Ferroelectric-type optical filter

Claim 2

A variable density optical filter comprising a ferroelectrictype ceramic plate having generally parallel optical quality surfaces of substantially greateR dimension than the cross section between said surfaces, said ferroelectric-type ceramic plate being an essentially optically isotropic lead zirconatelead titanate solid solution exhibiting electrically inducible ferroelectric and variable birefringence electrooptic effects, and a pair of spaced apart electrodes disposed on a surface of said plate; means coupled to said electrodes and including a photosensitive element controlled power source responsive to the amplitude of light radiation to which a surface of said plate is subjected for electrically inducing a ferroelectric state in said plate a birefringence in a direction in said plate to electrically controllable levels proportional to increase and decreases in amplitude of said light radiation within about 200 microseconds of said light amplitude changes; first polarizing means adjacent one of said surfaces for polarizing said light impinging on said plate; and second polarizing means adjacent the other surface of said plate positioned with polarizing axis at 90* with respect to said first polarizing means and coacting therewith for varying the level of light passing through the combination of said ferroelectric-type ceramic plate and said first and second polarizing means by controllable optical density changes through said combination of up to about 4 from an optical density of less than about 1 with said electrically induced changes in the birefringence of said plate, the direction of the polarizing axes of said polarizing means being other than said birefringence direction.

Claim 3

The filter of claim 1 together with means for portably supporting said entire filter on a person''s head.

Claim 4

The filter of claim 1 wherein said light radiation means includes means for electrically varying said birefringence to a plurality of levels proportional and responsive to levels of said light radiation.

Claim 5

The filter of claim 1 including a second ferroelectric-type ceramic plate optically aligned with said other ferroelectric-type ceramic plate adjacent said second polarizing means having generally parallel optical quality surfaces parallel to the surfaces of said other ferroelectric-type ceramic plate and of substantially greater dimension than the cross section between said surfaces, said second ferroelectric-type ceramic plate being an essentially optically isotropic lead zirconate-lead titanate solid solution exhibiting electrically inducible ferroelectric and variable birefringence electrooptic effects; a pair of spaced apart electrodes disposed on a surface of said second plate; means for coupling said light radiation responsive means in electrical parallel with said electrode pair of said second ferroelectric-type ceramic plate for electrically inducing a ferroelectric state in said second plate and birefringence in about the same direction in said second plate as said other plate to electrically controllable levels proportional to said increases and decreases in amplitude of said light radiation and corresponding with the birefringence level of said other ferroelectric-type ceramic plate within about 200 microseconds of said light amplitude changes; and a third polarizing means positioned adjacent a surface of said second ferroelectric-type ceramic plate sandwiching the same between said second polarizing means and said third polarizing means, said third polarizing means with polarizing axis parallel with said first polarizing means for coacting with said first and second polarizing means and said other ferroelectric-type ceramic plate and said second ferroelectric-type ceramic plate for varying the level of light passing through the combination of all of said polarizing means and said ferroelectric-type ceramic plates by controllable optical density changes of up to about 6 from an optical density of about 1 with said electrically induced changes in birefringence of said plates.