the glass surface and the water-absorbing gel layer, and the adhesion between the two can be greatly improved. In addition, since visible light or ultraviolet light is incident from the other end of the optical fiber and light is irradiated from the inside of the sharpened terminal portion 3 to the surface to cause photopolymerization, a gel film that is most effective as a sensor and a most efficient gel film are obtained. A gel film can be formed. In addition, this method makes it possible to simultaneously fix the dye on the gel membrane.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration and a manufacturing method of the present invention.

FIG. 2 is a photograph of a state where fluorescence is generated in the optical fiber sensor of the present invention.

FIG. 3 shows that the fluorescence spectrum of an optical fiber sensor in which sodium fluorescein dye is immobilized on the water-absorbing gel film 4 is pH
It is a figure showing how it changes with pH and the responsiveness to pH. The results show that the fixation of the dye on the water-absorbent gel membrane 4 improves the responsiveness to ions.

FIG. 4 is a diagram showing how the fluorescence spectrum of an optical fiber sensor in which sodium fluorescein dye is directly fixed on the surface of the sharpening terminal 3 changes with pH, and the response to pH. The results show that if the dye is not fixed to the water-absorbing gel film 4 but the dye is fixed directly to the surface of the sharpened terminal 3, the response to ions is not improved.

FIG. 5 is a diagram showing the response to pH (upper) and ethanol (lower) of an optical fiber sensor in which a plurality of dyes fluorescein (530 nm) and rhodamine B (595 nm) are immobilized on a water-absorbent gel film 4. We show that simultaneous measurement of pH and ethanol is possible.

FIG. 6 is a view showing Example 2; pH of an optical fiber sensor in which sodium fluorescein was fixed to a water-absorbing gel film 4;
The response characteristics are shown.

FIG. 7 is a view showing a third embodiment, and is a configuration diagram showing that the use of the optical fiber sensor of the present invention makes it possible to manufacture an ion measuring apparatus in which all parts are solidified.

Claims (7)

[Claims] An optical fiber end (2) from which a cladding layer (1) has been removed is heated and melted to be integrated and sharpened, and a water-absorbing gel layer (4) is formed on the surface of the sharpened end (3). After forming and fixing the fluorescent substance in the water-absorbing gel layer (4),
Excitation light is incident from one optical fiber end (5) toward the sharpened end portion (3) and the water-absorbing gel layer (4) to generate fluorescence, and the generated fluorescence is converted to the other optical fiber (6). Optical fiber sensor characterized by detecting through 2. An optical fiber sensor according to claim 1, wherein a sharpening angle of said sharpened terminal portion is in a range of 15 to 50 degrees. 3. A plastic optical fiber (POF) having a plastic material containing polymethyl methacrylate (PMMA) as a main component as a core material is used as an optical fiber used for manufacturing the optical fiber sensor.
The sharpened terminal portion (3) as the water-absorbing surface gel layer (4)
2. The optical fiber sensor according to claim 1, wherein a PMMA hydrolysis layer is formed on the surface. 4. A method for forming a hydrolyzed PMMA layer according to claim 3, wherein the surface of the sharpened end portion of the optical fiber (3) is brought into contact with concentrated sulfuric acid to cause a hydrolysis reaction of PMMA. 4. The method of manufacturing an optical fiber sensor according to claim 3, wherein 5. The fluorescent substance according to claim 1, wherein the fluorescent dye exhibits a change in fluorescence upon contact with ions or molecules.
3. The optical fiber sensor according to claim 1, wherein three types are used. 6. An optical fiber used for manufacturing the optical fiber sensor according to claim 1, wherein a silica glass core / plastic clad optical fiber (PCF) using silica glass as a core material is used. 2. A water-absorbent crosslinked polymer layer is formed on the surface of the sharpened terminal portion (3) as the water-absorbent surface gel layer described in (1).
Optical fiber sensor described 7. A method for forming the water-absorbent crosslinked polymer layer according to claim 6, wherein the glass surface of the sharpened end portion of the optical fiber according to claim 6 is treated with a silane coupling agent. A dye solution obtained by mixing a fluorescent dye with a photopolymerizable liquid containing a polymer, a water-absorbing polymer or oligomer, a monomer, a photosensitizer, a photocrosslinking agent, etc. is applied to the surface of the sharpened terminal section (3) or the terminal is coated. A visible light or ultraviolet ray is incident from the other end (5) of the optical fiber while the portion is immersed in the dye solution, thereby forming a water-absorbent crosslinked polymer layer on the surface of the sharpened terminal portion (3). 7. The method for manufacturing an optical fiber sensor according to claim 6, wherein