Optical device for modulating incident light

Abstract

According to one aspect of the present inventive concept, there is provided an optical device (1) for modulating incident light (L), which includes a resonance-defining layer structure (110) containing an optically state-changing material (112) and an electrode layer (120) containing at least two spaced-apart electrode elements (121, 122, 123). The electrode elements are individually addressable and are arranged to cause an optical state change of a portion of the optically state-changing material between a first state and a second state, wherein the portion forms a geometric structure (131, 132, 133, 134, 135, 136) defined by the arrangement of the at least two spaced-apart electrode elements. The optically state-changing material is configured to change the optical response of the optical device upon an optical state change between the first state and the second state, thereby determining the modulation of the incident light.

Description

Technical Field

[0001] The inventive concept relates to an optical device for modulating incident light. The inventive concept also relates to a method of modulating light incident on an optical device. Background Art

[0002] Holographic images are formed by controlling a three-dimensional light field. This is typically accomplished by an array of optical devices, each having an optical response, i.e., a particular way of altering incident light, to provide at least a portion of the light field. To form the optical response, the optical device may have a metasurface composed of an array of sub-wavelength features.

[0003] When a holographic image is to vary over time (e.g., to create a sequence of holographic images or generate a holographic video), it may be necessary to alter the optical response of the array of optical devices. In this regard, it is known to provide an array of optical devices, each having a separate addressing port and being electrically alterable, e.g., by a laser.

[0004] To obtain a sufficiently high efficiency, i.e., in terms of the ratio of modulated light to incident light, phase modulation is generally preferred over amplitude modulation. In the field of metasurfaces, it is known to use a modulation such as the Pancharatnam Berry (PB) phase modulation scheme, where the phase of light is determined by the geometry on which the light propagates rather than the distance. However, altering the optical properties between different states of such a metasurface is a challenging task, especially for visible light applications where component sizes are required to be less than one micron. Summary of the Invention

[0005] Accordingly, an object of the inventive concept is to provide an optical device whose optical response can be individually and reversibly altered to vary the modulation of incident light while maintaining overall efficiency.

[0006] This and other objects of the invention are at least partially met by the invention as defined in the independent claims. Preferred embodiments are stated in the dependent claims.

[0007] According to a first aspect of the inventive concept, there is provided an optical device for modulating incident light, comprising:

[0008] a resonance-defining layer structure including an optically state-changing material;

[0009] an electrode layer including at least two spaced-apart electrode elements;

[0010] wherein the electrode elements are individually addressable and arranged to cause an optical state change of a portion of the optically state-changing material between a first state and a second state;

[0011] wherein the portion forms a geometry defined by an arrangement of the at least two spaced-apart electrode elements,

[0012] wherein the optically variable material is configured to change an optical response of the optical device upon an optical state change between a first state and a second state, the optical response determining a modulation of incident light.

[0013] Accordingly, the optical response of the optical device can be changed by applying a voltage difference across the at least two electrodes, thereby changing a portion of the optically variable material. The geometry defined by the arrangement of the at least two spaced-apart electrode elements allows for generating a pattern of the optically variable material in two different states. A given geometry (i.e., a given pattern) can correspond to a given optical response, and the optical response of the optical device can thus be changed. Accordingly, there is no need to fabricate the geometry during manufacturing, enabling a simple and more cost-effective manufacturing.

[0014] By the individually addressable electrode elements, a voltage difference can be applied across the at least two electrode elements. Accordingly, a current, a current field, a magnetic field, an electric field, etc. can be induced in the resonance-defining layer structure and / or the optically variable material to change a portion of the optically variable material from the first state to the second state. Correspondingly, the portion of the optically variable material along the current, the current field, and / or the magnetic field can change state, thereby generating the geometry required to provide the desired optical response. By using the electrode elements described herein, it is possible to form geometries having dimensions of only a few hundred nanometers. In the present disclosure, "voltage difference" and "potential difference" can be used interchangeably, but both still refer to the concept of applying a potential difference across two or more elements.

[0015] In addition, when another voltage difference (such as a lower or higher voltage difference) is applied across the at least two electrode elements, the portion can be changed from the second state back to the first state. This in turn allows the optical device to obtain a first geometry, be "reset", i.e., have no geometry, and subsequently obtain another or the same geometry. Accordingly, the optical device can obtain various optical responses in a simple manner using the structure of the optical device.

[0016] In some embodiments, the first and second states of the optically variable material are stable states. The optically variable material can have more than two stable states. The optical state change can be achieved, for example, by Joule heating caused by a current, a current field, an electromagnetic field, etc. that affects the optically variable material. In some embodiments, the optically variable material is disposed in a layer structure.

[0017] According to one embodiment, the optically variable material may be a phase change material (PCM), preferably formed of a compound including a transition metal oxide or a chalcogenide glass such as germanium antimony telluride (GST), where the optically variable state is the phase change of the phase change material.

[0018] Thus, the optically variable state can be achieved by means of the state change of the PCM. By using a PCM, a substantial difference in optical properties between the first and second states can be achieved, thereby allowing better control of the optical response and thus of the scattered light. The difference in optical properties can be, for example, the complex refractive index or the complex dielectric constant of the PCM.

[0019] According to one embodiment, the electrode element may also be configured to repeatedly cause an optically variable material portion to change its optical state between a first state and a second state.

[0020] This again allows the use of the optical device to obtain a greater variety of different optical responses. In the case where the optically variable material is a PCM, the phase change of the portion from the first state to the second state can be achieved by applying a given voltage difference between both of at least two electrode elements.

[0021] According to one embodiment, the resonant confinement layer structure may further include a conductive layer and / or an electrically insulating layer.

[0022] Thus, current can flow through the insulating and / or conductive layer of the electrically insulating layer, but not through the optically variable layer. In some embodiments, the electrically insulating layer or the conductive layer may be inserted between the optically variable material and the electrode layer. In other embodiments, the current induced by at least two electrode elements can flow through the optically variable material to change its state. In other embodiments, the optical device may include two electrode layers disposed on each side of the resonant confinement layer structure such that when a voltage difference is applied between the electrodes of each layer, an electric field can be generated across the resonant confinement layer structure. Preferably, an electrically insulating layer may be provided between the resonant confinement layer structure and the corresponding electrode layer.

[0023] According to yet another embodiment, the electrode element may be configured to induce current into at least one layer of the resonant confinement layer structure in order to cause an optical state change of a portion of the optically variable material.

[0024] By inducing an electric current into at least one layer, local heating can occur along the current path, which can cause the portion of the phase optical state-changing material to change its optical state. Thereby, a simple and relatively easy-to-control optical state change of the desired portion can be achieved. Since the current path can be well-defined and the heat can be controlled by the current intensity, a well-defined portion of the optical state-changing material can be caused to transfer from a first state to a second state, or vice versa. This in turn enables the formation of geometric structures in the optical state-changing material (preferably in the main extension plane of the resonance-defining layer), where each geometric structure can have specific optical properties so as to modulate the incident light in a desired manner.

[0025] As an alternative or in combination therewith, the optical state change of the optical state-changing material can be caused or at least triggered by a magnetic field induced by an electric current or a potential difference. In some embodiments, the electric current will flow through the optical state-changing material, while in other embodiments, the electric current can travel in one or more other layers of the device.

[0026] According to one embodiment, an optical device can include at least three electrode elements arranged to define at least two different geometric structures in the main extension plane of the resonance-defining layer. The at least two different geometric structures can, for example, conform to a V-shape or an L-shape or other less complex anisotropic shapes, which can be rotated relative to each other within the plane of the resonance-defining layer. This allows phase modulation according to the Pancharatnam-Berry (PB) modulation scheme of the incident light. Since the geometric pattern is further rewritable and reconfigurable, the optical response of the optical device can be changed in a well-defined and controllable manner.

[0027] The incident light preferably impinges substantially perpendicular to the surface of the resonance-defining layer, such that the influence of the orientation of the at least two different geometric structures on the phase modulation can be increased.

[0028] According to one embodiment, a light-scattering device can be configured to modulate incident light having a wavelength in the range from 100 nm to 2000 nm, preferably in the range from 300 nm to 750 nm.

[0029] Therefore, the optical device can be used to modulate light in the visible range of the human eye. This also allows the optical device to be used to create 3D holographic images and / or videos.

[0030] According to yet another embodiment, the optical state-changing material in at least one of the first state and the second state can have plasmonic properties for incident light having a wavelength range from 100 nm to 2000 nm, preferably 300 nm to 750 nm.

[0031] This in turn allows the optical properties of the optically variable material to be highly dependent on the geometric structure formed in the optically variable material. The plasmonic properties can allow enhanced electromagnetic interaction with light and thus improve the modulation ability in a smaller volume. In addition, the visible wavelength range allows optical devices to be used to modulate light in the human visible spectrum, for example to provide holograms and the like.

[0032] According to one embodiment, the phase optically variable material may be arranged in a layer having a thickness less than the minimum wavelength of the incident light to be modulated.

[0033] Thus, in embodiments where light is transmitted through the device, light absorption by the optically variable material can be reduced. This in turn allows a larger portion of the incident light to be modulated and scattered by the optical device.

[0034] According to one embodiment, the first state of the optically variable material may be a primary crystalline state, while the second state of the optically variable material may be a primary amorphous state.

[0035] Thus, a strong response can be provided based on the material difference between the primary crystalline state and the primary amorphous state.

[0036] The primary crystalline state of the optically variable material refers to a state in which at least half of the optically variable material is in a crystalline state. At least half of the material can be interpreted as at least 50% of the mass of the optically variable material. Similarly, the primary amorphous state should be understood as a state in which more than half (e.g., more than 50% of the mass) of the optically variable material is in an amorphous state. It should be understood here that those skilled in the art will know the terms "crystalline state" and "amorphous state" with respect to optically variable materials (preferably phase change materials). Therefore, the details of these terms will not be further discussed in this disclosure. In some embodiments, the optically variable material may have more than one primary crystalline state and / or more than one primary amorphous state. In some embodiments, the primary crystalline state and / or the primary amorphous state may exhibit different properties of the optically variable material, such as optical properties.

[0037] According to yet another embodiment, the resonant confinement layer structure and the electrode layer may be arranged in a stacked structure, and when viewed in a direction perpendicular to the surface of the resonant confinement layer structure, the electrode layer may be arranged above and / or below the resonant confinement layer structure.

[0038] Thus, the electrode elements of the electrode layer may be capable of inducing current and / or generating a field within or around the resonance-defining layer with minimal losses, thereby enhancing the efficiency of the optical device. In some embodiments, current may flow from one electrode of the electrode layer, through at least a portion of the resonance-defining layer (e.g., a portion of the optically variable material), to a second electrode of the electrode layer. As an alternative or in combination therewith, a varying current or alternating current may be sent through the electrodes of the electrode layer to generate a magnetic field, for example, at least partially affecting a portion of the resonance-defining layer by altering the state of that portion of the resonance-defining layer.

[0039] In addition, a first and a second electrode layer may be provided on opposite sides of the resonance-defining layer. In such a case, a bias (such as a potential difference) may be applied between the electrode of the first layer and the corresponding electrode of the second layer (opposite to the electrode of the first layer) to generate a localized electric field through at least a portion of the resonance-defining layer.

[0040] In some embodiments, the electrode layer includes at least four electrode elements arranged at positions spanning a rectangle and / or a hexagon. This in turn allows for the formation of multiple different geometric configurations in the optically variable material of the resonance-defining layer, such as V-shaped, L-shaped, X-shaped, and I-shaped. Thus, various phase modulations of the incident light can be achieved by changing the optical properties of the optically variable material. The positions spanning the rectangle and / or the hexagon may be such that when viewed in a direction substantially perpendicular to the resonance-defining layer, each electrode may form one corner of the rectangle and / or the hexagon.

[0041] In some embodiments, an array for forming a distribution of three-dimensional light fields is provided, which includes a plurality of optical devices according to any of the above embodiments, wherein each of at least three electrode elements of each said optical device is individually addressable, such that the optical response of each optical device can be changed independently of the other optical devices of the array.

[0042] This in turn allows for the presentation of an array such as a hologram, for example, by modulating (such as phase modulating) the incident light while maintaining the high efficiency of using the optical device, the optical response of which can be easily reset and / or changed. According to one embodiment, the optical device may be configured to modulate polarized light. Specifically, the optical device may be configured to form an anisotropic geometry so as to allow for an increase in the difference in optical response during an optical state change between a first state and a second state. This embodiment is based on the recognition that light can be represented by a traveling wave having an electric field perpendicular to the propagation direction, where the polarization of the light wave describes the exact orientation of the electric field. Polarization can be described by a linear combination of orthogonal vectors in a plane perpendicular to the propagation direction, and depending on the weights of these orthogonal vectors, the light can be said to be linearly polarized, circularly polarized, or elliptically polarized.

[0043] As light travels, its magnetic and electric fields may interact differently with the surrounding environment. Thus, polarization becomes an important parameter when light passes through any structure, medium, or interface (such as an elliptical geometry or nanoparticles) that presents an anisotropic surrounding environment to the magnetic and electric fields. The weights of the orthogonal bases of polarization can determine how the light will interact with this anisotropy.

[0044] Accordingly, in the context of the present disclosure, polarization can be an important factor affecting the resulting modulation of light. For a particular (anisotropic) geometry, different polarizations can result in significantly different optical responses. Thus, these effects can be considered when designing the shape of the geometry. Advantageously, light having a fixed (or at least controlled) polarization can be used.

[0045] According to a second aspect of the inventive concept, there is provided a method of modulating light incident on an optical device, which can be configured similarly to the device described above with reference to the first aspect and related embodiments. The method may include the steps of:

[0046] Applying a first voltage difference across a pair of at least two electrode elements of the optical device to cause an optical state change of a portion of a phase optical state change material from a first state to a second state, and

[0047] Applying a second voltage difference across the pair of electrode elements, the second voltage difference being lower than the first voltage difference, to cause an optical phase state change of the phase optical state change material from the second state to the first state.

[0048] Similar to that described with reference to the device according to the first aspect, the optical state change can be reversible and depends on the voltage difference applied across the pair of electrode elements. This in turn allows for a controllable optical state change of portions of the phase optical state change material. Due to the reversibility, there is no need to pattern the resonant confinement layer during production, allowing for a simpler and more cost-effective production. Further, since the state of at least a portion of the phase optical state change material is defined by the electrodes of the electrode layer, no external source is required to reset the phase change of the material. This in turn allows for an optical device that can be easily configured.

[0049] According to one embodiment, the second voltage difference is applied for a longer period of time compared to the first voltage difference.

[0050] According to one embodiment, the electrode layer includes at least three electrode elements, and the method further includes the steps of:

[0051] Applying the first voltage difference across a second pair of electrode elements to cause an optical state change of another portion of the phase optical state change material from a first state to a second state, and

[0052] A second voltage difference is applied to the second pair of electrode elements to cause an optical state change of the other portion of the phase optical state change material from a second state to a first state.

[0053] According to a third aspect of the inventive concept, there is provided an array of optical devices, wherein each optical device in the array is an optical device according to the first aspect, and wherein each optical device forms a unit cell, and wherein each optical device in the array is individually controllable by controlling the electrode elements of the corresponding optical device. Accordingly, the optical device of the first aspect can be used in an array of individually controllable optical devices to define the optical response of the array of optical devices, which can be used, for example, to generate a holographic image.

[0054] According to an embodiment, each optical device includes a set of electrode elements.

[0055] Accordingly, each optical device can be individually controlled by controlling the set of electrode elements. The set may include at least three electrode elements, which are arranged to define at least two different geometries in a main extension plane of the resonance defining layer, such that the arrangement of the set of electrode elements can be used to define at least two different geometries formed by a portion of each optical device.

[0056] According to an embodiment, the set of electrode elements of a first optical device is different from the set of electrode elements of a second optical device. Accordingly, each of the first and second optical devices is controlled by its own set of electrode elements.

[0057] According to an embodiment, the array includes a single resonance defining layer common to all unit cells in the array.

[0058] This means that the resonance defining layer can be easily produced.

[0059] The different aspects of the present invention can be implemented in different ways, including an optical device, a method of modulating light incident on the optical device, and an array of optical devices as described above and below, each of which produces one or more benefits and advantages described in connection with at least one of the above aspects, and each of which has one or more preferred embodiments corresponding to the preferred embodiments described in connection with at least one of the above aspects.

[0060] Furthermore, it will be understood that embodiments described in connection with one aspect herein can equally be applied to another aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The above and other objects, features and advantages of the inventive concept will be better understood from the following detailed description, which is illustrative and non - limiting, with reference to the accompanying drawings. In the drawings, like reference numerals will be used for like elements unless otherwise noted.

[0062] Figure 1 is a perspective view of an optical device according to an embodiment.

[0063] FIG. 2 is a top view of an array of multiple optical devices according to an embodiment.

[0064] FIGS. 3a-d are perspective views of optical devices with different geometric structures formed in an optically state-changing material.

[0065] FIGS. 4a-b, 5a-b, and 6a-b schematically illustrate optical devices according to some embodiments of the present invention.

[0066] Figure 7 is a flowchart illustrating a method according to an embodiment. DETAILED DESCRIPTION

[0067] Referring now to Figure 1 , the optical device 1 will be generally described. The optical device 1 may include a resonance-defining layer structure 110 that includes an optically state-changing material 112 and an optional electrically insulating or conductive layer 114. Additionally, the device 1 may include an electrode layer that includes at least two spaced-apart electrode elements, such as a first electrode element 121, a second electrode element 122, and a third electrode element 123. In the present example, the resonance-defining layer structure 110 and the electrode elements 121, 122, 123 may be disposed on a substrate 140 such that the electrode elements 121, 122, 123 are disposed between the substrate 140 and the resonance-defining layer structure 110 and provide an electrical connection between a conductive structure (not shown) of the substrate 140 and the resonance-defining layer 110. As shown in this drawing, the optically state-changing material 112 and the electrically insulating or conductive layer 114 of the resonance-defining layer structure 110 may be disposed in a stacked structure, where the electrically insulating or conductive layer 114 is disposed between the electrode layer and the optically state-changing material 112.

[0068] The electrode elements 121, 122, 123 are individually addressable via, for example, the substrate 140, where conductive paths may be provided to supply power to the electrode elements 121, 122, 123. Thus, the electrode layer may be arranged such that electrical control of the optically state-changing material 112 is possible, and the optically state-changing material 112 may be configured to switch between at least a first and a second optical state when exposed to, for example, an electric current, an electric current field, a magnetic field, or heat provided by the electrode layer. Examples of these mechanisms will be discussed in connection with the following drawings.

[0069] The electrode layer can be formed, for example, by a conductive layer (such as a metal), and the conductive layer can be patterned into at least two electrode elements 121, 122, 123, which are laterally separated from each other in the main extension plane of the substrate 140. In other words, the electrode elements can form electrically addressable points or electrical contact areas on the resonant confinement layer structure 110. The separation and / or extension of the contact points between at least two electrode elements 121, 122, 123 and the resonant confinement layer structure 110 can define a geometric structure (not shown), which can be formed in the optically variable material 112 when an optical state change occurs in a part of the optically variable material 112. Examples of such geometric structures will be discussed in conjunction with, for example, Figure 6 The geometric structure formed by the optical state change of this part of the optically variable material 112 can be configured to change the optical response of the optical device 1, thereby determining the modulation of the light L incident on the device 1.

[0070] The optically variable material 112 can be provided as a substantially uniform layer that forms a surface on which the light to be modulated can be incident. Therefore, the geometric structure that can be used to affect the modulation of the incident light L can be defined by the pattern of the electrode layer 120 (or the arrangement of at least two electrical elements of the electrode layer) rather than by the direct patterning of the optically variable material 112 itself.

[0071] The optically variable material 112 can be, for example, a phase change material PCM, such as a transition metal oxide or a chalcogenide glass. Examples of transition metal oxides include VO2, V2O3, EuO, MnO, CoO, CoO2, LiCoO2, Ca2RuO4, SrLrO4, Ti2O3, LaCoO3, PrNiO3, Cd2OsO7, NdNiO3, Tl2Ru2O7, Ca 1-y Sr y VO3, Fe3O4, La 1-y Ca y MnO3, La 2-2y Sr 1+2u Mn2O7, Ti4O7, and La2NiO4. Examples of chalcogenide glasses and other phase change materials include NiS 2-y Se y , NiS, BaCo 1-y Ni y S2, PrRu4P 12, BaVS3, EuB6, CuCl, and compounds containing GeSbTe (also known as GST). The PCM can be configured to switch from a crystalline state to an amorphous state when exposed to high-power electrical pulses and return to the crystalline state when exposed to a series of low-power electrical pulses. Depending on the arrangement of the electrode elements 121, 122, 123, the geometric structures generated in the PCM can affect the optical response and thus the modulation of the incident light L.

[0072] The change of the state change material from one state to another can be determined by both the voltage amplitude and the duration of the electrical pulse. This can be illustrated by the PCM, where different phases can correspond to different percentages of crystallinity. Current and the generated Joule heat can be used to convert the atoms of the PCM from an ordered packing (crystalline phase) to a random packing (amorphous phase) and vice versa.

[0073] If the current injected into the PCM is high enough to melt the material, the atoms can enter the liquid phase. If the current and thus the heat are quickly removed, the atoms do not have the remaining energy to travel back to their preferred lattice positions. Therefore, they can be locked in the amorphous state. However, when the current and thus the heat are only gradually removed, the atoms can have sufficient energy to travel to their preferred lattice positions. The resulting state can then be crystalline.

[0074] If the injected current is not high enough to melt the PCM material, it can still provide enough heat and energy for the atoms to be able to move closer to their desired lattice positions. The more energy provided, the higher the percentage of atoms in the crystalline state.

[0075] Therefore, it will be understood that the state change can be affected by only the amplitude of the applied voltage pulse, only the duration of the pulse, or a combination of both. The electrode elements 121, 122, 123 can be arranged to cause an optical state change in a portion of the sub-wavelength scale geometric structure formed in the plane of the resonance defining layer 110 and with reference to the wavelength of the incident light to be modulated. The optical device 1 as shown in this figure can form one unit cell of an array of multiple unit cells, where each unit cell can be individually controlled in terms of optical response to control the wavefront of the incident electromagnetic wave by applying a local phase shift to the incoming wave.

[0076] The optical device 1 can be formed, for example, in an additive process, where the electrode layer 120 is deposited and patterned to form the electrode elements 121, 122, 123. In a later step, the resonance defining layer 110 can be provided by first depositing an intermediate layer 114 such as the conductive layer 114 above the electrode layer 120 and then depositing the optical state change material 112 above the intermediate layer 114.

[0077] Figures 2a-d schematically illustrate an optical device according to an embodiment, which may be configured similarly to the device shown in Figure 1 In the present embodiment, the resonance defining layer 110 includes an optically variable material 112 (such as, for example, the GST phase change material discussed above) and a first electrode element 121, a second electrode element 122, and a third electrode element 123. The electrode elements 121, 122, 123 are electrically connected to the GST layer 112 at laterally spaced-apart contact points, thereby defining a current path through the phase change material 112. Figures 2a-d show the device arranged in four different modulation states.

[0078] In Figure 2a, a current I1 passes between the first electrode element 121 and the third electrode element 123, such that a phase change is triggered in a portion of the phase change material 112 extending along the current path. The phase change portion may, for example, take an amorphous state along the current path, thereby forming a first geometric structure 131 extending between the first electrode element 121 and the third electrode element 123.

[0079] In Figure 2b, a current I2 passes between the first electrode element 121 and the second electrode element 122, thereby creating a second geometric structure 132 extending between the first and second electrode elements 121, 122.

[0080] In Figure 2c, a current I3 passes between the second electrode element 122 and the third electrode element 123, thereby generating a third geometric structure 133 between the second and third electrode elements 122, 123.

[0081] It will be appreciated that the above-described operation scheme of the optical device 1 is an example showing an embodiment of the inventive concept. Thus, different numbers of electrode elements and their arrangements may be used to achieve the desired geometric structure of the phase change region in the phase change material 122. Additionally, a current may also pass between three or more electrode elements. An example is shown in Figure 2d, where a current path is formed from the first electrode element 121 to both the second and third electrode elements 122, 123. The resulting geometry is formed by a combination of the second geometry 132 of Figure 2b and the third geometry 133 of Figure 2c. In the embodiment shown in Figures 2a-d, the optically variable material 112 is configured to change the optical response of the optical device in response to a current passing through the material. The current path through the optically variable material may cause an optical state change by means of Joule heating of the material itself. However, other configurations are also possible.

[0082] Figures 3a and b show that it can be associated with Figure 1An optical device configured similarly to the device of FIG. 2, except that the resonance-defining layer structure 110 includes an intermediate layer 114 disposed between the optically variable material 112 and the electrode layer 120. The intermediate layer 114, which may also be referred to as a stimulation-defining layer, may be configured to indirectly change the optical state of the optically variable material 112, for example, by Joule heating of the intermediate layer 114 itself. By disposing the intermediate layer 114 close to the optically variable material 112, the intermediate layer 114 can act as, for example, a heating layer that induces a phase change in the optically variable material 112. The intermediate layer may be, for example, an insulating layer, or a conductive layer through which currents I1, I2 can flow, for example, between a first electrical element 121 and a third electrical element 123 as shown in FIG. 3a, and between a first electrical element 121 and a second electrical element 122 as shown in FIG. 3b, to form desired geometries 131, 132 in the optically variable material 112.

[0083] FIGS. 4a and 4b illustrate another configuration of electrical elements disposed in an optical device that could otherwise be configured similarly to the embodiments of the previous figures. In this example, the optically variable material 112 may be configured to change its optical state in response to an electric field generated by a voltage bias on at least two of the electrode elements 121, 122, 123, 124. Thus, the optically variable material 112 may be an electro-optic material that exhibits a change in absorption or refractive index in the presence of an external electric field.

[0084] In this example, the first electrode element 121 may be disposed above the layer of the optically variable material 122 (not shown in FIGS. 4a and 4b in the stacking direction from the substrate surface), while the second electrode element 122 may be disposed below the optically variable material 112. Thus, the first and second electrode elements 121, 122 may form an electrode pair, with a portion of the optically variable material 112 located therebetween. When a potential difference is applied across the first and second electrode elements 121, 122, an electric field E may be generated between the electrodes and pass through the portion of the optically variable material 112 disposed between the electrical elements 121, 122. The electric field E may be used to cause a change in the optical state of this portion of the optically variable material 112, thereby creating a geometry extending along at least one of the electrode elements 121, 122 in the main extension plane of the resonance-defining layer structure 110. One or more electrode element pairs may be provided to allow the formation of other geometries. In FIG. 4b, a second electrode element pair 123, 124 disposed on opposite sides at another portion of the optically variable material 112 is used to generate an electric field E that forms another geometry.

[0085] Another example of an optical state change mechanism is disclosed in FIGS. 5a and 5b, where a magnetic field from an electrical conductor is used to cause a magneto-optical state change along a current path. Such an optical device may be configured similarly to the embodiments of Figure 1 FIGS. 2 to 4, except that the first electrode element 121 and the second electrode element 122 may be arranged to allow currents I1, I2 to pass through the respective electrode elements 121, 122 along the main extension plane of the resonance-defining layer structure 110. The magnetic field B generated by the currents I1, I2 flowing through the conductors formed by the electrode elements 121, 122 can be used to induce an optical state change in the optical state change material 112.

[0086] As shown in the examples illustrated in the above figures, several mechanisms can be employed to form geometric structures in the optical state change material, where the state change mechanism and the resulting extension and form of the geometric structure are determined by the arrangement and electrical operation of the electrode elements. Depending on the shape and orientation of the geometric structure, different optical responses can be provided to achieve modulation of the light incident on the optical device.

[0087] Figure 6 is a schematic top view of a plurality of optical devices 1 arranged in a two-dimensional array, which may be configured similarly to any of the above embodiments. Each of the optical devices 1 can be individually controlled to take into account the unit cells whose optical responses can be tuned accordingly. In this example, each of the optical devices 1 includes a set of electrode elements arranged to define six different portions in the optical state change material, each portion corresponding to a respective geometric structure in the extension plane of the resonance-defining layer structure. It should be noted that the unit cells formed by the optical devices 1 of the array can be defined by the arrangement of the electrode elements rather than the extension of the resonance-defining structure. Thus, the array can include a single resonance-defining layer common to all the unit cells of the array, and a plurality of unit cells defined by the pattern of the electrode layer.

[0088] For illustrative purposes only, each unit cell can be considered to have a resonance-defining layer with a quadrilateral shape and electrode elements arranged at each corner (or, in a configuration similar to that of FIGS. 4 and 5, extending along each side). Figure 6 Shows the resulting geometric structures 131-136 that can be formed when the optical state changes. In this illustrative example, six different geometric structures 131-136 can be achieved - four extending along the sides of the quadrilateral and two extending along its diagonals. Depending on the operation of the array, i.e., the voltage supplied to the electrode elements, the generated geometric structures can vary between different unit cells and over time. The geometric structures 131-136 can, for example, be combined in pairs to form V-shaped and L-shaped structures for modulating light. However, other shapes and configurations are also possible.

[0089] Figure 7is a flowchart showing a method for modulating light, where the light is incident on an optical device according to any one of the previous figures. The method includes applying a 10 first voltage difference to a pair of at least two electrode elements of the optical device to cause an optical state change of a portion of the optically state-changing material from a first state to a second state, and applying a 20 second voltage difference to the pair of electrode elements to cause an optical state change of the optically state-changing material from the second state to the first state. In one embodiment, the second voltage difference may be lower than the first voltage difference and is preferably provided in a plurality of pulses to return the optically state-changing material to the first state. For example, the first state may be a main crystalline state, and the second state may be a main amorphous state. Additionally, the electrode layer may include at least three electrode elements, thereby allowing the method to include the step of applying a 30 first voltage difference to a second pair of electrode elements to cause an optical state change of another portion of the optically state-changing material from the first state to the second state, and applying a 40 second voltage difference to the second pair of electrode elements to cause an optical state change of the another portion of the optically state-changing material from the second state to the first state.

[0090] Above, the inventive concept has been described mainly with reference to a limited number of examples. However, as will be readily understood by those skilled in the art, other examples besides those disclosed above are equally possible within the scope of the inventive concept defined by the appended claims.

Claims

1. An optical device (1) for modulating an incident light (L), comprising: A resonant confinement layer structure (110) including an optically state-changing material (112), the resonant confinement layer structure (110) being configured to receive the incident light on an upper surface; An electrode layer (120) including at least two spaced-apart electrode elements (121, 122, 123); Wherein the electrode elements are arranged together below a lower surface of the resonant confinement layer structure (110) or above an upper surface of the resonant confinement layer structure (110) at least one of them, wherein each electrode element is individually addressable and is arranged to cause an optical state change of a part of the optically state-changing material from a first state to a second state; Wherein the part forms a geometric structure (131, 132, 133, 134, 135, 136) defined by the arrangement of the at least two spaced-apart electrode elements, Wherein the optically state-changing material is configured to change an optical response of the optical device when undergoing an optical state change from the first state to the second state, and the optical response determines the modulation of the incident light.

2. The optical device according to claim 1, characterized in that, The optically state-changing material is a phase-change material selected from the group including at least one of transition metal oxides, chalcogens, or compounds containing germanium antimony telluride (GST), and wherein the optical state change is a phase change of the phase-change material.

3. The optical device according to claim 1 or 2, characterized in that, The electrode elements are further configured to repeatedly cause the optical state change of the part of the optically state-changing material between the first state and the second state.

4. The optical device according to claim 1 or 2 above, characterized in that, The resonant confinement layer structure further includes a conductive layer or an electrically insulating layer (114).

5. The optical device according to claim 1 or 2 above, characterized in that, The electrode elements are configured to induce currents (I1, I2, I3) into at least one layer of the resonant confinement layer structure to cause the optical state change of the part of the optically state-changing material.

6. The optical device according to claim 1 or 2 above, characterized in that, Including at least three electrode elements, the electrode elements being arranged to define at least two different geometric structures in the optically state-changing material.

7. The optical device according to claim 6, wherein When viewed in a direction perpendicular to the surface of the resonant confinement layer structure, the at least two different geometric structures together form a V shape and / or an L shape.

8. The optical device according to claim 1 or 2 above, characterized in that, The optical device is configured to modulate incident light having a wavelength in the range of 100 nm to 2000 nm.

9. The optical device according to claim 1 or 2 above, characterized in that, The optical device is configured to modulate incident light having a wavelength in the range of 300 nm to 750 nm.

10. The optical device according to claim 1 or 2 above, characterized in that, The device is configured to modulate polarized light.

11. The optical device according to claim 1 or 2 above, characterized in that, The optically state-changing material is arranged in a layer having a thickness less than the minimum wavelength of the incident light to be modulated.

12. The optical device according to claim 1 or 2 above, characterized in that, The first state of the optically state-changing material is a main crystalline state, and wherein the second state of the optically state-changing material is a main amorphous state.

13. The optical device according to claim 1 or 2 above, characterized in that, The resonant confinement layer structure and the electrode layer are arranged in a stacked structure.

14. A method of modulating light incident on an optical device according to any one of the preceding claims, comprising the steps of: Applying (10) a first voltage difference to a pair of at least two electrode elements of the optical device to cause an optical state change of the part of the optically state-changing material from a first state to a second state, and Apply (20) a second voltage difference to the pair of at least two electrode elements to cause an optical state change of the optically state-changing material from the second state to the first state.

15. The method according to claim 14, wherein The second voltage difference is lower than the first voltage difference, and / or the second voltage difference is applied for a longer period of time compared to the first voltage difference.

16. The method according to claim 14 or 15, characterized in that, The electrode layer includes at least three electrode elements, and the method further includes the steps of: Apply (30) the first voltage difference to a second pair of electrode elements to cause an optical state change of another portion of the optically state-changing material from the first state to the second state, and Apply (40) the second voltage difference to the second pair of electrode elements to cause an optical state change of the another portion of the optically state-changing material from the second state to the first state.

17. An array of optical devices, wherein each optical device in the array is an optical device according to any one of the preceding claims 1-13, and wherein each optical device forms a unit cell, and wherein each optical device in the array is individually controllable by controlling the electrode elements of the corresponding optical device.

18. The array according to claim 17, wherein Each optical device includes a set of electrode elements.

19. The array according to claim 18, wherein The set of electrode elements of the first optical device is different from the set of electrode elements of the second optical device.

20. The array according to any one of claims 17-19, characterized in that, The array includes a single resonance-defining layer shared by all unit cells in the array.

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