Filter array with reduced stray focused light

Abstract

To provide a favorable filter array with reduced stray focused light.SOLUTION: An apparatus is disclosed comprising an optical filter array (10) including an array of optical filter elements; where each optical filter element has opposing mutually parallel principal faces connected by sidewalls including at least one pair of opposing trapezoidal sidewalls and at least one pair of opposing sidewalls that are not mutually parallel; and where the opposing mutually parallel principal faces of the filter elements collectively define optical entrance and exit apertures of the optical filter array and include interference filters. Further disclosed is a method of illuminating such a filter array.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 62 / 250,272, filed November 3, 2015, the complete disclosure of which is incorporated herein by reference in its entirety.

[0002] The following relates to optical technologies, optical filter technologies, spectroscopic technologies, pricing information delivery technologies, and related technologies. [Background technology]

[0003] Optical interference filters with high spectral selectivity comprise a stack of layers with alternating refractive index values. These filters can be designed to provide passband, stopband, high-pass, low-pass, and notch filter outputs. The optical layers are typically deposited on a substrate plate that is optically transparent for the design-based spectrum, and thus the filter, sometimes referred to as a filter plate, is optically uniform across the area of ​​the plate.

[0004] On the other hand, optical interference filters with different pass or stop bands or cutoff wavelengths in different areas of the plate are useful for various multispectral applications, such as spectrometers or spectral analysis devices. Because it is difficult to controllably vary the layer thickness across the substrate plate during layer deposition, such multispectral filters are sometimes manufactured as so-called "marquetry" filter arrays. To build a marquetry filter array, a set of filter plates with different filter characteristics (e.g., different pass or stop bands and / or bandwidths) are formed by appropriate layer deposition. Each filter plate is designed to be uniform across the area of ​​the plate. The filter plates are then diced to form filter elements in the form of strips, which are then bonded together in a designed pattern to form the marquetry filter array. Two-dimensional filter arrays are manufactured by a similar process, except that the filter plates are diced to form filter elements, which are then bonded together into a desired two-dimensional array.

[0005] Some illustrative multispectral arrays of the type described above are described, for example, in U.S. Publication No. 2014 / 0307309A1 to Downing et al., published October 16, 2014, which is incorporated by reference in its entirety.

[0006] Several improvements are disclosed herein. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Publication No. 2014 / 0307309A1 Summary of the Invention [Means for solving the problem]

[0008] The present disclosure relates to an apparatus comprising an optical filter array including an array of optical filter elements, each optical filter element having opposing parallel major surfaces connected by sidewalls including at least one pair of opposing trapezoidal sidewalls and at least one pair of opposing sidewalls that are not parallel to one another, and the opposing parallel major surfaces of the filter elements collectively define optical entrance and exit apertures of the optical filter array and include an interference filter.

[0009] The present disclosure is also directed to a method of providing the aforementioned filter array and illuminating the optical filter array with converging or diverging light having a local angle that matches the sidewall angle of the sidewalls of the filter elements.

[0010] Additionally, the present disclosure is directed to an apparatus including an optical filter array comprising an array of internal optical filter elements that are not the outermost optical filter elements of the optical filter array, each internal optical filter element having larger and smaller opposing parallel major surfaces connected by sidewalls including at least one pair of opposing trapezoidal sidewalls and at least one pair of opposing sidewalls that are not parallel to one another, the larger major surface of the internal optical filter element comprising a diverging aperture of the optical filter array and the smaller major surface of the internal optical filter element comprising a converging aperture of the optical filter array. The present specification also provides, for example, the following items: (Item 1) An apparatus comprising: an optical filter array comprising an array of optical filter elements; Each optical filter element has opposing parallel major surfaces connected by sidewalls including at least one pair of opposing trapezoidal sidewalls and at least one pair of opposing sidewalls that are not parallel to one another; the opposing parallel major surfaces of the filter elements collectively define an optical entrance aperture and an optical exit aperture of the optical filter array and include an interference filter; Device. (Item 2) 2. The apparatus of claim 1, wherein each filter element is a strip with sidewalls including a pair of opposing trapezoidal end sidewalls and a pair of opposing long sidewalls that are not parallel to one another. (Item 3) Item 3. The apparatus of item 2, further comprising a linear or cylindrical light source having a long axis parallel to a long sidewall of the filter element. (Item 4) 2. The apparatus of claim 1, wherein each filter element includes two pairs of opposing trapezoidal sidewalls, where each pair of opposing trapezoidal sidewalls are not parallel to one another. (Item 5) Item 1, the apparatus further comprising an optical system configured to generate converging or diverging light, wherein opposing side walls of at least one pair of each filter element are aligned with a local angle of the converging or diverging light. (Item 6) 2. The device of claim 1, wherein a major surface of a filter element other than an outermost filter element of the filter array has a larger area at one of the optical entrance opening and optical exit opening than at the other of the optical entrance opening and optical exit opening. (Item 7) Item 2. The apparatus of item 1, wherein the optical filter element comprises a plurality of optical filter elements of different optical filter types defined by different interference filters. (Item 8) Item 1 , the apparatus of item 1 , wherein the interference filter of the optical filter element comprises a passband filter or a notch filter. (Item 9) 1. A method comprising: Providing an optical filter array according to item 1; illuminating the optical filter array with converging or diverging light having a local angle that matches a sidewall angle of a sidewall of the filter elements; A method comprising: (Item 10) An apparatus comprising: an optical filter array comprising an array of interior optical filter elements that are not outermost optical filter elements of the optical filter array; Each internal optical filter element includes larger and smaller opposing parallel major faces connected by sidewalls including at least one pair of opposing trapezoidal sidewalls and at least one pair of opposing sidewalls that are not parallel to one another; An apparatus, wherein a larger major surface of the internal optical filter element comprises a diverging aperture of the optical filter array and a smaller major surface of the internal optical filter element comprises a converging aperture of the optical filter array. (Item 11) Item 11. The apparatus of item 10, wherein each internal optical filter element is a strip with a pair of opposing trapezoidal end sidewalls and a pair of opposing long sidewalls that are not parallel to one another. (Item 12) Item 11. The apparatus of item 10, wherein each internal optical filter element includes two pairs of opposing trapezoidal sidewalls, where each pair of opposing trapezoidal sidewalls are not parallel to one another. (Item 13) Item 11. The apparatus of item 10, further comprising an optical system that generates converging light that enters the optical filter array at the diverging aperture and exits the optical filter array at the converging aperture. (Item 14) Item 11. The apparatus of item 10, further comprising an optical system that generates divergent light that enters the optical filter array at the converging aperture and exits the optical filter array at the diverging aperture.

[0011] These and other non-limiting aspects and / or objects of the present disclosure are more particularly described below. [Brief description of the drawings]

[0012] The following is a brief description of the drawings, presented for purposes of illustrating exemplary embodiments disclosed herein, and not for purposes of limiting same.

[0013] [Figure 1] FIG. 1 diagrammatically shows a cross-sectional side view of a filter array for filtering the focused light, along with ray tracing illustrating the focused light and a photodetector array. [Diagram 2] FIG. 2 shows a schematic cross-sectional side view of the optical filter array of FIG. [Diagram 3] FIG. 3 diagrammatically illustrates a single cross-sectional side view of an exemplary optical filter element of the filter array of FIGS. [Figure 4] Figures 4, 5, 6, and 7 diagrammatically show the front, top, right, and perspective views, respectively, of the filter array of Figures 1 and 2. In Figures 4-7, the number of illustrative optical filter elements has been reduced to a 4 x 4 array to reduce the complexity of the figures. [Diagram 5] Figures 4, 5, 6, and 7 diagrammatically show the front, top, right, and perspective views, respectively, of the filter array of Figures 1 and 2. In Figures 4-7, the number of illustrative optical filter elements has been reduced to a 4 x 4 array to reduce the complexity of the figures. [Figure 6] Figures 4, 5, 6, and 7 diagrammatically show the front, top, right, and perspective views, respectively, of the filter array of Figures 1 and 2. In Figures 4-7, the number of illustrative optical filter elements has been reduced to a 4 x 4 array to reduce the complexity of the figures. [Figure 7] Figures 4, 5, 6, and 7 diagrammatically show the front, top, right, and perspective views, respectively, of the filter array of Figures 1 and 2. In Figures 4-7, the number of illustrative optical filter elements has been reduced to a 4 x 4 array to reduce the complexity of the figures. [Figure 8] Figures 8, 9, 10, and 11 diagrammatically show front, top, right, and perspective views, respectively, of modified filter arrays for light converging or diverging in only one dimension, such as that generated by illustrative linear or cylindrical light sources. As in Figures 4-7, in Figures 8-11 the number of illustrative optical filter elements has been reduced to a 4x4 array to reduce the complexity of the figures. [Figure 9]Figures 8, 9, 10, and 11 diagrammatically show front, top, right, and perspective views, respectively, of modified filter arrays for light converging or diverging in only one dimension, such as that generated by illustrative linear or cylindrical light sources. As in Figures 4-7, in Figures 8-11 the number of illustrative optical filter elements has been reduced to a 4x4 array to reduce the complexity of the figures. [Figure 10] Figures 8, 9, 10, and 11 diagrammatically show front, top, right, and perspective views, respectively, of modified filter arrays for light converging or diverging in only one dimension, such as that generated by illustrative linear or cylindrical light sources. As in Figures 4-7, in Figures 8-11 the number of illustrative optical filter elements has been reduced to a 4x4 array to reduce the complexity of the figures. [Figure 11] Figures 8, 9, 10, and 11 diagrammatically show front, top, right, and perspective views, respectively, of modified filter arrays for light converging or diverging in only one dimension, such as that generated by illustrative linear or cylindrical light sources. As in Figures 4-7, in Figures 8-11 the number of illustrative optical filter elements has been reduced to a 4x4 array to reduce the complexity of the figures. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A more complete understanding of the processes and apparatus disclosed herein may be obtained by reference to the accompanying drawings, which are merely schematic representations for convenience and ease of illustrating existing technology and / or the present developments, and as such are not intended to indicate the relative sizes and dimensions of the assemblies or their components.

[0015] Although specific terms are used in the following description for purposes of clarity, these terms are intended to refer only to the particular structures of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the present disclosure. In the drawings and the description that follows, it should be understood that like numerical designations refer to components of similar function.

[0016] The singular forms "a," "an," and "the" include plural references unless the context clearly indicates otherwise.

[0017] The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes at least the degree of error associated with measurement of the particular quantity). When used in conjunction with a specific value, it should also be considered to disclose that value. For example, the term "about 2" also discloses the value "2" and the range "about 2 to about 4" also discloses the range "2 to 4."

[0018] With reference to FIG. 1, a disadvantage of the parquet-type filter arrays recognized herein is that they are not compatible with many practical optical systems that have a finite focal plane and act on converging or diverging light beams. FIG. 1 illustrates ray tracings for such a system with a focal plane P at a finite position along the optical axis OA. Due to the finite location of the focal plane P, the light passing through the optical system (schematically shown by the illustrative ray L) forms a conical beam with a conical half-angle A as shown in FIG. 1, which converges at the focal plane P. In the illustrative FIG. 1, the ray L travels from left to right on the drawing and is detected by a detector array 8 located in a plane close to the focal plane P, i.e., the ray L is therefore a converging ray. Alternatively, if the light travels away from the finite focal plane, e.g., emanating from a small light source at the focal plane, the light rays may diverge (alternative not shown). In either case, the light rays form either a converging (as shown) or diverging beam.

[0019] Marquetry-type filter arrays are composed of filter elements in the form of strips (for one-dimensional arrays) or blocks (for two-dimensional arrays) cut from a filter plate. A dicing saw produces vertical sidewalls for the strips or blocks. Downing et al., U.S. Publication No. 2014 / 0307309A1, discloses an improvement for use when the angle of incidence of light is not perpendicular to the surface of the filter array. In the design disclosed in Downing et al., U.S. Publication No. 2014 / 0307309A1, the strips or blocks are diced with sidewalls at an angle selected to match the angle of incidence of the light. This reduces light scattering and loss at the boundaries between the filter elements.

[0020] It is recognized herein that, for converging or diverging light, such filter arrays produce optical scattering and losses at the boundaries between adjacent filter elements. This scattering and optical losses cannot be reduced using the approach of Downing et al., U.S. Publication No. 2014 / 0307309 A1, because the angle of incidence of the converging or diverging light is not defined.

[0021] With continuing reference to FIG. 1 and further reference to FIG. 2, the improved optical filter array 10 has optical filter elements 12a, 12b, 12c, 12d, 12e, 12f, 12g, 12h, 12i, 12j with non-parallel sidewalls whose angles are designed to match the local convergence or divergence angles of light rays L for each filter element (optionally excluding the outer sidewalls of the outermost filter elements 12a, 12j, which form the perimeter of the filter array 10). The sidewall joints of adjacent filter elements are at the same local location on the surface of the filter array 10 and therefore have the same sidewall angle. As recognized herein, this matching of neighboring sidewall angles allows the filter elements to be affixed together at the sidewall joints, for example using an adhesive or other bond, to form the filter array 10. By way of example, the sidewall joints of filter elements 12b and 12c have the same sidewall angle, as labeled at interface 14 between filter elements 12b and 12c in FIG.

[0022] As can be further seen in Figures 1 and 2, the sidewall angle increases with increasing distance from the optical axis OA to match the increasing angle of the converging or diverging light beam with increasing distance from the optical axis OA.

[0023] With continued reference to Figures 1 and 2, and with further reference to Figure 3, the sidewalls of a given filter element are not parallel to one another. Rather, the inboard sidewalls of a given filter element have smaller sidewall angles than the outboard sidewalls ("inboard" and "outboard" denote relatively closer to and relatively farther from the optical axis OA, respectively). By way of example, Figure 3 shows filter element 12d in isolation. For filter element 12d, inboard sidewall 16 has a sidewall angle A smaller than that of outboard sidewall 18. O Smaller sidewall angle A compared to I (measured from the direction of the optical axis OA).

[0024] 3, for each filter element (e.g., illustrative filter element 12d), the filter element comprises a transparent substrate or body 20 bounded by four sidewalls 16, 18 (including, in addition to the sidewalls 16, 18, two sidewalls not depicted in the cross-sectional side view of FIG. 3) extending between opposing major surfaces 22, 24. One or both of these major surfaces may include an interference filter, e.g., illustrative major surface 22 of filter element 12d includes an interference filter 26, which may be deposited by techniques such as sputtering, vacuum deposition, plasma deposition, and the like. Interference filter 26 is typically constructed from an engineered stack of layers that provide optical interference to provide a design-based passband, stopband, high-pass, low-pass, or notch filter. The wavelength, full width at half maximum (FWHM), or other spectral characteristics of this interference filter 26 are designed for a particular application. Furthermore, since filter array 10 is typically a multispectral filter, each filter element 12a, 12b, 12c, 12d, 12e, 12f, 12g, 12h, 12i, 12j generally has a different interference filter (although some filter elements may be selected similarly. For example, if filter array 10 is intended to be symmetric about optical axis OA, the interference filters for filter elements 12a, 12j are the same, the interference filters for filter elements 12b, 12i are the same, the interference filters for filter elements 12c, 12h are the same, the interference filters for filter elements 12d, 12g are the same, and the interference filters for filter elements 12e, 12f are the same). Although not shown, an interference filter may additionally or alternatively be included on major surface 24 of filter element 12d.

[0025] The filter elements may generally be designed for any passband or stopband within the ultraviolet, visible, or infrared wavelength ranges. As an illustrative example, the filter elements (or more specifically, the filter element body or substrate, e.g., the filter element body or substrate 20 of the illustrative filter element 12d of FIG. 3) may be made of an optically transparent material, such as glass, sapphire, or another material with suitable transparency within the operating optical range. The interference filter 26 may include alternating layers of tantalum oxide (Ta2O5) and silicon dioxide (SiO2), or more generally, alternating layers of two (or more) materials with different refractive index values. The layers that make up the interference filter 26 are also preferably optically transparent for the operating optical range, but because they are thin layers, some optical absorption within the operating optical range may be acceptable. For example, as another illustrative example, the layers may be metal / metal oxide layers, such as titanium / titanium dioxide (Ti / TiO2). Known techniques for designing interference filters can be employed to design the layer thicknesses for a given passband or notch filter stopband, or to provide desired high-pass or low-pass filtering characteristics.

[0026] 1 and 2 depict filter 10 in a cross-sectional side view. This side view does not capture the three-dimensional shape of the convergent light L or filter array 10.

[0027] With reference to Figures 4-6, this three-dimensional shape is depicted diagrammatically by front (Figure 4), top (Figure 5), and right (Figure 6) views of filter 10, and Figure 7 shows a perspective view of filter 10 within its optical environment, including a converging light beam L and detector array 8 shown in a perspective view. In Figures 4-7, for diagrammatic simplicity, the number of filter elements shown is reduced to a 4x4 array of filter elements. It should be understood that the number of filter elements is a design parameter that is suitably selected based on the desired filter resolution and the total area of ​​the filter array.

[0028] The filter elements have two parallel bases 22, 24 (i.e., the bases 22, 24 are parallel to one another) with the same number of vertices (four vertices for the rectangular bases 22, 24 of the illustrative filter array 10) and are not parallelograms (different sidewall angles, e.g., different angle A for filter element 12d in illustrative FIG. 3). I , A O 3. Each filter element has a truncated pyramidal shape (see particularly illustrative filter element 12d in FIG. 3) with at least two trapezoidal sidewalls 16, 18. The two parallel base sides 22, 24 of the filter elements in the assembled filter array 10 collectively define the optical entrance and exit apertures (or vice versa) of the filter array 10, as best seen in FIGS.

[0029] With continuing reference to Figures 4-7, and with further reference to Figures 8-11, for light beams that diverge or converge in two dimensions, all four sidewalls of the filter elements are trapezoidal sidewalls, as best seen in Figures 4, 6, and 7. In these embodiments, each pair of opposing trapezoidal sidewalls (e.g., sidewalls 16, 18 in Figure 3) are not parallel to one another (i.e., not mutually parallel). On the other hand, for light beams that diverge or converge in only one dimension and are parallel in the orthogonal dimension (e.g., generated by a cylindrical or linear light source 30), as seen in Figures 8-11, to be multispectrally filtered only in the direction of divergence or convergence, the modified filter array 40 has filter elements in the form of strips, each filter element having two end sidewalls 46 that are trapezoidal. trap and the long side wall 46, which is a parallelogram. par In this embodiment, the trapezoidal end side walls 46 trap are opposed side walls that are parallel to each other (i.e., mutually parallel), while the two parallelogram long side walls 46 par are opposed side walls that are not parallel to each other. The linear or cylindrical light source 30 is aligned with the long side wall 46 of the filter element. par Parallel to the trapezoidal end side wall 46 trap It has a major axis 32 that is transverse to the

[0030] 1 and 2, typically, the interior filter elements (i.e., filter elements 12b, 12c, 12d, 12e, 12f, 12g, 12h, 12i, but not the outermost filter elements 12a, 12j of filter array 10) have one major surface (major surface 22 in FIG. 3) that has a larger area than the other major surface (major surface 24 in FIG. 3). The larger area major surfaces of the interior filter elements collectively constitute the diverging aperture 50 (labeled in FIG. 2) of filter array 10. The smaller area major surfaces of the interior filter elements collectively constitute the converging aperture 52 of filter array 10. In FIGS. 1 and 2, the left side of filter array 10 is diverging aperture 50, while the right side of filter array 10 is converging aperture 52. When a filter is applied to converging light (as in illustrative FIG. 1), the diverging aperture is the entrance aperture (i.e., the converging light enters diverging aperture 50) and the converging aperture is the exit aperture (i.e., the converging light exits from converging aperture 52 of filter array 10). Conversely, when a filter is applied to diverging light (as in the embodiment of FIG. 11), the converging aperture (the upper aperture of filter array 40, as shown in FIG. 11) is the entrance aperture and the diverging aperture (not visible in the perspective view shown in FIG. 11) is the exit aperture.

[0031] The outermost filter elements may optionally be "squared off" to have non-sloping peripheral sidewalls for the filter array 10 as a whole (as seen in outermost filter elements 12a and 12j, where the left major face is smaller than the right major face), which may be an exception to the above-described geometry as this may affect the area of ​​the major faces.

[0032] The sidewall angle of the filter element (e.g., angle A for illustrative filter element 12d in FIG. 3) I and A O When designing the filter element 10, the local angle of the diverging or converging light L at the sidewall is taken into account. This angle is preferably the angle in the material of the filter element, not the angle in air, due to the bending of light according to Snell's law. The angle θ of the light ray in the filter element material fe is the angle θ of the light ray in the air according to Snell's law, i.e., sin(θ)=nfe sin(θ fe ), wherein n fe is the refractive index of the filter element, and the surroundings are assumed to be air, vacuum, or another surroundings with refractive index n=1. For example, if the local ray angle is θ=15° at the filter element sidewall and n fe = 1.5, [ka] The side walls in this tournament are 10 o (The surroundings are preferably selected as n different from 1. ambient If the fluid is oil or some other material with ambient sin(θ)=n fe sin(θ fe ). The filter elements may be fabricated in a variety of ways, such as by first dicing a parallelepiped filter element, then grinding the individual diced filter elements, forming the sidewall angles, etc. Alternatively, dicing can employ a suitably angled cutting saw or an angled wafer mounting jig.

[0033] It is to be understood that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Further, it is to be understood that various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.

Claims

[Claim 1] The invention described in this specification.

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