Stress induced tunable optical waveplate

Abstract

Broadband optical waveplates and methods for their manufacture are described. Example stress induced tunable optical waveplates can operate in any one or the combination of the ultraviolet (UV), visible (VIS), near infrared (NIR), mid-wave infrared (MWIR) and long-wave infrared (LWIR) wavelength ranges. One example method for producing a waveplate with particular retardance characteristics includes selecting a target retardance for the waveplate, using a relationship between retardance, a stress property of a material from which the waveplate can be formed, a thickness of the waveplate, and stress to obtain an amount of stress that is needed to produce the target retardance, determining, based on the amount of stress, an amount of force or pressure that is needed to be applied to the waveplate to produce the target retardance, and providing the amount of force or pressure to the waveplate.

Description

Provisional Patent Application 044974.8144.WO00 (UA25-0 0)STRESS INDUCED TUNABLE OPTICAL WAVEPLATECROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to the provisional application with serial number 63 / 725,509 titled “STRESS INDUCED TUNABLE OPTICAL WAVEPLATE,” filed November 26, 2024. The entire contents of the above noted provisional application are incorporated by reference as part of the disclosure of this document.TECHNICAL FIELD

[0002] The technology described in this patent document relates to tunable optical waveplates and methods for their producing those tunable waveplates.BACKGROUND

[0003] Waveplates have several characteristics that include optical loss, depolarization, sensitivity to temperature, beam deviation and displacement, uniformity and stability, dispersion, toxicity and radioactivity, clear aperture size, birefringence and laser damage threshold. These characteristics generally depend on the material properties and design of the waveplate. Depending on the application, the requirements for the above characteristics can change. Other important (or desired) characteristics include low manufacturing cost, broadband achromatic operation and small form factors.SUMMARY

[0004] The disclosed embodiments, among other features and benefits, describe design methodologies and waveplates with improved characteristics, such as a broadband operation, without the undesirable limitations, such as toxicity. One example method for producing a waveplate with particular retardance characteristics includes selecting a target retardance for the waveplate, using a relationship between retardance, a stress property of a material from which the waveplate can be formed, a thickness of the waveplate, and stress to obtain an amount of stress that is needed to produce the target retardance, determining, based on the amount of stress, an amount of force or pressure that is needed to be applied to the waveplate to produce the target retardance, and providing the amount of force or pressure to the waveplate.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 compares strain in an example plate substrate with specific dimensions for different materials under the same in-plane external force.170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050)

[0006] FIG. 2 illustrates two optical mount designs for generating stress in a substrate in accordance with some example embodiments.

[0007] FIG. 3 shows experimental measurements illustrating change in transmittance, linear retardation and circular retardation of an example plate for zero and a finite externally applied force.

[0008] FIG. 4 illustrates stress distribution in an example crystal substrate under a compressive force applied normal to one facet of the crystal substrate.

[0009] FIG. 5 illustrates strain distribution in an example crystal substrate under a compressive force applied normal to one facet of the crystal substrate.

[0010] FIG. 6 illustrates stress distribution in an example crystal substrate under a shear force of 300N applied to one facet in +y direction.

[0011] FIG. 7 illustrates strain distribution in an example crystal substrate under a shear force applied to one facet in +y direction.

[0012] FIG. 8 illustrates an achromatic waveplate design that includes a combination of two half-wave waveplates and one quarter- wavepl ate in accordance with an example embodiment.

[0013] FIG. 9 illustrates a set of operations that can be carried out to produce a waveplate with particular retardance characteristics in accordance with an example embodiment.

[0014] FIG. 10 illustrates a set of operations that can be carried out to produce a retarder in accordance with an example embodiment.DETAILED DESCRIPTION

[0015] Existing waveplates generally have limited wavelength range, because there are few broadband birefringent materials with low optical loss covering the entire ultraviolet to infrared spectrum. The birefringent materials that exist, such as quartz and magnesium fluoride (MgF?), do not cover the long-wave infrared (LWIR) band, while materials such as cadmium sulfide (CdS), cadmium selenide (CdSe) and cadmium thiogallate (CdGa2S4), which cover the LWIR band, are poisonous and radioactive. On the other hand, transparent materials such as sodium chloride (NaCl), potassium bromide (KBr), and calcium fluoride (CaF2) are broadband transparent and nontoxic, but these materials have no intrinsic birefringent. There is therefore a need for waveplates and design methodologies that satisfy many of the benefits of an ideal waveplate, such as a broadband operation, without the undesirable limitations, such as toxicity.170142901.1Provisional Patent Application 044974.8144.WO00 (UA25-050)

[0016] The above and other shortcomings of the prior waveplates are addressed by the disclosed embodiments that utilize stress birefringence to construct a broadband optical waveplate that is non-toxic. The disclosed embodiments describe broadband optical waveplates and methods for their manufacture, and specifically optical waveplates that can operate in any one or the combination of the ultraviolet (UV), visible (VIS), near infrared (NIR), mid-wave infrared (MWIR) and long-wave infrared (LWIR) wavelength ranges.

[0017] When an external stress is applied to an isotropic material, strain is generated in the material, leading to deformation and anisotropy in thermal, electrical, magnetic, mechanical and optical properties. Stress birefringence can be induced in isotropic and anisotropic materials by application of stress. For small deformations, the process is reversible in the linear stress-strain region. While in many applications, stress birefringence is a property that is undesirable and should be minimized, the disclosed embodiments describe waveplate structure and design methodologies that rely on birefringence that results by applying stress to non-toxic and transparent materials.

[0018] Waveplates are generally made of birefringent materials that have anisotropic refractive indices. Two types of birefringent materials are uniaxial material and biaxial materials. Uniaxial materials include the tetragonal, hexagonal and trigonal crystal systems and have a dielectric tensor Euniaxiai given by:where £0is the vacuum permittivity, n0and neare the ordinary and extraordinary refractive indices. The linear birefringence of a material is defined by An;= ne— n0. Most waveplate has a fast and a slow axis. Light polarized along the slow axis encounters a higher index of refraction than light polarized along the fast axis.

[0019] Biaxial materials include the triclinic, monoclinic and orthorhombic crystal systems and have a dielectric tensorbiaxiai given bywhere nx, ny, nzare refractive indices along the three principal coordinate axes.170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050)

[0020] An important specification of a waveplate is its retardation, S, which is related to the thickness, d, wavelength, A, and birefringence, An as follows:

[0021] For a linear waveplate, the retardation is defined to be the phase shift between two orthogonal linear polarization states. For a circular waveplate, the retardation is defined to be the phase shift between two orthogonal circular polarization states. For an elliptical waveplate, the retardation is defined to be the phase shift between two orthogonal elliptical polarization states. A zero order waveplate has a retardation less than n, whereas a multiple order waveplate has a retardation of the order of 2mn, where m is an integer greater than or equal to 1. A multiple order waveplate is generally more sensitive to beam angle and temperature than a zero order waveplate. A quarter waveplate has a retardation of TT / 2, and a half waveplate has a retardation of n.

[0022] Waveplates can be made of single crystal materials such as quartz or calcite. One type of waveplate is made of a birefringent polymer such as a liquid crystal polymer. A polymer waveplate can be stacked and patterned and is compatible with roll-to-roll manufacturing. Polymer waveplates are used extensively in displays and generally have a low laser damage threshold. Other types of waveplates include metamaterial waveplates and form birefringence waveplates. Both types are made of periodically etched patterns on a transparent substrate. The patterns have subwavelength dimensions and require multiple micro and nanofabrication processing steps. These types of waveplates are generally narrow band. Some designs have high aspect ratio features with submicron dimensions, which are costly to manufacture especially those on a nonstandard substrate that is not silicon.

[0023] Waveplates can have either a reflective or a transmissive design. Existing transmissive waveplates operate in particular wavelength range, for example, in the ultraviolet or MWIR, due to availability of transparent material at those wavelengths. Existing reflective waveplates can operate in the LWIR and beyond. Notably, reflective waveplates that are based on mirrors are narrow band and utilize the phase shift between the 5- and / >-polarized light when light is reflected from a material, such as a metal, usually at an angle of 45 degrees. A common reflective waveplate is the quarter phase retarder mirror used in carbon dioxide lasers to convert a linear polarization to a circular polarization at 10.6 pm. However, the existing waveplates cannot operate from UV to LWIR wavelength range and beyond.170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050)

[0024] The disclosed embodiments, among other features and benefits, describe waveplates that can operate in the broadband range that spans from UV to LWIR by relying on stress birefringence as described herein.

[0025] To facilitate the understating of the disclosed technology, it is helpful to note that retardation, 8, of a material with a thickness, d, under stress, tr, is related to the stress optic coefficient, C^, as follow:

[0026] The stress optic coefficient is tabulated for several optical materials in various publications, such as in P. Szczesniak, D. Cuddeback, J. C. Corelli, “Stress-induced birefringence of solid transparent to 1- to 12-prn light,” J. Appl. Phys. 47, 5356-5359 (1976). is given in a unit of Brewsters (1 Brewster = 10'13cm2 / dyne) and has a typical magnitude of 0.5 to 25 Brewsters, depending on material and wavelength.

[0027] As an example, for a chalcogenide glass TI-1173, = 25.22 Brewsters, A = 10.6 pm, tr = 10 kg / cm2, 8 = 7T / 2, 1kg = 9.81 x 106dynes, the thickness of a zero-order quarter waveplate is 10.7 mm.

[0028] According to the disclosed embodiments, the retardation of a waveplate is tuned by stress, and thickness can further provide an additional tuning parameter. In some embodiments, stress in the substrate can be introduced by applying external forces to the substrate. For example, compressive stress due to an external planar force on a two-dimensional (2D) plate substrate leads to deformation in the plate. If we assume that stress is uniformly distributed in the plate, and inplane deformations are very small, whereas deformation in the plate thickness direction (z direction) is negligible, normal stress, cr, is proportionally related to strain, e, based on Hooke's law, as follows:

[0029] In Equation (5), E is the effective modulus of elasticity of a homogeneous, isotropic and linear elastic material, and v is the material’ s Poisson's ratio. It should be noted that the symbol £ in Equation (5) represents strain, and should not be confused with Epaxial inEquation (2) that represents dielectric tensor. Strain can be evaluated by the plate dimensions, material properties and applied force, as follow:170142901.1Provisional Patent Application 044974.8144.WO00 (UA25-050)L- L F(l+u)(l-2v)£ = - = — - - - - (6)L EA ’

[0030] In Equation (6), F is the normal force acting perpendicular to the area A of the plate, and AL is the deformation in the force direction.

[0031] For a given material, strain in the substrate due to normal compressive stress can be estimated based on Equation (6) and the material properties. FIG. 1 compares strain in a plate substrate with dimensions of 10 mm x 10 mm x 2 mm for different materials under the same inplane external force of 300N. An external force can create optical retardation in a material that can be determined based on Equations (4) and (5) above.

[0032] By leveraging the material and stress properties, a waveplate can be constructed using a material, such as NaCl, KBr, or a combination thereof, which is optically transparent from UV to LWIR. Other examples of optically transparent materials in the above range include chalcogenide or tellurite glass, which also have broad transmission band but are toxic when dissolved in the human body. Therefore, they may not be suitable for some applications.

[0033] FIG. 2 illustrates example optical mount designs for generating stress in the substrate in accordance with some example embodiments. Notably, panel (a) illustrates a design that generates stress by compression, and panel (b) illustrates an example design that generates stress by a sheer force. The design for generating normal stress in the substrate (panel (a)) includes a steel base and a steel block. The base is fixed on a stationary surface (x-y plane) with an open space at the base center to allow light from a light source to go through the planar surfaces (x-y plane) of the sample (e.g., at a normal angle) for detection. The steel block in FIG. 2 is connected to a micrometer, which is connected to the base. When the micrometer is advanced in the +x direction, the block moves freely in x-direction while being supported by the base. As shown in, for example, panel (a) of FIG. 2, the sample is suspended between the block’s side wall and the vertical wall of the base by surface contact with minimum force. Advancing the micrometer compresses the sample in the +x direction, resulting in induced optical birefringence in the substrate due to normal stress. Panel (b) of FIG. 2 illustrates the design for generating shear stress in the substrate, which similar to panel (a)’s design, is constructed with a steel base and a steel block. The steel base is fixed on a stationary surface (x-y plane) with open space at the base center for the light path to go through the sample’s planar surfaces (x-y plane) (e.g., at a perpendicular angle) for detection. The steel block is connected to a micrometer, which is connected to the base.170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050)When the micrometer is advanced in +x or -x direction, the block moves freely in x-direction while being supported by the base. Two facet edges (in x-z plane) of the sample are first fixed on the side walls of the base and the block, respectively, by adhesives, without external forces to the substrate. Advancing the micrometer in +x or -x direction generates shear stress in the sample, resulting in shear stress induced optical birefringence in the substrate.

[0034] For illustration purposes, the stress induced birefringence of a CaF2 plate (10mm x 10mm x 3mm) was investigated using a mount similar to that shown in panel (a) of FIG. 2. The Mueller matrix of the plate was measured from 400nm to 700nm using an Axometrics AxoScan polarimeter (Huntsville AL, USA). FIG. 3 shows the transmittance, linear retardation and circular retardation of the CaF2 plate for zero and a finite externally applied force. Tn general, a uniform stress distribution can create a change in linear retardation, and a nonuniform stress distribution can create a change in both linear and circular retardations. In some example embodiments, a mount with nonuniform applied force includes at least one block of a particular shape and dimension along with at least a means for applying stress, such as a micrometer, hydraulic press, pneumatic press, piezoelectric press, piezomagnetic press, thermomechanical press, and microelectro-mechanical systems (MEMS) and the like, which serve to tune the force on the block. The surface of the block in contact with the waveplate to apply force / pressure can be flat, curved or arbitrary, depending on the desired stress distribution. The force can be applied in one or more directions and can produce a combination of compression and shear stress. In some implementations, where a uniform stress / stain in the waveplate for uniform retardance is desired, the force / pressure is uniformly applied. In other applications a spatially varying retardance in a waveplate may be desired. Thus, by manipulating the magnitude, location and direction of applied force / pressure, a spatial varying stress field can be obtained in a waveplate, which allows achieving spatially varying retardance.

[0035] In some embodiments, the micrometer can be replaced by a fastener which applies a fixed (e.g., precomputed) or changeable force to obtain the desired retardation characteristics. In some embodiments, where a nonuniform retardation is needed, a mount with the desired force distribution that matches closely the required stress distribution is designed to generate the nonuniform retardation. In some implementations, the device that applies the force or pressure to the waveplates is electrically or mechanically driven from commands that are provided by a170142901.1Provisional Patent Application 044974.8144.WO00 (UA25-050) processor or controller. The processor or controller can, for example, use a look up table or compute the amount of force or pressure that is needed to be applied.

[0036] Stress distribution in a CaF crystal substrate with dimensions of 10mm x 10mm x 2mm was simulated based on a small deformation model to further illustrate some aspects of the disclosed technology. The crystal substrate was fixed at one facet (y-z plane) while its opposite facet (y-z plane) was subjected to a compressive force of 300N normal to the facet, as shown in FIG. 4. The stress in the substrate, and particularly, in the x-y planes where the light transmits through, is relatively uniform with a value about 15MPa. Lower stress values are shown close to the fixed facet whereas the maximum and minimum values are located at the corners and edges of the fixed facet respectively. Correspondingly, strain in the same example substrate shows a similar distribution, as shown in FIG. 5. Notably, in FIG. 5, a compressive force of 300N was applied normal to the illustrated facet. An average strain of 2.3xl0-4mm / mm is obtained in most of the surface area in the two x-y planes. The result also validates that deformation in the substrate is indeed small, about several microns for the 10mm long sample. In this example, practically the entire area of sample can provide a clear aperture with a desired retardance characteristic.

[0037] Stress distribution of the same substrate was also evaluated under shear stress. The same crystal substrate was fixed at one facet (y-z plane) while its opposite facet (y-z plane) was subjected to a shear force of 300N in the facet in +y direction, as illustrated in FIG. 6. The stress distribution, different from that under compressive force, is uniform in most (but not all) of the areas in the x-y planes with a value about 30MPa. Variations in stress are shown close to the facets with the maximum and minimum values located at the corners and edges of the fixed facet respectively. Correspondingly, FIG. 7 illustrates strain in the substrate under shear force, which exhibits uniform distribution in most (but not all) of the surface area in the x-y plane through the thickness of the waveplate; strain variation in any individual x-y plane through the thickness of the waveplate is small with an average value of 4xl0'4mm / mm. The results in FIGS. 6 and 7 indicate that it is feasible to obtain stress with uniform distribution covering more than 60% of the light-transmitting substrate area.

[0038] In some embodiments, the shape of the waveplate can be a triangle, a square, a rectangular, a parallelogram, a trapezoidal, a polygon, a circle or an arbitrary shape that allows the application of a normal or shear force. The thickness of the waveplate is determined by the required170142901.1Provisional Patent Application 044974.8144.WO00 (UA25-050) retardation (based on, for example, Equation (4)). The surfaces of the waveplate that receive light can be coated with anti -reflection coating to reduce optical loss. The surface(s) of the waveplate can also be coated with a multi-layer dielectric coating to pass and reflect different bands of wavelength, as may be necessary to tune for a specific band of wavelengths. In some embodiments, the facet of the waveplate can be coated with a layer of polarizer coating which transmits one polarization state and reflect the orthogonal polarization state. In other embodiments, the waveplate can be a prism with a uniform cross-section along its length.

[0039] As evident from the description herein, waveplates with practically any retardance can be designed and constructed, and further tuned to achieve a different retardance, by relying on stress birefringence, operable across a large range of wavelengths that can span from UV to LWIR. One example method for such a design includes selecting a target retardance. Equation (4) provides the relationship between retardance and stress optic coefficient of the material, thickness of the waveplate, and stress for a given wavelength. Accordingly, the amount of stress that is needed to produce the target retardance can be determined. For example, the amount of stress for a waveplate of a particular material and thickness, at a desired wavelength, can be obtained. Once the desired stress is determined, the amount of strain, and then the amount of force that is necessary to achieve the desired retardance can be obtained using Equations (5) and (6). All or some of the above determinations can be made using one or more tables, computations, iterations or neural networks of an artificial intelligence engine. The amount of force can then be applied to the waveplate using, for example, a calibrated micrometer. In some embodiments, the waveplate can be tested to determine whether it produces the desired amount of retardance, and the force can be fine-tuned if needed to achieve the proper retardance. The force can also be changed to coarsely tune the retardance to different value. It should be noted that in the above description, force has been used without limitation to facilitate the description; it is however understood that other related parameters, such as pressure which is force divided by area, can be used.

[0040] The above examples, for the sake of illustration, describe a single waveplate design that operates at a particular wavelength, or range of wavelengths. The disclosed technology can be implemented in some embodiments to include multiple waveplates operating over a broad range of wavelengths. For example, an achromatic and elliptical waveplate design can be made by stacking multiple waveplates of different orientation and retardation. A common achromatic170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050) quarter-wave waveplate can be designed by stacking two half-waveplates and a quarter- wavepl ate. Based on some example embodiments, a tunable broadband achromatic and elliptical waveplate can include a stack of multiple waveplates of different orientation and retardation caused by stress birefringence. The multiple waveplates can be stressed by a single mount and individually by multiple mounts. The waveplate can also be stacked with a separate polarizer and / or interference optical filter.

[0041] As one example of an achromatic waveplate design, an achromatic quarter waveplate can include a combination of two half-wave waveplates and one quarter- wavepl ate of the same material at a wavelength of Acat the center of the spectral range to be covered. The angle of the fast optical axis relative to the direction of the incident linear polarized light for the first half waveplate, second half waveplate and quarter-wave plate are equal to 6, 0and 0 + 01+ 02respectively. An achromatic waveplate design covering the wavelength range from I.325ACto 0.675Achas the angle values: 0 = 6°52', 0L= 27°40', and 02= 65°49'. A schematic of this combination is shown in FIG. 8. Notably, in FIG. 8, an achromatic waveplate design made of a combination of two half-wave waveplates and one quarter- wavepl ate of the same material is illustrated. In one embodiment for a MWIR achromatic waveplate, Ac= 4 pm, and the waveplate covers the wavelength from 2.7 pm to 5.3 pm. In another embodiment for a LWIR achromatic waveplate, Ac= 11 pm, and the waveplate covers the wavelength from 7.4 pm to 14.6 pm.

[0042] Other designs of achromatic waveplate can consider the exact wavelength dispersion of the plate material. In some embodiments, the plate material can be of different types. In other embodiments, the number of waveplate in the combination is not equal to three. In some embodiments, multiple stacks of waveplates can be used, where each stack can provide the desired retardance (based on stress birefringence) for one particular wavelength range, while allowing other wavelengths ranges to pass through. For example, a first stack provides the desired retardance in the UV range, and allows LWIR light to pass through, and a second stack allows the UV light to pass through while providing the desired retardance to the LWIR light. In some embodiments, the waveplate is connected to a heater and / or a cooler to maintain a constant operating temperature. Hot objects can emit MWIR and LWIR light which can interfere with the operation of the waveplate.

[0043] FIG. 9 illustrates a set of operations that can be carried out to produce a waveplate with170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050) particular retardance characteristics in accordance with an example embodiment. At 902, a target retardance for the waveplate is selected. At 904, using a relationship between retardance, a stress property of a material from which the waveplate can be formed, a thickness of the waveplate, and stress, an amount of stress that is needed to produce the target retardance is obtained. At 906, based on the amount of stress, an amount of force or pressure that is needed to be applied to the waveplate to produce the target retardance is obtained. At 908, the amount of force or pressure to the waveplate is provided.

[0044] In one example embodiment, the material comprises a material that is optically transparent in a broad range of wavelengths that span from ultraviolet (UV) to long-wave infrared (LWTR). Tn another example embodiment, the material comprises sodium chloride (NaCl), potassium bromide (KBr), or calcium fluoride (CaF2). In still another example embodiment, the stress property of the material is a stress optic coefficient of the material. In yet another example embodiment, the force or pressure includes an external normal compressive force or pressure, or an external sheer force or pressure.

[0045] According to one example embodiment, the waveplate is a first of a plurality of waveplates, the amount of stress that is needed to produce the target retardance is a first amount of stress that is needed to produce the target retardance for a first wavelength or range of wavelengths when applied to the first waveplate, and the method further comprises determining an amount of force or pressure that is needed to be applied to the remaining waveplates of the plurality of waveplates to produce the target retardance at one or more additional wavelengths or ranges of wavelengths different from the first wavelength or range of wavelengths. In another example embodiment, the plurality of waveplates consists of three waveplates. In another example embodiment, the plurality of waveplates produces the target retardance over one or part of: ultraviolet (UV) range of wavelength, visible (VIS) range of wavelength, near infrared (NIR) range of wavelength, mid-wave infrared (MWIR) range of wavelengths or long-wave infrared (LWIR) range of wavelengths. In yet another example embodiment, each of the plurality of waveplates is oriented at a different angle with respect to another one of the plurality of waveplates. In still another example embodiment, for each of the remaining waveplates, the method comprises providing the amount of force or pressure to the corresponding waveplate.

[0046] In one example embodiment, obtaining the amount of stress or determining the amount170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050) of force or pressure is performed at least in part by using: one or more lookup tables, a mathematical relationship, or an artificial intelligence engine. In another example embodiment, the method includes measuring an actual retardance provided by the waveplate, and upon a determination that the actual retardance measurement does not match the target retardance, changing the amount of force or pressure that is applied to the waveplate until the actual retardance measurement substantially matches the target retardance for a first wavelength or range of wavelengths.

[0047] In another example embodiment, the method includes selecting a different target retardance for the waveplate, using the relationship between retardance, the stress property of the material, the thickness of the waveplate, and stress to obtain a different amount of stress that is needed to produce the different target retardance, determining, based on the different amount of stress, an amount of force or pressure that is needed to be applied to the waveplate to produce the different target retardance, and providing the different amount of force or pressure to the waveplate. In yet another example embodiment, obtaining the amount of stress comprises selecting the material to consist of one of a plurality of materials that is optically transparent over a first range of wavelengths, and determining both the thickness of the waveplate and the amount of stress that is needed to produce the target retardance.

[0048] Another aspect of the disclosed embodiments relates to method for producing a retarder as illustrated in FIG. 10. At 1002, a target birefringence characteristic for one or more waveplates over a first wavelength or range of wavelengths is selected. At 1004, based on a relationship between birefringence characteristic, a stress property of a material from which the one or more waveplates can be formed, one or more dimensions of the one or more waveplates, and stress, determine an amount of force or pressure that is needed to be applied to each of the one or more waveplates to produce the target birefringence characteristic over the first wavelength or range of wavelengths. At 1006, the amount of force or pressure is provided to each of the one or more waveplates.

[0049] Another aspect of the disclosed embodiments relates to a tunable waveplate that includes one or more waveplates, each waveplate comprising a material that is transparent over a range of wavelengths; and means for applying a changeable force or pressure to one or more facets of the one or more waveplates, wherein the changeable force or pressure comprises a plurality of170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050) amounts of force or pressure, and each amount of force or pressure causes the tunable waveplate to exhibit a different retardance due to stress birefringence.

[0050] In one example embodiment, the material comprises sodium chloride (NaCl), potassium bromide (KBr), or calcium fluoride (CaF2). In another example embodiment, the tunable waveplate includes a plurality of waveplates, wherein: the means for applying the changeable force or pressure is operable to: apply a first amount or amounts of force or pressure to the one or more facets of a first set of waveplates such that the tunable waveplate exhibits a first target retardance over a first range of wavelengths, and apply a second amount or amounts of force or pressure to the one or more facets of a second set of waveplates such that the tunable waveplate exhibits the first target retardance over a second range of wavelengths.

[0051] In another example embodiment, the first range of wavelengths is mid-wave infrared (MWIR) and the second range of wavelengths is long-wave infrared (LWIR). In yet another example embodiment, one of the first range of wavelengths or the second range of wavelengths is an ultraviolet (UV) or visible range of wavelengths. In still another example embodiment, the tunable waveplate includes three waveplates, wherein each waveplates is oriented at different angles with respect to another one waveplates, and the means for applying the changeable force or pressure is operable at least two different amounts of force or pressure to two of the waveplates.

[0052] In yet another example embodiment, the means for applying the force or pressure comprises one or more of a micrometer, a fastener, a mount designed to exert one or more uniform or non-uniform forces to the one or more waveplates, a tunable piston, a hydraulic press, a pneumatic press, a piezoelectric press, a piezomagnetic press, a thermomechanical press, or a micro-electro-mechanical system. In one example embodiment, the tunable waveplate is coupled to a processor and a memory with instructions stored thereon, wherein the instructions upon execution by the processor cause the processor to provide one or more commands to apply one or more of the plurality of amounts of force or pressure. In another example embodiment, one or more of the plurality of amounts of force or pressure are determined using: one or more lookup tables, a mathematical relationship, or an artificial intelligence engine.

[0053] Another aspect of the disclosed embodiments relates to a retarder system that includes a plurality of waveplates, each waveplate comprising a material that is transparent over a range of wavelengths spanning at least one of ultraviolet (UV) range of wavelength, visible (VIS) range of170142901.1Provisional Patent Application 044974.8144.WO00 (UA25-050) wavelength, near infrared (NIR) range of wavelength, mid-wave infrared (MWIR) or long-wave infrared (LWIR), wherein each waveplate is positioned in the retarder system to experience an amount of force or pressure that causes the waveplate to exhibit a particular retardance, each waveplate is oriented at a different angle with respect to at least another waveplate, and a first set of the plurality of waveplates are positioned in cascade that collectively provide a target retardance in at least one of the UV, VIS, NIR, MWIR or LWIR ranges.

[0054] While this patent document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0055] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments.

[0056] It is understood that the various disclosed embodiments may be implemented individually, or collectively, in devices comprised of various optical components, electronics hardware and / or software modules and components. These devices, for example, may comprise a processor, a memory unit, an interface that are communicatively connected to each other, and may range from desktop and / or laptop computers, to mobile devices and the like. The processor and / or controller can perform various disclosed operations based on execution of program code that is stored on a storage medium. The processor and / or controller can, for example, be in communication with at least one memory and with at least one communication unit that enables the exchange of data and information, directly or indirectly, through the communication link with170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050) other entities, devices and networks. The communication unit may provide wired and / or wireless communication capabilities in accordance with one or more communication protocols, and therefore it may comprise the proper transmitter / receiver antennas, circuitry and ports, as well as the encoding / decoding capabilities that may be necessary for proper transmission and / or reception of data and other information.

[0057] Various information and data processing operations described herein may be implemented in one embodiment by a computer program product, embodied in a computer- readable medium, including computer-executable instructions, such as program code, executed by computers in networked environments. A computer-readable medium may include removable and non-removable storage devices including, but not limited to, Read Only Memory (ROM), Random Access Memory (RAM), compact discs (CDs), digital versatile discs (DVD), etc. Therefore, the computer-readable media that is described in the present application comprises non-transitory storage media. Generally, program modules may include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps or processes

[0058] Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document.170142901.1

Claims

Provisional Patent Application 044974.8144.WOOO (UA25-050)CLAIMSWHAT IS CLAIMED IS:

1. A method for producing a waveplate with particular retardance characteristics, comprising: selecting a target retardance for the waveplate; using a relationship between retardance, a stress property of a material from which the waveplate can be formed, a thickness of the waveplate, and stress to obtain an amount of stress that is needed to produce the target retardance; determining, based on the amount of stress, an amount of force or pressure that is needed to be applied to the waveplate to produce the target retardance; and providing the amount of force or pressure to the waveplate.

2. The method of claim 1, wherein the material comprises a material that is optically transparent in a broad range of wavelengths that span from ultraviolet (UV) to long-wave infrared (LWIR).

3. The method of claim 1, wherein the material comprises sodium chloride (NaCl), potassium bromide (KBr), or calcium fluoride (CaF?).

4. The method of claim 1, wherein the stress property of the material is a stress optic coefficient of the material.

5. The method of claim 1, wherein the force or pressure includes an external normal compressive force or pressure, or an external sheer force or pressure.

6. The method of claim 1, wherein: the waveplate is a first of a plurality of waveplates, the amount of stress that is needed to produce the target retardance is a first amount of stress that is needed to produce the target retardance for a first wavelength or range of wavelengths when applied to the first waveplate, and170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050) the method further comprises determining an amount of force or pressure that is needed to be applied to the remaining waveplates of the plurality of waveplates to produce the target retardance at one or more additional wavelengths or ranges of wavelengths different from the first wavelength or range of wavelengths.

7. The method of claim 6, wherein the plurality of waveplates consists of three waveplates.

8. The method of claim 6, wherein the plurality of waveplates produces the target retardance over one or part of: ultraviolet (UV) range of wavelength, visible (VIS) range of wavelength, near infrared (NIR) range of wavelength, mid-wave infrared (MWIR) range of wavelengths or longwave infrared (LWIR) range of wavelengths.

9. The method of claim 6, wherein each of the plurality of waveplates is oriented at a different angle with respect to another one of the plurality of waveplates.

10. The method of claim 6, comprising, for each of the remaining waveplates, providing the amount of force or pressure to the corresponding waveplate.

11. The method of claim 1, wherein obtaining the amount of stress or determining the amount of force or pressure is performed at least in part by using: one or more lookup tables, a mathematical relationship, or an artificial intelligence engine.

12. The method of claim 1, comprising: measuring an actual retardance provided by the waveplate, and upon a determination that the actual retardance measurement does not match the target retardance, changing the amount of force or pressure that is applied to the waveplate until the actual retardance measurement substantially matches the target retardance for a first wavelength or range of wavelengths.

13. The method of claim 1, comprising: selecting a different target retardance for the waveplate;170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050) using the relationship between retardance, the stress property of the material, the thickness of the waveplate, and stress to obtain a different amount of stress that is needed to produce the different target retardance; determining, based on the different amount of stress, an amount of force or pressure that is needed to be applied to the waveplate to produce the different target retardance; and providing the different amount of force or pressure to the waveplate.

14. The method of claim 1, wherein obtaining the amount of stress comprises selecting the material to consist of one of a plurality of materials that is optically transparent over a first range of wavelengths, and determining both the thickness of the waveplate and the amount of stress that is needed to produce the target retardance.

15. A method for producing a retarder, comprising: selecting a target birefringence characteristic for one or more waveplates over a first wavelength or range of wavelengths; based on a relationship between birefringence characteristic, a stress property of a material from which the one or more waveplates can be formed, one or more dimensions of the one or more waveplates, and stress, determining an amount of force or pressure that is needed to be applied to each of the one or more waveplates to produce the target birefringence characteristic over the first wavelength or range of wavelengths; and providing the amount of force or pressure to each of the one or more waveplates.

16. A tunable waveplate, comprising: one or more waveplates, each waveplate comprising a material that is transparent over a range of wavelengths; and means for applying a changeable force or pressure to one or more facets of the one or more waveplates, wherein the changeable force or pressure comprises a plurality of amounts of force or pressure, and each amount of force or pressure causes the tunable waveplate to exhibit a different retardance due to stress birefringence.170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050)17. The tunable waveplate of claim 16, wherein the material comprises sodium chloride (NaCl), potassium bromide (KBr), or calcium fluoride (CaF2).

18. The tunable waveplate of claim 16, comprising a plurality of waveplates, wherein: the means for applying the changeable force or pressure is operable to: apply a first amount or amounts of force or pressure to the one or more facets of a first set of waveplates such that the tunable waveplate exhibits a first target retardance over a first range of wavelengths, and apply a second amount or amounts of force or pressure to the one or more facets of a second set of waveplates such that the tunable waveplate exhibits the first target retardance over a second range of wavelengths.

19. The tunable waveplate of claim 18, wherein the first range of wavelengths is mid-wave infrared (MWIR) and the second range of wavelengths is long-wave infrared (LWIR).

20. The tunable waveplate of claim 18, wherein one of the first range of wavelengths or the second range of wavelengths is an ultraviolet (UV) or visible range of wavelengths.

22. The tunable waveplate of claim 16, comprising three waveplates, wherein each waveplates is oriented at different angles with respect to another one waveplates, and the means for applying the changeable force or pressure is operable at least two different amounts of force or pressure to two of the waveplates.

23. The tunable waveplate of claim 16, wherein the means for applying the force or pressure comprises one or more of a micrometer, a fastener, a mount designed to exert one or more uniform or non-uniform forces to the one or more waveplates, a tunable piston, a hydraulic press, a pneumatic press, a piezoelectric press, a piezomagnetic press, a thermomechanical press, or a micro-electro-mechanical system.

24. The tunable waveplate of claim 16, coupled to a processor and a memory with170142901.1Provisional Patent Application 044974.8144.WOOO (UA25-050) instructions stored thereon, wherein the instructions upon execution by the processor cause the processor to provide one or more commands to apply one or more of the plurality of amounts of force or pressure.

25. The tunable waveplate of claim 24, wherein one or more of the plurality of amounts of force or pressure are determined using: one or more lookup tables, a mathematical relationship, or an artificial intelligence engine.

26. A retarder system, comprising: a plurality of waveplates, each waveplate comprising a material that is transparent over a range of wavelengths spanning at least one of ultraviolet (UV) range of wavelength, visible (VIS) range of wavelength, near infrared (NIR) range of wavelength, mid-wave infrared (MWIR) or long-wave infrared (LWIR), wherein each waveplate is positioned in the retarder system to experience an amount of force or pressure that causes the waveplate to exhibit a particular retardance, each waveplate is oriented at a different angle with respect to at least another waveplate, and a first set of the plurality of waveplates are positioned in cascade that collectively provide a target retardance in at least one of the UV, VIS, NIR, MWIR or LWIR ranges.170142901.1

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