阅读说明：本技术 基于波导传输的高效太赫兹偏振分束器 (High-efficiency terahertz polarization beam splitter based on waveguide transmission ) 是由 焦晓飞 宋国峰 徐云 于 2020-06-16 设计创作，主要内容包括：一种太赫兹偏振分束器,包括：周期性金属-介质-金属波导层；所述周期性金属-介质-金属波导层由交替排列的金属条带与介质条带构成,一个周期内包含多个介质宽度不同的波导层；所述太赫兹偏振分束器能够将入射的TE模式偏振波与TM模式偏振波进行分束。本发明利用TE与TM波导模式对介质宽度的依赖性不同来实现偏振分束功能,而TE与TM波导模式在金属波导中具有低损耗的特质,具有高效的优点。对于不同频段的太赫兹波,本发明可以通过对波导介质宽度以及波导传输长度进行调节,从而实现偏振分束效果。(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, and a plurality of waveguide layers with different medium widths are contained in one period; the terahertz polarization beam splitter can split incident TE mode polarized waves and TM mode polarized waves. The invention realizes the polarization beam splitting function by utilizing the different dependence of the TE and TM waveguide modes on the width of the medium, and the TE and TM waveguide modes have the characteristics of low loss and high efficiency in the metal waveguide. For terahertz waves of different frequency bands, the invention can realize the polarization beam splitting effect by adjusting the width of the waveguide medium and the transmission length of the waveguide.)

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, and a plurality of waveguide layers with different medium widths are contained in one period;

the terahertz polarization beam splitter can split incident TE mode polarized waves and TM mode polarized waves.

2. The terahertz polarization beam splitter of claim 1, wherein the periodic metal-dielectric-metal waveguide layer requires adjacent waveguide layers to be equal in TE mode transmission phase difference.

3. The terahertz polarization beam splitter of claim 1, wherein the incident TM mode polarized wave excites surface plasmons on the surface of the metal strip for enhancing transmission efficiency.

4. The terahertz polarization beam splitter of claim 1, wherein the periodic metal-dielectric-metal waveguide layer realizes a function of adjusting and controlling an operating frequency band by changing a dielectric width.

5. The terahertz polarization beam splitter of claim 1, wherein the transmission phase of the TM mode is independent of a change in waveguide medium width.

6. The terahertz polarization beam splitter of claim 1, wherein the terahertz polarization beam splitter is capable of adjusting a phase gradient of a TE mode by adjusting a width of a medium of an adjacent waveguide layer within a period.

7. The terahertz polarization beam splitter of claim 1, wherein adjustment of transmission phase and transmission efficiency can be achieved by adjusting a transmission length of the periodic metal-dielectric-metal waveguide.

8. The terahertz polarization beam splitter of claim 1, wherein the terahertz polarization beam splitter operating wavelength is a terahertz waveband.

9. The terahertz polarization beam splitter of claim 1, wherein the absorption loss of the metal in the periodic metal-dielectric-metal waveguide layer near the terahertz waveband is very low, and the metal strip is aluminum, copper, gold, or silver.

10. The terahertz polarization beam splitter of claim 1, wherein the terahertz polarization beam splitter can adjust a beam splitting angle by designing the number of waveguide layers within one period.

Technical Field

The invention relates to the field of terahertz devices, in particular to a waveguide transmission-based efficient terahertz polarization beam splitter.

Background

Currently, the terahertz technology has become one of the very important subjects in this 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 the detector, functional devices such as a terahertz modulator, a filter, a beam splitter, a polarizer and the like are also indispensable in the terahertz system. Among these devices, the polarization beam splitter plays a very important role in terahertz polarization spectroscopy, polarization imaging, polarization state communication, and the like. In the terahertz range, the transmission efficiency of the device is particularly important due to low power, and the signal-to-noise ratio has a large influence due to free space path loss, atmospheric absorption and the like. The traditional terahertz polarization beam splitter relies on the birefringence effect of an optical crystal and utilizes the refractive index difference corresponding to the crystal in the transmission process of orthogonal polarization components to perform polarization beam splitting. However, these natural optical crystals are not only rare but also weak in birefringence and low in transmission efficiency, and require a large thickness of material.

The traditional metal super surface has the existence of surface plasmon resonance, but the plasma frequency of the metal is generally positioned in visible light and ultraviolet wave bands, the metal is close to an ideal conductor in THz wave bands, the surface plasmon resonance is difficult to excite, and most of the metal super surfaces are reflection super surfaces, so that complicated light paths need to be designed, and the application of most of transmission conditions is difficult to meet. With the trend of increasing integration of optical systems nowadays, the conventional polarization beam splitter cannot meet the application requirements. In view of the rapid development of terahertz technology, these drawbacks need to be addressed urgently. Recently, a new design idea is provided for the realization of terahertz polarization devices due to the appearance of metamaterials or metamaterials, the metamaterials can generate oscillation in different modes under the driving of an incident field, and the spectral response in various oscillation modes has a dependency on the shape, size, material and the like of the structure. By designing the structure, size and periodicity of the structure of the super-surface, researchers can realize that phase gradients are generated among different radiation fields.

Disclosure of Invention

In view of the above, the main object of the present invention is to provide a waveguide transmission based high-efficiency terahertz polarization beam splitter, which is intended to partially solve at least one of the above technical problems.

In order to achieve the above object, as an aspect of the present invention, there is provided a waveguide transmission-based high-efficiency terahertz polarization beam splitter, including:

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 plurality of waveguide layers with different medium widths are contained in one period;

the terahertz polarization beam splitter can split incident TE mode polarized waves and TM mode polarized waves.

Wherein the periodic metal-dielectric-metal waveguide layers require equal TE mode transmission phase differences of adjacent waveguide layers.

Wherein, the incident TM mode polarized wave excites surface plasmon on the surface of the metal strip to enhance the transmission efficiency.

The periodic metal-medium-metal waveguide layer realizes the function of regulating and controlling the working frequency band 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.

The terahertz polarization beam splitter can adjust the phase gradient of a TE mode by adjusting the width of a medium of an adjacent waveguide layer in a period.

Wherein, the transmission phase and the transmission efficiency can be adjusted by adjusting the transmission length of the periodic metal-dielectric-metal waveguide.

The working wavelength of the terahertz polarization beam splitter is a terahertz waveband.

The absorption loss of metal in a terahertz waveband is very low, and the metal strip is aluminum, copper, gold or silver.

The beam splitting angle can be adjusted by designing the number of waveguide layers in one period.

Based on the technical scheme, compared with the prior art, the efficient terahertz polarization beam splitter based on waveguide transmission at least has one of the following beneficial effects:

1. the invention realizes the polarization beam splitting function by utilizing the different dependence of the TE and TM waveguide modes on the width of the medium, and the TE and TM waveguide modes have the characteristics of low loss and high efficiency in the metal waveguide.

2. The number of waveguide layers in the period determines the change of the transmitted phase gradient, and the 2 pi phase gradient change can be covered by adjusting the width of the waveguide layers and the number of waveguide layers in the period, so that deflection at different angles can be realized.

3. For terahertz waves of different frequency bands, the invention can realize the polarization beam splitting effect by adjusting the width of the waveguide medium and the transmission length of the waveguide.

Drawings

Fig. 1 is a schematic diagram of a waveguide transmission-based efficient terahertz polarization beam splitter in an embodiment of the present invention;

fig. 2 is a schematic cross-sectional structure diagram of a waveguide transmission-based efficient terahertz polarization beam splitter in an embodiment of the present invention, where a z coordinate represents a device vertical direction, and x and y coordinate directions represent device horizontal directions;

FIG. 3 is a graph of transmission versus dielectric width for a waveguide transmission based polarizing beamsplitter in an embodiment of the present invention;

FIG. 4 is a graph showing the variation of the transmission phase of an incident light component with polarization along the x-axis (TM) and the polarization along the y-axis (TE) according to the width of a medium in an embodiment of the present invention;

FIG. 5 is a graph showing the distribution of the transmitted electric field for incident light with polarization in the x-axis direction (TM) and polarization in the y-axis direction (TE) in accordance with 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 (4) waveguide structure period.

Detailed Description

The invention discloses a waveguide transmission-based efficient terahertz polarization beam splitter, and belongs to the field of electromagnetic waves. The main structure of the invention is shown in figure 1 and is composed of a periodic metal-dielectric-metal waveguide layer with gradually changed dielectric width. The adjacent metal strips and the medium layer positioned in the metal strips form a metal-medium-metal waveguide which supports the transmission of a TE mode and a TM mode at the same time in an operating waveband. The transmission phase change of the TE mode in the operating band depends on the medium width, while the transmission phase change of the TM mode is independent of the medium width. And a plurality of waveguide structures with different dielectric interlayer thicknesses form a period, so that a transverse phase gradient appears at a waveguide exit port in a TE mode, the TE wave front direction is changed, the TM wave front is not changed, and the polarization beam splitting function is realized. The invention has the characteristics of high efficiency, adjustable beam splitting angle according to the structure, adjustable working frequency according to the parameters and the like.

Specifically, the invention discloses a waveguide transmission-based efficient terahertz polarization beam splitter, which mainly comprises:

a periodic metal-dielectric-metal waveguide layer; the periodic metal-dielectric-metal waveguide layer is composed of metal strips and dielectric strips which are alternately arranged, and a plurality of waveguide layers with different dielectric widths are contained in one period;

the periodic metal-dielectric-metal waveguide layer requires equal TE mode transmission phase difference of adjacent waveguide layers and can be realized by adjusting the dielectric width; the number of waveguide layers in a period determines the deflection angle of the TE mode; for TM mode incidence, exciting surface plasmons on the surface of the metal strip to enhance the transmission efficiency; the function of regulating and controlling the working frequency band is realized by changing the width of the medium.

Wherein the transmission phase of the TM mode is independent of the variation in the width of the waveguide medium.

Wherein the phase gradient of the TE mode can be adjusted by adjusting the width of the medium of the adjacent waveguide layer within the period.

The transmission phase and the transmission efficiency can be adjusted by adjusting the transmission length of the periodic metal-dielectric-metal waveguide.

The working wavelength of the high-efficiency terahertz polarization beam splitter based on waveguide transmission is a terahertz waveband.

The metal is an approximate perfect electric conductor in a terahertz waveband, the absorption loss is very little, and the metal strip is aluminum, copper, gold or silver.

The beam splitting angle can be adjusted by designing the number of waveguide layers in one period.

A high-efficiency terahertz polarization beam splitter based on waveguide transmission comprises a main body and a periodic metal-medium-metal waveguide layer, wherein the width of a waveguide medium in a period is in an increasing or decreasing trend.

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. The adjacent metal strips and the medium layer positioned in the metal strips form a metal-medium-metal waveguide which supports the transmission of a TE mode and a TM mode at the same time in an operating waveband. The mode refractive index of the TE mode is different from that of the TM mode, and the transmission phase of the TE mode in the operating band varies depending on the width of the medium, while the transmission phase of the TM mode varies independently of the width of the medium. The waveguide structures with the thickness of the multiple dielectric interlayers increasing or decreasing form a period, a transverse phase gradient appears at the waveguide exit port, the phase gradient covers 2 pi in the period, the TE wave front direction is changed, the TM wave front is not changed, and the polarization beam splitting function is realized.

Generally, the processes participating in the transmission of THz waves in the metal waveguide include direct transmission of THz in the waveguide, abnormal transmission caused by surface plasmon polarization waves, and induced localized surface plasmons, which are coupled to affect the resonance frequency and transmission. Unlike the slot resonators on the dielectric surface, the structural metal strips form a complete waveguide array, localized surface plasmon resonance is eliminated, and absorption loss is greatly reduced. The other point is different from the slit resonator in that surface electric resonance is generated on the upper surface and is used as a dipole source to excite magnetic resonance of the side wall, the magnetic resonance can be coupled back to the electric resonance, and the excited surface plasmon resonance can be propagated along the side wall of the waveguide, so that the polarization beam splitter with high-efficiency transmission is realized.

In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.

The terahertz polarization beam splitter based on waveguide transmission in the embodiment can split incident TE polarized waves and TM polarized waves, the working frequency band is 1THz, and the transmission efficiency is over 90%. Fig. 1 is a schematic diagram of a terahertz polarization beam splitter based on waveguide transmission, where 1 is a dielectric material quartz, 2 is a metal strip material aluminum, 3 is a transmission length a of a metal-dielectric-metal waveguide layer 1200 μm, 4 is one period of a waveguide structure, a dielectric layer has a width d1 of 135 μm along an x-axis direction, d2 of 143 μm, d3 of 153 μm, d4 of 167 μm, and a metal strip has a width w of 5 μm along the x-axis direction.

Fig. 2 is a cross-sectional view of a terahertz polarization beam splitter based on waveguide transmission.

Incident light is incident along the direction of a z axis, an electric vector is in an xy plane, the direction of the electric vector forms an included angle of 45 degrees with an x axis, and the intensity of incident light components with the polarization direction parallel to the direction of a strip (namely TE incident components and along the direction of the y axis) and the polarization direction perpendicular to the direction of the strip (namely TM incident components and along the direction of the x axis) is the same. Referring to fig. 3, which is a graph showing the variation of the transmittance of the terahertz polarization beam splitter based on waveguide transmission according to the width of the medium, 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. Referring to fig. 4, which shows a curve of a 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 medium width, in a range of 135 μm to 167 μm, a transmission phase of TE polarization and the medium width change nearly linearly, while a transmission phase of TM polarization is not affected by the medium width, and the transmission phase does not change according to the change of the medium width. Therefore, the structure in the embodiment can realize the phase gradient difference of the adjacent structures as pi/2 and realize the phase coverage of 2 pi.

Referring to fig. 5, it can be seen that the propagation direction of the TE polarized wave after transmission changes, and the propagation direction of the TM polarized wave after transmission does not change, showing the polarization beam splitting effect, as shown in fig. 5, the left side of fig. 5 shows the electric field distribution of the TE polarized wave, and the right side of fig. 5 shows the electric field distribution of the TM polarized wave.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.