Patent Description:
<CIT> discloses an optical filter with a passband in a spectral range around a center wavelength of approximately <NUM>, formed from alternating layers of high refractive index and low refractive index.

In a first aspect of the invention, an optical filter is provided in accordance with claim <NUM>.

The optical filter includes a substrate. The optical filter includes a set of alternating high refractive index layers and low refractive index layers disposed onto the substrate to filter incident light, wherein the high refractive index layers is provided by the first subset of layers and the low refractive index of layers is provided by the second subset of layers.

According to some possible implementations, an optical system may include an optical filter configured to filter an input optical signal and provide the filtered input optical signal. The input optical signal may include light from a first optical source and light from a second optical source. The optical filter may include a set of dielectric thin film layers. The set of dielectric thin film layers may include a first subset of layers of hydrogenated germanium with a first refractive index. The set of dielectric thin film layers may include a second subset of layers of a material with a second refractive index less than the first refractive index. The filtered input optical signal may include a reduced intensity of light from the second optical source relative to the input optical signal. The optical system may include an optical sensor configured to receive the filtered input optical signal and provide an output electrical signal.

An optical sensor device may include a sensor element array of sensor elements to receive light initiating from an optical source, such as an optical transmitter, a light bulb, an ambient light source, or the like. The optical sensor device may utilize one or more sensor technologies, such as a complementary metal-oxide-semiconductor (CMOS) technology, a charge-coupled device (CCD) technology, or the like. A sensor element (e.g., an optical sensor), of the optical sensor device, may obtain information (e.g., spectral data) regarding a set of electromagnetic frequencies. The sensor element may be an indium-gallium-arsenide (InGaAs) based sensor element, a silicon germanium (SiGe) based sensor element, or the like.

A sensor element may be associated with a filter that filters light to the sensor element to enable the sensor element to obtain information regarding a particular spectral range of electromagnetic frequencies. For example, the sensor element may be aligned with a filter with a passband in a spectral range of approximately <NUM> nanometers (nm) to approximately <NUM>, a spectral range of approximately <NUM> to approximately <NUM>, a spectral range with a center wavelength of approximately <NUM>, or the like to cause a portion of light that is directed toward the sensor element to be filtered. A filter may include sets of dielectric layers to filter the portion of the light. For example, a filter may include dielectric filter stacks of alternating high index layers and low index layers, such as alternating layers of hydrogenated silicon (Si:H or SiH) or germanium (Ge) as a high index material and silicon dioxide (SiO<NUM>) as a low index material. However, use of hydrogenated silicon as a high index material for a filter associated with a spectral range with a center wavelength centered at approximately <NUM> may result in an excessive angle shift (e.g., an angle shift greater than a threshold). Moreover, use of germanium as a high index material may result in less than a threshold transmissivity for the passband centered at approximately <NUM>, such as a transmissivity of less than approximate <NUM>% at a wavelength of approximately <NUM>.

The optical filter comprises hydrogenated germanium (Ge:H or GeH) as a high index material, thereby resulting in an angle-shift that is less than a threshold. The optical filter includes one or more layers of hydrogenated germanium, optionally annealed hydrogenated germanium. The optical filter includes one or more layers of silicon dioxide. The optical filter provides for a passband centered at a wavelength of approximately <NUM>, an angle shift of less than approximately <NUM> at an angle of incidence of <NUM> degrees, or an angle shift of less than approximately <NUM> at an angle of incidence of <NUM> degrees. Optionally, the optical filter provides an angle shift of less than approximately <NUM> at an angle of incidence of <NUM> degrees. Moreover, the optical filter using hydrogenated germanium and/or annealed hydrogenated germanium may provide greater than a threshold level of transmissivity for a passband centered at approximately <NUM>, such as a transmissivity greater than approximately <NUM>%, greater than approximately <NUM>%, greater than approximately <NUM>%, or the like. In this way, some implementations described herein filter light with less than a threshold angle shift and with greater than a threshold level of transmission.

<FIG> are diagrams of an overview of example implementations <NUM>/<NUM>'/<NUM>" described herein. As shown in <FIG>, example implementation <NUM> includes a sensor system <NUM>. Sensor system <NUM> may be a portion of an optical system, and may provide an electrical output corresponding to a sensor determination. Sensor system <NUM> includes an optical filter structure <NUM>, which includes an optical filter <NUM>, and an optical sensor <NUM>. For example, optical filter structure <NUM> may include an optical filter <NUM> that performs a passband filtering functionality. In another example, an optical filter <NUM> may be aligned to an array of sensor elements of optical sensor <NUM>.

Although some implementations, described herein, may be described in terms of an optical filter in a sensor system, implementations described herein may be used in another type of system, may be used external to a sensor system, or the like.

As further shown in <FIG>, and by reference number <NUM>, an input optical signal is directed toward optical filter structure <NUM>. The input optical signal may include but is not limited to light associated with a particular spectral range (e.g., a spectral range centered at approximately <NUM>), such as a spectral range of <NUM> to <NUM>, a spectral range of <NUM> to <NUM>, or the like. For example, an optical transmitter may direct the light toward optical sensor <NUM> to permit optical sensor <NUM> to perform a measurement of the light. In another example, the optical transmitter may direct another spectral range of light for another functionality, such as a testing functionality, a sensing functionality, a communications functionality, or the like.

As further shown in <FIG>, and by reference number <NUM>, a first portion of the optical signal with a first spectral range is not passed through by optical filter <NUM> and optical filter structure <NUM>. For example, dielectric filter stacks of dielectric thin film layers, which may include high index material layers and low index material layers of optical filter <NUM>, may cause the first portion of light to be reflected in a first direction, to be absorbed, or the like. In this case, the first portion of light may be a threshold portion of light incident on optical filter <NUM> not included in a bandpass of optical filter <NUM>, such as greater than <NUM>% of light not within a particular spectral range centered at approximately <NUM>. As shown by reference number <NUM>, a second portion of the optical signal is passed through by optical filter <NUM> and optical filter structure <NUM>. For example, optical filter <NUM> may pass through the second portion of light with a second spectral range in a second direction toward optical sensor <NUM>. In this case, the second portion of light may be a threshold portion of light incident on optical filter <NUM> within a bandpass of optical filter <NUM>, such as greater than <NUM>% of incident light in a spectral range centered at approximately <NUM>.

As further shown in <FIG>, based on the second portion of the optical signal being passed to optical sensor <NUM>, optical sensor <NUM> may provide an output electrical signal <NUM> for sensor system <NUM>, such as for use in imaging, ambient light sensing, detecting the presence of an object, performing a measurement, facilitating communication, or the like. In some implementations, another arrangement of optical filter <NUM> and optical sensor <NUM> may be utilized. For example, rather than passing the second portion of the optical signal collinearly with the input optical signal, optical filter <NUM> may direct the second portion of the optical signal in another direction toward a differently located optical sensor <NUM>.

As shown in <FIG>, another example implementation <NUM>' includes a set of sensor elements of a sensor element array forming optical sensor <NUM> and integrated into a substrate of optical filter structure <NUM>. In this case, optical filter <NUM> is disposed directly onto the substrate. Input optical signals <NUM>-<NUM> and <NUM>-<NUM> are received at multiple different angles and first portions <NUM>-<NUM> and <NUM>-<NUM> of input optical signals <NUM>-<NUM> and <NUM>-<NUM> are reflected at multiple different angles. In this case, second portions of input optical signals <NUM>-<NUM> and <NUM>-<NUM> are passed through optical filter <NUM> to a sensor element array forming optical sensor <NUM>, which provides an output electrical signal <NUM>.

As shown in <FIG>, another example implementation <NUM>" includes a set of sensor elements of a sensor element array forming optical sensor <NUM> and separated from an optical filter structure <NUM> (e.g., by free space in a free space optics type of optical system). In this case, optical filter <NUM> is disposed onto optical filter structure <NUM>. Input optical signals <NUM>-<NUM> and <NUM>-<NUM> are received at multiple different angles at optical filter <NUM>. First portions <NUM>-<NUM> and <NUM>-<NUM> of the input optical signals <NUM>-<NUM> and <NUM>-<NUM> are reflected and second portions <NUM>-<NUM> and <NUM>-<NUM> of the input optical signals <NUM>-<NUM> and <NUM>-<NUM> are passed by optical filter <NUM> and optical filter structure <NUM>. Based on receiving second portions <NUM>-<NUM> and <NUM>-<NUM>, the sensor element array provides an output electrical signal <NUM>.

As indicated above, <FIG> are provided merely as examples.

<FIG> is a diagram of an example optical filter <NUM>. <FIG> shows an example stackup of an optical filter using hydrogenated germanium as a high index material. As further shown in <FIG>, optical filter <NUM> includes an optical filter coating portion <NUM> and a substrate <NUM>.

Optical filter coating portion <NUM> includes a set of optical filter layers. For example, optical filter coating portion <NUM> includes a first set of layers <NUM>-<NUM> through <NUM>-N (N ≥ <NUM>) (e.g., high refractive index layers (H layers)) and a second set of layers <NUM>-<NUM> through <NUM>-(N+<NUM>) (e.g., low refractive index layers (L layers)). In some implementations, layers <NUM> and <NUM> may be arranged in a particular order, such as an (H-L)m (m ≥ <NUM>) order, an (H-L)m-H order, an (L-H)m order, an L-(H-L)m order, or the like. For example, as shown, layers <NUM> and <NUM> are positioned in an (H-L)n-H order with an H layer disposed at a surface of optical filter <NUM> and an H layer contiguous to a surface of substrate <NUM>. In some implementations, one or more other layers may be included in optical filter <NUM>, such as one or more protective layers, one or more layers to provide one or more other filtering functionalities (e.g., a blocker, an anti-reflection coating, etc.), or the like.

Layers <NUM> may include a set of hydrogenated germanium layers. In some implementations, another material may be utilized for the H layers, such as another material with a refractive index greater than the refractive index of the L layers, a refractive index greater than <NUM>, a refractive index greater than <NUM>, a refractive index greater than <NUM>, a refractive index greater than <NUM>, a refractive index greater the <NUM>, or the like, over a particular spectral range (e.g., the spectral range of approximately <NUM> to approximately <NUM>, the spectral range of approximately <NUM> to approximately <NUM>, the wavelength of approximately <NUM>, or the like). In another example, layers <NUM> may be selected to include a refractive index of approximately <NUM> at a wavelength of approximately <NUM>.

In some implementations, a particular hydrogenated germanium based material may be selected for the H layers <NUM>, such as hydrogenated germanium, annealed hydrogenated germanium, or the like. In some implementations, layers <NUM> and/or <NUM> may be associated with a particular extinction coefficient, such as an extinction coefficient, at approximately <NUM>, of less than approximately <NUM>, less than approximately <NUM>, less than approximately <NUM>, less than approximately <NUM>, an extinction coefficient of less than approximately <NUM>, an extinction coefficient of less than approximately <NUM>, or the like over a particular spectral range (e.g., the spectral range of approximately <NUM> to approximately <NUM>, the spectral range of approximately <NUM> to approximately <NUM>, the wavelength of approximately <NUM>, or the like).

According to the invention, layers <NUM> include a set of silicon dioxide (SiO<NUM>) layers. In some implementations, another material may be utilized for the L layers. In some implementations, a particular material may be selected for L layers <NUM>. The layers <NUM> include a set of silicon dioxide (SiO<NUM>) layers. In this case, layers <NUM> may be selected to include a refractive index lower than that of the layers <NUM> over, for example, a particular spectral range (e.g., the spectral range of approximately <NUM> to approximately <NUM>, the spectral range of approximately <NUM> to approximately <NUM>, the wavelength of approximately <NUM>, or the like). For example, layers <NUM> may be selected to be associated with a refractive index of less than <NUM> over a particular spectral range (e.g., the spectral range of approximately <NUM> to approximately <NUM>, the spectral range of approximately <NUM> to approximately <NUM>, a spectral range of approximately <NUM>, the wavelength of approximately <NUM>, or the like).

In another example, layers <NUM> may be selected to be associated with a refractive index of less than <NUM> over a particular spectral range (e.g., the spectral range of approximately <NUM> to approximately <NUM>, the spectral range of approximately <NUM> to approximately <NUM>, the wavelength of approximately <NUM>, or the like). In another example, layers <NUM> may be selected to be associated with a refractive index of less than <NUM> over a particular spectral range (e.g., the spectral range of approximately <NUM> to approximately <NUM>, the spectral range of approximately <NUM> to approximately <NUM>, the wavelength of approximately <NUM>, or the like). In another example, layers <NUM> may be selected to be associated with a refractive index of less than <NUM> over a particular spectral range (e.g., the spectral range of approximately <NUM> to approximately <NUM>, the spectral range of approximately <NUM> to approximately <NUM>, the wavelength of approximately <NUM>, or the like). In some implementations, the particular material may be selected for layers <NUM> based on a desired width of an out-of-band blocking spectral range, a desired center-wavelength shift associated with a change of angle of incidence, or the like.

In some implementations, optical filter coating portion <NUM> may be associated with a particular quantity of layers, m. For example, a hydrogenated germanium based optical filter may include approximately <NUM> layers of alternating H layers and L layers. In another example, optical filter <NUM> may be associated with another quantity of layers, such as a range of <NUM> layers to <NUM> layers, a range of <NUM> to <NUM> layers, or the like. In some implementations, each layer of optical filter coating portion <NUM> may be associated with a particular thickness. For example, layers <NUM> and <NUM> may each be associated with a thickness of between approximately <NUM> and approximately <NUM>, resulting in optical filter coating portion <NUM> being associated with a thickness of between approximately <NUM> and <NUM>, a thickness of between approximately <NUM> and <NUM>, or the like.

In some implementations, layers <NUM> and <NUM> may be associated with multiple thicknesses, such as a first thickness for layers <NUM> and a second thickness for layers <NUM>, a first thickness for a first subset of layers <NUM> and a second thickness for a second subset of layers <NUM>, a first thickness for a first subset of layers <NUM> and a second thickness for a second subset of layers <NUM>, or the like. In this case, a layer thickness and/or a quantity of layers may be selected based on an intended set of optical characteristics, such as an intended passband, an intended transmissivity, or the like. For example, the layer thickness and/or the quantity of layers may be selected to permit optical filter <NUM> to be utilized for a spectral range of approximately <NUM> to approximately <NUM>, at a center wavelength of approximately <NUM>, or the like.

In some implementations, optical filter coating portion <NUM> may be fabricated using a sputtering procedure. For example, optical filter coating portion <NUM> may be fabricated using a pulsed-magnetron based sputtering procedure to sputter alternating layers <NUM> and <NUM> on a glass substrate. In some implementations, optical filter coating portion <NUM> may be associated with a relatively low center-wavelength shift with change in angle of incidence. For example, optical filter coating portion <NUM> may cause a center-wavelength shift of less than approximately <NUM>, less than approximately <NUM>, less than approximately <NUM>, or the like in magnitude with a change in incidence angle from <NUM> degrees to <NUM> degrees; a center-wavelength shift of less than approximately <NUM>, less than approximately <NUM>, less than approximately <NUM>, or the like with a change in incidence angle from <NUM> degrees to <NUM> degrees; a center-wavelength shift of less than approximately <NUM>, less than approximately <NUM>, less than approximately <NUM>, less than approximately <NUM>, or the like with a change in incidence angle from <NUM> degrees to <NUM> degrees; or the like.

In some implementations, optical filter coating portion <NUM> is attached to a substrate, such as substrate <NUM>. For example, optical filter coating portion <NUM> may be attached to a glass substrate. In some implementations, optical filter coating portion <NUM> may be associated with an incident medium, such as an air medium or glass medium. In some implementations, optical filter <NUM> may be disposed between a set of prisms.

In some implementations, an annealing procedure may be utilized to fabricate optical filter coating portion <NUM>. For example, after sputter deposition of layers <NUM> and <NUM> on a substrate, optical filter <NUM> may be annealed to improve one or more optical characteristics of optical filter <NUM>, such as reducing an absorption coefficient of optical filter <NUM> relative to another optical filter for which an annealing procedure is not performed.

<FIG> is diagram of an example <NUM> of a sputter deposition system for manufacturing a hydrogenated germanium based optical filter described herein.

As shown in <FIG>, example <NUM> includes a vacuum chamber <NUM>, a substrate <NUM>, a cathode <NUM>, a target <NUM>, a cathode power supply <NUM>, an anode <NUM>, a plasma activation source (PAS) <NUM>, and a PAS power supply <NUM>. Target <NUM> may include a germanium material. PAS power supply <NUM> may be utilized to power PAS <NUM> and may include a radio frequency (RF) power supply. Cathode power supply <NUM> may be utilized to power cathode <NUM> and may include a pulsed direct current (DC) power supply.

With regard to <FIG>, target <NUM> is sputtered in the presence of hydrogen (H<NUM>), as well as an inert gas, such as argon, to deposit a hydrogenated germanium material as a layer on substrate <NUM>. The inert gas may be provided into the chamber via anode <NUM> and/or PAS <NUM>. Hydrogen is introduced into the vacuum chamber <NUM> through PAS <NUM>, which serves to activate the hydrogen. Additionally, or alternatively, cathode <NUM> may cause hydrogen activation (e.g., in this case, hydrogen may be introduced from another part of vacuum chamber <NUM>) or anode <NUM> may cause hydrogen activation (e.g., in this case, hydrogen may be introduced into vacuum chamber <NUM> by anode <NUM>). In some implementations, the hydrogen may take the form of hydrogen gas, a mixture of hydrogen gas and a noble gas (e.g., argon gas), or the like. PAS <NUM> may be located within a threshold proximity of cathode <NUM>, allowing plasma from PAS <NUM> and plasma from cathode <NUM> to overlap. The use of the PAS <NUM> allows the hydrogenated germanium layer to be deposited at a relatively high deposition rate. In some implementations, the hydrogenated germanium layer is deposited at a deposition rate of approximately <NUM>/s to approximately <NUM>/s, at a deposition rate of approximately <NUM>/s to approximately <NUM>/s, at a deposition rate of approximately <NUM>/s, or the like.

Although the sputtering procedure is described, herein, in terms of a particular geometry and a particular implementation, other geometries and other implementations are possible. For example, hydrogen may be injected from another direction, from a gas manifold in a threshold proximity to cathode <NUM>, or the like. Although, described, herein, in terms of different configurations of components, different relative concentrations of germanium may also be achieved using different materials, different manufacturing processes, or the like.

<FIG> show examples relating to optical filters using hydrogenated germanium as a high index material. <FIG> show characteristics relating to hydrogenated germanium based single layer films.

As shown in <FIG>, and by chart <NUM>, a filter response showing transmissivity for a set of films <NUM>-<NUM> through <NUM>-<NUM> is provided. Each film <NUM> may be an approximately <NUM> micrometer single layer film. Film <NUM>-<NUM> is associated with a concentration of hydrogen associated with a flow rate of <NUM> standard cubic centimeters per minute (SCCM). In other words, film <NUM>-<NUM> uses non-hydrogenated germanium. Films <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> are associated with concentrations of hydrogen associated with flow rates of <NUM> SCCM, <NUM> SCCM, <NUM> SCCM, and <NUM> SCCM. In other words, films <NUM>-<NUM> through <NUM>-<NUM> use hydrogenated germanium with increasing concentrations of hydrogen. In this case, the hydrogenated germanium films, such as films <NUM>-<NUM> through <NUM>-<NUM>, are associated with increased transmissivity relative to non-hydrogenated germanium film <NUM>-<NUM>. In this way, utilizing hydrogenated germanium in an optical filter can provide improved transmissivity. For example, based on a concentration of hydrogen in a hydrogenated germanium film, a hydrogenated germanium film may be associated with as a transmissivity greater than <NUM>%, greater than <NUM>%, greater than <NUM>%, greater than <NUM>%, greater than <NUM>%, greater than <NUM>%, or the like for a spectral range of <NUM> to <NUM>, a spectral range of <NUM> to <NUM>, a spectral range with a wavelength of <NUM>, or the like.

As shown in <FIG>, and by chart <NUM>, an index of refraction and an extinction coefficient for the films <NUM> are provided. At a wavelength of <NUM>, non-hydrogenated germanium film <NUM>-<NUM> is associated with an extinction coefficient of approximately <NUM>, which is greater than the extinction coefficients for hydrogenated germanium films <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, which are approximately <NUM>, approximately <NUM>, and approximately <NUM>, respectively. Similarly, at a wavelength of <NUM>, non-hydrogenated germanium film <NUM>-<NUM> is associated with a refractive index of <NUM>, which compares with hydrogenated germanium films <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, which are associated with refractive indices of <NUM>, <NUM> and <NUM>, respectively. In this case, hydrogenated-germanium films <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> are associated with a reduced extinction coefficient while maintaining a threshold refractive index (e.g., greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, etc.).

At a wavelength of <NUM>, a comparable non-hydrogenated germanium film <NUM>-<NUM> (that does not fall within the scope of the first subset of layers or the second subset of layers as provided by claim <NUM> but is discussed for exemplary purposes) is associated with an extinction coefficient of approximately <NUM>, which is greater than the extinction coefficients for hydrogenated germanium films <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, which are approximately <NUM>, approximately <NUM>, and approximately <NUM>, respectively. Similarly, at a wavelength of <NUM>, the non-hydrogenated germanium film <NUM>-<NUM> is associated with a refractive index of <NUM>, which compares with hydrogenated germanium films <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, which are associated with refractive indices of <NUM>, <NUM> and <NUM>, respectively. In this case, hydrogenated-germanium films <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> are associated with a reduced extinction coefficient while maintaining a threshold refractive index (e.g., greater than <NUM>, greater than <NUM>, greater than <NUM>, etc.).

At a wavelength of <NUM>, non-hydrogenated germanium film <NUM>-<NUM> (that does not fall within the scope of the first subset of layers or the second subset of layers as provided by claim <NUM> but is discussed for exemplary purposes) is associated with an extinction coefficient of approximately <NUM>, which is greater than the extinction coefficients for hydrogenated germanium films <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, which are approximately <NUM>, approximately <NUM>, and approximately <NUM>, respectively. Similarly, at a wavelength of <NUM>, non-hydrogenated germanium film <NUM>-<NUM> is associated with a refractive index of <NUM>, which compares with hydrogenated germanium films <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, which are associated with refractive indices of <NUM>, <NUM> and <NUM>, respectively. In this case, hydrogenated-germanium films <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> are associated with a reduced extinction coefficient while maintaining a threshold refractive index (e.g., greater than <NUM>, greater than <NUM>, greater than <NUM>).

As shown in <FIG>, and by chart <NUM>, an index of refraction for hydrogenated germanium film <NUM>-<NUM> and a hydrogenated silicon film <NUM>-<NUM> (that does not fall within the scope of the first subset of layers or the second subset of layers as provided by claim <NUM> but is discussed for exemplary purposes) is provided. In this case, the index of refraction for hydrogenated germanium film <NUM>-<NUM> is each greater than an index of refraction for hydrogenated silicon film <NUM>-<NUM>.

As shown in <FIG>, and by chart <NUM>, an index of refraction and an extinction coefficient are provided for hydrogenated germanium film <NUM>-<NUM> and an annealed hydrogenated germanium film <NUM>-<NUM>'. In this case, applying an annealing procedure, for example, at approximately <NUM> degrees Celsius for <NUM> minutes results in forming annealed hydrogenated germanium film <NUM>-<NUM>', results in an increased index of refraction (e.g., increased to approximately <NUM>) and a reduced extinction coefficient (e.g., reduced to approximately <NUM>) at a spectral range with a center wavelength of approximately <NUM> relative to hydrogenated germanium film <NUM>-<NUM>, thereby reducing angle shift and improving transmissivity.

<FIG> are diagrams of characteristics relating to an optical filter. <FIG> show characteristics relating to bandpass filters.

As shown in <FIG>, and by chart <NUM>, a filter response is provided for a hydrogenated germanium optical filter <NUM>. Optical filter <NUM> may include alternating layers of hydrogenated germanium and silicon dioxide. In some implementations, optical filter <NUM> may be associated with a thickness of approximately <NUM>, and may be associated with a bandpass centered at approximately <NUM> for an angle of incidence of <NUM> degrees. Moreover, optical filter <NUM> is associated with a transmissivity of greater than a threshold amount (e.g., greater than approximately <NUM>%) for angles of incidence from <NUM> degrees to <NUM> degrees.

As shown in <FIG>, and by chart <NUM>, a filter response is provided for a hydrogenated silicon based optical filter <NUM> (that does not fall within the scope of the first subset of layers or the second subset of layers as provided by claim <NUM> but is discussed for exemplary purposes). Optical filter <NUM> may include alternating layers of hydrogenated silicon and silicon dioxide. In some implementations, optical filter <NUM> may be associated with a thickness of approximately <NUM> micrometers (µm) and may be associated with a bandpass centered at approximately <NUM> for an angle of incidence of <NUM> degrees.

As shown in <FIG>, and by chart <NUM>, relative to optical filter <NUM> (Si:Ge), optical filter <NUM> (Si:H) is associated with a reduced angle shift for changes of angles of incidence from <NUM> degrees to approximately <NUM> degrees. For example, optical filter <NUM> is associated with a change in center wavelength of, for example, less than approximately <NUM> at an angle of incidence of approximately <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of approximately <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of approximately <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of approximately <NUM>-<NUM> degrees, or the like. Similarly, optical filter <NUM> is associated with a change in center wavelength of, for example, less than approximately <NUM> at an angle of incidence of <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of <NUM>-<NUM> degrees, or the like.

Similarly, optical filter <NUM> is associated with a change in center wavelength of, for example, less than approximately <NUM> at an angle of incidence of <NUM> degrees, less than approximately <NUM> at an angle of incidence of <NUM> degrees, less than approximately <NUM> at an angle of incidence of <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of <NUM>-<NUM> degrees, or the like. Similarly, optical filter <NUM> is associated with a change in center wavelength of, for example, less than approximately <NUM> at an angle of incidence of approximately <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of approximately <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of approximately <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of approximately <NUM>-<NUM> degrees, less than approximately <NUM> at an angle of incidence of approximately <NUM>-<NUM> degrees, or the like.

In this way, a hydrogenated germanium optical filter, such as an optical filter with hydrogenated germanium as a high index layer and another material as a low index layer, may provide improved angel shift, improved transmissivity, and reduced physical thickness relative to other materials for an optical filter associated with a spectral range with a center wavelength at approximately <NUM>.

Some implementations are described herein in connection with thresholds. As used herein, satisfying a threshold may refer to a value being greater than the threshold, more than the threshold, higher than the threshold, greater than or equal to the threshold, less than the threshold, fewer than the threshold, lower than the threshold, less than or equal to the threshold, equal to the threshold, etc..

Even though particular combinations of features are recited in the description, these combinations are not intended to limit the disclosure of possible implementations.

Claim 1:
An optical filter, comprising
a substrate (<NUM>);
a bandpass filter, comprising:
a set of layers including:
a first subset of layers (<NUM>) comprising hydrogenated germanium (Ge:H) with a first refractive index, and
a second subset of layers (<NUM>) comprising silicon dioxide with a second refractive index, the second refractive index being less than the first refractive index,
characterized in that the optical filter has a passband centered at a wavelength of approximately <NUM> nanometers (nm), and either (i) an angle shift of less than approximately <NUM> at an angle of incidence of <NUM> degrees, or (ii) an angle shift of less than approximately <NUM> at an angle of incidence of <NUM> degrees.