CN203688074U - System used for improving phase difference wavefront sensing performance - Google Patents

Abstract

The utility model relates to a system used for improving phase difference wavefront sensing performance. The system comprises a wavefront coding lens, a splitting element, a latus image focal plane CCD camera, an optical element capable of generating defocus, a defocus image focal plane CCD camera and a digital processing unit, wherein the wavefront coding lens and the splitting element are arranged on one same light path, the incident light of the splitting element is divided by the splitting element into the reflection light and the transmission light, the latus image focal plane CCD camera is arranged on the light path of the transmission light passing through the splitting element, the optical element capable of generating defocus and the defocus image focal plane CCD camera are sequentially arranged on the light path of the reflection light passing through the splitting element, and the latus image focal plane CCD camera and the defocus image focal plane CCD camera are respectively connected with the digital processing unit. The system used for improving phase difference wavefront sensing performance can greatly improve performance of the PD technology and can expand the application field.

Description

For promoting the system of the different wavefront sensing performance of phasic difference

Technical field

The utility model belongs to optical field, relates to a kind of for promoting the system of the different wavefront sensing performance of phasic difference.

Background technology

ADAPTIVE OPTICS SYSTEMS is made up of three parts conventionally: Wavefront sensor, wavefront rectifier and wavefront controller.Wherein, Wavefront sensor is being born the important task of obtaining system optics wavefront distortion, is the input end of whole ADAPTIVE OPTICS SYSTEMS.Even to this day, conventional wavefront sensing technology comprises: shearing interferometer, curvature sensor, rectangular pyramid mirror sensor and Shack-Hartmann sensor.These technology all with need to introduce special hardware, and some can only implement wavefront Inversion Calculation for pointolite, therefore aspect the range of application, is just being subject to certain restriction.At present, a kind of novel wavefront sensing technology based on image processing becomes study hotspot both domestic and external, Here it is the famous different PD(phase diversity of phasic difference) wavefront sensing technology.This technology only needs the positive burnt and out of focus image of two width of Same Scene (target is irrelevant), and build accordingly the objective function taking system wavefront zernike coefficient as variable, afterwards with global optimization approach such as simulated annealing or genetic algorithm minimize optimizing, thereby can inverting obtain the zernike coefficient of wavefront.Concise and to the point mathematical description is as follows:

The imaging process of any one noncoherence optics imaging system all can be expressed as formula (1) in frequency field,

G(u,v)=F(u,v)·OTF(u,v) （1）

Wherein, u and v represent respectively the spatial frequency after normalization.F represents dreamboat image spectrum, and G represents the actual image spectrum receiving.OTF represents the optical transfer function of imaging system, can be by optical system generalized pupil function

obtain by auto-correlation computation, wherein x and y represent respectively the normalization coordinate on pupil plane.φ is the unknown wave aberration in system, can carry out matching by zernike polynomial, and the coefficient of each rank zernike polynomial is exactly the direct sign of system wave aberration, is also the physical quantity that PD algorithm is wanted inverting.

the out of focus aberration that representative is introduced in positive Jiao and out of focus light path.

From formula (1), positive burnt light path and imaging process corresponding to out of focus light path are expressed as follows respectively,

G _I(u,v)=F(u,v)·OTF _I(u,v) （2）

G _D(u,v)=F(u,v)·OTF _D(u,v) （3）

Wherein I represents in-focus, and D represents defocus.

If will be by actual measured results to dreamboat image spectrum F, positive burnt optical transfer function OTF _iwith out of focus optical transfer function OTF _destimate simultaneously, so just can build following objective function,

$E=\underset{u}{\mathrm{\Σ}}\underset{v}{\mathrm{\Σ}}{|G_I-\tilde{F}\·D\tilde{T}{F}_I|}^2+{|G_D-\tilde{F}\·O\tilde{T}{F}_D|}^2---\left(4\right)$

Wherein "～" representative is estimated.

Make formula (4) ask local derviation to the frequency spectrum F of dreamboat image, and to make it be zero, can obtain the formula that is estimated as (5) of target image frequency spectrum,

$\tilde{F}=\frac{{|G_I\·O\tilde{T}{F^{*}}_D-G_D\·O\tilde{T}{F^{*}}_I|}^2}{{\left|O\tilde{T}{F}_I\right|}^2+{\left|O\tilde{T}{F}_D\right|}^2}---\left(5\right)$

And by formula (5) substitution formula again (4), just can obtain final objective function, it is as follows,

$E=\underset{u}{\mathrm{\Σ}}\underset{v}{\mathrm{\Σ}}\frac{{|G_I\·O\tilde{T}{F}_D-G_D\·O\tilde{T}{F}_I|}^2}{{\left|O\tilde{T}{F}_I\right|}^2+{\left|O\tilde{T}{F}_D\right|}^2}---\left(6\right)$

Because optical transfer function OTF can be obtained by the auto-correlation computation of pupil function P, pupil function is again the function of the unknown aberration φ of system, and φ can carry out matching by zernike polynomial, so formula (6) is actually taking system wavefront zernike coefficient as variable.Therefore, the estimation of system wavefront is equal to the searching of carrying out formula (6) minimum value at higher-dimension object space.By powerful global optimization approach, just can in limited iteration time, obtain the zernike coefficient of descriptive system wavefront, thereby realize wavefront sensing.

Compared with traditional wavefront sensing technology, PD has high computational accuracy, still can obtain the precision that is better than 1/20 wavelength under the impact that has actual measurement noise.But this technology also has its inferior position:

The first, the dynamic range of classical PD commercial measurement is less, generally can only be applied to the high precision inverting under little aberration state.If there is larger wavefront distortion in system, the computational accuracy of PD will be had a strong impact on so.Therefore, traditional PD technology still can not replace other wavefront sensing modes completely, just starts to bring into play and conventionally complete significantly rough grade in the mode of cascade in classic method the effect that high precision detects after detecting.

Second, existing research shows, classical PD technical requirement: the relative out of focus intensity of introducing between positive out of focus image can not exceed 1 wavelength, this is just to having proposed very high requirement for generation of the optical element of out of focus, also strictly define the relative positional accuracy of positive burnt light path focal plane and out of focus light path focal plane simultaneously, because if the deviation of the relative positional accuracy between positive out of focus imaging optical path focal plane has exceeded 1 wavelength, PD technology just faces the possibility of failure so.

Utility model content

In order to solve the above-mentioned technical matters existing in background technology, the utility model proposes and a kind ofly can greatly promote the performance of PD technology, and expand its application for promoting the system of the different wavefront sensing performance of phasic difference.

Technical solution of the present utility model is: the utility model provides a kind of for promoting the system of the different wavefront sensing performance of phasic difference, and its special character is: describedly comprise wavefront coded camera lens, beam splitter, positive burnt image focal plane CCD camera, the optical element that can produce out of focus, out of focus image focal plane CCD camera and digital processing element for promoting the system of the different wavefront sensing performance of phasic difference; Described wavefront coded camera lens and beam splitter are arranged in same light path; The light that is incident to beam splitter is divided into reflected light and transmitted light by described beam splitter; Described positive burnt image focal plane CCD camera is arranged in the transmitted light place light path after beam splitter; Described optical element and the out of focus image focal plane CCD camera that produces out of focus is successively set in the reflected light place light path after beam splitter; Described positive burnt image focal plane CCD camera and out of focus image focal plane CCD camera are connected with digital processing element respectively.

Above-mentioned wavefront coded camera lens comprises imaging lens and phase mask of wavefront coding system; Described imaging lens, phase mask of wavefront coding system and beam splitter are successively set in same light path.

Above-mentioned positive burnt image focal plane CCD camera and out of focus image focal plane CCD camera all can move axially along its optical axis direction.

The utility model has the advantages that:

It is a kind of for promoting the system of the different wavefront sensing performance of phasic difference that the utility model provides, this system has not only significantly been expanded effective computer capacity of primal algorithm wavefront inverting, can be applicable to the situation that system has larger aberration, and reduce the relative positional accuracy requirement of align/out of focus imaging optical path focal plane, thereby greatly promoted all round properties of the different wavefront inversion technique of phasic difference, make it tentatively possess the potentiality and the possibility that replace traditional wavefront sensing technology.The utility model provides a kind of method that effective computer capacity of traditional PD technology significantly can be expanded, and can reduce the relative positional accuracy between two focal planes of positive out of focus imaging optical path, thereby can General Promotion the performance of classical PD technology.Particularly, the utlity model has following advantage:

First, by introducing in system for the wavefront coded phase mask plate with particular phases distribution form, can reduce system to large aberration and the susceptibility of just/out of focus imaging optical path focal plane relative positional accuracy simultaneously, thereby can carry out the inverting of aberration zernike coefficient by classical PD technology, and then realize the high stability of expansion and the detection of PD dynamic range.

The second, PD and wavefront coded combination have expedited the emergence of a system new, that have wavefront distortion monitoring capability.There is following feature in this system: first, the phase mask plate that superposeed in pupil plane,, except system original wavefront, provides a large aberration disturbance artificially; Secondly, allow to there is larger " optical thickness " for introducing the optical element of known defocusing amount, thereby be convenient to processing and assembling; Finally, two focal planes in just/out of focus imaging optical path allow movable in the larger context, thereby are convenient to the system integration.

PD in conjunction with wavefront coded be a current techique, any one can be used for wavefront coded phase mask plate and all can be used for promoting the performance index of PD wavefront inverting.

Brief description of the drawings

Fig. 1 is the PD wavefront Inversion System structural representation of introducing wavefront coding technology;

Fig. 2 introduces after wavefront coding technology PD at the capability improving result figure that implements the inverting of large aberration wavefront;

Fig. 3 (a) in the time that phase-plate modulation parameter α is 20 wavelength, the disparity map between 4-13 rank zernike coefficient and the system ideal value being finally inversed by;

Fig. 3 (b) in the time that phase-plate modulation parameter α is 29 wavelength, the disparity map between 4-13 rank zernike coefficient and the system ideal value being finally inversed by;

Result figure when 0.5 wavelength of ideal position is departed from the positive burnt light path of Fig. 4 (a) focal plane;

Result figure when 1.5 wavelength of ideal position are departed from the positive burnt light path of Fig. 4 (b) focal plane;

Wherein:

The wavefront coded imaging lens of 1-; 2-beam splitter; The positive burnt image focal plane CCD camera of 3-; 4-out of focus image focal plane CCD camera; 5-produces the optical element of out of focus; 6-digital processing element.

Embodiment

Why traditional PD technology can only be carried out high-precision wavefront zernike coefficient in very limited dynamic range is calculated, because the optimization of traditional imaging system is carried out taking diffraction limited as prerequisite, so its final performance is highstrung often to the variation of system wavefront distortion.Therefore, if there is larger aberration in system, to such an extent as to positive Jiao or out-of-focus image spectrum information excessive deterioration, the global optimizing of formula (6) just possibly cannot converge to a significant solution so.In order to promote the dynamic range of PD technology, the most direct idea is exactly in system, to add an artificial disturbance, can make system insensitive to large aberration, so just likely realizes the expansion of PD wavefront inverting dynamic range.

The wavefront coded technology as a kind of effectively expansion optical system depth of field, was suggested so far from nineteen ninety-five, had obtained the extensive concern of academia and industry member.By add the phase mask plate of a slice through particular design in the aperture plane of imaging system, the optical transfer function that system has just can become insensitive while of out of focus, also can be simultaneously insensitive to causing the factor (as vibration, temperature variation) of out of focus.And more particularly, because the many aberrations of optical system all have the contact in mechanism with out of focus, so phase mask plate is in suppressing out of focus, also can effectively suppress many common aberrations.The basic point of departure that Here it is carries out combination by itself and PD technology.In addition, because wavefront coding technology can be realized effectively and suppressing out of focus, so also can reduce wavefront inversion accuracy and be subject to the impact of relative positional accuracy between positive out of focus imaging optical path focal plane.Therefore described above, wavefront coding technology is incorporated in PD technology, will obtain the benefit of two aspects simultaneously, great dynamic range detects and high stability detection.

In the utility model, by cube type phase mask plate (phase function f (x, the y)=α (x with classical ³+ y ³)) be example, illustrate that the introducing of wavefront coding technology affects PD technical feature.

Referring to Fig. 1, in based on the wavefront coded novel system form that realizes PD wavefront inversion principle, the first light path (transmitted light path) is for generation of positive burnt image, by wavefront coded imaging lens 1, and beam splitter 2, positive burnt image focal plane CCD camera 3 forms; The second light path (reflected light path) is for generation of out of focus image, and by wavefront coded imaging lens 1, beam splitter 2, produce the optical element 5 of out of focus, and out of focus image focal plane CCD camera 4 forms.CCD camera 3 and CCD camera 4 are all connected to digital processing element 6, for carrying out high-precision wavefront inverting.Wherein CCD3 two groups of dotted lines around represent that the focal plane of imaging optical path can move in wider scope.

PD shown in Fig. 1 is described below in conjunction with wavefront coded feature and the application mode that realizes wavefront inverting:

(1) combine with wavefront coded theoretical PD wavefront sensing.First, imaging optical path is divided into two-way, and a road is for generation of positive burnt image (main imaging optical path shown in redness in Fig. 1), and a road relies on special optical element to obtain out of focus image (imaging optical path of out of focus shown in blueness in Fig. 1).Secondly, utilize the different wavefront inversion technique of PD phasic difference, taking the positive burnt and out of focus image of two width images of Same Scene as data source, the objective function of structure taking wavefront distortion zernike coefficient as variable, and obtain system wave front aberration by global optimization approach.

Because PD wavefront inversion algorithm relates to the two-dimensional Fourier transform of image and wavefront, so if the pixel resolution of the image that participation is calculated is higher, will have a strong impact on so counting yield.In the time of simulation analysis, wavefront inverting is all carried out based on 128X128 pixel resolution grid, and the pixel resolution of the image obtaining in the middle of practical application is all far above this magnitude, so the inverting of wavefront is carried out in the 128X128 region that should intercept in original image.Can select arbitrarily for the region of implementing to calculate, because the constructed objective function of PD technology is actually irrelevant with the type of target to be imaged.

(2) the phase mask plate being positioned on pupil as shown in Figure 2, is classical cube type phase-plate (f (x, y)=α (x ³+ y ³)).In the time that the zernike coefficients corresponding to aberration such as the out of focus existing in system, astigmatism and coma approach 2 wavelength, while not carrying phase mask plate, there is very violent decline in PD inversion accuracy, this just means that the dynamic range of classical PD wavefront inverting is very limited.And in the time introducing modulate intensity in system and be the cube type phase mask plate of 20 wavelength, PD inversion accuracy even can be better than 1/10000 wavelength.In Fig. 2, solid black lines indicates the difference (variance is 0.0198) of inverting zernike coefficient and desirable zernike coefficient when wavefront coded, and pinkish red dotted line indicates the difference (variance is 6.324e-005) of inverting zernike coefficient and desirable zernike coefficient when wavefront coded, concrete data are as shown in table 1.This is explanation fully just: because wavefront coding technology can effectively suppress out of focus and the aberration relevant with out of focus, so PD technology in ensureing very high degree of precision, valid analysing range can obtain the lifting of matter.

Table 1 have wavefront coded with without wavefront coded PD inverting zernike coefficient

(3) due to the out of focus producing in effectively inhibition system of wavefront coding technology, so to apply PD technology in non-coding system different, now the out of focus difference between positive out of focus image can be amplified accordingly according to the modulate intensity of encoder element.As shown in Figure 3, in the time that the modulate intensity of phase mask plate is 20 wavelength, allow the defocusing amount of introducing can reach 4.75 wavelength; And in the time that the modulate intensity of phase mask plate is 29 wavelength, allow the defocusing amount of introducing even can reach 6.9 wavelength.This has all been far longer than the defocusing amount (being conventionally less than 1 wavelength) that traditional PD technology allows.As shown in Figure 3, for wavefront coded system, PD can realize the inverting (root-mean-square error between inverting zernike coefficient and desirable zernike coefficient is less than 0.002 wavelength) to the original wave aberration of system effectively, and wave aberration herein refers to the original aberration of camera lens of rejecting outside phase-plate.In Fig. 3, Fig. 3 (a) is in the time that phase-plate modulation parameter α is 20 wavelength, difference (each rank zernike coefficient numerical value is as shown in table 2) between 4-13 rank zernike coefficient and the system ideal value being finally inversed by, now, the defocusing amount just, between out of focus image at least can reach 4.75 wavelength.Fig. 3 (b) is in the time that phase-plate modulation parameter α is 29 wavelength, difference (each rank zernike coefficient numerical value is as shown in table 3) between 4-13 rank zernike coefficient and the system ideal value being finally inversed by, now, just, the defocusing amount between out of focus image at least can reach 6.9 wavelength.

Table 2 is corresponding to the data of Fig. 3 (a)

Table 3 is corresponding to the data of Fig. 3 (b)

4) phase mask plate is actually and in system, has introduced an artificial controlled aberration, has directly implemented the disturbance to wavefront, and when main imaging optical path CCD camera focal plane is because of certain reason drift (such as vibration)

Or in the time that conventional imaging camera lens is introduced out of focus aberration because of certain reason (such as interval variation etc.), can think to have added again extra uncertain aberration in system, indirectly participate in the disturbance of wavefront.For PD technology, this indirectly Wavefront Perturbation very likely causes the failure of PD technology, because: the first, the variation of conventional imaging lens optical wavefront may exceed the sensing range of PD; The second, thus focal plane drift can cause that the excessive deterioration of image spectrum makes to be difficult to convergence for the optimization of formula (6).But after having introduced wavefront coding technology, these two problems can be resolved.As shown in Figure 4, in the time that focal plane produces drift, under wavefront coded help, still can obtain high-precision wavefront inverting.

Result when 0.5 wavelength of ideal position is departed from the positive burnt light path of Fig. 4 (a) focal plane, the corresponding concrete data of table 4; Result when 1.5 wavelength of ideal position are departed from the positive burnt light path of Fig. 4 (b) focal plane, the corresponding concrete data of table 5.

Table 4 corresponding diagram 4(a) inversion result

Table 5 corresponding diagram 4(b) inversion result

Claims (3)

1. for promoting a system for the different wavefront sensing performance of phasic difference, it is characterized in that: describedly comprise wavefront coded camera lens, beam splitter, positive burnt image focal plane CCD camera, the optical element that can produce out of focus, out of focus image focal plane CCD camera and digital processing element for promoting the system of the different wavefront sensing performance of phasic difference; Described wavefront coded camera lens and beam splitter are arranged in same light path; The light that is incident to beam splitter is divided into reflected light and transmitted light by described beam splitter; Described positive burnt image focal plane CCD camera is arranged in the transmitted light place light path after beam splitter; Described optical element and the out of focus image focal plane CCD camera that produces out of focus is successively set in the reflected light place light path after beam splitter; Described positive burnt image focal plane CCD camera and out of focus image focal plane CCD camera are connected with digital processing element respectively.

2. according to claim 1 for promoting the system of the different wavefront sensing performance of phasic difference, it is characterized in that: described wavefront coded camera lens comprises imaging lens and phase mask of wavefront coding system; Described imaging lens, phase mask of wavefront coding system and beam splitter are successively set in same light path.

3. according to claim 1 and 2 for promoting the system of the different wavefront sensing performance of phasic difference, it is characterized in that: described positive burnt image focal plane CCD camera and out of focus image focal plane CCD camera all can move axially along its optical axis direction.

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