CN115728919A - Miniaturized high-resolution wide-temperature athermal infrared optical system - Google Patents

Abstract

The invention discloses a miniaturized high-resolution wide-temperature athermalized infrared optical system which consists of a first positive meniscus lens, a double-concave negative lens, a second positive meniscus lens and a negative meniscus lens which are coaxially arranged from an object space to an image space in sequence; the first meniscus positive lens, the second meniscus positive lens and the meniscus negative lens are all arranged in a bent mode towards the image side. The optical system can be adapted to a 1280 multiplied by 1024 high-resolution long-wave non-refrigeration type detector, works in a wide temperature range of minus 55 ℃ to plus 70 ℃, does not cause the reduction of the imaging quality of the system due to defocusing caused by the change of the ambient temperature, and realizes no thermalization; the chalcogenide glass with low refractive index temperature coefficient is introduced, and an optical passive athermalization mode is adopted, so that the simplification and miniaturization of the system structure are realized.

Description

Miniaturized high-resolution wide-temperature athermal infrared optical system

Technical Field

The invention relates to the technical field of uncooled infrared optical systems, in particular to a miniaturized high-resolution wide-temperature athermalized infrared optical system.

Background

With the rapid development of infrared night vision technology, infrared thermal imaging is receiving more and more extensive attention, and the development of an infrared detector of a core technology thereof has been greatly developed. Compared with a refrigeration type detector, the detection efficiency of the non-refrigeration detector is generally low, but the price of the non-refrigeration detector is gradually reduced along with the continuous reduction of the pixel size and the continuous improvement of the sensitivity of the non-refrigeration infrared detector. The uncooled infrared detector has the advantages of light weight, small size, low power consumption, high reliability, easiness in carrying and the like, and has a very wide application prospect in various fields of industry, agriculture, national defense, medical treatment, traffic, environmental protection and the like in recent years.

However, the refractive index of an optical material typically changes with temperature, which changes the focal length of the lens or optical system. The temperature coefficient of infrared optical materials is much larger than that of ordinary optical glasses, e.g. typical value of dn/dt for germanium single crystal is about 396 x 10 ^-6 /. Degree.C., and the temperature coefficient of K9 glass is only 2.8X 10 ^-6 V. C. Thus, the temperature effect on the refractive index is particularly pronounced in infrared systems. With the change of the environmental temperature, the refractive index, the curvature and the thickness of the optical lens, the part interval and the like all change, so that the infrared optical system generates heat defocusing, and the imaging quality of the system is poor. Therefore, athermal infrared optical systems are becoming a mainstream development direction for high-precision infrared optical systems.

There are three main methods for designing infrared systems without heating: the first is a mechanical passive compensation method, which is to use a temperature-sensitive mechanical material or memory alloy to make one or a group of lenses generate axial displacement, so as to compensate the displacement of the image plane caused by temperature variation. The method needs to calculate the position of the optimal phase surface at different temperatures, and compensates the displacement of the optimal image surface through different expansion and contraction amounts of the structural material according to the displacement of the optimal phase surface; the second method is an electronic active compensation method, which is to detect the variation of temperature by using a temperature sensor, then calculate the image plane displacement caused by the temperature variation, and drive a lens to generate axial displacement by using a motor so as to achieve the compensation effect; the third is an optical passive compensation method, in which the optical passive athermalization design utilizes the difference between the thermal properties of the optical materials to eliminate the influence of temperature by the reasonable combination of different property materials, thereby obtaining athermal effect. The mode has the advantages of relatively simple mechanism, small size, light weight, no need of power supply and good system reliability, and has the highest comprehensive efficiency, so that great attention is paid.

The optical system developed by the refraction/diffraction mixed element has incomparable advantages in the aspects of improving the imaging quality of the system, reducing the volume and weight of the system, reducing the cost and the like due to the fact that the diffraction optical element has negative dispersion characteristic and negative temperature characteristic, can realize random phase modulation on the wave surface and is matched with a common optical element.

The infrared detector with large area array scale needs to be matched with an infrared optical lens with a large target surface, otherwise, four corners of an infrared image output by the system are shiny. Therefore, the infrared optical system should be designed such that the target surface size is not smaller than the target surface size of the selected infrared detector.

The conventional optical passive athermal long-wave infrared optical system adopts infrared materials such as monocrystalline germanium, zinc selenide, zinc sulfide and the like, and the temperature coefficient of the conventional infrared materials is large, so that the optical system has the defects of more lenses, relatively complex structure and unfavorable miniaturization design in order to realize the system working in a wide temperature range.

Disclosure of Invention

The invention provides a miniaturized high-resolution wide-temperature athermalized infrared optical system. The optical system adopts chalcogenide glass with low temperature coefficient, ensures the adaptation of a 1280 multiplied by 1024 high-resolution long-wave non-refrigeration type detector and can well image in a wide temperature range of minus 55 ℃ to plus 70 ℃; because the number of system lenses is small and a complex temperature compensation mechanism is not needed, the miniaturization is realized.

In order to achieve the purpose, the invention adopts the specific scheme that:

a miniaturized high-resolution wide-temperature athermalized infrared optical system comprises a first positive meniscus lens, a double-concave negative lens, a second positive meniscus lens and a negative meniscus lens which are coaxially arranged from an object space to an image space in sequence; the first positive meniscus lens, the second positive meniscus lens and the negative meniscus lens are all arranged in a bent mode towards the image.

Furthermore, the material adopted by the first positive meniscus lens is single-crystal germanium; the materials used for the double concave negative lens, the second positive meniscus lens and the negative meniscus lens are all chalcogenide glass IRG206.

Further, let the focal length of the optical system be f, the effective focal length of each lens included in the optical system of the present invention satisfies the following condition:

the effective focal length f1 of the first meniscus positive lens meets the condition that f1/f is more than or equal to 1.0 and less than or equal to 1.2;

the effective focal length f2 of the biconcave negative lens satisfies: f2/f is more than or equal to-0.7 and less than or equal to-0.6;

the effective focal length f3 of the second meniscus positive lens satisfies: f3/f is more than or equal to 0.55 and less than or equal to 0.65;

the effective focal length f4 of the meniscus negative lens satisfies: f4/f is more than or equal to-2.9 and less than or equal to-2.7.

Further, an axial distance between the first positive meniscus lens and the double negative meniscus lens is T12, an axial distance between the double negative meniscus lens and the second positive meniscus lens is T23, and an axial thickness of the double negative meniscus lens is CT2, then T12, T23, and CT2 satisfy: (T12 + T23)/CT 2 is more than or equal to 3.2 and less than or equal to 3.6.

Further, the surface of the double concave negative lens facing the image side is an aspheric surface, and the surface of the double concave negative lens facing the image side satisfies the surface equation:

wherein z is a distance rise from a vertex of the aspheric surface when the aspheric surface is at a position having a height of R along the optical axis direction, C is a curvature, C =1/R, R represents a curvature radius of the lens surface, R is a radial coordinate perpendicular to the optical axis direction, k is a quadratic curve constant, a is a fourth order aspheric coefficient, B is a sixth order aspheric coefficient, C is an eighth order aspheric coefficient, and D is a tenth order aspheric coefficient.

Further, the aspheric coefficients of the surface of the biconcave negative lens facing the image side are respectively: k =0,A = -2.598806e-006, b = -1.788164e-009, c =2.378721e-012, d =0.

Furthermore, the surface of the side, facing the object, of the negative meniscus lens adopts a diffractive aspheric surface, and the surface of the side, facing the object, of the negative meniscus lens meets a surface equation:

wherein z is the distance rise from the aspheric surface vertex when the aspheric surface is at the position with the height of R along the optical axis direction, C is curvature, C =1/R, R represents the curvature radius of the lens surface, R is the radial coordinate vertical to the optical axis direction, k is a quadratic curve constant, A is a fourth order aspheric coefficient, B is a sixth order aspheric coefficient, and C is an eighth order aspheric coefficient; HOR is the diffraction order, C ₁ 、C ₂ 、C ₃ Is the diffraction surface coefficient, λ ₀ Designing a center wavelength; n is the refractive index of the lens, n ₀ Is the refractive index of air.

Further, aspheric coefficients of a surface of the meniscus negative lens facing the object side are respectively: k =0,A = -1.733180e-005, b = -3.923963e-008, c =4.173116e-011, hor =1, c ₁ ＝0.00016023，C ₂ ＝-5.00616326e-007，C ₃ ＝0。

Further, the optical system realizes the following technical parameters:

the working wave band is as follows: 8-12 μm; f ^# :1.0; focal length: 45mm; visual field: 19.4 ° x 15.5 °, image plane diameter: Φ 19.7mm, operating temperature range: -55 ℃ to +70 ℃;

wherein, F ^# The calculation formula is f/D, wherein f is the focal length of the optical system, and D is the diameter of the entrance pupil.

Furthermore, the detector matched with the optical system is a 1280 multiplied by 1024 uncooled infrared detector, and the size of a pixel is 12 mu m.

Has the advantages that:

1) The biconcave negative lens, the second positive meniscus lens and the negative meniscus lens all adopt chalcogenide glass materials with the brand number of IRG206, and the temperature coefficient of the refractive index of the chalcogenide glass IRG206 is 32 multiplied by 10 ^-6 /. Degree.C. is generalThe infrared material Ge passes through one tenth, so the introduction of chalcogenide glass can make the defocusing amount of an optical system caused by temperature change smaller, and the aim of no thermalization in a wide temperature range can be achieved under the condition of using less lenses, thereby realizing miniaturization.

2) Compared with the active athermalization mode and the mechanical passive athermalization mode, the optical passive athermalization mode has the advantages that a complex motion adjusting mechanism is not needed, the system structure is simple, the integral weight is reduced, and the reliability of the optical system is improved.

3) The diameter of the image surface of the system is phi 19.7mm, the target surface of the optical system is large, and the system can be adapted to a high-resolution detector with the current array scale of 1280 multiplied by 1024; the total length from the front surface of the first meniscus positive lens to the image plane is less than 70mm, and the total length is short, so that the structure light weight design is facilitated.

Drawings

FIG. 1 is a light path diagram of an optical system;

FIG. 2 is a diagram of the transfer function of the optical system at room temperature of 20 ℃;

FIG. 3 is a graph of the transfer function of the optical system at a low temperature of-55 ℃;

FIG. 4 is a graph of the transfer function of the optical system at high temperature +70 ℃;

FIG. 5 is a dot diagram of the optical system at room temperature of 20 ℃;

FIG. 6 is a dot-plot of the optical system at low temperature-55 ℃;

FIG. 7 is a dot-sequence diagram of the optical system at high temperature +70 ℃;

wherein, 1, a first meniscus positive lens, 2, a double concave negative lens, 3, a second positive meniscus lens, 4, a negative meniscus lens, 5, and an image plane.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to specific embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.

In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in further detail below. Disclosure of the inventionit is intended to protect all technical improvements within the scope of the present invention, and in the description of the present invention, it is to be understood that if there is an orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", etc., it is merely corresponding to fig. 1 of the present application, and it is convenient to describe the present invention, and it is not intended to indicate or imply that the indicated device or element must have a specific orientation. The terms "first," "second," and "third" are used for descriptive purposes only and refer to the order in which the types of lenses appear, and are not to be construed as indicating or implying relative importance.

First, the direction of the lens close to the object space is the object side, the direction of the lens close to the image space is the image side, and the two surfaces of the lens are the incident surface and the exit surface in this order from the object side to the image side.

As shown in fig. 1, the miniaturized high-resolution wide-temperature athermalized infrared optical system of the present invention is composed of a first positive meniscus lens 1, a biconcave negative lens 2, a second positive meniscus lens 3, and a negative meniscus lens 4, which are coaxially arranged in sequence from an object side to an image side. Light rays emitted by infrared radiation of an external scene are converged by the first meniscus positive lens 1 and then reach the biconcave negative lens 2, are diverged by the biconcave negative lens 2 and then reach the second meniscus positive lens 3, are converged by the second meniscus positive lens 3 and then reach the meniscus negative lens 4, and are diverged by the meniscus negative lens 4 and then are imaged on an image plane 5. The first positive meniscus lens 1, the second positive meniscus lens 3 and the negative meniscus lens 4 are all arranged in a curved manner towards the image side.

In detail, the material used for the first positive meniscus lens 1 is single-crystal Ge, and the material used for the double-concave negative lens 2, the second positive meniscus lens 3 and the negative meniscus lens 4 is IRG206.

Let the focal length of the optical system be f, the effective focal length of each lens included in the optical system of the present invention satisfies the following condition:

the effective focal length f1 of the first meniscus positive lens 1 meets the condition that f1/f is more than or equal to 1.0 and less than or equal to 1.2;

the effective focal length f2 of the biconcave negative lens 2 satisfies: f2/f is more than or equal to-0.7 and less than or equal to-0.6;

the effective focal length f3 of the second meniscus positive lens 3 satisfies: f3/f is more than or equal to 0.55 and less than or equal to 0.65;

the effective focal length f4 of the meniscus negative lens 4 satisfies: f4/f is more than or equal to-2.9 and less than or equal to-2.7.

Let the distance on the optical axis between the first positive meniscus lens 1 and the double negative meniscus lens 2 be T12, the distance on the optical axis between the double negative meniscus lens 2 and the second positive meniscus lens 3 be T23, and the thickness on the optical axis of the double negative meniscus lens 2 be CT2, then T12, T23, and CT2 satisfy the following conditions: (T12 + T23)/CT 2 is more than or equal to 3.2 and less than or equal to 3.6.

Table 1 shows technical indexes achieved by the present invention, wherein F ^# The formula (F number of the optical system) is F/D, and D is the diameter of the entrance pupil.

TABLE 1 technical index for the implementation of the present invention

Parameter(s)	Technical index
		Detector	1280 x 1024 uncooled infrared detector
Size of picture element	12μm
		Operating band
	8～12μm
		F # (optical System F number)	1.0
Focal length	45mm
		Field of view	19.4°×15.5°
Image plane diameter	Φ19.7mm

Table 2 lists detailed data for embodiments of optical systems according to the present invention including face type, radius of curvature, thickness, material for each lens. The unit of the curvature radius and the thickness of the lens are both mm, and the curvature radius of the spherical surface and the aspherical surface refers to the curvature radius at the intersection point of the lens surface and the optical axis. Wherein, the "serial number" in table 2 is counted along the light propagation direction, for example, the light beam incident surface of the first meniscus positive lens 1 is serial number S1, the light beam emergent surface is serial number S2, and the serial numbers of other mirror surfaces are analogized; the "radius" in table 2 represents the radius of curvature of the surface, and the positive and negative criteria are: the intersection point of the surface and the main optical axis is used as a starting point, and the center of the curved surface of the surface is used as an end point. If the connecting direction is the same as the light propagation direction, the connecting direction is positive, otherwise, the connecting direction is negative. If the surface is a plane, the curvature radius of the surface is infinite; the "thickness" in table 2 gives the distance between the two adjacent surfaces on the optical axis, and the positive and negative judgment principles are as follows: the current vertex is used as a starting point, and the next vertex is used as an end point. If the connecting direction is the same as the light propagation direction, the connecting direction is positive, otherwise, the connecting direction is negative. This thickness represents the lens thickness if the material between the two faces is infrared, and the air space between the two lenses if there is no material between the two faces.

Table 2 details of the optical system of the present invention

According to table 2, the curved surfaces of the first positive meniscus lens 1, the biconcave lens 2, the second positive meniscus lens 3, and the negative meniscus lens 4 in the direction from the object space to the image space are respectively marked as S1, S2, S3, S4, S5, S6, S7, and S8; the curved surface S4 of the double-concave negative lens 2 facing the image space is an aspheric surface, and the surface equation is:

wherein z is the distance rise from the aspheric surface vertex when the aspheric surface is at the position with the height of r along the optical axis direction; c is curvature, c =1/R, R denotes the radius of curvature of the lens surface; r is a radial coordinate perpendicular to the optical axis; k is a conic constant; a is a fourth order aspheric coefficient; b is a sixth-order aspheric coefficient; c is an eighth order aspheric coefficient; d is a tenth order aspheric coefficient.

The aspheric coefficients of the curved surface S4 facing the image side of the biconcave negative lens 2 of the present invention are shown in Table 3, wherein the aspheric coefficients are expressed by scientific notation, such as-2.598806 e-006-2.598806 × 10 ^-6 。

TABLE 3 aspherical surface coefficient of the image-side curved surface S4 of the biconcave negative lens 2

k	A	B	C	D
					0	-2.598806e-006	-1.788164e-009	2.378721e-012	0

The curved surface S7 of the meniscus negative lens 4 facing the object space is an aspheric surface, a continuous relief structure is machined on the aspheric substrate by diamond turning to form a diffraction surface, and the diffraction surface meets the equation:

z is the distance rise from the vertex of the aspheric surface when the aspheric surface is at the position with the height of R along the optical axis direction, C is the curvature, C =1/R, R represents the curvature radius of the lens surface, R is the radial coordinate vertical to the optical axis direction, k is a quadratic curve constant, A is a fourth-order aspheric coefficient, B is a sixth-order aspheric coefficient, and C is an eighth-order aspheric coefficient; HOR is diffraction order, C ₁ 、C ₂ 、C ₃ Is the diffraction surface coefficient, λ ₀ Designing a center wavelength; n is the refractive index of the lens, n ₀ Is the refractive index of air.

Table 4 diffractive aspherical surface coefficients of the curved surface S7 of the negative meniscus lens of the present invention facing the object side.

After simulation by optical design software, as shown in fig. 2, 3 and 4, when the spatial frequency of the uncooled detector with the pixel size of 12 μm and the pixel number of 1280 × 1024 is 42lp/mm, the transfer functions at the normal temperature of 20 ℃, the low temperature of-55 ℃ and the high temperature of 70 ℃ are all larger than 0.3. FIGS. 5, 6 and 7 are dot-sequence diagrams of the optical system at normal temperature of 20 deg.C, low temperature of-55 deg.C and high temperature of 70 deg.C, respectively, showing that the diameter of the diffuse spot of the system is smaller than that of the Airy spots.

The foregoing is merely a preferred embodiment of the invention and is not to be construed as limiting the invention in any way. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims (10)

1. The small high-resolution wide-temperature athermalized infrared optical system is characterized by comprising a first positive meniscus lens, a double-concave negative lens, a second positive meniscus lens and a negative meniscus lens which are coaxially arranged from an object space to an image space in sequence, wherein the first positive meniscus lens, the second positive meniscus lens and the negative meniscus lens are all arranged in a bent mode towards the image space.

2. The infrared optical system of claim 1, wherein the first positive meniscus lens is formed of a single crystal of germanium; the materials adopted by the double concave negative lens, the second meniscus positive lens and the meniscus negative lens are all chalcogenide glass IRG206.

3. A miniaturized, high-resolution, wide-temperature, athermalized infrared optical system according to claim 1, wherein the effective focal length of each lens included in the optical system of the present invention satisfies the following condition, if the focal length of the optical system is f:

the effective focal length f1 of the first meniscus positive lens meets the condition that f1/f is more than or equal to 1.0 and less than or equal to 1.2;

the effective focal length f2 of the biconcave negative lens satisfies: f2/f is more than or equal to-0.7 and less than or equal to-0.6;

the effective focal length f3 of the second meniscus positive lens satisfies: f3/f is more than or equal to 0.55 and less than or equal to 0.65;

the effective focal length f4 of the meniscus negative lens satisfies: f4/f is more than or equal to-2.9 and less than or equal to-2.7.

4. The infrared optical system as claimed in claim 1, wherein the distance between the first positive meniscus lens and the double concave negative lens on the optical axis is T12, the distance between the double concave negative lens and the second positive meniscus lens on the optical axis is T23, and the thickness of the double concave negative lens on the optical axis is CT2, then T12, T23 and CT2 satisfy: (T12 + T23)/CT 2 is more than or equal to 3.2 and less than or equal to 3.6.

5. The infrared optical system as set forth in claim 1, wherein the surface of the biconcave negative lens facing the image side is aspheric, and the surface of the biconcave negative lens facing the image side satisfies the equation of surface type:

wherein z is a distance rise from a vertex of the aspheric surface when the aspheric surface is at a position having a height of R along the optical axis direction, C is a curvature, C =1/R, R represents a curvature radius of the lens surface, R is a radial coordinate perpendicular to the optical axis direction, k is a quadratic curve constant, a is a fourth order aspheric coefficient, B is a sixth order aspheric coefficient, C is an eighth order aspheric coefficient, and D is a tenth order aspheric coefficient.

6. The infrared optical system as set forth in claim 5, wherein the aspheric coefficients of the surface of the biconcave negative lens facing the image side are: k =0,A = -2.598806e-006, b = -1.788164e-009, c =2.378721e-012, d =0.

7. The infrared optical system as claimed in claim 1, wherein the negative meniscus lens has a diffractive aspheric surface on the side facing the object, and the surface of the negative meniscus lens facing the object satisfies the equation of surface form:

wherein z is a distance rise from a vertex of the aspheric surface when the aspheric surface is at a position having a height of R in the optical axis direction, C is a curvature, C =1/R, R represents a curvature radius of the lens surface, R is a radial coordinate in a direction perpendicular to the optical axis, k is a conic constant, a is a fourth-order aspheric coefficient, B is a sixth-order aspheric coefficient, and C is an eighth-order aspheric coefficientAn aspheric coefficient; HOR is the diffraction order, C ₁ 、C ₂ 、C ₃ Is the diffraction surface coefficient, λ ₀ Designing a center wavelength; n is the refractive index of the lens, n ₀ Is the refractive index of air.

8. The infrared optical system as claimed in claim 7, wherein the aspheric coefficients of the object side surface of the negative meniscus lens are: k =0,A = -1.733180e-005, b = -3.923963e-008, c =4.173116e-011, hor =1, c ₁ ＝0.00016023，C ₂ ＝-5.00616326e-007，C ₃ ＝0。

9. The infrared optical system of claim 1, wherein the optical system implements the following technical parameters:

the working wave band is as follows: 8-12 μm; f ^# :1.0; focal length: 45mm; visual field: 19.4 ° x 15.5 °, image plane diameter: Φ 19.7mm, operating temperature range: -55 ℃ to +70 ℃;

wherein, F ^# The calculation formula is f/D, wherein f is the focal length of the optical system, and D is the diameter of the entrance pupil.

10. The infrared optical system as claimed in claim 1, wherein the detector fitted with the optical system is 1280 x 1024 uncooled infrared detector, and the pixel size is 12 μm.

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