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, and
a first blocking filter and a second blocking filter that are different from the bandpass filter,
wherein the bandpass filter is between the first blocking filter and the second blocking filter, and
wherein the bandpass filter includes:
one or more first layers, and
one or more second layers.
2. The optical filter of claim 1 , wherein the second blocking filter is disposed over a substrate.
3. The optical filter of claim 1 , wherein the one or more first layers include a first plurality of layers, and
wherein the one or more second layers include a second plurality of layers.
4. The optical filter of claim 3 , wherein the first plurality of layers alternate with the second plurality of layers.
5. The optical filter of claim 1 , wherein the one or more first layers include a first material, and
wherein the one or more second layers include a second material.
6. The optical filter of claim 1 , wherein thicknesses of the one or more first layers and the one or more second layers vary laterally in a direction x.
7. The optical filter of claim 1 , wherein a transmission wavelength λT varies based on a local thickness of the one or more first layers and the one or more second layers.
8. An optical filter comprising:
a first filter,
wherein the first filter is a bandpass filter that includes one or more first layers that include a first material and one or more second layers that include a second material;
a second filter,
wherein the second filter includes multiple other layers that include a third material and a fourth material,
wherein at least one of the third material or the fourth material includes at least silicon,
wherein each of a first refractive index of the first material, a second refractive index of the second material, and a third refractive index of the third material is less than a fourth refractive index of the fourth material, and
wherein the fourth refractive index of the fourth material is 2.6 or higher; and
a third filter,
wherein the bandpass filter is different from the third filter and the second filter, and
wherein the bandpass filter is between the third filter and the second filter.
9. The optical filter of claim 8 , wherein the second filter is a blocking filter.
10. The optical filter of claim 8 , wherein a first type of the first filter is different from a second type of the second filter, and
wherein the third filter is of the second type.
11. The optical filter of claim 8 , wherein the first filter is disposed in an optical path between the second filter and the third filter.
12. The optical filter of claim 8 , wherein the optical filter blocks wavelengths shorter and longer than a transmission wavelength λT of the first filter.
13. An optical filter comprising:
a bandpass section,
wherein the bandpass section includes:
a first cavity,
a second cavity, and
one or more silicon layers in one or more areas corresponding to local minima of an optical field inside the bandpass section.
14. The optical filter of claim 13 , wherein the first cavity includes a tantalum pentoxide spacer.
15. The optical filter of claim 14 , wherein the first cavity further includes a first quarter-wave reflector section and a second quarter-wave reflector section, and
wherein the tantalum pentoxide spacer is located between the first quarter-wave reflector section and the second quarter-wave reflector section.
16. The optical filter of claim 13 , wherein the first cavity includes:
a first reflector section that includes a first silicon layer of the one or more silicon layers, and
a second reflector section that includes a second silicon layer of the one or more silicon layers.
17. The optical filter of claim 13 , wherein the first cavity and the second cavity include four silicon layers, and
wherein the one or more silicon layers include the four silicon layers.
18. The optical filter of claim 13 , wherein the optical field is in a valley of a standing optical wave at a transmission wavelength λT inside the bandpass section.
19. The optical filter of claim 8 , wherein the bandpass filter is configured to provide a laterally variable transmission wavelength.
20. The optical filter of claim 8 , wherein the third filter is between the bandpass filter and a substrate.