Voltage imaging system using electro-optics

• US 5,124,635 A
• Filed: 02/13/1991
• Issued: 06/23/1992
• Est. Priority Date: 02/15/1990
• Status: Expired due to Term

• Current Assignee: Photon Dynamics Incorporated (KLA Corporation)
• Original Assignee: Photon Dynamics Incorporated (KLA Corporation)
• Inventors: Henley, Francois J.
• Primary Examiner(s): NGUYEN, VINH P
• Application Number:
  US07/654,709
• Time in Patent Office: 496 Days
• Field of Search: 324/96, 324/158 R, 324/158 D, 324/73.1, 350/356, 350/374, 350/376, 356/364, 356/367, 356/368, 356/2, 356/397, 382/8, 437/8
• US Class Current: 324/96
• CPC Class Codes: G01R 15/241 using electro-optical modulators, e.g. electro-absorption probes containing electro-optic elements G01R1/071
• CPC Class Codes: G01R 31/308 using non-ionising electromagnetic radiation, e.g. optical radiation investigating or analysing materials by the use of optical means G01N21/00; image analysis G06T7/00

Abstract

A two-dimensional image of the voltage distribution across a surface at a large plurality voltage test points of a panel under test is extracted by illuminating the surface with an input beam of optical energy through an electro-optic modulator wherein the modulator is disposed to allow longitudinal probing geometries such that a voltage differential on the surface of the panel under test causes a power modulation in the optical energy which can be observed through an area optical sensor (a camera) for use to directly produce a two-dimensional spatially-dependent power modulation image directly representative of the spatially corresponding differential voltage state on the surface of the panel under test. Surface cross-talk is minimized by placing the face of the modulator closer to the panel under test than the spacing of voltage sites in the panel under test. The device may operate in a pass-through mode or in a reflective mode.

Claims

1. An apparatus for observing voltage at a large plurality of positions on a surface of a panel under test comprising:

means for producing optical energy;

means for directing said optical energy into an input beam of any polerization state;

an electro-optic modulator means, said electro-optic modulator means having a first face and an opposing second face in an orientation to allow longitudinal probing geometries, said first face having a conductive coating electrically coupled to a voltage reference means for biasing said electro-optic modulator means and said second face being disposed to be adjacent an area of said surface of said panel under test, said panel under test being coupled to an excitation voltage means for applying voltages to selected portions of the panel under test, said modulator means being oriented to intercept at least a portion of said input beam directed into said modulator means through said first face to impinge on said second face adjacent said area of said surface in order to cause in an output beam spatiallydependent modulation along said input beam, said modulation being proportional to differences between voltages produced by the voltage reference means and the excitation voltage means at position on said surface; and

means for detecting said modulation in an image across said output beam.

2. The apparatus according to claim 1 wherein said electro-optic modulator means is transmissive of said output beam through said surface and said surface is transmissive of said output beam such that optical energy passes only once through said electro-optic modulator means.

3. The apparatus according to claim 1 wherein said second face of said electro-optic modulator means has an optically reflective coating such that said input beam and said output beam each pass through said electro-optic modulator means, further including means for separating said output beam from said input beam.

4. The apparatus according to claim 3 wherein said input beam and said output beam are collinear, and said separating means is a beam splitter.

5. The apparatus according to claim 1 wherein separations between said positions are greater than separation between said surface and said second face in order to minimize cross-talk between electric fields produced by said differences between voltages at said positions.

6. The apparatus according to claim 1 wherein said modulation is power modulation and wherein said detecting means comprises:

means for producing an observable map having features corresponding to magnitude of said differences between voltages.

7. The apparatus according to claim 6 wherein said map producing means is a camera.

8. The apparatus according to claim 1 wherein said electro-optic modulation means is a crystal.

9. The apparatus according to claim 1 wherein said electro-optic modulation means is a liquid crystal.

10. The apparatus according to claim 9 wherein said second face of said electro-optic modulator means has an optically reflective coating such that said input beam and said output beam each pass through said electro-optic modulator means, further including means for separating said output beam from said input beam and wherein said separating means is a beam splitter for splitting optical energy.

11. The apparatus according to claim 9 wherein separations between said positions are greater than separation between said surface and said second face in order to minimize cross-talk between electric fields produced by said differences between voltages at said positions.

12. The apparatus according to claim 1 wherein said electro-optic modulation means is a polymer-dispersed liquid crystal.

13. The apparatus according to claim 1 wherein said electro-optic modulation means is a solid crystal.

14. An apparatus for simultaneously observing differences between voltages produced by a voltage reference means and by an excitation voltage means at a plurality of positions on a surface of a panel under test comprising:

a light source for producing optical energy;

an electro-optic modulator means, said electro-optic modulator means having a first face and an opposing second face in an orientation to allow longitudinal probing geometries, said firs face having a conductive coating electrically coup led to the voltage reference means for biasing said electro-optic modulator means and said second face being disposed to be adjacent an area of said surface of said panel under test, said panel under test being coupled to the excitation voltage means for applying voltages to selected portions of the panel under test, said modulator means being oriented to intercept at least a portion of said input beam directed into said modulator means through said first face to impinge on said second face adjacent said area of said surface in order to cause in an output beam spatially-dependent change in light power along said input beam, said change in light power being proportional to differences between voltages produced by the voltage reference means and the excitation voltage means at positions on said surface; and

means disposed to intercept said spatiallydependent power modulation for producing an observable map having features corresponding to magnitude of said differences between voltages.

15. The apparatus according to claim 14 wherein said electro-optic modulator means is transmissive of said output beam through said surface and said surface is transmissive of said output beam such that optical energy passes only once through said electro-optic modulator means.

16. A method for observing voltage differentials at a large plurality of positions on a surface of a panel under test comprising:

directing an input beam of optical energy into an electro-optic modulator means, said electro-optic modulator means having a first face and an opposing second face in an orientation to allow longitudinal probing geometries, said first face having a conductive coating electrically coupled to a voltage reference means and said second face being disposed to be adjacent an area of said surface of said panel under test, said panel under test being coupled to the excitation voltage means for applying voltages to selected portions of the panel under test, said electro-optic modulator means being oriented to intercept at least a portion of said input beam directed into said modulator means through said first face to said second face adjacent said area of said surface of said panel under test in order to cause in an output beam a spatially-dependent modulation along said input beam, said modulation being proportional to differences between voltages produced by the voltage reference means and the excitation voltage means at positions on said surface; and

detecting said modulation in an image across said output beam.

17. The method according to claim 16 wherein said modulation is power modulation and wherein said detecting step comprises:

producing from said spatially-dependent power modulation an observable map having features corresponding to magnitude of said differences between voltages.

18. The method according to claim 16 further including the step of calibrating a voltage image for use in obtaining quantitative calibrated voltage information from said spatially-dependent power modulation in an observable map having features corresponding to a magnitude of said differences between voltages.

19. An apparatus for observing voltage at a large plurality of positions on a surface of a panel under test comprising:

means for producing optical energy;

means for directing said optical energy into an input beam of any polarization state;

an electro-optic modulator means, said electro-optic modulator means having a first face and an opposing second face in an orientation to allow longitudinal probing geometries, said first face having a conductive coating electrically coupled to a voltage reference means for producing a time-varying voltage to bias said electro-optic modulator means and said second face being disposed to be adjacent an area of said surface of said panel under test, said panel under test being coupled to an excitation voltage means for applying voltages to selected portions of the panel under test, said modulator means being oriented to intercept at least a portion of said input beam directed into said modulator means through said first face to impinge on said second face adjacent said area of said surface in order to cause in an output beam spatially-dependent modulation along said input beam, said modulation being proportional to differences between voltages produced by the voltage reference means and the excitation voltage means at positions on said surface; and

means for detecting said modulation in an image across said output beam.

20. A method for observing voltage differentials at a large plurality of positions on a surface of a panel under test comprising:

directing an input beam of optical energy into an electro-optic modulator means, said electro-optic modulator means having a first face and an opposing second face in an orientation to allow longitudinal probing geometries, said first face having a conductive coating electrically coupled to a voltage reference means and said second face being disposed to be adjacent an area of said surface of said panel under test, said panel under test being coupled to the excitation voltage means for applying voltages to selected portions of the panel under test, said electro-optic modulator means being oriented to intercept at least a portion of said input beam directed into said modulator means through said first face to said second face adjacent said area of said surface of said panel under test in order to cause in an output beam a spatially-dependent modulation along said input beam, said modulation being proportional to differences between voltages produced by the voltage reference means and the excitation voltage means at positions on said surface; and

detecting said modulation in an image across said output beam.