RU2388030C1 - Non-collinear acousto-optical filter - Google Patents

Abstract

FIELD: physics, optics.

SUBSTANCE: invention relates to acousto-optics and can be used as a tunable narrow-band filter in optical radiation spectrum analysers. The proposed non-collinear acousto-optical filter has an acousto-optical cell which is coaxial with an optical crystal, mainly paratellurite, which has first and second optical planes and an ultrasonic transducer on the third plane. The filter also has a polariser on the path of the light beam behind the first optical plane. The fourth plane is an optical and input plane for the light beam, and the reflecting second optical plane is slanted relative the fourth plane by 45°. The polariser is placed at the output of the light beam. Between the second and the fourth planes there is also a fifth optical plane which is perpendicular to the fourth plane. The filter also has turning roof prism fitted behind the polariser which is placed on the first optical plane on the path of the light beam, and an additional polariser placed behind the fifth plane of the acousto-optical cell.

EFFECT: simplification of the acousto-optical filter due to exclusion of at least one polariser from its composition.

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Description

The invention relates to acousto-optics and can be used as a tunable narrow-band filter in optical radiation spectrum analyzers.

A noncollinear acousto-optic filter (AOF) is known, in which an active optical crystal is made on the basis of a piezoelectric crystal, an ultrasound absorber is placed on its upper face, and the ultrasound transducer is made in the form of a lattice of antiphase excited electrodes of the type of interdigital / RF Patent No. 2208824, Cl. G02F 1/11, 2003 /.

A disadvantage of the known AOF is the complexity of its manufacture.

Known non-collinear AOF containing an acousto-optical cell (AOI), made in the form of a tetrahedral prism from a uniaxial optical crystal, mainly paratellurite, including the first and second optical faces and an ultrasonic transducer located on the third face of the prism, as well as a polarizer located along the light beam behind the first optical face of the prism / V.I. Balakshy et al. Physical foundations of acousto-optics. - M.: Radio and Communications, 1985, p. 236, 237 /.

This AOF is taken as a prototype.

The disadvantage of the prototype is the need to use two polarizers in it, which complicates the design of the filter.

The technical result obtained from the use of the invention is to simplify AOF by eliminating at least one of the polarizers from its composition.

The technical result is achieved due to the fact that in the known AOF containing AOI, made in the form of a tetrahedral prism from a uniaxial optical crystal, mainly paratellurite, including the first and second optical faces and ultrasonic scanning located on the third face of the prism, as well as a polarizer, located along the light beam behind the first optical face of the prism, the fourth face of the prism is made optical and input for the light beam, and the second optical face is beveled with respect to the fourth face at an angle om 45 °.

In addition, it is possible that between the second and fourth faces of the prism a fifth optical face is additionally arranged, which is perpendicular to the fourth face, while the filter further comprises a rotatable roof-shaped prism mounted behind the polarizer placed behind the first optical face in the direction of the light beam, and an additional polarizer, established beyond the fifth face of AOYA.

The invention is illustrated by drawings. In figure 1, 2 presents two options for filters.

AOF contains (Fig. 1) AOA made in the form of a tetrahedral prism from a uniaxial optical crystal (not digitized in the drawings), mainly from paratellurite.

The prism according to the first embodiment of AOI (FIG. 1) includes four faces 1, 2, 3, 4, and according to the second embodiment (FIG. 2), it also includes an additional face 5. (For convenience, the digitization of the faces in the claims and description coincides )

The optical face 2 of the crystal is beveled at an angle of 45 ° to the optical face 4, while face 4 is made optical, at least at the entrance of the light beam 6. There is also an ultrasonic scanner 7 installed on the face 3 of the prism, and a polarizer 8 installed at the output light beam 6 from a prism.

A feature of the AOF shown in FIG. 2 is the presence in the optical circuit of a pivoting roof-shaped prism 9 and a second polarizer 10 installed beyond face 5 (the non-skewed part of face 2).

It is easy to see that the second variant of the AOF implements the case of a double monochromator, usually including three or four polarizers / Acousto-optical, acoustic and X-ray spectral methods and measuring instruments in science and technology. Proceedings of VNIIFTRI, issue 48 (140), 2005, p. 129 /.

The rotary prism 9 or the AOI itself can be structurally combined with the polarizer 8.

In both AOF versions, the number of polarizers in the optical circuit is reduced by at least one polarizer, i.e., the delivered technical result is achieved.

AOF works as follows.

In the interaction of the ultrasonic wave 11 arising in the crystal during the operation of ultrasonic scanning 7 with a light wave, Bragg diffraction arises, which makes it possible to isolate a sufficiently narrow range of light wavelengths from a wide spectrum of optical radiation, since only those light waves with sufficient length effectively interact with a monochromatic sound satisfy the Bragg condition with accuracy.

By changing the frequency of sound, it is possible to move the measured interval over the optical spectrum over a wide range. This is the basis for the use of AOI as a spectral instrument, tunable optical filter.

Thus, anisotropic diffraction in birefringent crystals is used in AOF. Separation of transmitted and diaphragmed light is carried out by a system of polarizers. A beam of light 6 with an arbitrary polarization hits the AOJ. In this case, the reflecting face 2 serves as the input polarizer, on which the light beam 6 is divided into two beams with ordinary and extraordinary polarizations (not shown). The selection of the diffracted beam of the desired polarization is carried out by the polarizer 8.

In this case, a beam with an unusual polarization deviates from a beam with an ordinary polarization by a significant angle. This angle depends on the material and type of AOY. For example, for AOI from paratellurite with γ = 7 ° and θ = 16.4 ° (where in Fig. 1 s is the optical axis of the crystal) operating in the spectral range 400-800 nm, the angle between the ordinary and extraordinary rays at the output of the AOI is from 7 ° to 9 ° depending on the wavelength of light. Such a significant angle is sufficient to separate these rays or suppress the unusual beam by optical means.

The presence in the optical AOF optical circuit of the optical face 2, beveled at an angle of 45 ° to the optical face 4 (Fig. 1), allows one to exclude one polarizer from the scheme, since in this case the reflector face 2 effectively performs the role of the polarizer.

When implementing the dual monochromator circuit (FIG. 2), the light beam 6 interacts twice with the ultrasonic beam 11. In this case, one or two polarizers are excluded from the circuit. In addition, the input and output rays are spatially separated, which in many cases is important in the practical application of AOF.

Claims (2)

1. A noncollinear acousto-optic filter containing an acousto-optic cell made of a uniaxial optical crystal, mainly paratellurite, including the first and second optical faces and an ultrasonic transducer located on the third face, as well as a polarizer located along the light beam behind the first optical face, characterized in that the fourth face is made optical and input for the light beam, and the reflective second optical face is beveled with respect to the fourth face at an angle of 45 °, and a polarizer is installed at the output of the light beam. 2. The noncollinear acousto-optic filter according to claim 1, characterized in that between the second and fourth faces an additional fifth optical face is arranged perpendicular to the fourth face, the filter further comprising a rotatable roof-shaped prism mounted behind the polarizer located behind the first optical face in the direction light beam, and an additional polarizer mounted behind the fifth facet of the acousto-optic cell.

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