CN111999939A

CN111999939A - High-frequency wireless signal generator

Info

Publication number: CN111999939A
Application number: CN202010756240.XA
Authority: CN
Inventors: 李小明; 徐振华
Original assignee: Guangzhou Railway Polytechnic
Current assignee: Guangzhou Railway Polytechnic
Priority date: 2020-07-30
Filing date: 2020-07-30
Publication date: 2020-11-27

Abstract

The invention discloses a high-frequency wireless signal generator, which comprises a first substrate, a second substrate, a photo-alignment layer, a spacer and liquid crystals, wherein the photo-alignment layer is arranged on the first substrate; the liquid crystal display panel comprises a first substrate, a second substrate, a spacer, a liquid crystal layer and a liquid crystal layer, wherein the first substrate and the second substrate are arranged oppositely, the light control orientation layers are respectively arranged on the inner surface of the first substrate and the inner surface of the second substrate, the spacer is arranged between the light control orientation layers and forms a filling space together with the first substrate and the second substrate, and the liquid crystal is contained in the filling space; the light control orientation layer is a light control orientation film with a control pattern of continuous gradual distribution of director in the radial direction, which is formed by multi-step overlapping ultraviolet polarization exposure, and the control pattern of the light control orientation film is used for controlling the continuous gradual distribution of liquid crystal molecular director of liquid crystal in the radial direction. The terahertz broadband optical fiber has the characteristics of wide band applicability, miniaturization, easy integration, high efficiency, simplicity, convenience, low cost, light weight and great application potential in the aspects of terahertz mode multiplexing communication and the like.

Description

High-frequency wireless signal generator

Technical Field

The invention relates to the technical field of terahertz photoelectrons, in particular to a high-frequency wireless signal generator and a preparation method thereof.

Background

Terahertz (THz) waves are electromagnetic waves having an oscillation frequency of 0.1 to 10 THz. It is the most unknown and developed band, has different properties from microwave and visible light, and has great potential. THz waves have lower photon energy relative to x-rays, higher imaging resolution relative to ultrasound, higher frequency relative to microwaves, and greater penetration into many dielectric materials. The characteristics make the THz technology attractive in the wide fields of medical physical examination, remote sensing, high-speed wireless communication and the like. Bessel beams (Bessel beams) are typically non-diffractive beams, have the advantages of good directivity, large depth of focus, and low transmission loss, and are widely used for optical imaging, processing, and particle manipulation. Vortex beams are another specific electromagnetic field whose wave front exhibits a helical phase distribution. It brings a new dimension for optical manipulation, which can be quantitatively described by the topological charge, which refers to the number of rotations of a wave within one wavelength. Vortex beams have significant advantages in applications such as mode division multiplexing communication and large-capacity parallel quantum computing. The combination of the two beams is expected to further improve the level of THz photonics.

Over the past few years, a number of techniques have been developed for producing specific THz beams, such as specially designed phase plates, spatial light modulators, non-uniform birefringent crystals, and super-surface devices. By these methods, specific THz beams including vortex, airy, vector and bessel beams have been demonstrated. However, the current technology has some disadvantages. They are either affected by design and manufacturing complexity or lack functional adjustability and integration capability. Therefore, there is a pressing need to develop an efficient, tunable and easily integrated method to implement THz specific beam generators. The liquid crystal has broadband birefringence and excellent electro-optic tunability. Recently, both high transparency electrodes and high quality orientation technology of THz LC devices have been addressed. In particular, uv polarized exposure oriented LCs are well suited for controlling THz phase wavefronts in a geometrically phased manner. Meanwhile, the LC-based mode converter has advantages that a half-wave condition (mode conversion efficiency maximization) can be electrically tuned in a wide band; the local optical axis is accurately and freely controlled, and any wavefront operation is realized.

The existing method for generating the terahertz Bessel beam mainly comprises a polymer cone lens, a super-structure surface designed with a V-shaped antenna, half-wave plates spliced in different optical axis directions and the like. These generation methods have disadvantages in that the devices are large in size, difficult to process, and inefficient, and thus there is a strong demand for a device that is efficient, simple, low-cost, and light and thin to generate terahertz bessel beams.

Disclosure of Invention

The invention aims to provide a high-frequency wireless signal generator and a preparation method thereof, which solve the problems of large size, difficult processing, low efficiency and the like of the conventional device.

In order to achieve the above object, an embodiment of the present invention provides a high-frequency wireless signal generator, including a first substrate, a second substrate, a photo-alignment layer, a spacer, and a liquid crystal; the first substrate and the second substrate are arranged oppositely, the light control orientation layers are respectively arranged on the inner surface of the first substrate and the inner surface of the second substrate, the spacers are arranged between the light control orientation layers and form a filling space together with the first substrate and the second substrate, and the liquid crystal is contained in the filling space; the light control orientation layer is a light control orientation film with a control pattern of continuous and gradual distribution of director in the radial direction, which is formed by multi-step overlapping ultraviolet polarization exposure, and the control pattern of the light control orientation film is used for controlling the continuous and gradual distribution of the director of liquid crystal molecules of the liquid crystal in the radial direction.

In one embodiment, the photoalignment layer is made of a sulfur azo dye.

In one embodiment, the spacer is a 400 μm thick polyester film.

In one embodiment, the first substrate and the second substrate are both 500 μm thick quartz.

In one embodiment, the liquid crystal is NJU-LDn-4 which is a liquid crystal material with an average birefringence of 0.31 and is in a range of 0.5-1.5 THz.

The embodiment of the invention also provides a preparation method of the high-frequency wireless signal generator, which comprises the following steps:

providing a first substrate and a second substrate;

forming photoalignment layers on one side of the first substrate and one side of the second substrate, respectively;

arranging a spacer on one surface of the first substrate, which is provided with the photoalignment layer, and one surface of the second substrate, which is provided with the photoalignment layer, and packaging;

carrying out multi-step overlapped ultraviolet polarization exposure on the light control orientation layer to enable the light control orientation layer to form a control pattern with continuous and gradual distribution of a director in the radial direction;

and liquid crystal is poured between the first substrate and the second substrate, and the control graph of the photo-alignment film controls the molecular director of the liquid crystal to be in radial continuous gradient distribution.

In a certain embodiment, the forming the photoalignment layer on one side of the first substrate and one side of the second substrate respectively specifically includes:

spin coating alignment layers of sulfur azo dyes on the first substrate and the second substrate, respectively, to form the photoalignment layer.

In a certain embodiment, the disposing a spacer between the side of the first substrate on which the photoalignment layer is disposed and the side of the second substrate on which the photoalignment layer is disposed specifically includes:

the side of the first substrate provided with the photoalignment layer and the side of the second substrate provided with the photoalignment layer are separated by a 400 μm thick polyester film to form a filling space.

In one embodiment, the liquid crystal pouring between the first substrate and the second substrate specifically includes:

liquid crystal material NJU-LDn-4 with average birefringence of 0.31 in the range of 0.5-1.5THz is poured into the filling space.

In a certain embodiment, the performing multiple overlapping ultraviolet polarization exposures on the photoalignment layer to make the photoalignment layer form a control pattern with continuous and gradual distribution of a director in a radial direction specifically includes:

and controlling the local azimuth angle of the finger tip of the optical control orientation layer by using a digital micro-mirror device based on dynamic micro-lithography to form a control pattern with continuous gradient distribution of a director in the radial direction.

Compared with the prior art, the high-frequency wireless signal generator provided by the embodiment of the invention has the characteristics of wide-band applicability, miniaturization, easy integration, high efficiency, simplicity, low cost and light weight, and has great application potential in the aspects of terahertz mode multiplexing communication and the like.

Drawings

In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a high-frequency wireless signal generator according to an embodiment of the present invention;

fig. 2 is a schematic view of a control pattern of an photoalignment film according to an embodiment of the present invention for controlling a continuous and gradual distribution of liquid crystal molecular directors of liquid crystals in a radial direction;

fig. 3 is a schematic flow chart of a method for manufacturing a high-frequency wireless signal generator according to an embodiment of the present invention;

fig. 4 is a schematic flow chart of a method for manufacturing a high-frequency wireless signal generator according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a simulation of a high frequency wireless signal generator according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of a simulation of a high frequency wireless signal generator according to another embodiment of the present invention;

fig. 7 is a schematic diagram of a simulation of a high-frequency wireless signal generator according to another embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be understood that the step numbers used herein are for convenience of description only and are not intended as limitations on the order in which the steps are performed.

It is to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The terms "comprises" and "comprising" indicate the presence of the described features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The term "and/or" refers to and includes any and all possible combinations of one or more of the associated listed items.

Referring to fig. 1, an embodiment of the invention provides a high-frequency wireless signal generator 100, which includes a first substrate 10, a second substrate 20, a photo-alignment layer 30, a spacer 40, and a liquid crystal 50.

The first substrate 10 and the second substrate 20 are disposed opposite to each other, the photoalignment layers 30 are respectively disposed on the inner surface of the first substrate 10 and the inner surface of the second substrate 20, the spacers 40 are disposed between the photoalignment layers 30 and form a filling space together with the first substrate 10 and the second substrate 20, and the liquid crystal 50 is contained in the filling space; the photoalignment layer 30 is a photoalignment film having a control pattern of a continuous radial gradient distribution of directors formed through multi-step overlapping ultraviolet polarization exposure, and the control pattern of the photoalignment film is used for controlling a continuous radial gradient distribution of liquid crystal molecular directors of the liquid crystal 50.

In the embodiment of the present invention, a THz Bessel Vortex Beam (BVB) generator (i.e., the high frequency wireless signal generator 100 of the present invention) combining a spiral phase and a circular grating phase is proposed, and is designed by using a liquid crystal 50 by using a geometric phase modulation method. Numerical simulations were performed on the non-diffractive propagation characteristics and orbital angular momentum mode of the transmitted wavefront. The performance of the THz BVB generator was characterized using a scanning near-field THz microscope (SNTM). The THz BVB generated by the LC geometric phase cell was characterized in accordance with the simulation and showed high mode conversion efficiency in the wide band. Wherein the THz BVB generator is designed using a geometric phase, Pancharatnam-Berry phase. It originates from photon spin-orbit interactions and can be manipulated by directional control of anisotropic media, such as LCs and super-surface resonators. For an LC plate with an orientation angle α, its jones matrix can be expressed as:

where R is a rotation matrix, ζ ═ π nd/λ is half of the phase retardation (n, d, and λ are LC birefringence, liquid crystal 50 layer thickness, and wavelength, respectively), and I is an identity matrix. For circularly polarized light, the normalized jones vectors are χ (+) (1+ i) T/Left Circular Polarization (LCP) and χ (-) (1-i) T/circular polarization (RCP). When a circularly polarized wave is incident, the output wave is described as:

for an LCP incident wave, the output wave is split into two parts. One is the remaining LCP component, without additional phase modulation. The other is the converted RCP component, which has a phase factor of exp (i2 α) that is related only to α. And vice versa.

The designed phase diagram consists of vortex phase and circular grating phase. Final phase

The following equation is satisfied:

the first term on the right is the swirl term, where m is the topological charge. The second term describes the phase of a circular grating, where Λ is the period of 0-2 π alternation along the radius r. It can act as an axicon to generate a zero order bessel beam. The non-diffraction distance L of the zero-order Bessel beam can be obtained as follows:

where R is the radius of the entire phase plate. In one embodiment, as a demonstration of concept verification, as shown in fig. 2(a) and (b), a vortex step phase m of 2 and a circular grating phase Λ of 1728 μm are designed. In addition to the phase profile, the LC layer thickness is another important factor in determining Polarization Conversion Ratio (PCR). As in equation (2), PCR ═ sin ζ²That is, when d satisfies the half-wave condition, PCR is maximized. Deviation from the half-wave condition will result in a decrease in PCR. Here, the thickness d of the liquid crystal 50 layer is set to 400 μm, and the half-wave condition at 1.2THz is satisfied.

Referring to fig. 1, fig. 1 is a schematic cross-sectional view of a high-frequency wireless signal generator 100 according to an embodiment of the invention. Specifically, the high frequency wireless signal generator 100 includes upper and lower transparent substrates, a photoalignment layer 30 attached to an inner surface of the transparent substrates, and an innermost liquid crystal layer 50, and a spacer 40 for supporting the upper and lower substrates to form a filling space for the liquid crystal 50. The director distribution of the liquid crystal molecules in the liquid crystal 50 is shown in fig. 2(c), and fig. 2(d) is a photograph (indicated by two arrows) of a LC sample made under crossed polarizers, with a scale bar of 1 mm, to form the phase template required to produce bessel vortex rotation.

The THz LC BVB generator proposed in this embodiment has the following advantages: the principle is the geometric phase modulation of the anisotropic wave plate. The phase diagram is a combination of vortex phase and circular grating. The BVB produced has the characteristics of a vortex and a bessel beam. BVBs have the topological properties described by OAM and a remarkably good directivity without diffraction induction. These unique capabilities make BVBs an ideal choice for sounding, micro-manipulation, and mode-division-multiplexing-based communications. The geometric phase mechanism and broadband birefringence properties of LCs make them useful for a broad band. In addition, half-wave conditions determine the maximum mode conversion efficiency, and in combination with the adjustability of LCs due to the external field, an adjustable and even switchable mode converter is possible. Due to the high resolution of the directivity distribution control and the flexibility of wavefront manipulation, it is reasonably desirable to freely perform various mode encodings. The geometric phase LC element is further integrated with components, so that the function of the THz element is greatly expanded, and even the active dispersion operation and the spin multiplexing THz photonics can be realized.

Therefore, compared with the prior art, the high-frequency wireless signal generator 100 provided by the embodiment of the invention has the characteristics of wide-band applicability, miniaturization, easy integration, high efficiency, simplicity, low cost, light weight and great application potential in the aspects of terahertz mode multiplexing communication and the like.

In one embodiment, the photoalignment layer 30 is made of a sulfur azo dye.

In one embodiment, the spacer 40 is a 400 μm thick polyester film.

In one embodiment, the first substrate 10 and the second substrate 20 are both made of 500 μm thick quartz.

In one embodiment, the liquid crystal 50 is a liquid crystal material NJU-LDn-4 with an average birefringence of 0.31 in a range of 0.5-1.5 THz.

In the embodiment of the invention, NJU-LDn-4 is a large birefringence liquid crystal material, and the birefringence of the material reaches 0.3 in the vicinity of 1 THz.

Referring to fig. 3 and 4, an embodiment of the invention further provides a method for manufacturing a high-frequency wireless signal generator 100, including the following steps:

s120, providing a first substrate 10 and a second substrate 20;

s121, forming photoalignment layers 30 on one side of the first substrate 10 and one side of the second substrate 20, respectively;

s122, arranging spacers 40 on the surface of the first substrate 10 on which the photoalignment layer 30 is arranged and the surface of the second substrate 20 on which the photoalignment layer 30 is arranged, and packaging;

s123, performing multi-step overlapping ultraviolet polarization exposure on the photoalignment layer 30, so that the photoalignment layer 30 forms a control pattern with a radially continuous and gradually-changing distribution of a director;

and S124, liquid crystal 50 is poured between the first substrate 10 and the second substrate 20, and the control pattern of the photoalignment film controls the molecular director of the liquid crystal 50 to be continuously and gradually distributed in the radial direction.

In one embodiment, the step S121 of forming the photoalignment layer 30 on one side of the first substrate 10 and one side of the second substrate 20 respectively includes the following steps:

alignment layers of sulfur azo dyes were spin-coated on the first substrate 10 and the second substrate 20, respectively, to form the photoalignment layer 30.

In one embodiment, in the step S122, the step of providing a spacer 40 between the side of the first substrate 10 where the photoalignment layer 30 is disposed and the side of the second substrate 20 where the photoalignment layer 30 is disposed specifically includes the following steps:

the side of the first substrate 10 provided with the photoalignment layer 30 and the side of the second substrate 20 provided with the photoalignment layer 30 are separated by a 400 μm thick mylar film to form a filling space.

In one embodiment, in the step S124, the liquid crystal 50 is poured between the first substrate 10 and the second substrate 20, which includes the following steps:

In a certain embodiment, in step S123, the performing multiple overlapping ultraviolet polarization exposures on the photoalignment layer 30 to enable the photoalignment layer 30 to form a control pattern having a continuous radial gradual distribution of a director specifically includes the following steps:

the local azimuth angle of the finger tip of the photoalignment layer 30 is controlled by using a digital micromirror device based on dynamic microlithography to form a control pattern having a continuous and gradual distribution of the director in the radial direction.

In one embodiment, before forming the photoalignment layer 30 on the first substrate 10 side and the second substrate 20 side, respectively, in step S121, the method further includes the following steps:

the first substrate 10 and the second substrate 20 are ultrasonically cleaned.

In one embodiment, the THz LC BVB generator is fabricated as shown in fig. 4. Both substrates were 500 μm thick quartz. After ultrasonic cleaning, an alignment layer of sulfur azo dye (SD1, Dainippon Ink and Chemicals inc., Chiba, Japan) was spin coated onto the substrate. Thereafter, the two substrates were assembled, and a space filled with the liquid crystal 50 was formed by separating the substrates by a 400 μm thick polyester film. The local azimuthal angle of the LC fingers is controlled using a digital micromirror device based on dynamic microlithography, resulting in the desired phase diagram shown in fig. 2 (c). After filling the gap between the two substrates with a liquid crystal material NJU-LDn-4 with an average birefringence of 0.31(0.5-1.5THz), the resulting LC orientation (FIG. 2(d)) fits well with the design.

In order to verify the performance of the high-frequency wireless signal generator 100 designed according to the embodiment of the invention, the embodiment of the invention performs numerical simulation on the THz LC BVB generator by using commercial simulation software, logical FDTD Solutions. The simulation was performed based on the phase diagram of fig. 5 (c). A simulation model is built on the xy-plane consisting of many small LC pixels. Is arranged as each pixel200 μm.times.200. mu.m.times.400. mu.m (x. times.y. times.z). The liquid crystal 50 is arranged as a diagonal dielectric material, n_o1.60 (diagonal elements xx and yy) and n_e1.91 (diagonal element zz). The spatial distribution of the LC director directions is set by the LC orientation module. Planar THz waves are incident along the z-axis. FIG. 5(a) is a simulated THz intensity distribution in the xz plane at 1.2THz for LCP waves incident, with non-diffractive distances greater than 20 mm. The central dark region corresponds to the singularity of the vortex beam. FIGS. 5(b) and 5(c) are views in which the intensity distribution of a doughnut-like shape is observed in the xy plane. The intensity of the center ring decays exponentially along the radius due to the influence of far field diffraction. The diameter of the centering ring at z-20 mm is substantially the same as the diameter at z-5 mm, verifying the non-diffractive properties of BVB. In addition, the phase distribution of the xy plane at 1.2THz was also simulated. The two centers 0-2 pi alternately show the topological kernel number m of the OAM is 2.

According to the embodiment of the invention, the THz wave generation and detection based on the photoconductive antenna are carried out by using SNTM equipment (terahertz photonics, Inc., China), and the performance of the THz BVB generator can be represented. In this apparatus, the Ex field in the x-y plane is recorded with a scanning probe fixed on a motorized stage, with a step size of 0.2 mm. The sample is moved along the z-axis in steps of 0.5mm, capturing the Ex field in the x-z plane. The measured THz intensity distribution at 1.2THz in the x-z plane is shown in fig. 6 (a). Fig. 6(b) -6(e) are THz intensity and phase distributions measured at 1.2THz at z-5 mm, 10mm, 15mm and 20mm, respectively. The distinctive doughnut-type intensity profile and vortex phase are clearly apparent. Although the diameter of the central ring was gradually increased, the results fit better with the simulation, indicating no diffraction. In order to quantitatively evaluate the beam profile on the transmission section, the intensities along the x-axis and y-axis in fig. 6(b) are plotted in fig. 6 (f). The intensity along both the x-axis and the y-axis has a drop at r-0 mm, and two peaks beside it. Exponentially decaying side lobes were also observed in the transmission profile. All spin-converted waves have a designed phase, and therefore, the mode conversion efficiency is determined by PCR. The frequency dependence of PCR is shown in FIG. 6 (g). PCR at 1.2THz close to 1 is due to optimized half-wave conditions.

The LC BVB generator operates in a wide band due to the frequency independent geometric phase modulation. The inventive examples were characterized for performance at 1.1 and 1.4THz, as shown in fig. 7(c) and 7 (d). The intensity distribution in the xz plane (fig. 7(a) and 7(b)) indicates that BVB has good non-diffractive properties. The light intensity and phase distribution of the xy plane are very similar to those of 1.2THz, verifying its ability in broadband THz wave processing.

In summary, embodiments of the present invention propose and demonstrate a specially designed non-uniform LC wave plate based geometric phase modulated high frequency wireless signal generator 100 (i.e., THz BVB generator) that combines a helical phase and a circular grating phase. The generated BVB band has topological load and good directivity. These characteristics make it suitable for advanced THz applications. Its broadband operation capability is verified and its electrical tuning efficiency can be expected. The proposed period may be further integrated with the meta-device, which may lead to an upgrade of existing hardware devices.

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

Claims

1. The high-frequency wireless signal generator is characterized by comprising a first substrate, a second substrate, a photo-alignment layer, a spacer and liquid crystals;

the first substrate and the second substrate are arranged oppositely, the light control orientation layers are respectively arranged on the inner surface of the first substrate and the inner surface of the second substrate, the spacers are arranged between the light control orientation layers and form a filling space together with the first substrate and the second substrate, and the liquid crystal is contained in the filling space; the light control orientation layer is a light control orientation film with a control pattern of continuous and gradual distribution of director in the radial direction, which is formed by multi-step overlapping ultraviolet polarization exposure, and the control pattern of the light control orientation film is used for controlling the continuous and gradual distribution of the director of liquid crystal molecules of the liquid crystal in the radial direction.

2. The high frequency wireless signal generator of claim 1, wherein the photoalignment layer is made of sulfur azo dye.

3. The high-frequency wireless signal generator according to claim 1, wherein the spacer is a 400 μm thick polyester film.

4. The high-frequency wireless signal generator according to claim 1, wherein the first substrate and the second substrate are each 500 μm thick quartz.

5. The high frequency wireless signal generator of claim 1, wherein the liquid crystal is a liquid crystal material NJU-LDn-4 with an average birefringence of 0.31 in the range of 0.5-1.5 THz.

6. A method of making a high frequency wireless signal generator, comprising:

providing a first substrate and a second substrate;

7. The method according to claim 6, wherein the forming the photoalignment layer on each of the first substrate side and the second substrate side specifically comprises:

8. The method according to claim 6, wherein a spacer is provided between a surface of the first substrate on which the photoalignment layer is provided and a surface of the second substrate on which the photoalignment layer is provided, and specifically comprises:

9. The method according to claim 8, wherein the step of pouring liquid crystal between the first substrate and the second substrate comprises:

10. The preparation method according to claim 6, wherein the performing multiple overlapping ultraviolet polarization exposures on the photoalignment layer to make the photoalignment layer form a control pattern with a continuous and gradual distribution of director in a radial direction comprises: