Wavefront error correction of conformal optical component using planar lens

Abstract

To solve the problem in which, since correcting a wavefront error (WFE) of rotationally asymmetric optical components using conventional lenses usually requires multiple lenses, systems that use such conventional lens solutions are relatively bulky, especially in certain applications (e.g., aircraft).SOLUTION: An optical system 100 includes a conformal optical component 102 transmissive to electromagnetic radiation (EMR), which is propagated through the conformal optical component along an optical axis. The conformal optical component is rotationally asymmetric about the optical axis A. A planar corrector lens 108 is configured to correct a wavefront error (WFE) of the conformal optical component. The planar corrector lens defines a lens axis B. Accordingly, use of a single planar corrector lens for WFE correction of a conformal optical component reduces bulk and manufacturing complexity.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This application claims the benefit of U.S. patent application Ser. No. 16 / 812,975, filed Mar. 9, 2020, entitled "WAVEFRONT ERROR CORRECTION FOR CONFORMAL OPTICS USING FLAT LENSES," which is incorporated by reference in its entirety.

[0002] The present embodiments relate to optical systems, and in particular to correcting wavefront errors downstream of conformal optics using a flat lens. [Background technology]

[0003] Conformal optics have an outer surface that follows the shape of the host platform (e.g., in aerodynamic applications). For example, conformal optics are used in vehicles (e.g., aircraft) to modify aerodynamic drag and / or increase the difficulty of detection by radar systems. Optical elements that direct electromagnetic radiation (EMR) along an optical path inevitably introduce some aberrations into the wavefront of the EMR, and conformal shapes in particular degrade optical performance and cause significant optical aberrations. Such aberrations are referred to herein as wavefront errors (WFEs). WFEs degrade the performance of components in the optical path that utilize the EMR, such as focal plane arrays or other sensors. Additionally, the surface contour and / or orientation of conformal optics can cause the path through the conformal optic to be rotationally asymmetric, which can further contribute to wavefront errors.

[0004] Correction lenses may be used to correct such wavefront errors. However, current correction solutions can be bulky, expensive, and / or difficult to manufacture. For example, conventional lenses are typically curved, thick, and rotationally symmetric. Correcting the WFE of a rotationally asymmetric optical component using conventional lenses typically requires multiple lenses. Thus, systems using such conventional lens solutions are relatively bulky, especially in certain applications (e.g., aircraft).

[0005] Other potential solutions are generally complex and / or require special geometries that are difficult to manufacture using traditional grinding and / or polishing techniques. Summary of the Invention

[0006] Embodiments relate to a system and method for wavefront error (WFE) correction of a conformal optic using a flat lens. The embodiments include a conformal optic that is transmissive to electromagnetic radiation (EMR), where the electromagnetic radiation propagates through the conformal optic along an optical axis. The conformal optic is rotationally asymmetric with respect to the optical axis. A flat correction lens is configured to correct the WFE of the conformal optic. The flat correction lens defines a lens axis. Thus, using a single flat correction lens for WFE correction of the conformal optic reduces bulk and manufacturing complexity.

[0007] In one embodiment, the optical system includes a conformal optic that is transmissive to the EMR and a planar correction lens configured to correct a WFE of the EMR propagating along an optical axis through the conformal optic and through the planar correction lens to the detector. The planar correction lens defines a lens axis. The conformal optic is rotationally asymmetric about the optical axis.

[0008] In another embodiment, a method of correcting the WFE includes operating an interferometer, by a processor, to measure the WFE of the EMR downstream of the conformal optic and the planar correction lens. The planar correction lens defines a lens axis. The EMR propagates through the conformal optic along the optical axis. The conformal optic is rotationally asymmetric about the optical axis. The method further includes determining, by the processor, an indication of a refractive index that reduces the wavefront error. The method further includes operating, by the processor, an energy source to direct an energy beam to a surface of the planar correction lens according to the indication of the refractive index, thereby varying the surface, thereby varying the refractive index at a plurality of locations on the surface.

[0009] In another embodiment, a system for WFE correction includes an interferometer configured to measure the WFE of the EMR downstream of a conformal optic and a planar correction lens. The planar correction lens defines a lens axis. The EMR propagates through the conformal optic along the optical axis. The conformal optic is rotationally asymmetric about the optical axis. The system further includes determining, by a processor, a refractive index indication that mitigates the wavefront error. The system further includes an energy source configured to direct an energy beam at a surface of the planar correction lens according to the refractive index indication, thereby altering the surface, thereby altering the refractive index at a plurality of locations on the surface.

[0010] Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the embodiments in connection with the accompanying drawings. [Brief description of the drawings]

[0011] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several aspects of the disclosure and, together with the description, serve to understand the principles of the disclosure.

[0012] [Figure 1] FIG. 1 is a cross-sectional side view of an optical system including a conformal optic and a planar correction lens.

[0013] [Figure 2A] FIG. 2A is a perspective view of the planar correction lens of FIG.

[0014] [Figure 2B] FIG. 2B is a block diagram of the planar corrective lens of FIG. 2A including a front view, a close-up, and a side cross-sectional view.

[0015] [Diagram 3] FIG. 3 is a block diagram of a wavefront error (WFE) correction device, illustrating the identification and correction of WFE.

[0016] [Figure 4] FIG. 4 is a flow chart of a method for modifying the surface of the planar correction lens of FIGS. 1-3 to correct for WFE.

[0017] [Diagram 5] FIG. 5 is a diagram illustrating the first-order diffraction efficiency of one embodiment of the flat correction lens of FIGS.

[0018] [Figure 6A] FIG. 6A illustrates the improvement in modulation transfer function over a range of wavelengths using one embodiment of the planar corrector lens of FIGS. 1-3.

[0019] [Figure 6B] FIG. 6B is a diagram illustrating the improvement in modulation transfer function at a particular wavelength using one embodiment of the planar corrector lens of FIGS. 1-3.

[0020] [Figure 7] FIG. 7 illustrates a cylindrical planar corrector lens design for correcting a mid-wave infrared (MWIR) emitting conformal dome.

[0021] [Figure 8A] FIG. 8A is an image taken using the MWIR conformal dome of FIG.

[0022] [Figure 8B] FIG. 8B is an image taken using the MWIR conformal dome of FIG. 7 and a conventional cylindrical corrector lens.

[0023] [Figure 8C] FIG. 8C is an image taken using the MWIR conformal dome of FIG. 7 and the planar corrective lens of FIGS. 1-3.

[0024] [Figure 9]FIG. 9 is a block diagram of a system suitable for customizing the refractive index of a surface, according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The following embodiments represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of carrying out the embodiments. Upon reading the following description in light of the accompanying drawings, those skilled in the art will be able to understand the concepts of the present disclosure and recognize applications of these concepts not specifically addressed herein. It is understood that these concepts and applications are within the scope of the present disclosure and the appended claims.

[0026] Any flow charts detailed herein are necessarily set forth in a certain order for purposes of explanation, but unless expressly indicated otherwise, the embodiments are not limited to any particular order of steps. The use of ordinal numbers in connection with elements herein is merely to distinguish between what may otherwise be similar or identical labels, such as "first tier" and "second tier," and does not imply priority, type, importance, or other attributes, unless specifically stated herein. The term "about" as used herein in conjunction with a numerical value means any value within a range of 10% greater or less than that numerical value.

[0027] As used in this specification and the claims, the articles "a" and "an" referring to an element refer to "one or more" of that element, unless expressly specified otherwise. As used in this specification and the claims, the word "or" is inclusive unless the context requires otherwise. As an example, a description of A or B means A, or B, or both A and B.

[0028] The phrase "surface" as used herein refers to the outermost part of an article, and includes the thickness of the outermost part of the article. The exact thickness is generally not relevant to the embodiment unless otherwise stated herein. For example, a layer of material has a surface that includes not only the outermost part of the layer of material, but also a depth into the layer of material, which may be relatively shallow or may extend substantially into the layer of material. Although the sub-wavelength apertures described herein are formed in the surface, whether the depth of the sub-wavelength aperture extends beyond the depth of the surface is generally not relevant to the embodiment.

[0029] When an element, such as a layer, region, or substrate, is referred to as being "on" or extending "on" another element, it will be understood that it can be directly on or extending directly onto the other element, or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or extending "directly onto" another element, there are no intervening elements. Similarly, when an element, such as a layer, region, or substrate, is referred to as being "on" or extending "on" another element, it will be understood that it can be directly on or extending directly onto the other element, or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or extending "directly onto" another element, there are no intervening elements. Also, when an element is referred to as being "connected" or "coupled" to another element, it will be understood that it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

[0030] As used herein, relative terms such as "lower" or "top," "upper" or "bottom," "horizontal" or "vertical" may be used to describe the relationship of one element, layer or region to another element, layer or region as depicted in the figures. It should be understood that these terms, and those discussed above, are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

[0031] As used herein, the term "proximate" means in the position, next to, or near.

[0032] Embodiments include the creation of gradient index (GRIN) optics. Mechanisms for creating GRIN optics on the surface of a material are disclosed, for example, in U.S. Patent Nos. 9,340,446 and 9,772,255, the contents of which are incorporated herein by reference.

[0033] Embodiments relate to optical systems, and in particular to planar GRIN lenses (also referred to herein as metasurfaces, metalens, etc.) for correcting wavefront error (WFE) of conformal optics. Embodiments include at least one conformal optic having a surface portion that is transparent to electromagnetic radiation (EMR). Embodiments include an optical component having a sub-wavelength aperture at a surface of the planar corrective lens that corrects the WFE of the conformal optic by changing the refractive index at the air / surface.

[0034] Desired refractive index n eff can also be formed by a sub-wavelength aperture according to the following equation:

number

[0035] A pattern of subwavelength apertures at a particular fill factor, defined by the diameter D of the subwavelength apertures and the distance L between the subwavelength apertures formed on the surface of the medium, can change the refractive index of the medium. The term "subwavelength" refers to aperture diameters that are smaller than the wavelength of interest. For example, the examples herein are described in the context of wavelengths ranging from 3 micrometers (μm) (i.e., 3000 nanometers (nm)) to 5 μm (i.e., 5000 nm), and thus subwavelength apertures refer to apertures with diameters smaller than 3000 nm. In particular, a pattern of subwavelength apertures at a desired refractive index n eff can be fabricated in a material for a hexagonal pattern of subwavelength apertures by solving for D and L according to the following equation:

number

[0036] Disclosed herein is a GRIN planar correction lens (also sometimes referred to as a phase corrector). In certain embodiments, the planar correction lens is fabricated directly on a substrate (e.g., planar optics, wafer, etc.) using lithography tools (e.g., e-beam, UV lithography, nanoimprint lithography, etc.). Lithography can allow for high throughput and easy manufacturing (compared to traditional optical correction elements). In contrast to other solutions that require complex shapes / curvatures, denoted by Δt, to refract light and correct the output phase difference, the planar correction lens is fabricated by controlling the refractive index (Δn) across a planar mask while keeping the thickness constant so that there is no curvature.

number

[0037] Compared to other solutions, planar corrective lenses do not require complex curved surfaces that are difficult to manufacture, use high-throughput lithography techniques, are etched directly into the substrate material (minimizing potential delamination issues), are lower cost, and / or are easier to manufacture.

[0038] FIG. 1 is a cross-sectional side view of an optical system 100 including a conformal optic 102, an objective lens assembly 104 including objective lenses 106(1)-106(3) (collectively referred to herein as objective lenses 106), and a flat correction lens 108 (also referred to as a flat correction lens, etc.). In certain embodiments, the optical system 100 includes a detector 110, which may be part of a camera 112. The optical system 100 is configured to receive EMR from a target 114 through the conformal optic 102 and the objective lens assembly 104 to the detector 110. The flat correction lens 108 is configured to correct for any WFE generated by the conformal optic 102 and / or one or more objective lenses 106 in the objective lens assembly 104. The detector 110 (e.g., a focal plane array) is configured to capture an image based on the wavefront corrected EMR.

[0039] The conformal optic 102 is transmissive to the EMR. The EMR propagates along the optical axis A through the conformal optic 102 to the planar corrective lens 108. In certain embodiments, the conformal optic 102 includes a conformal optical window and / or a conformal dome. In certain embodiments, the conformal optic 102 has a rotationally asymmetric shape. In other embodiments, the conformal optic 102 has a rotationally symmetric shape but is oriented rotationally asymmetric with respect to the optical axis A. That is, the conformal optic 102 is rotationally asymmetric with respect to the optical axis. In certain embodiments, the conformal optic 102 may include shapes such as conical, pyramidal, and / or cylindrical. Furthermore, in certain embodiments, the conformal optic 102 is a single, integral component. In other embodiments, the conformal optic 102 includes multiple optical components.

[0040] In a particular embodiment, the objective lens assembly 104 includes multiple objective lenses 106, including a planar correction lens 108. Each objective lens 106 and planar correction lens 108 is transparent to EMR radiation. For example, as shown, the objective lens assembly 104 includes a first objective lens 106(1), a second objective lens 106(2), a third objective lens 106(3), and a planar correction lens 108. The planar correction lens 108 is disposed proximate to the detector 110 (e.g., between the objective lenses 106(1)-(3) and the detector 110) to correct for WFE potentially introduced by either the conformal optics 102 and / or the objective lenses 106. That is, the planar correction lens 108 is configured to correct for WFE of EMR propagating through the conformal optics 102 to the detector 110. The planar correction lens 108 defines a lens axis. In certain embodiments, the lens axis B is aligned with the optical axis A.

[0041] In certain embodiments, the planar corrector lens 108 comprises a GRIN lens. In certain embodiments, the planar corrector lens 108 comprises a GRIN surface etched into a substrate. In certain embodiments, the planar corrector lens 108 comprises a GRIN coating applied to a substrate. In certain embodiments, the planar corrector lens 108 comprises a thickness of less than 10 mm (e.g., about 0.5 mm).

[0042] In certain embodiments, the optical system 100 is configured for one or more of various types of EMR radiation, such as, for example, laser radiation, infrared radiation, ultraviolet light, visible light, etc. For example, in certain embodiments, the EMR includes at least one of mid-wave infrared radiation (MWIR) or long-wave infrared radiation (LWIR). The embodiments are generally designed for use within a particular band of light, referred to herein as a selected EMR band, which may include, by way of non-limiting example, short-wave infrared radiation (IR), mid-wave IR, long-wave IR, ultraviolet light, visible light, etc. Such bands may include, but are not limited to, wavelength bands between 30 μm and 1 mm, 3 μm and 30 μm, 700 nm and 3 μm, 400 nm and 700 nm, 200 nm and 400 nm, 1.4 μm and 3 μm, 3 μm and 8 μm, 8 μm and 15 μm, and / or 15 μm and 1000 μm.

[0043] Although not shown, the optical system 100 may also include one or more lenses and / or one or more reflectors disposed in the optical path between the target 114 and the detector 110 to focus or otherwise manipulate the EMR radiation for propagation throughout the optical system 100.

[0044] Figures 2A-2B are views of the flat corrective lens of Figure 1. Referring to Figure 2A, the flat corrective lens 108 has a flat front surface 116 and a flat back surface 118, and has a thickness T of less than 10 mm (e.g., 0.5 mm). In certain embodiments, the thickness T is less than 5 mm, less than 2.5 mm, or less than 1 mm.

[0045] The flat corrector lens 108 may comprise any suitable optical material and may be selected based on the particular wavelength or wavelength band for which the optical system 100 is designed. For example, in certain embodiments, the flat corrector lens 108 may comprise silicon, silicon dioxide, sapphire, germanium, Cleartran™ (ZnS), zinc selenide (ZnSe), chalcogenide glasses (e.g., AMTIR-4, AMTIR-5, IRG24), and the like. By way of example, for IR wavelengths, the flat corrector lens 108 may comprise germanium, silicon, and the like. In one embodiment, the flat corrector lens 108 comprises a glass-ceramic material having multiple states, including an amorphous state and a crystalline state. The material has one refractive index when in the amorphous state and another refractive index when in the crystalline state. The material thereby forms a surface of the flat corrector lens 108 that may be varied to correct the WFE associated with the conformal optic 102. In particular, a location within the material can be targeted with an energy beam source, such as a laser, according to the refractive index dictates, to change the location from an amorphous state to a crystalline state, thereby changing the refractive index to correct the WFE.

[0046] Referring to FIG. 2B, in one embodiment, the surface 116 is altered by forming openings in the surface 116 to alter the porosity of the surface 116, thereby altering the refractive index of the surface. In a particular embodiment, the planar corrector lens 108 may include a first portion 120(1) at a distance D(1) from the lens axis B (the center of the planar corrector lens 108) and a second portion 120(2) at a distance D(2) from the lens axis B. As an example, the distance D(1) is the same as the distance D(2) from the center C. Furthermore, the first portion 120(1) has a different refractive index than the second portion 120(2). In a particular embodiment, the planar corrector lens 108 has a refractive index that is rotationally asymmetric with respect to the lens axis B. In a particular embodiment, the planar corrector lens 108 has a refractive index that is rotationally symmetric only about a 180° rotation. Compared to conventional lenses, the planar corrector lens 108 does not require rotational symmetry.

[0047] In a particular embodiment, first portion 120(1) includes apertures 122(1) with a first fill factor and second portion 120(2) includes apertures 122(2) with a second fill factor (different from the first index of refraction). First portion 120(1) forms a plurality of first sub-wavelength apertures 122(1) with a first fill factor that changes the inherent index of refraction of surface 116 to a first desired index of refraction. Second portion 120(2) forms a plurality of second sub-wavelength apertures 122(2) with a second fill factor that changes the inherent index of refraction to a second desired index (different from the first desired index of refraction).

[0048] The diameter and / or depth of the first sub-wavelength opening 122(1) and the second sub-wavelength opening 122(2) may be the same or different. Additionally, the pitch L1 between the first sub-wavelength openings 122(1) may be the same or different from the pitch L2 between the second sub-wavelength openings 122(1). A combination of diameter 123, distance between openings 122(1), 122(2) (collectively referred to as openings 122), and calculated depths 124(1), 124(2) is determined and then formed on surface 116 to change the porosity of surface 116, thereby changing the refractive index at various locations of surface 116 to reduce or eliminate WFE. In some embodiments, diameter 123 may be less than about half the wavelength of the EMR of interest to minimize scattering.

[0049] The planar corrective lens 108 may have a variety of fill factors and resulting refractive indices across the length L and / or width W of the conformal optic 102. In one embodiment, the sub-wavelength apertures 122 are formed by directing an energy beam onto the surface 116 to imprint a mask of the sub-wavelength apertures 122, although the embodiment is not limited to a particular mask imprinting mechanism. The energy beam may include, by way of non-limiting examples, an ion beam, an electron beam lithography, or a laser beam. In certain embodiments, a lithographic manufacturing process may be used to reduce manufacturing costs. A subsequent chemical or physical etching procedure may then be performed to form the apertures 122 according to the mask. In certain embodiments, a layer may be deposited over the sub-wavelength apertures 122 by atomic layer deposition (ALD) or similar techniques.

[0050] 3 is a block diagram of the WFE corrector 126. In a particular embodiment, the WFE corrector 126 includes an interferometer 128 configured to measure the WFE of the EMR downstream of the conformal optic 102 and the planar corrector lens 108 of FIG. 1. The planar corrector lens 108 defines a lens axis B. In a particular embodiment, the planar corrector lens 108 has a refractive index that is rotationally asymmetric about the lens axis B. The EMR propagates through the conformal optic 102 along an optical axis A. The conformal optic 102 is rotationally asymmetric about the optical axis A.

[0051] In certain embodiments, the interferometer 128 measures the WFE using the laser beam 138. The WFE may be measured by the interferometer 128, for example, at an image plane 142 where a detector (e.g., a focal plane array 144) is located. In particular, by measuring the WFE at the image plane 142, a cumulative or collective WFE caused by the conformal optic 102 and the objective lens assembly 104 is measured. The interferometer 128 measures the WFE at the image plane 142, and the surface 116 of the planar correction lens 108 is altered to correct for the WFE. The interferometer 128 provides data to the computing device 130 that identifies the WFE or allows the WFE to be measured.

[0052] The interferometer 128 can measure the WFE associated with the conformal optic 102 and / or the objective lens 106. The interferometer 128 generates data quantifying the WFE in a particular format, such as an interferogram. Although an interferometer is used as an example herein, the WFE measurement component can include any device capable of measuring the WFE associated with an optical element. For example, in certain embodiments, a modulation transfer function (MTF) is measured and the WFE is measured based on the MTF (alternatively or in addition to using the interferometer 128).

[0053] The WFE correction apparatus 126 further includes a computing device 130 that receives and processes the data to determine refractive index instructions that specify modifications to be made to the surface 116 of the planar correction lens 108 to correct the WFE. The computing device 130 may include one or more microprocessors or processors 132, memory 134, and storage 136. In particular, the processor 132 is configured to determine refractive index instructions that reduce wavefront errors.

[0054] The WFE corrector 126 further includes an energy source 139 configured to direct an energy beam 140 to the surface 116 of the planar corrector lens 108 according to the refractive index instructions to change the surface 116 and thereby change the refractive index at multiple locations on the surface. In certain embodiments, the refractive index of the planar corrector lens 108 is rotationally asymmetric about the lens axis. In certain embodiments, the energy source 139 is an electron beam lithography system.

[0055] 4 is a flow chart of a method for modifying the surface of the planar correction lens of FIGS. 1-3 to correct for WFE. In step 152, the method includes operating interferometer 128 by processor 132 to measure the WFE of EMR downstream of conformal optic 102 and planar correction lens 108, where planar correction lens 108 defines a lens axis B. EMR propagates through conformal optic 102 along optical axis A. Conformal optic 102 is rotationally asymmetric with respect to optical axis A.

[0056] In step 154, the method further includes determining, by the processor 132, an indication of the refractive index that reduces the WFE.

[0057] In step 156, the method further includes operating the energy source 146 with the processor 132 to direct an energy beam 148 to the surface 116 of the planar corrector lens 108 according to the indication of the refractive index to vary the refractive index at a plurality of locations of the surface 116. In certain embodiments, the refractive index of the planar corrector lens 108 is rotationally asymmetric about the lens axis. In certain embodiments, the energy beam 148 comprises one of an ion beam and a laser beam.

[0058] FIG. 5 illustrates the first order diffraction efficiency of the planar corrector lens 108 of FIGS. 1-3. It should be noted that the planar corrector lens 108 may be optimized for a specific wavelength, but in certain embodiments, the planar corrector lens 108 provides broadband efficiency across multiple wavelengths. For example, in one embodiment, the planar corrector lens 108 has a 10 μm thick phase mask on a 0.5 mm germanium wafer (also sometimes referred to as a substrate). The planar corrector lens 108 is optimized for the 10 μm wavelength of the LWIR, yet has a focusing efficiency of over 80% in the 8 μm to 13 μm wavelength range. Additionally, in the figures, the apertures, for example, are 300 nm holes with various spacings.

[0059] FIG. 6A illustrates the improvement in modulation transfer function over various wavelengths using the planar correction lens of FIGS. 1-3. The figure shows theoretical and measured modulation transfer function (MTF) of an optical system with and without planar correction lens 108. Note that MTF is a measurement of image sharpness. The figure shows the MTF measured with planar correction lens 160 and the MTF measured with planar correction lens 162. Note that in this embodiment, the planar correction lens 160 did not have an anti-reflective coating, so the analysis of this particular planar correction lens 160 included ghosting. In a particular embodiment, the planar correction lens 160 is anti-reflective coated. As shown, the use of planar correction lens 108 provides an improvement in both the theoretical and measured values.

[0060] Figure 6B is a diagram illustrating the improvement in modulation transfer function at specific wavelengths using the planar correction lens 108 of Figures 1-3. In particular, the MTF 164 measured at 9 μm, the MTF 166 measured at 10 μm, the MTF 168 measured at 11 μm, and the MTF 170 measured at 12 μm are shown.

[0061] 7 is a diagram illustrating the design of a planar corrector lens 108' having a cylindrical shape for correcting a MWIR conformal dome. As shown, the density of apertures varies over the length of the planar corrector lens 108', varying the refractive index over the length of the planar corrector lens 108'.

[0062] FIG. 8A is an image taken using the MWIR conformal dome of FIG. 7. FIG. 8B is an image taken using the MWIR conformal dome and a conventional cylindrical corrector lens. FIG. 8C is an image taken using the MWIR conformal dome and the planar corrector lens 108 of FIGS. 1-3. The image of FIG. 8C taken using the MWIR conformal dome is sharper and eliminates aberrations through the conformal dome compared to the images of FIGS. 8A and 8B.

[0063] 9 is a block diagram of a system 174 suitable for customizing the refractive index of a surface, according to one embodiment. The system 174 may include one or more separate computing devices. The system 174 includes a processor device 176, a system memory 178, and a system bus 180. The system bus 180 provides an interface for system components including, but not limited to, the system memory 178 and the processor device 176. The processor device 176 can be any commercially available or dedicated processor.

[0064] The system bus 180 may be any of several bus architectures that may be further interconnected to a memory bus (with or without a memory controller), a peripheral bus, and / or a local bus using any of a variety of commercially available bus architectures. The system memory 178 may include non-volatile memory 182 (e.g., read only memory (ROM), erasable programmable read only memory (EPROM), electronic EPROM (EEPROM), etc.), and volatile memory 184 (e.g., RAM). A basic input / output system (BIOS) 186 may be stored in the non-volatile memory 182 and may include the basic routines that help transfer information between elements within the system 174. The volatile memory 184 may also include high-speed RAM, such as static RAM, for caching data.

[0065] The system 174 may further include or be coupled to a non-transitory computer-readable storage medium, such as a storage device 188, which may include, for example, an internal or external hard disk drive (HDD) (e.g., Enhanced Integrated Drive Electronics (EIDE) or Serial Advanced Technology Attachment (SATA)), HDD (e.g., EIDE or SATA), flash memory, and the like. The storage device 188, as well as other drives related to computer-readable and computer-usable media, may provide non-volatile storage of data, data structures, computer-executable instructions, and the like. Although the above description of computer-readable media refers to HDDs, it should be understood that other types of computer-readable media, such as Zip disks, magnetic cassettes, flash memory cards, cartridges, and the like, may also be used in the operating environment, and further, any such media may include computer-executable instructions for performing the novel methods of the disclosed embodiments. The storage device 188 may store one or more instructions 190 that specify how the surface is to be altered. For example, the instructions 190 may specify, for each of a number of different surface portions of the optical component, a particular fill factor, diameter, and pitch of sub-wavelength apertures to be formed in the surface of the optical component.

[0066] The storage device 188 and the volatile memory 184 may store a number of modules, including an instruction determiner 192 implementing the mechanisms described above with respect to FIG. 3A, for determining instruction content 190. All or a portion of the embodiments may be implemented as a computer program product stored on a temporary or non-transitory computer usable or computer readable storage medium, such as the storage device 188, and including complex programming instructions, such as complex computer readable program code, for causing the processor device 176 to perform the procedures described herein. Thus, the computer readable program code may include software instructions for implementing the functionality of the embodiments described herein when executed on the processor device 176. The processor device 176 may function as a controller, or control system, of the system 174 for implementing the functionality described herein.

[0067] An operator may also be able to input one or more configuration commands via a keyboard (not shown), a pointing device (not shown) such as a mouse, or a touch-sensitive surface (not shown) such as a display device. Such input devices may be connected to the processor device 176 via an input device interface 194 that is coupled to the system bus 180, but may also be connected by other interfaces such as a parallel port, a serial port, a universal serial bus (USB) port, an IR interface, etc.

[0068] System 174 may also include a communications interface 196 adapted to communicate with a network as needed or desired. System 174 may also include an electron beam lithography system 198 adapted to access instructions 190 and form a plurality of sub-wavelength apertures in a surface of the optical component according to the instructions 190 to change one or more portions of the surface from a natural refractive index to a desired refractive index.

[0069] Those skilled in the art will recognize improvements and modifications that may be made to the preferred embodiments of the present disclosure, and all such improvements and modifications are deemed to be within the scope of the concepts disclosed herein and the following claims.

Claims

1. 1. A method for correcting wavefront error (WFE), comprising: operating an interferometer by a processor to measure a WFE of electromagnetic radiation (EMR) downstream of the conformal optic and the objective lens, the EMR propagating along an optical axis through the conformal optic and the objective lens and through a flat correction lens, the flat correction lens defining a lens axis, the conformal optic having a rotationally symmetric shape and being oriented rotationally asymmetric with respect to the optical axis at an intersection of the optical axis and the flat correction lens, the flat correction lens having a substantially constant thickness; determining, by the processor, an indication of the refractive index of the planar correction lens that reduces the WFE; operating an energy source with said processor to direct an energy beam at a surface of said planar corrective lens in accordance with said indications of said refractive index to modify said surface thereby varying the refractive index at a plurality of locations of said surface; Equipped with A method comprising:

2. the conformal optic comprises a conformal optical window; 2. The method of claim 1 .

3. the conformal optic comprises a conformal dome; 2. The method of claim 1 .

4. The EMR comprises at least one of a mid-wave infrared (MWIR) wavelength band in the range of 3 μm to 5 μm or a long-wave infrared (LWIR) wavelength band in the range of 8 μm to 14 μm; 2. The method of claim 1 .

5. The planar correction lens is a single lens.

2. The method of claim 1 .

6. The planar correction lens comprises a gradient index (GRIN) lens.

2. The method of claim 1 .

7. The planar correction lens has a thickness of less than 10 mm.

2. The method of claim 1 .

8. 1. A system for wavefront error (WFE) correction, comprising: an interferometer configured to measure a WFE of electromagnetic radiation (EMR) downstream of a conformal optic and an objective lens, the EMR propagating along an optical axis through the conformal optic and the objective lens and through a single flat corrector lens, the single flat corrector lens defining a lens axis, the conformal optic being rotationally asymmetric with respect to the optical axis at an intersection of the optical axis and the single flat corrector lens, the single flat corrector lens having a substantially constant thickness; a processor configured to determine an indication of the refractive index of the single planar corrective lens that reduces the WFE; an energy source configured to direct an energy beam at a surface of the single planar corrective lens in accordance with the refractive index instructions to modify the surface, thereby modifying the refractive index at multiple locations of the surface; Equipped with A system characterized by:

9. the conformal optic comprises a conformal dome; The EMR comprises at least one of a mid-wave infrared (MWIR) wavelength band in the range of 3 μm to 5 μm or a long-wave infrared (LWIR) wavelength band in the range of 8 μm to 14 μm; the planar correction lens comprises a gradient index (GRIN) lens; The planar correction lens has a thickness of less than 10 mm.

9. The system of claim 8.

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