Tunable optical element

Abstract

A tunable optical element (10) is configured to modify electromagnetic radiation (15). The tunable optical element (10) comprises a carrier (100), a first electrode (101), and pillars (116) or ridges (117) of a first material (105). A pitch d of the pillars (116) or ridges (117) is smaller than a wave-length of the electromagnetic radiation (15). The pillars (116) or ridges (117) are arranged over the first electrode. The tunable optical element (10) further comprises a planarization layer (107) filling spaces between adjacent pillars (116) or ridges (117). The planarization layer comprises a second material. One of the first and the second materials comprises an electrooptical material and the other of the first and second materials comprises an inert material. The tunable optical element further comprises a transparent second electrode (102) over the planarization layer (105) and a power source (109), connected to the first and second electrode (101, 102), for tuning properties of the optical element (10).

Description

[0001] TUNABLE OPTICAL ELEMENT

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a tunable optical element .

[0004] BACKGROUND

[0005] Many consumer electronic devices comprise elements which rely on processing of electromagnetic radiation . Hence , there is a need for an optical element which may be tuned in an easy and fast manner .

[0006] SUMMARY

[0007] It is an obj ect of the present invention to provide an improved tunable optical element . Further, it is an obj ect to provide an improved electronic device .

[0008] According to embodiments , the above obj ects are achieved by the claimed matter according to the independent claims . Further developments are defined in the dependent claims .

[0009] A tunable optical element is configured to modi fy electromagnetic radiation . The tunable optical element comprises a carrier, a first electrode , and pillars or ridges of a first material . A pitch d of the pillars or ridges is smaller than a wavelength of the electromagnetic radiation . The pillars or ridges are arranged over the first electrode . The tunable optical element further comprises a planari zation layer filling spaces between adj acent pillars or ridges . The planari zation layer comprises a second material . One of the first and the second materials comprises an electrooptical material and the other of the first and second materials comprises an inert material . The tunable optical element further comprises a transparent second electrode over the planarization layer and a power source, connected to the first and second electrode, for tuning properties of the optical element.

[0010] In this context, the wording "a pitch is smaller than a wavelength" is intended to refer to the wavelength in the specific medium, e.g. the material of the pillars or ridges

[0011] For example, the electrooptical material may be selected from a ferroelectric material and an electrooptical polymer.

[0012] For example, the inert material may be selected from silicon oxide, aluminum oxide, beryllium oxide, germanium oxide, hafnium oxide, magnesium oxide, titanium nitride, magnesium fluoride, barium fluoride and cerium fluoride.

[0013] According to embodiments, the first electrode is arranged between the carrier and the pillars or ridges.

[0014] According to further embodiments, the pillars or ridges may be arranged adjacent to a first main surface of the carrier and the first electrode is arranged adjacent to a second main surface of the carrier.

[0015] The tunable optical element may further comprise a layer of the electrooptical material between the first electrode and the pillars or ridges and in contact with the pillars or ridges .

[0016] For example, the pillars or ridges are separated from each other .

[0017] By way of example, the pillars or ridges have identical size and are arranged at a constant pitch. For example , the first electrode may be assigned to a plurality of pillars and the second electrode comprises a plurality of address lines for addressing pillars of one group of pillars , respectively .

[0018] According to further examples , the first electrode is assigned to a plurality of pillars and the second electrode comprises a plurality of electrode segments .

[0019] According to embodiments , the electrode segments are addressable using address lines comprising a first subset of address lines extending in a first hori zontal direction and a second subset of address lines extending in a second hori zontal direction .

[0020] Each of the electrode segments may be assigned to one or a group of pillars .

[0021] The tunable optical element may further comprise a plurality of transistors , wherein each of the transistors is assigned to one electrode segment , respectively, a source or drain region of the transistor being electrically connected to an address line of the first subset of address lines , and a gate electrode of the transistor being electrically connected to an address line of the second subset of address lines .

[0022] For example , the pillars may comprise first pillars and second pillars . One of the first pillars and one of the second pillars may be arranged in unit cells having a si ze smaller than the wavelength of the electromagnetic radiation . According to implementations , the first electrode may be assigned to a plurality of pillars or ridges and the second electrode may be assigned to a plurality of pillars or ridges .

[0023] For example , at least a portion of the pillars may be arranged in circles and the second electrode comprises a ring-shaped portion for addressing pillars of a circle .

[0024] According to embodiments , the tunable optical element may further comprise a first resonator mirror adj acent to the first electrode and a second resonator mirror adj acent to the second electrode , an optical resonator being formed between the first and the second resonator mirrors .

[0025] According to further embodiments , a tunable optical element which is configured to modi fy electromagnetic radiation, comprises a carrier, a first electrode , and pillars or ridges of a first material . A pitch d of the pillars or ridges may be smaller than a wavelength of the electromagnetic radiation . The tunable optical element further comprises a planari zation layer filling spaces between adj acent pillars or ridges , the planari zation layer comprising a second material . The tunable optical element further comprises a piezoelectric layer on a side of the planari zation layer facing away from the carrier and a transparent second electrode over the piezoelectric layer . The tunable optical element further comprises a power source , connected to the first and second electrode , for deforming the piezoelectric layer to tune properties of the optical element .

[0026] For example , one of the first and the second materials comprises a perowskite material and the other of the first and second materials comprises an inert material . For example , the second electrode may be segmented .

[0027] According to further embodiments , a tunable optical element which is configured to modi fy electromagnetic radiation, comprises a carrier, a heater electrode , and pillars or ridges of a first material . A pitch d of the pillars or ridges is smaller than a wavelength of the electromagnetic radiation . The tunable optical element further comprises a planari zation layer filling spaces between adj acent pillars or ridges . The planari zation layer comprises a second material . One of the first and second materials comprises a thermooptical material and the other of the first and second materials comprises an inert material . The tunable optical element further comprises a power source connected to the heater electrode . The power source is configured to heat the heater electrode to tune properties of the optical element .

[0028] For example , the heater electrode may be segmented .

[0029] According to further embodiments , a tunable optical element that is configured to modi fy electromagnetic radiation, comprises a carrier, and a metaoptic structure arranged over the carrier . The metaoptic structure comprises an array of pillars or ridges of a first material , and a planari zation layer of a second material , the planari zation layer filling spaces between adj acent pillars or ridges . The tunable optical element further comprising a modulation device for changing optical properties of the array of pillars or ridges or of the second material to change optical properties of the metaoptic structure .

[0030] For example , the tunable optical element described above may be configured to implement an optical shutter, a lens or a deflector . BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this speci fication . The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles . Other embodiments of the invention and many of the intended advantages will be readily appreciated, as they become better understood by reference to the following detai led description . The elements of the drawings are not necessarily to scale relative to each other . Like reference numbers designate corresponding similar parts .

[0032] Fig . 1A shows a schematic cross-sectional view of a tunable optical element according to embodiments .

[0033] Fig . IB shows a schematic cross-sectional view of a tunable optical element according to further embodiments .

[0034] Fig . 1C shows a schematic cross-sectional view of a tunable optical element according to further embodiments .

[0035] Fig . ID is a hori zontal cross-sectional view of a portion of a tunable optical element according to embodiments .

[0036] Fig . IE is a hori zontal cross-sectional view of a portion of a tunable optical element according to further embodiments .

[0037] Figs . 2A and 2B are views for illustrating an addressing scheme of a tunable optical element according to embodiments . Figs . 3A and 3B are views for illustrating an addressing scheme of a tunable optical element according to further embodiments .

[0038] Fig . 3C shows an equivalent circuit diagram of a corresponding tunable optical element .

[0039] Fig . 3D shows voltage diagrams for illustrating the addressing of regions of the tunable optical element .

[0040] Fig . 3E is a schematic view of a tunable optical element according to further embodiments .

[0041] Fig . 4 shows a tunable optical element according to further embodiments .

[0042] Fig . 5A shows a schematic drawing of a tunable optical element according to further embodiments .

[0043] Fig . 5B shows a transmission / phase change characteristics in dependence from a refractive index .

[0044] Fig . 6A shows a schematic layout of a tunable optical element according to embodiments .

[0045] Fig . 6B shows a schematic layout of a further tunable optical element .

[0046] Fig . 6C shows a further configuration of a tunable optical element .

[0047] Fig . 7 shows a schematic cross-sectional view of a tunable optical element according to further embodiments . Fig. 8A shows a schematic cross-sectional view of a tunable optical element according to further embodiments.

[0048] Fig. 8B shows a schematic layout of a tunable optical element according to embodiments.

[0049] Fig. 8C shows a schematic cross-sectional view of a tunable optical element according to embodiments.

[0050] Figs. 9A to 9D illustrate cross-sectional views of a workpiece when performing a method of manufacturing a tunable optical element .

[0051] Figs. 10A to IOC are cross-sectional views of a workpiece when performing a further method of manufacturing a tunable optical element .

[0052] DETAILED DESCRIPTION

[0053] In the following detailed description reference is made to the accompanying drawings, which form a part hereof and in which are illustrated by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology such as "top", "bottom", "front", "back", "over", "on", "above", "leading", "trailing" etc. is used with reference to the orientation of the Figures being described. Since components of embodiments of the invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope defined by the claims. The description of the embodiments is not limiting . In particular, elements of the embodiments described hereinafter may be combined with elements of di f ferent embodiments .

[0054] The terms " lateral" and "hori zontal" as used in this speci fication intends to describe an orientation parallel to a first surface of a substrate or semiconductor body . This can be for instance the surface of a wafer or a die .

[0055] The term "vertical" as used in this speci fication intends to describe an orientation which is arranged perpendicular to the first surface of a substrate or semiconductor body .

[0056] As employed in thi s speci fication, the terms "coupled" and / or "electrically coupled" are not meant to mean that the elements must be directly coupled together - intervening elements may be provided between the "coupled" or "electrically coupled" elements . The term "electrically connected" may describe a low- ohmic electric connection between the elements electrically connected together .

[0057] The term "electrically connected" further comprises tunneling contacts between connected elements .

[0058] According to further embodiments and where appropriate , the term "electrically connected" may mean that the respective elements are "directly connected" or are "directly and permanently connected" .

[0059] The term " electrically connected" may describe a permanent low- resistive connection between electrically connected elements , for example a direct contact between the concerned elements or a low-resistive connection via a metal and / or heavily doped semiconductor material . The term " electrically coupled" may include that one or more intervening element ( s ) adapted for signal and / or power transmission may be connected between the electrically coupled elements , for example , elements that are controllable to temporarily provide a low-resistive connection in a first state and a high-resistive electric decoupling in a second state . An ohmic contact may be a non-recti fying electrical j unction .

[0060] The term "pitch of pillars" or "pitch of ridges" as used in the context of the present disclosure is intended to describe a sum of a width of a pillar and a distance between adj acent pillars or a sum o f a width of a ridge and a di stance between adj acent ridges , wherein the width and the distance are measured in a hori zontal direction . The use of the term "pitch" does not imply that the pillars or ridges are arranged in periodic arrangements having a fixed pitch between adj acent pillars or ridges . According to embodiments , the pitch may be variable . The use of the term "pitch" does not imply that e . g . the pillars are arranged in a rectangular lattice . For example , the pillars may be arranged in a hexagonal lattice . In this context , the term "pitch" may refer to a lattice constant or a length of the lattice vectors .

[0061] According to further embodiments , the pillars or ridges or sets of pillars or sets of ridges may be arranged in periodic patterns having a constant pitch or period .

[0062] The present disclosure relates to compounds such as silicon oxide or silicon nitride without further speci fying a stoichometric ratio . Where such unspeci fic compounds are described, it is intended that this description relates to any known stoichometric ratio including mixtures thereof . Accordingly, the term " silicon oxide" may refer to SiO, SiCy and mixtures of SiO and SiCy . The present disclosure relates to tunable metalenses . Generally, the term "metalens" or "metaoptic structure" refers to a lens that bends light using an array of nanostructures that are formed on a ( ideally flat ) surface of a substrate , instead of via refraction . More speci fically, a metalens includes a metasurface that includes an array of nanostructures , wherein the nanostructure array is configured to bend light incident thereon by altering its phase . As will be described, the phase change imparted by the metasurface can create a new wave front in a region down field of the lens . For example , a metalens consistent with the present disclosure can include an array of nanostructures that can impart a phase change to incident light having a spherical or hemispherical wave front up field of a lens , such that the light in a region down field of the lens has a planar wave front ( i . e . , a plane wave ) .

[0063] Stated more generally, metalenses are designed to shape light to a dedicated radiation pattern . Thi s may be accomplished due to phase shi fts and interference ef fects of geometrical structures having si zes below the wavelength of the electromagnetic radiation to be shaped by the metalenses . According to an approximation, the phase shi fts may be interpreted as waveguide modes propagating in the pillars , generating a phase shi ft dependent on the height of the pillar of a given geometry and si ze .

[0064] Furthermore , the propagation in materials may also change the polari zation direction of light . After passing areas having a structured pattern of polari zation rotation material , interferences may be generated, the interferences redirecting the light .

[0065] For example , nanostructures that may be a component of metalenses are generally configured to function as resonators or waveguides that impart a phase change to light incident thereon . As will be described below, the metalenses may comprise pillars or ridges and a planarization layer filling the spaces between adjacent pillars or ridges. In this context, the pillars / ridges or the planarization layer in between may constitute the nanostructures mentioned above.

[0066] As will be explained in the following, by suitable applying voltages to metalenses, the properties of the metalenses may be locally varied. As a result, the radiation pattern of the tunable metalens may be tuned without the need of using movable parts.

[0067] According to further embodiments, the properties of the metalenses may be varied by mechanical tension or heat.

[0068] For example, an electrooptical material may refer to a material that alters its optical properties, e.g. a refractive index when a voltage is applied.

[0069] A thermooptical material refers to a material that alters its optical properties, e.g. the refractive index when the temperature is changed.

[0070] Generally, materials which are suitable for use in the tunable optical element may comprise materials having an anisotropic crystal structure, e.g. materials which can form a dipole such as perovskite materials and transparent perovskite materials. These materials may be used as electrooptical material. Further, the optical properties of these materials may as well be modulated by applying mechanical tension or heat.

[0071] Further, transparent trigonal materials, e.g. birefringent materials may as well be used in the tunable optical element. Further examples comprise organic chromophores such as (E)-2- [2- ( 5-bromothiophen-2-yl ) vinyl] -4-oxo-4H-chromone-3-carboni- trile, (E ) -2- [ 2- ( 4-bromophenyl ) vinyl ] -4-oxo-4H-chromone-3-car- bonitrile, (E) -2- [2- ( 4-diethylaminophenyl ) -vinyl] -4-oxo-4H- chromone-3-carbonitrile, (E) -4- [2- ( 5-bromothiophen-2-yl ) -vinyl] -3-cyanocoumarin, (E) -4- [2- (2- (5- (4- (dimethylamino) phenyl) thiophen-2-yl ) vinyl) -4-oxo-4H-chromene-3-carbonitrile, (E) - 2- (2- (4- (4- (dimethylamino) phenyl) phenyl) vinyl) -4-oxo-4H- chromene-3-carbonitrile, (E) -2- (2- (5- (4- (dimethylamino) phenyl) thiophen-2-yl ) vinyl) -2-oxo-2H-chromene-3-carbonitrile, and DAST = 4-N, N-dimethylamino-4 , -N, -methyl-stilbazolium tosylate.

[0072] The term "inert" material refers to a material that hardly changes its optical properties e.g. the refractive index, when e.g. a voltage is applied, a mechanical stress or tension is applied or when the temperature is changed.

[0073] Fig. 1A shows a cross-sectional view of a tunable optical element 10 according to embodiments. As will be explained in the following, the tunable optical element 10 comprises a carrier 100, a first electrode 101 and pillars 116 or ridges 117 of a first material. A pitch of the pillars 116 or ridges 117 is smaller than a wavelength of electromagnetic radiation that is to be modified by the tunable optical element 10. The first electrode 101 is arranged between the carrier 100 and the pillars 116 or the ridges 117. The tunable optical element further comprises a planarization layer 107 comprising a second material which fills spaces between adjacent pillars 116 or ridges 117. The tunable optical element 10 further comprises a transparent second electrode 102 over the planarization layer 107. One of the first and the second materials comprises an electrooptical material and the other of the first and second materials comprises an inert material. Moreover, the tunable optical element 10 comprises a power source 109 which is connected to the first and second electrodes 101 , 102 . By applying a corresponding electrical field between the first electrode 101 and the second electrode 102 , the optical properties of the optical element 10 may be tuned .

[0074] As is shown in Fig . 1A, the first electrode 101 may be arranged between the carrier and the pillars 116 or the ridges 117 . Accordingly, the first electrode 101 may be arranged adj acent or directly adj acent to the electrooptical material . By keeping the electrodes in direct contact or contact through only a very thin insulating layer to the electrooptic materials , we minimi ze rej ection of the electric field by the electrooptic materials , due to the very high electrical permittivities of many electrooptic materials . For example , the risk that the electric field may be rej ected from the region of the electrooptical material when the distance between the electrooptical material and the first electrode 101 is too large , may be reduced .

[0075] For example , the electrooptical material may comprise a ferroelectric material such as BaTiOs, SrTiOa, LiNbOa, LiTaOs, PrScOa, SmScOa, TbScOa, DyScOa, Ba (BO2) 2 and others . The ferroelectric material may be a so-called "perovskite material" meaning that the crystal structure of the material is a perovskite crystal structure . According to further implementations , the electrooptical material 105 may comprise AIN, GaN or an organic material such as DAST = 4-N, N-dimethylamino-4 , -N, -methyl- stilbazolium tosylate or an organic chromophore having nonlinear optical properties . According to further embodiments , another organic material or polymer having electro-optic properties such as HLD or JRD1 , manufactured by NLM Photonics may be employed . For example, a height of the pillars 116 or ridges 117 may be less than 2 pm, e.g. 300 to 800 nm, e.g. approximately 500 nm. The height of the pillars 116 or ridges 117 may be larger than 100 nm. The height H of the pillars 116 or ridges may depend on the wavelength X of the electromagnetic radiation to be shaped and on the refractive index n of the material of the pillars or ridges. For example, the following relationship may hold :

[0076] 1 / 3*X < n*H <2*X.

[0077] The inert material may comprise SiCy, e.g. fused silica. Further examples of the inert material comprise aluminum oxide, beryllium oxide, germanium oxide, hafnium oxide, magnesium oxide, titanium nitride, magnesium fluoride, barium fluoride, and cerium fluoride. Further materials which are transparent for the emitted electromagnetic radiation may be taken. A refractive index of the inert material should be lower than the refractive index of the electrooptical material.

[0078] For example, the material of the first and the second electrode may comprise a transparent conductive oxide such as ITO ("indium tin oxide") or another transparent conductive material, e.g. another transparent conductive oxide. The carrier 100 may comprise a transparent material. For example, the carrier may be suitable for growth of the electrooptical material 105 having a predetermined growth direction. For example, a crystal orientation of the carrier or substrate may be selected such that e.g. a c-axis growth of the electrooptical material may be achieved, as will be explained with reference to Fig. 9A in more detail.

[0079] Fig. 1A further shows incident electromagnetic radiation 15 which is modified by the tunable optical element 10. As is further illustrated in Fig. 1A, the first electrode 101 and the second electrode 102 may be formed as continuous electrodes. When an electrical field is applied between the first electrode 101 and the second electrode 102, the optical properties of the electrooptical material may be modulated. In more detail, for example, the refractive index inside the nanostructures of the electrooptical material is changed. As a consequence, the propagation speed of the electromagnetic radiation in the electrooptical material is changed. As a consequence, the wavefront is shifted. Due to the shifted wavefront, interference effects which are resulting in a modification of the radiation pattern of the optical element are caused .

[0080] As is shown in Fig. 1A, the pillars or ridges 116, 117 may be arranged at an identical pitch. According to further implementations, the pillars 116 or ridges 117 may be arranged at different distances. The pillars 116 or ridges 117 may be identical in size and shape. According to further implementations, the pillars or ridges may have different sizes. Moreover, the pillars 116 or ridges 117 may have different shapes. For example, the pillars 116 or ridges 117 may be arranged at an identical pitch, forming a lattice. Further, the size and / or the shape of the individual pillars 116 or ridges 117 may vary. For example, using different diameters or horizontal sizes of the pillars 116 or the ridges 117, a lens action may be induced .

[0081] The tunable optical element 10 may accomplish a modulation of incident electromagnetic radiation without the need of movable mechanical components. Accordingly, the modulation may be performed at a very high speed. The tunable optical element 10 may be tuned using a direct electrostatic effect. Fig . IB shows a schematic cross-sectional view of a tunable optical element 10 according to further embodiments . As is shown, di f fering from embodiments illustrated in Fig . 1A, the pillars 116 or ridges 117 of the first material are arranged directly adj acent to the first main surface 201 of the carrier

[0082] 100 . The first electrode 101 may be arranged at a second main surface 202 of the carrier . For example , a material of the carrier 100 may be conductive . For example , the carrier 100 may comprise a doped semiconductor material . Examples of the semiconductor material comprise doped Si , InP when the incident radiation comprises wavelengths in the IR region . When the incident radiation comprises visible light , the semiconductor material may comprise GaN, AlGaN, ZnCy and others known in the art . For example , a doping level may be selected so that the carrier 100 has a high conductivity . In this case , the electric field may be ef fective in the region of the elec- trooptical material even though the distance between the elec- trooptical material and the first electrode 101 may be larger than according to embodiments shown in Fig . 1A.

[0083] The further components and features of the optical element 10 are similar to or identical with the components discussed with reference to Fig . 1A, so that a detailed description thereof is omitted here .

[0084] According to embodiments illustrated in Figs . 1A and IB, the first and the second electrodes 101 , 102 may be implemented as continuous electrodes . According to all embodiments described herein, at least one of the first and the second electrode

[0085] 101 , 102 may be segmented .

[0086] Fig . 1C shows a schematic cross-sectional view of the tunable optical element 10 according to further embodiments . Di f fering from embodiments illustrated in Fig . 1A, a layer of the electrooptical material 105 is arranged between the first electrode 101 and the pillars or ridges 116, 117. In more detail, according to e.g. Figs. 1A and IB, the pillars 116 or ridges 117 are patterned to the bottom side or to the first electrode 101. According to embodiments illustrated in Fig. 1C, the electrooptical material 105 is patterned so that only an upper portion of the electrooptical layer is patterned whereas the layer of electrooptical material 105 is maintained on a side adjacent to a first main surface 201 of the first electrode 101. A sum of the thickness of the layer of electrooptical material 105 and a height H of the ridges 117 or pillars 116 may be less than 4 pm, e.g. less than 2.5 pm. According to the implementation shown in Fig. 1C, the electrical field may penetrate into the patterned electrooptical material (e.g. the pillars 116 or ridges) with only moderate penalty in applied potential. As is illustrated in Fig. 1C, the first material of the pillars 116 or ridges 117 is an electrooptical material. As is clearly to be understood, instead, the second material of the planarization layer 107 may be an electrooptical material.

[0087] According to embodiments illustrated in Fig. 1C, the second electrode 102 may be segmented.

[0088] As has been explained above, for example, the pillars 116 or ridges 117 of the electrooptical material may change their optical properties in an electrical field. When the planarization layer between the pillars 116 or ridges 117 comprises an electrooptical material, the second material in the spaces between adjacent pillars 115 or ridges 117 may change its optical properties in an electrical field.

[0089] The left-hand portion of Fig. ID shows a horizontal cross-sectional view of the tunable optical element 10 according to embodiments . In particular, Fig . ID shows an example of an arrangement of pillars 116 . According to embodiments illustrated in Fig . ID, the single pillars 116 may be arranged in rows and in columns to form a cubic lattice . As is indicated in the left-hand portion of Fig . ID, the positions of the pillars may form a lattice and the si ze of the individual pillars may vary . For example , pillars of identical si ze may be arranged in a circular pattern .

[0090] The left-hand portion of Fig . IE shows a hori zontal cross-sectional view of the tunable optical element 10 according to further embodiments . Fig . IE shows a further example of an arrangement of pillars . According to embodiments illustrated in Fig . IE , the single pillars 116 may be arranged to form a hexagonal lattice . As is indicated in the left-hand portion of Fig . IE , the positions of the pillars may form the lattice and the si ze of the individual pillars may vary . In a corresponding manner as illustrated in Fig . ID, pillars of identical si ze may be arranged in concentric circles .

[0091] According to all embodiments disclosed herein, the tunable optical element 10 may be used as a transmissive optical element . For example , the components of the tunable optical element 10 may be selected to provide a desired degree of transparency . According to further embodiments , when the tunable optical element 10 is used as a transmissive optical element , the tunable metalens structure may be arranged over both surfaces of the carrier 100 .

[0092] According to all embodiments disclosed herein, the tunable optical element 10 may be used as a reflective optical element . For example , some components of the tunable optical element 10 may be selected to provide a desired degree of reflectivity . Figs. 2A and 2B illustrate a top view and a cross-sectional view of a tunable optical element 10 according to further embodiments. For example, the pillars 116 comprising a first material may be arranged in rows and columns. As is to be clearly understood, the pillars 116 may also be arranged in a different pattern. Further, the second electrode 102 may be segmented in address lines so that one address line may be assigned to one column of pillars. As is to be clearly understood, more than one column of pillars may be assigned to one address line. Further, different numbers of columns of pillars may be assigned to different address lines, respectively. By specifically addressing electrode segments assigned to selected rows or columns or other groups of the pillars 116, a specific pattern of a resulting refractive index may be generated so as to further modulate the properties of incident electromagnetic radiation.

[0093] In more detail, according to embodiments illustrated in Figs. 2A and 2B, the first electrode 101 may be constituted as a continuous conductive layer which is e.g. not patterned to lines. Moreover, the second electrode 102 may comprise a plurality of address lines 112i, 1122... 112n. For example, the single address lines may be assigned to one row or one column of pillars. In this way, a one-dimensional passive addressing may be implemented. This addressing scheme is easy to implement .

[0094] For example, the single address lines may be formed as conductive lines. Fig. 2B shows a cross-sectional view of the tunable optical element 10 which is taken in a direction intersecting an extension direction of the address lines 112i, ... 112n. For example, as is shown in Fig. 2B, an insulating material 114 may encapsulate the address lines 112i, ... 112nin order to avoid vacuum arcing. Fig. 3A shows a top view of a tunable optical element 10 according to further embodiments. According to embodiments illustrated in Fig. 3A, e.g. the second electrode 102 may be segmented to electrode segments 103 so that the electrode segments 103 are assigned to single pillars or to groups of adjacent pillars. For example, these groups may be arranged in rows and columns. The electrode segments 103 may be addressed via a plurality of address lines comprising a first subset 118 of address lines extending in a first horizontal direction, e.g. the y direction, and a second subset 119 of address lines extending in a second horizontal direction, e.g. the x-direc- tion. The electrode segments 103 may have an arbitrary shape. For example, a diameter or length of the electrode segments 103 may be less than 1 pm.

[0095] The tunable optical element 10 may further comprise a plurality of circuit elements 123 comprising a transistor 121, e.g. thin film transistors ("TFT") . Each of the transistors 121 may be assigned to a corresponding one of the segments. The address lines of the first subset 118 may be connected to the drain regions 136 of the transistors 121. Moreover, the address lines of the second subset 119 may be connected to the gate electrodes 137 of the transistors 121. The address lines of the first subset 118 may be connected to a drain line driver 128. Further, the address lines of the second subset 119 may be connected to a gate line driver 129. By applying a suitable drain voltage and a suitable gate voltage to the respective address lines via the drain line driver 128 and the gate line driver 129, selected ones of the electrode segments 103 may be addressed. In this way, a two-dimensional addressing may be implemented. For example, the transistors 121, e.g. the thin film transistors, may be transparent. For example, the transistors 121 may comprise a transparent conductive oxide such as ITO (" indium tin oxide" ) as an electrode , e . g . as a gate electrode .

[0096] Consequently, an arbitrary adj ustment of phase delays may be achieved . In particular, a local potential at individual pillars 116 or groups of pillars 116 may be set . In this way, Fresnel zones in lenses and deflectors may be generated and adj usted by applying suitable voltages to the respective address lines . The addressing scheme relies on active transistor-based addressing . In this way, electrical fields may be applied directly on selected pillars 116 . Due to the very high material permittivities of typical materials having a high electrooptical coef ficient , the pillars have a high capacitance . Accordingly, this addressing scheme may be implemented without the need of a separate capacitor to store charges during addressing sequencing .

[0097] For example , the electromagnetic radiation 15 incident on the tunable optical element 10 may be linearly polari zed . The voltages to be applied to the single address lines may be chosen using highly elaborate algorithms . For example , a lookup table may be used for choosing the voltages to be applied in dependence from the optical properties of the tunable optical element 10 to be achieved .

[0098] Fig . 3B shows a cross-sectional view of the tunable optical element 10 . Fig . 3B particularly shows a circuit element 123 comprising a transistor 121 which is assigned to an electrode segment 103 . The transistor 121 may be connected in a manner as will be described with reference to Fig . 3C . Moreover, the first electrode 101 is implemented as a continuous electrode . The first electrode 101 may be electrically connected to ground . The left-hand portion of Fig. 3C shows an example of a circuit diagram of a cell comprising a pillar 116 and a circuit element 123 including a transistor 121 and a diode 122. The lefthand portion of Fig. 3C shows the circuit element 123 for addressing an electrode segment 103 assigned to a specific pillar 116 or group of pillars 116. The left-hand portion of Fig. 3C further shows a line VGwhich is connected to a gate electrode of the transistor 121. Fig. 3C further shows a line VD(negative polarity) which is connected to a drain region 136 of the transistor 121. When a gate voltage VGand a drain voltage VDare applied to one of the transistors, the electrode segment 103 assigned to the transistor is addressed.

[0099] The right-hand portion of Fig. 3C shows an equivalent circuit diagram of the circuit element 123 for addressing the second electrode segments 103. The first electrode may be connected to a common reference potential.

[0100] Fig. 3D shows voltage diagrams for illustrating charging of a row i of M columns of electrode segments 103 to individual voltages VPfPj. The first diagram shows the voltage at the gate line for row i. The second diagram shows the voltage at the drain line for columns j, j+1, and the third diagram shows the voltage VPat an electrode segment 103 for row i and column j, j + 1-

[0101] At the beginning, it is assumed that the voltages for all electrode segments are equal to 0 V. For example, this may be the case after resetting all columns.

[0102] Referring to steps 101, 102 in row i, columns j, j+1 are addressed with a sequence of positive drain voltages VDj , VDj+i. First, at T1 the gate voltage for row i is set to VGP= VGH. Then, at T2, a column drain voltage VDj is applied. For example , a column drain voltage VDj which may correspond to the intended VPf Pj may be suf ficient to fully charge the pillar capacitance . I f the column drain voltage VDj is not suf ficient , it may be determined taking into account charging time and dynamic ID- VDs behavior . Then, at T3 , the process may move to the next row by setting VGP= 0 and Vgi+1= VGH (not illustrated in Fig . 3D) . Then, all VGiare set to 0 and then VDj is set to a value close to 0 and greater than 0 for the duration of a desired phase profile frame .

[0103] For resetting, at S 103 , all VDj are set to -VdlOde, forcing the diodes to conduct and reset VPf dj to approximately 0 V

[0104] The driver and driving schemes may be applied to other configurations , including addressing rings , ID structures , grouped pillars , etc . .

[0105] Further, although only the second electrode has been described to be segmented, any of the first and the second electrodes may be segmented . As a consequence , further addressing schemes may be used, and address lines for the first and the second electrodes 101 , 102 may be employed .

[0106] For some pillar / encapsulation materials , it may be possible to have address lines on top and bottom of pillars .

[0107] Fig . 3E shows a schematic view of a further tunable optical element which is based on the addressing scheme described with reference to Figs . 3A and 3B . As is shown, the tunable optical element comprises an array of first pillars 134 and an array of second pillars 135 . A unit cell may comprise a first pillar 134 and a second pillar 135 . For example , the first pillar 134 may have a shape that is di f ferent from the second pillar 135 . Further, a distance between adj acent first pillars 134 may be di f ferent from a distance between adj acent second pillars 135 . The unit cell may have a si ze smaller than a wavelength of incident light . The first pillar 134 and the second pillar 135 may be separately addressed by applying a corresponding voltage to the drain region of the associated transistor 121 . As a result , full wavefront control may be accomplished and both phase and amplitude control may be performed . This may eliminate many issues associated with speckle in digital holograms .

[0108] Using Va and Vb to generate phase shi fts <paand <pblead to overall unit cell phase shi ft <p0and amplitude coscpi

[0109] According to the embodiments described, lattice resonances and / or Mie resonances may enhance the refractive index ef fect changes . For example , i f the width t and the pitch of the pillars is appropriately selected, in dependence from a wavelength of incident electromagnetic radiation, the modulation may be ampli fied by ridge resonance or mode interference . For example , in the case of a one-dimensional arrangement of ridges 117 , this ef fect may be achieved when the width of the single pillars achieves a predetermined condition . This concept may be easily extendable to two-dimensional sub-wavelength lattices .

[0110] According to further embodiments , the height of the pillars 116 or ridges 117 may be appropriately selected so that nodes and standing waves are formed in the pillars 116 or ridges 177 . This may further enhance the ef fect of change of the refractive index with applied voltage . Fig . 4 shows a cross-sectional view of a tunable optical element 10 according to further embodiments . As is shown in Fig . 4 , the tunable optical element 10 further comprises a first resonator mirror 124 which is adj acent to the first electrode 101 and a second resonator mirror 125 which is adj acent to the second electrode 102 . Moreover, the distance s between the first and the second mirrors 124 , 125 is determined so that an optical resonator for the incident electromagnetic radiation is formed between the first and the second resonator mirrors 124 , 125 . For example , the first and the second resonator mirrors 124 , 125 may comprise an alternating sequence of layers having comparably high and low refractive indices . For example , the layers may be dielectric layers or may be semiconductor layers . The alternating sequence of layers may form a DBR ("distributed Bragg reflector" ) mirror .

[0111] For example , as is illustrated in Fig . 4 , the first resonator mirror 124 may be arranged between the carrier 100 and the first electrode 101 . Further, the second resonator mirror 125 may be arranged on a side of the second electrode 102 remote from the electrooptical material 105 . As is shown, in this way, a resonant Fabry-Perot cavity may be formed around the pillars . As a consequence , a number of light passes will be increased resulting in an increase of the modulation of the refractive index . This will greatly enhance the changes of the refractive index due to the cavity Q- factor for narrow-band incident light sources . As a consequence , the electrooptic ef fect is further enhanced . As is shown in Fig . 4 , the first electrode 101 and the second electrode 102 may be arranged directly adj acent to the pillars 116 or ridges 117 . Further, the resonator mirrors 124 , 125 may be arranged on a side of the electrodes 101 , 102 remote from the pillars 116 or ridges 117 . As a result , lossless conductors may be inside the cavity to prevent a loss of cavity-Q- f actor . According to further embodiments , the resonator mirrors 124 , 125 may be arranged on a side of the first and second electrodes 101 , 102 facing the pillars 116 or ridges 117 . For example , the resonator mirrors 124 , 125 may comprise doped semiconductor materials as a material of the first and the second resonator mirrors 124 , 125 . This may reduce a resistance of the electrodes 101 , 102 . As a consequence , a switching time needed to charge the pillars to full potential may be decreased .

[0112] Since most Bragg reflector coatings have a thickness of few wavelengths , the target spatial phase distribution will be modi fied by the Bragg reflectors . This should be taken into account for the desired output phase profi le . The tunable optical element 10 illustrated in Fig . 4 may be implemented as a transmissive or a as a reflective optical element . For example , a bandwidth of the electromagnetic radiation 15 to be modulated by the tunable optical element 10 may be very narrow, e . g . less than 10 nm or less than 5 nm or less than 2 nm .

[0113] For example , the structure illustrated in Fig . 4 may be applied to all embodiments described herein .

[0114] Fig . 5A shows a tunable optical element 10 which may implement a shutter . As is shown, the tunable optical element 10 comprises a first electrode 101 and a second electrode 102 and ridges 117 or pillars 116 of a first material . A planari zation layer 107 o f a second material fills the spaces between adj acent ridges 117 or pillars 116 . One of the first and second materials may be an electrooptical material as described above . The other of the first and second materials may be an inert material as described above .

[0115] All ridges 117 or pillars 116 are identical and spaced at an identical pitch according to sub-wavelength conditions . For example , pillars 116 having a space in a sub-wavelength range may be arrayed in rows and columns . For example , the light 15 incident into the tunable optical element may be linearly polari zed For example , when a hori zontal cross-section of the pillars 116 is circular or isotropic, the polari zation direction may be arbitrary . When the tunable optical element 10 comprises ridges 117 extending in a certain hori zontal direction, the polari zation direction may be paral lel or approximately paral lel to the extension direction of the ridges 117 . By suitably activating a power source 109 , the transmission at a certain refractive index which is induced by the special electrooptical material 105 may be quenched .

[0116] For the sake of example , one may consider ridges of TiCy on fused silica, where the height H of the ridges may be approximately 600 nm, the pitch P may be approximately 300 nm, and the ridge width W may be approximately 182 nm . For light with a free-space wavelength of 450 nm propagating as shown in Figure 5A, a sharp resonance in reflectance may be obtained at a refractive index of approximately 2 . 565 , as shown in the Figure 5B . This may be achieved by applying a suitable electric potential across the electrodes shown in Fig . 5A. Thus , by applying a suitable electrical potential , the device may strongly modulate the transmitted light intensity, functioning as a high-speed shutter or dynamic intensity filter .

[0117] In more detail , the potentials which are applied to the electrode segments assigned to individual pillars 116 or ridges 117 may be adj usted to generate corresponding 0-th order phase . As a result , a deflection of incident light may be appropriately adj usted . For example , a s i ze of the tunable optical element 10 may be 1 pm2to 1 mm2. The electrooptic ef fect may be very fast leading to a very short transmission time in a range of GHz . The incident electromagnetic radiation is polari zed . The shown tunable optical element implements a shutter which suppresses transmission at a specific refractive index which is induced by applying an electrical field .

[0118] Fig . 6A shows a general layout of a tunable optical element according to all embodiments described herein . As is shown, the pillars 116 may be arranged in rows and columns . The second electrode 102 may have a circular shape and may be arranged over the array of pillars . A power source 109 may be configured to apply an electrical field across the pillars .

[0119] According to further implementations , which are shown in Fig . 6B, the second electrode may be divided into several segments 1271 , 1272 , and 1273 . By selectively addressing the di f ferent segments 1271 , 1272 , 1273 , the respective pillars 116 may be selectively addressed . In this manner, an annular distribution of refractive indices may be achieved . The configuration described in Fig . 6B may be applied to all embodiments described herein .

[0120] Fig . 6C shows a configuration of a tunable optical element 10 in which pillars 116 arranged on subwavelength ring lattices . Accordingly, the single pillars 116 are arranged along circles . For example , each ring of pillars 116 may be addressed by a single conducting ring which may implement segments 1271 , 1272 , 1273 of an electrode . For example , groups of rings including pillars 116 of identical shape and distance may implement a Fresnel zone ( enclosed by dotted rings ) . The configuration described in Fig . 6C may be applied to all embodiments described herein . For example, different rings of pillars 116 may include pillars 116 of different shape, size or distance, respectively, to form different Fresnel zones.

[0121] Fig. 7 shows a cross-sectional view of a tunable optical element according to further embodiments. The tunable optical element comprises the same elements as the tunable optical element illustrated in Fig. 1A. In particular, the sizes, distances and heights of the pillars 116 or ridges 117 may be as has been described with reference to Fig. 1A.

[0122] Differing from embodiments illustrated in Fig. 1A, the optical element illustrated in Fig. 7 comprises a piezoelectric layer 130 which is arranged between the second electrode 102 and pillars 116 or ridges 117. The pillars 116 or ridges 117 are made of a first material. The tunable optical element 10 of Fig. 7 further comprises a planarization layer 107 of a second material. The planarization layer 107 fills the spaces between adjacent pillars 116 or ridges 117. The first or the second material may comprise a material that changes its optical properties when a mechanical tension is applied. Examples of such a material comprise materials having a Perovskite structure as has been explained above. The other of the first and the second material comprises an inert material.

[0123] When an electrical field is applied between the first and the second electrode 101, 102, a mechanical deformation of the piezoelectric layer 130 is generated. This mechanical deformation results in a mechanical tension on the array of pillars or ridges. As a result, a shift of a wavefront of incident electromagnetic radiation is caused. This shift of the wavefront results in a change of the radiation pattern transmitted or reflected by this tunable optical element. This modulation scheme is also referred to as an indirect electrostatic modulation scheme .

[0124] The second electrode 102 may be segmented in a similar manner as has been explained above with reference to Fig . 6B . Examples of transparent perowskite materials showing a piezoelectric ef fect comprise inter alia SrTiOa, PrScOa, SmScOa, TbScO3 , and DyScOa . Examples of biref ringent materials comprise LiNbOa, TiOa , and SiaN4. A further example of a material of the piezoelectric layer 130 comprises AIN .

[0125] For example , the pillars 116 or ridges 117 may be arranged adj acent to a first main surface 201 of the carrier 100 . The first electrode 101 may by arranged adj acent to a second main surface 202 of the carrier 100 .

[0126] According to further embodiments , the first electrode 101 may be arranged between the carrier 100 and the pillars 116 or ridges 117 .

[0127] As has been described with reference to Fig . 7 , the arrangement comprising the pillars 116 or ridges 117 may change its optical properties by application of mechanical tension . Accordingly, by changing a voltage appl ied across the piezoelectric layer 130 the optical properties of the tunable optical element 10 may be tuned .

[0128] The first and / or the second electrode 101 , 102 may be segmented in the manner as has been described with reference to Figs . 2 , 3 and 6 .

[0129] According to further embodiments , the optical properties of the pillars or ridges may be modulated by heat . For example , as is illustrated in Fig . 8A, a heater electrode 104 of the tunable optical element may be electrically connected to the power source 109 which acts as a thermal element. As a consequence, the heater electrode 104 is heated resulting in a local change of the refractive index of the pillars 116 or the ridges 117.

[0130] The tunable optical element illustrated in Fig. 8A comprises a carrier 100, pillars 116 or ridges 117 of a first material and a planarization layer 107 of a second material. The planarization layer 107 fills the spaces between adjacent pillars 116 or ridges 117. For example, the first material may comprise a thermooptical material or an inert material. When the first material comprises a thermooptical material, the second material comprises SiCy or another inert material. According to further implementations, the second material may comprise a thermooptical material and the first material may comprise SiCy or another material which is not thermooptical. For example, a thermooptical material may be a material that changes its optical properties when heat is applied. Examples of a thermooptical material comprise silicon nitride, TiCy, VO3, Ge-Sb-Te (GST) , CHaNHaPbCla, SiOC, LiNbO3, AIN, dedicated polymers, tellurite glasses, and chalcogenide glasses.

[0131] A material of the heater electrode 104 may for example comprise TiN. The arrangement, size or shape of the pillars 116 or ridges 117 may be identical to the arrangement, size or shape as has been discussed above with reference to Fig. 1A.

[0132] As is illustrated in Fig. 8B, according to embodiments, the heater electrode 104 is not formed to be a continuous plate. For example, the heater electrode 104 may have a meandering shape and may locally heat the pillars 116 or ridges 117 to locally change the refractive index. As is further shown in Fig . 8B, optionally the heater electrode 104 may be segmented so that a speci fic pattern of change of the refractive index may be implemented . For example , the power source 109 may be configured to be connected to a first segment 1271 and a second segment 1272 of the heater electrode 104 . As a consequence , the refractive index may be locally adj usted . Accordingly, the modulation scheme implemented according to Figs . 8A and 8B corresponds to a thermal modulation scheme . Fig . 8C shows an implementation of the tunable optical element 10 which may be implemented as a reflective optical element and which is operated according to the thermal modulation scheme . In this case , the heater electrode 104 may be made of a reflective material or an opaque material and may be connected to a power source 109 which generates heat inside the heater electrode 104 . A carrier 100 is arranged over the heater electrode 104 . Pillars 116 or ridges 117 of a first material are arranged over the carrier 100 . A planari zation layer 107 of a second material fills spaces between adj acent pillars 116 or ridges 117 . Incident electromagnetic radiation 15 is reflected and modulated by the tunable optical element 10 . By ( locally) changing the temperature of the heater electrode 104 , the phase of a wavefront of reflected light may be ( locally) changed resulting in tunable optical properties .

[0133] In the following, methods for manufacturing the tunable optical element according to embodiments wil l be explained . Fig . 9A shows a schematic cross-sectional view of a carrier 100 which may also be a growth substrate of the electrooptical material 105 . A material of the carrier 100 may be a doped semiconductor material which provides a suf ficient conductivity .

[0134] For example , a layer of the electrooptical material 105 may be formed by direct epitaxial deposition (MBE , CVD, PECVD) on a first main surface 201 of the heated carrier 100 . The lattice matching of the heated carrier 100 to a desired crystal plane will aid the direction of the c-axis growth . Accordingly, the crystal orientation of the growth substrate may be selected so that , for example , the c-axis of the grown material may have an angle of + 45 ° or - 45 ° with respect to the first main surface 201 . For example , a thickness of the layer of electrooptical material 105 may be less than a wavelength of electromagnetic radiation that is to be shaped by the tunable optical element 10 .

[0135] Thereafter, as is shown in Fig . 9B, the electrooptical material 105 is patterned using e . g . photolithographic and etching methods to pillars 116 or ridges 117 . Thereafter, an encapsulation material is applied to form a planari zation layer 107 . For example , the encapsulation material may comprise SiCy . Thereafter, the resulting surface is milled, e . g . ion-milled or polished so that the pillars 116 or ridges 117 are flush with the planarization layer 107 .

[0136] According to further implementations , the pillars 116 or ridges 117 may be masked by an appropriate masking material . Thereafter, the planari zation layer 107 may be deposited with an accurately known deposition rate . Then, a li ft-of f may be performed to remove the mask material from the pillars 116 or ridges 117 .

[0137] Fig . 9C shows an example of a resulting cross-sectional view of a workpiece . Thereafter, the second electrode 102 may be formed over the array of pillars 116 or ridges 117 . The second electrode 102 may optionally be suitably patterned . Further, a first electrode 101 may be formed over a second main surface 202 of the carrier 100 . When the tunable optical element 10 is to be used as a transmissive tunable optical element 10 , the first and the second electrodes 101 , 102 may be made of a suitable conductive material , e . g . a doped semiconductor material that is transparent for the electromagnetic radiation to be shaped by the resulting optical element 10 .

[0138] Fig . 9D shows a cross-sectional view of an example of a resulting workpiece .

[0139] According to further implementations , when the electrooptical material comprises an electrooptical polymer, a method of manufacturing the tunable optical element 10 may comprise forming a planari zation layer 107 , e . g . of SiCy and patterning holes in the planari zation layer 107 . Then the electrooptical material is filled in the holes to form pillars 116 or ridges 117 .

[0140] According to still further implementations , referring to Figs . 10A to 10B the electrooptical material 105 may be epitaxially grown over a speci fic growth substrate 132 which may, for example , comprise the material of the electrooptical material . For example , BaTiOs may be taken as a suitable growth substrate 132 . An interfacial layer 133 which may comprise a single-crystal line semiconductor material suitable for laser li ft-of f may be grown over the growth substrate 132 . For example , a suitable material of the interfacial layer 133 may comprise GaN, AIN or CeCy .

[0141] Thereafter, the electrooptical material 105 is epitaxially grown over the interfacial layer 133 . Then, as is indicated in Fig . 10B, the growth substrate 132 including the epitaxially grown electrooptical layer 105 is bonded to the first electrode 101 arranged over the carrier 100 . For example , this bonding process may comprise wafer bonding or metallic bonding . After attaching the electrooptical material 105 to the first electrode 101 , the growth substrate 132 is removed using a laser li ft-of f method . Fig . 10C shows an example of a resulting workpiece . Thereafter, the further proces sing steps illustrated with reference to Figs . 9B to 9D may be performed .

[0142] According to a more general approach, a tunable optical element 10 is configured to modi fy electromagnetic radiation 15 . The tunable optical element 10 comprises a carrier 100 , and a metaoptic structure arranged over the carrier . The metaoptic structure comprises an array of pillars 116 or ridges 117 of a first material , and a planari zation layer 107 of a second material . The planari zation layer 107 fills spaces between adj acent pillars 116 or ridges 117 . The tunable optical element 10 further comprises a modulation device for changing optical properties of the array of pillars 116 or ridges 117 or of the second material to change optical properties of the metaoptic structure .

[0143] For example , the change of optical properties may be reali zed by an electrostatic ef fect . For example , the tunable optical element 10 may comprise a first electrode 101 arranged at a first side of the pillars 116 or ridges 117 and a second electrode arranged at a second side of the pillars 116 or ridges 117 . The first or the second material may comprise an electrooptic material . The other of the first and second material comprises an inert material . The modulation device may be implemented as a voltage source 109 for applying a voltage between the first and the second electrode .

[0144] According to further embodiments , the change of the optical properties may be caused by mechanical tension . For example , the modulation device may comprise a piezoelectric layer and electrodes for applying a voltage across the piezoelectric layer . For example , a first electrode may be arranged on a first side of the ridges or pillars . Further, the piezoelectric layer and a second electrode may be arranged on a second side of the ridges or pillars . The modulation device may further comprise a voltage source 109 for applying a voltage between the first and the second electrode .

[0145] According to further embodiments , the change of the optical properties may be caused by a temperature ef fect . The first or the second material may comprise a thermooptic material . The other of the first and second material comprises an inert material . The modulation device may comprise a heater electrode 104 and a voltage source 109 for applying to the heater electrode 104 to increase the temperature of the heater electrode 104 .

[0146] While embodiments of the invention have been described above , it is obvious that further embodiments may be implemented . For example , further embodiments may comprise any subcombination of features recited in the claims or any subcombination of elements described in the examples given above . Accordingly, this spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein .

[0147] LIST OF REFERENCES

[0148] 10 tunable optical element

[0149] 15 electromagnetic radiation

[0150] 16 modi fied electromagnetic radiation

[0151] 100 carrier

[0152] 101 first electrode

[0153] 102 second electrode

[0154] 103 segment of second electrode

[0155] 104 heater electrode

[0156] 105 electrooptical material

[0157] 107 planari zation layer

[0158] 109 power source

[0159] 1121 , 1122 , 1123 address line

[0160] 114 insulating material

[0161] 116 pillar

[0162] 117 ridge

[0163] 118 first subset of address lines

[0164] 119 second subset of address lines

[0165] 121 transistor

[0166] 122 diode

[0167] 123 circuit element

[0168] 124 first resonator mirror

[0169] 125 second resonator mirror

[0170] 1271 , 1272 , 1273 segments of second electrode

[0171] 128 drain line driver

[0172] 129 gate line driver

[0173] 130 piezoelectric layer

[0174] 132 growth substrate

[0175] 133 interfacial layer

[0176] 134 first pillar

[0177] 135 second pillar

[0178] 136 drain region

[0179] 137 gate electrode 201 first main surface

[0180] 202 second main surface

Claims

CLAIMS1. A tunable optical element (10) configured to modify electromagnetic radiation (15) comprising: a carrier (100) ; a first electrode (101) ; pillars (116) or ridges (117) of a first material (105) , a pitch d of the pillars (116) or ridges (117) being smaller than a wavelength of the electromagnetic radiation (15) , the pillars (116) or ridges (117) being arranged over the first electrode; a planarization layer (107) filling spaces between adjacent pillars (116) or ridges (117) , the planarization layer comprising a second material, wherein one of the first and the second materials comprises an electrooptical material and the other of the first and second materials comprises an inert material; a transparent second electrode (102) over the planarization layer (105) ; and a power source (109) , connected to the first and second electrode (101, 102) , for tuning properties of the optical element (10) .

2. The tunable optical element (10) according to claim 1, wherein the electrooptical material (105) is selected from a ferroelectric material and an electrooptical polymer.

3. The tunable optical element (10) according to claim 1 or 2, wherein the inert material is selected from silicon oxide, aluminum oxide, beryllium oxide, germanium oxide, hafnium oxide, magnesium oxide, titanium nitride, magnesium fluoride, barium fluoride and cerium fluoride.The tunable optical element (10) according to any of the claims 1 to 3, wherein the first electrode (101) is arranged between the carrier (100) and the pillars (116) or ridges ( 117 ) .

5. The tunable optical element (10) according to any of claims 1 to 3, wherein the pillars (116) or ridges (117) are arranged adjacent to a first main surface (201) of the carrier (100) and the first electrode (101) is arranged adjacent to a second main surface (202) of the carrier (100) .

6. The tunable optical element (10) according to any of the preceding claims, further comprising a layer of the elec- trooptical material (105) between the first electrode (101) and the pillars (116) or ridges (117) and in contact with the pillars (116) or ridges (117) .

7. The tunable optical element (10) according to any of claims 1 to 5, wherein the pillars (116) or ridges (117) are separated from each other.

8. The tunable optical element (10) according to any of the preceding claims, wherein the pillars (116) or ridges (117) have identical size and are arranged at a constant pitch .

9. The tunable optical element (10) according to any of the preceding claims, wherein the first electrode (101) is assigned to a plurality of pillars (116) and the second electrode (102) comprises a plurality of address lines (1121, 1122, 1123) for addressing pillars (116) of one group of pillars, respectively.

10. The tunable optical element (10) according to any of claims 1 to 8, wherein the first electrode (101) is assigned to a plurality of pillars (116) and the second electrode (102) comprises a plurality of electrode segments (103) .

11. The tunable optical element (10) according to claim 10, wherein the electrode segments (103) are addressable using address lines comprising a first subset (118) of address lines extending in a first horizontal direction and a second subset (119) of address lines extending in a second horizontal direction .

12. The tunable optical element (10) according to claim 10, wherein each of the electrode segments (103) is assigned to one or a group of pillars.

13. The tunable optical element (10) according to claim 12, further comprising a plurality of transistors (121) , wherein each of the transistors is assigned to one electrode segment (103) , respectively, a source or drain region (136) of the transistor being electrically connected to an address line of the first subset of address lines, and a gate electrode (137) of the transistor being electrically connected to an address line of the second subset (119) of address lines.

14. The tunable optical element (10) according to any of claims 9 to 13, wherein the pillars (116) comprise first pillars (134) and second pillars (135) , one of the first pillars (134) and one of the second pillars (135) being arranged in unit cells having a size smaller than the wavelength of the electromagnetic radiation.

15. The tunable optical element (10) according to any of the preceding claims, wherein the first electrode (101) isassigned to a plurality of pillars (116) or ridges (117) and the second electrode (102) is assigned to a plurality of pillars (116) or ridges (117) .

16. The tunable optical element (10) according to any of the preceding claims 1 to 8, wherein at least a portion of the pillars (116) are arranged in circles and the second electrode (102) comprises a ring-shaped portion for addressing pillars (116) of a circle.

17. The tunable optical element (10) according to any of the preceding claims, further comprising a first resonator mirror (124) adjacent to the first electrode (101) and a second resonator mirror (125) adjacent to the second electrode (102) , an optical resonator being formed between the first and the second resonator mirrors (124, 125) .

18. A tunable optical element (10) configured to modify electromagnetic radiation (15) comprising: a carrier (100) ; a first electrode (101) ; pillars (116) or ridges (117) of a first material, a pitch d of the pillars (116) or ridges (117) being smaller than a wavelength of the electromagnetic radiation; a planarization layer (105) filling spaces between adjacent pillars (116) or ridges (117) , the planarization layer (105) comprising a second material; a piezoelectric layer (130) on a side of the planarization layer (105) facing away from the carrier (100) ; a transparent second electrode (102) over the piezoelectric layer (130) ; and a power source (109) , connected to the first and second electrode (101, 102) , for deforming the piezoelectric layer (130) to tune properties of the optical element (10) .

19. The tunable optical element according to claim 18, wherein one of the first and the second materials comprises a perovskite material and the other of the first and second materials comprises an inert material.

20. The tunable optical element (10) according to claim 18 or 19, wherein the second electrode (102) is segmented.

21. A tunable optical element (10) configured to modify electromagnetic radiation (15) comprising: a carrier (100) ; a heater electrode (104) ; pillars (116) or ridges (117) of a first material, a pitch d of the pillars (116) or ridges (117) being smaller than a wavelength of the electromagnetic radiation (15) ; a planarization layer (105) filling spaces between adjacent pillars (116) or ridges (117) , the planarization layer comprising a second material, wherein one of the first and second materials comprises a thermooptical material and the other of the first and second materials comprises an inert material; and a power source (109) , connected to the heater electrode (104) , configured to heat the heater electrode (104) to tune properties of the optical element (10) .

22. The tunable optical element (10) according to claim 21, wherein the heater electrode (104) is segmented.

23. A tunable optical element (10) configured to modify electromagnetic radiation (15) comprising: a carrier (100) , and a metaoptic structure arranged over the carrier, the metaoptic structure comprising:an array of pillars (116) or ridges (117) of a first material, and a planarization layer (107) of a second material, the planarization layer (107) filling spaces between adjacent pil- lars (116) or ridges (117) , the tunable optical element further comprising a modulation device for changing optical properties of the array of pillars or ridges or of the second material to change optical properties of the metaoptic structure.

24. The tunable optical element (10) according to any of the preceding claims being configured to implement an optical shutter, a lens or a deflector.

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