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 first filter,
the first filter comprising:
a first plurality of layers including a first material having a first refractive index, and
a second plurality of layers alternating with the first plurality of layers,
the second plurality of layers including a second material having a second refractive index,
the first refractive index being smaller than the second refractive index; and
a second filter including the first material.
2. The optical filter of claim 1 , wherein at least one of the first filter or the second filter is deposited directly on a photodetector array.
3. The optical filter of claim 1 , wherein the first filter is disposed over a substrate.
4. The optical filter of claim 1 , wherein at least one layer of the first plurality of layers is between at least one layer of the second plurality of layers and a substrate.
5. The optical filter of claim 1 , wherein at least one layer of the second plurality of layers is an external most layer.
6. The optical filter of claim 1 , wherein the first filter has a laterally variable thickness.
7. The optical filter of claim 1 , wherein the first refractive index is between 1.35 and 1.6.
8. The optical filter of claim 1 , wherein the first material includes silicon dioxide.
9. The optical filter of claim 1 , wherein the first material and the second material include dielectric materials.
10. The optical filter of claim 1 , wherein the second filter has a laterally variable thickness.
11. An optical filter comprising:
a bandpass filter including a first material; and
a blocking filter,
the blocking filter comprising:
a plurality of higher refractive index material layers having a refractive index between 2.6 and 4.5, and
a plurality of lower refractive index material layers alternating with the plurality of higher refractive index material layers,
the plurality of lower refractive index material layers including the first material.
12. The optical filter of claim 11 , wherein the blocking filter has a laterally variable thickness.
13. The optical filter of claim 11 , wherein the plurality of lower refractive index material layers include silicon dioxide.
14. The optical filter of claim 11 ,
wherein the plurality of higher refractive index material layers include a second material, and
wherein the second material has an absorption coefficient larger than an absorption coefficient of the first material.
15. The optical filter of claim 11 , wherein the bandpass filter includes a material having a refractive index between 1.35 and 1.6.
16. The optical filter of claim 11 , wherein the blocking filter is deposited directly on a photodetector array.
17. The optical filter of claim 11 , wherein the blocking filter is disposed over a substrate.
18. The optical filter of claim 11 , wherein at least one layer of the plurality of higher refractive index material layers is between at least one layer of the plurality of lower refractive index material layers and a substrate.
19. The optical filter of claim 11 , wherein at least one layer of the plurality of higher refractive index material layers is an external most layer.
20. The optical filter of claim 11 , wherein the bandpass filter includes a material having a refractive index between 1.8 and 2.5.