Optical filter
A bandpass filter may include a set of layers. The set of layers may include a first subset of layers. The first subset of layers may include hydrogenated germanium (Ge:H) with a first refractive index. The set of layers may include a second subset of layers. The second subset of layers may include a material with a second refractive index. The second refractive index may be less than the first refractive index.
1. A bandpass filter, comprising:
a set of layers including:
a first subset of layers,
the first subset of layers comprising hydrogenated germanium (Ge:H) with a first refractive index; and
a second subset of layers,
the second subset of layers comprising a material with a second refractive index,
the second refractive index being less than the first refractive index, and
the material including 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, or
a magnesium fluoride (MgF 2 ) material.
2. The bandpass filter of claim 1 , where the first subset of layers are high refractive index layers (H) and the second subset of layers are low refractive index layers (L); and
where the set of layers are arranged in at least one of:
an (H-L) m order,
an (H-L) m -H order,
an (L-H) m order, or
an L-(H-L) m order,
where m is a quantity of alternating H and L layers.
3. The bandpass filter of claim 1 , where the set of layers is configured to pass a threshold portion of light associated with a spectral range of between approximately 1100 nanometers (nm) and 2000 nm.
4. The bandpass filter of claim 1 , where the set of layers is configured to pass a threshold portion of light associated with a spectral range of between approximately 1400 nanometers (nm) and 2000 nm.
5. The bandpass filter of claim 1 , where the set of layers is configured to pass a threshold portion of light associated with a spectral range with a center wavelength of approximately 1550 nanometers.
6. The bandpass filter of claim 1 , where the first refractive index is greater than approximately 3.8 at a wavelength of approximately 1550 nanometers.
7. The bandpass filter of claim 1 , where the first refractive index is approximately 4.2 at a wavelength of approximately 1550 nanometers.
8. The bandpass filter of claim 1 , where the first subset of layers is associated with an extinction coefficient of less than approximately 0.01 at a spectral range centered at approximately 1550 nanometers.
9. The bandpass filter of claim 1 , where the second refractive index is less than 3 at a spectral range of approximately 1100 nanometers (nm) to approximately 2000 nm.
10. The bandpass filter of claim 1 , where a change to a center wavelength of a spectral range is less than 40 nanometers for angles of incidence from 0 degrees to 40 degrees.
11. The bandpass filter of claim 1 , where a change to a center wavelength of a spectral range is less than 30 nanometers for angles of incidence from 0 degrees to 40 degrees.
12. The bandpass filter of claim 1 , where a change to a center wavelength of a spectral range is less than 20 nanometers for angles of incidence from 0 degrees to 30 degrees.
13. The bandpass filter of claim 1 , where a change to a center wavelength of a spectral range is less than 10 nanometers for angles of incidence from 0 degrees to 20 degrees.
14. An optical filter, comprising:
a substrate; and
a set of alternating high refractive index layers and low refractive index layers disposed onto the substrate to filter incident light,
where the optical filter is configured to pass a first portion of the incident light within a spectral range with a center wavelength of approximately 1550 nanometers (nm) and reflect a second portion of incident light not within the spectral range,
the high refractive index layers being hydrogenated germanium (Ge:H), and
the low refractive index layers being silicon dioxide (SiO 2 ).
15. The optical filter of claim 14 , where the high refractive index layers are deposited using a sputtering procedure.
16. The optical filter of claim 14 , where the high refractive index layers are annealed.
17. An optical system, comprising:
an optical filter configured to filter an input optical signal and provide the filtered input optical signal,
the input optical signal including light from a first optical source and light from a second 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 hydrogenated germanium with a first refractive index,
a second subset of layers of a material with a second refractive index less than the first refractive index,
the material including 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, or
a magnesium fluoride (MgF 2 ) material, and
the filtered input optical signal including a reduced intensity of light from the second optical source relative to the input optical signal; and
an optical sensor configured to receive the filtered input optical signal and provide an output electrical signal.
18. The optical system of claim 17 , where the optical filter is disposed onto a sensor element array of the optical sensor.
19. The optical system of claim 17 , where the optical filter is separated from a sensor element by free space.
20. The optical system of claim 17 , where the optical filter is associated with a thickness of approximately 5.6 μm.