Topological insulator refractive index gradient sensing chip

Abstract

The invention discloses a topological insulator refractive index gradient sensing chip. Comprising a periodic topology common-vigness structure and a topology non-common-vigness structure which are connected through a bridge-shaped interface to form a first type of topology boundary state; a regular triangular cavity formed by topological non-trivialness units is arranged in the topological non-trivialness structure, the bottom edge of the cavity is parallel to a bridge-shaped interface, the upper vertex of the cavity and the bridge-shaped interface are spaced by a photonic crystal period, and the boundary of the cavity and the peripheral periodic topological non-trivialness units form a Zigzag boundary to form a second type of topological boundary state; the Zigzag boundary has a high group refractive index, and can significantly enhance the interaction between light and substances, thereby improving the response of the device to the medium change. Based on the natural advantages of the topological insulator, the structure is simple, the process complexity is low, the size is small, batch production is facilitated, and a wide-range refractive index test interval is realized by designing and adjusting topological common and non-common structural parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of optical sensors, and in particular to a topological insulator refractive index gradient sensing chip. Background Art

[0002] Refractive index has a wide range of applications in the field of optics, such as fiber optic communications, optical lens design, optical sensors, etc. By measuring the refractive index, the design of the optical system can be optimized and the performance of optical devices can be improved. In addition, the refractive index also has important application value in fields such as material science, biomedicine, and environmental monitoring. Existing refractive index sensors usually rely on effects such as interference, diffraction, or absorption of light. These methods have problems such as low sensitivity, complex structure, or high cost. Therefore, the development of a refractive index sensor with a simple structure, high sensitivity, and low cost has important practical application value. Summary of the invention

[0003] In view of the deficiencies in the prior art, the object of the present invention is to provide a topological insulator refractive index gradient sensing chip, which utilizes two types of topologically protected boundary states in a topological photonic crystal structure to achieve precise control of light field transmission and high-sensitivity refractive index detection.

[0004] The object of the present invention is achieved through the following technical solution: A topological insulator refractive index gradient sensing chip, comprising:

[0005] SiO2 substrate, periodic topological trivial photonic crystal unit structure and periodic topological non-trivial photonic crystal unit structure;

[0006] The photonic crystal unit structures are all composed of high refractive index materials, and the photonic crystal unit structures are provided with hexagonal air holes. When the scaling coefficients of the hexagonal air holes in the photonic crystal unit structures are C>1 and C<1, the topological Chern numbers of the two photonic crystals are opposite to each other (±1), and the scaling coefficients are scanned and optimized to ensure a larger photonic crystal band gap.

[0007] The periodic topological trivial photonic crystal unit structure and the topological non-trivial photonic crystal unit structure are connected via a bridge-shaped interface to form a first type of topologically protected boundary state;

[0008] An equilateral triangular cavity is provided in the periodic topological non-trivial photonic crystal unit structure, the equilateral triangular cavity is composed of a topologically trivial photonic crystal, and a SiO2 open window is provided above the equilateral triangular cavity;

[0009] The periodic topological trivial photonic crystal unit structure and the periodic topological non-trivial photonic crystal unit structure together constitute a photonic crystal slab, the SiO2 substrate is located below the entire photonic crystal slab, the SiO2 substrate in the non-triangular cavity region and the upper SiO2 open window constitute a closed vacuum space to ensure that the refractive index is constant at 1; the SiO2 substrate in the regular triangle cavity region and the photonic crystal slab constitute an open container at the top for carrying the filled pure refractive index medium;

[0010] When a wide spectrum of light is input into the incident end of the photonic crystal slab, a transmission spectrum with a loss mutation can be measured at the output end due to the difference between the conduction band frequency and the triangular cavity operating frequency. When the refractive index of the medium filling the open holes of the photonic crystal in the regular triangular cavity region is changed, the transmission spectrum will change significantly, achieving a one-to-one match with the refractive index.

[0011] The photonic crystal plate is fine-tuned through the photonic crystal unit structure to obtain different band gap ranges, and is connected in parallel through a wavelength division multiplexer to form a sensor array for expanding the operating frequency range of the sensor.

[0012] Furthermore, the high refractive index material is a silicon substrate.

[0013] Furthermore, the regular triangle cavity and the bridge-shaped interface are separated by a photonic crystal unit period.

[0014] Furthermore, the topologically trivial photonic crystal in the regular triangle cavity region and the external topologically non-trivial photonic crystal form a Zigzag boundary, and the Zigzag boundary has a high group refractive index, which manifests as a slow light effect.

[0015] Furthermore, it comprises a sensor array, which is composed of a plurality of sensor plates with fixed lattice constants and internal hole sizes of photonic crystal units finely adjusted according to a target frequency range.

[0016] Furthermore, the sensor array is connected to the incident light via a wavelength division multiplexer.

[0017] The beneficial effects of the present invention are:

[0018] 1. The transmission principle is based on topological insulator waveguides, which have topological protection characteristics. The light transmitted at the boundary is not affected by backscattering, and the changes in the transmission spectrum can be completely mapped to the changes in the refractive index of the filled medium;

[0019] 2. The Zigzag boundary at the equilateral triangle cavity has a high group refractive index and a slow light effect, which can significantly enhance the interaction between light and matter and improve the sensitivity of the sensor itself;

[0020] 3. Provide sensor integration in array form, customize the detection spectrum range through the geometric size difference of each sub-item in the array, and have flexibility in processing and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0022] Figure 1 A schematic diagram of a topological insulator refractive index sensor provided by one embodiment of the present invention;

[0023] Figure 2 A schematic diagram of the dimensions of a photonic crystal unit provided in one embodiment of the present invention;

[0024] Figure 3 A schematic diagram of the 3D structural layout of a regular triangle cavity portion provided in one embodiment of the present invention;

[0025] Figure 4 is the energy band diagram of the photonic crystal, where (a) is the energy band diagram of the topological non-trivial photonic crystal when the hole is not filled (i.e., air), and (b) is the energy band diagram of the topological trivial photonic crystal when the hole is filled with a medium with a refractive index of 1.1;

[0026] Figure 5 The projected band diagrams of the supercells of the two boundaries, where (a) is the projected band diagram of the bridge-type boundary supercell, and (b) is the projected band diagram of the Zigzag boundary supercell;

[0027] Figure 6 A graph showing the refractive index of a single refractive index sensor provided by an embodiment of the present invention under different conditions of the refractive index of the medium in the regular triangle cavity hole;

[0028] Figure 7 A schematic diagram of the transmission field distribution of the sensor plate provided in an embodiment of the present invention;

[0029] Figure 8 A topological insulator refractive index gradient sensing chip test flow chart provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. It should be noted that the features in the following embodiments and implementation methods can be combined with each other without conflict.

[0031] like Figure 1-Figure 3 As shown, this embodiment provides a topological insulator refractive index gradient sensing chip, and the sensor structure includes: an upper periodic topological trivial photonic crystal unit structure and a lower periodic topological non-trivial photonic crystal unit structure, the two are connected by a bridge-shaped interface to form a first type of topological protection boundary state; an equilateral triangular cavity composed of topological trivial photonic crystals is arranged in the periodic topological non-trivial photonic crystal unit structure, and the upper vertex of the equilateral triangular cavity is separated from the bridge-shaped interface by the distance of a photonic crystal unit, and a Zigzag boundary is formed between the topological trivial photonic crystal inside the equilateral triangular cavity and the topological non-trivial photonic crystal on the periphery, forming a second type of topological protection boundary state, and the Zigzag boundary has a high group refractive index, which enhances the interaction between light and matter.

[0032] Wherein, the sensor comprises the following structure:

[0033] Sensor array: A group of sensor plates with the same main structure, lattice constant and slightly different internal structures of the photonic crystal unit form an array to cover a wider refractive index test range.

[0034] Wavelength division multiplexer: The incident light is connected to the sensor array by a wavelength division multiplexer, which demultiplexes the broadband light in the incident optical fiber into four optical fibers corresponding to different frequency ranges, so that the photonic crystal slabs in the sensor array are in working state at the same time and always within the frequency range.

[0035] like Figure 2 As shown, the photonic crystal slab used in the topological insulator slab for realizing high-sensitivity response of refractive index is composed of two hexagons of different sizes, wherein L is the length of the long side of the left hexagon, R is the length of the small side, S is the length of the long side of the right hexagon obtained by scaling the left hexagon with a coefficient of C, and the outside is a high-refractive index contrast material such as Si / Si3N4. The size parameters adopted can obtain a larger photonic crystal band gap and thus a wider transmission spectrum.

[0036] like Figure 3As shown, above the equilateral triangular cavity is a SiO2 window with the same size as the equilateral triangular cavity and its Zigzag boundary, which can be used to fill the solid, liquid and gas three-state media into the holes of the photonic crystal in the cavity, and strictly limit the filling area to ensure the uniqueness of the transmission spectrum, thereby ensuring the one-to-one correspondence between the transmission spectrum and the refractive index; below the photonic crystal plate is a complete SiO2 to carry the medium injected from the upper window in the equilateral triangular cavity area, and ensure that the photonic crystal hole is in an air / vacuum environment in the non-triangular cavity area.

[0037] like Figure 4 As shown in Figs. 4a and 4b, the change of the refractive index of the filled medium can cause the energy band of the photonic crystal unit to change, which is reflected in the fact that as the refractive index of the medium filled in the equilateral triangle cavity increases, the energy band generally moves toward the low frequency direction.

[0038] like Figure 5 As shown in a, the resulting bridge-shaped boundary projected band diagram has a single topologically protected conduction band, which can support the transmission of topologically protected boundary states; while the resulting Zigzag boundary has two topologically protected conduction bands, as shown in Figure 5 As shown in b, according to the group refractive index formula:

[0039]

[0040] Where c is the speed of light in vacuum, k is the wave vector, ω is the normalized frequency, and n g is the group refractive index. It can be calculated that the mid-frequency region (i.e., the gray shaded area in the figure) has a high group refractive index, which supports topologically protected slow light transmission, greatly enhances the interaction between light and matter, and improves the sensitivity of the proposed sensor.

[0041] like Figure 6 As shown, when the refractive index of the equilateral triangle cavity hole part of the topological insulator refractive index sensor is changed, the transmission spectrum of the device changes significantly, and the transmission spectrum generally has one or two sudden peaks, which is conducive to monitoring the transmission spectrum and obtaining a one-to-one correspondence with the refractive index of the medium.

[0042] like Figure 7The figure shows the transmission field distribution of the sensor plate at 19.9 THz when the refractive index of the medium in the equilateral triangular cavity is 1. When the light wave entering from the incident end (left) approaches the equilateral triangular cavity, due to the near-field coupling between the bridge-shaped boundary and the Zigzag boundary of the equilateral triangular cavity, part of the light energy will enter the Zigzag boundary and undergo transmission related to the refractive index of the medium in the cavity. After the light wave resonates in the equilateral triangular cavity, it will return to the waveguide through the far-field coupling effect. This process is similar to input coupling, but in the opposite direction. The light wave coupled back to the bridge-shaped boundary continues to propagate along the boundary and is finally output from the output end of the waveguide. The light wave at the output end contains the original input light wave and the light wave generated after resonance and coupling in the equilateral triangular cavity.

[0043] like Figure 8 As shown, the input is λ in(1,2,3,4) The wide spectrum light is demultiplexed by the wavelength division multiplexer and divided into four different frequency ranges of λ1, λ2, λ3, and λ4. It is transmitted through the optical fiber and coupled into the corresponding photonic crystal plate. The light of different frequency ranges passes through the photonic crystal plates with different unit structures. A transmission spectrum with significant mutation can be measured at the output end of a certain photonic crystal plate. out By analyzing the sudden peaks, the refractive index of the medium filling the triangular cavity area in the photonic crystal slab can be obtained. When the medium environment changes, the transmission spectrum response may be generated by another photonic crystal slab at a different operating frequency, which significantly improves the working range and sensitivity of the sensor array.

[0044] The present invention realizes high-sensitivity detection of the refractive index of an external medium by measuring the spectrum shift caused by the change of the refractive index.

[0045] Those skilled in the art will readily appreciate other embodiments of the present application after considering the description and practicing the contents disclosed herein. The present application is intended to cover any variations, uses or adaptations of the present application, which follow the general principles of the present application and include common knowledge or customary technical means in the art that are not disclosed in the present application. The description and examples are intended to be exemplary only.

[0046] It should be understood that the present application is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof.

Claims

1. A topological insulator refractive index gradient sensing chip, characterized in that: include: SiO2 substrate, periodic topological trivial photonic crystal unit structure and periodic topological non-trivial photonic crystal unit structure; The photonic crystal unit structures are all composed of high refractive index materials, and the photonic crystal unit structures are provided with hexagonal air holes. When the scaling coefficients of the hexagonal air holes in the photonic crystal unit structures are C>1 and C<1, the topological Chern numbers of the two photonic crystals are opposite to each other, and the scaling coefficients are scanned and optimized to ensure a larger photonic crystal band gap; The periodic topological trivial photonic crystal unit structure and the topological non-trivial photonic crystal unit structure are connected via a bridge-shaped interface to form a first type of topologically protected boundary state; An equilateral triangular cavity is provided in the periodic topological non-trivial photonic crystal unit structure, the equilateral triangular cavity is composed of a topologically trivial photonic crystal, and a SiO2 open window is provided above the equilateral triangular cavity; The periodic topological trivial photonic crystal unit structure and the periodic topological non-trivial photonic crystal unit structure together constitute a photonic crystal slab, the SiO2 substrate is located below the entire photonic crystal slab, the SiO2 substrate in the non-triangular cavity region and the upper SiO2 open window constitute a closed vacuum space to ensure that the refractive index is constant at 1; the SiO2 substrate in the regular triangle cavity region and the photonic crystal slab constitute an open container at the top for carrying the filled pure refractive index medium; When a wide spectrum of light is input into the incident end of the photonic crystal slab, a transmission spectrum with a loss mutation can be measured at the output end due to the difference between the conduction band frequency and the triangular cavity operating frequency. When the refractive index of the medium filling the open holes of the photonic crystal in the regular triangular cavity region is changed, the transmission spectrum will change significantly. The photonic crystal plate is fine-tuned by the photonic crystal unit structure to obtain different band gap ranges, and is connected in parallel through a wavelength division multiplexer to form a sensor array for expanding the operating frequency range of the sensor.

2. A topological insulator refractive index gradient sensing chip as claimed in claim 1, characterized in that: The high refractive index material is a silicon substrate.

3. A topological insulator refractive index gradient sensing chip as claimed in claim 1, characterized in that: The regular triangle cavity and the bridge-shaped interface are spaced apart by a photonic crystal unit period.

4. A topological insulator refractive index gradient sensing chip as claimed in claim 1, characterized in that: The topologically trivial photonic crystal in the regular triangle cavity region and the external topologically non-trivial photonic crystal form a Zigzag boundary, and the Zigzag boundary has a high group refractive index.

5. A topological insulator refractive index gradient sensing chip as claimed in claim 1, characterized in that: The invention comprises a sensor array, which is composed of a plurality of sensor plates with fixed lattice constants and internal hole sizes of photonic crystal units finely adjusted according to a target frequency range.

6. A topological insulator refractive index gradient sensing chip as claimed in claim 5, characterized in that: The sensor array is connected to the incident light through a wavelength division multiplexer.

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