Patent Application
20240241366
This disclosure relates to optical metasurfaces and sensor systems, such as light detection and ranging (lidar) systems. This disclosure also relates to optical elements, such as lenses, mirrors, and prisms.
Previous approaches to optical systems have involved the use of fixed optical elements to manipulate light propagation and achieve desired optical effects. These fixed optical elements, such as lenses and mirrors, have limitations in terms of their ability to steer light and adapt to changing optical conditions. Scanner-based three-dimensional sensing systems, such as light detection and ranging (lidar) devices, that utilize fixed optical elements often incorporate mechanical movement that limits the operation, speed, and longevity of such devices. The field of view (FOV) of scanner-based three-dimensional sensing systems is often limited by mechanical constraints. For example, devices that utilize microelectromechanical (MEM) scanners usually have a FOV that is less than 60 degrees.
One approach to address these limitations has been the development of tunable optical metasurfaces. A metasurface may for example, include an array of subwavelength structures that can manipulate the phase, amplitude, and/or polarization of light. By controlling the properties of these subwavelength structures, the metasurface can selectively steer light to different angles.
Examples of metasurfaces include one-dimensionally steerable metasurfaces and two-dimensionally steerable metasurfaces. A dynamically tunable one-dimensionally steerable metasurface may be selectively steered to various steering angles within a first FOV in the steering direction (e.g., 100-140 degrees) and have a second, fixed FOV in the non-steering direction (e.g., 10-30 degrees). A dynamically tunable two-dimensionally steerable metasurface may be selectively steered to various steering angles within a first FOV in a first steering direction and selectively steered to various steering angles within a second FOV in a second steering direction. The first and second fields of view (FOVs) may be the same or different.
As described in greater detail in the patents and patent applications incorporated herein by reference below, a metasurface may be steered by applying a pattern or patterns of voltage differentials across liquid crystal deposited between arrays of metasurface elements (e.g., one-dimensional arrays of metal rails or two-dimensional arrays of metal pillars). Liquid crystal metasurfaces (LCMs) may be fabricated in a complementary metal-oxide-semiconductor (CMOS) foundry. As an example, a FOV of a one-dimensionally steerable LCM may have a steering FOV of 140 degrees in a steering direction (e.g., steerable in a steering direction to −70 degrees and +70 degrees in a steering direction) and have a static FOV of between 10 and 30 degrees in the non-steering direction (e.g., −10 degrees to +10 degrees for a 20-degree FOV in the non-steering direction).
The LCM may be physically capable of scanning beyond 140 degrees in the steering direction. For example, the LCM may be physically capable of scanning all the way up to 180 degrees (-−/+90 deg). However, the useful or effective FOV may be limited due to the optical performance limitations of an optically transparent cover of the LCM and/or an anti-reflective (AR) coating applied thereto.
Notably, the reflectance or Fresnel losses increase significantly at angles above approximately 70 degrees (e.g., >10% loss). Accordingly, a lidar or other sensing system that steers optical radiation to angles greater than approximately 70 degrees in either direction (e.g., a FOV of 140 degrees) experiences a loss in intensity in the output beam, which may cause a drop in performance (e.g., loss of range, ghost images, stray light, etc.). Thus, while a given metasurface may be physically steerable to a very wide FOV, the FOV of the metasurface may be limited to maintain the transmissivity above a threshold transmittance value. For example, to maintain transmission efficiencies above 95% (e.g., a threshold transmittance value of 95%), the FOV of a steerable metasurface may be limited to 120 degrees. Similarly, to maintain transmission efficiencies above 90%, the FOV of a steerable metasurface may be limited to 120 degrees. The specific FOV of the metasurface is based on a function of the physical steering capabilities of the metasurface, the optical properties of the transparent cover or anti-reflective coating, and a target threshold transmittance value.
The presently described systems and methods relate to expanding the FOV of a metasurface while still maintaining transmission efficiencies above a target threshold transmittance value by use of a freeform optic. In some embodiments, a freeform optic is used in combination with a prism. For example, a coupling prism may be used, inter alia, to prevent the obstruction of the output beam with the input incident beam. U.S. Pat. No. 11,567,390, granted on Jan. 31, 2023, entitled “Coupling Prisms for Tunable Optical Metasurfaces,” is hereby incorporated by reference in its entirety. As described herein, the presently described freeform optics and various configurations thereof allow for an expanded FOV of up to 180 degrees or even beyond 180 degrees (e.g., 210 degrees) in the steering direction. The freeform optic may operate to expand the fixed FOV of a metasurface in the non-steering direction from, for example, a fixed FOV of 20 degrees to an expanded fixed FOV of 90 degrees.
Any of a wide variety of tunable optical metasurfaces, advancements, variations, and improvements thereto may be utilized in conjunction with embodiments described herein, including one-dimensionally steerable optical metasurfaces and two-dimensionally steerable optical metasurfaces. In some embodiments, two-dimensional steering is accomplished using a one-dimensionally steerable optical metasurface in conjunction with selective activation of segmented lasers (e.g., VCSELs), as described in the disclosure incorporated by reference herein. Various metasurfaces, configurations, lidar components, transmitter subsystems, receiver subsystems, and the like that are applicable to this disclosure, may be utilized in combination with the embodiments of this disclosure, and/or may be otherwise be useful to understand this disclosure more fully are described in U.S. Pat. No. 10,451,800 granted on Oct. 22, 2019, entitled “Plasmonic Surface-Scattering Elements and Metasurfaces for Optical Beam Steering;” U.S. Pat. No. 10,665,953 granted on May 26, 2020, entitled “Tunable Liquid Crystal Metasurfaces;” U.S. Pat. No. 11,092,675 granted on Aug. 17, 2021, entitled “Lidar Systems based on Tunable Optical Metasurfaces;” U.S. Pat. No. 11,429,008 granted on Aug. 20, 2022, entitled “Liquid Crystal Metasurfaces with Cross-Backplane Optical Reflectors;” U.S. patent Publication No. 2012/0194399, published on Aug. 2, 2012, entitled “Surface Scattering Antennas;” U.S. patent Publication No. 2019/0285798 published on Sep. 19, 2019, entitled “Plasmonic Surface-Scattering Elements and Metasurfaces for Optical Beam Steering;” and U.S. patent Publication No. 2018/0241131 published on Aug. 23, 2018, entitled “Optical Surface-Scattering Elements and Metasurfaces;” each of which is hereby incorporated by reference in its entirety. Additional elements, applications, and features of surface scattering antennas are described in U.S. patent Publication No. 2014/0266946, published Sep. 18, 2014, entitled “Surface Scattering Antenna Improvements;” U.S. patent Publication No. 2015/0318618, published Nov. 5, 2015, entitled “Surface Scattering Antennas with Lumped Elements;” U.S. patent Publication No. 2015/0318620 published Nov. 5, 2015, entitled “Curved Surface Scattering Antennas;” U.S. patent Publication No. 2015/0380828 published on Dec. 31, 2015, entitled “Slotted Surface Scattering Antennas;” U.S. patent Publication No. 2015/0162658 published Jun. 11, 2015, entitled “Surface Scattering Reflector Antenna;” U.S. patent Publication No. 2015/0372389 published Dec. 24, 2015, entitled “Modulation Patterns for Surface Scattering Antennas;” PCT Application No. PCT/US18/19269 filed on Feb. 22, 2018, entitled “Control Circuitry and Fabrication Techniques for Optical Metasurfaces,” U.S. patent Publication No. 2019/0301025 published on Oct. 3, 2019, entitled “Fabrication of Metallic Optical Metasurfaces;” U.S. Publication No. 2018/0248267 published on Aug. 30, 2018, entitled “Optical Beam-Steering Devices and Methods Utilizing Surface Scattering Metasurfaces;” U.S. Pat. No. 11,747,446 issued on Sep. 5, 2023, entitled “Segmented Illumination and Polarization Devices for Tunable Optical Metasurfaces;” and U.S. Pat. No. 11,846,865 issued on Dec. 19, 2023, entitled “Two-Dimensional Metasurface Beam Forming Systems and Methods,” each of which is hereby incorporated by reference in its entirety.
The presently described systems and methods can be understood in the context of the above description and the patents and patent publications cited above. In various examples, an optical system includes a tunable optical metasurface (e.g., a one-dimensionally steerable LCM) that is selectively steerable in a steering direction to a plurality of steering angles. A freeform optic is positioned within an optical path of the metasurface. An air gap may exist between the freeform optic and the metasurface. The freeform optic gradually bends (refracts) the optical rays in terms of angle of incidence (and angle of departure) through the consecutive interfaces to bend (e.g., by refraction diffraction) the optical radiation with minimal losses.
For example, the optical path from the metasurface may include a metasurface cover-to-air interface, an air-to-freeform optic interface, and a freeform optic-to-air interface. In embodiments that include a prism, the optical path from the metasurface may include a metasurface cover-to-prism interface, a prism-to-air interface, an air-to-freeform optic interface, and a freeform optic-to-air interface. In a receiver configuration, a reverse optical path includes the same interfaces in the reverse order with the same cumulative optical properties.
The freeform optic may for example, include a concave first surface positioned proximate to the metasurface and a biconic second surface. In various embodiments, the second surface may have a first radius of curvature along a first axis in the steering direction of the metasurface and a second radius of curvature along a second axis in a non-steering direction of the metasurface, wherein the first radius of curvature along the first axis is different than the second radius of curvature along the second axis. The concave first surface may be rotationally symmetric in some embodiments. In other embodiments, the concave first surface may be a biconic surface, a biconic Zernike surface, an extended polynomial surface, a Zernike polynomial surface, or a Chebyshev polynomial surface.
As described herein, the freeform optic is positioned relative to the metasurface with an air gap between the concave first surface of the freeform optic and the metasurface. In some embodiments, a prism may also be positioned between the freeform optic and the metasurface, in which case an air gap exists between the prism and the freeform optic. The first surface of the freeform optic may for example, have a spherical or conical radius of curvature and/or may be rotationally symmetric. The first and second radii of curvature of the second surface (e.g., the surface opposing the first surface) of the freeform optic may be selected such that the second surface comprises a biconic surface, a biconic Zernike surface, an extended polynomial surface, a Zernike polynomial surface, or a Chebyshev polynomial surface.
In various embodiments, the first and second surfaces of the freeform optic may be shaped to compensate for one or more optical distortions introduced by the metasurface, adjust a steering line width of the metasurface, and/or correct a steering asymmetry of the metasurface. For example, the freeform optic may be configured to adjust for and/or compensate for one or more of the distortions or curvatures described in U.S. Pat. No. 11,092,675 granted on Aug. 17, 2021, entitled “Lidar Systems based on Tunable Optical Metasurfaces,” which is incorporated by reference above.
As described herein, including in conjunction with
The specific FOV of the metasurface may depend, in part, on an acceptable transmittance efficiency for a particular application. For example, a threshold transmittance value may be used between 80% and 99% that, for a given anti-reflective coating on a cover, a metasurface may limit the useable FOV for direct steering by the metasurface.
In some embodiments, the freeform optic may be embodied as and/or include one or more of a metalens formed on a curved substrate, a diffractive optical element, a refractive optical element, a reflective optical element, diffraction gratings, and/or the like.
The metasurface and freeform optic may be used as part of a transmitter system. The transmitter system may include an optical radiation source, such as a laser or laser array, to generate optical radiation to be reflected and/or refracted by the metasurface for transmission through the freeform optic. In such embodiments, the transmitted optical radiation is steered by the metasurface within the first FOV in the steering direction. For one-dimensionally steerable metasurfaces, the metasurface may reflect and/or refract the transmitted optical radiation with a second, fixed FOV in the non-steering direction (e.g., a fixed FOV of between 10 and 30 degrees).
As described herein, the first radius of curvature of the freeform optic along the first axis in the steering direction may operate (in conjunction with the concave first surface) to expand the first FOV. The second radius of curvature along the second axis in the non-steering direction of a one-dimensionally steerable metasurface may operate (in conjunction with the concave first surface to expand, narrow, or maintain the second, fixed FOV. For example, the second radius of curvature along the second axis in the non-steering direction may expand the native fixed FOV of the metasurface (or native fixed FOV of the metasurface and laser assembly) in the non-steering direction (e.g., 10-30 degrees) to an expanded fixed FOV in the non-steering direction (e.g., 60-120 degrees).
A controller (e.g., a driver) may control the operation of one or more optical radiation sources and/or the steering of the metasurface to scan a region of space with a sequence of scan lines (e.g., scan lines at a contiguous set of steering angles or a set of scan lines at arbitrary or discontiguous steering angles). In some embodiments, the optical radiation source includes a set of vertical-cavity surface-emitting lasers (VCSELs). Subsets of the VCSELs can be activated to attain narrower scan lines and/or to achieve some partial steering in the non-steering direction of the metasurface, as described in the patents and patent applications incorporated herein by reference.
Embodiments of this disclosure may be used for transmitter subsystems or devices, receiver subsystems or devices, and/or transceiver subsystems or devices of three-dimensional sensing systems (e.g., lidar systems). In various embodiments, an optical detector sensor (e.g., photodiodes) may operate to receive optical radiation reflected by the metasurface. For example, the metasurface may reflect optical radiation to the optical detector sensor that is received through the freeform optic at selective steering angles within a first FOV in the steering direction and within a fixed FOV in the non-steering direction.
In some embodiments, a freeform optic may be used in conjunction with a two-dimensionally steerable tunable optical metasurface. The two-dimensionally steerable metasurface may be selectively steerable in a first steering direction to a first plurality of steering angles within the first FOV and selectively steerable in a second steering direction to a second plurality of steering angles within a second FOV. As in other embodiments, the freeform optic may include a concave first surface positioned proximate to the metasurface. The concave first surface may be a spherical or conical rotationally symmetric surface, a biconic surface, a biconic Zernike surface, an extended polynomial surface, a Zernike polynomial surface, or a Chebyshev polynomial surface. The freeform optic also includes a biconic second surface that has a first radius of curvature along a first axis in the first steering direction of the metasurface and a second radius of curvature along a second axis in the second steering direction of the metasurface. The first radius of curvature along the first axis may still be different than the second radius of curvature along the second axis. However, in some embodiments in which the freeform optic is used in conjunction with a two-dimensionally steerable tunable optical metasurface, the biconic second surface of the freeform optic is rotationally symmetric.
Specific examples of freeform optics are described herein for use in conjunction with metasurfaces for transmitter and/or receiver subsystems of lidar or other three-dimensional sensor systems. A lidar transmitter may include a laser assembly (e.g., an array or set of VCSELs) to generate optical radiation. A one-dimensionally steerable tunable optical metasurface operates to selectively steer incident optical radiation in a steering direction for transmission at a plurality of steering angles within a first FOV. The first FOV may correspond to those steering angles for which the optical transmissivity is above a threshold transmittance value. The metasurface may operate to transmit the optical radiation at a fixed FOV in the non-steering direction.
As previously described, partial steering may be accomplished in the non-steering direction by the selective activation of subsets of the VCSELs). For example, a first subset of VCSELs may be activated for a 20-degree FOV from −20 degrees to 0 degrees in the non-steering direction, and a second subset of VCSELs may be activated for a different 20-degree FOV from 0 degrees to +20 degrees in the non-steering direction. In such embodiments, the one-dimensionally steerable metasurface still operates with a fixed FOV in the non-steering direction. In still other embodiments, a two-dimensionally steerable metasurface may be utilized. In embodiments in which partial or full steering is possible in the two different directions, the freeform optic may be configured to provide an expanded FOV in both steering directions while maintaining a higher transmittance value (optical transmission efficiency) than would be possible using the metasurface alone (e.g., due to Fresnel losses at extreme steering angles, as described in detail herein).
An optical assembly, such as one or more prisms, mirrors, lenses, waveguides, light guides, and/or the like, may be utilized to convey the optical radiation generated by the laser assembly to the metasurface. A lidar controller may cause the laser assembly to generate optical radiation and tune the metasurface to steer incident optical radiation as a sequence of transmit scan lines at various steering angles (contiguous or otherwise) within the first FOV. The freeform optic is positioned within the optical path of the metasurface and operates to expand the FOV of the metasurface in at least the steering direction, such that the optical radiation can be steered within an expanded FOV that is larger than the metasurface FOV while still maintaining an optical transmissivity above a target or selected threshold transmittance value.
Similarly, a lidar receiver may include an array of detector elements to detect optical radiation as a received scan line (e.g., a one-dimensional or two-dimensional array of photodiodes, various filters, collimators, microlenses, and/or the like). A tunable optical metasurface is steerable to reflect incident optical radiation to the array of detector elements at each of a plurality of receive steering angles within a first FOV in the steering direction. Again, the FOV of the metasurface may be limited (e.g., between 100 and 140 degrees) to achieve an optical transmissivity above a threshold transmittance value. The metasurface may operate to reflect incident optical radiation to the array of detector elements at each of the plurality of receive steering angles within a second, fixed FOV in the non-steering direction.
The lidar receiver may include a prism and/or other optical elements to convey the optical radiation reflected by the metasurface to the array of detector elements. Again, a controller may tune the metasurface (e.g., by driving a pattern of voltage differentials, as described in the references incorporated herein by reference) to receive optical radiation at a sequence of receive steering angles within the first FOV. The freeform optic is positioned within the optical path of the metasurface with an air gap between the freeform optic and the prism. The freeform optic has first and second surfaces that are configured to expand the first FOV in the steering direction to an expanded FOV while maintaining the optical transmissivity above the threshold transmittance value.
Similar to the other embodiments described herein, the freeform optic may be embodied as and/or include a metalens formed on a curved substrate, a diffractive optical element, a refractive optical element, a reflective optical element, a diffraction grating, a Fresnel lens, anti-reflective coatings, multiple layers, multiple elements, and/or the like. In various examples, the freeform optic includes a concave first surface positioned proximate to the metasurface (e.g., closest to the metasurface) and a biconic second surface that is farther from the metasurface. The concave first surface may be a spherical rotationally symmetric surface, a conical rotationally symmetric surface, a biconic surface, a biconic Zernike surface, an extended polynomial surface, a Zernike polynomial surface, or a Chebyshev polynomial surface. The second surface may have a first radius of curvature along a first axis in the steering direction of the metasurface and a second radius of curvature along a second axis in a non-steering direction of the metasurface.
Some of the infrastructure that can be used with embodiments disclosed herein is already available, such as general-purpose computers, computer programming tools and techniques, digital storage media, and communication links. Many of the systems, subsystems, modules, components, and the like that are described herein may be implemented as hardware, firmware, and/or software. Various systems, subsystems, modules, and components are described in terms of the function(s) they perform because such a wide variety of possible implementations exist.
It is also appreciated that two or more of the elements, devices, systems, subsystems, components, modules, etc. that are described herein may be combined as a single element, device, system, subsystem, module, or component. Moreover, many of the elements, devices, systems, subsystems, components, and modules may be duplicated or further divided into discrete elements, devices, systems, subsystems, components, or modules to perform subtasks of those described herein. Any aspect of any embodiment described herein may be combined with any other aspect of any other embodiment described herein and/or with the various embodiments described in the disclosures incorporated by reference, including all permutations and combinations thereof, consistent with the understanding of one of skill in the art reading this disclosure in the context of such other disclosures.
To the extent used herein, a computing device, system, subsystem, module, driver, or controller may include a processor, such as a microprocessor, a microcontroller, logic circuitry, or the like. The components of some of the disclosed embodiments are described and illustrated in the figures herein to provide specific examples. Many portions thereof could be arranged and designed in a wide variety of different configurations. In many instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of this disclosure.
Optical radiation from a laser assembly 310 is directed through a lens assembly 311 into the prism 320. The prism 320 allows the optical radiation to be directed from the laser assembly 310 for incidence on and steering by the metasurface 330 without obstructing the FOV of the metasurface. A transparent cover 340 (e.g., glass) on the metasurface 330 may have an anti-reflective coating to improve transmittance at various steering angles. However, as illustrated in
The freeform optic 350 is positioned above the prism 320 with a small air gap 345 therebetween. The airgap 345 is not visible in all the figures but may be present in any of the various embodiments to create an additional optical transition for bending the optical radiation gradually. The freeform optic 350 includes a first surface 352 (a lower surface as depicted) that is proximate to the metasurface 330 and a second surface 354 (an upper surface as depicted) that is opposite the first surface 352 and farther from the metasurface 330.
The first surface 352 includes surrounding planar sections outside the optical path that may be sized to support the freeform optic 350 and/or used for convenience in mounting. However, the portion of the first surface 352 that is within the optical path of the metasurface 330 is concave. In some embodiments, the concave first surface may be a biconic surface, a biconic Zernike surface, an extended polynomial surface, a Zernike polynomial surface, or a Chebyshev polynomial surface. In the illustrated example, the first surface 352 is rotationally symmetric and concave with a spherical radius of curvature or a conical radius of curvature. The biconic second surface 354 has a first radius of curvature along a first axis in the steering direction of the metasurface 330 and a second radius of curvature along a second axis in a non-steering direction of the metasurface 330. From the illustrated perspective, the first radius of curvature along the first axis in the steering direction is visible as a convex radius of curvature relative to the metasurface 330.
The freeform optic 350 expands the metasurface FOV of 120 degrees out of the prism 320 to an expanded FOV of 200 degrees. The freeform optic 350 allows the angle of incidence and the angle of departure of optical radiation at the interface of the metasurface 330 and the transparent cover 340 to be less than 60 degrees at all steering angles between −100 degrees and +100 degrees in the steering direction of the metasurface 330. The reflectance or Fresnel losses may be maintained at less than 1% while still allowing for a large effective FOV of at least 180 degrees. The freeform optic slowly (e.g., gradually) bends the optical rays in terms of angle of incidence (and angle of departure) through a sequence of three optical interfaces. The first interface is between the prism 320 and the air gap 345. The second interface is between the airgap 345 and the first surface 352 of the freeform optic 350. The third interface is between the second surface 354 of the freeform optic 350 and the air 347 outside of the device.
Accordingly, the freeform optic 350 includes a concave first surface 352 and a biconic second surface 354. A biconic surface is a surface that has a different radius of curvature along its two orthogonal axes. Each surface can be defined as various types of forms that have different design advantages based on symmetry, shape (e.g., round versus rectangular), and/or optical design optimization (computational convergence or speed). For instance, one or both of the first and second surfaces may be a biconic surface, a biconic Zernike surface, an extended polynomial surface, a Zernike polynomial surface, and a Cherbyshev polynomial surface. Complex biconic surfaces having two different spherical or conical radii of curvatures with different conic constants may be used to correct other asymmetries in the system, correct distortion, control an angle of incidence or an angle of departure on a surface, adjust line beam straightness, adjust a line beam pin cushion, adjust for barrel distortion, correct for conical diffraction of the metasurface, or the like.
For example, the laser assembly 310 may have a native divergence of approximately 20 degrees. The second radius of curvature of the second surface 354 (in conjunction with the concave first surface 352) operates to expand the native divergence such that the transmitted optical radiation has an expanded divergence or fixed FOV in the non-steering direction. In the illustrated example, the 20-degree native divergence of the laser assembly 310 is expanded to a fixed 90-degree FOV. The laser assembly 310 may include VCSELs, edge-emitting lasers, and/or another source, each of which may have unique or different divergence characteristics that can be expanded to a desired target FOV based on the second radius of curvature of the second surface 354. In some embodiments, the native intensity or power distribution profiles of the laser assembly 310 may be modified to be more even, more focused toward the center, and/or more focused toward one or both edges of the fixed FOV or divergence in the non-steering direction.
In the various illustrations, a steering direction is defined in the direction of the long edge 470, and a non-steering direction is defined in the direction of the short edge 460. The lower or first surface 452 is concave and may have a rotationally symmetric spherical or conical radius of curvature 453. Alternatively, the first surface 452 may be a concave biconic surface, a concave biconic Zernike surface, a concave extended polynomial surface, a concave Zernike polynomial surface, or a concave Chebyshev polynomial surface. The first surface 452 is positioned within an optical path of a metasurface with an airgap between the metasurface and the lower or first surface 452 (or between a prism and the lower or first surface 452 in embodiments that employ a prism between the metasurface and the freeform optic 450).
The upper surface 454, which is opposite the first surface 452, has a first radius of curvature 474 along the first axis in the steering direction (along the long edge 470) that is convex. The convex shape of the upper surface 454, as defined by the first radius of curvature 474, is emphasized in
The illustrated embodiments show the freeform optic 450 as being rectangular with a short edge 460 and a long edge 470. However, it is appreciated that in some embodiments, the freeform optic 450 may be square, circular, and/or have another polygonal, irregular, or freeform base shape.
A first spherical radius of curvature with a first conic constant is used in a first direction corresponding to the steering direction of the metasurface 830, and a second spherical radius of curvature with a second conic constant is used in a second direction corresponding to the non-steering direction of the metasurface 830. In various embodiments, the far field beam quality is improved by using a more complex freeform optic. The biconic upper surface 855 with higher order terms (spherical radii of curvature with different conic constants) exhibits sharper line beams for the higher steering angles than the spherical-only biconic upper surface 854 of the biconic freeform optic 850 in
The upper surface 855 of the biconic freeform optic 860 that opposes the lower surface 862 is also positioned within the optical path of the metasurface 830. The upper surface 865 forms an extended polynomial surface. The extended polynomial upper surface 865 has a first radius of curvature in a first direction corresponding to the steering direction of the metasurface 830. The extended polynomial upper surface 865 has a radius of curvature in a second direction corresponding to the non-steering direction of the metasurface 830. In various embodiments, the far field beam quality is improved through the use of the extended polynomial freeform optic.
The metasurface 830 steers optical radiation within a 120-degree FOV (e.g., steering between −60 degrees and +60 degrees). The upper surface 865 expands the FOV to 180 degrees (or more) to allow for beam steering in the steering direction between −90 degrees and +90 degrees. In the illustrated example, the metasurface 830 is illustrated as steering to angles −/+0°, 10°, 20°, 30°, 40°, 50°, 55°, and 60°, which are mapped by the biconic freeform optic 860 having an upper surface 865 that is an expended polynomial surface to angles −/+0°, 15°, 30°, 45°, 60°, 75°, 82.5°, and 90°. As previously described, the FOV or divergence of optical radiation in the non-steering direction may for example, be expanded from a native divergence (e.g., 20 degrees) to a target divergence (e.g., 90 degrees).
The optical radiation 905 is steered through the coupling prism 920, where it is refracted at the interface between the coupling prism 920 and the air gap. The optical radiation 905 is then refracted again as it enters the first surface of the freeform optic 950 (e.g., a rotationally symmetric spherical concave surface). The optical radiation 905 is refracted again as it departs the second surface of the freeform optic 950 into the air for free space transmission. The second surface of the freeform optic 950 may be biconic, as described herein. The freeform optic 950 expands the FOV in the steering direction 990 to an expanded FOV. As an example, the expanded FOV provided by the freeform optic 950 is approximately 160 degrees in some embodiments, approximately 170 degrees in some embodiments, approximately 180 degrees in some embodiments, and exceeds 180 degrees in some embodiments.
The optical radiation 905 is steered through the coupling prism 921, where it is refracted at the interface between the coupling prism 921 and the air gap. The optical radiation 905 is then refracted again as it enters the first surface of the freeform optic 950 (e.g., a rotationally symmetric spherical concave surface). The optical radiation 905 is refracted again as it departs the second surface of the freeform optic 950 into the air for free space transmission. The second surface of the freeform optic 950 may be biconic, as described herein. The freeform optic 950 expands the FOV in the steering direction 990 to an expanded FOV that is between 160 and 210 degrees, according to various embodiments.
The optical radiation 905 is steered through the coupling prism 922, where it is refracted at the interface between the coupling prism 922 and the air gap. The optical radiation 905 is then refracted again as it enters the first surface of the freeform optic 950 (e.g., a rotationally symmetric spherical concave surface). The optical radiation 905 is refracted again as it departs the second surface of the freeform optic 950 into the air for free space transmission. The second surface of the freeform optic 950 may be biconic, as described herein. The freeform optic 950 expands the FOV in the steering direction 990 to an expanded FOV that is between 160 and 210 degrees, according to various embodiments.
The optical radiation 905 is steered through the coupling prism 923, where it is refracted at the interface between the coupling prism 923 and the air gap. The optical radiation 905 is then refracted again as it enters the first surface of the freeform optic 950 (e.g., a rotationally symmetric spherical concave surface). The optical radiation 905 is refracted again as it departs the second surface of the freeform optic 950 into the air for free space transmission. The second surface of the freeform optic 950 may be biconic, as described herein. The freeform optic 950 expands the FOV in the steering direction 990 to an expanded FOV that is between 160 and 210 degrees, according to various embodiments.
The optical radiation 1005 is refracted at the interface between a transparent cover of the metasurface 1030 and the free space air between the freeform optic 1050 and the metasurface 1030. The optical radiation 1005 is then refracted at the interface of the air and the first surface of the freeform optic 1050 (e.g., a rotationally symmetric spherical concave surface or another concave surface). The optical radiation 1005 is refracted again as it departs the second surface of the freeform optic 1050 into the air for free space transmission. The second surface of the freeform optic 1050 may be biconic, as described herein. The freeform optic 1050 expands the FOV in the steering direction 1090 to an expanded FOV that is between 160 and 210 degrees, according to various embodiments.
The optical radiation 1005 is refracted at the interface between a transparent cover of the metasurface 1030 and the free space air between the freeform optic 1050 and the metasurface 1030. The optical radiation 1005 is then refracted at the interface of the air and the first surface of the freeform optic 1050 (e.g., a rotationally symmetric spherical concave surface). The optical radiation 1005 is refracted again as it departs the second surface of the freeform optic 1050 into the air for free space transmission. The second surface of the freeform optic 1050 may be biconic, as described herein. The freeform optic 1050 expands the FOV in the steering direction 1090 to an expanded FOV that is between 160 and 210 degrees, according to various embodiments.
The optical radiation 1005 is refracted at the interface between a transparent cover of the metasurface 1030 and the free space air. The optical radiation 1005 is then refracted at the interface of the air and the first surface of the freeform optic 1050 (e.g., a rotationally symmetric spherical concave surface or another concave surface). The optical radiation 1005 is refracted again as it departs the second surface of the freeform optic 1050 into the air for free space transmission. The second surface of the freeform optic 1050 may be biconic, as described herein. The freeform optic 1050 expands the FOV in the steering direction 1090 to an expanded FOV that is between 160 and 210 degrees, according to various embodiments.
According to various embodiments, any of the various biconic freeform optic devices and apparatuses may be fabricated using an injection molding plastic tool or other suitable manufacturing technique, depending on the material utilized. Suitable materials include but are not limited to, glass, sapphire, acrylics, plastics, and various transparent dielectric materials. The first and second surfaces of the biconic freeform optic may be cut on a metallic insert using a diamond point turning machine to create a mold. Injection molding can be used for a wide selection of available materials including, but not limited to, Cyclic olefin Polymer, Cyclic olefin copolymer, Acrylic, PMMA, Polycarbonate, Polyester, etc. In various embodiments, one or more surfaces of the biconic freeform optic 1250 may be coated with an AR coating to reduce reflections. In various embodiments, multiple freeform optics are used together (e.g., stacked or layered), at least one of which includes a biconic surface, to improve optical performance (e.g., expand a FOV, enhance a modulation transfer function (MTF) performance, etc.).
In some embodiments, a biconic freeform optic is fabricated with mechanical registering features (e.g., tabs, chamfers, pins, holes, etc.) to facilitate mounting the biconic freeform optic direction onto a prism, directly on a substrate around a metasurface, and/or directly onto an optically transparent cover of a metasurface. The mounting may create an air gap between the prism and the lower surface of the biconic freeform optic and/or an air gap between the metasurface and the biconic freeform optic.
The presently described embodiments support optical bandwidths and are, for example, suitable for optical sensing systems such as lidar, optical communications systems, optical computing systems, optical power transfer, and displays. For example, the systems and methods described herein can be configured with metasurfaces that operate in the sub-infrared, mid-infrared, high-infrared, and/or visible-frequency ranges (generally referred to herein as “optical” and understood in the context of feasibility and application). Given the feature sizes needed for sub-wavelength optical antennas and antenna spacings (e.g., sub-wavelength interelement spacings), the described metasurfaces may be manufactured using micro-lithographic and/or nano-lithographic processes, such as fabrication methods commonly used to manufacture CMOS integrated circuits.
This disclosure has been made with reference to various exemplary embodiments, including the best mode. However, those skilled in the art will recognize that changes and modifications may be made to the exemplary embodiments without departing from the scope of the present disclosure. While the principles of this disclosure have been shown in various embodiments, many modifications of structure, arrangements, proportions, elements, materials, and components may be adapted for a specific environment and/or operating requirements without departing from the principles and scope of this disclosure. These and other changes or modifications are intended to be included within the scope of the present disclosure.
This disclosure is to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope thereof. Likewise, benefits, other advantages, and solutions to problems have been described above with regard to various embodiments. However, benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element.
This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63/480,097, filed on Jan. 16, 2023, titled “Large Field-of-View Metasurface Optical Systems,” which application is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63480097 | Jan 2023 | US |
