INTERFERENCE FILTER REFLECTING A CERTAIN WAVE LENGTH BAND WITHIN A GIVEN WAVE LENGTH RANGE WHILE LETTING PASS OTHER WAVE LENGTH BANDS OF THE RANGE

• US 3,759,604 A
• Filed: 09/17/1971
• Issued: 09/18/1973
• Est. Priority Date: 09/18/1970
• Status: Expired due to Term

• Current Assignee: Alfred Thelen
• Original Assignee: Alfred Thelen
• Inventors: Thelen, Alfred
• Primary Examiner(s): Schonberg, David
• Assistant Examiner(s): Stern, Ronald J.
• Application Number:
  US05/181,433
• Time in Patent Office: 732 Days
• Field of Search: 350/163-166
• US Class Current: 359/588
• CPC Class Codes: G02B 5/285 comprising deposited thin solid films G02B5/281 - G02B5/289 take precedence; multilayered film filters for fibre optic multiplexing G02B6/29361

Abstract

The filter comprises a plurality of alternately high and low refracting light transmitting layers, applied on a light transmitting support, and reflecting a certain wave length band within a given wave length range while letting pass the other wave length bands of the range. The filter includes a periodically symmetrically constructed inner system between two reflection-reducing outer systems each constructed from a group of alternating high and low reflecting layers for the attenuation of undesired secondary reflection bands. The layers of one outer systm group have the same constant index of refraction nconst as a first layer group of the inner system. For any other layer of the outer system, having a variable index of refraction ni differing from nconst there is fulfilled the condition that the absolute value of the product nconst ni X d1 is less than this product for those inner system layers having an index of refraction differing from nconst and wherein d1 is the layer thickness. The constant index of refraction of one group of layers of an outer system may be equal to the index of refraction of the low refracting layers of the inner system or to the index of refraction of the high refracting layers of the inner system.

Claims

1. In an interference filter comprising a plurality of alternately high and low refracting light transmitting layers, applied on a light transmitting surface, reflecting a certain wave length band within a given wave length range while letting pass other wave length bands of the range, which filter includes a periodically symmetrically constructed inner system between two reflection-reducing outer systems each constructed from alternating high and low refracting layers, where all low refracting layers form one group of the outer systems and all high refracting layers form another group of the outer systems, and wherein all low refracting layers of said inner system form a first group and all high refracting layers of said inner system form a second group, for the attenuation of undesired secondary reflection bands:

the improvement comprising the layers of one outer system group having the same index of refraction nconst as one layer group of said inner system and each other layer of the outer systems having an index of refraction ni differing from nconst, and fulfilling the condition that the absolute value of the product nconst - ni X di is less than this product for the other group of inner system layers having an index of refraction differing from nconst, where di is the layer thickness.

2. In an interference filter, the improvement claimed in claim 1, in which the index of refraction of one group of layers of the outer sytems is equal to the index of refraction of the low-refracting layers of the inner system.

3. In an interference filter, the improvement claimed in claim 1, in which the index of refraction of one group of layers of the outer systems is equal to the index of refraction of the high-refracting layers of the inner system.

4. In an interference filter, the improvement claimed in claim 1, in which the outer systems have the layer sequence A/2, B1, A, B1, A/2, where A is a layer of lambda /4 optical thickness and B1 is a layer with a different index of refraction but also having lambda /4 optical thickness, lambda representing the wave length of minimum transmission of the filter.

5. In an interference filter, the improvement claimed in claim 1, in which the absolute value of the product nconst - ni di, for the additional layers of the outer system differing in their index of refraction from nconst of one group of layers thereof, decreases from the interior outwardly.