Variable Phase Devices

Abstract

The present embodiment relates to a variable phase device having a new device structure capable of solving various technical problems. The variable phase device has M (M is an integer greater than 2) pixels arranged in one dimension or two dimensions and each emitting light or modulating light. The arrangement period of the M pixels is lower than the wavelength of the incident light and is constant along a specified direction. Each of the M pixels includes N (N is an integer greater than 2) sub-pixels each having a structure that sets the phase of the emitted light to be variable. In each of the M pixels, the N partial light beams output from the N sub-pixels are synthesized into light with a single phase in the far field.

Description

Technical Field

[0001] The present invention relates to a variable phase device. Background Art

[0002] Patent Document 1 discloses a phase modulation type spatial light modulator having a plurality of pixels arranged two-dimensionally. Non-Patent Documents 1 and 2 disclose gate modulation type metasurfaces.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2008-250220

[0006] Non-patent literature

[0007] Non-patent document 1: Yao-Wei Huang et al., "Gate-Tunable Conducting Oxide Metasurfaces", Nano Letters, 2016, 16(9), pp 5319-5325

[0008] Non-patent document 2: Ghazaleh Kafaie Shirmanesh et al., "Dual-Gated Active Metasurface at 1550nm with Wide (>300°) Phase Tunability", Nano Letters, 2018, 18(5), pp 2957-2963 Summary of the invention

[0009] Problems to be solved by the invention

[0010] The inventors have studied the above-mentioned prior art and found the following technical problems. That is, currently, optical devices for spatially modulating the phase of light are being used. Such optical devices capable of phase modulation have a plurality of pixels arranged in one or two dimensions, and give different phases to each pixel, thereby performing spatial phase modulation. However, sometimes, due to different device structures, technical problems such as limitations on the variable range of phase due to structural limitations, or differences in the light intensity of each pixel corresponding to the phase, arise. It is expected that a new device structure that can solve such various technical problems will be obtained.

[0011] An object of one embodiment of the present invention is to provide a variable phase device having a new device structure that can solve various technical problems faced by existing optical devices capable of phase modulation.

[0012] Technical solutions to solve problems

[0013] In order to solve the above-mentioned technical problems, an example of the present embodiment provides a variable phase device, which has M (M is an integer greater than 2) pixels. The M pixels can each emit light or modulate light, and are arranged one-dimensionally along a first direction on a reference plane, or are arranged two-dimensionally along both the first direction and a second direction intersecting the first direction. The arrangement period defined by the distance between the centers of the M pixels adjacent to each other at least along the first direction is lower than the wavelength of the incident light and is constant along the first direction. In addition, each of the M pixels includes N (N is an integer greater than 2) sub-pixels each having a structure capable of changing the phase of the incident light. In addition, in each of the M pixels, the N partial light beams output from the N sub-pixels are synthesized into light with a single phase in the far field.

[0014] Effects of the Invention

[0015] According to an example of the present embodiment, a variable phase device having a new device structure that can solve various technical problems faced by conventional optical devices capable of phase modulation can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 FIG. 1 is a plan view showing a metasurface 1A as a variable phase device according to the first embodiment of the present invention.

[0017] Figure 2 is an enlarged top view of a pixel 10.

[0018] Figure 3 It is along Figure 2 The cross-sectional view taken along line III-III of shows the cross-sectional structure of each pixel 10 included in the supersurface 1A.

[0019] Figure 4 : is a circuit diagram showing the structure of the driving circuit 2.

[0020] Figure 5 It is a cross-sectional view showing a structure in which the metasurface 1A includes a driving circuit 2 .

[0021] Figure 6 (a)~ Figure 6 (d) is a diagram for explaining the operation of the driving circuit 2 of the pixels 10 in the m-th column.

[0022] Figure 7 It is a plan view showing the structure of the driving circuit 2 of each pixel 10 .

[0023] Figure 8 It is along Figure 7 The cross-sectional view taken along line VIII-VIII of EMBODIMENT 1 shows the cross-sectional structure of the driving circuit 2 of each pixel 10 .

[0024] Fig. 9 (a)~ Fig. 9 (d) is a cross-sectional view showing each step of an example of a method for manufacturing the metasurface 1A including the driving circuit 2 .

[0025] Fig.10 It is a graph showing a complex plane indicating the phase and intensity of the emitted light.

[0026] Fig.11 1 is a graph simulating a state where two partial light beams output from two sub-pixels 10 a and 10 b are combined, and shows a case where the phase difference between the partial light beams from the sub-pixels 10 a and 10 b is π / 2 (rad).

[0027] Fig.12 This is a graph simulating a state where two partial light beams output from two sub-pixels 10 a and 10 b are combined, and shows a case where the phase difference between the partial light beams from the sub-pixels 10 a and 10 b is 0 (rad).

[0028] Fig.13 As a comparative example, this is a graph simulating a case where the phase difference between the partial light beams from the sub-pixels 10 a and 10 b is set to 0 (rad) when the arrangement period of the pixels 10 is sufficiently larger than the wavelength of the incident light.

[0029] Fig.14 1 is a plan view showing a case where the number N of sub-pixels included in one pixel 10 is three.

[0030] Fig.15 It is along Fig.14 A cross-sectional view taken along line XV-XV is shown.

[0031] Fig.16 It is a graph showing a complex plane indicating the phase and intensity of the emitted light.

[0032] Fig.17 It is a plan view showing a case where the widths Wa and Wb of the partial films 11 a and 11 b are equal to each other.

[0033] Fig.18 It is along Fig.17 A cross-sectional view taken along line XVIII-XVIII is shown.

[0034] Fig.19It is a plan view showing a case where N1 sub-pixels having different partial film widths of the metal film 11 in the pixel 10 are repeatedly arranged with N2 periods (N1 and N2 are integers greater than or equal to 2).

[0035] Fig. 20 1 is a diagram showing a cross-sectional structure of a pixel 10A according to a fourth modification.

[0036] Fig.21 It is a plan view showing the shape of the metal film 11 as a fifth modification.

[0037] Fig. 22 This is a diagram showing an enlarged cross section of two mutually adjacent sub-pixels 10d and 10e.

[0038] Fig.23 FIG. 1 is a top view showing a metasurface 1B as a sixth variation.

[0039] Fig.24 It is a plan view showing one pixel 20 in an enlarged manner.

[0040] Fig.25 It is a diagram showing the structure of the driving circuit 2A.

[0041] Fig.26 It is a plan view showing an enlarged view of one pixel 30 included in the variable phase device according to the second embodiment of the present invention.

[0042] Fig. 27 It is along Fig.26 A cross-sectional view taken along line XXVII-XXVII is shown.

[0043] Fig.28 1 is a diagram showing a cross-sectional structure of one pixel 40 included in a variable phase device according to a third embodiment of the present invention.

[0044] Fig.29 It is a schematic diagram showing an enlarged view of one pixel 10 among a plurality of pixels 10 arranged along the direction D1.

[0045] Fig.30 This is a graph simulating a state where two partial light beams emitted from the sub-pixels 10 a and 10 b are combined, and shows a case where the period T is 1000 nm.

[0046] Fig.31 This is a graph simulating a state where two partial light beams emitted from the sub-pixels 10 a and 10 b are combined, and shows a case where the period T is 1600 nm.

[0047] Fig.32 Schematically shows four pixels 10 arranged along the direction D1.

[0048] Fig.33 1 is a graph simulating the state of light emission from four pixels 10 , and shows a case where the width U of the gap 50 is set to 0 nm.

[0049] Fig.34 This is a graph simulating the state of light emission from four pixels 10 , and shows a case where the width U of the gap 50 is set to 100 nm.

[0050] Fig.35 This is a graph simulating the state of light emission from four pixels 10 , and shows a case where the width U of the gap 50 is set to 200 nm.

[0051] Fig.36 This is a graph simulating the state of light emission from four pixels 10 , and shows a case where the width U of the gap 50 is set to 300 nm. DETAILED DESCRIPTION

[0052] [Description of Embodiments of the Invention of the Present Application]

[0053] First, the contents of the embodiments of the present invention will be described by individually giving examples.

[0054] (1) The variable phase device of this embodiment, as one mode thereof, has M (M is an integer greater than 2) pixels. The M pixels can each emit light or modulate light, and are arranged one-dimensionally along a first direction on a reference plane, or are arranged two-dimensionally along both the first direction and a second direction intersecting the first direction. The arrangement period defined by the distance between the centers of the M pixels adjacent to each other at least along the first direction is lower than the wavelength of the incident light and is constant along the first direction. In addition, the M pixels each include N (N is an integer greater than 2) sub-pixels each having a structure capable of changing the phase of the incident light. In addition, in each of the M pixels, the N partial light beams output from the N sub-pixels are synthesized into light with a single phase in the far field.

[0055] In a variable phase device having a structure as described above, the arrangement period of M pixels is less than the wavelength and is constant along a specific direction. According to the new understanding of the inventors, in such a structure, when N partial light beams with different wavelengths are output from N sub-pixels contained in one pixel, these partial light beams are synthesized with each other and synthesized into light (one light beam) with a single phase and uniform intensity in the far field (for example, a distance of 1 wavelength or several wavelengths from the pixel surface). The single phase and uniform intensity are not just the average of N values, but become the value of vector synthesis of the phase and intensity of each of the N partial light beams. Therefore, for example, even if a phase value cannot be achieved in the existing pixel structure due to various restrictions, the desired phase value can be achieved by appropriately controlling the phase of the partial light beams output from the N sub-pixels. In addition, as the phase changes, the light intensity of the sub-pixel also changes in various ways. Therefore, even if the light intensity is uneven for each pixel in the existing pixel structure, the light intensity of the M pixels can be uniformly close by appropriately combining the phases of the N sub-pixels. In this way, according to the variable phase device, a variable phase device with a new device structure that can solve various technical problems can be provided.

[0056] (2) As one method of the present embodiment, in each of the M pixels, the initial phases of the N sub-pixels may be different from each other. For example, with this structure, the variable range of the phase of each pixel can be expanded. In addition, as one method of the present embodiment, it is preferred that the initial phases of the N sub-pixels are staggered by 2π / N (rad). If the initial phases of the N sub-pixels are staggered by 2π / N (rad), the initial phase difference between the sub-pixels can be set to the maximum, and on the other hand, the phase change width of each sub-pixel is reduced, and a large phase change of each pixel is achieved.

[0057] (3) As one mode of the present embodiment, the variable phase device may also include a stacked structure, a first metal film, a second metal film, and a driving circuit. The stacked structure has a first surface consistent with the above-mentioned reference plane and a second surface opposite to the first surface, and includes a transparent conductive layer and a dielectric layer. The first metal film is arranged on the first surface side of the stacked structure. The second metal film is arranged on the second surface side of the stacked structure, and reflects the incident light entering the stacked structure through the first surface toward the first surface. The driving circuit controls the voltage applied between the first metal film and the second metal film. In particular, the first metal film includes a plurality of partial films arranged in N sub-pixels and separated from each other. The N sub-pixels respectively include a corresponding partial film and a pair of parts among the plurality of partial films. When viewed in the stacking direction from the first surface toward the second surface, the pair of parts are exposed from the first metal film in a manner of clamping the corresponding partial film. The driving circuit may also modulate the phase of each of the N partial light beams output from the N sub-pixels. In this case, the driving circuit individually controls the potential of each of the plurality of partial films of the first metal film.

[0058] In the variable phase device, each of the N sub-pixels defined in each of the M pixels on the first surface of the stacked structure includes a pair of parts (a pair of exposed parts). When viewed from the stacking direction of the stacked structure (the direction from the first surface to the second surface), the pair of parts is arranged in a state of being exposed from the first metal film in a manner of clamping a partial film included in the first metal film. The incident light reaching one of the pair of parts is reflected by the second metal film and outputted from the other direction of the pair of parts. When the width of the first metal film and the thickness of the stacked structure are sufficiently smaller than the wavelength of the incident light, when a driving voltage is applied between the first metal film and the second metal film, induced currents in opposite directions called gap surface plasmon modes are generated on each of the first metal film and the second metal film. That is, a strong magnetic resonance (plasma resonance) is generated in the stacked structure. Through this magnetic resonance, the phase of the incident light (modulated light) passing between the first metal film and the second metal film is modulated. Here, when a driving voltage is applied between the first metal film and the second metal film, the electron density near the interface between the transparent conductive layer and the dielectric layer becomes high. As a result, the transparent conductive layer is partially metallized near the interface, and the effective refractive index of the stacked structure changes. The modulation amount in the above-mentioned phase modulation depends on the effective refractive index of the stacked structure. Therefore, by changing the driving voltage, the effective refractive index can be controlled, and then the phase of the emitted light (the incident light reflected by the second metal film, that is, the light output after phase modulation) can be controlled. In addition, this structure is a kind of dynamic metasurface, called a gate modulation metasurface. In the variable phase device, in each of the N sub-pixels, the stacked structure includes the above-mentioned pair of parts. In addition, the first metal film includes a plurality of partial films respectively arranged in the sub-pixels and separated from each other. The driving circuit individually controls the potentials of the plurality of partial films, thereby enabling independent phase modulation to be performed on each sub-pixel. Therefore, according to the variable phase device, sub-pixels each having a structure that can change the phase of the incident light can be appropriately realized.

[0059] (4) As one mode of the present embodiment, the variable phase device may also further include a stacked structure, a first metal film, a second metal film, and a driving circuit. The stacked structure has a first surface that is consistent with a reference surface and to which incident light arrives, and a second surface opposite to the first surface, and includes a transparent conductive layer and a dielectric layer. The first metal film is arranged on the first surface side of the stacked structure. The second metal film is arranged on the second surface side of the stacked structure. In addition, the second metal film reflects the incident light incident into the stacked structure via the first surface toward the first surface. The driving circuit controls the voltage applied between the first metal film and the second metal film. In particular, the first metal film includes a plurality of partial films that are respectively arranged in N sub-pixels and separated from each other. The N sub-pixels respectively include a corresponding partial film among the plurality of partial films and a pair of portions exposed from the first metal film in a manner of clamping the corresponding partial film when viewed in the stacking direction from the first surface toward the second surface. In such a manner that the initial phases of the N sub-pixels are different from each other, the widths of the plurality of partial films arranged in each of the N sub-pixels, which are defined along the first direction, are different from each other. Alternatively, the drive circuit may modulate the phase of each of the N partial light beams output from the N sub-pixels. In this case, the drive circuit controls the potential of each of the plurality of partial films of the first metal film individually or collectively.

[0060] In this structure, each sub-pixel has the above-mentioned gate modulation metasurface structure. Therefore, the phase can be controlled for each sub-pixel. In addition, in the variable phase device, the initial phases of the N sub-pixels are different from each other, and the driving circuit controls the voltage between each of the multiple partial films and the second metal film individually or collectively. For example, through this structure, the variable range of the phase of each pixel can be enlarged. In addition, as a method of this embodiment, the initial phases of the N sub-pixels can also be staggered by 2π / N (rad). In this case, the initial phase difference between the sub-pixels is set to the maximum, and on the other hand, the phase change width of each sub-pixel is reduced, and a large phase change of each pixel is achieved.

[0061] (5) As one mode of the present embodiment, the variable phase device may also include a refractive index modulation layer, a Si film, a metal film, and a driving circuit. The refractive index modulation layer has a first surface consistent with a reference surface and a second surface corresponding to the first surface, and is composed of a dielectric. The Si film is arranged on the first surface side of the refractive index modulation layer. The metal film is arranged on the second surface side of the refractive index modulation layer. In addition, the metal film reflects the incident light that is incident into the refractive index modulation layer via the first surface toward the first surface. The driving circuit controls the voltage applied between the Si film and the metal film. In particular, the Si film includes a plurality of partial films that are respectively arranged in N sub-pixels and separated from each other. The driving circuit may also modulate the phases of the N partial light beams output from the N sub-pixels. In this case, the driving circuit individually controls the potentials of the plurality of partial films in the Si film. For example, even with this structure, each sub-pixel can be independently phase controlled.

[0062] (6) As one mode of the present embodiment, the variable phase device may also include an electro-optical crystal layer, a first transparent electrode film, a light reflecting surface, a second transparent electrode film, and a driving circuit. The electro-optical crystal layer has a first surface that is consistent with a reference surface and a second surface that is opposite to the first surface. The first transparent electrode film is arranged on the first surface side of the electro-optical crystal layer. The light reflecting surface is arranged on the second surface side of the electro-optical crystal layer. In addition, the light reflecting surface reflects the incident light that is incident into the electro-optical crystal layer via the first surface toward the first surface. The second transparent electrode film is arranged between the light reflecting surface and the second surface of the electro-optical crystal layer. The driving circuit controls the voltage applied between the first transparent electrode film and the second transparent electrode film. In particular, at least one of the first transparent electrode film and the second transparent electrode film includes a plurality of partial films that are respectively arranged in N sub-pixels and separated from each other. The driving circuit may also modulate the phases of each of the N partial light beams output from the N sub-pixels. In this case, the driving circuit individually controls the potentials of each of the plurality of partial films included in at least one of the first transparent electrode film and the second transparent electrode film. For example, with this structure, each sub-pixel can also be independently phase controlled.

[0063] (7) As one mode of the present embodiment, the variable phase device may also include an electro-optical crystal layer, a first transparent electrode film, a light reflecting surface, a second transparent electrode film, and a driving circuit. The electro-optical crystal layer has a first surface consistent with a reference surface and a second surface opposite to the first surface. The first transparent electrode film is arranged on the first surface side of the electro-optical crystal layer. The light reflecting surface is arranged on the second surface side of the electro-optical crystal layer. In addition, the light reflecting surface reflects the incident light that is incident into the electro-optical crystal layer via the first surface toward the first surface. The second transparent electrode film is arranged between the light reflecting surface and the second surface of the electro-optical crystal layer. The driving circuit controls the voltage applied between the first transparent electrode film and the second transparent electrode film. In particular, at least one of the first transparent electrode film and the second transparent electrode film includes a plurality of partial films that are respectively arranged in N sub-pixels and separated from each other. In such a way that the initial phases of the N sub-pixels are different from each other, the optical distance between the second transparent electrode film and the light reflecting surface is different between the N sub-pixels. The driving circuit may also modulate the phases of the N partial light beams output from the N sub-pixels. In this case, the potential of the plurality of partial films included in at least any one of the first transparent electrode film and the second transparent electrode film is controlled individually or collectively. For example, through this structure, each sub-pixel can also be independently phase controlled. In addition, in the variable phase device, the optical distance between the second transparent electrode film and the light reflecting surface is different between the N partial films of each pixel (one-to-one corresponding to the N sub-pixels, respectively), so that the initial phases of the N sub-pixels are different from each other. Moreover, the driving circuit controls the voltage of the plurality of partial films individually or collectively. For example, through this structure, the phase variable range of each pixel can be enlarged.

[0064] In addition, as one mode of this embodiment, the initial phases of the N sub-pixels are preferably shifted by 2π / N (rad). In this case, the initial phase difference between the sub-pixels can be set to the maximum, while on the other hand, the phase change width of each sub-pixel is reduced and a large phase change of each pixel is achieved.

[0065] Each aspect cited in the column of [Description of Embodiments of the Invention of the Present Application] is applicable to each of all the remaining aspects or all combinations of the remaining aspects.

[0066] [Details of the embodiments of the present invention]

[0067] The specific structure of the variable phase device of this embodiment is described in detail below with reference to the accompanying drawings. In addition, the present invention is not limited to these examples, and is represented by the claims, and is intended to include all changes within the scope and meaning equivalent to the claims. In addition, in the description of the drawings, the same elements are marked with the same symbols and repeated descriptions are omitted.

[0068] (First Embodiment)

[0069] Figure 1 1 is a top view of a metasurface 1A as a variable phase device as an embodiment of the present invention. The metasurface 1A of this embodiment is called a "gate modulation type metasurface". The "metasurface" is formed by arranging a plurality of unit structures that are sufficiently smaller than the wavelength of the incident light on a flat surface, and changing the phase, intensity, or polarization state of the incident light for each unit structure. There are various structures on the metasurface, but the metasurface 1A of this embodiment has a structure called a gap plasma type. The metasurface 1A is a flat-plate-shaped device extending along directions D1 and D2 that intersect (e.g., orthogonal) with each other, and the direction that intersects (e.g., orthogonal) with both directions D1 and D2 is set as the thickness direction (or stacking direction).

[0070] M (M is an integer greater than or equal to 2) pixels 10 are formed on the main surface 1a of the metasurface 1A. The M pixels 10 are arranged in one dimension along the direction D1 (first direction). The arrangement period W1 of the M pixels 10 (the distance between the centers of adjacent pixels 10 defined along the direction D1) is lower than the wavelength of the incident light and is constant along the direction D1. In addition, the arrangement period W1 may be less than 50% of the wavelength of the incident light. The wavelength of the incident light is, for example, in the range of 400 to 3000 nm, and in one example is 1550 nm. The arrangement period W1 corresponding to the wavelength of the incident light is, for example, in the range of 200 to 1500 nm, and in one example is 400 nm. The planar shape of each pixel 10 is rectangular (for example, the direction D2 intersecting the direction D1 as the arrangement direction is set to a rectangular shape with a long side direction). The width L1 of each pixel 10 in the direction D1 (the distance between the edges of each pixel defined along the direction D1) is, for example, in the range of 200 to 400 nm. The metasurface 1A is used for various purposes such as lens application and hologram formation by modulating the phase of incident light reaching the main surface 1 a for each pixel 10 individually.

[0071] Figure 2 is an enlarged top view of a pixel 10. Figure 2 As shown, each pixel 10 includes N (N is an integer greater than 2, and the figure illustrates the case of N=2) sub-pixels 10a and 10b. In addition, the number N of sub-pixels may be the same as or different from the number M of pixels 10. The sub-pixels 10a and 10b are equivalent to the above-mentioned unit structure, and each has a structure that can change the phase of the incident light. The N sub-pixels 10a and 10b are arranged in a row along the arrangement direction of the M pixels 10 (direction D1 in this embodiment). The arrangement direction of the sub-pixels 10a and 10b may also intersect with the arrangement direction of the M pixels 10. The widths of the sub-pixels 10a and 10b, defined along the arrangement direction, are equal to each other. When N is greater than 3, the arrangement period of the sub-pixels (the center-to-center distance between adjacent sub-pixels along the direction D1) is constant along the arrangement direction of the N sub-pixels.

[0072] Figure 3 It is along Figure 2 The cross-sectional view along the line III-III of FIG. 1 shows the cross-sectional structure of each pixel 10 included in the super surface 1A. Figure 3 As shown, the metasurface 1A includes a metal film 5, a stacked structure 7 stacked on the metal film 5, and a metal film 11 provided on the stacked structure 7. That is, the stacked structure 7 is provided between the metal film 5 and the metal film 11.

[0073] The stacked structure 7 is a flat film extending along the directions D1 and D2. The stacked structure 7 has a main surface 7a and a back surface 7b. Modulated light (incident light that should be output as output light after phase modulation) L is input as incident light to the main surface 7a. The modulated light L is, for example, a laser and has linear polarization. The main surface 7a and the back surface 7b are opposite to each other in the thickness direction of the stacked structure 7. The interval between the main surface 7a and the back surface 7b (i.e., the thickness of the stacked structure 7) is set to be sufficiently smaller than the wavelength of the modulated light L. The thickness of the stacked structure 7 is, for example, in the range of 10 to 100 nm. The stacked structure 7 has a semiconductor layer 3 and a dielectric layer 4 stacked along the thickness direction of the stacked structure 7.

[0074] The semiconductor layer 3 is an inorganic film (transparent conductive layer) having light transmittance and electrical conductivity. Light transmittance refers to a property of extremely low absorption (e.g., light absorption rate of 20% or less) with respect to the wavelength of the modulated light L. Also, electrical conductivity refers to an extremely low resistivity (e.g., resistivity of 10 -6 Ω·m or less). The semiconductor layer 3 of the present embodiment includes at least one of indium oxide (In2O3) and zinc oxide (Zn2O3) whose resistance is reduced by a dopant. The dopant for indium oxide is, for example, Sn. Indium oxide doped with Sn is called ITO. In addition, the dopant for zinc oxide is, for example, Al or Ga. Zinc oxide doped with Al is called AZO. Zinc oxide doped with Ga is called GZO. The thickness of the semiconductor layer 3 is, for example, in the range of 5 to 30 nm, and in one example is 20 nm.

[0075] The dielectric layer 4 is an inorganic film having light-transmitting properties and insulating properties. The insulating properties refer to a very high resistivity (for example, a resistivity of 10 -6 The dielectric layer 4 includes, for example, at least one of aluminum oxide (Al2O3), silicon oxide (SiO2), silicon nitride (Si3N4) and hafnium oxide (HfO2). The thickness of the dielectric layer 4 is, for example, in the range of 3 to 10 nm, and is 5 nm in one example. In the present embodiment, the dielectric layer 4 is located on the main surface 7a side relative to the semiconductor layer 3.

[0076] In addition, in the present embodiment, the semiconductor layer 3 is provided on the back surface 7b side, and the dielectric layer 4 is provided on the main surface 7a side, but the semiconductor layer 3 may be provided on the main surface 7a side, and the dielectric layer 4 may be provided on the back surface 7b side. In addition, in the present embodiment, the semiconductor layer 3 constitutes the back surface 7b, and the dielectric layer 4 constitutes the main surface 7a, but other layers may be provided between the semiconductor layer 3 and the dielectric layer 4 and the main surface 7a and / or the back surface 7b. In addition, other layers may be provided between the semiconductor layer 3 and the dielectric layer 4.

[0077] The metal film 11 is an example of the first metal film of the present embodiment, has electrical conductivity and light shielding properties, and functions as a nanoantenna of a super surface structure. The metal film 11 is disposed on the main surface 7a side of the stacked structure 7. The metal film 11 is a film made of a metal such as gold (Au). The film thickness of the metal film 11 is, for example, in the range of 30 to 100 nm, and is 50 nm in one example. The metal film 11 includes: a partial film 11a disposed on the stacked structure 7 of the sub-pixel 10a, and a partial film 11b disposed on the stacked structure 7 of the sub-pixel 10b. Figure 2 As shown, the partial films 11a and 11b are arranged along the direction D1 and are separated from each other. The center position of each partial film 11a and 11b in the direction D1 coincides with the center position of each sub-pixel 10a and 10b in the same direction. The widths Wa and Wb of the partial films 11a and 11b in the direction D1 are set smaller than the widths of the sub-pixels 10a and 10b in the same direction, and are set sufficiently smaller than the wavelength of the modulated light L. In addition, the widths Wa and Wb are different from each other. The arrangement period of the partial films 11a and 11b is, for example, in the range of 100 to 500 nm, and the ratio of the widths Wa and Wb to the thickness (duty ratio) is, for example, in the range of 0.1 to 0.9.

[0078] As described above, the widths Wa and Wb of the partial films 11a and 11b are smaller than the widths of the sub-pixels 10a and 10b, respectively. Moreover, the partial films 11a and 11b are arranged at the substantially central portions of the sub-pixels 10a and 10b in the direction D1. Figure 2 and Figure 3 As shown, the stacked structure 7 includes a pair of parts 71 and 72 in each sub-pixel 10a and 10b. When viewed from the thickness direction of the stacked structure 7, the pair of parts 71 and 72 are respectively arranged at a pair of positions sandwiching the partial film 11a (or 11b) and exposed from the metal film 11. The arrangement direction (i.e., direction D1) of the pair of parts 71 and 72 is consistent with the polarization direction of the modulated light L.

[0079] The metal film 5 is an example of the second metal film of the present embodiment. The metal film 5 is disposed on the back surface 7b side of the stacked structure 7. In one example, the metal film 5 is in contact with the back surface 7b. The metal film 5 reflects the modulated light L input into the stacked structure 7 toward the main surface 7a. The metal film 5 is composed of a metal such as gold (Au), for example. The film thickness of the metal film 5 is thicker than that of the metal film 11, for example, in the range of 80 to 200 nm, and in one example, 150 nm. The metal film 5 is disposed in each of the M pixels 10 and is located in each pixel 10. The metal films 5 of adjacent pixels 10 are separated from each other. The planar shape of the metal film 5 is substantially the same as the planar shape of the pixel 10. In one example, the planar shape of the metal film 5 is rectangular (for example, a rectangular shape with the direction D2 set as the long side direction).

[0080] Figure 4 2 is a circuit diagram showing the structure of the driving circuit 2. The driving circuit 2 controls the voltage applied between the metal film 11 and the metal film 5 for each pixel 10 independently. The driving circuit 2 of this embodiment sets the potential of the partial films 11a and 11b to a common reference potential (GND potential), and uses the transistor 25 to control the voltage of the metal film 5 for each pixel 10 individually. In addition, Figure 4 The driving circuits 2 for two pixels 10 are partially shown in FIG. 1 , but the structure of the driving circuits 2 for other pixels 10 is the same.

[0081] The drive circuit 2 has a gate drive wiring 23 and M voltage supply wirings 24. The gate drive wiring 23 extends along the arrangement direction (direction D1) of the M pixels 10. The M voltage supply wirings 24 extend respectively along the direction (direction D2) intersecting the arrangement direction of the M pixels 10, and are arranged in the direction D1. The gate drive wiring 23 is electrically connected to the control terminal (gate) of the transistor 25 provided in each pixel 10. The voltage supply wiring 24 of the mth column (m=1, 2, ..., M) is electrically connected to a current terminal (e.g., source) of the transistor 25 provided in the pixel 10 located in the mth column. The other current terminal (e.g., drain) of the transistor 25 is electrically connected to the metal film 5 of the pixel 10 via the wiring in the pixel 10.

[0082] In addition, the driving circuit 2 also has a plurality of capacitors 26 provided in each pixel 10. The capacitor 26 is an example of a voltage holding unit in the present embodiment, and the voltage applied to the metal film 5 of each pixel 10 is held in each metal film 5. As a voltage holding unit, in addition to a capacitor, various structures capable of holding a voltage can also be applied. The capacitor 26 is, for example, a parallel plate capacitor. One electrode of the capacitor 26 is connected to the metal film 5, and the other electrode is connected to a constant potential region (e.g., a reference potential region). The metal film 5 can also serve as one electrode of the capacitor 26.

[0083] Figure 5 1 is a cross-sectional view showing a structure in which the metasurface 1A is provided with a driving circuit 2. In this case, the driving circuit 2 can be configured as a substrate-shaped component including a plurality of transistors 25. The driving circuit 2 is located on the back side 7b relative to the stacked structure 7. Each transistor 25 is arranged corresponding to each pixel 10, and is located in each pixel 10 when viewed from the thickness direction of the stacked structure 7. The transistor 25 is, for example, a thin film transistor arranged on a substrate composed of a dielectric. On each transistor 25, a metal film 5 is arranged via an insulating film.

[0084] Figure 6 (a)~ Figure 6 (d) is a diagram for explaining the operation of the driving circuit 2 in the pixels 10 of the m-th column. Figure 6 In (a) to (d), the portion with the intended voltage value is indicated by a dotted line. Figure 6 In the state shown in (a), no voltage is applied to the gate drive wiring 23 and the m-th column voltage supply wiring 24, and the transistor 25 becomes non-conductive. Figure 6 As shown in (b), when a predetermined gate voltage Vg is applied to the gate drive wiring 23, the transistor 25 becomes conductive, and the m-th column voltage supply wiring 24 and the metal film 5 are connected to each other via the transistor 25. Figure 6 As shown in (c), a driving voltage Vd is applied to the m-th column voltage supply wiring 24. The voltage value of the driving voltage Vd is independently set for each pixel 10 based on the desired phase modulation pattern presented by the metasurface 1A. Thus, the driving voltage Vd is applied to the metal film 5 via the transistor 25, and at the same time, the driving voltage Vd is held by the capacitor 26. Then, as shown in Figure 6 As shown in (d), the gate voltage Vg is not applied from the gate drive wiring 23, and the supply of the drive voltage Vd from the m-th column voltage supply wiring 24 is stopped. At this time, the transistor 25 becomes non-conductive again, but the voltage of the metal film 5 is maintained at the drive voltage Vd by the capacitor 26. This operation is performed successively or simultaneously with respect to all pixels 10, and the drive circuit 2 individually controls the drive voltage Vd of the plurality of metal films 5, thereby presenting a desired phase modulation pattern on the metasurface 1A, and modulating the phase of the modulated light L for each pixel 10.

[0085] Figure 7 2 is a top view showing the structure of the driving circuit 2 of each pixel 10. Figure 8 It is along Figure 7 The cross-sectional view taken along the line VIII-VIII of FIG. 1 shows the cross-sectional structure of the driving circuit 2 of each pixel 10. Figure 8As shown, the driving circuit 2 has a semiconductor layer 21 of a first conductivity type (for example, p-type) and insulating layers 27 and 28 arranged on the semiconductor layer 21. The semiconductor layer 21 can be a semiconductor substrate itself, or a semiconductor film (single crystal film, polycrystalline film, or amorphous film) formed on a different type of substrate. A transistor 25 is provided on the surface 21c of the semiconductor layer 21 (that is, the main surface of the semiconductor substrate, or the main surface of a substrate-like component composed of a different type of substrate and a semiconductor film). In the case where the semiconductor layer 21 is a semiconductor film formed on a different type of substrate, the transistor 25 is called a thin film transistor. The semiconductor substrate constituting the semiconductor layer 21, or the different type of substrate and the semiconductor film constituting the semiconductor layer 21 make the surface 21c and the back side 7b of the stacked structure 7 (refer to Figure 3 ) are opposite to each other and are integrated with the stacked structure 7.

[0086] As an example, the semiconductor layer 21 is mainly composed of Si to which impurities of a first conductivity type (e.g., p-type) are added. Semiconductor regions 21a and 21b of a second conductivity type (e.g., n-type) are formed in the semiconductor layer 21. The semiconductor regions 21a and 21b are mainly composed of Si to which impurities of a second conductivity type are added. The semiconductor regions 21a and 21b are arranged at intervals from each other and exposed on the surface 21c of the semiconductor layer 21. The semiconductor region 21a forms an ohmic contact with the source electrode 25b of the transistor 25 provided on the surface 21c. The semiconductor region 21b forms an ohmic contact with the drain electrode 25c of the transistor 25 provided on the surface 21c. The source electrode 25b and the drain electrode 25c are arranged at intervals on the surface 21c.

[0087] The region on the surface 21c except for the source electrode 25b and the drain electrode 25c is covered with an insulating layer 27. Figure 7 In order to facilitate understanding, only the necessary part of the insulating layer 27 is shown in the figure. The insulating layer 27 mainly contains an insulating silicon compound such as SiO2. A gate electrode 25a of the transistor 25 is provided on the insulating layer 27. The gate electrode 25a is opposite to the region of the semiconductor layer 21 located between the semiconductor region 21a and the semiconductor region 21b via the insulating layer 27. The gate electrode 25a is covered by the insulating layer 28 provided on the insulating layer 27. Figure 8 As shown, the insulating layer 28 is a protective film for protecting the entire drive circuit 2. The insulating layer 28 mainly contains, for example, SiO2. On the insulating layer 28, the metal film 5 of the pixel 10 is provided.

[0088] like Figure 7 As shown in FIG. 2 , the source electrode 25b is connected to the voltage supply wiring 24 provided on the surface 21c. The gate electrode 25a is connected to the gate drive wiring 23 via the wiring provided on the insulating layer 27. Figure 8As shown, the drain electrode 25 c is connected to the metal film 5 via a wiring 25 d that penetrates the insulating layers 27 and 28 .

[0089] The capacitor 26 is composed of a portion of the metal film 5, the semiconductor layer 21 directly below the portion, and a dielectric layer 29 interposed between the two. In addition, the semiconductor layer 21 is set to a constant potential (for example, a reference potential). In this case, the metal film 5 also serves as one electrode of the capacitor 26, and the semiconductor layer 21 also serves as the other electrode of the capacitor 26. The dielectric layer 29 is set to bury the opening formed in the insulating layers 27 and 28. The lower surface of the dielectric layer 29 is in contact with the semiconductor layer 21, and the upper surface of the dielectric layer 29 is in contact with the metal film 5. The dielectric layer 29 mainly contains, for example, SiO2.

[0090] Fig. 9 (a)~ Fig. 9 (d) is a cross-sectional view showing each step in an example of a method for manufacturing a metasurface 1A including a driving circuit 2. Fig. 9 (a)~ Fig. 9 In (d), one pixel 10 is used as a representative, but other pixels 10 are also produced at the same time as the pixel 10 and can be produced by the same method. Fig. 9 As shown in (a) of FIG. 1 , as a first step, a drive circuit 2 is prepared. The drive circuit 2 is manufactured by a known method of forming a wiring layer on a substrate having a transistor. At this time, a metal film 5 is formed on the wiring layer on the drive circuit 2 by, for example, a PLD (Physical Layer Deposition) method.

[0091] Then, if Fig. 9 As shown in (b), a physical vapor deposition method such as sputtering or an atomic layer deposition (ALD) method is used to form a semiconductor layer 3 on the metal film 5. In the sputtering method, a target material composed of the material of the semiconductor layer 3 is set in a vacuum chamber, and an inactive gas ionized by a high voltage collides with the target material to scatter the material of the semiconductor layer 3 to form a film. In the case where the semiconductor layer 3 is composed of ITO, the material of the dielectric layer 4 is, for example, at least one of SiO2, Al2O3, and HfO2.

[0092] Then, if Fig. 9 As shown in (c), a dielectric layer 4 is formed on the semiconductor layer 3 using, for example, an ALD method. Specifically, for each element constituting the dielectric layer 4, a raw material gas is introduced and purged into a film forming device, and film formation is repeated to a thickness of, for example, several angstrom orders. When the dielectric layer 4 is composed of SiO2, the material of ALD is, for example, TDMAS and oxygen plasma.

[0093] Then, if Fig. 9 As shown in (d), for example, a metal film 11 including partial films 11a and 11b is formed on the dielectric layer 4 using a lift-off method. Specifically, first, a resist is applied to the dielectric layer 4, and a plurality of openings corresponding to the partial films 11a and 11b are formed by electron beam lithography. Next, a metal film (e.g., an Au film) is evaporated on the entire surface of the dielectric layer 4 including the plurality of openings of the resist. Then, the metal film deposited on the resist is removed by removing the resist. Through the above process, the metasurface 1A of this embodiment is produced.

[0094] The effect obtained by the metasurface 1A of the present embodiment described above is described. The metasurface 1A has a MIM structure in which a metal film 5 as a light-reflecting film is sequentially stacked; a stacked structure 7 including a semiconductor layer 3 and a dielectric layer 4; and a metal film 11 including partial films 11a and 11b having limited widths Wa and Wb. In this case, Figure 2 and Figure 3 As shown, the stacked structure 7 of each sub-pixel 10a, 10b includes a pair of parts 71, 72. When viewed from the stacking direction, the pair of parts 71, 72 are respectively arranged at a pair of positions sandwiching the partial films 11a, 11b, and are exposed from the metal film 11. The modulated light L of a part 71 (or 72) of each sub-pixel 10a, 10b input from the outside of the metasurface 1A is reflected on the metal film 5, and is output from the other part 72 (or 71) of each sub-pixel 10a, 10b to the outside of the metasurface 1A. At this time, when a driving voltage Vd is applied between the partial films 11a, 11b and the metal film 5, induced currents in opposite directions called gap surface plasmon modes are generated in both the partial films 11a, 11b and the metal film 5, and a strong magnetic resonance (plasmon resonance) is generated in the stacked structure 7. Due to the magnetic resonance, the phase of the modulated light L passing between the partial film 11 a and the metal film 5 and the phase of the modulated light L passing between the partial film 11 b and the metal film 5 are modulated individually.

[0095] Here, the following equation (1) represents the phase modulation amount of the modulated light L of the magnetic resonance: The width w (=Wa or Wb) of the partial film 11a or 11b, the wavelength λ of the modulated light L, and the effective refractive index N of the stacked structure 7 are gsp In addition, k is an integer.

[0096] [Formula 1]

[0097]

[0098] As can be seen from the above formula (1), the phase modulation amount It depends on the effective refractive index N of the stacked structure 7gsp Furthermore, by changing the driving voltage Vd applied between the partial films 11a, 11b and the metal film 5, the effective refractive index N can be controlled. gsp The reason is as follows. When a driving voltage Vd is applied between the partial films 11a, 11b and the metal film 5, the electron density near the interface between the semiconductor layer 3 and the dielectric layer 4 increases due to the electric field between the partial films 11a, 11b and the metal film 5. As a result, the layered portion near the interface of the semiconductor layer 3 is metallized. The metallized layer reacts with the modulated light L, and thus the effective refractive index N of the stacked structure 7 increases. gsp In addition, in the metasurface 1A of the present embodiment, the metal film 5 is provided for each pixel 10 and is separated from each other, and the driving circuit 2 controls the driving voltage Vd of the metal film 5 for each pixel 10 individually. Thus, the thickness of the metallization layer of the semiconductor layer 3 can be independently controlled for each pixel 10, and therefore, each pixel 10 can be independently phase modulated. That is, according to the metasurface 1A of the present embodiment, the phase of M pixels 10 arranged in a one-dimensional shape can be modulated.

[0099] In addition, as can be seen from the above formula (1), the phase modulation amount It also depends on the width w of the partial films 11a and 11b. Therefore, by making the widths Wa and Wb of the sub-pixels 10a and 10b different from each other, it is possible to set an arbitrary initial phase difference between the phase of the partial light beam output from the sub-pixel 10a and the phase of the partial light beam output from the sub-pixel 10b. In addition, the initial phase refers to the phase of the emitted light (the partial light beam output from each sub-pixel) when the driving voltage Vd of the metal film 5 is set to a certain initial value (for example, 0V).

[0100] Fig.10 : is a graph showing a complex plane indicating the phase and intensity of the emitted light. Fig.10 The vertical axis is the imaginary axis, and the horizontal axis is the real axis. The figure shows a plurality of vectors V11 to V15. The length of each vector refers to the light intensity of the emitted light, and the angle around the origin refers to the phase of the emitted light. Vector V11 is, for example, the initial state of sub-pixel 10a, and represents the emitted light with a phase of 0 (rad). Vector V12 is, for example, the initial state of sub-pixel 10b, and represents the emitted light with a phase of π / 2 (rad). When a voltage is applied to the metal film 5, the phase of sub-pixel 10a changes according to the magnitude of the voltage (from vector V11 to vector V13), and at the same time, the phase of sub-pixel 10b changes (from vector V12 to vector V14). At this time, the magnitude of the vector, that is, the intensity of the emitted light, also changes.

[0101] Here, vector V15 is a composite vector of vector V13 and vector V14. According to the understanding of the inventors, the arrangement period W1 of the pixel 10 including N sub-pixels is lower than the wavelength of the incident light, and when the arrangement direction of the N sub-pixels is constant, the N partial light beams (each of which is an emitted light) output from the N sub-pixels are synthesized into light (one light beam) with a single phase and uniform intensity in the far field. The single phase and uniform intensity are not just the average of N values, but are values ​​obtained by vector synthesis of the phases and intensities of the N partial light beams. In this example, the two partial light beams from the two sub-pixels 10a and 10b are synthesized into light with a single phase and uniform intensity in the far field. The phase and intensity are represented by vector V15.

[0102] Fig.11 and Fig.12 The following are graphs simulating the synthesis of two partial light beams from two sub-pixels 10a and 10b. In these graphs, the vertical axis represents the position y (unit: μm) in the normal direction relative to the surface of the sub-pixels 10a and 10b, and the horizontal axis represents the position x (unit: μm) in the direction D1. In addition, the phase of the emitted light is represented by the depth of the color. Fig.11 represents the case where the phase difference between the light emitted from the sub-pixels 10a and 10b is π / 2 (rad), Fig.12 The case where the phase difference between the light emitted from the sub-pixels 10a and 10b is 0 (rad) is shown. Detailed simulation conditions are as follows.

[0103] Wavelength of incident light: 1.55 μm

[0104] Pixel 10 arrangement period: 800nm

[0105] Arrangement period of sub-pixels 10a and 10b: 400nm

[0106] Light source size: 200nm

[0107] Boundary conditions: Direction D1... Periodic boundary conditions, normal direction of the pixel surface... PML (Perfectly Matched Layer) absorption boundary conditions

[0108] like Fig.12 As shown in FIG. 1 , when the phases of the partial light beams output from the sub-pixels 10a and 10b are in phase, a single-phase synthetic light is naturally propagated in the far field. Fig.11 As shown, when the phases of the partial light beams output from the sub-pixels 10a and 10b are different from each other, the phases are different in the near field, but they become synthetic light of a single phase in the far field. In addition, the far field mentioned here refers to a distance of one wavelength or several wavelengths from the pixel surface, for example. This insight is the insight discovered independently by the inventors.

[0109] also, Fig.13 As a comparative example, the diagram simulates the case where the phase difference of the partial light beams from the sub-pixels 10a and 10b is set to 0 (rad) when the arrangement period of the pixels 10 is sufficiently larger than the wavelength of the incident light. The detailed simulation conditions are as follows. Fig.13 As shown, in this case, the phase does not become single in the far field either, and the outputs from the sub-pixels 10a and 10b interfere with each other at high speed, resulting in only diffracted light.

[0110] Wavelength of incident light: 1.55 μm

[0111] Pixel 10 arrangement period: 3200nm

[0112] Arrangement period of sub-pixels 10a and 10b: 1600nm

[0113] Light source size: 200nm

[0114] Boundary conditions: Direction D1... Periodic boundary conditions, Normal direction of the pixel surface... PML absorption boundary conditions

[0115] As can be seen from the above, according to this embodiment, even if the phase value cannot be realized in the existing pixel structure due to various restrictions, its phase value can be realized by appropriately controlling the phase of the sub-pixels 10a and 10b. For example, if the phase modulation range of each pixel 10 is 2π (rad), there is no limit on the phase value, which can reduce the noise light contained in the emitted light from the metasurface 1A. In addition, as the phase changes, the light intensity of the sub-pixels 10a and 10b also changes in various ways. Therefore, even in the case where the light intensity is uneven for each pixel in the existing pixel structure, by appropriately combining the phases of the sub-pixels 10a and 10b, the light intensity of the M pixels 10 can be uniformly close. In this way, according to the metasurface 1A of this embodiment, a variable phase device with a new device structure that can solve various technical problems can be provided. In addition, this effect is also obtained when the number N of sub-pixels is 3 or more.

[0116] In addition, as in the present embodiment, in each pixel 10, the widths Wa and Wb of the partial films 11a and 11b are different from each other, so that the initial phases of the sub-pixels 10a and 10b can also be different from each other. For example, by such a structure, the variable range of the phase of each pixel 10 can be enlarged. Specifically, for example, even if the possible range of phase modulation of a pixel unit (in the existing metasurface, a pixel) is -π / 2 (rad) to π / 2 (rad) due to structural reasons, by shifting the initial phases of the sub-pixels 10a and 10b by π (rad), a phase modulation of -π (rad) to π (rad), that is, a phase modulation of a width of 2π (rad), can be performed. Therefore, in various purposes such as lens use and holographic formation, the degree of freedom of phase modulation can be increased to the limit. In addition, this effect is also obtained when the number of sub-pixels N is 3 or more. In particular, if the initial phases of N sub-pixels are shifted by 2π / N (rad), the initial phase difference between the sub-pixels can be maximized, the phase change width of each sub-pixel can be reduced, and a large phase change of each pixel 10 can be achieved.

[0117] In addition, in the present embodiment, the voltage between the partial film 11a of the sub-pixel 10a and the metal film 5, and the voltage between the partial film 11b of the sub-pixel 10b and the metal film 5 are controlled together (at the same voltage) in each pixel 10, but the voltage supply wiring 24 and the transistor 25 may be provided in the sub-pixels 10a and 10b, respectively, and their voltages may be controlled independently (individually). In this case, the degree of freedom of change of the phase and intensity of the emitted light from each pixel 10 can be further increased.

[0118] (First Modification)

[0119] Fig.14 1 is a plan view showing a case where the number N of sub-pixels included in one pixel 10 is three. Fig.15 It is along Fig.14 The pixel 10 shown in these figures includes three sub-pixels 10a to 10c. The sub-pixels 10a to 10c each have a structure for modulating the phase of incident light. The sub-pixels 10a to 10c are arranged in a row along the arrangement direction (direction D1) of the pixel 10. The widths of the sub-pixels 10a to 10c defined along the arrangement direction are equal to each other. The arrangement period of the sub-pixels 10a to 10c is constant.

[0120] The metal film 11 includes a partial film 11a provided on the stacked structure 7 of the sub-pixel 10a, a partial film 11b provided on the stacked structure 7 of the sub-pixel 10b, and a partial film 11c provided on the stacked structure 7 of the sub-pixel 10c. Fig.14As shown, the partial films 11a to 11c are arranged along the direction D1 and are separated from each other. The center position of each partial film 11a to 11c in the direction D1 coincides with the center position of each sub-pixel 10a to 10c in the same direction. The widths Wa to Wc of the partial films 11a to 11c in the direction D1 are set smaller than the widths of the sub-pixels 10a to 10c in the same direction, and are set sufficiently smaller than the wavelength of the modulated light L. In addition, the widths Wa to Wc are different from each other. In the illustrated example, the width Wa of the partial film 11a of the sub-pixel 10a located at one end of the direction D1 is the smallest, and the width of the partial film gradually increases toward the sub-pixel 10c located at the other end of the direction D1. The widths Wa to Wc of the partial films 11a to 11c are within the range of 100 to 300 nm, and in one example, Wa = 220 nm, Wb = 240 nm, and Wc = 260 nm.

[0121] As described above, the widths Wa to Wc of the partial films 11a to 11c are smaller than the widths of the sub-pixels 10a to 10c, respectively. Furthermore, the partial films 11a to 11c are arranged at substantially the center of the sub-pixels 10a to 10c in the direction D1. Fig.14 and Fig.15 As shown, the stacked structure 7 includes a pair of parts 71 and 72 in each sub-pixel 10a to 10c. When viewed from the thickness direction of the stacked structure 7, the pair of parts 71 and 72 are respectively provided at a pair of positions sandwiching the partial film 11a (11b or 11c) and exposed from the metal film 11. The arrangement direction (i.e., direction D1) of the pair of parts 71 and 72 is consistent with the polarization direction of the modulated light L.

[0122] Fig.16 is a graph showing the phase and intensity of the emitted light on a complex plane. The figure shows a plurality of vectors V21 to V27. Fig.10 Similarly, the length of each vector is equivalent to the light intensity of the emitted light, and the angle around the origin is equivalent to the phase of the emitted light. Vector V21 is, for example, the initial state of sub-pixel 10a, and represents the emitted light with a phase of 0 (rad). Vector V22 is, for example, the initial state of sub-pixel 10b, and represents the emitted light with a phase of 2π / 3 (rad). Vector V23 is, for example, the initial state of sub-pixel 10c, and represents the emitted light with a phase of 4π / 3 (rad). When a voltage is applied to the metal film 5, the phases of sub-pixels 10a to 10c change according to the magnitude of the voltage. That is, vector V21 changes to vector V24, vector V22 changes to vector V25, and vector V23 changes to vector V26.

[0123] Here, vector V27 is a composite vector of vectors V24 to V26. As described in the above embodiment, when the arrangement period of the pixel 10 including sub-pixels 10a to 10c is lower than the wavelength of the incident light, and the arrangement direction along the sub-pixels 10a to 10c is constant, the three partial light beams from the sub-pixels 10a to 10c are synthesized into light (one light beam) with a single phase and uniform intensity in the far field. Therefore, in this variant, by appropriately controlling the phase of the sub-pixels 10a to 10c, a phase value that cannot be achieved in the existing pixel structure due to various restrictions can be achieved. In addition, as the phase changes, the light intensity of the sub-pixels 10a to 10c also changes in various ways. Therefore, by appropriately combining the phases of the sub-pixels 10a to 10c, the light intensities of the M pixels 10 can be made uniformly close.

[0124] In addition, as in the present variation, in each pixel 10, the widths Wa to Wc of the partial films 11a to 11c are different from each other, and thus, the initial phases of the sub-pixels 10a to 10c may also be different from each other. For example, by means of such a structure, the variable range of the phase in each pixel 10 can be enlarged. Specifically, even if the possible range of phase modulation of a pixel unit (a pixel in the existing metasurface) is -π / 3 (rad) to π / 3 (rad) due to structural reasons, for example, by making the initial phases of the sub-pixels 10a to 10c staggered by 2π / 3 (rad), a phase modulation of -π (rad) to π (rad), i.e., a phase modulation of a width of 2π (rad), can be performed. Therefore, in various purposes such as lens applications and holographic formation, the degree of freedom of phase modulation can be increased to the limit. In addition, in this case, if the initial phases of the sub-pixels 10a~10c are shifted by 2π / 3 (rad), the initial phase difference between the sub-pixels 10a~10c can be set to the maximum, the phase change width of each sub-pixel 10a~10c can be reduced, and a large phase change of each pixel 10 can be achieved.

[0125] (Second Modification)

[0126] Fig.17 This is a plan view showing a case where the widths Wa and Wb of the partial films 11 a and 11 b according to the above embodiment are equal to each other. Fig.18 It is along Fig.17The cross-sectional view of the line XVIII-XVIII shown in FIG. 1 is a cross-sectional view of the line XVIII-XVIII shown in FIG. 1 . In this way, even when the widths Wa and Wb are equal to each other, by controlling the voltages of the partial films 11a and 11b to different values, the phases of the partial light beams output from the sub-pixels 10a and 10b can be made different from each other. Therefore, as in the above-mentioned embodiment, even if the phase value cannot be achieved in the existing pixel structure due to various restrictions, its phase value can be achieved by appropriately controlling the phases of the sub-pixels 10a and 10b. In addition, by appropriately combining the phases of the sub-pixels 10a and 10b, the light intensities of the M pixels 10 can be made uniformly close. This is also the case when the number N of sub-pixels is 3 or more.

[0127] (Third Modification)

[0128] Fig.19 This is a plan view showing a case where N1 sub-pixels having different widths of a portion of the metal film 11 are repeatedly arranged with N2 periods (N1 and N2 are integers greater than 2) in the pixel 10. In this case, the pixel 10 includes (N1×N2) sub-pixels. Fig.19 Herein, an example is given in which three sub-pixels 10a to 10c having different widths of partial films 11a to 11c are repeatedly arranged in three cycles, that is, N1 = 3 and N2 = 3. Even in this case, the same effects as those of the above embodiment can be achieved.

[0129] (Fourth Modification)

[0130] Fig. 20 : is a diagram showing a cross-sectional structure of a pixel 10A of a fourth variant of the above-mentioned embodiment. The difference between this variant and the above-mentioned embodiment is the structure of the stacked structure. In the above-mentioned embodiment, the stacked structure 7 includes a semiconductor layer 3 and a dielectric layer 4. In contrast, the stacked structure 7A of this variant has a structure in which two semiconductor layers 3 and two dielectric layers 4 are alternately stacked. Specifically, a semiconductor layer 3 is provided on a metal film 5, a dielectric layer 4 is provided on the semiconductor layer 3, another semiconductor layer 3 is provided on the dielectric layer 4, and another dielectric layer 4 is provided on the other semiconductor layer 3. Moreover, a metal film 11 is provided on the other dielectric layer 4.

[0131] As in this variation, in the stacked structure, a plurality of pairs consisting of the semiconductor layer 3 and the dielectric layer 4 may be repeatedly stacked. In this case, even if the phase modulation range of each sub-pixel 10a, 10b is limited in a single pair, the phase modulation range of each sub-pixel 10a, 10b can be enlarged by stacking a plurality of pairs. According to the knowledge of the inventors, the phase modulation range is limited to 5 / 3π (rad) in a single pair, but the phase modulation range can be enlarged to 2π (rad) by stacking a plurality of pairs.

[0132] (Fifth Modification)

[0133] Fig.21 This is a plan view showing the shape of the metal film 11 as a fifth modification of the above-mentioned embodiment. In this modification, six sub-pixels 10d to 10i are provided for one pixel 10A. Fig. 22 This is a diagram showing an enlarged cross-section of two adjacent sub-pixels 10d and 10e. The sub-pixels 10d to 10i are arranged in sequence along the direction D1, and are extended with the direction D2 as the long side direction. Partial films 11d to 11i of the metal film 11A are provided on each of the sub-pixels 10d to 10i. The wavelength of the modulated light L is, for example, 1550nm. In this case, the width of each of the sub-pixels 10d to 10i in the direction D1 is smaller than the wavelength of the modulated light L, for example, 800nm. A gap X is provided between adjacent pixels 10A.

[0134] The metal film 11A is the first metal film provided on the stacked structure 7. The metal film 11A has the same structure as the metal film 11 described above except for the following points. That is, the metal film 11A of this modification further includes a pair of partial films 11j, 11k and pad portions 11m, 11n. The partial film 11j is provided on one side of the direction D2 relative to the sub-pixels 10d to 10i, extends along the direction D1, and is integrally combined with the partial films 11d, 11f, and 11h. The pad portion 11m is provided on the opposite side of the sub-pixels 10d to 10i relative to the partial film 11j, is integrally combined with the partial film 11j, and is electrically connected to the driving circuit 2, for example, via a bonding wire. Therefore, a common variable voltage V1 (refer to Figure 2 ).

[0135] The partial film 11k is provided on the other side of the sub-pixels 10d to 10i in the direction D2, extends along the direction D1, and is integrally bonded to the partial films 11e, 11g, and 11i. The pad portion 11n is provided on the opposite side of the partial film 11k from the sub-pixels 10d to 10i, is integrally bonded to the partial film 11k, and is electrically connected to the drive circuit 2, for example, via a bonding wire. Therefore, a common variable voltage V2 (see Figure 2 ).

[0136] The widths of the partial films 11d, 11f, and 11h defined along the direction D1 are equal to each other. The widths of the partial films 11e, 11g, and 11i defined along the same direction D1 are also equal to each other. In addition, the widths of the partial films 11d, 11f, and 11h are different from the widths of the partial films 11e, 11g, and 11i. In the example shown in the figure, the widths of the partial films 11e, 11g, and 11i are larger than the widths of the partial films 11d, 11f, and 11h. The center-to-center distance between adjacent partial films is 1 / 2 of the width of the sub-pixel. When the widths of the sub-pixels 10d to 10i are each 800nm, the center-to-center distance between adjacent partial films is 400nm.

[0137] As in this variation, a common voltage V1 may be applied to the partial films 11d, 11f, 11h of one of the plurality of sub-pixels 10d to 10i included in one pixel 10A, and another common voltage V2 may be applied to the partial films 11e, 11g, 11i of the other sub-pixels 10e, 10g, 10i. In this case, the same effect as that of the above-mentioned embodiment can be achieved. In particular, as in this variation, the partial films 11d, 11f, 11h to which the voltage V1 is applied and the partial films 11e, 11g, 11i to which the voltage V2 is applied may be alternately arranged.

[0138] (Sixth Modification)

[0139] Fig.23 1 is a top view of a super surface 1B as a sixth variation of the above-mentioned embodiment. On the main surface 1a of the super surface 1B, M pixels 20 are formed instead of the M pixels 10 of the above-mentioned embodiment. The M pixels 20 are arranged in two dimensions as M1 rows and M2 columns with the direction D1 set as the row direction and the direction D2 set as the column direction. In addition, M1 and M2 are integers greater than 2, and M1×M2=M. The planar shape of each pixel 20 is rectangular (for example, square). The length L2 of one side of each pixel 20 is, for example, in the range of 200 to 400 nm.

[0140] The arrangement period W2 of the pixels 20 in the column direction (the distance between the centers of adjacent pixels 20 defined along the direction D1) is lower than the wavelength of the incident light and is constant along the arrangement direction of the M2 pixels 20. Similarly, the arrangement period W3 of the pixels 20 in the row direction (the distance between the centers of adjacent pixels 20 defined along the direction D2) is lower than the wavelength of the incident light and is constant along the arrangement direction of the M1 pixels 20. In addition, the specific values ​​of the wavelength of the incident light, the arrangement period W2 and W3 are the same as the wavelength of the incident light and the arrangement period W1 of the above-mentioned embodiment. The metasurface 1B is used for various purposes such as lens use and holographic formation by modulating the phase of the light (modulated light as the incident light) input to the main surface 1a for each pixel 20 individually.

[0141] Fig.24 2 is a top view showing a pixel 20 in an enlarged manner. Fig.24 As shown, each pixel 20 includes N (N is an integer greater than 2, and the figure illustrates the case of N=3) sub-pixels 20a~20c. In addition, in this modified example, the number N of sub-pixels may be the same as or different from the number M of pixels 20. The sub-pixels 20a~20c each have a structure for modulating the phase of the incident light. The sub-pixels 20a~20c are arranged in a row along one side of the arrangement direction of the pixels 20 (in this embodiment, direction D1). The widths of the sub-pixels 20a~20c, defined along the arrangement direction, are equal to each other. The arrangement period of the sub-pixels 20a~20c (the center-to-center distance between adjacent sub-pixels along the direction D1) is constant along the arrangement direction of the sub-pixels 20a~20c.

[0142] The metal film 11 of this modified example includes: a partial film 11d provided on the stacked structure 7 of the sub-pixel 20a, a partial film 11e provided on the stacked structure 7 of the sub-pixel 20b, and a partial film 11f provided on the stacked structure 7 of the sub-pixel 20c. The partial films 11d to 11f are arranged along the direction D1 and are separated from each other. The center position of each partial film 11d to 11f specified along the direction D1 and the direction D2 coincides with the center position of each sub-pixel 20a to 20c specified along the same direction D1 and the direction D2. The width Wg of each partial film 11d to 11f defined along the direction D1 is set smaller than the width of each sub-pixel 20a to 20c defined along the same direction D1, and is set sufficiently smaller than the wavelength of the modulated light L. Similarly, the widths Wd to Wf of the partial films 11d to 11f defined along the direction D2 are set smaller than the widths of the sub-pixels 20a to 20c defined along the same direction D2, and are set sufficiently smaller than the wavelength of the modulated light L. In addition, the widths Wd to Wf are different from each other. In the illustrated example, the width Wd of the partial film 11d of the sub-pixel 20a located at one end of the direction D1 is the largest, and the width of the partial film gradually decreases toward the sub-pixel 20c located at the other end of the direction D1. The widths Wd to Wf of the partial films 11d to 11f are within the range of 50 to 400 nm, and in one example, Wd = 160 nm, We = 240 nm, and Wf = 320 nm.

[0143] As described above, the widths Wd to Wf of the partial films 11d to 11f defined along the direction D2 are smaller than the widths of the sub-pixels 20a to 20c defined along the direction D2. Moreover, the partial films 11d to 11f are arranged at the approximate central portion of the sub-pixels 20a to 20c specified along the direction D2. Therefore, the stacked structure 7 includes a pair of portions 71 and 72 in each sub-pixel 20a to 20c. When viewed from the thickness direction of the stacked structure 7, the pair of portions 71 and 72 are respectively arranged at a pair of positions sandwiching the partial film 11d (11e or 11f) and exposed from the metal film 11. The arrangement direction of the pair of portions 71 and 72 (i.e., direction D2) is consistent with the polarization direction of the modulated light L.

[0144] The cross-sectional structure of the supersurface 1B of this modification is the same as the cross-sectional structure of the supersurface 1A of the above-mentioned embodiment (see Figure 3 ). In this variation, the metal film 5 is provided for M pixels 20 and is located in each pixel 20. The metal films 5 of adjacent pixels 20 are separated from each other. The planar shape of the metal film 5 is substantially the same as the planar shape of the pixel 20. In one example, the planar shape of the metal film 5 is a square.

[0145] Fig.25: is a diagram showing the structure of the driving circuit 2A. The metasurface 1B is provided with a driving circuit 2A, instead of the driving circuit 2 of the above embodiment. The driving circuit 2A of this modified example has M1 gate driving wirings 23 and M2 voltage supply wirings 24. The M1 gate driving wirings 23 extend respectively along the row direction (i.e., direction D1) and are arranged in the column direction (i.e., direction D2). The M2 voltage supply wirings 24 extend respectively along the column direction (i.e., direction D2) and are arranged in the row direction (i.e., direction D1). The gate driving wiring 23 of the m1th row (m1=1, 2, ..., M1) is electrically connected to the control terminal (gate) of the transistor 25 provided for each pixel 20 located in the m1th row. The voltage supply wiring 24 of the m2th column (m2=1, 2, ..., M2) is electrically connected to a current terminal (e.g., source) of the transistor 25 provided for the pixel 20 located in the m2th column. The other current terminal (eg, drain) of the transistor 25 is electrically connected to the metal film 5 of the pixel 20 via wiring within the pixel 20 .

[0146] The driving circuit 2A further includes a plurality of capacitors 26 provided for each pixel 20. The capacitor 26 is an example of a voltage holding unit in this modification, and holds a voltage applied to the metal film 5 of the pixel 20 for each metal film 5. The specific structure of the capacitor 26 is as described in the above embodiment.

[0147] As in this modification, M pixels may be arranged two-dimensionally. In this case, the same effects as those of the above embodiment can be achieved.

[0148] (Second Embodiment)

[0149] Fig.26 It is a plan view showing an enlarged view of one pixel 30 included in the variable phase device according to the second embodiment of the present invention. Fig. 27 It is along Fig.26 The variable phase device of this embodiment has M pixels 30 arranged in a Figure 1 One-dimensional shape as shown, or Fig.23 The arrangement period of the M pixels 30 is lower than the wavelength of the incident light and is constant along the arrangement direction of the M pixels 30.

[0150] Each pixel 30 includes N (N is an integer greater than 2, and the figure illustrates the case of N=2) sub-pixels 30a and 30b. The sub-pixels 30a and 30b each have a structure for modulating the phase of incident light. The sub-pixels 30a and 30b are arranged in a row along the arrangement direction of the pixels 30 (direction D1 in this embodiment). The widths of the sub-pixels 30a and 30b defined along the arrangement direction are equal to each other. When N is greater than 3, the arrangement period of the sub-pixels (the center-to-center distance between adjacent sub-pixels along the direction D1) is constant along the arrangement direction of the N sub-pixels.

[0151] The main difference between the first embodiment and the second embodiment is that a substrate 13 and a refractive index modulation layer 14 are provided instead of the stacked structure 7, and a Si film 12 is provided instead of the metal film 11. Except for the above-mentioned differences, the structure of the second embodiment is the same as that of the first embodiment. The variable phase device of the second embodiment has a so-called high contrast diffraction grating (HCG: High Contrast Gratings) structure, and modulates the phase of the modulated light L for each pixel 30 by changing the refractive index of the refractive index modulation layer 14.

[0152] The substrate 13 is made of, for example, GaAs or Si, and has a flat main surface 13a and a back surface 13b. The thickness of the substrate 13 is, for example, in the range of 100 to 2000 μm. The refractive index modulation layer 14 is an inorganic dielectric layer provided on the main surface 13a of the substrate 13. The refractive index modulation layer 14 is made of a material whose refractive index changes according to the magnitude of the electric field, such as KTN (oxide crystal composed of K, Nb, and Ta), LN (oxide crystal composed of Nb, Li, and O2), or an electro-optic polymer, and its thickness is, for example, in the range of 50 nm to 1000 μm.

[0153] The Si film 12 is disposed on a surface 14a of the refractive index modulation layer 14 (the opposite side to the substrate 13). In one example, the Si film 12 is disposed on the surface 14a of the refractive index modulation layer 14 and is in contact with the surface 14a. The Si film 12 has conductivity and functions as one of a pair of electrodes for applying an electric field to the refractive index modulation layer 14. The film thickness of the Si film 12 is, for example, in the range of 100 to 1000 nm, and is 850 nm in one example. The Si film 12 includes a partial film 12a disposed on the refractive index modulation layer 14 of the sub-pixel 30a and a partial film 12b disposed on the refractive index modulation layer 14 of the sub-pixel 30b. As Fig.26As shown, the partial films 12a and 12b are arranged along the direction D1 and are separated from each other. The center position of each partial film 12a and 12b specified along the direction D1 coincides with the center position of each sub-pixel 30a and 30b specified along the same direction D1. The widths Wa and Wb of the partial films 12a and 12b defined along the direction D1 are set smaller than the widths of the sub-pixels 30a and 30b defined along the same direction D1, and are set sufficiently smaller than the wavelength of the modulated light L. The widths Wa and Wb are equal to each other. The widths Wa and Wb of the partial films 12a and 12b are, for example, in the range of 100 to 360 nm, and in one example are 240 nm. The center-to-center distance of the partial films 12a and 12b (i.e., the arrangement period of the sub-pixels 30a and 30b) is, for example, in the range of 100 to 2000 nm, and in one example is 400 nm.

[0154] The metal film 5 is provided on the other surface 14b side of the refractive index modulation layer 14. In the present embodiment, the metal film 5 is provided on the back surface 13b of the substrate 13 and is in contact with the back surface 13b. The metal film 5 reflects the modulated light input to the refractive index modulation layer 14 toward the surface 14a. In addition, the specific structure of the metal film 5 is the same as that of the above embodiment.

[0155] The variable phase device of this embodiment further includes a driving circuit (not shown). The driving circuit controls the voltage applied between the partial films 12a and 12b of the Si film 12 and the metal film 5 individually for each of the partial films 12a and 12b. Figure 4 or Fig.25 However, the transistors 25 are provided in the sub-pixels 30a and 30b, respectively, and the current terminals of these transistors 25 are electrically connected to the partial films 12a and 12b, respectively.

[0156] When a voltage is applied between the partial film 12a (or 12b) and the metal film 5, the refractive index of the refractive index modulation layer 14 changes according to the magnitude of the electric field generated thereby. As a result, the optical distance from the surface 14a (light incident surface) of the refractive index modulation layer 14 to the surface (light reflecting surface) of the metal film 5 changes, and therefore, the phase of the partial light beam (outgoing light) output from the surface 14a after being reflected by the metal film 5 depends on the magnitude of the voltage. The voltage applied between the partial film 12a, 12b of the Si film 12 and the metal film 5 is controlled individually for each partial film 12a, 12b, and therefore, the phase of the modulated light is modulated for each sub-pixel 30a, 30b. That is, even in the structure of this embodiment, as in the above-mentioned embodiment, each sub-pixel 30a, 30b can be independently phase-controlled.

[0157] (Third Embodiment)

[0158] Fig.281 is a diagram showing a cross-sectional structure of one pixel 40 included in a variable phase device according to a third embodiment of the present invention. The variable phase device of this embodiment includes M pixels 40 arranged in a Figure 1 One-dimensional shape as shown, or Fig.23 The arrangement period of the M pixels 40 is lower than the wavelength of the incident light and is constant along the arrangement direction of the M pixels 40.

[0159] Each pixel 40 includes N (N is an integer greater than 2, and the figure illustrates the case of N=2) sub-pixels 40a and 40b. The sub-pixels 40a and 40b each have a structure for modulating the phase of incident light. The sub-pixels 40a and 40b are arranged in a row along the arrangement direction of the pixels 40 (direction D1 in this embodiment). The widths of the sub-pixels 40a and 40b defined along the arrangement direction are equal to each other. When N is greater than 3, the arrangement period of the sub-pixels (the center-to-center distance between adjacent sub-pixels along the direction D1) is constant along the arrangement direction of the N sub-pixels.

[0160] The variable phase device has the same structure as the variable phase device of the first embodiment described above, except that the electro-optic crystal layer 41 is provided instead of the stacked structure 7 of the first embodiment described above. The electro-optic crystal layer 41 mainly includes a material having an electro-optic effect (Pockels effect or Kerr effect) (for example, KTN (an oxide crystal composed of K, Nb, and Ta), LN (an oxide crystal composed of Nb, Li, and O2), etc.), and has a flat main surface 41a and a back surface 41b. The thickness of the electro-optic crystal layer 41 is, for example, in the range of 10 to 1000 nm. In addition, the variable phase device has a transparent electrode film 42 (a first transparent electrode film) provided on the main surface 41a side of the electro-optic crystal layer 41 and a transparent electrode film 43 (a second transparent electrode film) provided on the back surface 41b side. The transparent electrode film 42 is provided on the main surface 41a, and in one example is in contact with the main surface 41a. The transparent electrode film 43 is provided on the back surface 41b, and in one example is in contact with the back surface 41b. The transparent electrode films 42 and 43 mainly include a material having conductivity and transmitting modulated light (for example, ITO, AZO, GZO, etc.) The thickness of the transparent electrode films 42 and 43 is, for example, in the range of 10 to 1000 nm.

[0161] The transparent electrode film 42 functions as one of a pair of electrodes for applying an electric field to the electro-optical crystal layer 41. The transparent electrode film 42 includes a partial film 42a provided on the electro-optical crystal layer 41 of the sub-pixel 40a and a partial film 42b provided on the electro-optical crystal layer 41 of the sub-pixel 40b. The partial films 42a and 42b are arranged along the direction D1 and are separated from each other. The transparent electrode film 43 functions as the other of a pair of electrodes for applying an electric field to the electro-optical crystal layer 41. The transparent electrode film 43 includes a partial film 43a provided on the electro-optical crystal layer 41 of the sub-pixel 40a and a partial film 43b provided on the electro-optical crystal layer 41 of the sub-pixel 40b. The partial films 43a and 43b are arranged along the direction D1 and are separated from each other.

[0162] The variable phase device also includes a light reflecting film 45 having a light reflecting surface 45a. The light reflecting film 45 is respectively provided on the sub-pixels 40a and 40b, and the light reflecting surface 45a is opposite to the back surface 41b of the electro-optical crystal layer 41. The light reflecting surface 45a reflects the modulated light input to the electro-optical crystal layer 41 toward the main surface 41a. The light reflecting film 45 is, for example, a metal film formed on the transparent electrode film 43, and is composed of, for example, a metal such as Au or Al. The thickness of the light reflecting film 45 is, for example, in the range of 30 to 100 nm. In addition, the transparent electrode film 43 is provided between the light reflecting surface 45a and the electro-optical crystal layer 41.

[0163] In this embodiment, the optical distance between the transparent electrode film 43 and the light reflecting surface 45a is different between the sub-pixels 40a and 40b. Specifically, a light-transmitting layer 44 is provided between the partial film 43b of the transparent electrode film 43 and the light reflecting surface 45a in the sub-pixel 40b, whereas no light-transmitting layer 44 is provided between the partial film 43a of the transparent electrode film 43 and the light reflecting surface 45a in the sub-pixel 40a. The light-transmitting layer 44 is composed of, for example, SiO2, Si3N4, air, or a semiconductor substrate (for example, GaAs or Si).

[0164] The variable phase device of this embodiment further includes a driving circuit (not shown). The driving circuit controls the voltage applied between the partial films 42a and 42b of the transparent electrode film 42 and the partial films 43a and 43b of the transparent electrode film 43 for each partial film individually. Figure 4 or Fig.25 However, the transistors 25 are provided in the sub-pixels 40a and 40b, respectively, and the current terminals of these transistors 25 are electrically connected to the partial films 42a and 42b or the partial films 43a and 43b, respectively.

[0165] When a voltage is applied between the partial film 42a and the partial film 43a, the refractive index of the electro-optical crystal layer 41 of the sub-pixel 40a changes according to the size of the electric field generated thereby. As a result, the optical distance from the main surface 41a (light incident surface) of the electro-optical crystal layer 41 to the back surface 41b changes, so the phase of the partial light beam (emitting light) reflected on the light reflecting surface 45a and output from the main surface 41a depends on the size of the voltage. The same is true for the sub-pixel 40b. Moreover, the voltage applied between the transparent electrode film 42 and the transparent electrode film 43 is controlled individually for each partial film, so that the phase of the modulated light is modulated in the sub-pixels 40a and 40b respectively. That is, even with the structure of this embodiment, as in the above-mentioned embodiment, each sub-pixel 40a and 40b can be independently phase controlled.

[0166] In addition, in the present embodiment, the optical distance between the transparent electrode film 43 and the light reflecting surface 45a is different between the sub-pixels 40a and 40b depending on the presence or absence of the light-transmitting layer 44. As a result, the initial phase of the emitted light can be made different between the sub-pixels 40a and 40b, and thus, the variable range of the phase of each pixel 40 can be enlarged. This effect is also obtained when the number of sub-pixels N is 3 or more. In particular, if the initial phases of the N sub-pixels are each staggered by 2π / N (rad), the initial phase difference between the sub-pixels can be set to the maximum, the phase change width of each sub-pixel can be reduced, and a large phase change of each pixel 40 can be achieved.

[0167] In addition, in the present embodiment, in each pixel 40, the voltage between the partial film 42a and the partial film 43a of the sub-pixel 40a, and the voltage between the partial film 42b and the partial film 43b of the sub-pixel 40b are controlled independently (individually). However, when the optical distance between the transparent electrode film 43 and the light reflecting surface 45a is different between the sub-pixels 40a and 40b, these voltages can also be controlled together (same voltage).

[0168] (specific example)

[0169] Here, in order to reduce interference between mutually adjacent pixels, a model in which a space is provided between pixels to separate the pixels from each other is considered. Fig.29 1 is a schematic diagram showing an enlarged view of one pixel 10 among a plurality of pixels 10 arranged along a direction D1. The pixel 10 includes two sub-pixels 10a and 10b arranged along the direction D1. In addition, a gap 50 is provided between adjacent pixels 10. The gap 50 does not function as a pixel.

[0170] First, a model with a period T of 1000nm is studied relative to the wavelength of the incident light of 1550nm. When the width U of the gap 50 defined along the direction D1 is 200nm, the width L1 of the pixel 10 is 800nm, and the width S1 of each of the sub-pixels 10a and 10b is 400nm. On this metasurface, the intensity ratio of sub-pixel 10a to sub-pixel 10b is set to 1:1, and the phases are set to π / 2 (rad) and 0 (rad), respectively. When light with a Gaussian function-like light intensity distribution (light source size: 200nm) is incident, the two partial light beams emitted from the sub-pixels 10a and 10b are as follows: Fig.30 In addition, Fig.11 Same, Fig.30 This is a diagram simulating the situation of synthesizing two partial light beams output from sub-pixels 10a and 10b. In this way, if the period T is smaller than the wavelength of the incident light, even if a gap 50 is provided between pixels 10, the partial light beams output from each sub-pixel 10a and 10b can be appropriately synthesized.

[0171] Next, the model with a period T of 1600nm is studied relative to the wavelength of the incident light of 1550nm. The width L1 of the pixel 10 and the width S1 of each sub-pixel 10a and 10b are the same as above, with only the width U of the gap 50 changed to 800nm. On this metasurface, the intensity ratio of sub-pixel 10a and sub-pixel 10b is set to 1:1, and the phases are set to π / 2 (rad) and 0 (rad), respectively. When light with a Gaussian function-like light intensity distribution (light source size: 200nm) is incident, the two partial light beams output from the sub-pixels 10a and 10b will not be as Fig.31 Thus, even when the width L1 of the pixel 10 is smaller than the wavelength of the incident light, when the period T is larger than the wavelength of the incident light, the partial light beams output from the sub-pixels 10a and 10b will not be combined, but will only interfere.

[0172] The present inventors further studied the appropriate size of the gap 50 . Fig.32Schematically shows four pixels 10 arranged along the direction D1. Each of these pixels 10 has two sub-pixels 10a and 10b. The width L1 of the pixel 10 is set to 800nm ​​(fixed), and the width U of the gap 50 is changed to four types: 0nm, 100nm, 200nm, and 300nm. In addition, in all pixels 10, the intensity ratio of the sub-pixel 10a to the sub-pixel 10b is set to 1:1. In addition, the synthetic phase of each pixel 10 is set to 0 (rad), π / 2 (rad), π (rad), and 3π / 2 (rad) from the left end. Specifically, the phases of the sub-pixels 10a and 10b of the pixel 10 at the left end are set to 5π / 6 (rad) and 3π / 2 (rad), respectively, the phases of the sub-pixels 10a and 10b of the second pixel 10 from the left are set to 0 (rad) and 4π / 3 (rad), respectively, the phases of the sub-pixels 10a and 10b of the third pixel 10 from the left are set to π / 2 (rad) and 11π / 6 (rad), respectively, and the phases of the sub-pixels 10a and 10b of the pixel 10 at the right end are set to π (rad) and π / 3 (rad), respectively.

[0173] Figure 33 to Figure 36 This is a diagram simulating the state where light is emitted from four pixels 10 . Fig.33 This represents the case where the width U of the gap 50 is set to 0 nm. Fig.34 This indicates the case where the width U is set to 100 nm. Fig.35 This shows the case where the width U is set to 200 nm. Fig.36 This is the case where the width U is set to 300 nm. Fig.11 The wavelength of the incident light is 1550nm.

[0174] Refer to the gap 50 Figure 34 to Figure 36 When the gap is not set, Fig.33 By comparison, it can be seen that the interference (crosstalk) between pixels is reduced. In particular, when the width U of the gap 50 is 200nm (i.e., the ratio of the width U to the period T is 20%), the interference (crosstalk) is significantly reduced. In this way, by providing the gap 50, the interference between pixels can be suppressed and a good wavefront can be formed. In addition, the width U can also be, for example, greater than 0% and less than 20% relative to the period T of the pixel.

[0175] The variable phase device of this embodiment is not limited to the examples of the above-mentioned embodiments, and is indicated by the claims, and is intended to include all changes equivalent to the claims and within the scope. For example, the above-mentioned embodiments and modifications may be arbitrarily combined according to the desired purpose and effect. In addition, in the above-mentioned embodiments and modifications, the structure of the drive circuit, the stacked structure, the refractive index modulation layer or the electro-optical crystal layer integrated is described, but in the present invention, the drive circuit and the stacked structure, the refractive index modulation layer or the electro-optical crystal layer may also be constructed as separate bodies.

[0176] In addition, in the above-mentioned embodiments and modifications, an example of applying the present invention to a device that performs phase modulation on each pixel relative to the input modulated light is described, but the present invention can also be applied to a device that emits light for each pixel. That is, a variable phase device can also have M pixels arranged in a one-dimensional or two-dimensional shape to emit light, the arrangement period of the M pixels is lower than the wavelength of the light emission and is constant, and the M pixels each include N sub-pixels each having a structure that sets the phase of the emitted light to be variable. In this case, in each of the M pixels, the N partial light beams emitted from the N sub-pixels are also synthesized into light (one light beam) with a single phase in the far field. Therefore, the same effect as the above-mentioned embodiments and modifications can be achieved.

[0177] Explanation of symbols

[0178] 1A, 1B...metasurface, 1a...main surface, 2, 2A...driving circuit, 3...semiconductor layer (transparent conductive layer), 4...dielectric layer, 5...metal film, 7, 7A...stacked structure, 7a...main surface, 7b...back surface, 10, 10A...pixel, 10a, 10b, 10c...subpixel, 11...metal film, 11a to 11f...partial film, 12...Si film, 12a, 12b...partial film, 13...substrate, 13a...main surface, 13b...back surface, 14...refractive index modulation layer, 20...pixel, 20a, 20b, 20c...subpixel, 21...semiconductor layer, 21a, 21b...semiconductor region, 21c...surface, 23...gate drive wiring, 24... Voltage supply wiring, 25...transistor, 25a...gate electrode, 25b...source electrode, 25c...drain electrode, 25d...wiring, 26...capacitor, 27, 28...insulating layer, 29...dielectric layer, 30, 40...pixel, 30a, 30b, 40a, 40b...sub-pixel, 41...electro-optical crystal layer, 41a...main surface, 41b...back surface, 42, 43...transparent electrode film, 42a, 42b, 43a, 43b...partial film, 44...light-transmitting layer, 45...light-reflecting film, 45a...light-reflecting surface, 50...gap, 71, 72...part, D1, D2...direction, L...modulated light, Vd...driving voltage, Vg...gate voltage, W1, W2...arrangement period.

Claims

1. A variable phase device, characterized in that: The device comprises: M pixels arranged one-dimensionally along a first direction on a reference plane, or arranged two-dimensionally along both the first direction and a second direction intersecting the first direction, each of the M pixels performs light emission or light modulation, wherein M is an integer greater than 2, An arrangement period defined by a distance between centers of pixels adjacent at least along the first direction among the M pixels is lower than a wavelength of incident light and is constant along the first direction, Each of the M pixels includes N sub-pixels each having a structure capable of changing the phase of the incident light, wherein N is an integer greater than or equal to 2, In each of the M pixels, the N partial light beams output from the N sub-pixels are synthesized into light having a single phase in a far field, In each of the M pixels, initial phases of the N sub-pixels are different from each other.

2. The variable phase device according to claim 1, characterized in that: The initial phases of the N sub-pixels are each offset by 2π / N rad.

3. The variable phase device according to claim 1, characterized in that: Also available: a stacked structure including a transparent conductive layer and a dielectric layer, and having a first surface that coincides with the reference surface and to which the incident light reaches, and a second surface that is opposite to the first surface; a first metal film provided on the first surface side of the stacked structure; a second metal film provided on the second surface side of the stacked structure and reflecting the incident light incident into the stacked structure via the first surface toward the first surface; as well as a driving circuit that controls a voltage applied between the first metal film and the second metal film, The first metal film includes a plurality of partial films disposed in each of the N sub-pixels and separated from each other. The N sub-pixels each include: a corresponding partial film among the plurality of partial films, and a pair of portions exposed from the first metal film in a manner of sandwiching the corresponding partial film when viewed in a stacking direction from the first surface toward the second surface. The driving circuit individually controls the potential of each of the plurality of partial films of the first metal film in order to modulate the phase of each of the N partial light beams output from the N sub-pixels.

4. The variable phase device according to claim 1, characterized in that: Also available: a stacked structure including a transparent conductive layer and a dielectric layer, and having a first surface that coincides with the reference surface and to which the incident light reaches, and a second surface that is opposite to the first surface; a first metal film provided on the first surface side of the stacked structure; a second metal film provided on the second surface side of the stacked structure and reflecting the incident light incident into the stacked structure via the first surface toward the first surface; as well as a driving circuit that controls a voltage applied between the first metal film and the second metal film, The first metal film includes a plurality of partial films disposed in each of the N sub-pixels and separated from each other. The N sub-pixels each include: a corresponding partial film among the plurality of partial films, and a pair of portions exposed from the first metal film in a manner of sandwiching the corresponding partial film when viewed in a stacking direction from the first surface toward the second surface. The widths of the plurality of partial films provided in each of the N sub-pixels and defined along the first direction are different from each other in such a manner that the initial phases of the N sub-pixels are different from each other, The driving circuit controls the potential of each of the plurality of partial films of the first metal film individually or collectively in order to modulate the phase of each of the N partial light beams output from the N sub-pixels.

5. The variable phase device according to claim 4, characterized in that: The initial phases of the N sub-pixels are each offset by 2π / N rad.

6. The variable phase device according to claim 1, characterized in that: Also available: a refractive index modulation layer having a first surface consistent with the reference surface and a second surface corresponding to the first surface, and composed of a dielectric; A Si film provided on the first surface side of the refractive index modulation layer; a metal film disposed on the second surface side of the refractive index modulation layer and reflecting the incident light incident into the refractive index modulation layer via the first surface toward the first surface; as well as a driving circuit that controls a voltage applied between the Si film and the metal film, The Si film includes a plurality of partial films provided in each of the N sub-pixels and separated from each other, The driving circuit individually controls the potential of each of the plurality of partial films in the Si film in order to modulate the phase of each of the N partial light beams output from the N sub-pixels.

7. The variable phase device according to claim 1, characterized in that: Also available: an electro-optical crystal layer having a first surface consistent with the reference surface and a second surface opposite to the first surface; A first transparent electrode film disposed on the first surface side of the electro-optical crystal layer; a light reflecting surface disposed on the second surface side of the electro-optical crystal layer and reflecting the incident light incident into the electro-optical crystal layer via the first surface toward the first surface; A second transparent electrode film is disposed between the light reflecting surface and the second surface of the electro-optical crystal layer; as well as a driving circuit that controls a voltage applied between the first transparent electrode film and the second transparent electrode film, At least one of the first transparent electrode film and the second transparent electrode film includes a plurality of partial films provided in each of the N sub-pixels and separated from each other. The driving circuit individually controls the potential of each of the plurality of partial films included in at least one of the first transparent electrode film and the second transparent electrode film in order to modulate the phase of each of the N partial light beams output from the N sub-pixels.

8. The variable phase device according to claim 1, characterized in that: Also available: an electro-optical crystal layer having a first surface consistent with the reference surface and a second surface opposite to the first surface; A first transparent electrode film disposed on the first surface side of the electro-optical crystal layer; a light reflecting surface disposed on the second surface side of the electro-optical crystal layer and reflecting the incident light incident into the electro-optical crystal layer via the first surface toward the first surface; A second transparent electrode film is disposed between the light reflecting surface and the second surface of the electro-optical crystal layer; as well as a driving circuit that controls a voltage applied between the first transparent electrode film and the second transparent electrode film, At least one of the first transparent electrode film and the second transparent electrode film includes a plurality of partial films provided in each of the N sub-pixels and separated from each other. The optical distance between the second transparent electrode film and the light reflecting surface is different between the N sub-pixels in such a way that the initial phases of the N sub-pixels are different from each other, The driving circuit controls the potentials of the plurality of partial films included in at least one of the first transparent electrode film and the second transparent electrode film individually or collectively in order to modulate the phases of the N partial light beams output from the N sub-pixels.

9. The variable phase device according to claim 8, characterized in that: The initial phases of the N sub-pixels are each offset by 2π / N rad.

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