CN102012563A - Optical system of helmet mounted display based on free-form surface prism - Google Patents

Abstract

The invention relates to an optical system of a helmet mounted display based on a free-form surface prism. The optical system is the free-form surface prism formed by an S1 surface, an S2 surface and an S3 surface, wherein the S2 surface is a plane, and the S3 surface is a spherical surface. An overall coordinate system is firstly defined as follow: an original point O is positioned in the center of an entrance pupil; a Z axis is reversely traced from the center of the entrance pupil to the prism along a main optical axis L0; a Y axis is vertical to the Z axis and is positioned in the plane including the main optical axis L0; and an X axis is simultaneously vertical to the Y axis and the Z axis. A local coordinate system of each optical plane is then defined as follow: an original point is positioned on overall coordinates (SXi, SYi, SZi), a Zi axis passes through the original point of the local coordinate system and forms a thetai angle with the Z axis in the overall coordinate system, and a Yi axis passes through the original point and forms a right angle with the Zi axis in a symmetrical plane; and an Xi axis is vertical to coordinate axis of the Zi axis and the Yi axis, and a function expression of each optical plane is obtained according to the definition of the coordinate system, wherein a function expression of the S1 plane is a Zenike polynomial. The invention can realize the color display, effectively correct the aberration and improve the image quality.

Description

Optical system based on the Helmet Mounted Display of free curved surface prism

[technical field]

The present invention relates to optical technical field, particularly a kind of small-sized wide spectrum free curved surface prism helmet display refraction/diffraction mixed optical system belongs to optical system and device design field, is applicable to virtual reality and augmented reality field.

[background technology]

See also Fig. 1, (Helmet-mounted display HMD) is made up of microdrawing image source and optical system Helmet Mounted Display.This optical system shows to the infinite distance collimated image or place enough far away by partial reflection combination glass, so that the pilot normally observes.In perspective formula HMD, image will be superimposed with outside what comes into a driver's and throw in the human eye.Present most HMD optical system all is to adopt microscope positivie eyepiece form basically, and total system roughly is made up of three parts: relay optical system, eyepiece system and optical group combined glass glass.Among Fig. 1, relay optical system is a relay lens, eyepiece system is a reflection eyepiece, optical group combined glass glass adopts semi-transparent semi-reflecting sheet glass, in HMD, relay lens is imaged on image source on the focal plane of reflection eyepiece, is transformed into directional light through reflection eyepiece, by wearer's semi-transparent semi-reflecting sheet glass at the moment it is projected in wearer's the eye on the retina again.

Disclosed typical helmet display patent has United States Patent (USP) Pat.No.4, and 322,135 and 4,969,724, European patent Pat.No.0,583,116A2 and Jap.P. Pat.No.7-333551 etc.In above-mentioned patent, the reflecting surface or the transmission plane that constitute optical system adopt sphere, the symmetrical aspheric surface of rotation or the form of the foetus face etc., cause optical system can not proofread and correct hang down axial aberration and distortion simultaneously, and are difficult to realize miniaturization, have limited the application of Helmet Mounted Display.

See also Fig. 2, United States Patent (USP) Pat.No.5,959,780 and 6,292,301 utilize free curved surface prism (Free-Form surface Prism, FFSM) improve the HMD optical system, solved optical system the requirement of field angle, distance of exit pupil and the contradiction between the miniaturization and.But because the FFSM optical system only uses a kind of glass material, can't correcting chromatic aberration, realize that broadband shows.

[summary of the invention]

The technical problem to be solved in the present invention is exactly at above the deficiencies in the prior art, a kind of helmet display optical system of design based on free curved surface prism, can realize colored the demonstration, effectively aberration correction improves picture element, is fit to virtual reality or the augmented reality refraction/diffraction mixed optical system with Helmet Mounted Display.。

The present invention solves the problems of the technologies described above by the following technical programs: a kind of optical system of the Helmet Mounted Display based on free curved surface prism, it is a free curved surface prism of forming by S1 face, S2 face, S3 face, the image that generates as the liquid crystal micro display (LCD) of image source enters prism system after the refraction of S3 face, undertaken being transferred to the S1 face after the total internal reflection by the S2 face again, after the reflection of S1 face, reflect post-concentration in human eye to the S2 face once more, wherein the S2 face is the plane, the S3 face is a sphere, and at first define world coordinates and be: initial point O is at the entrance pupil center; The Z axle along the reverse trace of primary optical axis L0 from the entrance pupil center to prism; Y-axis vertical Z axle is in the plane that comprises primary optical axis L0; X-axis is vertical Y axle and Z axle simultaneously; The local coordinate that defines each optical surface then is: initial point is positioned at world coordinates (SXi, SYi, SZi) on, the Zi axle be one by the local coordinate system initial point, become a θ i angle with Z axle in the global coordinate system, the Yi axle is to meet at right angles in symmetrical plane and with the Zi axle by initial point; The Xi axle according to above-mentioned coordinate system definition, obtains the function expression of each optical surface perpendicular to the coordinate axis of Zi axle and Yi axle, and wherein the function expression of S1 face is a zernike polynomial, as shown in the formula:

$z=\frac{c_x{x}^2+c_y{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HSA00000292205800022.png"\; state="\{\{state\}\}">y</figure-callout>}}^2}{1+\sqrt{1-(1+{\mathrm{\&kappa;}}_x){c_x}^2{x}^2+(1+{\mathrm{\&kappa;}}_y){c_y}^2{y}^2}}$

$+c_1(x^2-y^2)$

$+c_2(-1+2x^2+2y^2)$

$+c_3(-2y+3x^{3}y+3y^3)$

$+c_4(3x^{2}y-y^3)$

$+c_5(x^4-6x^2{y}^2+y^4)$

$+c_6(-3x^2+4x^4+3y^2-4y^4)$

$+c_7(1-6x^2+6x^4-6y^2+12x^2{y}^2)$

$+c_8(3y-12x^{2}y+10x^{4}y-12y^3+20x^2{y}^2+10y^5)$

$+c_9(-12x^{2}y+15x^{4}y+4y^3+10x^2{y}^3-5y^5)$

$+c_{10}(5x^{4}y-10x^2{y}^3+y^5)$

$+c_{11}(x^6-15x^4{y}^2+15x^2{y}^4-y^6)$

$+c_{12}(6x^6-30x^2{y}^4-30\mathrm{xy}+6y^6-5x^4+30x^2{y}^2-5y^4)$

$+c_{13}(15x^6+15x^4{y}^2-15x^2{y}^4-15y^6-20x^4+20y^4+6x^2-6y^2)$

$+c_{14}(20x+60x^4{y}^2+60x^2{y}^4+20y^6-30x^4-60x^2{y}^2-30y^4+12x^2+12y^2-1)$

The y item adopts odd power in the formula; The x item adopts even power, the plane symmetry aspheric surface is changed according to the situation that we wish in the axial curvature of x, thereby reach the purpose of eliminating arc distortion aberration.

The value of Cx and Cy satisfies the Ke Dingdun equation in the function expression of adjustment S1 face, proofreaies and correct to realize astigmatic image error.

Show for broadband, except these monochromatic aberrations are proofreaied and correct, most critical be exactly the correction problem of aberration.And, only use a kind of glass material for own curved surface prism optical system, and can't correcting chromatic aberration, show that in order to realize broadband also help reducing simultaneously system bulk and weight, the present invention introduces binary optical elements in the own curved surface prism optical system.

On the S3 face, introduced binary optical elements, described binary optical elements adopts embossment structure, binary optical elements is placed on the plane of S3 face spherical lens, and described embossment is made up of the groove of a circle circle, a side arm of each groove is engraved as 8 steps, and all depths of groove are identical.

Because the equivalent Abbe number of binary optical elements is approximately-3.452, and the Abbe number of optical glass is all more than 20.Therefore the binary optical elements that forms on a positive lens surface can play the effect of negative lens, gives it just can achromatism with suitable focal power, is used for the broadband imaging.In addition, binary optical elements has PHASE DISTRIBUTION characteristic arbitrarily, thereby be the aberration that design of Optical System provides the more freedom degree to come corrective system, improve the image quality of optical system, also can play the lens number that reduces in the optical system, the effect of weight reduction simultaneously.

Advantage of the present invention is: can realize colored the demonstration, effectively aberration correction improves picture element, and the visual field is big, volume is little, in light weight, picture element good, the particularly important is the requirement of wide waveband particularly suitable virtual reality or the required optical system of augmented reality Helmet Mounted Display.

[description of drawings]

Fig. 1 is the optical principle synoptic diagram of one of prior art;

Fig. 2 is two an optical principle synoptic diagram of prior art;

Fig. 3 is a principle of the invention synoptic diagram;

Fig. 4 is the embossment structure synoptic diagram of binary optical elements.

[embodiment]

The invention will be further described in conjunction with the embodiments with reference to the accompanying drawings, can be implemented so that those skilled in the art can better understand the present invention also, but illustrated embodiment is not as a limitation of the invention.

For traditional HMD optical system such as Fig. 1 and Fig. 2, very difficult realization not only increases field angle, the colored demonstration of realization but also can reduce the optical system volume and weight, because realize colored the demonstration for traditional optical system, just must introduce the balsaming lens correcting chromatic aberration that the different optical material of refractive index is formed, cause optical system weight to increase.And, have to increase the optical system bore in order to increase the focal length (reducing the radius of concave mirror) that field angle will reduce optical system, cause system bulk to increase.Designed refraction/diffraction mixed optical system based on free curved surface prism for this reason.

As shown in Figure 3, the optical system that the present invention is based on the Helmet Mounted Display of free curved surface prism is a free curved surface prism of being made up of S1 face, S2 face, S3 face, the image that generates as the liquid crystal micro display (LCD) of image source enters prism system after the refraction of S3 face, undertaken being transferred to the S1 face after the total internal reflection by the S2 face again, after the reflection of S1 face, reflect post-concentration in human eye to the S2 face once more.For the clear structure that provides this optical system, at first define world coordinates and be: initial point O is at the entrance pupil center; The Z axle along the reverse trace of primary optical axis L0 from the entrance pupil center to prism; Y-axis vertical Z axle is in the plane that comprises primary optical axis L0; X-axis is vertical Y axle and Z axle simultaneously; The local coordinate of each optical surface is then: initial point be positioned at world coordinates (SXi, SYi, SZi) on, the Zi axle be one by the local coordinate system initial point, become a θ i angle with Z axle in the global coordinate system, as shown in Figure 3; The Yi axle is to meet at right angles in symmetrical plane and with the Zi axle by initial point; The Xi axle is perpendicular to the coordinate axis of Zi axle and Yi axle.According to above-mentioned coordinate system definition, can obtain the function expression of each optical surface, wherein the function expression of S1 face is a zernike polynomial, as (1) formula,

$z=\frac{c_x{x}^2+c_y{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HSA00000292205800022.png"\; state="\{\{state\}\}">y</figure-callout>}}^2}{1+\sqrt{1-(1+{\mathrm{\&kappa;}}_x){c_x}^2{x}^2+(1+{\mathrm{\&kappa;}}_y){c_y}^2{y}^2}}$

$+c_1(x^2-y^2)$

$+c_2(-1+2x^2+2y^2)$

$+c_3(-2y+3x^{2}y+3y^3)$

$+c_4(3x^{2}y-y^3)$

$+c_5(x^4-6x^2{y}^2+y^4)$

$+c_6(-3x^2+4x^4+3y^2-4y^4)$

$+c_7(1-6x^2+6x^4-6y^2+12x^2{y}^2)$

$+c_8(3y-12x^{2}y+10x^{4}y-12y^3+20x^2{y}^2+10y^5)$

$+c_9(-12x^{2}y+15x^{4}y+4y^3+10x^2{y}^3-5y^5)$

$+c_{10}(5x^{4}y-10x^2{y}^3+y^5)$

$+c_{11}(x^6-15x^4{y}^2+15x^2{y}^4-y^6)$

$+c_{12}(6x^6-30x^2{y}^4-30\mathrm{xy}+6y^6-5x^4+30x^2{y}^2-5y^4)$

$+c_{13}(15x^6+15x^4{y}^2-15x^2{y}^4-15y^6-20x^4+20y^4+6x^2-6y^2)$ (1)

$+c_{14}(20x+60x^4{y}^2+60x^2{y}^4+20y^6-30x^4-60x^2{y}^2-30y^4+12x^2+12y^2-1)$

The y item adopts odd power in the formula; The x item adopts even power, the S1 face is changed according to the situation that we wish in the axial curvature of x, thereby reach the purpose of eliminating arc distortion aberration; In addition, suitably adjust the value of Cx and Cy in (1) formula, satisfy Ke Dingdun equation (Coddington ' s Equation), can realize that astigmatic image error proofreaies and correct.The S2 face is the plane, and the S3 face is a sphere, helps device fabrication like this.

Be color difference eliminating simultaneously, on the S3 face, introduced binary optical elements.The embossment structure of this binary optical elements places binary optical elements on the plane of spherical lens as shown in Figure 4, can significantly reduce difficulty of processing, improves machining precision.Mask process is adopted in the processing of this binary optical elements, be processed into 8 ledge structures with three masks, embossment is made up of the groove of a circle circle as can be seen, a side arm of groove is engraved as 8 steps, all depths of groove are identical, but width difference, this structure can make binary optical elements have certain focal power, thereby realize its optical property.

Though more than described the specific embodiment of the present invention; but being familiar with those skilled in the art is to be understood that; our described specific embodiment is illustrative; rather than be used for qualification to scope of the present invention; those of ordinary skill in the art are in the modification and the variation of the equivalence of doing according to spirit of the present invention, all should be encompassed in the scope that claim of the present invention protects.

Claims (3)

1. optical system based on the Helmet Mounted Display of free curved surface prism, it is a free curved surface prism of forming by S1 face, S2 face, S3 face, the image that generates as the liquid crystal micro display (LCD) of image source enters prism system after the refraction of S3 face, undertaken being transferred to the S1 face after the total internal reflection by the S2 face again, after the reflection of S1 face, reflect post-concentration in human eye to the S2 face once more, wherein the S2 face is the plane, the S3 face is a sphere, it is characterized in that: at first defining world coordinates is: initial point O is at the entrance pupil center; The Z axle along the reverse trace of primary optical axis L0 from the entrance pupil center to prism; Y-axis vertical Z axle is in the plane that comprises primary optical axis L0; X-axis is vertical Y axle and Z axle simultaneously; The local coordinate that defines each optical surface then is: initial point is positioned at world coordinates (SXi, SYi, SZi) on, the Zi axle be one by the local coordinate system initial point, become a θ i angle with Z axle in the global coordinate system, the Yi axle is to meet at right angles in symmetrical plane and with the Zi axle by initial point; The Xi axle according to above-mentioned coordinate system definition, obtains the function expression of each optical surface perpendicular to the coordinate axis of Zi axle and Yi axle, and wherein the function expression of S1 face is a zernike polynomial, as shown in the formula:

$z=\frac{c_x{x}^2+c_y{y}^2}{1+\sqrt{1-(1+{\mathrm{\&kappa;}}_x){c_x}^2{x}^2+(1+{\mathrm{\&kappa;}}_y){c_y}^2{y}^2}}$

$+c_1(x^2-y^2)$

$+c_2(-1+2x^2+2y^2)$

$+c_3(-2y+3x^{2}y+3y^3)$

$+c_4(3x^{2}y-y^3)$

$+c_5(x^4-6x^2{y}^2+y^4)$

$+c_6(-3x^2+4x^4+3y^2-4y^4)$

$+c_7(1-6x^2+6x^4-6y^2+12x^2{y}^2)$

$+c_8(3y-12x^{2}y+10x^{4}y-12y^3+20x^2{y}^2+10y^5)$

$+c_9(-12x^{2}y+15x^{4}y+4y^3+10x^2{y}^3-5y^5)$

$+c_{10}(5x^{4}y-10x^2{y}^3+y^5)$

$+c_{11}(x^6-15x^4{y}^2+15x^2{y}^4-y^6)$

$+c_{12}(6x^6-30x^2{y}^4-30\mathrm{xy}+6y^6-5x^4+30x^2{y}^2-5y^4)$

$+c_{13}(15x^6+15x^4{y}^2-15x^2{y}^4-15y^6-20x^4+20y^4+6x^2-6y^2)$

$+c_{14}(20x+60x^4{y}^2+60x^2{y}^4+20y^6-30x^4-60x^2{y}^2-30y^4+12x^2+12y^2-1)$

The y item adopts odd power in the formula; The x item adopts even power.

2. the optical system of the Helmet Mounted Display based on free curved surface prism as claimed in claim 1 is characterized in that: adjust the value of Cx and Cy in the function expression of S1 face, satisfy the Ke Dingdun equation, proofread and correct to realize astigmatic image error.

3. the optical system of the Helmet Mounted Display based on free curved surface prism as claimed in claim 1 or 2, it is characterized in that: on the S3 face, introduced binary optical elements, described binary optical elements adopts embossment structure, binary optical elements is placed on the plane of S3 face spherical lens, described embossment is made up of the groove of a circle circle, a side arm of each groove is engraved as 8 steps, and all depths of groove are identical.

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