CN111610670B - Terahertz spatial light modulator, preparation method and application - Google Patents

Terahertz spatial light modulator, preparation method and application Download PDF

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Publication number
CN111610670B
CN111610670B CN202010517946.0A CN202010517946A CN111610670B CN 111610670 B CN111610670 B CN 111610670B CN 202010517946 A CN202010517946 A CN 202010517946A CN 111610670 B CN111610670 B CN 111610670B
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substrate
layer
electrode
terahertz
spatial light
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CN111610670A (en
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胡伟
沈志雄
葛士军
陆延青
徐飞
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Nanjing University
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Nanjing University
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1343—Electrodes
    • G02F1/134309—Electrodes characterised by their geometrical arrangement
    • G02F1/134336—Matrix
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133504—Diffusing, scattering, diffracting elements
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1339—Gaskets; Spacers; Sealing of cells
    • G02F1/13392—Gaskets; Spacers; Sealing of cells spacers dispersed on the cell substrate, e.g. spherical particles, microfibres
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1343—Electrodes
    • G02F1/13439—Electrodes characterised by their electrical, optical, physical properties; materials therefor; method of making
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering

Abstract

The embodiment of the invention discloses a terahertz spatial light modulator, a preparation method and application. The terahertz spatial light modulator comprises a first substrate, a second substrate and a liquid crystal layer which are oppositely arranged, wherein spacing particles are arranged between the first substrate and the second substrate to support the liquid crystal layer; one side of the first substrate, which is close to the liquid crystal layer, is provided with an electrode layer and a first orientation layer; the electrode layer comprises a plurality of interdigital electrodes arranged in an array; a super-structure surface layer and a second orientation layer are arranged on one side, close to the liquid crystal layer, of the second substrate; the super-structure surface layer comprises a plurality of split ring resonators arranged in an array; the first alignment layer and the second alignment layer have the same alignment direction, and the alignment direction intersects with the second direction. According to the technical scheme of the embodiment of the invention, the spatial light modulation function can be realized in the transmission and reflection modes according to different incident polarization directions, so that the technical problems of single function and low integration level of the terahertz spatial light modulator in the prior art are solved.

Description

Terahertz spatial light modulator, preparation method and application
Technical Field
The embodiment of the invention relates to a terahertz photoelectronic technology, in particular to a terahertz spatial light modulator, a preparation method and application.
Background
Terahertz waves are electromagnetic waves with frequencies between 0.1THz and 10THz (corresponding to wavelengths between 30 μm and 3000 μm), and have unique properties. Terahertz wave energy penetrates through nonpolar and nonmetallic materials, and ionizing radiation is small; in addition, many organic or biological molecules have collective vibration modes in this band, forming a unique "terahertz fingerprint". These characteristics provide huge opportunity for terahertz human body security inspection, industrial inspection and medical diagnosis. The carrier frequency of the terahertz wave is far higher than the commercial radio frequency wave band at present, so that the terahertz wave can be applied to future high-speed wireless communication, and the communication requirement of rapid expansion of information is met. In these applications relating to terahertz communication and imaging, the spatial light modulator has an indispensable role, and can be widely used for spatial modulation of the intensity and phase of a wavefront, and functions such as terahertz beam dynamic deflection and focusing, single-pixel imaging, and the like are realized.
The traditional terahertz spatial light modulator can realize intensity modulation of spatial light by loading visible light patterns on a digital micromirror array to irradiate doped silicon, and the mode has the defects of small modulation depth, multiple devices, cascade connection, large volume and difficulty in integration; the liquid crystal spatial light modulator can realize 0-2 pi full-phase modulation in a single pixel, the integration level is high, but the thickness of the liquid crystal layer is large due to the fact that the thickness of the liquid crystal layer needs to meet the half-wave condition of a terahertz wave band, the driving and responding performance is poor, and crosstalk is easy to occur between adjacent pixels. In recent years, spatial light modulators that integrate a metamaterial with a functional material having a dynamic response (such as a semiconductor, a liquid crystal, graphene, a phase change material, and the like) to realize high-efficiency dynamics have become a great hot spot in the research field. However, such devices typically can only operate in either a transmissive or reflective mode, limiting their practical range of use.
Disclosure of Invention
The embodiment of the invention provides a terahertz spatial light modulator, a preparation method and application, wherein the terahertz spatial light modulator can realize a spatial light modulation function in a transmission mode and a reflection mode according to different incident polarization directions, so that the technical problems of single function and low integration level of the terahertz spatial light modulator in the prior art are solved, and the terahertz spatial light modulator has great application potential in terahertz communication, imaging and other aspects.
In a first aspect, an embodiment of the present invention provides a terahertz spatial light modulator, including:
the liquid crystal display panel comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are oppositely arranged, and the liquid crystal layer is positioned between the first substrate and the second substrate;
an electrode layer and a first orientation layer are arranged on one side, close to the liquid crystal layer, of the first substrate, and the electrode layer is arranged between the first substrate and the first orientation layer;
the electrode layer comprises a plurality of interdigital electrodes arranged in an array, and each interdigital electrode comprises a first electrode and a second electrode;
the first electrode comprises a first electrode end and a plurality of first branch electrodes connected with the first electrode end, the first branch electrodes extend along a first direction and are arranged along a second direction, and the first electrode end extends along the second direction;
the second electrode comprises a second electrode end and a plurality of second branch electrodes connected with the second electrode end, the second branch electrodes extend along the first direction and are arranged along the second direction, the second electrode end extends along the second direction, and the first branch electrodes and the second branch electrodes are alternately arranged along the second direction;
a super-structure surface layer and a second orientation layer are arranged on one side, close to the liquid crystal layer, of the second substrate, and the super-structure surface layer is arranged between the second substrate and the second orientation layer;
the super-structure surface layer comprises a plurality of split ring resonators arranged in an array, each split ring resonator comprises a first fan ring and a second fan ring, the first fan ring and the second fan ring are positioned in the same circular ring, an opening between the first fan ring and the second fan ring is symmetrical relative to the first direction, and the central angle of the first fan ring is smaller than that of the second fan ring;
the first alignment layer and the second alignment layer have the same alignment direction, and the alignment direction intersects the second direction.
Optionally, each interdigital electrode forms a square region, and the side length of the square region is L1Wherein L is more than or equal to 500 mu m1≤2000μm。
Optionally, the number of the interdigital electrodes is n × m, wherein n is greater than or equal to 2 and less than or equal to 100, and m is greater than or equal to 2 and less than or equal to 100.
Optionally, the first branch electrode and the second branch electrode form a grating structure along the second direction, and a period L of the grating structure2Less than the wavelength of incident light to the terahertz spatial light modulator, wherein L is more than or equal to 10 mu m2≤50μm。
Optionally, each of the first branch electrode and the second branch electrode has a width L in the second direction3Wherein L is less than or equal to 5 mu m3≤25μm。
Optionally, the central angles of the first fan ring and the second fan ring are θ1And theta2The inner radius and the outer radius are R1And R2Wherein theta is more than or equal to 120 degrees1≤140°，160°≤θ2≤180°，20μm≤R1≤30μm，35μm≤R2≤45μm。
Optionally, the liquid crystal material of the liquid crystal layer is a birefringence material, and has a first refractive index and a second refractive index; when the frequency range of incident light to the terahertz spatial light modulator is 0.5 THz-2.5 THz, the difference value between the first refractive index and the second refractive index is delta n, and delta n is greater than or equal to 0.2 and less than or equal to 0.4.
Optionally, the spacer has an extension length L in a direction perpendicular to the first substrate4，3μm≤L4≤10μm。
Optionally, the first substrate and the second substrate are made of quartz, polyimide or intrinsic silicon; the electrode layer and the nanostructured surface layer comprise at least one of gold, silver, copper or aluminum.
In a second aspect, an embodiment of the present invention further provides a method for manufacturing a terahertz spatial light modulator, including:
providing a first substrate and a second substrate;
sequentially forming an electrode layer and a first orientation layer on one side of the first substrate, and sequentially forming a super-structure surface layer and a second orientation layer on one side of the second substrate;
arranging spacing particles on the first substrate and encapsulating the first substrate and the second substrate, wherein one side of the first alignment layer of the first substrate is opposite to one side of the second alignment layer of the second substrate;
carrying out polarized ultraviolet exposure orientation on the first orientation layer and the second orientation layer, and pouring a liquid crystal material between the first substrate and the second substrate so as to enable liquid crystal molecules to be arranged according to the orientation directions of the first orientation layer and the second orientation layer;
the electrode layer comprises a plurality of interdigital electrodes arranged in an array, and each interdigital electrode comprises a first electrode and a second electrode; the first electrode comprises a first electrode end and a plurality of first branch electrodes connected with the first electrode end, the first branch electrodes extend along a first direction and are arranged along a second direction, and the first electrode end extends along the second direction; the second electrode comprises a second electrode end and a plurality of second branch electrodes connected with the second electrode end, the second branch electrodes extend along the first direction and are arranged along the second direction, the second electrode end extends along the second direction, and the first branch electrodes and the second branch electrodes are alternately arranged along the second direction; the super-structure surface layer comprises a plurality of split ring resonators arranged in an array, each split ring resonator comprises a first fan ring and a second fan ring, the first fan ring and the second fan ring are positioned in the same circular ring, an opening between the first fan ring and the second fan ring is symmetrical relative to the first direction, and the central angle of the first fan ring is smaller than that of the second fan ring; the first alignment layer and the second alignment layer have the same alignment direction, and the alignment direction intersects the second direction.
In a third aspect, an embodiment of the present invention further provides an application of the terahertz spatial light modulator according to any one of the above, where each of the interdigital electrodes includes a powered state and a non-powered state;
the interdigital electrodes in the charged state and the non-charged state form a linear grating or a ring grating so as to deflect or focus an incident terahertz light beam.
The terahertz spatial light modulator provided by the embodiment of the invention comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are oppositely arranged, and the liquid crystal layer is positioned between the first substrate and the second substrate; an electrode layer and a first orientation layer are arranged on one side, close to the liquid crystal layer, of the first substrate, and the electrode layer is arranged between the first substrate and the first orientation layer; a super-structure surface layer and a second orientation layer are arranged on one side, close to the liquid crystal layer, of the second substrate, and the super-structure surface layer is arranged between the second substrate and the second orientation layer; the initial deflection direction of the liquid crystal is controlled through the first orientation layer and the second orientation layer, the electrode layer comprises a plurality of interdigital electrodes which are arranged in an array mode, each interdigital electrode forms a grating structure in the second direction, terahertz waves polarized along the second direction can be transmitted, and terahertz waves polarized along the first direction are reflected; by arranging the super-structure surface layer to comprise the split ring resonator, for terahertz waves polarized along the second direction, the asymmetric open ring structure of the split ring resonator can induce the terahertz waves to realize a Fano resonance type modulation effect, when different electric fields are applied to the interdigital electrodes, liquid crystals are caused to generate pointing deflection, the environmental refractive index of the super-structure surface layer is changed, and therefore the characteristic peak of the Fano resonance can generate frequency spectrum movement, and transmission type intensity modulation with large modulation depth is realized at specific frequency; for terahertz waves polarized along a first direction, an electric field of the terahertz waves and a split ring resonator generate an electric dipole resonance effect, induction ring current is generated between an interdigital electrode and the split ring resonator, a magnetic dipole is formed by the ring current, the direction of the magnetic dipole is consistent with the direction of a magnetic field of incident terahertz waves, and magnetic dipole resonance is generated, so that at a specific resonance frequency, the energy of the incident terahertz waves is completely lost in the structure, the complete absorption characteristic of a specific frequency is shown on a frequency domain spectrum, when different electric fields are applied to the interdigital electrode, liquid crystals are caused to generate directional deflection, the environmental refractive index of a super-structure surface layer is changed, and therefore, a characteristic absorption peak can also generate frequency spectrum movement, so that reflection-type intensity modulation with large modulation depth is realized at the specific frequency, and the terahertz dynamic wavefront modulation function of the terahertz spatial light modulator in a transmission mode and a reflection mode is realized, the terahertz spatial light modulator has a large modulation depth, solves the technical problems of single function and low integration level of the terahertz spatial light modulator in the prior art, and has great application potential in terahertz communication, imaging and other aspects.
Drawings
Fig. 1 is a schematic structural diagram of a terahertz spatial light modulator provided by an embodiment of the present invention;
fig. 2 is a schematic structural diagram of an electrode layer according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a super structured surface layer provided by an embodiment of the present invention;
FIG. 4 is a simulation diagram of polarization selective transmission characteristics of an interdigital electrode according to an embodiment of the present invention;
fig. 5 is an enlarged schematic view of a partial structure of an interdigital electrode provided in accordance with an embodiment of the present invention;
FIG. 6 is a schematic flow chart of a method for manufacturing a terahertz spatial light modulator according to an embodiment of the present invention;
FIG. 7 is a schematic structural flow chart of a method for manufacturing a terahertz spatial light modulator according to an embodiment of the present invention;
fig. 8 is a schematic diagram illustrating a terahertz transmittance simulation of a terahertz spatial light modulator in a transmission mode according to an embodiment of the present invention;
fig. 9 is a schematic diagram of a terahertz reflectivity simulation of a terahertz spatial light modulator in a reflection mode according to an embodiment of the present invention;
fig. 10 is a schematic diagram of a power-up mode of a terahertz spatial light modulator for deflecting a light beam according to an embodiment of the present invention;
fig. 11 is a schematic diagram of a power-on mode of the terahertz spatial light modulator for focusing a light beam according to the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. It should be noted that the terms "upper", "lower", "left", "right", and the like used in the description of the embodiments of the present invention are used in the angle shown in the drawings, and should not be construed as limiting the embodiments of the present invention. In addition, in this context, it is also to be understood that when an element is referred to as being "on" or "under" another element, it can be directly formed on "or" under "the other element or be indirectly formed on" or "under" the other element through an intermediate element. The terms "first," "second," and the like, are used for descriptive purposes only and not for purposes of limitation, and do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
Fig. 1 is a schematic structural diagram of a terahertz spatial light modulator according to an embodiment of the present invention, fig. 2 is a schematic structural diagram of an electrode layer according to an embodiment of the present invention, and fig. 3 is a schematic structural diagram of a super-structured surface layer according to an embodiment of the present invention. Referring to fig. 1, the terahertz spatial light modulator provided by the present embodiment includes: a first substrate 10, a second substrate 20 and a liquid crystal layer 30 between the first substrate 10 and the second substrate 20, which are oppositely arranged, wherein a spacer 40 is arranged between the first substrate 10 and the second substrate 20 to support the liquid crystal layer 30; an electrode layer 50 and a first alignment layer 60 are arranged on one side of the first substrate 10 close to the liquid crystal layer 30, and the electrode layer 50 is arranged between the first substrate 10 and the first alignment layer 60; referring to fig. 2, the electrode layer includes a plurality of interdigital electrodes 51 arranged in an array, and each interdigital electrode 51 includes a first electrode 511 and a second electrode 512; the first electrode 511 includes a first electrode end 5111 and a plurality of first branch electrodes 5112 connected to the first electrode end 5111, the plurality of first branch electrodes 5112 extend along the first direction y and are arranged along the second direction x, and the first electrode end 5111 extends along the second direction x; the second electrode 512 includes a second electrode end 5121 and a second electrodeA plurality of second branch electrodes 5122 connected to the terminal 5121, wherein the plurality of second branch electrodes 5122 extend along the first direction y and are arranged along the second direction x, the second electrode terminal 5121 extends along the second direction x, and the first branch electrodes 5112 and the second branch electrodes 5122 are alternately arranged along the second direction x; with continued reference to fig. 1, a side of the second substrate 20 close to the liquid crystal layer 30 is provided with a super-structured surface layer 70 and a second alignment layer 80, the super-structured surface layer 70 is disposed between the second substrate 20 and the second alignment layer 80; referring to fig. 3, the super-structured surface layer includes a plurality of split ring resonators 71 arranged in an array, each split ring resonator 71 includes a first fan ring 711 and a second fan ring 712, the first fan ring 711 and the second fan ring 712 are located in the same ring, an opening between the first fan ring 711 and the second fan ring 712 is symmetrical with respect to the first direction y, and a central angle θ of the first fan ring 711 is1Less than the central angle theta of the second ring2(ii) a The first alignment layer and the second alignment layer have the same alignment direction, and the alignment direction intersects with the second direction.
The first substrate 10 and the second substrate 20 are made of a material having high transmittance to terahertz waves, such as fused silica. The spacer 40 may be a quartz microsphere or a quartz column, and may be disposed at a boundary position of the first substrate 10 and the second substrate 20. The interdigital electrodes of the electrode layer 50 and the split-ring resonators 71 of the super-structured surface layer 70 may be made of a metal material with high conductivity and stable physical and chemical properties, such as gold. Optionally, the materials of the first substrate 10 and the second substrate 20 include quartz, polyimide, or intrinsic silicon; the electrode layer 50 and the super structured surface layer 70 comprise at least one of gold, silver, copper or aluminum, and the first alignment layer 60 and the second alignment layer 80 may be photo-alignment layers.
It is understood that the illustration of the electrode layer in fig. 2 including 9 interdigital electrodes 51 is merely exemplary and not limiting on the embodiments of the present invention. Referring to fig. 2, the first electrode 511 of each interdigital electrode 51 is sequentially connected to 9 electrodes D1-D9 by leading out wires, and the second electrodes 512 of all the interdigital electrodes 51 are connected to a common electrode C1, so that the electric field formed by each interdigital electrode 51 can be controlled respectively, the number of terminals can be reduced, and the cost can be reduced. In practice, each first electrode 511 can be controlled by a Field Programmable Gate Array (FPGA), so as to adjust and control the deflection direction of the liquid crystal in the corresponding region of each interdigital electrode 51. In other embodiments, each second electrode 512 may also be connected to a respective electrode, which is not limited in this embodiment of the present invention.
Fig. 4 is a simulation diagram of polarization selective transmission characteristics of an interdigital electrode according to an embodiment of the present invention. Referring to fig. 4, when the incident terahertz wave is a transverse magnetic wave (i.e., x-direction polarization), the terahertz wave in the frequency band of 0.5THz to 2.5THz is almost completely transmitted; when the incident terahertz wave is a transverse electric wave (i.e., y-direction polarization), the terahertz wave in the frequency band of 0.5THz to 2.5THz is almost completely reflected. By utilizing the characteristic, the polarization direction of incident light is set to be the transverse magnetic wave direction, so that the terahertz wave spatial light modulator can work in a transmission mode; by setting the polarization direction of incident light as the transverse electric wave direction, the terahertz wave front modulator can work in a reflection mode.
Referring to fig. 3, each split ring resonator 71 is formed by forming two openings on one ring, which are symmetric with respect to the y direction, and the two openings are asymmetric with respect to the x direction, that is, the central angles of the first fan ring 711 and the second fan ring 712 are different, and this design aims to make the terahertz wave incident in the x direction polarized to generate the pano resonance due to the asymmetry of the structure, and to show a sharp resonance peak on the transmission spectrum line, and the modulation depth corresponding to the spatial light modulator is large.
The principle of the spatial light modulator provided by the embodiment for modulating terahertz wave transmission or reflection is as follows:
when the terahertz waves polarized in the x direction are incident, the polarization direction is along the grating vector direction formed by the first branch electrode and the second branch electrode, so that the terahertz waves can completely penetrate through the grating and are modulated by the super-structure surface layer and the covered liquid crystal layer, the asymmetric open ring structure of the split ring resonator can induce the incident terahertz waves to realize the Fano resonance type modulation effect, a sharp resonance peak can be generated at a certain specific frequency on a terahertz frequency domain spectrum, and when the environmental medium liquid crystal generates directional deflection under the action of an electric field, the environmental refractive index of the super-structure surface is changed, so that the frequency spectrum of the characteristic peak of the Fano resonance can be shifted, and the transmission type intensity modulation with large modulation depth can be realized at the specific frequency.
When the terahertz wave polarized in the y direction enters, the terahertz wave firstly passes through the super-structure surface and the liquid crystal layer and then irradiates on the grating formed by the first branch electrode and the second branch electrode, because the polarization direction is vertical to the vector direction of the grating, the incident wave is completely reflected, and the interdigital electrode, the super-structure surface and the middle liquid crystal layer form an absorber structure. The electric field of the incident electromagnetic wave and the super-structure surface generate electric dipole resonance, induction loop current is generated between the interdigital electrode and the super-structure surface, the loop current forms a magnetic dipole, the direction of the magnetic dipole is consistent with the direction of the magnetic field of the incident electromagnetic wave, and magnetic dipole resonance is generated. Therefore, at a specific resonant frequency, the energy of incident electromagnetic waves is completely lost in the structure, the complete absorption characteristic at a specific frequency is shown on a frequency domain spectrum, when the environmental medium liquid crystal generates directional deflection under the action of an electric field, the environmental refractive index of a super-structure surface is changed, and therefore the characteristic absorption peak also generates spectrum shift, so that the reflection type intensity modulation with large modulation depth is realized at the specific frequency. The terahertz wave polarized in the x direction can be incident from the first substrate side or the second substrate side, and the terahertz wave polarized in the y direction is incident from the second substrate side.
According to the technical scheme of the embodiment, the initial deflection direction of the liquid crystal is controlled through the first orientation layer and the second orientation layer, the electrode layer comprises a plurality of interdigital electrodes which are arranged in an array mode, each interdigital electrode forms a grating structure in the second direction, terahertz waves polarized along the second direction can be transmitted, and terahertz waves polarized along the first direction are reflected; by arranging the super-structure surface layer to comprise the split ring resonator, for terahertz waves polarized along the second direction, the asymmetric open ring structure of the split ring resonator can induce the terahertz waves to realize a Fano resonance type modulation effect, when different electric fields are applied to the interdigital electrodes, liquid crystals are caused to generate pointing deflection, the environmental refractive index of the super-structure surface layer is changed, and therefore the characteristic peak of the Fano resonance can generate frequency spectrum movement, and transmission type intensity modulation with large modulation depth is realized at specific frequency; for terahertz waves polarized along a first direction, an electric field of the terahertz waves and a split ring resonator generate an electric dipole resonance effect, induction ring current is generated between an interdigital electrode and the split ring resonator, a magnetic dipole is formed by the ring current, the direction of the magnetic dipole is consistent with the direction of a magnetic field of incident terahertz waves, and magnetic dipole resonance is generated, so that at a specific resonance frequency, the energy of the incident terahertz waves is completely lost in the structure, the complete absorption characteristic of a specific frequency is shown on a frequency domain spectrum, when different electric fields are applied to the interdigital electrode, liquid crystals are caused to generate directional deflection, the environmental refractive index of a super-structure surface layer is changed, and therefore, a characteristic absorption peak can also generate frequency spectrum movement, so that reflection-type intensity modulation with large modulation depth is realized at the specific frequency, and the terahertz dynamic wavefront modulation function of the terahertz spatial light modulator in a transmission mode and a reflection mode is realized, the terahertz spatial light modulator has a large modulation depth, solves the technical problems of single function and low integration level of the terahertz spatial light modulator in the prior art, and has great application potential in terahertz communication, imaging and other aspects.
Based on the above technical solution, with continuing reference to fig. 2, optionally, each interdigital electrode 51 forms a square region with a side length L1Wherein L is more than or equal to 500 mu m1≤2000μm。
It can be understood that the side length of the square area determines the resolution of the spatial light modulation, the number of the square areas determines the modulation area of the spatial light modulation, and optionally, the number of the interdigital electrodes is n × m array, wherein n is greater than or equal to 2 and less than or equal to 100, and m is greater than or equal to 2 and less than or equal to 100.
Fig. 5 is an enlarged schematic view of a partial structure of an interdigital electrode provided in an embodiment of the present invention. Referring to fig. 5, alternatively, the first branch electrode 5112 and the second branch electrode 5122 form a grating structure along the second direction x, and the period L of the grating structure2Less than the wavelength of incident light to the terahertz spatial light modulator, wherein L is not less than 10 μm2Less than or equal to 50 mu m. Optionally, each of the first branch electrode 5112 and the second branch electrode 5122 has a width L in the second direction x3Wherein L is less than or equal to 5 mu m3≤25μm。
By setting different grating structure periods and the widths of the branch electrodes, terahertz waves with different wavelengths can be modulated, and the terahertz wave modulation device can be designed according to terahertz waves to be modulated during specific implementation.
Alternatively, with continued reference to FIG. 3, the first sector ring 711 and the second sector ring 712 each have a central angle θ1And theta2The inner radius and the outer radius are R1And R2Wherein theta is more than or equal to 120 degrees1≤140°，160°≤θ2≤180°，20μm≤R1≤30μm，35μm≤R2≤45μm。
Optionally, the liquid crystal material of the liquid crystal layer is a birefringence material, and has a first refractive index and a second refractive index; when the frequency range of incident light to the terahertz spatial light modulator is 0.5 THz-2.5 THz, the difference value between the first refractive index and the second refractive index is delta n, and delta n is more than or equal to 0.2 and less than or equal to 0.4.
Optionally, the spacer has an extension length L in a direction perpendicular to the first substrate4，3μm≤L4Less than or equal to 10 mu m. Therefore, the integration level of the terahertz spatial light modulator is improved, and the liquid crystal layer is used as an environment medium instead of a phase control unit, so that the thickness of the liquid crystal layer is much thinner than that of the traditional liquid crystal terahertz spatial light modulator, the response speed of the device is high, the driving voltage is low, the filling ratio is large, the problems of low response speed, large driving voltage and the like in the traditional liquid crystal terahertz modulator are solved, and the terahertz spatial light modulator has the advantages of being small in device performance.
Fig. 6 is a schematic flow chart of a method for manufacturing a terahertz spatial light modulator according to an embodiment of the present invention, and fig. 7 is a schematic structural flow chart of the method for manufacturing a terahertz spatial light modulator according to an embodiment of the present invention. The preparation method provided by the embodiment can be used for preparing any terahertz spatial light modulator provided by the above embodiment, and the preparation method includes:
step S110, providing a first substrate 10 and a second substrate 20.
The first substrate 10 and the second substrate 20 may be rigid substrates or flexible substrates with high transmittance to terahertz waves, such as quartz, intrinsic silicon, or polyimide.
Step S120 is to form the electrode layer 50 and the first alignment layer 60 in this order on the first substrate 10 side, and to form the super-structured surface layer 70 and the second alignment layer 80 in this order on the second substrate 20 side.
The electrode layer comprises a plurality of interdigital electrodes arranged in an array, and each interdigital electrode comprises a first electrode and a second electrode; the first electrode comprises a first electrode end and a plurality of first branch electrodes connected with the first electrode end, the plurality of first branch electrodes extend along a first direction and are arranged along a second direction, and the first electrode end extends along the second direction; the second electrode comprises a second electrode end and a plurality of second branch electrodes connected with the second electrode end, the second branch electrodes extend along the first direction and are arranged along the second direction, the second electrode end extends along the second direction, and the first branch electrodes and the second branch electrodes are alternately arranged along the second direction; the super-structure surface layer comprises a plurality of split ring resonators arranged in an array, each split ring resonator comprises a first fan ring and a second fan ring, the first fan ring and the second fan ring are positioned in the same circular ring, an opening between the first fan ring and the second fan ring is symmetrical relative to a first direction, and the central angle of the first fan ring is smaller than that of the second fan ring; the first alignment layer and the second alignment layer have the same alignment direction, and the alignment direction intersects with the second direction.
In specific implementation, both the electrode layer and the super-structure surface layer may be made of a metal material with high conductivity and stable physical and chemical properties, for example, at least one of gold, silver, copper, or aluminum, the interdigital electrode and the split ring resonator may be formed by a photolithography process, the first electrode and the second electrode may be disposed in the same layer or in different layers, and may be selected according to an actual process in specific implementation, which is not limited in the embodiment of the present invention. The first alignment layer and the second alignment layer may be photo-alignment layers, which are aligned using polarized ultraviolet light.
Step S130, disposing the spacer 40 on the first substrate 10 and encapsulating the spacer with the second substrate 20, wherein the first alignment layer 60 side of the first substrate 10 is disposed opposite to the second alignment layer 80 side of the second substrate 20.
Step S140, performing polarized ultraviolet exposure alignment on the first alignment layer 60 and the second alignment layer 80, and filling a liquid crystal material between the first substrate 10 and the second substrate 20 to align the liquid crystal molecules in the alignment direction of the first alignment layer 60 and the second alignment layer 80.
The terahertz spatial light modulator prepared by the preparation method provided by the embodiment can realize a dynamic terahertz wavefront modulation function in a transmission mode and a reflection mode, has a large modulation depth, solves the technical problems of single function and low integration level of the terahertz spatial light modulator in the prior art, has great application potential in terahertz communication, imaging and other aspects, and has the advantages of simplicity, convenience, high efficiency, low cost, batch production, stable device performance and various indexes meeting the practical requirements of terahertz photonic devices.
Illustratively, in a certain embodiment, the first substrate and the second substrate are made of fused silica, the interdigital electrodes and the split-ring resonators are made of gold, the first alignment layer and the second alignment layer are made of azo dye materials, and the initial alignment direction is the y direction (parallel to the extending direction of the first supporting electrode). The liquid crystal layer is made of a liquid crystal material with high birefringence in a terahertz waveband, and the first refractive index neAnd a second refractive index no1.9+0.005i and 1.6+0.01i, respectively, and a thickness of the liquid crystal layer of 5 μm, L2＝20μm，L 310 μm, the distance p between the centers of two adjacent split-ring resonators is 100 μm, and the inner diameter R of the ring127 μm, outer diameter R of the ring 240 μm, central angle θ of the first fan ring1130 °, central angle θ of the second fan ring2170 degrees, the splitting angles between the two fan rings are the same and are (2 pi-theta)1-θ2)/2。
Fig. 8 is a schematic diagram illustrating a terahertz transmittance simulation of a terahertz spatial light modulator in a transmission mode according to an embodiment of the present invention. Referring to fig. 8, in the transmission mode, the x-direction polarized terahertz waves are directly transmitted through the interdigital electrodes without electromagnetic interaction therewith. When no power is applied, the orientation direction of the liquid crystal is the y direction, and two resonance peaks are seen on the transmission spectrum, which are respectively located at 0.67THz and 1.05 THz. The former is that the asymmetry of the split ring resonator causes the terahertz wave and the generated Fano resonance, the electromagnetic wave is strongly localized on the surface of the super structure, and the electromagnetic scattering is inhibited due to the weak coupling with the free space, so the resonance peak is sharper and the quality factor is higher; the terahertz wave and the split ring resonator interact at the frequency to generate dipole resonance, and scattering loss is large, so that the spectral line of the resonance peak is wide, and the quality factor is low. When a saturation voltage is applied to the interdigital electrodes, the molecular orientation of the liquid crystal is reconstructed along with an electric field, the liquid crystal molecules positioned right above the electrodes tend to be oriented along the terahertz wave propagation direction, and the liquid crystal molecules positioned between adjacent electrodes tend to be oriented along the x direction, so that the environmental refractive index of the super-structure surface is changed, and the corresponding resonance frequency spectrum moves to the low-frequency direction. At 0.67THz, the transmittance changed from 0.07 when the "0 state" was not energized to 0.88 when the "1 state" was energized, and the modulation depth was as high as 0.81. At 1.05THz, the transmittance changes from 0 when the "0 state" is not applied to the electric field to 0.03 when the "1 state" is applied to the electric field, and the modulation depth is only 0.03. Since the spatial light modulator requires a large modulation depth between the "0 state" and the "1 state", 0.67THz is the operating frequency in the transmissive mode.
Fig. 9 is a schematic diagram illustrating a terahertz reflectivity simulation of a terahertz spatial light modulator in a reflection mode according to an embodiment of the present invention. Referring to fig. 9, in the reflection mode, the y-direction polarized terahertz wave is reflected on the interdigital electrode, and the interdigital electrode, the metamaterial surface, and the middle liquid crystal layer jointly interact with the incident terahertz wave electromagnetically. When not powered, a sharp resonance peak is seen on the reflection spectrum, at 1.23 THz. The principle of this line is as follows: when incident waves are completely reflected, the interdigital electrodes, the super-structure surface and the middle liquid crystal layer form a super-structure absorber structure, an electric field of incident electromagnetic waves acts with the super-structure surface to form electric dipole resonance, inductive loop current is generated between the sub-wavelength interdigital electrodes and the super-structure surface, and the loop current forms magnetic dipole resonance. At the resonance frequency, the energy of the incident electromagnetic wave is thus completely lost in the structure, exhibiting an absorber function. When saturation voltage is applied to the interdigital electrode, the molecular orientation of the liquid crystal is reconstructed along with an electric field, so that the environmental refractive index of the super-structure absorber is changed, the corresponding resonance frequency spectrum moves towards the low-frequency direction, the frequency at the frequency with the minimum reflectivity reaches 60GHz, the modulation depth reaches 0.95 when the frequency is 1.23THz and the frequency is from '0 state' to '1 state', and the dynamic modulation function of the terahertz wave beam in the reflection mode is realized.
In summary, the terahertz spatial light modulator provided by the embodiment of the invention has the advantages that the sub-wavelength interdigital electrode and the super-structure surface are arranged, the orientation directions of the first orientation layer and the second orientation layer are arranged to be perpendicular to the grating vector direction of the interdigital electrode, the initial deflection direction of liquid crystal in the liquid crystal layer is controlled through the first orientation layer and the second orientation layer, the deflection direction of the liquid crystal in the liquid crystal layer under the action of an electric field is controlled through the interdigital electrode and the super-structure surface, and the interdigital electrode is used as the electrode, so that the polarization selectivity, the high transmittance and the good electric field distribution and control of the terahertz spatial light modulator in the full terahertz frequency range are ensured; the liquid crystal can be driven to deflect in the direction of a director by applying voltage to the interdigital electrode, so that the liquid crystal is induced to be arranged along the direction of an electric field, the dynamic terahertz wave front modulation function of the terahertz spatial light modulator in a transmission mode and a reflection mode is realized by combining the super-structure surface, the terahertz wave front modulation function has larger modulation depth, and the technical problems of single function and low integration level of the terahertz spatial light modulator in the prior art are solved.
The terahertz spatial light modulator provided by the embodiment of the invention can be applied to terahertz communication systems and imaging systems. Large-scale array receiving antennas and large-scale array transmitting antennas are needed in a communication system, functions of beam scanning, coupling, shaping and the like are needed in the antennas, dynamic beam deflection and focusing can be achieved by using a spatial light modulator, and the antenna modulation function is met; because a large-area terahertz detector array is very expensive, a single-pixel imaging technology can realize rapid and high-resolution terahertz imaging, the cost is low, attention is paid to the technology, and the spatial light modulator plays an important functional role in single-pixel imaging.
The embodiment of the invention further provides an application of any terahertz spatial light modulator provided based on the above embodiment, where each interdigital electrode includes a powered state ("1 state") and a non-powered state ("0 state"); the interdigital electrodes in the charged state and the uncharged state form a linear grating or a ring grating so as to deflect or focus the incident terahertz light beam. By independently controlling the electrification of each interdigital electrode, the '0 state' and the '1 state' of the terahertz wave transmitted or reflected by each region can be independently controlled, wherein the '0 state' is a state with low transmittance or reflectivity, and the '1 state' is a state with high transmittance or reflectivity, so that the binary modulation of the terahertz space light intensity can be realized.
Fig. 10 is a schematic diagram illustrating an electrical mode of a terahertz spatial light modulator for deflecting a light beam according to an embodiment of the present invention. The black and white are respectively an independent interdigital electrode area formed by the 0 state and the 1 state. The application of such a periodically varying electrical energization along the x-direction can produce an effect similar to a diffraction grating, with the deflection angle of each diffraction order being determined by the following equation:
θ＝sin-1(kλ/d)；
where k is 0, ± 1, ± 2 … … is the diffraction order, λ is the wavelength of the incident wave, d is the period of the diffraction grating, and θ is the deflection angle. Dynamic changes in the beam deflection angle can be achieved by controlling the period d of the diffraction grating at a particular operating wavelength (frequency).
Fig. 11 is a schematic diagram of a power-up mode of the terahertz spatial light modulator for focusing a light beam according to the embodiment of the present invention. The annular grating can be formed by adopting the power-on mode which periodically changes along the radius direction, and the focusing effect similar to a Fresnel zone plate is generated. Changing the power-up period along the radius direction can achieve a dynamic change of the focal length.
In other embodiments, other power-up modes can be utilized to realize the application of the terahertz wave spatial light modulator in other scenes.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims (11)

1. A terahertz spatial light modulator, comprising:
the liquid crystal display panel comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are arranged oppositely, and the liquid crystal layer is positioned between the first substrate and the second substrate;
an electrode layer and a first orientation layer are arranged on one side, close to the liquid crystal layer, of the first substrate, and the electrode layer is arranged between the first substrate and the first orientation layer;
the electrode layer comprises a plurality of interdigital electrodes arranged in an array, and each interdigital electrode comprises a first electrode and a second electrode;
the first electrode comprises a first electrode end and a plurality of first branch electrodes connected with the first electrode end, the first branch electrodes extend along a first direction and are arranged along a second direction, and the first electrode end extends along the second direction;
the second electrode comprises a second electrode end and a plurality of second branch electrodes connected with the second electrode end, the second branch electrodes extend along the first direction and are arranged along the second direction, the second electrode end extends along the second direction, and the first branch electrodes and the second branch electrodes are alternately arranged along the second direction;
a super-structure surface layer and a second orientation layer are arranged on one side, close to the liquid crystal layer, of the second substrate, and the super-structure surface layer is arranged between the second substrate and the second orientation layer;
the super-structure surface layer comprises a plurality of split ring resonators arranged in an array, each split ring resonator comprises a first fan ring and a second fan ring, the first fan ring and the second fan ring are positioned in the same circular ring, an opening between the first fan ring and the second fan ring is symmetrical relative to the first direction, and the central angle of the first fan ring is smaller than that of the second fan ring;
the first alignment layer and the second alignment layer have the same alignment direction, and the alignment direction is parallel to the second direction.
2. The terahertz spatial light modulator of claim 1, wherein each interdigital electrode forms a square region having a side length L1Wherein L is more than or equal to 500 mu m1≤2000μm。
3. The terahertz spatial light modulator of claim 1, wherein the number of interdigitated electrodes is an n x m array, where 2 ≦ n ≦ 100, and 2 ≦ m ≦ 100.
4. The terahertz spatial light modulator of claim 1, wherein the first branch electrode and the second branch electrode form a grating structure along the second direction, and a period L of the grating structure2Less than the wavelength of incident light to the terahertz spatial light modulator, wherein L is more than or equal to 10 mu m2≤50μm。
5. The terahertz spatial light modulator of claim 1, wherein each of the first and second branch electrodes has a width L in the second direction3Wherein L is less than or equal to 5 mu m3≤25μm。
6. The terahertz of claim 1A spatial light modulator, wherein the first fan ring and the second fan ring have central angles θ1And theta2The inner radius and the outer radius are R1And R2Wherein theta is more than or equal to 120 degrees1≤140°，160°≤θ2≤180°，20μm≤R1≤30μm，35μm≤R2≤45μm。
7. The terahertz spatial light modulator of claim 1, wherein the liquid crystal material of the liquid crystal layer is a birefringent material having a first refractive index and a second refractive index; when the frequency range of incident light to the terahertz spatial light modulator is 0.5 THz-2.5 THz, the difference value between the first refractive index and the second refractive index is delta n, and delta n is greater than or equal to 0.2 and less than or equal to 0.4.
8. The terahertz spatial light modulator of claim 1, wherein the spacer has an extension length L in a direction perpendicular to the first substrate4，3μm≤L4≤10μm。
9. The terahertz spatial light modulator of claim 1, wherein the first substrate and the second substrate are made of quartz, polyimide or intrinsic silicon; the electrode layer and the nanostructured surface layer comprise at least one of gold, silver, copper or aluminum.
10. A preparation method of a terahertz spatial light modulator is characterized by comprising the following steps:
providing a first substrate and a second substrate;
sequentially forming an electrode layer and a first orientation layer on one side of the first substrate, and sequentially forming a super-structure surface layer and a second orientation layer on one side of the second substrate;
arranging spacing particles on the first substrate and encapsulating the first substrate and the second substrate, wherein one side of the first alignment layer of the first substrate is opposite to one side of the second alignment layer of the second substrate;
carrying out polarized ultraviolet exposure orientation on the first orientation layer and the second orientation layer, and pouring a liquid crystal material between the first substrate and the second substrate so as to enable liquid crystal molecules to be arranged according to the orientation directions of the first orientation layer and the second orientation layer;
the electrode layer comprises a plurality of interdigital electrodes arranged in an array, and each interdigital electrode comprises a first electrode and a second electrode; the first electrode comprises a first electrode end and a plurality of first branch electrodes connected with the first electrode end, the first branch electrodes extend along a first direction and are arranged along a second direction, and the first electrode end extends along the second direction; the second electrode comprises a second electrode end and a plurality of second branch electrodes connected with the second electrode end, the second branch electrodes extend along the first direction and are arranged along the second direction, the second electrode end extends along the second direction, and the first branch electrodes and the second branch electrodes are alternately arranged along the second direction; the super-structure surface layer comprises a plurality of split ring resonators arranged in an array, each split ring resonator comprises a first fan ring and a second fan ring, the first fan ring and the second fan ring are positioned in the same circular ring, an opening between the first fan ring and the second fan ring is symmetrical relative to the first direction, and the central angle of the first fan ring is smaller than that of the second fan ring; the first alignment layer and the second alignment layer have the same alignment direction, and the alignment direction intersects the second direction.
11. Use of the terahertz spatial light modulator according to any one of claims 1 to 9, wherein each interdigital electrode comprises a powered state and a non-powered state;
the interdigital electrodes in the charged state and the non-charged state form a linear grating or a ring grating so as to deflect or focus an incident terahertz light beam.
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