A kind of absorptive broadband bandpass terahertz filter

Abstract

The invention discloses an absorptive broadband bandpass terahertz filter, comprising a plurality of square filter units arranged in a periodic manner, each filter unit comprising a loss absorbing film, an intermediate dielectric layer and a lossless transmission film, the intermediate dielectric layer adopts a silicon dioxide dielectric substrate, the loss absorbing film is a cross-shaped metal resonator, four metal arms of which are respectively loaded with a graphene sheet, and four ends are respectively provided with a bald Baogai-shaped metal graphic structure, and the lossless transmission film comprises four square metal sheets, each square metal sheet is surrounded by a first square metal ring at equal intervals, and the four first square metal rings are surrounded by a second square metal ring at equal intervals. The filter realizes impedance matching in an ultra-wide frequency band of 0.47 to 1.74 THz, wherein 0.33 THz to 1.16 THz realizes broadband signal low-loss transmission, the relative transmission bandwidth is 111.4%, the minimum insertion loss is 0.89 dB, and the filter realizes out-of-band absorption at 1.37 to 1.77 THz at the same time.

Description

Technical Field

[0001] The invention relates to an optical component, in particular to an absorptive broadband bandpass terahertz filter. Background Art

[0002] Terahertz (THz) has been initially applied in imaging, security inspection, electronic countermeasures, etc. due to its short wavelength, strong penetration, and non-destructive characteristics. In the field of communications, due to the high bandwidth and high rate characteristics of terahertz, the 6G system based on terahertz communication provides an important solution for future massive data transmission and high-speed wireless communication. With the rapid development of optical micro-nano technology, the contradiction between high integration and multi-function in terahertz systems has become increasingly prominent, the optical electromagnetic environment has become increasingly complex, and the communication system has higher and higher requirements for electromagnetic compatibility. As an important optical component in the terahertz system, the bandpass filter can selectively transmit signals of specified frequencies and suppress noise. However, in the design of traditional bandpass filters, out-of-band signals are often only eliminated by enhancing reflection. This part of the reflected stray signals will still affect other devices and sharply deteriorate the technical indicators of broadband communication systems. How to increase the bandwidth of the in-band working band and truly suppress out-of-band interference signals, thereby improving the integration and stability of terahertz optical devices, is of great significance.

[0003] In the microwave band, the frequency selective rasorber (FSR) can be regarded as an absorptive filter structure. Due to its characteristics of in-band transmission and out-of-band absorption, it has been increasingly studied in the field of antennas and communications in recent years. Generally, FSR is designed by cascading a bandpass frequency selective surface with an absorption layer, and has achieved certain results in the microwave band, but there are few reports in the terahertz band. At present, terahertz absorptive filters face the following bottlenecks: First, existing designs are based on multilayer structures and hollow 3-D structure technologies, and generally have air spacing layers. Although some performance has been improved, the complexity of the filter has been greatly increased, which is not conducive to the actual processing and on-chip integration of the terahertz band; second, the loss mechanism of the absorption layer in the microwave band is generally based on components such as resistors / capacitors / variable diodes, and its physical size and operating frequency limitations are difficult to extend to terahertz; third, most FSR transmission passbands are narrow, and there are often interference signals between them and the absorption band, and full-band impedance matching is not achieved. Summary of the invention

[0004] In order to solve the problem of high integration and multifunctionality of optical devices in the terahertz frequency band, the present invention proposes an absorptive broadband bandpass terahertz filter, which realizes impedance matching in the ultra-wide band of 0.47~1.74THz, wherein 0.33THz~1.16THz realizes low-loss transmission of broadband signals, with a relative transmission bandwidth of 111.4% and a minimum insertion loss of 0.89dB. The filter also realizes out-of-band absorption in 1.37~1.77THz, providing a solution for the integrated filter design of broadband communication and wave absorption. The filter also realizes a rapid conversion from transmission performance to absorption performance, improves the selectivity of the terahertz filter, and uses a single-layer dielectric substrate structure to simplify the system complexity, meet the requirements of on-chip integration of terahertz optical devices, improve the integration and stability of terahertz optical devices, and provide a wider range of practical application value for the design of terahertz optical devices.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: an absorptive broadband bandpass terahertz filter, comprising a plurality of square filter units arranged in a periodic manner, each of the filter units comprising a loss absorbing film, an intermediate dielectric layer and a lossless transmission film, the loss absorbing film and the lossless transmission film are respectively attached to the front and back of the intermediate dielectric layer, the intermediate dielectric layer adopts a silicon dioxide dielectric substrate, the loss absorbing film is a cross-shaped metal resonator, four metal arms of the cross-shaped metal resonator are respectively loaded with a graphene sheet, four ends of the cross-shaped metal resonator are respectively provided with a bald treasure cover metal graphic structure, the opening of each bald treasure cover metal graphic structure faces the center of the cross-shaped metal resonator, the lossless transmission film comprises four square metal sheets, the four square metal sheets are uniformly distributed in the four directions of the intermediate dielectric layer in a field shape, the periphery of each square metal sheet is surrounded by a first square metal ring at equal intervals, the four first square metal rings are arranged at intervals, and the periphery of the four first square metal rings is surrounded by a second square metal ring at equal intervals.

[0006] The absorptive broadband bandpass terahertz filter of the present invention realizes integrated integration technology by using a single-layer dielectric substrate. Compared with the traditional terahertz filter, the present invention reduces the number of design layers and greatly reduces the difficulty of micro-nano processing.

[0007] The absorptive broadband bandpass terahertz filter of the present invention introduces a loss absorption film of a cross-shaped metal resonator structure as a super-surface metal superstructure unit on the front side of the intermediate dielectric layer, and the cross-shaped metal resonator loaded with a graphene sheet enhances surface plasmons, utilizes its resonance characteristics, and combines the graphene sheet to produce a high-impedance absorption frequency response, thereby achieving broadband impedance matching, being able to strongly absorb terahertz waves in a wide range, and reducing interference with other components, and the cross-shaped metal resonator achieves broadband absorption of terahertz waves on the high-frequency side by exciting non-radiative annular dipoles. In addition, the absorptive broadband bandpass terahertz filter of the present invention has a tunable characteristic, and the tunable absorption intensity can be achieved by adjusting the chemical potential of the graphene sheet.

[0008] The absorptive broadband bandpass terahertz filter of the present invention introduces a lossless transmission film with a nested square metal ring structure on the back of the intermediate dielectric layer. The four square metal sheets, four first square metal rings and one second square metal ring are equivalent to a circuit in which lossless components, an inductor and a capacitor, are connected in parallel, which can generate strong resonance and realize low-frequency and broadband terahertz wave transmission. The transmission bandwidth can reach 111.4%. Compared with traditional terahertz filters, the present invention realizes broadband impedance matching, and simultaneously realizes broadband signal transmission and out-of-band absorption, providing a solution for the integrated filter design of broadband communication and wave absorption.

[0009] Preferably, the side length of the outer edge of the second square metal ring is the same as the periodic side length of one of the filter units.

[0010] Preferably, the cross-shaped metal resonator is a centrosymmetric graphic structure, a square metal graphic structure is integrally arranged at the center of the cross-shaped metal resonator, and a centrosymmetric cross-shaped hollow graphic is etched in the middle of the square metal graphic structure.

[0011] Preferably, the periodic side length P1 of each of the filter units is 40-43 μm; in each of the filter units, the thickness H1 of the intermediate dielectric layer is 50-60 μm, the thickness H2 of the loss absorbing film is the same as the thickness H3 of the lossless transmission film and H2=H3=0.5-1 μm.

[0012] Preferably, in each of the filtering units, the length of each metal arm of the cross-shaped metal resonator is L1=25~29 μm, and the width is w1=1~3 μm, the length of each graphene sheet is L2=0.5~2 μm, and the width is w2=1~3 μm, each of the bald treasure cover-shaped metal graphic structures is composed of metal strips with a side width of w3=1~3 μm, the maximum length of each of the bald treasure cover-shaped metal graphic structures is A1=3~4 μm, and the maximum width is A2=9~11 μm, and the length of each hollow arm of the cross-shaped hollow graphic is L3=7~9 μm, and the width is g=0.8~1 μm.

[0013] Preferably, the side length B1 of the square metal graphic structure is 11~13 μm, the side length B2 of each square metal sheet is 28~30 μm, each first square metal ring is composed of a metal strip with a side width w4=0.5~1 μm, the spacing w5 between the outer edge of each square metal sheet and the inner edge of the first square metal ring around it is 3~4 μm, the spacing w6 between two adjacent first square metal rings is 1~2 μm, the spacing w7 between the outer edges of the four first square metal rings and the inner edges of the second square metal ring is 1~3 μm, and the second square metal ring is composed of a metal strip with a side width w8=0.5~1.5 μm.

[0014] Preferably, the operating temperature of each graphene sheet is 300 K, the relaxation time is 0.09-0.2 ps, and the chemical potential is 0.5-0.7 eV.

[0015] Preferably, the relative dielectric constant of the silicon dioxide dielectric substrate is 1.5, and the loss tangent value is 0.001.

[0016] Compared with the prior art, the present invention has the following advantages: the absorptive broadband bandpass terahertz filter of the present invention realizes integrated integration technology by using a single-layer dielectric substrate, introduces a loss-absorbing film with a cross-shaped metal resonator structure as a metasurface metal metastructure unit on the front of the intermediate dielectric layer, and introduces a lossless transmission film with a nested square metal ring structure on the back of the intermediate dielectric layer, the filter realizes impedance matching in an ultra-wideband of 0.47~1.74 THz, wherein 0.33 THz~1.16 THz realizes low-loss transmission of broadband signals, the relative transmission bandwidth is 111.4%, and the minimum insertion loss is 0.89 dB, and the filter realizes out-of-band absorption at 1.37~1.77 THz, providing a solution for the integrated filter design of broadband communication and wave absorption. The filter realizes a rapid conversion from transmission performance to absorption performance, improves the selectivity of the terahertz filter, and simplifies the system complexity by using a single-layer dielectric substrate structure, meets the requirements of on-chip integration of terahertz optical devices, improves the integration and stability of terahertz optical devices, and provides a wider range of practical application value for the design of terahertz optical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a front view of the absorptive broadband bandpass terahertz filter in Example 1;

[0018] Figure 2 is a front view of a single filter unit in Example 1;

[0019] Figure 3 This is a schematic diagram of the dimensions of a single filter unit in Example 1;

[0020] Figure 4 For the corresponding Figure 2 Left view of;

[0021] Figure 5 is a back view of the absorptive broadband bandpass terahertz filter in Example 1;

[0022] Figure 6 for Figure 5 Schematic diagram of the dimensioning of the part above the dotted line in the upper left corner;

[0023] Figure 7 is a simulation curve diagram of S parameters of terahertz filtering in Example 1 when electromagnetic waves are incident along the -Z direction;

[0024] Figure 8 is a simulated curve diagram of the wave absorption rate of the terahertz filter in Example 1 when the electromagnetic wave is incident along the -Z direction;

[0025] Fig. 9 is a simulation curve diagram of S parameters of terahertz filtering in Example 2 when electromagnetic waves are incident along the -Z direction;

[0026] Fig.10 is a simulated curve diagram of the wave absorption rate of the terahertz filter in Example 2 when the electromagnetic wave is incident along the -Z direction;

[0027] The specific reference numerals in the figure are as follows:

[0028] 1-filter unit, 2-loss absorption film, 21-metal arm, 22-graphene sheet, 23-bald Baogai-shaped metal graphic structure, 24-square metal graphic structure, 25-cross-shaped hollow graphic, 3-intermediate dielectric layer, 4-lossless transmission film. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to the accompanying drawings.

[0030] The absorptive broadband bandpass terahertz filter of embodiment 1 is as follows Figure 1~Figure 5 As shown, it includes nine square filter units 1 arranged in a periodic manner, each filter unit 1 includes a loss absorbing film 2, an intermediate dielectric layer 3 and a lossless transmission film 4, the loss absorbing film 2 and the lossless transmission film 4 are respectively attached to the front and back of the intermediate dielectric layer 3, the intermediate dielectric layer 3 adopts a silicon dioxide dielectric substrate, the relative dielectric constant of the silicon dioxide dielectric substrate is 1.5, and the loss tangent value is 0.001, the loss absorbing film 2 is a cross-shaped metal resonator, and a graphene sheet 22 is loaded on each of the four metal arms 21 of the cross-shaped metal resonator, and the working temperature of each graphene sheet 22 is 300 K, the relaxation time is 0.11 ps, and the chemical potential is 0.6 eV, a bald T-shaped metal graphic structure 23 is integrally provided at each end of the cross-shaped metal resonator, the opening of each bald T-shaped metal graphic structure 23 faces the center of the cross-shaped metal resonator, the lossless transmission film 4 includes four square metal sheets 41, the four square metal sheets 41 are evenly distributed in the four directions of the middle dielectric layer 3 in a T-shaped shape, a first square metal ring 42 is evenly spaced around the periphery of each square metal sheet 41, the four first square metal rings 42 are spaced apart from each other, a second square metal ring 43 is evenly spaced around the periphery of the four first square metal rings 42, and the side length of the outer edge of the second square metal ring 43 is the same as the periodic side length of a filter unit 1.

[0031] In Example 1, the cross-shaped metal resonator is a centrosymmetric pattern structure, a square metal pattern structure 24 is integrally provided at the center of the cross-shaped metal resonator, and a centrosymmetric cross-shaped hollow pattern 25 is etched in the middle of the square metal pattern structure 24 .

[0032] In Example 1, the periodic side length P1 of each filter unit 1 is 41 μm; in each filter unit 1, the thickness H1 of the intermediate dielectric layer 3 is 55.4 μm, the thickness H2 of the loss absorption film 2 is the same as the thickness H3 of the lossless transmission film 4 and H2=H3=0.5 μm; in each filter unit 1, the length L1=27 μm and the width w1=2 μm of each metal arm 21 of the cross-shaped metal resonator, the length L2=0.65 μm and the width w2=2 μm of each graphene sheet 22, each bald treasure cover metal graphic structure 23 is composed of a metal strip with a side width w3=2 μm, the maximum length A1=3.5 μm and the maximum width A2=10 μm of each bald treasure cover metal graphic structure 23, the length L3=8 μm and the width g=0.8 μm of each hollow arm of the cross-shaped hollow graphic 25; the side length B1=12 μm, the side length B2 of each square metal sheet 41 is 29 μm, each first square metal ring 42 is composed of a metal strip with a side width w4=0.675 μm, the spacing w5 between the outer edge of each square metal sheet 41 and the inner edge of the first square metal ring 42 around it is 3.4 μm, the spacing w6 between two adjacent first square metal rings 42 is 1.5 μm, the spacing w7 between the outer edges of the four first square metal rings 42 and the inner edges of the second square metal rings 43 is 1.25 μm, and the second square metal ring 43 is composed of a metal strip with a side width w8=0.75 μm.

[0033] In Example 1, the loss absorbing film 2 and the lossless transmission film 4 are not electrically connected, and terahertz waves are transmitted through the intermediate dielectric layer 3, wherein the four square metal sheets 41, the four first square metal rings 42 and the one second square metal ring 43 in the lossless transmission film 4 are equivalent to a circuit in which lossless elements of inductance and capacitance are connected in parallel, and low insertion loss and wide-band transmission of terahertz waves are achieved at low frequencies by constructing a low-frequency transmission path; the loss absorbing film 2 is mainly used to absorb out-of-band electromagnetic waves at high frequencies, and generates strong resonance with the entire surface of the loss absorbing film 2 at high frequencies through graphene, and can absorb high-frequency terahertz waves within a wide frequency band, thereby achieving impedance matching and out-of-band absorption of terahertz waves through the graphene sheet 22, and preventing electromagnetic waves from being reflected at low frequencies.

[0034] The absorptive broadband bandpass terahertz filter of Example 2 is different from that of Example 1 only in that the values ​​of some size parameters are different. Specifically, in Example 2, w4=1 μm, w8=1.5 μm, and L2=2 μm.

[0035] Figure 7 This is a simulation curve of the S parameters of the absorptive broadband bandpass terahertz filter in Example 1 when the electromagnetic wave is incident vertically along the -Z direction, the incident electric field is in the y direction, and the incident magnetic field is in the x direction. For specific directions, refer to Figure 1 The three-dimensional coordinate system shown. Figure 7 In the figure, S11 represents the simulated reflection coefficient curve, and S21 represents the simulated transmission coefficient curve. Figure 7 It can be seen that when the electromagnetic wave polarization mode is TE polarization, the S11 of the filter is ≤-10 dB in the frequency range of 0.42~1.62 THz, and the relative bandwidth is 117.7%. It can be considered that the magnetic wave is not reflected, and ultra-wideband impedance matching is achieved; the S21 of the filter is ≥-3 dB in the frequency range of 0.34~0.94 THz, and the relative bandwidth is 93.75%. The electromagnetic wave can be transmitted within this frequency range, the transmission peak frequency is 0.52 THz, and the minimum insertion loss is 1.02 dB.

[0036] Figure 8 This is a simulated curve diagram of the absorptive rate of the absorptive broadband bandpass terahertz filter in Example 1 when the electromagnetic wave is vertically incident along the -Z direction. A strong absorption peak is observed at 1.67 THz, and both S11 and S21 are strongly suppressed. The absorption efficiency is 97%, and the frequency range for the absorption efficiency to be higher than 80% is 1.12 THz to 1.61 THz.

[0037] Fig. 9 This is a simulation curve of the S parameters of the absorptive broadband bandpass terahertz filter in Example 2 when the electromagnetic wave is incident vertically along the -Z direction. The incident electric field is in the y direction and the incident magnetic field is in the x direction. For specific directions, refer to Figure 1 The three-dimensional coordinate system shown. Fig. 9 In the figure, S11 represents the simulated reflection coefficient curve, and S21 represents the simulated transmission coefficient curve. Fig. 9 It can be seen that when the polarization mode of the electromagnetic wave is TE polarization, the S11 of the absorptive bandpass terahertz filter is ≤-10 dB in the frequency range of 0.47~1.74 THz, and the relative bandwidth is 114.9%. It can be considered that the magnetic wave is not reflected, and ultra-wideband impedance matching is achieved; the S21 of the absorptive bandpass terahertz filter is ≥-3 dB in the frequency range of 0.33~1.16 THz, and the relative bandwidth is 111.4%. The electromagnetic wave can be transmitted within this frequency range, the transmission peak frequency is 0.65 THz, and the minimum insertion loss is 0.89 dB.

[0038] Fig.10 This is a simulated curve diagram of the absorptive rate of the absorptive broadband bandpass terahertz filter in Example 2 when the electromagnetic wave is vertically incident along the -Z direction. A strong absorption peak is observed at 1.67 THz, and both S11 and S21 are strongly suppressed. The absorption efficiency is 97%, and the frequency range for the absorption efficiency to be higher than 80% is 1.37 THz to 1.77 THz.

[0039] The above-mentioned absorptive broadband bandpass terahertz filter achieves good impedance matching in a wide frequency band, and its reflection coefficient is less than -10dB and the bandwidth reaches 114.9%. At the same time, it realizes broadband and low-loss terahertz wave transmission at low frequency, with a relative transmission bandwidth of 111.4%. At 0.65THz, the minimum insertion loss is 0.89dB. At the same time, it realizes a rapid conversion from transmission performance to absorption performance, improves the selectivity of terahertz filtering, and can meet the requirements of multi-radar transceiver communication systems. While meeting the working frequency band bandwidth requirements, the use of a single-layer dielectric substrate structure simplifies the system complexity, improves the integration and stability of terahertz optical devices, and provides a wider range of practical application value for the design of terahertz optical devices.

Claims

1. An absorptive broadband bandpass terahertz filter, characterized in that: The invention comprises a plurality of square filter units arranged in a periodic manner, each of the filter units comprises a loss absorbing film, an intermediate dielectric layer and a lossless transmission film, the loss absorbing film and the lossless transmission film are respectively attached to the front and back sides of the intermediate dielectric layer, the intermediate dielectric layer adopts a silicon dioxide dielectric substrate, the loss absorbing film is a cross-shaped metal resonator, four metal arms of the cross-shaped metal resonator are respectively loaded with a graphene sheet, four ends of the cross-shaped metal resonator are respectively provided with a bald Bao Gai-shaped metal graphic structure, the opening of each bald Bao Gai-shaped metal graphic structure faces the center of the cross-shaped metal resonator, the lossless transmission film comprises four The invention relates to a square metal sheet, wherein the four square metal sheets are evenly distributed in the four directions of the intermediate dielectric layer in a field shape, each of the square metal sheets is surrounded by a first square metal ring at equal intervals, the four first square metal rings are arranged at intervals, the four first square metal rings are surrounded by a second square metal ring at equal intervals, the side length of the outer edge of the second square metal ring is the same as the periodic side length of one of the filtering units, the cross-shaped metal resonator is a centrally symmetrical graphic structure, the center of the cross-shaped metal resonator is integrally provided with a square metal graphic structure, and the middle of the square metal graphic structure is etched with a centrally symmetrical cross-shaped hollow graphic.

2. The absorptive broadband bandpass terahertz filter according to claim 1, characterized in that: The periodic side length P1 of each of the filter units is 40-43 μm; in each of the filter units, the thickness H1 of the intermediate dielectric layer is 50-60 μm, the thickness H2 of the loss absorption film is the same as the thickness H3 of the lossless transmission film, and H2=H3=0.5-1 μm.

3. The absorptive broadband bandpass terahertz filter according to claim 2, characterized in that: In each of the filtering units, each metal arm of the cross-shaped metal resonator has a length L1=25~29 μm and a width w1=1~3 μm, each graphene sheet has a length L2=0.5~2 μm and a width w2=1~3 μm, each of the bald treasure cover-shaped metal graphic structures is composed of metal strips with a side width w3=1~3 μm, each of the bald treasure cover-shaped metal graphic structures has a maximum length A1=3~4 μm and a maximum width A2=9~11 μm, and each hollow arm of the cross-shaped hollow graphic has a length L3=7~9 μm and a width g=0.8~1 μm.

4. The absorptive broadband bandpass terahertz filter according to claim 2 or 3, characterized in that: The side length B1 of the square metal graphic structure is 11~13 μm, the side length B2 of each square metal sheet is 28~30 μm, each first square metal ring is composed of a metal strip with a side width w4=0.5~1 μm, the spacing w5 between the outer edge of each square metal sheet and the inner edge of the first square metal ring around it is 3~4 μm, the spacing w6 between two adjacent first square metal rings is 1~2 μm, the spacing w7 between the outer edges of the four first square metal rings and the inner edges of the second square metal ring is 1~3 μm, and the second square metal ring is composed of a metal strip with a side width w8=0.5~1.5 μm.

5. The absorptive broadband bandpass terahertz filter according to claim 1, characterized in that: The operating temperature of each graphene sheet is 300 K, the relaxation time is 0.09-0.2 ps, and the chemical potential is 0.5-0.7 eV.

6. The absorptive broadband bandpass terahertz filter according to claim 1, characterized in that: The relative dielectric constant of the silicon dioxide dielectric substrate is 1.5, and the loss tangent value is 0.001.

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