Optical system applicable to improving the dynamic range of Shack-Hartmann sensors

• US 20050275946A1
• Filed: 05/18/2005
• Published: 12/15/2005
• Est. Priority Date: 05/19/2004
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Choo, Hyuck, Muller, Richard S.
• Granted Patent: US 7,355,793 B2
• Time in Patent Office: Days
• US Class Current: 359/619
• CPC Class Codes: B29D 11/00365 Production of microlenses lenticular sheets B29D11/00278
• CPC Class Codes: G02B 26/0875 by means of one or more refracting elements
• CPC Class Codes: G02B 27/0933 Systems for active beam shaping by rapid movement of an element
• CPC Class Codes: G02B 27/0961 Lens arrays lens arrays per se G02B3/0006
• CPC Class Codes: G02B 27/46 Systems using spatial filters

Abstract

An addressable array of lenses is disclosed. Two electrical connections per row address specific lenses within that row. Carriages support individual lenses, thus forming resonant units with frequencies unique within each row. A voltage, having the same frequency as a selected resonant unit is applied. The selected lens produces a resonating image. Testing has verified proper resonance addressing within a 5-by-5 array of microlenses. The array can be applied to a Shack-Hartmann (SH) sensor. To compensate for errant images formed outside of their image area, resonating images are identified by a processor. The array thus improves the dynamic range of the wavefront aberration that can be measured by an SH sensor. The inventors currently estimate the improvement over conventional designs to be about a factor of 30.

Claims

1. A microlens array comprising

a plurality of microlenses;

a plurality of detectors;

means for moving the focal point of one or more of the microlenses; and

means for detecting the moved focal point by using the plurality of detectors.

2. The microlens array of claim 1, further comprising

a lens-support carriage associated with each of the plurality of microlenses, wherein two or more lens-support carriages have different resonant frequencies;

means for vibrating a lens-support carriage at its resonant frequency to effect movement of the focal point of one or more of the microlenses; and

drive means for generating a vibration of one or more of the lens-support carriages.

3. The microlens array of claim 2, wherein microlenses are arranged in a rectangular array in rows and columns, wherein two drive voltages per row are used to cause a selected lens-support carriage to vibrate.

4. The microlens array of claim 1, wherein the plurality of detectors includes

an array of charge-coupled devices.

5. The microlens array of claim 1, further comprising

one or more flextures associated with a particular microlens, wherein a flexture'"'"'s geometry determines, at least in part, a resonant vibration frequency for the particular microlens.

6. The microlens array of claim 1, wherein the microlenses include Shack-Hartmann-type microlens array characteristics.

9. The microlens array of claim 1, wherein the plurality of microlenses is arranged in a microlens array having rectangular cells, wherein each microlens occupies every other cell in a row of cells, the microlens array comprising

an actuator in each cell that that is not occupied by a microlens, wherein each actuator is associated with a microlens to move the microlens when the actuator is actuated;

and

a shifting mechanism for shifting the microlens array from a first position to a second position;

wherein the shifting mechanism shifts the microlens array by an amount equal to or less than a width of a cell (pitch) as a mean to improve effective clear aperture and wavefront measurement accuracy (especially spatial resolution) of the system; and

wherein a focal point of one or more microlenses is detected in at least the first and second positions.

7. A method for determining a focal point of a microlens, wherein a microlens array is in a predetermined position with respect to a plurality of detectors, the method comprising

causing a movement of a subgroup of the microlenses;

and

using the detector to detecting a movement in a focal point of at least one of the microlenses in the subgroup.

8. The method of claim 7, further comprising

using a resonant frequency to cause the focal points of less than the total number of microlenses in the microlens array to move.

10. A method for fabricating and integrating a microlens on a low stress silicon nitride membrane comprising using surface tension and polymer-jet technology

12. The method of claim 10, further comprising

forming a ground plane below a device layer.

13. The method of claim 10, wherein a deposition condition used in the fabrication is approximately (100DCS/25HN3/140 mTorr/835°

C.).

11. A method for fabricating a microlens, comprising using low stress silicon nitride to form a lens in a lithography process.

14. A method for identifying a structure in an micro-electromechanical (MEMS) system (MEMS) having a plurality of structures, the method comprising

setting an inertial property of a particular structure;

and

causing a mechanical vibration of two or more of the structures so that the particular structure vibrates at a resonant frequency dependent upon the inertial property; and

detecting the vibration of the particular structure.

15. The method of claim 14, wherein the MEMS includes an array selected from a Hartmann array and a Shack-Hartmann array.

16. An optical system comprising:

a plurality of resonant units, each having a path that transmits light and having a resonant frequency that is unique among the plurality of resonant units; and

an actuator configured to provide force having a frequency selected to correspond to that of a selected unit.

17. The optical system of claim 16, where each light path includes a component selected from a pin hole, a microlens having a diameter between about 25 microns (μ

m) and about 4000 μ

m in diameter, or a macro lens.

18. The optical system of claim 16, where the actuator is selected from at least one of:

a voltage controlled electrostatic actuator including a voltage source and at least two conductors electrically coupled thereto, where the resonant components are positioned between the conductors, and where the voltage has a frequency corresponding to the selected frequency;

a current controlled electromagnetic actuator including a current source and at least one conductor electrically coupled thereto and configured to generate a magnetic field within the resonant components, the magnetic field having a frequency corresponding to the selected frequency;

or

a vibrator mechanically coupled to the plurality of resonant units and having a vibration frequency corresponding to the selected frequency.

19. The optical system of claim 16, where each resonant component further includes a material is selected from at least one of a piezoelectric material, a ferromagnetic material, or a thermo-pneumatic material.

20. The optical system of claim 16, further comprising:

a handling layer having a through hole for each light path;

a plurality of supports, each attached both to the handling layer and to one of the resonant units; and

a set of fixed combs, each corresponding to one of the resonant units;

where each resonant unit includes;

a lens frame;

a flexure attached both to the lens frame and to one of the supports; and

a moving comb attached to the lens frame and interleaved with the particular fixed comb corresponding to that particular resonant unit.

21. The optical system of claim 16, where the optical system further comprises:

at least one additional plurality of resonant units; and

at least one additional actuator, where each additional actuator corresponds to one of the additional plurality of resonant units.

22. The optical system of claim 16, further comprising an electro-optic imaging device configured to generate an electrical signal indicative of images of a light beam that passes through the resonant units.

23. The optical system of claim 23, further comprising a second actuator configured to displace the entire plurality of resonant units with respect to the electro-optical imaging device.

24. The optical system of claim 23, further comprising:

a processor configured to receive the electrical signal, to determine the selected frequency and control the actuator to produce the selected frequency, and to identify which particular resonant unit generates which particular light beam image based on detecting vibration of the particular light beam image.

25. The optical system of claim 24, where the processor is further configured to determine a wavefront aberration of the light beam based on the electrical signal, thereby forming a Shack-Hartmann (SH) sensor.

26. The optical system of claim 25, further comprising:

an adaptive optical element having adjustable properties, where the adaptive optical element is positioned within the light beam prior to the resonant units; and

a beam splitter, positioned within the light beam between the adaptive optical element and the resonant units, and configured to split the light beam into a component that is incident on the resonant units and a second component;

where the processor controls the adjustable properties based on the determined wavefront aberration so as to control wavefront aberration in the second component.

27. The optical system of claim 25, further comprising:

a light source configured to generate the light beam;

where the optical system is adapted for use with an optical element under test that is positioned within the light beam between the light source and the resonant units; and

where the processor is further configured to determine optical properties of the optical element under test based on the determined wavefront aberration.

28. An optical system comprising:

means for forming a plurality of images of a light beam that is incident of the forming means;

means for inducing vibration in a selected subset of the images; and

means for detecting which a particular one of the images is generated from a particular location on the forming means based on detecting the vibration.

29. The optical system of claim 28, further comprising:

means for displacing the images;

means for generating an electrical signal indicative of the images;

means for determining a wavefront aberration of the light beam based on the electrical signal;

means for controlling the wavefront aberration of the light beam based on the determined wavefront aberration;

means for generating the light beam; and

means for determining properties of an optical element under test through which the light beam passes, where the determining is based on the determined wavefront aberration.

30. A method of analyzing a light beam, the method comprising:

dissecting a light beam into a plurality of segments and forming images thereof;

inducing vibration in a selected subset of the images; and

determining which particular segments forms which particular image based on detecting the vibration.

31. The method of claim 30, further comprising:

displacing the images;

generating an electrical signal indicative of the images;

determining a wavefront aberration of the light beam based on the electrical signal;

controlling the wavefront aberration based on the determined wavefront distortion;

generating the light beam; and

determining properties of an optical element under test through which the light beam passes, where the determining is based on the measured wavefront aberration.

32. A method of fabricating a micro-optical device, the method comprising:

thermally growing an oxide layer on a device layer of a silicon on insulator (SOI) wafer that also includes a buried oxide layer and a handling layer;

patterning the buried oxide layer to form a buried mask that patterns carriages, lenses, and contacts;

using a deep reactive ion etch (DRIE) of the device layer to form holes for the contacts, the holes extending through both the device layer and the insulation layer;

forming the contacts by depositing a polysilicon layer within the contact holes and extending there beyond, the depositing being a low pressure chemical vapor deposition (LPCVD);

using a second DRIE of the device layer to form lens trenches extending though the device layer;

depositing and patterning a low stress silicon nitride layer to form a substrate layer of the microlenses on the lens trenches;

using a third DRIE of the device layer, where the DIRE is patterned by the buried mask to form the carriages, while using a photoresist layer to protect the contacts and the low stress silicon nitride layer;

using a fourth DRIE of the handling layer to remove the handling layer from beneath the lenses;

using a hydrofluoric acid (HF and H₂O) bath to remove the buried oxide layer from underneath the lenses and carriages;

using polymer jet printing to form a polymer layer of the microlenses.

33. An resonance addressable array of microlenses produced by a process comprising:

thermally growing an oxide layer on a device layer of a silicon on insulator (SOI) wafer that also includes a buried oxide layer and a handling layer;

patterning the buried oxide layer to form a buried mask that patterns carriages, lenses, and contacts;

using a deep reactive ion etch (DRIE) of the device layer to form holes for the contacts, the holes extending through both the device layer and the insulation layer;

forming the contacts by depositing a polysilicon layer within the contact holes and extending there beyond, the depositing being a low pressure chemical vapor deposition (LPCVD);

using a second DRIE of the device layer to form lens trenches extending though the device layer;

depositing and patterning a low stress silicon nitride layer to form a substrate layer of the microlenses;

using a third DRIE of the device layer, where the DIRE is patterned by the buried mask to form the carriages, while using a photoresist layer to protect the contacts and the low stress silicon nitride layer;

using a fourth DRIE of the handling layer to remove the handling layer from beneath the lenses;

using a hydrofluoric acid (HF and H₂O) bath to remove the buried oxide layer from underneath the lenses and carriages;

using polymer jet printing to form a polymer layer of the microlenses.

34. A method of fabricating a microlens, the method comprising:

using a deep reactive ion etch (DRIE) of a device layer of a silicon on insulator (SOI) wafer that also includes a buried oxide layer and a handling layer, where the DRIE forms lens trenches extending though the device layer;

depositing and patterning a low stress silicon nitride layer to form a substrate layer of the microlenses on the lens trenches;

using a second DRIE of the handling layer to remove the handling layer from beneath the lenses;

using a hydrofluoric acid (HF and H₂O) bath to remove the buried oxide layer from underneath the lenses;

using polymer jet printing to form a polymer layer of the microlenses.

35. A microlens produced by a process comprising:

using a deep reactive ion etch (DRIE) of a device layer of a silicon on insulator (SOI) wafer that also includes a buried oxide layer and a handling layer, where the DRIE forms lens trenches extending though the device layer;

depositing and patterning a low stress silicon nitride layer to form a substrate layer of the microlenses on the lens trenches;

using a second DRIE of the handling layer to remove the handling layer from beneath the lenses;

using a hydrofluoric acid (HF and H₂O) bath to remove the buried oxide layer from underneath the lenses;

using polymer jet printing to form a polymer layer of the microlenses.