Long-wave infrared athermalized optical system

Abstract

A long-wave infrared athermalization optical system. It relates to the field of optical technology, in particular to the field of optical instrument manufacturing technology. It solves the problems of complex structure and low imaging quality of the existing long-wave infrared athermalization optical system. The system comprises a protective cover, a first lens, a second lens, a third lens, a detector window and an image plane arranged in sequence along the propagation direction of the incident light on the same optical axis; the protective cover is a zinc sulfide lens, the first lens is a meniscus positive lens, the second lens is a meniscus positive lens, the third lens is a meniscus negative lens, the detector window is a germanium flat glass, and the image plane is a non-cooled detector focal plane.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and more specifically to the field of optical instrument manufacturing technology. Background Technology

[0002] Uncooled infrared lenses offer advantages such as low cost and simple structure, leading to increasing market demand in both military and civilian applications. Uncooled infrared lenses typically require an f / # of less than 1.4 to achieve a reasonably clear image; increasing the f / # reduces the lens's sensitivity and light throughput. Therefore, a lower f / # corresponds to a larger relative aperture and better image quality. Due to the thermal effects of optical and lens barrel materials, the refractive index, radius of curvature, thickness, and spacing of optical elements change under varying ambient temperatures. This disrupts the system's original aberration balance and reduces imaging performance. Therefore, anechoic design is necessary in infrared system design to maintain image clarity over a relatively wide temperature range.

[0003] There are three commonly used athermalization design methods: electromechanical active, mechanical passive, and optical passive. Among these, the electromechanical active and electromechanical passive methods cannot correct aberration imbalances, have complex structures, and require high precision in manufacturing and assembly, making them unsuitable for lightweight designs. Summary of the Invention

[0004] To address the problems of complex structure and low imaging quality in existing long-wave infrared athermalized optical systems, this invention provides a long-wave infrared athermalized optical system.

[0005] The system includes a protective cover, a first lens, a second lens, a third lens, a detector window, and an image plane, which are arranged sequentially along the same optical axis along the propagation direction of the incident light. The protective cover is a zinc sulfide negative lens, the first lens is a meniscus positive lens, the second lens is a meniscus positive lens, the third lens is a meniscus negative lens, the detector window is germanium flat glass, and the image plane is the focal plane of an uncooled detector.

[0006] Furthermore, the radii of curvature of the front and rear surfaces of the protective cover are 40mm and 37-38mm, respectively, and the thickness is 2mm-3mm. The air gap between the rear surface of the protective cover and the front surface of the first lens is 2mm-4mm.

[0007] Furthermore, the front surface of the first lens is spherical, and the rear surface is a diffractive aspherical surface; the radii of curvature of the front and rear surfaces of the first lens are 30.04mm~32.86mm and 40.41mm~42.18mm, respectively, and the thickness is 5mm~5.2mm; the air gap between the rear surface of the first lens and the front surface of the second lens is 24mm~26mm.

[0008] Furthermore, both the front and rear surfaces of the second lens are spherical; the radii of curvature of the front and rear surfaces of the second lens are 18.15mm~20.87mm and 18.09mm~20.89mm, respectively, and the thickness is 3mm~4mm. The air gap between the rear surface of the second lens and the front surface of the third lens is 6mm~7mm.

[0009] Furthermore, the front surface of the third lens is spherical, and the rear surface is an even-order aspherical surface; the radii of curvature of the front and rear surfaces of the third lens are -54.46mm to -52.14mm and -65.22mm to -62.48mm, respectively, and the thickness is 2mm to 3mm; the air gap between the rear surface of the third lens and the front surface of the detector window is 5mm to 6mm.

[0010] Furthermore, the thickness of the detector window is 0.6mm to 1mm; the air gap between the rear surface of the detector window and the front surface of the image plane is 1.3mm to 1.8mm.

[0011] The beneficial effects of the structure described in this invention are as follows:

[0012] This invention provides a long-wave infrared athermalized optical system that can achieve clear imaging in environments ranging from -40℃ to +60℃ without the need for focusing. This system boasts advantages such as simple structure, low cost, high light throughput, good image quality, and high system reliability. While existing technologies also offer long-wave infrared athermalized optical systems capable of imaging in environments ranging from -40℃ to +60℃ without focusing, they can only guarantee a relatively large f / #, not a relatively large relative aperture. The structure described in this invention can simultaneously possess a small f / # and a large relative aperture, providing a large-aperture long-wave infrared athermalized optical system for clear imaging.

[0013] The system described in this invention can be applied in military fields such as infrared night vision and individual weapons, as well as civilian fields such as security and vehicle-mounted applications. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of the long-wave infrared athermalized optical system of the present invention;

[0015] Figure 2 The MTF plot of a long-wave infrared calorimetric optical system at room temperature (20°C);

[0016] Figure 3 A dot plot of a long-wave infrared calorimetric optical system at room temperature (20°C);

[0017] Figure 4 The MTF plot of a long-wave infrared athermalized optical system at a low temperature of -40℃;

[0018] Figure 5 A dot plot of a long-wave infrared athermalized optical system at a low temperature of -40℃;

[0019] Figure 6 The MTF plot of a long-wave infrared calorimetric optical system at a high temperature of 60°C;

[0020] Figure 7 This is a dot plot of a long-wave infrared calorimetric optical system at a high temperature of 60°C. Detailed Implementation

[0021] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0022] Example 1

[0023] like Figure 1 As shown, the long-wave infrared athermalized optical system of the present invention includes a protective cover 1, a first lens 2, a second lens 3, a third lens 4, a detector window 5, and an image plane 6, which are arranged sequentially along the propagation direction of the incident light on the same optical axis.

[0024] The protective cover 1 is a zinc sulfide lens with a radius of curvature of 40mm and 37-38mm on its front and rear surfaces, respectively, and a thickness of 2mm-3mm. The air gap between the rear surface of the protective cover and the front surface of the first lens 2 is 2mm-4mm, which has good chemical stability and plays the role of protecting the lens.

[0025] The first lens 2 is a meniscus lens with its convex surface facing the protective cover, and its material is IRG206. The radii of curvature of the front and rear surfaces of the first lens 2 are 30.04mm to 32.86mm and 40.41mm to 42.18mm, respectively, and its thickness is 5mm to 5.2mm. The air gap between the rear surface of the first lens 2 and the front surface of the second lens 3 is 24mm to 26mm.

[0026] The front surface of the first lens 2 is spherical, and the rear surface is a diffractive aspherical surface.

[0027] The phase distribution functions of the diffraction surfaces all satisfy the equation:

[0028] M(B1r 2 +B2r 4 );

[0029] In the formula, M represents the diffraction order, M = 1; B1 and B2 are diffraction phase coefficients, B1 is -0.7438 to -0.1866, B2 is -1.3817E-4 to -6.3817E-5, and En represents ×10⁻⁶. -n .

[0030] The surface shape equation of an aspherical surface satisfies the following equation:

[0031]

[0032] Z represents the distance vector from the vertex of the aspherical surface at a height of r along the optical axis; c is the radius of curvature; k is the conic coefficient; a4 and a6 are aspherical coefficients. In aspherical data, En represents ×10. -n a4 ranges from 3.8561E-6 to 6.3874E-6, and a6 ranges from 1.9745E-8 to 3.1257E-8.

[0033] The second lens 3 is a meniscus lens with its convex surface facing the protective cover, and the material is IRG206. The radii of curvature of the front and rear surfaces of the second lens 3 are 18.15mm~20.87mm and 18.09mm~20.89mm, respectively, and the thickness is 3mm~4mm. The air gap between the rear surface of the second lens 3 and the front surface of the third lens 4 is 6mm~7mm.

[0034] The third lens 4 is a meniscus negative lens made of single-crystal germanium. The radii of curvature of the front and rear surfaces of the third lens 4 are -54.46 mm to -52.14 mm and -65.22 mm to -62.48 mm, respectively, and the thickness is 2 mm to 3 mm. The air gap between the rear surface of the third lens 4 and the front surface of the detector window is 5 mm to 6 mm.

[0035] The front surface of the third lens 4 is spherical, and the rear surface is an even-order aspherical surface. The surface shape equation of the even-order aspherical surface satisfies the following equation:

[0036]

[0037] Its aspherical data a4 ranges from -6.2003E-7 to -3.4547E-7, and a6 ranges from 3.5619E-9 to 7.18494E-9.

[0038] The detector window 5 is made of germanium flat glass. Its thickness is 0.6 mm to 1 mm, and the air gap between the rear surface of the detector window 5 and the front surface of the image plane 6 is 1.3 mm to 1.8 mm.

[0039] Image plane 6 is the focal plane of the uncooled detector. Its pixel size is 12um×12um, resolution is 640*512, and target surface size is 7.68×6.144mm.

[0040] like Figure 2 , Figure 3 As shown, at room temperature of 20℃, the long-wave infrared athermal optical system provided by this invention has a transfer function value greater than 0.37 at a frequency of 42lp / mm in the entire field of view within the wavelength range of 8 to 12 μm, an RMS blur spot diameter less than 12 μm pixel size, and an imaging quality close to the diffraction limit.

[0041] like Figure 4 , Figure 5 As shown, at a low temperature of -40℃, the long-wave infrared athermal optical system provided by this invention has a transfer function value greater than 0.36 at a frequency of 42lp / mm across the entire field of view, and a blur spot diameter less than 12µm pixel size. The imaging quality still meets the requirements at low temperatures.

[0042] like Figure 6 , Figure 7 As shown, at a high temperature of 60°C, the long-wave infrared athermal optical system provided by this invention has a transfer function value greater than 0.32 at a frequency of 42 lp / mm across the entire field of view, and a blur spot diameter less than 12 μm pixel size. The imaging quality still meets the requirements at high temperatures.

[0043] By combining common chalcogenide infrared materials with single-crystal germanium and rationally allocating the optical power and materials of the lenses, the number of lenses is reduced, achieving system miniaturization and weight reduction. The combination of diffraction and aspherical surfaces enables aberration balance, resulting in good system imaging quality. A passive optical compensation method is employed for calorimetric design, utilizing the differences in the thermal properties of infrared materials, allowing the optical system to maintain clear large-aperture imaging without focusing in ambient temperatures ranging from -40℃ to 60℃. This invention features a simple structure, small size, light weight, good imaging quality, and high system reliability.

[0044] Example 2

[0045] This embodiment further defines Embodiment 1, and implements the technical solution described in Embodiment 1 through a specific set of parameter settings, as shown in Table 1:

[0046] Table 1:

[0047]

[0048]

[0049] The equation for the phase distribution function of the diffraction surface of mirror 4 is:

[0050] M(B1r 2 +B2r 4 In the formula:

[0051] M=1; B1=-0.6751; B2=-1.0824E-4

[0052] The equation for the aspherical surface of mirror 4 is:

[0053]

[0054] In the formula:

[0055] k=0; a4=4.1043E-6; a6=2.4762E-8;

[0056] The equations for even-order aspherical surfaces of mirror 8 are:

[0057]

[0058] In the formula:

[0059] k=0; a4=-6.1578E-7; a6=3.8354E-9;

[0060] In Example 2, the infrared anechoic optical system composed of the optical elements in Table 1 achieved the following optical specifications: system focal length f = 44 mm; F / # = 1; field of view 2ω = 12.8°; band λ = 8~12 μm; full field of view MTF@42lp / mm = 0.37.

[0061] Example 3

[0062] This embodiment further defines Embodiment 1, and implements the technical solution described in Embodiment 1 through a specific set of parameter settings, as shown in Table 2:

[0063] Table 2:

[0064]

[0065] The phase distribution function equation for the diffraction surface of mirror 4 is: M(B1r 2 +B2r 4 In the formula:

[0066] M=1; B1=-0.4383; B2=-9.5017E-5

[0067] The equation for the aspherical surface of mirror 4 is:

[0068]

[0069] In the formula:

[0070] k=0; a4=6.1585E-6; a6=3.0287E-8;

[0071] The equations for even-order aspherical surfaces of mirror 8 are:

[0072]

[0073] In the formula:

[0074] k=0; a4=-4.8543E-7; a6=3.6867E-9;

[0075] In Example 3, the infrared anechoic optical system composed of the optical elements in Table 2 achieved the following optical specifications: system focal length f = 44 mm; F / # = 1; field of view 2ω = 12.8°; band λ = 8~12 μm; full field of view MTF@42lp / mm = 0.37.

[0076] Example 4

[0077] This embodiment further defines Embodiment 1, and implements the technical solution described in Embodiment 1 through a specific set of parameter settings, as shown in Table 3:

[0078] Table 3:

[0079]

[0080]

[0081] The phase distribution function equation for the diffraction surface of mirror 4 is: M(B1r 2 +B2r 4 In the formula:

[0082] M = 1; B1 = -0.2486; B2 = -1.2157E-4; The equation of the aspherical surface of mirror 4 is:

[0083]

[0084] In the formula:

[0085] k = 0; a4 = 5.5487E-6; a6 = 2.1585E-8; The even-order aspherical equation of mirror 8 is:

[0086]

[0087] In the formula:

[0088] k=0; a4=-5.1528E-7; a6=3.6895E-9;

[0089] In Example 4, the infrared anechoic optical system composed of the optical elements in Table 3 achieved the following optical specifications: system focal length f = 44 mm; F / # = 1; field of view 2ω = 12.8°; band λ = 8~12 μm; full field of view MTF@42lp / mm = 0.37.

Claims

1. A long-wave infrared athermalized optical system, characterized in that, The system consists of a protective cover (1), a first lens (2), a second lens (3), a third lens (4), a detector window (5), and an image plane (6) arranged sequentially along the same optical axis along the direction of incident light propagation. The protective cover (1) is a zinc sulfide negative lens, the first lens (2) is a meniscus positive lens, the second lens (3) is a meniscus positive lens, the third lens (4) is a meniscus negative lens, and the material is single-crystal germanium. The detector window (5) is germanium flat glass, and the image plane (6) is the focal plane of an uncooled detector. The radii of curvature of the front and rear surfaces of the protective cover (1) are 40 mm and 37-38 mm, respectively, and the thickness is 2 mm-3 mm. The air gap between the rear surface of the protective cover (1) and the front surface of the first lens (2) is 2 mm-4 mm. The front surface of the first lens (2) is spherical, and the rear surface is a diffractive aspherical surface. The radii of curvature of the front and rear surfaces of the first lens (2) are 40 mm and 37-38 mm, respectively, and the thickness is 2 mm-3 mm. The radii of curvature of the first lens (2) are 30.04mm to 32.86mm and 40.41mm to 42.18mm, respectively, and the thickness is 5mm to 5.2mm; the air gap between the rear surface of the first lens (2) and the front surface of the second lens (3) is 24mm to 26mm; both the front and rear surfaces of the second lens (3) are spherical; the radii of curvature of the front and rear surfaces of the second lens (3) are 18.15mm to 20.87mm and 18.09mm to 20.89mm, respectively, and the thickness is 3mm to 4mm; the air gap between the rear surface of the second lens (3) and the front surface of the third lens (4) is 6mm to 7mm; the front surface of the third lens (4) is spherical, and the rear surface is an even-order aspherical; the radii of curvature of the front and rear surfaces of the third lens (4) are -54.46mm to -52.14mm and -65.22mm to -62.48mm, respectively. The thickness is 2mm to 3mm; the air gap between the rear surface of the third lens (4) and the front surface of the detector window (5) is 5mm to 6mm; the thickness of the detector window (5) is 0.6mm to 1mm; the air gap between the rear surface of the detector window (5) and the front surface of the image plane (6) is 1.3mm to 1.8mm.

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