Chiral transmission device based on metamaterial waveguide

Abstract

The application discloses a chiral transmission device based on a metamaterial waveguide and belongs to the field of optical field mode regulation. The device comprises a substrate, double-coupled silicon-based metamaterial waveguides and a cladding. The double-coupled silicon-based metamaterial waveguides are composed of two embedded nano-porous metamaterial waveguides. By adjusting the waveguide spacing, the waveguide width and the period of the nano-pores, the parameters of the double-coupled silicon-based metamaterial waveguides can be mapped to the parameter space of a non-hermitian system, so that the change trajectory of the parameter space can surround singular points, thereby realizing the singular characteristics of chiral mode transmission, 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 particularly, to a chiral transmission device based on metamaterial waveguide. Background Art

[0002] In recent years, non-Hermitian systems have attracted considerable attention due to their non-conservative properties, such as open boundary conditions or gain / loss interactions. These systems exhibit numerous physical phenomena that are difficult to intuitively understand. Degenerate singularities of eigenvalues ​​in non-Hermitian Hamiltonians are known as exceptional points (EPs), and they have been extensively studied theoretically and experimentally in advanced fields such as thermodynamics, quantum mechanics, electronics, and acoustics. In photonics, various optical structures that manipulate gain and loss have been used to explore and demonstrate exotic effects based on EPs. These phenomena, including loss-induced transparency, enhanced sensitivity, single-mode lasing, and unidirectional cloaking, lay the foundation for next-generation 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 research demonstrates that mapping the dynamic surrounding of Hamiltonian parameters to coupled waveguide configurations enables chiral mode switching, where the properties of the output mode are fully determined by the handedness of the surrounding path. However, in conventional chiral switching devices based on EPs, chiral transmission efficiency is generally low due to path-dependent losses near the EPs. To address this issue, several techniques have been proposed, including mobile EPs surrounding, Hamiltonian hopping, and rapid parameter evolution, to achieve efficient chiral switching across optical communication bands. With the rapid development of wavelength division multiplexing technology, traditional communication bands are facing a "capacity bottleneck." The recent 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, extending the wavelength of chiral mode switching devices beyond 1.55 microns, particularly to the 2-micron band, is of great significance. However, achieving high-performance chiral mode switching in the 2-micron band remains challenging.

[0004] Furthermore, previous chiral mode switching devices suffered from wavelength-dependent mode mismatch, resulting in a limited operating wavelength range and reduced mode purity. 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 exhibit strong coupling coefficients and flat dispersion, laying the foundation for the realization of high-performance mode devices. Therefore, metamaterial engineering holds great promise for the development of high-performance chiral mode switching devices. Summary of the Invention

[0005] In view of the defects of the prior art, the present application aims to provide a chiral transmission device based on a metamaterial waveguide, which introduces a metamaterial waveguide to solve the wavelength-related mode mismatch problem of the previous on-chip chiral transmission device and realize a chiral transmission device with large bandwidth, high efficiency and high purity in multiple wavebands.

[0006] To achieve the above-mentioned purpose, the present application provides a chiral transmission device based on a metamaterial waveguide, comprising a substrate, a double-coupling metamaterial waveguide located on the surface of the substrate, and a cladding layer located above the substrate and covering the double-coupling metamaterial waveguide; the double-coupling metamaterial waveguide comprises a first wide waveguide, two embedded nano-hole metamaterial waveguides (a first metamaterial waveguide and a second metamaterial waveguide), and a second wide waveguide; the output of the first wide waveguide is connected with the input of the first metamaterial waveguide and the second metamaterial waveguide respectively, the input of the second wide waveguide is connected with the output of the first metamaterial waveguide and the second metamaterial waveguide respectively, the first metamaterial waveguide and the second metamaterial waveguide maintain a preset interval, and the first metamaterial waveguide and the second metamaterial waveguide are both embedded with nano-holes; the two embedded nano-hole metamaterial waveguides can adjust the structural parameters (waveguide width, waveguide interval and nano-hole period) to correspond to the parameter space (tuning parameter and loss) of the non-hermitian system, so that the change trajectory of the parameter space can surround the singular point, thereby realizing the singular characteristics of low-loss, high-purity and large-bandwidth chiral mode transmission;

[0007] The parameter space of the non-hermitian system is a space in which a Riemann surface is located, with the tuning parameter and the loss as independent variables, and the eigenvalue and the corresponding eigenvector of the Hamiltonian operator of the non-hermitian system as dependent variables; the non-hermitian system can have degenerate eigenvalues and eigenvectors at the singular point;

[0008] The singular characteristics of the chiral mode transmission are 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, only the fundamental mode is output at the output end, and when the fundamental mode and the high-order mode are input from the output end, only the high-order mode is output at the input end.

[0009] Preferably, the nano-hole shape embedded in the first metamaterial waveguide and the second metamaterial waveguide is circular, square, elliptical, rhombic or the like; when the nano-hole period of 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 nano-hole period of the metamaterial waveguide matches the working wavelength, the metamaterial waveguide exhibits the high-loss characteristics of a photonic crystal waveguide.

[0010] Preferably, the nano-hole period of the first metamaterial waveguide is constant, which can realize low-loss optical transmission; and the waveguide width gradually decreases from left to right (L c1 region), then widens (L s1 region), and finally remains unchanged (L s2 region and Lc2 Region).

[0011] Preferably, the second metamaterial waveguide nanohole period is first unchanged (L c1 Region) from left to right, then first increases and then decreases (L s1 Region and L s2 Region), and finally unchanged (L c2 Region), and the high-loss transmission of the optical field can be realized in the period change region; the L s1 Region and L s2 Region are cascaded photonic crystal waveguides, and wideband reflection loss can be realized; the waveguide width is first unchanged (L s1 Region and L c1 Region) from left to right, then decreases (L s2 Region), and finally increases (L c2 Region).

[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 the fundamental mode and high-order modes.

[0014] Preferably, the working waveband of the chiral transmission device can be designed in the communication waveband and the two-micron waveband, and even the visible light waveband to realize wideband 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, and polymer.

[0016] Compared with the prior art, the above technical scheme of the present application has the following beneficial effects:

[0017] 1. The present application discloses a chiral transmission device based on a metamaterial waveguide, which fully utilizes the advantages of artificial adjustment and design of the refractive index and dispersion characteristics of the metamaterial waveguide, overcomes the wavelength-dependent mode mismatch problem, and provides a new idea for improving the performance of the chiral transmission device compared with the use of traditional strip waveguides.

[0018] 2. The present application utilizes the tailorable characteristics of the waveguide performance of the metamaterial waveguide to control the waveguide loss, which can switch the light transmission between the lossless subwavelength grating waveguide and the lossy photonic crystal waveguide state by changing the size of the nanohole of the metamaterial waveguide, realize precise control of the loss, do not need to introduce additional materials for absorption, or set special surrounding singular point lines, reduce the difficulty of system parameter control, and can also realize fine control of the loss, realize high-efficiency transmission of the device.

[0019] 3、The present application uses the easy processing characteristics of metamaterial waveguide, compared with the traditional sub-wavelength grating using rectangular block, the present application has larger feature size, also has larger processing tolerance characteristics.

[0020] 4、The present application uses the universality of constructing metamaterial waveguide, which can also be applied to other various integrated photon platforms. BRIEF DESCRIPTION OF DRAWINGS

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

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

[0023] Figure 3 is the band gap diagram and transmission transmittance of metamaterial waveguide as sub-wavelength grating waveguide, and the band gap diagram and transmission transmittance of metamaterial waveguide as photonic crystal grating waveguide.

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

[0025] Figure 5 is a simulation transmission spectrum diagram of a chiral transmission device based on metamaterial waveguide at a 2-micron waveband.

[0026] Figure 6 is an experimental transmission spectrum diagram of a chiral transmission device based on metamaterial waveguide at a 2-micron waveband.

[0027] Figure 7 is a simulation transmission spectrum diagram of a chiral transmission device based on metamaterial waveguide at a communication waveband. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0029] Example one:

[0030] A chiral transmission device based on metamaterial waveguide, as shown in Figure 1 , is composed of two silicon metamaterial waveguides, and the substrate and cladding are both silicon dioxide. The entire device can be represented by the Hamiltonian . Wherein β , gammaand kappa are the tuning parameter, 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 beta / kappa = 0, gamma / kappa = 2, the eigenvalue and eigenvector are degenerate at the singular point. By adjusting the size of the metamaterial waveguide nanopore, 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, to achieve the surrounding singularity, the period of the nanoholes in the first metamaterial waveguide (2-2) remains unchanged at 200nm; while the period of the nanoholes in the second metamaterial waveguide (2-3) is:

[0031] Where n is the number of corresponding nanopores from left to right.

[0032] The adjustment of the waveguide width mainly corresponds to the adjustment of the system parameter tuning amount. Figure 3 As can be seen from (a), 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 .in, w 0 is 600 nm, Δ w It is 100nm.

[0033] 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 the figure, 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: in, d 0 is 50 nm, d 1 is 750nm.

[0034] 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) is shown. 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 0 dB ((Figure 5 mode purity is greater than 98.7% (see (a) in FIG. 6 Figure 5 Figure 6 From the simulated transmission spectrum of (b) in FIG. 6, it can be seen that the transmission efficiency of the device is greater than 1 dB in the wavelength range of 1.945 - 2.03 μm Figure 6 mode purity is greater than 95% (see (a) in FIG. 6 Figure 6

[0035] Example Two:

[0036] A high-performance chiral transmission device based on a metamaterial waveguide, which not only can work in the 2-micron waveband, but also can achieve high-performance chiral transmission in the communication waveband by adjusting the parameters of the device. In order to demonstrate the robustness to the waveguide thickness, the device adopts a 220-nm-thick silicon wave super material guide. The waveguide width of the second super material waveguide (2-3) remains unchanged, and the waveband width of the first super material waveguide (2-2) is shown as follows:

[0037]

[0038] wherein, w 00 is 450 nm, Δ w 0 is 100 nm. x is the propagation distance from 0 μm to 137.4 μm.

[0039] The nanohole period of the first super material waveguide (2-2) remains unchanged, and the nanohole period of the second super material waveguide (2-3) is shown as follows:

[0040]

[0041] The distance between the two super material waveguides is first increased and then decreased:

[0042]

[0043] wherein d 00 is 50 nm, d 01 is 800 nm.

[0044] Figure 7 ​​(a) in FIG. 6 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 the purity of the mode is greater than 99.6% in the wavelength range of 1.25 - 1.75 μm, as shown in Figure 7 (c) in FIG. 6. Figure 7 (b) in FIG. 6 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 the purity of the mode is greater than 98.9% in the wavelength range of 1.25 - 1.75 μm, as shown in Figure 7 (d) in FIG. 6.

[0045] In general, the high-performance chiral transmission device based on the metamaterial waveguide has super-high performance in the 2 μm waveband, and also has super-high performance in the communication waveband, and even in other visible light wavebands.

[0046] Those skilled in the art can easily understand that the above description is only preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

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 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 connected to the input end of the first metamaterial waveguide (2-2) and the second metamaterial waveguide (2-3), respectively; the input of the second wide waveguide (2-4) is connected to the input end of the first metamaterial waveguide (2-1), respectively. 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 the non-Hermitian system, and by adjusting the structural parameters of the first metamaterial waveguide (2-2) and the second metamaterial waveguide (2-3), the change trajectory of the parameter space surrounds the singularity point, 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 with the tuning parameters and losses 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; 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 operating wavelength, the metamaterial waveguide exhibits the low-loss characteristics of a subwavelength grating waveguide; when the period of the embedded nanoholes matches the operating 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 from L s1 Area to L s2 The area first becomes larger and then smaller, and finally L c2 The region remains unchanged; The waveguide width is first L s1 Area and L c1 The area remains unchanged, then L s2 The area becomes smaller, and finally L c2 The area becomes larger.

7. The chiral transmission device based on metamaterial waveguide according to claim 1, characterized in that: The spacing 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-micron 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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