JPS5951302A - Optical fiber loop of optical fiber gyroscope - Google Patents

Abstract

PURPOSE:To enhance the accuracy of an optical fiber gyroscope, by providing an optical fiber loop to the outer periphery of a transport mechanism such as an automobile or a vessel to widen the area of said loop. CONSTITUTION:An optical loop 3 is provided so as to surround the periphery of the roof 2 of an automobile 1 while an optical system and circuit part 4 is provided to one place in the car body so as to be spaced apart from the loop 3. In the case of a vessel, an optical fiber loop 7 is attached to the peripheral edge of a ship 6 so as to draw the loop with a wide area. In this case, the sensitivity to the speed of a rotary angle is proportional to the area of the optical fiber loop and, therefore, by widening the area of the optical fiber loop as mentioned above, the speed of the rotary angle can be detected in good sensitivity. As the result, the accuracy of an optical fiber gyroscope can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an optical fiber that increases the area of the optical fiber loop as much as possible and improves the detection limit of rotational angular velocity even if the optical fiber loop has a limited overall length. Concerning the gyro fiber optic loop.

FIG. 4 is a basic optical system configuration diagram showing the principle of an optical fiber gyro.

The light emitted from the light source 21 is split into two beams by a beam splitter 22. The two light beams are wound around each other, and the two light beams pass through the loop either clockwise (CW) or counterclockwise (CaW). The light flux that has passed through the loop passes through the lens 23 from the loop end, is combined again by the beam splitter 22, enters the photodetector 26, and is detected there.

When the optical fiber loop is rotating with an angular velocity Ω, Sa
Due to the GMC effect, a phase difference Δθ appears between clockwise and counterclockwise light.

The phase difference Δθ is given by 4 kANΩ Δθ: '□ (1). k is the wave number of light, A is the area of the optical fiber loop, C is the speed of light in vacuum, N is the number of turns of the optical fiber loop, and Ω is the rotational angular velocity of the loop.

Equation (1) does not include the refractive index or other physical constants of the material of the optical fiber at all. k is determined by the wavelength of light.

Conventionally, when assembling an optical fiber gyro as a device,
Generally, the optical system/circuit section and the optical fiber loop were housed in the same case.

FIG. 5 is an exploded perspective view of a conventional optical fiber gyro.

An optical fiber 125 wound in many layers is housed in a square case 27. An electronic circuit section 29 and an optical system 30 are housed in the space inside the optical fiber 125.

A lid 28 is fitted into the case 27 and is fixed. In this example, the box body including the case and lid is 200 x 20
0 tlM x 40 MM. The diameter of the optical fiber loose is 2001 RM or less.

Optical fiber gyros can be widely used to detect the direction of transportation vehicles such as automobiles, ships, and aircraft, and of various moving bodies.

However, when the angular velocity Ω to be detected is small, a sufficient phase difference does not occur, so it is difficult to accurately detect Δθ. The sensitivity was poor.

In order to increase the sensitivity, it is sufficient to increase the proportionality constant for Ω in equation (1). All you have to do is increase the product AND.

As the number of turns N increases, the sensitivity improves in proportion to the number of turns. The total length of the optical fiber is proportional to the number of turns N, assuming the loop diameter is constant. Therefore, in the method of increasing the number of turns, the length of the optical fiber and the sensitivity are directly proportional.

However, increasing the total length of the optical fiber requires a large amount of optical fiber, which increases costs.

On the other hand, the area Ai may be increased. If the number of turns N is constant and the area A is multiplied by m, the total length of the required optical fiber becomes /W times. In order to increase the sensitivity by a factor of m, the total length of the optical fiber need only be increased by a factor of Jl.

Let R be the radius of the optical fiber loose.

The area A of the loop is A = πR2 (2) The total length of the fiber is L = NX2πR (3) Therefore, the product AN is given by L AN ==: - (4). Assuming that the total length is constant, the sensitivity of the fiber optic gyro is directly proportional to the radius H of the loop. (
4) That is the meaning of the expression.

Furthermore, for fiber optic gyros with the same sensitivity, the product of radius R and total length is constant.

In order to increase the sensitivity of the optical fiber gyro, it is effective to increase the radius of the loop. If the total length is fixed, multiplying the loop radius by m reduces the number of turns to 17 m. Since the area is multiplied by m2, the product of the number of turns N and the area A is multiplied by m.

The present invention was made based on such an idea, and is characterized in that the optical fiber loop is widely installed around the outer periphery of the intended transportation vehicle to increase the loop area.

Rather than housing the optical fiber loop along with the optical system and circuit section in a small box, the optical fiber loop and the optical system/circuit section are separated, and the optical fiber loop is installed around the periphery of a car, ship, or aircraft. .

FIG. 1 is a perspective view of an automobile equipped with an optical fiber loop of an optical fiber gyro according to an embodiment of the present invention.

In FIG. 1, an optical fiber loop 3 is installed around the roof 2 of an automobile 1. Optical system/circuit section 4
is provided at a location within the vehicle body, apart from the optical fiber loop 3. The rotational angular velocity Ω or a parameter determined by Ω can also be displayed on the display unit 5.

FIG. 2 is a schematic diagram showing an example of a ship. An optical fiber loop 17 is attached to the periphery of the ship 6 in a wide area loop.

In addition, in the case of aircraft, it is also possible to
The area A of the optical fiber loose is made as large as possible.

Figure 8 shows the sensitivity of the optical fiber gyro as a parameter.
It is a graph showing the relationship between fiber loop radius R and fiber length.

The horizontal axis is the loop radius (Crn), and the vertical axis is the total length (m) of the optical fiber.

Equation (1) is It can be rewritten as

Let me give you a conventional example.

L=385m, R=0.1m, C=8X108
n7s,.

When S=8×10 m, we obtain the following formula: Δθ=20 (6). A factor of 2 gives the sensitivity K. The detection limit of Δθ was Q, 3 deg in this example. Then, the limit of Ω becomes Q, 15 deg/sec.

To get the same sensitivity = 2, L R = 88.5
It is sufficient if it is m2. This is what the inverse proportion graph at the bottom of Figure 3 means.

If R = 1 m, L = 88.5 m would be sufficient.

A case where the detection limit of Δθ is Q, 6 degrees is also illustrated.

In this case, the graph is inversely proportional to LR=77m2.

If R = 0.1m as in the conventional example, L = 770
m optical fibers are required. For example, if R=1 m as in the present invention, L=77 m is sufficient.

The optical fiber (optical fiber) of the optical fiber gyro of the present invention is installed on the outer periphery of a transportation vehicle such as a car, a ship, or an aircraft so as to surround a wide area, so even if the optical fiber is short, it can be used with high sensitivity and rotational angular velocity. Ω can be detected. Can improve the accuracy of fiber optic gyro,
This is a useful invention.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing an example in which the present invention is applied to an automobile. FIG. 2 is a schematic perspective view showing an example in which the present invention is implemented on a ship. FIG. 3 is a graph illustrating the length of the optical fiber loop L required to obtain the same sensitivity as a function of the loop radius H. At wavelength λ = 800 nm, the detection limit of Δθ is Q,
3 deg, Ω detection limit is 0.15 deg, L R
= 38.5 m2 (7) is also O (A), the detection limit of 80 is Q, 6 deg, the detection limit of Ω is 0.15 deg
, L R = 77 m2 (B). FIG. 4 is a diagram showing the basic optical system configuration of a conventional example of an optical fiber cable. FIG. 5 is an exploded perspective view showing a specific example of a conventional optical fiber gyro. 1 ・・・・・・・・・ Automobile 2
・・・・・・・・・ Roof 3 ・
・・・・・・・・・ Optical fiber loop 4 ・・・・・・
... Optical system/circuit section 5 ......
Display section 6... Ship 7 ...... Optical fiber loop invention
Person Yoshi 1) Ken --4 Kono゛
Public, □ 3 - Yu Nishiwaki Hiroshi Kazu - Figure 1 Figure 2 Figure 4 Figure 5 Continued from page 1 0 Inventor Hiroshi Tsuno - 1-1-3 Shimaya, Konohana-ku, Osaka 9-

Claims (1)

[Claims] An optical fiber loop wound with a single-mode optical fiber, a beam splitter that splits the light into two beams, or a beam splitter that combines the two beams that have been split and passed through the optical fiber, and the intensity of the combined light. In optical fiber gyros, which are similar to photodetectors for detecting