CN1455282A - Infrared refraction-diffraction three-piece heat-abstraction optical imaging system structure - Google Patents

Abstract

The refraction/ diffraction mixed heat difference abstraction infrared optical system of dual optical elements can obtain the imaging quality close to diffraction limit in wide visual field and very good chromatic aberration correction in wide temperature range. The defocus quantity of the system is less than the focal depth. Moreover, it is simple, small size and lightweight. Thus, the dual optical diffraction elements possesses the high applied cost in the abstraction of heat design and chromatic aberration correction of the infrared optical system as well as in consideration of zoom design and the abstraction of heat difference design of multi band system.

Description

Infrarefraction diffraction three-piece formula reduction of heat difference optical imaging system structure

Technical field: the invention belongs to improvement, relate to a kind of optical imaging system structure of infrarefraction diffraction three-piece formula to the optical design imaging arrangement of infrared band.

Background technology: the reduction of heat difference design of infrared optical system is to make infrared system keep the stable of image quality in a very big temperature range by technology such as certain machinery, optics, electronics.Generally there are following three kinds: active, the mechanical passive type of machinery, PASSIVE OPTICAL formula.Because PASSIVE OPTICAL formula reduction of heat difference system has in light weight, simple in structure, be more suitable for the demand of infrared optical system, therefore paid close attention to widely, Kanagawa Y, people such as Wakabayashi S and Tajime T have proposed good method, but curvature that can only be by changing curved surface in traditional dioptric system or use different materials to come aberration correction, need the material more than at least three kinds, make lens numbers increase, need expensive infrared exotic material, make system effectiveness than descending, the system architecture complexity, when temperature drift, the aberration quality of system seriously descends especially, cause system not use, then can not be suitable for Military Application.

Summary of the invention: the objective of the invention is problem at above-mentioned existence, designed a kind of simple in structure, without special material, long back work distance from the optical imaging system structure formed of infrarefraction/diffraction three-piece formula, hyperthermy, silicon germanium material.

For achieving the above object, introduce binary optical elements in the infrared optical system of the present invention and promptly reflect the diffraction hybrid lens as shown in Figure 1, on same optical axis, be equipped with lens 1 successively, refraction diffraction hybrid lens 2, refraction diffraction hybrid lens 3, cold light hurdle 4 is picture plane 5 at last, adopt refraction diffraction hybrid lens 2 and refraction diffraction hybrid lens 3 to be mainly used to proofread and correct the infrared optical system aberration by one of focal power adjusting them, it is poor that another is mainly used to reduce infrared optical system heat; The diffraction surfaces of refraction diffraction hybrid lens 2 is positioned at a side of refraction diffraction hybrid lens 3, or the diffraction surfaces of refraction diffraction hybrid lens 2 is positioned at a side that also can be positioned near lens 1; The diffraction surfaces of refraction diffraction hybrid lens 3 is positioned at the side near picture plane 5, or the diffraction surfaces of refraction diffraction hybrid lens 3 also can be positioned at the side near refraction diffraction hybrid lens 2; Put behind in cold light hurdle 5; It is on plane, sphere or the aspheric surface that the diffraction surfaces of refraction diffraction hybrid lens 2 and refraction diffraction hybrid lens 3 can prepare in substrate, and uses silicon germanium material; The temperature range that makes optical system is-80 ℃～+ 280 ℃; Lens 1, refraction diffraction hybrid lens 2, refraction diffraction hybrid lens 3 other face except that diffraction surfaces had both adopted sphere or aspheric surface, utilized aspheric surface to coordinate the coma and the spherical aberration of corrective system.

When the present invention works; Because the thermal constant of the used refractive material of the present invention is for just, and the diffraction thermal constant all is negative, when the system works temperature raises, the lens with positive light coke feature of system will be at optical axis directions and are radially expanded (because radially little to the quality influence of system, so can ignore), so focal power will increase, the power of lens with negative power feature will reduce, and the focal power that two diffraction surfaces are born will reduce, and the lens barrel material also will expand this moment.So the focal power of system will change, because the refraction thermal constant greater than the diffraction thermal constant, so the total focal power of system will increase, Jiao is taken place move.Since lens barrel material generation polar expansion, both same moved further, and system Jiao who has then solved the temperature change generation moves, when temperature reduces, with above-mentioned opposite.One of the diffraction surfaces of binary optical mainly plays the aberration and the spherochromatism of corrective system, and another then mainly plays the effect of reduction of heat difference.

Good effect of the present invention:, increased the degree of freedom in the optical design process because the refraction diffraction hybrid optical system of diffraction element and traditional refracting element composition has utilized light refraction and diffraction two specific characters in the air.Have negative dispersion owing to diffraction element simultaneously, negative diffraction thermal constant, the characteristics of positive light coke have irreplaceable positive role for color correction difference of the present invention and the design of reduction of heat difference.The thermal constant and the lens barrel material coefficient of thermal expansion coefficient of lens material well can be cooperated, the out of focus that the lens thermal constant causes when making temperature variation is just in time consistent with the image planes mobile phase that the lens barrel material thermal expansion coefficient causes.Wherein the effect of diffraction optical element promptly can be played the task of the color correction difference of system, can also play the double action of the heat difference that disappears in addition.Utilize diffraction optical element reduction of heat difference and utilize it to come the color correction difference similar, all be to distribute by suitable focal power to realize, because the heat difference of diffactive lens heat difference and refractor is similar, bear too much focal power for fear of a diffraction element, make diffraction element produce big chromatic dispersion, the designed system of the present invention uses two diffraction elements, and a slice is used for the aberration of corrective system, and another sheet heat that is used for disappearing is poor.The present invention illustrates the photo-thermal expansion coefficient of diffraction optical element and the photo-thermal expansion coefficient opposite in sign of most infra-red material, with the irrelevant photo-thermal expansion coefficient of the thermal refractive index coefficient of material.So adopt the refraction/diffraction mixing reduction of heat difference infrared optical system of binary optical elements, can not only in big visual field, obtain image quality near diffraction limit, very wide temperature working range, and also simple in structure, volume is little, and is in light weight.Therefore diffraction optical element is in the reduction of heat design of infrared optical system, and the reduction of heat difference design of color correction difference aspect and varifocal and multiband system has very big using value.

Description of drawings:

Fig. 1 is an embodiment of the present invention structure cut-open view

Fig. 2 is the optical transfer function figure of the present invention when different temperatures

Fig. 3 be the present invention-80 during ℃ to 280 ℃ wavefront difference and the relation curve of temperature

Fig. 4 is an aberration curve of the present invention

Embodiment:, enforcement of the present invention is described further below in conjunction with accompanying drawing

As Fig. 1 is designed infrarefraction/diffraction three-piece formula, hyperthermy, the most preferred embodiment structural representation of silicon germanium material optical system and the optical schematic diagram of the present invention.The system design wave band is 3.2～4.5 μ m, and bore is that 30mm, field angle are 5, system's focal length is the infrared system of 68mm.

Lens 1 can adopt the refraction spherical mirror among Fig. 1, the lens that lens 2 and 3 adopt the refraction diffraction to mix, and lens 2 and 3 minute surface 6 can adopt diffraction surfaces, minute surface 7 can adopt aspheric surface, and minute surface 8 can adopt diffraction surfaces, and minute surface 9 can adopt aspheric surface, minute surface 10,11 can adopt sphere.Wherein minute surface 5,6, and 7,8 can select diffraction surfaces as required.The substrate of diffraction surfaces can be used sphere or plane, and other face of not doing diffraction surfaces can use sphere or aspheric surface.

The present invention adopts the reduction of heat difference design proposal that contains diffraction element, adopts 3 slice systems, and wherein lens 2 and 3 adopt Silicon respectively for rolling over/spread out hybrid element, two kinds of materials of Germanium.

Temperature range is infrarefraction/diffraction system of-80 ℃～+ 280 ℃.Then this system must satisfy: one, focal power is distributed and need be satisfied total focal power, and two, the axial chromatic aberration that disappears, three, three equations of reduction of heat difference design.Can explain with 1,2 and 3 formulas: $\underset{1}{\overset{3}{\mathrm{\Σ}}}{h}_i{\mathrm{\φ}}_i=\mathrm{\φ}........\left(1\right)$ φ in the formula _iBe power of lens, h _iBe the height of incidence of paraxial rays on lens, φ is the focal power of system. ${\mathrm{\Δf}}_b^T={\left(\frac{1}{h_1\mathrm{\φ}}\right)}^2\mathrm{\Σ}\left(h_i^2{\mathrm{\ω}}_i{\mathrm{\φ}}_i\right)=0........\left(2\right)$ ω is the chromatic dispersion factor of element in the formula, the relative variation of the focal power that chromatic dispersion just causes, here, h ₁Be the height of incidence of paraxial rays on lens.As can be seen, the definition of the definition of the chromatic dispersion factor and photo-thermal expansion coefficient is close, so can draw by the caused out of focus of the temperature effect of optical element.For the reduction of heat difference system of PASSIVE OPTICAL formula, the out of focus that requires optical element to produce is cancelled out each other with the out of focus of physical construction, thereby total system does not produce the temperature out of focus, can obtain following formula: ${\mathrm{df}}_b^T/\mathrm{dT}={\left(\frac{1}{h_1\mathrm{\φ}}\right)}^2\mathrm{\Σ}\left(h_i^2{x}_i{\mathrm{\φ}}_i\right)={\mathrm{\α}}_{h}L....\left(3\right)$ X in the formula _iBe the thermal constant of system, α _hBe the linear expansion coefficient of optical system external structure, L is the length of structure.

Obtain initial configuration by finding the solution above-mentioned equation.Optimize by ZEMAX, the structure that obtains system as shown in Figure 1.Wherein face 9 and face 7 are high order aspheric surface, and the purpose that adds high order aspheric surface is more to help anaberration.Face 6 and face 8 are the diffraction optics diffraction surfaces.The cold light hurdle connects airtight in the rear surface of lens 3.

Fig. 2 is the optical transfer function situation of optical system of the present invention in the time of-80 ℃, 40 ℃, 280 ℃, illustrates that this system can operate as normal in 360 ℃ temperature range.Can find out also that from the wavefront difference curve of Fig. 3 this system can think flawless, very good of heat difference that disappear of illustrative system.Fig. 4 illustrative system is very little at-80 ℃ and 280 ℃ of aberrations of locating, illustrates that the binary diffractive optic element plays extraordinary color correction difference effect.According to the relational expression of wave aberration and depth of focus, the maximum defocus amount of this system in-80 ℃ to 280 ℃ temperature ranges is about the depth of focus (76 μ m) of 35.9 μ m less than system simultaneously.

Fig. 2 A is the optical transfer function figure of the present invention in the time of-80 ℃

Fig. 2 B is the optical transfer function figure of the present invention in the time of 40 ℃

Fig. 2 C is the optical transfer function figure of the present invention in the time of 280 ℃

Vertical axial aberration curve when Fig. 4 A is-80 ℃

Axial aberration curve when Fig. 4 B is-80 ℃

Fig. 4 C is the vertical axial aberration curve of aberration curve in the time of 280 ℃

So this system of axial aberration curve when Fig. 4 D is 280 ℃ can use.

Claims (3)

1, infrarefraction diffraction three-piece formula reduction of heat difference optical system structure, comprise lens 1, cold light hurdle 4, picture plane 5, it is characterized in that comprising refraction diffraction hybrid lens 2, refraction diffraction hybrid lens 3, on same optical axis, be equipped with lens 1 successively, refraction diffraction hybrid lens 2, refraction diffraction hybrid lens 3, cold light hurdle 4 is picture plane 5 at last, adopt refraction diffraction hybrid lens 2 and refraction diffraction hybrid lens 3 to be mainly used to proofread and correct the infrared optical system aberration by one of focal power adjusting them, it is poor that another is mainly used to reduce infrared optical system heat; The diffraction surfaces of refraction diffraction hybrid lens 2 is positioned at a side of refraction diffraction hybrid lens 3, or the diffraction surfaces of refraction diffraction hybrid lens 2 is positioned at a side that also can be positioned near lens 1; The diffraction surfaces of refraction diffraction hybrid lens 3 is positioned at the side near picture plane 5, or the diffraction surfaces of refraction diffraction hybrid lens 3 also can be positioned at the side near refraction diffraction hybrid lens 2; Put behind in cold light hurdle 5; It is on plane, sphere or the aspheric surface that the diffraction surfaces of refraction diffraction hybrid lens 2 and refraction diffraction hybrid lens 3 can prepare in substrate; The temperature range that makes optical system is-80 ℃～+ 280 ℃; Lens 1, refraction diffraction hybrid lens 2, refraction diffraction hybrid lens 3 other face except that diffraction surfaces had both adopted sphere or aspheric surface, utilized aspheric surface to coordinate the coma and the spherical aberration of corrective system.

2, require described infrarefraction diffraction three-piece formula reduction of heat difference optical system structure according to right 1, its feature is that also lens 1, refraction diffraction hybrid lens 2 and refraction diffraction hybrid lens 3 use silicon germanium material.

3, require described infrarefraction diffraction three-piece formula reduction of heat difference optical system structure according to right 1, its feature is that also one of diffraction surfaces is mainly used to proofread and correct the infrared optical system aberration, and it is poor that another is mainly used to reduce infrared optical system heat.

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