JP2003130934A - Optical fiber magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber magnetic sensor which has a simple construction and is excellent in extendability. SOLUTION: An FBG 13 covered with metal, a power source 15 for causing a current to flow in this metal covering 3, a light source 27 which causes light to enter the FBG, and a wavelength measuring instrument 29 for measuring the wavelength of light emitted from the FBG 13, are provided. A change of expansion or shrinkage of the FBG 13 is found from a detected wavelength of light emitted when a current is caused to flow in the metal covering 3, and information on external magnetic flux 17 is obtained from this change of expansion or shrinkage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor using an optical fiber, and more particularly to an optical fiber magnetic sensor having a simple structure and excellent expandability.

[0002]

2. Description of the Related Art As a sensor for detecting magnetism by means of an optical fiber, for example, a multipoint type sensor utilizing electromagnetic force is known (Japanese Patent Laid-Open No. 1-35284). This is shown in a block diagram in FIG.

Two optical fibers are connected to the light source 31 via a coupler 32, and these two optical fibers are connected to a photodetector 35 via a coupler 34 to form a Mach-Zehnder interferometer. Magnetic detection elements 40, 43, 4
Different frequencies are set in 6 as the resonance point and the drive current frequency. The output of the light receiver 35 is connected to the synchronous detectors 42, 45 and 48.

The light emitted from the light source 31 is branched into two optical paths by the coupler 32, one optical path passes through the optical phase modulator 39, and the other optical path is detected by the magnetic detection elements 40, 4.
After passing through 3 and 46, they are multiplexed by the coupler 34. The electric signal obtained from the light receiver 35 is synchronously detected at each frequency by the transmitters 41, 44 and 47, and the magnetic information at each point is extracted.

Further, in order to remove the fading, a DC component of a difference component between the output of the photoreceiver 35 and the output of the photoreceiver 36 is taken out from the compensator 37, and this output is amplified by an amplifier 38 to be an optical phase modulation element. In addition to 39, optical feedback is performed to control so that the DC component becomes zero.

[0006]

The conventional magnetic sensor using the above-mentioned optical fiber is likely to be able to relatively easily perform measurement over a wide range by lengthening the optical fiber, but has the following problems. is there.

(1) There are many electric signal lines between each sensor section and the base section.

For example, the following arrangement can be considered for the sensor at the left end of FIG.

A) When both the transmitter 41 and the synchronous detector 42 are installed in the sensor section (in the vicinity of the magnetic detection element 40), the base section (base station collecting the output of each sensor, the light receiver 35, etc.) is installed. (Provided) and the sensor section,
A signal line for sending an electric signal from the light receiver 35 to the sensor unit and a signal line for sending a sensor output from the sensor unit to the base unit are required.

B) When the oscillator 41 is installed in the vicinity of the sensor unit and the synchronous detector 42 is installed in the base unit, a power line is provided between the base unit and the sensor unit, and the transmitter 4 is provided from the sensor unit to the base unit.
A signal line for transmitting the 1 signal is required.

C) When both the transmitter 41 and the synchronous detector 42 are installed in the base unit, a power line is provided between the base unit and the sensor unit, and a signal from the transmitter 41 is sent from the base unit to the sensor unit. A signal line for sending is required.

Since an alternating current directly related to magnetic information flows through these signal lines, noise from the outside causes a large error factor. Further, if the interval between the sensor units is set longer or the distance between each sensor unit and the base unit is longer, the cable to be routed becomes longer accordingly, resulting in a decrease in S / N and deterioration in workability.

(2) The expandability and compatibility of each sensor unit are insufficient.

If one sensor unit is added, a part of a complete single sensor (one magnetic detection element) is inserted into the Mach-Zehnder interferometer, and the compatibility with the complete single sensor is poor. .

(3) The fail-safe property is lacking.

When one of the arms of the Mach-Zehnder interferometer, which is extended due to the increase in the number of points, has an abnormality such as a break or an increase in loss, all the sensor parts become unusable.

(4) It is difficult to remove fading.

As the length of the two arms of the interferometer increases with the increase in the number of points or the number of connectors used increases, the amount of disturbance added increases, or the fading changes due to a decrease in light coherence. Variations in the amount and changing frequency increase, and fading removal becomes difficult.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide an optical fiber magnetic sensor having a simple structure and excellent expandability.

[0020]

In order to achieve the above object, the present invention provides an FBG coated with a metal, a power supply for energizing the metal coating, a light source for making light incident on the FBG, and an FBG. A wavelength measuring device for measuring the wavelength of the emitted light is provided, the expansion / contraction change of the FBG is obtained from the detection wavelength of the light when the metal coating is energized, and the information of the external magnetic flux is obtained from this expansion / contraction change.

An optical coupler may be provided to guide the light from the light source to the FBG and branch the reflected light from the FBG to the wavelength measuring device.

The light from the light source is split into a plurality of FBGs.
And a plurality of optical couplers that combine the reflected lights of the FBGs with each other.

The light from the light source is split into a plurality of FBGs.
It is also possible to provide a plurality of optical couplers for guiding to the wavelength measuring device and a plurality of optical couplers for multiplexing the transmitted light of each FBG and guiding them to the wavelength measuring device.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

According to the present invention, when the metal coating of an optical fiber coated with a metal is energized, the force acting on the metal coating due to the interaction with the external magnetic flux gives expansion / contraction or lateral pressure change in the longitudinal or radial direction of the optical fiber. Therefore, the information of the external magnetic flux is extracted by optically detecting these changes. As an optical fiber coated with metal, the FBG in which the refractive index of the core of the optical fiber is changed at a constant cycle
To use. The expansion / contraction change of the FBG can be obtained from the detection wavelength of light when the metal coating is energized, and the information of the external magnetic flux can be obtained from this expansion / contraction change.

The metal-coated FBG used in the present invention is shown in FIG. The metal-coated FBG changes the refractive index of the core portion 2 of the optical fiber 1 at a constant period L, and the incident light is reflected by this refractive index changing portion. The reflection wavelength λ is determined by the period L and the core refractive index n as in the following equation.

Λ = 2 × L × n (1) This FBG is coated with metal 3. Metal to cover 3
There are, for example, nickel and gold, nickel is coated on the optical fiber, and gold is further coated thereon.

An optical fiber magnetic sensor using this metal-coated FBG is shown in FIG. In this configuration, the metal-coated FBG
13 is connected to the coupler 28, and the light source 27 is connected to the coupler 28.
And the wavelength meter 29 are connected. That is, the coupler 28 guides the light from the light source 27 to the metal-coated FBG 13 and branches the reflected light from the metal-coated FBG 13 to guide it to the wavelength meter 29. The light source 27 emits light in a sufficiently wide wavelength range. The light reflected by the metal-coated FBG 13 and returning to the wavemeter 29 has a wavelength λ obtained by the equation (1), as shown in FIG. This wavelength λ is measured by the wavelength meter 29.

As shown in FIG. 4, a metal-clad FBG 13 is stretched in a straight line using a fixing jig 11 and a fixing material 12 fixed to an insulating casing 14 to fix both ends, and between the both ends of the metal coating. A voltage is applied from the AC power supply 15 to the. 16 is a power supply line. The metal-coated FBG 13 has the same structure as in FIG.
A light source and a wavelength meter are connected via a coupler.

At this time, as shown in FIG. 5, when a magnetic field 17 is applied from the outside, an external force represented by the following equation is applied to the metal-coated FBG 13 in the arrow direction.

F = B × I (2) Since the metal coating FBG 13 is fixed to the insulating casing 14 so as to maintain a constant tension, the metal coating FBG 13 is displaced by a constant length by an external force. As a result, the FBG is expanded, and the cycle L is lengthened.

As described above, since the reflection wavelength λ of the FBG is determined by the period L, the reflection wavelength λ changes as the period L changes. Therefore, a change in external force, that is, a change in magnetism can be obtained by measuring the reflection wavelength λ.

In this system, since a DC power source can be used as the power source, the influence of disturbance can be easily removed by a filter or the like. Further, in the change due to magnetism, since the change in wavelength with respect to the initial value is taken out by the wavelength meter 29, it is not necessary to refer to an electrical signal.

Although an example using a coupler has been described with reference to FIG. 2, as shown in FIG. 6, the light source 27 and the metal-coated FBG are used.
13. The wavelength meter 29 may be connected in series. in this case,
In the light transmitted through the metal-coated FBG 13, the wavelength λ obtained by the equation (1) decreases. Therefore, the wavelength distribution waveform of the light received by the wavelength meter 29 is as shown in FIG. This attenuated wavelength λ is measured by the wavelength meter 29.

Next, an embodiment in which optical fiber magnetic sensors are connected at multiple points will be described.

The optical fiber magnetic sensor shown in FIG. 8 guides the light from the light source 27 to the FBG side at a position close to the light source 27, branches the reflected light from the FBG side and guides it to the wavelength meter 29. Is provided, and the light from the light source side is branched at a position farther from the optical coupler 28, and a plurality of metal-coated FBG1s are provided.
3a, 13b, 13c, each metal coated FBG13
A plurality of optical couplers 28 that combine reflected lights of a, 13b, and 13c and return them to the light source side are provided. Here, the metal-coated FBGs 13a, 13b, 13c reflect lights having different wavelengths.

The optical fiber magnetic sensor shown in FIG. 9 branches the light from the light source 27 into a plurality of metal-coated FBGs 13.
A plurality of optical couplers 28 that lead to a, 13b, and 13c are provided,
A plurality of optical couplers 28 are provided to combine the transmitted lights of the metal-coated FBGs 13a, 13b, 13c and guide them to the wavelength meter 29. Here, the metal-coated FBGs 13a, 13b, 1
3c attenuates and transmits light of different wavelengths.

The optical fiber magnetic sensor of FIGS. 8 and 9 is
Individual sensor parts, that is, metal-coated FBGs 13a, 13
b and 13c are independent of each other and can be increased in number by a coupler connection, and thus are excellent in expandability, compatibility, and fail-safe property.

Since the sensor output basically depends on the period L of the FBG, a stable output can be obtained.

Although the three metal-coated FBGs 13 are used in FIGS. 8 and 9, the number of connectable metal-coated FBGs 13 is limited by the dynamic range of the wavemeter 29, but is not limited in principle.

In the embodiment of FIG. 4, the metal-coated FBG 13 is linearly stretched between the insulating casings 14 and 14, but as shown in FIG.
It may be made longer than 14 and formed in a circular shape or a spiral shape so as not to come into contact with each other, and may be held by using a clamp (not shown) or another jig so as to keep a constant radius. Even in this case, when a voltage is applied from both ends of the metal coating by the AC power supply 15, the FBG is extended according to the magnetic field 17 and the reflection or transmission wavelength λ is changed.

[0042]

The present invention exhibits the following excellent effects.

(1) The electric signal line is only the power supply line 16 for supplying a current to the metal coating, the number of electric signal lines is reduced as compared with the conventional one, and the structure is simplified.

(2) The expandability and compatibility of each sensor unit are high, and the fail-safe property is also excellent. Also, there is no problem of fading removal.

(3) A stable output can be obtained.

[Brief description of drawings]

FIG. 1 is a side sectional view of a metal-coated FBG showing an embodiment of the present invention.

FIG. 2 is an optical circuit diagram of an optical fiber magnetic sensor showing an embodiment of the present invention.

FIG. 3 is an optical signal characteristic diagram of the optical fiber magnetic sensor according to the present invention.

FIG. 4 is a mechanical configuration diagram of an optical fiber magnetic sensor showing an embodiment of the present invention.

FIG. 5 is an operation explanatory diagram of the optical fiber magnetic sensor according to the present invention.

FIG. 6 is an optical circuit diagram of an optical fiber magnetic sensor showing an embodiment of the present invention.

FIG. 7 is an optical signal characteristic diagram of the optical fiber magnetic sensor according to the present invention.

FIG. 8 is an optical circuit diagram of an optical fiber magnetic sensor showing an embodiment of the present invention.

FIG. 9 is an optical circuit diagram of an optical fiber magnetic sensor showing an embodiment of the present invention.

FIG. 10 is a mechanical configuration diagram of an optical fiber magnetic sensor according to an embodiment of the present invention.

FIG. 11 is an optical / electrical circuit diagram of a conventional optical fiber magnetic sensor.

[Explanation of symbols]

1 optical fiber 2 core parts 3 metal 13 Metal coated FBG 15 AC power supply 17 magnetic field 27 light source 28 Coupler 29 Wavemeter

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shuichi Sunahara             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. F-term (reference) 2G017 AA01 AD11                 2H038 AA04 BA24 BA25

Claims (4)

[Claims] 1. A fiber Bragg grating (hereinafter referred to as FBG) coated with a metal, a power supply for energizing the metal coating, a light source for making light incident on the FBG, and a wavelength of light emitted from the FBG. A fiber optic magnetic sensor, comprising: a wavelength measuring device for measuring; obtaining expansion / contraction change of the FBG from a detection wavelength of light when the metal coating is energized; and obtaining information of external magnetic flux from the expansion / contraction change. 2. The optical fiber magnetism according to claim 1, further comprising an optical coupler for guiding the light from the light source to the FBG and branching the reflected light from the FBG to the wavelength measuring device. Sensor. 3. The plurality of FBs are formed by branching the light from the light source.
3. The optical fiber magnetic sensor according to claim 1, further comprising a plurality of optical couplers that guide the light to G and combine the reflected light of each FBG. 4. A plurality of FBs are formed by branching light from the light source.
2. The optical fiber magnetic sensor according to claim 1, wherein a plurality of optical couplers for guiding to G and a plurality of optical couplers for multiplexing the transmitted light of each FBG and guiding to the wavelength measuring device are provided.