RU52488U1 - DEVICE FOR FORMING AND TEMPERATURE COMPENSATION OF THE IMAGE IN THE INFRARED SPECTRUM - Google Patents

Abstract

Usage: in the field of optical instrumentation in thermal imaging observational devices, the receivers of which are sensitive in the infrared range of the spectrum (8-12 microns). Objective: expanding the functionality of the device by ensuring its operability for receivers of various configurations, as well as increasing the relative aperture to 1: 1 or more, expanding the angular field while maintaining high image quality. SUBSTANCE: in a device for forming and temperature compensation of an image in the infrared region of the spectrum, comprising a housing in which a frame with a lens is movably mounted with a lens including two menisci, an athermalized assembly mounted on the housing, and one of the ends on a frame with a lens, and made in the form of rods made of a material with a low coefficient of expansion, the lens is supplemented with a third meniscus, the first of which is made with a negative facing concave surface to the object, the second and third with positive optically by the forces facing convex surfaces to the object, the third meniscus is set at a distance d from the second, while the following relationships are true:

-0.2 <φ _{I /} φ _equiv <-0.15

0.6 <φ _{II /} φ _equiv <0.7

0.9 <φ _{III /} φ _equiv <1.1

0.4 <φ _{I, II /} φ _equiv <0.6

0.8≤dφ _equiv ≤0.9,

where φ _I , φ _II , φ _III , are the optical forces of menisci I, II, III,

φ _{I, II} - the optical power of the component consisting of I and II menisci,

φ _eq. - optical power of the lens.

In addition, the device is supplemented by a receiver, while the frame with the lens and the receiver are connected to the ends of the rods of the athermalized node using fasteners whose lengths l ₁ and l _{2 are} selected from the condition:

-dn / [φ _equiv (n-1) α ₀ ] = l ₁ + l ₂ + dl ₃ α ₁ ,

where dn are the changes in the refractive index of the lens material from temperature changes,

n is the refractive index of the lens material of the lens,

l ₁ - the length of the mounting element, with which the frame with the lens is connected to the rods of the athermalized node;

l ₂ is the length of the fastener with which the receiver is connected to the rods of the athermalized node;

l ₃ - the length of the rods athermalized node;

α ₀ - coefficient of linear expansion of the material of the fastening elements;

α ₁ - the coefficient of linear expansion of the material of the rods of the athermalized site.

Description

The proposed utility model relates to the field of optical instrumentation and can be used in thermal imaging devices, the receivers of which are sensitive in the infrared (IR) range of the spectrum.

Currently, most of the existing observational infrared optical devices are designed to operate in the ranges of 3-5 microns and 8-12 microns, corresponding to the "windows" of transparency of atmospheric moisture and self-radiation from the observation source. At the same time, systems operating in the region of 8–12 μm have the advantage that they can observe their own infrared radiation from all objects whose temperature is different from 0 ° K, which allows them to register signals from very distant objects.

Until recently, the main drawback of systems operating in the far infrared range was the imperfection of receivers requiring special protection against spurious illumination, mainly deep cooling of surrounding mechanical parts. In this case, the optical system of the lens should have an exit pupil placed in the image space to combine it with the input window of the cryostat [1]. However, with the advent of bolometric detectors [2], the need for these measures disappeared, and, therefore, it became possible to significantly simplify the design of both the entire device and the lens.

Due to the limited number of optical materials that are transparent in the region of 8-12 microns, IR lenses are usually

are made of single-crystal germanium, which is characterized by a large refractive index (n≈4) and high cost. Therefore, when designing optical systems from Germany, it is necessary to minimize the number of optical parts in them in order to reduce reflection losses from surfaces and product prices. At the same time, such lenses should have a large aperture, since they, as a rule, serve to detect distant objects.

Based on these considerations, many modern optical IR systems have a relatively simple design, including 2-3 lenses with significant aperture ratio (aperture value less than 1). At the same time, to achieve a satisfactory image quality, aspherical surfaces are used, including higher orders, which leads to an increase in the cost of such systems [3, 4]. In lenses, for one reason or another lacking aspherical lenses, in order to ensure the required level of image quality, it is usually necessary to significantly reduce the aperture ratio and the angular field, for example [5]. In this regard, the task of creating a device with a lens [6] for an IR system, which would provide the required image quality, aperture ratio and field angle without the use of complex aspherical surfaces and with a moderate number of optical parts, is becoming increasingly relevant.

Another important problem of creating IR lenses using germanium is a significant change in its refractive index from temperature. This causes a defocusing dS 'equal to

dS '= f' dn / (n-1),

where f 'is the focal length of the lens; dn is the change in the refractive index n with a change in temperature by ΔT.

For example, for germanium n = 4, dn = 0.025 with a change in temperature from T = 20 ° C to T = -40 ° C and with f '= 40 mm, dS' = 0.33 mm.

Such defocusing leads to a complete loss of image quality and special temperature compensation devices are needed to compensate for it.

Closest to the claimed technical solution is a temperature compensation device for an optical device [7], comprising a housing in which the frame is movably mounted with a lens including two menisci, an athermalized unit, one end mounted on the body, and the other on the frame.

The thermalized unit is made in the form of rods and ensures the movement of the frame relative to the body when the temperature changes.

On the athermalized assembly and the housing or frame, counterparts are made, respectively elastically mating with each other, which allows to eliminate the gaps between the connected parts.

The disadvantages of the known device include its limited capabilities, since only a lens (optical device) is made thermostatically controlled, this means that the position of the image plane is stable relative to the lens body and this design is intended only for a specific receiver, the image plane of which is aligned with the installation plane .

The main task, which the proposed utility model is aimed at, is to expand the functionality of the device by ensuring its operability for receivers of various configurations, as well as increasing the relative aperture to 1: 1 or more, expanding the angular field while maintaining high image quality.

To solve this problem, a device for the formation and temperature compensation of the image in the infrared region of the spectrum is proposed, which, like the prototype, contains a housing in which a frame with a lens, including two menisci, an athermalized unit mounted on

case, and one of the ends - on a frame with a lens, and made in the form of rods of material with a low coefficient of expansion (α ₁ ).

In contrast to the prototype, the lens is supplemented by a third meniscus, the first of which is made with a negative facing concave surface to the object, the second and third with positive optical forces facing convex surfaces to the object, the third meniscus is set at a distance d from the second, with the following relations :

-0.2 <φ _{I /} φ _equiv <-0.15

0.6 <φ _{II /} φ _equiv <0.7

0.9 <φ _{III /} φ _equiv <1.1

0.4 <φ _{I, II /} φ _equiv <0.6

0.8≤dφ _equiv ≤0.9,

where φ _I , φ _II , φ _III , are the optical forces of menisci I, II, III,

φ _{I, II} - the optical power of the component consisting of I and II menisci,

φ _eq . - optical power of the lens.

In addition, the device is supplemented by a receiver, while the frame with the lens and the receiver are connected to the ends of the rods of the athermalized node using fasteners whose lengths l ₁ and l _{2 are} selected from the condition:

-dn / [φ _equiv (n-1) α ₀ ] = l ₁ + l ₂ + dl ₃ α ₁ ,

where dn is the change in the refractive index of the lens material from temperature changes,

n is the refractive index of the lens material of the lens,

l ₁ - the length of the mounting element, with which the frame with the lens is connected to the rods of the athermalized node;

l ₂ is the length of the fastener with which the receiver is connected to the rods of the athermalized node;

l ₃ - the length of the rods athermalized node;

α ₀ - coefficient of linear expansion of the material of the fastening elements;

α ₁ - the coefficient of linear expansion of the material of the rods of the athermalized site.

The essence of the proposed utility model lies in the fact that, thanks to the proposed design of the lens, the first, second and third menisci act as a single force-correction element, which simultaneously allows expanding the angular field by at least 1.4 times and compensating for higher order aberrations of wide beams while increasing the relative aperture to 1: 1.

At the same time, the first meniscus of the lens, being negative, is oriented with a concave surface toward the object, which compensates for the asymmetry of off-axis beams relative to the main rays while increasing the angular field.

Another advantage of the proposed scheme is that, despite a significant increase in the output aperture, the size of the posterior segment in it is at least 0.35f ' _Σ .

Thus, the proposed device for the formation and temperature compensation of the image in the infrared region of the spectrum with a lens working with a relative aperture of 1: 1 and an angular field of 25 °, providing high image quality, and an athermalized node, provides full compensation for defocusing in the temperature range of -15 ° ÷ + 50 °.

The essence of the claimed utility model is illustrated in the drawing, where Fig. 1 shows a general view of a device for forming and temperature compensation of an image in the infrared region of the spectrum; figure 2 is an optical diagram of the lens and the Appendix, which shows the design parameters and optical characteristics of a particular sample.

The proposed device for the formation and temperature compensation of the image in the infrared region of the spectrum comprises a housing 1, in which a frame 2 with a lens 3 is movably mounted, an athermalized assembly 4 mounted on the housing 1, and one end on a frame 2 with a lens 3.

The thermalized unit 4 is made in the form of rods of material with a small coefficient of expansion (α ₁ ).

Lens 3 consists of three menisci 5, 6 and 7, the first of which meniscus 6 is made with a negative facing concave surface to the object, the second meniscus 6 and the third meniscus 7 with positive optical forces facing convex surfaces to the object, the third meniscus 7 is set to the distance d from the second meniscus 6, while the following relationships are true:

-0.2 <φ _{I /} φ _equiv <-0.15

0.6 <φ _{II /} φ _equiv <0.7

0.9 <φ _{III /} φ _equiv <1.1

0.4 <φ _{1, II /} φ _equiv <0.6

0.8≤dφ _equiv ≤0.9,

where φ _I , φ _II , φ _III , are the optical forces of menisci I, II, III,

φ _{1, II} - the optical power of the component, consisting of I and II menisci,

φ _eq. - optical power of the lens.

The device is supplemented by a receiver 8, while the frame 2 with the lens 3 and the receiver 8 are connected to the ends of the rods of the athermalized node 4 using fasteners 9 and 10, the lengths of which l ₁ and l _{2 are} selected from the condition:

-dn / [φ _equiv (n-1) α ₀ ] = l ₁ + l ₂ + dl ₃ α ₁ ,

where dn is the change in the refractive index of the lens material from temperature changes,

n is the refractive index of the lens material of the lens,

l ₁ - the length of the mounting element 9, through which the frame 2 with the lens 3 is connected to the rods of the athermalized node 4;

l ₂ - the length of the mounting element 10, with which the receiver 8 is connected to the rods of the athermalized node 4;

l ₃ - the length of the rods athermalized node 4;

α ₀ - coefficient of linear expansion of the material of the fastening elements 9 and 10;

α ₁ - coefficient of linear expansion of the material of the rods of the athermalized node 4.

The proposed device for forming and temperature compensation of the image in the infrared spectrum works as follows.

Menisci 5 and 6 of positive optical power form an image in the intermediate plane located behind the focal plane of the lens 3, free from lower order aberrations for the axial point. The meniscus 7 of positive optical power re-projects the intermediate image into the focal plane of the lens and minimizes off-axis points to the coma and additionally has a corrective effect in the region of higher orders of spherical aberration, as well as image curvature.

When the temperature changes, for example, by ΔT, the focal plane shifts by - dS '. The frame 2 with the lens 3 is shifted to the right to the focal plane by the value Δl ₁ , determined by the length of the mount 9 - l ₁ :

Δl ₁ = l ₁ · α ₀ ΔT,

while the rods of the athermalized node 4 practically do not change in length, because they are made of material with a linear coefficient of expansion α ₁ ≪ α ₀ .

On the other hand, the receiver 8 is shifted to the left towards the lens 3 by the value Δl ₂ , determined by the length of the mounting element 10 of the receiver 8:

Δl _{2 =} l ₂ · α ₀ ΔT.

Thus, the fastening elements 9 and 10 provide a part of the defocus compensation dS ′ equal to Δl ₁ + Δl ₂ .

The selected gap d between menisci 6 and 7, in addition to correcting field aberrations of astigmatism and coma, provides an additional shift of the focal plane by

Δd ₌ d · α ₀ ΔT,

Thus, due to the fact that when the temperature changes by + ΔT, the focal plane shifts by - dS ', the proposed device for the formation and temperature compensation of the image in the infrared region of the spectrum compensates for defocusing and ensures good image quality at wide temperature differences.

Appendix 1 shows a lens with the following parameters:

φ _I = -0.18

φ _II = 0.65

φ _III = 0.94

φ _{I, II} = 0.53

dφ _equiv = 0.85

The lens provides an angular field of 25 ° relative aperture 1: 1.07, f ' _eq = 42.8 mm

Image quality: at a frequency of 10 lines / mm, a contrast of at least 0.6 across the entire image field.

INFORMATION SOURCES

1. Orlov V.A., Petrov V.I. Surveillance devices at night and with limited visibility. M. Military ed., 1989.

2. Malyarov V.G. Uncooled thermal infrared matrices. Optical Magazine. 2002. T 69. No. 10. S.60-72.

3. United States Patent No. 6292293, IPC: G 02 B 1/00 of 09/18/2001

4. United States Patent No. 6236501, IPC: G 02 B 1/00 of 05.22.2002

5. Russian Federation, patent No. 2187135, IPC: G 02 B 13/34 from 08/10/2002

6. Russian Federation, patent No. 2183340, IPC: G 02 B 13/34 from 06/10/2002

7. USA, patent No. 6631040, IPC: G 02 B 7/02 of 05/08/2002 - prototype.

Claims (1)

A device for forming and temperature compensating an image in the infrared region of the spectrum, comprising a housing in which a frame with a lens is mounted movably with two menisci, an athermalized assembly mounted on the housing, and one end on a frame with a lens, and made in the form of rods of material with a low coefficient of expansion, characterized in that the lens is supplemented by a third meniscus, the first of which is made negative, facing a concave surface to the object, the second and third with positive optical forces facing convex surfaces to the object, the third meniscus is set at a distance d from the second, while the following relationships are true: -0.2 <φ _{I /} φ _equiv <-0.15 0.6 <φ _{II /} φ _equiv <0.7 0.9 <φ _{III /} φ _equiv <1.1 0.4 <φ _{I, II /} φ _equiv <0.6 0.8≤dφ _equiv ≤0.9, where φ _I , φ _II , φ _III , are the optical forces of menisci I, II, III; φ _{I, II} - the optical power of the component consisting of I and II menisci; φ _equiv - the optical power of the lens, in addition, the device is supplemented by a receiver, while the frame with the lens and the receiver are connected to the ends of the rods of the athermalized node using fasteners whose lengths l ₁ and l _{2 are} selected from the condition: -dn / [φ _equiv (n-1) α ₀ ] = l ₁ + l ₂ + dl ₃ α ₁ , where dn - changes in the refractive index of the lens material from temperature changes; n is the refractive index of the lens material of the lens; l ₁ - the length of the mounting element, with which the frame with the lens is connected to the rods of the athermalized node; l ₂ is the length of the fastener with which the receiver is connected to the rods of the athermalized node; l ₃ - the length of the rods athermalized node; α ₀ - coefficient of linear expansion of the material of the fastening elements; α ₁ - the coefficient of linear expansion of the material of the rods of the athermalized site.