RU2617130C2 - Optical interference mixer for laser gyro - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: optical interference mixer consists of a semitransparent plane mirror, wherein the first surface with a semitransparent reflective coating or film formed by the hemispherical recess surface of radius R1. Second surface is made translucent plane mirror focusing lens radius R2. Wherein R2>R1. Wherein the longitudinal axis of the focusing lens coincides with the longitudinal axis of the hemispherical surface and the axis of the gyroscope photodetector. Thickness of the semitransparent plane mirror is much greater than the recess.

EFFECT: technical result of the invention is to improve the reliability, accuracy and stability of measurement of the angular velocity of the laser gyro with a triangular optical circuit monoblock expulsion and technological focus points of the interference of the mixer, the focusing lens and the photodetector.

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Description

The invention relates to the field of measurement technology, and in particular to devices for measuring angular velocity in orientation systems and navigation of moving objects, and can be used to organize systems for removing and processing output information from ring laser gyroscopes in the form of an interference pattern.

Registration of a phase shift in a ring interferometer is based on the phenomenon of interference arising from the summation of oncoming light rays. For the first time this phenomenon was used in 1904 by A. Michelson in experiments in the study of the "Ether" hypothesis. Similar experiments in 1913 in order to verify the Newtonian "luminiferous ether" were carried out by M. Sagnac [Bayborodin Yu.V. The basics of laser technology. - 2nd ed., Revised. and add. - Kiev: High school. Head Publishing House, 1988 .-- 383 p. - S. 188].

To isolate the signal of the difference frequency of counterpropagating radiation in a laser gyroscope emerging through one of the reflective elements of the ring resonator, the latter are combined in a special optical device - an optical interference mixer. It should be noted that in a laser gyroscope only a small fraction of the energy of the optical signal (approximately 1 ... 10%) interferes on the working face of the optical mixer. For the interference of counterpropagating waves of a laser gyroscope, various schemes of optical mixers are used. It is customary to distinguish between three types of optical mixer circuits: mirror, prism, and holographic [Bayborodin Yu.V. The basics of laser technology. - 2nd ed., Revised. and add. - Kiev: High school. Head Publishing House, 1988 .-- 383 p. - S. 288].

For monoblock designs of a laser gyroscope, the well-known prism scheme is most preferable for matching accuracy [AD Bogdanov Laser gyroscopes. - M .: Military Publishing, 1973. - 72 p. - S. 36].

The structural solution of the optical design of an interference mixer based on an asymmetric prism is shown in FIG. 1. The main elements of this scheme are a translucent flat mirror, which on one side (mirrored) faces the optical channels of the gas laser and the other side is interfaced with the base of the asymmetric prism. When passing through a translucent flat mirror of the 1st and 2nd optical rays, taking into account the passage of the 1st optical beam through an asymmetric prism, interference of the opposing waves occurs on its working face. This leads to the appearance in the working plane AA of the interference pattern, which can be technically processed, for example, using a photodetector. For stable operation of the photodetector, a focusing optical lens is usually added to the processing chain.

The advantage of this optical design should be considered the possibility of its application for almost any optical design of a ring laser.

The disadvantages include:

1) the presence of two components - a translucent flat mirror and an asymmetric prism conjugated with it. This provision does not allow the creation of an integrated structure and imposes restrictions on the technology for creating such a design: pairing two glass surfaces with specified optical characteristics;

2) for the normal operation of the photodetector, a focusing lens is required, which is an external additional element at the output of the optical circuit of the interference mixer. This imposes additional requirements of a technological nature when adjusting the photodetector, focusing lens and directly the interference mixer.

Closest to the claimed device is an optical circuit that implements the alignment function of the optical ring triangular scheme of a laser gyroscope and is made on the basis of a flat mirror of full reflection with a hemispherical surface in its geometric center [I. Gorenstein, I. A. Shulman Inertial navigation systems. / Ed. Cand. tech. Sciences I.A. Gorenstein - M.: Mechanical Engineering, 1970 .-- 230 p. - S. 161-164].

The essence of the technical solution of the prototype is shown in FIG. 2.

In a planar mirror (1) of thickness B, a hemispherical region (3) of radius R is technologically formed. The hemispherical surface is recessed into the first surface (2) of the planar mirror by an amount of h. On the first surface (2) of the flat mirror (1), a film of the corresponding materials / layers of the required thickness is optically opaque for the laser electromagnetic wave. The second surface (4) of the planar mirror (1), unlike the first (2), is optically transparent. In the constructive plan, as a rule, the following basic geometric dimensions of this device are realized: h = 1.0 ... 1.5 mm; B = 3.0 ... 5.0 mm.

The advantage of this scheme is its high degree of integration - all work surfaces are made within one element - a flat mirror (1).

The disadvantage of this scheme is the lack of a real opportunity to provide the interference mode of counterpropagating waves when realizing full reflection in a plane mirror. However, if we change the properties of the film on the surface (2), i.e. to realize a translucent mode, then interference transformation is possible in the structure, but it is practically impossible to technically process it.

Common features of known optical laser gyro interference mixers are:

1) a translucent flat mirror coupled to an asymmetric prism, and a focusing lens;

2) the longitudinal axis of the focusing lens coincides with the perpendicular axis of the working face of the asymmetric prism, a translucent mirror and the axis of the photodetector.

The technical result of the invention consists in increasing the reliability, accuracy and stability of measuring the angular velocity of a laser gyro with a triangular optical monoblock scheme and eliminating the technological aspects of focusing an interference mixer, focusing lens and photodetector due to the creation of a highly integrated optical interference mixer.

The inventive device contains:

1) a translucent flat mirror, the first surface of which is covered with a translucent reflective coating / film, and its thickness is sufficient to implement the process of interference of counterpropagating waves in a monoblock of a ring laser gyro at the interface of its second surface and the area of the focusing lens and photodetector, which ensures the achievement of technical processing the resulting interference pattern using a photodetector at a given distance of the interference screen area;

2) a hemispherical surface of a given radius, integrated with a flat mirror and formed on its first surface to a predetermined depth, the hemispherical surface facing the optical channels of a monoblock ring laser gyroscope;

3) a focusing lens of a given radius, integrated with a flat mirror and formed on its second surface, and the radius of the focusing lens is greater than the radius of the hemispherical surface, and the longitudinal axis of the focusing lens coincides with the longitudinal axis of the hemispherical surface and the axis of the photodetector.

Common to the claimed device and prototype are the following features:

1) a translucent flat mirror of a given thickness, the first surface of which is covered with a translucent reflective coating / film;

2) a hemispherical surface of a given radius, integrated with a flat mirror and formed on its first surface, with the hemispherical surface facing the optical channels of the monoblock ring laser gyroscope.

Different from the prototype are the following features:

1) the thickness of the translucent flat mirror is sufficient to implement the process of interference of counterpropagating waves in a monoblock of a ring laser gyro at the interface between its second surface and the area of the focusing lens and photodetector, which allows you to perform technical processing of the resulting interference pattern using a photodetector at a given distance from the screen area interference

2) a focusing lens of a given radius, integrated with a flat mirror and formed on its second surface, the radius of the focusing lens being greater than the radius of the hemispherical surface, and the longitudinal axis of the focusing lens coinciding with the longitudinal axis of the hemispherical surface and the axis of the photodetector.

The essence of the technical solution of the claimed device discloses a drawing of the device in FIG. 3. The inventive device contains: 1 - a translucent flat mirror; 2 - the first surface of a flat mirror on which a translucent reflective coating / film is applied; 3 - hemispherical surface; 4 - the second surface of a flat mirror, which is optically transparent for interfering counterpropagating waves; 5 - focusing lens.

The device optical interference mixer of a laser gyro operates as follows. The principle of operation is illustrated in FIG. 4. Assume for convenience of analysis that the inventive device of the optical interference mixer is used with a monoblock gyro with open optical channels [RF Patent for the invention. Laser gyroscope, No. 2488773, G01C 19/66, application No. 20111144273/28, 11/01/2011, publ. 07/27/2013, bull. No. 21].

In the working area of the hemispherical surface 3, which is formed on the working surface of the flat mirror 2 and has a working radius R1, two beams simultaneously come from the channels of the optical ring contour of the monoblock. By moving the flat mirror 2 in a certain region perpendicular to the plane of the optical annular contour of the monoblock, the optical rays of the laser source are aligned. As a result, the system of mirrors implements a closed optical ring loop of a monoblock. The maximum deepening of the hemispherical surface 3 into a flat mirror 1 is a predetermined value of h, which in practical cases does not exceed the value of 1.0 ... 1.5 mm.

In the case of a triangular optical monoblock design, both optical beams come to the operating point of the hemispherical surface 3 at the same angles of 30 °. At the interface between the two air-glass media, the angle of refraction will be approximately 27 °, which does not create full optical reflection at the next glass-air interface (second surface 4 of the planar mirror 1) and determines the specific efficiency of the interference process.

For the case of a quadrangular optical monoblock design, both optical beams arrive at the operating point of the hemispherical surface 3 at the same angles, but already equal to 45 °. This leads to the fact that the known angle of refraction will be approximately 42 °, which creates the effect of total optical reflection at the next glass-air interface (second surface 4 of the plane mirror 1). This means that both beams cannot go beyond the surface 4 of the translucent flat mirror 1. This position indicates that the proposed device can only function with a triangular optical monoblock circuit.

Given that the transmittance of the flat mirror 1 is not more than 10%, then 90% of the energy of the oncoming rays is returned to the optical annular contour of the monoblock. This provides a stable mode of operation of the gyroscope.

Part of the energy of the opposing optical rays (approximately 10%), having passed the interface of the working surface 2, penetrate into the volume of the flat mirror 1 with angles of approximately 27 °. Upon reaching the second surface 4, both beams can exit onto the surface 4 of the plane mirror 1, forming an interference pattern of counterpropagating waves in the area of the interference screen at a distance L from surface 4. However, the distance between the interference fringes depends on the distance of the screen L and the distance between the points of exit of the opposing waves d on the surface 4. To ensure the technical processing of the interference pattern, it is advisable to bring the screen area as close to surface 4. 4, the parameters L and d are reciprocal. It follows that it is necessary to increase the parameter d, which proportionally depends on the thickness H of the flat mirror 1. This position determines the following restriction on the ratio of the thickness parameters of the flat mirror 1: H >> h. Practical values of the thickness of a flat mirror 1 can be H = 10 ... 20 mm with h = 1.0 ... 1.5 mm.

Further improving the quality of the technical processing of the interference pattern requires focusing the oncoming optical signals in the plane of the screen zone. For this, a focusing lens 5 integrally formed with a radius R2 is integrally formed on the surface 4 of the planar mirror 1. For confident capture of refracted oncoming optical beams at the mixer output, the following restrictions must be met:

1) the radii of the spherical surfaces must satisfy the condition R2> R1;

2) the longitudinal axis of the focusing lens 5 should coincide with the longitudinal axis of the hemispherical surface 3 and the axis of the photodetector.

The test was performed on a prototype created on the basis of optical glass of the KOI-8 type 12 mm thick with a mirror surface based on an aluminum film created by vacuum deposition and providing 10% transmittance of the optical signal power of counterpropagating waves at an operating wavelength of 1550.0 nm. When realizing spherical surfaces R2 = 50 mm and R1 = 20 mm, it was possible to obtain an interference pattern in the screen area at a distance of 5 cm and to provide technical processing of the interference pattern using a differential photodetector type BPX 48 from Siemens.

The use of the inventive device can significantly reduce the technological costs of both the process of creating interference mixers and the process of aligning ring monoblock laser gyroscopes with a triangular optical scheme, while achieving increased reliability, accuracy and stability of measuring the angular velocity of a laser gyroscope.

Claims (1)

Optical interference mixer of a laser gyroscope, including a translucent flat mirror of thickness H, the first surface of which is covered with a translucent reflective coating / film, a hemispherical surface of radius R1, which is integrated with a flat mirror and formed on its working surface by deepening by an amount of h, with the hemispherical surface facing optical channels of a monoblock ring laser gyroscope, characterized in that a focusing lens of radius R2 is created, which integ is aligned with the second surface of the translucent plane mirror and is limited by the ratio of the radii of the spherical surfaces R2> R1, the longitudinal axis of the focusing lens coincides with the longitudinal axis of the hemispherical surface and the axis of the photodetector of the gyroscope, and the thickness of the translucent plane mirror is significantly increased and limited by the ratio H >> h, which enough to implement the process of interference of counterpropagating waves in a monoblock of a ring laser gyro at the interface of its second surface and the region of positioning of the focusing lens and ensures the achievement of technical processing of the resulting interference pattern using a photodetector at a given distance of the interference screen area.

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