Electrically-controlled dynamic optical component comprising a planar metasurface

Abstract

An optical component comprising a planar metasurface arranged on a surface of a first substrate and a top layer arranged in a height direction Z above the metasurface, wherein the metasurface comprises a plurality of scattering structures, wherein a dielectric material is deposited on a subset of the plurality of scattering structures, wherein an active media is sandwiched between the metasurface and the top layer, wherein an incident electromagnetic radiation is transmitted or reflected by the optical component, wherein a phase profile modulation is induced on the incident electromagnetic radiation during the reflection or transmission.

Claims

1-11. (canceled)

12. An optical component comprising a planar metasurface arranged on a surface of a first substrate and a top layer arranged in a height direction Z above the metasurface, wherein the metasurface comprises a plurality of scattering structures, wherein a dielectric material is deposited on a subset of the plurality of scattering structures, wherein an active media is sandwiched between the metasurface and the top layer, wherein an incident electromagnetic radiation is transmitted or reflected by the optical component, and wherein a phase profile modulation is induced on the incident electromagnetic radiation during the reflection or transmission.

13. The optical component according to claim 12, wherein the phase profile modulation is a switchable phase profile modulation.

14. The optical component according to claim 12, wherein the scattering structures are deployed as optical antennas in the form of rods, which are orientated in the plane of the metasurface, wherein the scattering structures comprise spatially varying orientations, wherein the dimensions of the scattering structures are smaller than the wavelength λ of an incident electromagnetic radiation, wherein the spacing between the scattering structures is smaller than half of the wavelength λ of the incident electromagnetic radiation, and wherein the scattering structures comprise identical geometric parameters.

15. The optical component according to claim 14, wherein the scattering structures consist of a metal.

16. The optical component according to claim 14, wherein the scattering structures consist of gold.

17. The optical component according to claim 12, wherein the phase profile modulation, induced on the incident electromagnetic radiation, comprises a geometric phase component, wherein the geometric phase component is introduced due to a phase retardation of the incident electromagnetic radiation, and wherein the phase retardation depends on the orientation of the scattering structures.

18. The optical component according to claim 12, wherein the phase profile modulation, induced on the incident electromagnetic radiation, comprises a propagation phase component, wherein the propagation phase component is modulated by the dielectric material, which is deposited on a subset of the plurality of scattering structures, and the refractive index of the active media, wherein the dielectric material is deposited on the scattering structures in the form of a dielectric pillar, comprising a height along the height direction Z, and wherein the modulation of the propagation phase component depends on the height of the dielectric pillar along the height direction Z.

19. The optical component according to claim 12, wherein the refractive index of the active media is tunable by an external input, wherein the external input is an applied electric field, and wherein the active media comprises highly birefringent liquid crystals.

20. The optical component according to claim 19, wherein the external input to tune the refractive index of the active media is electromagnetic radiation.

21. The optical component according to claim 19, wherein the external input to tune the refractive index of the active media is a temperature change.

22. The optical component according to claim 12, wherein the metasurface is an array of scattering structures, wherein the array is a repeating pattern of unit cells, wherein a unit cell comprises at least two scattering structures, wherein a first scattering structure is covered with the dielectric material, and wherein a second scattering structure is not covered with the dielectric material.

23. The optical component according to claim 22, wherein the optical component is an array of unit cells, wherein each unit cell is addressable by the external input.

24. The optical component according to claim 12, wherein the top layer comprises a second substrate, which is coated with a metallic layer, wherein the second substrate is made of dielectric material, wherein the first substrate serves as a first electrode and the metallic layer serves as a second electrode, and wherein an electric voltage is applicable on the two electrodes.

25. The optical component according to claim 12, wherein the second substrate is made of glass.

26. The optical component according to claim 12, wherein the the metallic layer is an indium tin oxide (ITO) layer.

27. The optical component according to claim 12, wherein at least one spacer element is placed between the metasurface and the top layer.

28. The optical component according to claim 27, wherein the at least one spacer element is spherical.

29. The optical component according to claim 28, wherein the at least one spacer element consists of silica.

30. An optical device comprising the optical component according to claim 12, wherein an application of an electric field causes a modulation of an optical functionality of the optical device due to a modulated phase profile of an incident electromagnetic radiation, which is transmitted through or reflected by the optical component.

31. An optical device according to claim 30, wherein the optical device is a holographic device or a lens or a beam steering device.

Description

[0038] In the drawings:

[0039] FIG. 1 shows an optical component according to an embodiment

[0040] FIG. 2 shows a metasurface according to an embodiment;

[0041] FIG. 3 shows a side view of an optical component according to an embodiment;

[0042] FIG. 4 shows an optical component according to an embodiment

[0043] FIG. 5 shows a schematic of a phase mask;

[0044] FIG. 6 shows an example holographic pattern upon electrical control.

[0045] In the FIGS. 1 to 5 an optical component (1) is displayed comprising a planar metasurface (2) arranged on a surface of a first substrate (3) and a top layer (4) arranged in a height direction Z above the metasurface (2), wherein the metasurface (2) comprises a plurality of scattering structures (5, 5a, 5b, 5c), wherein a dielectric material (6, 6a) is deposited on a subset of the plurality of scattering structures (5, 5a, 5b, 5c), wherein an active media (7) is sandwiched between the metasurface (2) and the top layer (4), wherein an incident electromagnetic radiation (8) is transmitted or reflected by the optical component (1), wherein a phase profile modulation is induced on the incident electromagnetic radiation during the reflection or transmission.

[0046] The optical device extends along a height direction Z a two in-plane directions X, Y. The metasurface (2) extends in the plane spanned by the two in-plane directions X, Y.

[0047] The scattering structures (5, 5a, 5b, 5c) consist of a metal, in particular gold, and are deployed as optical antennas (5a) in the form of rods. The rods are orientated in the plane of the metasurface (2) with spatially varying in plane orientations The dimensions of the scattering structures (5, 5a, 5b, 5c) are smaller than the wavelength A of an incident electromagnetic radiation (8). Further, the spacing (9) between the scattering structures (5, 5a, 5b, 5c) is smaller than half of the wavelength A of the incident electromagnetic radiation (8). Additionally, the scattering structures (5, 5a, 5b, 5c) comprise identical geometric parameters.

[0048] For an electromagnetic radiation (8) with a wavelength of λ=633 nm, the scattering structures (5, 5a, 5b, 5c) in the form of gold nanorods, which are employed as optical antennas, have an optimal dimension of 200 nm*80 nm. The spacing (9) between scattering elements is 300 nm, which is smaller than half of the wavelength of the incident electromagnetic radiation. The dimension of the optical antennas (5a) is optimized in order to achieve the maximum reflection efficiency under the incident wavelength of 633 nm.

[0049] The top layer (4) comprises a second substrate (16), which is coated with a metallic layer (15). The second substrate is made of dielectric material, preferably glass, and the metallic layer (15) is a indium tin oxide (ITO) layer. Further, a layer of rubbed polymide (18) may be provided at the second substrate (16).

[0050] The active media in the form of liquid crystals are held in cell. The liquid crystal (LC) cell is constructed by sandwiching the LC between the first substrate (3) with the metasurface (2) and a glass substrate. Between the metasurface (2) and the top layer (4) at least one spacer element (17) is placed, which is spherical and consists of silica. This is depicted in FIG. 3. The silica sphere is employed as spacer to fix the inside thickness of the LC cell to 5 μm. A highly birefringence (Hi-Bi) LC with ne=1.92 and no=1.53 at the operating wavelength of 633 nm is placed inside the cell in direct contact with the metasurface. The high birefringence (Hi-Bi) LC is encapsulated inside the cell and is in direct contact with the metasurface (2). On the sides of the optical component (1) seals (19) might be provided to seal the cell.

[0051] The refractive index of the active media (7) in the form of high birefringence liquid crystals is tunable by an external input (11), wherein the external input (11) is an applied electric field. The first substrate (3) serves as a first electrode and the metallic layer (15) serves as a second electrode, wherein an electric voltage is applicable on the two electrodes. The electric field does not influence on the optical properties of optical antennas (5a). The electric field might have a possible value of 4 V/μm. Of course, it is conceivable that an external input of a different nature like a temperature change or an incident electromagnetic radiation is applied.

[0052] The phase profile, induced on the incident electromagnetic radiation (8), comprises a geometric phase component and a propagation phase component. The geometric phase component is introduced due to a phase retardation of the incident electromagnetic radiation (8), which depends on the orientation of the scattering structures (5, 5a, 5b, 5c). Based on the principle of PB phase, the phase delay from each scattering structures (5, 5a, 5b, 5c) is equal to 2φ, where φ is the orientation angle of the scattering structures (5, 5a, 5b, 5c). Thus, arbitrary phase profile is achieved by arranging the scattering structures (5, 5a, 5b, 5c) with different orientations on the metasurface (2).

[0053] The propagation phase component is modulated by the dielectric material (6, 6a), which is deposited on a subset of the plurality of scattering structures (5, 5a, 5b, 5c) and the refractive index of the active media (7). The dielectric material (6, 6a) is deposited on the scattering structures (5, 5a, 5b) in the form of a dielectric pillar (6a), comprising a height (10) along the height direction Z. The modulation of the propagation phase component depends on the height (10) of the dielectric pillar (6, 6a) along the height direction Z.

[0054] The metasurface (2) is an array (12) of scattering structures (5, 5a, 5b, 5c). The array (12) is a repeating pattern of unit cells (13). A unit cell (13) comprises at least two scattering structures (5, 5a, 5b, 5c), wherein a first scattering structure (5, 5a, 5b) is covered with the dielectric material (6, 6a) and a second scattering structure (5, 5a, 5c) is not covered with the dielectric material (6, 6a). There are two nanorods (5a) in each unit cell (13), which are vertical to each other. One of the nanorods (5a, 5b) is covered with the dielectric material (6, 6a) in order to generate propagation phase, which is different between two nanorods (5, 5a, 5b, 5c). Therefore, the pattern of covering with the dielectric pillar (6, 6a) is determined by the relative location of two nanorods (5, 5a, 5b, 5c) in the unit cell (13).

[0055] The dielectric material (6, 5a) covering the scattering structures (5, 5a, 5b) is used to introduce propagation phase on certain optical antennas (5, 5a, 5b). Thus, propagation phase difference is generated between the optical antennas with (5, 5a, 5b) and without (5, 5a, 5c). covering. Such phase difference could be adjusted by changing the orientation of the surrounding liquid crystal molecules (7) due to an appropriate external input (11), for instance an electric field.

[0056] The optical component (1) can be designed as an array of unit cells (13). Each unit cell (13) is addressable by the external input (11) and comprises at least one scattering structure (5, 5a, 5b, 5c). This is depicted in FIG. 4. Addressability is achieved by local control of liquid crystal.

[0057] The unit cells (13) may be considered as the pixels of a phase mask (20). This means the optical component (1) is divided into discrete pixels where each pixel provides a specific, local, phase shift indicated by φ.sub.ij which represents a discretized version of a phase map (20), depicted in FIG. 5. For the shaping of an incident beam a phase profile φ(x,y), φ(x,y) is induced. Preferably, after the incident beam is reflected from or transmitted through the metasurface (2) and propagates a distance z.

[0058] The selective combination of the geometric phase component and a propagation phase component on individual subwavelength pixels achieves a pixel-level addressability. This concept is universal and works for any active materials, which exhibit refractive index changes upon electrical, light, thermal, or other external stimuli.

[0059] The metasurface (2) comprises scattering structures (5, 5a, 5b, 5c) in the form of optical antennas (5a) that have been designed according to the PB phase. At least one optical antenna is caged in a cell (13), which is filled with highly birefringent liquid crystals (7). Some of the antennas (5a) are selectively covered with dielectric pillars (6a). This introduces an additional propagation phase on such scattering structures (5, 5a, 5b) and meanwhile isolates them from the liquid crystals (7), deactivating the response of these scattering structures (5, 5a, 5b) to electrical control.

[0060] The optical component (1) could be comprised in an optical device (100). The optical component (1) might also be an optical device (100). An application of an electric field causes a modulation of an optical functionality of the optical device (100) due to a modulated phase profile of an incident electromagnetic radiation (8), which is transmitted through or reflected by the optical component (1).

[0061] The phase profile consists of geometric phase and propagation phase. The geometric phase profile is a static part, which depends on the orientation of optical antenna. The propagation phase profile is achieved by the dielectric materials covering a liquid crystal layer, which could be switched by applying electric field to adjust refractive index of liquid crystal. Thus, the switching is realized due to the changeable phase profile.

[0062] With proper phase-profile designs, completely interchangeable functionalities, for instance, switching between different holographic patterns within a hologram, or multi-function switching among beam steering, focusing, holography, optical vortices, etc., can be successfully implemented within milliseconds and with excellent reversibility under electrical control at visible frequencies. In FIG. 6 an example of a switching of holographic patterns within a hologram upon electrical control is depicted.

[0063] This invention features great potentials to achieve diversified optical functions, such as optical switch for communication systems and dynamic holographic for data storage.

[0064] All the features disclosed in the application documents are claimed as being essential to the invention if, individually or in combination, they are novel over the prior art.

LIST OF REFERENCE NUMERALS

[0065] 1 optical component

[0066] 2 pump signal generator

[0067] 3 first substrate

[0068] 4 top layer

[0069] 5 scattering structures

[0070] 5a optical antennas

[0071] 6 dielectric material

[0072] 6a dielectric pillar

[0073] 7 active media

[0074] 8 electromagnetic radiation

[0075] 9 spacing between scattering structures

[0076] 10 height of the dielectric pillar

[0077] 11 external input

[0078] 12 array of scattering structures

[0079] 13 unit cell

[0080] 15 metallic layer

[0081] 16 second substrate

[0082] 17 spacer element

[0083] 18 layer of rubbed polymide

[0084] 19 seal

[0085] 20 phase mask

[0086] X in-plane direction

[0087] Y in-plane direction

[0088] Z height direction