On-chip dynamic control device based on terahertz metasurface transmission wave or surface wave front

Abstract

The invention relates to an on-chip dynamic control device for the wavefront of a terahertz metasurface transmission wave or surface wave, and belongs to the technical field of electromagnetic wave wavefront control devices. Since the traditional phase gradient metasurface fails to dynamically control the wavefront of a transmission wave or surface wave, the present invention combines an integrated photosensitive material metasurface with a spatially coded light source to realize on-chip dynamic control of the wavefront of a terahertz transmission wave or surface wave. The device deposits a dielectric layer on a metal reflective bottom plate, and the top layer of the dielectric layer is divided into two regions: an excitation region and an intrinsic region. The excitation region is composed of a metal ring array with multiple openings uniformly distributed and photosensitive materials deposited at the openings. By controlling the intensity of the pump light source irradiating the photosensitive material, a 2-bit coding unit is formed. The excitation region is constructed according to a preset coding sequence. When a circularly polarized wave is incident on the surface of the excitation region, a transmission wave or surface wave can be generated. By changing the coding sequence, the phase of the transmission wave or surface wave is reconstructed, and the wavefront of the transmission wave or surface wave is dynamically controlled, thereby realizing an on-chip dynamic control device for the wavefront of a transmission wave or surface wave.

Description

Technical Field

[0001] The present invention relates to dynamic control of terahertz transmission waves or surface waves, and belongs to the technical field of electromagnetic wave front dynamic control devices. Background Art

[0002] Electromagnetic waves can be divided into two types: transmission waves and surface waves. Transmission waves propagate in free space, while surface waves propagate on the surfaces of two different dielectric materials. Since the wavelength of surface waves is short, their wave vector is an imaginary number in the normal direction of the interface, resulting in their wave vector being larger than that of the transmission wave. Therefore, transmission waves and surface waves cannot be directly coupled and transmitted. In traditional surface wave excitation methods, gratings or prisms are usually required to excite and control surface waves. These methods have problems such as multi-mode, low efficiency, large size, and difficulty in integration. This makes it very challenging to integrate dynamic control of transmission waves and surface waves on wavefronts.

[0003] A metasurface is an artificial two-dimensional metamaterial structure composed of planar subwavelength microstructures with a customizable electromagnetic response. In modern technology, metasurfaces have demonstrated powerful manipulation capabilities for electromagnetic waves. By adjusting the geometry, material composition, and arrangement of the subwavelength unit structures, the phase, amplitude, and polarization of propagating or surface waves can be controlled. However, existing metasurfaces are primarily used for propagating wavefront manipulation. To achieve on-chip integrated dynamic manipulation of propagating and surface wavefronts, a phase gradient metasurface is constructed. By designing an appropriate phase gradient to form an excitation region, the excitation region provides an additional wave vector for the incident wave, converting the incident circularly polarized wave into a surface wave. The surface wave is then propagated along the surface of the adapted eigenregion. Therefore, the excitation region of a phase gradient metasurface can manipulate the wavefronts of both propagating and surface waves. However, conventional phase gradient metasurfaces are typically composed of metallic structures. Once the unit structures are fabricated, their electromagnetic parameters, such as phase and amplitude, cannot be flexibly manipulated. This results in the inability of phase gradient metasurfaces to dynamically manipulate the wavefronts of propagating or surface waves on-chip, limiting their scope and applications. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that traditional phase gradient metasurfaces cannot dynamically control the wavefront of transmission waves or surface waves on-chip, and propose an on-chip dynamic control device for transmission waves or surface waves based on terahertz metasurfaces.

[0005] A device for dynamically controlling a terahertz metasurface transmission wave or a surface wave front, comprising a dielectric layer, a metal reflective bottom plate, a metal ring, a photosensitive material, and a pump light source;

[0006] A dielectric layer is deposited on a metal reflective base plate, and the top surface of the dielectric layer is divided into two areas. One area is provided with metal rings distributed in an array as an excitation area, and the other area is used as an intrinsic area. Each metal ring is evenly distributed with multiple openings, and a layer of photosensitive material is deposited at each opening.

[0007] By regulating the pump light source to irradiate the photosensitive material at a specific opening position on the metal ring, the conductivity of the excited photosensitive material increases, forming different metal opening rings corresponding to different coding units, achieving full 2π phase coverage;

[0008] Taking the length direction of the excitation area as the y-axis direction, the width direction of the excitation area as the x-axis direction, the x-axis as the row, and the y-axis as the column, by presetting the coding unit of each metal open ring in the excitation area, the coding unit array in the excitation area satisfies two coding sequences. The first coding sequence is: presetting the coding unit of each metal open ring on any column in the excitation area, and making the coding units of the metal open rings on each row of the excitation area the same, and the phase of each coding unit in the first coding sequence is composed of the phase of each coding unit in the y-axis direction; the second coding sequence is: presetting the coding unit of each metal open ring on any column in the excitation area, and keeping the phase difference of the coding units of each two adjacent metal open rings on each row of the excitation area at 90 degrees, and the phase of each coding unit in the second coding sequence is composed of the phase of each coding unit in the y-axis direction and the phase gradient in the x-axis direction;

[0009] When a circularly polarized wave is incident on an array of coding units arranged according to a first coding sequence, a transmission wave front is formed in a direction perpendicular to the upper surface of the excitation region. When the coding unit of the metal open ring in the excitation region is changed by a pump light source, the phase of the changed coding unit is correspondingly changed and the changed coding unit satisfies the first coding sequence, the transmission wave front will become a new transmission wave front, thereby realizing dynamic control of the transmission wave front. When a circularly polarized wave is incident on an array of coding units arranged according to a second coding sequence, a surface wave front is transmitted along the surface of the intrinsic region. When the coding unit in the excitation region is changed by a pump light source, the phase of the changed coding unit is correspondingly changed and the changed coding unit satisfies the second coding sequence, the surface wave front will become a new surface wave front, thereby realizing dynamic control of the surface wave front.

[0010] Preferably, it further comprises a plurality of spatial coding structures;

[0011] A spatial coding structure is suspended above each metal ring. Each spatial coding structure is a baffle with a through hole. The position of the through hole on each baffle corresponds to the position of the photosensitive material at the opening of each metal ring.

[0012] The pump light source irradiates the photosensitive material at a set position through the set through hole.

[0013] Preferably, the photosensitive material is germanium, and the wavelength of the light source is 1600 nm or less.

[0014] Preferably, the material of the metal reflective bottom plate is gold, and the material of the dielectric layer is SiO2.

[0015] Preferably, when the transmission wave front is a transmission wave focused beam, the phase of each coding unit in the first coding sequence is the transmission wave focused beam phase; when the transmission wave front is a transmission wave Bessel beam, the phase of each coding unit in the first coding sequence is the transmission wave Bessel beam phase; when the transmission wave front is a transmission wave Airy beam, the phase of each coding unit in the first coding sequence is the transmission wave Airy beam phase.

[0016] Preferably, the transmission wave focused beam phase is expressed as:

[0017]

[0018] Where, is the phase of the transmission wave focused beam, k is the wave vector of the transmission wave, y' is the y-axis coordinate of the center point of the metal ring corresponding to the excited photosensitive material, F is the distance from the starting point to the focus of the focused beam,

[0019] The phase of the transmitted Bessel beam is expressed as:

[0020]

[0021] Where, is the transmission wave Bessel beam phase, NA is the numerical aperture,

[0022] The phase of the transmitted Airy beam is expressed as:

[0023]

[0024] Where, is the phase of the transmitted wave Airy beam, b is the lateral transmission distance, θ is the radiation direction of the beam, and Ai is the Airy function.

[0025] Preferably, when the surface wave wavefront is a surface wave focused beam, the phase of each coding unit in the first coding sequence is the surface wave focused beam phase; when the surface wave wavefront is a surface wave Bessel beam, the phase of each coding unit in the first coding sequence is the surface wave Bessel beam phase; when the surface wave wavefront is a surface wave Airy beam, the phase of each coding unit in the first coding sequence is the surface wave Airy beam phase.

[0026] Preferably, the surface wave focused beam phase is expressed as:

[0027]

[0028] Where, is the phase of the surface wave focused beam, k x is the eigenwave vector of the surface wave, x is the x-coordinate of the center point of the metal ring corresponding to the excited photosensitive material, y' is the y-axis coordinate of the center point of the metal ring corresponding to the excited photosensitive material, F is the distance from the starting point to the focus of the focused light beam,

[0029] The phase of the surface wave Bessel beam is expressed as:

[0030]

[0031] Where, is the surface wave Bessel beam phase, NA is the numerical aperture,

[0032] The phase of the surface wave Airy beam is expressed as:

[0033]

[0034] Where, is the surface wave Airy beam phase, b is the lateral transmission distance, θ is the radiation direction of the beam, and Ai is the Airy function.

[0035] The beneficial effects of the present invention are:

[0036] According to the transmission wave focused beam phase formula, the transmission wave Bessel beam phase formula or the transmission wave Airy beam phase formula, the transmission wave focused beam phase, the transmission wave Bessel beam phase or the transmission wave Airy beam phase is obtained. According to the phase, the pump light source is controlled to irradiate each metal ring so that the metal ring presents different metal opening rings corresponding to different coding units, so that the coding unit array in the excitation area is encoded according to two coding sequences. When the circularly polarized wave is incident on the first coding sequence, a transmission wave front is formed in a direction perpendicular to the upper surface of the excitation area. By changing the coding units in the first coding sequence, the transmission wave front is dynamically controlled. When the circularly polarized wave is incident on the second coding sequence, a surface wave front is transmitted along the surface of the intrinsic area. By changing the coding units in the second coding sequence, the surface wave front is dynamically controlled.

[0037] The present invention arranges metal rings with multiple openings evenly distributed in an array, and places photosensitive materials at the openings of the metal rings. When a coding controller controls a pump light source to illuminate the photosensitive materials, the illuminated photosensitive materials are excited to generate photogenerated carriers, causing the photosensitive germanium on each metal ring to transition between an insulating state and a metallic state, resulting in a different opening structure for each metal ring. Under the incidence of a left-handed circularly polarized wave, cross-polarization can obtain a 2-bit coding unit with complete 2π phase coverage. An excitation region is established based on the coding units of a preset coding sequence. The coding controller controls the irradiation intensity of the pump light source on the photosensitive material at the corresponding position on each metal ring, dynamically regulating the coding sequence of the coding units. The excitation region can convert the incident circularly polarized wave into a reflected transmission wave or couple it into a surface wave, and dynamically regulate the wavefront of the transmission wave or surface wave.

[0038] The wavefront dynamic control device, designed based on the dimensions of the metal ring and unit period, operates at a frequency of 0.74 THz, enabling dynamic switching between transmission waves and surface waves. It operates stably at this frequency, ensuring stable transmission waves or surface waves. The dimensions of the metal ring and unit period, as well as the structure of the intrinsic region, can also be varied to enable operation in other frequency ranges. Within the transmission wave, dynamic switching between focused beams, Bessel beams, and Airy beams can be achieved to obtain a desired output beam.

[0039] Therefore, compared to previous metasurface wavefront manipulation devices, this invention utilizes the same device to dynamically manipulate both the transmission and surface wavefronts. This device boasts subwavelength-level control capabilities, high efficiency, high integration, and dynamic switching, significantly changing the flexibility of electromagnetic wave manipulation. This technology holds enormous potential for both far-field radiation and near-field manipulation applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of a dynamic control device based on a terahertz metasurface transmission wave or surface wave front;

[0041] Figure 2 Schematic diagram of the structure of the photosensitive material being excited, where Figure 2 (a) is a diagram showing the relationship between the spatial coding structure and the spatial coding structure. Figure 2 (b) is a schematic diagram of the structure of the light source irradiating the photosensitive material;

[0042] Figure 3 is the metasurface unit encoding and equivalent diagram, where Figure 3 (a) is a schematic diagram of the position number of the photosensitive material; Figure 3 (b) is a schematic diagram of the light position number on the spatial coding structure; Figure 3(c) Schematic diagram of the coding method of the pump light of the spatial coding structure and the coding equivalent diagram of the metal ring;

[0043] Figure 4 is the amplitude and phase of the excitation region coding unit, where Figure 4 (a) is the amplitude of the coding unit in the excitation area, Figure 4 (b) is the phase of the coding unit in the excitation area;

[0044] Figure 5 is the intrinsic region structure and dispersion curve, where Figure 5 (a) is a schematic diagram of the intrinsic region unit; Figure 5 (b) is the dispersion curve of the intrinsic region;

[0045] Figure 6 is the dynamic control phase diagram of the transmission wavefront, where Figure 6 (a) is the wavefront phase of the focused beam; Figure 6 (b) is the Bessel beam wavefront phase; Figure 6 (c) is the wavefront phase of the Airy beam;

[0046] Figure 7 is the electric field diagram of the transmission wave front control, where Figure 7 (a) is the electric field diagram of the focused beam wavefront; Figure 7 (b) is the electric field diagram of the Bessel beam wavefront; Figure 7 (c) is the electric field diagram of the Airy beam wavefront;

[0047] Figure 8 is the dynamic control phase of the surface wave front, where Figure 8 (a) is the wavefront phase of the surface focused beam; Figure 8 (b) is the surface Bessel beam wavefront phase; Figure 8 (c) is the surface Airy beam wavefront phase;

[0048] Figure 9 is the electric field diagram of the surface wave front control, where Figure 9 (a) is the electric field diagram of the surface focused beam wavefront; Figure 9 (b) is the electric field diagram of the surface Bessel beam wavefront; Figure 9 (c) is the electric field diagram of the surface Airy beam wavefront; DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0050] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0051] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0052] Example:

[0053] Combine Figures 1 to 9 This embodiment is described, based on a terahertz metasurface transmission wave or a surface wave front on-chip dynamic control device, comprising a dielectric layer 1, a metal reflective bottom plate 2, a metal ring 3, a photosensitive material 4 and a pump light source;

[0054] A dielectric layer 1 is deposited on a metal reflective base plate 2. The top surface of the dielectric layer 1 is divided into two regions. One region is provided with an array of metal rings 3, serving as an excitation region 6, and the other region serves as an intrinsic region 5. Each metal ring 3 has multiple openings evenly distributed on it, and a layer of photosensitive material 4 is deposited at each opening.

[0055] By regulating the pump light source to irradiate the photosensitive material 4 at a specific opening position on the metal ring 3, the conductivity of the excited photosensitive material 4 increases, forming different metal opening rings corresponding to different coding units, achieving full 2π phase coverage;

[0056] Taking the length direction of the excitation region 6 as the y-axis direction, the width direction of the excitation region 6 as the x-axis direction, the x-axis as the row, and the y-axis as the column, by presetting the coding unit of each metal open ring in the excitation region 6, the coding unit array in the excitation region 6 satisfies two coding sequences. The first coding sequence is: presetting the coding unit of each metal open ring on any column in the excitation region 6, and making the coding units of the metal open rings on each row of the excitation region 6 the same, and the phase of each coding unit in the first coding sequence is composed of the phase of each coding unit in the y-axis direction; the second coding sequence is: presetting the coding unit of each metal open ring on any column in the excitation region 6, and keeping the phase difference of the coding units of each adjacent two metal open rings in each row of the excitation region 6 at 90 degrees, and the phase of each coding unit in the second coding sequence is composed of the phase of each coding unit in the y-axis direction and the phase gradient in the x-axis direction;

[0057] When a circularly polarized wave is incident on an array of coding units arranged according to a first coding sequence, a transmission wave front is formed in a direction perpendicular to the upper surface of the excitation region 6. When the coding unit of the metal open ring in the excitation region 6 is changed by a pump light source, the phase of the changed coding unit is correspondingly changed and the changed coding unit satisfies the first coding sequence, the transmission wave front will become a new transmission wave front, thereby realizing dynamic control of the transmission wave front. When a circularly polarized wave is incident on an array of coding units arranged according to a second coding sequence, a surface wave front is transmitted along the surface of the intrinsic region 5. When the coding unit in the excitation region 6 is changed by a pump light source, the phase of the changed coding unit is correspondingly changed and the changed coding unit satisfies the second coding sequence, the surface wave front will become a new surface wave front, thereby realizing dynamic control of the surface wave front.

[0058] Specifically, Figure 1 In the figure, reference numeral 8 represents a transmission wave Airy beam, reference numeral 9 represents a transmission wave focused beam, reference numeral 10 represents a transmission wave Bessel beam, reference numeral 11 represents a left-handed circularly polarized wave, reference numeral 12 represents a surface wave focused beam, reference numeral 13 represents a surface wave Bessel beam, and reference numeral 14 represents a surface wave Airy beam; the incident wave is a left-handed circularly polarized wave, which can be reflected into a transmission wave or converted into a surface wave.

[0059] Function of the metal reflective base plate: The metal reflective base plate can increase the reflectivity, reduce energy loss, and the incident left-hand circularly polarized wave cannot be transmitted through it; Function of the dielectric layer: The dielectric layer not only plays a supporting and isolating role, but also can adjust the electromagnetic field distribution; at the same time, because the refractive index and space of the dielectric layer are different, it can enhance the optical performance and facilitate integration.

[0060] like Figure 1 As shown, in actual application, the amount of photosensitive material can be set according to the number of openings on the metal ring 3 and the phase requirement. Figure 3 As shown, each metal ring 3 can be evenly distributed with 8 openings, and 8 rectangular photosensitive materials are set at the openings; there are 8 photosensitive materials on each metal ring 3, and only 6 photosensitive materials are excited each time. The conductivity of the excited photosensitive materials increases and becomes similar to metal, while the unexcited photosensitive materials are insulating media, which is equivalent to the opening of the metal ring 3 not being closed. In this way, 4 metal open rings with different opening positions can be formed, with 4 different phases (coding sequences). Figure 3 (c) Represents four different coding sequences.

[0061] The structural parameters of the excitation region subunit and the intrinsic region subunit are optimized using the finite time-domain difference method, as follows: Figure 2The period length of the subunit in the middle excitation region is p1 = 89 μm, the thickness of the dielectric layer is d1 = 30 μm, the thickness of the metal reflective base plate is t1 = 1 μm, the inner and outer radii of the ring are r1 = 29 μm, r2 = 39 μm, the germanium thickness is t1 = 1 μm, l1 = 55 μm, l2 = 79 μm, and w = 7 μm; Figure 5 The period length of the intrinsic region subunit in (a) is p2 = 89 μm, the thickness of the dielectric layer is d2 = 30 μm, and the thickness of the metal layer is t2 = 1 μm; the wavefront control device after the above structural optimization achieves stable operation at a center frequency of 0.74 THz.

[0062] The preset phase coding sequence is calculated through the phase formula, and the phase coding sequence is used to set the state of the photosensitive material at the opening of each metal ring to achieve dynamic control of the terahertz transmission wave and surface wave front. The specific process is as follows:

[0063] Step 1: Photosensitive material 4 (photosensitive semiconductor material germanium) can be excited by pump light with wavelengths of 1600nm and below. Therefore, a pump light source with a wavelength of 1550nm can be selected to excite the photosensitive semiconductor material germanium. By changing the spatial structure light encoding method, the conductivity of each photosensitive semiconductor germanium in the metal ring on the top layer of the metasurface can be controlled to achieve transitions between insulating and metallic states. This method can form metal rings with different opening positions and realize a 2-bit encoding unit for the phase of left-handed circular cross-polarization waves, thereby achieving 2π full phase coverage. Figure 3 The number of the photosensitive material (12345678) on (a) also represents the number of the point light source (12345678) of the corresponding upper spatial coding structure; at the same time, the number 0 indicates that the photosensitive germanium material at the position is not excited by the corresponding coding structure pump light, and the number 1 indicates that the photosensitive germanium material at the corresponding position is excited by the pump light. Figure 3 As shown in (c), when the coding sequences of the spatial coding structure pump light source are 01110111, 10111011, 11011101 and 11101110, respectively, the 2-bit coding units of the left-hand circular cross-polarization wave phase can be realized, which are 00, 01, 10 and 11 structural units, respectively, thereby achieving 2π full phase coverage, as shown in Figure 4 (b)

[0064] Step 2: Use the transmission wave focused beam phase formula to calculate the phase A1 of the focused beam with a focal distance of 1700 μm (as shown in Figure 6 (a), different colors indicate different phases), and the phase formula of the Bessel beam is used to calculate the phase A2 of the Bessel beam (as shown in Figure 6 (b)), the phase A3 of the Airy beam is calculated using the phase formula of the transmitted wave Airy beam (as shown in Figure 6(c)), the phase B1 of the surface focused beam with a focal length of 1700 μm is calculated using the surface wave focused beam phase formula (as shown in Figure 8 (a)), the phase formula of the surface wave Bessel beam is used to calculate the phase B2 of the surface Bessel beam (as shown in Figure 8 (b)) or use the surface wave Airy beam phase formula to calculate the surface Airy beam phase B3 (as shown in Figure 8 (c)

[0065] Step 3: Based on the distribution results of the transmission wave phase A1, phase A2, phase A3, surface wave phase B1, phase B2 or phase B3 calculated in step 2, control the light source to illuminate the photosensitive germanium corresponding to each metal ring, stimulate the photosensitive germanium to produce the corresponding phase, realize the switching of transmission wave or surface wave control, and dynamically control the wavefront of the transmission wave or surface wave respectively.

[0066] Therefore, based on the combination of a spatial coding structure pump light source and a metasurface, a dynamic control device for terahertz transmission waves or surface waves is realized. The corresponding phase is calculated through the transmission wave and surface wave wavefront formulas. Combined with the spatial coding structure pump light source, the coding sequence of the pump light source is changed to 01110111, 1011101, 11011101, and 11101110, respectively, to obtain the required 2-bit coding unit (00, 01, 10, 11). According to numerical simulation calculations, the dynamic control results of the transmission wave and surface wave wavefront at 0.74THz are obtained. Figure 7 (a) is the electric field diagram of the transmission wave focused beam with F = 1700 μm; Figure 7 (b) Electric field diagram of the transmitted Bessel beam with NA = 0.38; Figure 7 (c) b = 250 μm -1 The electric field diagram of the propagation wave Airy beam. Figure 9 (a) is the electric field diagram of the surface focused beam with F = 1700 μm; Figure 9 (b) Electric field diagram of the surface Bessel beam with NA = 0.38; Figure 9 (c) b = 250 μm -1 Electric field diagram of the Airy beam on the surface.

[0067] The structure for controlling the light source to irradiate the photosensitive material 4 at a set position is further described below:

[0068] The wavefront control device further includes a plurality of spatial coding structures;

[0069] A spatial coding structure is suspended above each metal ring 3. Each spatial coding structure is a baffle 7 with a through hole. The position of the through hole on each baffle 7 corresponds to the position of the photosensitive material 4 at the opening of each metal ring 3.

[0070] The pump light source irradiates the photosensitive material 4 at a set position through the set through hole.

[0071] The following is a further introduction to photosensitive materials and the wavelength of the light source they receive when excited:

[0072] The photosensitive material 4 is germanium, and the wavelength of the light source is 1600 nm or less.

[0073] Specifically, germanium materials can only be excited by light sources with a wavelength of 1600 nm or less.

[0074] The materials of the metal reflective bottom plate 2 and the dielectric layer 1 are further described below: the material of the metal reflective bottom plate 2 is gold, and the material of the dielectric layer 1 is SiO2.

[0075] The following describes the encoding unit phase settings required to generate a transmission wave focused beam, a transmission wave Bessel beam, or a transmission wave Airy beam:

[0076] When the transmission wave front is a transmission wave focused beam, the phase of each coding unit in the first coding sequence is the transmission wave focused beam phase; when the transmission wave front is a transmission wave Bessel beam, the phase of each coding unit in the first coding sequence is the transmission wave Bessel beam phase; when the transmission wave front is a transmission wave Airy beam, the phase of each coding unit in the first coding sequence is the transmission wave Airy beam phase.

[0077] The following describes the phase expression of the transmission wave focused beam:

[0078]

[0079] Where, is the phase of the transmission wave focused beam, k is the wave vector of the transmission wave, y' is the y-axis coordinate of the center point of the metal ring corresponding to the excited photosensitive material, F is the distance from the starting point to the focus of the focused beam,

[0080] The phase of the transmitted Bessel beam is expressed as:

[0081]

[0082] Where, is the transmission wave Bessel beam phase, NA is the numerical aperture,

[0083] The phase of the transmitted Airy beam is expressed as:

[0084]

[0085] Where, is the phase of the transmitted wave Airy beam, b is the lateral transmission distance, θ is the radiation direction of the beam, and Ai is the Airy function.

[0086] Specifically, NA may be equal to 0.38, and b may be equal to 250 μm. -1 , θ represents the radiation direction of the beam. When the direction is 0, the generated Airy beam is perpendicular to the metasurface. At the same time, the coding units in each row are uniformly phased. In other words, the coding of the pump light source in each row of the spatial coding structure is the same.

[0087] When it is desired to generate a transmission wave focused beam, a transmission wave Bessel beam or a transmission wave Airy beam, the center coordinates of the metal ring are brought into the transmission wave focused beam to obtain the phase of the transmission wave focused beam, the transmission wave Bessel beam or the transmission wave Airy beam. According to this phase, the pump light source is controlled to irradiate the photosensitive material 4 at the corresponding position on each metal ring 3, and the metal ring is encoded so that the phase of the coding unit is the phase of the transmission wave focused beam, the transmission wave Bessel beam or the transmission wave Airy beam, that is, Formula 1, Formula 2 or Formula 3. When the circularly polarized wave is incident on the coding unit array, a transmission wave focused beam, a transmission wave Bessel beam or a transmission wave Airy beam is generated; therefore, according to the transmission wave focused beam, the transmission wave Bessel beam or the transmission wave Airy beam to be generated, the coding array is controlled to realize dynamic control of the transmission wavefront. Formulas 1 to 3 all satisfy the phase Relationship: in, is the phase distribution function of the coding unit in the first coding sequence in the y-axis direction, is the phase distribution function of the coding unit in the first coding sequence in the x-axis direction, is a constant; it can be seen that by adjusting the phase in the y-axis direction, the incident left-handed circular wave can be converted into a transmission wave front.

[0088] The following describes the coding unit phase settings required to generate a surface wave focused beam, a surface wave Bessel beam, or a surface wave Airy beam:

[0089] When the surface wave wavefront is a surface wave focused beam, the phase of each coding unit in the first coding sequence is the surface wave focused beam phase; when the surface wave wavefront is a surface wave Bessel beam, the phase of each coding unit in the first coding sequence is the surface wave Bessel beam phase; when the surface wave wavefront is a surface wave Airy beam, the phase of each coding unit in the first coding sequence is the surface wave Airy beam phase.

[0090] The phase of the surface wave focused beam is expressed as follows:

[0091]

[0092] Where, is the phase of the surface wave focused beam, k x is the eigenwave vector of the surface wave, x is the x-coordinate of the center point of the metal ring corresponding to the excited photosensitive material, y' is the y-axis coordinate of the center point of the metal ring corresponding to the excited photosensitive material, F is the distance from the starting point to the focus of the focused light beam,

[0093] The phase of the surface wave Bessel beam is expressed as:

[0094]

[0095] Where, is the surface wave Bessel beam phase, NA is the numerical aperture,

[0096] The phase of the surface wave Airy beam is expressed as:

[0097]

[0098] Where, is the surface wave Airy beam phase, b is the lateral transmission distance, θ is the radiation direction of the beam, and Ai is the Airy function.

[0099] Specifically, Formulas 4 to 6 all satisfy the phase Relational in, is the phase distribution function of the coding unit in the second coding sequence in the y-axis direction, is the phase distribution function of the coding unit in the second coding sequence in the x-axis direction, and ξ is the phase gradient of the coding unit in the second coding sequence in the x-axis direction. From this relationship, it can be seen that when generating surface waves, an additional phase gradient is required in, Here, the period length P = p1 = p2, meaning that the phases of two adjacent metal rings on the x-axis differ by 90 degrees. This phase gradient couples the incident circularly polarized wave into a surface wave, which propagates toward the left intrinsic region and is confined there. By varying the spatial structure of the coding units on each row, surface waves can be excited and their wavefronts dynamically manipulated. Figure 5 (a) is the intrinsic region structure, the metal structure is gold, the dielectric layer is an isotropic uniform dielectric SiO2, Figure 5 (b) The dispersion curve can be used to calculate the wave vector k of the surface wave at 0.74 THz. x k x =1.138k, k x =ξ(such as Figure 5 (b)), left-handed circularly polarized light generates surface waves in the left intrinsic region.

[0100] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be employed in conjunction with other described embodiments.

Claims

1. A device for dynamically controlling a terahertz metasurface transmission wave or a surface wave front, characterized in that: It comprises a dielectric layer (1), a metal reflective bottom plate (2), a metal ring (3), a photosensitive material (4) and a pump light source; A dielectric layer (1) is deposited on a metal reflective bottom plate (2), and the top surface of the dielectric layer (1) is divided into two regions. One region is provided with metal rings (3) distributed in an array as an excitation region (6), and the other region is used as an intrinsic region (5). Multiple openings are evenly distributed on each metal ring (3), and a layer of photosensitive material (4) is deposited at each opening. By regulating the pump light source to irradiate the photosensitive material (4) at a specific opening position on the metal ring (3), the conductivity of the excited photosensitive material (4) increases, forming different metal opening rings corresponding to different coding units, thereby achieving full 2π phase coverage; The length direction of the excitation region (6) is the y-axis direction, the width direction of the excitation region (6) is the x-axis direction, the x-axis is the row, and the y-axis is the column. By presetting the coding unit of each metal open ring in the excitation region (6), the coding unit array in the excitation region (6) satisfies two coding sequences. The first coding sequence is: the coding unit of each metal open ring on any column in the excitation region (6) is preset, and the coding units of the metal open rings on each row of the excitation region (6) are all the same, and the phase of each coding unit in the first coding sequence is composed of the phase of each coding unit in the y-axis direction; the second coding sequence is: the coding unit of each metal open ring on any column in the excitation region (6) is preset, and the phase difference of the coding units of each adjacent two metal open rings on each row of the excitation region (6) is maintained at 90 degrees, and the phase of each coding unit in the second coding sequence is composed of the phase of each coding unit in the y-axis direction and the phase gradient in the x-axis direction; When a circularly polarized wave is incident on an array of coding units arranged according to a first coding sequence, a transmission wave front is formed in a direction perpendicular to the upper surface of the excitation region (6). When the coding unit of the metal open ring in the excitation region (6) is changed by a pump light source, the phase of the changed coding unit is correspondingly changed and the changed coding unit satisfies the first coding sequence, the transmission wave front will become a new transmission wave front, thereby realizing dynamic control of the transmission wave front. When a circularly polarized wave is incident on an array of coding units arranged according to a second coding sequence, a surface wave front is transmitted along the surface of the intrinsic region (5). When the coding unit in the excitation region (6) is changed by a pump light source, the phase of the changed coding unit is correspondingly changed and the changed coding unit satisfies the second coding sequence, the surface wave front will become a new surface wave front, thereby realizing dynamic control of the surface wave front.

2. The on-chip dynamic control device based on terahertz metasurface transmission wave or surface wave wavefront according to claim 1, characterized in that: It also includes multiple spatial encoding structures; A spatial coding structure is suspended above each metal ring (3), and each spatial coding structure is a baffle (7) with a through hole. The position of the through hole on each baffle (7) corresponds to the position of the photosensitive material (4) at the opening of each metal ring (3). The pump light source is transmitted through the set through hole to irradiate the photosensitive material (4) at the set position.

3. The on-chip dynamic control device based on terahertz metasurface transmission wave or surface wave wavefront according to claim 1, characterized in that: The photosensitive material (4) is germanium, and the wavelength of the light source is 1600 nm or less.

4. The on-chip dynamic control device based on terahertz metasurface transmission wave or surface wave wavefront according to claim 1, characterized in that: The material of the metal reflective bottom plate (2) is gold, and the material of the dielectric layer (1) is SiO2.

5. The on-chip dynamic control device based on terahertz metasurface transmission wave or surface wave wavefront according to claim 1, characterized in that: When the transmission wave front is a transmission wave focused beam, the phase of each coding unit in the first coding sequence is the transmission wave focused beam phase; when the transmission wave front is a transmission wave Bessel beam, the phase of each coding unit in the first coding sequence is the transmission wave Bessel beam phase; when the transmission wave front is a transmission wave Airy beam, the phase of each coding unit in the first coding sequence is the transmission wave Airy beam phase.

6. The on-chip dynamic control device based on terahertz metasurface transmission wave or surface wave wavefront according to claim 5, characterized in that: The phase of the transmission wave focused beam is expressed as: Where, is the phase of the transmission wave focused beam, k is the wave vector of the transmission wave, y' is the y-axis coordinate of the center point of the metal ring corresponding to the excited photosensitive material, F is the distance from the starting point to the focus of the focused beam, The phase of the transmitted Bessel beam is expressed as: Where, is the transmission wave Bessel beam phase, NA is the numerical aperture, The phase of the transmitted Airy beam is expressed as: Where, is the phase of the transmitted wave Airy beam, b is the lateral transmission distance, θ is the radiation direction of the beam, and Ai is the Airy function.

7. The on-chip dynamic control device based on terahertz metasurface transmission wave or surface wave wavefront according to claim 1, characterized in that: When the surface wave wavefront is a surface wave focused beam, the phase of each coding unit in the first coding sequence is the surface wave focused beam phase; when the surface wave wavefront is a surface wave Bessel beam, the phase of each coding unit in the first coding sequence is the surface wave Bessel beam phase; when the surface wave wavefront is a surface wave Airy beam, the phase of each coding unit in the first coding sequence is the surface wave Airy beam phase.

8. The on-chip dynamic control device based on terahertz metasurface transmission wave or surface wave wavefront according to claim 7, characterized in that: The phase of the surface wave focused beam is expressed as: Where, is the phase of the surface wave focused beam, k x is the eigenwave vector of the surface wave, x is the x-coordinate of the center point of the metal ring corresponding to the excited photosensitive material, y' is the y-axis coordinate of the center point of the metal ring corresponding to the excited photosensitive material, F is the distance from the starting point to the focus of the focused light beam, The phase of the surface wave Bessel beam is expressed as: Where, is the surface wave Bessel beam phase, NA is the numerical aperture, The phase of the surface wave Airy beam is expressed as: Where, is the surface wave Airy beam phase, b is the lateral transmission distance, θ is the radiation direction of the beam, and Ai is the Airy function.

Images