RU134671U1 - LIGHT LIGHT FOR IR IR SPECTRUM - Google Patents

Abstract

1. A fast lens for the infrared region of the spectrum, containing four menisci located along the rays from the objects, the third of which is facing the image plane with a convex surface, the rest are concave, and the following relationships occur between the meniscus optical forces in the lens: ϕ: ϕ: ϕ : ϕ = (0.7 ÷ 0.9) :-( 0.25 ÷ 0.5) :-( 0.3 ÷ 0.6) :( 1.5 ÷ 2), where ϕ, ϕ, ϕ, ϕ - relative optical powers of the first, second, third and fourth menisci, respectively, while the first, third and fourth menisci are made of germanium, and the second - of material with a refractive index Nia not lower than 2.2, transmissive infrared radiation in the wavelength range of from 8 to 14 microns, a fourth meniscus arranged to progress along the optical focusing osi.2. The lens according to claim 1, characterized in that zinc selenide is used as the material for the second meniscus.

Description

The invention relates to the field of optical instrumentation, and in particular to lenses for the infrared (IR) region of the spectrum, and can be used in thermal imagers built on the basis of infrared array IR detectors that do not require cooling to cryogenic temperatures, sensitive in the spectral range from 8 to 14 microns .

A known lens for the infrared region of the spectrum [Patent PM RU 115514, 2009], containing four menisci located along the rays, the distance between the first and second meniscus being (0.8 ÷ 0.95) of the equivalent focal length of the lens, which results in a large lens length (i.e., the distance along the optical axis between the apex of the first refracting surface and the image plane).

The closest analogue to the claimed device by technical nature is a fast lens for the infrared region of the spectrum [Patent RU 2477502, 2013, claim 1 of the formula]. The latter contains four menisci located along the rays, the third of which faces the image plane with a convex surface, the rest are concave. The spectral range of operation is from 8 to 12 microns. The relative aperture of the lens is 1: 1. Moreover, the lens length is not less than (1.67 ÷ 1.75) times greater than the focal length of the lens.

The large relative length of the lens is a disadvantage of the closest analogue.

Reducing the relative length of the lens in the closest analogue cannot be achieved while maintaining the ratios stated in the claims between the parameters and characteristics of the lens, the form of the lenses and their materials included in it while maintaining high relative apertures, image quality and manufacturability.

High manufacturability of the lens design means the use of only spherical (in particular case, flat) refractive surfaces in the lens device, the manufacturing technology of which corresponds to the economic level of accuracy and is provided on standard equipment for the production and assembly of lenses.

The technical result achieved by the proposed device is to reduce the relative length of the lens while maintaining a high relative aperture, image quality and manufacturability.

The technical result is achieved by the fact that in a high-aperture lens for the infrared region of the spectrum containing four menisci located along the rays from the object, the third of which is facing the image plane with a convex surface, the rest are concave, the following relationships between the meniscus optical powers are provided:

where φ ₁ , φ ₂ , φ ₃ , φ ₄ are the relative optical powers of the first, second, third and fourth menisci, respectively,

the first, third and fourth menisci are made of germanium, and the second is made of material with a refractive index of at least 2.2, transmitting infrared radiation in the wavelength range from 8 to 14 μm, the fourth meniscus is mounted with the possibility of focusing movement along the optical axis.

In the particular case of execution, zinc selenide was used as the material for the second meniscus.

Providing the relative meniscus optical powers in the lens in accordance with the stated relation (1), meniscus orientation in the manner described above, making the first, third and fourth meniscus from germanium, and the second from a material with a refractive index of at least 2.2, transmitting infrared radiation in the range wavelengths from 8 to 14 microns, as well as the installation of the fourth meniscus with the possibility of focusing movement along the optical axis, can provide such a device lens, which is achieved by reducing the relative length of the lens while maintaining a high relative aperture, image quality and manufacturability.

The specified solution, in our opinion, has novelty and is industrially applicable. All lenses of the lens are made with spherical refracting surfaces, made of materials, the technology of which is known and tested for manufacturing lenses for the infrared region of the spectrum at enterprises specializing in the production of thermal imaging devices and their elements. At the same time, the authors are not aware of the optical schemes of lenses for the infrared region of the spectrum in which a combination of these features would be implemented.

The proposed device is illustrated by the following graphic materials:

FIG. 1 is an optical diagram of an aperture lens for the infrared region of the spectrum;

FIG. 2 - graphs of the frequency-contrast characteristic (TSC);

FIG. 3 - graphs of the function of energy concentration (FFE) in the spot;

FIG. 4 is a graph of distortion.

The optical system of the fast lens for the infrared region of the spectrum (Fig. 1) contains a positive meniscus 1 facing a concave surface to the image plane and made of germanium; negative meniscus 2, facing a concave surface to the image plane and made of material with a refractive index of at least 2.2, transmitting infrared radiation in the wavelength range from 8 to 14 microns; negative meniscus 3 facing a convex surface to the image plane and made of germanium; positive meniscus 4, facing a concave surface to the image plane and made of germanium. The meniscus optical forces satisfy relation (1). The meniscus 4 is mounted with the possibility of focusing movement along the optical axis. All the refracting surfaces of menisci 1-4 are spherical. Pos. 5, in the form of a plane-parallel plate, a protective glass of a matrix IR radiation detector is additionally shown. At focal length f ', the lens has a length L. Shown in FIG. 1 axial stroke on oblique beams confirms the relationship between the focal length and the lens length along the axis.

In the particular case of execution, meniscus 2 is made of zinc selenide.

The implementation of the device is as follows. Menisci 1-4 focus IR radiation coming from each point of distant objects within the angular field determined by the size of the IR matrix detector and the focal length of the lens, and create real images of objects in the image plane, providing focus for each point of the object into a small spot, comparable in magnitude to the diffraction spot. The plane of the sensitive elements of the matrix receiver of infrared radiation (not shown in Fig. 1) is aligned with the plane of the image of the lens.

To focus radiation coming from objects located at a finite distance from the lens, as well as lens operating temperatures other than the calculated temperature, the meniscus 4 moves within the limits of the focusing movement along the optical axis, the position of the remaining components of the circuit and the IR radiation receiver remains unchanged. This ensures the preservation of image quality and a small error in changing the focal length of the lens.

Table 1 shows the values of optical forces, materials, distances between menisci and their diameters in a specific example of a high-aperture lens for the infrared region of the spectrum. The values of the parameters are given with the normalization f '= 1.

Table 1 Parameters of a specific example of execution The number in accordance with FIG. one Optical power Material Axis distance Diameter one 0.83 Ge 0.10 0.53 2 -0.35 Znse 0.38 0.44 3 -0.41 Ge 0.32 0.39 four 1.70 Ge 0.27 0.42

As follows from table 1, the optical forces of menisci 1-4 are related as follows: φ ₁ : φ ₂ : φ ₃ : φ ₄ = 0.83: -0.35: -0.41: 1.7, and satisfy in this relation (1). Menisci 1, 3 and 4 are made of germanium, meniscus 2 is made of zinc selenide. The meniscus orientation corresponds to the lens circuit shown in FIG. 1. The total value of the focusing movement of the meniscus 4 for focusing and thermal compensation does not exceed 1.6% of the focal length. The lens length L is 1.57.

With the industrial applicability of the inventive lens in a thermal imaging device, based on the values given in table 1 and using standard least squares optimization, which is part of all modern programs for optical calculations, the exact values of the optical forces, radii of refractive surfaces and thicknesses along the optical axis are established for a specific value of the focal length of the lens, the value of which is consistent with the size of the sensitive area of the FPU and the required angular field in space ve items. The presence of only spherical refracting surfaces provides industrial implementation on standard equipment for the production and assembly of lenses, in other words - high adaptability.

An example of the implementation of an aperture lens for the infrared region of the spectrum was analyzed for a focal length f '= 33.2 mm, an entrance pupil diameter of 33.2 mm, a relative aperture of 1: 1, a receiver format of 640 × 480, a pixel pitch of 0.017 mm, (receiver diagonal 2y '= 13.6 mm), L = 52 mm. The relative length of the lens is L / f '= 52: 33.2 = 1.57, i.e. less than in the closest analogue.

In FIG. 2 shows graphs of the frequency response of the lens for an example implementation. On the graph, the abscissa axis shows the values of spatial frequencies (cycle / mm), referred to the plane of the image of the lens, the ordinate axis shows the values of the contrast transfer coefficients in relative units. The frequency response graphs are shown for meridional and sagittal sections (designation T and C, respectively) for different points of the image: on the axis (designation 0 mm), on the edge of the image (designation 6.8 mm), along the image field (designations 4.08 and 5, 4 mm), as well as the diffraction frequency response for a point on the axis (designation Dip. Limit). The imposition of the frequency response curves for different points of the field and their proximity to the diffraction frequency response indicate that the proposed lens retained a high, diffraction-limited image quality, not lower than in the closest analogue. As another criterion confirming the high image quality in the proposed lens, in FIG. Figure 3 shows the FFE graphs for various points of the field: on the axis, along the field, and on the edge of the image field (point designations are similar to Fig. 2), as well as diffractive FCE. From the above graphs, it follows that for image points with coordinates whose values are less than half the horizontal size of the sensitive area of the matrix receiver of infrared radiation, on the site, the side of which corresponds to the pixel pitch of the receiver, the value of the photomultiplier is higher than 0.7. The latter value, according to modern requirements for the image quality of lenses for the infrared region of the spectrum, corresponds to high image quality.

From the distortion graph (Fig. 4) it follows that the latter at the edge of the field does not exceed 0.6%, which meets the criterion of high image quality for lenses of thermal imaging devices.

The above estimates of image quality confirm the industrial applicability of the proposed lens in thermal imaging devices built on modern infrared detectors.

Thus, in comparison with the closest analogue, the proposed aperture lens device for the infrared region of the spectrum provides a reduction in the relative length of the lens to 1.57 while maintaining the relative aperture (not lower than 1: 1), diffractive image quality and high adaptability.

Thus, the technical implementation of the proposed aperture lens for the infrared region of the spectrum, having a combination of these distinguishing features, allows it to be paired with modern matrix IR detectors that do not require cooling to cryogenic temperatures, sensitive in the spectral range from 8 to 14 μm, and obtain small-sized thermal imaging device with high technical and consumer characteristics.

Literature

1. Patent PM RU 115514, 2009.

2. Patent RU 2477502, 2013.

Claims (2)

1. A fast lens for the infrared region of the spectrum, containing four menisci located along the rays from the objects, the third of which faces the image plane with a convex surface, the rest are concave, and the following relationships occur between the meniscus optical forces in the lens: ϕ ₁ : ϕ ₂ : ϕ ₃ : ϕ ₄ = (0.7 ÷ 0.9) :-( 0.25 ÷ 0.5) :-( 0.3 ÷ 0.6) :( 1.5 ÷ 2 ), where ϕ ₁ , ϕ ₂ , ϕ ₃ , ϕ ₄ are the relative optical powers of the first, second, third and fourth menisci, respectively, the first, third and fourth menisci are made of germanium, and the second is made of material with a refractive index of at least 2.2, transmitting infrared radiation in the wavelength range from 8 to 14 μm, the fourth meniscus is mounted with the possibility of focusing movement along the optical axis. 2. The lens according to claim 1, characterized in that zinc selenide is used as the material for the second meniscus.

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