A Graphene-Based Metawaveguide Phase Dynamic Modulator

Abstract

The present invention provides a metasurface waveguide phase dynamic modulator based on graphene. Its characteristics are as follows: It is composed of Ⅰ a silicon waveguide, Ⅱ a metasurface composed of artificial microstructured metal units, and Ⅲ a bilayer graphene capacitor; the bilayer graphene is separated by an insulating material, hexagonal boron nitride; by applying a voltage to the metal electrodes, the bilayer graphene forms a capacitor, ensuring that the voltage at each point of the graphene is consistent, thereby changing the Fermi level of the graphene and affecting the interaction of the metal structural unit with the optical field; the signal light source is incident from one end of the waveguide, and after passing through the phase modulation structure - the metal structure and the graphene, it exits from the port on the other side, realizing the phase regulation of the output signal. The present invention can be used in a Mach-Zehnder interferometer or a ring resonator to realize various functions such as optical switching, filtering, wave selection, and beam splitting, and can be widely applied to the field of micro-nano photon device integration.

Description

(1) Technical Field

[0001] The present invention relates to a metasurface waveguide phase dynamic modulator based on graphene, which can be used in a Mach-Zehnder interferometer or a ring resonator to realize functions such as optical switching, beam splitting, filtering, and wave selection, and belongs to the field of photonic integration. (2) Background Art

[0002] A phase modulator is a key component for modulating high-speed optical signals in a photonic integration system, and it is of great significance for the effective manipulation of guiding electromagnetic waves. A waveguide is a low-loss transmission medium that can confine electromagnetic waves in a closed space and has the advantages of small volume and easy integration. Therefore, a silicon waveguide with a relatively large relative permittivity is often used to fabricate a phase modulator.

[0003] There are currently various methods for modulating the phase. The electro-optic modulator based on lithium niobate is relatively large in size and has a relatively high driving voltage in terms of technology; the silicon modulator based on the plasma dispersion effect is accompanied by chirping and a limited extinction ratio, which deteriorates its performance; the modulator based on the thermo-optic effect has a slow modulation speed, high cost, and poor repeatability; the hybrid plasmonic waveguide modulator based on nonlinear polymers has working instability and incompatibility with CMOS technology.

[0004] To solve the above problems, two-dimensional materials have been used in recent years to achieve the modulation target, such as new bandgap-tunable materials like graphene, vanadium dioxide, and Dirac semimetals. Among them, graphene has excellent optical properties such as high conductivity, high modulation efficiency, broadband width, and tunable light absorption. The Fermi level can be actively adjusted by applying a driving voltage, and the complex permittivity of graphene can be adjusted. However, the interaction between single-atom-thick graphene and vertically incident light is very weak (only ~2.3% absorption), which limits its application in optical modulators.

[0005] At the same time, a metasurface is an array of artificial microstructural units, which can provide a powerful ability to manipulate electromagnetic waves by changing the geometric structure and size of the units. However, most metamaterials are simulated, evaluated, and operated in free space, and in actual use, it is difficult to control the loss in free space. Attempts have been made to combine the metasurface and the waveguide. The waveguide can avoid scattering in free space, and the metasurface can shorten the modulation length. Chinese Patent: 201910357092.1 discloses a silicon-based artificial microstructural metasurface waveguide coupler that couples vertically incident light into the waveguide. Although a phase delay of 0 - 2π is achieved, the optical field transmitted in the waveguide cannot be regulated; Chinese Patent: 201711334825.7 discloses a waveguide structure for phase regulation of a chip lidar based on a metasurface. Although large-angle phase regulation is achieved, it is not dynamically adjustable.

[0006] The present invention discloses a metasurface waveguide phase dynamic modulator based on graphene. It can be used for signal modulation, and can realize functions such as optical switches, filtering, and wave selection in combination with Mach-Zehnder interferometers or micro-ring resonators, and can be widely applied to the field of integration of micro-nano photon devices. It combines the adjustable bandgap feature of graphene and the powerful electromagnetic wave manipulation ability of the metasurface, thereby achieving large-angle phase modulation. Compared with lithium niobate phase modulators, it reduces energy consumption; compared with electro-optic graphene phase modulators, it shortens the working distance; compared with thermo-optic phase modulators, it improves stability and repeatability; and compared with plasma phase modulators, it can be combined with existing CMOS processing technologies. (III) Summary of the Invention

[0007] The object of the present invention is to provide a waveguide phase dynamic modulator combining graphene and metasurface, which has a simple and compact structure, large modulation amplitude, low energy consumption, high stability, and can be combined with existing CMOS processing technologies.

[0008] The object of the present invention is achieved as follows:

[0009] The graphene-based metasurface waveguide phase dynamic modulator is characterized in that: it is composed of I silicon waveguide, II metasurface composed of artificial microstructural metal units, and III bilayer graphene; the bilayer graphene is separated by the insulating material hexagonal boron nitride; by applying a voltage to the metal electrode connected to the graphene, the bilayer graphene forms a capacitor to ensure that the voltage at each point of the graphene is consistent, thereby changing the Fermi level of the graphene and affecting the action of the metal structure unit on the optical field; the signal light source is incident from one end of the waveguide, and after passing through the graphene-covered area, it exits from the port on the other side, realizing the phase regulation of the output signal.

[0010] Among them, the modulation process involves the principle of phase transmission:

[0011]

[0012] The beneficial effects of the present invention are as follows:

[0013] 1. The present invention effectively combines the waveguide and the metasurface, and the use of metal split rings generates an intuitive absorption peak in the transmission spectrum.

[0014] 2. When the Fermi level of the graphene is adjusted to change from 0.4 eV to 1 eV in the present invention, a 360° change in phase can be achieved, realizing the phase modulation function.

[0015] 3. When the Fermi level of the graphene is adjusted to change from 0.4 eV to 1 eV at 1550 nm in the present invention, a change in transmittance from 0.08 to 0.71 can be achieved, realizing the intensity modulation function.

[0016] 4. When the Fermi level of graphene is adjusted to vary from 0.4 eV to 1 eV in the present invention, a drift of the absorption peak exceeding 50 nm can be achieved, realizing the function of wave selection. (IV) BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram of the present invention. The number of the above unit structures can be increased or decreased according to the usage requirements. I is a silicon waveguide with a cross-section of 2 μm × 1 μm and a length of 4 - 10 μm. II is a gold split ring. III is a graphene capacitor composed of bilayer graphene and hexagonal boron nitride.

[0018] Figure 2 is a side view of the schematic structural diagram of the present invention. 1 is a silicon waveguide, 2 is a gold split ring, 3 is graphene, and 4 is hexagonal boron nitride.

[0019] Figure 3 is a top view of the schematic structural diagram of the present invention. The distance dx between the metal units is between 100 - 500 nm, the slit s is less than 50 nm, and ro and ri are respectively the outer ring radius and inner ring radius of the metal split ring, which are between 100 - 300 nm.

[0020] Figure 4 is the phase varying with the Fermi level of graphene.

[0021] Figure 5 is the absorption peak varying with the Fermi level of graphene.

[0022] Figure 6 is the transmittance at 1550 nm varying with the Fermi level of graphene. (V) SPECIFIC EMBODIMENTS

[0023] The following further describes the specific embodiments of the present invention with reference to the accompanying drawings.

[0024] Figure 1 、 Figure 2 As shown, the present invention provides a metasurface waveguide phase dynamic modulator based on graphene. The device is composed of I silicon waveguide, II metasurface composed of artificial microstructural metal units, and III bilayer graphene; the bilayer graphene is separated by an insulating material, hexagonal boron nitride; by applying a voltage on the metal electrode, the bilayer graphene forms a capacitor to ensure that the voltages at each point of the graphene are consistent, thereby changing the Fermi level of the graphene and affecting the action of the metal structural unit on the optical field; the signal light source is incident from one end of the waveguide, and after passing through the phase modulation structure - the metal structure and graphene, it exits from the port on the other side, realizing the phase regulation of the output signal.

[0025] As an example, the specific dimensions are as follows: in the cross-section of the waveguide, the width is 480 nm, the height is 0.35 nm, the thickness of the metal unit is 40 nm, the thickness of hexagonal boron nitride is 10 nm, the gap dx between metal units is 300 nm, the outer ring radius ro of the metal unit is 190 nm, the inner ring radius ri is 140 nm, the graphene coverage length is 3.4 microns, there are five metal units on each of the upper and lower surfaces of the waveguide, and the incident frequency ranges from 180 THz to 210 THz.

[0026] The Fermi level of graphene varies from 0 to 1 eV, and the phase change is as Figure 4 shown, the absorption peak shift is as Figure 5 shown, and the transmittance change at 1550 nm is as Figure 6 shown. The phase changes by 40°, the absorption peak shifts by 30 nm, and the transmittance changes by 0.3. This is only the result that can be achieved with five units. If a larger 360° is desired, more units can be used, such as more than 30 units.

Claims

1. A graphene-based metasurface waveguide phase dynamic modulator, characterized in that: The modulator includes a silicon waveguide, a metasurface composed of artificial microstructured metal units, and a graphene capacitor; both the upper and lower surfaces of the silicon waveguide are simultaneously provided with graphene and artificial microstructured metal units. The double-layer graphene is close to the upper and lower surfaces of the silicon waveguide and is symmetrically arranged up and down. The artificial microstructured metal units are arranged on the side of the double-layer graphene facing away from the silicon waveguide and are symmetrically arranged up and down; the graphene is separated by the insulating material hexagonal boron nitride to form a graphene capacitor. The thickness of the single-layer graphene is 0.34 nm, and the thickness of the hexagonal boron nitride is 10 nm; the artificial microstructured metal unit is an open-loop, and a slit is dug on the open-loop, so that it is divided into two left and right semi-circles along the transmission direction of the waveguide; the graphene capacitor applies a voltage through a metal electrode connected to the graphene to change the Fermi level of the graphene, thereby affecting the effect of the artificial microstructured metal unit on the optical field; the signal light source is incident from one end of the waveguide, passes through the artificial microstructured metal unit and the graphene capacitor, and exits from the other port to realize the phase regulation of the output signal.

2. The metamaterial waveguide phase dynamic modulator based on graphene according to claim 1, wherein It effectively combines the waveguide and the metasurface composed of artificial microstructured metal units. By applying a voltage to the metal electrode connected to the graphene, the double-layer graphene forms a capacitor to ensure that the voltages at each point of the graphene are consistent, thereby changing the Fermi level of the graphene, and thus regulating the optical field in the waveguide.

3. The metamaterial waveguide phase dynamic modulator based on graphene according to claim 1, characterized in that: The wavelength range of the signal light source is 1500 - 1600 nm.

4. The metamaterial waveguide phase dynamic modulator based on graphene according to claim 1, characterized in that: When the Fermi level of the graphene changes from 0.4 ev to 1 ev, the phase of the output light can achieve continuous change within 360°.

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