A topological insulator refractive index gradient sensing chip

Abstract

The present invention discloses a topological insulator refractive index gradient sensing chip. It includes a periodic topologically trivial structure and a topologically nontrivial structure, which are connected by a bridge-shaped interface to form a first type of topological boundary state; in the topologically nontrivial structure, an equilateral triangle cavity composed of topologically trivial units is provided. The bottom edge of the cavity is parallel to the bridge-shaped interface and there is a gap of one photonic crystal period between the upper vertex and the bridge-shaped interface. The boundary of the cavity and the surrounding periodic topologically nontrivial units form a Zigzag boundary, forming a second type of topological boundary state. At the Zigzag boundary, there is a high group refractive index, which can significantly enhance the interaction between light and matter, thereby improving the response of the device to changes in the medium. Based on the natural advantages of topological insulators, the present invention has a simple structure, low process complexity, small size, and is convenient for mass production. By designing and adjusting the parameters of the topologically trivial and nontrivial structures, a wide range of refractive index test intervals can be achieved.

Description

Technical Field

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

[0002] The refractive index has a wide range of applications in the field of optics, such as optical fiber communication, optical lens design, optical sensors, etc.; by measuring the refractive index, the design of optical systems can be optimized and the performance of optical devices can be improved. In addition, the refractive index also has important application values in the fields of materials science, biomedicine, and environmental monitoring. Existing refractive index sensors usually rely on effects such as light interference, diffraction, or absorption. These methods have problems such as low sensitivity, complex structure, or high cost. Therefore, it is of great practical application value to develop a refractive index sensor with a simple structure, high sensitivity, and low cost. Summary of the Invention

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

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

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

[0006] The photonic crystal unit structures are all composed of high-refractive-index materials, and hexagonal air holes are opened on the photonic crystal unit structures. When the scaling factor C of the hexagonal air holes in the photonic crystal unit structure is C>1 and C<1, the topological Chern numbers of the two photonic crystals are opposite to each other (±1), and at the same time, the scaling factor is scanned and optimized to ensure a relatively large photonic crystal bandgap;

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

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

[0009] The periodic topologically trivial photonic crystal unit structure and the periodic topologically 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 and the SiO2 open window above form a sealed vacuum space in the non-triangular cavity region, ensuring that the refractive index is constantly 1. The SiO2 substrate and the photonic crystal slab form an upward-open container in the equilateral triangular cavity region for carrying the filled pure refractive index medium.

[0010] When broadband light is input at the incident end of the photonic crystal slab, due to the difference between the conduction band frequency and the operating frequency of the triangular cavity, a transmission spectrum with a sudden change in loss can be measured at the output end. When the refractive index of the medium filled in the open holes of the photonic crystal in the equilateral 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 slab is finely tuned through the photonic crystal unit structure to obtain different bandgap ranges, and a sensor array is formed in parallel through a wavelength division multiplexer to expand the operating frequency range of the sensor.

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

[0013] Further, there is a photonic crystal unit period between the equilateral triangular cavity and the bridge-shaped interface.

[0014] Further, the topologically trivial photonic crystal in the equilateral triangular 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 is manifested as the slow light effect.

[0015] Further, it includes a sensor array, and the sensor array is composed of a plurality of sensor slabs with a fixed lattice constant and the internal hole size of the photonic crystal unit being finely tuned according to the target frequency range.

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

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

[0018] 1. Based on the topological insulator waveguide in terms of the transmission principle, it has topological protection characteristics, and the light transmitted at the boundary is not affected by backscattering, and can completely map the change of the transmission spectrum line to the change of the refractive index of the filled medium.

[0019] 2. The Zigzag boundary at the equilateral triangular cavity has a high group refractive index and the 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 an 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 following will briefly introduce the drawings required for description in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 Schematic diagram of a topological insulator refractive index sensor provided in an embodiment of the present invention;

[0023] Figure 2 Schematic diagram of the size of a photonic crystal unit provided in an embodiment of the present invention;

[0024] Figure 3 Schematic diagram of the 3D structure layout of the equilateral triangle cavity part provided in an embodiment of the present invention;

[0025] Figure 4 Band diagram of a photonic crystal, where (a) is the band diagram of a topologically non-trivial photonic crystal when the hole has no filler (i.e., air), and (b) is the band diagram of a topologically trivial photonic crystal when the hole is filled with a medium with a refractive index of 1.1;

[0026] Figure 5 Projection band diagrams of two types of boundaries, where (a) is the projection band diagram of a supercell with a bridge-type boundary, and (b) is the projection band diagram of a supercell with a Zigzag boundary;

[0027] Figure 6 Curve diagram of a single refractive index sensor provided in an embodiment of the present invention under different refractive indices of the medium in the equilateral triangle cavity hole;

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

[0029] Figure 8 Test flow chart of a topological insulator refractive index gradient sensing chip provided in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. It should be noted that, without conflict, the features in the following embodiments and implementation manners can be combined with each other.

[0031] As Figures 1-3 shown, this embodiment provides a topological insulator refractive index gradient sensing chip. The sensor structure includes: a periodic topologically trivial photonic crystal unit structure above and a periodic topologically non-trivial photonic crystal unit structure below. The two are connected by a bridge-shaped interface to form a first type of topologically protected boundary state. A regular triangular cavity composed of topologically trivial photonic crystals is arranged in the periodic topologically non-trivial photonic crystal unit structure. The distance between the upper vertex of the regular triangular cavity and the bridge-shaped interface is one photonic crystal unit. A Zigzag boundary is formed between the topologically trivial photonic crystals inside the regular triangular cavity and the surrounding topologically non-trivial photonic crystals, forming a second type of topologically protected boundary state. The Zigzag boundary has a high group refractive index, enhancing the interaction between light and matter.

[0032] Among them, the sensor includes the following structures:

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

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

[0035] As Figure 2 shown, the photonic crystal plate used for the topological insulator plate with high-sensitivity refractive index response is composed of two hexagons with different sizes. Among them, L is the long side length of the left hexagon, R is its short side length, S is the long side length of the right hexagon obtained by scaling the left hexagon with a coefficient of C, the inside is a hole while the outside is a high refractive index contrast material such as Si / Si3N4. The adopted size parameters can obtain a large photonic crystal bandgap and thus a wide transmission spectrum.

[0036] As Figure 3As shown, above the equilateral triangle cavity is a SiO2 window with the same size as the equilateral triangle cavity and its Zigzag boundary, which can be used to fill solid, liquid, and gaseous 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 a one-to-one correspondence between the transmission spectrum and the refractive index; below the photonic crystal slab is a complete SiO2 to support the media injected from the upper window in the equilateral triangle cavity area, and ensure that the holes of the photonic crystal are in an air / vacuum environment in the non-triangle cavity area.

[0037] As Figure 4 shown in Figs. a and 4b, the change in the refractive index of the filled medium can cause the energy band change of the photonic crystal unit, manifested as the overall directional shift of the energy band to the low frequency with the increase in the refractive index of the medium filled in the equilateral triangle cavity.

[0038] As Figure 5 shown in Fig. a, the formed bridge-shaped boundary projected energy band diagram has a single topologically protected conduction band, which can support the transmission of topologically protected boundary states; while the formed Zigzag boundary has two topologically protected conduction bands. As Figure 5 shown in Fig. 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 middle frequency region (i.e., the gray shaded region in the figure) has a high group refractive index, supports topologically protected slow light transmission, can greatly enhance the interaction between light and matter, and improve the sensitivity of the proposed sensor.

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

[0042] As Figure 7As shown, it is the transmission field distribution of the sensor flat plate at 19.9 THz when the refractive index of the medium in the equilateral triangle cavity is 1. When the light wave entering from the incident end (left) approaches the equilateral triangle cavity, due to the near-field coupling between the bridge-shaped boundary and the Zigzag boundary of the equilateral triangle 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 triangle cavity, it will return to the waveguide again through the far-field coupling effect. This process is similar to the input coupling but in the opposite direction. The light wave coupled back to the bridge-shaped boundary continues to propagate along the boundary and finally outputs from the output end of the waveguide. The light wave at the output end includes the original input light wave and the light wave generated after resonance and coupling in the equilateral triangle cavity.

[0043] As Figure 8 shown, the input is broadband light with a wavelength of λ in(1,2,3,4) which is demultiplexed by a wavelength division multiplexer into four different frequency ranges of λ1, λ2, λ3, and λ4, transmitted through an optical fiber and coupled into the corresponding photonic crystal flat plates. The light with different frequency ranges passes through the photonic crystal flat plates with different unit structures, and a transmission spectrum with a significant mutation can be measured at the output end of a certain photonic crystal flat plate. By analyzing the transmission spectrum λ out and the mutation spikes therein, the refractive index of the medium filled in the triangular cavity region of the photonic crystal flat plate can be obtained. When the medium environment changes, the photonic crystal flat plate operating at a different working frequency may generate a transmission spectrum response, significantly improving 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 spectral shift caused by the refractive index change.

[0045] After considering the specification and practicing the content disclosed herein, those skilled in the art will easily think of other implementation schemes of this application. This application aims to cover any variations, uses, or adaptive changes of this application, which follow the general principles of this application and include the common general knowledge or conventional technical means in this technical field not disclosed in this application. The specification and embodiments are only regarded as exemplary.

[0046] It should be understood that this application is not limited to the precise structure already described and shown in the drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A topological insulator refractive index gradient sensing chip, characterized in that Including: A SiO2 substrate, a periodic topologically trivial photonic crystal unit structure, and a periodic topologically non-trivial photonic crystal unit structure; Both of the photonic crystal unit structures are composed of high refractive index materials. Hexagonal air holes are opened on the photonic crystal unit structures. When the scaling factor C of the hexagonal air holes in the photonic crystal unit structure is C > 1 and C < 1, the topological Chern numbers of the two photonic crystals are opposite to each other, and at the same time, the scaling factor is scanned and optimized to ensure a relatively large photonic crystal bandgap; The periodic topologically trivial photonic crystal unit structure and the topologically non-trivial photonic crystal unit structure are connected by a bridge-shaped interface to form a first type of topologically protected edge state; A regular triangular cavity is provided in the periodic topologically non-trivial photonic crystal unit structure. The regular triangular cavity is composed of a topologically trivial photonic crystal. A SiO2 open window is provided above the regular triangular cavity; There is a photonic crystal unit period between the regular triangular cavity and the bridge-shaped interface; The topologically trivial photonic crystal in the regular triangular cavity region and the external topologically non-trivial photonic crystal form a Zigzag boundary, and the Zigzag boundary has a high group refractive index; The periodic topologically trivial photonic crystal unit structure and the periodic topologically non-trivial photonic crystal unit structure together form a photonic crystal slab. The SiO2 substrate is located below the entire photonic crystal slab. The SiO2 substrate and the upper SiO2 open window form a sealed vacuum space in the non-triangular cavity region to ensure that the refractive index is constantly 1; The SiO2 substrate and the photonic crystal slab form an upper-open container in the regular triangular cavity region for carrying the filled pure refractive index medium; For the photonic crystal slab, when broadband light is input at the incident end, due to the difference in the conduction band frequency and the working frequency of the triangular cavity, a transmission spectrum with a sudden change in loss can be measured at the output end. When the refractive index of the medium filled in the open holes of the photonic crystal in the regular triangular cavity region is changed, the transmission spectrum will change significantly; The photonic crystal slab is fine-tuned by the photonic crystal unit structure to obtain different bandgap ranges, and is connected in parallel through a wavelength division multiplexer to form a sensor array for expanding the working frequency range of the sensor.

2. The refractive index gradient sensing chip of a topological insulator according to claim 1, characterized in that The high refractive index material is a silicon substrate.

3. The refractive index gradient sensing chip of a topological insulator according to claim 1, characterized in that Including a sensor array, the sensor array is composed of a plurality of sensor slabs with a fixed lattice constant and the internal hole size of the photonic crystal unit being fine-tuned according to the target frequency range.

4. The refractive index gradient sensing chip of a topological insulator according to claim 3, characterized in that The sensor array is connected to the incident light through a wavelength division multiplexer.

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