Functional metasurfaces for arbitrary polarization filtering

Abstract

An optical apparatus is configured to filter incident light by polarity, propagating a first polarity away from the apparatus and redirecting a second polarity to evanescence. The apparatus effectively filters the second polarity so that the second polarity does not propagate away from the apparatus, and beneficially does not reflect toward the source of the incident light. Illustrative embodiments include a metasurface device disposed to receive the light from a light source, the metasurface device having a substrate and an array of birefringent pillars disposed on the substrate such that adjacent pillars of the plurality of pillars in a first direction are separated by a first pitch less than or equal to half the wavelength of the received light. In illustrative embodiments, each such pillar is configured to diffract, into the array, received light having a second polarity, which second polarity is orthogonal to the first polarity.

Description

[0001] 128174-10302

[0002] 8 / 15 / 2025

[0003] 1

[0004] Functional Metasurfaces for Arbitrary Polarization Filtering

[0005] RELATED APPLICATIONS

[0006] This application claims priority to U.S. Provisional Application No. 63 / 684,262, filed August 16, 2024 and titled “Functional Metasurfaces for Arbitrary Polarization Filtering” and naming Mohammadrasoul Taghavi, Ali Forouzmand, and Pawel Latawiec as inventors [Attorney Docket No. 128174-10301].

[0007] The disclosure of each of the foregoing is incorporated herein by reference, in its entirety.

[0008] The disclosure of each of the following documents is also incorporated herein by reference, each in its entirety: US patent 9,739,918, titled “Simultaneous Polarization and Wavefront Control using a Planar Device” issued August 22, 2017 to California Institute of Technology.

[0009] FIELD

[0010] Illustrative embodiments generally relate to optics and, more particularly, various embodiments relate to polarization filtering.

[0011] BACKGROUND

[0012] Metasurfaces include a plurality of metasurface elements . Metasurface elements are diffractive optical elements in which individual waveguide elements have subwavelength spacing and have a planar profile. Metasurface elements have recently been developed for application in the UV- IR bands (300-10,000 nm). Compared to traditional refractive optics, metasurface elements may introduce phase shifts onto the light field and / or alter the polarization state of the light. Metasurface elements have thicknesses or cross-sectional dimensions on the order of the wavelength of light at which they are designed to operate, whereas traditional refractive surfaces have thicknesses that are 10-100 times (or more) larger than the wavelength of light at which they are designed to operate. Additionally, metasurface elements may have no variation in thickness along or parallel to the optical axis in the constituent elements and thus are able to shape light without any curvature, as typically included in refractive optics. Compared to traditional diffractive optical elements (DDEs), for example binary diffractive optics, metasurface elements have the ability to impart a range of phase shifts on an incident light field, at a minimum the metasurface elements can have phase shifts between 0-2a: with at least 5 distinct values from that range, whereas binary DDEs are only able to impart two distinct functional values of phase shift and are often limited to phase shifts of either 0 or ljr. Compared to multi-level DOE’s, metasurface elements do not require height variation of its constituent elements along the optical axis, only the in-plane geometries of the metasurface element features vary.

[0013] SUMMARY OF VARIOUS EMBODIMENTS

[0014] An optical apparatus is configured to filter incident light by polarity, propagating a first polarity away from the apparatus and redirecting a second polarity to evanescence. The apparatus 128174-10302

[0015] 8 / 15 / 2025

[0016] 2 effectively filters the second polarity so that the second polarity does not propagate away from the apparatus, and beneficially does not reflect toward the source of the incident light. Illustrative embodiments include a metasurface device disposed to receive the light from a light source, the metasurface device having a substrate and an array of birefringent pillars disposed on the substrate such that adjacent pillars of the plurality of pillars in a first direction are separated by a first pitch less than or equal to half the wavelength of the received light. In illustrative embodiments, each such pillar is configured to diffract, into the array, received light having a second polarity, which second polarity is orthogonal to the first polarity.

[0017] In accordance with one embodiment, an optical apparatus includes a light source which outputs light with a wavelength less than or equal to 1350 nm, and a metasurface device disposed to receive the light from the light source (said light being received light). The metasurface device includes a substrate having a substrate surface, and an array comprising a plurality of pillars, each pillar being a structurally birefringent pillar disposed on the substrate surface such that adjacent pillars of the plurality of pillars in a first direction are separated by a first pitch less than or equal to half the wavelength of the received light. Each such pillar is configured to propagate received light having a first polarity away from the metasurface device, and to diffract, into the array, received light having a second polarity, which second polarity is orthogonal to the first polarity.

[0018] In some embodiments of the optical apparatus, the plurality birefringent pillars include a plurality of super cells, each super cell including a first birefringent pillar and a second birefringent pillar spaced from the first birefringent pillar in the first direction by the first pitch. In some embodiments, the first birefringent pillar and the second birefringent pillar have a non-zero phase gradient.

[0019] In some embodiments adjacent pillars of the plurality of pillars in a second direction are separated by a second pitch, wherein the first pitch is less than the second pitch, and wherein the first direction and the second direction are orthogonal. In some such embodiments, the first pitch is about a third of the wavelength of the received light.

[0020] In some embodiments, the first polarity and the second polarity define an elliptical polarization of the received light. In some embodiments, the elliptical polarization is a circular polarization. In some embodiments, the elliptical polarization is a linear polarization.

[0021] In some embodiments, the metasurface device has a broad band efficiency such that the metasurface device propagates the first polarity of the received light away from the metasurface device and diffracts the second polarity of the received light until evanescence for a range of different wavelengths. In some embodiments, the range of different wavelengths is from 900 nm to 1350 nm.

[0022] In some embodiments, the metasurface device is configured to: reflect the first polarity of received light, and to diffract the second polarity of received light until evanescence.

[0023] In some embodiments, the light source includes a vertical-cavity surface-emitting laser (VCSEL). In some embodiments, the light source includes a light emitting diode (LED). 128174-10302

[0024] 8 / 15 / 2025

[0025] 3

[0026] In some embodiments, the plurality birefringent pillars includes a plurality of super cells, each super cell comprising a first birefringent pillar and a second birefringent pillar spaced from the first birefringent pillar in the first direction by the first pitch, and the plurality of super cells comprise a plurality of super cells that repeat having a period.

[0027] In some embodiments, each pillar is configured to diffract received light having a second polarity in a direction parallel to the surface of the substrate.

[0028] In some embodiments, the wavelength is 1350 nm, and the pitch is less than or equal to 675 nm but greater than 100 nm.

[0029] In some embodiments, the wavelength is 940 nm, and the pitch is less than or equal to 470 nm but greater than 100 nm.

[0030] In some embodiments, the wavelength is 940 nm, and the pitch is less than or equal to 315 nm but greater than 100 nm.

[0031] BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Those skilled in the art should more fully appreciate advantages of various embodiments from the following “Description of Illustrative Embodiments,” discussed with reference to the drawings summarized immediately below.

[0033] Figure 1A schematically illustrates the operation of an embodiment of a metasurface while under illumination of incident light;

[0034] Figure IB schematically illustrates an embodiment of a birefringent pillar;

[0035] Figure 1C schematically illustrates the operation of an embodiment of a an apparatus in which a light source is configured to transmit light to a metasurface;

[0036] Figure 2 schematically illustrates an example plot of Equation 2;

[0037] Figure 3 schematically illustrates an embodiment of a metasurface;

[0038] Figure 4 schematically illustrates an embodiment of plots of transmitted polarization components and extinguished polarization component with respect to wavelength for a metasurface.

[0039] Figure 5A schematically illustrates an embodiment of a metasurface;

[0040] Figure 5B schematically illustrates an embodiment of a metasurface.

[0041] DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0042] In illustrative embodiments, an optical apparatus is configured to filter incident light by polarity, propagating a first polarity away from the apparatus and redirecting a second polarity to evanescence. The apparatus effectively filters the second polarity so that the second polarity does not propagate away from the apparatus, and beneficially does not reflect toward the source of the incident light. Illustrative embodiments include a metasurface device disposed to receive the light from a light source, the metasurface device having a substrate and an array of birefringent pillars disposed on the substrate such that adjacent pillars of the plurality of pillars in a first direction are separated by a first pitch less than or equal to half the wavelength of the received light. In illustrative embodiments, each such pillar is configured to diffract, into the array, received light 128174-10302

[0043] 8 / 15 / 2025

[0044] 4 having a second polarity, which second polarity is orthogonal to the first polarity. Details of illustrative embodiments are discussed below.

[0045] In illustrative embodiments, an optical apparatus capable of propagating a first polarity of light while filtering out a second polarity of light that is orthogonal to the first polarity of light does not include or require diffractive optical elements and / or lenses in addition to a metasurface as described herein. In illustrative embodiments, an optical apparatus capable of propagating a first polarity of light while filtering out a second polarity of light that is orthogonal to the first polarity of light, and beam shaping the propagated light, does not include or require diffractive optical elements and / or lenses in addition to a metasurface as described herein.

[0046] Filtering embodiments

[0047] Various embodiments include a metasurface that has a substrate and an array of pillars. Each pillar is birefringent. Each pillar may comprise amorphous silicon. Each pillar can be rectangular (not square) or elliptical in shape. The birefringence is a function of the dimensions of the pillar. The dimensions are measured in a plane parallel to the substrate. The dimensions may be referred to as length and width, or as major axis and minor axis.

[0048] With regard to impinging light having a wavelength and two orthogonal polarization states, each pillar passes a first polarization of the impinging light, but redirects a second polarization (which is orthogonal to the first polarization) of the impinging light along a path parallel to the plane of the substrate. In this way, the metasurface, in effect, filters out the portion of the impinging light that has the second polarization. From the point of view of the transmitted light, it is as if the metasurface has extinguished the light having a second polarization.

[0049] The ability of the metasurface to filter the light depends on specific characteristics of the pillars. This is done by (1) designing the metasurface birefringent pillars such that one of the polarizations can fade away and other radiate and (2) selecting the pitch of the pillars to be strictly less than half of the effective wavelength, in order to operate in the shadow region as shown in Figure 2 described herein. In other words, a first characteristic is that the pitch between two adjacent pillars must be less than or equal to half of the wavelength. However, there are limitations on the selection of pitch. Generally, achieving larger operating wavelengths and angular bandwidths involves limiting the pitch size of unit cells. However, there exists a limit beyond which the pitch size cannot be further decreased. This limitation is directly related to satisfying the condition necessary for obtaining the required phase span, which is crucial for generating the phase gradient needed to extinguish the polarization component.

[0050] Second, the phase gradient between two adjacent pillars must be properly selected. Structurally birefringent meta-atoms pave the way for simultaneous control over the two orthogonal polarization states in a single nanopillar. Using the mentioned property, it is possible to select two independent phase gradients for the two arbitrary orthogonal polarizations. The inventors discovered that, if the pitch size of the metasurface is smaller than half of the effective operating 128174-10302

[0051] 8 / 15 / 2025

[0052] 5 wavelength it is possible to extinguish one of the orthogonal polarization components by using a proper phase gradient.

[0053] Beam shaping embodiments

[0054] In addition to the filtering described above, in some embodiments the metasurface also imposes beam shaping on the transmitted light by manipulating the wavefront of the transmitted light.

[0055] This is achieved by proper selection of phase gradient between two adjacent pillars. Metasurfaces can control the characteristics of the transmitted (or propagated) polarization components thanks to the possibility of applying different phase-gradients between the two adjacent subwavelength elements (e.g., pillars). By applying different phase-gradients between the two adjacent subwavelength elements (pillars), the device can further control the characteristics of the transmitted polarization components, e.g. to shape the beam. This is the most compact way of doing so: other methods require additional optics to be used after polarization filtering. Examples of beam shaping are to create an illumination that is diffused (“flood”) or patterned (e.g. dots or lines as for optical 3D sensing), or of other beam shapes.

[0056] As disclosed in more detail below, in illustrative embodiments, where impinging light includes a first polarization orthogonal to a second polarization, a metasurface can control each such polarization independently through the rotation / length / width of the metasurface’s pillars. In other words, where two polarization are orthogonal, the metasurface's response to them can be independent.

[0057] Definitions: As used in this description and the accompanying claims, the following terms shall have the meanings indicated, unless the context otherwise requires.

[0058] The term “DOE” means “diffractive optical element.”

[0059] The “period” of a series of super cells e.g., a first super cell and a super cell) is the nonzero distance between them.

[0060] The term “propagate” with respect to a metasurface device receiving incident light means to transmit (or pass) a portion of the incident light or to reflect a portion of the incident light.

[0061] The “phase gradient” of two pillars is the difference in phase imposed by the two pillars on a light wave passing through both pillars. For example, if a first pillar imposes a first phase shift on an impinging light wave, and a second pillar imposes a second phase shift on that impinging light wave, then the phase gradient of the first pillar and second pillar is the quantitative difference between the first phase shift and the second phase shift. The target phase gradient is determined by the intended optical functionality (e.g. beamforming, lensing, etc.) the designer intends to achieve. Phase gradient is designed by the intended optical function, e.g., (lensing, beamshaping, etc.). One way to select or specify the desired phase gradient is to analytically choose a phase such as a hyperbolic phase profile \phi(r) = f - \sqrt{fA2 - rA2}. Selection of the phase gradient or phase, for achieving a desired phase function, they can perform polarization extinction in the orthogonal polarization. 128174-10302

[0062] 8 / 15 / 2025

[0063] 6

[0064] The “phase span” with respect to a plurality of pillars in which each pillar imposes a corresponding phase on a light wave, is the range of phases of the plurality of pillars. For example, consider a set of metasurface elements that map to a phase for a particular polarization: \phi_i, where \phi is the phase induced on the polarization for metasurface i. The phase span of that metasurface refers to the range of the phases: max(\phi_i) - min(\phi_i). Note that the phase spans for two orthogonal polarizations may be different. The requisite phase span in order to enable some optical functionality is achieved by selecting metasurface geometry (pillar pitch, width, length, or other characterizing parameters) such that at, under the design constraints, there is a representative metasurface unit cell with minimal phase impact, and a representative metasurface unit cell with maximal phase impact, meeting the requirement of the phase span. The necessary phase span itself is calculated from the optical functionality necessary from the device, and is typically at least 2pi. In some circumstances, the designer may make a tradeoff in the system design to have a smaller phase span, so long as the optical functionality still meets requirements.

[0065] In some embodiments, a set of unit cells with a desired phase span is arrived at by simulations of a set of candidate unit cells, varying the in-plane geometries or cross-sections of the pillars. For each unit cell, the phase at the output of the unit cell is noted to give that unit cell's phase response, for that particular polarization. To wit, to calculate the phase response of a particular unit cell, we solve Maxwell's equations given a plane-wave incident field with wavevector k_0 and polarization p. At a plane on the other side of the unit cell, we calculate the central Fourier coefficient of the plane-wave response (the "zero order" Fourier mode) for the copolarized field. The argument of this complex-valued coefficient gives the phase response of a particular unit cell. The phase span is then calculated across the set of candidate unit cells with the previous reduction.

[0066] A “pillar” is a birefringent structure disposed on a substrate. A pillar has a length and a width, measured in the plane of the substrate (or in a plane parallel to the plane of the substrate) and has structural birefringence where the length of the pillar is not equal to the width of the pillar. A pillar also has a height measured as the distance between the bottom of the pillar (or measured from the surface of the substrate) and the top of the pillar. In illustrative embodiments, each pillar of a super cell has the same length and width. A first pillar of a super cell may have a different height than the second pillar of that super cell.

[0067] The “pitch” between two pillars (e.g., a first pillar and a second pillar) is the non-zero distance between them. The distance between a first pillar and a second pillar is typically specified as the distance between the center of the first pillar and the center of the second pillar. When the first pillar is adjacent to the second pillar, pitch may be described as the distance between centers of adjacent pillars.

[0068] A “set” includes at least one member. Unless otherwise specified, a set may include as few as a single member, or may include a plurality of members. 128174-10302

[0069] 8 / 15 / 2025

[0070] 7

[0071] A “super cell” is a set of pillars. In illustrative embodiments, a super cell includes two or more pillars. In illustrative embodiments, a metasurface may have a plurality of super cells, each super cell separated from an adjacent super cell by a period.

[0072] A “meta-atom” or “unit cell” is a single pillar.

[0073] Various embodiments include a metasurface including a planar layer of pillars which transmit a desired polarization component of an incident beam and arbitrarily manipulate its wavefront while filtering out another orthogonal component by making it evanescent, rather than reflected. The transmitted polarization can be elliptical, circular, or linear, unlike traditional polarizer filters that may only be linear polarizers. Furthermore, the planar layer maintains its functionality in a wide-band wavelength range and incident angle may make it compatible with standard light sources such as light emitting diodes (LEDs) and vertical cavity surface emitting lasers (VCSELs).

[0074] Additionally, the metasurface may shape the transmitted polarization component into various beam shapes. This is unlike other polarization filters where additional optical elements are included for beam shaping. The metasurface is compact and can replace other layers of conventional optical elements. In conventional optical elements, other layers provide beam shaping while the polarizer provides merely polarization filtering. While conventional metasurfaces may provide polarization filtering, this polarization filtering is narrow-band in operating wavelength and ultra-sensitive to the incident angle and lacking the ability to perform any beam-manipulation (e.g. beam shaping).

[0075] Various embodiments of the disclosed metasurface may be applied to a compact class of light sources (e.g. illuminators) and light detectors (e.g. imagers) which would otherwise be agnostic to the transmitted / received polarization.

[0076] The metasurface may be a metasurface polarizer that radiates one polarization and extinguishes the other orthogonal, undesired polarization by making it evanescent. The polarization can be arbitrary, e.g. elliptical, circular, or linear, or partially polarized.

[0077] The metasurface may include metasurface birefringent pillars which may be structured such that one of the polarizations can fade away (e.g. propagate within the pillars until evanescent) and others radiate through the metasurface. The metasurface birefringent pillars may include a pitch of the pillars to be less than or equal to half of the effective wavelength of the incident light. In some embodiments, each pillar may derive its birefringent property by including one or more anisotropic materials.

[0078] Extinguishing the other polarization by making it evanescent is advantageous. In examples of conventional metasurface polarizers that reflect the orthogonal polarization, the metasurface cannot further shape the transmitted polarization. For these conventional metasurface and other types of polarizers such as wire gride polarizers, reflecting the orthogonal polarization is also undesirable as they can create stray light in the system, as well as negatively impacts the emitter. Those negative impacts include an increase of the junction temperature caused by the photons 128174-10302

[0079] 8 / 15 / 2025

[0080] 8 reabsorbed by the light emitter, which is detrimental to the emitter light conversion efficiency, or returning back in the lasing cavity in the case of a VCSEL which can create instability.

[0081] Further advantages of the disclosed metasurface include dissipating the light by leveraging longer propagation distance, enhanced field confinement, and efficiency energy transfer of the proposed mechanism so the tightly bound beam may be dissipated, not reflected / transmitted in case of presence of loss mechanism in the system.

[0082] Unlike most conventional polarizer filters, which are strictly linear polarizers, e.g. wire-grid or dichroic polarizer filters, the metasurface may be utilized on a wide variety of polarization. For example, not only linear polarization may be utilized, but also elliptical polarization, of which circular and linear polarizations are a subset. In one example, the transmitted polarization can be left circular polarization (FCP), and the orthogonal polarization extinguished or dissipated by evanescence is then right circular polarization (RCP). These arbitrary polarizations may be utilized to calculate the Stokes parameter S3 in a polarization camera. A polarization camera sensitive to circular polarization may be used for stress measurements and various biomedical imaging applications.

[0083] The disclosed metasurface includes a pitch smaller than half the effective operating wavelength of the incident light. The inventors have discovered that limiting pitch to smaller than half the effective operating wavelength of the incident light is a critical feature for configuring a metasurface to diffract a given polarization of light as described herein, to configure the metasurface to reduce or eliminate propagation of that given polarization away from the metasurface and / or to reduce or eliminate redirection of that given polarization back to its source.

[0084] The metasurface may include a wide-band wavelength range and wide-band incident angle. This is unlike other approaches utilizing metasurfaces for polarization filtering which are narrowband in operating wavelength and ultra- sensitive to the incident angle. Wide-band wavelength range and incident angle may provide compatibility with standard light sources such as light emitting diodes (FEDs) and vertical cavity surface emitting lasers (VCSEEs).

[0085] By applying different phase-gradients between the two adjacent subwavelength elements, the device can further control the characteristics of the transmitted polarization components, e.g. beam-shaping. Each nano pillar can control the local phase of a first polarization light extinguished or dissipated by evanescence and a second polarization of light transmitted. The first polarization may be sent to evanescent channel and a phase gradient may be applied between adjacent two elements but at the same time to perform beam-steering on the second polarization light which is radiated so that the required phase gradient is applied for that polarization component. These two happen by controlling the length and width of the pillars. The sub wavelength elements can provide multifunctionality into an optical system where different phase profiles may be applied to different polarization vectors. Thus, the first polarization light may be provided in an evanescent mode and the second polarization light may be transmitted with beam forming / shaping (e.g., steering, focusing, holography). 128174-10302

[0086] 8 / 15 / 2025

[0087] 9

[0088] Typically, polarizers include additional optics to be used after polarization filtering in order to provide beam shaping. However, various embodiments include beam shaping in addition to polarization filtering. Examples of beam shaping include creating an illumination that is diffused (“flood”) or patterned (e.g. dots or lines as for optical 3D sensing), or of other beam shapes.

[0089] Figure 1A is a schematic illustrating the operation of a metasurface while under illumination of incident light in accordance with an embodiment.

[0090] The metasurface 110 includes a plurality of birefringent pillars (121, 122, 123, etc.) disposed on substrate 111. In illustrative embodiments, the substrate 111 has as first surface 112, which may be a planar surface, and a second surface 113 on a side of the substrate 111 opposite the first surface 112.

[0091] In some embodiments, the metasurface 110 includes a light source 199. The light source 199 may be a light-emitting diode (“LED”), or a vertical-cavity surface-emitting laser (“VCSEL”), to name but a few examples. In some embodiments, the light source 199 is disposed and configured to transmit light away from the metasurface 110 in a direction defined by an arrow extending from the first surface 112 towards the second surface 113. In such embodiments, the transmitted light may reflect from a distal surface and be received by the metasurface 110 as received light. Such a distal surface may impose on the transmitted light a first polarity and a second polarity that is orthogonal to the first polarization, or may change one or more polarities of transmitted light.

[0092] In some embodiments, the light source 199 is disposed and configured to transmit light to the metasurface 110, as schematically illustrated in Figure 1C.

[0093] Figure IB schematically illustrates an embodiment of a structurally birefringent pillar 170. The embodiment of Figure IB is rectangular in cross-section where the pillar 170 meets the substrate 111, or in a plane parallel to the substrate 111. The structurally birefringent pillar 170 has a width 171 (which may also be referred-to as its minor axis), a length 172 (which may also be referred-to as its major axis), and a height 173. The width 171 and length 172 are each measured in a plane parallel to the substrate 111, and the height 173 is measured along a line normal to the substrate 111. In illustrative embodiments, the width 171 is not equal to the length 172, such that the pillar 170 does not have a square cross-section or a circular cross-section where the pillar 170 meets the substrate 111, or in a plane parallel to the substrate 111. In some embodiments, the pillar has an elliptical cross-section, having a major axis 172 and a minor axis 171 where the pillar 170 meets the substrate 111, or in a plane parallel to the substrate 111. In some embodiments, the pillars have a cross-sectional shape that does not exhibit four-fold symmetry.

[0094] The incident light 102 includes a first polarization and a second polarization. The first polarization component of light is Pl (151). P2 (152) is the second polarization component of light. Pl and P2 are arbitrary orthogonal polarizations. The metasurface polarizer 104 diffracts the incident light 102 such that the first polarization component Pl is evanescent. Moreover, the metasurface polarizer 104 may control the characteristics of the second polarization component P2 which is transmitted through the metasurface polarizer 104. 128174-10302

[0095] 8 / 15 / 2025

[0096] 10

[0097] In some embodiments, different phase-gradients may be applied between two adjacent subwavelength elements of the metasurface polarizer 104 in order to control the characteristics of the transmitted light.

[0098] Unlike traditional polarizers, the first polarization component Pl is not reflected back to the system or absorbed but instead it is converted to an evanescent beam that does not radiate to the transmission side.

[0099] The metasurface polarizer 104 may utilize bandgap generation. The bending angle in a generic metasurface can be calculated using the generalized Snell’s law for anomalous diffraction using Equation 1 :

[0100] A< > + 2mn = fc0A sin(0). (1)

[0101] Then, it is possible to derive the following equation which determines the required 40 for a chosen pitch size A in order to remain in the shadow region where is no radiation from the metasurface layer using E <2>

[0102] Figure 2 is an example plot of Equation 2. In this plot, A =940nm and A =400 nm which is A <2 / 2 and hence a shadowing region is generated between the radiated anomalous diffraction orders. The pitch size A becomes larger when the shadowing region becomes narrower which decreases the operating wavelength and angular bandwidth of the filter. Thus, the pitch may be A < / 2.

[0103] Structurally birefringent meta-atoms may provide simultaneous control over two orthogonal polarization states in a single nanopillar. In some embodiments, two independent phase gradients may be utilized for the two arbitrary orthogonal polarizations. In some embodiments, the pitch size of the metasurface is smaller than half of the effective operating wavelength which may extinguish one of the orthogonal polarization components by using a proper phase gradient. With the pitch size smaller than half of the effective operating wavelength, the device may have a large operating angular and wavelength bandwidth and thus may be utilized with VCSELs and LEDs. Additionally, an arbitrary beam-shaping technique may be applied to the unfiltered polarization component.

[0104] There may be limitations on the selection of pitch size. Achieving larger operating wavelengths and angular bandwidths may include reducing the pitch size of unit cells. However, there may be limitations on decreasing the pitch size. This limitation may be directly related to satisfying the condition necessary for obtaining the required phase span, which is crucial for generating the phase gradient needed to extinguish the polarization component. In illustrative embodiments, the pitch size is not less than 100 nm. In some embodiments, the pitch size is not less than 200 nm; in some embodiments the pitch size is not less than 300 nm; in some embodiments the pitch size is not less than 50 nm.

[0105] Figure 3 is a schematic illustration of an example metasurface in accordance with an embodiment. As illustrated, the metasurface includes a plurality of pillars. The pillars are spaced apart by a period A. The period A is less than half a wavelength of an incident light. For example, the pitch 128174-10302

[0106] 8 / 15 / 2025

[0107] 11 may be 380 nm while the wavelength of incident light may be 940 nm. The plurality of pillars may have different cross-sectional sizes. In some examples, adjacent pillars in one direction may have different widths and / or lengths. In some examples, adjacent pillars are another direction may have the same widths and / or lengths. The cross-section of the pillars may direct the TE polarization to the first diffraction order and filter the TM polarization by directing it to the evanescent diffraction order. The array may act as both a polarizer and a beam-shaper for the desired polarizations. Also, there may be a large operating wavelength bandwidth. The metasurface may be integrated in a polarization-controlled illuminator which may benefit from a large operating wavelength bandwidth. The phase gradients applied to the TE and TM wave are such that TM becomes evanescent and TE radiates from the metasurface.

[0108] Figure 4 is an embodiment of plots of transmitted polarization components and extinguished polarization component with respect to wavelength for the metasurface. The metasurface includes a period of less than half a wavelength as discussed above. The operating wavelength of the metasurface is wide enough to be used with a wide-band illuminators such as LED and overall, the ratio of the targeted diffraction order remains considerably large with respect to the extinguished one.

[0109] Figure 5A is an example perspective view of a metasurface in accordance with an embodiment. The metasurface decouples the radiating and cut-off channels. Pl is an undesired polarization component. P2 is a desired polarization component. Pl and P2 may be arbitrary orthogonal polarizations. For example, Pl and P2 may be orthogonal elliptical, linear, or circular polarizations. As illustrated, the desired polarization component P2 is reflected while the undesired polarization component Pl is propagated through the metasurface in order to make it evanescent.

[0110] Figure 5B is an example perspective view of a metasurface in accordance with an embodiment. The device of Figure 5B is similar to the device described in connection with Figure 5A and this description is applicable here and will not be repeated. In the device of Figure 5B, the desired polarization component P2 is transmitted through the metasurface while the undesired polarization component Pl is propagated through the metasurface in order to make it evanescent.

[0111] As illustrated in Figure 5A and Figure 5B, each metasurface- is configured to propagate received light having a first polarity away from the metasurface 110, and to diffract, into the array 120, received light having a second polarity, which second polarity is orthogonal to the first polarity. In illustrative embodiments, each pillar is configured to diffract received light having a second polarity in a direction parallel to the surface of the substrate.

[0112] For both devices of Figure 5A and Figure 5B, this isolates the evanescent and radiating field channels. There may be a ratio between the desired and undesired polarization transmittance which may be determined by the pitch size in the direction of the applied phase gradient. Large pitch size (e.g. A-A / 2) may be advantageous for achieving the desired phase span and minimizing the coupling between the neighboring elements. However, smaller pitch sizes (e.g. A -2 / 3) may help with increasing the operating wavelength and angular bandwidth of the cut-off channel. The constraints inherent in these two tradeoffs create a compromise that may restrict the overall efficiency of the 128174-10302

[0113] 8 / 15 / 2025

[0114] 12 filter's performance. The metasurface decouples the cut-off and propagating channels and pitch size requirement by directing the radiating and evanescent waves into different directions, increasing the efficiency and operational bandwidth of the nanoscale polarizers. The metasurface includes two different pitch pxas the pitch 310 in the x direction and pyas the pitch 320 in the y direction. pxcontrols the radiating channel and can be selected large enough to cover the 2TT phase span and pycontrols the evanescent channel and can be selected much smaller to get large operating bandwidth. In some examples, pxmay be smaller than, bigger than, or equal to X / 2 whereas pymay be smaller than or equal to 2 / 2.

[0115] Unlike conventional polarizer filters, such as the wire-grid polarizer, the metasurface may interact with elliptical polarizations. In various embodiments, the metasurface may be used to measure the Stokes parameter S3 in polarimetry applications. For example, circular polarization polarimetry may be used in stress measurements and various biomedical imaging applications. Additionally, the metasurface allows for beam-shaping and polarization control within a single layer, increasing device efficiency. Furthermore, this filter can be applied to the design of vertical-cavity surface-emitting lasers (VCSELs) with polarization control in illuminators. Unlike existing designs where polarization filtering occurs during the lasing process inside the cavity, the metasurface is configured to provide polarization filtering while also providing beam shaping. Thus, attaching a single layer of the proposed metasurface to the VCSEL, both beam-shaping and polarization filtering can be achieved.

[0116] The metasurface 110 may be included in flood illuminators used for example in 2D near infrared (NIR) imaging and 3D sensing, patterned beam illuminators such as dot pattern projectors for 3D sensing methods including Structured Light (SL), ToF, LiDAR. The 3D sensing may include various techniques such as stereovision or ToF (Time of Flight). 2D NIR imaging and 3D sensing may be used in various applications such as consumer electronics (e.g. biometrics in palm readers, payment kiosks, cell phones, smart door locks), 3D point clouds, avatars, AR / VR for gaming, heads up displays (HUD), automotive (e.g. LiDAR for autonomous vehicle driving, cabin and driver monitoring), drones, robotic applications (e.g. optical inspection, machine vision, navigation, object detection).

[0117] A listing of certain reference numbers is presented below.

[0118] 110: Metasurface polarizer;

[0119] 111: Substrate;

[0120] 112: First of substrate;

[0121] 113. Second surface of substrate;

[0122] 120: Pillar array;

[0123] 121: Pillar;

[0124] 122: Pillar;

[0125] 123: Pillar;

[0126] 150: Incident light 128174-10302

[0127] 8 / 15 / 2025

[0128] 13

[0129] 151: First component (“Pl”) of incident light having a first polarization;

[0130] 152: Second component (“P2”) of incident light having a second polarization distinct from the first polarization;

[0131] 161: Filtered light component;

[0132] 162: Output (e.g., propagated) light component;

[0133] 170: Birefringent pillar;

[0134] 171: Width;

[0135] 172: Length;

[0136] 173: Height;

[0137] 199: Light source.

[0138] Various embodiments may be characterized by the potential claims listed in the paragraphs following this paragraph (and before the actual claims provided at the end of the application). These potential claims form a part of the written description of the application. Accordingly, subject matter of the following potential claims may be presented as actual claims in later proceedings involving this application or any application claiming priority based on this application. Inclusion of such potential claims should not be construed to mean that the actual claims do not cover the subject matter of the potential claims. Thus, a decision to not present these potential claims in later proceedings should not be construed as a donation of the subject matter to the public.

[0139] Without limitation, potential subject matter that may be claimed (prefaced with the letter “PC” so as to avoid confusion with the actual claims presented below) includes: PCI. An optical device comprising: a light source which outputs incident light with a wavelength; a metasurface device comprising: a substrate; a plurality of pillars positioned on the substrate, wherein adjacent pillars of the plurality of pillars in a first direction are separated by a first period, and wherein the first period is less than or equal to half the wavelength of the incident light.

[0140] PC2. The optical device of PCI, wherein adjacent pillars of the plurality of pillars in a second direction are separated by a second period, wherein the first period is less than the second period, and wherein the first direction and the second direction are orthogonal.

[0141] PC3. The optical device of PC2, wherein the first period is about half the wavelength of the incident light, wherein the second period is about a third of the incident light. 128174-10302

[0142] 8 / 15 / 2025

[0143] 14

[0144] PC4. The optical device of any of PC1-PC3, wherein the metasurface is transparent to a first polarization of the incident light and propagates a second polarization of the incident light until evanescence, wherein the first polarization and the second polarization are orthogonal.

[0145] PC5. The optical device of PC4, wherein the first polarization and second polarization are elliptical polarizations.

[0146] PC6. The optical device of PC5, wherein the elliptical polarizations are circular polarizations.

[0147] PC7. The optical device of PC5, wherein the elliptical polarizations are linear polarizations.

[0148] PC8. The optical device of PC4, wherein the metasurface has a broad band efficiency such that the metasurface transmits the first polarization of the incident light and propagates the second polarization of the incident light until evanescence for a range of different wavelengths.

[0149] PC9. The optical device of PC8, wherein the range of different wavelengths is from 900 nm to 980 nm.

[0150] PC10. The optical device of PC8, wherein the metasurface performs beam forming to the first polarization of the incident light.

[0151] PCI 1. The optical device of PCI, wherein the metasurface is reflective to a first polarization of the incident light and propagates a second polarization of the incident light until evanescence, wherein the first polarization and the second polarization are orthogonal.

[0152] PC12. The optical device of PC11, wherein the first polarization and second polarization are elliptical polarizations.

[0153] PC13. The optical device of PC 12, wherein the elliptical polarizations are circular polarizations.

[0154] PC14. The optical device of PCI 1, wherein the elliptical polarizations are linear polarizations.

[0155] PC15. The optical device of PC11, wherein the metasurface has a broad band efficiency such that the metasurface is reflective to the first polarization of the incident light and propagates the second polarization of the incident light until evanescence for a range of different wavelengths.

[0156] PC 16. The optical device of PC 15, wherein the range of different wavelengths is from 900 nm to 980 nm. 128174-10302

[0157] 8 / 15 / 2025

[0158] 15

[0159] PC17. The optical device of any of PC1-PC16, wherein the light source comprises a vertical-cavity surface-emitting laser (VCSEL) or a light emitting diode (LED). PCI 8. The optical device of any of PCI -PC 17, wherein each of the pillars of the plurality of pillars has about the same height, length, and width.

[0160] PC 19. The optical device of any of PCI -PC 18, wherein each of the pillars in a second direction has different length and / or width, and wherein each of the pillars in the first direction have about the same length and width.

[0161] PC20. The optical device of PC, wherein the pillars in the second direction form a unit which repeats after a number of pillars.

[0162] The embodiments described above are intended to be merely exemplary; numerous variations and modifications will be apparent to those skilled in the art. Such variations and modifications are intended to be within the scope of the present disclosure as defined by any of the appended claims.

Claims

128174-103028 / 15 / 202516What is claimed is:

1. An optical apparatus comprising: a light source which outputs light with a wavelength less than or equal to 1350 nm; a metasurface device disposed to receive the light from the light source, said light being received light, the metasurface device comprising: a substrate having a substrate surface; and an array comprising a plurality of pillars, each pillar being a structurally birefringent pillar disposed on the substrate surface such that adjacent pillars of the plurality of pillars in a first direction are separated by a first pitch less than or equal to half the wavelength of the received light; the pillars configured to propagate received light having a first polarity away from the metasurface device, and to diffract, into the array, received light having a second polarity, which second polarity is orthogonal to the first polarity.

2. The optical apparatus of claim 1, wherein: the plurality birefringent pillars comprise a plurality of super cells, each super cell comprising a first birefringent pillar and a second birefringent pillar spaced from the first birefringent pillar in the first direction by the first pitch.

3. The optical apparatus of claim 2, wherein the first birefringent pillar and the second birefringent pillar have a non-zero phase gradient.

4. The optical apparatus of claim 1, wherein adjacent pillars of the plurality of pillars in a second direction are separated by a second pitch, wherein the first pitch is less than the second pitch, and wherein the first direction and the second direction are orthogonal.

5. The optical apparatus of claim 1, wherein the first pitch is about a third of the wavelength of the received light.

6. The optical apparatus of claim 1, wherein the first polarity and the second polarity define an elliptical polarization of the received light.

7. The optical apparatus of claim 6, wherein the elliptical polarization is a circular polarization.

8. The optical apparatus of claim 7, wherein the elliptical polarization is a linear polarization.128174-103028 / 15 / 2025179. The optical apparatus of claim 1 wherein the metasurface device has a broad band efficiency such that the metasurface propagates the first polarity of the received light away from the metasurface and diffracts the second polarity of the received light until evanescence for a range of different wavelengths.

10. The optical apparatus of claim 9 wherein the range of different wavelengths is from 900 nm to 1350 nm.

11. The optical apparatus of claim 1, wherein the metasurface device is configured to: reflect the first polarity of received light, and to diffract the second polarity of received light until evanescence.

12. The optical apparatus of claim 1, wherein the light source comprises a vertical-cavity surfaceemitting laser (VCSEL).

13. The optical apparatus of claim 1, wherein the light source comprises a light emitting diode (LED).

14. The optical apparatus of claim 1, wherein: the plurality birefringent pillars comprise a plurality of super cells, each super cell comprising a first birefringent pillar and a second birefringent pillar spaced from the first birefringent pillar in the first direction by the first pitch, and the plurality of super cells comprise a plurality of super cells that repeat having a period.

15. The optical apparatus of claim 1, wherein each pillar is configured to diffract received light having a second polarity in a direction parallel to the surface of the substrate.

16. The optical apparatus of claim 1, wherein the wavelength is 1350 nm, and the pitch is less than or equal to 675 nm but greater than 100 nm.

17. The optical apparatus of claim 1, wherein the wavelength is 940 nm, and the pitch is less than or equal to 470 nm but greater than 100 nm.

18. The optical apparatus of claim 1, wherein the wavelength is 940 nm, and the pitch is less than or equal to 315 nm but greater than 100 nm.

19. The optical apparatus of claim 1, wherein the wavelength is 940 nm, and the pitch is 400 nm.

Images