JPS6184571A - Optical fiber magnetometer - Google Patents

Abstract

PURPOSE:To reduce the capacity of an optical fiber magnetism sensing part and reduce the influence of a magnetic noise from an aircraft, etc., by using plural optical fibers which are bent and arranged. CONSTITUTION:The magnetometer uses optical fibers, which are bent and fixed on a nonmagnetic plate 9. Straight parts of odd-numbered optical fibers are coated with a ferromagnetic material fibers by using a splitter 2 and also guided to fibers B which are not coated with the magnetic material by using another splitter 3. Outputs of optical fibers A which shift in phase owing to external magnetism and outputs of fibers B which do not shift in phase are led to phase detectors 8 to detect the intensity of the external magnetic field applied to each fiber A, and outputs of the phase detectors 8 are summed up by an adder 11.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides an optical device that can measure weak magnetic fields as strong as the earth's magnetic field with a sensitivity that is more than one order of magnitude higher than the sensitivity (Q, 01nT)' of conventional optical pumping magnetometers. It concerns fiber magnetometers.

[Prior art]

FIG. 1 is a configuration diagram showing a conventional optical fiber magnetometer, in which (1) is a light source and (2) is a beam splitter.

(3) is a total reflection mirror, (4) is an optical fiber, (
5) is a ferromagnetic material, (6) is a photodetector, (7) is an amplifier,
(8) is a phase detector. The light source (1) is, for example, a single mode semiconductor laser. A laser beam from a light source (1) is split into equal light intensities by a beam splitter (2) and guided to each optical fiber (4). Here, one optical fiber (4) is coated or applied with a ferromagnetic material (5) such as Nickel Cobal to the required thickness.

The ferromagnetic material (5) produces magnetostriction in the external magnetic field 1 (Q), and this magnetostriction gives mechanical distortion to this optical fiber (4), so the laser beam passing through the optical fiber (4) The two laser beams are converted into electric signals by a photodetector (6) and amplified by an amplifier (7), and then an optical fiber without ferromagnetic material (5) is (4
) with the electrical signal corresponding to the phase detector (8) as a reference signal.
), the intensity HQ of the external magnetic field can be determined.

The optical fiber magnetometer with the above configuration is as follows.

Optical fiber (4) with 9 ferromagnetic bodies (5) 1
It has a high sensitivity of 0.001 to 0.0001 nTO per m. However, optical fiber (4)
It is difficult with current technology to uniformly coat or apply the ferromagnetic material (5) over a length of 1 m. Also.

In the field where this magnetometer is mounted on an aircraft and used for detecting water ships, etc., the long magnetic sensing part of about 11 rL makes it susceptible to the magnetic noise of the aircraft, and it also measures the total magnetic force HQ. If the three axes are orthogonal to each other, the volume of the magnetically sensitive part will increase.

Measurement accuracy deteriorated and it was easily affected by magnetic noise from aircraft, making it difficult to put it into practical use.

[Summary of the invention]

In this invention, an optical fiber is bent and arranged a required odd number of times within the same plane corresponding to the X, Y, and Z axes, and a ferromagnetic material is coated or applied only to the straight portions of the optical fiber. While maintaining the high sensitivity of the fiber magnetometer, the volume of the magnetically sensitive area is reduced.

It is less susceptible to magnetic noise from aircraft, etc.

[Embodiments of the invention]

FIG. 2 is a configuration diagram of an optical fiber magnetometer showing an embodiment of the present invention, and (9) is a nonmagnetic plate.

α[ is a non-magnetic fastener, (lυ is an adder, α2 is an X-axis separator/
(13 is the center point YO of the Y-axis sensor
, a4) is the center point za of the two-axis sensor. Non-magnetic plate (9) and non-magnetic fastener (1G made of Teflon, for example.

The function is to fix the optical fibers (4) corresponding to each axis and the reference beam, respectively, on the same plane. (1) Although not shown, the center points of the senna of each axis (The origin of the x, y, and two axes mentioned above and the center point of the sensor of each axis Xo, Y.

In order to accurately match zO and zO, the optical fiber (4) is bent an odd number of times in each axis. In addition, in order to eliminate disturbances caused by changes in the direction of the external magnetic field, the portions of the optical fibers (4) on each axis where the ferromagnetic material (5) is coated or applied are placed on the surface of each non-magnetic grating (9). This is limited to only the straight part at the top. X-axis, Y-axis and 2 with phase detector (8)
The process of obtaining the signal of the axis sensor is the same as that explained in FIG. By selecting the reflectance of the mirror, the laser beam is distributed to the four optical fibers (4) with uniform light intensity. The adder U has a function of adding up the outputs of three phase detectors (8) corresponding to each axis and outputting the total magnetic force such as earth's magnetism as an output.

[Effects of the Invention] As described above, according to the present invention, an optical fiber magnetometer, which is originally a vector sensor, can be made into a total magnetic force measurement sensor with a small volume of the magnetically sensitive part while maintaining its sensitivity, and can be used in aircraft. When using it on a
It can be less affected by magnetic noise from aircraft.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional optical fiber magnetometer, and FIG. 2 is a block diagram showing an optical fiber magnetometer according to an embodiment of the present invention. (1)...Light source, (2)...Beam splitter, (
3)... Total reflection mirror, (41... Optical fiber, (5) - ferromagnetic material. (6)... Photodetector, (7)... Amplifier, (8)...
・・Phase detector, (9) ・・Nonmagnetic plate, (In
...Non-magnetic fastener, α-to...adder, (13...X
Center point of axis sensor, (13... center point of Y-axis sensor,
(14... Center point of the Z-axis sensor. In Figure 1, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] means for transmitting the light intensity from one light source to four optical fibers almost equally; means for bending and fixing each of the optical fibers a required odd number of times within the same plane; 3
means for coating or applying a ferromagnetic material with a predetermined thickness only on the straight portions of the optical fibers; means for making the three optical fibers orthogonal to each other; means for providing an optical fiber coated or not coated with a ferromagnetic substance, means for converting an optical signal passed through the four optical fibers into an electrical signal, and an optical fiber coated or not coated with a ferromagnetic substance. Using the electrical signal as a reference signal,
An optical device comprising means for phase-detecting the electric signals corresponding to the three orthogonal optical fibers, and means for synthesizing the three phase-detected signals, and measuring the total magnetic force of earth's magnetism or the like. Fiber magnetometer.