Variable optical filter and a wavelength-selective sensor based thereon
A variable optical filter is disclosed including a bandpass filter and a blocking filter. The bandpass filter includes a stack of alternating first and second layers, and the blocking filter includes a stack of alternating third and fourth layers. The first, second and fourth materials each comprise different materials, so that a refractive index of the first material is smaller than a refractive index of the second material, which is smaller than a refractive index of the fourth material; while an absorption coefficient of the second material is smaller than an absorption coefficient of the fourth material. The materials can be selected to ensure high index contrast in the blocking filter and low optical losses in the bandpass filter. The first to fourth layers can be deposited directly on a photodetector array.
1. An optical filter comprising:
a bandpass filter including a first layer comprising a first material and a second layer comprising a second material,
wherein the first layer and the second layer having first laterally varying thicknesses for providing a laterally variable transmission wavelength; and
a blocking filter including a third layer comprising a third material and a fourth layer comprising a fourth material, wherein
the third layer and the fourth layer have second laterally varying thicknesses, coordinated with the first laterally varying thicknesses, for blocking wavelengths, within a wavelength range, that are different than the laterally variable transmission wavelength, and
the bandpass filter further includes an additional layer, comprising the fourth material, disposed in an area of a local minimum of a standing optical wave inside the bandpass filter.
2. The optical filter of claim 1 , wherein the optical filter is disposed on a substrate.
3. The optical filter of claim 2 , wherein the substrate is a photodetector array.
4. The optical filter of claim 1 , wherein
the blocking filter is a first blocking filter, and
the optical filter further includes a second blocking filter.
5. The optical filter of claim 4 , wherein the bandpass filter is located between the first blocking filter and the second blocking filter.
6. The optical filter of claim 1 , wherein
the blocking filter includes a plurality of portions,
each portion, of the plurality of portions, is associated with a blocking band, and
each blocking band is cascaded to cover a particular wavelength range.
7. The optical filter of claim 1 , wherein the first material, the second material, and the third material are each different.
8. The optical filter of claim 1 , wherein the bandpass filter includes a dielectric spacer layer located between first and second reflector stacks.
9. The optical filter of claim 1 , wherein the bandpass filter includes a plurality of cavities.
10. An optical filter comprising:
a bandpass filter; and
a blocking filter, wherein
the bandpass filter comprises:
a first layer comprising a first material,
a second layer comprising a second material, and
a third layer disposed in an area of a local minimum of a standing optical wave inside the bandpass filter, and
the blocking filter comprises:
a fourth layer comprising a third material, and
a fifth layer comprising a fourth material.
11. The optical filter of claim 10 , wherein
the third layer comprises the fourth material, and
the first material, the second material, and the fourth material are each different.
12. The optical filter of claim 10 , wherein
the first layer and the second layer have laterally varying thicknesses, and
the fourth layer and the fifth layer have other laterally varying thicknesses coordinated with the laterally varying thicknesses.
13. The optical filter of claim 10 , wherein
the blocking filter is a first blocking filter,
the optical filter further includes a second blocking filter, and
the bandpass filter is located between the first blocking filter and the second blocking filter.
14. The optical filter of claim 10 , wherein the optical filter is disposed on a substrate.
15. The optical filter of claim 14 , wherein the substrate is a photodetector array.
16. The optical filter of claim 10 , wherein
the blocking filter includes a plurality of portions,
each portion, of the plurality of portions, is associated with a blocking band, and
each blocking band is cascaded to cover a particular wavelength range.
17. The optical filter of claim 10 , wherein the bandpass filter includes:
a dielectric spacer layer located between first and second reflector stacks, and
a plurality of cavities.
18. A method of manufacturing an optical filter, the method comprising:
providing a substrate, a bandpass filter, and a blocking filter;
depositing the bandpass filter on the blocking filter,
wherein the bandpass filter comprises:
a first layer comprising a first material,
a second layer comprising a second material, and
a third layer disposed in an area of a local minimum of a standing optical wave inside the bandpass filter; and
depositing the blocking filter on the substrate,
wherein the blocking filter comprises:
a fourth layer comprising a third material, and
a fifth layer comprising a fourth material.
19. The method of claim 18 , further comprising:
forming, in the substrate, an array of photodetectors; and
polishing a surface to expose the array of photodetectors.
20. The method of claim 18 , further comprising:
forming, in the substrate, a bond pad.