Switchable controller for terahertz circular dichroism and linear dichroism

Abstract

This invention discloses a controller capable of switching terahertz wave circular dichroism (CD) and linear dichroism (LD). The controller comprises a dielectric layer embedded in a U-shaped silicon rod, a dielectric layer embedded in a metal open square ring, a dielectric layer, and a base layer. The interaction between the top composite structure and the dielectric layer generates strong circular dichroism (CD). The controller can also achieve switching between CD and LD by varying the conductivity of the photosensitive silicon pump light. The controller has a simple structure and can achieve dual-polarization dichroism. It has broad application prospects in fields such as polarization detection and near-field imaging.

Description

Technical Field

[0001] The present invention relates to the field of terahertz wave controllers, and in particular to a terahertz wave circular dichroism and linear dichroism switchable controller. Background Art

[0002] Terahertz waves (0.1-10 THz) lie in the transition region between electronics and photonics, between microwaves and infrared in the electromagnetic spectrum. Their unique spectral position enables terahertz waves to possess microwave penetration and optical imaging capabilities. They also exhibit many electromagnetic properties not found in microwave and infrared bands, such as broadband, coherence, transient behavior, and low photon energy. An object's structure cannot be transformed into its mirror image through translation or rotation, resulting in chirality. Many natural substances, such as proteins, amino acids, and DNA, possess chirality. Therefore, chirality is crucial to life, and detecting the chirality of matter has become a hot topic for many researchers. Chiral materials exhibit different absorption for right-handed and left-handed circular polarization, a phenomenon known as circular dichroism (CD). CD can be defined as the difference in absorption / reflection of a chiral medium for waves with different circular polarizations. The difference is called circular dichroism. Linear dichroism can be defined as the difference in absorption / reflection for waves with different linear polarizations. Circular dichroism and linear dichroism can be used to detect the chirality of a material or structure. The optical chiral response (circular dichroism and linear dichroism) brought about by chiral structures has important application prospects in polarization imaging, biomedical detection, optical communications, circular dichroism spectroscopy, and other fields.

[0003] Since the chiral signals of biological molecules in nature are relatively weak and difficult to detect, by studying artificial chiral metasurfaces and constructing different chiral metasurfaces, the chiral signal testing of biomolecules can be easily realized. Designing simple and adjustable chiral metasurface devices has become an inevitable trend. At the same time, it is necessary to comprehensively consider multiple factors such as materials, processes, efficiency and functions. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problem that the existing technology cannot achieve circular dichroism and linear dichroism at the same time, overcome the shortcomings of complex structure, practical production difficulties and high cost, and provide a terahertz wave circular dichroism and linear dichroism switchable controller.

[0005] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0006] A terahertz wave circular dichroism and linear dichroism switchable controller, comprising a composite structure consisting of four layers with identical square outer contours, comprising, from top to bottom, a first BCB dielectric layer, a second BCB dielectric layer, a third BCB dielectric layer, and a silicon substrate. The first BCB dielectric layer is embedded with a U-shaped silicon rod made of photosensitive silicon. The U-shaped silicon rod consists of a first rectangular silicon rod and two second rectangular silicon rods arranged at the long sides of the first rectangular silicon rod at both ends, with the first rectangular silicon rods arranged along the diagonals of the first BCB dielectric layer. The second BCB dielectric layer is embedded with a metal open square ring, which has two openings symmetrically provided on two opposite sides. The silicon substrate is made of photosensitive silicon.

[0007] Preferably, the composite structure is periodically arranged on a plane, with a period of 25 μm to 35 μm in the x-direction and a period of 25 μm to 35 μm in the y-direction.

[0008] Preferably, the thickness of the first BCB dielectric layer and the U-shaped silicon rod are both 0.1μm to 1.0μm; in the U-shaped silicon rod, the length of the first rectangular silicon rod is 15μm to 25μm, and the width is 1μm to 3μm, and the length of the second rectangular silicon rod is 1μm to 2μm, and the width is 1μm to 2μm.

[0009] Furthermore, the dielectric constant of the U-shaped silicon rod is 11.9.

[0010] Preferably, the thickness of the second BCB dielectric layer and the metal open square ring are both 0.1 μm to 1.0 μm, wherein the length of the metal open square ring is 15 μm to 25 μm, the width is 1 μm to 5 μm, and the length of the opening on a single side is 1 μm to 5 μm.

[0011] Furthermore, the metal open square ring is made of gold, and its electrical conductivity is 4.561×10 7 S / m.

[0012] Preferably, the thickness of the third BCB dielectric layer is 5 μm to 15 μm.

[0013] Preferably, the dielectric constants of the BCB dielectric materials in the first BCB dielectric layer, the second BCB dielectric layer and the third BCB dielectric layer are all 2.67.

[0014] Preferably, the silicon substrate has a thickness of 0.5 μm to 1.5 μm.

[0015] Preferably, the controller controls the photosensitive silicon in the device to be in a metallic state by pumping light, thereby realizing both circular dichroism and linear dichroism in different frequency bands; and realizes dynamic tuning of the circular dichroism and linear dichroism amplitudes by changing the conductivity of the photosensitive silicon.

[0016] The terahertz wave circular dichroism and linear dichroism switchable controller designed in this invention generates strong circular dichroism (CD) due to the interaction between the top composite structure and the dielectric layer. The device's conductivity can be altered by varying the photosensitive silicon pump light, enabling the device to simultaneously achieve both circular dichroism and linear dichroism in different frequency bands without crosstalk. This device can achieve dual-polarization dichroism and offers advantages such as ease of large-scale integration, simple structure, compact size, low cost, and ease of fabrication. It has broad application prospects in fields such as polarization detection and near-field imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the three-dimensional structure of the controller that can switch between terahertz circular dichroism and linear dichroism;

[0018] Figure 2 It is a top view schematic diagram of the dielectric layer embedded in the U-shaped silicon rod;

[0019] Figure 3 It is a top view schematic diagram of the dielectric layer embedded with the metal split square ring;

[0020] Figure 4 is the conductivity of photosensitive silicon σ Si =5×10 5 S / m, the reflection coefficient curve of the designed structure under the incident circularly polarized wave;

[0021] Figure 5 is the conductivity of photosensitive silicon σ Si =5×10 5 S / m, the reflectivity and circular dichroism curves of the designed structure under circularly polarized wave incidence;

[0022] Figure 6 is the conductivity of photosensitive silicon σ Si =5×10 5 S / m, the circular dichroism spectrum of the designed structure when the incident angle of circularly polarized wave increases from -60° to 60°;

[0023] Figure 7 is the conductivity of photosensitive silicon σ Si =5×10 5 S / m, the circular dichroism spectrum of the designed structure when the polarization angle of circularly polarized wave increases from 0° to 90°;

[0024] Figure 8 The conductivity of photosensitive silicon increases from 1S / m to 5×10 5 The change of circular dichroism peak when S / m.

[0025] Figure 9 is the conductivity of photosensitive silicon σ Si =5×105 S / m, the reflection coefficient curve of the designed structure under the incidence of linearly polarized wave;

[0026] Figure 10 is the conductivity of photosensitive silicon σ Si =5×10 5 S / m, the absorptivity and linear dichroism curves of the designed structure under linearly polarized wave incidence;

[0027] Figure 11 is the conductivity of photosensitive silicon σ Si =2×10 5 S / m, the linear dichroism spectrum of the designed structure when the incident angle of the linear polarization wave increases from -0° to 50°;

[0028] Figure 12 The conductivity of photosensitive silicon increases from 1S / m to 5×10 5 The change of linear dichroism peak at S / m. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0030] In a preferred embodiment of the present invention, a terahertz wave circular dichroism and linear dichroism switchable controller is provided. Figure 1 As shown in the figure, it consists of a composite structure consisting of four layers with the same square outer contour, namely, the first BCB dielectric layer 1, the second BCB dielectric layer 2, the third BCB dielectric layer 3 and the silicon substrate 4. The outer contours of the four layers are the same, so the planar contour of the entire device is also a square. The main bodies of the first BCB dielectric layer 1, the second BCB dielectric layer 2 and the third BCB dielectric layer 3 are all made of BCB material (Benzocyclobutene). A U-shaped silicon rod made of photosensitive silicon is embedded in the first BCB dielectric layer 1, as shown in the figure. Figure 2 As shown, the U-shaped silicon rod consists of a first rectangular silicon rod and two second rectangular silicon rods. The two second rectangular silicon rods are arranged at both ends of the first rectangular silicon rod and are located on one side of a long side of the rectangle. The whole is equivalent to a rectangular ring with one long side missing. The first rectangular silicon rod is arranged along the diagonal line of the first BCB dielectric layer 1. A metal open square ring is embedded in the second BCB dielectric layer 2, as shown in FIG. Figure 3As shown, the metal open square ring has two openings symmetrically formed on two opposite sides. The material of the silicon substrate 4 is photosensitive silicon.

[0031] The composite structure is arranged periodically on the plane, with a period P in the x direction. x 25μm~35μm, y direction period P y 25μm~35μm, that is to say, the plane outline of the device composed of a single composite structure and the outer outline of the four-layer body are both P x ×P y .

[0032] The specific materials and parameters of the terahertz wave circular dichroism and linear dichroism switchable controller are as follows:

[0033] The thickness of the first BCB dielectric layer 1 and the U-shaped silicon rod are both 0.1μm to 1.0μm; in the U-shaped silicon rod, the length of the first rectangular silicon rod is 15μm to 25μm, the width is 1μm to 3μm, and the length of the second rectangular silicon rod is 1μm to 2μm, the width is 1μm to 2μm (here, the length direction of the second rectangular silicon rod is defined as parallel to the length direction of the first rectangular silicon rod, and the width direction of the second rectangular silicon rod is defined as perpendicular to the length direction of the first rectangular silicon rod). The dielectric constant of the U-shaped silicon rod is 11.9. The thickness of the second BCB dielectric layer 2 and the metal open square ring are both 0.1μm to 1.0μm, the length of the metal open square ring is 15μm to 25μm, the width is 1μm to 5μm, and the length of the opening on a single side is 1μm to 5μm. The metal open square ring is made of gold, and its conductivity is 4.561×10 7 The thickness of the third BCB dielectric layer 3 is 5 μm to 15 μm. The dielectric constant of the BCB dielectric material in the first BCB dielectric layer 1, the second BCB dielectric layer 2, and the third BCB dielectric layer 3 is 2.67. The thickness of the silicon substrate 4 is 0.5 μm to 1.5 μm.

[0034] The controller controls the photosensitive silicon in the device to be in a metallic state by pumping light, thereby realizing both circular dichroism and linear dichroism in different frequency bands; and by changing the conductivity of the photosensitive silicon, dynamic tuning of the circular dichroism and linear dichroism amplitudes can be achieved.

[0035] The above-mentioned terahertz wave circular dichroism and linear dichroism switchable controller is applied to a specific example below to demonstrate its technical effect.

[0036] Example

[0037] In this embodiment, the shapes of the components of the terahertz wave circular dichroism and linear dichroism switchable controller are as described above. Figures 1 to 3 , I will not go into details here. However, the specific parameters of each component are as follows:

[0038] The composite structure is arranged periodically on the plane, with a period P in the x direction. x 28μm, y direction period P y The thickness of the first BCB dielectric layer 1 and the U-shaped silicon rod are both 0.2 μm. In the U-shaped silicon rod, the length of the first rectangular silicon rod is 17 μm and the width is 2 μm, and the length of the second rectangular silicon rod is 2 μm and the width is 1 μm. The dielectric constant of the U-shaped silicon rod is 11.9. The thickness of the second BCB dielectric layer 2 and the metal open square ring are both 0.3 μm. The length of the metal open square ring is 17 μm and the width is 1 μm, and the length of the opening on a single side is 4 μm. The metal open square ring is made of gold, and its conductivity is 4.561×10 7 The thickness of the third BCB dielectric layer 3 is 9 μm. The dielectric constants of the BCB dielectric materials in the first BCB dielectric layer 1, the second BCB dielectric layer 2, and the third BCB dielectric layer 3 are all 2.67. The thickness of the silicon substrate 4 is 0.6 μm.

[0039] In this device, the conductivity of the photosensitive silicon can be controlled by inputting pump light from the upper surface of the first BCB dielectric layer 1, thereby achieving functional control of the device. Si =5×10 5 S / m), the device can realize circular dichroism and linear dichroism functions. When circularly polarized waves are incident, a circular dichroism effect with a bandwidth of about 0.74THz can be achieved in the frequency band of 3.66~4.40THz; when linearly polarized waves are incident, the linear dichroism values ​​of the device at frequencies of 6.76THz, 7.45THz and 8.39THz are 0.71, -0.57 and 0.33 respectively. By changing the conductivity of photosensitive silicon, the amplitudes of circular dichroism and linear dichroism can be dynamically tuned, and the amplitude modulation depths reach 98% and 96.1% respectively. Figure 4 As shown in the figure, the co-polarization reflection curve of the left circularly polarized wave (r -- ) and the co-polarization reflection curve of right-hand circularly polarized wave (r ++ ) is consistent with the cross-polarization reflection curve of right-hand circularly polarized wave (r -+ ) and the cross-polarization reflection curve of left-hand circularly polarized wave (r +- ) have a large difference. When the frequency is 4.03THz, r -+ Greater than 0.9, r +- is close to 0, indicating that at this frequency, the designed structure reflects most of the right-hand circularly polarized waves, but does not reflect the left-hand circularly polarized waves. Figure 5As shown in the figure, at a frequency of 4.03THz, the reflectivity of the designed structure for left-hand circularly polarized waves is 0, and the reflectivity for incident right-hand circularly polarized waves reaches 86.7%. At this time, the circular dichroism value is close to 1, and in the frequency band of 3.66~4.40THz, the circular dichroism is greater than 0.9, and the bandwidth is about 0.74THz. Figure 6 As shown in the figure, when the incident angle of the circularly polarized wave is less than 50°, the circular dichroism of the designed structure is greater than 0.85 in the range of 3.84 to 4.33 THz, and the bandwidth is 0.49 THz, indicating that the structure has good wide incident angle characteristics. Figure 7 As shown in Figure 2, in the frequency range of 3.61 to 4.55 THz, increasing the polarization angle of the incident terahertz wave from 0° to 90° has no effect on the circular dichroism value, and the amplitude is always greater than 0.85. Figure 8 As shown, when the conductivity of photosensitive silicon increases from 5×10 5 When S / m drops to 1S / m, the circular dichroism value of the designed structure drops from 0.98 to 0 at a frequency of 4.03THz, and the amplitude modulation depth is 98%. Figure 9 As shown in the figure, in the frequency band of 4.50~9.00THz, the cross reflection curve r corresponding to the linear polarization wave yx =r xy , and the co-polarization reflection curve r xx and r yy There are obvious differences. Figure 10 As shown in the figure, at a frequency of 6.76THz, the absorption rates of x-polarization and y-polarization are significantly different. The absorption rate is 0.87 under x-polarization wave incidence and 0.16 under y-polarization wave incidence. At this time, the linear dichroism amplitude is 0.71, indicating that the structure strongly absorbs x-polarization waves and reflects y-polarization waves. At 7.45THz and 8.39THz, the corresponding linear dichroisms are -0.57 and 0.33, respectively. Figure 11 As shown, when the conductivity of photosensitive silicon σ Si =2×10 5 When the incident angle changes from 0° to 50°, the linear dichroism amplitude gradually decreases and produces a slight blue shift. Figure 12 As shown, the conductivity of photosensitive silicon increases from 2×10 5 When S / m is reduced to 1S / m, the linear dichroism value of the structure decreases from 0.77 to 0.03, and the amplitude modulation depth is 96.1%.

[0040] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A terahertz wave circular dichroism and linear dichroism switchable controller, characterized in that: The invention relates to a composite structure composed of four layers with the same square outer contour, which are, from top to bottom, a first BCB dielectric layer (1), a second BCB dielectric layer (2), a third BCB dielectric layer (3) and a silicon substrate (4); the first BCB dielectric layer (1) is embedded with a U-shaped silicon rod made of photosensitive silicon, the U-shaped silicon rod being composed of a first rectangular silicon rod and two second rectangular silicon rods arranged on the long sides of both ends of the first rectangular silicon rod, and the first rectangular silicon rod is arranged along the diagonal line of the first BCB dielectric layer (1); the second BCB dielectric layer (2) is embedded with a metal open square ring, the metal open square ring having two openings symmetrically opened on two opposite sides; the material of the silicon substrate (4) is photosensitive silicon.

2. The terahertz wave circular dichroism and linear dichroism switchable controller according to claim 1, characterized in that: The composite structure is periodically arranged on a plane, with a period of 25 μm to 35 μm in the x-direction and a period of 25 μm to 35 μm in the y-direction.

3. The terahertz wave circular dichroism and linear dichroism switchable controller according to claim 1, characterized in that: The thickness of the first BCB dielectric layer (1) and the U-shaped silicon rod are both 0.1 μm to 1.0 μm; in the U-shaped silicon rod, the length of the first rectangular silicon rod is 15 μm to 25 μm and the width is 1 μm to 3 μm, and the length of the second rectangular silicon rod is 1 μm to 2 μm and the width is 1 μm to 2 μm.

4. The terahertz wave circular dichroism and linear dichroism switchable controller according to claim 3, characterized in that: The dielectric constant of the U-shaped silicon rod is 11.

9.

5. The terahertz wave circular dichroism and linear dichroism switchable controller according to claim 1, characterized in that: The thickness of the second BCB dielectric layer (2) and the metal open square ring are both 0.1 μm to 1.0 μm, wherein the length of the metal open square ring is 15 μm to 25 μm, the width is 1 μm to 5 μm, and the length of the opening on a single side is 1 μm to 5 μm.

6. The terahertz wave circular dichroism and linear dichroism switchable controller according to claim 5, characterized in that: The metal open square ring is made of gold, and its electrical conductivity is 4.561×10 7 S / m.

7. The terahertz wave circular dichroism and linear dichroism switchable controller according to claim 1, characterized in that: The thickness of the third BCB dielectric layer (3) is 5 μm to 15 μm.

8. The terahertz wave circular dichroism and linear dichroism switchable controller according to claim 1, characterized in that: The dielectric constants of the BCB dielectric materials in the first BCB dielectric layer (1), the second BCB dielectric layer (2) and the third BCB dielectric layer (3) are all 2.

67.

9. The terahertz wave circular dichroism and linear dichroism switchable controller according to claim 1, characterized in that: The silicon substrate (4) has a thickness of 0.5 μm to 1.5 μm.

10. The terahertz wave circular dichroism and linear dichroism switchable controller according to claim 1, characterized in that: The controller controls the photosensitive silicon in the device to be in a metallic state by pumping light, thereby realizing circular dichroism and linear dichroism in different frequency bands; and realizes dynamic tuning of the circular dichroism and linear dichroism amplitudes by changing the conductivity of the photosensitive silicon.

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