Free-form Offner spectrometer

Abstract

The spectrometer is configured to form a spectrally resolved image of the electromagnetic radiation from the electromagnetic radiation source. The spectrometer can include a light guiding device configured to guide the electromagnetic radiation along an optical path. The light guiding device can include a first prism positioned in the optical path. The light guiding device can further include focusing optics. The first prism can have at least one freeform prism face including at least some cylindrical curvature having a freeform polynomial term formed thereon, and the face can be a substantially cylindrical, substantially non-cylindrical, or substantially flat surface having the freeform polynomial term formed thereon.

Description

[Technical Field]

[0001] The present invention relates to a freeform Offner spectrometer. [Background Art]

[0002] In optical applications, groups and arrangements of prisms, gratings, and / or mirrors are often used to direct, separate, and / or combine electromagnetic radiation within optical systems that serve a variety of different purposes. For example, in hyperspectral imaging, wide-field spectrometers are often used to acquire, image, and / or analyze spectral components of electromagnetic radiation from an object. The spectrometer directs electromagnetic radiation from the object through an optical system provided with dispersive elements (e.g., prisms, mirrors, gratings) to split the light into different spectral components, and directs the light to a capture sensor configured to image / analyze the spectral components contained in the light from the object. Such analysis can be used to determine properties of the object, such as chemical composition and other properties.

[0003] In order for a spectrometer to accurately image / analyze the spectral components of an imaged object, it is desirable for the spectrometer to have high-quality imaging characteristics. For manufacturing a spectrometer with a large, high-resolution, well-corrected image field, it is desirable to optimize not only image quality, resolution, distortion correction, light throughput, and total dispersion, but also the mass and volume of the spectrometer. Improved designs for optical elements and spectrometers are continually being developed to produce spectrometers with improved image quality, distortion correction, throughput, and other imaging characteristics. [Brief Description of the Drawings]

[0004] Features and advantages of the present technology will become apparent from the following detailed description when read in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the present technology.

[0005] [Figure 1] This is a schematic diagram of a spectrometer according to an example of the disclosure. [Figure 2a] This is a front view of a lens configuration according to an example of the disclosure. [Figure 2b] This is a cross-sectional view of an exemplary lens according to the examples of the present disclosure. [Figure 2c] This is a cross-sectional view of an exemplary lens according to the examples of the present disclosure. [Figure 2d] This is a cross-sectional view of an exemplary lens according to the examples of the present disclosure. [Figure 3a] This is a front view of a lens configuration according to an example of the disclosure. [Figure 3b] This is a cross-sectional view of an exemplary lens according to the examples of the present disclosure. [Figure 3c] This is a cross-sectional view of an exemplary lens according to the examples of the present disclosure. [Figure 3d] This is a cross-sectional view of an exemplary lens according to the examples of the present disclosure. [Figure 3e] This is an exemplary cross-sectional view of a lens according to the present disclosure, on which freeform features are formed. [Figure 3f] This is an exemplary cross-sectional view of a lens according to the present disclosure, on which freeform features are formed. [Figure 3g] This is an exemplary cross-sectional view of a lens according to the present disclosure, on which freeform features are formed. [Figure 3h] This is a cross-sectional view of an exemplary lens according to the example of the present disclosure, on which freeform features are formed. [Figure 3i] This is a cross-sectional view of an exemplary lens according to the example of the present disclosure, on which freeform features are formed. [Figure 4] This is a schematic diagram of a spectrometer according to an example of the disclosure. [Figure 5] This is a schematic diagram of a spectrometer according to an example of the disclosure. [Figure 6] This figure shows a method for configuring an optical guide device according to an example of the present disclosure. [Figure 7a] This is a diagram showing a Ferry spectrometer. [Figure 7b] This is a diagram of a free-form spectrometer. [Figure 8] Figures a and b show various experimental results comparing the distortion of a ferry spectrometer with that of a freeform spectrometer. [Figure 9] Figures a and b show various experimental results comparing the distortion of a ferry spectrometer with that of a freeform spectrometer. [Modes for carrying out the invention]

[0006] Illustrative embodiments are referenced here, and specific language is used to describe them in this specification. However, it should be understood that this is not intended to limit the scope of the Art.

[0007] As used herein, the term “substantially” refers to the extent of a complete or near-complete action, feature, characteristic, state, structure, item, or result. For example, “substantially” enclosed means that the object is completely or nearly completely enclosed. The exact acceptable range of deviation from absolute completeness may vary depending on the specific circumstances. However, generally speaking, approaching completeness results in the same overall outcome as if absolute and complete completeness had been achieved. The use of “substantially” also applies when used in a negative sense to refer to the complete or near-complete absence of an action, feature, characteristic, state, structure, item, or result.

[0008] As used herein, “adjacent” means that two structures or elements are in close proximity. In particular, elements identified as “adjacent” may be either touching or connected. Such elements may be close or near to each other, even if they are not in contact with each other. The exact degree of proximity may depend on the specific context.

[0009] A preliminary overview of the concept of the present invention is given below, followed by a more detailed description of specific embodiments. This preliminary overview is intended to help the reader more quickly understand the embodiments, but is not intended to identify any important or essential features of the embodiments, nor is it intended to limit the scope of the claims.

[0010] This specification discloses an optical guiding device configured to guide electromagnetic radiation along an optical path. The optical guiding device may include a first prism positioned in the optical path. The optical guiding device may further include a focusing optical system positioned in the optical path. The first prism may include at least one freeform prism surface.

[0011] Furthermore, this specification discloses a spectrometer configured to form a spectrally resolved image of electromagnetic radiation from a source. The spectrometer may include a slit configured to receive electromagnetic radiation. The spectrometer may further include an optical guide device positioned in the optical path downstream from the slit. The optical guide device may be configured to guide electromagnetic radiation along the optical path. The optical guide device may include a first prism positioned in the optical path. The optical guide device may further include a focusing optical system positioned in the optical path. The first prism may comprise at least one freeform prism surface having at least some degree of cylindrical curvature with a freeform polynomial term formed thereon. The freeform prism surface may include at least one of cylindrical, non-cylindrical, or substantially planar surfaces.

[0012] Further disclosed herein is a method of configuring a light guide device. The method may comprise the step of configuring the light guide device to include a first prism in an optical path. The method may further comprise the step of configuring the light guide device to include a condensing optical system positioned in the optical path. The method may further comprise the step of configuring the first prism to include at least one freeform prism surface having at least a certain degree of cylindrical curvature with a freeform polynomial term formed thereon. The freeform prism surface may comprise at least one of a cylindrical surface, a non-cylindrical surface, or a substantially planar surface.

[0013] Further disclosed herein is an optical system. The optical system may comprise an electromagnetic radiation inlet configured to receive electromagnetic radiation from a source. The optical system may further comprise a light guide device configured to guide electromagnetic radiation along an optical path from the electromagnetic radiation inlet to a focal plane. The light guide device may comprise a first prism positioned in the optical path. The light guide device may further comprise a condensing optical system positioned in the optical path. The first prism may comprise at least one freeform prism surface comprising at least a certain degree of cylindrical curvature with a freeform polynomial term formed thereon. The freeform prism surface may comprise at least one of a cylindrical surface, a non-cylindrical surface, or a substantially planar surface.

[0014] To further illustrate the present technology, examples are provided herein with reference to the drawings. Referring to Figure 1, an optical system according to an example of the present disclosure is shown. The optical system may be a spectrometer 100, which is operable to collect light from an object 101 for imaging / analysis by the spectrometer 100. The spectrometer 100 includes a light guide device 102, which may be configured to direct electromagnetic radiation and split the electromagnetic radiation into various spectral components.

[0015] The light guide device 102 can include a condensing optical system 104, and can include one or more reflective surfaces. For example, the condensing optical system 104 can be configured as an Offner relay including a first reflective surface 108, a second reflective surface 110, and a third reflective surface 112, each of which can be configured to receive electromagnetic radiation and reflect it in a desired direction. As shown in FIG. 1, the first reflective surface 108 and the third reflective surface 112 can be formed on a single mirror 114. The first reflective surface 108 and the third reflective surface 112 may not be separate discrete surfaces, but may alternatively be different sections of a single continuous reflective surface 115 each formed on the mirror 114. In other words, in the spectrometer 100, the first reflective surface 108 and the third reflective surface 112 are not separated from each other, which means that the first reflective surface 108 and the third reflective surface 112 are different parts of one single continuous reflective surface. The first reflective surface 108 and the third reflective surface 112 are not separate reflective surfaces even if such separate reflective surfaces are in contact or formed on the same substrate. Instead, the first reflective surface 108 and the third reflective surface 112 are formed such that there is no discontinuity in the reflective surface 115, and there is no discontinuity between the first reflective surface 108 and the third reflective surface 112. The second reflective surface 110 can be formed on a second mirror 116 spaced apart from the mirror 114 in the configuration of the Offner relay. Alternatively, the second mirror 116 can be a diffraction grating instead of a mirror. As described below with reference to FIG. 5, the condensing optical system can be a condensing optical system other than an Offner relay, such as the Dyson spectrometer shown in FIG. 5.

[0016] The optical guide device 102 may further comprise a first prism 118 including a first surface 118a and a second surface 118b. The optical guide device 102 may further comprise a second prism 120 including a first surface 120a and a second surface 120b. As shown in Figure 1, the first prism 118 and the second prism 120 may be prisms having one or more surfaces (e.g., 118a, 118b, 120a, and 120b) configured to collimate, reflect, refract, and / or direct incident light. It should be understood that either the first prism 118 or the second prism 120 may be a Ferry prism, a standard prism, or other prism, and the other may be the same, similar, or different type of prism. A standard prism, such as a Ferry prism, may have a planar, spherical, cylindrical, aspherical, non-cylindrical, or freeform surface. Any number of additional standard or Ferry prisms having planes, spheres, cylindrical surfaces, aspherical surfaces, non-cylindrical surfaces, and / or freeform surfaces can be added.

[0017] The optical guide device 102 includes various components (e.g., prism 118, mirror 114, mirror 116, and prism 120) that can define the optical path to which electromagnetic radiation is directed. As shown in Figure 1, the optical path can be as follows: Light incident on the first surface 118a of the first prism 118 can pass through the first prism 118 and exit from the second surface 118b of the first prism 118. Light from the first prism 118 can be directed toward the first reflecting surface 108 of the focusing optical system 104. The first reflecting surface 108 can be located in the optical path downstream from the first prism 118 and can reflect light from the first prism 118 toward the second reflecting surface 110 of the focusing optical system 104. The second reflecting surface 110 of the focusing optical system 104 can direct light toward the third reflecting surface 112 of the focusing optical system 104, which is located in the optical path downstream from the second reflecting surface 110. Light incident on the third reflective surface 112 can be reflected towards the second prism 120, which is positioned in the optical path downstream from the third reflective surface 112. The light can be incident on the first surface 120a of the second prism 120, pass through the second prism 120, and exit from the second surface 120b of the second prism 120.

[0018] The optical guide device 102 can be used as an optical guide device within the spectrometer 100. The spectrometer 100 may further include a slit 103 that functions as an electromagnetic radiation inlet, through which light 122a from a source or object 101 enters the spectrometer 100. Alternatively, the slit can be a beam slicer. Light 122b from the slit 103 can travel along the optical path to the optical guide device 102, specifically to the first prism 118. Light incident on the first surface 118a of the first prism 118 can pass through the first prism 118 and exit as light 122c from the second surface 118b of the first prism 118. Light 122c can be directed toward the first reflective surface 108 of the focusing optical system 104, which can reflect the light 122c from the first prism 118 toward the second reflective surface 110 of the focusing optical system 104 as light 122d. The second reflective surface 110 of the focusing optical system 104 can direct light 122d as light 122e towards the third reflective surface 112, which is located in the optical path downstream from the second reflective surface 110. Light 122e incident on the third reflective surface 112 can be reflected as light 122f towards the second prism 120, which is positioned in the optical path downstream from the third reflective surface 112. Light 122f can be incident on the first surface 120a of the second prism 120, pass through the second prism 120, and be emitted as light 122g from the second surface 120b of the second prism 120.

[0019] Next, the light 122g can travel to and be incident on the reflective surface 124 of a reflective field corrector 126 (e.g., a field flattener) positioned downstream from the second prism 120 and configured to provide correction to the incident light 122g to ensure a high-quality, high-resolution, well-corrected field for imaging / analysis by the spectrometer 100. The light 122h reflected by the field corrector 126 can then travel to a focal plane 128 configured to receive spectrally separated light in a well-corrected field or image. The focal plane 128 may include a capture sensor 130 configured to analyze light or capture and image it for later analysis, such as a CCD imaging sensor, a CMOS imaging sensor, or any other sensor or capture device. Devices, sensors, or other objects located within the focal plane 128 are not intended to be limited in any way by this disclosure.

[0020] As shown in Figure 1, spectrometer 100 is a prism-based spectrometer including prisms 118 and 120, and reflectors 108, 110, and 112. Alternatively, the spectrometer may be a diffraction grating-based spectrometer, which includes a diffraction grating to direct and split the light. However, diffraction grating spectrometers have low optical efficiency and require complex order-sorting filters that are difficult to manufacture. Therefore, diffraction grating-based spectrometers tend to negatively impact several desirable image quality metrics, such as image quality, modulation transfer function (MTF), optical transfer function (OTF), spot size, wavefront error, optical throughput, total dispersion, and image distortion. In contrast, prism-based spectrometers, such as the spectrometer described herein, offer significant performance advantages over diffraction grating-based spectrometers, including improvements in each of the image quality metrics listed above. Modern optical design, including computer-aided design of lenses, prisms, mirrors, and their surfaces, enables the manufacture of highly specialized and unique surfaces on lenses, mirrors, and prisms, allowing for the provision of precisely image-corrected and high-resolution images from the spectrometer. In other words, the spectrometer described herein provides hyperspectral imaging with a well-corrected imaging field of desired size.

[0021] In spectrometers such as spectrometer 100, optical elements and their surfaces can be designed and manufactured to have uniquely highly specialized surfaces in order to provide high-quality, large-scale, and well-corrected imaging. For example, prisms 118 and 120 can be designed and manufactured to include one or more free-form surfaces, which are further detailed below.

[0022] The surfaces of lenses, mirrors, and prisms can be of several types and designs. In one example, an optical element with a spherical surface can be manufactured. Figure 2a shows a front view of an exemplary optical element 200 (e.g., a surface, lens, mirror, or prism) having a circular contour. An example of a spherical optical element 200 is shown in a cross-sectional view of an example of optical element 200a shown in Figure 2b. The cross-section can be taken along any diameter of the optical element 200 (e.g., line AA, BB, CC, or DD, or any other arbitrary diameter). The spherical surface 202a may be characterized by having a consistent radius of curvature across the entire surface, such that the surface of the optical element 200a is a partial cross-section of a geometric sphere. The spherical surface 202a may exhibit rotational symmetry across the entire surface and may be symmetric with respect to any diameter of the optical element 200a (e.g., the diameter specified and shown in Figure 2a, and any other arbitrary diameter that bisects the optical element).

[0023] The optical element 200 may also include an aspherical surface. An example of an aspherical surface of the optical element 200 is shown in the cross-sectional view of the example optical element 200b shown in Figure 2c. The cross-section can be taken along any diameter of the optical element 200 (e.g., line AA, BB, CC, or DD, or any other arbitrary diameter). The aspherical surface is characterized by its non-spherical and non-cylindrical shape. Unlike a sphere, the aspherical surface has a radius of curvature that varies from the center of the optical element 200b to the edge of the optical element 200b. However, like a sphere, the aspherical surface also exhibits rotational symmetry. As shown in Figure 2c, the spherical surface 202b can exhibit rotational symmetry across its entire surface and can be symmetric with respect to any diameter of the optical element 200b (e.g., the diameter specified and shown in Figure 2a, and any other arbitrary diameter that bisects the optical element).

[0024] Furthermore, those skilled in the art will understand that a cylindrical surface 202d can be formed on the optical element 200a having the radius of curvature shown in Figure 2b, but lacking rotational symmetry over the entire surface. In other words, the cylindrical surface of the optical element is characterized by having curvature in one axis (e.g., line AA) and being flat with respect to a perpendicular axis (e.g., line CC). This gives the cylindrical optical element the unique property of functioning as a lens or focusing element only in one axis. The cylindrical lens forms a line focus rather than a point focus. For example, a cylindrical surface 202d can be formed on the optical element 200. However, the cylindrical surface may be symmetric only with respect to a specific diameter, such as line CC and line AA perpendicular to line CC, and may be asymmetric with respect to lines BB and DD. Similarly, a non-cylindrical surface 202e can be formed on the optical element 200 and may have the same symmetry relationship with respect to line CC and line AA perpendicular to line CC, and may be asymmetric with respect to lines BB and DD of the optical element 200.

[0025] Optical element 200 can be configured as an example of optical element 200c. As shown in Figure 2d, optical element 200c may have a freeform surface 202c. In contrast to aspherical, spherical, cylindrical, and non-cylindrical surfaces 202a, 202b, 202d, and 202e, the freeform surface 202c can be specifically designed and highly customized to include curvature with peaks P and valleys V, and / or other features formed on its surface that are not symmetrical on the surface. In other words, the freeform surface may lack rotational symmetry and may also lack symmetry with respect to any diameter of optical element 200c. It should be understood that the freeform polynomial terms may be formed on substantially spherical, cylindrical, or flat surfaces, which are different from the freeform terms formed on the surface.

[0026] While Figure 2d shows an exemplary surface curvature, it should be understood that any cross-section of the optical element 200c taken along any diameter (e.g., diameters AA, BB, CC, and DD shown in Figure 2a) can have a different contour than the surface 202c shown in Figure 2d. With the assistance of computer design and manufacturing, freeform surfaces can be formed or imparted to lenses, mirrors, and prisms, providing highly localized and customized features and enabling precise image and light correction by specific and predictable quantities. Using freeform surfaces, it becomes possible to manufacture mirrors, lenses, and / or prisms with highly specific and unusual geometric shapes that are nearly flat while providing desired image correction. Because freeform surfaces can have highly customized geometric shapes defined by custom-tuned polynomials (e.g., defining the shape and contour along the x, y, and z axes), specifically tailored image correction within a very specific region of the image is possible. Furthermore, the highly specific surface geometric shape of a freeform surface allows for the application of highly specific correction amounts to the image without exceeding or falling below the desired correction amount. For example, by enabling odd-order polynomial terms, such as cubic or quintic terms, and special shapes on the surfaces of prisms, lenses, or mirrors, image problems such as coma can be corrected without inducing astigmatism or anamorphic distortion. In other words, nearly flat freeform surfaces make it possible to correct aberrations and distortions in multiple images, even by very small amounts, without further inducing undesirable image distortion.

[0027] Similar to the example of the circular optical element in Figure 2a, other optical elements with various different surfaces can also be manufactured. For example, a front view of an optical element 300 having a rectangular or square contour is shown in Figure 3a. Similar to optical element 200, optical element 300 can be formed by any of the following: a spherical surface 302a, an aspherical surface 302b, a cylindrical surface 302d, and a non-cylindrical surface 302e, symmetric with respect to lines EE and FF. The cylindrical surface of the optical element is characterized by having curvature in one axis (e.g., line EE) and being flat in the orthogonal axis (e.g., line FF). This gives the cylindrical optical element the unique property that it functions as a lens or focusing element only in one axis. A cylindrical lens forms a line focus rather than a point focus.

[0028] Similar to the optical element 200, the optical element 300 can also be formed to have a free-form surface 302c. In contrast to the aspherical, spherical, cylindrical, and non-cylindrical surfaces 302a, 302b, 302d, and 302e shown in Figures 3B and 3C, respectively, the free-form surface 302c can be specifically designed and highly customized on the optical element 300 to include curvature with peaks P and valleys V, and / or other features formed on its surface that are not symmetrical on the surface with respect to line EE or line FF. In other words, the free-form surface 302c can lack rotational symmetry and further lack symmetry with respect to a line bisecting the optical element 300. While an exemplary surface curvature is shown in Figure 3d, it should be understood that any cross-section of the optical element 300 taken along any cutting line passing through the optical element 300 may have a different contour from the surface 302c shown in Figure 3d.

[0029] With the assistance of computer design and manufacturing, freeform surfaces can be formed or imparted to lenses, mirrors, and prisms, providing highly localized and customized features that enable precise image and light correction in specific and predictable quantities. Using freeform surfaces, it becomes possible to manufacture mirrors, lenses, and / or prisms with specific geometric shapes that are nearly flat yet provide desired image correction. For example, by enabling odd polynomial terms and special shapes on the surface of prisms, lenses, or mirrors, image problems such as coma can be corrected without inducing astigmatism or anamorphic distortion. In other words, nearly flat freeform surfaces allow for the correction of aberrations and distortions in multiple images without further inducing undesirable image distortion.

[0030] It should be understood that freeform polynomial terms and shapes can be formed on substantially spherical, cylindrical, or flat surfaces, which are different from freeform terms formed on a surface. For example, Figures 3e to 3i show freeform portions on a lens having shapes corresponding to substantially spherical, cylindrical, or flat shapes. For example, Figure 3e shows a cross-section of a substantially spherical lens 310a taken along the axis of the lens (e.g., line EE in Figure 3a). Figure 3f shows a cross-section of a substantially spherical lens 310a taken along the orthogonal axis of the lens (e.g., line FF in Figure 3a). In the case of a substantially spherical lens 310a, it should be understood that the lens exhibits substantially the same radius of curvature at any position along the spherical contour of the lens 310a. As shown, the lens 310a may have a substantially spherical shape 312a on the lens 310a, and the freeform portion 314a or freeform polynomial is formed on the substantially spherical shape 312a of the lens 310a.

[0031] Figure 3g shows a cross-section of a substantially cylindrical lens 310b taken along the axis of the lens (e.g., line EE in Figure 3a). Figure 3h shows a cross-section of a substantially spherical lens 310b taken along the orthogonal axis of the lens (e.g., line FF in Figure 3a). As shown in Figure 3g, a substantially cylindrical lens 310b can exhibit a radius of curvature only along one axis of the lens 310b (e.g., line EE in Figure 3a), as shown in Figure 3g, but the orthogonal axis (e.g., line FF in Figure 3a) has substantially no curvature, as shown in Figure 3h. As illustrated, lens 310a can have a substantially cylindrical shape 312b on lens 310b, and a freeform portion 314b or freeform polynomial can be formed on the substantially cylindrical shape 312b of lens 310b.

[0032] Furthermore, Figure 3i shows a cross-section of a substantially flat lens 310c. As shown in Figure 3i, a substantially flat lens 310c may exhibit substantially no curvature along the flat shape 312c of the lens 310c, as shown in Figure 3i. As illustrated, the lens 310c may have a substantially flat shape 312c on top of the lens 310b, and a freeform portion 314c or freeform polynomial may be formed on the substantially flat shape 312c of the lens 310c. Although the flat shape 312c, cylindrical shape 312b, and spherical shape 312a are shown as discrete layers or surfaces in the figure, it should be understood that this simply means that shapes 312a-c represent the substantially general shape of the lens, and not that they represent separate surfaces or layers of the lens. Instead, it should be understood that freeform portions 314a-c can be formed on lenses of any shape.

[0033] In the spectrometers 100 / 400, optical guide devices 102 / 402, and focusing optical systems 104 / 404 described herein, freeform surfaces can be formed with extremely near-flatness by only slight variations in the peaks or valleys of the surface due to polynomial terms in the equation defining the freeform surface. In such freeform surfaces of the Disclosure, most or all of the correction to the image can be attributed to the freeform polynomial terms rather than to any radius of curvature of any element. For example, prisms 118 and 120 can be ferry prisms having radii of curvature common to ferry prisms. However, it will be understood that one or more freeform surfaces may have substantially cylindrical or non-cylindrical surfaces, and that their surfaces have at least some degree of cylindrical curvature in a uniaxial direction (e.g., line EE), are flat in orthogonal directions (e.g., line FF), and form line foci rather than point foci.

[0034] Since the image correction is due to the freeform term rather than the radius of curvature of prisms 118 and 120 (which is common in ferry prisms with spherical surfaces), the freeform surfaces of prisms 118 and 120 can be formed on one or more surfaces, such as the substantially flat surface of prisms 118 and 120 (i.e., the surface is not flat or planar but contains a small degree of cylindrical or non-cylindrical curvature (almost zero)), a cylindrical surface, or a non-cylindrical surface. Similarly, the surfaces of mirror 114, second mirror 116, field corrector 126, surface 408, and surface 412 can also have freeform surfaces formed on them to ensure that most or all of the image correction is performed by the freeform polynomial term rather than by any curvature or radius of the respective elements.

[0035] According to the principles described herein, in order to improve image correction in an Offner spectrometer, one or more of the prisms 118 and 120 may have one or more freeform surfaces that are substantially cylindrical, substantially non-cylindrical, or substantially flat, having freeform polynomial terms formed thereon, as opposed to having a spherical surface on which freeform polynomial terms are formed. More than one surface of a prism may consist of substantially cylindrical, substantially non-cylindrical, or substantially flat surfaces having freeform polynomial terms thereon, but not all prisms are required to include one or more such surfaces. The shape and configuration of the prism surfaces may be any shape or configuration, but are not particularly limited by this disclosure, and may instead have freeform polynomial terms formed thereon.

[0036] Therefore, to improve imaging and light directivity within the spectrometer 100, free-form surfaces (e.g., substantially cylindrical, substantially non-cylindrical, or substantially flat surfaces having free-form polynomial terms formed thereon) can be formed on the prisms 118 and 120 to improve image quality, correct image distortion and aberrations, and provide a highly corrected image from the spectrometer. An example of quantifying experimental data collected for the improved image quality and corrected image distortion of the spectrometer disclosed herein is described. In the above example, an Offner spectrometer including a ferry prism having a spherical surface ("ferry-offner") is compared to an Offner spectrometer of the type shown in Figure 1 ("free-form-offner") where the ferry prism has a free-form surface formed thereon. Figure 7a shows an example of a ferry-offner, with ferry prisms 718 and 720 having spherical surfaces 718a, 718b, 720a, and 720b. Figure 7b shows an example of a freeform offner, and freeform prisms 728 and 730 according to the principles of the present disclosure, each prism having one face of the XY polynomial type and one flat (plano) face.

[0037] Both the ferry offner and the freeform offner use a combination of a first reflective surface 108 and a third reflective surface 112 formed on a single mirror 114 as a continuous freeform surface as described herein. Both designs are constructed to cover a field of view of 40 mm with an f-number of f / 7.7 and to cover the spectrum from 400 nm to 700 nm. In the freeform offner spectrometer, the spectrometer is designed such that each ferry prism (e.g., 118 and 120) has one surface that is an XY polynomial type freeform surface (e.g., 118a or 118b, and 120a or 120b), and one planar surface (e.g., another 118a or 118b, and another 120a or 120b).

[0038] The results obtained from experimental data for both ferry-offners and free-form offners are as follows: Compared to ferry-offners, free-form offners showed 3.5 times better wavefront error correction, 33% better smile distortion correction, 30% better keystone distortion correction, and less than 1% anamorphic distortion, compared to 8% for ferry-offners. Figures 8A to 9B show the results of various distortions and errors when comparing ferry-offners with free-form offners. Figure 8a shows the smile distortion that appeared when comparing free-form offners with ferry-offners. Figure 8b shows the keystone distortion that appeared when comparing free-form offners with ferry-offners. Figure 9a shows the wavefront errors that appeared in the red, green, yellow, and blue wavelengths for ferry-offners. Figure 9b shows the wavefront errors that appeared in the red, green, yellow, and blue wavelengths for free-form offners.

[0039] It should be understood that the spectrometers and optical devices of this disclosure are not limited to the freeform offner configurations described in the experimental results above. Other configurations are possible and contemplated within the scope of the principles of this disclosure. One or more of the surfaces 118a and 118b of the first prism 118 may be formed as a freeform surface (e.g., substantially cylindrical, substantially non-cylindrical, or substantially planar) to provide correction to the light traveling within the spectrometer. One or more of the surfaces 120a and 120b of the second prism 120 may be formed as a freeform surface (e.g., substantially cylindrical, substantially non-cylindrical, or substantially planar) to provide further correction to the light traveling within the spectrometer. According to the above disclosure, the first prism 118 and the second prism 120 may be ferry prisms having one or more freeform surfaces (e.g., substantially cylindrical, substantially non-cylindrical, or substantially planar) formed thereon. Furthermore, only one of the Ferry prisms, the first prism 118 and the second prism 120, may have a single free-form surface, while the other prism does not have a free-form surface. It will be understood that, in order to achieve the advantage of this disclosure of limiting the complexity of manufacture, only one free-form surface may be used on one of the prisms. However, if it is desirable to achieve the advantage of this disclosure, any number of additional free-form surfaces may be formed on the surfaces of any number of prisms.

[0040] Furthermore, a free-form surface can be formed on the mirror 114. As shown in Figure 1, the mirror 114 can be a single mirror 114 containing a single continuous free-form surface 115. Having a single continuous free-form surface 115, the mirror 114 can be surface-treated to include two distinct parts of the single continuous free-form surface 115 (for example, a first reflective surface 108, which is one part of the continuous free-form surface 115, and a third reflective surface 112, which is the other part of the continuous free-form surface 115). This is in contrast to certain Offner relay imaging systems where the first and third reflective surfaces are separate discrete surfaces, even if such discrete surfaces are formed on a common substrate or if such discrete surfaces are in contact with each other. The first reflective surface 108 can be a free-form surface configured to reflect light to the surface 110 of the mirror 116, and the third reflective surface 112 can be a free-form surface configured to receive light from the mirror 116 and reflect the light to the second prism 120.

[0041] By forming a single continuous freeform reflective surface 115 that functions as both the first reflective surface 108 and the third reflective surface 112, advantages over conventional separate reflective surfaces in an Offner relay are obtained. For example, by limiting the amount of adjustment and motion that can occur between the first reflective surface 108 and the third reflective surface 112, the first and third reflective surfaces can be correctly positioned relative to each other, reducing the possibility of misalignment. This is achieved by manufacturing both the first reflective surface 108 and the third reflective surface 112 as a single surface. By manufacturing as a single surface, the first reflective surface 108 and the third reflective surface 112 are clearly aligned and fixed relative to each other, being part of the same single surface. Because they are fixed relative to each other in this way, the first reflective surface 108 and the third reflective surface 112 cannot be misaligned, as they are formed from a single piece of glass or metal. In other words, the first reflective surface 108 and the third reflective surface 112 can be manufactured as one large mirror rather than two small mirrors during production. Furthermore, by forming a single mirror to provide both the function of a first and third reflecting surface, the manufacturing process for producing the mirrors and reflecting surfaces of a spectrometer can be simplified and minimized.

[0042] The surface 110 of the mirror 116 is not intended to be limited in any way by the present disclosure. The reflective surface 110 of the mirror 116 can be any type of surface, including but not limited to spherical, aspherical, cylindrical, non-cylindrical, and freeform surfaces.

[0043] As further shown in Figure 1, the spectrometer 100 may include a reflective field corrector 126, positioned downstream of the second prism 120, which may be configured to correct the incident light 122g and reflect the light toward the focal plane 128. The reflective surface 124 of the reflective field corrector 126 may be any type of surface, including but not limited to spherical, aspherical, cylindrical, non-cylindrical, or freeform surfaces. The reflective field corrector 126 may be a folding optical component, such as a folding mirror. The field corrector 126 can correct residual field aberrations, also known as aberrations that vary across the field of view, including curvature and field-dependent astigmatism.

[0044] From the above disclosure, it will be understood that any combination of surfaces included in the spectrometer 100, the focusing optical system 104, and the optical guide device 102 can be free-form surfaces (for example, substantially cylindrical, substantially non-cylindrical, or substantially planar surfaces having free-form polynomial terms formed thereon). For example, any element in the optical guide device may include one or more free-form surfaces.

[0045] In the first example, only the first prism 118, the focusing optical system 104, and the optical guide device 102 of the spectrometer 100 have one or more freeform surfaces (e.g., substantially cylindrical, substantially non-cylindrical, or substantially planar surfaces having freeform polynomial terms formed thereon). The first surface 118a may be a freeform prism surface, or the second surface 118b may be a freeform surface, or both surfaces 118a and 118b may be freeform surfaces.

[0046] In the second example, only the second prism 120, the focusing optical system 104, and the optical guide device 102 of the spectrometer 100 have one or more freeform surfaces. The first surface 120a can be a freeform prism surface, or the second surface 120b can be a freeform surface, or both surfaces 120a and 120b can be freeform surfaces.

[0047] In the third example, only the mirror 114, focusing optical system 104, and optical guide device 102 of the spectrometer 100 have one or more freeform surfaces. The first reflective surface 108 may be a freeform surface, or the third reflective surface 112 may be a freeform surface, or both reflective surfaces 108 and 112 may be freeform surfaces. Furthermore, reflective surfaces 108 and 112 may also be formed from a single continuous freeform reflective surface, as described elsewhere in this specification.

[0048] In another example, the surface 110 of the second mirror 116 can be a freeform surface. In yet another example, the surface 124 of the field corrector 126 can be a freeform surface.

[0049] This disclosure will be understood to mean that, without limitation, any combination of surfaces described and illustrated in the spectrometer 100, the focusing optical system 104, and the optical guide device 102 can be free-form surfaces, as long as one or more of the elements of the spectrometer 100, the focusing optical system 104, and / or the optical guide device 102 include at least one free-form surface.

[0050] An alternative configuration for spectrometer 400 is shown in Figure 4. Elements having the same configuration and function as spectrometer 100 are labeled in Figure 4 by the same numbers used for the same elements in Figure 1. As shown in Figure 4, the optical guide device 402 and focusing optical system 404 can be modified relative to optical guide device 102 and focusing optical system 104 by using two discrete reflective surfaces / mirrors, the first reflective surface 408 and the third reflective surface 412. Two discrete reflective surfaces 408 and 412 are used instead of a single continuous reflective surface 115, but the optical paths and functions of each spectrometer 400, optical guide device 402, and focusing optical system 404 can remain the same. However, in the exemplary spectrometer 400, the first reflective surface 408 and the third reflective surface 412 can also be separate to provide adjustability between the alignment and angle of the first reflective surface 408 and the third reflective surface 412.

[0051] From the above disclosure, it will be understood that any combination of surfaces included in the spectrometer 400, the focusing optical system 404, and the optical guide device 402 can be free-form surfaces. For example, any element in the optical guide device may include one or more free-form surfaces.

[0052] In the first example, only the first prism 118, the focusing optical system 404, and the optical guide device 402 of the spectrometer 400 have one or more freeform surfaces. The first surface 118a can be a freeform prism surface, or the second surface 118b can be a freeform surface, or both surfaces 118a and 118b can be freeform surfaces.

[0053] In the second example, only the second prism 120, the focusing optical system 404, and the optical guide device 402 of the spectrometer 400 have one or more freeform surfaces. The first surface 120a can be a freeform prism surface, or the second surface 120b can be a freeform surface, or both surfaces 120a and 120b can be freeform surfaces.

[0054] In the third example, only the first reflecting surface 408, the focusing optical system 404, and the optical guide device 402 of the spectrometer 400 have one or more free-form surfaces. The first reflecting surface 408 can be a free-form surface. Alternatively, only the third reflecting surface 412 can be a free-form surface. Alternatively, both the reflecting surface 408 and the reflecting surface 412 can be free-form surfaces.

[0055] In another example, the surface 110 of the second mirror 116 can be a free-form surface. In yet another example, the surface 124 of the field corrector 126 can be a free-form surface. By this disclosure, it will be understood that, without limitation, any and all combinations of surfaces described and illustrated in the spectrometer 400, the focusing optical system 404, and the optical guide device 402 can be free-form surfaces, as long as one or more of the elements of the spectrometer 400, the focusing optical system 404, and / or the optical guide device 402 include at least one free-form surface.

[0056] While the above examples specifically pertain to spectrometers, it should be understood that the focusing optical systems (e.g., focusing optical systems 104 and 404) and optical guide devices (e.g., devices 102 and 402) described herein can be used without limitation in any other suitable optical system. Any optical system used to receive and direct electromagnetic radiation can incorporate the focusing optical systems (e.g., focusing optical systems 104 and 404) and optical guide devices (e.g., devices 102 and 402) according to the principles described herein.

[0057] The examples of spectrometers, focusing optics, Offner relays, and optical guide devices described herein offer numerous advantages and benefits. For example, computer-aided design of prism optical surfaces makes it possible to impart specific and unique shapes to the free-form surfaces of optical elements. Such specific and unique free-form surfaces can be used on one or more of the optical components (e.g., prism 118, prism 120, reflector 108, reflector 112, reflector 115, reflector 110, field corrector 126). Because they are precisely designed using computer-aided design and manufacturing, it becomes possible to manufacture surfaces on optical elements that are specifically and uniquely designed to correct specific aberrations and distortions of images and electromagnetic radiation that were previously difficult to correct. By using special surfaces designed with computer-aided design tools, it becomes possible to precisely correct specific aberrations. Thus, as a result of the principles described herein, relays, optical guide devices, optics, and spectrometers can be made that have well-corrected imaging fields and high resolution.

[0058] The above description primarily pertains to Offner spectrometers that include an Offner relay as a focusing optical system. However, other focusing optical systems designed according to the principles described herein can be used in spectrometers while obtaining the above benefits and advantages. For example, Figure 5 shows another optical system according to an example of this disclosure. The optical system may be a spectrometer 500 and is operable to focus light from an object 501 for imaging / analysis by the spectrometer 500. The spectrometer 500 includes an optical guide device 502 which may be configured to direct electromagnetic radiation and split that electromagnetic radiation into various spectral components.

[0059] The optical guide device 502 may include a focusing optical system 504, which may include one or more reflective surfaces. In this example, the focusing optical system 504 is configured as a relay, so that the spectrometer 500 can be a Dyson spectrometer. In such an example, the focusing optical system 504 may include a first reflective surface 508, which may be configured to receive electromagnetic radiation and reflect it in a desired direction.

[0060] The optical guide device 502 may further include a prism 518, which may include a first surface 518a and a second surface 518b configured to collimate, reflect, refract, and / or direct incident light. The optical guide device 502, comprising its various components (e.g., the prism 518 and the reflecting surface 508), can define an optical path that directs electromagnetic radiation. As shown in Figure 5, the optical path may be as follows: Light incident on the first surface 518a of the prism 518 can pass through the prism 518 and exit from the second surface 518b of the prism 518. Light from the first prism 518 can be directed towards the first reflecting surface 508 of the focusing optical system 504. The first reflecting surface 508 may be located in the optical path downstream from the prism 518 and can reflect light from the first prism 518 back towards the first prism 518 of the focusing optical system 504. Light from the reflective surface 508 can be directed toward the second surface 518b of the prism 518. Light incident on the second surface 518b can pass through the prism 518, exit the prism 518, and exit from the first surface 518a.

[0061] The optical guide device 502 can be used as an optical guide device within the spectrometer 500. The spectrometer 500 may further include a slit 503 that functions as an electromagnetic radiation inlet, through which light 522a from a source or object 501 enters the spectrometer 500. Alternatively, the slit can be a beam slicer. Light 522b from the slit 103 can travel along the optical path to the optical guide device 502, specifically to the first prism 518. Light incident on the first surface 518a of the prism 518 can pass through the first prism 518 and exit as light 522c from the second surface 518b of the prism 518. Light 522c can be directed toward the reflective surface 508 of the focusing optical system 504, which can reflect the light 522c from the prism 518 as light 522d and return it toward the second surface 518b of the prism 518. Light 522d can pass through prism 518 and exit from the first surface 518a of prism 518 as light 522e. Light 522e may then proceed to enter or pass through a field corrector 526 (e.g., a field flattener) positioned downstream from prism 518 and configured to provide correction to the incident light 522e to ensure a high-quality, high-resolution, well-corrected field for imaging / analysis by spectrometer 500. Subsequently, or alternatively, light 522e may proceed to a focal plane 528 configured to receive spectrally separated light in a well-corrected field or image. The focal plane 528 may include a capture sensor configured to analyze light or capture and image it for later analysis, such as a CCD imaging sensor, a CMOS imaging sensor, or any other sensor or capture device. Devices, sensors, or other objects located within the focal plane 528 are not intended to be limited in any way by this disclosure.

[0062] As shown in Figure 5, the spectrometer 100 is a prism-based spectrometer including a prism 518 and a reflecting surface 508. Modern optical design, including computer-aided design of lenses, prisms, mirrors, and their surfaces, makes it possible to manufacture special and unique surfaces on the lenses, mirrors, and prisms to provide precisely image-corrected and high-resolution images from the spectrometer. Similar to the prism described in the spectrometer 100, the prism 518 can be formed by a freeform surface. One or more of the surfaces 518a and 518b may be freeform surfaces that provide correction of incident light, as described elsewhere in this disclosure. One surface of the prism 518 (518a or 518b) may be freeform, and the other surface (the non-freeform surface of 518a or 518b) may be flat. Alternatively, both surfaces 518a and 518b may be freeform surfaces, as needed. The freeform surface(s) of the prism 518 can be specifically designed to provide correction for specific amounts of specific aberrations in the incident light, similar to those described above for the spectrometer 100.

[0063] Further described herein is a method 600 for configuring the optical guide device shown in Figure 6. Method 600 may include step 602 of configuring the optical guide device to include a first prism in the optical path. Method 600 may further include step 604 of configuring the optical guide device to include a focusing optical system in the optical path from the first prism. Method 600 may further include step 606 of configuring the first prism to include at least one freeform prism surface. These methods can be performed by the spectrometer described herein.

[0064] Refer to the examples illustrated in the drawings, and use specific language in this specification to explain them. However, it should be understood that this is not intended to limit the scope of the Art. Modifications and further changes to the features illustrated herein, as well as additional uses of the examples illustrated herein, should be considered within the scope of description.

[0065] This disclosure may not expressly disclose that some embodiments or features described herein can be combined with other embodiments or features described herein, but this disclosure should be read to describe any such combinations that are feasible to those skilled in the art. Where “or” is used herein, unless otherwise specified herein, it should be understood to mean non-exclusive or, i.e., “and / or”.

[0066] Furthermore, the described features, structures, or properties can be combined in any preferred manner in one or more embodiments. The preceding description provides many specific details, including examples of various configurations, to ensure a full understanding of the described art. However, it is understood that the art can be implemented without using one or more of these specific details, or using other methods, components, or apparatus. In other instances, well-known structures or operations are not illustrated or described in detail to avoid obscuring aspects of the art.

[0067] While the subject matter is described in a language specific to its structural features and / or operations, it should be understood that the subject matter defined in the attached claims is not necessarily limited to the specific features and operations described. Rather, the specific features and operations described above are disclosed as exemplary forms that implement the claims. Many modifications and alternative arrangements can be devised without departing from the spirit and scope of the described art.

Claims

1. An optical guide device configured to guide electromagnetic radiation along an optical path, A first prism positioned within the aforementioned optical path, Includes a focusing optical system positioned within the optical path, The first prism includes (i) at least one freeform prism surface containing an XY polynomial type freeform surface, and (ii) another flat prism surface. An optical guide device wherein the at least one freeform prism surface has cylindrical curvature along a first axis, is flat along a second axis perpendicular to the first axis, and has a freeform polynomial term formed thereon.

2. The optical guide device according to claim 1, further comprising a second prism positioned downstream of the first prism in the optical path.

3. The optical guide device according to claim 2, wherein the focusing optical system is positioned downstream of the first prism in the optical path and upstream of the second prism in the optical path.

4. The optical guide device according to claim 2, wherein one or more of the first prism and the second prism are ferry prisms.

5. The optical guide device according to claim 2, wherein the second prism includes at least one freeform prism surface.

6. The optical guide device according to claim 2, wherein at least one of the first prism and the second prism includes at least two freeform prism surfaces.

7. The optical guide device according to claim 1, wherein the focusing optical system is positioned downstream or upstream of the first prism in the optical path.

8. The aforementioned focusing optical system is A first reflective surface positioned within the optical path, A second reflective surface positioned in the optical path downstream from the first reflective surface, The optical guide device according to claim 1, further comprising a third reflective surface positioned in the optical path downstream from the second reflective surface.

9. The optical guide device according to claim 8, wherein the first reflective surface, the second reflective surface, and the third reflective surface of the focusing optical system are arranged to form an Offner relay.

10. The optical guide device according to claim 8, wherein the first reflective surface is formed on a first mirror, and the third reflective surface is formed on a second mirror separate from the first mirror.

11. The first reflective surface and the third reflective surface are arranged on a common substrate. The optical guide device according to claim 8, wherein at least one of the first reflective surface and the third reflective surface is a free-form surface.

12. The optical guide device according to claim 8, wherein both the first reflective surface and the third reflective surface are portions of a single continuous freeform reflective surface formed on the first mirror.

13. The optical guide device according to claim 12, wherein the second reflective surface is formed on a second mirror separate from the first mirror.

14. The optical guide device according to claim 13, wherein one or more of the first reflective surface and the third reflective surface are free-form surfaces.

15. The optical guide device according to claim 1, further comprising a field corrector disposed in the optical path downstream from the first prism and the focusing optical system.

16. The optical guide device according to claim 15, wherein the field corrector is a reflective field corrector.

17. The optical guide device according to claim 16, wherein the field corrector includes a free-form surface.

18. The optical guide device according to claim 1, wherein the at least one freeform prism surface further includes at least one of a cylindrical surface, a non-cylindrical surface, or a substantially planar surface.

19. A spectrometer configured to form a spectrally resolved image of electromagnetic radiation from a source, A slit configured to receive the aforementioned electromagnetic radiation, A spectrometer comprising an optical guide device according to any one of claims 1 to 18, positioned in the optical path downstream from the slit.

20. A method for constructing an optical guide device, The optical guide device is configured to include a first prism within the optical path, The optical guide device is configured to include a focusing optical system positioned within the optical path, The first prism is configured such that it includes (i) at least one freeform prism surface including an XY polynomial type freeform surface, and (ii) another flat prism surface. A method wherein the at least one freeform prism surface has cylindrical curvature along a first axis, is flat along a second axis perpendicular to the first axis, and has a freeform polynomial term formed thereon.

21. An optical system, An electromagnetic radiation inlet configured to receive electromagnetic radiation from a source, The optical guide device includes an optical guide device configured to guide electromagnetic radiation along the optical path from the electromagnetic radiation inlet to the focal plane, The optical guide device includes a prism positioned within the optical path and a focusing optical system positioned within the optical path. The prism includes (i) at least one freeform prism surface containing an XY polynomial type freeform surface, and (ii) another flat prism surface. An optical system in which at least one freeform prism surface has cylindrical curvature along a first axis, is flat along a second axis perpendicular to the first axis, and has a freeform polynomial term formed thereon.

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