JPS5842635B2 - Laser Shilo using ring laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a unidirectional traveling wave ring laser (Unidirect) to measure the angular velocity or angular displacement of a moving object.
The present invention relates to a laser gyro using the ional Ring La5er (hereinafter referred to as URL).

Conventionally, what is called a laser gyro includes a conventional bidirectional traveling wave ring laser (Conventional Ring La5er).
; hereafter referred to as CRL), and an optical interferometer type laser gyro that uses laser light as a light source and creates a closed circuit with a magnetic fiber.

Since this invention uses a ring laser,
First, a laser gyro using a conventional ring laser will be explained.

FIG. 1 is a schematic diagram of a conventional CRL.

In this figure, LT is a laser oscillator, Ll is a clockwise laser beam, L2 is a counterclockwise laser beam, PM is a total reflection mirror, TM is a partially transmission mirror, and PD is a photodetector or optical beat frequency. Detector, IA is the input shaft,
ω is the angular velocity around the input axis IA.

When the input shaft IA rotates, each component rotates in the same manner without changing its relative position.

As is generally well known, the CRL transmits laser beams L1 . As L2 progresses and a ring laser oscillation is formed, the input axis IA
In the region where the angular velocity ω is small, the oscillation frequencies of the lasers KL, L2 traveling in opposite directions approach each other, so they fall into a standing wave state, and there is a region where even if there is a small input, it is not sensed. .

This is shown in the characteristic diagram of FIG. In FIG. 2, the vertical axis shows the beat frequency Δf, and the horizontal axis shows the angular velocity ω.

In this way, the laser gyro using the conventional CRL has a dead area L I (Loc
k -in) occurs.

Therefore, the existence of the dead area LI is a serious obstacle to increasing the precision of the ring laser gyro, and various methods have been attempted to solve this problem.

Among these, the ones that have been successfully put into practical use include the dithering method by Honeywell Corporation of the United States and the method using the Faraday effect by Sveri-Land Corporation of the United States.

The one-type dither provides a stable mechanical vibration rate around the human axis, eliminating insensitivity during minute inputs, but since the device that provides mechanical dither (vibration) is mechanical,
There are drawbacks in terms of reliability.

In the Faraday effect method, a Faraday shell is inserted into the optical path inside the optical resonator of a ring laser, and by applying a magnetic field of appropriate strength along the optical path, the phase of the light wave traveling in the direction of the magnetic field is advanced. Even in the state of zero input, the insensitivity around zero input is eliminated by giving a large difference in the oscillation frequency of each light wave traveling in opposite directions (by giving a constant bias), but due to the temperature of the Faraday shell and the magnetic field. It has drawbacks such as requiring high precision in control (affecting bias stability).

The optical interferometer type laser gyro is a so-called passive interferometer (Pa5sive Interferometer).
) and is based on the same principle as the Michelson interferometer.

Therefore, this laser gyro has drawbacks such as requiring an extremely long closed optical path in order to increase sensitivity.

This invention was made to eliminate the above-mentioned drawbacks of the conventional laser gyro, and provides a highly accurate URL that eliminates the laser gyro and white insensitive area.

The present invention will be explained below based on the drawings.

.・FIG. 3 is a schematic configuration diagram showing an embodiment of the present invention, and shows a case where the range gyro has one axis.

As shown in the figure, the present invention is comprised of two URLs whose traveling light waves are directed in opposite directions, and one photodetector ROD that detects the beat frequency of the outputs of both lasers.

The URL is an optical resonator that forms a closed circuit with one laser oscillator LT, two fully reflective mirrors PM, and one partially transmissive mirror TM, and among the reniza light that travels bidirectionally within the optical resonator. , basically consists of a unidirectional traveling wave device UD that stops laser oscillation in one direction and allows only laser light traveling in the other direction to exist.

R, OD are total reflection mirrors PM; beam splitter BS,
It is composed of a photodetector PD.

Next, the operating principle will be explained.

FIG. 4 is a diagram showing the principle of operation of this invention.

In the diagram, enter the URL that oscillates 'L' on the laser.
Lcw, U'RL the URL that oscillates the laser beam L1
Let c c *.

It is assumed that the closed optical path surfaces of U RL''cw and U RL c'cvJ are arranged parallel to each other, and the input axis coincides with a common normal of the respective closed optical path surfaces.

First, focusing on the URL "ccw, when the input angular velocity ω=0, the laser beam L2 oscillated from the URL ccw
The oscillation frequency of is determined by its closed optical path length (Optic'aiCmv
:'i ty'Leng'th) and takes a constant value.

Now, if the angular velocity ω is applied around the input axis (sensitivity axis), the laser oscillation frequency of U′1(Lccv changes in proportion to the angular velocity ω due to the Doppler effect (apparently) of light).

Similarly, the oscillation frequency of the laser JL of URLcw in □ is also frequency modulated by the application of the field.

Since the directions of frequency modulation of Ll and L2 are contradictory (in Figure 4, the oscillation frequency of Ll is low and that of L2 is high), these laser beams are transmitted through the ROD as the same traveling wave. If they are integrated and interfered, they will interfere with each other through the likely heterodyne effect and generate a likely beat signal.

Since this beat frequency is proportional to ω, ω can be known by measuring this frequency.

Next, the above qualitative explanation will be explained quantitatively below.

In Figure 4, the radius of the circular closed likelihood path of URLccw is R1
The input angular velocity is ω, the laser beam L3 oscillates counterclockwise from the point P (the observation point at the same time as the light emitting point), and the time it takes to return to the original position is t.

Now, when ω-〇, the time for the light to go around the circular closed likelihood path is to
, where C is the speed of light in vacuum.

When the angular velocity ω is applied in the clockwise direction, the time tCcw for the light to make one revolution is: □
'Therefore, when the angular velocity is (2), ω = O and ω - ω, the □ time difference △t required for the light to make one revolution is given by Equation (1),
From Equation (2), the apparent difference △L at the same optical distance when ω = 0 and when ω - ω is obtained by subtracting Equation 5 (3) given by Equation (4) below. By substituting it into equation (4), we get that A−πR2 is U
RI, 'cc state is the area enclosed by the circularly closed likelihood path.

On the other hand, the oscillation condition of the ring-nuzzer is expressed by the following equation (6).

From ν=C/λ (Sh: laser oscillation frequency, λ: laser wavelength), equation (6) becomes the following equation (7).

Here, m: positive integer, From equation (7), L: closed optical path length of optical resonator, Equation (8) can be approximately expressed by the following equation (9).

Therefore, by substituting equation (5) into equation (9), Δν is the laser oscillation frequency ν when ω-0 due to the application of ω.

means the amount of frequency change from .

Therefore, the laser oscillation frequency fCCW of URLccw is expressed by the following equation 01).

ω is positive in the clockwise direction.

Regarding the laser oscillation frequency fcw of URLcw, UR
It can be expressed in the same way as in the case of Lccw, but in that case, the sign of Δν becomes opposite, and it can be expressed by the following equation (12).

However, it is assumed that URLcw is created exactly the same as URLccw (the traveling directions of the laser beams in each optical resonator are opposite to each other).

The beat frequency Δf of the lasers KL1 and L2 is given by the following equation 03) from equations 00 and 02.

FIGS. 5 and 6 are schematic configuration diagrams showing still other embodiments of the present invention, and graphically illustrate cases in which the laser gyro has two axes and three axes, respectively, based on the configuration shown in FIG. It is something.

The operation of the embodiment shown in FIGS. 5 and 6 is basically the same as that of the single-axis Lenizza gyro shown in FIG. 3, so the explanation thereof will be omitted.

Among the components of the laser gyro according to the embodiment of the present invention, a particularly important one is the unidirectional traveling wave device UD.

This is inserted along the optical path inside the ring laser's resonator, allowing waves traveling in one direction to pass through without any disturbance, and passing waves traveling in the opposite direction through its linear deflection surface ( It is assumed that the light wave emitted from the laser oscillator LT is plane-polarized.

As a result, the laser light that is stimulated and emitted within the resonator becomes only the world-class component that passes through U and D without being subjected to any disturbance.
Directional traveling laser light is output from that 'URL.

As explained above, since the present invention configures a gyro using a URL, the laser light amplified within the optical resonator of the URL travels in only one direction, so the conventional bidirectional traveling wave ring There is essentially no risk of standing wave phenomenon occurring at minute input angular velocities, as seen in lasers, so insensitivity at minute input angular velocities can be eliminated and high accuracy can be achieved.

Furthermore, since this invention uses a combination of two URLs with the same configuration, there is an advantage that manufacturing becomes easy.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the conventional CRL, and Figure 2 is the CRL shown in Figure 1.
RL characteristic diagram, FIG. 3 is a schematic configuration diagram showing one embodiment of the present invention, FIG. 4 is a modeled version of FIG. 3, and FIGS. 5 and 6 are further diagrams of the present invention. FIG. 2 is a schematic configuration diagram showing an example.

Claims (1)

[Claims] 1 A unidirectional traveling wave ring laser that rotates together with the input shaft that is the object to be detected, and a unidirectional traveling wave ring that also rotates with the human power shaft and generates laser light in the opposite direction to the unidirectional traveling wave ring laser.・Laser and
A laser gyro using a ring laser, comprising a photodetector that detects the beat frequency of the outputs of both the lasers.