JP3443686B2 - How to measure the refractive index - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a refractive index, and more particularly, to a method for measuring a refractive index with a high measurement accuracy using a contact-type optical fiber sensor. And a method for measuring a refractive index. 2. Description of the Related Art As a contact type optical fiber sensor, a third type is known.
Proc. Of Bioengineering Symposium No.
940-5 (Date of lecture; January 20, 1994, 21
Date) are known. In this contact type optical fiber sensor, one light source-side optical fiber, one spacer optical fiber, and a detector-side optical fiber are arranged in parallel, a tip portion is melted and integrated, and the tapered shape is extended. A contact portion is brought into contact with a test substance, and the output light amount of the detector-side optical fiber is measured. In the above-mentioned contact type optical fiber sensor, the size of the contact portion can be made extremely small, so that, for example, blood flowing through a blood vessel can be measured. [0004] The above-mentioned conventional contact type optical fiber sensor is used for measuring a flow rate, but not for measuring a refractive index. Therefore, an object of the present invention is to
It is an object of the present invention to provide a method for measuring a refractive index by which a refractive index can be measured with high measurement accuracy using a contact-type optical fiber sensor. According to a first aspect of the present invention, a light source-side optical fiber, a spacer optical fiber, and a detector-side optical fiber are aligned substantially in parallel to each other, and the tip portions are fused and integrated. The melted and integrated tip portion is brought into contact with the test substance as a contact portion, and the temperature of the test substance is adjusted by a temperature controller.
Changing, little different temperatures and the reference temperature is continuously therewith
The output light quantity of the detector-side optical fiber is measured at least at two points , and the reference temperature is measured based on the measurement value of the output light quantity at the reference temperature.
The measured value of the output light amount at a temperature different from the
Provided is a method for measuring a refractive index, which comprises calculating a refractive index of a test substance . In the method of measuring a refractive index according to the first aspect, the contact portion of the contact type optical fiber sensor is brought into contact with the test substance, and the temperature of the test substance is changed by the temperature controller.
And continuously measure the output light quantity of the optical fiber on the detector side at the reference temperature and a different temperature, and based on the measurement value of the output light quantity at the reference temperature, calculate the output light quantity at different temperatures.
The refractive index of the test substance is calculated by normalization . As will be described later with reference to FIG. 9, there is a variation in the output light amount due to the measurement. However, when normalization is performed based on the output light amount at an appropriate reference temperature, it is possible to eliminate the variation due to the measurement. Therefore, it differs based on the measured value of the output light quantity at the reference temperature.
If the refractive index is calculated by normalizing the measured value of the output light amount at the temperature, the refractive index of the test substance can be measured with high measurement accuracy. An embodiment of the present invention will be described below with reference to the drawings. It should be noted that the present invention is not limited by this. FIG. 1 is a configuration diagram of a contact type optical fiber sensor 10 used in the method for measuring a refractive index according to the present invention. The contact type optical fiber sensor 10 includes a contact portion 1 that contacts a test substance and a heat-resistant glass tube 2 that supports the contact portion 1.
And a stainless steel tube 6 supporting the heat-resistant glass tube 2
A light source-side optical cable 14 and a detector-side optical fiber 15 derived from the stainless steel tube 6; a light source-side optical connector 8 attached to an end of the light source-side optical cable 14; And a detector-side optical connector 9 attached to the end. [0008] The light source side optical cable 14 includes a light source side optical fiber 4. The detector-side optical cable 15 includes a detector-side optical fiber 5. In the stainless steel tube 6, the heat-resistant glass tube 2, the optical fibers 4 and 5 inserted into the heat-resistant glass tube 2, the spacer optical fiber (3) described later, and the optical cables 14 and 15 are connected by a ceramic bond. Are integrated. FIG. 2A is an enlarged front view of the contact portion 1, and FIG. 2B is an enlarged bottom view of the contact portion 1. The contact portion 1 is formed in such a manner that the light source side optical fiber 4, the two spacer optical fibers 3, 3 and the detector side optical fiber 5 are aligned substantially in parallel, and the distal end portion 1a is melted and integrated to form a substantially spherical shape. . As shown in FIG. 3, the light source side optical fiber 4 is a PANDA type (Polarization Maintaining and
Reducing Fiber polarization-maintaining optical fiber (Single-pol)
arization single mode fiber). A core 4a has a diameter of, for example, 10 μm. Reference numeral 4b denotes a clad having an outer diameter of, for example, 125 μm. As shown in FIG. 4, the detector side optical fiber 5 is a multi mode fiber.
It is. 5a is a core having a diameter of, for example, 80 μm.
It is. 5b is a clad whose outer diameter is, for example, 12
5 μm. The spacer optical fiber 3 is a silica-based single mode fiber. Its outer diameter is, for example, 125 μm. FIG. 5 is a sectional view taken along the line AA 'of FIG. The light source side optical fiber 4, the two spacer optical fibers 3, 3 and the detector side optical fiber 5 are aligned substantially in parallel, and the periphery thereof is surrounded by a number of spacer optical fibers 3, and the heat-resistant glass tube 2 is inserted. It has become. FIG. 6 is an explanatory diagram of a two-dimensional optical path simulation based on the Fresnel reflection equation. The formula for the Fresnel reflection is: (Equation 1) It is assumed that light having a wavelength of 1300 nm is radiated from the light-emitting side core 4a (diameter: 10 μm) at a light intensity of 1 mw in a normal distribution, and a light-receiving side core 5a is used for a polarization component perpendicular to the incident surface. The intensity (output light quantity I) of the reflected light incident on (diameter 80 μm) was calculated (almost the same result is obtained in the case of a polarized light component parallel to the incident surface). Standard deviation σ
Represents the degree of spread of the emitted light and corresponds to the numerical aperture of the light source side optical fiber 4, and was set to 0.2. The refractive index of the test substance is 1.00 (air), 1.33.
(Water), a refractive index of 1.36 (ethyl alcohol), and a refractive index of 1.40 (prepared substance). FIG. 7A shows a calculation result when one spacer optical fiber 3 is sandwiched between the light source side optical fiber 4 and the detector side optical fiber 5. From this calculation result, the radius R at which the change rate of the output light amount is as large as possible in the change range of the refractive index of the test substance from 1.0 to 1.40 is 126
It can be seen that the range is from μm to 140 μm. More specifically, the change range of the refractive index of the test substance is 1.33.
In the vicinity of (water), it can be seen that the radius R at which the rate of change of the output light quantity becomes as large as possible is about 137 μm. Also, when the change range of the refractive index of the test substance is in the vicinity of 1.36 (ethyl alcohol), the radius R at which the change rate of the output light quantity becomes as large as possible is about 134 μm. In addition, when the change range of the refractive index of the test substance is near 1.40, the radius R at which the change rate of the output light amount becomes as large as possible is about 129 μm. FIG. 7B shows two spacer optical fibers 3 and 3 as a light source side optical fiber 4 and a detector side optical fiber 5.
It is a calculation result when sandwiched between. From this calculation result, the radius R at which the change rate of the output light amount becomes as large as possible in the change range of the refractive index of the test substance from 1.0 to 1.40 is:
It turns out that it is the range of 191 micrometers-210 micrometers. More specifically, the change range of the refractive index of the test substance is 1.3.
In the vicinity of 3 (water), it can be seen that the radius R at which the rate of change of the output light quantity becomes as large as possible is about 206 μm.
Also, when the change range of the refractive index of the test substance is near 1.36 (ethyl alcohol), the radius R at which the change rate of the output light amount becomes as large as possible is about 201 μm. Also, when the change range of the refractive index of the test substance is near 1.40, the radius R at which the change rate of the output light quantity becomes as large as possible is about 194 μm. 7 (a) and 7 (b), the radius R is such that the change rate of the output light quantity becomes as large as possible in the change range of the refractive index of the test substance from 1.0 to 1.40. The range is shown in FIG.
(B) is wider. For this reason, it is preferable to adopt a structure in which the two spacer optical fibers 3 and 3 are sandwiched between the light source side optical fiber 4 and the detector side optical fiber 5 because the manufacturing becomes easier. In addition, in order to adjust the radius R of the contact portion 1, the heating temperature and / or the heating time when the tip portions of the optical fibers 4, 3, and 5 are melted and integrated may be controlled. The above contact type optical fiber sensor 10 includes:
There are the following advantages. The detector-side optical fiber 5 is a multi-mode optical fiber and has a large core diameter (for example, 80 μm), so that the light reflected by the contact portion 1 can easily enter and the output light amount can be increased. Since the contact portion 1 is formed in a substantially spherical shape with a radius such that the rate of change of the output light amount with respect to the change of the refractive index increases, high specific sensitivity can be obtained. A structure in which optical fibers 4, 3, and 5 are inserted through a glass tube 2, the glass tube 2 is inserted through a stainless steel tube 6, and optical connectors 8 and 9 are provided at ends of a light source side optical cable 14 and a detector side optical cable 15, respectively. Therefore, the mechanical strength and the chemical stability are improved, and the handling is facilitated. FIG. 8 is a block diagram of a refractive index measuring apparatus 100 for implementing the method of measuring a refractive index according to the present invention. In the refractive index measuring device 100, reference numeral 109 denotes a laser diode light source (Q8142A manufactured by Advantest) having an output of 1 mw, an output stability of 0.05 db or less, and a wavelength of 1300 nm. 14 is a light source side optical fiber, 1 is a contact part, and 15 is a detector side optical fiber. Reference numeral 110 denotes a power meter (Q8214A manufactured by Advantest) having a measurement accuracy of ± 5%.
102 is a 0.5 mm sheath thermocouple, 111 is measurement accuracy ±
0.3 ℃ multi thermometer (TR2114 manufactured by Advantest)
H). Reference numeral 101 denotes a glass container for containing a test substance, 1
04 is a copper block, 106 is a heat insulating container, and 105 is a temperature controller. 107 is a stirrer. Reference numeral 108 denotes a vibration isolation table. Reference numeral 112 denotes a personal computer which receives the signal output I. Reference numeral 113 denotes a printer. FIG. 9 shows the results of repeating the measurement on distilled water five times to confirm the reproducibility of the measurement. As can be seen, the signal output I is different for each measurement. However, when normalized with the signal output I of 20 ° C., one characteristic curve is obtained. Therefore, it is understood that the refractive index can be measured with high measurement accuracy by calculating the refractive index based on the measured value of the output light amount I at at least two temperatures. That is, the personal computer 112
Stores the normalized signal output normalized by the signal output I at 20 ° C. and the refractive index calibration curve. Then, the temperature of the subject substance is changed by the temperature controller 105 and the 0.5 mm sheath thermocouple 102, the output light quantity I is measured at at least two different temperatures, and the obtained output light quantity at at least two temperatures is obtained. The measured value is normalized from I, and the refractive index is calculated based on the result and the calibration curve. Further, the obtained refractive index is printed on the printer 113. According to the refractive index measuring device 100 described above, the refractive index of the test substance can be measured with high measurement accuracy using the contact type optical fiber sensor 10. According to the method for measuring the refractive index of the present invention,
Using a contact-type optical fiber sensor, the refractive index of a test substance can be measured with high measurement accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram showing a contact-type optical fiber sensor used for carrying out the present invention. FIG. 2 is an enlarged view of a contact portion of the contact type optical fiber sensor of FIG. FIG. 3 is a sectional view of a main part of a light source side optical fiber. FIG. 4 is a sectional view of a main part of a detector-side optical fiber. FIG. 5 is a sectional view taken along line AA ′ of FIG. 1; FIG. 6 is an explanatory diagram of a two-dimensional optical path simulation based on the Fresnel reflection equation. FIG. 7 is a graph showing calculation results of a two-dimensional optical path simulation based on the Fresnel reflection equation. FIG. 8 is a configuration diagram showing a refractive index measuring device embodying the present invention. FIG. 9 is a graph showing a result of repeating measurement of distilled water five times. [Description of Signs] 10 Contact type optical fiber sensor 1 Contact part 2 Heat resistant glass tube 3 Spacer optical fiber 4 Light source side optical fiber 5 Detector side optical fiber 6 Stainless steel tube 8 Light source side optical connector 9 Detector side optical connector 14 Light source side Optical cable 15 Detector side optical cable R Radius of contact part 100 Refractive index measuring device 101 Glass container 102 Sheath thermocouple 104 Copper block 105 Temperature controller 106 Insulated container 109 Laser diode light source 110 Power meter 111 Multi thermometer 112 Personal computer 113 Printer

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-57-39317 (JP, A) JP-A-6-12947 (JP, U) JP-A-60-165852 (JP, U) JP-A-60-165 31654 (JP, U) Japanese Utility Model 60-176164 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21/00-21/01 G01N 21/17-21/61 Practical File (PATOLIS) Patent file (PATOLIS)

Claims (1)

(57) [Claims 1] A light source side optical fiber, a spacer optical fiber, and a detector side optical fiber are aligned substantially parallel to each other, and the tip portions are melted and integrated. The sample is brought into contact with a test substance as a contact portion, and the test substance is
, The output light quantity of the detector-side optical fiber is continuously measured at at least two points of the reference temperature and a temperature different from the reference temperature, and the reference temperature is determined based on the measurement value of the output light quantity at the reference temperature. Normalize output light measurement at different temperatures
And measuring the refractive index of the test substance .