RU2132076C1 - Photomixing pair of optical prisms for laser gyro with prisms of total internal reflection - Google Patents

Abstract

FIELD: gyroscopes. SUBSTANCE: photomixing pair of optical prisms for laser gyro with prisms of total internal reflection has first prism with two refracting and one reflecting faces, second prism with inlet, outlet, reflecting and setting faces. Optical contact between setting face of second prism and reflecting face of first prism lies outside generation field of laser gyro. Value of distance from reflecting face of first prism to inlet face of second prism changes smoothly from zero close to rib formed by setting and inlet faces of second prism to three lengths of radiation wave near rib formed by inlet and reflecting faces of second prism. EFFECT: increased level of precision of laser gyro operating in wide temperature range. 4 dwg

Description

 The technical field to which the invention relates.

 Laser gyroscopy; IPC G 01 C 19/66.

 A known photo-mixing pair of optical prisms of a laser gyroscope, which is a prototype, operating on the principle of total internal reflection (PVO) violation by the small gap between the first (ring laser resonator prism) and the second prism, having a constant transmittance over the radiation aperture area and providing a rigid diaphragm for the radiation beam, moreover, the second prism is fixed on the first glue [1]. Rigid diaphragm refers to the diaphragm of a laser beam, in which a small shift of the radiation beam (of the order of 0.05 mm) or a change in the beam diameter corresponds to a significant (of the order of 100%) change in the introduced diffraction loss. In the temperature range, adjustments can reach values of the order of 0.1 mm. Rigid diaphragm reduces the accuracy of the laser gyroscope in the presence of adjustments of different origin. The glue connection does not provide sufficient mechanical rigidity and strength of the connection, especially in a wide temperature range, because of which the constancy of the gap between the first and second prisms, and hence the transmittance, is not ensured.

 The invention aims to increase the accuracy of a laser gyroscope operating in a wide temperature range by reducing at least an order of magnitude the steepness of the dependence of diffraction loss on the input of the diaphragm deeper into the generation field.

 The design of the prototype is illustrated in FIG. 1. Prism 1 has two refracting faces 2, 3 and a reflecting face (air defense face) 4. Prism 5 has a reflecting face (air defense face) 6, an input face 7 and an output face 8. Face 6 is perpendicular to face 7 with a small deviation from perpendicularity ( about 1 ') for the formation of an interference pattern. Facets 6 and 7 form an interference rib. The second prism is fixed on the first filling of the gap with glue outside the generation zone, while there is a sputtering on the input face of the second prism, which sets the clearance to 3 radiation wavelengths between the input face of the second prism and the reflective face of the first prism. In this case, the input face partially overlaps the spot of generation on the reflective face of the first prism. The presence of a small gap leads to the appearance of an air defense violation, which consists in the fact that when the conditions of total internal reflection are fulfilled, the radiation is nevertheless not completely reflected. Due to this phenomenon, the input face of the second prism, partially overlapping the generation spot on the reflective face of the second prism, outputs a small (of the order of 0.01%) part of the radiation of counterpropagating radiation waves of a ring laser, simultaneously performing the function of iris diaphragm. The radiation from one of the counterpropagating waves extracted from the resonator propagates to the output face of the second prism. The extracted radiation of the second counterpropagating wave is deflected by the reflection face of the second prism so that the reflected radiation propagates to the output face of the second prism with a small angle (of the order of 1 ′) with respect to the radiation of the first wave. In this case, a running interference pattern is formed in the plane of the photodetector, from which the gyro rotation parameters are then extracted.

 This design is inoperative in a wide temperature range for the following reasons: significant thermal readjustments of the order of 0.1 mm, leading to a change in the diffraction properties of the photo-mixing pair of prisms and the power of the output radiation; unstable properties of the adhesive, leading to instability of the gap between the first and second prisms of the pair, as a result of which the diffraction properties of the pair and the power of the output radiation also change.

 All these physical phenomena lead to a change in the difference in intensities for counterpropagating waves. The difference in intensities leads to an additional difference in the frequencies of the opposite waves, described by formula (15.6) from [2]. This frequency difference leads to an error called the zero-shift of the laser gyro. In rearrangements (thermal, mechanical), the diffraction conditions change unequally for counterpropagating waves, which leads to an additional change in the magnitude of the zero shift. A constant zero shift can be taken into account when calibrating a laser gyro, however, in the temperature range, the zero shift becomes a variable, which reduces the accuracy of the laser gyro.

 To stabilize the zero shift, a design of a photo-mixing pair of prisms is required, which is slightly sensitive to rearrangements.

 A proposed photo-mixing pair of prisms is shown in FIG. 2. A mounting face 9 is introduced into the structure, the second prism being installed by optical contact along this face onto the reflective face of the first prism. The installation and input faces of the second prism form the installation rib. The input face of the second prism completely covers the generation spot, and the gap varies smoothly from 0 at the mounting edge to 3 (depending on the required transmittance of radiation) radiation wavelengths at the interference edge. The optical contact between the mounting face of the second prism and the reflecting face of the first prism is an essential feature due to the fact that during optical contact, firstly, a new property arises - the intermolecular interaction between the mounting face of the second prism and the reflective face of the first prism; secondly, the reflection coefficient of the reflecting face of the first prism will be close to zero in the zone of optical contact, which is the basis for choosing the law of a smooth change in the distance from the reflective face of the first prism to the input face of the second prism.

 The proposed design provides the output of radiation due to the effect of violation of air defense by a small (up to 3 radiation wavelengths) variable gap between the prisms of the pair. Soft aperture is ensured by the transmittance gradient arising due to the variability of the gap. Soft aperture refers to aperture in which a small shift in the radiation beam or a small change in the diameter of the beam corresponds to a small change in the introduced diffraction loss. Thanks to the ability to diaphragm, there is no need for a specially introduced diaphragm, which reduces diffraction loss and backscattering of radiation. The stability of the radiation bias is provided by fixing the prisms with a rigid and strong optical contact.

 Thus, the proposed combination of three essential features: installation face; optical contact between the mounting face of the second prism and the reflective face of the first prism; a smooth change in the distance from the reflective face of the first prism to the input face of the second prism from zero at the installation face to three radiation wavelengths at the interference edge of the second prism; gives a new property: increasing the accuracy of the laser gyroscope in the temperature range, and each individual symptom does not give this positive effect.

The list of figures of drawings and other materials:
FIG. 1 is a drawing of a prototype of a photo-mixing pair of prisms,
FIG. 2 is a drawing of the proposed photo-mixing pair of prisms, the relative location of the prisms of the pair, the optical axis,
FIG. 3 is a graph of the distribution of the reflection coefficient of radiation over the cross section of the gap,
FIG. 4 is a graph of sensitivity to readjustment for the proposed mixing prism and prototype.

 Information confirming the possibility of carrying out the invention.

 The design of the photo-mixing pair of prisms is shown in FIG. 2. In FIG. Figure 3 shows the distribution of the energy reflection coefficient over the cross section in the case of a wedge-shaped gap, i.e. gap, in which the gap varies linearly from 0 at the mounting edge of the second prism to 3 radiation wavelengths at the interference edge of the second prism. In FIG. 3, the X coordinate corresponds to the distance from the middle of the wedge-shaped gap.

 The wedge-shaped gap has a variable transmittance over the gap section.

ik_2zd = α;

где τ - коэффициент пропускания по интенсивности зазора размером d;
n - показатель преломления материала призм;
θ - угол падения излучения внутри первой призмы;
ε₁ - диэлектрическая проницаемость материала призм;
ε₂ - диэлектрическая проницаемость воздуха;

волновой вектор излучения в призмах;
λ - длина волны излучения.The dependence of the energy transmittance of radiation on the magnitude of the gap has the form

ik _2z d = α;

where τ is the transmission coefficient for the intensity of the gap of size d;
n is the refractive index of the material of the prisms;
θ is the angle of incidence of radiation inside the first prism;
ε ₁ - dielectric constant of the material of the prisms;
ε ₂ - dielectric constant of air;

wave vector of radiation in prisms;
λ is the radiation wavelength.

 To confirm the receipt of the above technical result, comparative calculations of sensitivity to rearrangements were made. Sensitivity to adjustments is defined as the ratio of the change in insertion loss to the shift of the optical beam during thermal adjustments. The calculation results are shown in figure 4 for the prototype and the proposed design. In figure 4, ΔS is the amount of adjustment, ΔA is the change in insertion loss.

 It is obvious that the sensitivity to rearrangements is significantly lower for the proposed version of the mixing prism.

Literature
1. II St. Petersburg International Conference on Gyroscopic Engineering and Navigation. Part 1. - St. Petersburg, 1995, p. 125-127.

 2. Zeiger S.G., Klimontovich Yu.L., Landa P.S. et al. Wave and fluctuation processes in lasers / Ed. Yu.L. Klimontovich - Moscow: Nauka, 1974.

Claims (1)

 A photomixing pair of optical prisms for a laser gyro with total internal reflection prisms, including the first and second prisms, the first prism containing two refracting faces and one reflecting face, and the second prism containing input, output and reflecting faces, characterized in that the second prism is introduced mounting face, there is an optical contact between the mounting face of the second prism and the reflecting face of the first prism outside the laser gyroscope generation field, the distance from the reflecting face being of the first prism to the input face of the second prism smoothly changes from zero at the edge formed by the installation and input faces of the second prism to three radiation waves at the edge formed by the input and reflecting faces of the second prism.

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