IPC분류정보
국가/구분 |
United States(US) Patent
등록
|
국제특허분류(IPC7판) |
|
출원번호 |
US-0743539
(2008-11-06)
|
등록번호 |
US-8422822
(2013-04-16)
|
우선권정보 |
EP-07121009 (2007-11-19) |
국제출원번호 |
PCT/EP2008/065082
(2008-11-06)
|
§371/§102 date |
20100723
(20100723)
|
국제공개번호 |
WO2009/065740
(2009-05-28)
|
발명자
/ 주소 |
- Beghuin, Didier
- Joannes, Luc
|
출원인 / 주소 |
|
대리인 / 주소 |
|
인용정보 |
피인용 횟수 :
0 인용 특허 :
8 |
초록
▼
The present invention relates to a Fourier transform deflectometry system (1) and method for the optical inspection of a phase and amplitude object (2) placed in an optical path between a grating (3) and an imaging system (4), at a distance h of said grating 3. The grating (3) forms a contrast-based
The present invention relates to a Fourier transform deflectometry system (1) and method for the optical inspection of a phase and amplitude object (2) placed in an optical path between a grating (3) and an imaging system (4), at a distance h of said grating 3. The grating (3) forms a contrast-based periodic pattern with spatial frequencies μ0, v0 in, respectively, orthogonal axes x,y in an image plane, and the imaging system (4) comprises an objective (5) and an imaging sensor (6) comprising a plurality of photosensitive elements. Spatial frequencies μ0, v0 are equal or lower than the Nyquist frequencies of the imaging system in the respective x and y axes. According to the method of the invention, a first image of said pattern, distorted by the phase and amplitude object (2), is first captured through the objective (5) by the imaging sensor (6). Then, a Fourier transform of said first image in a spatial frequency domain is calculated, at least one first- or higher-order spectrum of said Fourier transform is selected and shifted in said frequency domain, so as to substantially place it at a central frequency of said Fourier transform, and a reverse Fourier transform said at least one shifted first- or higher-order spectrum of said Fourier transform is performed so as to obtain a complex function g(x,y)=l(x,y)eiφ(x,y), wherein l(x,y) is an intensity and φ(x,y) a phase linked to optical deflection angles θx, θy in, respectively, the directions of the x and y axes, in the following form: φ(x,y)=−2ττh(μ0 tan θx+v0 tan θy).
대표청구항
▼
1. A deflectometry method for the optical inspection of a phase and amplitude object placed in an optical path between a single grating and an imaging system, at a distance h of the grating, wherein the grating forms a contrast-based periodic pattern with the spatial frequencies μ0, v0 in, respectiv
1. A deflectometry method for the optical inspection of a phase and amplitude object placed in an optical path between a single grating and an imaging system, at a distance h of the grating, wherein the grating forms a contrast-based periodic pattern with the spatial frequencies μ0, v0 in, respectively, orthogonal axes x,y in an image plane, and the imaging system comprises an objective and an imaging sensor comprising a plurality of photosensitive elements, wherein this method comprises the step of: capturing through the objective, with the imaging sensor, a first image of said pattern distorted by the phase and amplitude object;and is characterised in that said spatial frequencies μ0, v0 are not higher than the respective Nyquist frequencies of the imaging system on said axes x,y, and this method also comprises the steps of:calculating a Fourier transform of said first image in a spatial frequency domain;selecting at least one first— or higher-order spectrum of said Fourier transform and shifting it in said frequency domain so as to substantially place it at a central frequency of said Fourier transform; andcarrying out a reverse Fourier transform of said at least one shifted first- or higher-order spectrum of said Fourier transform so as to obtain a complex function g(x,y)=I(x,y)eiφ(x,y), wherein I(x,y) is an intensity and φ(x,y) a phase linked to optical deflection angles θx, θy in, respectively, the directions of the x and y axes, according to the following formula: φ(x,y)=−2πh(μ0 tan θx+V0 tan θy). 2. The deflectometry method according to claim 1, wherein several first- and/or higher order spectra of said Fourier transform are selected and shifted in said frequency domain so as to substantially place them at a central frequency of said Fourier transform. 3. The deflectometry method according to claim 1, further comprising a step of unwrapping said phase. 4. The delfectometry method according to claim 1, further comprising a step of filtering said intensity below a certain threshold. 5. The deflectometry method according to claim 1, wherein said steps are carried out with two patterns crossed at an angle with respect to each other. 6. The deflectometry method according to claim 1, wherein said steps are carried out with the grating in a first position with respect to the object and with the grating in a second position with respect to the object, said first and second positions being offset by a known distance along the optical path. 7. The deflectometry method according to claim 1, wherein several distorted images of the pattern are captured, with the object at several distances in said optical path with respect to the grating, and additionally comprising the steps of: combining said several distorted images to obtain a composite image;calculating a Fourier transform of said composite image in a spatial frequency domain;selecting at least one first- or higher-order spectrum of said Fourier transform of the composite image and shifting it in said frequency domain so as to substantially place it at a central frequency of said Fourier transform; andcarrying out a reverse Fourier transform of said at least one shifted first- or higher-order spectrum of said Fourier transform of the composite image so as to obtain a complex function gM (x, y)=IM(x,y)eiφM(x,y) wherein IM(x,y) is an intensity and φM(x,y) a phase, and IM(x,y) is linked to the contrast level in the composite image. 8. The deflectometry method according to claim 7, wherein said pattern comprises two crossed sets of parallel fringes with different spatial frequencies μO,A, vO,A and μO,B vO,B and said steps of calculating a Fourier transform of the composite image, selecting and shifting said spectrum of said Fourier transform of the composite image, and carrying out a reverse Fourier transform of said shifted spectrum of the Fourier transform of the composite image may be carried out first with a shift close to μO,A, VO,A , and then with a shift close to μO,B, VO,B so as to obtain two amplitude maps, respectively IMA(x,y) and IMB(x,y). 9. The deflectometry method according to claim 8, further comprising a step of combining said two amplitude maps by superposition, addition, and/or multiplication. 10. The deflectometry method according to claim 1, further comprising the steps of: capturing a moire image of the distorted pattern, either by aliasing or by superposition with an additional grating at a different distance in the optical axis with respect to the object;calculating a Fourier transform of said moire image in a spatial frequency domain;selecting at least one first- or higher-order spectrum of said Fourier transform of the moire image and shifting it in said frequency domain so as to substantially place it at a central frequency of said Fourier transform; andcarrying out a reverse Fourier transform of said at least one shifted first— or higher-order spectrum of said Fourier transform of the moire image so as to obtain a complex function gM(x,y)=IM (x,y)ei φ(x,y) wherein IM(x,y) is an intensity and φm(x,y) a phase, and IM(x,y) is linked to the contrast level in the moiré image. 11. The deflectometry method according to claim 10, wherein said steps are carried out with the additional grating in a plurality of different distances in the optical path with respect to the object. 12. The deflectometry method according to claim 7, wherein said pattern comprises two crossed sets of parallel fringes. 13. The deflectometry method according to claim 1, wherein said phase and amplitude object is a refractive object, and said first image is an image of said pattern through said refractive object. 14. The deflectometry method according to claim 1, wherein said phase and amplitude object is a reflective object, and said first image is an image of said pattern reflected by the reflective object. 15. A deflectometry system for the optical inspection of a phase and amplitude object, comprising: a grating forming a contrast-based periodic pattern with the spatial frequencies μ0, V0 in, respectively, orthogonal axes x,y in an image plane;an imaging system comprising an objective and an imaging sensor comprising a plurality of photosensitive elements;a data processing system connected to said imaging sensor; andmeans for holding said object in an optical path between said grating and the imaging system, at a distance h of said grating;this deflectometry system being characterised in that said spatial frequencies μ0, v0 are not higher than the respective Nyquist frequencies of the imaging system on said axes x,y, and in that said data processing system is programmed to:capture through the objective, with the imaging sensor, a first image of said pattern distorted by the phase and amplitude object;calculate a Fourier transform, in a spatial frequency domain, of said first image of said pattern distorted by said phase and amplitude object;select at least one first- or higher-order spectrum of said Fourier transform and shifting it in said frequency domain towards a central frequency of said Fourier transform; andcarry out a reverse Fourier transform of said shifted first-order spectrum of said Fourier transform so as to obtain a complex function g(x,y)=I(x,y)ei φ(x,y), wherein I(x,y) is an intensity and φ(x,y) a phase linked to optical deflection angles θx, θy in, respectively, the directions of the x and y axes, according to the following formula: φ(x,y)=−2πh(μ0 tan θx+v0 tan θy). 16. The deflectometry system according to claim 15, wherein said objective is a telecentric objective. 17. The deflectometry system according to claim 15, wherein said phase and amplitude object is a reflective object, the deflectometry system further comprising a beam splitter for reflecting said pattern towards the reflective object while transmitting its distorted reflection towards the imaging system. 18. The deflectometry system according to claim 15, wherein said pattern comprises at least one set of equally-spaced parallel fringes, preferably in the form of a Ronchi pattern. 19. The deflectometry system according to claim 15, wherein those equally-spaced parallel fringes said spatial frequencies μ0,μ0 are about ½ the respective Nyquist frequencies of said imaging system on said axes x, y. 20. The deflectometry system according to claim 15, wherein said pattern comprises two substantially perpendicular sets of equally-spaced parallel fringes. 21. The deflectometry system according to claim 15, wherein said grating is formed by a contrast pattern, preferably a metal lithographic pattern, printed on a glass plate. 22. The deflectometry system according to claim 15, wherein said grating is formed by an active matrix screen, such as, for example, an LCD screen.
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