JP2000180299A - Reflection center wavelength measuring method of fiber grating element using disc type variable wavelength filter and measuring device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve measuring accuracy and likelihood by using a disc type variable wavelength filter DTF, admitting Bragg's reflecting light from a fiber grating element FBG, and detecting an anticipated angle based on the intensity of the transmitting light and a fixed mark for computation processing. SOLUTION: The light of the spontaneous emission light ASE light source 1 of an erbium dope fiber amplifier passes through ten pieces of FBG (3-1)-(3-10) of different wavelength in the reflection center, light comformed to Bragg's wavelength of FBG is reflected and passed through DTF 6, and the intesity of the light is detected by a light receiver 12. The DTF 6 is constantly rotated, the detected signal of an angular position detecting mark is synchronized with the transmitter of a control circuit 10, and the anticipated angle of the DTF 6 is detected. A computer 13 decides transmitting wavelength by the detected anticipated angle and the temperature from a temperature sensor 14. From information of the wavelength and the intensity of the obtained reflecting light in this way, the computer 13 computes the number of FBG connected with wavelength of maximum intensity, and decides the wavelength of the reflection center of the FBG.

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 a 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 concerns the device.

[0002]

2. Description of the Related Art Conventional FBG reflection center wavelength measuring systems include an edge filter, a sweep type wavelength variable etalon filter driven by a piezo element, a wavelength variable filter using an FBG driven by a piezo element, and an angle adjustment type. Discrimination of wavelength is performed by 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 wavelength discrimination method. In the wavelength discrimination by the edge filter, high-speed measurement is possible because there is no mechanical operation part. However, since the measurement range and the measurement accuracy are inversely proportional, it is not compatible with a wide measurement range and a high measurement accuracy. In the wavelength discrimination using a sweep-type variable wavelength etalon filter driven by a piezo element, it is difficult to improve the measurement accuracy although the measurement range is wide because the finesse of the etalon filter must be improved. In wavelength discrimination by a wavelength variable filter using an FBG driven by a piezo element, high measurement accuracy and high measurement accuracy can be realized, but the measurement range is narrow because the wavelength variable width of the wavelength variable filter using the FBG is narrow. In the wavelength discrimination by the angle-adjusting dielectric multilayer film, there is a limitation in an applicable band due to a polarization dependent loss. In wavelength discrimination by an interferometer, high-accuracy and high-accuracy measurement can be performed in a short time, but the measurement configuration is complicated, and a long optical path length is required, so that miniaturization is difficult. Each of these measurement methods has advantages and disadvantages, and it is difficult to realize a measurement that satisfies all the conditions of high accuracy, high accuracy, high speed measurement, and miniaturization. Therefore, an object of the present invention is to broaden the center wavelength measurement method of the FBG, improve the measurement accuracy, improve the measurement accuracy, and shorten the measurement time.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problem, and the present invention is not intended to use the conventional method for discriminating the wavelength in the measurement of the reflection center wavelength of the FBG.
Disc type wavelength tunable filter (hereinafter abbreviated as DTF) enables wavelength discrimination over a wide measurement range, high measurement accuracy, high measurement accuracy,
It is characterized by performing at high speed.

According to a first aspect of the present invention, a step of causing light from a broadband light source to enter at least one FBG element, a step of Bragg-reflecting light of a predetermined wavelength by the at least one FBG element, and It has a function of a filter that transmits only light of a wavelength, and has a mark for detecting an angular position, and the DTF is changed to a DTF in which the wavelength of transmitted light changes according to an expected angle with respect to the mark for detecting the angular position. Rotating the reflected light or transmitted light from the one or more FBG elements while rotating, detecting the expected angle, receiving the light transmitted through the DTF by a light receiving element, A step of calculating information on reflected light or transmitted light received by the element in association with the detected expected angle, and measuring the reflection center wavelength of the FBG element using the DTF.

According to a second aspect of the present invention, the thermal expansion correction of the DTF is performed in the operation processing step.

According to a third aspect of the present invention, the plurality of FBG elements include:
The optical switch is selectively controlled, 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 connected to the other end of a star coupler branched from a broadband light source, respectively.
The reflected light or the transmitted light from the G element is detected by each individual light receiving element, and parallel processing is performed.

According to a fifth aspect of the present invention, the expected angle detecting step is performed using a magnetic head.

According to a sixth aspect of the present invention, the expected angle detecting step is performed using an optical pickup.

According to a seventh aspect of the present invention, there is provided a broadband light source, one or more FBG elements for Bragg-reflecting light of a predetermined wavelength among the light incident from the broadband light source, and the one or more FB devices.
Among the light incident from the reflected light or transmitted light from the G element, the filter has a function of transmitting only light of a specific wavelength, and includes a mark for detecting an angular position. A DTF in which the wavelength of transmitted light changes according to a reference expected angle, a rotation mechanism for rotating the DTF, a rotation control mechanism for the DTF, an angular position detection mechanism for detecting the expected angle of the DTF, and the DTF An FBG element using a DTF, comprising: a light receiving element that receives light transmitted through the light receiving element; and an arithmetic unit that performs arithmetic processing by associating light receiving information of the light receiving element with detection information of the angular position detecting mechanism. Is a reflection center wavelength measuring device. It is an invention of an apparatus using the method of claim 1.

A system for measuring the center wavelength of an FBG according to the present invention is a DTF having a broadband light source, an optical system including the FBG, and 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 and a collimator lens system for connecting the light source to the FBG and the DTF, and a DTF.
A motor for rotating the motor, a controller for controlling the motor, an angle position detecting element for detecting an angle (hereinafter abbreviated as an expected angle) with reference to a DTF mark, a temperature sensor,
An arithmetic unit for calculating a reflection center wavelength of the FBG and the like based on a signal of an expected angle of the TF and an intensity signal of light from the light receiving element.

The DTF has a structure in which the transmission center wavelength changes linearly with respect to the expected angle and continuously changes over a wide band, so that the measurement wavelength can be broadened easily. The DTF is rotated at a constant speed by a motor. Further, a mark on the DTF is detected by an angular position detecting element, and by rotating the motor in synchronization with a controller of the motor, an expected angle of the DTF is detected with high accuracy for each rotation, and highly accurate wavelength discrimination is performed. In addition, by storing in an arithmetic unit in advance the correspondence between the expected angle and the transmission wavelength using the absolute wavelength reference with temperature and atmospheric pressure as parameters, a simple measurement system configuration without using an external reference light source or the like is achieved. Perform accurate wavelength discrimination. Further, the measurement time can be easily reduced only by increasing the rotation speed of the DTF. By the means as described above, the measurement of the reflection center wavelength of the FBG is realized in a wide measurement range, high measurement accuracy, high measurement accuracy, and high speed.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 is a view for explaining a first embodiment of the present invention, and shows a method for measuring distortion with high accuracy according to the present invention. This strain measurement system has an oscillation wavelength from 1530 nm to 163
A spontaneous emission (hereinafter abbreviated as ASE) light source 1 of an erbium-doped fiber amplifier up to 0 nm, a fiber coupler 2,
FBG3-1 to 3-10, collimating lenses 4, 4 ',
Mirror 5, 5 ', DTF 6, spindle 7, DC servo motor 8, angular position detecting element 9 composed of photocoupler,
Control circuit 10 by phase locked loop, single mode optical fiber 11, light receiving element 1 composed of photodiode
2. It comprises an arithmetic unit 13 composed of a microcomputer and a temperature sensor 14 composed of an infrared radiation thermometer.

In this embodiment, an example of an ASE light source will be described as the light source 1. However, the same effect as in this embodiment can be obtained by using a broadband light source such as a broadband LED (light emission diode) or a superluminescent diode as the light source. . Further, the angle position detecting element 9 is not limited to a photocoupler, and a known magnetic head used for 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, it is possible to perform angular position detection 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 a temperature sensor including an infrared radiation thermometer, but may be a known sensor such as a thermistor or a thermocouple.

FIG. 2 is a diagram showing the structure of DTF7. D
The TF 7 is formed by depositing a high-reflection film 16, a dielectric multilayer film 17 whose film thickness changes according to 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. 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 half width is about 0.8 nm.

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 differing between 630 nm
Pass through zero. When passing through each of the FBGs 3-1 to 3-10, light matching 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, changes the direction of light by 90 degrees by the mirror 5 ′, enters the collimating lens 4 ′ again, and enters the single mode optical fiber 11.
And the light intensity is detected by the light receiver 12. DT
F6 is fixed to the spindle 7 and is rotated at a constant rotation speed of 6000 rpm or more by the DC servo motor 8. A rotary encoding signal is obtained by detecting an angular position detecting mark 19 drawn on the DTF 6 with high accuracy by an angular position detecting element 9 using a photocoupler, and the signal is transmitted to a transmitter inside a control circuit 10 by a phase locked loop. A method is used in which the expected angle of the DTF 6 on the time axis is precisely detected every rotation by rotating the DC servo motor 8 in synchronization with.

A temperature sensor 14 composed of an infrared radiation thermometer was arranged near the DTF 6, and the temperature of the DTF 6 was measured. The DTF 6 is stored in the arithmetic unit 13 in association with the expected angle and the transmission absolute wavelength using the absolute wavelength reference with the temperature as a parameter in advance for the expected angle from the mark position. Therefore, the transmission wavelength at that time is determined based on the detected expected angle and the temperature signal from the temperature sensor 14. As a result, the arithmetic unit can correct the thermal expansion of the DTF 6.
On the other hand, the intensity of the light detected by the photodiode 12 was taken into the arithmetic unit 13 by the microcomputer in synchronization with the oscillator of the control circuit 10 by the phase-locked loop, thereby obtaining the information on the wavelength and the intensity of the reflected light. The reflection center wavelengths of the FBGs 3-1 to 3-10 are determined by calculating the number of the FBGs 3-1 to 3-10 connected to the wavelengths having the maximum intensity from the information on the wavelength and the intensity of the reflected light taken into the arithmetic unit 13. did. By the above measurement method, FB
Measurement of the reflection center wavelength of G3-1 to 3-10 is about 100n.
It was realized with a measurement range of m, an accuracy of 1 pm or less, an accuracy of ± 3 pm or less, and a measurement speed of 100 Hz or more.

In the FBG, the refractive index of the fiber core 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. This allows FB
When an external force such as a strain or a temperature that changes the period of the grating is applied to G, the Bragg wavelength changes.

Here, assuming that a strain is applied to the FBG as an external force that changes the Bragg wavelength, a highly accurate strain measurement can be performed by the above-described measurement system. In the above measurement system,
When distortion is applied to the FBG, the period of the grating of the FBG changes, the Bragg wavelength also changes, and the detected reflection center wavelength changes in proportion thereto. From this wavelength change,
The applied distortion was calculated and measured by the calculator 13. 1.
Since the amount of change in the wavelength of 2 pm corresponds to the amount of change in the strain of 1 μ strain, the above-described measurement configuration realizes the strain measurement with an accuracy of ± 3 μ strain or less and an accuracy of 1 μ strain or less at a measurement speed of 100 Hz or more. . Further, since the range of wavelengths that can be distinguished is wide, a plurality of FBGs having different reflection center wavelengths can be connected in series, thereby realizing distortion measurement at multiple points.

In this embodiment, the calibration of the DTF 6 is performed only with the temperature, but the accuracy of measurement can be further improved by using a pressure sensor. At that time, not only the temperature but also the atmospheric pressure are stored in the computing unit in correspondence with the expected angle and the transmission absolute wavelength using the absolute wavelength reference as a parameter.

[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 denoted by the same reference numerals (the same applies to the following embodiments). The light emitted from the ASE light source 1 is a fiber coupler 2
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
The reflection center wavelength of 3-8 is measured. With the above-described measurement configuration, the FB can be connected to the same optical switch 20 but can be measured without expanding the wavelength band of the light source and the DTF 6 because the FBG 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 that does not require measurement speed but is useful for using a large amount of FBG for measurement. In this embodiment, a 1 × 8 optical switch having a switching time of 10 ms was used. This resulted in a measurement speed of 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 a 1 × 8 star coupler 21, and fiber couplers 2-1, 2-2.
1, 3, 2 ..., collimating lens 4-1, 4-2
.., 4'-1, 4'-2 ..., mirrors 5-1 and 5-
2 ..., 5'-1, 5'-2 ..., optical fiber 11
-1, 11-2..., Light receiving elements 12-1, 12-2.
・ ・ Inject the light into 8 sets of optical systems consisting of The eight optical systems are installed on the circumference of the DTF 6 and share the DTF 6. The arithmetic unit 13 can perform parallel arithmetic processing on 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-mentioned measuring system is used as another measuring system for each optical system, the cost per measuring system can be reduced by sharing the DTF 6 among a plurality of measuring systems.

[0025]

Embodiment 4 FIG. 5 is a diagram for explaining a fourth embodiment of the present invention, and is a diagram showing a measuring method in which the measuring system is downsized by simplifying the light receiving optical system. Light emitted from the ASE light source 1 passes through the fiber coupler 2 and FBGs 3-1 to 3
Pass through -10. When passing through the FBGs 3-1 to 3-10, 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 collimator lens 4 as parallel light, and passes through the DTF 6. Then, the light intensity is detected by the light receiver 12 immediately below the DTF 6. With the above measuring system, the mirror, collimating lens and optical fiber on the light receiving element side can be omitted, the size can be reduced, and the measuring system can be made more 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 of simply configuring a measurement system by measuring a reflection center wavelength from transmitted light of an FBG. . The light emitted from the ASE light source 1 is FBG3-1 to 3-
Pass 10 When passing through the FBGs 3-1 to 3-10, light other than light that matches the Bragg wavelength of the FBGs 3-1 to 3-10 is transmitted, passes through the fiber coupler 2, is emitted from the collimating lens 4 as parallel light, and is reflected by the mirror 5. The direction of the light is changed by 90 degrees, passes through the DTF 6, is changed by 90 degrees by the mirror 5 ', enters the collimating lens 4' again, passes through the optical fiber 11, passes through the optical receiver 12,
Detects the light intensity. 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 performing the measurement using the method described above, it is possible to reduce the cost and to measure the FBG reflection center wavelength with small size and high accuracy.

[0027]

Sixth Embodiment FIG. 7 is a diagram for explaining a sixth embodiment of the present invention, and shows a configuration in which the present invention is applied to a rockfall management system. The principle of measuring the amount of distortion is the same as in the first embodiment. FB
G3 is attached to the surface of the wire rope of the falling rock 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 FBG 3 attached to the surface of the wire rope is also distorted. As a result, the Bragg wavelength of the FBG 3 changes, and the detected reflection wavelength also changes. The amount of change in the strain applied to the falling rock wire net 22 can be detected from the amount of change. The arithmetic unit 13 determines whether this distortion is likely to exceed the predicted rock collapse threshold.
To monitor the falling rocks.

FBG changes its Bragg wavelength not only with strain but also with temperature changes. Therefore, even if no distortion is applied to the FBG, which is a distortion sensor, the detected reflection wavelength changes due to a temperature change. Therefore, a temperature compensating fiber grating (hereinafter, abbreviated as temperature compensating FBG) 23 is provided immediately adjacent to the strain sensor FBG 3. The temperature compensating FBG 23 is not fixed to the surface of the wire rope, and the Bragg wavelength changes only with respect to the temperature. Therefore, the temperature compensation is realized by subtracting the change in the reflection wavelength from the temperature compensation FBG 23 from the reflection wavelength from the strain sensor FBG 3.

[0029]

The present invention is embodied in the form described above and has the following effects. By measuring the center wavelength of the FBG using the DTF for discrimination of the wavelength, it is possible to widen the measurement range, improve the measurement accuracy, improve the measurement accuracy, and shorten the measurement time. In addition, high-precision measurement is realized by using the above-described measurement system for measuring strain and temperature. In addition, a high-precision rockfall management system can be constructed by applying the above-described strain measurement system to a rockfall management system.

[Brief description of the 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 illustrating a structure of a disk-type wavelength tunable filter.

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

FIG. 4 is a diagram illustrating an example of a measurement 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 illustrating an example of a measurement method in which a measurement 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 lens 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 detecting element 10 Controller 11, 11-1, 11-2 ... Single mode optical fiber 12, 12-1, 12-2 .. Receiver 13 Computing unit 14 Temperature sensor 15 Glass substrate 16, 16 'High reflection film 17 Dielectric multilayer film 18 Antireflection film 19 Angle position detection mark 20 Optical switch 21 Star coupler 22 Rockfall prevention wire net 23 For temperature compensation Fiber grating

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideo Teruya 1-3-1 Gotenyama, Musashino-shi, Tokyo NTT Advanced Technology Co., Ltd. (72) Inventor Eiichi Sugai Gotenyama, Musashino-shi, Tokyo 1-3-1 NTT Advanced Technology Corporation (72) Inventor Shoga Katagiri 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Suzuki Kenichi Fukui term (reference) in Nippon Telegraph and Telephone Corporation, 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo 2G020 AA03 CA05 CB27 CB42 CC07 CC31 CC55 CC65 CD24 2G086 EE05 EE06 EE12 KK07

Claims (7)

[Claims] 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 by the one or more fiber grating elements; It has the function of a filter that allows only transmission, and has a mark for angular position detection,
A disk-type wavelength tunable filter in which the wavelength of transmitted light changes according to an expected angle based on the mark for detecting the angular position,
While rotating the disk-type tunable filter,
Receiving reflected light or transmitted light from at least one fiber grating element, detecting the expected angle, receiving light transmitted through the disk-type wavelength tunable filter with a light receiving element, Measuring the reflection center wavelength of the fiber grating element using the disk-type wavelength tunable filter, wherein the information processing means performs an arithmetic process in which information on the reflected light or the transmitted light received in the step is associated with the detected expected angle. Method. 2. The reflection center wavelength measurement of a fiber grating element using a disk-type wavelength tunable filter according to claim 1, wherein the step of performing the arithmetic processing corrects the thermal expansion of the disk-type wavelength tunable filter. Method. 3. A step of injecting light from a broadband light source into the one or more fiber grating elements, wherein a plurality of the fiber grating elements are selectively controlled in a time series by an optical switch, and the subsequent steps are also performed in a time series manner. 3. The fiber grating element using a disk-type wavelength tunable filter according to claim 1, wherein the central processing is performed to measure the reflection center wavelength of each fiber grating element in time series. Of measuring the reflection center wavelength. 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 are provided. The reflected light or transmitted light from is received by the light receiving elements provided for each optical system in the receiving step, and the reflected light or transmitted light received by the plurality of light receiving elements in the arithmetic processing step 3. The method of measuring a reflection center wavelength of a fiber grating element using a disk-type wavelength tunable filter according to claim 1, wherein parallel operation processing is performed based on the information. 5. The method according to claim 1, wherein the step of detecting the expected angle is performed using a magnetic head.
3. A method for measuring a reflection center wavelength of a fiber grating element using the disk-type wavelength tunable filter described in 1. above. 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 using an optical pickup. Wavelength measurement method. 7. A broadband light source, at least one fiber grating element for Bragg-reflecting light of a predetermined wavelength among light incident from the broadband light source, and light reflected from the one or more fiber grating elements or Of the light incident from the transmitted light, it has the function of a filter that transmits only light of a specific wavelength, and includes a mark for angular position detection,
A disk-type variable wavelength filter in which the wavelength of transmitted light changes according to an expected angle based on the mark for detecting the angular position,
A rotation mechanism for rotating the disk-type variable wavelength filter, a rotation control mechanism for the disk-type variable wavelength filter,
An angular position detecting mechanism for detecting the expected angle of the disk-type variable wavelength filter, a light receiving element for receiving light transmitted through the disk-type variable wavelength filter, and detecting the light receiving information of the light receiving element by the angular position detecting mechanism An apparatus for measuring the reflection center wavelength of a fiber grating element using a disk-type wavelength tunable filter, comprising: a calculation unit for performing a calculation process in association with information.