AN OPTICAL DEVICE FOR MODULATING INCIDENT LIGHT

Abstract

According to an aspect of the present inventive concept there is provided an optical device (1) for modulating incident light (L), comprising a resonance defining layer structure (110) comprising an optical state change material (112), and an electrode layer (120) comprising at least two spaced-apart electrode elements (121, 122, 123). The electrode elements are individually addressable and arranged to cause an optical state change of a portion of the optical state change 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 optical state change material is configured to alter an optical response of the optical device upon the optical state change between the first state and the second state, thereby determining the modulation of the incident light.

Claims

1. An optical device for modulating incident light, comprising: a resonance defining layer structure comprising an optical state change material; an electrode layer comprising at least two spaced-apart electrode elements; wherein said electrode elements are individually addressable and arranged to cause an optical state change of a portion of the optical state change material between a first state and a second state; wherein said portion forms a geometric structure defined by the arrangement of the at least two spaced-apart electrode elements, wherein the optical state change material is configured to alter an optical response of the optical device upon the optical state change between the first state and the second state, said optical response determining the modulation of the incident light.

2. An optical device according to claim 1, wherein the optical state change material is a phase change material, said phase change material preferably being formed of a compound comprising germanium-antimony-tellurium, GST, and wherein an optical state change is a phase change of the phase change material.

3. An optical device according to claim 1, wherein said electrode elements are further configured to repeatedly cause an optical state change of the portion of the optical state change material between the first state and the second state.

4. An optical device according to claim 1, wherein the resonance defining layer structure further comprises an electrically conducting and/or an electrically insulating layer.

5. An optical device according to claim 1, wherein the electrode elements are configured to induce a current into at least one layer of the resonance defining layer structure so as to cause the optical state change of the portion of the optical state change material.

6. An optical device according to claim 1 comprising at least three electrode elements, arranged to define at least two different geometric structures in the optical state change material.

7. An optical device according to claim 6, wherein the at least two different geometric structures together form a V-shape and/or a L-shape, when seen in a direction perpendicular to the surface of the resonance defining layer structure.

8. An optical device according to claim 1, wherein the optical device is configured to modulate incident light having a wavelength in the range from 100 nm to 2000 nm, preferably from 300 nm to 750 nm.

9. An optical device according to claim 1, wherein the device is configured to modulate polarized light.

10. An optical device according to claim 1, wherein the optical state change material is arranged in layer having a thickness smaller than a minimum wavelength of the incident light to be modulated.

11. An optical device according to claim 1, wherein the first state of the optical state change material is a dominantly crystalline state, and wherein the second state of the optical state change material is a dominantly amorphous state.

12. An optical device according to claim-1, wherein the resonance defining layer structure and the electrode layer is arranged in a stack structure, and wherein the electrode layer is arranged above and/or below the resonance defining layer structure when seen in a direction perpendicular to the surface of the resonance defining layer structure.

13. A method of modulating light incident to an optical device according to claim 1, comprising the steps of: applying a first voltage difference to a pair of the at least two electrode elements of the optical device so as to cause an optical state change of the portion of optical state change material from a first state to a second state, and applying a second voltage difference to the pair of electrode elements, so as to cause an optical state change of the optical state change material from the second state to the first state.

14. A method according to claim 13, wherein the second voltage difference is lower than the first voltage difference and/or applied for a longer period of time than the first voltage difference.

15. A method according to claim 13, wherein the electrode layer comprises at least three electrode elements, the method further comprising the steps of: applying the first voltage difference to a second pair of electrode elements so as to cause an optical state change of a further portion of the optical state change material from the first state to the second state, and applying the second voltage difference to the second pair of electrode elements so as to cause an optical state change of the further portion of the optical state change material from the second state to the first state.

16. An array of optical devices, wherein each optical device in the array is an optical device according to claim 1 and wherein each optical device forms a unit cell, wherein each optical device in the array is individually controllable by controlling the electrode elements of the respective optical device.

17. The array according to claim 16, wherein each of the optical devices comprises a set of electrode elements.

18. The array according to claim 17, wherein the set of electrode elements of a first optical device differs from the set of electrode elements of a second optical device.

19. The array according to claim 16, wherein the array comprises a single resonance defining layer common to all unit cells in the array.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description, with reference to the appended drawings. In the drawings like reference numerals will be used for like elements unless stated otherwise.

[0068] FIG. 1 is a perspective view of an optical device according to an embodiment.

[0069] FIG. 2 is a top view of an array of a plurality of optical devices according to an embodiment.

[0070] FIGS. 3a-d are perspective views of an optical device in which different geometrical structures are formed in the optical state change material.

[0071] FIGS. 4a-b, 5a-b and 6a-b schematically illustrate optical devices according to some embodiments of the present invention.

[0072] FIG. 7 is a flow chart illustrating a method according to an embodiment.

DETAILED DESCRIPTION

[0073] Referring now to FIG. 1, an optical device 1 will be generally described. The optical device 1 may comprise a resonance defining layer structure 110 comprising an optical state change material 112 and, optionally, an electrically insulating or conducting layer 114. Further, the device 1 may comprise an electrode layer comprising at least two spaced-apart electrode elements, such as a first electrode element 121, a second 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 arranged on a substrate 140, such that the electrode elements 121, 122, 123 are arranged between the substrate 140 and the resonance defining layer structure 110 and provide an electrical connection between conducting structures of the substrate 140 (not shown) and the resonance defining layer 110. As shown in the present figure, the optical state change material 112 and the electrically insulating or conducting layer 114 of the resonance defining layer structure 110 may be arranged in a stacked structure, with the electrically insulating or conducting layer 114 arranged between the electrode layer and the optical state change material 112.

[0074] The electrode elements 121, 122, 123 may be individually addressable via for example the substrate 140, in which conductive paths may be provided for supplying electrical power to the electrode elements 121, 122, 123. Thus, the electrode layer may be arranged to enable an electrical control of the optical state change material 112, which may be configured switch between at least a first and a second optical state when exposed to for example a current, a current field, a magnetic field or a heat provided by the electrode layer. Examples of these mechanisms will be discussed in connection with the following figures.

[0075] The electrode layer may for example be formed of an electrically conducing layer, for example of a metal, that may be patterned into at least two electrode elements 121, 122, 123 that are laterally separated from each other in the main plane of extension of the substrate 140. Put differently, the electrode elements may form electrically addressable points or regions of electrical contact on the resonance defining layer structure 110. The separation and/or extension of the contact points between at least two electrode elements 121, 122, 123 and the resonance defining layer structure 110 may define a geometric structure (not shown) that can be formed in the optical state change material 112 upon an optical state change in a portion of the optical state change material 112. Examples of such geometrical structures will be discussed in connection with for example FIG. 6. The geometric structure formed by the optical state change of the portion of the optical state change material 112 may be configured to alter an optical response of the optical device 1, determining the modulation of light L impinging on the device 1.

[0076] The optical state change material 112 may be provided as a substantially uniform layer forming a surface onto which the light to be modulated can be brought to impinge. The geometric structures, which can be used for affecting the modulation of the incident light L, may therefore be defined by the patterning of the electrode layer 120 (or the arrangement of the at least two electrical elements of the electrode layer) rather than by a direct patterning of the optical state material 112 itself.

[0077] The optical state change material 112 may for example be a phase change material, PCM, such as for example a transition metal oxide or a chalcogenide glass. Examples of transition metal oxides include VO.sub.2, V.sub.2O.sub.3, EuO, MnO, CoO, CoO.sub.2, LiCoO.sub.2, Ca.sub.2RuO.sub.4, SrLrO.sub.4, Ti.sub.2O.sub.3, LaCoO.sub.3, PrNiO.sub.3, Cd.sub.2OsO.sub.7, NdNiO.sub.3, Tl.sub.2Ru.sub.2O.sub.7, Ca.sub.1−ySr.sub.yVO.sub.3, Fe.sub.3O.sub.4, La.sub.1−yCa.sub.yMnO.sub.3, La.sub.2−2ySr.sub.1+2uMn.sub.2O.sub.7, Ti.sub.4O.sub.7 and La.sub.2NiO.sub.4. Examples of chalcogenide glasses, and other phase change materials, include NiS.sub.2−ySe.sub.y, NiS, BaCo.sub.1−yNi.sub.yS.sub.2, PrRu.sub.4P.sub.12, BaVS.sub.3, EuB.sub.6, CuCl and compounds comprising GeSbTe, also referred to as GST. The PCM may be configured to switch from a crystalline state to an amorphous state when exposed to a high-power electrical pulse, and to 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 resulting geometrical structure in the PCM may affect the optical response and thus the modulation of the incident light L.

[0078] The change of a state change material from one state to another may be determined by both the voltage amplitude and the duration of the electrical pulse. This can be exemplified by a PCM, in which the different phases may correspond to different percentages of crystallinity. Current and generated Joule heat may be used to switch the atoms of the PCM from being orderly packed (crystalline phase) to randomly packed (amorphous phase) and vice versa.

[0079] If the current injected in the PCM is high enough to melt the material, the atoms may go to a liquid phase. It the current, and thus the heat, is then promptly taken away, the atoms have no remaining energy to travel back to their preferred crystalline lattice position. They may hence be locked in the amorphous state. However, when the current, and thus the heat, is only gradually taken away, the atoms may have sufficient energy to travel to their preferred crystalline position. The resulting state may then be crystalline.

[0080] If the injected current is not high enough to melt the PCM material, it can still provide heat and thus energy to the atoms that is sufficient to allow them to move closer to their desired crystalline lattice location. The more energy provided, the more percentage of the atoms may be in a crystalline state.

[0081] Thus, it is appreciated that the state change may be effected by the amplitude of the applied voltage pulse alone, by the duration of the pulse alone or by a combination of both.

[0082] The electrode elements 121, 122, 123 may be arranged to cause an optical state change of a portion forming a subwavelength-scaled geometric structure in the plane of the resonance defining layer 110 and with reference to the wavelength of the of the incident to be modulated. The optical device 1 as shown in the present figure may form a unit cell of an array of a plurality of unit cells, wherein each unit cell may be individually controlled in terms of optical response to control a wave front of incident electromagnetic waves by imparting local phase shifts to the incoming waves.

[0083] The optical device 1 may for example be formed in an additive process, in which the electrode layer 120 is deposited and patterned to form the electrode elements 121, 122, 123. In a following step, the resonance defining layer 110 may be provided by first depositing for example an intermediate layer 114, such as an electrically conducting layer 114, above the electrode layer 120, and then the optical state change material 112 above the intermediate layer 114.

[0084] FIGS. 2a-d schematically illustrate an optical device according to an embodiment, which may be similarly configured as the device shown in FIG. 1. In the present embodiment, the resonance defining layer 110 comprises an optical state change 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 separated contact points, defining electrical current paths through the phase change material 112. FIGS. 2a-d shows the device when arranged in four different modulation states.

[0085] In FIG. 2a, an electrical current I.sub.1 is passed 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 changed portion may for example assume an amorphous state along the current path, forming a first geometrical structure 131 extending between the first electrode element 121 and the third electrode element 123.

[0086] In FIG. 2b, an electrical current I.sub.2, is passed between the first electrode element 121 and the second electrode element 122, resulting in a second geometrical structure 132 extending between the first and the second electrode element 121, 122.

[0087] In FIG. 2c, an electrical current I3 is passed between the second electrode element 122 and the third electrode element 123, such that a third geometrical structure 133 is generated between the second and third electrode element 122, 123.

[0088] It will be appreciated that the above operation schemes of the optical device 1 are examples illustrating the embodiments of the inventive concept. Thus, different numbers of electrode elements and arrangements of the same may be employed to achieve the desired geometrical structures of phased changed regions in the phase change material 122. Further, a current may be passed between three or more electrode elements as well. An example of is shown in FIG. 2d, in which a current flow path is formed from the first electrode element 121 to both the second and the third electrode element 122, 123. The resulting geometrical shape is formed of a combination of the second geometrical shape 132 of FIG. 2b and the third geometrical shape 133 of FIG. 2c.

[0089] In the embodiment shown in FIGS. 2a-d, the optical state change material 112 is configured to alter the optical response of the optical device in response to an electrical current being passed through the material. The current path through the optical state change material may cause the optical state change by means of Joule heating in the material itself. However, other configurations are also possible.

[0090] FIGS. 3a and b show an optical device that may be similarly configured as the devices of FIGS. 1 and 2, with the difference that the resonance defining layer structure 110 comprises an intermediate layer 114 arranged between the optical state change material 112 and the electrode layer 120. The intermediate layer 114, which also may be referred to as a stimulus defining layer, maybe configured o indirectly change the optical state of the optical state change material 112, for example through Joule heating of the intermediate layer 114 itself. By arranging the intermediate layer 114 close to the optical state change material 112, the intermediate layer 114 may act as a heating layer inducing for example a phase change in the optical state change material 112. The intermediate layer may for example be an insulating layer, or an electrically conducting layer through which a current I.sub.1, I.sub.2 may flow for example between the first electrical element 121 and the third electrical element 123 as illustrated in FIG. 3a, and between the first electrical element 121 and the second electrical element 122 as illustrated in FIG. 3b, to form the desired geometrical structures 131, 132 in the optical state change material 112.

[0091] FIGS. 4a and b show another configuration of the electrical elements arranged in an optical device that otherwise may be similarly configured as the embodiments of the previous figures. In the present example, the optical state change material 112 may be configured to change optical state in response to an electric field generated by a voltage bias over at least two of the electrode elements 121, 122, 123, 124. The optical state change material 112 may hence be an electro-optic material exhibiting a change in absorption or refractive index under the presence of an external electric field.

[0092] In the present example, the first electrode element 121 may be arranged above a layer of the optical state change material 122 (as seen in a stacking direction from a surface of the substrate, not shown in FIGS. 4a and b), whereas the second electrode element 122 may be arranged below the optical state change material 112. Hence, the first and the second electrode element 121, 122 may form an electrode pair with a portion of the optical state change material 112 in between. When applying an electric potential difference over the first and second electrode element 121, 122, an electric field E may be generated between the electrodes, and passing through the portion of the optical state change material 112 arranged between the electrical elements 121, 122. The electric field E may be used to cause an optical state change of the portion of the optical state change material 112, resulting in a geometrical structure extending along at least one of the electrode elements 121, 122 in main plane of extension of the resonance defining layer structure 110.

[0093] One or several electrode element pair may be provided so as to allow the formation of other geometric structures. In FIG. 4b, a second electrode element pair 123, 124, arranged on opposite sides at another portion of the optical state change material 112, is used to generate an electric field E forming another geometric structure.

[0094] A further example of an optical state change mechanism is disclosed in FIGS. 5a and b, in which a magnetic field from an electrical conductor is used to cause a magneto-optic state change along a current path. Such an optical device may be similarly configured as the embodiments of FIGS. 1 to 4, with the difference that the first electrode element 121 and the second electrode element 122 may be arranged to allow a current I.sub.1, I.sub.2 to pass through the respective electrode element 121, 122 along the main plane of extension of the resonance defining layer structure 110. The magnetic field B generated by the electric current I.sub.1, I.sub.2 through the conductors formed by the electrode elements 121, 122 may be employed to induce an optical state change in the optical state change material 112.

[0095] As shown in the illustrating examples of the above figures, several mechanisms may be employed to form a geometric structure in the optical state change material, wherein the state change mechanism, as well as the extension and form of the resulting geometrical structure are determined by the arrangement and electrical operation of the electrode elements. Depending on the shape and orientation of the geometrical structure, different optical responses may be provided to achieve a modulation of light impinging on the optical device.

[0096] FIG. 6 is a schematic top view of a plurality of optical devices 1, which may be similarly configured as any of the above embodiments, arranged in a two-dimensional array. Each of the optical devices 1 may be individually controlled to allow for a unit cell whose optical response can be tuned accordingly. In the present example, each of the optical devices 1 comprises a set of electrode elements arranged to define six different portions in the optical state change material, each of which corresponding to a respective geometrical structure in the plane of extension of the resonance defining layer structure. It should be noted that a unit cell, formed by an optical device 1 of the array, may be defined by the arrangement of the electrode elements rather than the extension of the resonance defining structure. Thus, the array may comprise a single resonance defining layer that is common to all unit cells of the array, and a plurality of unit cells defined by the pattern of the electrode layer.

[0097] For illustrative purposes only, each of the unit cells may be considered to have a resonance defining layer with a shape conforming to a quadrilateral and an electrode element arranged in each corner (or, in the case of a configuration similar to the ones in FIGS. 4 and 5, extending along each side). The resulting geometrical structures 131-136 that can be formed upon an optical state change are indicated in FIG. 6. In the present, illustrative example, six different geometrical structures 131-136 can be achieved—four extending along the sides of the quadrilateral, and two along its diagonals. Depending on the operation of the array, i.e., the voltages supplied to the electrode elements, the generated geometrical structures may vary between different unit cells and over time. The geometrical structures 131-136 may for example be combined in pairs to form V-shapes and L-shapes for modulating the light. Other shapes and configurations are however possible.

[0098] FIG. 7 is a flowchart illustrating a method for modulating light according to an embodiment, wherein the light is incident on an optical device according to any one of the previous figures. The method comprises applying 10 a first voltage different to a pair of the at least two electrode elements of the optical device to cause an optical state change of the portion of optical state change material from a first state to a second state, and applying 20 a second voltage different to the pair of electrode elements to cause an optical state change of the optical state change material from the second state to the first state. In an embodiment, the second voltage different may be lower than the first voltage different, and preferably provided in a plurality of pulses, so as to cause the optical state change material to return to the first state. The first state may for example be a predominantly crystalline state, whereas the second state may be a predominantly amorphous state. Further, the electrode layer may comprise at least three electrode elements, allowing the method to comprise the steps of applying 30 the first voltage difference to a second pair of electrode elements to cause an optical state change of a further portion of the optical state change material from the first state to the second state, and applying 40 the second voltage difference to the second pair of electrode elements to cause an optical state change of the further portion of the optical state change material from the second state to the first state.

[0099] In the above the inventive concept has mainly been described with reference to a limited number of examples. However, as is readily appreciated by a person skilled in the art, other examples than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.