Chiral transmission device based on metamaterial waveguide

Abstract

The invention discloses a chiral transmission device based on a metamaterial waveguide, and belongs to the field of light field mode regulation and control. The device comprises a substrate, a double-coupling silicon-based metamaterial waveguide and a cladding. The double-coupling silicon-based metamaterial waveguide is composed of two metamaterial waveguides embedded with nano-pores, and parameters of the double-coupling silicon-based metamaterial waveguide can be mapped to a parameter space of a non-Hermi system by adjusting the waveguide distance, the waveguide width and the period of the nano-pores, so that the change track of the parameter space can surround a singular point, and the accuracy of the singular point is improved. Therefore, the singular characteristic of chiral mode transmission is realized, that is, when the fundamental mode and the high-order mode are input from the left side, only the fundamental mode is output from the right side, and when the fundamental mode and the high-order mode are input from the right side, only the high-order mode is output from the left side. The chiral transmission device based on the metamaterial waveguide can realize low-loss, high-purity and large-bandwidth chiral mode transmission, and has the characteristics of simple process, large manufacturing tolerance and the like.

Description

Technical Field

[0001] The present invention relates to the field of light field mode manipulation, and more specifically, to a chiral transmission device based on metamaterial waveguide. Background Art

[0002] In recent years, non-Hermitian systems have attracted much attention due to their non-conservative properties, such as open boundary conditions or gain / loss interactions. This type of system exhibits many physical phenomena that are difficult to understand intuitively. In the non-Hermitian Hamiltonian, the degenerate singularities of the eigenvalues ​​are called Exceptional Points (EPs), which have been widely studied theoretically and experimentally in many advanced fields such as thermodynamics, quantum mechanics, electronics, and acoustics. In the field of photonics, various optical structures that manipulate gain and loss have been used to explore and demonstrate exotic effects based on EPs. These phenomena include loss-induced transparency, enhanced sensitivity, single-mode lasing, and unidirectional stealth, which lay the foundation for the next generation of optical technologies.

[0003] Among the many exotic effects, chiral topological responses can be observed in non-Hermitian systems when system parameters are tuned to dynamically surround EPs. Recent studies have shown that mapping the dynamic surround of Hamiltonian parameters to coupled waveguide configurations enables chiral mode switching, where the properties of the output mode are completely determined by the handedness of the surround path. However, in conventional EPs-based chiral switching devices, chiral transmission efficiency is generally low due to path-dependent losses near EPs. To address this issue, several technical approaches have been proposed, including mobile EPs surround, Hamiltonian hopping, and fast parameter evolution, to achieve efficient chiral switching across optical communication bands. With the rapid development of wavelength division multiplexing technology, conventional communication bands are facing a "capacity bottleneck". Recently, the emergence of low-loss hollow-core fibers and high-gain low-noise holmium-doped fiber amplifiers has made the 2-micron band a potential solution to this problem. Therefore, it is of great significance to extend the wavelength of chiral mode switching devices to above 1.55 microns, especially to the 2-micron band. However, achieving high-performance chiral mode switching in the 2-micron band remains challenging.

[0004] In addition, previous chiral mode switching devices have limited operating wavelength range and reduced mode purity due to wavelength-dependent mode mismatch. In recent years, silicon-based metamaterials have been introduced to construct artificial effective dielectric waveguides with tunable refractive index and dispersion properties, providing unprecedented flexibility for nanophotonic devices. Silicon-based metamaterial waveguides demonstrate strong coupling coefficients and flat dispersion, laying the foundation for the realization of high-performance mode devices. Therefore, the use of metamaterial engineering technology is expected to develop high-performance chiral mode switching devices. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of the present invention is to provide a chiral transmission device based on metamaterial waveguide, aiming to introduce metamaterial waveguide to solve the wavelength-related mode mismatch problem of previous on-chip chiral transmission devices and realize chiral transmission devices with large bandwidth, high efficiency and high purity in multiple bands.

[0006] To achieve the above-mentioned purpose, the present invention provides a chiral transmission device based on metamaterial waveguide, comprising a substrate, a dual-coupled metamaterial waveguide located on the surface of the substrate, and a cladding located above the substrate and covering the dual-coupled metamaterial waveguide; the dual-coupled silicon-based metamaterial waveguide comprises a first wide waveguide, two embedded nanohole metamaterial waveguides (a first metamaterial waveguide and a second metamaterial waveguide) and a second wide waveguide; the output of the first wide waveguide is respectively connected to the input ends of the first metamaterial waveguide and the second metamaterial waveguide, the input of the second wide waveguide is respectively connected to the output ends of the first metamaterial waveguide and the second metamaterial waveguide, the first metamaterial waveguide and the second metamaterial waveguide maintain a preset spacing, and the first metamaterial waveguide and the second metamaterial waveguide are both embedded with nanoholes; the two embedded nanohole metamaterial waveguides can adjust structural parameters (waveguide width, waveguide spacing and nanohole period) to correspond to the parameter space (tuning parameters and loss) of a non-Hermitian system, so that the change trajectory of the parameter space can surround the singularity point, thereby achieving the singularity characteristics of low loss, high purity and large bandwidth chiral mode transmission;

[0007] The parameter space of the non-Hermitian system is a space where the Riemann surface is formed by taking the tuning parameters and the loss as independent variables and the eigenvalues ​​and corresponding eigenvectors of the Hamiltonian operator of the non-Hermitian system as dependent variables; the non-Hermitian system may have degenerate eigenvalues ​​and eigenvectors at singular points;

[0008] The unique characteristic of the chiral mode transmission is that the output mode is only related to the input and output ports, that is, when the fundamental mode and the high-order mode are input from the input end, the output end only outputs the fundamental mode, and when the fundamental mode and the high-order mode are input from the output end, the input end only outputs the high-order mode.

[0009] Preferably, the shapes of the embedded nanoholes in the first metamaterial waveguide and the second metamaterial waveguide are circular, square, elliptical, diamond-shaped, etc.; when the period of the embedded nanoholes in the metamaterial waveguide is much smaller than the working wavelength, the metamaterial waveguide exhibits the low-loss characteristics of a subwavelength grating waveguide; when the period of the embedded nanoholes in the metamaterial waveguide far matches the working wavelength, the metamaterial waveguide exhibits the high-loss characteristics of a photonic crystal waveguide.

[0010] Preferably, the nanopore period of the first metamaterial waveguide remains unchanged, so that low-loss light transmission can be achieved; and the waveguide width gradually decreases from left to right (L c1 area), then widens (L s1 area), and finally remain unchanged (L s2 Area and Lc2 area).

[0011] Preferably, the period of the second metamaterial waveguide nanopores is constant from left to right (L c1 area), then it first gets bigger and then gets smaller (L s1 Area and L s2 area), and finally unchanged (L c2 region), high-loss transmission of the light field can be achieved in the periodic variation region; the L s1 Area and L s2 The region is a cascaded photonic crystal waveguide, which can achieve broadband reflection loss; the waveguide width remains unchanged from left to right (L s1 Area and L c1 area), then becomes smaller (L s2 area), and finally becomes larger (L c2 area).

[0012] Preferably, the waveguide spacing between the first metamaterial waveguide and the second metamaterial waveguide increases first and then decreases from left to right.

[0013] Preferably, the first wide waveguide and the second wide waveguide are strip waveguides, which can support low-loss transmission of fundamental mode and high-order modes.

[0014] Preferably, the operating band of the chiral transmission device can be designed to be in the communication band and the two-micrometer band, or even the visible light band to achieve broadband operation.

[0015] Preferably, the materials of the first metamaterial waveguide and the second metamaterial waveguide are high refractive index media such as silicon, silicon nitride, silicon carbide, lithium niobate, polymer, etc.

[0016] Through the above technical solution conceived by the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The present invention discloses a chiral transmission device based on a metamaterial waveguide, which makes full use of the advantage that the refractive index and dispersion characteristics of the metamaterial waveguide can be manually adjusted to overcome the wavelength-related mode mismatch problem. Compared with the method of using traditional strip waveguides, it provides a new idea for improving the performance of chiral transmission devices.

[0018] 2. The present invention utilizes the tailorable characteristics of the waveguide performance of the metamaterial waveguide. For the regulation of waveguide loss, the size of the nanoholes of the metamaterial waveguide can be changed to switch the light transmission between the lossless subwavelength grating waveguide and the lossy photonic crystal waveguide states, thereby achieving precise control of the loss. There is no need to introduce additional materials for absorption or set up special lines around the singularity point, which reduces the difficulty of regulating the system parameters. It can also achieve fine regulation of the loss and realize high-efficiency transmission of the device.

[0019] 3. The present invention utilizes the easy processing characteristics of metamaterial waveguides. Compared with the traditional sub-wavelength gratings using rectangular blocks, the present invention has a larger characteristic size and a larger processing tolerance.

[0020] 4. The present invention utilizes the universality of constructing metamaterial waveguides and can also be applied to various other integrated photonic platforms. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of a chiral transmission device based on metamaterial waveguide.

[0022] Figure 2 This is a schematic diagram of light field transmission in a chiral transmission device based on metamaterial waveguide.

[0023] Figure 3 It is the bandgap diagram and transmission transmittance when the metamaterial waveguide behaves as a subwavelength grating waveguide, and the bandgap diagram and transmission transmittance when the material waveguide behaves as a photonic crystal grating waveguide.

[0024] Figure 4 It is the reciprocal of the propagation constant tuning parameter and coupling coefficient of the subwavelength grating waveguide and the traditional strip waveguide.

[0025] Figure 5 This is the simulated transmission spectrum of the chiral transmission device based on metamaterial waveguide in the 2-micron band.

[0026] Figure 6 This is the experimental transmission spectrum of the chiral transmission device based on metamaterial waveguide in the 2-micron band.

[0027] Figure 7 This is the simulated transmission spectrum of the chiral transmission device based on metamaterial waveguide in the communication band. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] Embodiment 1:

[0030] A chiral transmission device based on metamaterial waveguide, such as Figure 1 As shown in Figure 1, it consists of two silicon metamaterial waveguides, with both the substrate and the cladding being silicon dioxide. The entire device can be represented by the Hamiltonian In other words, β, γ and κ are tuning parameters, relative loss rate and coupling coefficient respectively. To further simplify the parameters, the Hamiltonian can be expressed as When the system parameters are tuned to β / κ=0, γ / κ=2, the eigenvalues ​​and eigenvectors are degenerate at the singular point. By adjusting the size of the metamaterial waveguide nanohole, the loss can be precisely controlled. Figure 2 As shown in Figure 2, when the waveguide width is 600nm and the period is 200nm ( Figure 2 (a) in the figure, the metamaterial waveguide behaves as a low-loss subwavelength grating; when the waveguide width is 600nm and the period is 500nm ( Figure 2 In (b), the metamaterial waveguide behaves as a high-loss photonic crystal grating. Specifically, in order to realize the surrounding singularity, the period of the nanohole of the first metamaterial waveguide (2-2) remains unchanged and is maintained at 200nm; while the period of the nanohole of the second metamaterial waveguide (2-3) is: Where n is the number of corresponding nanopores from left to right.

[0031] The adjustment of waveguide width mainly corresponds to the adjustment of system parameter tuning. Figure 3 As can be seen from (a) in the figure, the tuning amounts of subwavelength grating waveguides of different wavelengths are almost overlapping, showing a relatively flat dispersion compared to the strip waveguide. Among them, the width parameters of the first metamaterial waveguide (2-2) and the second metamaterial waveguide (2-3) are Among them, w0 is 600nm and Δw is 100nm.

[0032] The adjustment of the waveguide spacing mainly corresponds to the adjustment of the system parameter coupling coefficient. Figure 3 As can be seen from (b) in FIG. 1 , compared with the strip waveguide, the subwavelength grating waveguide has a larger coupling coefficient, which can relax the adiabatic constraint and improve the performance of the chiral transmission device. Specifically, the waveguide spacing of this embodiment is: Among them, d0 is 50nm and d1 is 750nm.

[0033] Figure 4 The simulated light field diagram of the high-performance chiral transmission device based on metamaterial waveguide inputting TE0 mode from the left (a) and the right (b). Among them, the mode output from the right is still TE0 mode, but the mode output from the left is TE1 mode. Figure 5 It can be seen from the simulated transmission spectrum that in the wavelength range of 1.75-2.25μm, the transmission efficiency of the device is close to 0dB (( Figure 5 (a))), the pattern purity is greater than 98.7% ( Figure 5 (b) in the figure). Figure 6It can be seen from the simulated transmission spectrum that in the wavelength range of 1.945-2.03μm, the transmission efficiency of the device is greater than 1dB ( Figure 6 (a) in the figure), the pattern purity is greater than 95% ( Figure 6 (b) in Figure 1). Some deviations between the experimental and simulation results originate from fabrication issues such as sidewall errors, etching roughness, and fabrication accuracy. Therefore, the performance of the fabricated chiral mode switching device can be further improved by optimizing the fabrication process.

[0034] Embodiment 2:

[0035] A high-performance chiral transmission device based on a metamaterial waveguide can not only work in the 2-micron band, but also achieve high-performance chiral transmission in the communication band by adjusting the parameters of the device. In order to demonstrate the robustness to the waveguide thickness, the device uses a 220nm thick silicon wave metamaterial guide. The waveguide width of the second metamaterial waveguide (2-3) remains unchanged, and the band width of the first metamaterial waveguide (2-2) is shown in the following formula:

[0036]

[0037] Among them, w 00 is 450nm, Δw0 is 100nm, and x is the propagation distance from 0μm to 137.4μm.

[0038] The nanopore period of the first metamaterial waveguide (2-2) remains unchanged, and the nanopore period of the second metamaterial waveguide (2-3) is as shown in the following formula:

[0039]

[0040] The distance between the two metamaterial waveguides also increases first and then decreases:

[0041]

[0042] where d 00 is 50nm, d 01 It is 800nm.

[0043] Figure 7 (a) shows the transmittance of TE0 mode and TE1 mode when TE0 mode and TE1 mode are input from the left. It can be found that the mode output from the right is always TE1 mode, and its mode purity is greater than 99.6% in the wavelength range of 1.25–1.75μm, as shown in Figure 1. Figure 7 As shown in (c) in . Figure 7(b) shows the transmittance of TE0 mode and TE1 mode when TE0 mode and TE1 mode are input from the right. It can be found that the mode output from the left is always TE0 mode, and its mode purity is greater than 98.9% in the wavelength range of 1.25-1.75μm, as shown in Figure 1. Figure 7 As shown in (d) in .

[0044] In general, the high-performance chiral transmission devices based on metamaterial waveguides are not limited to having ultra-high performance in the 2-micron operating band, but also have ultra-high performance in the communication band and even in other visible light operating bands.

[0045] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A chiral transmission device based on metamaterial waveguide, characterized in that: The invention comprises a substrate (1), a dual-coupled metamaterial waveguide (2) located on the surface of the substrate (1), and a cladding (3) located above the substrate (1) and covering the dual-coupled metamaterial waveguide (2); the dual-coupled silicon-based metamaterial waveguide comprises a first wide waveguide (2-1), a first metamaterial waveguide (2-2), a second metamaterial waveguide (2-3), and a second wide waveguide (2-4); the output of the first wide waveguide (2-1) is respectively connected to the input end of the first metamaterial waveguide (2-2) and the input end of the second metamaterial waveguide (2-3); the input of the second wide waveguide (2-4) is respectively connected to the input end of the first metamaterial waveguide (2-1), and the output of the second wide waveguide (2-4) is respectively connected to the input end of the first metamaterial waveguide (2-2). The output ends of the first metamaterial waveguide (2-2) and the second metamaterial waveguide (2-3) are connected, the first metamaterial waveguide (2-2) and the second metamaterial waveguide (2-3) maintain a preset distance, and the first metamaterial waveguide (2-2) and the second metamaterial waveguide (2-3) are both embedded with nanopores; the structural parameters of the first metamaterial waveguide (2-2) and the second metamaterial waveguide (2-3) correspond to the parameter space of a non-Hermitian system, and the change trajectory of the parameter space surrounds a singular point by adjusting the structural parameters of the first metamaterial waveguide (2-2) and the second metamaterial waveguide (2-3), thereby realizing chiral mode transmission.

2. The chiral transmission device based on metamaterial waveguide according to claim 1, characterized in that: The parameter space of the non-Hermitian system is a space where the Riemann surface is formed by taking the tuning parameters and the loss as independent variables and the eigenvalues ​​and corresponding eigenvectors of the Hamiltonian operator of the non-Hermitian system as dependent variables; the non-Hermitian system has degenerate eigenvalues ​​and eigenvectors at the singular points.

3. The chiral transmission device based on metamaterial waveguide according to claim 1, characterized in that: The output mode of the chiral mode transmission is only related to the input and output ports, that is, when the fundamental mode and the high-order mode are input from the input end, the output end only outputs the fundamental mode, and when the fundamental mode and the high-order mode are input from the output end, the input end only outputs the high-order mode.

4. The chiral transmission device based on metamaterial waveguide according to claim 1, characterized in that: The shapes of the embedded nanoholes of the first metamaterial waveguide (2-2) and the second metamaterial waveguide (2-3) are circular, square, elliptical, and diamond-shaped; when the period of the embedded nanoholes is much smaller than the working wavelength, the metamaterial waveguide exhibits the low-loss characteristics of a subwavelength grating waveguide; when the period of the embedded nanoholes far matches the working wavelength, the metamaterial waveguide exhibits the high-loss characteristics of a photonic crystal waveguide.

5. The chiral transmission device based on metamaterial waveguide according to claim 4, characterized in that: From the input to the output, it is divided into L c1 Area, L S1 Area, L s2 Area and L c2 In the region, the nanopore period of the first metamaterial waveguide remains unchanged, and the waveguide width is L c1 The area gradually becomes smaller, and then L s1 The area widens, and finally L s2 Area and L c2 The region remains unchanged.

6. The chiral transmission device based on metamaterial waveguide according to claim 4, characterized in that: From the input to the output, it is divided into L c1 Area, L S1 Area, L s2 Area and L c2 region, the nanopore period of the second metamaterial waveguide is first in L c1 The area remains unchanged, then L s1 Area and L s2 The area first becomes larger and then smaller, and finally L c2 The region remains unchanged; The waveguide width is L s1 Area and L c1 The area remains unchanged, then L s2 The area becomes smaller, and finally L c2 The area gets bigger.

7. The chiral transmission device based on metamaterial waveguide according to claim 1, characterized in that: The distance between the first metamaterial waveguide (2-2) and the second metamaterial waveguide (2-3) first increases and then decreases from the input end to the output end.

8. The chiral transmission device based on metamaterial waveguide according to claim 1, characterized in that: The first wide waveguide (2-1) and the second wide waveguide (2-4) are strip waveguides.

9. The chiral transmission device based on metamaterial waveguide according to claim 1, characterized in that: The working band of the chiral transmission device is a communication band, a two-micrometer band or a visible light band.

10. The chiral transmission device based on metamaterial waveguide according to claim 4, characterized in that: The materials of the first metamaterial waveguide (2-2) and the second metamaterial waveguide (2-3) are silicon, silicon nitride, silicon carbide, lithium niobate or polymer.

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