CN113805272B - High-efficiency terahertz polarization beam splitter based on waveguide transmission - Google Patents

High-efficiency terahertz polarization beam splitter based on waveguide transmission Download PDF

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CN113805272B
CN113805272B CN202010551120.6A CN202010551120A CN113805272B CN 113805272 B CN113805272 B CN 113805272B CN 202010551120 A CN202010551120 A CN 202010551120A CN 113805272 B CN113805272 B CN 113805272B
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metal
polarization beam
waveguide
beam splitter
medium
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CN113805272A (en
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焦晓飞
宋国峰
徐云
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Institute of Semiconductors of CAS
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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/105Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type having optical polarisation effects
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12Light 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
    • G02B6/122Basic optical elements, e.g. light-guiding paths
    • G02B6/125Bends, branchings or intersections
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12Light 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
    • G02B6/126Light 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 using polarisation effects
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12Light 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
    • G02B2006/12083Constructional arrangements
    • G02B2006/1209Multimode

Abstract

A terahertz polarization beam splitter, comprising: a periodic metal-dielectric-metal waveguide layer; the periodic metal-medium-metal waveguide layer is formed by alternately arranging metal strips and medium strips, and a plurality of waveguide layers with different medium widths are contained in one period; the terahertz polarization beam splitter can split an incident TE mode polarized wave and a TM mode polarized wave. The invention realizes the polarization beam splitting function by utilizing the different dependence of TE and TM waveguide modes on the medium width, and the TE and TM waveguide modes have the characteristic of low loss in the metal waveguide and have the advantage of high efficiency. For terahertz waves in different frequency bands, the polarization beam splitting effect can be realized by adjusting the width of the waveguide medium and the transmission length of the waveguide.

Description

High-efficiency terahertz polarization beam splitter based on waveguide transmission
Technical Field
The invention relates to the field of terahertz devices, in particular to a high-efficiency terahertz polarization beam splitter based on waveguide transmission.
Background
Currently, terahertz technology has become one of the very important subjects in the century, and has unique advantages and huge application prospects in important fields such as imaging, communication, astronomy, medical treatment and the like. In addition to the terahertz source and detector, functional devices such as terahertz modulator, filter, beam splitter, polarizer, etc. are also indispensable in the terahertz system. Among these devices, the polarizing beam splitter plays a very important role in terahertz polarization spectrum analysis, polarization imaging, polarization state communication, and the like. In the terahertz range, the transmission efficiency of the device is particularly important due to lower power, and the signal to noise ratio can have a relatively large influence due to free space path loss, atmospheric absorption and the like. The conventional terahertz polarization beam splitter relies on the birefringent effect of an optical crystal, and performs polarization beam splitting by utilizing the refractive index difference corresponding to the crystal in the process of propagating orthogonal polarization components. However, these natural optical crystals are not only rare but also weak in birefringence, and also not high in transmission efficiency, and require a thicker material thickness.
The traditional metal super-surface has surface plasmon resonance, but the plasma frequency of the metal is generally positioned in visible light and ultraviolet band, the metal is close to an ideal conductor in THz band, the surface plasmon resonance is difficult to excite, most of the metal super-surface is a reflecting super-surface, a complex light path is required to be designed, and the application of most of the transmission conditions is difficult to meet. With the trend of continuously increasing integration level of optical systems nowadays, the conventional polarizing beam splitter cannot meet application requirements. In view of the rapid development of terahertz technology, these drawbacks need to be resolved urgently. Recently, the appearance of a metamaterial or a super surface provides a new design idea for realizing a terahertz polarization device, and a super surface structure can generate different modes of oscillation under the drive of an incident field, and the spectral response in various oscillation modes has a dependency relationship on the shape, the size, the material and the like of the structure. By designing the structure, size and periodicity of the super-surface, researchers can achieve phase gradients between different radiation fields.
Disclosure of Invention
Accordingly, a primary object of the present invention is to provide a high-efficiency terahertz polarization beam splitter based on waveguide transmission, so as to partially solve at least one of the above technical problems.
To achieve the above object, as an aspect of the present invention, there is provided a high-efficiency terahertz polarization beam splitter based on waveguide transmission, comprising:
a periodic metal-dielectric-metal waveguide layer;
the periodic metal-medium-metal waveguide layer is formed by alternately arranging metal strips and medium strips, and a plurality of waveguide layers with different medium widths are contained in one period;
the terahertz polarization beam splitter can split an incident TE mode polarized wave and a TM mode polarized wave.
Wherein the periodic metal-dielectric-metal waveguide layer requires that the adjacent waveguide layers have equal TE mode transmission phase differences.
The incident TM mode polarized wave excites surface plasmons on the surface of the metal strip, so that the transmission efficiency is enhanced.
The periodic metal-medium-metal waveguide layer realizes the function of regulating and controlling the working frequency band by changing the medium width.
Wherein the transmission phase of the TM mode is independent of the variation of the waveguide medium width.
The terahertz polarization beam splitter can adjust the phase gradient of the TE mode by adjusting the medium width of adjacent waveguide layers in the period.
Wherein, by adjusting the transmission length of the periodic metal-medium-metal waveguide, the adjustment of the transmission phase and transmission efficiency can be realized.
The working wavelength of the terahertz polarization beam splitter is terahertz wave band.
The metal band is made of aluminum, copper, gold or silver, and the absorption loss of the metal near the terahertz wave band is very small.
Wherein the beam splitting angle can be adjusted by designing the number of waveguide layers in one period.
Based on the technical scheme, the high-efficiency terahertz polarization beam splitter based on waveguide transmission has at least one of the following beneficial effects compared with the prior art:
1. the invention realizes the polarization beam splitting function by utilizing the different dependence of TE and TM waveguide modes on the medium width, and the TE and TM waveguide modes have the characteristic of low loss in the metal waveguide and have the advantage of high efficiency.
2. The number of waveguide layers in the period determines the phase gradient change of transmission, and the phase gradient change of 2 pi can be covered by adjusting the width of the waveguide layers and the number of waveguide layers in the period, so that deflection of different angles can be realized.
3. For terahertz waves in different frequency bands, the polarization beam splitting effect can be realized by adjusting the width of the waveguide medium and the transmission length of the waveguide.
Drawings
FIG. 1 is a schematic diagram of a high-efficiency terahertz polarization beam splitter based on waveguide transmission in an embodiment of the invention;
FIG. 2 is a schematic cross-sectional structure of a waveguide-based efficient terahertz polarization beam splitter according to an embodiment of the present invention, where the z-coordinate represents the vertical direction of the device and the x-and y-coordinate directions represent the horizontal direction of the device;
FIG. 3 is a graph showing the transmittance of a polarization beam splitter based on waveguide transmission as a function of the width of a medium in an embodiment of the present invention;
FIG. 4 is a graph showing the phase of transmission of the incident light component of polarization along the x-axis (TM) and polarization along the y-axis (TE) as a function of the width of the medium, according to an embodiment of the present invention;
FIG. 5 is a graph showing the distribution of the transmitted electric field of incident light with polarization in the x-axis direction (TM) and polarization in the y-axis direction (TE) in an embodiment of the present invention.
In the above figures, the reference numerals have the following meanings:
1. a quartz material; 2. a metallic aluminum material; 3. a transmission length; 4. and (3) a waveguide structure period.
Detailed Description
The invention discloses a high-efficiency terahertz polarization beam splitter based on waveguide transmission, and belongs to the field of electromagnetic wave inventions. The main structure of the invention is shown in figure 1, and consists of a periodic metal-medium-metal waveguide layer with gradually changed medium width. Adjacent metal strips and dielectric layers located therein form metal-dielectric-metal waveguides that support both TE mode and TM mode transmissions in the operating band. The transmission phase change of TE mode in the operating band depends on the medium width, whereas the transmission phase change of TM mode is independent of the medium width. And a plurality of waveguide structures with different medium interlayer thicknesses form a period, so that transverse phase gradient occurs to TE modes at the waveguide exit, the TE wavefront direction is changed, and the TM wavefront is unchanged, thereby realizing the polarization beam splitting function. The invention has the characteristics of high efficiency, adjustable beam splitting angle according to the structure, adjustable working frequency according to parameters and the like.
Specifically, the invention discloses a high-efficiency terahertz polarization beam splitter based on waveguide transmission, which mainly comprises the following components:
a periodic metal-dielectric-metal waveguide layer; the periodic metal-medium-metal waveguide layer is composed of metal strips and medium strips which are alternately arranged, and a period comprises a plurality of waveguide layers with different medium widths;
the periodic metal-medium-metal waveguide layer requires equal TE mode transmission phase difference of adjacent waveguide layers, and can be realized by adjusting the medium width; the number of waveguide layers in a period determines the deflection angle of the TE mode; for TM mode incidence, surface plasmons are excited on the surface of the metal strip to enhance transmission efficiency; the function of regulating and controlling the working frequency range is realized by changing the width of the medium.
Wherein the transmission phase of the TM mode is independent of the variation of the waveguide medium width.
Wherein the phase gradient of the TE mode can be adjusted by adjusting the dielectric widths of adjacent waveguide layers in the period.
Wherein, the transmission phase and transmission efficiency can be adjusted by adjusting the transmission length of the periodic metal-medium-metal waveguide.
The working wavelength of the efficient terahertz polarization beam splitter based on waveguide transmission is terahertz wave band.
The metal is a perfect electric conductor in the terahertz wave band, the absorption loss is very little, and the metal strip is aluminum, copper, gold or silver.
Wherein the beam splitting angle can be adjusted by designing the number of waveguide layers in one period.
The body comprises a periodic metal-medium-metal waveguide layer, wherein the width of the waveguide medium in the period is gradually increased or gradually decreased.
The efficient terahertz polarization beam splitter based on waveguide transmission is composed of a metal-medium-metal waveguide layer with gradually changed medium width in a period. Adjacent metal strips and dielectric layers located therein form metal-dielectric-metal waveguides that support both TE mode and TM mode transmissions in the operating band. The TE mode has a mode refractive index different from that of the TM mode, and the transmission phase change of the TE mode in the operating band depends on the medium width, whereas the transmission phase change of the TM mode is independent of the medium width. The waveguide structure with the thickness of the medium interlayers increasing or decreasing gradually forms a period, so that a transverse phase gradient appears at the exit of the waveguide, the phase gradient covers 2 pi in one period, the TE wave front direction is changed, the TM wave front is unchanged, and the polarization beam splitting function is realized.
In general, the processes involved in the transmission of THz waves in metal waveguides include direct transmission of THz in the waveguide, extraordinary transmission caused by surface plasmon polarized waves, and localized surface plasmons that are induced, which will couple to affect the resonant frequency as well as transmission. Unlike a slot resonator on the surface of the dielectric, the structural metal strip forms a complete waveguide array, localized surface plasmon resonance is eliminated, and absorption losses are greatly reduced. Another point is that unlike a slot resonator, surface electrical resonance is generated on the upper surface, where it is used as a dipole source to excite magnetic resonance of the sidewall, which can be coupled back into electrical resonance, and the excited surface plasmon resonance can propagate along the waveguide sidewall, thereby realizing a polarization beam splitter with efficient transmission.
The present invention will be further described in detail below with reference to specific embodiments and with reference to the accompanying drawings, in order to make the objects, technical solutions and advantages of the present invention more apparent.
The terahertz polarization beam splitter based on waveguide transmission in the embodiment can split the incident TE polarized wave and TM polarized wave, the working frequency band is 1THz, and the transmission efficiency is more than 90%. Fig. 1 is a schematic diagram of a terahertz polarization beam splitter based on waveguide transmission, in which fig. 1 is a dielectric material quartz of the polarization beam splitter, in which fig. 2 is a metal strip material aluminum, in which fig. 3 is a transmission length a=1200 μm of a metal-dielectric-metal waveguide layer, in which fig. 4 is one period of a waveguide structure, the width of the dielectric layer along the x-axis direction is d1=135 μm, d2=143 μm, d3=153 μm, d4=167 μm, and the width of the metal strip along the x-axis direction is w=5 μm.
Fig. 2 shows a cross-sectional view of a terahertz polarization beam splitter based on waveguide transmission.
The incident light is incident along the z-axis direction, the electric vector is in the xy-plane, the electric vector direction forms an included angle of 45 degrees with the x-axis, and the polarization direction is parallel to the stripe direction (namely TE incident component along the y-axis direction) and the intensity of the incident light component with the polarization direction perpendicular to the stripe direction (namely TM incident component along the x-axis direction) is the same. As shown in fig. 3, which shows a change curve of transmittance of the terahertz polarization beam splitter based on waveguide transmission with the width of the medium, referring to fig. 3, the transmittance of the polarization beam splitter is almost 90% or more in the range of 135 μm to 167 μm of the medium width. As shown in fig. 4, which is a graph showing a change in transmission phase between a transmitted light component polarized in an x-axis direction and a transmitted light component polarized in a y-axis direction according to a width of a medium, with reference to fig. 4, a transmission phase of TE polarization changes approximately linearly with the width of the medium in a range of 135 μm to 167 μm, while a transmission phase of TM polarization is not affected by the width of the medium, and does not change with the change of the width of the medium. Therefore, the structure in the embodiment can realize the phase gradient difference of pi/2 of the adjacent structure and realize the phase coverage of 2 pi.
As shown in fig. 5, the electric field distribution of the TE polarized wave is shown on the left side of fig. 5, and the electric field distribution of the TM polarized wave is shown on the right side of fig. 5, and referring to fig. 5, it can be seen that the propagation direction of the TE polarized wave after transmission is changed, and the propagation direction of the TM polarized wave after transmission is unchanged, so as to exhibit the polarization beam splitting effect.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the invention thereto, but to limit the invention thereto, and any modifications, equivalents, improvements and equivalents thereof may be made without departing from the spirit and principles of the invention.

Claims (8)

1. A terahertz polarization beam splitter, comprising:
a periodic metal-dielectric-metal waveguide layer;
the periodic metal-medium-metal waveguide layer is composed of metal strips and medium strips which are alternately arranged;
the terahertz polarization beam splitter can split an incident TE mode polarized wave and a TM mode polarized wave;
the beam splitting angle can be adjusted by adjusting the width of the dielectric strips adjacent to the waveguide layer in one period so that the width of the dielectric strips of the waveguide layer in one period is increased or decreased, or by adjusting the number of the waveguide layers in one period, the phase gradient change of TE mode 2 pi can be covered.
2. The terahertz polarization beam splitter of claim 1 wherein the periodic metal-medium-metal waveguide layers require equal phase differences in TE mode transmissions of adjacent waveguide layers.
3. The terahertz polarization beam splitter of claim 1 wherein the incident TM mode polarized wave excites surface plasmons at the surface of the metal strip for enhancing transmission efficiency.
4. The terahertz polarization beam splitter of claim 1 wherein the periodic metal-medium-metal waveguide layer performs the function of regulating the operating frequency band by varying the medium width.
5. The terahertz polarization beam splitter of claim 1 wherein the transmission phase of the TM mode is independent of variations in waveguide medium width.
6. The terahertz polarization beam splitter of claim 1 wherein the adjustment of the transmission phase and transmission efficiency is achieved by adjusting the transmission length of the periodic metal-dielectric-metal waveguide.
7. The terahertz polarization beam splitter of claim 1 wherein the terahertz polarization beam splitter operates at a terahertz band.
8. The terahertz polarization beam splitter of claim 1 wherein the metal in the periodic metal-dielectric-metal waveguide layer has very little absorption loss near the terahertz band and the metal strip is aluminum, copper, gold or silver.
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Publication number Priority date Publication date Assignee Title
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CN107765359A (en) * 2017-11-10 2018-03-06 中国科学院半导体研究所 Efficient wave plate based on resonator enhancing waveguide transmission

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US9122820B2 (en) * 2013-02-28 2015-09-01 Board Of Regents, The University Of Texas System Subwavelength grating coupler

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CN104297844A (en) * 2014-10-31 2015-01-21 中国计量学院 TeraHertz wave polarization beam splitter of periodically staggered rectangular structure
CN105372758A (en) * 2015-12-02 2016-03-02 中国计量学院 Bar-type terahertz wave polarization beam splitter
CN107765359A (en) * 2017-11-10 2018-03-06 中国科学院半导体研究所 Efficient wave plate based on resonator enhancing waveguide transmission

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