Wavefront on-chip dynamic regulation and control device based on terahertz metasurface transmission wave or surface wave

Abstract

The invention discloses a wavefront on-chip dynamic regulation and control device based on terahertz metasurface transmission waves or surface waves, and belongs to the technical field of electromagnetic wave wavefront regulation and control devices. Due to the fact that a traditional phase gradient metasurface cannot dynamically regulate and control the wavefront of transmission waves or surface waves, the metasurface of the integrated photosensitive material is combined with a space coding light source, and on-chip dynamic regulation and control of the wavefront of terahertz transmission waves or surface waves are achieved. According to the device, a dielectric layer is deposited on a metal reflection bottom plate, and the top layer of the dielectric layer is divided into two regions, namely an excitation region and an intrinsic region. The excitation area is composed of a metal ring array, a plurality of openings are evenly distributed in the metal ring array, light-sensitive materials are deposited at the openings, and 2-bit coding units are formed by controlling the intensity of the light-sensitive materials irradiated by the pump light source. An excitation region is constructed according to a preset coding sequence, when a circularly polarized wave enters the surface of the excitation region, a transmission wave or a surface wave can be generated, the coding sequence is changed to reconstruct the phase of the transmission wave or the surface wave, and the wavefront of the transmission wave or the surface wave is dynamically regulated and controlled, so that the on-chip dynamic regulation and control device for the wavefront of the transmission wave or the surface wave is realized.

Description

Technical Field

[0001] The invention relates to dynamic control of wavefronts of terahertz transmission waves or surface waves, and belongs to the technical field of electromagnetic wave wavefront 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 vectors are imaginary numbers in the normal direction of the interface, which causes their wave vectors to be larger than the wave vectors of transmission waves. 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. There are problems such as multi-mode, low efficiency, large size and difficulty in integration, which makes it very challenging to integrate dynamic control of transmission waves and surface waves on the wavefront.

[0003] Metasurface is an artificial two-dimensional metamaterial structure composed of planar subwavelength microstructures with customized electromagnetic response. In modern technology, metasurfaces have shown powerful manipulation capabilities for electromagnetic waves. The phase, amplitude and polarization of transmission waves or surface waves can be controlled by adjusting the geometry, material composition and arrangement of subwavelength unit structures. However, existing metasurfaces are mainly used for transmission wavefront control. In order to achieve on-chip integrated dynamic control of transmission wave and surface wave wavefront, a phase gradient metasurface is constructed. The excitation region is formed by designing a suitable phase gradient. The purpose is to provide an additional wave vector for the incident wave, which can convert the incident circularly polarized wave into a surface wave, and transmit the surface wave along the surface of the intrinsic region through the adapted intrinsic region. Therefore, the excitation region of the phase gradient metasurface can control the wavefront of both transmission waves and surface waves. However, traditional phase gradient metasurfaces are usually composed of metal structures. Once the unit structure is prepared, its electromagnetic parameters such as phase and amplitude cannot be flexibly controlled, resulting in the failure of the phase gradient metasurface to dynamically control the wavefront of transmission waves or surface waves on-chip, limiting the scope and field of application. 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 bottom 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; a plurality of openings are evenly distributed on each metal ring, 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] The length direction of the excitation region is taken as the y-axis direction, the width direction of the excitation region is taken as the x-axis direction, the x-axis is taken as the row, and the y-axis is taken as the column. By presetting the coding unit of each metal open ring in the excitation region, the coding unit array in the excitation region 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, and making the coding units of the metal open rings on each row in the excitation region 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, and keeping the phase difference of each adjacent two metal open rings in each row of the excitation region 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 changes accordingly 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 changes accordingly 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 also includes a plurality of spatial coding structures;

[0011] A space coding structure is suspended above each metal ring, and each space coding structure is a baffle with a through hole, and 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 focusing beam, the phase of each coding unit in the first coding sequence is the transmission wave focusing 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] In the formula, 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 of the focused beam to the focus,

[0019] The transmission wave Bessel beam phase is expressed as:

[0020]

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

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

[0023]

[0024] In the formula, 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 front is a surface wave focusing beam, the phase of each coding unit in the first coding sequence is the phase of the surface wave focusing beam; when the surface wave front is a surface wave Bessel beam, the phase of each coding unit in the first coding sequence is the phase of the surface wave Bessel beam; when the surface wave front is a surface wave Airy beam, the phase of each coding unit in the first coding sequence is the phase of the surface wave Airy beam.

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

[0027]

[0028] In the formula, is the phase of the surface wave focused beam, k x is the eigenvector 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 of the focused light beam to the focus,

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

[0030]

[0031] In the formula, 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] In the formula, is the phase of the surface wave Airy beam, 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 focusing beam phase formula, the transmission wave Bessel beam phase formula or the transmission wave Airy beam phase formula, the transmission wave focusing 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, and the transmission wave front is dynamically controlled by changing the coding unit in the first coding sequence; when the circularly polarized wave is incident on the second coding sequence, the surface wave front is transmitted along the surface of the intrinsic area, and the surface wave front is dynamically controlled by changing the coding unit in the second coding sequence.

[0037] The present invention arranges a plurality of metal rings with evenly distributed openings in an array form, and arranges photosensitive materials at the openings on the metal rings. When a coding controller controls a pump light source to irradiate the photosensitive materials, the irradiated photosensitive materials are excited to generate photogenerated carriers, so that the photosensitive germanium on each metal ring is converted between an insulating state and a metallic state, resulting in each metal ring forming a different opening structure. Under the incidence of a left-handed circularly polarized wave, cross-polarization can obtain a 2-bit coding unit with a complete 2π phase coverage. An excitation region is established according to a coding unit of a preset coding sequence, and the irradiation intensity of the pump light source on the photosensitive material at the corresponding position on each metal ring is controlled by a coding controller to dynamically adjust the coding sequence of the coding unit. The excitation region can realize the conversion of the incident circularly polarized wave into a reflected transmission wave or couple it into a surface wave, and dynamically adjust the wavefront of the transmission wave or the surface wave.

[0038] The wavefront dynamic control device designed according to the size of the metal ring and the unit period has an operating frequency of 0.74 THz, which realizes the dynamic switching between the transmission wave and the surface wave. It works stably at this frequency, so that the generated transmission wave or surface wave is stable. The size and intrinsic region structure of the metal ring and the unit period can also be changed to make the present invention work in other frequency ranges. In the transmission wave, dynamic switching between the focused beam, the Bessel beam and the Airy beam can be realized to obtain a beam that is desired to be output.

[0039] Therefore, compared with the previous metasurface wavefront control devices, the present invention can dynamically control both the transmission wavefront and the surface wavefront using the same device. The present invention has the characteristics of sub-wavelength control capability, high efficiency, high integration, and dynamic switching, which greatly changes people's flexibility in electromagnetic wave control. This technology has great potential in far-field radiation and near-field control applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of the structure of a dynamic control device on a wavefront chip based on a terahertz metasurface transmission wave or surface wave;

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

[0042] Figure 3 is the encoding and equivalent diagram of the hypersurface unit, 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) is a schematic diagram showing the coding method of the pump light of the spatial coding structure and the coding of the metal ring equivalent diagram;

[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 of the excitation area;

[0044] Figure 5 is the intrinsic region structure and dispersion curve diagram, 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 wave front, 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 phase control of the surface wave front, where Figure 8 (a) is the surface focused beam wavefront phase; Figure 8 (b) is the surface Bessel beam wavefront phase; Figure 8 (c) is the surface Airy beam wavefront phase;

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

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are 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] Combination Figures 1 to 9 This embodiment is described, based on the terahertz metasurface transmission wave or surface wave front on-chip dynamic control device, including 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 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; a plurality of openings are evenly distributed on each metal ring 3, 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, thereby achieving full coverage of the 2π phase;

[0056] The length direction of the excitation region 6 is taken as the y-axis direction, the width direction of the excitation region 6 is taken as the x-axis direction, the x-axis is taken as the row, and the y-axis is taken 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: 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 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;

[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 changes accordingly and the changed coding unit satisfies the first coding sequence, the transmission wave front will become a new transmission wave front, thereby realizing dynamic regulation 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 changes accordingly and the changed coding unit satisfies the second coding sequence, the surface wave front will become a new surface wave front, thereby realizing dynamic regulation 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 metal reflective baseplate: The metal reflective baseplate can increase reflectivity, reduce energy loss, and prevent incident left-handed circularly polarized waves from transmitting through it; Function of 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, the optical performance can be enhanced and integration is facilitated.

[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, 8 openings can be evenly distributed on each metal ring 3, and 8 rectangular photosensitive materials are respectively 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 opening rings with different opening positions can be formed, with 4 different phases (coding sequences). Figure 3 (c) Represents 4 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=89μm, the thickness of the dielectric layer is d1=30μm, the thickness of the metal reflective bottom plate is t1=1μm, the inner and outer radii of the ring are r1=29μm, r2=39μm, the thickness of germanium is t1=1μm, l1=55um, l2=79um, and w=7um; Figure 5 In (a), the period length of the intrinsic region subunit is p2=89μm, the thickness of the dielectric layer is d2=30μm, and the thickness of the metal layer is t2=1μm; the wavefront control device after the above structural optimization can achieve stable operation at a center frequency of 0.74THz.

[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: The photosensitive material 4 (photosensitive semiconductor material germanium) can be excited by pump light with a wavelength of 1600nm or less, so 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 top metal ring of the metasurface can be controlled to achieve the conversion between the insulating state and the metallic state. This method can form metal opening rings with different opening positions and realize the 2-bit encoding unit of the left-handed circular cross-polarization wave phase, thereby achieving 2π full phase coverage. Figure 3 The number (12345678) of the photosensitive material in (a) also represents the number (12345678) of the corresponding point light source of the 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, the 2-bit coding units of the left-handed 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 (such as 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 transmission wave Airy beam phase formula (as shown in Figure 6(c)), the phase B1 of the surface focused beam with a focal distance 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, according to 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 irradiate the photosensitive germanium corresponding to each metal ring, stimulate the photosensitive germanium to produce the corresponding phase, realize the transmission wave or surface wave control switching, and dynamically control the wavefront of the transmission wave or surface wave respectively.

[0066] Therefore, based on the combination of the spatial coding structure pump light source and the metasurface, a dynamic control device for terahertz transmission wave or surface wave wavefront is realized. The corresponding phase is calculated through the transmission wave and surface wave wavefront formula. Combined with the pump light source of the spatial coding structure, the coding sequence of the pump light source is changed to 01110111, 10111011, 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 0.74 THz are obtained. Figure 7 (a) is the electric field diagram of the transmission wave focused beam with F = 1700um; Figure 7 (b) is the electric field diagram of the transmission wave Bessel beam with NA = 0.38; Figure 7 (c) b = 250 um -1 The electric field diagram of the propagating Bo Airy beam. Fig. 9 (a) is the electric field diagram of the surface focused beam at F = 1700um; Fig. 9 (b) is the electric field diagram of the surface Bessel beam with NA = 0.38; Fig. 9 (c) b = 250 um -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 the set position is further described below:

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

[0069] A space coding structure is suspended above each metal ring 3, and each space coding structure is a baffle 7 with a through hole, and 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 1600nm 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 coding 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 introduces the phase expression of the transmission wave focused beam:

[0078]

[0079] In the formula, 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 of the focused beam to the focus,

[0080] The transmission wave Bessel beam phase is expressed as:

[0081]

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

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

[0084]

[0085] In the formula, 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 in phase. 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 coordinate of the metal ring is 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 adjusted to realize dynamic control of the transmission wavefront. Formulas 1 to 3 all satisfy the phase Relational formula: 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 front 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 front 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 front 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] In the formula, is the phase of the surface wave focused beam, k x is the eigenvector 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 of the focused light beam to the focus,

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

[0094]

[0095] In the formula, 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] In the formula, is the phase of the surface wave Airy beam, 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, Among them, the period length P = p1 = p2, that is, the phase difference between the two adjacent metal rings in the x-axis direction is 90 degrees. This phase gradient just couples the incident circularly polarized wave into a surface wave, which propagates to the left intrinsic region and is bound in the intrinsic region. By changing the spatial structure coding of the coding unit on each row, the surface wave can be excited and the surface wave front can be dynamically controlled. Figure 5 (a) is the intrinsic region structure, the metal structure is gold, the dielectric layer is 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 examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A device for dynamically controlling the wavefront of a terahertz metasurface transmission wave or surface wave, 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); a plurality of 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 coverage of 2π phases; The length direction of the excitation region (6) is taken as the y-axis direction, the width direction of the excitation region (6) is taken as the x-axis direction, the x-axis is taken as the row, and the y-axis is taken 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: the coding unit of each metal open ring in any column in the excitation region (6) is preset, and the coding units of the metal open rings in 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 in any column in the excitation region (6) is preset, and the phase difference of the coding units of each adjacent two metal open rings in 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 an excitation region (6); when a coding unit of a 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 regulation 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 an intrinsic region (5); when a 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 regulation 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), each spatial coding structure is a baffle (7) with a through hole, and 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 irradiates the photosensitive material (4) at a set position through the set through hole.

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 1600nm or less.

4. The on-chip dynamic control device based on terahertz metasurface transmission wave or surface wave front 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 front according to claim 5, characterized in that: The phase of the transmission wave focused beam is expressed as: In the formula, 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 of the focused beam to the focus, The transmission wave Bessel beam phase is expressed as: In the formula, is the transmission wave Bessel beam phase, NA is the numerical aperture, The phase of the transmitted Boairy beam is expressed as: In the formula, 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 front 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 front 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 front 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: In the formula, is the phase of the surface wave focused beam, k x is the eigenvector 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 of the focused light beam to the focus, The surface wave Bessel beam phase is expressed as: In the formula, is the surface wave Bessel beam phase, NA is the numerical aperture, The phase of the surface wave Airy beam is expressed as: In the formula, is the phase of the surface wave Airy beam, b is the lateral transmission distance, θ is the radiation direction of the beam, and Ai is the Airy function.

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