RU2542790C1 - Infrared system - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: infrared system consists of a first channel, comprising an afocal attachment and a focusing lens arranged in series, a second comprising an input lens and a projection lens and a photodetector which are common for the first and second channels and are arranged in series. The system also comprises devices for switching radiation flux from the first and second channel to the photodetector. In the first channel, the focusing lens has a discretely variable focal distance. In the second channel the input lens has a smoothly variable focal distance. The radiation flux switching device is installed in front of the projection lens.

EFFECT: longer detection range and high spatial resolution of the system owing to smoother variation of the focal distance by expanding the variation range of focal distance towards the maximum value.

5 cl, 1 dwg, 4 tbl

Description

The invention relates to the field of instrumentation and can be used in optoelectronic systems for the detection and recognition of objects in security systems.

Known are fully reflective optical systems with a discretely variable angular field of view (see patents EP 1679538 A1, publ. 12.07.2006, US 6084727 A, publ. 04.07.2000), in which the change in the field of view is carried out by a system of switching flat mirrors . Also known are lens optical systems with discrete and continuously variable focal lengths (see patents RU 2460101, publ. 12/20/2011, RU 2400784, publ. 09/27/2010, RU 2310217, publ. 10.11.2007), in of which a discrete change in the focal length is carried out by introducing an additional lens group into the optical path or by moving one of the components, and a continuous change in the focal length is carried out by simultaneously moving the two components.

, при этом значение максимального фокусного расстояния не превышает 500 мм.In these systems, the focal length variation (angular field of view) does not exceed 9 ^× $$(M=f_{\max }^{\text{'}\text{'}}/f_{\min }^{\text{'}\text{'}})$$

while the maximum focal length does not exceed 500 mm.

Closest to the technical nature of the claimed optical system, selected as a prototype, is an infrared front view system (see patent EP 1335176 A1, IPC ⁷ G02B 13/14, publ. 08/13/2003), including two channels that work with with its input windows and interacting with flat mirrors:

- the first channel of a narrow field of view;

- the second channel of medium and wide fields of view.

The first channel contains an afocal nozzle consisting of an input lens and an ocular part, a focusing lens, a projection lens, and a photodetector. The second channel also contains an afocal nozzle consisting of an input lens and an ocular part, a focusing lens, a projection lens, and a photodetector. The input lenses of the afocal nozzles are separate for the first and second channels, while in the first channel the input lens has a fixed value of the field of view (focal length), and in the second channel the field of view (focal length) of the input lens is discretely changed, and the change is made by entering into the optical a path or a conclusion from it of mobile lens groups. The ocular part of the afocal nozzles, the focusing lens, the projection lens, and the photodetector are common to the first and second channels. Switching the radiation fluxes of the first and second channels to the photodetector, as well as changing the field of view in the second channel, is carried out using a device containing a movable flat mirror and two movable lens groups. When a moving mirror is inserted into the optical path, the system switches to work in the first channel in the narrow field of view mode; when a movable mirror is withdrawn from the optical path and the first movable lens group is input, the system switches to work in the second channel in the medium field of view mode; when a movable mirror is withdrawn from the optical path and a second movable lens group is introduced, the system switches to work in the second channel in the wide field of view mode.

The prototype system operates in the spectral range of 8-10 μm, the diameter of the entrance pupil (D ₀ ) is 220.2 mm

Given the fact that in the indicated spectral range it is not practical to use optical circuits with a diaphragm number exceeding the value of 2.8 (K = f ′ / D ₀ ), the maximum focal length of the prototype system does not exceed 620 mm.

The problem to which the invention is directed is to increase the rate of change of the focal length of the infrared system by expanding the range of the focal length to the maximum value, which will increase the detection range and increase the spatial resolution of the system.

This goal is achieved by the fact that in an infrared system consisting of a first channel containing a series-mounted afocal lens and a focusing lens, a second channel containing an input lens, and a projection lens and a photodetector, as well as a switching device, common to the first and second channels radiation fluxes of the first and second channels to the photodetector; in the first channel, the focusing lens is made with a discretely variable focal length and in the second channel the input lens is made with a continuously variable focal length, while the device switching the radiation flux is installed in front of the projection lens.

And also the fact that the afocal nozzle of the first channel is made in the form of two reflective elements.

And also the fact that the focusing lens of the first channel is made in the form of sequentially mounted fixed positive convex-concave lenses, movable negative convex-concave and concave-convex lenses mounted to move along the optical axis from one fixed position to another, while the distance between the vertices of the surfaces of the movable lens remains unchanged, and the stationary positive plano-convex lens.

And also the fact that the input lens of the second channel is made in the form of sequentially mounted fixed convex-concave lenses, movable negative convex-concave and biconcave lenses mounted with the possibility of simultaneous movement along the optical axis, while the distance between the vertices of the surfaces of the moving lenses changes, two fixed positive convex-concave lenses and a fixed negative convex-concave lens.

And also the fact that the projection lens is made in the form of a positive convex-concave lens.

The drawing shows an optical diagram of an infrared system with the arrangement of elements in the channels corresponding to the maximum focal length.

The infrared system contains the first channel I, which includes an afocal nozzle installed in series along the optical axis, which can be made in the form of two reflective elements 1 and 2, a flat mirror 3, a focusing lens containing a fixed positive convex-concave lens 4, movable negative convex-concave lens 5 and concave-convex lens 6, mounted with the possibility of movement along the optical axis from one fixed position to another, while the distance between the vertices of the surfaces of the movable lenses remains unchanged, a stationary positive plano-convex lens 7, a flat mirror 8, a second channel II, comprising an input lens made in the form of sequentially mounted stationary positive convex-concave lens 9, movable negative convex-concave lens 10 and biconcave lens 11 mounted with the possibility of simultaneous movement along the optical axis, while the distance between the vertices of the surfaces of the moving lenses changes, two fixed positive convex-concave lenses 12 and 13, a stationary negative convex-concave lens 14, and sequentially mounted projection lens common to the first I and second II channels, comprising a positive convex-concave lens 15, and a photodetector 16, as well as a device for switching radiation fluxes the first I and second II channels to the photodetector 16, made in the form of a movable flat mirror 17 and mounted in front of the projection lens 15.

Technical characteristics of the infrared system operating in the spectral range of 3 ... 5 microns are shown in table 1.

Table 1 Specifications First channel Second channel Focal length mm 1200/600 400 ... 50 Diameter of entrance pupil, mm 300/150 100 ... 12.5 Central Shielding Ratio 0.25 / 0.5 - Linear field of view in the image space, mm 9.6 × 7.68 9.6 × 7.68

The design parameters of channel I of the infrared system are shown in table 2, channel II in table 3.

table 2 Item no. Surface radius mm Axial thickness, mm Material one r ₁ = -1000 ¹⁾ d ₁ = -375 2 r ₂ = -250 ²⁾ d ₂ = 445 3 r ₃ = ∞ / -45 ° d ₃ = 94 four r ₄ = 106.86 d ₄ = 7 Silicon r ₅ = 188.59 d ₅ = 50/35 5 r ₆ = 681.8 d ₆ = 4 Germanium r ₇ = 84.43 d ₇ = 21.7 6 r ₈ = -80.81 d ₈ = 4 Germanium r ₉ = -114.22 d ₉ = 10/25 7 r ₁₀ = ∞ d ₁₀ = 6 Silicon r ₁₁ = -125.9 ³⁾ 8 r ₁₂ = ∞ / -45 ° d ₁₁ = 28.8 17 (I) r ₁₃ = ∞ / -45 ° d ₁₂ = 141.7 fifteen r ₁₄ = 45.195 d ₁₄ = 4 Germanium r ₁₅ = 181.4 ^{4) 1), 2), 3)} - aspherical surfaces; ⁴⁾ - aspheric-diffraction surface

Table 3 Item no. Surface radius mm Axial thickness, mm Material 9 r ₁ = 129.06 d ₁ = 10 Silicon r ₂ = 192.93 ⁵⁾ d ₂ = 66 10 r ₃ = 74.49 d ₃ = 6 Silicon r ₄ = 59.72 ⁶⁾ d ₄ = 66 eleven r ₅ = -87.93 ⁷⁾ d ₅ = 4 Germanium r ₆ = 137.3 d ₆ = 5.2 12 r ₇ = 99.47 d ₇ = 6 Silicon r ₈ = 459.1 d ₈ = 30.6 13 r ₉ = 28.02 d ₉ = 7 Silicon r ₁₀ = 40.84 d ₁₀ = 1 fourteen r ₁₁ = 41.77 d ₁₁ = 5 Germanium r ₁₂ = 26.38 ⁸⁾ 17 (II) r ₁₃ = ∞ / 45 ° d ₁₂ = 48.4 d ₁₃ = 18.8 fifteen r ₁₄ = 43.22 d ₁₄ = 4 Germanium r ₁₅ = 151.18 ^{9) 5), 9)} - aspheric-diffraction surfaces; ^{6), 7), 8)} - aspherical surfaces

In channel I, the system operates as follows: the radiation flux enters element 1 of the afocal nozzle, is reflected from it, falls onto element 2, is reflected from it, and, deflecting with a flat mirror 3, enters the first lens 4 of the focusing lens, passes through lenses 4, 5 , 6, 7 (in this case, the movable lenses 5 and 6 occupy a position corresponding to the focal length f ′ = 1200 mm), is deflected by a flat mirror 8 and focused in the plane of the intermediate image PPI (I), then deflected by a flat mirror 17 of the device for switching radiation fluxes Ia channels installed in position 17 (I), passes through a lens of the projection lens 15 and enters the photodetector 16, in the plane of the sensitive elements of which an image is formed.

When moving the lenses 5 and 6 of the focusing lens by 15 mm relative to the occupied position, the focal length changes discretely and takes the value f ′ = 600 mm, while the image is formed in the same plane of the sensitive elements of the photodetector.

In channel II, the system operates as follows: the radiation flux enters the first lens 9 of the input lens, passes through the lenses 9, 10, 11, 12, 13, 14 (while the movable lenses 10 and 11 occupy a position corresponding to the focal length f ′ = 400 mm) and focuses in the plane of the intermediate image PPI (II), then it is deflected by a flat mirror 17 of the channel radiation flux switching device installed in position 17 (II), passes through the lens 15 of the projection lens and enters the photodetector 16, whereby the image is formed in the same plane photodetector device sensitive elements.

With the simultaneous movement of the lenses 10 and 11 of the input lens (each of the lenses moves according to its own law), the focal length is smoothly changed to f ′ = 50 mm, while the image is formed in the same plane of the sensitive elements of the photodetector.

Table 4 shows some values of the variable air gaps d ₂ , d ₄ , d _{6 of the} input lens of channel II.

Table 4 Focal length mm d ₂ mm d ₄ mm d ₆ mm 400 66 66 5.2 200 69.5 47.95 19.75 one hundred 58.3 50.3 28.6 fifty 31 73 33,2

, в канале II минимальное значение фокусного расстояния $$f_{\min }^{\text{'}}=50мм$$

, общая кратность изменения фокусного расстояния $$M=f_{\max }^{\text{'}}/f_{\min }^{\text{'}}=1200/50={24}^{\times }$$

. При этом изменение происходит в три ступени: при перемещении линз 5 и 6 в канале I фокусное расстояние изменяется дискретно, кратность его изменения составляет M₁=1200/600=2^×, при переключении подвижного плоского зеркала 17 из положения 17 (I) в положение 17 (II) фокусное расстояние дискретно изменяется, кратность его изменения составляет M₂=600/400=1,5^×, а при перемещения линз 10 и 11 в канале II фокусное расстояние изменяется плавно и кратность его изменения составляет M₃=400/50=8^×. Общая кратность изменения фокусного расстояния инфракрасной системы M=M₁·M₂·M₃=2·1,5·8=24^×.In channel I, the maximum focal length of the infrared system $$f_{\max }^{\text{'}\text{'}}=1200mm$$

, in channel II, the minimum value of the focal length $$f_{\min }^{\text{'}\text{'}}=\mathrm{fifty}mm$$

, the total zoom ratio $$M=f_{\max }^{\text{'}\text{'}}/f_{\min }^{\text{'}\text{'}}=1200/\mathrm{fifty}={24}^{\times }$$

. In this case, the change occurs in three stages: when the lenses 5 and 6 are moved in channel I, the focal length changes discretely, its multiplicity of change is M ₁ = 1200/600 = 2 ^× , when the movable flat mirror 17 is switched from position 17 (I) to 17 (II), the focal length changes discretely, the rate of change is M ₂ = 600/400 = 1.5 ^× , and when the lenses 10 and 11 move in channel II, the focal length changes smoothly and the frequency of change is M ₃ = 400/50 = 8 ^× . The total rate of change in the focal length of the infrared system is M = M ₁ · M ₂ · M ₃ = 2 · 1.5 · 8 = 24 ^× .

Thus, the implementation of the infrared system in accordance with the formula of the claimed materials allows you to increase the rate of change of the focal length by expanding the range of the focal length in the direction of the maximum value, which increases the resolution and increase the detection range.

Claims (5)

1. An infrared system consisting of a first channel containing a sequentially mounted afocal lens and a focusing lens, a second channel containing an input lens, and common projection lens and photodetector common to the first and second channels, as well as a device for switching radiation fluxes of the first and second channels to a photodetector, characterized in that in the first channel, the focusing lens is made with a discretely variable focal length, and in the second Nala input lens configured to continuously variable focal length, the radiation flow switching device is mounted in front of the projection lens. 2. The system according to claim 1, characterized in that the afocal nozzle of the first channel is made in the form of two reflective elements. 3. The system according to claim 1, characterized in that the focusing lens of the first channel is made in the form of sequentially mounted fixed positive convex-concave lenses, movable negative convex-concave and concave-convex lenses mounted to move along the optical axis from one fixed position to another, while the distance between the vertices of the surfaces of the movable lenses remains unchanged, and the stationary positive plano-convex lens. 4. The system according to claim 1, characterized in that the input lens of the second channel is made in the form of sequentially mounted fixed positive convex-concave lenses, movable negative convex-concave and biconcave lenses mounted with the possibility of simultaneous movement along the optical axis, while the distance between the vertices of the surfaces of the movable lenses changes, two fixed positive convex-concave lenses and a fixed negative convex-concave lens. 5. The system according to claim 1, characterized in that the projection lens is made in the form of a positive convex-concave lens.