Two-dimensional metasurface beamforming system and method

Abstract

The metasurface may include a substrate layer and a two-dimensional array of metal optical columns arranged in parallel rows and extending vertically relative to the substrate layer. Gaps between adjacent columns form an optical resonator, and a tunable dielectric material is located in the optical resonator between the columns. The reflective layer between the substrate layer and the two-dimensional array of pillars may include a two-dimensional array of elongated rectangular reflector patches arranged in parallel rows with electrically isolated gaps between adjacent rows of reflector patches. A plurality of reflector patches may be arranged longitudinally within each row with a non-resonant gap between adjacent reflective patches. The reflector patches in adjacent rows may be offset relative to each other such that a non-resonant gap between adjacent reflector patches in one row is not aligned with a non-resonant gap between adjacent reflector patches in adjacent rows.

Description

Related Applications

[0001] This application claims priority to U.S. Patent Application No. 18 / 459,310 filed on August 31, 2023 (titled “Two-Dimensional Metasurface Beam Forming Systems and Methods”), which claims priority to and benefits under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 63 / 376,129 filed on September 19, 2022 (titled “Two-Dimensional Metasurface Beam Forming Systems and Methods”), both of which are incorporated herein by reference in their entirety. Technical Field

[0002] The present disclosure relates to optical metasurfaces, including tunable resonant optical metasurfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Figure 1A A perspective view showing a simplified block diagram of the reflective layer and resonator layer of a two-dimensional optical metasurface according to one embodiment.

[0004] Figure 1B An exploded perspective view of a simplified block diagram of the reflective layer and resonator layer of a two-dimensional optical metasurface is shown according to one embodiment.

[0005] Figure 1C A top perspective view of a simplified block diagram of the reflective layer and resonator layer of a two-dimensional optical metasurface is shown according to one embodiment.

[0006] Figure 1D A side perspective view of a simplified block diagram of the reflective layer and resonator layer of a two-dimensional optical metasurface according to one embodiment is shown.

[0007] Figure 2 An example diagram of a control layer of a two-dimensional optical metasurface with passive matrix addressing is shown according to one embodiment.

[0008] Figure 3 An example diagram of a control layer of a two-dimensional optical metasurface with active matrix addressing is shown according to one embodiment.

[0009] Figure 4 A side view of the layers of a portion of a tunable optical metasurface is shown according to one embodiment.

[0010] Figure 5AAn example diagram showing the light field in an optical resonator of a resonator layer of a tunable optical metasurface according to one embodiment.

[0011] Figure 5B A tunable dielectric material is shown between two pillars aligned in a first direction to provide a first refractive index in the absence of any applied voltage, according to one embodiment.

[0012] Figure 5C A tunable dielectric material is shown between pillars aligned in a second direction to provide a second refractive index with an applied voltage of 5 volts, according to one embodiment.

[0013] Figure 5D A graph showing the phase response of a resonant unit with respect to applied voltage values ​​according to one embodiment.

[0014] Fig. 6A Shown is a top view of a portion of a tunable optical metasurface with offset rows of posts, according to one embodiment.

[0015] Figure 6B An example diagram showing an offset non-resonant gap in a reflector layer of a tunable optical metasurface to reduce or eliminate coupling between cells, according to one embodiment.

[0016] Figure 6C An example diagram showing aligned non-resonant gaps in a reflector layer of a tunable optical metasurface according to one embodiment.

[0017] Fig.6D An example diagram of the light field in a resonator layer of a tunable optical metasurface with offset rows of pillars, according to one embodiment, is shown.

[0018] Fig. 7A Shown is a top view of a portion of a tunable optical metasurface with row-aligned posts according to one embodiment.

[0019] Figure 7B An example diagram of a non-resonant gap in a reflector layer of a tunable optical metasurface is shown to reduce or eliminate coupling between cells, according to one embodiment.

[0020] Figure 7C An example diagram showing the light field in row-aligned pillars in a resonator layer of a tunable optical metasurface according to one embodiment.

[0021] Figure 8 An exemplary diagram illustrating another example of a metasurface according to one embodiment is shown.

[0022] Fig. 9An example of an active matrix driver architecture with a tiled aperture is shown, where each tile represents a diffraction-limited building block of individually addressable elements, according to one embodiment.

[0023] Fig. 10A An example diagram showing a top view of the XY plane of a tunable optical metasurface according to one embodiment.

[0024] Fig. 10B According to one embodiment, Fig. 10A An example diagram of a first cross-sectional side view of the XZ plane of a tunable optical metasurface.

[0025] Fig. 10C According to one embodiment, Fig. 10A An example diagram of a second cross-sectional side view of the XZ plane of the tunable optical metasurface.

[0026] Fig. 10D According to one embodiment, Fig. 10A Top view of the XY plane of the tunable optical metasurface showing the angle of the light field in the resonator layer. DETAILED DESCRIPTION

[0027] Tunable optical metasurfaces can be dynamically tuned to spatially modulate incident optical radiation. Modulating the phase and / or amplitude of incident optical radiation can be used to produce output optical radiation with a target profile. Spatial light modulation can be used for beam shaping, beam forming, beam control, etc. The systems and methods currently described can be applied to tunable metasurfaces using various architectures and designs to deflect optical radiation within an operating bandwidth. In various embodiments, a controller or metasurface driver selectively applies a voltage pattern to a two-dimensional array of optical structures located on a reflective layer. The voltage difference between adjacent optical structures changes the refractive index of the dielectric material therebetween. The phase delay combination generated by the applied voltage pattern can be used to produce constructive interference.

[0028] Various examples of tunable optical metasurfaces are described herein and depicted in the figures. For example, the tunable optical metasurface may include a two-dimensional array of metal optical posts (e.g., antenna elements, elongated post elements, metal post pairs, etc.). Liquid crystal or another dielectric material with a tunable refractive index is located in the gap or channel between adjacent metal optical posts. Liquid crystal is used in many examples provided in the present disclosure. However, it will be appreciated that in many cases, alternative dielectric materials with tunable refractive indices and / or combinations of different dielectric materials with tunable refractive indices may be used instead of liquid crystals. Examples of suitable tunable dielectric materials with tunable refractive indices include liquid crystals, electro-optic polymers, electro-optic crystals, chalcogenide glasses, and / or various semiconductor materials.

[0029] In various embodiments, biasing the liquid crystals in the metasurface with a voltage bias pattern changes the reflection phase of the optical radiation. For example, each different voltage pattern applied to the metasurface corresponds to a different reflection phase pattern. Each different reflection phase corresponds to a unique spatial modulation, steering, beamforming, or other controlled optical transmission. A digital or analog controller (controlling current and / or voltage), such as a passive or active switch matrix driver, can apply a differential voltage bias pattern to achieve a target phase modulation pattern on a two-dimensional array. The metasurface can be controlled to perform optical spatial modulation to achieve target beam shaping, one-dimensional beam steering (i.e., steering in one direction), two-dimensional beam steering (i.e., steering in two directions), wavelength filtering, beam divergence, beam convergence, beam focusing, and / or controlled deflection, refraction, and / or reflection of incident optical radiation.

[0030] Additional descriptions, variations, functions, and uses of optical metasurfaces are described in the following patents: U.S. Patent No. 10,451,800, issued on October 22, 2019, entitled “Plasmonic Surface-Scattering Elements and Metasurfaces for Optical Beam Steering”; U.S. Patent No. 10,665,953, issued on May 26, 2020, entitled “Tunable Liquid Crystal Metasurfaces”; U.S. Patent No. 11,092,675, issued on August 17, 2021, entitled “Lidar Systems based on Tunable Optical Metasurfaces”; and U.S. Patent No. 11,429,008, issued on August 20, 2022, entitled “Liquid Crystal Metasurfaces with Cross-Backplane Optical Reflectors,” each of which is incorporated herein by reference in its entirety.

[0031] The present disclosure includes various embodiments and variations of tunable optical metasurface devices and methods of making the same. It is noteworthy that the metasurface technology described herein can be combined with or otherwise utilize previous advances in surface scattering antennas, such as described in the following patents: U.S. Patent No. 2012 / 0194399, published on August 2, 2012, entitled "Surface Scattering Antennas"; U.S. Patent No. 2019 / 0285798, published on September 19, 2019, entitled "Plasmonic Surface-Scattering Elements and Metasurfaces for Optical Beam Steering"; and U.S. Patent No. 2018 / 0241131, published on August 23, 2018, entitled "Optical Surface-Scattering Elements and Metasurfaces"; each of which is incorporated herein by reference in its entirety.Additional elements, applications, and features of surface scattering antennas are described in the following documents: U.S. Patent Publication No. 2014 / 0266946, published on September 18, 2014, entitled “Surface Scattering Antenna Improvements”; U.S. Patent Publication No. 2015 / 0318618, published on November 5, 2015, entitled “Surface Scattering Antennas with Lumped Elements”; U.S. Patent Publication No. 2015 / 0318620, published on November 5, 2015, entitled “Curved Surface Scattering Antennas”; U.S. Patent Publication No. 2015 / 0380828, published on December 31, 2015, entitled “Slotted Surface Scattering Antennas”; U.S. Patent Publication No. 2015 / 0162658, published on June 11, 2015, entitled “Surface Scattering Reflector Antenna”; U.S. Patent No. 2015 / 0372389, published on December 24, 2015, entitled “Modulation Patterns for Surface Scattering Antennas”; PCT Application No. PCT / US18 / 19269, filed on February 22, 2018, entitled “Control Circuitry and Fabrication Techniquesfor Optical Metasurfaces”, U.S. Patent No. 2019 / 0301025, published on October 3, 2019, entitled “Fabrication of Metallic Optical Metasurfaces”; and U.S. Patent No. 2018 / 0248267, published on August 30, 2018, entitled “Optical Beam-Steering Devices and Methods Utilizing Surface Scattering Metasurfaces”, each of which is incorporated herein by reference in its entirety.

[0032] In some examples, the tunable optical device includes a substrate layer, a reflective layer, and a two-dimensional array of metal optical columns. The two-dimensional array of metal optical columns can be arranged in parallel rows extending vertically relative to the substrate layer. The gaps between adjacent rows of columns form optical resonators so that each row of columns includes multiple optical resonator gaps or cavities. In various embodiments, the columns in each row are spaced less than the minimum wavelength in the operating bandwidth (referred to as sub-wavelength spacing). In other embodiments, the columns in each row are spaced greater than the maximum wavelength or multiple wavelengths of the operating bandwidth. A tunable dielectric material (e.g., liquid crystal) with a tunable refractive index is located between the columns, which is included in the optical resonator formed by the gaps between adjacent rows of columns. The reflective layer is located between the substrate layer and the two-dimensional column array to reflect light radiation.

[0033] In some examples, the width of each pillar along each row is less than half the minimum wavelength of the operating bandwidth, and the length of each pillar in a direction perpendicular to each row is less than the minimum wavelength of the operating bandwidth.

[0034] The reflective layer includes a two-dimensional array of elongated rectangular reflector patches arranged in parallel. Electrically isolated gaps separate the reflector patches in adjacent rows, while non-resonant gaps separate the reflector patches in the same row. The reflector patches are arranged longitudinally along the rows (perpendicular to the length of the corresponding column). In some embodiments, the reflector patches of parallel rows are offset relative to each other so that the non-resonant gaps between adjacent reflector patches in a row are not aligned (e.g., misaligned or staggered) with the non-resonant gaps between adjacent reflector patches in an adjacent row. In other embodiments, the reflector patches can be aligned relative to each other so that the non-resonant gaps between adjacent reflector patches are aligned with each other in the column direction.

[0035] In some examples, the width of each reflector patch combined with the electrical isolation gap between adjacent rows of reflector patches is less than the length of each post, so that each post spatially overlaps with reflector patches in at least two adjacent rows of reflector patches. In some examples, the electrical isolation gaps between adjacent rows of reflector patches and / or the non-resonant gaps between adjacent reflector patches in the same row can be filled with dielectric material. The metasurface can be controlled by a controller. For example, the controller can include a passive or active control line switch matrix to selectively apply a voltage differential bias pattern to the tunable dielectric material between adjacent metal optical posts.

[0036] Metasurfaces may also be described in the context of resonant units. A two-dimensional optical metasurface may include a two-dimensional array of dynamically tunable resonant units arranged in rows and columns. Each resonant unit may include first and second elongated optical columns extending vertically relative to a substrate. The columns in each resonant unit may be positioned with sides parallel to each other and spaced less than the minimum wavelength in the operating bandwidth to form a gap therebetween. The columns of the resonant unit extend longitudinally in a first direction, with the tunable dielectric material positioned to fill (at least partially) the gap.

[0037] In addition to the columns extending longitudinally in the first direction, the resonant unit also includes a reflector patch extending longitudinally in a second direction perpendicular to the first direction. The reflector patch is part of a reflective layer located between the first and second elongated optical columns and the substrate. The reflector patches in each resonant unit are electrically isolated from each other (e.g., by an electrically isolating gap). A non-resonant gap (for wavelengths within an operating bandwidth) separates the reflector patch of each resonant unit from an adjacent reflector patch of an adjacent resonant unit. The non-resonant gaps of each resonant unit can be offset relative to each other so that the non-resonant gaps between the reflector patches of adjacent resonant units are staggered.

[0038] Examples of metasurfaces that can be used for transmitting or receiving are described herein. Systems containing metasurfaces described herein can be used as transmitters only, receivers only, transmitters and receivers at the same time, time multiplexing transmitters / receivers, frequency multiplexing transmitters / receivers, where the first metasurface acts as a transmitter and the second metasurface acts as a receiver, or operate in another transmit / receive configuration or operating technique. The metasurfaces described herein can be used to control, adjust, or modify reflection phase patterns. For example, one or more metasurfaces can be used to control (i) reflection phase, (ii) reflection amplitude, or (iii) reflection phase and reflection / transmission amplitude of an optical signal. Therefore, metasurfaces can be used in any of the embodiments described herein to control the complex phase and / or complex amplitude of reflected optical radiation.

[0039] Various embodiments of any of the embodiments described herein can be fabricated with dimensions suitable for optical bandwidths of optical sensing systems such as LiDAR, optical communication systems, optical computing systems, and displays. For example, the systems and methods described herein can be configured with a metasurface that operates with optical radiation, including but not limited to wavelengths of light in the near infrared, mid-infrared, long-wave infrared, and / or visible wavelength ranges. Given the feature sizes required for subwavelength optical antennas and antenna spacing, the metasurface can be fabricated using microlithography and / or nanolithography processes, such as those commonly used to fabricate complementary metal oxide semiconductor (CMOS) integrated circuits.

[0040] Some infrastructures that can be used together with the embodiments disclosed herein are already available, such as general-purpose computers, computer programming tools and techniques, digital storage media, and communication links. Many systems, subsystems, modules, and components described herein can be implemented as hardware, firmware, and / or software. Because there are so many possible implementations, they are described according to the functions performed by various systems, subsystems, modules, and components. For example, it is understood that many existing programming languages, hardware devices, frequency bands, circuits, software platforms, network infrastructures, and / or data storage devices can be used alone or in combination to implement specific control functions.

[0041] It is also understood that two or more elements, devices, systems, subsystems, parts, modules, etc. described herein can be combined into a single element, device, system, subsystem, module or part. In addition, many elements, devices, systems, subsystems, parts and modules can be replicated or further divided into discrete elements, devices, systems, subsystems, parts or modules to perform the subtasks described herein. Any aspect of any embodiment described herein can be combined with any other aspect of any other embodiment described in other disclosures described herein or incorporated by reference, including all permutations and combinations thereof, which is consistent with the understanding of those skilled in the art when reading the disclosure in the context of such other disclosures.

[0042] As used herein, a computing device, system, subsystem, module, driver, or controller may include a processor, such as a microprocessor, a microcontroller, a logic circuit, etc. The processor may include one or more special processing devices, such as an application specific integrated circuit (ASIC), a programmable array logic (PAL), a programmable logic array (PLA), a programmable logic device (PLD), a field programmable gate array (FPGA), or another customizable and / or programmable device. The computing device may also include a machine-readable storage device, such as a non-volatile memory, an optical memory, a flash memory, or another transient or non-transient machine-readable storage medium. Various aspects of some embodiments may be implemented or enhanced using hardware, software, firmware, or a combination thereof.

[0043] The parts of some disclosed embodiments are described and illustrated in the drawings herein to provide specific examples. Many parts thereof can be arranged and designed into various configurations. In addition, the features, structures and operations relevant to an embodiment can be applied to or combined with the features, structures or operations described in conjunction with another embodiment. In many cases, well-known structures, materials or operations are not shown or described in detail to avoid blurring aspects of the present disclosure.

[0044] Figure 1AA perspective view of a simplified block diagram of a reflective layer 110 and a resonator layer 120 of a two-dimensional optical metasurface 100 according to one embodiment is shown. As shown, the resonator layer 120 includes a two-dimensional array of metal optical pillars 125 arranged in parallel rows. Each pillar 125 in the resonator layer 120 extends vertically relative to the underlying substrate layer (not shown). The spacing between the pillars 125 in each row can be less than the minimum wavelength in the operating bandwidth. The width (W) of each pillar 125 along each row can be less than half the minimum wavelength of the operating bandwidth. The length (L) of each pillar 125 in a direction perpendicular to each row (e.g., along a column) can be less than the minimum wavelength of the operating bandwidth.

[0045] The gaps between adjacent pillars 125 in each row of pillars form an optical resonator. The tunable dielectric material can be deposited within the resonator layer to fill the spaces between the pillars 125 in all directions, such that the tunable dielectric material is located within the optical resonator formed by the gaps between adjacent rows of pillars 125. Examples of suitable tunable dielectric materials having a tunable refractive index include liquid crystals, electro-optic polymers, electro-optic crystals, chalcogenide glasses, and / or various semiconductor materials.

[0046] In alternative embodiments, the spacing between the pillars 125 in each row can be greater than the wavelength in the operating bandwidth (e.g., ten times the maximum wavelength in the operating bandwidth). Similarly, in some embodiments, the width (W) of each pillar 125 along each row can be greater than half the minimum wavelength, and the length (L) of each pillar 125 along a direction perpendicular to each row (e.g., along a column) can be many times greater than the maximum wavelength in the operating bandwidth.

[0047] The reflective layer 110 includes a two-dimensional array of elongated rectangular reflector patches 115 extending longitudinally along parallel rows. That is, as shown, the reflector patches 115 extend longitudinally in a direction perpendicular to the lengthwise direction of the pillars 125. Electrically isolated gaps 130 separate the reflector patches 115 in adjacent rows. Non-resonant gaps 140 separate adjacent reflector patches 115 in the same row. The direction of the electrically isolated gaps 130 is non-resonant with the incident electric field, so there is no resonant coupling. The non-resonant gaps 140 between adjacent reflector patches 115 are perpendicular to the incident electric field. Therefore, for a certain range of optical radiation wavelengths, the size of the non-resonant gaps 140 is selected to minimize or avoid any possible resonance between the reflector patches 115 in the same row. The size of the non-resonant gaps 140 can be different from the size of the electrically isolated gaps 130.

[0048] The dielectric via layer 150 may be located between the reflective layer 110 and the resonator layer 120. Each post 125 may be electrically connected to one of the underlying reflector patches 115 via a conductor via 155 within the dielectric via layer 150. For clarity, the dielectric of the dielectric via layer 150 has been removed from the figure to show the positioning of the conductor vias 155.

[0049] Figure 1B An exploded perspective view of a simplified block diagram of a reflective layer 110 and a resonator layer 120 of a two-dimensional optical metasurface 100 is shown. As shown, the parallel rows of reflector patches 115 are offset relative to each other so that the non-resonant gaps 140 between adjacent reflector patches 115 in one row are not aligned (e.g., misaligned or staggered) with the non-resonant gaps 140 between adjacent reflector patches 115 in an adjacent row. Each conductor via 155 of the dielectric via layer 150 (shown with the dielectric material around the conductor via 155 removed) connects one post 125 to one of the underlying reflector patches 115. Notably, because the posts 125 extend longitudinally in a direction perpendicular to the direction in which the underlying reflector patches 115 extend, half of the posts 125 in a first row of posts 125 (alternating every other one) are connected to reflector patches 115 in the first row of reflector patches 115, while the other half (alternating) are connected to reflector patches 115 in the second row of reflector patches 115.

[0050] Figure 1C A top perspective view of a simplified block diagram of a reflective layer 110 and a resonator layer 120 of a two-dimensional optical metasurface 100 is shown. The top perspective view shows that the posts 125 are aligned in rows and columns, where the posts extend longitudinally in a first direction (e.g., perpendicular to the angle of incident optical radiation). In the example shown, the length of each post 125 is less than the minimum wavelength of the operating bandwidth, and the width of each post 125 is less than half the minimum wavelength. The gaps between adjacent posts 125 in the same row also have sub-wavelength dimensions. As described herein, in some embodiments, the length, width, and spacing dimensions may be larger.

[0051] The specific dimensions of the pillars 125, including height and inter-element spacing (gap), are selected based on the target operating bandwidth, as described in detail in the patents and patent publications incorporated herein by reference. For example, for operation with optical radiation having a wavelength of 905 nanometers, the gaps filled with tunable dielectric material between adjacent pillars 125 forming a unit can be about 150 nanometers. The height of the pillars 125 can be about 400 nanometers and provide a second-order resonance.

[0052] Figure 1DA side perspective view of a simplified block diagram of a reflective layer 110 and a resonator layer 120 of a two-dimensional optical metasurface 100 is shown. The illustrated view is rotated so that the rows of reflector patches 115 and posts 125 extend from the bottom of the page to the top of the page. As previously described, the reflector patches 115 extend longitudinally in the direction of the rows, while the posts 125 extend transversely in the direction of the rows. The relative sizes of the posts 125 and reflector patches 115 are selected so that there are two rows of reflector patches 115 below each row of posts 125.

[0053] Figure 2 An example diagram of a control layer 200 of a two-dimensional optical metasurface with passive matrix addressing is shown according to one embodiment. A controller can be connected to voltage control lines on rows 210 and columns 220 of resonator units (e.g., metal optical posts connected to each resonant unit). The control lines of the control layer 200 can be integrated within the substrate of the metasurface or within a separate dielectric layer between the substrate and the reflective layer. The control lines can be electrically connected to reflector patches, which in turn are connected to the posts through conductor vias in the dielectric via layer. The passive matrix control line addressing scheme facilitates two-dimensional, M x N addressing of M rows 210 and N columns 220 of metal optical posts. The beam steering or other spatial phase modulation (Φ) of the metasurface (illustrated as wavefront 250) can be represented by a row modulation f(x) function and a column modulation g(y) function, such that Φ = f(x) + g(y).

[0054] Figure 3 An example diagram of a control layer 300 of a two-dimensional optical metasurface with active matrix addressing according to one embodiment is shown. The active matrix control system includes rows and columns of transistors. Each transistor is connected to a unique metal optical column through a corresponding reflector patch and a conductor via. The control lines of the control layer 300 can be integrated within the substrate of the metasurface or within a separate dielectric layer between the substrate and the reflective layer. The active matrix control system can drive voltages on one or more rows and use column select lines to turn on transistors associated with a particular column. The active matrix architecture enables the resonant unit of the metasurface to exhibit a unique phase response pattern (Φ), which is a function of the row drive (x) and the column select (y), which can be expressed as Φ=f(x,y), as shown in 350.

[0055] As described herein, each resonant unit cell includes two metal optical pillars separated by a sub-wavelength gap that is filled (partially, fully, or overflowing) with a tunable dielectric material having a tunable refractive index. The tunable refractive index of the tunable dielectric material of each resonant unit cell is selected by generating a voltage difference between the two metal optical pillars of the cell. The voltage difference is used to tune the phase (and / or amplitude) of the incident optical radiation (e.g., laser). The size of each resonant unit cell in the plane direction of the incident optical radiation can be less than half the wavelength of the light, thereby achieving large field of view beam control without grating lobes. The size of the resonant unit cell (e.g., the width of the two metal optical pillars and the gap therebetween) is configured to be less than half the wavelength of the incident optical radiation in the plane direction (λ / 2) to prevent the resonant unit cell from diffraction. The size of the resonant unit cell can be larger in the out-of-plane or lateral direction (e.g., up to the maximum wavelength) while still maintaining a large beam control field of view without introducing diffraction. In applications where the angle of incidence is close to the metasurface plane normal, the cell size can be relaxed (e.g., having a size greater than half a wavelength (λ / 2) in the plane direction and / or a size greater than one wavelength in the out-of-plane or lateral direction).

[0056] Figure 4 A side view of the layers of a portion of a tunable optical metasurface 400 with active matrix addressing according to one embodiment is shown. In the cross-sectional view shown, metal optical posts 425 in the resonator layer 420 form a single row of optical resonators. The posts 425 extend vertically relative to the substrate layer (not shown) and extend longitudinally into the page. The dielectric via layer 450 includes conductor vias 455 that connect the posts 425 to reflector patches 415 within the reflective layer 410. As shown, the reflector patches 415 are staggered or offset from each other so that the reflector patches 415 of each other post 425 are not visible in the cross-sectional view. The example shown includes a second via layer 460 having conductor vias 465 for connecting the posts 425 to control lines and transistors 475 within the control layer 470.

[0057] The active matrix architecture enables the resonant units of the metasurface 400 to exhibit a unique phase response pattern (Φ), which is a function of the row drive (x) and column selection (y), which can be expressed as Φ = f(x, y). The incident field and k-vector of the wavefront of the optical radiation 490 are shown. The metasurface 400 can be used to perform arbitrary phase modulation on the incident optical radiation 490 to achieve beam steering, lensing or other optical functions.

[0058] As shown, the active matrix addressing scheme includes a transistor 475 located below each resonant unit. In some embodiments, each resonant unit includes only a single transistor connected to one of the pillars, while the other pillar is connected to a fixed voltage. In other embodiments, each resonant unit includes two transistors, one of which is connected to each metal optical pillar, so that each metal optical pillar can be driven with a unique voltage. Although an absolute voltage is applied to each metal optical pillar, the phase of each resonant unit depends on the voltage difference between adjacent metal optical pillars.

[0059] According to various embodiments, the dielectric via layer 450 also serves as a waveguide layer between the resonator layer 420 and the reflector layer 410. The thickness of the waveguide layer is such that destructive interference of the fields occurs at the bottom of the optical resonator (e.g., the gaps between adjacent rows of optical metal pillars), thereby confining most of the optical energy to the vertical pillars and minimizing optical energy leaking into the waveguide layer.

[0060] The resonant cell is tuned by a refractive index tunable material 485 between adjacent metal optical pillars 425. For example, a liquid crystal with a high refractive index tuning range can be used. As described herein, a differential voltage is applied between adjacent metal optical pillars 425, which causes the liquid crystal in the resonant cell to rotate, thereby changing the refractive index experienced by the x-component of the optical electric field. This thus changes the effective length of the metal optical pillar 425, thereby changing the phase experienced by the incident optical radiation 490 at that location on the metasurface. Since the resonant cell is resonant, in many embodiments, the change in phase is coupled to a change in the amplitude response, which is a typical feature of a Lorentz-type resonator. In such an embodiment, each metal optical pillar 425 is programmed with a unique voltage (and therefore phase) to achieve a desired spatial phase gradient. This gradient can be used for beam steering or other optical functions, such as focusing, collimation, or any arbitrary optical transformation.

[0061] Again, the metal optical pillar 425 can be implemented using conventional CMOS manufacturing processes, such as processes based on copper inlay metallization, deposition processes, etching processes, photolithography processes, patterning processes, chemical mechanical planarization processes, etc. In addition to copper, other metals such as aluminum, silver, and gold can also be used to form the metal core of each metal optical pillar. Copper is attractive because it is widely used in the semiconductor industry to manufacture transistor interconnects with the dimensions required to implement these resonant units. In addition, copper has excellent optical properties in the near-infrared and short-wave infrared wavelength ranges.

[0062] Figure 5AAn example diagram of an optical field 590 within a tunable dielectric material 585 is shown, the optical field 590 being located in the gap between a pair of metallic optical posts 525 and 526 forming an optical resonator, with reflector patches 515 and 516 underneath. In the example shown, the height of the metallic optical posts 525 and 526 is selected to be in second order resonance with two magnetic field antinodes 590. According to various embodiments, as shown, each metallic optical post 525 and 526 includes a metallic core 527 and 528 and a passivation coating 521 and 522.

[0063] The passivation coatings 521 and 522 may be deposited as a single or uniform layer covering the sidewalls and top walls of each metal optical post 525. The passivation coatings 521 and 522 may be, for example, a thin silicon nitride (SiN) layer to passivate the metal cores 527 and 528 of each metal optical post 525. The passivation coatings 521 and 522 may be used to prevent the metal of the metal optical posts 525 and 526 from diffusing into the tunable dielectric material (e.g., liquid crystal) and / or to prevent corrosion of the metal optical posts 525 and 526. The passivation coatings 521 and 522 may be SiN, SiCN, aluminum oxide, or another suitable passivation material.

[0064] Passivation coatings 521 and 522 may be optically transparent and / or reflective for wavelengths within the operating bandwidth of the metasurface to complement the underlying reflective conductive metal cores 527 and 528 (e.g., copper). Passivation coatings 521 and 522 may alternatively (or additionally) include silicon carbide nitride, silicon carbide, aluminum oxide (AlO x ), hafnium oxide (HfO2), silicon oxide (SiO2), aluminum nitride (AlN), boron nitride (BN), and / or another passivating dielectric material. A transistor 575 within the control layer is connected to the pillar 525 through the reflector patch 515 and the intermediate conductor vias 555 and 565 within the dielectric via layers 550 and 560. The controller can drive the pillar 525 to a target voltage through the transistor 575 to generate a voltage difference within the optical resonator formed by the gap between the pillars 525 and 526. The refractive index of the tunable dielectric material 585 can be adjusted to a target refractive index based on the voltage difference applied between the pillars 525 and 526.

[0065] Figure 5B A tunable dielectric material 585 is shown between two pillars 525 and 526 aligned in a first direction to provide a first refractive index within the optical resonator in the absence of any applied voltage (eg, zero volt differential at 501 ), according to one embodiment.

[0066] Figure 5C Tunable dielectric material 585 is shown between posts 525 and 526 aligned in a second direction to provide a second index of refraction at 502 within the optical resonator with an applied voltage of 5 volts, according to one embodiment.

[0067] Figure 5D A graph 599 showing the phase response of a resonant cell with respect to applied voltage values ​​according to one embodiment is shown. It will be appreciated that the phase response and voltage range may vary based on the specific dimensions of the pillars 525 and 526, the width of the gap forming the optical resonator (the gap being filled with the tunable dielectric material 585), and / or the specific material used as the tunable dielectric material 585 (e.g., liquid crystal).

[0068] Fig. 6A A top view of a portion of a tunable optical metasurface 600 with offset rows of posts 625 is shown, according to one embodiment. Each resonant cell 621 consists of two metallic optical posts 625 and 626. Each metallic optical post 625 and 626 is connected to one of the reflector patches 615 and 616 through conductive vias 655 and 656. The metasurface 600 operates only under transverse magnetic (TM) polarization. Therefore, the x-component of the electric field (perpendicular to the longitudinal or long sidewalls and parallel to the transverse or short sidewalls) is coupled in the resonant cell 621 metallic optical posts 625 and 626. The gap or slot 603 between the metallic optical posts 625 and 626 in the y-direction does not couple to the field because the field is parallel to the walls of the metal posts (e.g., copper) and is therefore excluded from the slot 603. As shown Figure 4 As shown in the cross-sectional view of FIG. 1 , each reflector patch 615 is connected to the underlying transistor (e.g., via Figure 4 Conductor via 465 in the second via layer 460).

[0069] The reflector layer 610 of the reflector patches 615 and 616 includes a non-resonant gap 612 on the x-axis. The non-resonant gap 612 provides electrical isolation between adjacent reflector patches 615 and 616 in the same row. The non-resonant gap 612 has a width dimension selected to be non-resonant with the incident field, thereby limiting the amount of field that leaks into the reflector patches 615 and 616 of the reflector layer 610. In addition, an electrically isolating gap 613 or channel is created on the y-axis to electrically isolate adjacent reflector patches 615 and 616 in adjacent rows. Since the E-field is parallel to the metal walls of the reflector patches 615 and 616, the optical field does not couple into the electrically isolating gap 613, and therefore the size of the electrically isolating gap 613 may be different (e.g., smaller) than the size of the non-resonant gap 612 that is more carefully selected to be non-resonant.

[0070] Figure 6BAn example diagram of offset non-resonant gaps 612 between adjacent reflector patches 615 of a reflector layer 610 according to one embodiment is shown to reduce or eliminate coupling between reflector patches 615 in the same row. Electrically isolating gaps 613 can be used to electrically isolate reflector patches 615 in different rows without regard to avoiding resonance. As described herein, reflector patches 615 of one row are staggered or offset relative to reflector patches 615 in adjacent rows to ensure that the non-resonant gaps 612 are staggered and not aligned with each other.

[0071] Figure 6C An example diagram of aligned non-resonant gaps in a reflector layer of a tunable optical metasurface according to one embodiment is shown. Electrically isolating gaps 613 electrically isolate reflector patches 615 in different rows. Reflector patches 615 of one row are aligned relative to reflector patches 615 in an adjacent row. Non-resonant gaps 612 are used to reduce coupling between reflector patches in the same row.

[0072] Fig.6D An example diagram of a light field in a resonator layer of a tunable optical metasurface with row offset posts according to one embodiment is shown. As shown, metal optical posts 625 and 626 are part of a first resonant unit. A first light field 623 is shown between metal optical posts 625 and 626. The example shown includes staggered or offset posts 625 and 626. Thus, metal optical posts 627 and 628 of a second resonant unit are offset, staggered, or misaligned relative to metal optical posts 625 and 626 of the first resonant unit. Thus, a second light field 624 in a second resonant cell is also staggered or offset relative to the first light field 623.

[0073] Fig. 7A A top view of a portion of a tunable optical metasurface 700 with row-aligned posts 725 is shown, according to one embodiment. Each resonant unit cell 721 includes two metallic optical posts 725 and 726. Each metallic optical post 725 and 726 is connected to one of the reflector patches 715 and 716 through conductive vias 755 and 756. The metasurface 700 operates only under transverse magnetic (TM) polarization. Therefore, the x-component of the electric field (perpendicular to the longitudinal or long sidewalls and parallel to the transverse or short sidewalls) is coupled in the metallic optical posts 725 and 726 of the resonant unit cell 721. The gap or slot 703 between the metallic optical posts 725 and 726 in the y-direction does not couple to the field because the field is parallel to the walls of the metallic posts and is therefore excluded from the slot 703. As shown in FIG. Figure 4 As shown in the cross-sectional view of FIG. 1 , each reflector patch 715 is connected to the underlying transistor (e.g., via Figure 4 Conductor via 465 in the second via layer 460).

[0074] The reflector layer 710 of the reflector patches 715 and 716 includes a non-resonant gap 712 on the x-axis. The non-resonant gap 712 provides electrical isolation between adjacent reflector patches 715 and 716 in the same row. The non-resonant gap 712 has a width dimension selected to be non-resonant with the incident field, thereby limiting the amount of field that leaks into the reflector patches 715 and 716 of the reflector layer 710. In addition, an electrically isolating gap 713 or channel is created on the y-axis to electrically isolate adjacent reflector patches 715 and 716 in adjacent rows. Since the E-field is parallel to the metal walls of the reflector patches 715 and 716, the optical field does not couple into the electrically isolating gap 713, and therefore the size of the electrically isolating gap 713 may be different (e.g., smaller) than the size of the non-resonant gap 712 that is more carefully selected to be non-resonant.

[0075] Figure 7B An example diagram of non-resonant gaps in a reflector layer of a tunable optical metasurface according to one embodiment is shown to reduce or eliminate coupling between resonant units. Electrically isolating gaps 713 can be used to electrically isolate reflector patches 715 located in different rows without regard to avoiding resonance. As described herein, reflector patches 715 of one row are staggered or offset relative to reflector patches 715 in adjacent rows to ensure that non-resonant gaps 712 are staggered and not aligned with each other.

[0076] Figure 7C An example diagram of a light field in a row-aligned resonator layer of a tunable optical metasurface with row-aligned posts according to one embodiment is shown. As shown, metal optical posts 725 and 726 are part of a first resonant unit. A first light field 723 is shown between metal optical posts 725 and 726. The example shown includes a column-aligned post. Therefore, metal optical posts 727 and 728 of a second resonant unit are aligned relative to metal optical posts 725 and 726 of the first unit. Therefore, a second light field 724 in the second resonant unit is also aligned relative to the first light field 723.

[0077] Figure 8An example diagram of another example of a metasurface 800 according to one embodiment is shown. In the example shown, the metasurface 800 includes a plurality of blocks 801, 802, 803, and 804. Each block 801, 802, 803, and 804 includes a plurality of metal optical posts 825 having a length of a plurality of wavelengths in the out-of-plane direction (vertical axis). The horizontal axis includes the pitch or interelement spacing of the metal optical posts 825, which is less than the diffraction limit (e.g., half the operating wavelength). The illustrated metasurface 800 can be used to generate grating lobes in the vertical direction. For example, the metasurface 800 can be used to comb discrete light beams along the vertical axis, which can then be guided together. The metasurface 800 does not generate grating lobes in the horizontal axis because the interelement spacing of the metal optical posts 825 is below the diffraction limit. Each metal optical post 825 is connected to the underlying elongated reflector patch 815 by a conductor via 855.

[0078] Fig. 9 An example of an active matrix driver architecture 900 with a tiled aperture is shown, where each tile 901 represents a diffraction-limited building block of individually addressable elements, according to one embodiment. As the aperture size of the metasurface increases, the number of elements grows as the square of the linear size. In addition, all or many voltage-controlled or tunable elements (e.g., metal optical posts) may need to be updated for each change in the phase modulation pattern (e.g., for a given steering angle). In some embodiments of liquid crystal tuning of the metasurface based on copper posts, typical switching speeds are 50 microseconds, and the entire array is updated on this time scale.

[0079] The active matrix driver architecture 900 shown reduces the complexity, power and / or size of the driver electronics by decoupling the aperture size from the angular resolution. The angular resolution on each axis is determined by the number of individually addressed resonant units on each axis. The aperture size of a particular optical design is typically much larger than the diffraction limited aperture dictated by the angular resolution requirements. Each tile 901 can share the same set of source drivers, such as a digital-to-analog converter 981 or "DAC" for column addressing and a gate driver 982 for row addressing. The active matrix architecture 900 of the tile metasurface, including the various control lines, capacitors and / or transistors, as well as the DAC 981 and gate drivers 982, is referred to herein as part of the controller or control layer of the metasurface.

[0080] Alternatively, the cell architecture can be implemented with passive matrix addressing. In this case, each cell can have two columns, including a first column driven by a wire propagating along the x-axis (carrying the row drive voltage) and another column connected to a wire propagating along the y-axis (carrying the column drive voltage). If the cell is below the diffraction limit, the light will experience scattering (phase delay) from both columns. Therefore, an optical function of the form phi = f(x) + f(y) can be achieved.

[0081] Fig. 10A An example diagram of a top view of the XY plane of a tunable optical metasurface 1000 according to one embodiment is shown. In the example shown, the unit 1080 includes four metal optical pillars, including a metal optical pillar 1025 connected to a continuous control line 1005 that provides a driving voltage (x voltage). All metal optical pillars connected to the continuous control line 1005 (represented by connection points) are driven to the same voltage by the continuous control line 1005.

[0082] According to one embodiment, Fig. 10B Shows Fig. 10A An example diagram of a first cross-sectional side view 1001 of the tunable optical metasurface 1000 in the XZ plane at the indicated "cut A" location. As shown, each metal optical post 1025 is connected to the underlying reflector patch 1015 through a conductor via 1055 and to a control line and / or transistor in the "Y voltage layer" 1075.

[0083] According to one embodiment, Fig. 10C Shows Fig. 10A 1002 is an example of a second cross-sectional side view 1002 of a tunable optical metasurface in the XZ plane at the indicated “cut B” location. As shown, every other (alternating) metal optical post 1026 is connected to the continuous reflector patch 1016 via a conductor via 1055 in the dielectric via layer 1050.

[0084] Fig. 10D According to one embodiment, Fig. 10A A top view of the XY plane of the tunable optical metasurface 1000 looking at the optical field 1018 and 1019 between the metal optical pillars 1025 in the resonator layer.

[0085] The present disclosure has been made with reference to various exemplary embodiments (including best mode). However, those skilled in the art will recognize that the exemplary embodiments may be changed and modified without departing from the scope of the present disclosure. Although the principles of the present disclosure have been shown in various embodiments, many modifications of structure, arrangement, ratio, elements, materials and assemblies may be adjusted for specific environments and / or operational requirements without departing from the principles and scope of the present disclosure. These and other changes or modifications are intended to be included within the scope of the present disclosure.

[0086] The present disclosure should be considered illustrative rather than restrictive, and all such modifications are intended to be included within the scope of the present disclosure. Likewise, benefits, other advantages, and solutions to problems have been described above for various embodiments. However, benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more apparent should not be construed as critical, required, or essential features or elements. The claims are also intended to be a part of this disclosure.

Claims

1. A tunable optical device comprising: substrate layer; a two-dimensional array of metallic optical posts arranged in parallel rows and extending vertically relative to the substrate layer, wherein each row includes a plurality of posts and the gaps between adjacent posts form a plurality of optical resonators for operating on optical radiation within a bandwidth; a tunable dielectric material located within the gaps between adjacent pillars, having a tunable refractive index; as well as A reflective layer is located between the substrate layer and the two-dimensional array of pillars to reflect optical radiation, the reflective layer comprising a two-dimensional array of reflector patches, wherein each pillar is electrically connected to at least one of the reflector patches.

2. The apparatus of claim 1, wherein at least some of the reflector patches comprise elongated rectangular reflector patches.

3. The apparatus of claim 2, wherein the elongated rectangular reflector patches are arranged in parallel rows with electrically isolating gaps between reflector patches in adjacent rows.

4. The apparatus of claim 3, wherein the electrically isolating gaps between adjacent rows of reflector patches are filled with a dielectric material.

5. The apparatus of claim 3, wherein the elongated rectangular reflector patches in each row are positioned with non-resonant gaps between adjacent reflector patches.

6. The apparatus of claim 5, wherein the non-resonant gaps between adjacent reflector patches in each row are filled with a dielectric material.

7. The apparatus of claim 5, wherein the parallel rows of reflector patches are offset from one another such that non-resonant gaps between adjacent reflector patches in one row are not aligned with non-resonant gaps between adjacent reflector patches in an adjacent row.

8. The apparatus of claim 5, wherein the gaps between adjacent pillars in each row of pillars each have a width less than a minimum wavelength of the operating bandwidth.

9. The device according to claim 8, wherein: The width of each column along each row is less than half the minimum wavelength of the operating bandwidth.

10. The device according to claim 9, wherein: Wherein the length of each column in a direction perpendicular to each row is less than the minimum wavelength of the operating bandwidth.

11. The device according to claim 10, wherein: The width of each reflector patch combined with the electrical isolation gap between adjacent rows of reflector patches is less than the length of each post such that each post spatially overlaps reflector patches in at least two adjacent rows of reflector patches.

12. A device according to any one of claims 1 to 11, wherein the length of each pillar in a direction perpendicular to each row is greater than the maximum wavelength of the operating bandwidth.

13. The apparatus according to any one of claims 1 to 11, wherein: The gaps between adjacent pillars in each row of pillars each have a width that is at least ten times the maximum wavelength of the operating bandwidth.

14. The apparatus of any one of claims 1 to 11, wherein the tunable dielectric material comprises one or more of: a liquid crystal, an electro-optic polymer, an electro-optic crystal, and a chalcogenide glass.

15. The apparatus of any one of claims 1 to 11, wherein each post comprises one of: copper, silver, gold, aluminum, and silver-coated copper.

16. The apparatus according to any one of claims 1 to 11, further comprising: A passivating coating of optically transparent dielectric material is applied to each post.

17. The apparatus according to any one of claims 1 to 11, further comprising: A controller is configured to selectively apply a voltage differential bias pattern to the tunable dielectric material between adjacent pillars by driving the pillars with a voltage pattern.

18. The apparatus according to any one of claims 1 to 11, further comprising: A control layer between the substrate layer and the reflective layer comprises a two-dimensional active switch matrix of transistors connected to at least some of the pillars through one or more dielectric via layers.

19. The device of claim 18, wherein each transistor is connected to one of the reflector patches, and wherein each reflector patch connected to a transistor is connected to one of the pillars through a conductor via in a first dielectric via layer between the reflective layer and the two-dimensional array of pillars.

20. The device of claim 19, wherein each transistor is connected to one of the reflector patches by a conductor via in a second dielectric via layer between the control layer and the reflective layer.

21. The apparatus of claim 19, further comprising: A controller is used to selectively apply a voltage differential bias pattern to the tunable dielectric material between adjacent pillars by driving the pillars in a voltage pattern via an active switching matrix of the transistors.

22. The apparatus according to any one of claims 1 to 11, wherein: The parallel rows of posts are offset relative to each other.

23. The apparatus according to any one of claims 1 to 11, wherein: The parallel rows of posts are aligned relative to each other.

Images