Method and system for managing light at an optical interface
An interface between two different optical materials can comprise a stack of thin film layers that manage light incident on that interface. One of the optical materials can have a first composition and a first refractive index, while the other optical material can have a second composition and a second refractive index. The stack can comprise thin film layers of the first optical material interleaved between thin film layers of the second optical material. The layers of the stack can be configured to provide the stack with an aggregate composition of at least one of the optical materials that progressively varies from one end of the stack to the other end. To provide the progressive variation in composition, the layers of one of the optical materials can have a progressively increased thickness across the stack, or can progressively increase in number, for example.
1. A method for providing an optical filter that provides rugate optical characteristics, comprising:
providing on a substrate a plurality of resonant cavities, each comprising:
a first and a second bank of thin film structures, each bank comprising first high index layers interleaved with first low index layers to provide reflective optical interfaces at a dimensional periodicity corresponding to approximately one half of a wavelength of filtered light; and
a spacer layer sandwiched between the first and the second bank; and
providing each reflective optical interface with a respective refractive index transition that comprises an interleaved series of second high index layers and second low index layers, wherein a plurality of the second high index layers are disposed in a first low index layer of the each reflective optical interface, and wherein a plurality of the second low index layers are disposed in a first high index layer of the each reflective optical interface.
2. The method of claim 1 , wherein the respective refractive index transitions provide a sinusoidal refractive index profile for each of the first bank and the second bank with periodicity corresponding to the dimensional periodicity.
3. The method of claim 1 , wherein each interleaved series is distributed substantially across a period of the first and second thin film structures.
4. The method of claim 1 , wherein each interleaved series comprises progressively thinner layers.
5. The method of claim 1 , wherein each interleaved series comprises progressively larger layer spacing.
6. The method of claim 1 , wherein the plurality of the second high index layers each has a thickness that is less than about one percent of the wavelength, and
wherein the plurality of the second low index layers each has a thickness that is less than about one percent of the wavelength.
7. The method of claim 1 , wherein the first and second banks have smoothed square wave refractive index profiles.