US 5,212,374 A · Method and apparatus for positioning and biasing an electro-optic modulator of an electro-optic imaging system

Abstract

An imaging method creates a two-dimensional image of a voltage distribution or a capacitance distribution across a surface of a substrate under test using an electro-optic modulator which is positioned and biased with respect to the surface of the substrate. The method involves a first coarse offsite calibrating step to compensate for nonuniformities in the light emerging from the modulator. Then, for each successive portion of the substrate over which the modulator is to detect characteristics of the substrate, the system undergoes a modulator relocating step, a modulator levelling step, a modulator gapping step, a fine onsite calibrating step, and a measuring step. An apparatus is disclosed for levelling the bottom surface of a modulator into a substantially coplanar spacial relationship with a portion of top surface of the underlying substrate being tested monitors light emerging from at least three regions on the top surface of the modulator in order to determine the relative distances of three corresponding regions of the bottom surface of the modulator from the underlying top surface of the substrate being tested. In one embodiment, three transducers are used to control the spacial orientation of the modulator. The method and apparatus see special application in detecting defects in LCD display panels.

Claims18

Dependent claims

A method of positioning an electro-optic material in relation to a surface of a substrate, optical energy emerging from said electro-optic material, comprising the steps of:

detecting said optical energy;
and
controlling a positioning of said electro-optic material in relation to said surface of said substrate in response to at least one characteristic of said optical energy.

A method of imaging a substrate under test using an electro-optic modulator and a conductive plate disposed in a substantially coplanar relationship to a planar surface of the electro-optic modulator, comprising the steps of:

(a) detecting a gain G.sub.c of each of a plurality of regions of said electro-optic modulator by detecting light emerging from each of said plurality of regions when a first voltage and a second voltage is present between the electro-optic modulator and said conductive plate while the electro-optic modulator is fixed with respect to said conductive plate;
(b) repositioning the electro-optic modulator with respect to said substrate under test;
(c) detecting a gain G.sub.f of each of said plurality of regions of said electro-optic modulator by detecting light emerging from each of said plurality of regions when a first voltage and a second voltage is present between the electro-optic modulator and said substrate under test while the electro-optic modulator is fixed with respect to said substrate under test;
(d) detecting light emerging from each of said plurality of regions when a fixed voltage is present between each of the plurality of regions of the electro-optic modulator and said substrate under test while the electro-optic modulator is fixed with respect to said substrate under test as it was in step (c);
and
(e) using G.sub.c and G.sub.f to compensate the light detecting in step (d) for each region of said plurality of regions.

3 more elements

Dependencies are inferred from the claim text.

Method and apparatus for positioning and biasing an electro-optic modulator of an electro-optic imaging system

Life of this patent

Method and apparatus for positioning and biasing an electro-optic modulator of an electro-optic imaging system

Life of this patent

Abstract

Claims18