A terahertz wave tunable waveguide type narrowband filter

Abstract

The application provides a terahertz wave tunable waveguide type narrow-band filter and a manufacturing method thereof. The filter comprises a cavity with a rectangular structure, the upper surface and the lower surface of the cavity are low-loss metal surfaces with a periodic groove structure, a wedge-shaped protruding area is arranged in the middle of the cavity, and the two side walls are flat. The application has the advantages of simple structure, small size, low cost, easy integration, high Q value, small insertion loss, small transmission loss, and the like. The tuning of the output center frequency of the filter can be realized by adjusting the transverse position of the filter. The filter bandwidth and the transmissivity of the filter can be changed by changing the number of waveguide periods, the distance between the upper and lower flat plates, and the groove depth.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optical devices and optical communication technology, specifically relating to a terahertz wave tunable waveguide narrowband filter. Background Technology

[0002] Terahertz waves are electromagnetic waves with a frequency range of 0.1 THz to 10 THz and wavelengths between microwaves and far-infrared. Because terahertz waves occupy a special region at the transition from electronics to photonics, they possess many unique advantages and have broad research value and application prospects in fields such as broadband communication, non-destructive testing, and security inspection. However, in practical applications, terahertz systems are limited by environmental noise and application requirements. To improve the performance of terahertz systems and promote the application of terahertz waves in the field of communication, it is necessary to filter out unwanted frequency ranges and noise. Therefore, functional devices such as tunable narrowband terahertz filters have significant research significance and value.

[0003] Currently, terahertz filters are mainly based on photonic crystal structures, quantum well structures, and waveguide-based terahertz filters, and significant progress has been made in research both domestically and internationally. In 2010, Rajin Mendis et al. studied low-pass, high-pass, band-pass, and band-stop terahertz filters based on planar waveguides. In 2020, Kehui Jia, Lina Fan, and Zhaoliang Cao proposed a narrowband terahertz filter based on undulating parallel planar waveguide bandgap modulation, with a bandwidth of 5.8 GHz and a transmittance of 99.8%. Liquid crystal was added to achieve tunable filter frequency. In 2011, Zhao Dongmei, Zhou Qingli, and Li Lei et al. proposed a tunable narrowband terahertz filter based on a subwavelength array structure simulated by FDTD, achieving adjustable filtering frequency within the range of 2.5 THz to 20 THz, with a minimum bandwidth of 0.04 THz. In 2016, Chen Heming, Teng Chenchen, Zhou Wen, and others proposed a terahertz filter using garnet-type ferrite magnetic material. By changing the magnitude of the external magnetic field, they achieved low-loss narrowband filtering of THz waves, with an insertion loss of 0.0997 dB. Chinese Patent Application No. 201710585750.3 disclosed a narrowband selective and frequency-tuned terahertz narrowband filter and its method, addressing the need for narrowband filters within a bandwidth of several GHz in the terahertz band. Chinese Patent Application No. 201721274742.9 proposed a tunable terahertz narrowband filter, realizing a voltage-tunable terahertz narrowband filter that exhibits excellent transmission efficiency. Compared to the above terahertz filters, waveguide-type terahertz filters have a simpler structure, simpler manufacturing process, and are easier to integrate.

[0004] Currently, terahertz filter structures researched both domestically and internationally are mainly based on metamaterials and photonic crystals. These filter structures are relatively complex, require advanced fabrication techniques, and are difficult to manufacture, significantly impacting the application of terahertz filters. Furthermore, these non-waveguide filters are difficult to integrate, have complex tuning processes, and are challenging to implement. The tunable waveguide narrowband filter proposed in this invention has advantages such as simple structure, ease of fabrication, tunable band, and ease of integration, meeting the application requirements of terahertz waves, especially the development needs of future 6G communication technologies. Summary of the Invention

[0005] To address the aforementioned issues, the inventors, through multiple design and research efforts, have developed a terahertz-tunable waveguide narrowband filter that features low transmission loss, low insertion loss, and ease of integration.

[0006] According to the technical solution of the present invention, a terahertz tunable waveguide narrowband filter is provided, which includes a cavity with a rectangular structure. The upper and lower surfaces of the cavity are low-loss metal surfaces with periodic groove structures, and a wedge-shaped protrusion region is included in the middle. The two side walls are planar. The number of waveguide periods, the spacing between the upper and lower metal plates, the tilt angle of the symmetrical structure, and the period size in the terahertz tunable waveguide narrowband filter can all be changed according to the actual application scenario.

[0007] Furthermore, the filter bandwidth and transmittance are altered by changing the number and size of waveguide periods; the center frequency is changed by adjusting the filter's lateral position, thus achieving tunable narrowband filtering of terahertz signals. The filter linewidth is 0.001 THz, and the transmittance is higher than 97%.

[0008] Preferably, the upper and lower surfaces of the rectangular cavity are periodic groove structures with wedge-shaped protrusions and a certain tilt angle, which are symmetrical about the center. The periodic structure parameters can be designed according to the actual operating frequency band, and the tilt angle of the wedge-shaped protrusions can be selected according to the tuning accuracy. The tilt angle of the wedge-shaped protrusions is 2 to 5 degrees. The upper and lower surfaces of the rectangular cavity are made of low-loss metallic materials in the terahertz frequency band. The rectangular cavity is achieved by photolithography on a non-metallic material followed by metal coating.

[0009] More preferably, the non-metallic material is acrylic, glass, or silicon wafer; the metal is gold or silver, and the coating thickness is greater than 100 nm.

[0010] Compared with existing technologies, the terahertz-tunable waveguide narrowband filter of this invention has the following technical advantages:

[0011] 1. This invention has the advantages of simple structure, small size, low cost and easy integration; it has high Q value, low insertion loss and low transmission loss; the output center frequency of the filter can be tuned by adjusting the lateral position of the filter; the filtering bandwidth and transmittance of the filter can be changed by changing the number of waveguide periods, the distance between the upper and lower plates and the groove depth.

[0012] 2. Narrow linewidth, small size, simple structure, simple manufacturing process, and easy integration; the filter has a narrow bandwidth, the filter linewidth can reach 0.001THz, and the transmittance is higher than 97%.

[0013] 3. The filtering bandwidth and transmittance of the filter can be changed by adjusting the number of waveguide periods, the spacing between parallel plate waveguides, and the groove depth.

[0014] 4. The filter has a symmetrical structure, is bidirectional, and has no directional requirements; it has low transmission loss and low insertion loss.

[0015] 5. Compared with existing terahertz filters, the filter materials are readily available, the bandwidth is narrow, the transmittance is high, the Q value is high, and the center frequency is easy to adjust. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the terahertz-tunable waveguide narrowband filter according to the present invention;

[0017] Figure 2 yes Figure 1 A top view of the upper and lower flat surfaces used in the terahertz tunable waveguide narrowband filter.

[0018] Figure 3 This is the spectrum diagram of a terahertz-tunable waveguide narrowband filter.

[0019] The reference numerals in the attached figures are as follows: 1 for the terahertz wave incident direction, 2 for the terahertz wave emission direction, 3 for the micrometer, d and b for the filter periodic structure defect lengths, and a and c for the filter periodic structure period length and groove length, respectively. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In addition, the scope of protection of the present invention should not be limited to the specific structures, components or parameters described below.

[0021] The terahertz-tunable waveguide narrowband filter provided by this invention is a terahertz functional device that can filter out interference signals in a terahertz system, thereby improving the system's performance. The terahertz-tunable waveguide narrowband filter provided by this invention can confine terahertz waves to a certain area for transmission, resulting in low transmission loss and low insertion loss.

[0022] Furthermore, the terahertz tunable waveguide narrowband filter of the present invention includes a cavity with a rectangular structure. The upper and lower surfaces of the cavity are low-loss metal surfaces with periodic groove structures, and a wedge-shaped protrusion region is included in the middle. The side walls are planar. The number of waveguide periods, the spacing between the upper and lower metal plates, the tilt angle of the symmetrical structure, and the period size can all be changed according to the actual application scenario. By changing the number and size of the waveguide periods, the filtering bandwidth and transmittance of the filter can be changed; by adjusting the lateral position of the filter, its center frequency can be changed, thereby achieving tunable narrowband filtering of terahertz signals. The filter linewidth can reach 0.001THz, and the transmittance is higher than 97%. The filter of the present invention has the advantages of simple structure, small size, low cost, easy integration, narrow bandwidth, and low loss (insertion and transmission).

[0023] In embodiments of the present invention, such as Figure 1 As shown, a terahertz-wave tunable waveguide narrowband filter includes a cavity with a rectangular structure. The upper and lower surfaces of the cavity are low-loss metal surfaces with periodic groove structures. The upper surface of the cavity includes a wedge-shaped protrusion region in the middle, and the two side walls are planar. By adjusting the lateral position of the terahertz-wave tunable waveguide narrowband filter, the center frequency of the terahertz-wave tunable waveguide narrowband filter can be changed, thereby realizing tunable narrowband filtering of terahertz signals. Figure 1 In this process, a rectangular cavity filter is mounted on a horizontally adjustable micrometer bracket. The output center frequency of the terahertz wave tunable waveguide narrowband filter is tuned by adjusting the lateral position of the filter, thereby achieving tunable narrowband filtering of the terahertz signal. Furthermore, the terahertz wave is incident from the left incident point 1 of the terahertz wave tunable waveguide narrowband filter, passes through the filter, and exits from the right exit point 2 of the filter. Figure 3 The spectrum diagrams show the different positions of the terahertz tunable waveguide narrowband filter, with corresponding filter periodic structure protrusion lengths of 600, 800, 1000, 1200, and 1400 micrometers, respectively.

[0024] The upper and lower surfaces of the rectangular cavity are both periodic groove structures with wedge-shaped protrusions and a certain tilt angle, symmetrical about the center. The periodic structure parameters can be designed according to the actual operating frequency band, and the tilt angle of the wedge-shaped protrusions can be selected according to the tuning accuracy, typically 2 to 5 degrees. The filtering bandwidth and transmittance of the terahertz tunable waveguide narrowband filter can be changed by altering the number of waveguide periods and the depth of the periodic groove structure, and can be selected according to actual needs. In a preferred embodiment, the upper and lower surfaces of the rectangular cavity are made of low-loss metal materials in the terahertz frequency band. Their structure can be achieved by photolithography on non-metallic materials (such as acrylic, glass, silicon wafers, etc.) followed by metal (gold, silver, etc.) coating (preferably, film thickness greater than 100 nm). The structure of the upper and lower surfaces can be directly photolithographically processed on the metal surface, and the material is a low-loss metal material in the terahertz frequency band such as gold, silver, aluminum alloy, stainless steel, etc. The rectangular cavity can be encapsulated according to the design parameters after the upper and lower surfaces are fabricated.

[0025] In another embodiment, the cross-section of the periodic groove structure on the upper and lower surfaces of the rectangular cavity can be rectangular, trapezoidal, sawtooth, sine or cosine function, etc., and can be selected according to actual needs and processing methods.

[0026] like Figure 2 As shown, the width of the waveguide wedge-shaped protrusions on the upper and lower flat surfaces of the terahertz tunable waveguide narrowband filter is adjustable by adjusting the lateral position of the filter, ranging from d micrometers (μm) to b micrometers (μm), where 'a' represents the period length of the filter's periodic structure and 'c' represents the width of the photolithographic groove. The shape of the periodic grooves on the upper and lower surfaces of the cavity can be selected as rectangular, trapezoidal, sawtooth, sine, cosine, etc., depending on the actual requirements. By adjusting the lateral position of the filter, the center frequency of the filter can be changed, thereby achieving tunable narrowband filtering of terahertz signals.

[0027] Furthermore, the groove structure on the upper and lower surfaces of the waveguide is fabricated directly on the Al (aluminum) alloy surface using photolithography. The photolithography surface material can be other low-loss metal materials in the terahertz frequency band, such as gold, silver, aluminum alloy, stainless steel, etc. The shape of the periodic structure on the upper and lower surfaces of the cavity is trapezoidal, and the shape of the periodic structure on the cavity surface can be selected according to actual needs, such as rectangular, sawtooth, sine, cosine, etc. The number of waveguide periods, the spacing between the parallel plate waveguides, the tilt angle of the symmetrical structure, and the period size are variable. Changing the number of waveguide periods, the spacing between the parallel plate waveguides, and the period size can change the filter bandwidth and transmittance.

[0028] Furthermore, in Figure 2In the upper and lower surface plates shown, the waveguide structure has 10 periods on both sides of the wedge shape, the waveguide spacing between the parallel plates is 250 meters (m), and the period size 'a' is 200 meters (m). The variable-width periodic structure of the wedge shape on the upper and lower surfaces of the cavity is a groove structure with a certain tilt angle and is symmetrical about the center. The periodic structure parameters can be designed according to the actual operating frequency band, and the tilt angle can be selected according to the tuning accuracy. The waveguide tilt angle about the center is 2 degrees, and the adjustable range of the filter wedge protrusion width is from 320 meters (m) to 2000 meters (m).

[0029] Figure 3 The spectrum diagram of a terahertz-tunable waveguide narrowband filter is shown, based on... Figure 3 As can be seen, by adjusting the transverse position of the waveguide according to the order of the wedge protrusion width, transmission spectra at different output frequencies can be obtained. The center frequency of the narrowband filter shifts to lower frequencies as the wedge protrusion width increases, enabling tunable narrowband filtering of terahertz signals.

[0030] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Those skilled in the art will understand that various modifications in form and detail can be made without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A terahertz-tunable waveguide narrowband filter, characterized in that, It includes a cavity with a rectangular structure, the upper and lower surfaces of the cavity are low-loss metal surfaces with a periodic groove structure, the middle of which contains a wedge-shaped protrusion area, and the two side walls are planar. In terahertz tunable waveguide narrowband filters, the number of waveguide periodic grooves, the spacing between the upper and lower metal plates, the tilt angle of the periodic grooves, and the period size are all changed according to the actual application scenario. The filtering bandwidth and transmittance of the filter can be changed by altering the number and period size of the waveguide period grooves. The upper and lower surfaces of the rectangular cavity are periodic groove structures with wedge-shaped protrusions and a certain tilt angle that are symmetrical about the center. The parameters of the periodic groove structure are designed according to the actual operating frequency band, and the tilt angle of the wedge-shaped protrusions is selected according to the tuning accuracy. The inclination angle of the wedge-shaped protrusion is 2 to 5 degrees; The rectangular cavity filter is mounted on a horizontally adjustable micrometer bracket. The output center frequency of the terahertz wave tunable waveguide narrowband filter is tuned by adjusting the lateral position of the filter.

2. The terahertz-tunable waveguide narrowband filter according to claim 1, characterized in that, The filter linewidth is 0.001THz, and the transmittance is higher than 97%.

3. The terahertz-tunable waveguide narrowband filter according to claim 1, characterized in that, The upper and lower surfaces of the rectangular cavity are made of low-loss metallic materials in the terahertz frequency band. The rectangular cavity is achieved by photolithography on a non-metallic material and then by metal coating.

4. The terahertz-tunable waveguide narrowband filter according to claim 3, characterized in that, The non-metallic material is acrylic, glass, or silicon wafer.

5. The terahertz-tunable waveguide narrowband filter according to claim 3, characterized in that, The metal is gold or silver.

6. The terahertz-tunable waveguide narrowband filter according to claim 3, characterized in that, The coating thickness is greater than 100 nm.

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