JPH0968435A - Passive ring resonant optical gyro - Google Patents

Abstract

(57) Abstract: A passive ring resonance type optical gyro that improves the detection performance of the input angular velocity by narrowing the frequency distribution of the laser light used as the detection light of the passive ring resonance type optical gyro. A passive ring resonance type optical gyro having an optical filter (9) for narrowing the frequency distribution of laser light oscillated and radiated by a laser light source (1) interposed between the laser light source (1) and a ring resonator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive ring resonance type optical gyro, and more particularly, to narrowing the frequency distribution of laser light used as detection light of the passive ring resonance type optical gyro to detect the input angular velocity. An improved passive ring resonant optical gyro.

[0002]

2. Description of the Related Art A conventional example of a passive ring resonance type optical gyro will be described with reference to FIGS. FIG. 4 is a diagram for explaining a conventional example of a passive ring resonance type optical gyro,
FIG. 5 is a diagram showing input / output characteristics of the passive ring resonance type optical gyro of FIG. The laser light emitted from the laser light source 1 is transmitted through an optical directional coupler 13 arranged in the vicinity of the partial transmission mirror 2 and is transmitted through a ring resonance constituted by the mirror 2, the mirror 3, the mirror 5 and the mirror 6. It is incident on the ring-shaped optical path 4 of the container. The laser light incident on the ring-shaped optical path 4 is sequentially reflected by the mirror 3, the mirror 5, the mirror 6 and the mirror 2, and circulates in the clockwise direction on the ring-shaped optical path 4. A part of this circulating laser light is partially directional coupler 13
The circulating light thus extracted is made to interfere with the incident light entering the optical directional coupler 13, and the interference light is detected by the light receiver 7. The characteristic of the detection intensity I of the interference light detected by the light receiver 7 is as shown by the curve 18. That is, at the optical frequency f ₀ that satisfies the resonance condition, the detection intensity I decreases in a sharp pulse shape and becomes a dark state.
The characteristic indicated by the curve 18 detected by the light receiver 7 is generally called a reflection characteristic, and this can be used to configure an optical gyro. This resonator causes resonance at a resonance frequency f ₀ corresponding to the length of the ring-shaped optical path 4,
The peak resulting from the multiple interference shown by the solid line in FIG. 5 is created on the photodetector 7. When the angular velocity ω is input around the central axis 8 orthogonal to the optical path surface of the ring resonator, the resonance frequency f ₀ increases / decreases in accordance with the increase / decrease in the input angular velocity ω.

The principle of the optical gyro generally relies on the Sagnac effect. The Sagnac effect means that when the ring-shaped optical path 4 surrounding the finite closed area S makes a motion with an angular velocity ω about the axis 8 in the direction of the closed area normal as a rotation axis, the ring-shaped optical path 4 rotates in opposite directions in the ring-shaped optical path 4. A difference occurs in the frequency of the circling light, and the resonance frequency difference Δf ₀ between the circling light is Δf ₀ = (4S / λL) ω, where λ is the optical wavelength, L is the optical path length of the ring-shaped optical path, and S is the circumference of the optical path. Area.

An optical ring resonator as shown in FIG. 4 is constructed, and laser light which is coherent light is made incident on the optical ring resonator from an external laser light source 1 to the ring-shaped optical path 4 in a clockwise direction and a counterclockwise direction. By rotating the two-way light of, the resonance frequency difference Δf ₀
By detecting, the input angular velocity ω input to the optical ring resonator can be measured. The optical gyro that inputs the laser light, which is the coherent light, from the laser light source 1 arranged outside the resonator to the optical ring resonator is called a passive ring resonance type optical gyro. In an actual ring resonance type optical gyro, a modulation signal is input from the outside so that the resonance frequency f ₀ becomes constant, the frequency of the modulation signal that keeps the resonance frequency f ₀ constant is measured, and the input angular velocity ω In many cases, the method of converting to (the details of the passive ring resonant optical gyro are described in Japanese Patent Application No. 3-321715.
See the specification).

[0005]

The resolution of the ring resonance type optical gyro is mainly determined by the finesse representing the resonator characteristics of the gyro. Here, the resolution ΔΩ of the passive ring resonance type optical gyro is represented by ΔΩ = πc ₀ · Δf · λL / 2S, where c _{0 is a} constant and Δf is the half width of the resonance peak. The finesse is the loss c ₀ of the optical member of the resonator of the ring resonance type optical gyro and the full width at half maximum Δf of the laser light resonating.
Determined by That is, the smaller the loss, the higher the resolution, and the narrower the half width, the larger the finesse and the higher the resolution. Conventionally, the loss has been reduced by improving the performance of the mirror, and the half width has been narrowed by using a light source that oscillates laser light with high coherence.

As a laser light source having a high coherence, conventionally, a gas laser having a Fabry-Perot resonator at both ends of the laser or a semiconductor laser having a cleavage plane at both ends has been used. This gas laser has a large outer dimension, and the semiconductor laser has a small outer dimension but is expensive. In particular, the passive ring resonant optical gyro requires a laser light source that outputs a narrow-band laser light in order to improve the detection performance of the input angular velocity, but this is not always easy in terms of manufacturing technology. The cost is also high. The semiconductor laser requires a current control device or other control device to stabilize the oscillation wavelength.

The present invention is intended to improve the performance of a passive ring resonance type optical gyro without depending only on the height of coherence of the light source. A narrow ring optical filter with an extremely narrow pass band is interposed between the and the narrow band optical filter to narrow the band of the laser light incident on the resonator of the optical gyro, thereby improving the detection performance of the input angular velocity. A resonant optical gyro is provided.

[0008]

A passive ring resonance type optical gyro having an optical filter 9 for narrowing the frequency distribution of laser light oscillated and radiated by a laser light source 1 is interposed between the laser light source 1 and a ring resonator. Configured. The optical filter 9 is a passive ring resonance type optical gyro which is a resonance type optical filter in which two very low loss multilayer film mirrors are opposed to each other or of the same type.

Further, the mirror constitutes a passive ring resonance type optical gyro which is a multilayer film mirror for a ring laser gyro. Further, the optical filter constitutes a narrow-band multilayer optical filter on a large-area substrate and cuts it into a filter having a small area required, or a narrow-band multilayer on a substrate cut into a small area required. A passive ring-resonance optical gyro composed of a film optical filter was formed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIGS. This invention is a laser light source 1
A narrow band optical filter 9 for narrowing the frequency distribution of the laser light oscillated and radiated is placed between the laser light source 1 and the ring resonator. The ring resonator comprises a partially transmissive mirror 2, a mirror 3, a mirror 5 and a mirror 6. Reference numeral 4 denotes a ring-shaped optical path formed in the ring resonator. The laser light emitted from the laser light source 1 passes through the narrow band optical filter 9 to be narrowed, and then passes through the optical directional coupler 13 arranged in the vicinity of the partial transmission mirror 2 to form the partial transmission mirror 2. The light enters the ring resonator formed by the mirror 3, the mirror 5, and the mirror 6. Looking at the laser light that is incident on the ring resonator and is rotated in the clockwise direction a number of times while being reflected in the ring resonator, a part of the laser light is extracted to the outside through the optical directional coupler 13 and the extracted circular light is extracted. And the incident light incident on the optical directional coupler 13 can be interfered with each other to form a peak on the photodetector 7 as a result of the multiple interference shown by the solid line in FIG.

The narrow band optical filter 9 will be described with reference to FIG.
I will tell. FIG. 3A shows a cross section of the narrow band optical filter 9.
(B) is a narrow band generated by the laser light source 1
Showing the laser light incident on the bandpass optical filter 9, (c)
Is the laser beam emitted from the narrow band optical filter 9.
Show. The narrow band optical filter 9 is, for example, a ring with low loss.
Two multi-layer mirrors for laser gyro facing each other,
Or, a resonance type optical filter having an effect equivalent to this.
It consists of. s₁ Is a transparent substrate. Board s₁ 
First, the thickness d of the transparent high refractive index material is₁ High
Refractive index thin layer n₁Is formed. High refractive index thin layer n₁ On the surface
Is a thickness d of a transparent low refractive index material. ₂ Low refractive index thin
Layer n₂ Is formed. High refractive index thin layer n₁ And low refractive index
Thin layer n₂Are alternately formed in this order in multiple layers. T₁ Is transparent
A clear intermediate material layer is shown. Intermediate material layer T₁ To the right of
Inter-material layer T₁ Is a symmetry plane, and the low refractive index thin layer n₂ and
High refractive index thin layer n₁ In this order, a large number of layers are alternately formed.
Where n₁ And n₂ Also indicates the refractive index of the thin layer
Then, the high refractive index thin layer n₁ And a low refractive index thin layer n₂Is
For thickness and refractive index, n₁ d₁ = N₂ d₂ = Λ / 4, and the layers are stacked. In this case, the intermediate material layer T
₁ Has a thickness of λ / 2. (In addition, ring laser gyi
(B) Resonant optical film with two multi-layer film mirrors facing each other
For details of the data, see Japanese Patent Application No. 7-46857).

The narrow band optical filter 9 which is the resonance type optical filter described here is a filter of extremely low loss and high efficiency, and when it is used as a mirror, it is 1.0.
It shows a measured value of 6 ppm in total loss with respect to light having a wavelength of 6 μm, and has high wavelength selectivity. Then, the narrow band multilayer optical filter is formed on the surface of a large transparent laminated substrate s ₁ and cut out into a required small area filter with a diameter of about 1 mm, or into a required small area. By constructing the narrow band multilayer optical filter on the cut-out substrate, it can be manufactured at low cost. Therefore, the manufacturing cost of the narrow-band multilayer optical filter itself is low. The laser light source 1 oscillates and radiates the narrow band optical filter 9
The laser light incident on the laser beam includes a large number of emission peaks as shown in FIG. 3 (b) and has a wide band. Then, the output radiated light of the narrow band optical filter 9 can be radiated light having an emission peak having a very narrow band as shown in FIG. 3C. That is, the laser light source 1
Between the ring resonator and the ring resonator, a narrow band optical filter 9 for narrowing the frequency distribution of the laser light oscillated and emitted by the laser light source 1 is interposed so that the resonance peak having a narrow half width Δf as shown by the solid line in FIG. Can occur. When the resonance peak when the narrow band optical filter 9 is not used is shown as a reference, it is as shown by the dotted line in FIG. The above is the discussion on the laser light that rotates in the clockwise direction a number of times while reflecting in the ring resonator, but the same holds for the laser light that rotates in the counterclockwise direction. The passive ring resonance type optical gyro can detect the input angular velocity by detecting the resonance frequency difference between the resonance peak of the clockwise rotating laser light and the resonance peak of the counterclockwise rotating laser light. The fact that the half widths of both are narrower makes it easier to separate the two resonance peaks, which means that the resolution of the passive ring resonance optical gyro is improved accordingly. Therefore, the input angular velocity detection performance is improved.

[0013]

As described above, according to the present invention, resonance is achieved by interposing a low-cost multilayer narrow band optical filter having high efficiency and high stability and high frequency selection performance between the light source and the resonator. It is possible to increase the coherence of the light incident on the vessel and improve the resolution of the passive ring resonance type optical gyro.

Further, it is not always easy in terms of manufacturing technology to construct a laser light source which outputs a narrow band light, and it is costly, but a laser light source which outputs a wide band light is compared with this. Easy to manufacture and inexpensive. in this case,
It is easier to manufacture a laser light source that outputs a wide band of light and is cheaper, and it is easier to manufacture and is cheaper to combine the narrow band optical filter of the multilayer film as described above to generate a narrow band laser light. In the end, it is technically and cost-effective to generate the narrow band laser light only by the laser light source that outputs the narrow band light.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an example.

FIG. 2 is a diagram showing frequency characteristics of optical output according to the embodiment.

FIG. 3 is a diagram illustrating a narrow band optical filter.

FIG. 4 is a diagram illustrating a conventional example.

FIG. 5 is a diagram showing a frequency characteristic of optical output of a conventional example.

[Explanation of symbols]

 1 Laser Light Source 2 Partial Transmission Mirrors 3, 5, 6 Mirror 4 Ring Optical Path 7 Photodetector 9 Narrow Band Optical Filter

Claims (4)

[Claims] 1. A passive ring resonance type optical gyro, wherein an optical filter for narrowing a frequency distribution of laser light emitted by a laser light source is interposed between the laser light source and the ring resonator. 2. The passive ring resonance type optical gyro according to claim 1, wherein the optical filter is a resonance type optical filter in which two very low loss multilayer mirrors are opposed to each other or of the same type. A passive ring resonant optical gyro characterized by: 3. The passive ring resonance type optical gyro according to claim 2, wherein the mirror is a multilayer film mirror for a ring laser gyro. 4. The passive ring resonance type optical gyro according to claim 3, wherein the optical filter comprises a narrow band multilayer optical filter on a large area substrate, and the optical filter is used as a small area filter required. A passive ring resonance type optical gyro, which is formed by forming a narrow band multilayer optical filter on a substrate that is cut out or cut out into a required small area.