Silicon-germanium based optical filter

1. An optical filter, comprising:

a substrate;

a set of optical filter layers disposed onto the substrate,

the set of optical filter layers including:

a first subset of optical filter layers,

the first subset of optical filter layers comprising silicon-germanium (SiGe) with a first refractive index; and

a second subset of optical filter layers,

the second subset of optical filter layers comprising a material with a second refractive index,

the second refractive index being less than the first refractive index.

2. The optical filter of claim 1 , where the material includes at least one of:

a silicon dioxide (SiO 2 ) material,

an aluminum oxide (Al 2 O 3 ) material,

a titanium dioxide (TiO 2 ) material,

a niobium pentoxide (Nb 2 O 5 ) material,

a tantalum pentoxide (Ta 2 O 5 ) material,

a magnesium fluoride (MgF 2 ) material,

a zirconium oxide (ZrO 2 ) material,

a yttrium oxide (Y 2 O 3 ) material,

a silicon nitride (S 3 N 4 ),

a boron based material, or

a phosphorous based material.

3. The optical filter of claim 1 , where the first subset of optical filter layers are high refractive index material layers (H) and the second subset of optical filter layers are low refractive index material layers (L); and

where the set of optical filter layers are arranged in at least one of:

an (H-L) m order,

an (H-L) m -H order, or

an L-(H-L) m order,

where m is a quantity of alternating H and L layers.

4. The optical filter of claim 1 , where the first refractive index is greater than 3 at a spectral range of approximately 800 nanometers (nm) to approximately 1100 nm.

5. The optical filter of claim 1 , where the first refractive index is greater than 3.5 at a spectral range of approximately 800 nanometers (nm) to approximately 1100 nm.

6. The optical filter of claim 1 , where the first refractive index is approximately 4 at a wavelength of approximately 900 nanometers (nm) to approximately 1100 nm.

7. The optical filter of claim 1 , where the first refractive index is greater than approximately 3 at a spectral range of approximately 1400 nanometers (nm) to approximately 1700 nm.

8. The optical filter of claim 1 , where the first refractive index is greater than approximately 3.4 at a spectral range of approximately 1500 nanometers (nm) to approximately 1600 nm.

9. The optical filter of claim 1 , where the first refractive index is greater than approximately 3.6 at a spectral range of approximately 1500 nanometers (nm) to approximately 1600 nm.

10. The optical filter of claim 1 , where the first subset of optical filter layers is annealed.

11. The optical filter of claim 1 , where the first subset of optical filter layers is hydrogenated.

12. The optical filter of claim 1 , where the first subset of optical filter layers is nitrogenated.

13. The optical filter of claim 1 , where the first subset of optical filter layers includes between 5% and 100% gennanium.

14. The optical filter of claim 1 , where the first subset of optical filter layers is doped with at least one of:

a phosphorous based dopant,

a nitrogen based dopant, or

a boron based dopant.

15. The optical filter of claim 1 , where the second refractive index is less than 3 at a spectral range of approximately 800 nanometers (nm) to approximately 1100 nm.

16. The optical filter of claim 1 , where the second refractive index is less than 2.5 at a spectral range of approximately 800 nanometers (nm) to approximately 1100 nm.

17. The optical filter of claim 1 , where the second refractive index is less than 2 at a spectral range of approximately 800 nanometers (nm) to approximately 1100 nm.

18. The optical filter of claim 1 , where the optical filter is a band pass filter.

19. The optical filter of claim 1 , where the optical filter is annealed.

20. An optical filter, comprising:

a substrate; and

a high refractive index material layer and a low refractive index material layer disposed onto the substrate to filter incident light,

wherein a first portion of the incident light with a first spectral range is to be reflected by the optical filter and a second portion of the incident light with a second spectral range is to be passed through by the optical filter,

the high refractive index material layer being hydrogenated silicon-germanium (SiGe:H), and

the low refractive index material layer being silicon dioxide (SiO 2 ).

21. The optical filter of claim 20 , where layers of the optical filter are deposited via a sputtering procedure.

22. The optical filter of claim 20 , further comprising:

an anti-reflective coating.

23. An optical system, comprising:

an optical transmitter to emit near-infrared (NIR) light;

an optical filter to filter an input optical signal and provide a filtered input optical signal,

the input optical signal including the NIR light from the optical transmitter and ambient light from an optical source,

the optical filter including a set of dielectric thin film layers,

the set of dielectric thin film layers including:

a first subset of layers of silicon-germanium with a first refractive index, and

a second subset of layers of a material with a second refractive index less than the first refractive index, and

the filtered input optical signal including a reduced intensity of ambient light relative to the input optical signal; and

an optical receiver to receive the filtered input optical signal and provide an output electrical signal.

24. The optical system of claim 23 , where the optical filter is associated with greater than 80% transmissivity at approximately 950 nm.

25. The optical system of claim 23 , where the optical filter is associated with greater than 80% transmissivity at approximately 1550 nm.

26. The optical system of claim 23 , where the first subset of layers are hydrogenated.

27. The optical system of claim 23 , where the optical filter is annealed.