United States Patent  [ii] Patent Number: 4,756,602
Southwell et al.  Date of Patent: Jul. 12,1988
 NARROWBAND OPTICAL FILTER WITH PARTITIONED CAVITY
 Inventors: William H. Southwell, Thousand
Oaks; William J. Gunning, Newbury
Park, both of Calif.
 Assignee: Rockwell International Corporation, El Segundo, Calif.
 Appl. No.: 58,495
 Filed: Jun. 5,1987
 Int. CL* G02B 5/28
 U.S. CI 350/166; 350/1.6
 Field of Search 350/166, 1.6
 References Cited
U.S. PATENT DOCUMENTS
3,039,362 6/1962 Dobrowolski 350/166
3,579,130 5/1971 Smiley 350/166
4,583,822 4/1986 Southwell 350/164
4,666,250 5/1987 Southwell 350/166
Berning, "Use of Equivalent Films in the Design of Infrared Multilayer Anti-Reflection Coatings," /. of the Optical Soc. of America, vol. 52 No. 4, pp. 431-436 (1962).
Epstein, "The Design of Optical Filters," Journal of the Optical Society of America, vol. 42 No. 11, pp. 806-810 (1952).
Southwell, "Coating Design Using Very Thin High-and Low-Index Layers," Applied Optics, vol. 24 No. 4, pp. 457-460 (1985).
Southwell, "Gradient-Index Antireflection Coatings", Optics Letters, vol. 8 No. 11, pp. 584-586 (Nov. 1983). Yadava et al., "Optical Behavior of Gradient-Index Multilayer Films," Thin Solid Films, vol. 21, pp. 297-312 (1974).
Primary Examiner—Bruce Y. Arnold
Attorney, Agent, or Firm—Hamann H. Fredrick; Craig
O. Malin; John J. Deinken
A method of designing a thin film optical bandpass filter, for transmitting light in a narrow band of wavelengths centered about a bandpass wavelength, begins by defining a first quarter-wave stack, including a first plurality of layers each having an optical thickness equal to one fourth the bandpass wavelength. A second quarter-wave stack includes a second plurality of layers each having an optical thickness equal to one fourth the bandpass wavelength. Next, a cavity layer is defined with an optical thickness equal to an integral multiple of one half the bandpass wavelength, to be interposed between the first quarter-wave stack and the second quarter-wave stack. The cavity layer is then replaced with a partitioned cavity, including at least one layer of a first optical material with a relatively high index of rfraction and at least one layer of a second optical material with a relatively low index of refraction. The partitioned cavity layers, which initially have a total optical thickness equivalent to the optical thickness of the cavity layer, are adjusted in physical thickness to center the transmission peak of the filter on the bandpass wavelength. Thin film optical bandpass filters produced according to the method are also disclosed.
15 Claims, 9 Drawing Sheets