Patent Description:
The invention is as defined in independent claim <NUM>. Optional features are defined in the dependent claims.

At least one of the three or more different materials may be an oxide material, the oxide material may include at least one of: niobium titanium oxide (NbTiOx), silicon dioxide (SiO<NUM>), aluminum oxide (Al<NUM>O<NUM>), titanium dioxide (TiO<NUM>), niobium pentoxide (Nb<NUM>O<NUM>), tantalum pentoxide (Ta<NUM>O<NUM>), zirconium oxide (ZrO<NUM>), yttrium oxide (Y<NUM>O<NUM>), hafnium dioxide (HfO<NUM>), or a combination thereof.

At least one of three or more different materials may include at least one of: a nitride material, a fluoride material, a sulfide material, a selenide material, or a combination thereof.

At least one of the first mirror or the second mirror may include a hydrogenated silicon (Si:H) material.

The spacer may be a hydrogenated silicon (Si:H) spacer.

At least one of the three or more different materials may be associated with a refractive index, at a spectral range of between approximately <NUM> and approximately <NUM>, greater than <NUM>.

At least one of the three or more different materials may be associated with a refractive index, at a spectral range of between approximately <NUM> and approximately <NUM>, less than <NUM>.

The optical filter may be associated with a <NUM>% relative bandwidth of between approximately <NUM> and approximately <NUM> at a center wavelength of <NUM>.

The optical filter may be deposited onto a substrate associated with a set of sensor elements of a sensor element array, the spacer of the optical filter may include a plurality of layers forming a plurality of channels corresponding to the set of sensor elements of the sensor element array.

The optical filter may be an array of optical filters corresponding to a set of sensor elements of a sensor element array.

A difference between a refractive index of a high index material of a quarterwave stack, of the plurality of quarterwave stacks, and a low index material of the quarterwave stack, of the plurality of quarterwave stacks, may be greater than a threshold.

A sensor element (e.g., an optical sensor) may be incorporated into an optical sensor device to obtain information (e.g., spectral data) regarding a set of electromagnetic frequencies. For example, the optical sensor device may include an image sensor, a multispectral sensor, or the like that may perform a sensor measurement of light. 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. The optical sensor device may include multiple sensor elements (e.g., an array of sensor elements) each configured to obtain information.

A sensor element may be associated with a filter that filters light to the sensor element. For example, the sensor element may be aligned with a linear variable filter (LVF), a circular variable filter (CVF), a Fabry-Perot filter, or the like to cause a portion of light directed toward the sensor element to be filtered. For a binary filter structure, such as a Fabry-Perot filter, hydrogenated silicon (Si:H) may be selected for layers of a spacer that is positioned between mirrors of a filter. The mirrors may be manufactured from metal layers (e.g., silver) or dielectric layers (e.g., quarterwave stacks of alternating high-index layers and low-index layers (HL pairs)). For example, a multispectral filter may include a first mirror, which includes a set of quarterwave stacks of alternating hydrogenated silicon layers and silicon dioxide layers, and a second mirror, which includes another set of quarterwave stacks of alternating hydrogenated silicon layers and silicon dioxide layers. The multispectral filter may result in a particular filter response. For example, the multispectral filter may be associated with a particular center wavelength of a spectral range passed toward the sensor, a particular bandwidth of the spectral range passed toward the sensor element, or the like. The filter response may be altered by altering a thickness of the spacer or by altering the quantity of quarterwave stacks between which the spacer is positioned.

However, altering the thickness of the spacer for a single cavity type of filter and/or altering a quantity of quarterwave stacks may result in a change to the filter response that exceeds a threshold. For example, an alteration from a set of two hydrogenated silicon and silicon dioxide quarterwave stacks to a set of three hydrogenated silicon and silicon dioxide quarterwave stacks may reduce a bandwidth of a filter from a first bandwidth that is greater than a first threshold to a second bandwidth that is less than a second threshold. Implementations, described herein, may utilize a mixed quarterwave stack configuration, an altered quarterwave stack layer thickness, or the like to permit altering a multispectral filter response. For example, implementations, described herein, may utilize three or more coating materials for quarterwave stacks of a multispectral filter. In this case, a filter response of a multispectral filter may be changed from, for example, an initial bandwidth that is greater than the first threshold to a target bandwidth that is between the first threshold and the second threshold. In this way, a greater granularity in tuning of multispectral filter performance is achieved.

<FIG> is a diagram of an overview of an example implementation <NUM> described herein. As shown in <FIG>, a multispectral filter <NUM> (e.g., a binary structure optical filter array) may include a first mirror <NUM>-<NUM>, a second mirror <NUM>-<NUM>, and a spacer <NUM>.

As further shown in <FIG>, first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM> may sandwich spacer <NUM>. In other words, spacer <NUM> may separate first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM> by a threshold distance, and/or faces of spacer <NUM> may be enclosed by first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM>. In some implementations, mirrors <NUM> may be associated with a particular material. For example, mirrors <NUM> may include a set of dielectric mirror layers (e.g., alternating hydrogenated silicon layers and silicon dioxide layers) or the like to reflect a portion of light directed from a light source toward sensor elements associated with multispectral filter <NUM>. Mirrors <NUM> may align with each sensor element of a sensor element array associated with each channel of multispectral filter <NUM>.

In some implementations, spacer <NUM> may include one or more spacer layers <NUM>. For example, spacer <NUM> may include a set of spacer layers <NUM>-<NUM> through <NUM>-<NUM> (e.g., dielectric layers, such as hydrogenated silicon layers). In some implementations, a thickness of one or more spacer layers <NUM> may be associated with ensuring a minimum spacer thickness for a particular wavelength. In some implementations, spacer <NUM> may be associated with a single cavity configuration. Additionally, or alternatively, spacer <NUM> may be associated with a multicavity configuration.

In some implementations, a thickness of one or more spacer layers <NUM> may be related based on a binary progression. For example, spacer layer <NUM>-<NUM> may be associated with a thickness of approximately half a thickness of spacer layer <NUM>-<NUM>, spacer layer <NUM>-<NUM> may be associated with a thickness of approximately half the thickness of spacer layer <NUM>-<NUM>, and spacer layer <NUM>-<NUM> may be associated with a thickness of approximately half the thickness of spacer layer <NUM>-<NUM>.

In some implementations, multispectral filter <NUM> may be deposited onto a substrate associated with an optical sensor device. For example, mirror <NUM>-<NUM> may be deposited (e.g., via a deposition process and/or a photolithographic lift-off process) onto a substrate that includes an array of sensor elements to capture information (e.g., spectral data). In some implementations, spacer <NUM> may permit capture of information relating to multiple wavelengths. For example, a first portion of spacer <NUM> aligned with a first sensor element (e.g., a back illuminated optical sensor or a front illuminated optical sensor of a sensor element array) may be associated with a first thickness and a second portion of spacer <NUM> aligned with a second sensor element may be associated with a second thickness. In this case, light, which is directed toward the first sensor element via a first channel corresponding the first portion and toward the second sensor element via a second channel corresponding to the second portion, may correspond to a first wavelength at the first sensor element based on the first thickness and a second wavelength at the second sensor element based on the second thickness. In this way, multispectral filter <NUM> permits multispectral sensing by an optical sensor device using a spacer (e.g., spacer <NUM>) associated with multiple portions, which are associated with multiple thicknesses, aligned to multiple sensor elements of the optical sensor device.

<FIG> are diagrams of characteristics relating to a multispectral filter not according to the claimed invention. <FIG> show an example of a multispectral filter with a first set of two quarterwave stacks and a second set of two quarterwave stacks sandwiching a spacer.

As shown in <FIG>, and by chart <NUM>, a filter <NUM> may include a substrate, a first set of two quarterwave stacks, a spacer, and a second set of two quarterwave stacks. The first set of quarterwave stacks include layers <NUM> through <NUM> of alternating hydrogenated silicon (shown as "Si_H" or sometimes termed Si:H) layers and silicon dioxide (shown as "SiO2") layers. The spacer may include layer <NUM> of hydrogenated silicon spacer. The second set of two quarterwave stacks include layers <NUM> through <NUM> of alternating hydrogenated silicon layers and silicon dioxide layers.

The hydrogenated silicon layers of the first quarterwave stack and the second quarterwave stack may each be associated with a refractive index of approximately <NUM> at a spectral range of approximately <NUM>, a physical thickness of approximately <NUM>, and a quarterwave optical thickness (shown as "Q. ") of approximately <NUM>. Quarterwave optical thickness of a layer corresponds to the physical thickness and refractive index of the layer. In some implementations, the high index layers of the quarterwave stacks (e.g., the hydrogenated silicon layers, which are associated with a higher index than the low-index layers of the quarterwave stack-the silicon dioxide layers) may be associated with a refractive index greater than a threshold value. For example, the high index layers may be associated with a refractive index, at a spectral range of approximately <NUM> to approximately <NUM>, that is greater than approximately <NUM>, approximately <NUM>, approximately <NUM>, approximately <NUM>, approximately <NUM>, approximately <NUM>, or the like. In some implementations, a difference between a refractive index of the high index material layers and a refractive index of the low index material layers may be greater than a threshold, such as greater than approximately <NUM>, greater than approximately <NUM>, greater than approximately <NUM>, or the like.

The silicon dioxide layers of the first set of two quarterwave stacks and the second set of two quarterwave stacks may each be associated with a refractive index of approximately <NUM> at a spectral range of approximately <NUM>, a physical thickness of approximately <NUM>, and a quarterwave optical thickness of approximately <NUM>. In some implementations, the low index layers of the quarterwave stacks (e.g., the silicon dioxide layers) may be associated with a refractive index less than a threshold value at a spectral range of approximately <NUM> to approximately <NUM>, such as a refractive index less than the refractive index of the high index layers, less than approximately <NUM>, less than approximately <NUM>, less than approximately <NUM>, less than approximately <NUM>, less than approximately <NUM>, or the like.

The hydrogenated silicon spacer layer is associated with a refractive index of approximately <NUM>, a physical thickness of approximately <NUM>, and a quarterwave optical thickness of approximately <NUM>. Although described herein as a hydrogenated silicon spacer layer, the hydrogenated silicon spacer layer may include multiple spacer layers of hydrogenated silicon of multiple thicknesses selected to form multiple channels. For example, in a first case, the hydrogenated silicon spacer layer may be formed using multiple layers to form <NUM> channels. Similarly, in a second case, the hydrogenated silicon spacer layer may be formed using multiple layers to form <NUM> channels. Additionally, or alternatively, a spacer layer may be utilized to form another threshold quantity of channels, such as <NUM> channels, <NUM> channels, <NUM> channels, <NUM> channels, or the like. In some implementations, the spacer layer may be associated with a refractive index greater than a threshold at a spectral range of approximately <NUM> to approximately <NUM>, such as a refractive index greater than approximately <NUM>, approximately <NUM>, approximately <NUM>, approximately <NUM>, approximately <NUM>, approximately <NUM>, or the like.

As shown in <FIG>, chart <NUM> represents a refractive index profile of filter <NUM>. As shown, filter <NUM> includes a substrate, a first mirror <NUM>-<NUM> deposited on the substrate, a second mirror <NUM>-<NUM>, and a hydrogenated silicon spacer <NUM> disposed between first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM>. First mirror <NUM>-<NUM> includes a first quarterwave stack <NUM>-<NUM> and a second quarterwave stack <NUM>-<NUM>. Similarly, second mirror <NUM>-<NUM> includes a third quarterwave stack <NUM>-<NUM> and a fourth quarterwave stack <NUM>-<NUM>. Each quarterwave stack <NUM>-<NUM> through <NUM>-<NUM> includes a hydrogenated silicon layer and a silicon dioxide layer forming a high-index layer/low-index layer (HL) pair.

As shown in <FIG>, and by chart <NUM>; and in <FIG>, and by chart <NUM>, a filter response for filter <NUM> is provided. For example, filter <NUM> is associated with a transmissivity (shown as "T[%]") of greater than approximately <NUM>% at a wavelength (shown as "λ[nm]") of approximately <NUM>. As shown in <FIG>, and by reference number <NUM>, filter <NUM> is associated with a relative <NUM>% bandwidth (e.g., a bandwidth for transmissivity greater than <NUM>% surrounding a center wavelength representing a peak transmissivity) of approximately <NUM> in a spectral range from approximately <NUM> to approximately <NUM>.

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

<FIG> are diagrams of characteristics relating to a multispectral filter not according to the claimed invention. <FIG> show an example of a multispectral filter with a first set of three quarterwave stacks and a second set of three quarterwave stacks sandwiching a spacer.

As shown in <FIG>, chart <NUM> represents a refractive index profile of a filter <NUM>. As shown, filter <NUM> includes a substrate, a first mirror <NUM>-<NUM> deposited on the substrate, a second mirror <NUM>-<NUM>, and a hydrogenated silicon spacer <NUM> disposed between first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM>. First mirror <NUM>-<NUM> includes a set of three quarterwave stacks <NUM>-<NUM> through <NUM>-<NUM>. Second mirror <NUM>-<NUM> includes a set of three quarterwave stacks <NUM>-<NUM> through <NUM>-<NUM>. Each quarterwave stack <NUM> includes a hydrogenated silicon layer and a silicon dioxide layer forming an HL pair.

As shown in <FIG>, and by chart <NUM>; in <FIG>, and by chart <NUM>; and in <FIG>, and by chart <NUM>, the filter response for filter <NUM> and a filter response for filter <NUM> are provided. For example, as shown in <FIG>, and by reference number <NUM> and <NUM>', based on filter <NUM> including an additional hydrogenated silicon and silicon dioxide quarterwave stack for each mirror of filter <NUM> relative to filter <NUM>, filter <NUM> is associated with a reduced peak transmissivity and a reduced relative <NUM>% bandwidth. In this case, as shown in <FIG> and by reference number <NUM>, filter <NUM> is associated with a transmissivity of approximately <NUM>% at approximately <NUM> and a <NUM>% relative bandwidth of <NUM>. In contrast, as shown in <FIG>, and by reference number <NUM>', filter <NUM> is associated with a peak transmissivity of approximately <NUM>% at approximately <NUM>, and is associated with a <NUM>% relative bandwidth of approximately <NUM>. As shown in <FIG>, and by reference numbers <NUM> and <NUM>', filter <NUM> is associated with a reduced out of band transmission relative to filter <NUM>, and a minimum transmissivity is reduced from approximately <NUM>% to approximately <NUM>% for filter <NUM> relative to filter <NUM>. In some implementations, transmissivity for filter <NUM> may be further improved by matching a configuration of filter <NUM> to a substrate and another medium (e.g., air).

In these cases, changing a quantity of quarterwave stacks in mirrors of a multispectral filter (e.g., from two quarterwave stacks in each mirror to three quarterwave stacks in each mirror) causes a change to optical characteristics of the multispectral filter, thereby enabling tuning the multispectral filter for a particular spectral range, a particular transmissivity, or the like. However, the change in optical characteristics may be greater than a threshold change. For example, a multispectral filter may be desired that is associated with a <NUM>% relative bandwidth that is between approximately <NUM> and approximately <NUM>.

<FIG> are diagrams of characteristics relating to a multispectral filter not according to the claimed invention. <FIG> show an example of a multispectral filter with an additional low index layer (e.g., a silicon dioxide layer) disposed contiguous to each of a first set of three quarterwave stacks and a second set of three quarterwave stacks, and a spacer disposed between the first set of three quarter wave stacks, the second set of three quarterwave stacks, and the additional low index layers.

As shown in <FIG>, chart <NUM> represents a refractive index profile of a filter <NUM>. As shown, filter <NUM> includes a substrate, a first mirror <NUM>-<NUM> deposited on the substrate, a second mirror <NUM>-<NUM>, and a spacer <NUM> disposed between first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM>. First mirror <NUM>-<NUM> includes a set of quarterwave stacks <NUM>-<NUM> through <NUM>-<NUM> and an unpaired silicon dioxide layer <NUM>-<NUM> (e.g., a low index silicon dioxide layer not paired with a high index hydrogenated silicon layer or another high index layer). Similarly, second mirror <NUM>-<NUM> includes a set of quarterwave stacks <NUM>-<NUM> through <NUM>-<NUM> and an unpaired silicon dioxide layer <NUM>-<NUM>. Each quarterwave stack <NUM> is disposed between unpaired silicon dioxide layers <NUM>-<NUM> and <NUM>-<NUM>, and includes a hydrogenated silicon layer and a silicon dioxide layer forming an HL pair. Although silicon dioxide layers <NUM> are not paired with corresponding high index layers (e.g., hydrogenated silicon layers), each silicon dioxide layer <NUM> may be termed a quarterwave stack for a respective mirror <NUM>. In some implementations, filter <NUM> may be an array of optical filters aligned to a set of sensor elements of a sensor element array.

As shown in <FIG>, and by chart <NUM>; and in <FIG>, and by chart <NUM>, a set of filter responses for filter <NUM>, filter <NUM>, and filter <NUM> is provided. For example, as shown in <FIG>, and by reference number <NUM>, <NUM>', and <NUM>", based on filter <NUM> including a set of unpaired silicon dioxide layers for each mirror of filter <NUM>, filter <NUM> is associated with a peak transmissivity at approximately <NUM> that is between that of filter <NUM> and filter <NUM>, and a <NUM>% relative bandwidth that is between that of filter <NUM> and filter <NUM>. In this case, as shown in <FIG> and by reference number <NUM>, filter <NUM> is associated with a peak transmissivity of greater than <NUM>% at approximately <NUM> and is associated with a <NUM>% relative bandwidth of approximately <NUM>. As shown in <FIG> and by reference number <NUM>', filter <NUM> is associated with a peak transmissivity of approximately <NUM>% at approximately <NUM> and a <NUM>% relative bandwidth of approximately <NUM>. In contrast, as shown in <FIG>, and by reference number <NUM>", filter <NUM> is associated with a peak transmissivity of approximately <NUM>% at approximately <NUM> and a <NUM>% relative bandwidth of approximately <NUM>.

In this case, adding the unpaired set of silicon dioxide layers causes a change to optical characteristics of a multispectral filter, thereby enabling tuning the multispectral filter for a particular spectral range, a particular transmissivity, a particular bandwidth, or the like with a greater granularity than altering a quantity of quarterwave stacks.

<FIG> are diagrams of characteristics relating to a multispectral filter according to the claimed invention. <FIG> show an example of a multispectral filter with mixed sets of quarterwave stacks, and a spacer disposed between the mixed sets of quarterwave stacks.

As shown in <FIG>, chart <NUM> represents a refractive index profile of a filter <NUM>. As shown, filter <NUM> includes a substrate, a first mirror <NUM>-<NUM> deposited on the substrate, a second mirror <NUM>-<NUM>, and a spacer <NUM> disposed between first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM>. First mirror <NUM>-<NUM> includes a set of quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM>, a quarterwave stack <NUM>-<NUM>, and an unpaired silicon dioxide layer <NUM>-<NUM>. Similarly, second mirror <NUM>-<NUM> includes a set of quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM>, a quarterwave stack <NUM>-<NUM>, and an unpaired silicon dioxide layer <NUM>-<NUM>. Each quarterwave stack <NUM> includes hydrogenated silicon and silicon dioxide forming an HL pair. Each quarterwave stack <NUM> includes niobium titanium oxide (NbTiOx) forming an HL pair. In this case, filter <NUM> utilizes mixed sets of quarterwave stacks, with each mirror <NUM> including different types of HL pairs. Utilization of the mixed sets of quarterwave stacks permits characteristics of filter <NUM> to be controlled with a greater granularity than another technique that utilizes increased or decreased quantities of quarterwave stacks to control characteristics. Although described herein in terms of niobium titanium oxide, silicon dioxide, and hydrogenated silicon for quarterwave stacks of filter <NUM>, another group of three or more materials may be used for a set of mixed quarterwave stacks, such as utilizing as an oxide material, such as silicon dioxide (SiO<NUM>), niobium pentoxide (Nb<NUM>O<NUM>), tantalum pentoxide (Ta<NUM>O<NUM>), titanium dioxide (TiO<NUM>), aluminum oxide (Al<NUM>O<NUM>), zirconium oxide (ZrO<NUM>), yttrium oxide (Y<NUM>O<NUM>), hafnium dioxide (HfO<NUM>), or the like; a nitride material, such as silicon nitride (Si3N4); a fluoride material, such as magnesium fluoride (MgF); a sulfide material, such as zinc sulfide (ZnS); a selenide material, such as zinc selenide (ZnSe); a combination thereof; or the like.

As shown in <FIG>, and by chart <NUM>; and in <FIG>, and by chart <NUM>, the filter response for filter <NUM>, the filter response for filter <NUM>, and a filter response for filter <NUM> are provided. For example, as shown in <FIG>, and by reference numbers <NUM>, <NUM>', and <NUM>", based on filter <NUM> including the set of unpaired silicon dioxide layers <NUM> and utilizing the mixed set of quarterwave stacks, filter <NUM> is associated with a peak transmissivity at approximately <NUM> and a <NUM>% relative bandwidth that is between that of filter <NUM> and filter <NUM>. In this case, as shown in <FIG> and by reference number <NUM>, filter <NUM> is associated with a peak transmissivity of greater than <NUM>% at approximately <NUM> and a <NUM>% relative bandwidth of approximately <NUM>, and as shown in <FIG> and by reference number <NUM>', filter <NUM> is associated with a peak transmissivity of approximately <NUM>% at approximately <NUM> and a <NUM>% relative bandwidth of approximately <NUM>. In contrast, as shown in <FIG>, and by reference number <NUM>", filter <NUM> is associated with a peak transmissivity of approximately <NUM>% at approximately <NUM> and a <NUM>% relative bandwidth of approximately <NUM>.

In this case, utilizing the set of mixed quarterwave stacks causes a change to optical characteristics of the multispectral filter, thereby enabling tuning the multispectral filter for a particular spectral range, a particular transmissivity, or the like with a greater granularity than altering a quantity of quarterwave stacks.

<FIG> are diagrams of characteristics relating to a multispectral filter not according to the claimed invention. <FIG> show an example of a multispectral filter with detuned sets of quarterwave stacks, and a spacer disposed between the detuned sets of quarterwave stacks.

As shown in <FIG>, chart <NUM> represents a comparison of a refractive index profile of filter <NUM> and a refractive index profile of a filter <NUM>. As shown, filter <NUM> includes a substrate, a first mirror <NUM>-<NUM> deposited on the substrate, a second mirror <NUM>-<NUM>, and a hydrogenated silicon spacer <NUM> disposed between first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM>. First mirror <NUM>-<NUM> includes a set of quarterwave stacks <NUM>-<NUM> through <NUM>-<NUM> and an unpaired silicon dioxide layer <NUM>-<NUM>. Similarly, second mirror <NUM>-<NUM> includes a set of quarterwave stacks <NUM>-<NUM> through <NUM>-<NUM> and an unpaired silicon dioxide layer <NUM>-<NUM>. Each quarterwave stack <NUM> includes a hydrogenated silicon layer and a silicon dioxide layer forming an HL pair. In some implementations, another set of materials may be used for quarterwave stacks <NUM>. In some implementations, quarterwave stacks <NUM> may be a mixed set of quarterwave stacks using three or more materials.

As further shown in <FIG>, and by reference number <NUM>, filter <NUM> (e.g., of mirrors <NUM>) includes silicon dioxide layers that are associated with a threshold reduction in thickness relative to silicon dioxide layers of filter <NUM> (e.g., of mirrors <NUM>). As shown by reference number <NUM>, filter <NUM> includes hydrogenated silicon layers associated with a threshold increase in thickness relative to hydrogenated silicon layers of filter <NUM>. In some implementations, the threshold increase or reduction may be a selected to detune the quarterwave stacks from a quarterwave thickness (e.g., a thickness associated with a center wavelength of light that is to be incident on the quarterwave stacks), thereby centering filter <NUM> at a selected center wavelength for a peak transmissivity and/or altering a <NUM>% relative bandwidth for filter <NUM>, such as by utilizing an approximately <NUM>% increase or an approximately <NUM>% reduction in thickness. Additionally, or alternatively, an increase or reduction in thickness between approximately <NUM>% and <NUM>%, between approximately <NUM>% and <NUM>%, between approximately <NUM>% and <NUM>%, or the like may be selected for filter <NUM>.

As shown in <FIG>, and by chart <NUM>; and in <FIG>, and by chart <NUM>, a set of filter responses for filter <NUM>, filter <NUM>, and filter <NUM> is provided. For example, as shown in <FIG>, and by reference numbers <NUM>, <NUM>', and <NUM>", based on filter <NUM> including a set of detuned quarterwave stacks (e.g., quarterwave stacks using altered layer thicknesses), filter <NUM> is associated with a peak transmissivity at approximately <NUM> and a <NUM>% relative bandwidth that is between that of filter <NUM> and filter <NUM>. In this case, as shown in <FIG> and by reference number <NUM>, filter <NUM> is associated with a peak transmissivity of greater than <NUM>% at approximately <NUM> and a <NUM>% relative bandwidth of approximately <NUM>, and as shown in <FIG> and by reference number <NUM>', filter <NUM> is associated with a peak transmissivity of approximately <NUM>% at approximately <NUM> and a <NUM>% relative bandwidth of approximately <NUM>. In contrast, as shown in <FIG>, and by reference number <NUM>", filter <NUM> is associated with a peak transmissivity of approximately <NUM>% at approximately <NUM> and a <NUM>% relative bandwidth of approximately <NUM>.

In this case, utilizing the set of detuned quarterwave stacks causes a change to optical characteristics of the multispectral filter, thereby enabling tuning the multispectral filter for a particular spectral range, a particular transmissivity, or the like with a greater granularity than altering a quantity of quarterwave stacks. For example, detuning a thickness of quarterwave stacks permits configuration of an optical filter with a selected bandwidth, such as a bandwidth between bandwidths associated with different quantities of quarterwave stacks, a bandwidth overlapping with bandwidths associated with different quantities of quarterwave stacks, or the like.

<FIG> are diagrams of characteristics relating to a set of multispectral filters. <FIG> show examples of multispectral filters with mixed sets of quarterwave stacks.

As shown in <FIG>, chart <NUM> represents a refractive index profile of filter <NUM> not according to the claimed invention. As shown, filter <NUM> includes a substrate, a first mirror <NUM>-<NUM> deposited on the substrate, a second mirror <NUM>-<NUM>, and a hydrogenated silicon spacer <NUM> disposed between first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM>. First mirror <NUM>-<NUM> includes a set of quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> of hydrogenated silicon and silicon dioxide as HL pairs and a quarterwave stack <NUM>-<NUM> of niobium titanium oxide and silicon dioxide as an HL pair. Second mirror <NUM>-<NUM> includes a set of quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> of hydrogenated silicon and silicon dioxide as HL pairs and a quarterwave stack <NUM>-<NUM> of niobium titanium oxide and silicon dioxide as an HL pair. In this case, quarterwave stack <NUM>-<NUM> is disposed between quarterwave stack <NUM>-<NUM> and hydrogenated silicon spacer <NUM>, and quarterwave stack <NUM>-<NUM> is disposed between quarterwave stack <NUM>-<NUM> and hydrogenated silicon spacer <NUM>.

As shown in <FIG>, chart <NUM> represents a refractive index profile of filter <NUM> according to the claimed invention. As shown, filter <NUM> includes a substrate, a first mirror <NUM>-<NUM> deposited onto the substrate, a second mirror <NUM>-<NUM>, and a hydrogenated silicon spacer <NUM> disposed between first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM>. First mirror <NUM>-<NUM> includes a set of quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> of hydrogenated silicon and silicon dioxide as HL pairs, a quarterwave stack <NUM>-<NUM> of niobium titanium oxide and silicon dioxide as an HL pair, and an unpaired silicon dioxide layer <NUM>-<NUM>. Similarly, second mirror <NUM>-<NUM> includes a set of quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> of hydrogenated silicon and silicon dioxide as HL pairs, a quarterwave stack <NUM>-<NUM> of niobium titanium oxide and silicon dioxide as an HL pair, and an unpaired silicon dioxide layer <NUM>-<NUM>. In this case, quarterwave stack <NUM>-<NUM> is disposed between quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM>, and quarterwave stack <NUM>-<NUM> is disposed between quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM>.

As shown in <FIG>, chart <NUM> represents a refractive index profile of filter <NUM> according to the claimed invention. As shown, filter <NUM> includes a substrate, a first mirror <NUM>-<NUM> deposited on the substrate, a second mirror <NUM>-<NUM>, and a hydrogenated silicon spacer <NUM> disposed between first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM>. First mirror <NUM>-<NUM> includes a quarterwave stack <NUM>-<NUM> of hydrogenated silicon and tantalum pentoxide (Ta<NUM>O<NUM>) as an HL pair, a set of two quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> of hydrogenated silicon and silicon dioxide as HL pairs, and an unpaired tantalum pentoxide layer <NUM>-<NUM>. Similarly, second mirror <NUM>-<NUM> includes a quarterwave stack <NUM>-<NUM> of hydrogenated silicon and tantalum pentoxide as an HL pair, a set of two quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> of hydrogenated silicon and silicon dioxide as HL pairs, and an unpaired tantalum pentoxide layer <NUM>-<NUM>. In this case, quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> are disposed between quarterwave stack <NUM>-<NUM> and hydrogenated silicon spacer <NUM>, and quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> are disposed between quarterwave stack <NUM>-<NUM> and hydrogenated silicon spacer <NUM>.

As shown in <FIG>, chart <NUM> represents a refractive index profile of filter <NUM> according to the claimed invention. As shown, filter <NUM> includes a substrate, a first mirror <NUM>-<NUM> deposited on the substrate, a second mirror <NUM>-<NUM>, and a hydrogenated silicon spacer <NUM> disposed between first mirror <NUM>-<NUM> and second mirror <NUM>-<NUM>. First mirror <NUM>-<NUM> includes a set of two quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> of hydrogenated silicon and niobium titanium oxide as HL pairs, a set of two quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> of hydrogenated silicon and silicon dioxide as HL pairs, and an unpaired niobium titanium oxide layer <NUM>-<NUM>. Similarly, second mirror <NUM>-<NUM> includes a set of two quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> of hydrogenated silicon and niobium titanium oxide as HL pairs, a set of two quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> of hydrogenated silicon and silicon dioxide as HL pairs, and an unpaired tantalum pentoxide layer <NUM>-<NUM>. In this case, quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> are disposed between quarterwave stack <NUM>-<NUM> and hydrogenated silicon spacer <NUM>, and quarterwave stacks <NUM>-<NUM> and <NUM>-<NUM> are disposed between quarterwave stack <NUM>-<NUM> and hydrogenated silicon spacer <NUM>.

<FIG> and <FIG> are diagrams of characteristics relating to a set of multispectral filters. <FIG> and <FIG> show examples of <NUM>% relative bandwidths for filters described herein.

As shown in <FIG>, and by table <NUM>, a set of <NUM>% relative bandwidths for filters described herein is provided for a center wavelength of approximately <NUM>. As shown, filter <NUM> is associated with a <NUM>% relative bandwidth of approximately <NUM>. Adding an additional quarterwave stack to form filter <NUM> results in a <NUM>% relative bandwidth of approximately <NUM>. As described herein, multiple techniques may be utilized to tune a multispectral filter with a greater degree of granularity (e.g., to tune a multispectral filter to a <NUM>% relative bandwidth that is between approximately <NUM> and approximately <NUM> or another range of <NUM>% relative bandwidths associated with another set of multispectral filters). For example, filter <NUM> results in a <NUM>% relative bandwidth of approximately <NUM>, filter <NUM> results in a relative bandwidth of approximately <NUM>, filter <NUM> results in a <NUM>% relative bandwidth of <NUM>, filter <NUM> results in a <NUM>% relative bandwidth of approximately <NUM>, filter <NUM> results in a <NUM>% relative bandwidth of approximately <NUM>, filter <NUM> results in a <NUM>% relative bandwidth of approximately <NUM>, and filter <NUM> results in a <NUM>% relative bandwidth of approximately <NUM>. In this way, a multispectral filter may utilize three or more different materials for quarterwave stack mirrors, detuned quarterwave stack thicknesses, unpaired quarterwave stack layers, or the like to achieve a particular spectral range, transmissivity, or the like.

As shown in <FIG>, and by chart <NUM>, a set of <NUM>% relative bandwidths for filters described herein is provided at a set of center wavelengths. For example, based on tuning a multispectral filter described herein to a particular center wavelength (e.g., by altering a spacer thickness for the multispectral filter), a <NUM>% relative bandwidth may be determined. As shown, for a spectral range of center wavelengths of between approximately <NUM> and approximately <NUM>, each of filters <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> is associated with a <NUM>% relative bandwidth between that of filters <NUM> and <NUM>. For example, at a center wavelength of approximately <NUM>, filters <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are associated with a <NUM>% relative bandwidth of between approximately <NUM> and approximately <NUM>. Similarly, at a center wavelength of approximately <NUM>, filters <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are associated with a <NUM>% relative bandwidth of between approximately <NUM> and approximately <NUM>.

As indicated above, <FIG> and <FIG> are provided merely as examples. Other examples are possible and may differ from what was described with regard to <FIG> and <FIG>.

Although some implementations, described herein, are described in terms of a granularity of tuning of spectral range relative to another optical filter with two quarterwave stacks or three quarterwave stacks, some implementations described herein may provide greater granularity of tuning relative to other quantities of quarterwave stacks. For example, utilizing a third coating material, fourth coating material, or the like or detuning a thickness of quarterwave stacks may permit improve granularity of tuning of an optical filter for a particular spectral range, transmissivity, or the like relative to an addition or subtraction of one quarterwave stack, an addition or subtraction of two quarterwave stacks, an addition or subtraction of three quarterwave stacks, an addition or subtraction of four quarterwave stacks, or the like.

In this way, utilization of a mixed set of quarterwave stacks or a detuned set of quarterwave stacks results in a greater granularity for controlling a transmissivity, bandwidth, or the like relative to another technique involving utilizing additional quantities of quarterwave stacks. Based on improving a granularity of control of multispectral filters, sensing is improved for sensor elements attached to the multispectral filters.

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 claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of possible implementations. Although each dependent claim listed below may directly depend on only one claim, the disclosure of possible implementations includes each dependent claim in combination with every other claim in the claim set.

Claim 1:
An optical filter, comprising:
a first mirror (<NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>), and
a second mirror (<NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>),
each of the first mirror and the second mirror including three or more quarterwave stacks,
a first quarterwave stack, of the three or more quarterwave stacks, including a set of alternating paired layers (<NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) of a first material and a second material,
the first material having a higher refractive index than the second material,
a second quarterwave stack, of the three or more quarterwave stacks, including a set of alternating paired layers (<NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) of a third material and a fourth material,
the third material having a higher refractive index than the fourth material,
the first material, the second material, the third material, and the fourth material comprising three or more different materials;
a spacer (<NUM>, <NUM>, <NUM>, <NUM>) disposed between the first mirror and the second mirror; and
the first and second mirrors including an unpaired lower refractive index layer (<NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>),
wherein the unpaired lower refractive index layer is not paired with a higher refractive index layer, and wherein each and every quarterwave stack is disposed between the unpaired lower refractive index layers.