JP3054860B2 - Fiber Bragg grating temperature sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION A fiber Bragg grating (FBG) temperature sensor of the present invention improves the disadvantage that a temperature sensor employing only one FBG lacks accuracy. , And other medical optical fiber sensors are used together to achieve a biomedical product or environmental temperature measuring instrument that has achieved the purpose of determining the scale. Since 1980, fiber optic temperature sensors have been widely studied. Various fiber optic sensors are applied to temperature measurement in many areas. Primarily, the advantages of optical fibers are small, light, resistant to chemical corrosion, free from electromagnetic interference, and compact (bio-compacti).
bility) is high. For this reason, it is used as an excellent physiological temperature sensor. Currently, in the development of a medical sensor, a physiological signal sensor is manufactured by combining an optical fiber and a chemically sensitive head. Due to the change in the chemically sensitive head spectrum, the optical fiber can transmit the change of the optical signal to the outside, analyze and measure. However, each of these sensors basically requires a temperature scale, and thus temperature accuracy is very important.

The present invention operates a double FBG to provide accurate temperature measurement and scale determination functions, and is less susceptible to fluctuations in optical frequency, while at the same time a biomedical fiber optic sensor adds a thermocouple. It solves the problem that packaging cannot be done unless it is used, and at the same time, operates an optical fiber temperature sensor, pushes the optical fiber sensor toward all optics, and reduces the volume.

[0003]

2. Description of the Related Art S. Bracci et al.
"Sensor and Acturators" was published in "A: psysical", Vol. 37, 2nd term, pp. 180-186, and the measurement method of pH value optical fiber sensor was submitted. Also, in 1992, R. Wolthius et al.
omed. Eng., Vol. 39, 2nd period, pages 185-193, discloses a technique for measuring oxygen content in the body using an optical fiber sensor. Fox et al. (1990)
Proceeding of Northeast Conference `` Bioengineeri
n ”on pages 101-102
A method for monitoring blood glucose level using the measurement method was submitted.

[0004] Recently, AGMignani et al.
995, "IEEE J. Lightwave Technol" Vol.13, No.7
We introduced a multifunctional fiber optic monitoring sensor for use in vivo on pages 1396-1406. This uses an optical sensor to measure the pH, oxygen content,
The carbon dioxide component can be measured simultaneously. This research emphasizes the attractiveness of measuring biological signals with optical sensors in medicine, and it is a future trend that integration of biological optical fiber sensors will push for all-optical technology. In the optical fiber sensor submitted by Mignani, the body temperature is measured using a thermocouple, but other optical fiber temperature sensors correct errors. We know that when other electromedical sensors become contaminated with blood, they can cause other side effects and even death. The use of thermocouples as temperature sensors in the body in the past will be replaced by fiber optic temperature sensors in the future. For this reason, sensors made of optical fibers are suitable for medical use and flexible. Waltius et al., In 1991, described IEEE Trans.
omed. Eng., Vol. 38, 10th period, pages 974 to 981, reported a physiological fiber optic temperature sensor. This is a manufacturing problem because a temperature sensor was added on the optical fiber in the system. Temperature sensors applied externally to optical fibers are a type of chemical that can emit fluorescence. The life cycle of fluorescence and temperature are related,
The temperature is measured using this signal. Since the subsequent signal processing circuit is complicated, real-time measurement cannot be performed.

In the field of photoelectrons, many sensors using FBG have been studied. For example, Arabi (AT
Alavie) et al., 1993, "IEEE photon.Technol.Let
t. ", Vol. 9, ninth period, pages 1112 to 1114, and Shin (MGXn) et al. in 1993," Electron. Lett. " The temperature can be measured and the survey signal can be processed immediately. In this type of FBG, the frequency stabilization changes due to a temperature change. Since all of the conventional techniques use the wavelength of the maximum value of the reflection spectrum for temperature measurement, these techniques have a limitation in measurement accuracy. Spectrum analyzers for measuring light wavelengths have further limitations and uncertainties in accuracy. For this reason, the prior art has significant disadvantages in practical applications, especially in medical applications. The present invention ameliorates these shortcomings of the prior art and is readily applied to the biomedical field in conjunction with other fiber optic sensors.

[0006]

SUMMARY OF THE INVENTION The main object of the present invention is to:
By providing a highly accurate temperature sensor, the low accuracy of a conventional temperature sensor using only one FBG is improved. The FBG temperature sensor employs an FBG having two different materials, and accurately calculates the temperature based on the amount of reflected laser light. This FBG temperature sensor
No optical spectrum or optical wavelength detector is required, and errors in the sensor due to fluctuations in spectrum or optical wavelength are prevented, and the resolution and accuracy of temperature measurement are increased. In particular, it applies to medical temperature measurement or other internal fiber optic sensor calibration. Another object of the present invention is to improve the structure of the body temperature sensor in the past,
It also provides a temperature measurement device that is compatible with fiber optic sensors, effectively reducing the volume of the sensor so that biological signals can be measured in minute tissues such as blood vessels. The resolution of the present invention has been increased to 0.01 ° C., and can be measured in a range of ± 10 ° C. of 36 ° C., which is a general human body temperature. Therefore, it can be used as a biological sensor or an environmentally accurate temperature measuring instrument. can do.

[0007]

The high-precision double FBG temperature sensor according to the present invention has two F coefficients having different temperature coefficients.
Including BG, it is possible to obtain a highly accurate temperature measurement effect with a small laser frequency stabilization. The present invention uses one FB
This is to improve the low accuracy of the temperature sensor using G. The present FBG temperature sensor can be used together with other fiber optic sensors to determine the scale.
The present invention can be a temperature measurement article in biomedical or environmental temperature measurement articles.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS High precision double FB according to the present invention
FIG. 1 shows a system structure diagram of the G temperature sensor. Laser light source 1, fiber coupler (Fiber Coupler, hereafter,
Recorded as FC. ) A temperature sensor 5 composed of 2, 21, 22, an FBG (1) 51 and an FBG (2) 52;
Each unit of the photodetector 6 and the microprocessor 8 is included. The present invention provides a narrow spectrum laser 1
Is used as a light source, a light beam emitted from the light source passes through the FC2, is split into two, and the light beam of the optical fiber branch (1) 3 reaches the FBG (1) 51 through the FC. The light beam of the optical fiber branch (2) 4 also passes through another FC22 and
Arrives at BG (2) 52. FBG (1) 51 and FBG
(2) 52 are arranged in parallel to constitute the temperature sensor 5. Light beams reflected from the FBG (1) 51 and the FBG (2) 52 are introduced into the photoelectric signal converter 6 through the FCs 21 and 22. The reflected light efficiency signals measured through the photodetector (1) 61 and the photodetector (2) 62, respectively, are converted into electric signals, sent to the microprocessor 8 through the electric cable 7, perform calculations, and calculate an accurate temperature. .

The present invention refers to a narrow-spectrum laser light source whose optical frequency width is less than the FBG perforation or reflection spectrum for any laser light source. The FC therein has a spectral function, and can be replaced with any optical component having a spectral function, such as a spectroscope or a waveguide connector. Regarding the operation of the spectral range, the FC is not affected by frequency stabilization, and if frequency stabilization occurs, first determine the scale of the survey and correct the data in the database in the microprocessor. it can.

[0010] FBGs come in many forms. Figures 2-4
As shown, the diffraction grating of the FBG component can be fabricated on a fiber core, core cladding, or core and core cladding. Generally, the FBG is fabricated in the core 91 of the fiber 9.
The core 91 is made of a photosensitive material, employs ultraviolet interference or phase mask exposure, and generates a periodic change in reflectivity (Refractiveindex).
Create G. As shown in FIG. 2, the reflectance before the core exposing the n _1. The reflectance of the exposed location and n _3. The reflectance n ₂ of the cladding 92 of the created FBG 93 is
Must be smaller than n ₁ and n ₃ . In addition, as shown in FIG. 3, the cladding 102 of the fiber 10 can be made of a photosensitive material. The reflectivity of the cladding 101 after exposure does not change, and the cladding reflectivity changes periodically to form the FBG 103. Thus, an FBG having cladding can be manufactured. Alternatively, as shown in FIG. 4, the fiber 11 having the D-type FBG can be manufactured by polishing. The method optically polishes the cladding 112 to near the core 111. Further, a diffraction grating waveguide 113 having a periodic reflectance change depending on the reflectances n ₃ and n ₄ is manufactured, and a light beam is transmitted in the optical fiber, so that an FBG effect can be obtained.

The reflected light efficiency when one Bragg is FBG is expressed by the following formula.

(Equation 1) That is,

(Equation 2) It is. Among them, L indicates the length of the FBG in FIG. κ indicates a couple coefficient.

The difference between this coefficient and the FBG reflectance is Δn (FIG. 2).
△ n = n ₂ −n ₃ ), which is related to the optical frequency.

(Equation 3)

C is the speed of light (= 3 × 10 ⁸ m / s), δ is the detuning factor, and is expressed by the following equation.

(Equation 4) It can be seen from the above equation that δ is related to the grating pitch Λ (grating pitch).

When the temperature changes by ΔT, the relationship between the center frequency of the reflected light spectrum of the FBG (optical frequency of the reflection maximum value) and the temperature change ΔT is as follows.

(Equation 5) α is the coefficient of thermal expansion, ζ is the coefficient of heat and light, λ _B is the Bragg wavelength (=
2nλ), where n is the core effective reflectance (Effective Refractive ind)
ex) respectively.

A feature of the optical fiber temperature sensor of the present invention is that two or more sets of FBGs having different coefficients of thermal expansion and thermo-optics are used. If the coefficients such as α and の of FBG (1) and FBG (2) are different,
The center frequency of the reflected light changes with temperature. In addition since the length L of the lattice spacing Λ and the FBG varying any, also different light reflection efficiency of light P _R. The light efficiency output of the two FBGs can be easily adjusted by a formula consisting of frequency and temperature.

## _EQU6 ## P _R1 = M ₁ (f, T) P _R2 = M ₂ (f, T)

M ₁ and M ₂ denote the transfer functions of FBG, respectively, and the linear inverse function of M ₁ and M ₂ can be easily obtained. The optical frequency and the temperature can be calculated in reverse from the reflected light efficiencies P _R1 and P _R2 obtained by the measurement.

(Equation 7)

The signal obtained by the photodetector measurement is sent to a microprocessor, and the real-time optical frequency and temperature are calculated based on the function values in the database. This can provide a thermometer that is accurate and is not affected by the optical frequency. Different materials are used in the present invention.
It can be used for BG. Different materials can be used respectively on the core, cladding, core and cladding. Also, one, two or all of the core, cladding, core and cladding may be plated with materials having different coefficients of thermal expansion. FBG has different grating pitch
And different grating structures can be designed. F
The BG also employs a polished D-type optical fiber, so that diffraction grating waveguides having different coefficients of thermal expansion and thermal light can be manufactured on a flat core surface. D-type FBGs can have plated films of different materials, different grating lengths, different grating structures, or different coefficients of thermal expansion.

The optical fiber temperature sensor of the present invention employs a digital operation circuit or an analog operation circuit. This FBG sensor can simultaneously measure temperature and light source frequency. In addition, various microcomputers can be employed to assist the measurement. The microcomputer includes a memory device. After the microcomputer measures the frequency, the frequency of the laser is stabilized by a feedback circuit. As a material of the FBG , an optical amplifier material mixed with a rare earth element may be used . FBG temperature sensors are used on biomedical, especially large falling within vessels of the human
The biomedical signals inside the body, such as in blood vessels.
Can be measured. The FBG temperature sensor can also be combined with and used with other biomedical sensors .
Thus, according to the present invention, the objects of volume reduction and integration can be achieved. FBG temperature sensor of the present invention, the stabilization of the reflected light spectrum of the temperature first, measured at optical frequency measuring instrument, establishes the database in mathematical theory model, used for the subsequent temperature measurements. Optical frequency measuring instruments have high analytical power. Anritsu's ANRITSU
1319 in the case of an optical frequency measurement device of the “MF9630A type”.
The resolution in nm reaches 1 MHz and the accuracy reaches 12 MHz. In the embodiment, in order for the analysis power to reach 0.1 ° C., the frequency resolution of the database needs to achieve 4 GHz. The above "ANRITSU MF9630A
The "type" is sufficient to provide a database with an analysis power of 0.01 ° C. Therefore, even if the optical frequency fluctuates,
According to the above equations ( 6) and ( 7 ), the present invention can accurately measure the temperature. Therefore, the present invention does not adversely affect the FBG accuracy due to the frequency fluctuation of the laser.
Indeed, it can be said that it is a temperature sensor required in current medical equipment for measuring signals in the body .

[0019]

As described above, the FBG temperature sensor of the present invention includes a laser light source, a fiber connector, two FBGs having different thermal stabilization, a photodetector, and a microprocessor, and ensures high-precision temperature measurement. It has the ability to be used in conjunction with other fiber optic sensors, especially for measuring biomedical signals in the body, such as in blood vessels. Furthermore, the degree of analysis is 0.01 ° C. or less, and the operation range is at least 20 ° C. It is more accurate than conventional sensors and has other functions such as determining the scale of biomedical fiber optic sensors. In addition, it is suitable for use with an optical fiber sensor, and can reduce the volume.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an FBG temperature sensor according to the present invention.

FIG. 2 is a perspective view showing an FBG using a core as a photosensitive material according to the present invention.

FIG. 3 is a graph showing the relationship between F and F of the present invention using a cladding as a photosensitive material
It is a perspective view showing BG.

FIG. 4 is a perspective view showing a D-type FBG of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Fiber connector 21 Fiber connector 22 Fiber connector 3 Optical fiber branch (1) 4 Optical fiber branch (2) 5 Temperature sensor 51 FBG (1) 52 FBG (2) 6 Photoelectric signal converter 61 Photodetector ( 1) 62 Photodetector (2) 7 Electric cable 8 Microprocessor 9 Fiber 91 Core 92 Cladding 93 FBG 10 Fiber 101 Core 102 Cladding 103 FBG 11 Fiber 111 Core 112 Cladding 113 Diffraction grating waveguide

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-11078 (JP, A) JP-A-8-240451 (JP, A) JP-A-8-2324051 (JP, A) JP-A-7- JP-A-4-307328 (JP, A) JP-A-7-29430 (JP, U) JP-A-6-507728 (JP, A) JP-T-62-500052 (JP, A) Special Table 1986-501587 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01K 11/32

Claims (7)

(57) [Claims] 1. A laser light source and three fiber connections
Device, two fiber Bragg gratings,
Detector and microprocessor
A bar Bragg grating temperature sensor, The laser light emitted from the laser light source is
After passing through one of the fiber splicers,
Each of the laser beams branched in the two directions
The above fibers connected to the fiber connector
Laser light of a specific wavelength is incident on the Bragg diffraction grating.
Reflected from the reflected light to the above photodetector
To measure the change in spectrum due to temperature.
A configuration that calculates the temperature with a processor, The microprocessor is the photodetector
From the two spectra of the reflected light measured in
Calculate efficiency and calculate temperature
Iver Bragg grating temperature sensor. 2. A laser light source and three fiber connections
Device, two fiber Bragg gratings,
Detector and microprocessor
A bar Bragg grating temperature sensor, The laser light emitted from the laser light source is
After passing through one of the fiber splicers,
Each of the laser beams branched in the two directions
The above fibers connected to the fiber connector
Laser light of a specific wavelength is incident on the Bragg diffraction grating.
Reflected from the reflected light to the above photodetector
To measure the change in spectrum due to temperature.
A configuration that calculates the temperature with a processor, The two fiber Bragg gratings are
The Bar Bragg grating itself expands and contracts with temperature
Temperature sensor that can measure temperature
Have different coefficients of thermal expansion and heat and light,
Different grating spacing or different grating
Fiber Bragg diffraction grating characterized by its structure
Child temperature sensor. 3. The two fiber Bragg gratings
The fiber Bragg grating itself depends on the temperature
Temperature that can measure temperature by expanding and contracting With a degree sensor
And different thermal expansion coefficients and heat-light coefficients.
Have different grating intervals or different
2. A grating structure according to claim 1.
Fiber Bragg grating temperature sensor. 4. The microprocessor according to claim 1, wherein
In addition, the optical frequency of the laser light source is also measured, and the
Through the feedback circuit, the optical frequency of the laser
4. The method according to claim 1, wherein the stabilization is performed.
2. The fiber Bragg diffraction grating temperature sensor according to claim 1. 5. The fiber Bragg diffraction grating is constituted.
The core and the cladding are made of different materials
And at least one of the core and the cladding
Is characterized by providing a diffraction grating in one of the
The fiber bragg according to any one of claims 1 to 4,
Diffraction grating temperature sensor. 6. The fiber Bragg diffraction grating
And adopt D-type optical fiber after polishing, different thermal expansion
Grating wavegauge with coefficient and thermo-optic coefficient
The flat cladding surface of the D-type optical fiber
6. The method according to claim 1, wherein the second member is formed in
2. The fiber Bragg diffraction grating temperature sensor according to claim 1. 7. A file system for use in the biomedical field.
A bar Bragg grating temperature sensor, and
Size of the sensor part including the Inver Bragg grating
Characterized in that it is large enough to enter human blood vessels
The fiber brush according to any one of claims 1 to 6.
Grating temperature sensor.