Multiple line rugate filter with index clipping
AssigneeRockwell International Corporation
InventorWilliam H. Southwell
Life of this patent
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Abstract
A gradient index codeposition process involving refractive index clipping is used to fabricate rugate filters having multiple reflectance bands. During the codeposition process, whenever the superimposed sine wave profiles extend beyond either the upper or lower refractive index limits of the optical materials involved, the index is held at its bound (i.e., clipped). A rugate filter having a multiplicity of stop bands can be fabricated using a rather limited range of refractive index excursions during the codeposition process. Loss of optical density from index clipping can be corrected by a compensating increase in filter thickness.
Claims10
A method of making a gradient index thin film having a plurality of reflectance bands, comprising the steps of:
- determining a thin film refractive index profile corresponding to each of the plurality of reflectance bands;
- summing the plurality of refractive index profiles in parallel to produce a superimposed refractive index profile;
- determining upper and lower refractive index limits of optical material to be deposited, said superimposed refractive index profile having peak-to-peak amplitude variations exceeding said upper and lower refractive index limits;
- and
- depositing a film of said optical material having an actual refractive index profile corresponding to said superimposed refractive index profile bounded by said upper and lower limits.
A method of making a rugate filter having a plurality of stop bands, comprising the steps of:
- determining a thin film refractive index profile corresponding to each of the plurality of stop bands;
- summing the plurality of refractive index profiles in parallel to produce a superimposed refractive index profile;
- determining upper and lower refractive index limits based on optical characteristics of materials to be codeposited, said superimposed refractive index profile having peak-to-peak amplitude variations exceeding said upper and lower refractive index limits;
- and
- codepositing a film of said optical materials, said film forming a rugate filter having an actual refractive index profile corresponding to said superimposed refractive index profile clipped at said upper and lower limits.
A rugate filter having multiple reflectance bands, comprising:
- a thin film comprising a first optical material producing an upper refractive index limit codeposited with a second optical material producing a lower refractive index limit;
- said thin film having a gradient refractive index profile derived from a parallel sum of individual refractive index profiles required to produce each of the multiple reflectance bands, said parallel sum having peak-to-peak amplitude variations exceeding said upper and lower refractive index limits;
- and
- said gradient refractive index profile having upper and lower refractive index excursions bounded by said upper and lower refractive index limits.
Dependencies are inferred from the claim text.