Iso-index coupled-wave electro-optic filters
AssigneeHughes Aircraft Company
InventorJames F. Lotspeich
Life of this patent
Estimating the term…
Abstract
Narrow-band optical filters are disclosed utilizing a birefringent crystal exhibiting a change in sign in birefringence at a predetermined wavelength and relying upon wave coupling between ordinary and extraordinary polarizations of light at or near the predetermined wavelength. The crystal is disposed along the light path between appropriately oriented polarizers, and a dc electric field is applied to the crystal either parallel or perpendicular to the light path. The dc electric field produces the aforementioned wave coupling for light at the center wavelength of the filter which normally is equal to the predetermined wavelength. The filter center wavelength may be displaced from the predetermined wavelength by employing a spatially periodic electric field.
Claims8
An optical filter comprising:
- first and second polarizers spaced from one another along a predetermined path and having their respective pass directions for polarized light oriented at a desired angular relationship with respect to one another;
- a crystal of birefringent material in which the birefringence becomes zero and changes sign at a predetermined wavelength disposed along said path between said first and second polarizers and oriented with its optic axis perpendicular to said path;
- means for directing light at a plurality of wavelengths including a preselected wavelength in the vicinity of said predetermined wavelength through said first polarizer and said crystal along said path;
- and
- means for applying a dc electric field to said crystal to produce wave coupling therein between ordinary and extraordinary polarizations of light at said preselected wavelength, whereby light at said preselected wavelength is selectively passed or blocked by said second polarizer.
An optical filter comprising:
- first and second polarizers spaced from one another along a predetermined path and having their respective pass directions for polarized light oriented at a desired angular relationship with respect to one another;
- a crystal of birefringent material in which the birefringence becomes zero and changes sign at a predetermined wavelength disposed along said path between said first and second polarizers and oriented with its optic axis perpendicular to said path;
- means for directing light at a plurality of wavelengths including a preselected wavelength in the vicinity of said predetermined wavelength through said first polarizer and said crystal along said path;
- and
- means for applying to said crystal a dc electric field which spatially periodically varies along said path with a period .LAMBDA. satisfying the relation
- (2 /.lambda.)C(.lambda.-.lambda..sub.o)-(2 /.LAMBDA.)=0,
- where .lambda. is said preselected wavelength, .lambda..sub.o is said predetermined wavelength, and C is the rate of change of the birefringence of said crystal with respect to wavelength at said preselected wavelength to produce in said crystal wave coupling between ordinary and extraordinary polarizations of light at said preselected wavelength, whereby light at said preselected wavelength is selectively passed or blocked by said second polarizer.
Dependencies are inferred from the claim text.