JPS6348283B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention has high sensitivity and high S/N characteristics.
This invention relates to a block version of a modulation detection type optical fiber coil.

An optical fiber gyro is a device that detects the rotational angular velocity of a rotating body.

FIG. 4 is a plan view showing the basic structure of the optical fiber gyroscope.

The coherent light emitted from the laser 51 is split into two beams by a beam splitter 52, and passes through condensing lenses 53, 53 into an optical fiber loop 54.
incident on both ends of. The two light beams pass through the optical fiber loop 54 clockwise (or clockwise CW) or counterclockwise (or counterclockwise CCW), and exit from the other end. Optical fiber loop 54
is a single mode fiber, which is wound multiple times.

The two beams of light emitted from the optical fiber loop pass through condensing lenses 53, 53, and enter beam splitter 5.
2 and enters the photodetector 55.

Clockwise light (CW) and counterclockwise light (CCW)
The optical paths are equal. If the optical fiber loop 54 is rotating at an angular velocity Ω, a phase difference Δφ will appear between the CW light and the CCW light. Δφ is given by Δφ=8πAΩ/λC (1). C is the speed of light, λ is the wavelength of the laser beam,
A is the total area encompassed by the optical fiber loop.

The amplitude of CW light and CCW light are equal, and the phase difference is Δφ
, the photodetector 55 detects 2 of the sum of both.
Since it produces an output proportional to the power, the output I(t) is
It is given by the proportional expression I(t)∝E ₀ ² (1+cosΔφ) (2). E ₀ is CCW, CW light vibration.

Such an optical fiber gyroscope has poor sensitivity in a low angle region, that is, when Δφ is small. (1+
This is because the output changes depending on cos(Δφ)).

Furthermore, there is a drawback. Since level changes of DC components are detected, the S/N ratio is low.

FIG. 5 is a plan view of another conventional optical fiber gyroscope. In order to solve the above-mentioned difficulties, this method separates part of the optical path and modulates the amplitude of one of the lights.

An amplitude modulation element 56 is added to the optical path of clockwise light.

To separate clockwise light and counterclockwise light,
Beam splitters 57, 58, and 59 are newly added, and the beam splitters 52, 57, 58, and 59 are arranged so as to form a rectangle.

The clockwise light is amplitude modulated, focused by a condensing lens 53, enters an optical fiber loop 54, passes through the loop, passes through the condensing lens 53, and is separated by a beam splitter 58. Enter the light path. A phase shifter 6 is installed in the separated optical path.
0 is set. This provides a phase difference of π/2.

The wave of clockwise light can be written as E ₀ (1+msinω _n t)e ⁱ⁽ 〓 ^t+ 〓〓 ⁾⁺ⁱ 〓 ^/2 (3).

Counterclockwise light can be written as E ₀ e ⁱ 〓 ^t (4).

Since the output I(t) of the photodetector is the square of the sum of (3) and (4), it consists of a DC component, a frequency ω _n component, and a frequency 2ω _n component.

If we extract only the component whose frequency is ω _n , we get
This is I(t)=2mE ₀ ² (1−sinΔφ)sinω _n t (5). By extracting the ω _n component, it is possible to know the phase difference Δφ and detect the angular frequency Ω.

In such a conventional optical fiber coil, the laser, beam splitter, and lens are made up of separate devices and members. It is difficult to always align the optical axes and keep the distance relationship constant.

Optical system instability can cause the photodetector output to drift.

When the relative positions of the laser, beam splitter, condensing lens, and optical fiber vary, the coupling efficiency between the optical fiber and other optical systems varies, causing the output of the photodetector to drift.

Furthermore, the overlapping area of the clockwise light and the counterclockwise light may vary on the surface of the photodetector, which may cause the output of the photodetector to vary.

These drawbacks are due to the fact that the relative positions of the optical systems are not firmly fixed.

The present invention provides a modulation type optical fiber coil.
An optical fiber iron made by combining glass blocks with improved stability of the optical system is provided.

Hereinafter, the present invention will be explained with reference to drawings showing examples.

FIG. 1 is a perspective view of a block optical system of an optical fiber coil according to an embodiment of the present invention.

1st glass block 1 to 10th glass block 1
0's are combined to form a U-shaped block.

The glass blocks have a triangular or quadrangular prism shape and are bonded together using an optically uniform adhesive with good transmittance, such as epoxy resin adhesive or balsam.

First glass block 1 and second glass block 2
is a triangular prism whose base is a right-angled isosceles triangle. The slope is coated with a thin film of metal (Ag, Al, etc.) so that the light transmittance and reflectance are 50% each. This metal thin film functions as a beam splitter 11.

On the side of the second glass block 2, fused quartz,
An ultrasonic propagation medium 12 such as LiNbO ₃ or YAG is bonded. The propagation medium 12 is a rectangular parallelepiped-shaped transparent body, and an amplitude modulation element 16 consisting of an electrode 13, an ultrasonic transducer 14, and an electrode 15 is fixed to the upper surface of the propagation medium 12.

A modulated voltage of frequency ω _n is applied from the power source 17 to the electrode 1
It is applied between 3 and 15.

The ultrasonic transducer 14 uses a piezoelectric effect to generate ultrasonic waves. For example, crystal, barium titanate, PZT, Bi ₁₂ SiO ₂₀ , etc. are used as the ultrasonic transducer.

The ultrasonic wave having a frequency of ω _n generated by the ultrasonic transducer travels through the propagation medium 12 from top to bottom, reaches the ultrasonic absorber 18, and is absorbed therein.

The propagation medium 12 has an acousto-optic effect. A periodic change in refractive index occurs in the propagation medium in the direction of the ultrasound. Light traveling perpendicularly to the direction of propagation of the ultrasonic wave is diffracted due to periodic changes in the refractive index. The direction of diffraction oscillates up and down with ω _n . Therefore, the intensity of light is subjected to amplitude modulation of frequency ω _n .

The amplitude modulation element 16 consisting of the propagation medium 12, the electrode 13, the ultrasonic transducer 14, and the electrode 15 is an acousto-optic modulation element.

Next to the first glass block 1, a third glass block 3 is attached at a position symmetrical to the amplitude modulation element 16 with respect to the beam splitter 11.
The third glass block 3 is a rectangular parallelepiped.

A fourth glass block 4 in the form of an isosceles right triangular prism is attached to the other end surface of the third glass block 3.

The fifth glass block 5 is in the shape of an isosceles right triangular prism, and is bonded to the slope of the fourth glass block 4 to form a square prism.

Fourth glass block 4, fifth glass block 5
A beam splitter 19 coated with a metal thin film (Ag, Al, etc.) in advance is provided on the adhesive surface of the beam splitter 19 .

Fourth glass block 4, fifth glass block 5
On the other hand, a sixth glass block 6 at a diagonal position,
Similarly, the seventh glass block 7 is an isosceles right triangular prism. Similarly, the beam splitter 20 coated with a metal thin film is provided on a 45° slope.

The surface of the sixth glass block 6 is bonded to the surface of the propagation medium 12, and the glass blocks 1 and 2, the propagation medium 12, and the glass blocks 6 and 7 are aligned on the same straight line.

There is a space between the seventh glass block 7 and the eighth glass block 8, and the phase plate 21 is located between the eighth glass block 7 and the eighth glass block 8.
It is glued to the front surface of the glass block 8. The phase plate 21 shifts the phase of light by π/2.

The eighth and ninth glass blocks 8 and 9 are isosceles right triangular prisms, and a beam splitter 22 is provided on the slope, and the glass blocks 8 and 9 are bonded to each other on the slope.

Fifth glass block 5 and ninth glass block 9
and are connected by a tenth glass block 10.

The four beam splitters 11 are arranged radially from the center of the glass block group.

One end surface of a collimating lens 23 is adhered to the side surface of the first glass block 1.

The collimating lens 23 has a cylindrical shape and is a gradient index lens whose refractive index changes continuously in the radial direction.

A laser diode 24 is attached to the other end surface of the collimator lens 23. The collimating lens 23 converts the light from the laser diode 24 into parallel light.

The light emitted from the collimating lens 23 is reflected by the beam splitter 11 and travels straight to the third glass block 3, fourth glass block 4, and fifth glass block 5. One end of a collimating lens 25 is bonded to the fifth glass block 5 at the position of the optical axis.

A portion of the light emitted from the collimating lens 23 passes through the beam splitter 11 and travels straight to the second glass block 2, the propagation medium 12, the 16th glass block 6, and the seventh glass block 7. A collimating lens 26 is bonded to the end face of the seventh glass block 7 on the axis of this light.

Optical fibers 27 at both ends of the optical fiber loop are fixed to the collimating lenses 25 and 26.
The optical fiber 27 is a single mode fiber consisting of a core and a cladding. Collimating lens 2
5 and 26, the parallel laser light is focused and irradiated onto the end face of the optical fiber 27.

A photodiode 28 as a photodetector is attached to the end face of the ninth glass block 9.

The operation of the above configuration will be explained.

The coherent light excited by the laser diode 24 enters the first glass block 1.

In the beam splitter 11, the laser beam is split into two beams.

The reflected light passes through the third glass block 3 and the fourth glass block.
Proceed to glass block 4 and fifth glass block 5. The collimating lens 23 converts the laser beam into parallel light. It passes through the collimating lens 25 attached to the fifth glass block 5 and is focused here.
The light enters the optical fiber 27. This light flux rotates clockwise in the loop of the optical fiber 27 and returns to the seventh glass block 7 from the collimating lens 26 on the opposite side.

The clockwise light is reflected by the beam splitter 20, exits into space, passes through the phase plate 21, enters the glass blocks 8 and 9, and is detected by the photodiode 28. When passing through the phase plate 21, the phase shifts by π/2.

On the other hand, the light that exits the laser diode 24 and goes straight through the beam splitter 11 passes through the second glass block 2 and the propagation medium 12 of the amplitude modulation element 16. The propagation direction of ultrasonic waves and the traveling direction of light are orthogonal. Since the propagation medium 12 has an acousto-optic effect, its refractive index changes periodically and the laser beam is diffracted. The diffraction angle oscillates up and down at the angular frequency ω _n of the ultrasonic wave.

The diffracted light passes through the sixth glass block 6, the beam splitter 20, and the seventh glass block 7, and enters the optical fiber 27 from the collimating lens 26. Since the laser beam is diffracted, the amount of light entering the collimating lens 26 will oscillate by ω _n , and the light entering the optical fiber 27 will undergo amplitude modulation (1+msinω _n t) (6) become.

The modulated light passes counterclockwise through the optical fiber 27, reaches the collimating lens 25, and enters the fifth glass block 5. This light is reflected by the beam splitter 19 and passes through the tenth glass block 1.
0, passes through the ninth glass block 9, is reflected by the beam splitter 22, and enters the photodiode 28.

If the loop of the optical fiber 27 is rotating at an angular velocity Ω, a phase difference Δφ of equation (1) will occur.

The fact that the phase is shifted by π/2 by the phase plate 21, that the amplitude is modulated, and that the ω _n component of the output is ideally expressed by equation (5) is shown in Fig. 6. It is no different from the optical fiber.

The optical fiber iron of the present invention is characterized in that the optical system is integrated into a block and a modulation method is used. The type of modulation and modulation method are arbitrary.

FIG. 2 is a perspective view showing an embodiment using a light modulation element utilizing the electro-optic effect.

This also applies amplitude modulation to one of the lights and extracts only the component of the modulation frequency ω _n .

The amplitude modulation element 30 has an electro-optic material 31 sandwiched between a polarizer 32 and an analyzer 33. Electrodes are provided on the upper and lower surfaces of the electro-optic material 31, and a modulation voltage is applied by a power source 34.

Electro-optic materials include Bi ₁₂ SiO ₂₀ ,
Crystals such as Bi ₁₂ GeO ₂₀ and LiNbO ₃ can be used.

The laser beam becomes linearly polarized light by the polarizer 32, but the plane of polarization rotates in proportion to the modulation voltage. Since this light passes through the analyzer 33, the rotation angle of the plane of polarization is converted into amplitude. In other words, the electro-optic material, polarizer, and analyzer function as an amplitude modulation element.

If the analyzer 33 is omitted, it functions as a phase modulation element.

Furthermore, a magneto-optic effect may be used.

FIG. 3 is a perspective view of an embodiment including an optical modulator using the magneto-optic effect.

The amplitude modulator 35 has a coil 37 wound around a magneto-optical material 36, an alternating current is caused to flow by a power source 38, and a polarizer 39 and an analyzer 40 are provided on both sides.

YIG crystal, GGG crystal, etc. can be used as the magneto-optical material.

When coil 37 is energized, a magnetic field is generated within magneto-optic material 36 . The plane of polarization of the light that passes through the polarizer 39 and becomes linearly polarized light is rotated by the magneto-optic effect. Since the light passes through the analyzer 40 in this state, the amplitude decreases in accordance with the polarization plane rotation. Therefore, these as a whole function as an optical amplitude modulator.

As explained in detail above, the optical fiber coil of the present invention consists of glass blocks bonded together to form an optical path and a beam splitter, and a collimating lens, laser diode, photodiode, etc.
directly or indirectly adheres to the glass block,
Furthermore, the optical paths of clockwise light and counterclockwise light are separated, and a modulator is provided on either one.

Since it does not use a separate optical system and is made into a block, it is small and lightweight, making it convenient to handle. There is no need for alignment or adjustment.

The relative distance of the optical system and the relative position of the axes do not change. Therefore, it becomes a highly reliable measuring instrument.

Furthermore, since a modulated optical signal is used, the S/N is also high.

The optical fiber gyroscope of the present invention is most suitable as a gyroscope to be mounted on a moving object such as an automobile, a ship, an aircraft, a robot, etc., especially a moving object with large external vibrations.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an optical fiber coil according to an embodiment in which an amplitude modulator utilizing an acousto-optic effect is provided. FIG. 2 is a perspective view of an optical fiber gyro according to a second embodiment, which is provided with an amplitude modulator that utilizes the electro-optic effect. FIG. 3 is a perspective view of an optical fiber gyro according to a third embodiment, which is provided with an amplitude modulator that utilizes the magneto-optic effect. FIG. 4 is a diagram showing the basic optical system configuration of a conventional optical fiber coil. FIG. 5 is an optical system configuration diagram of a conventional modulation type optical fiber gyro. 1 to 10... Glass block, 11... Beam splitter, 12... Propagation medium, 13, 15...
Electrode, 14... Ultrasonic transducer, 16...
... Amplitude modulation element, 17 ... Power supply, 18 ... Ultrasonic absorber, 19, 20 ... Beam splitter, 21
...Phase plate, 22...Beam splitter, 23...
...Collimating lens, 24... Laser diode, 25... Collimating lens, 26... Collimating lens, 27... Optical fiber, 28... Photodiode, 30... Amplitude modulator, 31... Electro-optic material, 32... Polarizer, 33...Analyzer, 3
4... Power source, 35... Amplitude modulator, 36... Magneto-optical material, 37... Coil, 38... Power source, 39
... polarizer, 40 ... analyzer, 41 ... frequency shift modulator, 42 ... propagation medium, 43 ... ultrasonic transducer, 44 ... ultrasonic absorber.

Claims (1)

[Scope of Claims] 1. Beam splitters 11, 20, 19, 22 were made by coating a thin film on the hypotenuse surface of a transparent glass block in the form of a right-angled isosceles triangular prism and bonding the same.
A glass block 3 consists of two square prism-shaped glass blocks, these glass blocks are arranged at the four corners so that the beam splitters are lined up diagonally, and they are bonded together to form a square block body. ,10,21,12,...
and a light emitting element 4 which is attached directly to the side surface of the glass block constituting the first beam splitter 11 or through a collimating lens and which produces monochromatic light.
, a collimating lens 26 affixed to the side surface of a glass block constituting the second beam splitter 20 on the extension of the optical axis of the light emitting element 4, and a first
A third beam splitter 19 is located at a position symmetrical to the collimating lens 26 with respect to the beam splitter 11.
The fourth beam splitter 22 is composed of a collimating lens 25 affixed to the side surface of the glass block constituting the beam splitter, and an optical fiber 27 wound in a loop shape and having both ends connected to the collimating lenses 25 and 26. The side surface of the glass block where the light emitted from the collimating lenses 26 and 25 is reflected by the second and third beam splitters 20 and 19, and is incident after being reflected or transmitted by the fourth beam splitter 22. A light-receiving element 28 attached directly or through a collimating lens, and an amplitude modulator installed in a portion of the glass block forming a square optical path that allows only clockwise light or counterclockwise light to pass through. Optical fiber gyro that is characterized by 2 The ultrasound transducer is bonded to the propagation medium in which the amplitude modulator has an acousto-optic effect, so that the ultrasound propagates at right angles to the propagation direction of the light, and the intensity of the 0th order diffracted light is The optical fiber gyroscope according to claim 1, characterized in that the optical fiber gyroscope is an amplitude modulator adapted to perform modulation at a modulation frequency of . 3 The amplitude modulator is an electro-optic material with a polarizer and an analyzer glued to both sides, and the electro-optic material is provided with electrodes, and by applying a modulation voltage to the electrodes, linearly polarized light is transmitted through the electro-optic material. 2. The optical fiber gyro according to claim 1, wherein the optical fiber gyro is an amplitude modulator that modulates the intensity of light by rotating the plane of polarization of the light and passing it through an analyzer. 4 The amplitude modulator is a magneto-optical material with a coil wound around it, with a polarizer and an analyzer glued to both sides, and by passing a modulation current through the coil, the plane of polarization of linearly polarized light transmitted through the magneto-optic material can be changed. The optical fiber gyro according to claim 1, characterized in that it is an amplitude modulator that modulates the intensity of light by rotating it and passing it through an analyzer.