Variable optical filter and a wavelength-selective sensor based thereon

1. A method comprising:

providing an array of photodetectors spaced apart along a length dimension of an optical filter,

the array of photodetectors being responsive to different wavelengths of light; and

depositing, on the array of photodetectors, a bandpass filter and a blocking filter,

the bandpass filter comprising first and second layers comprising first and second materials, respectively, and having a first laterally varying thicknesses for providing a laterally variable transmission wavelength, and

the blocking filter comprising third and fourth layers comprising third and fourth materials, respectively, and having a second laterally varying thicknesses, coordinated with the first laterally varying thicknesses of the first and second layers, for blocking wavelengths, within a wavelength range, that are larger or smaller than the laterally variable transmission wavelength,

the bandpass filter further comprising at least one fifth layer comprising the fourth material and disposed in an area of a local minimum of a standing optical wave inside the bandpass filter.

2. The method of claim 1 ,

wherein the first, second and fourth materials are different materials,

wherein a refractive index of the first material is smaller than a refractive index of the second material, and

wherein the refractive index of the second material is smaller than a refractive index of the fourth material.

3. The method of claim 1 , wherein the first and third materials are comprised of a dielectric material.

4. The method of claim 3 , wherein the first and third materials are comprised of the dielectric material.

5. The method of claim 4 , wherein the dielectric material comprises silicon dioxide.

6. The method of claim 1 , wherein the fourth material comprises a semiconductor material.

7. The method of claim 6 ,

wherein the semiconductor material comprises silicon, and

wherein the first and third materials comprise silicon dioxide.

8. The method of claim 1 , wherein the second material comprises one of titanium dioxide, tantalum pentoxide, niobium pentoxide, or an alloy of tantalum pentoxide and niobium pentoxide.

9. The method of claim 1 ,

wherein a refractive index of the first and third materials is between 1.35 and 1.6,

wherein a refractive index of the second material is between 1.8 and 2.5, and

wherein a refractive index of the fourth material is between 2.6 and 4.5.

10. The method of claim 1 ,

wherein the wavelength range spans from 900 nm to 1700 nm, and

wherein the bandpass filter and the blocking filter have a total thickness of less than 20 micrometers at a location corresponding to a transmission wavelength of 1300 nm.

11. The method of claim 1 ,

wherein the blocking filter comprises first and second portions for blocking wavelengths larger and smaller than the laterally variable transmission wavelength, respectively, and

wherein the bandpass filter is disposed in an optical path between the first and second portions of the blocking filter.

12. The method of claim 1 ,

wherein the first and third materials comprise silicon dioxide,

wherein the second material comprises tantalum pentoxide or niobium pentoxide,

wherein the fourth material comprises silicon,

wherein the bandpass filter comprises no more than 20 layers, and

wherein the blocking filter comprises no more than 60 layers.

13. The method of claim 12 , wherein the bandpass filter and the blocking filter have a total thickness of no greater than 10 micrometers.

14. The method of claim 1 ,

wherein two or more photodetectors, in the array of photodetectors, have different heights,

wherein the array of photodetectors comprises a planarization layer disposed over the two or more photodetectors, and

wherein the two or more photodetectors support the optical filter.

15. The method of claim 1 ,

wherein two or more photodetectors, in the array of photodetectors, are separated by a plurality of laterally spaced gaps, and

wherein the array of photodetectors further comprises an opaque isolation material disposed in the plurality of laterally spaced gaps, for optical isolation of each individual photodetector of the two or more photodetectors.

16. The method of claim 15 ,

wherein the optical filter comprises a plurality of slots each disposed above a corresponding one of the plurality of laterally spaced gaps, and

wherein the opaque isolation material is disposed in the slots for additional optical isolation of each individual photodetector of the two or more photodetectors.

17. The method of claim 1 ,

wherein the array of photodetectors comprises a device chip having opposed first and second surfaces,

wherein the array of photodetectors is disposed in the first surface of the device chip, and

wherein the optical filter is disposed on the first surface over the array of photodetectors.

18. The method of claim 17 , wherein, prior to deposition of the bandpass filter and the blocking filter, the method further comprises:

providing a device wafer having first and second opposing surfaces;

forming, in the second surface of the device wafer, the array of photodetectors facing towards the first surface; and

polishing the first surface of the device wafer to expose the array of photodetectors.

19. The method of claim 18 , wherein the array of photodetectors further comprises a carrier chip bonded to the second surface of the device chip.

20. The method of claim 1 ,

wherein the array of photodetectors comprises a substrate having opposed first and second surfaces,

wherein photodetectors, of the array of photodetectors, are disposed in the first surface, and

wherein the optical filter is disposed on the second surface of the substrate.

21. The method of claim 20 , further comprising:

providing a multiplexer chip for reading photoelectric signals of the array of photodetectors,

wherein the multiplexer chip is flip-chip bonded to the first surface of the substrate.