JPH0126197B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention rotates and advances two almost monochromatic laser beams in opposite directions by sequentially reflecting them by a plurality of reflecting mirrors to form an annular optical path. The present invention relates to a laser angular velocity sensor that detects an input angular velocity by detecting an oscillation frequency difference, and particularly relates to a sensor that reduces lock-in errors.

<Prior art> In this type of laser angular velocity sensor, when the difference in oscillation frequency between two laser beams is small, both light beams have the same frequency due to a lock-in phenomenon. To solve this problem, a typical conventional method is to mechanically swing the entire laser angular velocity sensor around an axis perpendicular to the annular optical path to shorten the time it stays in the lock-in region and further reduce random noise. This method randomizes the effect of the lock-in during the period in which the oscillations are superimposed and reversed. Although there are other examples in which direct frequency separation is performed using a Faraday element, it is the method described above that has produced a laser gyro of a practical level. However, this method uses crystallized glass with a side of 10
Since the entire block, which is approximately 2.5 cm long and 2.5 cm thick, is oscillated, it becomes a source of large vibrations for the entire system, and when applied to an inertial navigation system, eliminating and reducing this vibration is a design issue. It's summery. Further, the driving power of this rocking device accounts for a large portion of the power consumption, which is disadvantageous when it is mounted on a rocket, for example.

<Summary of the Invention> An object of the present invention is to provide a laser angular velocity sensor that does not cause the entire sensor to swing, therefore does not generate large vibrations, and has low power consumption.

According to this invention, means is provided for vibrating the angle of one of the reflecting mirrors around an axis that passes through the reflection point and is perpendicular to the optical path, so that the optical path is shifted from the input axis by vibrations having a predetermined amplitude and frequency. The lock-in error is reduced. The plurality of reflecting mirrors constituting the annular optical path are composed of one plane mirror and a plurality of concave mirrors, or all of them are composed of concave mirrors having a radius of curvature sufficiently longer than the optical path length; in the former case, the plane mirror is The angle can be changed.

<Example> FIG. 1 shows an example of a laser angular velocity sensor according to the present invention. Passages 12, 13, 14 forming each side of a substantially equilateral triangle within the crystallized glass block 11
is formed, and the passages 12, 13, and 14 are made into one continuous discharge space. Reflecting mirrors 15, 16, 17 are arranged at each intersection of the passages 12, 13, 14, that is, at each vertex of the equilateral triangle. Passage 12,1
An anode 18, 19 is provided at each intermediate position of the passageway 13, and a cathode 21 is provided at an intermediate portion of the passageway 13. A laser medium such as helium or neon is sealed in the discharge space, and a laser discharge is performed between the anodes 18 and 19 and the cathode 21, and the laser beam is reflected by the reflecting mirror 1.
The circular optical path is sequentially reflected by mirrors 5, 16, and 17, and the circular optical path is sequentially reflected by reflecting mirrors 15, 17, and 16. In other words, the triangular optical path 22
Two laser beams are generated that travel clockwise and counterclockwise. When the angular velocity Ω around the axis 23 passing perpendicularly through the center of the optical path 22 is input, a difference occurs in the frequencies of the two laser beams traveling in opposite directions, and the difference in frequency between the two laser beams is detected. The input angular velocity Ω is thereby measured. That is, for example, a part of the two laser beams is taken out from a part of one reflecting mirror 15, and the two taken out laser beams are made to interfere with each other using a prism or mirror, and the interference is caused by the movement speed and direction of the interference plate. and measure the magnitude and direction of the input angular velocity.

Conventionally, in order to control the laser oscillation wavelength λ constant, one reflecting mirror 16 is connected to the piezoelectric driver 2.
It is fixed to the movable part of 0. The piezoelectric driver 20 is driven with alternating current to vibrate the reflecting mirror 16 in the normal direction of the annular optical path 22, that is, in the radial direction with respect to the axis 23. This vibration controls the oscillation wavelength to be at the Doppler center of the laser medium, and the optical path 2 is centered around that point with a width of about 1 to 2 wavelengths.
The length of 2 has been varied.

In this embodiment, one reflecting mirror 17 is a plane mirror, and all other reflecting mirrors 15 and 16 are concave mirrors. A vibrating means 24 is provided for vibrating the angle around an axis perpendicular to the optical path passing through the reflection point of the plane mirror 17. The vibration means 24 is composed of, for example, a piezoelectric driver similar to the piezoelectric driver 20, and a plane mirror 17 is attached to its movable portion, and a piezoelectric element 25 is interposed between the facing surfaces of the movable portion and the fixed portion. be done. By driving this piezoelectric element 25 with an alternating current signal, the angle of the plane mirror 17 with respect to the circumference of the axis 23, that is, the angle with respect to the passage 12, changes in a vibrational manner. That is, for example, as shown in FIG. 2, from the state where the reflecting mirrors 15, 16, and 17 are indicated by solid lines,
Only the reflecting mirror 17 is tilted by an angle of θ ₁ and returned again, as indicated by a dotted line 17', which is repeated. This θ ₁
is small, since the reflecting mirrors 15 and 16 are concave mirrors, the laser oscillation condition is maintained even if the plane mirror 17 is tilted by θ ₁ , and the same equilateral triangle tilted by θ ₁ with respect to the optical path 22 of the equilateral triangle ABC is maintained. Optical path 2 of a′b′c′
6 is formed. Therefore, the annular optical path 22 is vibratedly rotated around the input shaft 23 by the vibratory tilting of the plane mirror 17, and the same effect as conventional mechanical rocking is obtained.

When the optical paths 22 and 26 are vibrated, the optical path length changes between the optical paths 22 and 26. That is, optical path 2
If the length of one side ac of the equilateral triangle 2 is L, then the change in optical path length is expressed by the following equation.

ac−a′c′=L[1−sin30゜／cos(30゜−θ ₁ )｜t
anθ ₁
+ tan (30°-θ ₁ )}] (1) This change in optical path length is due to the change in optical path length (approximately 1 to 2 wavelengths) due to vibration of the reflecting mirror 16 to keep the oscillation wavelength constant. also needs to be made smaller. In other words, ac−a′c′≦λ/100 (2). For example, if a mixture of helium and neon is used as the laser medium and the oscillation wavelength λ is 6328 Å,
The vibration inclination angle θ ₁ that satisfies equation (2) is approximately 6 seconds from equation (1). In FIG. 2, points a and a' are drawn on the same plane, but in reality points a and a' are on the concave mirror 15, so correction for this is required. When the radius of curvature of the concave mirror 15 is R, the correction amount Δx is Δx=R(1−cosθ ₁ )cos 30°. When R = 3000mm, θ ₁ = 6 seconds, the correction amount △
x is approximately 10 Å, which is sufficiently small compared to the wavelength. Therefore, while controlling the optical path length using the piezoelectric driver 20, it is possible to control the plane mirror 17 without contradicting this by controlling the angular vibration with a vibration angle θ ₁ of several seconds or less.
The lock-in error can be made sufficiently small by swinging the optical path 22 by giving a

When the entire conventional laser angular velocity sensor is mechanically oscillated, the relationship between the maximum dither rate (oscillation angular velocity) Ω _D , the dither (oscillation) frequency ωd, and the maximum dither angle φd is Ω _D = ωd It is given by ×φd (3). The oscillation strength in the conventional method is usually
The rate is approximately 100 to 150 degrees/second, which corresponds to a rocking angle of 200 to 300 degrees and a rocking frequency of several hundred hertz. In the angular vibration of the plane mirror 17, 150
To obtain the maximum dither rate Ω _D in degrees/second (3)
It is understood from the formula that the vibration frequency ωd should be about 14 KHz. Vibration at this level of frequency can be performed by the piezoelectric driver 24. Therefore, while maintaining the selected oscillation wavelength λ, the plane mirror 1
7 is angularly oscillated around the input shaft 23 to form the optical path 2.
2 can be vibrated.

Although three reflecting mirrors are used in the above description, four or more reflecting mirrors may be used and arranged in a regular polygon. Further, although one of the reflecting mirrors is a plane mirror, all the reflecting mirrors may be concave mirrors. In that case, the radius of curvature of each concave mirror is made sufficiently larger than the length of the optical path 22.

<Effects> As described above, according to the present invention, the entire laser angular velocity sensor is not mechanically vibrated, but only one reflecting mirror is vibrated, and there is no risk of it becoming a large source of vibration. , power consumption for vibration can also be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an example of a laser angular velocity sensor according to the present invention, and FIG. 2 is a diagram showing the inclination of an optical path due to the inclination of a plane mirror. 15, 16: Concave mirror, 17: Plane mirror, 18, 1
9: anode, 21: cathode, 22: annular optical path, 23:
Input shaft, 24: piezoelectric driver as plane mirror vibration means.

Claims (1)

[Claims] 1. Two almost monochromatic laser beams are sequentially reflected from a plurality of reflecting mirrors to form an annular optical path and rotate in opposite directions, and the rotational angular velocity is determined by detecting the frequency difference between the two light beams. In the laser angular velocity sensor for detection, the plurality of reflecting mirrors are composed of one plane mirror and a plurality of concave mirrors, or all of them are composed of concave mirrors having a radius of curvature sufficiently longer than the optical path length of the optical path, and the plurality of reflecting mirrors are composed of a plane mirror. In this case, the plane mirror, and in the case where all of the concave mirrors are composed of concave mirrors, one of the concave mirrors is provided with a vibrating means that vibrably changes the angle around an axis perpendicular to the annular optical path. A laser angular velocity sensor, wherein the optical path is oscillatorically rotated about the axis by oscillations in amplitude and frequency.