阅读说明：本技术 一种超薄的透射式太赫兹圆偏振非对称聚焦透镜 (Ultrathin transmission-type terahertz circularly-polarized asymmetric focusing lens ) 是由 臧小飞 姚冰双 朱亦鸣 陈麟 谢静雅 于 2020-07-21 设计创作，主要内容包括：本发明公开了一种超薄的透射式太赫兹圆偏振非对称聚焦透镜,提出的双层矩形金属阵列结构加薄膜衬底太赫兹聚焦透镜首次在太赫兹波段实现了超薄的透射式太赫兹圆偏振光的非对称聚焦,能够在右旋圆偏振从正面入射时产生焦点,从反面入射时不能聚焦,通过两层矩形金属结构的叠加打破了结构的对称性,实现了普通透镜不能实现的功能。两层金属矩形阵列结构附着在薄膜衬底层上,厚度仅仅25.3um,并且可根据实际应用场合及要求,通过调整结构参数和结构旋转角度来实现转换频点的调节和焦距的调节。具有损耗低、超薄、体积小、易集成等优点；且该聚焦透镜结构简单,取材广泛,便于加工制备。(The invention discloses an ultrathin transmission-type terahertz circular polarization asymmetric focusing lens, which is characterized in that the ultrathin transmission-type terahertz circular polarization asymmetric focusing lens with a double-layer rectangular metal array structure and a film substrate is used for realizing the asymmetric focusing of ultrathin transmission-type terahertz circular polarization in a terahertz waveband for the first time, can generate a focus when right-handed circular polarization is incident from the front side and cannot be focused when the right-handed circular polarization is incident from the back side, and the symmetry of the structure is broken through the superposition of two layers of rectangular metal structures, so that the function which cannot be realized by a common lens is realized. The two layers of metal rectangular array structures are attached to the thin film substrate layer, the thickness is only 25.3um, and the adjustment of conversion frequency points and the adjustment of focal length can be realized by adjusting structure parameters and structure rotation angles according to actual application occasions and requirements. The device has the advantages of low loss, ultra-thinness, small volume, easy integration and the like; and the focusing lens has simple structure, wide material sources and convenient processing and preparation.)

1. The utility model provides an ultra-thin transmission-type terahertz circular polarization asymmetric focusing lens which characterized in that: the device has a periodic structure and comprises a film substrate layer (3), a first rectangular metal array layer and a second rectangular metal array layer, wherein the first rectangular metal array layer and the second rectangular metal array layer are used for connecting the front side and the back side of the film substrate layer (3);

the rectangular metal array layer I is arranged on the front side of the thin film substrate layer (3), comprises a plurality of rectangular metal I (1) which are distributed in an array mode and have different rotating angles, and is used for adjusting the phase of the transmission terahertz wave to enable the transmission terahertz wave to have a focusing phase and converting incident circularly polarized light into cross polarization terahertz wave;

the rectangular metal array layer II is arranged on the reverse side of the film substrate layer (3), and comprises a plurality of rectangular metal array layers (2) which are distributed in an array mode and have a rotation angle of 45 degrees, and the rectangular metal array layers are used for breaking structural symmetry;

the first rectangular metal (1) and the second rectangular metal (2) have different lengths and widths, and a single first rectangular metal (1) and a single second rectangular metal (2) and the middle film substrate layer (3) form a single periodic structure of the lens.

2. The ultra-thin transmissive terahertz circularly polarized asymmetric focusing lens of claim 1, wherein: the film substrate layer (3) is a polyimide film or a polyethylene naphthalate film or a polyester film.

3. The ultra-thin transmissive terahertz circularly polarized asymmetric focusing lens of claim 1, wherein: the thickness of the thin film substrate layer (3) is 25 microns.

4. The ultra-thin transmissive terahertz circularly polarized asymmetric focusing lens of claim 1, wherein: the frequency point is adjusted by changing the length and the width of the rectangular metal I (1) and the rectangular metal II (2), and the focal length is adjusted by changing the rotating angle of the rectangular metal I (1).

5. The ultra-thin transmissive terahertz circularly polarized asymmetric focusing lens of claim 1, wherein: the first rectangular metal array layer and the second rectangular metal array layer are coated on the film substrate layer (3) through photoetching or magnetron sputtering.

6. The ultra-thin transmissive terahertz circularly polarized asymmetric focusing lens of claim 1, wherein: the right-handed circularly polarized light is focused when entering from the front side of the film substrate layer (3), is unfocused when entering from the back side of the film substrate layer (3), and is unfocused when entering from the front side of the film substrate layer (3) and is focused when entering from the back side of the film substrate layer (3).

Technical Field

The invention relates to a terahertz lens, in particular to an ultrathin transmission-type terahertz circularly-polarized asymmetric focusing lens.

Background

Terahertz (THz) waves are electromagnetic waves having a frequency between 0.1THz and 10THz, and are located between microwaves and far infrared. With the generation of terahertz waves and the development of detection technologies, terahertz technologies have raised a research trend in the international range. The terahertz wave has the characteristics of strong penetrability, high use safety, good directionality and the like, so the terahertz technology is widely applied to the fields of biomedicine, safety inspection, communication and the like. The research of the terahertz technology mainly focuses on three major contents, namely the application research of a terahertz source, terahertz detection and a terahertz functional device. In order to meet the actual application requirements, researchers are struggling to develop miniaturized and integrated terahertz systems. The existing terahertz functional device is low in efficiency and large in size, such as a quartz wave plate, a polyethylene lens and the like. This current situation hinders the development of terahertz technology and the development process of miniaturized terahertz systems.

In recent years, due to the fact that the terahertz superlens design based on the super-surface design causes heat tide, the terahertz focusing lens is realized in the terahertz waveband at present. In this year, Xiaorong Hong, the central ethnic university, realized a transmissive terahertz lens at 1THz with a cylindrical silicon structure having different diameters. However, the thickness of the super-surface lens of most of the medium-based super-lenses is far larger than that of the metal-based super-surface lens, and the medium super-surface lens is more easily damaged than the metal-based super-surface lens, thereby limiting the application field of the medium super-surface lens.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the problem that the existing terahertz lens is too large in size and difficult to integrate a terahertz device is solved.

In order to solve the above problems, the technical solution of the present invention is to provide an ultrathin transmissive terahertz circularly polarized asymmetric focusing lens, which is characterized in that: the device has a periodic structure and comprises a film substrate layer, a first rectangular metal array layer and a second rectangular metal array layer, wherein the first rectangular metal array layer and the second rectangular metal array layer are used for connecting the front side and the back side of the film substrate layer;

the rectangular metal array layer I is arranged on the front side of the film substrate layer, comprises a plurality of rectangular metal I with different rotation angles, is distributed in an array manner, and is used for adjusting the phase of the transmission terahertz wave to enable the transmission terahertz wave to have a focusing phase and converting incident circularly polarized light into cross polarization terahertz waves;

the rectangular metal array layer II is arranged on the reverse side of the film substrate layer and comprises a plurality of rectangular metal array layers which are distributed in an array mode and rotate at an angle of 45 degrees, and the rectangular metal array layers are used for breaking structural symmetry;

the first rectangular metal and the second rectangular metal have different lengths and widths, and a single first rectangular metal, a single second rectangular metal and the middle film substrate layer form a single periodic structure of the lens.

Preferably, the film substrate layer is a polyimide film or a polyethylene naphthalate film or a polyester film.

Preferably, the thin film substrate layer has a thickness of 25 microns.

Preferably, the frequency point is adjusted by changing the length and width of the first rectangular metal and the second rectangular metal, and the focal length is adjusted by changing the rotation angle of the first rectangular metal.

Preferably, the first rectangular metal array layer and the second rectangular metal array layer are coated on the film substrate layer by a photoetching or magnetron sputtering method.

Preferably, the right-handed circularly polarized light is focused when incident from the front side of the film substrate layer, and is unfocused when incident from the back side of the film substrate layer, and the left-handed circularly polarized light is unfocused when incident from the front side of the film substrate layer, and is focused when incident from the back side of the film substrate layer.

Compared with the prior art, the invention has the beneficial effects that:

the double-layer rectangular metal array structure and film substrate terahertz focusing lens provided by the invention realizes asymmetric focusing of ultrathin transmission type terahertz circularly polarized light in a terahertz waveband for the first time, can generate a focus when right-handed circular polarization is incident from the front side and cannot focus when the right-handed circular polarization is incident from the back side, breaks through the symmetry of the structure through the superposition of the two layers of rectangular metal structures, and realizes the function which cannot be realized by a common lens.

The 1/4 wave plate, the lens and the polarizer are combined together to realize the asymmetric focusing of the circular polarization by adopting the traditional method, the system structure is huge, and the light loss is large after passing through the thick lens. The two layers of metal rectangular array structures provided by the invention are attached to the film substrate layer, the thickness is only 25.3um, and the adjustment of conversion frequency points and the adjustment of focal length can be realized by adjusting structure parameters and structure rotation angles according to actual application occasions and requirements. The device has the advantages of low loss, ultra-thinness, small volume, easy integration and the like; and the focusing lens has simple structure, wide material sources and convenient processing and preparation.

Drawings

FIG. 1 is a top view of a front surface of a single periodic structure of an ultra-thin transmissive terahertz circularly polarized asymmetric focusing lens according to the present invention;

FIG. 2 is a top view of the reverse side of a single periodic structure of the ultra-thin transmissive terahertz circularly polarized asymmetric focusing lens of the present invention;

FIG. 3 is a left side view of a single periodic structure of the ultra-thin transmissive terahertz circularly polarized asymmetric focusing lens of the present invention;

FIG. 4 is a front top view of a sixteen-period structure of the ultra-thin transmissive terahertz circularly-polarized asymmetric focusing lens of the present invention;

FIG. 5 is a reverse top view of a sixteen-period structure of the ultra-thin transmissive terahertz circularly-polarized asymmetric focusing lens of the present invention;

FIG. 6 is a left side view of a sixteen-period structure of the ultra-thin transmissive terahertz circularly-polarized asymmetric focusing lens of the present invention;

FIG. 7 is a phase diagram of the phase of cross-polarized light transmitted by a rectangular metal array layer on the front side of a single periodic structure of the ultrathin transmissive terahertz circularly-polarized asymmetric focusing lens according to the present invention under the incidence of circularly polarized light, varying with the rotation angle of the rectangular metal array layer;

FIG. 8 is a transmittance diagram of circularly polarized transmission light of the ultrathin transmission terahertz circularly polarized asymmetric focusing lens under the vertical incidence of right-handed circularly polarized light;

fig. 9 is a transmittance diagram of the ultrathin transmission-type terahertz circularly polarized asymmetric focusing lens according to the present invention when the upper and lower rectangular metal array layers are not completely aligned, under the incidence of right-handed circularly polarized light.

Detailed Description

In order to make the invention more comprehensible, preferred embodiments are described in detail below with reference to the accompanying drawings.

The invention discloses an ultrathin transmission-type terahertz circularly-polarized asymmetric focusing lens which is of a periodic structure and comprises three layers, wherein the first layer is a rectangular metal array layer I and is used for adjusting the phase of transmitted light to enable the transmitted light to have a focusing phase and converting incident circularly-polarized light into cross-polarized light; the second layer is a film substrate layer 3 which is used for connecting an upper layer structure and a lower layer structure; the third layer is a rectangular metal array layer II with a rotation angle fixed at 45 degrees and is used for breaking the structural symmetry. The rectangular metal array layer I and the rectangular metal array layer I on and under the film substrate layer 3 are prepared by a photoetching process or a magnetron sputtering coating method.

The film backing layer 3 may be a polyimide film, a polyethylene naphthalate film, or a polyester film, and has a thickness of 25 um. The front side and the back side of the film substrate layer 3 are respectively etched with a plurality of rectangular metal I1 and rectangular metal II 2 which are distributed in an array mode to form a rectangular metal array layer I and a rectangular metal array layer II, and the rectangular metal I1 and the rectangular metal II 2 have different lengths and widths. The single rectangular metal I1 and the single rectangular metal II 2 and the intermediate thin film substrate layer 3 form a single periodic structure of the lens.

The terahertz circularly polarized asymmetric focusing lens can focus right-handed circularly polarized light incident from the front side of the film substrate layer 3 at 0.6THz, and cannot focus light incident from the back side of the film substrate layer 3; for left-handed circularly polarized light, the light can be focused when entering from the back side of the thin film substrate layer 3, and can not be focused when entering from the front side of the thin film substrate layer 3, so that the asymmetric focusing function of circular polarization is realized.

As shown in FIGS. 1, 2 and 3, the length of a single periodic structure of the ultrathin transmission type terahertz circularly-polarized asymmetric focusing lens is p, and the total thickness is t₁+d+t₂The polyimide film comprises two rectangular metal array layers I and two rectangular metal array layers II which are periodically arranged and a polyimide film. The thickness of the first rectangular metal array layer is t₁The length and width of the rectangular metal I1 are respectively l₁、w₁For regulating and controlling the polarization state and phase of incident terahertz wavesModulating the phase of incident circularly polarized terahertz waves to focus the incident circularly polarized terahertz waves; the thickness of the second polyimide film is d, so that the effect of reducing loss and realizing ultrathin property can be achieved in the transmission process of electromagnetic waves, and the polyimide film is not limited to the polyimide film; the thickness of the second rectangular metal array layer of the third layer is t₂The length and width of the rectangular metal II 2 are respectively l₂、w₂The rotation angle is fixed to be 45 degrees, and the rotation angle is used for breaking structural symmetry to enable the right-handed circular polarization to be focused when entering from the front side of the polyimide film, the right-handed circular polarization cannot be focused when entering from the back side of the polyimide film, the left-handed circular polarization can be focused when entering from the back side of the polyimide film, and the left-handed circular polarization cannot be focused when entering from the front side of the polyimide film. The structural parameters of the first rectangular metal 1 and the second rectangular metal 2 can be adjusted to realize adjustment of conversion frequency points and adjustment of focal lengths, the frequency points are adjusted by changing the length and the width of the first rectangular metal 1 and the second rectangular metal 2, and the focal lengths are adjusted by changing the rotation angle of the first rectangular metal.

The ultrathin transmission-type terahertz circularly-polarized asymmetric focusing lens disclosed by the invention is composed of a plurality of periodic structures, wherein the top views and the left views of the front surface and the back surface of the ultrathin transmission-type terahertz circularly-polarized asymmetric focusing lens shown in the figures 3, 4 and 5 show sixteen periodic structures.

In this example, a polyimide film with a refractive index of 3.5(1+0.01i) was selected, and rectangular metal array layers arranged periodically were prepared on the front and rear surfaces of the polyimide film using a photolithography process and a magnetron sputtering coating technique. The ultrathin transmission-type terahertz circularly-polarized asymmetric focusing lens is tested by a traditional terahertz time-domain spectroscopy system, and the polarization state of terahertz light excited by the terahertz time-domain spectroscopy system is linear polarization, so that a quarter-wave plate is arranged between terahertz source samples to convert the linearly-polarized terahertz wave into circularly-polarized terahertz wave, and right-handed circularly-polarized light obtained by rotating the angle of the wave plate is incident on the front surface of the superlens and finally converged on a probe through the superlens. The sample was then inverted so that right-handed circularly polarized light was incident from the opposite side of the superlens. In the test, the time domain signal detected by the probe is subjected to Fourier transform to obtain required phase and amplitude information, and finally, time domain difference numerical simulation is carried out to obtain field distribution information of the super lens. As shown in fig. 7, the rectangular metal array layer i on the front surface of the ultra-thin terahertz circularly-polarized asymmetric focusing lens mainly performs phase control to generate a focusing phase, and the phase Φ, which is 2 θ, can be obtained by rotating the angle θ between the long axis of the rectangular metal 1i on the front surface of the rectangular metal array layer i and the x axis, so that the phase can be easily controlled by rotating the direction of the rectangular metal 1i in the range of 0.5-0.9 THz. As shown in fig. 8, since another rectangular metal array layer two with a rotation angle fixed at 45 ° is covered on the reverse side of the film substrate layer 3 on the rectangular metal 1 of the original focused rectangular metal array layer one, the structural symmetry of the superlens is broken, at 0.6THz, the transmittance of right-handed circularly polarized terahertz Light (LCP) incident from the front side of the superlens reaches 30%, and the transmittance of right-handed circularly polarized terahertz light incident from the reverse side is almost 0%, so that the asymmetric transmission of circularly polarized terahertz light is realized. In addition, although the upper and lower rectangular metal one 1 and rectangular metal two 2 structures are designed, the incomplete alignment of the two rectangular metal one 1 and rectangular metal two 2 structures does not affect the functions thereof, and as shown in fig. 9, when the two rectangular metal structures are deviated from the center by 5.9um and 11.8um, the transmission curves when the right-handed circularly polarized light is incident from the front and the back are hardly affected. Because the polarization converter is manufactured on the polyimide film, the polarization converter has the advantages of being ultrathin, small in size, small in loss and the like.