JPH0545370A - Laser gyro - Google Patents

Abstract

PURPOSE:To reduce influence of mode coupling and an error in basic characteristics by making thickness of an uppermost thin film of a multi-layered film mirror different from that of a thin film of a dielectric of a similar kind in the multi-layered films. CONSTITUTION:A mirror constituting a resonator comprises two kinds of thin films including a dielectric 12 of a low refractory index n2 such as SiO2 and a dielectric 11 of a high refractory index n1 such as TiO2 for example alternately laminated to form a multi-layered film mirror, while thickness d3 of its uppermost layer 13 is different from thickness d2 of a thin film of the similar dielectric 12 in the multi-layered film. The mirror thus constituted makes reflectance of laser light wavelength 100% and also it can reduce reflectance with respect to wavelength approximately a half of the laser light wavelength to extremely low, so that an output with respect to an input angle speed with little influence of mode coupling and a small error in basic characteristics can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser gyro using a ring laser used for detecting various angular velocities.

[0002]

2. Description of the Related Art Conventionally, as a laser gyro using a ring laser, what is called an internal mirror type laser gyro as shown in FIG. 4 is known. Since such a laser gyro is well known, its details will be omitted, but in FIG. 4, reference numeral 1 is a substantially triangular glass block made of low-expansion and transparent glass, and mirrors 2-1 and 2-1 are provided at respective apexes thereof. 2-2 and 2-3 are fixed respectively.
In the glass block 1, three pores 3-1 and 3 are provided which communicate with each other and serve as a laser optical path and form a discharge path.
-2, 3-3 are formed along each side of the triangle, and these pores 3-1, 3-2, 3-3 form these three mirrors 2.
A resonator is configured with -1, 2, 2 and 2-3. still,
3-1 ', 3-2', 3-3 'are pores 3-1, 3-2,
The central axes of 3-3 are shown respectively.

An anode 4 is provided on each side of the glass block 1.
-1, 4-2 and the cathode 5 are pores 3-1 and 3-, respectively.
It is attached facing 2, 3-3. Pores 3-1 and 3-
The internal spaces 2 and 3-3 are made completely airtight, and a gas (laser medium such as helium or neon) for oscillating laser light is enclosed inside.

Reference numeral 6 denotes a composite prism provided outside the mirror 2-3, for example, and is used to combine the clockwise and counterclockwise laser lights in the resonator to extract the angular velocity output.

Now, when the angular velocity is actually measured by a ring laser gyro, the characteristics shown in FIG. 5 are obtained. Figure 5
The dotted line shows the characteristics of an ideal ring laser gyro with no error. On the other hand, as shown by the solid line, in the measured value, the angular velocity output is usually lost when the input angular velocity Ω is very small. This is a phenomenon that has long been known as the "lock-in phenomenon" of the ring laser gyro. On the other hand, when the input angular velocity exceeds a certain value, the actual output becomes larger than the ideal value. This is called a positive error. In the ring laser gyro, the following means is usually used to eliminate such an error.

That is, in FIG. 4, reference numeral 7 denotes a hinge, which elastically supports the whole body including the glass block 1 about an axis (0) perpendicular to the paper surface of FIG.
Cooperating with an electric circuit such as an amplifier connected to this, the glass block 1 has an alternating angular vibration about the axis (0),
That is, the dither movement is given.

However, even if such a method is used, it is impossible to eliminate the error altogether. If the error shown in FIG. 5 is small, the final error is always reduced. Therefore, as shown in FIG. It is no exaggeration to say that "improvement of basic characteristics" is always the greatest research theme of the ring laser gyro.

It has been conventionally said that the mirror is a key part of the ring laser gyro. In particular, regarding the lock-in phenomenon, which is an obstacle to improving the performance, it is considered that the backscattering of the mirror is the main cause, and many researchers have been working to reduce this scattering. However, according to a recent research, a clue for improving the performance has been found by integrating and analyzing the lock-in phenomenon and the positive error by the concept of mode coupling. According to this idea, if the wavelength of the light of the laser currently used is λn, it is exactly half of this wavelength, that is,

[0009]

[Equation 1]

Mode coupling occurs under the influence of the "electric susceptibility" of the substance on the optical path with respect to the wavelength of, and as a result, the characteristics of the gyro include lock-in phenomenon and positive error. It has become clear that is caused.

The electrical susceptibility is theoretically treated as a complex number, but its real part x'is the wavelength λ of the substance.
_When the refractive index for _h is n _h ,

[0012]

[Equation 2]

There is a relationship of

However, the inventors of the present invention have made various studies, but even if it is called a substance on the optical path, the refractive index of helium / neon gas close to vacuum is sufficiently close to "1", and the "electric susceptibility" of the internal gas. Is almost zero, and it turns out that it is the mirrors that dominate this phenomenon.

Here, conventional mirrors 2-1, 2-2, 2-
3 will be described. FIG. 6 shows a cross section of a "multi-thin film" mirror that is currently used in laser gyros. The substrate 10 is a glass substrate made of the same material as the glass block 1 in FIG. On this layer, dielectrics 11 having a refractive index of n ₁ and dielectrics 12 having a refractive index of n ₂ are alternately stacked, and when P pairs of layers are stacked, a mirror having a second P layer as shown in the figure is obtained. Become.

In the ring laser, the central axis 3 is used as a resonator.
Since it is necessary for the optical path matching −1 ′, 3-2 ′, 3-3 ′ to have an extremely good resonance property, it is possible to have almost perfect 100% reflectance for the wavelength λn of the oscillation laser light. It is known that, in such a case, the thicknesses d ₁ and d ₂ of each layer need to have the following relationship except for the final layer 13.

[0017]

[Equation 3]

Where θ ₁ and θ ₂ are dielectrics 11 and 1
The respective refraction angles of 2 are obtained by the following Snell's law.

[0019]

[Equation 4]

Here, the refractive index of the laser medium on the optical path is "1", and the incident angle of the laser light on the mirrors 2-1, 2-2, 2-3 is θ _i . The final layer 13 is typically doubled in the case of FIG. 6 to 2d ₂ .

As a specific example, the odd-numbered layer dielectric 1
It is typical that 1 is TiO ₂ (titanium dioxide) and the even-numbered dielectric layer 12 is SiO ₂ (silicon dioxide).
In this case, when P is 10 or more, that is, when P exceeds 20 layers in total, a reflectance close to 100% is obtained.

In FIG. 7, TiO ₂ having a thickness of d ₁ and d having a thickness of d ₁
SiO ₂ in 13 pairs of _2, satisfies the number of three conditions to 26 layers, the example in which the thickness of the top layer 13 is 2d _2, showing the measured values of reflectivity for the wavelength of the incident light. The wavelength of the laser light of the helium and neon lasers is 632.8 nanometers (n
m), and the reflectance of the mirror as shown in FIG. 6 for this wavelength λn is 100% as planned.

[0023]

[Problems to be Solved by the Invention]
Λn / 2 = λ _h 316.4 nm involved in coupling
The reflectance corresponding to is around 20 to 30% as shown in FIG. The insides of the pores 3-1, 3-2 and 3-3 have, as already mentioned, only a slight amount of gas in the vacuum,
Since this refractive index is "1", to say that there is reflection, the equivalent refractive index n _m of the mirror is shown that not "1", the n _m the number 2 instead of n _h As you can see by substituting, it shows that at least the real part of the electric susceptibility exists. Therefore, if this mirror is used, mode coupling always exists.

Therefore, in the conventional laser gyro using the mirror as shown in FIG. 6, there is a disadvantage that a lock-in phenomenon and a positive error as shown in FIG. 5 occur. As a solution to this, in the past, for the deterioration of performance due to this mode coupling, among the mirrors made by the same method at best, it is possible to select and use the best one, or change the position where the light hits within the same mirror. However, there is a problem that there is no way to deal with it, such as using a position with less coupling, and the above method cannot provide a basic solution.

The present invention has been made in view of the above problems, and an object thereof is to propose an excellent laser gyro that is less affected by mode coupling and has less error in basic characteristics.

[0026]

The laser gyro according to the present invention includes a mirror 2-1 as shown in FIGS. 1, 2 and 4, for example.
In a laser gyro having a resonator using 2-2 and 2-3 and a ring laser that oscillates using this resonator, the mirrors 2-1, 2-2 and 2-3 have low refraction. first dielectric example SiO ₂ 12 and high refractive index rate n ₂ n
A second dielectric of ₁ , for example, a multilayer mirror formed by alternately stacking two kinds of thin films of TiO ₂ 11 is used, and the thin film of the uppermost layer 13 of the multilayer mirror is the same kind of dielectric 12 in the multilayer film.
The thickness of the thin film is set to be different from the thickness of the thin film, so that the reflectance of the mirror with respect to the wavelength λ _h which is approximately ½ of the wavelength λ n of the laser light is extremely lowered.

Further, the laser gyro according to the present invention includes mirrors 2-1 and 2-2 as shown in FIGS. 2, 3 and 4, for example.
In a laser gyro having a resonator using 2-3 and a ring laser that oscillates using this resonator,
The mirrors 2-1, 2-2, 2-3 are of two types: a first dielectric material having a low refractive index n ₂ such as SiO ₂ 12 and a _second dielectric material having a high refractive index n ₁ such as TiO ₂ 11. Laser light is obtained by forming a multilayer film mirror formed by alternately laminating the thin films of (1) and (2P + 1) as the first dielectric 12 for both the lowermost layer and the uppermost layer of the multilayer film mirror. This mirror has an extremely low reflectance for a wavelength λ _h that is approximately ½ of the wavelength λ n.

[0028]

According to the present invention, the reflectance of the laser light at the wavelength λn is set to 100% as a mirror constituting the resonator, and the reflectance of the laser light at the wavelength λ _h about ½ of the wavelength λn is shown. Since an extremely low value is used as shown in FIG. 2, it is possible to obtain an output with respect to the input angular velocity .OMEGA. With a small error close to the broken line in FIG.

[0029]

EXAMPLE The present invention will be described with reference to FIGS. 1, 2 and 4 below.
Let us explain one example of the Ming Laser Gyro. Figure 1
In FIG. 6, the same reference numerals are given to the portions corresponding to FIG.
Detailed description is omitted. The laser gyro of this example is shown in Fig. 4.
It is made of glass with low expansion and is almost triangular.
Mirrors 2-1, 2-2, 2 are provided at each vertex of the lath block 1.
Fix -3 respectively. In this glass block 1
The optical path and the discharge path are in communication with each other.
3 small holes 3-1, 3-2, 3-3 on each side of the triangle
Formed along these pores 3-1, 3-2, 3-3
Together with these three mirrors 2-1, 2-2, 2-3,
Configure a resonator. Each side of the glass block 1
The cathodes 4-1 and 4-2 and the cathode 5 are pores 3-1 and 3 respectively.
It is attached facing -2, 3-3. Pores 3-1 and 3-
The inner space of 2,3-3 is made completely airtight, and
Gas for laser oscillation (laser medium such as helium, neon, etc.
Quality) is enclosed. In addition, a composite pre-print is placed outside the mirror 2-3.
The prism 6 is provided, and the synthetic prism 6 is used to
The angular velocity output is obtained by synthesizing the laser light in the counterclockwise and counterclockwise directions.
Take out. In this example, the glass block 1
The mirrors 2-1, 2-2 and 2-3 fixed to the apex are shown in FIG.
It is configured as shown in. In FIG. 1, 10 is a glass block
Click here for a glass substrate of the same material as
10 has thickness d₁And high refractive index n₁Dielectric, for example
If TiO₂11 and thickness d₂And low refractive index n₂Invitation
Electric body, eg SiO₂Alternately stacked up to (2P-1) layers
And the top layer 13 on top of it has a thickness d₃And low refractive index
n₂Dielectric, eg SiO₂Stack up. That is, 2P
Even number of layers In this example, there are 26 layers. Thickness of each layer
d₁, D₂Is the relation of Equation 3, that is, n₁d₁cos θ₁= N
₂d ₂cos θ₂= Λn / 4. However, θ₁as well as
θ₂Are the refraction angles of the dielectrics 11 and 12, respectively.
It is calculated according to Snell's law of Equation 4. n₁sin θ₁= N₂sin θ₂= Sin θi Here, the refractive index of the laser medium on the optical path is “1”, and
Let θi be the incident angle of light on the mirrors 2-1, 2-2, 2-3.
is doing. The wavelength of the laser light used is λn
is doing. Further, in this example, the thickness d of the uppermost layer 13 is₃To

[0030]

[Equation 5]

The case of k = 2 in the relation of is taken. Here, n ₂ ′ is the wavelength λn = λ _h / 2 of the low refractive index dielectric material 12.
Is the index of refraction for the wavelength n
₂ is generally different. θ ₂ ′ also

[0032]

[Equation 6]

Is the refraction angle according to. Such a configuration of FIG.
As shown in Fig. 2, the reflection characteristics of the
Of the laser light of the laser at the wavelength λn632.8 nm
This wave is 100% and is involved in mode coupling
1/2 wavelength of long λn_hThe reflectance at 316.4 nm
It was about 0%. The characteristic d as shown in FIG. 2 is obtained.
₃The value of is not only the above value, but any value that satisfies the equation 5.
It was confirmed that This example is as described above
Characteristics of mirrors 2-1, 2-2, 2-3 forming the resonator
As shown in Fig. 2, the reflection of the wavelength λn of the laser light used
The ratio is 100% and the wavelength λn of this laser light is 1
1/2 wavelength λ_hSince the reflectance of is almost zero, this
Λn / 2 = λ of optical path_hHas zero electrical susceptibility,
Do_,The coupling is eliminated, and the laser
According to Iro, this basic characteristic is as shown by the broken line in FIG.
It is possible to obtain a good output angular velocity for a good input angular velocity Ω.
There is a profit Also, an example of the mirror used in the present invention
Then, the one shown in FIG. 3 can also be used. This Figure 3
The same reference numerals are given to the parts corresponding to those in FIGS.
The detailed description is omitted. The example in Figure 3 is a glass substrate
If the layers of the dielectric film of the plate 10 are odd layers (2P + 1)
Both have the thickness d of the first layer on the glass substrate 10.₂With low refractive index
n₂Dielectric, eg SiO₂12 and the thickness of the second layer
Is d₁And high refractive index n₁Dielectric, eg TiO₂11 and
Then, stack these layers one after the other up to the 2P layer,
The thickness of the upper layer 13 is d _FourAnd low refractive index n₂Dielectric, example
For example SiO₂Stack up. In this example, the number of layers is 27. This
Thickness of each layer of₁, D₂Is the relation of Equation 3, that is, n₁d₁cos θ₁= N₂d₂cos θ₂= Λn / 4. Thickness d of this uppermost layer 13_FourTo

[0034]

N ₂ ′ d ₄ cos θ ₂ ′ = kλn / 4 k = 1, 2, 3 ...

The relationship is as follows. Such a mirror as shown in FIG.
Also has a reflectance of 100 at the wavelength λn of the laser light as shown in FIG.
%, And a wavelength λ that is 1/2 of this wavelength λn_hThe reflectance of
It turned out to be almost zero. Such a Mira as shown in FIG.
The laser gyro mirrors 2-1, 2-2, 2-3
When used as, the same effects as above can be obtained.
Of course. Further, in the above embodiment, the low refractive index n₂of
SiO as a dielectric₂Was used instead of Mg
F₂Other low refractive index dielectrics can be used, and
Folding rate n₁As a dielectric of₂I used
Instead Ta₂O _FiveOther high refractive index dielectrics can be used
Of course you can. Further, the present invention is limited to the above embodiment
Without departing from the spirit of the present invention
Of course, it is possible.

[0036]

According to the present invention, the reflectance of the laser light at the wavelength λn is set to 100% as a mirror constituting a resonator, and the reflectance of the laser light at the wavelength λ _h which is approximately ½ of the wavelength λn is obtained. Since the value of is extremely low and substantially zero is used, there is an advantage that an output for an input angular velocity with a small error can be obtained in the basic characteristic that the influence of mode coupling is small.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a mirror used in a laser gyro of the present invention.

FIG. 2 is a diagram showing a reflection characteristic of the mirror of FIG.

FIG. 3 is a cross-sectional view showing another example of a mirror used in the laser gyro of the present invention.

FIG. 4 is a configuration diagram showing an example of a laser gyro.

FIG. 5 is a diagram for explaining the present invention.

FIG. 6 is a sectional view showing an example of a conventional mirror.

FIG. 7 is a diagram showing a reflection characteristic of the mirror of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass block 2-1, 2-2, 2-3 Mirror 3-1, 3-2, 3-3 Micropores 4-1, 4-2 Anode 5 Cathode 6 Synthetic prism 7 Hinge 10 Substrate 11, 12 Dielectric material 13 top layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Ishikawa 2-16-46 Minami-Kamata, Ota-ku, Tokyo Within Tokimetsu Co., Ltd. (72) Inventor Kenmori Masushima 2-16-46 Minami-Kamata, Ota-ku, Tokyo No. Stock Company Tokimetsu

Claims (2)

[Claims] 1. A laser gyro having a resonator using a mirror and a ring laser oscillating using the resonator, wherein the mirror comprises a first dielectric material having a low refractive index and a high refractive index material. A multilayer mirror formed by alternately stacking two kinds of thin films of the second dielectric, and by making the uppermost thin film of the multilayer mirror different from the film thickness of the thin film of the same dielectric in the multilayer film, A laser gyro, wherein the reflectance of the mirror is extremely low for a wavelength that is approximately ½ the wavelength of the laser light. 2. A laser gyro having a resonator using a mirror and a ring laser oscillating using the resonator, wherein the mirror comprises a first dielectric material having a low refractive index and a first dielectric material having a high refractive index. A multilayer film mirror formed by alternately stacking two kinds of thin films with two dielectrics, and a mirror composed of an odd number layer in which both the lowermost layer and the uppermost layer of the multilayer film mirror are first dielectrics. Thus, the reflectance of the mirror for the wavelength of about ½ of the wavelength of the laser light is extremely low, and the laser gyro.