JPH0633367Y2 - Light fiber gyro - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical fiber gyroscope for measuring the rotational angular velocity of a moving body, and more specifically, it is a cause of deterioration of the sensitivity of the detected angular velocity. The present invention relates to an optical fiber gyro in which the influence of reflected light on the exit surface of the optical branching optical element is reduced.

2. Description of the Related Art Currently, a gyro is used as an angular velocity sensor for navigation and attitude control of aircrafts, flying vehicles, automobiles, robots and the like. If this gyro is used, not only the angular velocity but also the data such as the azimuth can be obtained by integrating it.

Among such gyros, the optical fiber gyro can be used in any environment without the problem of shielding because the light and the optical fiber through which the light propagates are not easily affected by the magnetic field or the electric field. It is completely compact and can be downsized, and is superior to conventional gyros in terms of minimum detectable angular velocity (sensitivity), drift, measurable range (dynamic range), and stability of scale factor. Therefore, it has been noticed and developed in recent years.

Examples of such fiber optic gyros are, for example, Gallorange. Gee. , Bukalogger. A. Other "Optical Fiber Sensor Technology" IE Journal of Quantum Electronics (Giallorenz
i TG, Bucaro JA et al “Optical Fiber Sensor Tech
nology ", IEEE J. of Quantum Electronics) QE-18, NO.
4, PP626-662 (1982) and krasho and eye. Pee. Gilles "Optical Fiber Gyroscope" Journal of Physics Electronics Science Instruments (Culshaw and IPGiles “Fiber Optic Gyros
copes "J.Phys.E: Sci Instrum.) 16 pp5-15, (1983)
Tsubokawa and Otsuka “Optical Fiber Gyroscope” Laser Research, 11 , NO.12, pp889-902 (1983).

Here, the principle of the optical fiber gyro will be described with reference to FIG.

The light from the light emitting element 1 is split by the beam splitter 2 and is input to both ends of an optical fiber loop, that is, a sensor coil 5 in which a single mode optical fiber 4 is wound in a coil shape many times, that is, a clockwise rotation to the sensor coil 5 ( Propagate light in CW) and counterclockwise (CCW). At that time, the sensor coil 5
Is rotating at an angular velocity Ω, a phase difference Δθ occurs between clockwise light and counterclockwise light, and the angular velocity Ω is measured by measuring Δθ.
Is to detect.

Strength E _cw electric field of light propagated in the optical and counterclockwise propagated clockwise through the sensor coil 5, E _ccw is expressed as follows.

However, E _r , E _L : amplitude of left-handed light and right-handed light ω: angular frequency of light t: time Δθ: phase difference due to Sagnac effect Left-handed light and right-handed light having such a phase difference Δθ Are combined by the beam splitter 2 and are incident on the light receiving element 3. The phase difference Δθ can be known from the detected intensity of the light receiving element 3. The phase difference Δθ can be expressed as follows.

However, L: Fiber length of sensor coil a: Radius of sensor coil c: Light velocity in vacuum λ: Wavelength of light Ω: Angular velocity of rotation This is called the Sannyak effect.

Problems to be Solved by the Invention In the above-described optical fiber, the beam splitter 2 forming the optical element for optical branching has a right-angled isosceles triangular cross-section that is superposed so that a semi-reflective surface is formed therebetween. It is composed of two prisms in the form of. In addition to the light propagating counterclockwise and clockwise in the sensor coil 5, the light detected by the light receiving element 3 enters the beam splitter 2 from the light emitting element 1, passes through the semi-reflective surface 6, and exits from the emitting end surface. Light reflected by A, further reflected by the semi-reflecting surface 6 and incident on the light receiving element 3, and light incident on the beam splitter 2 from the light receiving element 1, reflected by the semi-reflective surface 6, reflected by the emitting end surface B, and further Light that passes through the semi-reflective surface 6 and enters the light receiving element 3 is included. The reflected lights are noise lights for measurement, and when they interfere with each other and are detected by the light receiving element 3, the combined light amount slightly changes due to a slight change in the optical path, so that the sensitivity of angular velocity detection is high. to degrade.

Therefore, an object of the present invention is to provide an optical fiber gyro that eliminates such drawbacks and realizes highly sensitive angular velocity detection.

Means for Solving the Problems That is, according to the present invention, an optical element for branching and multiplexing incident light and a sensor coil portion formed by winding a part of a plurality of times are included. One optical fiber having a pair of two end faces, a light emitting element for generating light to be injected into both ends of the optical fiber via the optical element, and a light beam emitted from both ends after propagating through the optical fiber. A light receiving element for receiving light via the optical element, and further, an optical path length from the light branch point of the optical element to the emission end surface of the optical element with respect to the first end surface, and the optical branch point from the light branch point to the first end surface. In an optical fiber gyro configured such that the optical path lengths from the two end faces to the emission end face of the optical element are different from each other, the optical element includes a semi-reflecting surface that branches or combines incident light, and Right angle to the reflective surface Provided is an optical fiber gyro characterized by being configured by a prism beam splitter having a rectangular cross-sectional shape by a flat surface.

In the optical fiber gyro having the above-described structure, the branching optical element causes the optical path difference between the optical path to the exit end face of one of the optical fibers and the optical path to the exit end face of the other optical fiber. There is. Therefore, the optical path length from the light emitting element entering the branching optical element to the light that becomes the branched light to one end of the optical fiber is reflected by the end face of the branching optical element and returns to enter the light receiving element. And the optical path length from the light emitting element entering the branching optical element to the light that becomes the branched light to the other end of the optical fiber is reflected by the end surface of the branching optical element and returns to enter the light receiving element. There can be a difference. Therefore, the phases of both reflected lights, which become noise, are sufficiently separated, and the interference can be reduced. Therefore, the combined light amount of the noise light detected by the light receiving element becomes a constant value, and the influence on the detection sensitivity can be reduced, so that the sensitivity of the optical fiber gyro can be increased.

Embodiment An embodiment of the optical fiber gyro according to the present invention will be described below with reference to FIG. The parts in the embodiment of FIG. 1 corresponding to the parts of the conventional optical fiber gyro shown in FIG. 2 are designated by the same reference numerals.

The optical fiber gyro shown in FIG. 1 is composed of two prisms stacked as a beam splitter 2A for splitting the light from the light emitting element 1 so that a semi-reflecting surface is formed therebetween. As shown in FIG. 1, is a rectangular parallelepiped shape in which the cross section of the plane including the incident light and the branched light and perpendicular to the branching semi-reflecting surface is rectangular.

The light split by such a beam splitter 2A is input to both ends of a sensor coil 5 composed of an optical fiber formed by winding a single mode optical fiber 4 in a coil shape many times, and the sensor coil 5 is rotated clockwise ( Propagate to CW) and counterclockwise (CCW).

Then, the light emitted from both ends of the sensor coil 5 is again combined with the beam splitter 2A to be combined, and the light receiving element 3
Incident on.

In such an optical fiber gyro, since the beam splitter 2A is a rectangular parallelepiped, it enters the beam splitter 2A from the light emitting element 1 and enters the semi-reflecting surface 6, that is, the branch point O.
Noise light which is transmitted through and is reflected by the end face A ′, further reflected by the semi-reflective surface 6 and incident on the light receiving element 3, and the light beam incident from the light emitting element 1 on the beam splitter 2A at the semi-reflective surface 6, that is, the branch point O A large optical path difference is generated between the reflected light, the reflected light at the end face B ′, the transmitted light through the semi-reflective surface, and the incident noise light on the light receiving element 3. In general, the spectrum width of a semiconductor laser used as a light source of an optical fiber gyro is about 0.2 nm, so the coherence length is about 3 mm. Therefore, the optical path difference of the light reflected by the end faces A'and B ', that is, twice the distance between the branch point O and the end face A'and twice the distance between the branch point O and the end face B'. If the shape of the rectangular parallelepiped is such that the difference is 3 mm or more, they do not interfere with each other, the combined light quantity of the noise light detected by the light receiving element 3 becomes a constant value, and the detection sensitivity is not significantly affected.

The shape of the beam splitter 2A does not necessarily have to be a rectangular parallelepiped, and may be any shape as long as the distance from the branch point O to the emitting end surface differs on the transmission side and the opposite side.

Effect of the Invention As is apparent from the above description, in the optical fiber gyro according to the present invention, the optical element that branches the light to both ends of the sensor coil has a sufficient optical path difference in the optical path from the branch point to the two emission end faces. Since the noise lights reflected by the exit end faces of the branching optical elements do not interfere with each other, even if they are detected by the light receiver, they only give a certain amount of light and do not become noise. Therefore, a highly sensitive optical fiber gyro can be obtained.

[Brief description of drawings]

 FIG. 1 is an explanatory diagram of an optical fiber gyro to which the present invention is applied, and FIG. 2 is a principle diagram of a conventional optical fiber gyro. (Main reference numbers) 1 ... Light source, 2, 2A ... Beam splitter, 3 ... Photodetector, 4 ... Optical fiber, 5 ... Sensor coil

Claims (1)

[Scope of utility model registration request] Claim: What is claimed is: 1. An optical element for branching and multiplexing incident light, and a single coil having a pair of first and second end faces including a sensor coil portion formed by winding a part of the light multiple times. An optical fiber, a light emitting element that generates light to be injected into both ends of the optical fiber through the optical element, and a light receiving element that receives light emitted from both ends after propagating through the optical fiber through the optical element An optical path length from the light branch point in the optical element to the exit end surface of the optical element with respect to the first end face, and an optical path length from the light branch point to the exit end surface of the optical element with respect to the second end face. Are configured to be different from each other, and when the sensor coil portion is rotated, the first propagating light that is incident from the first end face and is emitted from the second end face, and the second
In an optical fiber gyro that detects the rotational angular velocity of the sensor coil from the phase difference generated between the second propagating light that enters from the end face and exits from the first end face, the optical element branches or combines the incident light. An optical fiber gyro, which is a prism beam splitter having a corrugated semi-reflective surface and having a rectangular cross-section due to a surface perpendicular to the semi-reflective surface.