Zero angle offset bandpass filter

Abstract

The invention relates to a zero angle offset bandpass filter. In some embodiments, an optical filter assembly includes an optical filter disposed on a first side of a substrate, where the optical filter has a thickness greater than a first threshold, and wherein the optical filter is configured to experience a center wavelength shift less than a second threshold for a particular operating center wavelength and a range of angles of incidence from 0 degrees to at least a third threshold.

Description

[0001] Cross Reference to Related Applications

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 672,084, filed July 16, 2024, entitled “ZERO ANGLE SHIFT BANDPASS FILTER.” The disclosure of the prior application is considered part of this patent application and is hereby incorporated by reference into this patent application. BACKGROUND

[0003] Optical filters are used to select a spectral band or spectral component of incident light. For example, a high-pass filter selects light with a wavelength greater than the filter edge wavelength. Conversely, a low-pass filter selects light with a wavelength less than the edge wavelength. A bandpass filter is a unique filter that selects light with a wavelength close to a center wavelength within the filter bandwidth. An adjustable bandpass filter is an optical filter whose center wavelength is adjustable or tunable.

[0004] The performance of an optical filter can degrade when the angle of incidence (AOI) of light directed at the optical filter varies from a configured angle of incidence (e.g., 0 degrees, 45 degrees, 90 degrees) to a threshold angle of incidence (e.g., more than about 30 degrees deviation from the configured angle of incidence). In this case, the band edges can shift to different wavelengths, such as a blue shift to shorter wavelengths. SUMMARY

[0005] In some implementations, an optical filter assembly includes an optical filter disposed on a first side of a substrate, where the optical filter has a thickness greater than a first threshold, and where the optical filter is configured to experience a center wavelength shift less than a second threshold for a particular working center wavelength and for a range of angles of incidence from 0 degrees to at least a third threshold.

[0006] In some implementations, an optical filter includes a filter stack formed of alternating layers of a first material having a first refractive index and a second material having a second refractive index, where the filter stack has at least a first threshold level of transmittance at a configured center wavelength, and where the filter stack is configured to introduce a red shift less than a second threshold for an angle of incidence between 0 degrees and 30 degrees.

[0007] In some implementations, an optical system includes an electro-optical component; and an optical filter disposed on a first side of a substrate, where a thickness of the optical filter is greater than a first threshold, and where the optical filter is configured to experience a center wavelength shift less than a second threshold for a particular working center wavelength and for a range of angles of incidence from 0 degrees to at least a third threshold. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1is a schematic diagram of example implementations described herein.

[0009] Figure 2 is a schematic diagram of an example optical filter assembly.

[0010] Figures 3A-3C is a characteristic plot of an example optical filter.

[0011] Figures 4A-4D is a characteristic plot of an example optical filter. DETAILED DESCRIPTION

[0012] The following detailed description of example implementations refers to the accompanying drawings. The same reference numbers in different drawings can identify the same or similar elements. The following description is presented with reference to a spectrometer. However, the techniques, principles, procedures, and methods described herein can be used with any sensor, including but not limited to other optical sensors and spectral sensors.

[0013] An optical sensor device can include an array of sensor elements for receiving light emitted from a light source (e.g., an optical emitter, a light bulb, or an ambient light source, etc.). For example, in a spectrometer, the optical sensor device can include an array of sensor elements for receiving light reflected from a target object, enabling identification of the target object. The sensor elements can be aligned with optical filters that filter light to the sensor elements to enable the sensor elements to acquire information about a particular electromagnetic frequency spectral range. For example, the sensor elements can be aligned with optical filters that have a passband in the near-infrared (NIR) spectral range, the visible spectral range, the ultraviolet spectral range, etc.

[0014] In other words, an optical system can include an optical filter, such as a bandpass filter, to filter out light at wavelengths other than a measurement wavelength of interest. This light at wavelengths other than the measurement wavelength of interest causes noise, thereby reducing performance of the optical system, for example, by obscuring weak signals and reducing the signal-to-noise ratio of the optical system, thereby making accurate detection and measurement difficult. The optical system can include a bandpass filter that has a passband at the measurement wavelength of interest and blocks light at other wavelengths. However, angular misalignment can cause the wavelength of light incident on the bandpass filter to change. For example, in the case of light incident on the optical filter at a high angle of incidence, the optical filter can cause an angular misalignment, i.e., a shift in the center wavelength of the light that passes through. Thus, light directed at the optical filter at a first wavelength and at an angle greater than a threshold angle can be shifted by the optical filter to a second wavelength. This angular misalignment can cause light that the optical system is intended to measure, such as light emitted from an emitter toward a target for spectral analysis, to be shifted outside of the passband of the bandpass filter and blocked by the bandpass filter, thereby resulting in failure to measure the target.

[0015] Conversely, angular deviation can cause unintended light to deviate into the wavelength of interest, to be within the passband of the bandpass filter, and to be passed by the bandpass filter, thereby causing excess 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 angularly deviate into the passband of the bandpass filter and pass through the bandpass filter along with light from the intended light source (e.g., an optical emitter). When both the stray light and the intended light are directed toward the sensor element at the same time, the sensor element can produce an erroneous reading of the intended light.

[0016] Additionally, in certain applications, it can be desirable to make precise measurements of light that is incident on an optical element at a relatively high angle of incidence. In such cases, angular deviation can change the center wavelength of the light, causing the optical sensor device to make inaccurate measurements of the light due to the relatively high angle of incidence. Accordingly, it is desirable for an optical filter to minimize or eliminate angular deviation of the center wavelength of light incident on the optical filter at an increased angle. For example, it is desirable for light intended to be measured not to angularly deviate beyond the passband range of the bandpass filter, and / or for light not intended to be measured not to angularly deviate into the passband range of the bandpass filter. Additionally, when measurements are to be made of light at a relatively high angle of incidence, it is desirable for the light not to be affected by angular deviation due to the relatively high angle of incidence.

[0017] Some embodiments described herein provide an optical filter assembly, optical device, optical element, optical module, or optical system with reduced angular shift. For example, an optical filter can include a layer structure that achieves a center wavelength shift of less than 0.1% of the center wavelength of the optical filter passband. Thus, as a specific example, for a 940 nanometer (nm) passband filter, the optical filter layer structure can achieve an angular shift of less than 4 nm, less than 1 nm, or less than 0.25 nm, etc. In some implementations, the optical filter can include a zero angular shift (ZAS) filter that achieves an angular shift of ±0.1% of the center wavelength of the passband. In some implementations, the optical filter can cause any residual angular shift of a light beam to be a red shift, rather than a blue shift, as occurs with other low angular shift (LAS) filters, such as a high low angular shift (HLAS) filter. In this way, the optical filter can transmit light without angular shift, even at relatively high angles of incidence. When the optical filter is a bandpass filter with a configured passband, the optical filter can reflect or block light at wavelengths outside the configured passband without angular shift of light outside the configured passband being shifted into the configured passband (and passing through), thereby avoiding excess noise or crosstalk in an optical sensor or array of sensor elements. Additionally, the optical filter can also reflect or block light at wavelengths outside the configured passband without angular shift of light inside the configured passband being shifted outside the configured passband (and being blocked), thereby avoiding measurement errors. Additionally, when the optical filter is included in an optical system for measuring light at oblique angles (e.g., greater than a threshold angle of incidence), the optical filter can avoid angular shift related measurement errors for light at oblique angles.

[0018] The zero angular shift filter described herein improves the blocking of ambient light and increases the stability of the passband, enabling optical systems incorporating the zero angular shift filter to operate at lower transmitter power, as less ambient light reaches the detector and lower signal strength can be used to achieve high signal-to-noise ratio. This can extend the battery life of portable devices such as smartphones and enable longer detection ranges in applications such as light detection and ranging (LIDAR), for example, allowing automotive LIDAR systems to detect objects at greater distances without increasing output power. Thus, the zero angular shift filter helps enable more energy-efficient, higher-performing optical systems.

[0019] Figure 1 is a schematic diagram of an example implementation 100 described herein. As Figure 1As shown, example implementation 100 includes an optical system 110. The optical system 110 may be part of an optical system and may provide electrical output corresponding to sensor measurements. For example, the optical system 110 may be part of a LIDAR system, a three-dimensional sensing system, a spectral 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, as well as other examples.

[0020] In some embodiments, the optical system 110 may include an optical filter assembly 120, which may include a substrate 130 and an optical filter 140. In some embodiments, the optical filter assembly 120 may include a bandpass filter. For example, the optical filter assembly 120 may include one or more layers forming a bandpass interference filter configured to allow a first portion of light in a first wavelength range to pass through and block a second portion of light in a second wavelength range. Additionally or alternatively, the optical filter assembly 120 may include a long wavelength passband (LWP) filter, a short wavelength passband (SWP) filter, a wide wavelength passband (BWP) filter, an infrared cut-off (IR Cut) filter, a notch filter, etc. In some embodiments, the optical filter assembly 120 may have a bandpass between 200 nm and 14000 nm and may be used in the visible spectrum, NIR spectrum, mid-wave infrared (MWIR) spectrum, long-wave infrared (LWIR) spectrum, or ultraviolet spectrum, etc.

[0021] In some embodiments, optical filter 140 may include a zero-angle offset filter. For example, optical filter 140 may include one or more layers forming an angle-sensitive filter configured to allow light to pass through without experiencing an angular offset (e.g., having a minimum angular offset, such as an angular offset less than a threshold, as described herein). In this case, by minimizing or eliminating the angular offset of light, even at relatively high angles of incidence, optical filter assembly 120 can ensure that stray light entering the cavity of optical system 110 is not deflected into the wavelength of interest of optical system 110 (or the passband of optical filter 140). In other words, when optical system 110 is configured to measure the properties of light at a wavelength (e.g., 980 nm), zero-angle offset optical filter 140 ensures that emitted light at a wavelength of 980 nm and having a threshold angle of incidence (e.g., greater than 30 degrees or less than -30 degrees) does not deviate from 980 nm, which would otherwise prevent optical system 110 from measuring the emitted light. Conversely, optical system 110 ensures that stray light with a wavelength of (e.g.) 1000 nm and a threshold angle of incidence does not deviate from 980 nm, which could otherwise lead to erroneous measurements. Therefore, by reducing angular offset, optical system 110 can measure light with improved measurement accuracy, reduced noise, or reduced crosstalk. Furthermore, when optical system 110 is configured with multiple optical bands, zero-angle offset optical filter 140 ensures that the first emitted beam (e.g., 985 nm) does not deviate to the wavelength of the second emitted beam (e.g., 980 nm), thereby preventing the first beam from interfering with the measurement of the second beam. In this way, by reducing the possibility of crosstalk caused by angular offset, optical system 110 and optical filter 140 can use closer optical bands, thereby improving spectral density and / or system efficiency.

[0022] In some embodiments, the optical filter assembly 120 may include one or more other filters. For example, the optical filter assembly 120 may include an anti-reflective filter. For instance, the optical filter assembly 120 may include an anti-reflective filter configured to have the same bandpass region as the bandpass filter of the optical filter assembly 120. In this case, the anti-reflective filter may be coated on the surface of the bandpass filter or included within the bandpass filter. Additionally or alternatively, the optical filter assembly 120 may include a long-wavelength bandpass filter, a short-wavelength bandpass filter, or a wide-bandpass filter, etc.

[0023] While some embodiments described herein may be described as one or more optical filters in a sensor system, certain (other) embodiments may be used in other types of systems, external optical elements of a sensor system, optically packaged optical elements, etc. In some embodiments, 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.

[0024] In some embodiments, substrate 130 may be a transparent substrate, such as a glass substrate, a silicon substrate, a germanium substrate, etc. In some embodiments, substrate 130 may include a silicon dioxide substrate. In some embodiments, substrate 130 may be disposed on a specific side of optical filter 140. For example, substrate 130 may have optical filter 140 (e.g., a zero-angle offset filter) disposed on the surface of substrate 130. In this case, substrate 130 may include one or more other optical filters disposed on top of optical filter 140 (e.g., such that optical filter 140 is sandwiched between one or more other optical filters and substrate 130). Additionally or alternatively, substrate 130 may have optical filters on opposite 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., such that optical filter 140 and one or more other optical filters sandwich substrate 130 between).

[0025] In some embodiments, the substrate 130 may be omitted. For example, the optical filter 140 may be directly disposed on the optical sensor 160, or another optical filter may be disposed therewith, without the need for a substrate between them, or either filter may be disposed on the optical sensor 160. In this case, the optical filter 140 is matched with other optical elements to ensure light coherence. In some embodiments, in addition to the substrate separating the optical elements of the optical system 110 (such as the optical filter 140 and another optical filter or optical sensor 160), another medium may separate the optical elements of the optical system 110, such as an air gap, a gas gap, or a liquid gap.

[0026] In some embodiments, the optical filter 140 may include an alternating collection of high-refractive-index layers and low-refractive-index layers (e.g., an alternating arrangement of multiple high-refractive-index layers and multiple low-refractive-index layers). For example, the optical filter 140 may include a high-refractive-index material, such as amorphous silicon or niobium titanium oxide. Additionally or alternatively, the 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 combinations thereof. Additionally or alternatively, the optical filter 140 may include another type of high-refractive-index material layer with a refractive index greater than 2.0, greater than 2.5, greater than 3.0, greater than 3.5, etc.

[0027] In some embodiments, the optical filter 140 may include a low-refractive-index material, such as silicon dioxide. Additionally or alternatively, the optical filter 140 may include another type of low-refractive-index material layer with a refractive index less than 2.5, less than 2.0, less than 1.5, etc. For example, for a bandpass filter operating at 940 nm, the optical filter 140 may include a collection of alternating layers of silicon hydride and silicon dioxide. In some embodiments, the optical filter 140 may include three or more different materials. In this case, using three or more different types of layers, compared to using only two different materials, can allow the optical filter 140 to achieve higher transmittance and / or even further reduced angular offset at certain wavelengths.

[0028] like Figure 1 Further, as shown by reference numeral 170, the input optical signal is directed to the optical filter assembly 120 at one or more incident angles θ. For example, input optical signals 150-1 and 150-2 may be directed to the optical filter assembly 120 at incident angles θ0 (e.g., configured incident angles) and θ, respectively. For example, an electro-optic component of an optical emitter such as optical system 110 may emit a beam including input optical signals 150-1 and 150-2. As shown by reference numeral 175, a first portion of the input optical signal is reflected by the optical filter assembly 120. For example, based on a portion of the input optical signal located outside the passband of a bandpass filter in the set of optical filters 140, the set of optical filters 140 may reflect this portion of the input optical signal.

[0029] like Figure 1 As further shown by reference numeral 180, another portion of the optical signal is transmitted through the optical filter assembly 120. For example, a portion of the input optical signal within the passband of the optical filter assembly 120 passes through the optical filter assembly 120, as described in more detail herein.

[0030] As indicated by reference numeral 185 in the accompanying drawings, the optical sensor 160 may provide an output electrical signal to the optical system 110 based on a portion of the optical signal transmitted to another optoelectronic component, such as the optical sensor 160 (e.g., an optical detector or a photodetector). For example, the optical sensor 160 may provide an output electrical signal identifying light intensity, light characteristics (e.g., spectral features), light wavelength, etc.

[0031] As mentioned above, Figure 1 Provided as an example only. Other examples may be related to... Figure 1 The content described in the text is different.

[0032] Figure 2 This is a schematic diagram of an example optical filter assembly 200. (As shown) Figure 2 As shown, the optical filter assembly 200 includes a substrate 210 on which an optical filter 220 is disposed. A set of light beams 240-1 to 240-6 can be incident on the optical filter 220 at different angles.

[0033] In some embodiments, optical filter 220 may be a passband filter exhibiting a low angular offset, such as zero (or near-zero) angular offset. For example, optical filter 220 may be a low-angle-offpass filter. In this case, optical filter 220 may be a low-angle-offpass filter made using silicon hydride (Si:H) or amorphous silicon. In some embodiments, optical filter 220 may be associated with angular offsets less than a threshold when the incident angle is greater than a threshold, as described in more detail below. For example, within a specific incident angle range, optical filter 220 may be associated with angular offsets less than 5% (e.g., expressed as a percentage of the center wavelength of light in the passband of optical filter 220), less than 1%, less than 0.5%, less than 0.1%, etc. In this case, the specific range of incident angles may be approximately 0 degrees to approximately 60 degrees, approximately 0 degrees to approximately 45 degrees, approximately 0 degrees to approximately 30 degrees, etc.

[0034] In some embodiments, a zero-angle offset filter (such as optical filter 220) may include a bandpass filter whose passband center angular offset is, 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 in an angular range of about 0 to about 30 degrees in the near-infrared (NIR) spectral range. In some embodiments, the zero-angle offset filter (such as optical filter 220) may exhibit an angular offset less than ±0.1% or less than ±0.05% of the center wavelength of the incident light. In some embodiments, the minimum angular offset (such as an angular offset less than the aforementioned thresholds) may be along a redshift direction (e.g., along the positive direction of a longer wavelength), rather than along a blueshift direction as in other optical filters. In some embodiments, the zero-angle offset filter (such as optical filter 220) can use a narrower passband bandwidth compared to low-angle offset and ultra-low-angle offset filters. Because zero-angle offset filters essentially eliminate angular offset across a certain range of incident angles, the passband can be designed to be narrower while still maintaining its spectral selectivity for the wavelength of interest. This allows the bandpass filter to block a larger proportion of ambient or stray light, thereby improving the signal-to-noise ratio of the optical system. Therefore, even in well-lit environments, optical systems incorporating zero-angle offset filters can achieve higher measurement accuracy and significantly reduce interference from unwanted wavelengths.

[0035] In some embodiments, the optical filter 220 may include multiple layers. For example, multiple layers may be deposited and / or patterned (e.g., by using a photolithography process) to form the optical filter 220. In some embodiments, the optical filter assembly 200 may be associated with a specific size. For example, the optical filter 220 may be associated with a thickness between about 10 nm and 5000 nm. Additionally or alternatively, the optical filter 220 may be associated with a thickness up to 10000 nm or greater than 10000 nm.

[0036] In some implementations, light exceeding a threshold percentage can pass through optical filter 220 at an incident angle less than the threshold (or less than a threshold deviation from the configured incident angle). For example, for light with incident angles less than about 60 degrees, less than about 45 degrees, less than about 30 degrees, etc., optical filter 220 may allow transmittance greater than about 75%, greater than about 90%, greater than about 95%, greater than about 99%, or greater than about 99.9%, respectively, and other examples.

[0037] In some embodiments, the optical filter assembly 200 may be associated with a specific spectral range that makes it transmissive over a configured incident angle range. For example, the optical filter assembly 200 may be associated with spectral ranges such as about 600 nm to about 1200 nm, about 700 nm to about 1100 nm, and about 800 nm to about 1000 nm. Additionally or alternatively, the optical filter assembly 200 may be associated with spectral ranges such as about 1200 nm to about 2000 nm, about 1400 nm to about 1800 nm, and about 1500 nm to about 1700 nm. Additionally or alternatively, the optical filter assembly 200 may be associated with spectral ranges such as about 200 nm to about 4000 nm, about 1000 nm to about 3000 nm, and about 1500 nm to about 2500 nm. In some embodiments, the optical filter assembly 200 may be associated with a spectral range of about 100 nm to about 14000 nm or a subrange thereof. Additionally or alternatively, the optical filter assembly 200 may be associated with spectral ranges such as the visible spectral range, the near-infrared spectral range, the ultraviolet spectral range, or combinations thereof.

[0038] In some embodiments, the optical filter assembly 200 may include one or more other filters, such as a blocker, edge filter, bandpass filter, etc. In some embodiments, the optical filter assembly 200 may include a protective covering (e.g., for protecting the optical filter 220). In some embodiments, the optical filter assembly 200 may include a layer of one or more other materials. For example, for optical filter 220, optical filter assembly 200 may include silicon (Si)-based materials, silicon hydride (Si:H)-based materials, germanium (Ge)-based materials, germanium hydride (Ge:H)-based materials, silicon-germanium (SiGe)-based materials, aluminum (Al)-based materials, silver (Ag)-based materials, silicon dioxide (SiO2) materials, aluminum oxide (Al2O3) materials, titanium dioxide (TiO2) materials, niobium pentoxide (Nb2O5) materials, tantalum pentoxide (Ta2O5) materials, magnesium fluoride (MgF2) materials, niobium titanium oxide (NbTiOx) materials, niobium pentoxide tantalum material (NbTa2O5) materials, zinc oxide (ZnO) materials, platinum (Pt) materials, gold (Au) materials, fluorescent materials, etc. In some embodiments, a spacer layer or material may be included in one or more optical filters.

[0039] In some implementations, the optical filter assembly 200 can be bidirectional. For example, although the optical filter assembly 200 shown in the figure allows light to pass through in a particular direction, the optical filter assembly 200 can also be configured to allow light to pass through from another direction.

[0040] As mentioned above, Figure 2This is provided as an example only. Other examples are also possible and may relate to [the topic of...]. Figure 2 The content described in the text is different.

[0041] Figures 3A-3C This is a characteristic diagram of an example optical filter. For example... Figure 3A As shown, Example 300 of an ultra-low angle offset (HLAS) optical filter may include a stack of alternating silicon hydride (Si:H) layers and silicon dioxide (SiO2) layers. The HLAS optical filter may include 26 layers with a total thickness of approximately 3233 nm. In contrast, as... Figure 3B As shown, an example 350 of a zero-angle offset (ZAS) optical filter (such as optical filter 140 or optical filter 220 described herein) may include alternating stacks of silicon hydride and silicon dioxide layers, wherein the number of layers is 63 and the total thickness is approximately 9003 nm. Figure 3C Example 370 of another ZAS optical filter is shown, which may include alternating layers of silicon hydride (SiH) and silicon dioxide (SiO2), with a substrate at a first end and an air interface at a second end. In some embodiments, the zero-angle offset filter can be fabricated as a multilayer thin-film structure, including alternating layers of a high-refractive-index material (e.g., silicon hydride) and a low-refractive-index material (e.g., silicon dioxide). For a center wavelength of approximately 940 nm, the zero-angle offset filter may include 50 to 100 alternating layers, wherein the physical thickness of each high-refractive-index layer is in the range of 1 nm to 1200 nm, and the thickness of the low-refractive-index layer is in the range of 1 nm to 700 nm. The total stack thickness may be in the range of 5000 nm to 15000 nm.

[0042] Typically, the number of layers and total thickness of a ZAS optical filter can be much greater than that of an HLAS optical filter (and a low-angle offset (LAS) optical filter). This results in a reduction in the angular offset (e.g., center wavelength (CWL) offset) of the ZAS optical filter relative to both HLAS and LAS optical filters. Figure 3C And as shown in Figure 370. For example, in Figure 3C The diagram shows the target Figure 3A HLAS optical filters, Figure 3B The angular offsets of the ZAS optical filter and the example LAS optical filter are shown. As illustrated, the ZAS optical filter has an angular offset of less than 2.0 degrees (e.g., about 0.2 degrees) between 0 and 30 degrees of incident angle (AOI), while the HLAS and LAS optical filters have much higher angular offsets, up to 8.0 degrees and 14.0 degrees, respectively.

[0043] Additionally or alternatively, ZAS optical filters, based on a greater number of layers and a larger total thickness, can compensate for spectral ripple (e.g., transmission or blocking variations occurring at higher incident angles). For example, by doubling the number of layers and increasing the total thickness relative to HLAS and LAS optical filters, ZAS optical filters can control and align ripple to enhance the desired passband or expand the blocking 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 with increased incident angles. The increased number of layers provides additional design freedom, enabling precise control of the spectral response of the ZAS optical filter across a relevant angular range.

[0044] In some implementations, a ZAS optical filter may cause the light beam to exhibit a redshift as it passes through. For example, when a ZAS optical filter causes the light beam to experience a minimum angular shift at various incident angles (e.g., less than 0.2 degrees between 0 and 30 degrees of AOI), the minimum angular shift that a ZAS optical filter may cause is a redshift to a longer wavelength. In contrast, HLAS and LAS optical filters cause the light beam to exhibit a blueshift as it passes through. Therefore, when considering the minimum angular shift, a ZAS optical filter can be selected if it is desired that the wavelength of the light that has passed through the ZAS optical filter is not shorter than the wavelength before passing through the ZAS optical filter. In other words, when emitting light with a specific wavelength, an HLAS or LAS optical filter may cause that specific wavelength to be blueshifted to a shorter wavelength. Therefore, a detector configured to detect at least a configured wavelength may fail to detect the light when it is blueshifted to a shorter wavelength. In contrast, ZAS optical filters ensure that a specific wavelength is redshifted only to a longer wavelength (by a minimum), and the detector can still detect the light even when it is shifted to a specific wavelength. Therefore, ZAS optical filters are particularly suitable for bandpass filters, detectors, or other optical elements with wavelength cutoff for shorter wavelengths.

[0045] Additionally or alternatively, ZAS optical filters may offer greater durability than HLAS or LAS optical filters. For example, due to their greater number of layers and / or thickness, ZAS filters can exhibit stronger resistance to environmental degradation and / or damage associated with physical impact. However, ZAS filters may not be as miniaturized as HLAS or LAS optical filters, which may make them unsuitable for some miniaturized applications.

[0046] Additionally or alternatively, in other conventional multilayer interferometric filters, an equation relating the effective refractive index of the stack to the incident angle 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 no longer holds, because a ZAS optical filter achieving zero angular shift would mathematically result in an infinite effective refractive index. Therefore, the behavior of ZAS optical filters differs from theoretical mathematical models, achieving zero or near-zero angular shift through a complex multilayer structure rather than through control of the effective refractive index.

[0047] As mentioned above, Figures 3A-3C Provided as an example only. Other examples may be provided. Figures 3A-3C The content described in the text is different.

[0048] Figures 4A-4D This is a characteristic diagram of an example optical filter. For example... Figure 4A As shown, Example 400 of an LAS filter having a given refractive index distribution (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 offset of approximately -13 nm between incident angles of 0 degrees and 30 degrees. Figure 4B As shown, Example 410 of an HLAS filter having a given refractive index distribution (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 offset of approximately -7.4 nm between incident angles of 0 degrees and 30 degrees. Figure 4C As shown, Example 420 of the ZAS filter described herein, having a given refractive index distribution (e.g., a substrate and a set of alternating high (H) and low (L) refractive index layers in a stacked configuration), can have a center wavelength of approximately 940 nm and can exhibit an angular offset of less than approximately 1 nm between incident angles of 0 to 30 degrees. Figure 4C As further shown, the transmittance of the ZAS optical filter remains approximately the same (e.g., approximately 95%) across the range of incident angles from 10 to 30 degrees. Figure 4DExample 430 illustrates a comparison of LAS, HLAS, and ZAS optical filters. As shown, the ZAS optical filter exhibits a lower angular offset than the HLAS and LAS optical filters across an incident angle range of 0 to 30 degrees. Furthermore, the ZAS optical filter can present a lower angular offset than non-LAS optical filters (e.g., a bandpass filter not configured for low angular offset, which has an angular offset of approximately 34 nm across an incident angle range of 0 to 30 degrees). While some embodiments describe an incident angle range of 0 to 30 degrees, it is conceivable that the ZAS optical filter described herein can achieve reduced angular offset relative to other filters across a wider range of incident angles, such as 0 to 40 degrees, 0 to 50 degrees, 0 to 60 degrees, or a greater range.

[0049] As mentioned above, Figures 4A-4D Provided as an example only. Other examples may be provided. Figures 4A-4D The content described in the text is different.

[0050] The foregoing disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Modifications and variations can be made based on the foregoing disclosure, and can also be derived from practice of the embodiments.

[0051] The term "component" as used herein should be broadly understood to mean a combination of hardware, firmware, or software and hardware. It is evident that the systems and / or methods described herein can be implemented in various forms of hardware, firmware, and / or software and hardware combinations. The actual dedicated control hardware or software code used to implement these systems and / or methods does not limit these implementations. Therefore, the operation and behavior of the systems and / or methods described herein do not refer to any specific software code—it should be understood that the systems and / or methods can be implemented using software and hardware based on the description herein.

[0052] As used in this article, the threshold can be defined in context as greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, etc.

[0053] Even if specific combinations of features are listed in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of various embodiments. In fact, many features can be combined in ways not expressly listed in the claims and / or not disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various embodiments includes a combination of each dependent claim with all other claims in the claim set. As used herein, “at least one” refers to any combination of a series of items, including a single item. For example, “at least one of a, b, or c” is intended to cover a, b, c, ab, ac, bc, and abc, as well as any combination with multiple identical items.

[0054] Unless explicitly stated otherwise, no element, action, or instruction used herein should be construed as essential or necessary. Furthermore, the articles “a” and “one” as used herein are intended to encompass one or more items and may be used interchangeably with “one or more.” The article “the” as used herein is intended to encompass one or more items associated with the article “the” and may be used interchangeably with “one or more.” The term “set” as used herein is intended to encompass one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items) and may be used interchangeably with “one or more.” If referring to only one item, the phrase “only one” or a similar expression is used. Furthermore, the terms “have,” “possess,” “have,” etc., as used herein are intended to indicate open-ended terms. Furthermore, unless explicitly stated otherwise, the phrase “based on” is intended to mean “at least partially based on.” Furthermore, as used herein, the term “or” is intended to be inclusive in a series of uses and may be used interchangeably with “and / or” unless explicitly stated otherwise (e.g., in combination with “any” or “only one”).

Claims

1. An optical filter assembly, comprising: An optical filter is disposed on the first side of the substrate. The thickness of the optical filter is greater than the first threshold, and The optical filter is configured to experience a center wavelength offset of less than a second threshold for a specific operating center wavelength and for an incident angle range from 0 degrees to at least a third threshold.

2. The optical filter assembly of claim 1, wherein the first threshold is at least 10,000 nanometers.

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

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

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

6. The optical filter assembly of claim 1, wherein the third threshold is at least 30 degrees.

7. The optical filter assembly of claim 1, further comprising at least one of the following: Anti-reflective filter Long-wavelength passband filter, Short-wavelength passband filter, or Wide passband filter.

8. The optical filter assembly of claim 1, wherein the optical filter is a zero-angle offset ZAS bandpass filter.

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

10. An optical filter, comprising: The filter stack is formed by alternating layers of a first material having a first refractive index and a second material having a second refractive index. The filter stack has a transmittance of at least a first threshold level at the configured center wavelength, and The filter stack is configured to introduce a redshift of less than a second threshold for incident angles between 0 and 30 degrees.

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

12. The optical filter of claim 10, wherein the first material comprises at least one of the following: Amorphous silicon layer, or Silicon hydrogenation layer.

13. The optical filter of claim 10, wherein the second material comprises at least one of the following: silicon oxide layer Titanium oxide layer, tantalum oxide layer, Alumina layer, or Niobium oxide layer.

14. The optical filter of claim 10, wherein the center wavelength of the configuration is in the range of 100 nanometers (nm) to 14000 nm.

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

16. An optical system comprising: Electro-optical components; as well as An optical filter is disposed on the first side of the substrate. The thickness of the optical filter is greater than the first threshold, and The optical filter is configured to experience a center wavelength offset of less than a second threshold for a specific operating center wavelength and for an incident angle range from 0 degrees to at least a third threshold.

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

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

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

20. The optical system of claim 16, wherein the center wavelength shift is a shift towards a shorter wavelength as the incident angle increases.

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