Spectral filter with integral antireflection coating

United States Patent

Hall et al.

[li] Patent Number: [45] Date of Patent:

4,826,267 May 2, 1989

[54] SPECTRAL FILTER WITH INTEGRAL ANTTREFLECriON COATING

[75] Inventors: Randolph L. Hall, Newbury Park;

Frank J. Woodberry, Malibu; William
H. Southwell, Thousand Oaks, all of
Calif.

[73] Assignee: Rockwell International Corporation, El Segundo, Calif.

[21] Appl. No.: 126,809

[22] Filed: Nov. 30,1987

[51] Int. CI.4 G02B 1/10; G02B 5/28

[52] U.S. CI 350/1.6; 350/164;

350/166

[58] Field of Search 350/1.6, 164-166

[56] References Cited

U.S. PATENT DOCUMENTS

2,281,474 4/1942 Cartwright et al 350/164

2,338,234 1/1944 Dimmick 427/10

2,376,428 5/1945 Hansell 350/164

2,397,929 4/1946 Dimmick 350/164

3,271,179 9/1966 Smith 350/166 X

3,781,090 12/1973 Sumita 350/164

4,229,066 10/1980 Rancourt et al 350/1.6

4,293,732 10/1981 Rancourt et al 136/257

4,583,822 4/1986 Southwell 350/164

4,666,250 5/1987 Southwell 350/166

4,707,611 11/1987 Southwell 250/560

OTHER PUBLICATIONS

Berning, "Use of Equivalent Films in the Design of Infrared Multilayer Antireflection Coatings," J.O.S.A., vol. 52, p. 431, 1962.

Epstein, "The Design of Optical Filters," J.O.S.A., vol. 42, p. 806, 1952.

Minot, "Single-Layer, Graded Refractive Index Antireflection Films Effective from 0.35 to 2.5fx," J.O.S.A., vol. 66, p. 515, 1976.

Southwell, "Coating Design Using Very Thin HighINDEX

A gradient index filter can be fabricated with integral antireflection properties without degrading the inband performance of the filter. The filter is for placement between an incident medium and a substrate to reflect incident electromagnetic energy having wavelengths within a predetermined band of wavelengths and to transmit incident electromagnetic energy having wavelengths outside of the reflection band. The filter includes an antireflecting portion having a nominal refractive index profile selected to reflect a minimum amount of electromagnetic energy from a theoretical interface between a first medium having a first predetermined refractive index and a second medium having a second predetermined refractive index. A band rejecting portion has a periodic refractive index profile whose periodicity and amplitude are selected to reflect a maximum amount of electromagnetic energy within the relfection band. At least part of the nominal refractive index profile is modulated by the superposition thereon of at least part of the periodic refractive index profile. The entire periodic refractive index profile maybe superimposed on the monial refractive index profile, while the periodic refractive index profile may be a rugate profile. In addition, the nominal incident and substrate refractive index profiles may be quintic refractive index profiles.

22 Claims, 14 Drawing Sheets