Sequential wavefront sensor
View Patent ↗A sequential wavefront sensor comprises a light beam scanning module, a sub-wavefront focusing lens, a detector with more than one photosensitive area and a processor for calculating the sequentially obtained centroids of a number focused light spots from the sub-wavefronts to determine the aberration of the input wavefront. A sequential wavefront sensing method comprises the steps of; sequentially projecting a number of sub-wavefronts onto a sub-wavefront focusing lens and a detector with more than one photosensitive areas, calculating the centroid of the focused light spot from each sub-wavefront, and processing the centroid information to determine the aberration of the wavefront. In particular, a method for auto-focusing and/or auto-astigmatism-correction comprises the steps of sequentially projecting a number of sub-wavefronts around an annular ring of a wavefront to a sub-wavefront focusing lens and a detector, calculating the centroid of focused light spot from each sub-wavefront to figure out the centroid trace and hence the defocus and/or astigmatism, adjusting the focus and/or astigmatism of the optical imaging system before the wavefront sensor so that the measured defocus and/or astigmatism is minimized.
1. A sequential wavefront sensor comprising:
a wavefront scanning device adapted to sequentially shift an incident wavefront by a first displacement in a first dimension and a second displacement in a second dimension
an aperture positioned to intercept and configured to select a portion of the incident wavefront shifted by the sequential scanning device;
a focusing element configured to focus the portion of the shifted incident wavefront selected by the aperture onto a position sensing device; and
with the position sensing device configured to indicate the two-dimensional displacement from a reference point of the portion of the shifted incident wavefront focused by the focusing element onto the position sensing device.
2. The sequential wavefront sensor of claim 1 where the wavefront scanning device further comprises:
a wavefront scanner for sequentially shifting the incident wavefront in a transverse direction.
3. The sequential wavefront sensor of claim 2 where the wavefront scanner comprises:
an electric motor having a shaft; and
a tilted mirror located on the shaft.
4. The sequential wavefront sensor of claim 3 wherein:
the motor is a stepper motor and the tilted mirror is mounted at a fixed angle on the end of the shaft so that a number of sub-wavefronts around an annular ring of the incident wavefront are selected when the shaft is rotated.
5. The sequential wavefront sensor of claim 2 where the wavefront scanner comprises:
an electric motor having a shaft; and
an asymmetric multiple-faceted drum mirror mounted on the shaft.
6. The sequential wavefront sensor of claim 1 wherein the position sensing device is a quad detector having four photo-sensitive areas.
7. The sequential wavefront sensor of claim 2 where the wavefront scanner comprises:
a MEMS-based scanner.
8. The sequential wavefront sensor of claim 2 where the wavefront scanner comprises:
a transmissive optical beam scanner.
9. The sequential wavefront sensor of claim 1 wherein:
the aperture is a variable aperture for controlling the size of the portions of the selected incident wavefront.
10. A method for detecting aberration of an incident wavefront, said method comprising:
sequentially shifting an incident wavefront by a first displacement in a first dimension and a second displacement in a second dimension
intercepting and selecting a portion of a shifted incident wavefront with an aperture;
focusing the portion of the shifted incident wavefront selected by the aperture onto a position sensing device; and
determining the two-dimensional deflection of the portion of the incident wavefront focused on the position sensing device from a reference point on the position sensing device.
11. The method of claim 10 further comprising:
analyzing a plurality of two-dimensional deflections to characterize the aberration of the incident wavefront.
12. The method of claim 11 where the position sensing device is a quad detector having a reference point and said step of determining the deflection further comprises:
calculating two-dimensional deflection coordinates of the portion of the incident wavefront focused on the quad detector.
13. The method of claim 12 where selecting further comprises:
sequentially selecting a portion of a shifted incident wavefront disposed around an annular ring of the incident wavefront, and where analyzing further comprises:
determining the scattering of the two-dimensional deflections.
14. The method of claim 12 where selecting further comprises:
sequentially selecting a portion of the shifted incident wavefront disposed around an annular ring of the incident wavefront; and where analyzing further comprises:
detecting a sign change in the location of a focused portion to indicate a change of the input waveform between a convergent waveform and a divergent waveform.
15. The method of claim 10 further comprising:
pulsing or bursting a light source that generates the wavefront.
16. The method of claim 11 further comprising:
displaying the two-dimensional deflections to form a pattern on a display device.
17. The method of claim 12 where the position sensing device is a quad detector having a reference point and where displaying the deflections further comprises:
displaying each focused portion based on its calculated coordinates.
18. The method of claim 14 further comprising:
displaying two-dimensional deflections on a display device in real time.
19. A method for compensating aberrations of an incident wavefront, said method comprising:
sequentially shifting an incident wavefront by a first displacement in a first dimension and a second displacement in a second dimension;
intercepting and selecting a portion of the shifted incident wavefront with an aperture;
focusing the portion of the shifted incident wavefront selected by the aperture onto a position sensing device;
measuring the two-dimensional deflection of the focused portion of the shifted incident wavefront focused onto the position sensing device from a reference point on the position sensing device to determine the aberration of the incident wavefront; and
forming a feedback criteria based on the two-dimensional deflection of the focused portion of the shifted incident wavefront.
20. The method of claim 19 further comprising:
controlling an optical wavefront compensation device with the feedback criteria to compensate aberration of the incident wavefront.
21. The method of claim 19 where selecting further comprises:
sequentially selecting a number of portions of the shifted incident wavefront around an annular ring of the incident wavefront.
22. The method of claim 21 further comprising:
displaying the two-dimensional deflections on a display device in real time.
23. The method of claim 21 where said step of forming a feedback criteria further comprises:
minimizing the scattering of the deflections as a criteria to correct defocus of the wavefront.
24. The method of claim 21 where said step of forming a feedback criteria further comprises:
detecting a sign change of the deflection of a focused portion as a criteria to indicate when an optical system in front of the wavefront is in focus.
25. The method of claim 21 where said step of forming a feedback criteria further comprises:
detecting the deviation of a deflection-formed pattern from a circle as a feedback criteria to correct astigmatism of the wavefront.
26. The method of claim 21 where said step of forming a feedback criteria further comprises:
detecting abnormal rotation of a deflection-formed pattern as a feedback criteria for correcting an astigmatic wavefront.
27. The method of claim 21 where said step of forming a feedback criteria further comprises:
detecting ellipticity of the deflection-formed pattern as a feedback criteria for correcting astigmatism.
28. A wavefront compensation system comprising:
a wavefront scanning device adapted to sequentially shift an incident wavefront by a first displacement in a first dimension and a second displacement in a second dimension
an aperture positioned to intercept and configured to select a portion the incident wavefront shifted by the sequential scanning device;
a focusing element configured to focus the portion of the shifted incident wavefront selected by the aperture onto a position sensing device;
with the position sensing device configured to indicate the two-dimensional displacement from a reference point of the portion of the shifted incident wavefront focused by the focusing element onto the position sensing device;
a wavefront aberration analyzing device that generates a feedback signal based on detected locations of the sequentially selected portions of the shifted incident wavefront; and
a wavefront compensation device for compensating aberrations in the wavefront that utilizes the feedback signal in a closed loop control system to activate compensation.
29. The system of claim 28 with the wavefront compensation device comprising:
an axially driven optical lens for focusing the wavefront.
30. The system of claim 28 with the wavefront compensation device comprising:
an rotationally driven astigmatism correction element.
31. A sequential wavefront sensor comprising:
a wavefront scanning device adapted to sequentially shift an incident wavefront so that an annular ring is sampled;
an aperture positioned to intercept and configured to select a portion the incident wavefront shifted by the wavefront scanning device;
a focusing element configured to focus the portion of the shifted incident wavefront selected by the aperture onto a position sensing device; and
with the position sensing device configured to indicate the two-dimensional displacement from a reference point of the portion of the shifted incident wavefront focused by the focusing element onto the position sensing device.
32. A sequential wavefront sensor comprising:
a wavefront scanning device adapted to sequentially shift an incident wavefront by a first displacement in a first dimension and a second displacement in a second dimension;
a variable aperture positioned to intercept and configured to select a portion the incident wavefront shifted by the wavefront scanning device, with the size of the aperture being variable so that the sensitivity and resolution can be controlled;
a focusing element configured to focus the portion of the shifted incident wavefront selected by the aperture onto a position sensing device; and
with the position sensing device configured to indicate the two-dimensional displacement from a reference point of the portion of the shifted incident wavefront focused by the focusing element onto the position sensing device.
33. A system comprising:
a position sensing device configured to indicate the two-dimensional displacement of an incident image spot;
an aperture configured to pass through a portion of a wavefront to project an image spot onto the position sensing device; and
a scanning device configured to sequentially direct any portion of an incident wavefront to pass through the aperture.
34. The system of claim 33 where the scanning device comprises:
a reflective element configured to be stepped in arbitrary radial and azimuthal directions.
35. The system of claim 33 where the scanning device comprises:
a reflective element configured to continually shift the incident wavefront in arbitrary radial and azimuthal directions.
36. An apparatus comprising:
an aperture disposed along an aperture plane;
an optical system configured to replicate an incident wavefront onto the aperture plane,
a wavefront positioning device, included in the optical system, configured to project the incident wavefront with a selected two-dimensional transversal displacement onto the aperture plane so that any portion of the projected replicate of the incident wavefront can be selected to pass through the aperture;
a focusing element configured to focus the portion of the projected replicate of the incident wavefront selected to pass through the aperture onto a position sensing device; and
with the position sensing device configured to indicate the two-dimensional displacement from a reference point of the portion of the incident wavefront focused by the focusing element onto the position sensing device.