Hyperphosphorimetric chain metal-lined hole hyperplane optical fiber tunable terahertz filter

Abstract

The utility model discloses a kind of super rhombus chain metal lining hole superplane optical fiber tunable terahertz filter, comprising: super rhombus chain structure and metal lining hole superplane optical fiber, wherein super rhombus chain structure is integrated in the plane area of metal lining hole superplane optical fiber.The filter can realize high Q value, frequency tunable and larger maximum stopband attenuation filtering in 0.1~3THz range with the change of rotation angle and carrier concentration of super rhombus chain structure.Adopt metal lining hole superplane optical fiber, the utility model can effectively solve the terahertz wave loss and the restriction of integration difficulty of other free space terahertz filter;Super rhombus chain structure can fully interact with evanescent field leaked in superplane optical fiber plane area, and good tunable filtering effect can be obtained under the irradiation of pump light.

Description

Technical Field

[0001] This invention belongs to the field of terahertz wave application technology, specifically relating to a tunable terahertz filter made of super-rhomboid chain metal-lined hyperplane fiber, which is suitable for terahertz wave signal processing in fields such as medical treatment, sensing, communication and imaging. Background Technology

[0002] Terahertz (THz) waves, located between microwaves and infrared radiation, possess advantages such as high transmission rate, large capacity, strong directionality, enhanced security, and good penetration, making them widely used in medical, sensing, communication, and imaging fields. However, the practical application of terahertz technology is limited by the development of high-performance devices, among which filters, as a core component, directly affect the accuracy and efficiency of signal processing.

[0003] Although researchers have recently developed a series of high-performance spatial optical terahertz filters using cutting-edge techniques such as metasurfaces, metamaterials, and integration technologies to construct resonant modes such as localized surface plasmon resonance and continuum bound states, these technologies still face many challenges in practical applications. On the one hand, the high cost limits the feasibility of large-scale production; on the other hand, the high loss of terahertz waves in free space affects signal transmission efficiency. Furthermore, the complex and difficult integration process further hinders its widespread adoption in practical applications. Simultaneously, the short distance between light and matter leads to a low resonant quality factor (Q value) and insufficient filter selectivity. Moreover, these filters often lack or only possess narrow-range frequency tunability, significantly reducing their ability to process complex signals. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by providing a tunable terahertz filter and its terahertz filtering method using a super-rhombohedral chain metal-apertured hyperplane fiber. This method reduces transmission loss through metal apertures and utilizes the interaction between the evanescent field enhancement of the hyperplane fiber and the super-rhombohedral chain, combined with optical pump carrier concentration modulation, to achieve wide-range, high-Q frequency tuning. This solves the key problems of high cost, high loss, difficult integration, difficult tuning, and low Q value of traditional terahertz filters.

[0005] The above-mentioned objectives of the present invention are achieved through the following technical solutions:

[0006] A tunable terahertz filter made of super-rhombic chain metal-lined hyperplane fiber is characterized by comprising:

[0007] The metal-lined superplanar optical fiber (1) has a cross-section comprising large air holes (5) with a metal film (4) deposited on the inner wall of the outer ring and small air holes (6) arranged periodically in the inner layer. The metal-lined superplanar optical fiber (1) has a planar region (3) extending along the optical fiber axis. The planar region (3) is a semi-circular cross-sectional structure formed by processing.

[0008] The super-rhomboid chain structure (2) is integrated on the longitudinal centerline of the planar region (3) and is made of semiconductor material. Its cross-section consists of a rectangular body and a rhomboid body. The rhomboid body is composed of multiple congruent rhomboids connected in series. One end of the rhomboid body is connected to the rectangular body, and the apex of the rhomboid body at the other end is ground flat and connected to the planar region (3) of the metal-filled super-planar optical fiber (1) to ensure that the super-rhomboid chain structure (2) and the planar region (3) form optical coupling and generate electromagnetic resonance to achieve terahertz wave filtering.

[0009] When a terahertz wave couples into a filter, its evanescent field excites electromagnetic resonance on the superrhombic chain structure during transmission. This electromagnetic resonance mechanism can form a narrow-bandwidth filter stopband, thereby achieving a high-Q filtering effect.

[0010] Metal-filled fiber is a type of optical fiber used for transmitting terahertz waves. Its cross-section contains hollow metal fillers and small air holes. The metal fillers are large air holes with an inner wall of a metal film. The thickness of the metal film can be any of 10–200 nm, and the material of the metal film can be gold, silver, or aluminum. The diameter of the large air holes is any of 20–80 μm, and the diameter of the small air holes is any of 8–40 μm. The annular arrangement of metal fillers outside the fiber core can resonate within a specific terahertz frequency range, thereby localizing the terahertz wave within the fiber core and reducing transmission loss.

[0011] Hyperplanar fiber is a specially processed type of optical fiber. Typically, through microfabrication techniques such as physical cutting or chemical etching, the cladding and core of a specific length of the fiber are removed, resulting in a unique structure with a semi-circular end face. This planar region acts as a "leakage window" for light transmission within the core, allowing evanescent field energy to more easily leak out and interact with the hyperrhombic chain structure within the planar region.

[0012] The super-rhombohedral chain structure has a cross-section composed of multiple congruent rhombohedral shapes arranged in a line, with one end connected to a rectangle and the other end having one corner of a rhombohedral shape ground flat. This structure, at specific dimensions, produces a strong band-stop filtering effect for terahertz waves in a specific frequency band. After the terahertz wave couples into the filter, the evanescent field generates electromagnetic resonance on the super-rhombohedral chain structure, thereby forming a narrow-bandwidth filter stopband.

[0013] Optionally, the metal-filled optical fiber is a terahertz optical fiber composed of polymer material and metal film, with hollow metal fillers and small air holes distributed in its cross-section. The metal fillers are large air holes with metal film as the inner wall, the thickness of the metal film is 10~200 nm, the diameter of the large air hole is 20~80 μm, and the diameter of the small air hole is 8~40 μm.

[0014] Optionally, the number of rhombuses in the super-rhombus chain structure is 3 to 10, the side length of the rhombus is 20 to 100 μm, and the length of the rectangle is 10 to 200 μm; the overlapping area of ​​each rhombus accounts for 20 to 50% of the area of ​​a single rhombus, and the flattened part accounts for 1 to 40% of the area of ​​a single rhombus; the depth of all rectangular pillars and rhombus pillars is consistent at 10 to 200 μm; the super-rhombus chain structure is integrated into the longitudinal centerline of the hyperplane fiber, and the whole structure presents a super-rhombus chain structure in the planar region of the hyperplane fiber; the rotation angle of the super-rhombus chain structure is 0 to 90°, and the rotation axis is the longitudinal centerline of the fiber center.

[0015] Optionally, the length of the planar region (3) is 1-5 mm, and it is formed by precision machining using a CNC machine tool, with a surface roughness of less than 100 nm.

[0016] Optionally, the semiconductor material of the superrhombic chain structure is one of silicon, germanium, or III-V compound semiconductors, and its carrier concentration can be adjusted by external pump light.

[0017] The super-rhomboid chain structure (2) achieves frequency tuning in the following way:

[0018] Mechanical tuning: The coupling state between the super-rhomboid chain structure (2) and the optical fiber is changed by rotating the chain structure. The tuning range is 1.12-1.16 THz.

[0019] Optical tuning: The carrier concentration can be changed by pump light (8), and the tuning range can reach 35.95 GHz.

[0020] The present invention also discloses a terahertz filtering method based on the above-mentioned filter, characterized by the following steps: (1) a terahertz wave (7) is coupled into the input end of a metal-perforated hyperplane fiber (1); (2) during transmission, the terahertz wave interacts with the super-rhomboid chain structure (2) through the evanescent field of the planar region (3) to form a stopband at the resonant frequency; (3) a terahertz wave at a non-resonant frequency is output from the output end; (4) the carrier concentration of the super-rhomboid chain structure (2) is changed by adjusting the intensity of the pump light (8) to achieve dynamic tuning of the resonant frequency.

[0021] Furthermore, it also includes performance optimization steps:

[0022] Determine the optimal structural parameters through finite element simulation;

[0023] Super-rhombic chain structures were prepared using high-precision micromachining technology (2);

[0024] The filtering performance was tested using a terahertz time-domain spectroscopy system.

[0025] Fine-tune the structural parameters based on the test results to obtain the optimal Q value and stopband attenuation.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] Employing a metal-coated metaplanar fiber structure effectively reduces terahertz wave loss in free space, enhances the interaction distance between the super-rhombic chain structure and terahertz waves, improves stopband attenuation, and reduces insertion loss. Using a super-rhombic chain structure as a filter structure effectively improves the Q value of the terahertz filter. Optical tuning techniques allow for the control of carrier concentration in the super-rhombic chain structure by introducing photogenerated carriers, thereby adjusting the filter's resonant frequency. Attached Figure Description

[0028] Figure 1 is a schematic diagram of the structure of the terahertz filter according to an embodiment of the present invention;

[0029] Figure 2 is a schematic diagram of the terahertz fiber end face structure according to an embodiment of the present invention;

[0030] Figure 3 is a schematic diagram of the cross-sectional structure of the planar region of the metal-filled superplanar optical fiber according to an embodiment of the present invention;

[0031] Figure 4 is a schematic diagram of the super-rhomboid chain structure according to an embodiment of the present invention;

[0032] Figure 5 is a schematic diagram of the working principle of the terahertz filter according to an embodiment of the present invention;

[0033] Figure 6 is a simulated electric field diagram of the planar region cross-section of the metal-filled superplanar optical fiber according to an embodiment of the present invention;

[0034] Figure 7 shows the transmission spectra of terahertz filters at different angles according to an embodiment of the present invention;

[0035] Figure 8 This is a diagram showing the effect of angle change on the Q value and maximum stopband attenuation of the terahertz filter in an embodiment of the present invention.

[0036] Figure 9 shows the effect of angle change on the resonant frequency of the terahertz filter according to an embodiment of the present invention.

[0037] Figure 10 shows the transmission spectra of terahertz filters with different carrier concentrations according to an embodiment of the present invention.

[0038] Figure 11 shows the effect of carrier concentration variation on the Q value and maximum stopband attenuation of the terahertz filter in an embodiment of the present invention.

[0039] Figure 12 shows the effect of carrier concentration variation on the resonant frequency of the terahertz filter according to an embodiment of the present invention.

[0040] Icons: 1-Metal-lined superplanar fiber; 2-Super rhombic chain structure; 3-Planar region; 4-Metal film; 5-Large air hole; 6-Small air hole; 7-Terahertz wave; 8-Pump light; 9-Cross-section of super rhombic chain structure. Detailed Implementation

[0041] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate the following embodiments, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0042] Please refer to the following first. Figure 1 Figure 1 is a schematic diagram of the terahertz filter structure according to an embodiment of the present invention. As shown in Figure 1, this embodiment of the present invention provides a tunable terahertz filter using a super-rhombic chain metal-apertured hyperplane fiber, comprising: an upper super-rhombic chain structure 2 and a lower processed metal-apertured hyperplane fiber 1. The super-rhombic chain structure 2 is integrated on the planar region 3 of the metal-apertured hyperplane fiber 1. When a terahertz wave couples into the metal-apertured hyperplane fiber 1, the terahertz wave at the resonant frequency is localized in the upper super-rhombic chain structure 2 and filtered by the structure during transmission. The remaining frequency bands are output from the metal-apertured hyperplane fiber 1 to achieve filtering. By changing the carrier concentration of the super-rhombic chain structure by applying an external vertical pump light, the resonant frequency of the filter is significantly shifted, thus achieving tunable filtering.

[0043] The metal-perforated hyperplane fiber 1 used in this embodiment of the invention is made of high-density polyethylene. As shown in Figure 2, the end face of the metal-perforated hyperplane fiber 1 has an outer layer consisting of multiple large air holes 5 arranged in a ring, and an inner wall coated with a metal thin film 4, forming a metal-dielectric composite waveguide structure. The inner layer has a uniformly distributed array of small air holes 6, constituting a photonic bandgap structure. In this embodiment, the diameter of the metal-perforated hyperplane fiber 1 is 1 mm, suitable for transmitting terahertz waves with frequencies of 0.1-3 THz, effectively reducing terahertz wave loss.

[0044] Using a CNC machine tool, the fiber cladding and part of the fiber core are cut to obtain a semi-circular cross-section of the planar region 3. The planar region is approximately 2 mm long, forming a "leakage window" for light transmission in the fiber core. Evanescent field energy easily leaks out from the planar region 3 and is localized within the super-rhomboid chain structure 2 designed with a side-polished surface. Adjusting the parameters of the CNC machine tool can also change the length and remaining amount of the planar region. A longer planar region results in a stronger interaction between the leaked terahertz waves and the planar structure. The metal-filled perforated superplanar fiber 1 used in this embodiment of the invention can effectively reduce the transmission loss of terahertz waves. Furthermore, by changing the length and remaining amount of the planar region, the interaction strength between the terahertz waves and the structure on the polished area can be effectively enhanced.

[0045] As shown in Figure 4, the upper layer of this embodiment of the invention has a carrier concentration of 1×10⁻⁶. 15 / cm 3 A super-rhombohedral chain structure 2, with a carrier migration rate of 100 cm² / (V·s) and made of silicon, is integrated in the longitudinal centerline of the planar region 3 shown in Figure 3. The super-rhombohedral chain structure 2 is constructed by high-precision physical cutting technology, cutting a smooth circular silicon substrate with a diameter of 50 cm into a structure consisting of multiple congruent rhombohedrals and a rectangle at one end arranged in a line using a high-precision mechanical cutter. One corner of each rhombohedral is ground flat. There are 5 rhombohedrals, each with a side length of 45 μm, and the rectangles are 100 μm long. The overlapping area of ​​each rhombohedral is 45% of the area of ​​a single rhombohedral, and the ground area is 10% of the area of ​​a single rhombohedral. All rectangular and rhombohedral pillars have a uniform depth of 100 μm. The rotation angle of the super-rhombohedral chain structure is 10°, and the rotation axis is the longitudinal centerline of the geometric center of the complete optical fiber cross-section. The super-rhomboid chain structure 2, under specific dimensions and rotation angles, can effectively localize and filter terahertz waves with a center frequency of 1.1648 THz and a half-width of 0.0009986 THz, achieving a maximum stopband attenuation of 2.77 dB and a Q value of 1149.8. The Q value is an important indicator for measuring filter performance. The higher the Q value, the better the selectivity of the filter, that is, it can more accurately filter terahertz waves of specific frequencies and reduce interference from terahertz waves of other frequencies.

[0046] like Figure 5The diagram illustrates the working principle of this embodiment, with a terahertz source and a terahertz detector connected to both ends of the optical fiber. After the terahertz wave couples into the metal-perforated hyperplane optical fiber 1, filtering is achieved. Upon input of the terahertz wave, the evanescent field leaks out from the planar region. On one hand, the metal perforation efficiently localizes the terahertz wave within the fiber core, reducing transmission loss and ensuring stable signal transmission. On the other hand, the super-rhomboid chain structure 2 has an extremely high Q value, enabling filtering within a very narrow half-width range, laying the foundation for precise terahertz wave filtering. Furthermore, this modulator employs a hyperplane optical fiber structure, ensuring a sufficiently long flat region, increasing the interaction length between the terahertz wave and the super-rhomboid chain, effectively improving the efficiency of light-matter interaction, achieving better maximum stopband attenuation for the terahertz wave, and enhancing the filtering effect.

[0047] like Figure 6 The figure shows the electric field distribution at the resonant frequency of the embodiment. This figure presents the electric field distribution of the terahertz filter at a specific resonant frequency, and the terahertz filter is simulated and analyzed using the finite element method. As can be seen from Figure 6, most of the terahertz wave is localized within the super-rhomboid chain structure. A significant electric field localization effect is particularly evident in the lower and middle parts of the super-rhomboid chain structure. This phenomenon indicates that the terahertz wave at the resonant frequency is first absorbed by the super-rhomboid chain structure, then oscillates in three main regions, thereby consuming most of the terahertz energy and significantly reducing the transmittance of the terahertz wave, ultimately achieving efficient filtering. This simulation result not only verifies the crucial role of the super-rhomboid chain structure in the terahertz filter but also provides important theoretical basis for further optimizing filter performance.

[0048] Figure 7 shows the transmission spectra of the embodiment at different angles. The finite element method was used to simulate the terahertz filter, demonstrating the impact of angle changes on filter performance. As the angle increased from 0° to 15°, the resonant frequency showed a decreasing trend, but the sharpness of the resonant peak exhibited a pattern of first increasing and then decreasing. Specifically, the sharpness of the resonant peak reached its maximum at an angle of 10°, corresponding to a resonant frequency of 1.14823 THz. This phenomenon is because too small an angle causes the three localized electric field locations to be too far from the optical fiber, resulting in some terahertz waves escaping into the air during transmission, thus reducing the efficiency of the localized electric field. Conversely, too large an angle causes the structure to be too far from the other side of the optical fiber, making it impossible to uniformly localize the terahertz waves within the fiber, leading to a decrease in filtering performance. Therefore, choosing an appropriate angle is crucial for achieving higher Q values ​​and better filtering performance. Furthermore, different angles cause changes in the equivalent refractive index of the filter, thereby altering the filter's resonant frequency.

[0049] Figure 8 shows the changes in Q value and stopband attenuation of the resonant peak at different angles of the cross section in the embodiment. The terahertz filter was simulated using the finite element method. As can be seen from Figure 8, the maximum Q value of 1149.8 and the stopband attenuation of 2.77 dB can be achieved at the 10° angle of cross section 9 in Figure 6. At the same time, Q values ​​of more than 500 and stopband attenuation of more than 1 dB can be achieved at angles between 0 and 15°.

[0050] Figure 9 shows the variation of the maximum stopband attenuation depth for different cross-sectional dimensions in the embodiment. The terahertz filter was simulated using the finite element method. As can be seen from Figure 9, increasing the angle will reduce the resonant frequency of the filter.

[0051] As shown in Figures 10 and 11, when a pump light is applied vertically to the superrhombic chain structure, the carrier concentration increases from 1 × 10⁻⁶. 15 / cm 3 Increased to 1.5×10 16 / cm 3 During the process, the absolute value of the stopband attenuation gradually decreases; simultaneously, as shown in Figure 12, the resonant frequency gradually increases from 1.14823 THz to 1.18418 THz, achieving a maximum frequency tuning range of 35.95 GHz. This is because the refractive index and conductivity of the superrhombic chain structure change with the increase in carrier concentration, leading to changes in the optical properties of the filter and thus altering its resonant frequency, achieving a wide range of tunable filtering.

[0052] As can be seen from the above, this invention can effectively improve the high cost, high loss, difficult integration, difficult tuning, and low Q value of other terahertz filters, and obtain a low-cost, low-loss, easy-to-integrate, easy-to-tunable, and high-Q filter based on a super-rhomboid chain structure 2 with metal aperture superplane fiber 1, which has outstanding and significant technical effects.

[0053] While the embodiments disclosed in this invention are as described above, their content is merely for the purpose of facilitating understanding of the technical solutions of this invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and changes to the form and details of the implementation without departing from the core technical solutions disclosed in this invention; however, the scope of protection defined by this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A tunable terahertz filter using a super-rhombic chain metal-coated hyperplane fiber, characterized in that, include: The metal-lined superplanar optical fiber (1) has a cross-section comprising large air holes (5) with a metal film (4) deposited on the inner wall of the outer ring and small air holes (6) arranged periodically in the inner layer. The metal-lined superplanar optical fiber (1) has a planar region (3) extending along the optical fiber axis. The planar region (3) is a semi-circular cross-sectional structure formed by processing. The super-rhomboid chain structure (2) is integrated on the longitudinal centerline of the planar region (3) and is made of semiconductor material. Its cross-section consists of a rectangular body and a rhomboid body. The rhomboid body is composed of multiple congruent rhomboids connected in series. One end of the rhomboid body is connected to the rectangular body, and the apex of the rhomboid body at the other end is ground flat and connected to the planar region (3) of the metal-filled super-planar optical fiber (1) to ensure that the super-rhomboid chain structure (2) and the planar region (3) form optical coupling and generate electromagnetic resonance to achieve terahertz wave filtering.

2. The tunable terahertz filter with a super-rhombic chain metal-coated hyperplane fiber as described in claim 1, characterized in that: The diameter of the metal-coated superplanar optical fiber is 0.5~3 mm, the remaining thickness of the planar region (3) is 0.4~1.2 mm, the metal film is made of gold, silver or aluminum, and has a thickness of 10~200 nm, the diameter of the large air hole is 20~80 μm, the center-to-center distance between adjacent large air holes is 40-160 μm, and the diameter of the small air hole is 8~40 μm.

3. The tunable terahertz filter with a super-rhombic chain metal-coated hyperplane fiber as described in claim 1, characterized in that: The specific parameters of the super-rhombic chain structure (2) satisfy: The side length of the rhombus is 20~100 μm, the overlapping area of ​​adjacent rhombuses accounts for 20~50% of the area of ​​a single rhombus, and the flattened part accounts for 1~40% of the area of ​​a single rhombus; The length of the rectangular body is 10~200 μm; All rectangular prisms and rhombuses have a consistent depth of 10~200 μm. It can rotate 0~90° around the longitudinal centerline of the optical fiber.

4. The tunable terahertz filter with a super-rhombic chain metal-coated hyperplane fiber as described in claim 1, characterized in that: The semiconductor material of the super-rhomboid chain structure (2) is one of silicon, germanium or III-V compound semiconductors, and its carrier concentration can be adjusted by external pump light (8).

5. The tunable terahertz filter of super-rhombic chain metal-coated hyperplane fiber as described in claim 1, characterized in that: The length of the planar region (3) is 1-5 mm, and it is formed by precision machining of a CNC machine tool with a surface roughness of less than 100 nm.

6. The tunable terahertz filter with a super-rhombic chain metal-coated hyperplane fiber as described in any one of claims 1-5, characterized in that: The filter operates in the 0.1-3 THz frequency band, has a Q value greater than 500 at the resonant frequency, and a stopband attenuation greater than 1 dB, with the Q value exceeding 10 under optimal parameters. 3 The maximum stopband attenuation exceeds 2 dB.

7. The tunable terahertz filter with a super-rhombic chain metal-coated hyperplane fiber as described in any one of claims 1-5, characterized in that: The super-rhomboid chain structure (2) achieves frequency tuning in the following way: Mechanical tuning: By rotating the super-rhomboid chain structure (2), its coupling state with the optical fiber is changed, and the tuning range is greater than 30 GHz; Optical tuning: Optical tuning is performed by pump light (8), with a tuning range greater than 30 GHz.

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