Zero angle shift bandpass filter

Abstract

When the angle of incidence (AOI) of the light directed to the optical filter changes from a set angle of incidence (e.g., 0 °, 45 °, 90 °) to a threshold angle of incidence (e.g., the deviation from the set angle of incidence is greater than about 30 °), the filter performance of the optical filter may degrade. In this case, the band edge may shift to a different wavelength, such as a blue shift to a shorter wavelength.SOLUTION: In some embodiments, the optical filter assembly 120 includes an optical filter 140 disposed on a first side of the substrate 130, the optical filter 140 having a thickness greater than a first threshold, and the optical filter 140 configured to have a central wavelength shift less than a second threshold at an angle of incidence range of 0 ° to at least a third threshold at a particular center operating wavelength.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] [Cross-reference to related art] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 672,084, entitled "ZERO ANGLE SHIFT BANDPASS FILTER," filed July 16, 2024. The disclosure of this prior application is considered a part of this patent application and is incorporated by reference into this patent application. [Background technology]

[0002] Optical filters are used to select spectral bands or components of incident light. For example, a high-pass filter selects light with wavelengths longer than the edge wavelength of the filter. Conversely, a low-pass filter selects light with wavelengths shorter than the edge wavelength. A band-pass filter is a different type of filter that selects light with wavelengths within the filter's bandwidth that are close to the filter's center wavelength. A tunable band-pass filter is an optical filter whose center wavelength can be adjusted or tuned. Summary of the Invention [Problem to be solved by the invention]

[0003] When the angle of incidence (AOI) of light directed at an optical filter changes from a set angle of incidence (e.g., 0°, 45°, 90°) to a threshold angle of incidence (e.g., deviation from the set angle of incidence greater than about 30°), the filtering performance of the optical filter can degrade, potentially causing the band edge to shift to a different wavelength, such as a blue shift to shorter wavelengths. [Means for solving the problem]

[0004] In some embodiments, the optical filter assembly includes an optical filter disposed on a first side of a substrate, the optical filter having a thickness greater than a first threshold, and the optical filter configured to have a center wavelength shift at a particular operating center wavelength that is less than a second threshold over a range of incident angles from 0° to at least a third threshold.

[0005] In some embodiments, the optical filter includes a filter stack of alternating layers of a first material having a first refractive index and a second material having a second refractive index, the filter stack having a transmittance of at least a first threshold level at a set center wavelength, and the filter stack configured to introduce a red-shift less than a second threshold at angles of incidence between 0° and 30°.

[0006] In some embodiments, the optical system includes an electro-optical component and an optical filter disposed on a first side of a substrate, the optical filter having a thickness greater than a first threshold, and the optical filter configured to have, at a particular operating center wavelength, a center wavelength shift less than a second threshold over a range of incident angles from 0° to at least a third threshold. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram of an embodiment described herein. [Figure 2] FIG. 1 is a diagram of an exemplary optical filter assembly. [Figure 3A] FIG. 1 is a characteristic diagram of an exemplary optical filter. [Figure 3B] FIG. 1 is a characteristic diagram of an exemplary optical filter. [Figure 3C] FIG. 1 is a characteristic diagram of an exemplary optical filter. [Figure 4A] FIG. 1 is a characteristic diagram of an exemplary optical filter. [Figure 4B] FIG. 1 is a characteristic diagram of an exemplary optical filter. [Figure 4C] FIG. 1 is a characteristic diagram of an exemplary optical filter. [Figure 4D] FIG. 1 is a characteristic diagram of an exemplary optical filter. DETAILED DESCRIPTION OF THE INVENTION

[0008] The following detailed description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings may refer to the same or similar elements. The following description uses a spectrometer as an example. However, the techniques, principles, procedures, and methods described herein can be used with any sensor, including but not limited to other optical and spectroscopic sensors.

[0009] An optical sensor device may include a sensor element array of sensor elements that receive light emitted from a light source, such as, for example, a light transmitter, a light bulb, an ambient light source, among others. For example, in a spectrometer, the optical sensor device may include an array of sensor elements for receiving light reflected from an object, thereby enabling identification of the object. The sensor elements may be associated with optical filters that filter the light to the sensor elements, allowing the sensor elements to obtain information about specific ranges of the electromagnetic frequency spectrum. For example, the sensor elements may be aligned with optical filters having passbands in the near-infrared (NIR) spectral range, the visible spectral range, the ultraviolet spectral range, and / or similar ranges.

[0010] In other words, an optical system may include an optical filter, such as a bandpass filter, to filter light of wavelengths other than the wavelength of interest. This light causes noise at wavelengths other than the wavelength of interest, degrading the performance of the optical system by, for example, obscuring weak signals and reducing the signal-to-noise ratio of the optical system, thereby making accurate detection and measurement difficult. An optical system may include a bandpass filter that has a passband for the wavelength of interest and blocks light of other wavelengths. However, an angular shift can cause a change in the wavelength of light incident on the bandpass filter. For example, if the angle of incidence of light incident on the optical filter is large, the optical filter can cause an angular shift, which is a shift in the center wavelength of the light that passes through. Thus, light of a first wavelength directed at the optical filter at an angle greater than a threshold angle can be shifted to a second wavelength by the optical filter. This angular shift can cause light to be measured by the optical system, such as light emitted from an emitter toward a target for spectroscopic analysis, to fall outside the passband of the bandpass filter and be blocked by the bandpass filter, thereby making it impossible to measure the target.

[0011] Conversely, the angular shift can cause unintended light to shift to the wavelength of interest, fall within the passband of the bandpass filter, and pass through the bandpass filter, causing excessive noise in the measurement of the target. For example, stray light from an unintended light source (e.g., the sun or a light bulb in a room) can be angularly shifted into the passband of the bandpass filter and pass through the bandpass filter along with light from an intended light source (e.g., a light emitter). If both stray light and intended light are directed at a sensor element, the sensor element may produce an erroneous reading of the intended light.

[0012] Furthermore, in some applications, it may be desirable to generate accurate measurements of light incident on an optical element at relatively large angles of incidence. In such scenarios, the optical sensor device may generate inaccurate measurements of the light as a result of the relatively large angles of incidence because the central wavelength of the light changes with the angular shift. Therefore, it may be desirable for the optical filter to minimize or eliminate the angular shift in the central wavelength that occurs as the angle of incidence of light incident on the optical filter increases. For example, it may be desirable to ensure that light of interest is not angularly shifted outside the passband of the bandpass filter and / or that light not of interest is not angularly shifted within the passband of the bandpass filter. Additionally, when measurements are performed with light at relatively large angles of incidence, it may be desirable that the light is not affected by the angular shift as a result of the relatively large angles of incidence.

[0013] Some embodiments described herein provide an optical filter assembly, optical device, optical element, optical module, or optical system with reduced angular shift. For example, the optical filter may have a layer structure that achieves a center wavelength shift of less than 0.1% of the center wavelength of the bandpass of the optical filter. Thus, as a specific example, for a 940 nanometer (nm) bandpass filter, the optical filter layer structure may achieve an angular shift of less than 4 nm, less than 1 nm, or less than 0.25 nm, among others. In some embodiments, the optical filter may include a zero angle shift (ZAS) filter that achieves an angular shift of ±0.1% of the center wavelength of the bandpass. In some embodiments, the optical filter may impart a residual angular shift to the beam that is a red shift rather than a blue shift, as occurs with other low angle shift (LAS) filters, such as ultra-low angle shift (HLAS) filters. In this way, the optical filter can transmit light without angular shifting the light, even at relatively large angles of incidence. When the optical filter is a bandpass filter having a set passband, the optical filter can reflect or block light of wavelengths outside the set passband without angularly shifting the light outside the set passband to shift into (and pass through) the set passband, thereby avoiding excessive noise or crosstalk in the optical sensor or sensor element array. Furthermore, the optical filter can reflect or block light of wavelengths outside the passband without angularly shifting the light within the set passband to shift out of (and be blocked from) the set passband, thereby avoiding measurement errors. Additionally, when the optical filter is included in an optical system that measures light at an oblique angle (e.g., greater than a threshold angle of incidence), the optical filter avoids measurement errors associated with angular shifts of light at oblique angles.

[0014] The improved ambient light rejection and passband stability provided by zero-angle-shift filters, as described herein, allows optical systems incorporating zero-angle-shift filters to operate at lower emitter powers because less ambient light reaches the detector, enabling a high signal-to-noise ratio to be achieved using lower signal strengths. This can extend battery life in portable devices such as smartphones and can increase the detection range in applications such as light detection and ranging (LIDAR), allowing, for example, automotive LIDAR systems to detect objects at greater distances without increasing power. Thus, zero-angle-shift filters enable energy-efficient, high-performance optical systems.

[0015] FIG. 1 is a diagram of an embodiment 100 described herein. As shown in FIG. 1, embodiment 100 includes an optical system 110. Optical system 110 may be part of an optical system and may provide an electrical output corresponding to a sensor determination. For example, optical system 110 may be part of a LIDAR system, a three-dimensional sensing system, a spectroscopy system, a gesture recognition system, a facial recognition system, an object recognition system, an imaging system, an iris recognition system, a motion tracking system, or a communication system, among others.

[0016] In some embodiments, the optical system 110 can include an optical filter assembly 120, which can include a substrate 130 and an optical filter 140. In some embodiments, the optical filter assembly 120 can include a bandpass filter. For example, the optical filter assembly 120 can include one or more layers forming a bandpass interference filter configured to pass a first portion of light in a first range of wavelengths and block a second portion of light in a second range of wavelengths. Additionally or alternatively, the optical filter assembly 120 can include a long wavelength passband (LWP) filter, a short wavelength passband (SWP) filter, a wide wavelength passband (BWP) filter, an infrared cut (IR Cut) filter, a notch filter, and / or the like. In some embodiments, the optical filter assembly 120 can have a bandpass of 200 nm to 14,000 nm and can be used in the visible, NIR, mid-wave infrared (MWIR), long-wave infrared (LWIR), or ultraviolet spectral ranges, among others, by way of example.

[0017] In some implementations, optical filter 140 may include a zero-angle-shift filter. For example, optical filter 140 may include one or more layers forming an angle-sensitive filter configured to pass light without the light being angularly shifted (e.g., with a minimum amount of angular shift, such as an angular shift less than a threshold, as described herein). In this case, by minimizing or eliminating the angular shift of light, even at relatively large angles of incidence, optical filter assembly 120 can ensure that stray light entering the cavity of optical system 110 is not shifted to the wavelength of interest of optical system 110 (or does not fall within the passband of optical filter 140). In other words, if optical system 110 is configured to measure the properties of light at a wavelength of, for example, 980 nm, zero-angle-shift optical filter 140 ensures that 980 nm emitted light having a threshold angle of incidence (e.g., greater than 30° or less than −30°) is not shifted from 980 nm to prevent optical system 110 from being unable to measure the emitted light. Conversely, optical system 110 prevents stray light having a wavelength of, for example, 1000 nm and a threshold angle of incidence from shifting to 980 nm and resulting in erroneous measurements. Thus, by reducing the angular shift, optical system 110 may measure light with, among other things, increased measurement accuracy, reduced noise, or reduced crosstalk. Furthermore, if optical system 110 is configured with multiple bands of light, zero-angle-shift optical filter 140 may prevent a first radiation beam, for example, at 985 nm, from being shifted to a second radiation beam, for example, at 980 nm, thereby preventing the first beam from interfering with the measurement of the second beam. Thus, by reducing the possibility of crosstalk caused by the angular shift, optical system 110 and optical filter 140 may enable the use of closely spaced bands of light, thereby improving spectral density and / or system efficiency.

[0018] In some embodiments, optical filter assembly 120 may include one or more other filters. For example, optical filter assembly 120 may include an anti-reflection filter. For example, optical filter assembly 120 may include an anti-reflection filter configured in the same bandpass region as the bandpass filter of optical filter assembly 120. In this case, the anti-reflection filter may be coated on a surface or may be included within the bandpass filter. Additionally or alternatively, optical filter assembly 120 may include a long-wavelength passband filter, a short-wavelength passband filter, or a wide-wavelength passband filter, among others, by way of example.

[0019] Although some embodiments described herein may be described in terms of one or more optical filters within a sensor system, some (other) embodiments may be used in other types of systems, optical elements external to the sensor system, optical elements in an optical package, and / or the like. In some embodiments, the optical system 110 may include a photodetector system, an avalanche photodetector system, a single-photon avalanche diode (SPAD) detector system, or a complementary metal-oxide semiconductor (CMOS) detector system.

[0020] In some embodiments, substrate 130 may be a transparent substrate such as a glass substrate, a silicon substrate, a germanium substrate, and / or the like. In some embodiments, substrate 130 may include a silicon dioxide substrate. In some embodiments, substrate 130 may be disposed on a particular side of optical filter 140. For example, substrate 130 may have optical filter 140 (e.g., a zero-angle shift filter) disposed on a surface of substrate 130. In this case, substrate 130 may include one or more other optical filters disposed on optical filter 140 (e.g., sandwiched between optical filter 140 and one or more other optical filters). Additionally or alternatively, substrate 130 may have optical filters on opposing sides of substrate 130. For example, optical filter 140 may be disposed on a first side of substrate 130, and one or more other optical filters may be disposed on a second side of substrate 130 (e.g., sandwiched between optical filter 140 and one or more other optical filters).

[0021] In some embodiments, substrate 130 may be omitted. For example, optical filter 140 may be disposed directly on optical sensor 160 or another optical filter without a substrate. In this case, optical filter 140 and another optical element are aligned to have optical coherence. In some embodiments, rather than a substrate separating optical elements of optical system 110, such as optical filter 140 and another optical filter or optical sensor 160, the optical elements of the optical system may be separated by another medium, such as an air gap, a gas gap, or a liquid gap, among others.

[0022] In some implementations, optical filter 140 may include a set of alternating high and low refractive index layers (e.g., multiple high and multiple low refractive index layers alternating with each other). For example, optical filter 140 may include a high refractive index material, such as amorphous silicon or niobium titanium oxide, among others. Additionally or alternatively, optical filter 140 may include a silicon layer, a silicon dioxide layer, a silicon hydride layer, a tantalum pentoxide layer, a niobium pentoxide layer, a germanium layer, a silicon germanium layer, a silicon germanium hydride layer, a niobium tantalum oxide layer, a titanium dioxide layer, a silicon nitride layer, an aluminum oxide layer, a niobium oxide layer, an aluminum nitride layer, or a combination thereof, among others. Additionally or alternatively, optical filter 140 may include another type of high refractive index material layer having a refractive index greater than 2.0, greater than 2.5, greater than 3.0, greater than 3.5, and / or similar.

[0023] In some implementations, optical filter 140 may include a low-refractive index material, such as silicon dioxide. Additionally or alternatively, optical filter 140 may include layers of another type of low-refractive index material having a refractive index less than 2.5, less than 2.0, less than 1.5, and / or similar. For example, optical filter 140 may include a set of alternating layers of amorphous silicon and silicon dioxide for a bandpass filter operating at 940 nm. In some implementations, optical filter 140 may include three or more different materials. In this case, using three or more different types of layers may enable optical filter 140 to achieve higher transmittance and / or further reduced angular shift at some wavelengths compared to using only two different materials.

[0024] 1 and indicated by reference numeral 170, input optical signals are directed toward optical filter assembly 120 at one or more angles of incidence θ. For example, input optical signals 150-1 and 150-2 may be directed toward optical filter assembly 120 at angles of incidence θ (e.g., set angles of incidence) and θ, respectively. For example, an electro-optical component, such as an optical emitter, of optical system 110 may transmit a beam including input optical signals 150-1 and 150-2. As indicated by reference numeral 175, a first portion of the input optical signal is reflected by optical filter assembly 120. For example, based on the portion of the input optical signal being outside the passband of a bandpass filter of the set of optical filters 140, the set of optical filters 140 may reflect that portion of the input optical signal.

[0025] 1 and as indicated by reference numeral 180, another portion of the optical signal is transmitted through optical filter assembly 120. For example, a portion of the input optical signal within the passband of optical filter assembly 120 passes through optical filter assembly 120, as described in more detail herein.

[0026] As indicated by reference numeral 185, a portion of the input optical signal may be transmitted to another electro-optical component, such as optical sensor 160 (e.g., an optical detector or photodetector), which may provide an output electrical signal for optical system 110. For example, optical sensor 160 may provide an output electrical signal that identifies the intensity of the light, a property (e.g., a spectroscopic property) of the light, a wavelength of the light, and / or the like.

[0027] As noted above, Figure 1 is presented as an example only. Other examples may differ from those described with respect to Figure 1.

[0028] Figure 2 is a diagram of an exemplary optical filter assembly 200. As shown in Figure 2, the optical filter assembly 200 includes a substrate 210 on which an optical filter 220 is disposed. Two sets of beams 240-1 to 240-6 may be incident on the optical filter 220 at different angles.

[0029] In some embodiments, optical filter 220 may be a passband filter exhibiting a small amount of angular shift, such as zero (or near-zero) angular shift. For example, optical filter 220 may be a low-angle-shift passband filter. In this case, optical filter 220 may be a low-angle-shift passband filter fabricated using hydrogenated silicon (Si:H) or amorphous silicon. In some embodiments, optical filter 220 may be associated with an angular shift less than a threshold value at angles of incidence greater than a threshold, as described in more detail herein. For example, optical filter 220 may be associated with an angular shift of less than 5% (e.g., as a percentage of the center wavelength of light within the passband of optical filter 220), less than 1%, less than 0.5%, less than 0.1%, and / or the like, over a particular range of angles of incidence. In this case, the particular range of angles of incidence may be between about 0° and about 60°, between about 0° and about 45°, between about 0° and about 30°, and / or the like.

[0030] In some embodiments, a zero-angle-shift filter, such as optical filter 220, may comprise a bandpass filter that exhibits an angular shift of the center of the passband of, for example, less than about 10 nm, less than 5 nm, less than 1 nm, less than 0.5 nm, or less than 0.2 nm over an angular range of, for example, about 0° to about 30° in the near-infrared (NIR) spectral range. In some embodiments, a zero-angle-shift filter, such as optical filter 220, may exhibit an angular shift of less than ±0.1% or less than ±0.05% of the center wavelength of the incident light. In some embodiments, the minimum angular shift, such as an angular shift below the threshold mentioned above, may occur in a red-shift direction (e.g., positively toward longer wavelengths) rather than a blue-shift direction as occurs with other optical filters. In some embodiments, a zero-angle-shift filter, such as optical filter 220, may enable the use of narrower bandwidths in the passband compared to low-angle-shift and ultra-low-angle-shift filters. Because zero-angle-shift filters substantially eliminate angular shift over a range of incident angles, the passband can be designed to be narrower while maintaining spectral selectivity at the wavelengths of interest. This improves the signal-to-noise ratio in optical systems by allowing the bandpass filter to block a greater percentage of ambient or stray light. As a result, optical systems incorporating zero-angle-shift filters can achieve higher measurement accuracy and significantly reduced interference from unwanted wavelengths, even in environments with high ambient illumination.

[0031] In some embodiments, optical filter 220 may include multiple layers. For example, multiple layers may be deposited and / or patterned, such as by using photolithographic techniques, to form optical filter 220. In some embodiments, optical filter assembly 200 may be associated with a particular size. For example, optical filter 220 may be associated with a thickness of approximately 10 nm to 5000 nm. Additionally or alternatively, optical filter 220 may be associated with a thickness of 10,000 nm or less or a thickness greater than 10,000 nm.

[0032] In some embodiments, a percentage of light greater than a threshold may pass through optical filter 220 at angles of incidence less than the threshold (or angles of incidence that deviate less than the threshold from the set angle of incidence). For example, optical filter 220 may allow greater than about 75% transmittance, greater than about 90% transmittance, greater than about 95% transmittance, greater than about 99% transmittance, or greater than about 99.9% transmittance, among others, for light having angles of incidence less than about 60°, less than about 45°, less than about 30°, and / or the like.

[0033] In some embodiments, the optical filter assembly 200 may be associated with a particular spectral range over which the optical filter assembly 200 is transmissive within a set range of angles of incidence. For example, the optical filter assembly 200 may be associated with spectral ranges from about 600 nm to about 1200 nm, from about 700 nm to about 1100 nm, from about 800 nm to about 1000 nm, and / or similar spectral ranges. Additionally or alternatively, the optical filter assembly 200 may be associated with spectral ranges from about 1200 nm to about 2000 nm, from about 1400 nm to about 1800 nm, from about 1500 nm to about 1700 nm, and / or similar spectral ranges. Additionally or alternatively, the optical filter assembly 200 may be associated with spectral ranges from about 200 nm to about 4000 nm, from about 1000 nm to about 3000 nm, from about 1500 nm to about 2500 nm, and / or similar spectral ranges. In some embodiments, the optical filter assembly 200 may be associated with a spectral range of about 100 nm to about 14,000 nm, or any subrange thereof. Additionally or alternatively, the optical filter assembly 200 may be associated with a visible spectral range, a near-infrared spectral range, an ultraviolet spectral range, combinations thereof, and / or the like.

[0034] In some embodiments, optical filter assembly 200 may include one or more other filters, such as blockers, edge filters, bandpass filters, and / or the like. In some embodiments, optical filter assembly 200 may include a protective cover (e.g., to protect optical filter 220). In some embodiments, optical filter assembly 200 may include one or more layers of other materials. For example, the optical filter assembly 200 may be configured to use, for example, a silicon (Si)-based material, a silicon hydride (Si:H)-based material, a germanium (Ge)-based material, a germanium hydride (Ge:H)-based material, a silicon germanium (SiGe)-based material, an aluminum (Al)-based material, a silver (Ag)-based material, a silicon dioxide (SiO2) material, an aluminum oxide (Al2O3) material, a titanium dioxide (TiO2) material, a niobium pentoxide (Nb2O5) material, a tantalum pentoxide (Ta2O5) material, a magnesium fluoride (MgF2) material, a niobium titanium oxide (NbTiO x ) material, niobium tantalum pentoxide (NbTaO) material, zinc oxide material (ZnO), platinum (Pt) material, gold (Au) material, fluorescent material, and / or the like. In some embodiments, a spacer layer or material may be included in one or more optical filters.

[0035] In some embodiments, optical filter assembly 200 may be bidirectional. For example, while optical filter assembly 200 is shown as transmitting light in a particular direction, optical filter assembly 200 may be configured to transmit light in another direction.

[0036] As noted above, Figure 2 is presented as an example only, and other examples are possible and may differ from those described with respect to Figure 2.

[0037] 3A-3C illustrate characteristic diagrams of exemplary optical filters. As shown in FIG. 3A, an example very low angle shift (HLAS) optical filter 300 can include a stack of alternating silicon hydride (Si:H) and silicon dioxide (SiO2) layers. The HLAS optical filter can include 26 layers and have a total thickness of approximately 3233 nm. In contrast, as shown in FIG. 3B, an example zero angle shift (ZAS) optical filter 350, such as optical filter 140 or optical filter 220 described herein, can include a stack of alternating silicon hydride and silicon dioxide layers with 63 layers and a total thickness of approximately 9003 nm. FIG. 3C illustrates another example ZAS optical filter 370, which can include alternating silicon hydride (Si:H) and silicon dioxide (SiO2) layers with a substrate (sub) at a first end and an air interface at a second end. In some embodiments, the zero angle shift filter may be fabricated as a multilayer thin film structure including alternating layers of high refractive index material (e.g., silicon hydride) and low refractive index material (e.g., silicon dioxide). For a center wavelength of about 940 nm, the zero angle shift filter may include 50 to 100 alternating layers, with the individual high refractive index layers having physical thicknesses ranging from 1 nm to 1200 nm and the low refractive index layers having thicknesses ranging from 1 nm to 700 nm. The overall stack thickness may range from 500 nm to 15000 nm.

[0038] ZAS optical filters generally can have a substantially larger number of layers and a substantially larger overall thickness than HLAS optical filters (and low angle shift (LAS) optical filters), which results in a reduced angle shift (e.g., center wavelength (CWL) shift) in ZAS optical filters compared to HLAS and LAS optical filters.

[0039] Additionally or alternatively, due to the large number of layers and large overall thickness of ZAS optical filters, ZAS optical filters can compensate for spectral ripple (e.g., variations in transmission or rejection that occur at high angles of incidence). By doubling the number of layers and increasing the overall thickness compared to, for example, HLAS and LAS optical filters, ZAS optical filters can control or align ripple so that the ripple enhances the desired bandpass or extends the rejection range. This compensation mechanism ensures that the passband of the ZAS optical filter remains stable and that out-of-band transmission or leakage is minimized even as the angle of incidence increases. Increasing the number of layers provides greater design freedom, allowing for precise control of the spectral response of the ZAS optical filter over the relevant angular range.

[0040] In some embodiments, a beam may exhibit a red shift when passing through a ZAS optical filter. For example, if a ZAS optical filter causes a minimal amount of angular shift in a beam at various angles of incidence (e.g., an angular shift of less than 0.2° between an AOI of 0° and 30°), the ZAS optical filter may attribute that minimal angular shift to a red shift toward longer wavelengths. In contrast, a beam may exhibit a blue shift when passing through HLAS and LAS optical filters. Therefore, a ZAS optical filter may be selected when it is desirable to ensure that the wavelength of light passing through the ZAS optical filter is not shorter than the wavelength of the light before passing through the ZAS optical filter, taking into account the minimal amount of angular shift. In other words, when light is emitted at a specific wavelength, HLAS and LAS optical filters may blue-shift the specific wavelength toward shorter wavelengths. Therefore, if the light blue-shifts toward shorter wavelengths, a detector configured to detect at least a set wavelength may not be able to detect the light. In contrast, a ZAS optical filter may cause only specific wavelengths to be red-shifted (minimally) toward longer wavelengths, so that the detector still detects the light even if the light shifts from the specific wavelength. Thus, ZAS optical filters can be particularly useful in combination with bandpass filters, detectors, or other optical elements that have wavelength cutoffs on the short wavelength side.

[0041] Additionally or alternatively, ZAS optical filters may have greater durability than HLAS or LAS optical filters. For example, due to their greater number of layers and / or greater thickness, ZAS optical filters may be more resistant to damage related to environmental degradation and / or physical impact. However, ZAS optical filters may not be as miniaturized as HLAS or LAS optical filters, and therefore may not be suitable for some miniaturized use cases.

[0042] Additionally or alternatively, in other conventional multilayer interference filters, an equation relating the effective refractive index of the stack to the angle of incidence can be used to predict the angle-dependent shift of the passband. However, in the case of ZAS optical filters as described herein, such an equation does not hold because a ZAS optical filter that achieves zero angular shift mathematically has an infinite effective refractive index. Therefore, the behavior of ZAS optical filters differs from theoretical mathematical models, and they achieve zero or near-zero angular shift not by manipulating the effective refractive index but by complex multilayer structures.

[0043] As noted above, Figures 3A-3C are provided as examples only, and other examples are possible and may differ from those described with respect to Figures 3A-3C.

[0044] 4A-4D are characteristic diagrams of exemplary optical filters. As shown in FIG. 4A, an example LAS filter 400 having a given refractive index profile (e.g., a substrate and a set of alternating high (H) and low (L) refractive index layers) can have a center wavelength of approximately 940 nm and exhibit an angular shift of approximately −13 nm at angles of incidence between 0° and 30°. As shown in FIG. 4B, an example HLAS filter 410 having a given refractive index profile (e.g., a substrate and a set of alternating high (H) and low (L) refractive index layers) can have a center wavelength of approximately 940 nm and exhibit an angular shift of approximately −7.4 nm at angles of incidence between 0° and 30°. As shown in FIG. 4C, an example ZAS filter 420 having a given refractive index profile (e.g., a substrate and a set of alternating high (H) and low (L) refractive index layers) can have a center wavelength of approximately 940 nm and can exhibit an angular shift of less than approximately 1 nm at angles of incidence between 0° and 30°. FIG. 4D shows an example comparison 430 of an LAS optical filter, an HLAS optical filter, and a ZAS optical filter. As shown, the ZAS optical filter has a smaller angular shift than the HLAS and LAS optical filters over the range of angles of incidence between 0° and 30°. Furthermore, the ZAS optical filter can exhibit a smaller angular shift than a non-LAS optical filter (e.g., a bandpass filter that is not configured with a low angular shift, which can have an angular shift of approximately 34 nm over the range of angles of incidence between 0° and 30°). Although some embodiments are described with respect to an incident angle range of 0° to 30°, it is contemplated that the ZAS optical filters described herein may achieve reduced angular shift compared to other filters over incident angle ranges of 0° to 40°, 0° to 50°, 0° to 60°, or even greater ranges, etc.

[0045] As noted above, Figures 4A-4D are provided as examples only, and other examples are possible and may differ from those described with respect to Figures 4A-4D.

[0046] The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Modifications and variations may be made in light of the foregoing disclosure or may be acquired from practice of the embodiments.

[0047] As used herein, the term "component" is intended to be broadly interpreted as hardware, firmware, or a combination of hardware and software. It will be apparent that the systems and / or methods described herein may be implemented in various forms, such as hardware, firmware, and / or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and / or methods is not intended to limit the embodiments. Thus, the operation and behavior of the systems and / or methods are described herein without reference to specific software code, and it will be understood that the systems and / or methods can be implemented using software and hardware based on the description herein.

[0048] As used herein, meeting a threshold may refer to a value exceeding the threshold, being greater than or equal to the threshold, being less than the threshold, being less than or equal to the threshold, being equal to the threshold, not being equal to the threshold, etc., depending on the context.

[0049] Although particular combinations of features are recited in the claims and / or disclosed herein, these combinations are not intended to limit the disclosure of various embodiments. Indeed, many of these features can be combined in ways not specifically recited in the claims and / or disclosed herein. Although each dependent claim may depend directly on only one claim, the disclosure of various embodiments includes each dependent claim in combination with all other claims in that group. As used herein, phrases referring to "at least one" of listed items refer to any combination of those items, including single components. By way of example, "at least one of a, b, and c" is intended to encompass a, b, c, ab, ac, bc, and abc, as well as any combination with multiples of the same item.

[0050] No element, act, or instruction used herein should be construed as critical or required unless expressly stated as such. Also, herein, the indefinite articles "a" and "an" are intended to include one or more items and can be used interchangeably with "one or more." Furthermore, herein, the definite article "the" is intended to include one or more items referenced in connection with the definite article "the" and can be used interchangeably with "one or more." Furthermore, herein, the term "set" is intended to include one or more items (e.g., related items, unrelated items, a combination of related and unrelated items, etc.) and can be used interchangeably with "one or more." Where only one item is intended, the phrase "only one" or similar language is used. Also, herein, terms such as "comprise" are intended to be open-ended terms. Furthermore, the phrase "based on" is intended to mean "based at least in part on," unless expressly stated otherwise. Also, as used herein, the term "or" is intended to be inclusive when used in a sequence and can be used interchangeably with "and / or" unless otherwise specified (e.g., when used in combination with "either" or "only one of").

Claims

1. 1. An optical filter assembly comprising: an optical filter disposed on a first side of the substrate the optical filter having a thickness greater than a first threshold; The optical filter assembly is configured such that, at a particular operating center wavelength, the center wavelength shift is less than a second threshold value over a range of angles of incidence from 0° to at least a third threshold value.

2. 10. The optical filter assembly of claim 1, wherein the first threshold is greater than or equal to 10,000 nanometers.

3. 10. The optical filter assembly of claim 1, wherein the second threshold is less than 4 nanometers.

4. 10. The optical filter assembly of claim 1, wherein the second threshold is less than 1 nanometer.

5. 10. The optical filter assembly of claim 1, wherein the second threshold is less than 0.25 nanometers.

6. 10. The optical filter assembly of claim 1, wherein the third threshold is greater than or equal to 30 degrees.

7. 10. The optical filter assembly of claim 1, Anti-reflection filters, Long wavelength passband filters, Short wavelength passband filter, or Wide Passband Filter The optical filter assembly further comprising at least one of:

8. 10. The optical filter assembly of claim 1, wherein the optical filter is a zero angle shift (ZAS) bandpass filter.

9. 2. The optical filter assembly of claim 1, wherein the center wavelength shift is in a positive direction.

10. An optical filter, A filter stack of alternating layers of a first material having a first refractive index and a second material having a second refractive index. the filter stack having a transmittance of at least a first threshold level at a set center wavelength; The filter stack is an optical filter configured to introduce a red-shift less than a second threshold at angles of incidence between 0° and 30°.

11. 11. The optical filter of claim 10, wherein the first refractive index is higher than the second refractive index.

12. 11. The optical filter of claim 10, wherein the first material is: an amorphous silicon layer, or hydrogenated silicon layer An optical filter comprising at least one of:

13. 11. The optical filter of claim 10, wherein the second material is: a silicon oxide layer, titanium oxide layer, tantalum oxide layer, an aluminum oxide layer, or Niobium oxide layer An optical filter comprising at least one of:

14. 11. The optical filter according to claim 10, wherein the set center wavelength is in the range of 100 nanometers (nm) to 14,000 nm.

15. 11. The optical filter of claim 10, wherein the second threshold has a magnitude less than 0.2 nanometers.

16. 1. An optical system comprising: an electro-optical component; an optical filter disposed on a first side of the substrate; the optical filter having a thickness greater than a first threshold; The optical filter is configured such that, at a particular operating center wavelength, the center wavelength shift is less than a second threshold value over a range of angles of incidence from 0° to at least a third threshold value.

17. 17. The optical system of claim 16, wherein the electro-optical component is an optical emitter configured to emit at the particular operating center wavelength.

18. 17. The optical system of claim 16, wherein the electro-optical component is an optical detector configured to detect at the particular operating center wavelength.

19. 17. The optical system of claim 16, wherein the substrate is a glass substrate.

20. 17. The optical system of claim 16, wherein the center wavelength shifts toward shorter wavelengths as the angle of incidence increases.

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