JPS6348003B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention combines block optical systems,
It constitutes a small and lightweight optical fiber gyroscope.

An optical fiber coil is a device that transmits monochromatic light clockwise or counterclockwise into an optical fiber loop made of multiple layers of optical fibers, detects the difference in phase, and determines the rotational angular velocity. be.

FIG. 2 shows a diagram of the optical system configuration of a conventional optical fiber gyroscope.

The coherent light emitted from the laser 31 is split into two beams by a beam splitter 32.

The two beams are incident on both ends of the optical fiber 34 by condenser lenses 33, 33. optical fiber 3
4 is wound many times into a loop shape.

Clockwise light (CW light) and counterclockwise light (CCW light) are clockwise light (CW light) and counterclockwise light (CCW light), respectively.
Pass through the loop counterclockwise.

Optical fiber 34 is a single mode fiber.

The transmitted light exits from the end face of the optical fiber 34, passes through the lenses 33, 33, is transmitted or reflected by the beam splitter 32, and reaches the photodetector 35.

If the optical fiber loop 35 is stationary, the optical paths of the CW light and the CCW light are strictly equal, so there is no phase difference between the two.

When the optical fiber loop 35 rotates at the rotational angular velocity Ω, the optical path lengths of the CW light and CCW light change, so
A phase difference Δθ appears.

If the total area of the optical fiber loop 35 is A, the wave number of the laser beam is k, the wavelength is λ, and the speed of light is c, then the phase difference Δθ is Δθ=4kAΩ/c (1) where k=2π/λ (2) Given.

The output of the photodetector is 2 of the sum of CW light and CCW light.
Proportional to the power. In other words, the photodetector output is proportional to cosΔθ. From the output value, the phase difference Δθ can be determined, and the angular velocity Ω of the optical fiber loop can be determined.

Conventionally, optical fiber coils have been constructed by combining separate optical systems as shown in FIG. The combination of individual optical systems had the following drawbacks.

Optical systems such as lasers, photodetectors, lenses, and optical fibers are fixed on a surface plate with a stand or in a casing using a suitable holder. No matter how fixed they are, the optical systems are spatially separated and are likely to change their positions relatively.

When the position of the optical system changes relative to another, the coupling efficiency between the optical fiber and other optical systems changes, causing the output of the photodetector to drift.

The area of the overlap between the CW light and the CCW light may vary on the surface of the photodetector.

This instability of the optical system causes the output of the photodetector to drift. It is difficult to distinguish between output drift due to optical system instability and output fluctuation due to cosΔθ.

Therefore, it is difficult to correctly detect an accurate phase difference.

The present invention aims to solve these drawbacks.

The optical fiber iron of the present invention consists of optical elements made up of blocks, which are joined together to create a compact, lightweight,
This realizes a highly reliable optical system.

Furthermore, an isolator is provided between the light emitting element and the block body to prevent light from returning to the light emitting element. Further, a polarizing beam splitter is provided between the light receiving element and the block.

Hereinafter, the configuration, operation, and effects of the present invention will be explained with reference to drawings showing examples.

FIG. 1 is a schematic plan view of an optical fiber coil according to the present invention.

The optical system is integrated.

Glass block 1 and glass block 2 are triangular prism-shaped transparent bodies. Each base is an isosceles right triangle, which are overlapped at the hypotenuses to form a square prism.

On the slope that forms the boundary between glass blocks 1 and 2,
For example, it is coated with metal such as Al or Ag, and has a transmittance of 50%.

The metal coating layer serves as a beam splitter 3 that transmits or reflects light. The beam splitter 3 is not an independent optical system, but is a coated surface of the glass block 1 or 2.

For example, after coating with metal by vapor deposition or sputtering, the glass blocks 1 and 2 are bonded on the slope.

On the side surfaces of the glass blocks 1 and 2, condensing lenses 6 and 7 are arranged at symmetrical positions with respect to the beam splitter 3.
is attached.

The condensing lenses 6 and 7 are cylindrical rod lenses having a square distribution of refractive index in the radial direction.

An isolator 13 and a polarizing beam splitter 14 are bonded to the sides of the glass blocks 1 and 2 facing the condensing lenses 6 and 7.

A light emitting element 4 is bonded onto the isolator 13 so as to be on an extension of the optical axis of the rod lens 6.

A light receiving element 5 is placed above the polarizing beam splitter 14 so as to be on an extension of the optical axis of the rod lens 7.
Glue.

The isolator 13 has a structure in which a Faraday element 10 is sandwiched between polarizing plates 11 and 12. A magnetic field is applied to the Faraday element 10 so that the Faraday rotation angle is 45°.

The polarizing plates 11 and 12 have their polarization directions twisted by 45 degrees.

The light emitted from the light emitting element 4 passes through the isolator 13 and enters the glass block 2. The beam splitter 3 separates the light into reflected light and transmitted light.

Each light passes through glass blocks 1 and 2,
Enter lenses 7 and 6.

light emitting element 4, light receiving element 5, isolator 13,
Polarizing beam splitter 14, condensing lenses 6, 7
is adhered to the glass blocks 1 and 2 using an adhesive that is optically homogeneous, has high transmittance, and has excellent environmental resistance.

For example, epoxy adhesive, balsam, etc. are used.

These optical elements and the glass block are integrated into a block shape.

The optical fiber 8 is formed by winding a long single mode fiber many times to form an optical fiber loop 9.

Both ends of the optical fiber 8 are connected to condensing lenses 6 and 7.

The operating principle of the fiber optic coil is similar to that shown in FIG.

The optical fiber coil according to the present invention has the conventionally separated optical system integrated into one block, and is provided with an isolator and a polarizing beam splitter, so that it has the following effects.

A light emitting element, a light receiving element, a beam splitter, a condensing lens, an isolator, a polarizing beam splitter, etc. are coupled through a glass block.

Fluctuations in the optical axis and distance cannot occur. It is highly reliable and produces less noise.

Since the isolator is placed in front of the light emitting element, there is no possibility of return light entering the light emitting element.

The light emitting element is a semiconductor laser that emits monochromatic light, a superluminescent diode, or the like. Operation is stable because the returned light does not enter the light emitting element.

The left-handed light and the right-handed light are made incident on the light receiving element through the polarizing beam splitter. When the plane of polarization of light propagating through the optical fiber varies randomly, this causes the output of the light receiving element to vary. Since the polarizing beam splitter passes only light with a fixed plane of polarization, it is possible to eliminate the influence of rotation of the plane of polarization.

The optical fiber gyroscope of the present invention is (1) Gyroscopes installed in automobiles, ships, and aircraft.

(2) It can be mounted on a moving object such as a robot and used as a position sensor to know its own position.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of an optical fiber coil according to the present invention. FIG. 2 is a plan view of a conventional optical fiber gyro. 1, 2... Glass block, 3... Beam splitter, 4... Light emitting element, 5... Light receiving element, 6,
7... Rod lens, 8... Optical fiber, 9...
Optical fiber loop, 10... Faraday element, 1
1, 12...Polarizing plate, 13...Isolator, 1
4...Polarizing beam splitter.

Claims (1)

[Claims] 1. Two glass blocks having a right-angled isosceles triangular base, whose slopes are coated with a thin film to form a beam splitter, and which are bonded to each other on the slopes;
A rod lens is glued at a symmetrical position with respect to the beam splitter of the glass block, an optical fiber loop whose both ends are connected to the rod lens and wound many times into a loop shape, and a rod lens is glued to the glass block at a position opposite to the rod lens. An optical fiber coil comprising an isolator, a polarizing beam splitter, a light emitting element bonded to the isolator, and a light receiving element bonded to the polarizing beam splitter.