Extended depth of field optical systems

• US 7,218,448 B1
• Filed: 05/01/1998
• Issued: 05/15/2007
• Est. Priority Date: 03/17/1997
• Status: Expired due to Term

• Current Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Original Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Inventors: Dowski, Edward Raymond Jr., Cathey, Wade Thomas Jr.
• Primary Examiner(s): Chang; Audrey Y.
• Application Number:
  US09/070,969
• Time in Patent Office: 3,301 Days
• Field of Search: 359/558, 359/565, 359/566, 359/569, 359/707, 359/556, 386/124.5, 382/212, 382/213, 382/210, 382/211, 382/284, 382/265, 382/260, 382/100, 382/254, 235/462
• US Class Current: 359/558
• CPC Class Codes: G01S 11/12 using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 3/7835 using coding masks
• CPC Class Codes: G02B 21/14 affording illumination for phase-contrast observation
• CPC Class Codes: G02B 27/0025 for optical correction, e.g. distorsion, aberration
• CPC Class Codes: G02B 27/46 Systems using spatial filters
• CPC Class Codes: G02B 27/52 Phase contrast optics in microscopes G02B21/14
• CPC Class Codes: G02B 5/00 Optical elements other than lenses light guides G02B6/00; optical logic elements G02F3/00
• CPC Class Codes: G02B 7/365 by analysis of the spatial frequency components of the image
• CPC Class Codes: G02B 7/40 using time delay of the reflected waves, e.g. of ultrasonic waves

Abstract

A system for increasing the depth of field and decreasing the wavelength sensitivity of an incoherent optical system incorporates a special purpose optical mask into the incoherent system. The optical mask has been designed to cause the optical transfer function to remain essentially constant within some range from the in-focus position. Signal processing of the resulting intermediate image undoes the optical transfer modifying effects of the mask, resulting in an in-focus image over an increased depth of field. Generally the mask is placed at or near an aperture stop or image of the aperture stop of the optical system. Preferably, the mask modifies only phase and not amplitude of light, though amplitude may be changed by associated filters or the like. The mask may be used to increase the useful range of passive ranging systems.

Claims

1. An optical system for increasing a depth of field, the optical system characterized at least by an ambiguity function and a point spread function (PSF), which ambiguity function is a function of a normalized spatial frequency parameter u and a vertical variable v related to a misfocus parameter ψ

, and which PSF is at least a function of the misfocus parameter ψ

, the optical system comprising;

a plastic element configured for imaging light from an object to form an image, the light including at least phase and amplitude and the plastic element being configured to maintain the amplitude of light passing through the plastic element;

a mask optically connected with the plastic element and configured for altering the phase of the light while maintaining the amplitude of the light passing through the mask such that a main lobe of the ambiguity function is broader in v for a given value of u over an optical bandpass of the imaging system, and the PSF has a functionally different form for a given value of ψ

, in comparison to a main lobe of an ambiguity function, a PSF and the optical bandpass, respectively, characterizing the optical system without the mask for those given values of u and ψ

, over a range of object distances between the object and the plastic element; and

a signal processor configured for removing from the image, in accordance with the PSF, an imaging effect induced by the altering of the phase by the mask.

2. The optical system of claim 1, wherein the mask comprises a phase plate configured for effecting a phase modulation of the light.

3. The optical system of claim 2, wherein the phase modulation comprises a selected one of a linear phase modulation and a cubic phase modulation.

4. The optical system of claim 1, further comprising a storing arrangement optically connected with the mask for storing the image.

5. The optical system of claim 4, wherein the signal processor comprises a filter connected with the storing arrangement for removing the imaging effect.

6. In an optical system for imaging light from an object to form an image, which light is characterized at least by phase and amplitude, and which optical system is characterized at least by an ambiguity function and a point spread function (PSF), which ambiguity function is a function of a normalized spatial frequency parameter u and a vertical variable v related to a misfocus parameter ψ

, and which PSF is at least a function of the misfocus parameter ψ

, an improvement for increasing a depth of field of the optical system, the improvement comprising;

an optical mask, configured for altering the phase while maintaining the amplitude of the light transmitted therethrough such that a main lobe of the ambiguity function is broader in v for a given value of u over an optical bandpass of the imaging system, and the PSF has a functionally different form for a given value of ψ

, in comparison to a main lobe of an ambiguity function, a PSF and the optical bandpass, respectively, characterizing the optical system without the optical mask for those given values of u and ψ

, over a range of object distances between the object and the optical system; and

a signal processor configured for removing from the image, in accordance with the PSF, an imaging effect induced by the altering of the phase by the optical mask to render an in-focus electronic image over the range of object distances.

7. In the optical system of claim 6, the further improvement wherein the mask comprises a phase plate configured for effecting a phase modulation of the light.

8. In the optical system of claim 7, the further improvement wherein the phase modulation comprises a selected one of a linear phase modulation and a cubic phase modulation.

9. In the optical system of claim 6, the further improvement comprising a storing arrangement optically connected with the optical mask for storing the image.

10. In the optical system of claim 9, the further improvement wherein the signal processor comprises a filter connected with the storing arrangement for removing the imaging effect.