High-sensitivity chiral sensing flat photonic crystal

Abstract

The invention discloses a chiral sensing flat photonic crystal with high sensitivity. Comprising a dielectric plate and a four-hole structure which is arranged on the dielectric plate in a two-dimensional periodic manner, the period of the two-dimensional periodic arrangement is lambda, the centers of four holes in the four-hole structure form a square with the side length of g, two groups of parallel sides of the square are respectively parallel to the periodic arrangement direction, and each hole in the four-hole structure is a cylindrical through hole with the diameter of d. The chiral sensing panel photonic crystal is of a C4v structure, TE and TM guided modes can be coupled to generate a super-chiral field with high optical chirality density by selecting proper geometric structure parameters, and high-sensitivity chiral sensing is achieved. The invention has the advantages of simple structure, easiness in processing, obvious improvement of the optical response of chiral molecules and the like.

Description

Technical Field

[0001] This invention relates to a highly sensitive chiral sensing flat-panel photonic crystal, belonging to the field of photonic crystal technology. Background Technology

[0002] The core objective of chiral planar photonic crystals is to enhance the chiral interaction between light and matter through structural design, thereby amplifying the chiral signal and optimizing chiral sensing. For intrinsically chiral planar photonic crystals that rely on their own chirality, their inherent chiral characteristics introduce significant background signals, leading to a decrease in the detection signal-to-noise ratio. However, a high optical chirality density hyperchiral field achieved through strong local electric and magnetic field coupling can not only avoid background interference caused by reliance on inherent chirality but also effectively improve the sensitivity of chiral sensing.

[0003] While plasmonic nanostructures can also achieve high optical chirality density hyperchiral fields, their material losses and weak electromagnetic field confinement significantly limit further improvements in chiral sensing sensitivity. This has led to a shift in focus towards high-refractive-index dielectric nanostructures, which possess low material losses and high Q-resonance characteristics. These nanostructures can achieve high optical chirality density hyperchiral fields through strong electric and magnetic field coupling, thus laying the foundation for high-sensitivity chiral sensing.

[0004] Although there have been reports of high optical chirality density hyperchirality fields achieved by some dielectric nanostructure metamaterials and planar photonic crystals, the main problems are that the proposed structures either cannot be fabricated or are too complex to be fabricated and therefore too expensive, or the optical chirality density hyperchirality fields cannot be effectively controlled. Summary of the Invention

[0005] This invention proposes a highly sensitive chiral sensing planar photonic crystal.

[0006] To overcome the shortcomings of the prior art, the technical solution adopted by the present invention is as follows:

[0007] A highly sensitive chiral sensing planar photonic crystal includes a dielectric substrate and a four-hole structure arranged in a two-dimensional periodic pattern on the substrate. The period of the two-dimensional periodic arrangement is Λ, and the center of each of the four holes in the four-hole structure forms a side length of Λ. g A square, wherein the two sets of parallel sides of the square are parallel to the periodic arrangement direction, and each hole in the four-hole structure has a diameter of [missing information]. d A cylindrical through hole.

[0008] The thickness of the dielectric plate t = 0.4Λ, the diameter of the through hole satisfies 0.1Λ ≤ d ≤ 0.3Λ, 0.2 ≤ g ≤0.5Λ.

[0009] During operation, circularly polarized light is incident, with the direction of the height of the dielectric substrate defined as the Z-axis. The upper or lower surface of the dielectric substrate is taken as the XOY plane, the direction of the line connecting the centers of two through-holes on the same horizontal line in the XOY plane is defined as the X-direction, and the direction perpendicular to the line connecting the centers of the two through-holes is defined as the Y-direction. Compared with the prior art, the present invention has the following advantages:

[0010] (1) The flat photonic crystal is composed of a single material, has a simple structure, and is easy to prepare and apply.

[0011] (2) The flat-panel photonic crystal has higher sensitivity than the current chiral sensing flat-panel photonic crystal with metal material.

[0012] (3) The flat-panel photonic crystal can be easily selected. g This enables the effective control of a hyperchiral field with high optical chirality density. Attached Figure Description

[0013] Figure 1 A schematic diagram of a sensing planar photonic crystal structure is provided for a specific embodiment of the present invention;

[0014] Figure 2 This is a top view of the unit structure of the present invention;

[0015] Figure 3 for Figure 1 The structure shown is in d = Dispersion curves of TE and TM guided modes at 70 micrometers;

[0016] Figure 4 for Figure 1 The dispersion curves of the TE and TM guided modes of the structure shown are displayed at d = 73.3 μm.

[0017] Figure 5 for Figure 1 The structure shown is in d The effective enhancement factor EF of the optical chirality density of the hyperchiral field at 73.3 micrometers c ;

[0018] Figure 6 for Figure 1 The circular dichroism CD of the structure shown is observed when the test object is attached to the inner wall of the through hole.

[0019] Figure 7 for Figure 1 The structure shown is in different g and d EF in the super-chiral field c . Specific implementation methods

[0020] To better understand the present invention, further detailed description is provided below in conjunction with the accompanying drawings.

[0021] Figure 1 and Figure 2 This invention illustrates a high-sensitivity chiral sensing planar photonic crystal, comprising a dielectric substrate and a four-hole structure arranged in a two-dimensional periodic pattern on the substrate. The period of each two-dimensional periodic arrangement is Λ, and the center of each of the four holes in the four-hole structure forms a side length of... g A square, wherein the two sets of parallel sides of the square are parallel to the periodic arrangement direction, and each hole in the four-hole structure has a diameter of [missing information]. d Cylindrical through-holes. The Z-axis is defined as the direction along the height of the dielectric substrate, the XOY plane is defined as the upper or lower surface of the dielectric substrate, the X-axis is defined as the line connecting the centers of two through-holes on the same horizontal line in the XOY plane, and the Y-axis is defined as the line perpendicular to the line connecting the centers of the two through-holes. t The thickness of the dielectric substrate.

[0022] In the implementation of this invention, while keeping other structural parameters fixed, appropriate parameters are selected. d By coupling the guided modes of TE and TM to achieve a superchiral field, high-sensitivity detection of enantiomers can be realized.

[0023] The technical effects of the present invention will be illustrated below with specific embodiments.

[0024] In the terahertz band, the period Λ in both the X and Y directions is selected to be 300 micrometers. The dielectric substrate is made of high-resistivity silicon with a dielectric constant of 11.67 and a thickness of [missing information]. t It is 120 micrometers. g The aperture diameter is 120.5 micrometers. d .

[0025] When the geometric parameters of the structure of the present invention are under the above parameters, when d At 70 micrometers, two frequency-degenerate transverse conductance modes (TE-A and TE-B) and two frequency-degenerate transverse magnetic conductance modes (TM-A and TM-B) were found within the operating frequency range using electromagnetic wave calculation software. Figure 3 As shown. In k = 0, the frequencies of TE-A and TE-B are 0.549 THz, and the frequencies of TM-A and TM-B are 0.561 THz. To obtain a high optical chirality density superchiral field, strong near-field coupling between the TE guided mode and the TM guided mode must be achieved. This can be achieved by adjusting... d So that the four guide modules are in k = 0 is achieved by having the same frequency.

[0026] like Figure 4 As shown, whend At a wavelength of 73.3 micrometers, the TE and TM guided modes coincide at 0.572 THz, representing the point where the maximum optical chirality density of the hyperchiral field can be achieved. To illustrate and evaluate the potential of the hyperchiral field generated by the coupling of the TE and TM guided modes in enhancing the interaction between light and chiral molecules, we simulated the effective enhancement factor EF of the optical chirality density of the hyperchiral field under normal incidence of a left-handed circularly polarized terahertz wave on a planar photonic crystal. c ,like Figure 5 As shown, the maximum EF c It reached 704.

[0027] Currently, chiral sensing measurements based on superchiral fields generally use circular dichroism (CD) as the detection index, and its value is related to the EF of the superchiral field. c Closely related. For example... Figure 6 As shown, in practical CD detection applications, the chiral biomolecular layer to be tested is attached to the inner wall of the through-hole of a planar photonic crystal. Assuming the Pasteur parameter κ = 0 + 0.0001j used for the chiral biomolecules and a thickness of 10 micrometers, we calculated the transmittance of the planar photonic crystal sensor under normal incidence of left-handed and right-handed circularly polarized terahertz waves, respectively, and obtained a maximum CD value of 0.013. However, without a planar photonic crystal sensor, the calculated CD value for this 10-micrometer-thick biomolecular layer is only 1.7 × 10⁻⁶. -5 That is, the sensitivity of our designed chiral sensor is amplified by 765 times, compared to the maximum EF. c The values ​​are close. When the chiral medium adheres to the structural surface, the calculated magnification is 118 times. When the chiral medium adheres to both the structural surface and the inner wall of the through-hole, the magnification is 270 times.

[0028] In addition, we also simulated and calculated different g and d The superchiral field EF generated by the coupling of TE and TM guided modes c The impact. For example... Figure 7 As shown, when g When increased to 123 micrometers, the calculations yielded... d At 70.7 micrometers, planar photonic crystals exhibit the strongest superchirality field, with a maximum EF. c It was 1859. When g = 126 micrometers, d At 68.1 micrometers, the maximum EF of the hyperchiral field in a planar photonic crystal is... c Increased to 3671. EF c The increase in g can be attributed to the Q values ​​of the TE and TM guided modes increasing with... g As the value increases, the superchiral field generated by its coupling also continuously strengthens.

Claims

1. A high-sensitivity chiral sensing slab photonic crystal, characterized in that: The application relates to a medium plate comprising a medium plate and four-hole structures arranged in a two-dimensional periodic array on the medium plate, the period of the two-dimensional periodic array being Lambda, the four-hole structures being square-shaped with a side length of Lambda / 2, the square-shaped two-hole structures being arranged with two parallel sides of the square-shaped two-hole structures being parallel to the direction of the periodic array, and each of the four-hole structures being a cylindrical through-hole with a diameter of Lambda / 2. g d ​​ 2. The high-sensitivity chiral sensing flat photonic crystal according to claim 1, characterized in that: The range of the chiral sensing flat photonic crystal Λ is 0.4-0.8 times the working wavelength.

3. The high-sensitivity chiral sensing flat photonic crystal according to claim 2, characterized in that: The thickness of the medium plate t = 0.4Λ, the diameter of the through hole and the side length of the square satisfy 0.1Λ ≤ d ≤ 0.3Λ, 0.2Λ≤ g ≤ 0.5Λ respectively.

4. The high-sensitivity chiral sensing flat photonic crystal according to any one of claims 1-3, characterized in that: In operation, circularly polarized light is used for incidence, wherein the direction in which the medium plate is high is the Z-axis direction, the upper surface or the lower surface of the medium plate is the XOY plane, the direction in which the line connecting the centers of the two through-hole circles on the same horizontal line of the XOY plane is the X direction, and the direction perpendicular to the line connecting the centers of the two through-hole circles is the Y direction.

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