WO2020237744A1 - 一种太赫兹波导 - Google Patents

一种太赫兹波导 Download PDF

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Publication number
WO2020237744A1
WO2020237744A1 PCT/CN2019/091643 CN2019091643W WO2020237744A1 WO 2020237744 A1 WO2020237744 A1 WO 2020237744A1 CN 2019091643 W CN2019091643 W CN 2019091643W WO 2020237744 A1 WO2020237744 A1 WO 2020237744A1
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Prior art keywords
waveguide
microstructure
input
output
wavelength
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English (en)
French (fr)
Inventor
陈明阳
徐航
张媛
白彤彤
姚建铨
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Jiangsu University
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Jiangsu University
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Priority to GB2115277.2A priority Critical patent/GB2596771B/en
Priority to US17/280,920 priority patent/US11137545B1/en
Publication of WO2020237744A1 publication Critical patent/WO2020237744A1/zh
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02295—Microstructured optical fibre
    • G02B6/02314—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes
    • G02B6/02342—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes characterised by cladding features, i.e. light confining region
    • G02B6/02366—Single ring of structures, e.g. "air clad"
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P3/00—Waveguides; Transmission lines of the waveguide type
    • H01P3/10—Wire waveguides, i.e. with a single solid longitudinal conductor
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02295—Microstructured optical fibre
    • G02B6/02314—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes
    • G02B6/02319—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes characterised by core or core-cladding interface features
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02295—Microstructured optical fibre
    • G02B6/02314—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes
    • G02B6/02342—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes characterised by cladding features, i.e. light confining region
    • G02B6/02347—Longitudinal structures arranged to form a regular periodic lattice, e.g. triangular, square, honeycomb unit cell repeated throughout cladding
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/032—Optical fibres with cladding with or without a coating with non solid core or cladding
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/107—Subwavelength-diameter waveguides, e.g. nanowires
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/1225—Basic optical elements, e.g. light-guiding paths comprising photonic band-gap structures or photonic lattices
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02295—Microstructured optical fibre
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/262—Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements

Definitions

  • the invention relates to the field of terahertz, in particular to a terahertz waveguide.
  • the terahertz wave has some characteristics in the electromagnetic field that other electromagnetic bands cannot match, such as low energy, water absorption characteristics, strong penetration, etc., it is very important in the fields of medical imaging, chemistry, biology, and communications. Application value. Because the terahertz signal is greatly affected by water vapor absorption and atmospheric scattering, the attenuation coefficient is so large when it is transmitted in free space that it cannot be transmitted over long distances. Therefore, the study of terahertz waveguides is helpful to promote the development of terahertz technology. Very significant meaning.
  • Some researchers have proposed a sapphire fiber with a fiber diameter of 150-325 ⁇ m, which realizes low-loss single-mode transmission of terahertz waves.
  • a sub-wavelength terahertz solid core fiber with a core diameter of about 200 ⁇ m, the air outside the core is the fiber cladding, and the core is made of polyethylene (PE) material, which is around 0.3THz
  • PE polyethylene
  • sub-wavelength solid core optical fiber The main disadvantage of sub-wavelength solid core optical fiber is that the optical fiber needs special supporting elements during application process, and the system stability is poor, and the fiber core is directly exposed to the air, and the transmission performance is affected by the external environment and is easily interfered by surrounding signals. In addition, due to the small cross-sectional size of the core, the coupling between it and the terahertz source is also difficult.
  • the present invention provides a terahertz waveguide, which solves the problem that conventional subwavelength waveguides require mechanical support in the entire transmission direction, and at the same time ensures that the structure at both ends of the internal terahertz wave is in the main transmission section.
  • the transmission impact is minimal, and the transmission waveguide is isolated from the environment.
  • the present invention achieves the above technical objectives through the following technical means.
  • a terahertz waveguide including:
  • the input end includes an input end waveguide and an input end microstructure waveguide, one end of the input end waveguide is connected to one end of the core of the input end microstructure waveguide;
  • the transmission end includes a sub-wavelength waveguide, an air layer surrounding the sub-wavelength waveguide, and an outer cladding layer surrounding the air layer.
  • One end of the sub-wavelength waveguide is connected to the other end of the core of the input end microstructure waveguide, and the outer cladding layer One end of is connected to the cladding of the input end microstructure waveguide;
  • the output end includes an output end microstructure waveguide and an output end waveguide.
  • the other end of the subwavelength waveguide is connected to one end of the core of the output end microstructure waveguide, and the other end of the outer cladding layer is connected to the output end microstructure waveguide.
  • the cladding of the structural waveguide is connected, and the other end of the core of the output end microstructure waveguide is connected to one end of the output end waveguide;
  • the diameter d c of the sub-wavelength waveguide satisfies d c ⁇ 0 , where ⁇ 0 is the working wavelength, and the cladding layers of the input microstructure waveguide and the output microstructure waveguide are both made of matrix material and regularly arranged
  • the fiber cores of the input microstructure waveguide and the output microstructure waveguide are both composed of matrix material.
  • the input end includes an input end tapered waveguide and an input end straight waveguide, the narrow end of the input end tapered waveguide is connected to one end of the input end straight waveguide, and the other end of the input end straight waveguide is connected to One end of the core of the input microstructure waveguide is connected;
  • the output end waveguide is a tapered waveguide, and the narrow end of the output end waveguide is connected to the other end of the core of the output end microstructure waveguide.
  • the input end tapered waveguide, the input end straight waveguide, the input end microstructure waveguide, the output end microstructure waveguide and the output waveguide are all circular in cross section, and the input end A tapered waveguide, the straight waveguide at the input end and the microstructure waveguide at the input end are coaxial, and the microstructure waveguide at the output end is coaxial with the output waveguide;
  • the narrow end diameter of the output waveguide is d ts2
  • the core diameter of the output end microstructure waveguide is d m2
  • the narrow end diameter of the input end tapered waveguide is d ts1
  • the numerical aperture of the straight waveguide at the input end is NA 0
  • the numerical aperture of the input microstructure waveguide is NA 1
  • the numerical aperture of the sub-wavelength waveguide is NA 2
  • the numerical aperture of the output microstructure waveguide is The numerical aperture is NA 3
  • the numerical aperture of the narrow end of the output waveguide is NA 4
  • the mode field diameter of the input microstructure waveguide is W 1
  • the mode field diameter of the output microstructure waveguide is W 3 , where , NA 4 ⁇ d ts2 >NA 0 ⁇ d z >NA 1 ⁇ W 1 >NA 2 ⁇ d c >NA 3 ⁇ W 3 .
  • NA 0 ⁇ d z k 1 ⁇ NA 1 ⁇ W 1 ,
  • NA 1 ⁇ W 1 k 2 ⁇ NA 2 ⁇ d c ,
  • NA 2 ⁇ d c k 3 ⁇ NA 3 ⁇ W 3 ,
  • NA 4 ⁇ d ts2 k 4 ⁇ NA 3 ⁇ W 3 .
  • k 1 , k 2 , k 3 , and k 4 are proportional coefficients, the value range of k 1 is 1.5 to 4, the value range of k 2 is 1 to 2, and the value range of k 3 is 1 to 2.
  • the value range of k 4 is 10-20; d z is the diameter of the straight waveguide at the input end, and d c is the diameter of the sub-wavelength waveguide.
  • the transmission end includes at least two sub-wavelength waveguides arranged side by side, wherein at least one end of the sub-wavelength waveguide is connected to the core of the input end microstructure waveguide, and at least one of the sub-wavelength waveguides One end of the wavelength waveguide is connected to the core of the output end microstructure waveguide.
  • the transmission end includes two sub-wavelength waveguides arranged side by side, one end of the sub-wavelength waveguide is connected to the core of the input end microstructure waveguide, and the other is One end is connected to the core of the output microstructure waveguide.
  • the transmission end includes three sub-wavelength waveguides arranged side by side, one end of the sub-wavelength waveguide in the middle position is connected to the core of the input end microstructure waveguide, and the other two sub-wavelength waveguides have one end respectively The two cores of the microstructure waveguide at the output end are connected in a one-to-one correspondence.
  • the number of air hole layers in the input microstructure waveguide is greater than one, and the number of air holes in the output microstructure waveguide is not less than one;
  • the diameter of each layer of air holes gradually increases from the corresponding core in the radially outward direction ,
  • the diameter of the air hole ranges from ⁇ 0 /20 to 3 ⁇ 0 .
  • the arrangement of the air holes in the input-end microstructure waveguide or the output-end microstructure waveguide both satisfies: arranged in a regular triangle grid or arranged on a circle centered on the center of the corresponding core .
  • the input microstructure waveguide and the output microstructure waveguide are respectively arranged at both ends of the transmission end, which overcomes the shortcomings of conventional sub-wavelength waveguides that require mechanical support in the entire transmission direction, thereby distributing the mode field and reducing confinement loss
  • the outer covering of the transmission end realizes the isolation of the sub-wavelength waveguide from the external environment, avoiding environmental interference; in sensing applications, the method of cutting the outer covering locally can also remove the external medium Introduce to realize special sensing function.
  • the input end is composed of a tapered waveguide at the input end, a straight waveguide at the input end, and a microstructure waveguide at the input end to realize the conversion of a large input mode field into a matching mode field of a subwavelength waveguide, thereby realizing low loss transmission.
  • the output end waveguide of the present invention is a tapered waveguide, and the output end is composed of an output end waveguide and an output end microstructure waveguide, which can effectively couple the mode field transmitted by the subwavelength waveguide.
  • the structure of the present invention can easily form a multi-waveguide transmission structure to realize functions such as mode coupling and conversion between waveguides; and the present invention can form a cascade structure to form more complex functional devices, because the input and output ends are both With solid core waveguide structure, as long as the connection ends are matched, sub-wavelength waveguides of different sizes can be connected with low loss.
  • Fig. 1 is a schematic structural diagram of a preferred embodiment of a terahertz waveguide of the present invention
  • Fig. 2 is a schematic cross-sectional view of the input end of the terahertz waveguide shown in Fig. 1;
  • Fig. 3 is a schematic cross-sectional view of the input end microstructure waveguide of the input end shown in Fig. 1;
  • FIG. 4 is a schematic cross-sectional view of the output end of the terahertz waveguide shown in FIG. 1;
  • FIG. 5 is a schematic cross-sectional view of the output end microstructure waveguide of the output end shown in FIG. 4;
  • Fig. 6 is a cross-sectional view of the transmission end of the terahertz waveguide shown in Fig. 1;
  • Figure 7 is a graph of the k value of the terahertz waveguide shown in Figure 1, where (a) is the scatter plot of k 1 with the diameter d z of the straight waveguide at the input end, and (b) is the graph of k 2 with the microstructure waveguide at the input end The scatter plot of the diameter d in-3 of the innermost hole, (c) is the scatter plot of the change of k 3 with the subwavelength waveguide diameter d c , (d) is the scatter plot of k 4 with the air hole of the microstructure waveguide at the output end Scatter plot of changes in diameter d out ;
  • Figure 8 is the mode field diagram of the terahertz waveguide shown in Figure 1, where (a) is the fundamental mode diagram of the straight waveguide at the input end, (b) is the fundamental mode diagram of the input end microstructure waveguide, and (c) is the transmission end waveguide The archetype diagram;
  • FIG. 9 is a cross-sectional view of a derivative dual waveguide structure of a terahertz waveguide according to an embodiment of the present invention.
  • FIG. 10 is a cross-sectional view of a derivative three-waveguide structure of a terahertz waveguide according to an embodiment of the present invention.
  • Fig. 11 is a transmission efficiency spectrum diagram of a terahertz waveguide according to an embodiment of the present invention.
  • Input end waveguide 1-1. Input end tapered waveguide; 1-2 Input end straight waveguide; 2. Input end microstructure waveguide; 3. Subwavelength waveguide; 4. Output end microstructure waveguide; 5. Output end Tapered waveguide; 6. Outer layer.
  • first and second are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined with “first” and “second” may explicitly or implicitly include one or more of these features. In the description of the present invention, “plurality” means two or more than two, unless specifically defined otherwise.
  • the terms “installed”, “connected”, “connected”, “fixed” and other terms should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection. , Or integrally connected; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal communication between two components.
  • installed can be a fixed connection or a detachable connection.
  • it can be a mechanical connection or an electrical connection
  • it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal communication between two components.
  • the specific meaning of the above-mentioned terms in the present invention can be understood according to specific circumstances.
  • a terahertz waveguide according to an embodiment of the present invention includes an input end, a transmission end and an output end.
  • the input end includes an input end waveguide 1 and an input end microstructure waveguide 2
  • the transmission end includes a sub-wavelength waveguide 3, an air layer surrounding the sub-wavelength waveguide, and an outer cladding layer 6 surrounding the air layer.
  • the terminal includes an output-end microstructure waveguide 4 and an output-end waveguide 5.
  • One end of the input end waveguide 1 is connected to one end of the core of the input end microstructure waveguide 2; the other end of the input end microstructure waveguide 2 is connected to one end of the subwavelength waveguide 3, and one end of the outer cladding layer 6 is connected to the input
  • the cladding layer of the end microstructure waveguide 2 is connected, the other end of the outer cladding layer 6 is connected with the cladding layer of the output end microstructure waveguide 4, the other end of the subwavelength waveguide 3 is connected with one end of the core of the output end microstructure waveguide 4, and the output The other end of the core of the end microstructure waveguide 4 is connected to one end of the output end waveguide 5.
  • the diameter d c of the sub-wavelength waveguide 3 satisfies d c ⁇ 0 , where ⁇ 0 is the working wavelength.
  • the sub-wavelength waveguide 3 can reduce the transmission ratio of terahertz waves in the waveguide, thereby reducing material absorption loss.
  • the cladding layers of the input microstructure waveguide 2 and the output microstructure waveguide 4 are composed of matrix material and regularly arranged air holes, and the cores of the input microstructure waveguide 2 and the output microstructure waveguide 4 are both composed of matrix material .
  • the input microstructure waveguide and the output microstructure waveguide are respectively provided at both ends of the transmission end to support the sub-wavelength waveguide 3 and provide support for the outer cladding layer 6.
  • the outer cladding layer of the transmission end isolates the sub-wavelength waveguide 3 from the external environment, so that the terahertz wave is sub-
  • the wavelength waveguide 3 transmits in the air layer, avoiding environmental interference; and the terahertz waveguide according to the embodiment of the present invention requires no support unit in the longitudinal direction except that a microstructure waveguide is required at both ends to support the sub-wavelength waveguide. Since there is no restraint loss introduced by the supporting unit, the transmission loss of the waveguide is effectively reduced.
  • the input microstructure waveguide 2 and the output microstructure waveguide 4 also play a role in effectively converting the mode field of the terahertz waveguide mode, so that the terahertz wave from the input port can be effectively coupled into the subwavelength waveguide 3, and The terahertz wave output by the sub-wavelength waveguide 3 is effectively coupled to the output port.
  • the terahertz waveguide according to the embodiment of the present invention can easily form a cascade structure, thereby forming a more complicated waveguide device and realizing more complicated functions.
  • the input end includes an input end tapered waveguide 1-1 and an input end straight waveguide 1-2, and the narrow end of the input end tapered waveguide 1-1 is connected to one end of the input end straight waveguide 1-2.
  • the other end of the input straight waveguide 1-2 is connected to one end of the core of the input microstructure waveguide 2.
  • the output end waveguide 5 is a tapered waveguide, and the narrow end of the output end waveguide 5 is connected to the other end of the core of the output end microstructure waveguide 4.
  • the input end is composed of taper waveguide 1-1 at the input end, straight waveguide 1-2 at the input end, and microstructure waveguide 2 at the input end, which can convert a large input mode field into a matching mode field of a subwavelength waveguide, thereby achieving low loss transmission.
  • different terahertz wave sources have different spot sizes, and the wide end of the tapered waveguide 1-1 at the input end can be flexibly changed to meet different wave sources.
  • the straight waveguide 1-2 can play a transitional role, adjusting the waveform, so that the wave is better coupled into the microstructure waveguide 4 at the input end.
  • the output end is composed of a tapered output end waveguide 5 and an output end microstructure waveguide 4, which can effectively couple the mode field transmitted by the sub-wavelength waveguide, and can expand the mode field diameter of the waveform to a certain extent to adapt to the existing The equipment caliber of the terahertz detector.
  • the input tapered waveguide 1-1, the input straight waveguide 1-2, and the output waveguide 5 all have larger cross-sectional dimensions, thereby effectively reducing the energy ratio of the terahertz wave in the air, and can be effective with terahertz sources, etc. connection.
  • the cross-sections of the input tapered waveguide 1-1, the input straight waveguide 1-2, the input microstructure waveguide 2, the output microstructure waveguide 4, and the output waveguide 5 are all circular.
  • the input tapered waveguide 1-1, the input straight waveguide 1-2 and the input microstructure waveguide 2 are coaxial, and the output microstructure waveguide 4 and the output waveguide 5 are coaxial.
  • the narrow end diameter of the output waveguide 5 is d ts2
  • the core diameter of the output microstructure waveguide 4 is d m2
  • the narrow end diameter of the input tapered waveguide 1-1 is d ts1
  • the core diameter of the input microstructure waveguide 2 is d m1
  • the core radius of the input microstructure waveguide 2 and the output microstructure waveguide 4 is defined as the distance between the center of the core and the center of the innermost air hole Subtract the radius of the innermost air hole, and the diameter of the core is twice the radius of the core.
  • the tapered input waveguide length at the input end is 1/2 ⁇ 0 ⁇ 5 ⁇ 0
  • the straight waveguide length at the input end is 1/2 ⁇ 0 ⁇ 5 ⁇ 0
  • the microstructure waveguide length at the input end is 1/2 ⁇ 0 ⁇ 5 ⁇ 0
  • the transmission end The length is 5-100cm, which is selected according to the required length and absorption loss.
  • the length of the microstructure waveguide at the output end is ⁇ 0 ⁇ 30 ⁇ 0
  • the length of the tapered output waveguide at the output end is ⁇ 0 ⁇ 30 ⁇ 0 .
  • the input microstructure waveguide 2 and the output microstructure waveguide 4 are composed of a cladding matrix material and air holes arranged on the matrix material, their numerical aperture is smaller than that of the subwavelength waveguide 3, so the output microstructure waveguide
  • the core diameter of 4 needs to be larger than the core diameter of the input microstructure waveguide 2 so that the terahertz wave output by the subwavelength waveguide 3 can be effectively coupled into the output microstructure waveguide 4.
  • the numerical aperture of the straight waveguide 1-2 at the input end is NA 0
  • the numerical aperture of the input microstructure waveguide 2 is NA 1
  • the numerical aperture of the subwavelength waveguide 3 is NA 2
  • the numerical aperture of the output microstructure waveguide 4 is Is NA 3
  • the numerical aperture of the narrow end of the output waveguide 5 is NA 4
  • the mode field diameter of the input microstructure waveguide 2 is W 1
  • the mode field diameter of the output microstructure waveguide 5 is W 3
  • the mode field diameter gradually decreases from the large diameter end of the tapered waveguide 1-1 at the input end of the terahertz wave, so that most of the terahertz wave can be effectively coupled into the subwavelength waveguide 3 to the output end.
  • the waveguide 5 begins to expand the beam, and the mode field diameter increases, so that the wave is coupled into the corresponding receiving device.
  • d z is an input terminal 1-2 straight waveguide diameter
  • d c is the diameter of a subwavelength waveguide 3
  • k 1, k 2, k 3 is a coefficient of proportion
  • k takes 1
  • the value range is 1.5 ⁇ 4
  • the value range of k 2 is 1 ⁇ 2
  • the value range of k 3 is 1 ⁇ 2
  • the value range of k 4 is 10 ⁇ 20.
  • the input-end straight waveguide 1-2 and the sub-wavelength waveguide 3 are very different in terms of mode field distribution and mode field size.
  • the cladding of the input straight waveguide 1-2 is air, and the core of the input microstructure waveguide 2 is surrounded by air holes. Therefore, the refractive index distribution of the two is similar, thereby effectively reducing the connection loss between the two ;
  • the core diameter of the input microstructure waveguide 4 is larger than the diameter of the sub-wavelength waveguide 3, its numerical aperture is smaller than that of the sub-wavelength waveguide 3, so low-loss connections can still be achieved.
  • the number of air hole layers in the microstructure waveguide 2 at the input end is greater than 1, and the number of air hole layers in the microstructure waveguide 4 at the output end is not less than 1, usually 1-8 layers;
  • the diameter of each layer of air holes gradually increases from the corresponding core in the radially outward direction. This is due to the core
  • the outer air hole and the dielectric material together form a cladding. The lower the equivalent cladding refractive index, the lower the absorption loss, and the higher the efficiency of outputting terahertz waves.
  • the diameter of the air hole ranges from ⁇ 0 /20 to 3 ⁇ 0 , A value within the range can ensure the stability of the mechanical structure.
  • the arrangement of the air holes in the input microstructure waveguide 2 and the output microstructure waveguide 4 can be selected according to the function of the waveguide to realize a waveguide beam splitter, a coupler, and the like.
  • the core is a solid polymer material, and there may be multiple layers of air holes arranged outside the core.
  • the air holes in the input microstructure waveguide 2 are arranged in a regular triangular grid. It should be noted that the air holes in the input microstructure waveguide 2 in this embodiment are parallel to each other. It is not limited to being arranged in a regular triangular grid, but can also be arranged on a circle centered on the center of the core. The arrangement of the air holes in the microstructure waveguide 4 at the output end is also the same.
  • the transmission end includes at least two sub-wavelength waveguides 3 arranged side by side, wherein one end of at least one sub-wavelength waveguide 3 is connected to the core of the input end microstructure waveguide 2, and at least one sub-wavelength waveguide One end of the wavelength waveguide 3 is connected to the core of the output microstructure waveguide 4.
  • the transmission end includes two sub-wavelength waveguides 3 arranged side by side, one end of one sub-wavelength waveguide 3 is connected to the core of the input end microstructure waveguide 2, and the other sub-wavelength waveguide One end of 3 is connected to the core of the microstructure waveguide 4 at the output end.
  • This structure can couple the input terahertz wave to another port and output it. Utilizing the characteristics of different coupling lengths of different wavelengths, this structure can realize functions such as filtering.
  • the transmission end includes three sub-wavelength waveguides 3 arranged side by side, one end of the sub-wavelength waveguide 3 in the middle position is connected to the core of the input end microstructure waveguide 2, and the remaining two sub-wavelength waveguides One end of 3 is respectively connected to the two cores of the output microstructure waveguide 4 in a one-to-one correspondence.
  • This structure can realize the uniform splitting of an input terahertz wave to the sub-wavelength waveguides on both sides, and effectively couple them out, thereby achieving a uniform beam splitting function.
  • the waveguide structure is as shown in FIG. 1.
  • the diameter of the input tapered waveguide 1-1 is 710 ⁇ m, the narrow end diameter is 250 ⁇ m, and the length is 1000 ⁇ m, and the input straight waveguide 1-2 has a diameter of 250 ⁇ m and the length is 1000 ⁇ m.
  • the value of k 1 is 3.11.
  • the terahertz wave with a wavelength of 270 ⁇ m is used for incidence, and the material is polyethylene with very low terahertz absorption loss, and the material has a refractive index of 1.53.
  • the air holes are arranged in a regular triangular grid.
  • the period P 1 of the air holes is 200 ⁇ m
  • the diameter of the first layer of air holes is 112 ⁇ m
  • the diameter of the second layer is 126 ⁇ m
  • the diameter of the third layer is 176 ⁇ m.
  • the length of the input microstructure waveguide 2 is 1400 ⁇ m
  • the total diameter is 1680 ⁇ m
  • the value of k 2 is 1.18.
  • the sub-wavelength waveguide 3 is a solid-core polyethylene waveguide with a diameter of 70 ⁇ m, and the length of the main waveguide can be flexibly selected. In this embodiment, the length is 5 cm.
  • the outer diameter D 2 of the outer cladding layer 6 is 1490 ⁇ m, the inner diameter D 1 is 1300 ⁇ m, the cladding thickness D c is 190 ⁇ m, and the value of k 3 is 1.17.
  • the output microstructure waveguide 4 has a layer of air holes.
  • the air holes are arranged in a regular triangular grid.
  • the period P 2 of the air holes is 240 ⁇ m.
  • the distance between the center of the air hole and the center of the cross section of the subwavelength waveguide 3 on the same horizontal plane is 720 ⁇ m.
  • the diameter of the air hole is 120 ⁇ m.
  • the narrow end of the output waveguide 5 and the output microstructure waveguide 4 are connected and fixed on the basis of the central axis, and the narrow end has a diameter of 1140 ⁇ m. Finally, the terahertz wave is emitted from the wide end of the output waveguide 5 with a diameter of 1440 ⁇ m. When the terahertz time-domain spectroscopy system is connected, the value of k 4 is 14.12.
  • this embodiment needs to meet:
  • the above waveguide components whether the input microstructure waveguide 2, the output microstructure waveguide 4 or the sub-wavelength waveguide 3, adopt a transmission mode of total reflection. Considering the structural loss, as shown in Figure 11, the final emission efficiency of the fundamental mode can reach about 80%.

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Abstract

本发明提供了一种太赫兹波导，包括：输入端，包括依次连接的输入端波导和输入端微结构波导；传输端，包括亚波长波导、包围亚波长波导的空气层和包围空气层的外包层，亚波长波导的一端与输入端微结构波导的纤芯的另一端连接，外包层的一端与输入端微结构波导的包层连接；及输出端，包括输出端微结构波导和输出端波导，亚波长波导的另一端与输出端微结构波导的纤芯的一端连接，外包层的另一端与输出端微结构波导的包层连接，输出端微结构波导的纤芯的另一端与输出端波导的一端连接；本发明解决了常规亚波长波导在整个传输方向均需要机械支撑的问题，同时又保证两端结构对内部太赫兹波在主传输段的传输影响最小，并实现传输波导与环境的隔离。

Description

一种太赫兹波导 技术领域
本发明涉及太赫兹领域，尤其涉及一种太赫兹波导。
背景技术
由于太赫兹波在电磁领域中具有其他电磁波段所无法比拟的一些特点，例如能量低、吸水特性、穿透性强等等，从而使它在医学成像、化学、生物、通信等领域具有很重要的应用价值。由于太赫兹信号受水蒸汽吸收和大气散射的影响非常大，使它在自由空间中传输时衰减系数很大，以至于不能远距离传输，所以太赫兹波导的研究对促进太赫兹技术的发展有非常重大的意义。
有研究人员提出了一种蓝宝石光纤，光纤直径为150-325μm，实现了太赫兹波的低损耗单模传输。在此基础上，有研究人员提出一种亚波长太赫兹实芯光纤，光纤纤芯直径约为200μm，纤芯外空气为光纤包层，纤芯采用聚乙烯(PE)材料，在0.3THz附近损耗低于0.01cm -1，由于纤芯截面尺寸小，其与太赫兹源之间的耦合效率仅为20％左右。
亚波长实芯光纤的主要缺点是光纤在应用过程中需要特殊的支撑元件，系统稳定性较差，而纤芯直接暴露在空气中，传输性能受外界环境影响，也易受周围信号的干扰。此外，由于纤芯截面尺寸小，其与太赫兹源之间的耦合也比较困难。
发明内容
针对现有技术中存在不足，本发明提供了一种太赫兹波导，解决了常规亚波长波导在整个传输方向均需要机械支撑的问题，同时又保证两端结构对内部太赫兹波在主传输段的传输影响最小，并实现传输波导与环境的隔离。
本发明是通过以下技术手段实现上述技术目的的。
一种太赫兹波导，包括：
输入端，包括输入端波导和输入端微结构波导，所述输入端波导的一端与所述输入端微结构波导的纤芯的一端连接；
传输端，包括亚波长波导、包围亚波长波导的空气层和包围空气层的外包层，所述亚波长波导的一端与所述输入端微结构波导的纤芯的另一端连接，所述外包层的一端与所述输入端微结构波导的包层连接；及
输出端，包括输出端微结构波导和输出端波导，所述亚波长波导的另一端与所述输 出端微结构波导的纤芯的一端连接，所述外包层的另一端与所述输出端微结构波导的包层连接，所述输出端微结构波导的纤芯的另一端与所述输出端波导的一端连接；
其中，所述亚波长波导的直径d c满足d c＜λ 0，其中λ 0为工作波长，所述输入端微结构波导和所述输出端微结构波导的包层均由基质材料和规则排布的空气孔组成，所述输入端微结构波导和所述输出端微结构波导的纤芯均由基质材料组成。
优选地，所述输入端包括输入端锥形波导和输入端直波导，所述输入端锥形波导的窄端与所述输入端直波导的一端连接，所述输入端直波导的另一端与所述输入端微结构波导的纤芯的一端连接；
所述输出端波导为锥形波导，所述输出端波导的窄端与所述输出端微结构波导的纤芯的另一端连接。
优选地，所述输入端锥形波导、所述输入端直波导、所述输入端微结构波导、所述输出端微结构波导和所述输出波导的横截面均为圆形，所述输入端锥形波导、所述输入端直波导的和所述输入端微结构波导同轴，所述输出端微结构波导和所述输出波导同轴；
所述输出波导的窄端直径为d ts2，所述输出端微结构波导的纤芯直径为d m2，所述输入端锥形波导的窄端直径为d ts1，所述输入端直波导的直径d z，所述输入端微结构波导的纤芯直径为d m1，其中，d m2>d ts2>d m1>d ts1＝d z>d c。
优选地，所述输入端直波导的数值孔径为NA 0，所述输入端微结构波导的数值孔径为NA 1，所述亚波长波导的数值孔径为NA 2，所述输出端微结构波导的数值孔径为NA 3，所述输出波导的窄端的数值孔径为NA 4，所述输入端微结构波导的模场直径为W 1，所述输出端微结构波导的模场直径为W 3，其中，NA 4·d ts2＞NA 0·d z＞NA 1·W 1＞NA 2·d c＞NA 3·W 3。
优选地，满足如下关系：
NA 0·d z＝k 1·NA 1·W 1，
NA 1·W 1＝k 2·NA 2·d c，
NA 2·d c＝k 3·NA 3·W 3，
NA 4·d ts2＝k 4·NA 3·W 3。
其中，k 1、k 2、k 3、k 4为比例系数，k 1的取值范围为1.5～4，k 2的取值范围为1～2，k 3的取值范围为1～2，k 4的取值范围为10～20；d z是所述输入端直波导的直径、d c是所述亚波长波导的直径。
优选地，所述传输端包括至少两根并列排布的亚波长波导，其中，至少有一根所述 亚波长波导的一端与所述输入端微结构波导的纤芯连接，至少有一根所述亚波长波导的一端与所述输出端微结构波导的纤芯连接。
优选地，所述传输端包括两根并列排布的亚波长波导，其中一根所述亚波长波导的一端与所述输入端微结构波导的纤芯连接，另一根所述亚波长波导的一端与所述输出端微结构波导的纤芯连接。
优选地，所述传输端包括三根并列排布的亚波长波导，位于中间位置的所述亚波长波导的一端与所述输入端微结构波导的纤芯连接，其余两根亚波长波导的一端分别与所述输出端微结构波导的两个纤芯一一对应连接。
优选地，所述输入端微结构波导内的空气孔层数大于1，所述输出端微结构波导内的空气孔层数不小于1；
当所述输入端微结构波导或所述输出端微结构波导内的空气孔的层数不小于2时，从对应纤芯沿着径向向外的方向，每层空气孔的直径逐渐增大，空气孔的直径取值范围为λ 0/20～3λ 0。
优选地，所述输入端微结构波导或所述输出端微结构波导内的空气孔的排布均满足：排布在正三角网格中或排布在以对应纤芯中心为圆心的圆周上。
本发明的有益效果：
1)本发明在传输端的两端分别设置输入端微结构波导和输出端微结构波导，克服了常规亚波长波导需要在整个传输方向均需要机械支撑的缺点，从而在模场分布、减少束缚损耗等方面实现了优化，同时传输端的外包层实现了将亚波长波导与外界环境的隔离，避免了环境的干扰；在传感应用中，通过在外包层局部进行切割的方法，还可以将外界介质引入，实现特殊传感功能。
2)本发明以输入端锥形波导、输入端直波导、输入端微结构波导组成输入端，实现将大的输入模场转换为亚波长波导的匹配模场，从而实现低损耗传输。
3)本发明的输出端波导为锥形波导，并以输出端波导和输出端微结构波导组成输出端，能够将亚波长波导传输的模场有效耦合出来。
4)本发明结构可以很容易地组成多波导传输结构，实现波导间模式耦合、转换等功能；并且本发明可以组成级联结构，组建更为复杂的功能器件，由于输入端和输出端均为实芯的波导结构，只要连接端匹配，不同尺寸的亚波长波导可以实现低损耗连接。
附图说明
图1是本发明一种太赫兹波导一较佳实施例的结构示意图；
图2是图1所示太赫兹波导的输入端剖面示意图；
图3是图1所示输入端的输入端微结构波导截面示意图；
图4是图1所示太赫兹波导的的输出端剖面示意图；
图5是图4所示输出端的输出端微结构波导截面示意图；
图6是图1所示太赫兹波导的传输端截面图；
图7是图1所示太赫兹波导的k值图，其中(a)为k 1随输入端直波导的直径d z的变化散点图，(b)为k 2随输入端微结构波导的最内层孔的直径d in-3的变化散点图，(c)为k 3随亚波长波导直径d c的变化散点图，(d)为k 4随输出端微结构波导的空气孔直径d out的变化散点图；
图8是图1所示太赫兹波导的模场图，其中(a)为输入端直波导的基模图，(b)为输入端微结构波导的基模图，(c)为传输端波导的基模图；
图9为根据本发明实施例的一种太赫兹波导的衍生双波导结构剖视图；
图10为根据本发明实施例的一种太赫兹波导的衍生三波导结构剖视图。
图11为根据本发明实施例的一种太赫兹波导的传输效率频谱图；
附图标记：
1.输入端波导；1-1.输入端锥形波导；1-2输入端直波导；2.输入端微结构波导；3.亚波长波导；4.输出端微结构波导；5.输出端锥形波导；6.外包层。
具体实施方式
下面详细描述本发明的实施例，所述实施例的示例在附图中示出，其中自始至终相同或类似的标号表示相同或类似的元件或具有相同或类似功能的元件。下面通过参考附图描述的实施例是示例性的，旨在用于解释本发明，而不能理解为对本发明的限制。
在本发明的描述中，需要理解的是，术语“中心”、“纵向”、“横向”、“长度”、“宽度”、“厚度”、“上”、“下”、“轴向”、“径向”、“竖直”、“水平”、“内”、“外”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本发明和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本发明的限制。此外，术语“第一”、“第二”仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”的特征可以明示或者隐含地包括一个或者更多个该特征。在本发明的描述中，“多个”的含义是两个或两个以上，除非另有明确具体的限定。
在本发明中，除非另有明确的规定和限定，术语“安装”、“相连”、“连接”、“固定” 等术语应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或一体地连接；可以是机械连接，也可以是电连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个元件内部的连通。对于本领域的普通技术人员而言，可以根据具体情况理解上述术语在本发明中的具体含义。
下面首先结合附图具体描述根据本发明一较佳实施例的一种太赫兹波导。
请参阅图1至图9，根据本发明实施例的一种太赫兹波导包括输入端、传输端和输出端。
具体而言，如图1所示，输入端包括输入端波导1和输入端微结构波导2，传输端包括亚波长波导3、包围亚波长波导的空气层和包围空气层的外包层6，输出端包括输出端微结构波导4和输出端波导5。输入端波导1的一端与所述输入端微结构波导2的纤芯的一端连接；输入端微结构波导2的纤芯的另一端与亚波长波导3的一端连接，外包层6的一端与输入端微结构波导2的包层连接，外包层6的另一端与输出端微结构波导4的包层连接，亚波长波导3的另一端与输出端微结构波导4的纤芯的一端连接，输出端微结构波导4的纤芯的另一端与输出端波导5的一端连接。
亚波长波导3的直径d c满足d c＜λ 0，其中λ 0为工作波长，亚波长波导3可以减少太赫兹波在波导内的传输比例，从而减小材料吸收损耗。输入端微结构波导2和输出端微结构波导4的包层均由基质材料和规则排布的空气孔组成，输入端微结构波导2和输出端微结构波导4的纤芯均由基质材料组成。
由此，根据本发明实施例的太赫兹波导，通过在传输端的两端分别设置输入端微结构波导和输出端微结构波导，对亚波长波导3形成支撑作用，并为外包层6提供支撑，克服了常规亚波长波导需要在整个传输方向均需要机械支撑的缺点；同时，如图6所示，传输端的外包层实现了将亚波长波导3与外界环境的隔离，使太赫兹波在内部亚波长波导3与空气层中传输，避免了环境的干扰；并且根据本发明实施例的太赫兹波导，除了在两端需要微结构波导对亚波长波导进行支撑以外，在纵向不再需要支撑单元，因不存在支撑单元引入的束缚损耗，从而有效减少波导的传输损耗。输入端微结构波导2和输出端微结构波导4还起到对太赫兹波导模式的模场进行有效转换作用，从而使得从输入端口进来的太赫兹波能有效耦合地进入亚波长波导3，以及使亚波长波导3输出的太赫兹波有效耦合到输出端口。
如需要将两个根据本发明实施例的太赫兹波导连接，例如将第一太赫兹波导的输出端与第二太赫兹波导的输入端连接，则只需设计两个太赫兹波导的结构，使得第一太赫 兹波导的输出端波导的输出端面尺寸与第二太赫兹波导的输入端波导的输入端面尺寸相同，即可实现两者的低损耗连接。因而，根据本发明实施例的太赫兹波导可以很容易组成级联结构，从而组成更为复杂的波导器件和实现更复杂的功能。
优选地，本实施例中，输入端包括输入端锥形波导1-1和输入端直波导1-2，输入端锥形波导1-1的窄端与输入端直波导1-2的一端连接，输入端直波导1-2的另一端与输入端微结构波导2的纤芯的一端连接。输出端波导5为锥形波导，输出端波导5的窄端与输出端微结构波导4的纤芯的另一端连接。
以输入端锥形波导1-1、输入端直波导1-2、输入端微结构波导2组成输入端，能够实现将大的输入模场转换为亚波长波导的匹配模场，从而实现低损耗传输。并且考虑波源光斑直径与波导口径的匹配度，不同太赫兹波源光斑大小不同，输入端锥形波导1-1的宽端可以通过灵活改变尺寸来满足不同波源。而直波导1-2可以起到过渡的作用，调整波形，使波更好的耦合进输入端微结构波导4。
以锥形的输出端波导5和输出端微结构波导4组成输出端，能够将亚波长波导传输的模场有效耦合出来，并且可以对波形的模场直径进行一定程度的扩束以适应现有太赫兹检测仪的设备口径。输入端锥形波导1-1、输入端直波导1-2、输出端波导5均具有较大的截面尺寸，从而有效减少太赫兹波在空气中的能量比例，并能够与太赫兹源等有效连接。
优选地，本实施例中，输入端锥形波导1-1、输入端直波导1-2、输入端微结构波导2、输出端微结构波导4和输出波导5的横截面均为圆形，输入端锥形波导1-1、输入端直波导1-2的和输入端微结构波导2同轴，输出端微结构波导4和输出波导5同轴。输出波导5的窄端直径为d ts2，输出端微结构波导4的纤芯直径为d m2，输入端锥形波导1-1的窄端直径为d ts1，输入端直波导1-2的直径d z，输入端微结构波导2的纤芯直径为d m1，输入端微结构波导2和输出端微结构波导4的纤芯半径定义为纤芯中心与最内层空气孔中心之间的间距减去最内层空气孔的半径，并且纤芯的直径为纤芯的半径的两倍。上述参数满足：d m2>d ts2>d m1>d ts1＝d z>d c，满足上述关系是考虑波导制作的实际条件与波导机械结构的稳定性，防止气孔被覆盖或破坏。
进一步的，输入端锥形输入波导长度取1/2λ 0～5λ 0，输入端直波导长度取1/2λ 0～5λ 0，输入端微结构波导长度取1/2λ 0～5λ 0，传输端长度取5～100cm，具体根据所需长度与吸收损耗选取，输出端微结构波导长度取λ 0～30λ 0，输出端锥形输出波导长度取λ 0～30λ 0。
由于输入端微结构波导2和输出端微结构波导4由包层基质材料和排布在基质材料 上的空气孔组成，其数值孔径小于亚波长波导3的数值孔径，为此输出端微结构波导4的纤芯直径需大于输入端微结构波导2的纤芯直径，从而能够将亚波长波导3输出的太赫兹波有效耦合进输出端微结构波导4。
进一步的，输入端直波导1-2的数值孔径为NA 0，输入端微结构波导2的数值孔径为NA 1，亚波长波导3的数值孔径为NA 2，输出端微结构波导4的数值孔径为NA 3，输出波导5的窄端的数值孔径为NA 4，输入端微结构波导2的模场直径为W 1，输出端微结构波导5的模场直径为W 3，根据亚波长波导基模直径公式
Figure PCTCN2019091643-appb-000001
(NA为单模波导最大理论数值孔径)，以及实验得出的基模纤芯所占功率与纤芯直径关系等条件，得到：NA 4·d ts2＞NA 0·d z＞NA 1·W 1＞NA 2·d c＞NA 3·W 3。该数值关系是由计算所得，模场直径从太赫兹波进入输入端锥形波导1-1的大直径端开始逐渐缩小，使大部分太赫兹波可以有效耦合进亚波长波导3，直至输出端波导5开始扩束，模场直径增大，使波耦合进相应的接收设备中。
进一步的，上述各个数值孔径还满足以下关系：NA 0·d z＝k 1·NA 1·W 1，NA 1·W 1＝k 2·NA 2·d c，NA 2·d c＝k 3·NA 3·W 3，NA 4·d ts2＝k 4·NA 3·W 3。
其中，d z是输入端直波导1-2的直径、d c是亚波长波导3的直径，k 1、k 2、k 3、k 4为比例系数，有图7可得，k 1的取值范围为1.5～4，k 2的取值范围为1～2，k 3的取值范围为1～2，k 4的取值范围为10～20，满足上述关系时，能够高效传输太赫兹波。
从图8中可见，输入端直波导1-2和亚波长波导3在模场分布和模场大小方面均存在很大的不同。输入端直波导1-2的包层为空气，而输入端微结构波导2的纤芯被空气孔所包围，因而，两者在折射率分布上相似，从而有效减少两者之间的连接损耗；而输入端微结构波导4的纤芯直径虽然大于亚波长波导3的直径，但其数值孔径小于亚波长波导3的数值孔径，因而仍然可以实现低损耗连接。
优选地，本实施例中，输入端微结构波导2内的空气孔层数大于1，输出端微结构波导4内的空气孔层数不小于1，通常取1-8层；当输入端微结构波导2或输出端微结构波导4内的空气孔的层数不小于2时，从对应纤芯沿着径向向外的方向，每层空气孔的直径逐渐增大，这是由于纤芯外气孔与介质材料共同形成包层，等效的包层折射率越低，吸收损耗越低，输出太赫兹波的效率越高，空气孔的直径取值范围为λ 0/20～3λ 0，在范围内取值能够保证机械结构的稳定性。
进一步的，对于输入端微结构波导2和输出端微结构波导4内的空气孔的排布，可 以根据波导功能的选取，以实现波导分束器、耦合器等。一般的，纤芯为实心聚合物材料，纤芯外可以有多层空气孔排布。进一步的，如图3所示，输入端微结构波导2内的空气孔的排布在正三角网格中，需要说明的是，本实施例中的输入端微结构波导2内的空气孔并不限于排布在正三角网格中，也可排布在以纤芯中心为圆心的圆周上。输出端微结构波导4内的空气孔的排布也是如此。
优选地，本实施例中，传输端包括至少两根并列排布的亚波长波导3，其中，至少有一根亚波长波导3的一端与输入端微结构波导2的纤芯连接，至少有一根亚波长波导3的一端与输出端微结构波导4的纤芯连接。
进一步的，如图9所示，传输端包括两根并列排布的亚波长波导3，其中一根亚波长波导3的一端与输入端微结构波导2的纤芯连接，另一根亚波长波导3的一端与输出端微结构波导4的纤芯连接。此结构可实现将输入的太赫兹波耦合到另一端口，并输出。利用不同波长的耦合长度不同等特性，此结构可以实现滤波等功能。
进一步的，如图10所示，传输端包括三根并列排布的亚波长波导3，位于中间位置的亚波长波导3的一端与输入端微结构波导2的纤芯连接，其余两根亚波长波导3的一端分别与输出端微结构波导4的两个纤芯一一对应连接。此结构可实现将输入的一束太赫兹波均分到两侧的亚波长波导，并有效耦合出来，从而实现均匀分束功能。
优选地，本实施例中，波导结构如图1所示。输入端锥形波导1-1的直径为710μm，窄端直径为250μm，长度为1000μm，输入端直波导1-2直径为250μm，长度为1000μm。对于该实施例，k 1取值为3.11。采取270μm波长太赫兹波入射，材料选取太赫兹吸收损耗很低的聚乙烯，材料折射率1.53。
输入微结构波导2纤芯外有三层空气孔排布，空气孔排布在正三角网格中，空气孔的周期P 1为200μm，第一层空气孔直径为112μm，第二层直径为126μm，第三层直径为176μm。输入微结构波导2的长度为1400μm，总直径为1680μm，k 2取值为1.18。
亚波长波导3为直径70μm实芯聚乙烯波导，主波导长度可灵活选取，本实施例取长度5cm。外包层6的外径D 2为1490μm，内径D 1为1300μm，包层厚度D c为190μm，k 3取值为1.17。
输出端微结构波导4有一层空气孔，空气孔排布在正三角网格中，空气孔的周期P 2为240μm，空气孔圆心与同水平面亚波长波导3横截面圆心相距最远距离为720μm，空气孔直径为120μm。
输出端波导5的窄端与输出端微结构波导4以中心轴线为基准连接固定，窄端直径 为1140μm，最终太赫兹波由输出端波导5的宽端出射，宽端直径为1440μm，可与太赫兹时域光谱系统等设备连接，k 4的取值14.12。
根据计算，本实施例需满足：
NA 4·d ts2＞NA 0·d z＞NA 1·W 1＞NA 2·d c＞NA 3·W 3。
以上的波导部件无论是输入端微结构波导2、输出端微结构波导4还是亚波长波导3采取的传输方式均为全反射式。考虑结构损耗，如图11所示，最终的基模出射效率可达80％左右。
在本说明书的描述中，参考术语“一个实施例”、“一些实施例”、“示例”、“具体示例”、或“一些示例”等的描述意指结合该实施例或示例描述的具体特征、结构、材料或者特点包含于本发明的至少一个实施例或示例中。在本说明书中，对上述术语的示意性表述不一定指的是相同的实施例或示例。而且，描述的具体特征、结构、材料或者特点可以在任何的一个或多个实施例或示例中以合适的方式结合。
尽管上面已经示出和描述了本发明的实施例，可以理解的是，上述实施例是示例性的，不能理解为对本发明的限制，本领域的普通技术人员在不脱离本发明的原理和宗旨的情况下在本发明的范围内可以对上述实施例进行变化、修改、替换和变型。

Claims (10)

  1. 一种太赫兹波导，其特征在于，包括：
    输入端，包括输入端波导(1)和输入端微结构波导(2)，所述输入端波导(1)的一端与所述输入端微结构波导(2)的纤芯的一端连接；
    传输端，包括亚波长波导(3)、包围亚波长波导的空气层和包围空气层的外包层(6)，所述亚波长波导(3)的一端与所述输入端微结构波导(2)的纤芯的另一端连接，所述外包层(6)的一端与所述输入端微结构波导(2)的包层连接；及
    输出端，包括输出端微结构波导(4)和输出端波导(5)，所述亚波长波导(3)的另一端与所述输出端微结构波导(4)的纤芯的一端连接，所述外包层(6)的另一端与所述输出端微结构波导(4)的包层连接，所述输出端微结构波导(4)的纤芯的另一端与所述输出端波导(5)的一端连接；
    其中，所述亚波长波导(3)的直径d c满足d c＜λ 0，其中λ 0为工作波长，所述输入端微结构波导(2)和所述输出端微结构波导(4)的包层均由基质材料和规则排布的空气孔组成，所述输入端微结构波导(2)和所述输出端微结构波导(4)的纤芯均由基质材料组成。
  2. 根据权利要求1所述的太赫兹波导，其特征在于，所述输入端包括输入端锥形波导(1-1)和输入端直波导(1-2)，所述输入端锥形波导(1-1)的窄端与所述输入端直波导(1-2)的一端连接，所述输入端直波导(1-2)的另一端与所述输入端微结构波导(2)的纤芯的一端连接；
    所述输出端波导(5)为锥形波导，所述输出端波导(5)的窄端与所述输出端微结构波导(4)的纤芯的另一端连接。
  3. 根据权利要求2所述的太赫兹波导，其特征在于，所述输入端锥形波导(1-1)、所述输入端直波导(1-2)、所述输入端微结构波导(2)、所述输出端微结构波导(4)和所述输出波导(5)的横截面均为圆形，所述输入端锥形波导(1-1)、所述输入端直波导(1-2)的和所述输入端微结构波导(2)同轴，所述输出端微结构波导(4)和所述输出波导(5)同轴；
    所述输出波导(5)的窄端直径为d ts2，所述输出端微结构波导(4)的纤芯直径为d m2，所述输入端锥形波导(1-1)的窄端直径为d ts1，所述输入端直波导(1-2)的直径d z，所述输入端微结构波导(2)的纤芯直径为d m1，其中，d m2>d ts2>d m1>d ts1＝d z>d c。
  4. 根据权利要求3所述的太赫兹波导，其特征在于，所述输入端直波导(1-2)的数 值孔径为NA 0，所述输入端微结构波导(2)的数值孔径为NA 1，所述亚波长波导(3)的数值孔径为NA 2，所述输出端微结构波导(4)的数值孔径为NA 3，所述输出波导(5)的窄端的数值孔径为NA 4，所述输入端微结构波导(2)的模场直径为W 1，所述输出端微结构波导(5)的模场直径为W 3，其中，NA 4·d ts2＞NA 0·d z＞NA 1·W 1＞NA 2·d c＞NA 3·W 3。
  5. 根据权利要求4所述的太赫兹波导，其特征在于，满足如下关系：
    NA 0·d z＝k 1·NA 1·W 1，
    NA 1·W 1＝k 2·NA 2·d c，
    NA 2·d c＝k 3·NA 3·W 3，
    NA 4·d ts2＝k 4·NA 3·W 3。
    其中，k 1、k 2、k 3、k 4为比例系数，k 1的取值范围为1.5～4，k 2的取值范围为1～2，k 3的取值范围为1～2，k 4的取值范围为10～20；d z是所述输入端直波导(1-2)的直径、d c是所述亚波长波导(3)的直径。
  6. 根据权利要求1所述的太赫兹波导，其特征在于，所述传输端包括至少两根并列排布的亚波长波导(3)，其中，至少有一根所述亚波长波导(3)的一端与所述输入端微结构波导(2)的纤芯连接，至少有一根所述亚波长波导(3)的一端与所述输出端微结构波导(4)的纤芯连接。
  7. 根据权利要求6所述的太赫兹波导，其特征在于，所述传输端包括两根并列排布的亚波长波导(3)，其中一根所述亚波长波导(3)的一端与所述输入端微结构波导(2)的纤芯连接，另一根所述亚波长波导(3)的一端与所述输出端微结构波导(4)的纤芯连接。
  8. 根据权利要求6所述的太赫兹波导，其特征在于，所述传输端包括三根并列排布的亚波长波导(3)，位于中间位置的所述亚波长波导(3)的一端与所述输入端微结构波导(2)的纤芯连接，其余两根亚波长波导(3)的一端分别与所述输出端微结构波导(4)的两个纤芯一一对应连接。
  9. 根据权利要求1所述的太赫兹波导，其特征在于，所述输入端微结构波导(2)内的空气孔层数大于1，所述输出端微结构波导(4)内的空气孔层数不小于1；
    当所述输入端微结构波导(2)或所述输出端微结构波导(4)内的空气孔的层数不小于2时，从对应纤芯沿着径向向外的方向，每层空气孔的直径逐渐增大，空气孔的直径取值范围为λ 0/20～3λ 0。
  10. 根据权利要求1或9所述的太赫兹波导，其特征在于，所述输入端微结构波导(2)或所述输出端微结构波导(4)内的空气孔的排布均满足：排布在正三角网格中或排 布在以对应纤芯中心为圆心的圆周上。
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