RU2629704C1 - Method of measuring complex communication factors in ring resonators of laser gyroscopes - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: in the circuit resonator, counter-propagating waves are formed by exciting the natural-oscillation waves in opposite directions by means of the external laser radiation. In this case, the counter waves are formed of equal intensity, a phase shift is introduced between them and the values of the complex coupling coefficients are determined from the time dependences of the intensities of the waves emerging from the ring resonator.

EFFECT: increasing the accuracy of measuring complex coupling coefficients of ring resonators.

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Description

The invention relates to instrumentation and can be used in monitoring systems of parameters of ring resonators (CR) of laser gyroscopes (LG).

The proposed method relates to the field of laser gyroscopes based on ring He-Ne lasers with a wavelength of 632.8 nm, used to solve many problems of navigation, measuring angular displacements, geodesy and geophysics.

One of the main sources of LG error is backscattering (OR) on the mirrors of a ring resonator, which leads to the appearance of a deadband at low rotational speeds (the so-called capture threshold) and nonlinear distortions of the scale factor [F. Aronowitz. Optical Gyros and their Applications. RTO AGARDograph 339, 3-1, 1999].

When analyzing the frequency characteristics of a ring laser, it is convenient to use complex values S ₊ and S _- , which are, respectively, the sum and difference of the complex coupling coefficients of counterpropagating waves of the ring laser in the clockwise direction r _cw exp (iϕ _cw ) and the complex conjugate coupling coefficient in the opposite direction clockwise r _ccw exp (-iϕ _ccw ):

S ₊ = [r _cw exp (iϕ _cw ) + r _ccw exp (-iϕ _ccw )],

S _- = [r _cw exp (iϕ _cw ) -r _ccw exp (-iϕ _ccw )].

,

имеем следующее соотношение:In the case of weak coupling, when Ω <

,

we have the following relation:

where ω is the CR beat frequency, Ω is the frequency stand, c is the speed of light, L is the Raman perimeter. The frequencies in the ratio for the beat frequency have dimensions [rad / sec].

It should also be noted that this relation was written for zero detuning of the laser generation frequency relative to the center of the gain line of the active medium. The parameter Ω _G is represented as the following relation:

The coefficients β and θ are, respectively, the parameters of self and mutual nonlinear saturation of counterpropagating waves in the active medium, and α is the gain of the active medium.

It is easy to obtain the following relations for the modules S ₊ and S _- :

Thus, the frequency response of the laser gyroscope is determined by the values of the complex coupling coefficients (CS), or, more precisely, by the three OP parameters: two CS modules and the total phase shift that occurs during backscattering of light (ϕ = ϕ _CW + ϕ _CCW ). Moreover, the CR capture threshold Ω _L is determined by the value of the module S ₊ :

In the manufacturing process of LG, a complex technological cycle takes place, including assembly and adjustment of the RC, vacuum-technological processing, filling with a working gas mixture. At the final stage of the assembly, the basic operational accuracy parameters of the LG are checked. After this, the screening of suitable LH is carried out.

The introduction of methods for monitoring complex coupling coefficients directly in the ring resonator allows rejecting unfit resonators already at the stage of its assembly, which allows not only to avoid labor-intensive technological processes, but also ultimately increase the number of suitable LG.

A known method of controlling the parameters of ring resonators of laser gyroscopes [F. Aronowitz and R.J. Collins, "Mode coupling Due to Backscattering in a He-Ne Traveling-wave Ring Laser", Applied Physics Letters, 9, 55, 1966], which makes it possible to estimate the values of complex CSs by measuring the dependence of the beat frequency of counterpropagating waves of a ring resonator on rotation speed.

The disadvantage of this method is the relatively high complexity, because information on the magnitude of the complex coupling coefficients is formed after a long and expensive complex of vacuum-technological processing and filling a monoblock ring resonator with a working He-Ne gas mixture.

There is also a method [US 4884283 A, 11.28.1989], which consists in the fact that in a ring resonator using radiation from an external He-Ne laser with a wavelength of 632.8 nm, they excite their own vibration in one of the directions and determine the backscattering by the results of measurements the value of the capture threshold, after exceeding the permissible value of which a decision is made from rejection of the ring resonator.

The authors of this method tried to eliminate the disadvantage of the method described above and introduced control of the intensity of backscattering at the stage of adjustment of Raman scattering. In fact, this made it possible to measure the coefficient of coupling coefficient in one of the directions, which, as follows from the above relations, is not enough to predict LG errors associated with OR.

Closest to the proposed is the method [RU 2570096, C1, H01S 3/083, G01C 19/66 of 12/10/2015], which consists in the fact that excite waves of natural vibrations in the ring resonator using radiation from an external laser and additionally excite in the ring resonator own oscillation in the opposite direction by installing at the output mirror of the ring resonator a return mirror, measure the time dependences of the intensities of the counterpropagating waves emerging from the ring resonator, with a longitudinal movement of the return mirror at a distance exceeding half the wavelength of the laser radiation.

The disadvantage of this method is the relative low accuracy of measurements, associated mainly with the asymmetric method of excitation of the resonator modes in opposite directions. As a result, the contrasts of recorded interference patterns for counterpropagating waves vary significantly.

The required technical result is to increase the accuracy of measuring complex coupling coefficients of ring resonators.

The problem is solved, and the required technical result is achieved by the fact that in the method according to which counterpropagating waves are generated in the ring resonator by exciting natural waves in counterpropagating directions using external laser radiation, according to the invention, the counterpropagating waves are formed of equal intensity, a phase shift between them is introduced and determine the values of the complex coupling coefficients from the time dependences of the intensities of the waves emerging from the ring resonator.

In addition, the required technical result is achieved by the fact that for the formation of counterpropagating waves of equal intensity in the ring resonator, the radiation of an external laser is divided by radiation of equal intensity using a translucent beam splitting mirror, the output radiation of which is introduced by rotating mirrors into the ring resonator in opposite directions.

The drawing shows:

in FIG. 1 is a diagram of the optical part of a device that implements the proposed method for measuring complex coupling coefficients in ring resonators of laser gyroscopes;

in FIG. 2 is a functional diagram of a device for measuring complex coupling coefficients in a ring resonator based on the proposed method;

in FIG. 3 - measurement results of complex coupling coefficients in a ring resonator during the antiphase course of two piezoelectric correctors (here the predicted values of the LG capture threshold obtained using the measured values of the complex coupling coefficients are presented here).

In the drawing are indicated:

1 - ring resonator, 2 - translucent beam splitting mirror, 3 - He-Ne laser with a wavelength of 632.8 nm, 4 - optical isolator, 5, 6, 7 - rotary mirrors, 8 - first photodetector, 9 - second photodetector 10 — a unit for recording optical signals, 11, 12, 13, 14, 15 — piezoelectric correctors, 16 — a frequency stabilization unit, 17 — a control unit for piezoelectric correctors, 18 — a personal computer, 19 — a piezoelectric corrector power supply.

The proposed method for measuring the complex coupling coefficients in the ring resonators of laser gyroscopes is implemented as follows.

First, we give a theoretical description of the proposed method for measuring complex coupling coefficients in ring resonators of laser gyroscopes.

Relations for the waves emerging from the ring resonator can be written as follows:

Here, χ _cw and χ _ccw are the phases of counterpropagating waves in the clockwise and counterclockwise directions, respectively, and δ are the losses of the ring resonator in intensity.

For a symmetric scheme, we can assume that the intensities of the counterpropagating waves are equal to:

E ₀ = E _cw = E _ccw .

Then the relationship for the intensity of the waves emerging from the resonator can be written as:

Thus, when introducing a phase difference between counterpropagating waves in the wave intensities, an alternation of maxima and minima will be observed. The contrasts of these extrema are directly proportional to the modules of the coupling coefficients and allows us to determine their values. In this case, the positions of the extrema are shifted relative to each other. The magnitude of this shift determines the magnitude of the total phase shift due to backscattering.

For example, in the case when the position of the minimum intensity of one of the waves coincides with the position of the maximum of the counterpropagating wave, the total phase shift is π radian. As a rule, in ring resonators the value ϕ = ϕ _CW + ϕ _CCW differs slightly from π. For clarity, in FIG. Figure 3 shows the dependence for the phase shift in the form of a difference between its value and π, i.e. for ψ = ϕ-π.

According to the scheme of the optical part of the device that implements the proposed method for measuring complex coupling coefficients in the ring resonators of laser gyroscopes (Fig. 1), the laser radiation enters the ring resonator 1 through a mixing system consisting of a translucent beam splitting mirror 2 and two rotary mirrors 5 and 6, exciting own vibrations in opposite directions. The phase difference between the opposing waves is introduced by moving the rotary mirrors 5 and 6. In FIG. 2 shows a complete functional diagram of a device for measuring complex coupling coefficients in a ring resonator based on the proposed method. Previously, before the measurement behavior, the generation frequency of the He-Ne laser 4 with a wavelength of 632.8 nm is “linked” to the natural frequency of the ring resonator 1. For this, the power resonance signal detected by the second photodetector 9 is fed to the input of block 16 frequency stabilization. The output of the frequency stabilization unit 16 is connected to the input of the piezoelectric corrector 14 mounted on one of the mirrors of the ring resonator 1 and allowing to control the natural frequency of the ring resonator 1. The piezoelectric correctors 11, 12, 13 are connected to the control unit 17 that performs the necessary modes of movement of the rotary mirrors 12 , 13, as well as one of the mirrors of the He-Ne laser 4 with a wavelength of 632.8 nm. The movement of the piezoelectric corrector 15 is controlled by the piezoelectric corrector power unit 19. To reduce the influence of backward reflections of waves emerging from the ring resonator 1 and entering the He-Ne laser 3 with a wavelength of 632.8 nm, an optical insulator 4 is installed in front of its output mirror.

The intensities of the counterpropagating waves emerging from the ring resonator 1 are recorded using the first 8 and second 9 photodetector devices, as well as using the optical signal recording unit 10, made, for example, in the form of an analog-to-digital converter. The output of this unit is connected to a personal computer 18, where the processing of the recorded signals is carried out and the values of the complex coupling coefficients are determined. As a result, the magnitudes of the coupling coefficients of the counterpropagating waves and the total phase shift due to backscattering are determined.

In FIG. Figure 3 presents the results of measurements of the complex coupling coefficients in the ring resonator of a ring He-Ne laser with a wavelength of 632.8 nm, in particular, the dependences of the backscattering parameters during the antiphase course of the piezoelectric correctors controlling the perimeter of the ring resonator. For this, the piezoelectric corrector 15 was connected to the power supply unit 19 and all measurements were performed when this voltage was changed in the range 0-200 V. FIG. Figure 3 also shows the dependence of the predicted value of the LG capture threshold.

Thus, due to the improvement of the known method in the proposed invention, the required technical result is achieved, which consists in increasing the accuracy of measuring the complex coupling coefficients of the ring resonators, since, in particular, a symmetric method for exciting the resonator modes in opposite directions is provided.

Claims (2)

1. A method for measuring complex coupling coefficients in ring resonators of laser gyroscopes, according to which counterpropagating waves are generated in the ring resonator by exciting natural waves in counterpropagating directions using external laser radiation, characterized in that the counterpropagating waves form with equal intensity and introduce a phase shift between them and determine the values of the complex coupling coefficients from the time dependences of the intensities of the waves emerging from the ring resonator. 2. The method according to p. 1, characterized in that for the formation of counterpropagating waves of equal intensity in the ring resonator, the radiation of an external laser is divided by radiation of equal intensity using a translucent beam splitting mirror, the output radiation of which is introduced by rotating mirrors into the ring resonator in opposite directions.

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