JP3403657B2 - Method for measuring reflection center wavelength of fiber grating element using disk-type tunable filter and measuring apparatus using the method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring method and a measuring method for measuring the reflection center wavelength of one or a plurality of fiber grating (hereinafter abbreviated as FBG) elements in a wide band, with high accuracy, high accuracy and high speed. It relates to the device.

[0002]

2. Description of the Related Art In a conventional FBG reflection center wavelength measuring system, an edge filter, a tunable etalon filter of a sweep type driven by a piezo element, a wavelength tunable filter using an FBG driven by a piezo element, and an angle adjustment type. Discrimination of wavelengths is performed using a dielectric multilayer film or a system using an interferometer.

[0003]

These FBG reflection center wavelength measuring systems have the following problems depending on the respective wavelength discriminating methods. With wavelength discrimination using an edge filter, high-speed measurement is possible because there is no mechanical operating part, but the measurement range and measurement accuracy are in inverse proportion, so a wide measurement range and high measurement accuracy cannot be achieved at the same time. In wavelength discrimination by a tunable etalon filter of the sweep type driven by a piezo element, the measurement range is wide, but it is difficult to improve the measurement accuracy because the finesse of the etalon filter must be improved. In wavelength discrimination using a wavelength tunable filter that uses an FBG driven by a piezo element, high measurement accuracy and high measurement accuracy can be realized, but the wavelength tunable width of the wavelength tunable filter that uses an FBG has a narrow measurement range. In wavelength discrimination using an angle-adjustable dielectric multilayer film, the applicable band is limited due to polarization-dependent loss. With the wavelength discrimination by the interferometer, highly accurate and highly accurate measurement can be performed in a short time, but the measurement configuration is complicated, and a long optical path length is required, which makes miniaturization difficult. Each of these measuring methods has advantages and disadvantages, and it is difficult to realize the measurement satisfying all the conditions of high accuracy, high accuracy, high speed measurement, and miniaturization. In view of this, the present invention has an object to broaden the FBG center wavelength measuring method, improve measurement accuracy, improve measurement accuracy, and shorten measurement time.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the wavelength discrimination in the FBG reflection center wavelength measurement is not performed by a conventional method.
Disc type wavelength tunable filter (hereinafter abbreviated as DTF) allows wavelength discrimination with wide measurement range, high measurement accuracy, high measurement accuracy,
It is characterized by high speed.

According to a first aspect of the present invention, a step of injecting light from a broadband light source into one or more FBG elements, a step of Bragg-reflecting light of a predetermined wavelength by the one or more FBG elements, having the function of filter that transmits only light of wavelengths, comprising a mark for detecting the angular position, the wavelength of the transmitted light against the apparent angle relative to the mark for detecting the angle position
A step of causing reflected light or transmitted light from the one or more FBG elements to be incident on a linearly and continuously changing DTF while rotating the DTF, and detecting the mark to detect the DTF.
By synchronizing with the rotation of
A step of detecting, a step of receiving light transmitted through the DTF by a light receiving element, and a step of performing arithmetic processing in association with information of reflected light or transmitted light received by the light receiving element in association with the detected prospective angle. FB using DTF characterized by having
This is a method of measuring the reflection center wavelength of the G element.

The invention of claim 2 is characterized in that the thermal expansion of the DTF is corrected in the step of performing the arithmetic processing.

According to a third aspect of the invention, a plurality of FBG elements are
It is characterized in that it is selectively controlled by an optical switch, and the reflection center wavelength of each FBG element is measured in time series.

According to a fourth aspect of the present invention, a plurality of optical systems including a fiber grating element are respectively connected to the other ends of the star couplers branched from the broadband light source, and a plurality of FBs are provided.
Reflected light or transmitted light from the G element is detected by each individual light receiving element, and parallel arithmetic processing is performed.

The invention of claim 5 is characterized in that the prospective angle detecting step is performed using a magnetic head.

The invention of claim 6 is characterized in that the prospective angle detecting step is performed by using an optical pickup.

According to a seventh aspect of the present invention, a broadband light source, at least one FBG element that Bragg-reflects light having a predetermined wavelength of the light incident from the broadband light source, and the at least one FB.
Of the light incident from the reflected light or the transmitted light from the G element, it has the function of a filter that transmits only the light of a specific wavelength, and is provided with a mark for detecting the angular position. for the apparent angle of the reference wavelength of the transmitted light
A DTF continuously varies linearly, a rotation mechanism for rotating the DTF, a rotation control mechanism of the DTF, the mer
Detected once and synchronized with the rotation of the DTF once
An angular position detection mechanism for detecting the expected angle at each turn , and the D
A DT including a light-receiving element that receives light transmitted through the TF, and a calculation unit that performs calculation processing by associating light-receiving information of the light-receiving element with detection information of the angular position detection mechanism.
It is a reflection center wavelength measuring device of an FBG element using F.
It is an invention of an apparatus using the method of claim 1.

A center wavelength measuring system for an FBG according to the present invention comprises a broadband light source, an optical system including the FBG, and a DTF including a mark for detecting an angular position for discriminating the center wavelength of light reflected or transmitted from the FBG. A light receiving element for receiving the discriminated light, a fiber coupler for connecting the light source to the FBG and DTF, a collimator lens system, and a DTF.
A motor for rotating the motor, a controller for controlling the motor, an angular position detecting element for detecting an angle (hereinafter referred to as a prospective angle) with respect to the DTF mark as a reference, a temperature sensor, and D.
It is configured by an arithmetic unit that calculates the reflection center wavelength of the FBG and the like based on the signal of the apparent angle of TF and the intensity signal of the light from the light receiving element.

The DTF has a structure in which the transmission center wavelength changes linearly and continuously with respect to the expected angle over a wide band, and it is possible to easily broaden the measurement wavelength band. The DTF is rotated at a constant rotation speed by a motor. Further, the mark on the DTF is detected by the angular position detecting element and rotated in synchronization with the controller of the motor, so that the expected angle of the DTF is detected with high precision for each rotation, and the wavelength is discriminated with high precision. In addition, by using the absolute wavelength reference with temperature and atmospheric pressure as parameters, and correlating the expected angle and the transmission wavelength in the calculator, it is possible to achieve a high measurement system configuration without using an external reference light source. Perform accurate wavelength discrimination. Also, the measurement time can be easily shortened by simply increasing the rotation speed of the DTF. By the means as described above, it is possible to measure the reflection center wavelength of the FBG at a wide measurement range, high measurement accuracy, high measurement accuracy, and high speed.

[0014]

DETAILED DESCRIPTION OF THE INVENTION

[Embodiment 1] FIG. 1 is a view for explaining a first embodiment of the present invention and shows a highly accurate strain measuring method according to the present invention. This distortion measurement system has an oscillation wavelength of 1530 nm to 163
Erbium-doped fiber amplifier up to 0 nm spontaneous emission light (hereinafter abbreviated as ASE) light source 1, fiber coupler 2,
FBG3-1-3-10, collimating lenses 4, 4 ',
Mirrors 5, 5 ', DTF 6, spindle 7, DC servo motor 8, angle position detection element 9 composed of photo coupler,
Phase-locked loop control circuit 10, single-mode optical fiber 11, light-receiving element 1 including photodiode
2. Comprised of a calculator 13 including a microcomputer and a temperature sensor 14 including an infrared radiation thermometer.

In the present embodiment, an example of an ASE light source will be described as the light source 1, but a wide band light source such as a wide band LED (light emission diode) or a super luminescence diode can also obtain the same effect as this embodiment. . Further, the angular position detecting element 9 is not limited to the photocoupler, and a known magnetic head used in a magnetic disk can be used. The magnetic head can perform highly accurate angular position detection without contact. Similarly, by using a known optical pickup used for a compact disc, the angular position can be detected with higher accuracy without contact. Further, as the arithmetic unit 13, not only a microcomputer but also a personal computer can be used. Further, the temperature sensor 14 is not limited to the temperature sensor including an infrared radiation thermometer, and a known one such as a thermistor or a thermocouple can be used.

FIG. 2 is a diagram showing the structure of DTF 6 . D
The TF 6 is formed by depositing a high reflection film 16, a dielectric multilayer film 17 having a film thickness that changes depending on an expected angle, and a high reflection film 16 ′ on a glass substrate 15. An antireflection film 18 is provided on the back of the glass substrate. Further, an angle position detection mark 19 is drawn on the upper surface of the substrate with high accuracy.
Wavelength variable width is 100n from 1530nm to 1630nm
m. The full width at half maximum is about 0.8 nm.

The light emitted from the ASE light source 1 passes through the fiber coupler 2 and has a reflection center wavelength of 1530 nm to 1
10 FBGs 3-1 to 3-1 different between 630 nm
Pass 0. When passing through the FBGs 3-1 to 3-10, the light that matches the Bragg wavelength of each of the FBGs 3-1 to 3-10 is reflected, passes through the fiber coupler 2 again, and is emitted from the collimating lens 4 as parallel light. The direction of light is changed by 90 degrees by the mirror 5, passes through the DTF 6, and the direction of light is changed by 90 degrees by the mirror 5 ', and then enters the collimator lens 4'against the single mode optical fiber 11
The intensity of light is detected by the light receiver 12 after passing through. DT
F6 is fixed to the spindle 7 and is rotated by the DC servo motor 8 at a constant rotation speed of 6000 rpm or more. The angle position detection mark 19 drawn with high precision on the DTF 6 is detected by the angle position detection element 9 by a photocoupler to obtain a rotary encode signal, and the signal is generated by the oscillator inside the control circuit 10 by the phase locked loop. A method of precisely detecting the expected angle of the DTF 6 on the time axis by rotating the DC servo motor 8 in synchronism with the above was used.

A temperature sensor 14 consisting of an infrared radiation thermometer was arranged near the DTF 6 to measure the temperature of the DTF 6. The DTF 6 uses the absolute wavelength reference with the temperature as a parameter for the projected angle from the mark position, and stores the projected angle and the transmission absolute wavelength in the calculator 13 in association with each other. Therefore, the transmission wavelength at that time is determined by the detected angle of sight and the temperature signal from the temperature sensor 14. This allows the arithmetic unit to perform thermal expansion correction of the DTF 6.
On the other hand, the information on the wavelength and the intensity of the reflected light was acquired by synchronizing the light intensity of the light detected by the photodiode 12 with the oscillator of the control circuit 10 by the phase locked loop and fetching it into the calculator 13 by the microcomputer. The reflection center wavelength of the FBGs 3-1 to 3-10 is determined by calculating the number of the FBGs 3-1 to 3-10 having the maximum intensity from the wavelength and intensity information of the reflected light taken into the calculator 13. did. With the above-mentioned measuring method, FB
About 100n for the measurement of the reflection center wavelength of G3-1 to 3-10
Measurement range of m, accuracy of 1 pm or less, accuracy of ± 3 pm or less, measurement speed of 100 Hz or more.

In the FBG, the refractive index of the core of the fiber changes periodically in the longitudinal direction of the fiber. Only a predetermined wavelength, called the Bragg wavelength, which is proportional to the period of the grating is reflected by the FBG. Because of this, FB
The Bragg wavelength changes when G is given an external force such as a strain that changes the grating period or temperature.

If strain is applied to the FBG as an external force that changes the Bragg wavelength, the strain can be measured with high precision by the above-mentioned measurement system. In the above measurement system,
When strain is applied to the FBG, the period of the FBG grating changes, the Bragg wavelength also changes, and the reflection center wavelength detected proportionally changes. From the variation of this wavelength,
The applied strain was calculated and measured by the calculator 13. 1.
Since the amount of change in wavelength of 2 pm corresponds to the amount of change in strain of 1 μ strain, the above-described measurement configuration realizes strain measurement with an accuracy of ± 3 μ strain or less and accuracy of 1 μ strain or less at a measurement speed of 100 Hz or more. . In addition, since the range of wavelengths that can be discriminated is wide, it is possible to connect a plurality of FBGs having different reflection center wavelengths in series, thereby realizing distortion measurement at multiple points.

Although the DTF 6 is calibrated only by the temperature in this embodiment, the atmospheric pressure sensor can be used to improve the measurement accuracy. At that time, not only the temperature but also the atmospheric pressure is stored as a parameter in the computing unit in association with the expected angle and the transmission absolute wavelength by using the absolute wavelength reference.

[0022]

[Embodiment 2] FIG. 3 is a view for explaining a second embodiment of the present invention, and is a view showing a measuring method in which FBGs 3 are connected in parallel using an optical switch. The same components as those in FIG. 1 are designated by the same reference numerals (the same applies to the following embodiments). The light emitted from the ASE light source 1 is the fiber coupler 2
Pass through the optical switch 20. The optical switch 20 has eight output fibers, and one or a plurality of FBGs 3-1 to 3-8 are connected to each fiber. The FBG 3-1 connected to each output fiber in time series by switching the optical switch 20 in synchronization with one rotation of the DTF 6.
Measure the reflection center wavelength of 3-8. With the above measurement configuration, the FBs connected to the same optical switch 20 can be measured without expanding the wavelength band of the light source and the DTF 6 because FBGs having the same reflection center wavelength can be used between different output fibers.
It is possible to increase the number of G. However, in this configuration, since the measurement is performed in synchronization with the switching speed of the optical switch 20, the measurement speed decreases in inverse proportion to the number of output fibers of the optical switch. Therefore, it is a measurement system which does not require a measurement speed but is useful when a large amount of FBG is used for measurement. In this example, a 1 × 8 optical switch with a switching time of 10 ms was used. As a result, the measurement speed was about 10 Hz.

[0023]

[Embodiment 3] FIG. 4 is a view for explaining a third embodiment of the present invention, and is a view showing a measuring method in which FBGs are connected in parallel by preparing a plurality of sets of optical systems. The light emitted from the ASE light source 1 is divided into eight by the 1 × 8 star coupler 21, and the fiber couplers 2-1, 2-2, ..., FBG3-
1, 3-2 ..., Collimating lenses 4-1 and 4-2.
...., 4'-1, 4'-2 ..., Mirrors 5-1, 5-
2 ... 5'-1, 5'-2 ..., Optical fiber 11
-1, 11-2 ..., Light receiving elements 12-1, 12-2 ...
.., and is made incident on eight sets of optical systems. The eight optical systems are installed on the circumference of the DTF 6 and share the DTF 6. In addition, the calculator 13 can perform parallel calculation processing for each optical system. Since each optical system is independent, the number of FBGs can be increased without increasing the measurement time as long as the optical system can be installed.

When it is considered that the above measurement system is used as a separate measurement system for each optical system, the cost per measurement system can be suppressed by sharing the DTF 6 among a plurality of measurement systems.

[0025]

[Embodiment 4] FIG. 5 is a view for explaining a fourth embodiment of the present invention, and is a view showing a measuring method in which the measuring system is downsized by simplifying the light receiving optical system. The light emitted from the ASE light source 1 passes through the fiber coupler 2 and FBGs 3-1 to 3-3.
Pass -10. When passing through the FBGs 3-1 to 3-10, the light that matches the Bragg wavelength of the FBGs 3-1 to 3-10 is reflected, passes through the fiber coupler 2 again, is emitted from the collimating lens 4 as parallel light, and passes through the DTF 6. Then, the light intensity of the light is detected by the light receiver 12 immediately below the DTF 6. With the above-described measuring system, the mirror on the light receiving element side, the collimating lens, and the optical fiber can be omitted, the size can be reduced, and the measuring system can be made economical.

[0026]

[Embodiment 5] FIG. 6 is a view for explaining a fifth embodiment of the present invention, and is a view showing a method for simply constructing a measuring system by measuring a reflection center wavelength from transmitted light of an FBG. . The light emitted from the ASE light source 1 is FBG 3-1 to 3-3-
Pass 10. When passing through the FBGs 3-1 to 3-10, the light other than the light that matches the Bragg wavelength of the FBGs 3-1 to 3-10 is transmitted, passes through the fiber coupler 2, and is emitted from the collimator lens 4 as parallel light. The direction of the light can be changed by 90 degrees, the light can pass through the DTF 6, and the direction of the light can be changed by 90 degrees by the mirror 5 '.
Detects the intensity of light. The transmitted light is discriminated by the DTF 6, the wavelength having the minimum intensity is calculated by the calculator 13, and the reflection center wavelength of the FBGs 3-1 to 3-10 is determined. By measuring with the method as described above, it is possible to reduce the cost and realize the measurement of the reflection center wavelength of the FBG that is small and highly accurate.

[0027]

[Sixth Embodiment] FIG. 7 is a diagram for explaining a sixth embodiment of the present invention, showing a configuration in which the present invention is applied to a rockfall management system. The principle of measuring the strain amount is the same as that in the first embodiment. FB
G3 is attached to the surface of the wire rope of the rockfall wire net 22 and used as a strain sensor. The wire rope is attached to rocks where rocks may fall to prevent rocks from falling. When the bedrock is about to collapse, the wire rope is distorted, and the FBG3 attached to the surface of the wire rope is also distorted. As a result, the Bragg wavelength of the FBG 3 changes and the reflected wavelength detected also changes. From this change amount, it is possible to detect the change amount of the strain applied to the rockfall wire net 22. Calculating whether this distortion is likely to exceed the predicted rock collapse threshold 13
Safety management of rockfall is carried out by monitoring by.

The FBG changes its Bragg wavelength not only with strain but also with changes in temperature. Therefore, even if strain is not applied to the FBG, which is a strain sensor, the reflected wavelength to be detected changes due to temperature changes. Therefore, the temperature compensating fiber grating (hereinafter abbreviated as temperature compensating FBG) 23 is installed in the immediate vicinity of the strain sensor FBG 3. The temperature compensating FBG 23 is not fixed to the surface of the wire rope, but the Bragg wavelength is changed only with respect to the temperature. Therefore, temperature compensation is realized by subtracting the change in the reflection wavelength from the temperature compensating FBG 23 from the reflection wavelength from the strain sensor FBG 3.

[0029]

The present invention is carried out in the form as described above and has the following effects. To the angle of view
Discrimination of wavelength by DTF whose transmission center wavelength changes continuously
By using the FBG to measure the center wavelength,
Wide bandwidth, improved measurement accuracy, improved measurement accuracy, and
Short measurement time by controlling the rotation speed of the DTF disk
Achieve contraction. Further, by using the above measuring system for measuring strain and temperature, highly accurate measurement can be realized. Further, it is possible to construct a highly accurate rockfall management system by applying the above strain measurement system to a rockfall management system.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a highly accurate strain measuring method according to the present invention.

FIG. 2 is a diagram showing a structure of a disk type wavelength tunable filter.

FIG. 3 is a diagram showing an example of a measuring method in which FBGs are connected in parallel using an optical switch.

FIG. 4 is a diagram showing an embodiment of a measuring method in which FBGs are connected in parallel by preparing a plurality of optical systems.

FIG. 5 is a diagram showing an embodiment of a measuring method in which the measuring system is downsized by simplifying the light receiving optical system.

FIG. 6 is a diagram showing an example of a measuring method in which a measuring system is simply configured by measuring a transmission center wavelength of an FBG.

FIG. 7 is a diagram showing an embodiment in which the present invention is applied to a rockfall management system.

[Explanation of symbols]

1 ASE light source 2, 2-1, 2-2 ... Fiber coupler 3, 3-1, 3-2 ... Fiber grating 4, 4-1, 4-2 ... 4 ', 4'- 1, 4'-2
... Collimating lenses 5, 5-1, 5-2, 5 ', 5'-1, 5'-2
... Mirror 6 Disk type wavelength tunable filter 7 Spindle 8 DC servo motor 9 Angular position detection element 10 Controllers 11, 11-1, 11-2 ... Single mode optical fiber 12, 12-1, 12-2 ... .. Photodetector 13 Operation unit 14 Temperature sensor 15 Glass substrate 16, 16 'High reflection film 17 Dielectric multilayer film 18 Antireflection film 19 Angular position detection mark 20 Optical switch 21 Star coupler 22 Rockfall prevention wire net 23 Temperature compensation Fiber grating

Front page continuation (72) Inventor Eiichi Sugai 1-3-1, Gotenyama, Musashino-shi, Tokyo NTT Advance Technology Co., Ltd. (72) Inventor Yoshimasa Katagiri 3-chome, Nishishinjuku, Shinjuku-ku, Tokyo 19 No. 2 Nihon Telegraph and Telephone Corporation (72) Inventor Kenichi Suzuki 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nihon Telegraph and Telephone Corporation (56) Reference JP-A-9-178609 (JP, A) JP-A-8-313348 (JP, A) JP-A-2000-30162 (JP, A) International Publication 98/036252 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01M 11/00-11/08 G01J 3/00-4/04

Claims (7)

(57) [Claims] 1. A step of injecting light from a broadband light source into one or more fiber grating elements, a step of Bragg-reflecting light of a predetermined wavelength with the one or more fiber grating elements, and light of a specific wavelength. Has the function of a filter that allows only light to pass through, and is equipped with a mark for angle position detection.
The disc-type wavelength tunable filter wavelength of for the apparent angle <br/> transmitted light relative to the mark for the angle position detection is continuously changed in a linear, while rotating the disk-type wavelength tunable filter, a step of incident reflected light or transmitted light from the one or more fiber grating element, wherein Ma
Detected and detected the rotation of the disk tunable filter.
To detect the above-mentioned prospective angle for each rotation.
And a step of receiving light transmitted through the disc type wavelength tunable filter by a light receiving element, and processing of information of reflected light or transmitted light received by the light receiving element in association with the detected prospective angle. A method of measuring a reflection center wavelength of a fiber grating element using a disk-type wavelength tunable filter, which comprises: 2. The reflection center wavelength measurement of a fiber grating element using a disk type wavelength tunable filter according to claim 1, wherein thermal expansion correction of the disk type wavelength tunable filter is performed in the arithmetic processing step. Method. 3. In the step of injecting light from a broadband light source into the one or more fiber grating elements, a plurality of the fiber grating elements are selectively controlled by an optical switch in time series, and the subsequent steps are also time series. 3. The fiber grating element using the disk-type wavelength tunable filter according to claim 1 or 2, wherein the reflection center wavelength of each fiber grating element is measured in a time-series manner. Method of measuring the center wavelength of reflection. 4. A plurality of optical systems including the one or more fiber grating elements are respectively connected to the other ends of star couplers branched from the broadband light source, and the one or more fiber grating elements in each optical system. The reflected light or transmitted light from the received light is received by the light receiving element provided for each optical system in the light receiving step, and the reflected light or transmitted light received by the plurality of light receiving elements in the arithmetic processing step 3. A reflection center wavelength measuring method for a fiber grating element using a disk-type wavelength tunable filter according to claim 1, wherein parallel calculation processing is performed based on information. 5. The method according to claim 1, wherein the step of detecting the expected angle is performed by using a magnetic head.
A method for measuring a reflection center wavelength of a fiber grating element using the disk-type wavelength tunable filter described in. 6. The reflection center of a fiber grating element using a disk type wavelength tunable filter according to claim 1, wherein the step of detecting the expected angle is performed by using an optical pickup. Wavelength measurement method. 7. A broadband light source and at least one fiber grating element that Bragg-reflects light having a predetermined wavelength of light incident from the broadband light source, and reflected light from the one or more fiber grating elements. Of the light incident from the transmitted light, it has the function of a filter that transmits only the light of a specific wavelength, and is equipped with a mark for angular position detection.
A disk-type variable wavelength filter wavelengths for the apparent angle <br/> transmitted light varies continuously linear relative to the mark for the angle position detection, a rotation mechanism for rotating the disk type tunable wavelength filter And a rotation control mechanism of the disk-type variable wavelength filter and the disk-type wavelength detecting the mark.
Every rotation by synchronizing with the rotation of the variable filter
And angular position detecting mechanism for detecting the apparent angle, the disc-type variable and a light receiving element for receiving the light of the wavelength filter transmitted through, in association with processing the detection information of the angle position detecting mechanism receiving information light receiving element A reflection center wavelength measuring device for a fiber grating element using a disk-type wavelength tunable filter, comprising: