PATENT DOCUMENT

Publication Number: US-11550163-B2
Application Number: US-202217581926-A
Country: US
Kind Code: B2

Title: Tunable blazed grating

Abstract:
Apparatus for deflection of a beam of light includes a case, which is configured to be positioned in a path of the beam, and a liquid, which is contained within the case. An array of plates is disposed across a surface of the liquid. The plates are configured to rotate on the surface about respective axes, which are mutually parallel and are spaced apart by a predefined pitch. An actuator is configured to drive a rotation of the plates about the respective axes so as deflect the beam that is incident on the plates.

Claims:
The invention claimed is: 
     
       1. Apparatus for deflection of a beam of light, the apparatus comprising:
 a case, which is configured to be positioned in a path of the beam; 
 a liquid, which is contained within the case; 
 an array of plates, which are disposed across a surface of the liquid and are configured to rotate on the surface about respective axes, which are mutually parallel and are spaced apart by a predefined pitch; and 
 an actuator, which is configured to drive a rotation of the plates about the respective axes so as deflect the beam that is incident on the plates. 
 
     
     
       2. The apparatus according to  claim 1 , wherein the case, the liquid, and the plates are transparent to the light, and the beam is deflected upon transmission through the apparatus. 
     
     
       3. The apparatus according to  claim 2 , and comprising cylindrical microlenses, which are fixed to the case in alignment with the plates. 
     
     
       4. The apparatus according to  claim 1 , wherein the beam is deflected by reflection from the plates. 
     
     
       5. The apparatus according to  claim 1 , wherein the array is configured to diffract the incident beam into a plurality of diffraction orders, having an angular spacing between the orders that is dependent on a ratio of a wavelength of the light to the pitch of the array, and wherein the actuator is configured to rotate the plates among a set of two or more blaze angles selected to direct the deflected light respectively into two or more different ones of the diffraction orders. 
     
     
       6. The apparatus according to  claim 5 , wherein the two or more of the diffraction orders comprise a zero diffraction order and a first diffraction order. 
     
     
       7. The apparatus according to  claim 1 , wherein the liquid comprises an oil. 
     
     
       8. The apparatus according to  claim 7 , wherein the oil across which the plates are disposed is a first liquid having a first refractive index, and wherein the apparatus further comprises a second liquid, which is immiscible with the oil and has a second refractive index different from the first refractive index, and which is disposed within the case over the array of plates. 
     
     
       9. The apparatus according to  claim 1 , and comprising a flexible membrane covering the surface of the liquid, wherein the plates are disposed on the flexible membrane, which is deformed by the rotation of the plates. 
     
     
       10. The apparatus according to  claim 9 , wherein the case comprises a reservoir having a volume that varies with the rotation of the plates so as to receive and expel the liquid that is displaced by deformation of the flexible membrane. 
     
     
       11. The apparatus according to  claim 10 , and comprising a pump, which is configured to draw the liquid into the reservoir and drive the liquid out of the reservoir in conjunction with the rotation of the plates. 
     
     
       12. The apparatus according to  claim 1 , wherein the axes about which the plates rotate are disposed along respective edges of the plates. 
     
     
       13. The apparatus according to  claim 1 , wherein the axes about which the plates rotate are disposed along respective centerlines of the plates. 
     
     
       14. The apparatus according to  claim 1 , and comprising a plurality of hinges, which secure the plates to the case at points along the respective axes of the plates. 
     
     
       15. The apparatus according to  claim 1 , wherein the actuator comprises a plurality of piezoelectric beams, which are coupled to apply rotational forces to the plates. 
     
     
       16. The apparatus according to  claim 15 , wherein the piezoelectric beams are oriented along the respective axes of the plates. 
     
     
       17. The apparatus according to  claim 15 , wherein the piezoelectric beams are oriented perpendicular to the respective axes of the plates. 
     
     
       18. The apparatus according to  claim 1 , wherein the array of plates comprises a first array of the plates, which are disposed across a first surface of the liquid and are configured to rotate about respective first axes, and wherein the apparatus comprises a second array of the plates, which are disposed across a second surface of the liquid, opposite the first surface, and are configured to rotate about respective second axes, which are mutually parallel. 
     
     
       19. The apparatus according to  claim 18 , wherein the second axes are parallel to the first axes. 
     
     
       20. The apparatus according to  claim 18 , wherein the second axes are perpendicular to the first axes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application 63/170,609, filed Apr. 5, 2021, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to optical components, and particularly to tunable optical elements. 
     BACKGROUND 
     Diffractive optical elements (DOEs) are optical components with micro-structure patterns that modulate the phase of incident beams of optical radiation. (The term “optical radiation” is used in the present description and in the claims, interchangeably with the term “light,” to refer to electromagnetic radiation in any of the visible, ultraviolet, and infrared spectral ranges.) DOEs may operate on either transmitted or reflected radiation (or both). The optical effect of the DOE depends on the spacing and depth of the diffractive micro-structure pattern. 
     A diffraction grating is a type of DOE with a periodic structure that diffracts incident light into multiple, distinct beams by either transmission through or reflection from the grating. The beams correspond to diffraction orders of the grating, which emanate from the grating at angles θ m  determined by the grating pitch d and the wavelength λ of the incident light: θ m =sin −1 (mλ/d). The fraction of the incident optical power that is emitted into a given diffraction order is referred to as the efficiency of the grating for that order. 
     The efficiency of a grating for a particular order at a particular wavelength can be optimized by appropriate choice of the blaze angle θ B , which is defined as the angle between the facets of the grating and the surface plane of the grating. For example, in a transmission grating, when the blaze angle is chosen such that the angle at which the beam is refracted at the facets is equal to the diffraction angle of a particular diffraction order, the light will be diffracted into that order with high efficiency. 
     SUMMARY 
     Embodiments of the present invention that are described hereinbelow provide tunable diffraction gratings and methods for their manufacture and use. 
     There is therefore provided, in accordance with an embodiment of the invention, apparatus for deflection of a beam of light. The apparatus includes a case, which is configured to be positioned in a path of the beam, and a liquid, which is contained within the case. An array of plates is disposed across a surface of the liquid. The plates are configured to rotate on the surface about respective axes, which are mutually parallel and are spaced apart by a predefined pitch. An actuator is configured to drive a rotation of the plates about the respective axes so as deflect the beam that is incident on the plates. 
     In some embodiments, the case, the liquid, and the plates are transparent to the light, and the beam is deflected upon transmission through the apparatus. In one embodiment, the apparatus includes cylindrical microlenses, which are fixed to the case in alignment with the plates. 
     Additionally or alternatively, the beam is deflected by reflection from the plates. 
     In some embodiments, the array is configured to diffract the incident beam into a plurality of diffraction orders, having an angular spacing between the orders that is dependent on a ratio of a wavelength of the light to the pitch of the array, and the actuator is configured to rotate the plates among a set of two or more blaze angles selected to direct the deflected light respectively into two or more different ones of the diffraction orders. In a disclosed embodiment, the two or more of the diffraction orders include a zero diffraction order and a first diffraction order. 
     Additionally or alternatively, the liquid includes an oil. In one embodiment, the oil across which the plates are disposed is a first liquid having a first refractive index, and the apparatus further includes a second liquid, which is immiscible with the oil and has a second refractive index different from the first refractive index, and which is disposed within the case over the array of plates. 
     In some embodiments, the apparatus includes a flexible membrane covering the surface of the liquid, wherein the plates are disposed on the flexible membrane, which is deformed by the rotation of the plates. In a disclosed embodiment, the case includes a reservoir having a volume that varies with the rotation of the plates so as to receive and expel the liquid that is displaced by deformation of the flexible membrane. The apparatus may also include a pump, which is configured to draw the liquid into the reservoir and drive the liquid out of the reservoir in conjunction with the rotation of the plates. 
     In one embodiment, the axes about which the plates rotate are disposed along respective edges of the plates. In another embodiment, the axes about which the plates rotate are disposed along respective centerlines of the plates. Additionally or alternatively, the apparatus includes a plurality of hinges, which secure the plates to the case at points along the respective axes of the plates. 
     In some embodiments, the actuator includes a plurality of piezoelectric beams, which are coupled to apply rotational forces to the plates. In one embodiment, the piezoelectric beams are oriented along the respective axes of the plates. In another embodiment, the piezoelectric beams are oriented perpendicular to the respective axes of the plates. 
     In some embodiments, the array of plates includes a first array of the plates, which are disposed across a first surface of the liquid and are configured to rotate about respective first axes, and the apparatus includes a second array of the plates, which are disposed across a second surface of the liquid, opposite the first surface, and are configured to rotate about respective second axes, which are mutually parallel. In a disclosed embodiment, the second axes are parallel to the first axes. In another embodiment, the second axes are perpendicular to the first axes. 
     Methods for producing apparatus as described above and methods for deflecting a beam of light as implemented in the apparatus described above are also within the scope of the present invention. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is schematic side view of apparatus for optical beam steering, in accordance with an embodiment of the invention; 
         FIGS.  2 A and  2 B  are schematic sectional views of a tunable diffraction grating at two different blaze angles, in accordance with an embodiment of the invention; 
         FIG.  2 C  is a schematic frontal view of the tunable diffraction grating of  FIGS.  2 A and  2 B ; 
         FIGS.  3 ,  4  and  5    are schematic sectional views of tunable diffraction gratings, in accordance with embodiments of the invention; 
         FIGS.  6  and  7    are schematic frontal views of plates in tunable diffraction gratings with piezoelectric actuators, in accordance with embodiments of the invention; 
         FIG.  8    is a schematic pictorial view of a plate in a tunable diffraction grating with piezoelectric actuators, in accordance with another embodiment of the invention; 
         FIGS.  9 A and  9 B  are schematic sectional and frontal views, respectively, of plates in a tunable diffraction grating with hinges, in accordance with an embodiment of the invention; 
         FIGS.  10 A and  10 B  are schematic sectional and frontal views, respectively, of plates in a tunable diffraction grating with hinges, in accordance with another embodiment of the invention; 
         FIGS.  11 A and  11 B  are schematic sectional and frontal views, respectively, of plates in a tunable diffraction grating with hinges, in accordance with yet another embodiment of the invention; 
         FIGS.  12 A and  12 B  are schematic sectional and frontal views, respectively, of plates in a tunable diffraction grating with hinges, in accordance with a further embodiment of the invention; 
         FIG.  13    is a schematic sectional view of a tunable diffraction grating with integral microlenses, in accordance with an embodiment of the invention; 
         FIG.  14    is a schematic sectional view of a tunable diffraction grating, in accordance with a further embodiment of the invention; 
         FIG.  15 A  is a schematic sectional view of a tunable diffraction grating, in accordance with yet another embodiment of the invention; and 
         FIGS.  15 B and  15 C  are schematic top and bottom views, respectively, of the tunable diffraction grating of  FIG.  15 A . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A wide variety of beam deflection and scanning devices are known in the art. In general, as the required deflection angle grows, the size and energy consumption of the device increases concomitantly. There is a need for ultra-compact, power-efficient devices that can rapidly switch or scan an incident beam of light between two or more different output angles. 
     Embodiments of the present invention that are described herein address this need by providing beam deflection apparatus with a novel, liquid-based structure. In the disclosed embodiments, the liquid is contained in a case, and an array of plates is disposed across the surface of the liquid in the container. (In some embodiments, the plates are disposed on a flexible membrane, which covers the surface of the liquid.) The plates rotate on the surface of the liquid about respective axes, which are mutually parallel and are spaced apart by a predefined pitch. An actuator drives the rotation of the plates about the respective axes so as to deflect a beam of light that is incident on the plates. The incident beam may be directed to reflect from the plates or to be refracted at the surface of the plates as it is transmitted through the apparatus (assuming that the case, liquid, and plates are all transparent at the wavelength of the beam). Because the apparatus uses an array of plates on a liquid substrate, only minimal energy is expended in rotating the plates, and little or no free space is required above the surface of the liquid to accommodate the rotation. 
     The pitch of the plates is selected in accordance with application requirements. In embodiments in which the pitch is substantially larger than the wavelength of the incident beam, the apparatus deflects the beam continuously by reflection or refraction at the surfaces of the plates. On the other hand, for smaller values of pitch (for example, below about 100 times the wavelength), the array of plates functions as a diffraction grating, diffracting the incident beam into multiple diffraction orders with an angular spacing between the orders that is dependent on the ratio of the wavelength to the pitch. In such embodiments, the actuator rotates the plates among a set of two or more blaze angles, which efficiently direct the deflected light into different diffraction orders. By appropriate selection of the blaze angles, the apparatus can serve as a switchable blazed grating over a large range of wavelengths. 
       FIG.  1    is schematic side view of apparatus  20  for optical beam steering, in accordance with an embodiment of the invention. Apparatus  20  comprises a light source, such as a laser  22 , which emits a beam  24  of light along a direction that is identified, for the sake of convenience, as the Z-axis in this and subsequent figures. Beam  24  is incident on a deflection device  26 , which is configured in this embodiment as a diffraction grating operating in a transmission mode. Device  26  diffracts beam  24  into two or more diffraction orders, which include, in this embodiment, a zero order  28  and a first order  30 . Actuators in device  26  control the blaze angle of the grating in order to direct the light in beam  24  selectively into one of the diffraction orders, as described below in greater detail. 
     In the pictured embodiment, deflection device  26  operates as a transmission grating. In other embodiments, deflection device  26  has a larger pitch, relative to the wavelength of beam  24 , and operates as an adjustable prism, which deflects the beam by refraction. In alternative embodiments (not shown in the figures), the beam is deflected by reflection from device  26 . Depending again on the pitch, the device may operate either as a reflection grating or as a rotating mirror array. 
     Reference is now made to  FIGS.  2 A- 2 C , which schematically show details of deflection device  26 , which is configured as a tunable diffraction grating in accordance with an embodiment of the invention.  FIGS.  2 A  and  2 B are sectional views at two different blaze angles of the grating, while  FIG.  2 C  is a frontal view. 
     Device  26  comprises a case  32 , which is positioned in the path of beam  24  ( FIG.  1   ). The case is filled with a liquid  36 , which is covered by a flexible membrane  34 . An array of plates  38  is fixed to the surface of membrane  34 , extending across the surface of liquid  36 . As illustrated in  FIGS.  2 A and  2 B , plates  38  rotate on the surface about respective axes, which are mutually parallel and are spaced apart by a predefined pitch. A number of different axis configurations are shown in the figures that follow. In these and the subsequent figures, the axes of plates  38  are assumed to extend along the Y-axis, and the pitch corresponds to the distance, measured along the X-axis, between the axes of neighboring plates. Although membrane  34  and plates  38  are disposed only across one side of case  32  in the present embodiment, in alternative embodiments (as shown in  FIGS.  14  and  15 A -C), there may be membranes and arrays of plates on both sides of the case. 
     As device  26  operates in transmission mode, case  32 , liquid  36 , membrane  34 , and plates  38  are all transparent to the light in beam  24 . For this purpose, case  32  and plates  38  typically comprise a suitable rigid glass or polymer material, and membrane  34  comprises a thin, flexible polymer or inorganic material. Alternatively, for operation at infrared wavelengths, plates  38  and/or case  32  may comprise suitable semiconductor materials, such as silicon. Assuming the wavelength of beam  24  to be approximately 1 μm, plates  38  will be between about 1 μm and 100 μm wide in the X-direction. To achieve a high fill factor and thus high efficiency of deflection, the pitch of the array is typically only slightly larger than the width of the plates. 
     Membrane  34  may comprise, for example, a siloxane-based polymer, polymethyl methacrylate (PMMA), or any other polymer with appropriate optical properties (for example, high optical transmittance, inter alia), low Young&#39;s Modulus, and stable residual stress. Alternatively, membrane  34  may comprise inorganic materials, such as SiO 2  or SiN. The thickness of polymer membranes used in the present embodiments is typically in the range of a few microns up to several tens of microns. The thickness of inorganic membranes in these embodiments is typically in the range of a few tens of nanometers up to several hundred nanometers. Membrane  34  may alternatively comprise a combination of polymer and inorganic materials. 
     Liquid  36  may include any suitable transparent liquid, desirably with a high refractive index to promote refraction in the configuration of  FIG.  2 B . Optical oils perform well in this capacity, such as silicone, phenyl-based, or perfluoro-polyether oils. Nanoparticles may be added to the oil in order to further increase its refractive index. 
     One or more actuators (shown in the figures that follow) drive the rotation of plates  38  about the respective axes so as deflect the beam that is incident on the plates. In the present example, the angles of plates  38  in  FIGS.  2 A and  2 B  correspond to different grating blaze angles that are selected to optimize diffraction into the zero and first diffraction orders, respectively (orders  28  and  30  in  FIG.  1   ).  FIG.  2 A  shows the rest position of the plates, while  FIG.  2 B  shows the actuated position. (Although for the sake of simplicity of illustration, the representation of membrane  34  in  FIG.  2 B , as well as in the figures that follow, has sharp transitions between plates  38 , in practice the membrane bends smoothly in response to the pressure exerted by the plates.) In one embodiment, the actuators apply downward pressure at points  40  along the edges of plates  38 . Alternatively, the actuators may apply uniform downward pressure along the lengths of the edges of the plates. Additionally or alternatively, the actuators may apply upward pressure at certain points or along the edges of the plates, possibly in conjunction with downward pressure on the opposite edges of the plates. As yet another alternative, the actuators may apply a rotational moment directly along the axes of rotation of the plates. 
     In the pictured embodiments, the actuators rotate all the plates concurrently at the same angle. Alternatively, the actuators may be controlled to rotate certain plates selectively, at the same or different angles. 
       FIG.  3    is a schematic sectional view of a tunable diffraction grating  50 , in accordance with an embodiment of the invention. Grating  50  can be identical in structure and functionality to device  26 , as described above, and is shown here to illustrate the location of axes  52  of rotation, which run along the respective centerlines of plates  38 . This axis position is advantageous in that the liquid  36  that is displaced by the downward motion of the right sides of the plates is taken up in the additional space created by the upward motion of the left sides of the plates. Thus, the total liquid volume is conserved, and the only resistance to the rotation of plates  38  is due to the viscosity of liquid  36  and the elasticity of membrane  34 . Therefore, only minimal actuation force is required in order to rotate the plates. 
       FIG.  4    is a schematic sectional view of a tunable diffraction grating  60 , in accordance with another embodiment of the invention. Grating  60  can also be similar in structure and functionality to device  26 , as described above, but in this case axes  62  of rotation are located along the respective edges of plates  38 . As a result, rotation of plates  38  about axes  62  reduces the available volume for liquid  36  in the area beneath the plates. To alleviate this problem, one or more reservoirs  64  receive the liquid that is displaced as plates  38  rotate downward and then expel this liquid when the plates rotate back up to their rest position. Membrane  34  over reservoirs  64  expands and contracts depending on the amount of liquid displaced into the reservoirs. Although reservoirs  64  in  FIG.  4    are located outside the area of the array of plates  38 , the gaps between an alongside plates  38  may be used, additionally or alternatively, as reservoir areas. 
     In the pictured embodiment, grating  60  comprises piezoelectric actuators  66 , which are fixed to membrane  34  over reservoirs  64 . Actuators  66  are driven to bend, as shown in  FIG.  4   , in order to draw liquid into reservoirs  64  when plates  38  rotate downward, and to straighten in order to expel the liquid from the reservoirs when the plates rotate back up. Actuators  66  thus function as a pump, which can assist in reducing the force that must be exerted in order to rotate plates  38  (and may even obviate the need to apply force directly to the plates themselves). This sort of pump can also be useful in adjusting for changes in the volume of liquid  36  due to thermal expansion and contraction. Alternatively, other sorts of miniature pumping mechanisms may be applied for these purposes. 
       FIG.  5    is a schematic sectional view of a tunable diffraction grating  70 , in accordance with an alternative embodiment of the invention. The principle of operation of grating  70  is similar to that of device  26 , but in this embodiment there is no membrane covering the liquid. Rather, grating  70  comprises two immiscible liquids  74  and  76  inside a closed case  72 . Plates  38  are disposed directly over the surface of liquid  74 , which is assumed to be heavier than liquid  76 . For example, liquids  74  and  76  may comprise two different optical oils, with different refractive indexes. (The larger the difference in refractive index, the smaller will be the required rotation of plates  38  in order to switch between diffraction orders.) 
     This embodiment is advantageous in reducing the force that must be applied in order to rotate plates  38 , since mechanical resistance due to the elasticity of the membrane used in the preceding embodiments is eliminated. In another embodiment, liquid  76  is replaced by a gas, such as air. 
       FIGS.  6  and  7    are schematic frontal views of plates in tunable diffraction gratings with piezoelectric actuators  80  and  84 , respectively, in accordance with embodiments of the invention. These figures show individual plates  38  within an array in a deflection device, such as device  26  in  FIG.  2 C . The structures shown in these and the succeeding figures may be produced, for example, by processes of thin film deposition, photolithographic patterning, and etching, as are known in the art of fabrication of semiconductor devices and microelectromechanical systems (MEMS). 
     Actuators  80  and  84  comprise piezoelectric beams, which are oriented along the respective axes of plates  38  and are coupled by mechanical connectors  82  to apply rotational forces to the edges of plates  38 . Actuators  80  are rectangular, while actuators  84  are trapezoidal, for example, but other geometrical configurations may alternatively be used. In one embodiment, these actuators comprise a layer of lead zirconate titanate (PZT) deposited on a silicon substrate. To deflect plates  38  downward (in the −Z direction in the view shown in  FIGS.  6  and  7   ), actuators  80  and  82  are disposed with the PZT layer below the silicon layer. 
       FIG.  8    is a schematic pictorial view of plate  38  in a tunable diffraction grating, with piezoelectric actuators  86  in accordance with another embodiment of the invention. In this case, actuators  86  comprise piezoelectric beams that are oriented perpendicular to the axis of plate  38  and are coupled by mechanical connectors  88  to apply rotational forces to the edge of the plate. Because the piezoelectric beams are short in this case, they can achieve only a limited range of motion. To increase the range of motion, two or more beams can be arranged in serpentine fashion at each side of plate  38 . 
       FIGS.  9 A and  9 B  are schematic sectional and frontal views, respectively, of plates  38  in a tunable diffraction grating, with hinges  90  in accordance with an embodiment of the invention. Hinges  90  secure plates  38  to anchors  92  in case  32  at points along respective axes  94  of rotation of the plates. In this example, axes  94  are located along the centerlines of plates  38 . Hinges  90  extend downward through fluid  36  to anchors  92 , in a direction perpendicular to axes  94 . Hinges  90  and anchors  92  (as well as the hinges and anchors in the embodiments that follow) can be produced together with case  32 , for example using a process of photolithography and etching, and then bonded to membrane  34  and plates  38 . 
       FIGS.  10 A and  10 B  are schematic sectional and frontal views, respectively, of plates  38  in a tunable diffraction grating, with hinges  96  in accordance with another embodiment of the invention. As in the preceding embodiment, hinges  96  secure plates  38  to anchors  92  in case  32  at points along respective axes  98  of rotation of the plates; but in this case axes  98  are located along the edges of plates  38 . 
       FIGS.  11 A and  11 B  are schematic sectional and frontal views, respectively, of plates  38  in a tunable diffraction grating, with hinges  100  in accordance with yet another embodiment of the invention. In this example, hinges  100  extend in a direction parallel to the axes of plates  38  and are anchored to the edges of case  32 , rather than to the bottom. Hinges  100  (as well as the hinges in the embodiment of  FIGS.  12 A /B) can be produced on membrane  34  by processes of thin film deposition, photolithography, and etching, for example, or by a nanoimprint process. Hinges  100  support membrane  34  along respective lines that are parallel to plates  38 , and thus secure plates  38  to case  32  without actually being attached directly to the plates. This arrangement allows the plates greater freedom of motion over liquid  36 . 
       FIGS.  12 A and  12 B  are schematic sectional and frontal views, respectively, of plates  38  in a tunable diffraction grating, with hinges  102  in accordance with a further embodiment of the invention. In this example, hinges  102  are attached along the edges of plates  38  above membrane  34 , and thus secure the plates to the edges of case  32 . 
       FIG.  13    is a schematic sectional view of a tunable diffraction grating  110  with integral microlenses  112 , in accordance with an embodiment of the invention. This embodiment addresses the problem that a portion of the light beam that is incident on the grating can pass through the gaps between plates  114  and thus reduce the efficiency of deflection. It is assumed in this embodiment that beam ( FIG.  1   ) is incident on and transmitted through the lower surface of case  32 . An array of cylindrical microlenses  112  is fixed to case in alignment with plates  114  and with the same pitch as the plates. Microlenses  112  focus the incident light sufficiently so that nearly all the light energy is directed toward the areas of the plates and not the intervening gaps. Plates  114  have the form of diverging cylindrical lenses, which are complementary to microlenses  112  so that the diffracted light transmitted through grating  110  is collimated. 
       FIG.  14    is a schematic sectional view of a tunable diffraction grating  120 , in accordance with a further embodiment of the invention. In this embodiment, case  122  is covered by transparent membranes  126  and  129  on the opposing upper and lower sides of liquid  36 . (The terms “upper” and “lower” are used here solely for the sake of convenience, since grating  120  can be used in substantially any desired orientation.) An array of transparent plates  124  is fixed to membrane  126 , while another array of transparent plates  128  is fixed to membrane  129 . The axes of rotation of plates  124  and  128  are mutually parallel. In the pictured embodiment, plates  128  rotate in the opposite angular direction to plates  124 , thus increasing the effective blaze angle of grating  120 . Alternatively, the plates may be actuated to rotate in the same direction. In the rest position (as illustrated in  FIG.  2 A , for example), plates  124  are all coplanar, as are plates  128 . 
     Reference is now made to  FIGS.  15 A-C , which schematically illustrate a tunable diffraction grating  130 , in accordance with yet another embodiment of the invention.  FIG.  15 A  is a sectional view, while  FIGS.  15 B and  15 C  are top and bottom views, respectively, of the tunable diffraction grating. 
     As in the preceding embodiment, grating  130  comprises a case  132 , with membranes  136  and  140  on the opposing upper and lower sides of liquid  36 . An array of transparent plates  134  is fixed to membrane  136 , while another array of transparent plates  138  is fixed to membrane  140 . (The plates in these figures are shown in their rest positions.) In contrast to the preceding embodiment, however, the axes of rotation of plates  138  are oriented along the X-axis, perpendicular to those of plates  134 , which are oriented along the Y-axis. This configuration makes it possible for grating  130  to deflect an incident beam in either the X-direction or the Y-direction or both, depending on the respective angles of plates  134  and  138 . 
     It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Metadata:
Filing Date: 20220123
Publication Date: 20230110
Grant Date: 20230110
Priority Date: 20210405
Inventors: BOLIS, SEBASTIEN
POUYDEBASQUE, ARNAUD
CHIDAMBARAM, NACHIAPPAN
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B27/0944", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/4244", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/4244", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0944", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/4244", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0944", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 83450136