A high-frequency polarization signal conversion method

Abstract

The present invention discloses a method for converting high-frequency polarization signals, which is implemented by a polarization converter. The polarization converter includes a metal plate, an insulating plate, and a metal ring, wherein the insulating plate is sandwiched between the metal plate and the metal ring. The metal plate and the insulating plate are both square. The center of the metal ring is located at the intersection of the diagonals of the square. The metal ring has two notches, which are symmetrically distributed about the diagonal of the square. The polarization converter performs the following steps: receiving a terahertz polarized wave with a preset resonant frequency and incident angle; after inputting the terahertz polarized wave, the current in the metal ring resonates with the current in the metal plate, simultaneously converting the linearly polarized wave into a circularly polarized wave. The present invention optimizes the polarization converter with a metasurface structure to achieve control of the polarization and phase of the electromagnetic wave, thereby achieving a higher polarization conversion rate in the terahertz band.

Description

Technical Field

[0001] The present invention relates to the technical field of optical communication and information processing, and in particular to a high-frequency polarization signal conversion method. Background Art

[0002] Terahertz technology has important application value in spectroscopy, imaging, security inspection, communications and other fields. Therefore, research on terahertz functional devices such as polarization converters, filters, and beam splitters has gradually become a hot topic.

[0003] A polarization converter is a functional device that adjusts the polarization state of electromagnetic waves. Traditional polarization converters utilize dichroic crystals or half-wave plates. Due to the limitations of crystal properties, these devices suffer from low conversion efficiency and narrow bandwidth. Metasurfaces, through artificially designed microstructures, can achieve physical properties not possessed by natural materials, thereby controlling the polarization and phase of electromagnetic waves. Designing structures that enable polarization converters to achieve wider bandwidths and higher conversion efficiency has become a hot topic of research. When the incident angle and polarization angle vary within a certain range, the polarization converter's signal conversion performance is affected, limiting the converter's usefulness. By studying the effects of varying incident and polarization angles on polarization conversion efficiency, the polarization converter can be made more versatile and adaptable. Summary of the Invention

[0004] To address the above technical issues, the present invention provides a high-frequency polarization signal conversion method. By optimizing the polarization converter of the metasurface structure, the polarization and phase of the electromagnetic wave can be controlled, thereby achieving a higher polarization conversion rate in the terahertz band. The technical solution is as follows:

[0005] The present invention provides a high-frequency polarization signal conversion method, which is implemented by a polarization converter. The polarization converter includes a metal plate, an insulating plate, and a metal ring. The insulating plate is sandwiched between the metal plate and the metal ring. The metal plate and the insulating plate are both square. The center of the metal ring is located at the intersection of the diagonals of the square. The metal ring has two notches, which are symmetrically distributed with the diagonal of the square as the symmetry axis.

[0006] The conversion steps of the polarization converter are:

[0007] receiving a terahertz polarized wave of a preset resonant frequency and incident angle;

[0008] After the terahertz polarized wave is input, the current of the metal ring resonates with the current of the metal plate, and the linear polarized wave is converted into a circular polarized wave.

[0009] As a preferred solution, the side lengths of the square metal plate and the insulating plate are both 100 μm.

[0010] As a preferred solution, the metal plate and the metal ring are made of any one of gold, silver, copper and aluminum.

[0011] As a preferred solution, the thickness of the metal plate and the metal ring is 0.2 μm.

[0012] As a preferred solution, the outer radius of the metal ring is 34.5 μm, and the inner radius is 29.5 μm.

[0013] As a preferred solution, the insulating plate is made of silicon dioxide, and the thickness of the insulating plate is 44.5 μm.

[0014] As a preferred solution, the high-frequency polarization signal conversion method further includes:

[0015] When the resonant frequency of the terahertz polarized wave is 0.578 THz, the current in the metal ring induces a reverse current in the metal plate;

[0016] When the resonant frequency of the terahertz polarized wave is 1.6868 THz, the current in the metal ring induces a current in the same direction in the metal plate.

[0017] As a preferred solution, in the high-frequency polarization signal conversion method, the incident angle of the terahertz polarized wave is adjusted in the range of 0 to 20 degrees.

[0018] As a preferred solution, in the high-frequency polarization signal conversion method, the polarization angle of the terahertz polarized wave is adjusted in a range of -10 degrees to 10 degrees.

[0019] As a preferred solution, the metal ring is symmetrically divided into a first semicircular ring and a second semicircular ring with the line connecting the two gaps as the symmetry axis, and the central angles of the first semicircular ring and the second semicircular ring are both 150 degrees.

[0020] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0021] The present invention provides a high-frequency polarization signal conversion method capable of achieving broadband polarization conversion of linearly polarized terahertz waves. Based on the structural optimization of a dual-open-ring resonant ring unit structure, the polarization converter is not only simpler than other polarization converters, but also forms a resonant cavity between the metal ring and the metal plate, enhancing device efficiency. Furthermore, the polarization converter achieves a wide operating bandwidth of 1.39 THz within the frequency range of 0.4934-1.883 THz. It rotates the polarization direction of incident linearly polarized terahertz waves by 90 degrees, ensuring a polarization conversion efficiency of 80%. By applying this polarization converter, the efficiency and information processing capabilities of terahertz space optical communications can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a front view of the structure of a polarization converter according to an embodiment of the present invention;

[0023] Figure 2 is a side view of the structure of a polarization converter according to an embodiment of the present invention;

[0024] Figure 3 is a rear view of the structure of a polarization converter according to an embodiment of the present invention;

[0025] Figure 4 This is a reflectivity curve diagram of a polarization converter in an embodiment of the present invention in which the thickness of the insulating plate is adjusted to 35 μm on the existing basis;

[0026] Figure 5 This is a reflectivity curve diagram of a polarization converter in an embodiment of the present invention, in which the outer ring radius is adjusted to 36 μm on the existing basis;

[0027] Figure 6 This is a reflectivity curve diagram of a polarization converter in an embodiment of the present invention, in which the inner ring radius is adjusted to 28 μm on the existing basis;

[0028] Figure 7 is a reflectivity curve of a polarization converter in which the side lengths of the insulating plate and the metal plate are both 110 μm in an embodiment of the present invention;

[0029] Figure 8 is a reflectivity curve diagram of a polarization converter with an optimized structure according to an embodiment of the present invention;

[0030] Figure 9 is the reflection coefficient r of a polarization converter in an embodiment of the present invention yx 、r xx Reflectivity curve of

[0031] Figure 10is a polarization conversion ratio (PCR) curve diagram of a polarization converter according to an embodiment of the present invention;

[0032] Figure 11 is a reflection wave phase difference curve diagram of a polarization converter in an embodiment of the present invention;

[0033] Figure 12 This is a first effect diagram of a high-frequency polarization signal conversion method according to an embodiment of the present invention;

[0034] Figure 13 This is a second effect diagram of a high-frequency polarization signal conversion method according to an embodiment of the present invention;

[0035] Figure 14 This is a third effect diagram of a high-frequency polarization signal conversion method according to an embodiment of the present invention;

[0036] Figure 15 is a polarization conversion rate (PCR) curve diagram of a conversion method of a polarization converter in an embodiment of the present invention, in which the incident angle adjustment range is 0 to 20 degrees;

[0037] Figure 16 is a polarization conversion rate (PCR) curve diagram of a polarization converter in an embodiment of the present invention, wherein the polarization angle adjustment range is from -10 degrees to 10 degrees;

[0038] Among them, 1. Metal ring; 2. Insulating plate; 3. Metal plate; 4. Current direction of the metal plate; 5. Current direction of the metal ring. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] See Figures 1 to 3 , which shows an exemplary polarization converter according to an embodiment of the present invention, comprising at least one structural unit, wherein the structural unit comprises a metal plate, an insulating plate, and a metal ring, wherein the insulating plate is sandwiched between the metal plate and the metal ring;

[0041] The metal plate and the insulating plate are both square; the center of the metal ring is located at the intersection of the diagonals of the square;

[0042] The metal ring has two notches, and the two notches are symmetrically distributed with the diagonal of the square as the symmetry axis, and symmetrically divide the metal ring into a first semicircle and a second semicircle;

[0043] Among them, the outer ring radius is set to R1, the inner ring radius is R2, the side length of a unit structure square is p, the metal thickness is d1, and the dielectric thickness between the two layers of metal is d2; the unit is μm.

[0044] See Figure 4 , which shows the reflectivity of one possible polarization converter, wherein p=100, d1=0.2, d2=35, R1=35, R2=30;

[0045] See Figure 5 , which shows the reflectivity of one possible polarization converter, wherein p=100, d1=0.2, d2=45, R1=36, R2=30;

[0046] See Figure 6 , which shows the reflectivity of one possible polarization converter, wherein p=100, d1=0.2, d2=45, R1=35, R2=28;

[0047] See Figure 7 It shows the reflectivity of one possible polarization converter, wherein p=110, d1=0.2, d2=45, R1=35, and R2=30;

[0048] See Figure 8 It shows the reflectivity of one possible polarization converter, where the side lengths of the square metal plate and the insulating plate are both 100 μm.

[0049] Preferably, the metal plate and the metal ring are made of one of gold, silver, copper and aluminum.

[0050] Preferably, the thickness of the metal plate and the metal ring is 0.2 μm.

[0051] Preferably, the outer radius of the metal ring is 34.5 μm, and the inner radius is 29.5 μm.

[0052] Preferably, the insulating plate is made of silicon dioxide and has a thickness of 44.5 μm.

[0053] In addition, an embodiment of the present invention provides a polarization converter array device, which is formed by periodically arranging a plurality of polarization converters as described above.

[0054] In this embodiment, the structure is simulated using CST microwave studio software. Since the structure itself is anisotropic, the reflected wave has two components: co-polarization and cross-polarization. The reflectivity of the x-polarized wave to the x-polarized wave is called the co-polarization reflectivity: Corresponding to SZmax(2) and Zmax(2) in the CST software; the reflectivity of the x-polarized wave to the y-polarized wave is called the cross-polarization reflectivity: Corresponding to SZmax(1), Zmax(2) in CST software. xr and E xi They represent the amplitudes of the reflected terahertz polarized wave and the incident terahertz polarized wave with polarization directions along the x-axis, and E yr The polarization conversion ratio (PCR) is related to the phase difference of the reflected terahertz wave as follows:

[0055]

[0056] Δψ=ψ yx -ψ xx (2)

[0057] In formula (2), Δψ represents the phase difference between the y component and the x component of the reflected terahertz polarization wave, ψ xx represents the phase of the reflected wave from the x-polarized wave to the x-polarized wave, ψ yx Indicates the phase of the reflected wave from the x-polarized wave to the y-polarized wave.

[0058] See Figures 9 to 11 , simulate the reflection characteristics of the double open resonant ring and obtain the reflection coefficient r yx 、r xx and the polarization conversion ratio (PCR), where Figure 9 is the reflection coefficient r yx 、r xx The reflectivity curve of Figure 10 is the polarization conversion rate (PCR) curve. From this we can know the cross polarization reflection coefficient r yx In the frequency range of 0.4934-1.883THz (bandwidth is 1.39THz), it is always greater than 90%. The polarization conversion rate is highest at 0.542THz, 1.0388THz, and 1.6616THz, and the reflection coefficient r yx are 0.99, 0.99 and 0.973 respectively, and the reflection coefficient r xxThe reflection coefficients of the co-polarized and cross-polarized waves are equal at 0.4628THz and 1.8974THz, indicating that the incident terahertz linear polarization wave can be converted into a reflected terahertz circular polarization wave. When the polarization conversion rate is 80%, the structure can rotate the polarization direction of the incident terahertz linear polarization wave by 90 degrees in the frequency range of 0.4934-1.883THz (bandwidth is 1.39THz). The CST software can be used to obtain the co-polarized reflectivity and cross-polarized reflectivity of the reflected wave, and then the phase difference of the reflected wave can be calculated according to formula (2), as shown in the following example: Figure 11 As shown, at frequencies of 0.4628 and 1.8974 THz, the co-polarized reflectivity and cross-polarized reflectivity of the reflected wave are equal, and the phase difference between the co-polarized reflected wave and the cross-polarized reflected wave is 90 degrees, indicating that the linear polarization wave is converted into a circular polarization wave.

[0059] In this embodiment, in order to deeply understand the working mechanism of the polarization converter, we can use symmetry to analyze it through coordinate transformation. The coordinate plane formed by the x-axis and the y-axis is rotated 45 degrees clockwise to obtain the u and v axes, as shown in Figure 2. Figure 1 As shown, the incident terahertz polarization wave in the y direction is composed of two components on the u and v axes. The electric field of the incident terahertz wave can be expressed as:

[0060]

[0061] The electric field of the reflected terahertz wave can be expressed as:

[0062]

[0063] Among them, the reflection coefficient r uu It represents the reflectivity of the u-polarized wave to the u-polarized wave. Indicates the reflected wave phase of the u-polarized wave to the u-polarized wave, and the reflection coefficient r vv It represents the reflectivity of the polarized wave in the v direction to the polarized wave in the v direction. Represents the phase of the reflected wave from the polarized wave in the v direction to the polarized wave in the v direction. Reflection coefficient r uv Represents the reflectivity of the polarized wave in the v direction to the polarized wave in the u direction, the reflection coefficient r vu Indicates the reflectivity of u-polarized waves to v-polarized waves.

[0064] In the u and v axis coordinate system, the reflection coefficient r is calculated uv and r vu , the two cross-polarization reflectivities are almost 0, so the electric field of the reflected terahertz wave is only related to the same polarization reflectivity, and equation (4) can be approximately expressed as:

[0065]

[0066] Co-polarization phase difference:

[0067]

[0068] In the u and v axis coordinate system, the reflection coefficient r is calculated uu and r vv , the reflectivity of the two co-polarized waves is above 95%, and three resonance peaks appear at 0.578THz, 1.1288THz, and 1.6868THz. The phase difference of the co-polarized reflected waves of the incident terahertz waves along the u and v directions is calculated, and the phase difference of the co-polarized reflected waves is obtained. In the frequency range of 0.9704-1.523THz, the phase difference range is -180 to -140 degrees. At this time, the polarization converter converts the incident linearly polarized terahertz wave into a right-handed elliptically polarized terahertz wave; in the range of 0.6086-0.9704THz and 1.523-1.958THz, the phase difference range is 150 to 220 degrees. At this time, the polarization converter converts the incident linearly polarized terahertz wave into a left-handed circularly polarized terahertz wave, and there is a phase mutation near the resonance point. According to the conditions of formula (6), the polarization direction of the reflected terahertz wave can be rotated 90 degrees. Calculations show that the polarization conversion rate of the polarization converter reaches over 90% in the range of 0.4934-1.883 THz.

[0069] According to the polarization converter and its conversion principle described above, the following conversion method is obtained:

[0070] Setting the resonant frequency and electric field strength of the terahertz polarized wave;

[0071] adjusting the incident angle of the terahertz polarized wave;

[0072] An output terahertz polarized wave is obtained, which has a phase difference of 90 degrees with the input terahertz polarized wave.

[0073] One possible implementation is that when the terahertz polarized wave is incident perpendicular to the notch of the metal ring, the first semicircular ring guides the current to the two notches respectively, and the second semicircular ring converges the current in the middle of the second semicircular ring.

[0074] See Figure 12 The terahertz polarized wave is incident along the u-axis with a resonant frequency of 0.578 THz. At this point, a double dipole resonance occurs. At the same time, the current on the double-open resonant ring structure induces a reverse current on the underlying metal plate, forming a magnetic resonance. The first semicircular ring and the second semicircular ring guide the current in the direction of the terahertz polarized wave emission.

[0075] See Figure 13The terahertz polarized wave is incident along the v-axis direction with a resonant frequency of 0.578 THz. At this point, a four-dipole resonance occurs. The first semicircular ring forms a first inductor and a second inductor, the second semicircular ring forms a third inductor and a fourth inductor, and the two gaps of the metal ring form a first capacitor and a second capacitor respectively. When the terahertz polarized wave is incident perpendicular to the gap direction of the metal ring, the current of the first semicircular ring flows toward the two gaps, and the current of the second semicircular ring converges toward the middle of the second semicircular ring. At the same time, the current on the double-open resonant ring structure induces a reverse current on the underlying metal plate, forming magnetic resonance.

[0076] One possible implementation is that when the terahertz polarized wave is incident parallel to the gap of the metal ring, the first semi-circular ring and the second semi-circular ring guide the current to the gap of the same metal ring.

[0077] See Figure 14 The terahertz polarized wave is incident along the u-axis with a resonant frequency of 1.6868 THz. A double dipole resonance occurs at this point. At the same time, the current on the double-open resonant ring structure induces the same-direction current on the underlying metal plate, forming an electric resonance. The first semicircular ring and the second semicircular ring guide the current in the direction of the incident terahertz polarized wave.

[0078] It's easy to understand that the resonant ring can be considered an LC resonant circuit, where L1, L2, L3, and L4 are the equivalent inductances of the split resonant ring, and C1 and C2 are the equivalent capacitances of the two split resonant rings. Therefore, the polarization converter reflects different phases for u- and v-polarized incident waves, and this phase difference in the reflected waves causes the polarization of the terahertz wave.

[0079] In this embodiment, the incident angle of the terahertz polarized wave is adjustable in a range of 0 to 20 degrees.

[0080] See Figure 15 The relationship between polarization conversion rate and incident angle is an important indicator to measure the performance of polarization converter. By changing the size of the incident angle, the polarization conversion rate is simulated and analyzed. Figure 6 It can be seen that when the terahertz wave is incident at an angle of 0-20 degrees, the polarization converter achieves a polarization conversion efficiency of over 70% within the frequency range of 0.4934-1.883THz. Compared to existing technologies, when the incident angle is 20 degrees, the polarization conversion efficiency is still above 80% in the frequency ranges of 0.4934-1.1054THz and 1.1396-1.8038THz, thus ensuring a high polarization conversion efficiency while achieving a wide range of incident angle adjustment.

[0081] See Figure 16The polarization angle also affects the polarization conversion rate. When the frequency is 0.4934-1.883THz and the polarization angle is between -10 degrees and 10 degrees, the polarization conversion rate is greater than 70%.

[0082] See Figure 8 , which shows the optimal effect of the polarization converter. In a preferred embodiment of the polarization converter, the polarization converter includes a metal plate, an insulating plate, and a metal ring. The insulating plate is sandwiched between the metal plate and the metal ring. The thickness of the metal plate and the metal ring is 0.2 μm. The insulating plate is made of silicon dioxide, and the thickness of the insulating plate is 44.5 μm.

[0083] The metal plate and the insulating plate are both square; wherein the side lengths of the square metal plate and the insulating plate are both 100 μm.

[0084] The outer radius of the metal ring is 34.5 μm, and the inner radius is 29.5 μm. The metal ring is symmetrically divided into a first semicircle ring and a second semicircle ring with the line connecting the two gaps as the symmetry axis, and the central angles of the first semicircle ring and the second semicircle ring are both 150 degrees.

[0085] When the frequency of the received terahertz polarized wave is 0.4934-1.883THz, the polarization direction of the incident terahertz linear polarized wave is rotated 90 degrees; the polarization conversion rate is greater than 80%, and the polarization conversion rate is highest at 0.542THz, 1.0388THz, and 1.6616THz, with the reflection coefficients ryx being 0.99, 0.99, and 0.973, respectively, and the reflection coefficients rxx being 0.01, 0.005, and 0.01, respectively. At 0.4628THz and 1.8974THz, the reflection coefficients of the co-polarized and cross-polarized waves are equal.

[0086] Embodiments of the present invention provide a high-frequency polarization signal conversion method capable of achieving broadband polarization conversion of linearly polarized terahertz waves. Based on the structural optimization of a dual-slit resonant ring unit structure, the polarization converter not only has a simpler structure than other polarization converters, but also forms a resonant cavity with the metal ring and the metal plate, enhancing the efficiency of the device. Furthermore, when the input wave frequency is within the range of 0.4934-1.883 THz, the polarization converter achieves a polarization conversion rate greater than 80%. With this polarization conversion rate, the bandwidth is 1.39 THz, achieving a wide operating bandwidth while maintaining excellent polarization conversion performance. By applying this polarization converter, the efficiency and information processing capabilities of terahertz space optical communications can be improved.

[0087] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A high-frequency polarization signal conversion method, characterized in that: The invention is implemented by a polarization converter, which includes a metal plate, an insulating plate, and a metal ring, wherein the insulating plate is sandwiched between the metal plate and the metal ring; the metal plate and the insulating plate are both square; the center of the metal ring is located at the intersection of the diagonals of the square; the metal ring has two notches, which are symmetrically distributed with the diagonal of the square as the symmetry axis; the polarization converter is used to rotate the polarization direction of the incident terahertz linear polarization wave by 90 degrees within the frequency range of 0.4934-1.883THz; The conversion steps of the polarization converter are: Receive a terahertz polarized wave with a preset resonant frequency and incident angle; the incident angle of the terahertz polarized wave can be adjusted in a range of 0 to 20 degrees; and the polarization angle of the terahertz polarized wave can be adjusted in a range of -10 to 10 degrees; After the terahertz polarized wave is input, the current of the metal ring resonates with the current of the metal plate, and the linear polarized wave is converted into a circular polarized wave.

2. The high-frequency polarization signal conversion method according to claim 1, wherein: The side lengths of the square metal plate and the insulating plate are both 100 μm.

3. The high-frequency polarization signal conversion method according to claim 1, wherein: The metal plate and the metal ring are made of any one of gold, silver, copper and aluminum.

4. The high-frequency polarization signal conversion method according to claim 1, wherein: The thickness of the metal plate and the metal ring is 0.2 μm.

5. The high-frequency polarization signal conversion method according to claim 1, wherein: The outer radius of the metal ring is 34.5 μm, and the inner radius is 29.5 μm.

6. The high-frequency polarization signal conversion method according to claim 1, wherein: The insulating plate is made of silicon dioxide, and has a thickness of 44.5 μm.

7. The high-frequency polarization signal conversion method according to claim 1, wherein: The metal ring is symmetrically divided into a first semicircular ring and a second semicircular ring with the line connecting the two notches as the symmetry axis, and the central angles of the first semicircular ring and the second semicircular ring are both 150 degrees.

8. The high-frequency polarization signal conversion method according to any one of claims 1 to 7, wherein: Also includes: When the resonant frequency of the terahertz polarized wave is 0.578 THz, the current in the metal ring induces a reverse current in the metal plate; When the resonant frequency of the terahertz polarized wave is 1.6868 THz, the current in the metal ring induces a current in the same direction in the metal plate.

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