EP4367535A1

EP4367535A1 - Optical device

Info

Publication number: EP4367535A1
Application number: EP21742120.5A
Authority: EP
Inventors: Harald Giessen; Julian KARST; Mario Hentschel
Original assignee: Baden Wuerttemberg Stiftung gGmbH
Current assignee: Baden Wuerttemberg Stiftung gGmbH
Priority date: 2021-07-09
Filing date: 2021-07-09
Publication date: 2024-05-15
Also published as: WO2023280426A1

Abstract

The present invention relates to an optical device (1), having ˗ at least one first surface (3) comprising at least one first nanostructure (5), wherein ˗ the at least one first nanostructure (5) comprises at least one conductive polymer material, wherein ˗ the optical device (1) comprises at least one conductor (7) in electrical contact to the at least one first nanostructure (5), wherein ˗ the at least one first nanostructure (5) is adapted to change its dielectric function when an electric quantity of the at least one conductor (7) is changed.

Description

DESCRIPTION

Optical device

The invention is related to an optical device.

Optical devices of the kind as referred to herein in particular allow spatiotemporal control of light, i.e., a control of at least one of the amplitude, the phase, and the polarization of light, in particular a control of a combination of at least two of these quantities, in particular all three quantities. However, commercially available optical devices like spatial light modulators (SLM), spatially variable phase plates, LIDARs, in particular beam steering devices in LIDARs, devices for generating a switchable hologram, augmented reality displays, virtual reality displays, and endoscopes, typically rely on liquid crystals which call for improvement both with respect to efficiency and miniaturization. In particular, due to the need to pile up multiple layers of liquid crystals on each other in order to achieve phase shifts from 0 to 2p, such devices typically have a thickness of several micrometers, e.g., 6 pm. Further, pixel sizes of liquid-crystal displays are typically also of at least several micrometers, e.g., 3 pm. Still further, such optical devices only have a limited field of view of only a few degrees.

In principle, nanostructures, sometimes also referred to as nanoantennas, may be used as pixels for optical devices. However, up to now it has been a cumbersome task to switch the optical properties of such nanostructures, either by modifying the dielectric function of the environment of such a nanostructure (see, e.g., EP 3 101 464 Al), or by directly influencing the dielectric function of the nanostructure itself (see, e.g., DE 102014203 488 Al). While at least in principle it is possible to electrically change the dielectric properties of the environment, a device relying on such a mechanism is low in contrast and difficult to miniaturize. The dielectric properties of the nanostructure itself may be influenced chemically, in particular by hydrogenating or dehydrogenating the nanostructured material. However, this is not possible on short timescales, in particular not at video rates, and typically lacks sufficient reversibility.

It is therefore an object of the invention to provide an optical device at least partly not having the above-referenced disadvantages or being preferably free from these disadvantages. The object is achieved by providing the technical teachings suggested herein, in particular the subject matter of the independent claims as well as the embodiments disclosed in the dependent claims and in the description.

The object is in particular achieved by providing an optical device, the optical device having at least one first surface comprising at least one first nanostructure, wherein the at least one first nanostructure comprises at least one conductive polymer material, wherein the optical device comprises at least one conductor in electrical contact to the at least one first nanostructure, wherein the at least one first nanostructure is adapted to change its dielectric function when an electric quantity of the at least one conductor is changed. The inventors have recognized that it is possible to directly influence the dielectric function of a conductive polymer material by making electrical contact to the material and changing the electrical properties of the contact. By nanostructuring such a conductive polymer material, i.e., making at least one nanostructure from the material, it is possible to provide a miniaturized optical device with electrically switchable optical properties on fast timescales, in particular at video rates. In particular, it is possible to provide an optical device having subwavelength pixel sizes, in particular in the range of several hundred nanometers or even several nanometers, wherein further one pixel has a very small height of several 10 nm or at most 200 nm, and a small width of less than 1 pm. The optical device can have a spatial resolution, in particular between 100 nm to 200 nm, in particular more than 1000 dpi or even more than 2000 dpi. Further, the optical device allows for a large field of view of more than 30°, preferably more than 45°. Further, the device allows for switching with rates of more than 30 Hz. The conductive polymer material in particular allows for fully reversible on and off switching.

In the context of the present technical teachings, an optical device is a device which is adapted to influence electromagnetic radiation, in particular light. In particular, the optical device has adjustable, in particular switchable properties, such that the influence of the device on the electromagnetic radiation may be changed, in particular upon an internal stimulus, i.e., a stimulus of the device itself, or upon an external stimulus. In particular, the optical device allows for spatiotemporal control of electromagnetic radiation, i.e., a control of at least one of the amplitude, the phase, and the polarization of the electromagnetic radiation, in particular a control of a combination of at least two of these quantities, in particular all three quantities.

In an embodiment, the first surface is a surface of a substrate. Preferably, the substrate comprises a dielectric material or is a dielectric. The substrate preferably comprises or consists of: glass, in particular quartz glass, quartz, fused silica, CaF2, or silicon. In an embodiment, the first surface, preferably the substrate, is flexible. In particular, in an embodiment, the first surface, preferably the substrate, may be curved in at least one direction.

The at least one nanostructure is preferably arranged on the first surface.

In an embodiment, the first surface comprises a plurality of- preferably identical - nanostructures. In particular, the plurality of nanostructures is arranged on the first surface. Preferably, each nanostructure is a pixel of the optical device.

In the context of the present technical teachings, a nanostructure, also referred to as a nanoantenna, in particular is a structure whose characteristic dimension lies in a size range from several nanometers to several hundred nanometers. Preferably, all dimensions of the nanostructure lie in the respective size range.

In particular, the characteristic dimension lies in a size range in which plasmonic resonance occurs at least in one state of the material of the nanostructure. Accordingly, the characteristic dimension of the nanostructure is in particular at most large enough to still observe a plasmonic resonance in the at least one state.

The term "characteristic dimension" refers to a dimension of the nanostructure on which a spectral position of the plasmonic resonance - in particular a peak wavelength - at least most strongly depends. For example, the characteristic dimension is a length of the nanostructure along a direction in which a dipole oscillation is excited within the plasmonic resonance, where the resonance frequency depends on the length. If the nanostructure has different dimensions in different directions, typically a dimension in one of the directions determines the spectral position of the plasmonic resonance. For example, if a rod-shaped nanostructure is considered, typically the length of the rod-shaped nanostructure determines the spectral position of the plasmonic resonance, while a width and a height play at most a minor role. Therefore, in this example, the length of the rod-shaped nanostructure is to be regarded as the characteristic dimension.

The nanostructure can be tuned to desired spectral properties, i.e., spectral position of the plasmonic resonance, in particular by a suitable choice of the characteristic dimension, wherein the spectral position of the plasmonic resonance further depends on a charge carrier density of the conductive polymer material. "Plasmonic resonance" refers to a localized charge carrier oscillation in a nanostructure having delocalized charge carriers, in particular electrons, holes, polarons, or bipolarons, in particular in a metallic state of the material of the nanostructure, the wavelength of the oscillation being in the range of the wavelength of the exciting electromagnetic radiation. Thereby it is possible to influence the plasmonic resonance of a nanostructure in particular by changing its size, shape and material.

In an embodiment, the nanostructure is selected from a group consisting of a rod-shaped structure, a disk-shaped or spherical structure, and elliptically-shaped structure, a square-shaped structure, a rectangular-shaped structure, a wire-shaped structure, a lattice-shaped or grid-shaped structure, a spiral-shaped structure, a cross-shaped structure, an oligomeric structure, a curved structure, a three-dimensional arrangement, and a combination of at least two of these structures.

In the context of the present teachings, a rod-shaped structure is in particular understood to mean a structure that has a larger dimension in a selected direction than in the other two directions oriented perpendicularly thereto. This selected direction is called the longitudinal direction of the nanostructure. The characteristic dimension of the nanostructure is its size measured in the longitudinal direction, i.e., its length. In an embodiment, the nanostructure is rod-shaped with a length and thus characteristic dimension from at least 10 nm to at most 500 nm. Preferably, the characteristic dimension is from at least 50 nm to at most 400 nm, or from at least 100 nm to at most 380 nm. Alternatively, or additionally, the rod-shaped nanostructure has a height - measured from the surface - of at least 10 nm to at most 200 nm, preferably of 90 nm. Alternatively, or additionally, the nanostructure has a width - measured perpendicular to the height and the longitudinal direction - that is from at least 10 nm to at most 200 nm, preferably 160 nm.

In an embodiment, a plurality of rod-shaped nanostructures is arranged one behind the other in rows oriented parallel to each other, the nanostructures in particular being lined up one behind the other along their longitudinal direction. In this case, measured in the longitudinal direction, the result is preferably a periodic structure with a period of at least 20 nm to at most 1000 nm, preferably 400 nm, relative to a unit cell of the periodic structure, the unit cell having exactly one nanostructure. Alternatively, or additionally, the periodic structure of nanostructures has a corresponding period of at least 20 nm to at most 1000 nm, preferably 400 nm, in a direction perpendicular to the longitudinal direction and lying in the surface. The optical properties of such a periodic structure can be influenced, on the one hand, by the characteristic dimension of the nanostructures and, on the other hand, by the choice of the period in at least one of the directions mentioned herein.

A periodic arrangement of the nanostructures has the advantage of enabling a stronger and, in particular, also more homogeneous signal of the entire device than it is the case with a random structure.

However, it is also possible that the nanostructures are arranged in a disordered or random manner.

Alternatively, the nanostructures are arranged in a quasi -periodic structure, or in more complex structures, having a super period and comprising unit cells having more than one nanostructure.

A structured, in particular periodic arrangement of the nanostructures is advantageous not only in connection with rod-shaped nanostructures, but also in connection with nanostructures formed in other ways, for example disk-shaped, spherical, wire-shaped, lattice-shaped, spiral-shaped, cross shaped, oligomeric, curved, or three-dimensional structures. Combinations of these structures are also preferably arranged periodically, resulting in the advantages described.

In the case of a wire-shaped structure, the extension in the longitudinal direction is preferably much greater than the extension of the structure in the two directions oriented perpendicular thereto.

A lattice-shaped structure can be created by lattice-like superposition or arrangement of rod shaped and/or wire-shaped structures.

Similarly, a cross-shaped structure can be generated, for example, by crossing two rod-shaped structures, two wire-shaped structures, or a rod-shaped and a wire-shaped structure.

An oligomeric structure preferably has a plurality of individual nanostructures grouped relatively to each other, which are combined by the grouping into a superordinate nanostructure.

A curved structure preferably has either nanostructures that are curved within themselves or an arrangement of a plurality of nanostructures positioned along a curved line. It is possible that the curvature is in a plane and thus two-dimensional. Alternatively, it is possible that the curvature runs in three dimensions, so that a three-dimensional curved structure is realized. Such a curved structure may have a super period resulting from the curved geometry, in particular selected with respect to a desired diffraction angle for a beam steering application.

Finally, a three-dimensional nanostructure or arrangement of nanostructures is also possible. In this regard, it is possible that the optical properties of the device result especially from the three- dimensional arrangement of the nanostructures.

In an embodiment, the first surface is a metasurface, in particular a plasmonic metasurface. A metasurface is in particular understood to be a surface which is either structured or unstructured with subwavelength- scaled patterns in the horizontal dimensions. In electromagnetic theory, a metasurface modulates the behavior of electromagnetic waves through specific boundary conditions, rather than constitutive parameters in three-dimensional (3D) space, which is commonly exploited in natural materials and metamaterials. The term “metasurface” also refers to the two-dimensional counterpart of a metamaterial. The first surface is in particular structured with subwavelength-scaled patterns by the arrangement of the first nanostructures on the first surface.

In an embodiment, all nanostructures have the same material. However, it is also possible to combine different materials. In particular, different adjacent nanostructures may comprise different materials.

In particular, the at least one first nanostructure is made of or consists of the at least one conductive polymer material.

In the context of the present technical teachings, a conductive polymer material is a polymer material which is electrically conducting at least in one state of the material, in particular in a metallic state of the material. Preferably, the conductive polymer material comprises at least one conductive polymer. It is possible that the conductive polymer material comprises more than one conductive polymer, in particular a mixture of at least two conductive polymers. In particular, a conductive polymer is a polymer which is electrically conducting at least in one state of the polymer, in particular in a metallic state of the polymer. Preferably, the conductive polymer material comprises in addition to the at least one conductive polymer at least one dopant. In particular, a dopant is a chemical substance which is adapted to influence the electronic structure of the conductive polymer, in particular to donate or push charge carriers to the conductive polymer, or to draw or pull charge carriers from the conductive polymer. It is possible that the conductive polymer material comprises more than one dopant, in particular at least two dopants. In the context of the present technical teachings, a conductor in particular is a structure or a substance which is adapted to conduct the electric current. The conductor may be solid, liquid or comprise a viscous material. In an embodiment, the conductor is selected from a group consisting of a solid structure and an electrolyte. In an embodiment, the conductor preferably is a solid structure and comprises or consists of a metallic or semiconducting material. Preferably, the conductor comprises or consists of indium tin oxide (ITO) or InGaZnO (IGZO). In an embodiment, the conductor is arranged on the first surface, preferably by physical vapor deposition or sputtering. In an embodiment, the first surface is completely covered by the conductor, in particular by a layer of the metallic or semiconducting material, in particular of indium tin oxide or InGaZnO (IGZO). In another embodiment, the first surface comprises a plurality of separate conductors, in particular made by structuring a layer of the metallic or semiconducting material, in particular indium tin oxide or InGaZnO (IGZO). In another embodiment, the conductor is a liquid electrolyte or a solid- state electrolyte. Preferably, the conductor is arranged on the first surface. In particular, the at least one first nanostructure is immersed in the conductor.

In an embodiment, the at least one first nanostructure further is in electrical contact with at least one counter-conductor. The electric quantity of the at least one conductor is in particular defined with respect to the at least one counter-conductor or with respect to a reference electrode in electrical contact with the counter-conductor. In particular, an electric potential or a voltage of the at least one conductor is defined with respect to or measured against the at least one counter conductor or the reference electrode. The counter-conductor may be solid, liquid or comprise a viscous material. In an embodiment, the counter-conductor is selected from a group consisting of a solid structure and an electrolyte. In an embodiment, the counter-conductor is a liquid electrolyte or a solid-state electrolyte. Preferably, the counter-conductor is arranged on the first surface. In particular, the at least one first nanostructure is immersed in the counter-conductor. In another embodiment, the counter-conductor preferably is a solid structure and comprises or consists of a metallic or semiconducting material. Preferably, the counter-conductor comprises or consists of indium tin oxide (ITO) or InGaZnO (IGZO). In an embodiment, the counter-conductor is arranged on the first surface, preferably by physical vapor deposition or sputtering. In an embodiment, the first surface is completely covered by the counter-conductor, in particular by a layer of the metallic or semiconducting material, in particular of indium tin oxide or InGaZnO (IGZO). In another embodiment, the first surface comprises a plurality of separate counter-conductors, in particular made by structuring a layer of the metallic or semiconducting material, in particular indium tin oxide or InGaZnO (IGZO). In an embodiment, the conductor is a solid structure, in particular comprising or consisting of a metallic or semiconducting material, preferably indium tin oxide or InGaZnO (IGZO), and the counter-conductor is a liquid electrolyte or a solid-state electrolyte. However, in another embodiment, the conductor is a liquid electrolyte or a solid-state electrolyte, and the counter conductor is a solid structure, in particular comprising or consisting of a metallic or semiconducting material, preferably indium tin oxide or InGaZnO (IGZO).

In the context of the present technical teachings, the electric quantity in particular is a physical variable from the field of electricity, in particular electrostatics or electrodynamics, in particular a quantity applied to or measurable at the conductor, preferably an electric potential, a voltage, or an electric current.

Advantageously, in particular the dielectric function of the at least one first nanostructure can be changed at low voltages, in particular CMOS-compatible voltages, in particular up to 3.3 V. In one embodiment, the at least one first nanostructure adopts its first insulating state at - 1 V and its second metallic state at + 1 V.

In the context of the present technical teachings, that a first element is in electrical contact with a second element means that electric current can flow between the first element and the second element, i.e., from the first element to the second element or vice versa.

In the context of the present technical teachings, that a dielectric function is changed in particular means that at least a progress of a real part of the dielectric function (real permittivity) depending on the wavelength of incident electromagnetic radiation is changed.

A maximum switching rate for fully reversible on and off switching of the at least one nanostructure is determined in particular by the height of the at least one nanostructure, in particular as measured from the surface.

In an embodiment of the invention, the at least one first nanostructure is adapted to switch between at least a first insulating state and a second metallic state when the electric quantity of the at least one conductor is changed. In particular, the at least one first nanostructure exhibits its plasmonic resonance only in the second metallic state (on state), wherein the plasmonic resonance is not present in the first insulating state (off state). Thus, the plasmonic resonance of the at least one first nanostructure can advantageously be switched on and off, in particular reversibly, by switching between the first state and the second state. In particular, the real part of the dielectric function of the material of the first nanostructure - also designated in short as the dielectric function of the first nanostructure - is approximately constant with the wavelength of the incident electromagnetic radiation in the first insulating state, whereas the real part of the dielectric function drops with ascending wavelength in the second metallic state, showing a crossing from positive values to negative values at a specific crossing wavelength, which is in particular determined by the charge carrier density of the material of the at least one first nanostructure - also designated in short as the charge carrier density of the first nanostructure. In particular, the at least one first nanostructure exhibits its plasmonic resonance for wavelengths which are greater than the specific crossing wavelength. The position of the specific crossing wavelength can be selected by the charge carrier density of the material of the at least one first nanostructure. The peak wavelength of the plasmonic resonance can be selected in particular by defining the geometry, in particular the characteristic dimension, and the charge carrier density of the at least one first nanostructure.

In the context of the present technical teachings, a metallic state in particular is a state wherein the first nanostructure, in particular the conductive polymer material, is optically metallic, which in particular means that the real part of the dielectric function is negative (si < 0) for wavelengths greater than the specific crossing wavelength, or frequencies lower than a certain limit frequency corresponding to the specific crossing wavelength, which is the plasma frequency of the conductive polymer material in its second state. In particular, a metallic state is the state in which the first nanostructure exhibits the plasmonic resonance. The insulating state in particular is a state wherein the real part of the dielectric function is positive (si > 0) at least for a certain wavelength range comprising the specific crossing wavelength corresponding to the plasma frequency of the second metallic state. In particular, the insulating state is a dielectric state. The insulating state and the metallic state in particular differ from each other in the charge carrier density of the first nanostructure, in particular of the conductive polymer material. The charge carrier density is higher in the metallic state than in the insulating state. In particular, by changing the electric quantity of the conductor, charge carriers are supplied to the first nanostructure in order to switch it into its second metallic state, or pulled from the first nanostructure in order to switch it to its first insulating state.

In an embodiment of the invention, the at least one first nanostructure is adapted to adopt a plurality of states between the first state and the second state depending on the electric quantity of the at least one conductor. This advantageously allows for intermediary states between the on state of the plasmonic resonance and the off state of the plasmonic resonance. In particular, an intensity of the optical response of the at least one nanostructure is different in the different intermediary states. In this way, in particular a greyscale in the optical response of the at least one nanostructure is accessible. In particular, a different dielectric function is assigned to each of the states, i.e., to the first state, the second state and each intermediary state. In particular, the behavior of the real part of the dielectric function shifts from its approximately constant behavior with the wavelength towards its fully descending behavior when the state of the at least one first nanostructure shifts from the first state towards the second state.

In an embodiment of the invention, the at least one first nanostructure is adapted to adopt the plurality of states between the first state and the second state depending on the electric quantity of the at least one conductor in a continuous manner. This advantageously allows for complete flexibility in the optical response of the at least one first nanostructure.

In another embodiment of the invention, the at least one first nanostructure is adapted to adopt the plurality of states between the first state and the second state depending on the electric quantity of the at least one conductor in a discrete manner. This advantageously offers access to a certain number of well-defined states having well-defined intensities of the optical response.

In an embodiment of the invention, the at least one first nanostructure is adapted to have - in the second metallic state - a peak wavelength of the plasmonic resonance within a range from 100 nm to 20000 nm. The at least one first nanostructure comprising the at least one conductive polymer material can advantageously be tuned to a selected peak wavelength within a broad wavelength range, in particular ranging from far ultraviolet up to medium infrared, in particular by choosing a suitable geometry, in particular characteristic dimension, and charge carrier density for the at least one first nanostructure.

In an embodiment of the invention, the at least one first nanostructure is adapted to have the peak wavelength of the plasmonic resonance in a range from 100 nm to 400 nm. In this case, the peak wavelength is advantageously in the ultraviolet spectral range.

In another embodiment of the invention, the at least one first nanostructure is adapted to have the peak wavelength of the plasmonic resonance in a range from 400 nm to 800 nm. In this case, the peak wavelength is advantageously in the visible spectral range. Then, the optical device is in particular suitable for video applications. In another embodiment of the invention, the at least one first nanostructure is adapted to have the peak wavelength of the plasmonic resonance in a range from 800 nm to 1500 nm. In this case, the peak wavelength is advantageously in the near infrared spectral range.

In another embodiment of the invention, the at least one first nanostructure is adapted to have the peak wavelength of the plasmonic resonance in a range from 1500 nm to 20000 nm. In this case, the peak wavelength is advantageously in the medium infrared spectral range.

In an embodiment of the invention, the plasmonic resonance of the at least one first nanostructure has a bandwidth in a range from 1 nm to 1000 nm. Advantageously, the at least one first nanostructure may be selected to have either a small or a large bandwidth, in particular depending on the application of the optical device. The bandwidth is dominantly influenced by the characteristic dimension of the at least one first nanostructure. Further, the selection of a specific conductive polymer material for the at least one first nanostructure influences the bandwidth (complex refractive index of polymer).

In an embodiment of the invention, the optical device comprises a control device adapted to change the electric quantity of the at least one conductor. Advantageously, in this way the actual dielectric function of the at least one first nanostructure can be selected directly by the control device in an easy, fast and well-defined manner.

Preferably, the electric quantity of the at least one conductor is the electrical potential of the at least one conductor, or the electric current through the at least one conductor. In particular, the electric quantity of the at least one conductor is a voltage with respect to a reference electrode. The reference electrode may be grounded or embodied as an electrochemical standard reference electrode, e.g., the silver chloride electrode (Ag/AgCl electrode).

In an embodiment, the control device is embodied as an adjustable voltage source. In another embodiment, the control device is embodied as an adjustable current source. In still another embodiment, the control device is embodied as an adjustable power source. In the context of the present teachings, “adjustable” means in particular “switchable” between at least two states, i.e., a neutral state or off state and an on state, wherein in the neutral state no voltage, power or current is applied, wherein in the on state a predetermined voltage, a predetermined power, or a predetermined current is applied; or it means “switchable” between two states, i.e., a positive on state and a negative on state, wherein the sign of the voltage or the direction of the current or of the power flow is reversed in the on state with respect to the off state; or it means “switchable” between three states, i.e., the neutral state or off states, the positive on state, and the negative on state.

In an embodiment of the invention, the at least one first surface comprises a plurality of first nanostructures, wherein the first nanostructures are connected to a common conductor as the at least one conductor. In this way, the optical device is most simple and cost-efficient, and it can have a high intensity optical response, wherein the nanostructures are all switched collectively.

In another embodiment of the invention, the at least one first surface comprises a plurality of first nanostructures, wherein the first nanostructures are arranged in at least two groups, wherein each group of first nanostructures is connected to a separate conductor assigned to the group as the at least one conductor. While still providing high intensity, this embodiment allows for spatial complexity in the optical response by differently addressing the different groups of nanostructures.

In still another embodiment of the invention, the at least one first surface comprises a plurality of first nanostructures, wherein each first nanostructure of the plurality of first nanostructures is connected to a separate conductor assigned to the first nanostructure as the at least one conductor. This embodiment allows for full spatial resolution, wherein each nanostructure forms a pixel of the optical device, which can be addressed individually.

In an embodiment of the invention, the at least one conductive polymer material comprises at least one conductive polymer which is adapted to be electrochemically doped. In particular this property advantageously allows for electrically addressing the at least one first nanostructure, in particular by electrochemically, i.e., electrically, changing a charge carrier density of the at least one conductive polymer upon a change in the electric quantity of the at least one conductor. In particular by choosing the electric potential or voltage of the conductor, charge carriers are pushed into or pulled from the electronic system of the conductive polymer, thereby electrochemically doping the conductive polymer. In particular, in this way the conductive polymer can be switched between its first insulating state and its second metallic state. Moreover, this can be done at fast timescales, in particular at video rates greater than 30 Hz.

In an embodiment of the invention, the at least one conductive polymer material comprises at least one conductive polymer selected from a group consisting of poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3-hexylthiophene) (P3HT), polyaniline (PANI), poly diacetylene, poly-vinyl- carbazole, and bicarbazole.

In an embodiment of the invention, the at least one conductive polymer material comprises or is made of at least one conductive polymer. In particular, in an embodiment of the invention, the at least one conductive polymer material is free from a dopant, or, in other words, does not comprise a dopant. In particular, the at least one conductive polymer material consists of the at least one conductive polymer.

In another embodiment of the invention, the at least one conductive polymer material comprises at least one conductive polymer and a dopant. As the dopant is adapted to push charge carriers to or pull charge carriers from the conductive polymer, the pristine state of the conductive polymer material when the conductor is neutral, in particular at 0 V, can be determined by suitably choosing the dopant. For example, a conductive material which would as taken alone, without the dopant, be in its first insulating state when the conductor is in its neutral state, can be shifted to the second metallic state by the presence of the dopant.

In an embodiment of the invention, the dopant is selected from a group consisting of PSS poly(styrenesulfonate) (PSS), trifluoromethanesulfonate (OTf), preferably doped with trifluoromethanesulfonic acid (TfOH), OTf in combination or doped with H2SO4 (suit), para- toluenesulfonate (OTs), and FeCl·,.

In an embodiment, the conductive polymer material is PEDOT:PSS. In another embodiment, the conductive polymer material is PEDOT:sulf. In another embodiment, the conductive polymer material is PEDOTOTf. In still another embodiment, the conductive polymer material is PEDOT Ts.

In an embodiment of the invention, the at least one first surface is adapted to transmit electromagnetic radiation. In this way, the optical device can work in transmission, which is particularly suitable for beam steering applications.

The property of the at least one first surface to transmit, absorb or reflect electromagnetic radiation in particular refers to the peak wavelength of the plasmonic resonance of the at least one first nanostructure. In another embodiment of the invention, the at least one first surface is adapted to absorb electromagnetic radiation. In this way, the optical device can be provided as an absorber with changeable, in particular switchable properties.

In another embodiment of the invention, the at least one first surface is adapted to reflect electromagnetic radiation. In this way, the optical device can work in reflection, which is particularly suitable for display applications.

In another embodiment of the invention, the at least one first surface is adapted to partly transmit and partly absorb electromagnetic radiation.

In another embodiment of the invention, the at least one first surface is adapted to partly transmit and partly reflect electromagnetic radiation.

In another embodiment of the invention, the at least one first surface is adapted to partly reflect and partly absorb electromagnetic radiation.

In another embodiment of the invention, the at least one first surface is adapted to partly transmit, partly reflect, and partly absorb electromagnetic radiation.

The respective property of the first surface to transmit, reflect and/or absorb electromagnetic radiation may be determined by an appropriate selection of a material of the substrate comprising the first surface, or by appropriate adjustments to this material.

In an embodiment, the optical properties of the at least one first surface, in particular the optical properties of the substrate, are adjustable, in particular switchable, in particular in response to an electric signal, preferably a voltage or a current, applied to the surface material or the substrate. Preferably, in this way it is possible to selectively choose whether the first surface shall transmit, absorb, or reflect electromagnetic radiation, or to which extent the first surface shall transmit, absorb, or reflect electromagnetic radiation, in particular by simply applying a suitable electric signal to the first surface.

Additionally, or alternatively, the at least one first surface, in particular the substrate, comprises an elastic material, such that the at least one first surface can selectively be mechanically stretched and released, thereby changing the environment for the at least one first nanostructure, and in particular changing a distance between at least two adjacent nanostructures of the at least one first nanostructure. In this way, the optical properties of the optical device may be changed in an even more complex manner.

In an embodiment of the invention, the at least one first nanostructure is adapted to maintain a state which it has priorly assumed upon applying the electric quantity to the conductor, even after the conductor is reset, in particular switched to its neutral state, in particular grounded. Advantageously, the state of the at least one first nanostructure can be changed simply by applying a short pulse of the electric quantity; it is not necessary to maintain the electric quantity in order to maintain the respective state of the at least one first nanostructure. Thus, the optical device is extremely efficient in terms of energy consumption. That the at least one first nanostructure is adapted to maintain its priorly assumed state after the conductor is reset implies, that the least one first nanostructure exhibits a hysteresis. In particular, the dielectric function of the at least one first nanostructure exhibits a hysteresis in its response to the electric quantity of the conductor.

In an embodiment of the invention, the optical device comprises a plurality of first surfaces superimposed on each other as the at least one first surface, wherein at least one separate conductor is assigned to each of the first surfaces as the at least one conductor. In this way, each first surface is individually electrically addressable. In particular, each first surface comprises at least one first nanostructure in electrical contact to the respective at least one conductor.

In an embodiment of the invention, the optical device further comprises at least one second surface. The at least one second surface preferably is above or below the at least one first surface, i.e., the at least one second surface and the at least one first surface are superimposed on each other. The optical properties of the optical device can advantageously be further determined or modified by choosing the properties and arrangement of the at least one second surface. In particular, by suitably choosing the at least one second surface, the optical device can be embodied as a perfect absorber, in particular as a switchable perfect absorber.

The terms “above” and “below” refer to a direction perpendicular to the at least one first surface.

In an embodiment of the invention, the at least one second surface comprises a metallic material.

In another embodiment of the invention, the at least one second surface comprises a dielectric material. In another embodiment of the invention, the at least one second surface comprises a material having switchable properties, in particular switchable upon an electric signal, i.e., electrically switchable, as explained above with respect to the at least one first surface.

In another embodiment of the invention, the at least one second surface is a metasurface.

In another embodiment of the invention, the at least one second surface comprises a metallic material and a dielectric material.

In another embodiment of the invention, the at least one second surface comprises a metallic material and a material having switchable properties.

In another embodiment of the invention, the at least one second surface comprises a metallic material and the at least one second surface is a metasurface.

In another embodiment of the invention, the at least one second surface comprises a dielectric material and a material having switchable properties.

In another embodiment of the invention, the at least one second surface comprises a dielectric material and the at least one second surface is a metasurface.

In another embodiment of the invention, the at least one second surface comprises a material having switchable properties and the at least one second surface is a metasurface.

In another embodiment of the invention, the at least one second surface comprises a metallic material, and a dielectric material, and a material having switchable properties.

In another embodiment of the invention, the at least one second surface comprises a metallic material, and a dielectric material, and the at least one second surface is a metasurface.

In another embodiment of the invention, the at least one second surface comprises a metallic material, and a material having switchable properties, and the at least one second surface is a metasurface.

In another embodiment of the invention, the at least one second surface comprises a dielectric material, and a material having switchable properties, and the at least one second surface is a metasurface. In another embodiment of the invention, the at least one second surface comprises a metallic material, and a dielectric material, and a material having switchable properties, and the at least one second surface is a metasurface.

In an embodiment of the invention, the optical device further comprises at least one second nanostructure in addition to the at least one first nanostructure. By choosing the at least one second nanostructure, the optical properties of the optical device can be further tuned. Even additional properties, like sensing properties, be it chemical sensing or electromagnetic sensing, can be applied to the optical device by suitably providing the at least one second nanostructure. In an embodiment, the at least one second nanostructure is arranged on the same surface, i.e., on the at least one first surface, as the at least one first nanostructure. In another embodiment, the at least one second nanostructure is arranged on another surface, in particular on the at least one second surface, or on at least one third surface, in particular above or below the at least one first surface and thus above or below the at least one first nanostructure.

In an embodiment, the optical device comprises a plurality of second nanostructures. The different second nanostructures may have different sizes, geometries, and/or materials. Alternatively, the second nanostructures may be identical to each other.

In an embodiment, the at least one second nanostructure is a passive nanostructure, i.e., a nanostructure which cannot be switched. In another embodiment, the at least one second nanostructure is switchable with respect to at least one property, in particular with respect to its dielectric function, upon a certain stimulus, which preferably can be an electric quantity or signal, or a chemical stimulus. If the stimulus is a chemical stimulus, the optical properties of the optical device may depend on the presence or concentration of a certain chemical substance, e.g., hydrogen. Thus, the optical device may have chemical sensing properties.

The at least one first nanostructure and the at least one second nanostructure may be arranged relative to each other in a way to form a superordinate structure, e.g., stacked antennas or a chiral arrangement. In particular, the optical device can be embodied as a chirality sensor. Further, the optical device can be embodied as a perfect absorber in particular by choosing a suitable arrangement of the at least one second nanostructure relative to the at least one first nanostructure.

In an embodiment of the invention, the at least one second nanostructure comprises a metallic material. In another embodiment of the invention, the at least one second nanostructure comprises a dielectric material.

In another embodiment of the invention, the at least one second nanostructure comprises a second conductive polymer material different from the - first - conductive polymer material comprised by the at least one first nanostructure. The second conductive polymer material may differ from the first conductive polymer material in its conductive polymer. Alternatively, or additionally, the second conductive polymer material may differ from the first conductive polymer material in its dopant.

In another embodiment of the invention, the at least one second nanostructure comprises a first second nanostructure comprising a metallic material, and the at least one second nanostructure comprises a second second nanostructure comprising a dielectric material.

In another embodiment of the invention, the at least one second nanostructure comprises a first second nanostructure comprising a metallic material, and the at least one second nanostructure comprises a second second nanostructure comprising a second conductive polymer material different from the first conductive polymer material.

In another embodiment of the invention, the at least one second nanostructure comprises a first second nanostructure comprising a dielectric material, and the at least one second nanostructure comprises a second second nanostructure comprising a second conductive polymer material different from the first conductive polymer material.

In another embodiment of the invention, the at least one second nanostructure comprises a first second nanostructure comprising a metallic material, and the at least one second nanostructure comprises a second second nanostructure comprising a dielectric material, and the at least one second nanostructure comprises a third second nanostructure comprising a second conductive polymer material different from the first conductive polymer material.

In an embodiment, the optical device comprises at least one electrically addressable liquid crystal in addition to the at least one first nanostructure, on the at least one first surface or on another surface, in particular above or below the at least one first surface. This further enhances the complexity of the optical device and the possibilities to influence the optical response of the optical device. Preferably, the optical device comprises a plurality of, in particular individually, electrically addressable liquid crystals.

In an embodiment, at least two first nanostructures of the at least one first nanostructure are arranged relative to each other as a switchable plasmonic electromagnetically induced transparency (EIT) device. Preferably, a plurality of the first nanostructures is arranged relative to each other such that a dipole couples with a quadrupole. For example, it is possible that three rod shaped first nanostructures are arranged relative to each other in such a way that two of the first nanostructures are aligned parallel to each other on the first surface, while a third first nanostructure of the first nanostructures is arranged perpendicular to and in front of the two parallel nanostructures on the first surface or on another surface - in particular the second surface or a third surface above or below the first surface -, so that a quasi-U-shaped structure is created - albeit with the nanostructures spaced apart from each other. Alternatively, a quasi-H-shaped structure may be provided by placing the third, perpendicular first nanostructure between the two parallel nanostructures - on the first surface or on another surface above or below the first surface. It is also possible that the third first nanostructure is arranged on the first surface and the other two first nanostructures are arranged on another surface above or below the first surface. Upon electromagnetic excitation, the two first nanostructures oriented parallel to each other form a quadrupole, while the third first nanostructure oriented perpendicular to this forms a dipole, whereby the dipole couples with the quadrupole. This results in a retardation for electromagnetic waves in the spectral range of the plasmonic excitation of the nanostructure arrangement. Such a switchable nanoplasmonic retarder - also referred to as a phase plate - is particularly suitable for use in telecommunications applications. In an analogous manner, an absorber based on the switchable plasmonic electromagnetically induced transparency can also be formed.

In another embodiment, a switchable plasmonic electromagnetically induced transparency arrangement (EIT arrangement) as described above, is made from the second nanostructures and provided in addition to the at least one first nanostructure. The EIT arrangement may be located at the first surface together with the at least one first nanostructure, or on the second or a third surface, in particular above or below the at least one first surface, or distributed over different surfaces, as explained above.

By providing an EIT arrangement, the optical device may advantageously be embodied as a switchable optical filter having a small bandwidth. In an embodiment, the at least one first nanostructure is embedded in a matrix material. Advantageously, the matrix material defines an embodiment, in particular a dielectric embodiment, of the at least one first nanostructure and thereby also influences the optical properties of the optical device. In particular, the matrix material influences the plasmonic resonance of the at least one first nanostructure. Preferably, the matrix material has properties, in particular a dielectric function, which is switchable upon a certain stimulus, preferably upon an electric quantity or signal. In this case, the optical properties of the optical device can further be tuned by selectively switching the properties, in particular the dielectric function, of the matrix material. In an embodiment, the matrix material may be switchable from a transmitting to an absorbing or reflecting state, or vice versa.

In an embodiment of the invention, the optical device is a device selected from a group consisting of a LIDAR, a device for generating a switchable hologram, a spatially variable phase plate, a spatial light modulator, an augmented reality display, a virtual reality display, an endoscope, and a CMOS controlled device. The optical device advantageously may provide for a variable focus, in particular for zooming in and/or zooming out, in particular depending on the dielectric function of the at least one first nanostructure.

In another embodiment of the invention, the optical device is a part of a device selected from the group consisting of a LIDAR, a device for generating a switchable hologram, a spatially variable phase plate, a spatial light modulator, an augmented reality display, a virtual reality display, an endoscope, and a CMOS controlled device; in particular a part used for beam shaping, beam steering, generating a hologram or picture, dynamic focusing, zooming in and/or zooming out.

In an embodiment, a plurality of first nanostructures is arranged on the first surface such that a Fresnel-lens type metasurface is formed, which is adapted to operate as a switchable lens. Then, in the second metallic state of the first nanostructures - which preferably can be switched collectively - the metasurface acts as a lens focusing electromagnetic radiation, wherein in the insulating state the focusing effect is switched off.

The invention also comprises a use of the optical device in a device, in particular for beam shaping, beam steering, generating a hologram or a picture, dynamic focusing, zooming in and/or out. The device, in which the optical device is used, is preferably selected from the group consisting of a LIDAR, a device for generating a switchable hologram, a spatially variable phase plate, a spatial light modulator, an augmented reality display, a virtual reality display, an endoscope, and a CMOS controlled device.

In an example of the invention, the optical device comprises a substrate having the first surface, the first surface being at least in parts coated with a conducting layer forming the at least one conductor, wherein the at least one first nanostructure is arranged on the first surface and in electrical contact with the conductor, and wherein further the at least one first nanostructure is in electric contact with an electrolyte as the counter-conductor, in particular surrounded by or immersed in the electrolyte, wherein the electrolyte further is in electrical contact with a reference electrode. The electrolyte may be a liquid electrolyte or a solid-state electrolyte. If the electrolyte is a liquid electrolyte, the reference electrode is preferably immersed in the electrolyte. If the electrolyte is a solid-state electrolyte, the reference electrode may be arranged on the electrolyte. Preferably, in order to change the dielectric function of the at least one first nanostructure, a voltage of the conductor is changed with respect to the reference electrode. The conducting layer may be structured in order to provide separate conductors, isolated from each other, for individually addressing separate first nanostructures. The reference electrode may be a silver/silver chloride electrode. The optical device may comprise a counter electrode also in contact with the electrolyte, wherein the voltage between the at least one conductor and the reference electrode is controlled by varying an electrical current between the conductor and the counter electrode.

The invention also comprises a method for manufacturing an optical device according to the invention or an optical device in accordance with at least one of the above-described embodiments. The method comprises the steps of providing a first surface, arranging at least one conductor on the first surface, arranging at least one first nanostructure on the first surface in electrical contact with the at least one conductor, wherein the at least one first nanostructure is selected to comprise at least one conductive polymer material, and wherein the at least one first nanostructure is selected such that it is adapted to change its dielectric function when an electric quantity of the at least one conductor is changed.

Preferably, a conductor material is coated onto the first surface in order to form the at least one conductor. Preferably, the conductor material is structured in order form a plurality of separate conductors, electrically isolated from each other.

Preferably, a plurality of first nanostructures is arranged on the first surface in electrical contact with the at least one conductor, preferably each first nanostructure in electrical contact with an individually assigned, separate conductor, in particular electrically isolated from other conductors assigned to other first nanostructures.

In particular, a preferably structured layer (preferably 20 nm) of indium tin oxide (ITO), or InGaZnO (IGZO), as the at least one conductor is deposited on the first surface provided at a substrate, preferably a glass substrate. Then, a conductive polymer material is spin-coated onto the first surface, preferably with a thickness of 90 nm. The conductive polymer material is overcoated with poly(methyl methacrylate) (PMMA) as positive tone-resist for electron beam lithography (EBL). After development a S1O2 etch mask is deposited via electron-gun evaporation, followed by a lift-off, preferably in acetone. The thickness of the S1O2 etch mask (preferably 30 nm) is chosen in accordance to the etching rate of the conductive polymer material and S1O2 in a subsequent argon (Ar) etching process. This causes no remaining S1O2 after the Ar etching and a pure polymer nanoantenna from the conductive polymer material on ITO.

The invention is further explained with respect to the appended drawing, wherein

Figure 1 shows a first embodiment of an optical device;

Figure 2 schematically shows the fundamental functionality of the optical device;

Figure 3 shows an embodiment of a method for manufacturing the optical device, and

Figure 4 shows a second embodiment of an optical device as well as a schematic representation of temporal switching of the optical device.

Fig. 1 shows an embodiment of an optical device 1, the optical device 1 having a first surface 3, wherein the first surface 3 comprises at least one first nanostructure 5, in the embodiment according to figure 1 in particular a plurality of first nanostructures 5 of which only one has been assigned the respective reference numeral for clarity’s sake. In particular, the at least one first nanostructure 5 is arranged on the first surface 3. The first nanostructures 5 each comprise at least one conductive polymer material. The optical device 1 further comprises at least one conductor 7 in electrical contact to the at least one first nanostructure 5, which is only schematically shown for the leftmost one of the first nanostructures 5. Indeed, in the embodiment according to figure 1, all first nanostructures 5 are in electrical contact with the same common conductor 7; in particular, the first surface 3 is coated with a conducting material, in particular indium tin oxide (ITO) or InGaZnO (IGZO), forming the conductor 7, and the first nanostructures 5 are arranged on the conductor 7 and thus in electrical contact with the same. In this way, the first nanostructures 5 can only be electrically addressed collectively in this embodiment.

However, in other embodiments, the first nanostructures 5 may be arranged in at least two groups, wherein each group of first nanostructures 5 is connected to a separate conductor 7 assigned to the group, or, each first nanostructure 5 of the plurality of first nanostructures 5 may be connected to a separate conductor 7 individually assigned to the respective first nanostructure 5. In such embodiments, the first nanostructures 5 can either be addressed in groups, or individually. In order to address individual groups of first nanostructures 5 or even individual first nanostructures 5 electrically, the conducting material arranged on the first surface 3 as the at least one conductor 7 can be structured in order to form separate conductors 7 electrically isolated from each other.

The first nanostructures 5 are adapted to change their dielectric function when an electric quantity of the conductor 7 is changed. In particular, the first nanostructures 5 are adapted to switch between at least a first insulating state and a second metallic state when the electric quantity of the conductor 7 is changed. Preferably, the first nanostructures 5 are adapted to adopt a plurality of states between the first state and the second state, preferably in a continuous manner, or, alternatively, in a discrete manner, depending on the electric quantity of the conductor 7. In particular, the first nanostructures 5 exhibit a plasmonic resonance in the second metallic state, and they do not exhibit the plasmonic resonance in the first insulating state.

The at least one conductive polymer material comprises at least one conductive polymer which is adapted to be electrochemically doped. In particular, the at least one conductive polymer material comprises at least one conductive polymer selected from a group consisting of PEDOT, P3HT, PANI, polydiacetylene, poly-vinyl-carbazole, and bicarbazole. Additionally, or alternatively, the at least one conductive polymer material comprises at least one conductive polymer and a dopant, wherein the dopant is preferably selected from a group consisting of PSS, OTf, sulf, FeCh, and OTs.

The optical device 1 comprises a control device 9 which is adapted to change the electric quantity of the conductor 7. In particular, the control device 9 is adapted to change an electrical potential of the conductor 7 or an electric current through the conductor 7.

In the embodiment according to figure 1, the optical device 1 comprises an electrolyte 11 as a counter-conductor in electrical contact with the first nanostructures 5. The control device 9, preferably embodied as a potentiostat, comprises a voltage source 13 which on the one hand is in electrical contact with the conductor 7 via a working electrode 15, and on the other hand is in electrical contact with a counter electrode 17 immersed in the electrolyte 11. The control device 9 further comprises a voltmeter 19 on the one hand in electrical contact with the working electrode 15, and on the other hand in electrical contact with a reference electrode 21 immersed in the electrolyte 11. The reference electrode 21 may be adapted to provide a standard reference potential. Preferably, the reference electrode 21 is embodied as a silver/silver chloride electrode. The control device 9 is adapted to apply a voltage between the working electrode 15, and thus the conductor 7, and the reference electrode 17, and preferably to control this voltage by varying an electrical current between the working electrode 15 and the counter electrode 17.

The electrolyte 11 may be a liquid electrolyte. Alternatively, the electrolyte 11 may be a solid- state electrolyte.

In the embodiment according to figure 1, the first surface 3 is adapted to transmit electromagnetic radiation. In other embodiments, the first surface 3 may, additionally, or alternatively, be adapted to absorb or reflect electromagnetic radiation.

In figure la), it is shown that a voltage of + 1 V is applied to the conductor 7. In this case, the first nanostructures 5 are in their second metallic state and exhibit a plasmonic resonance at a wavelength of an incident beam of light 23. Due to the plasmonic resonance and the particular arrangement of the first nanostructures 5 on the first surface 3, the incident beam 23 is partly transmitted as a transmitted beam 25 and partly diffracted as a diffracted beam 27. The transmitted beam 25 and the diffracted beam 27 can be observed with a camera 29.

In figure lb), a voltage of - 1 V is applied to the conductor 7. In this case, the first nanostructures 5 are in their first insulating state and do not exhibit the plasmonic resonance. Thus, the incident beam 23 is only transmitted, and consequently, only the transmitted beam 25 can be observed on the camera 29. The diffracted beam 27 is not present. Thus, 100 % contrast with respect to the diffracted beam 27 can be obtained by switching between the first state and the second state.

Specifically, figure 1 shows an example, where the electrolyte 11 is 0.1 mol/1 TBAPF₆ in Acetonitrile. The reference electrode 21 is a silver/silver chloride electrode. The length of the individual first nanostructures 5 made of PEDOT:PSS is 380 nm, the width is 160 nm, and the height is 90 nm. Incremental rotation angles of 6° with a periodicity of 500 nm in x and y direction in the first surface 3 result in a super period of 15 pm. It comprises a total of 30 individual first nanostructures 5, leading to a diffraction angle of f = 10.2°. The incident beam 23 is right- circularly polarized laser beam at 2.65 pm. The diffracted beam 27 shows opposite handedness relative to the incident beam 23.

Preferably, the first nanostructures 5 are adapted to maintain a priorly - upon applying the electric quantity to the conductor 7 - assumed state even after the conductor 7 is reset, in particular grounded. Thus, the first nanostructures 5 exhibit a hysteresis with respect to their different states, such that energy efficient switching between the states is possible by just giving a short voltage pulse in order to switch the states, rather than permanently applying a certain voltage assigned to the respective state. In particular, at voltage zero, depending on the direction of the scan (either going from + 1 V to 0 V or going from - 1 V to 0 V), the resulting optical signal will be different. Thus, non-volatile operation is possible, which in particular means that for future holographic and display applications the plasmonic resonance of the first nanostructures 5 can be set ON or OFF in a powerless operation.

Preferably, in an embodiment not shown in the drawing, the optical device 1 comprises a plurality of first surfaces 3 - each having at least one first nanostructure 5 - superimposed on each other as the at least one first surface 3, wherein at least one separate conductor 7 is assigned to each of the first surfaces 3, such that each first surface 3 is individually electrically addressable.

Additionally, or alternatively, the optical device 1 further comprises at least one second surface 31, only schematically shown in figure lb), wherein the at least one second surface 31 comprises a metallic material, or a dielectric material, or a material having switchable properties, or wherein the at least one second surface 31 is a metasurface.

Additionally, or alternatively, the optical device 1 further comprises at least one second nanostructure 33, also only schematically shown in figure lb), in addition to the at least one first nanostructure 5, wherein preferably the at least one second nanostructure 33 comprises a metallic material or a dielectric material. The at least one second nanostructure 33 may be arranged on the at least one second surface 31, or, together with the first nanostructures 5, on the first surface 3.

Preferably, the optical device l is a device selected from a group consisting of a LIDAR, a device for generating a switchable hologram, a spatially variable phase plate, a spatial light modulator, an augmented reality display, a virtual reality display, an endoscope, and a CMOS controlled device.

Fig. 2 schematically shows the fundamental functionality of the optical device 1.

Identical or functionally equivalent features are assigned the same reference numerals in all the figures, such that reference is made, respectively, to the description as given above.

In figure 2a), on the left, the first insulating state of the first nanostructure 5 is depicted, whereas on the right the second metallic state of the first nanostructure 5 is shown. It is schematically shown that switching between the states may be carried out at video rates of at least 30 Hz. Further, the absorbance of the first nanostructure 5 as a function of the wavelength is given for both the first insulating state on the left in a first diagram 35 and the second metallic state on the right in a second diagram 37. While the first diagram 35 shows virtually no absorbance in the first insulating state, the second diagram 37 shows a prominent plasmonic resonance of the first nanostructure 5 in the second metallic state, in particular a transverse magnetic (TM) mode. The plasmonic resonance preferably has a peak wavelength in a range from 100 nm to 20000 nm, in particular from 100 nm to 400 nm, or from 400 nm to 800 nm, or from 800 nm to 1500 nm, or from 1500 nm to 20000 nm, wherein preferably the plasmonic resonance has a bandwidth in a range from 1 nm to 1000 nm, in particular depending on a characteristic dimension, in particular length, of the first nanostructure 5 and further on a charge carrier density of the conductive polymer material of the first nanostructure 5. The nanostructure 5 of an example according to figure 2 is made of PEDOT:PSS as the conductive polymer material, has a characteristic dimension, in particular length, of 300 nm, and a peak resonance wavelength at 2.2 pm in its second metallic state. Thus, as one single nanostructure 5 may form a pixel of the optical device 1, it is shown that sub wavelength pixel sizes are accessible with the technical teachings disclosed herein.

In figure 2b), the real part of the dielectric function is given for both states of the first nanostructure 5: a first solid line 39 shows the real part of the dielectric function in the first insulating state, wherein the real part of the dielectric function is positive and approximately constant over the total wavelength range shown; a second dashed line 41 shows the real part of the dielectric function in the second metallic state, wherein the real part crosses the zero line and thus becomes negative at a wavelength of 1.3 pm. Thus, the first nanostructure 5 is indeed optically metallic for wavelengths greater than 1.3 pm. In an inset of the diagram, the principal mechanism of the switching between the first insulating state and the second metallic state (metal-insulator transition) is shown for PEDOT as the conductive polymer, wherein it is in particular shown that connectivity in the second metallic state is based on a polaron/bipolaron mechanism.

Fig. 3 shows an embodiment of a method for manufacturing the optical device.

The method comprises the steps of providing the first surface 3, arranging the at least one conductor 7 on the first surface 3, arranging the at least one first nanostructure 5 on the first surface 3 in electrical contact with the at least one conductor 7, wherein the at least one first nanostructure 5 is selected to comprise at least one conductive polymer material, and wherein the at least one first nanostructure 5 is selected such that it is adapted to change its dielectric function when an electric quantity of the at least one conductor 7 is changed.

Preferably, a conductor material is coated onto the first surface 3 in order to form the at least one conductor 7. Preferably, the conductor material is structured in order to form a plurality of separate conductors 7, electrically isolated from each other.

Preferably, a plurality of first nanostructures 5 is arranged on the first surface 3 in electrical contact with the at least one conductor 7, preferably each first nanostructure 5 in electrical contact with an individually assigned, separate conductor 7, in particular electrically isolated from other conductors 7 assigned to other first nanostructures 5.

In particular, a preferably structured layer 43 (preferably 20 nm) of indium tin oxide (ITO) as the at least one conductor 7 is deposited, preferably via physical vapor deposition or sputtering, on the first surface 3 provided at a substrate 45, preferably glass substrate. Then, a conductive polymer material 47, preferably PEDOT:PSS, is spin-coated onto the first surface 3, preferably with a thickness of 90 nm. The conductive polymer material 47 is overcoated with PMMA 49 as positive tone-resist for electron beam lithography (EBL). After development, a SiCk etch mask 51 is deposited via electron-gun evaporation, followed by a standard lift-off, preferably in acetone. The thickness of the SiCk etch mask 51 (preferably 30 nm) is chosen in accordance to the etching rate of the conductive polymer material 47 and SiCk in a subsequent argon (Ar) etching process. This causes no remaining SiCk after the Ar etching and a pure polymer nanoantenna, i.e. the first nanostructure 5, from the conductive polymer material 47 on ITO.

Fig. 4 shows a second embodiment of an optical device 1 as well as a schematic representation of temporal switching of the optical device 1. At a), the setup for investigating the temporal behavior is shown. The characteristic dimension, i.e., length, for the first nanostructure 5 made of PEDOT:PSS in this embodiment is 300 nm. The electrolyte 11 is 0.1 mol/l TBAPF₆ in Acetonitrile. The reference electrode 21 is a silver/silver chloride electrode.

At b), an intensity of the transmitted beam 25 at l = 2.15 pm in arbitrary units is shown while the applied voltage is switched, as sketched on the right. The intensity of the transmitted beam is modulated according to the state of the first nanostructures 5, depending on the applied voltage. The lower graphs show the set voltage switching between + 1 V and - 1 V. The top graphs depict the transmitted intensity cycling between the ON and OFF state as well as a 10 % to 90 % modulation. Cycles 1 to 10 (left curves) and 261 to 290 (right curves) are plotted, where the first nanostructures 5 are switched with a frequency of f = 1 Hz and f = 30 Hz, respectively. In both cases, more than a 10 % to 90% modulation is observed.

The optical device 1 suggested here greatly boosts the integrability of plasmonic systems into, e.g., commercial smart and small-scale electro-optical devices, in particular as it possesses several favorable properties: It has a very high switching modulation efficiency with a full ON- and OFF- state, it is electrically switchable, it requires comparably low voltages/electric potentials, and it is switchable at video-rate frequencies.

The nanostructures 5 in particular allow a new level of flexibility for the fabrication on flexible substrates for curved optical devices. This is in particular important to realize augmented reality (AR) and virtual reality (VR) technologies that work in transmission, e.g., on contact lenses or glasses. In particular, applications are conceivable which project a 3D world directly in front of the eyes. Ultimately, this could even enable pixel densities of over 2000 lines/mm, which would support full-color holographic movies at very large field of view. All this is aided by the fact that the extremely small first nanostructures 5 operate at only ± 1 V, which in particular is very favorable for low-voltage CMOS compatibility (0 to 3.3V) at moderate local electric fields.

The first nanostructures 5 also allow for the generation of dynamic holograms, in particular electrically switchable holograms, in particular with a large field of view in the region of more than 30°, in particular more than 45°. In particular, the first nanostructures 5 allow for the generation of amplitude and phase holograms.

A spatial resolution in the region from 100 nm to 200 nm in particular for visible light is possible.

Claims

1. Optical device (1), having

- at least one first surface (3) comprising at least one first nanostructure (5), wherein

- the at least one first nanostructure (5) comprises at least one conductive polymer material, wherein

- the optical device (1) comprises at least one conductor (7) in electrical contact to the at least one first nanostructure (5), wherein

- the at least one first nanostructure (5) is adapted to change its dielectric function when an electric quantity of the at least one conductor (7) is changed.

2. Optical device (1) according to claim 1, wherein the at least one first nanostructure (5) is adapted to switch between at least a first insulating state and a second metallic state when the electric quantity of the at least one conductor (7) is changed.

3. Optical device (1) according to at least one of the preceding claims, wherein the at least one first nanostructure (5) is adapted to adopt a plurality of states between the first state and the second state, preferably in a continuous manner, depending on the electric quantity of the at least one conductor (7).

4. Optical device (1) according to at least one of the preceding claims, wherein the at least one first nanostructure (5) is adapted to have a plasmonic resonance with a peak wavelength in a range from 100 nm to 20000 nm, in particular from 100 nm to 400 nm, or from 400 nm to 800 nm, or from 800 nm to 1500 nm, or from 1500 nm to 20000 nm, wherein preferably the plasmonic resonance has a bandwidth in a range from 1 nm to 1000 nm.

5. Optical device (1) according to at least one of the preceding claims, wherein the optical device (1) comprises a control device (9) adapted to change the electric quantity of the at least one conductor (7), preferably the electrical potential of or the electric current through the at least one conductor (7).

6. Optical device (1) according to at least one of the preceding claims, wherein the at least one first surface (3) comprises a plurality of first nanostructures (5), wherein the first nanostructures (5) are connected to a common conductor as the at least one conductor (7), or are arranged in at least two groups, wherein each group of first nanostructures (5) is connected to a separate conductor assigned to the group as the at least one conductor (7), or

- each first nanostructure (5) of the plurality of first nanostructures (5) is connected to a separate conductor assigned to the first nanostructure (5) as the at least one conductor (7).

7. Optical device (1) according to at least one of the preceding claims, wherein the at least one conductive polymer material comprises at least one conductive polymer which is adapted to be electrochemically doped.

8. Optical device (1) according to at least one of the preceding claims, wherein the at least one conductive polymer material comprises at least one conductive polymer selected from a group consisting ofPEDOT, P3HT, PANI, polydiacetylene, poly-vinyl-carbazole, and bicarbazole.

9. Optical device (1) according to at least one of the preceding claims, wherein the at least one conductive polymer material comprises at least one conductive polymer and a dopant, wherein the dopant is preferably selected from a group consisting of PSS, OTf, sulf, OTs, and FeCh.

10. Optical device (1) according to at least one of the preceding claims, wherein the at least one first surface (3) is adapted to transmit, absorb, or reflect electromagnetic radiation.

11. Optical device (1) according to at least one of the preceding claims, wherein the at least one first nanostructure (5) is adapted to maintain a state priorly assumed upon applying the electric quantity to the conductor (7) after the conductor (7) is reset.

12. Optical device (1) according to at least one of the preceding claims, wherein the optical device (1) comprises a plurality of first surfaces (3) superimposed on each other as the at least one first surface (3), wherein at least one separate conductor (7) is assigned to each of the first surfaces (3), such that each first surface (3) is individually electrically addressable.

13. Optical device (1) according to at least one of the preceding claims, wherein the optical device (1) further comprises at least one second surface (31), wherein the at least one second surface (31) comprises a metallic material, or a dielectric material, or a material having switchable properties, or wherein the at least one second surface (31) is a metasurface.

14. Optical device (1) according to at least one of the preceding claims, wherein the optical device (1) further comprises at least one second nanostructure (33) in addition to the at least one first nanostructure (5), wherein preferably the at least one second nanostructure (33) comprises a metallic material or a dielectric material.

15. Optical device (1) according to at least one of the preceding claims, wherein the optical device (1) is a device selected from a group consisting of a LIDAR, a device for generating a switchable hologram, a spatially variable phase plate, a spatial light modulator, an augmented reality display, a virtual reality display, an endoscope, and a CMOS controlled device.