A broadband transmissive infrared light modulator based on graphene plasmon

Abstract

The present invention belongs to the field of optical devices. In order to improve the modulation depth and bandwidth of the modulator, a broadband transmission infrared light modulator based on graphene plasma is proposed, comprising a substrate, a graphene modulation layer is covered on the substrate, a non-metallic grating layer is provided on the modulation layer by coating-etching, a metal grating layer is provided on the non-metallic grating layer by coating, and electrodes 1 and 2 are provided on both sides of the substrate by coating. By coupling the graphene with the non-metallic grating layer, the excellent polarization characteristics of the metal grating and the field confinement capability of further enhancing the graphene localized surface plasmon polaritons are utilized, thereby greatly improving the modulation depth and modulation bandwidth of the device. The structure has strong reflection for TE linearly polarized incident light, and can realize transmission modulation with high modulation depth in a wide band range for TM linearly polarized incident light. This characteristic can realize the modulation function of high modulation depth and wide modulation bandwidth for the transmitted light when natural light is incident.

Description

Technical Field

[0001] The invention relates to the technical field of optical devices, and in particular to a broadband transmission-type infrared light modulator based on graphene plasma. Background Art

[0002] Graphene is a two-dimensional material composed of a single layer of carbon atoms arranged in a honeycomb lattice structure. Its flexibility and bendability enable it to be combined with supersurface structures. Graphene also has an ultra-wide regulation bandwidth (from near-infrared to terahertz) and an ultra-high carrier mobility of up to 200,000 cm 2 / (V×s), which makes it possible to realize broadband ultrafast optoelectronic devices. As the core device in chip optical interconnection, optical modulators have very important application prospects in the future. In recent years, the research on graphene optical modulators has been widely studied by scholars at home and abroad.

[0003] In order to improve the modulation depth and modulation bandwidth of graphene optical modulators, it is necessary to enhance the interaction between light and graphene. At present, the research on graphene optical modulators mainly includes: graphene optical modulators based on waveguide structures and graphene optical modulators based on metasurfaces. For graphene optical modulators based on waveguide structures, their modulation ability has a strong dependence on the waveguide length. For example, Liu et al. coupled a single layer of graphene with a silicon waveguide and achieved a modulation depth of ~0.1 dB / μm within a 40 μm waveguide length in the near-infrared band of 1.35μm to 1.60μm by adjusting the Fermi level of graphene (see [Ming Liu, et. al., "A Graphene-Based Broadband Optical Modulator", Nature, vol. 474, no. (7349), pp. 64-67, 2011]). In addition to using waveguides to enhance the modulation ability of graphene, graphene surface plasmons can also be combined with metasurfaces to enhance the interaction between graphene and light. For example, Gao et al. laid a single-layer graphene on a silicon grating and used guided mode resonance to modulate the transmission of TM light by applying a bias voltage to graphene. When the Fermi level increased from 0.4 eV to 0.9 eV, the resonance peak frequency could be increased from 1000 cm -1 Migration to 1400 cm -1(about 7 – 10 μm), and the modulation depth can reach 10 dB (see [Weilu Gao, et. al., "Excitation of Plasmonic Waves in Graphene by Guided-Mode Resonances", Acs Nano, vol. 6, no.(9), pp. 7806-7813, 2012]). Although the above-mentioned graphene-based optical modulators have different mechanisms, the weak interaction between graphene and the electric field limits the modulation depth and modulation bandwidth of the device. Summary of the invention

[0004] The object of the present invention is to provide a broadband transmission infrared light modulator based on graphene plasma to solve the technical problems of low modulation depth and modulation bandwidth existing in the existing modulators.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a broadband transmission infrared light modulator based on graphene plasma, comprising a substrate, the substrate is covered with a modulation layer, a non-metallic grating layer is provided on the modulation layer by coating-etching, a metal grating layer is provided on the non-metallic grating layer by coating, an electrode one and an electrode two are provided on both sides of the substrate by coating respectively, and the modulation layer is graphene.

[0006] Preferably, the graphene can be directly grown or transferred onto the substrate, and can be a single layer or multiple layers of the graphene, and can be in the form of a complete piece of graphene or a graphene nanoribbon array.

[0007] Preferably, the material of the non-metallic grating layer is silicon, and is deposited on the modulation layer by a coating process to form a uniform silicon film, and the non-metallic grating layer is formed by an etching process.

[0008] Preferably, the material of the metal grating layer is aluminum, which is uniformly deposited on the upper surface of the non-metallic grating layer by a coating process and is located above the modulation layer in the slits of the non-metallic grating layer.

[0009] Preferably, the electrode is deposited on the substrate not covered by the modulation layer, and the material of the electrode can be gold, silver, or copper, and the material of the substrate is silicon.

[0010] Preferably, the second electrode is deposited above the modulation layer extending from the non-metallic grating layer, and the material of the electrode may be gold, silver or copper.

[0011] Preferably, the number of graphene layers is 15, the period of the non-metallic grating layer is P=250 nm, the height H1=700 nm, the width W=110 nm, and the thickness of the metal grating layer is H2=50 nm.

[0012] Preferably, a DC bias voltage in a vertical direction is applied to the graphene layer.

[0013] Beneficial Effects

[0014] The broadband transmission infrared light modulator based on graphene plasma provided by the present invention couples the modulation layer of graphene with the non-metallic grating layer, and utilizes the excellent polarization characteristics of the metal grating and the field confinement capability of further enhancing the graphene localized surface plasmon polaritons, thereby greatly improving the modulation depth and modulation bandwidth of the device. The structure has strong reflection for TE linearly polarized incident light, and can realize transmission modulation within a wide band for TM linearly polarized incident light. This characteristic enables the present invention to realize the modulation function of high modulation depth and wide modulation bandwidth for transmitted light when natural light is incident. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the cross-sectional structure of the present invention;

[0016] Figure 2 It is a schematic diagram of the three-dimensional structure of the present invention;

[0017] Figure 3 It is the transmittance spectrum of graphene at different Fermi levels when the incident light is TM linearly polarized light;

[0018] Figure 4 It is the transmittance spectrum of graphene at different Fermi levels when the incident light is TE linearly polarized light;

[0019] Figure 5 The electric field distribution diagram of graphene with a Fermi level of 0.3 eV and a resonance wavelength of 13.5 μm;

[0020] Figure 6 The electric field distribution diagram of graphene with a Fermi level of 0.3 eV and a wavelength of 7 μm (far away from the resonance peak);

[0021] Figure 7 It is the transmittance spectrum of different Fermi levels when the height of silicon grating H1=500 nm;

[0022] Figure 8 It is the transmittance spectrum of different Fermi levels when the height of silicon grating H1=600 nm;

[0023] Fig. 9The transmittance spectra at different Fermi levels when the height of the silicon grating is H1=700 nm.

[0024] Reference numerals

[0025] 1-substrate, 2-modulation layer, 3-non-metal grating layer, 4-metal grating layer, 5-electrode one, 6-electrode two, H1-silicon grating height, H2-metal grating layer thickness, W-silicon grating width, P-period. DETAILED DESCRIPTION

[0026] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments. Example

[0027] like Figure 1-2 As shown, a broadband transmission infrared light modulator based on graphene plasma includes a substrate 1, a modulation layer 2 is covered on the substrate 1, a non-metallic grating layer 3 is provided on the modulation layer 2 by coating-etching, a metal grating layer 4 is provided on the non-metallic grating layer 3 by coating, and an electrode 1 5 and an electrode 2 6 are provided on both sides of the substrate 1 by coating, and the modulation layer 2 is graphene.

[0028] The modulation mechanism of the present invention can be explained by the localized surface plasmon resonance excited by graphene in the infrared band. Figure 1 In the 1-substrate shown in the figure, since silicon has good transmittance in the mid-infrared and far-infrared bands, the incident light passes through the 1-substrate and reaches the 2-modulation layer, where it interacts with graphene. In the mid-infrared to terahertz bands, the special optical properties of graphene can excite surface plasmon polaritons (SPPs) and generate resonance peaks. Figure 1In the structure shown, TE linear polarized light with the electric field perpendicular to the grating line direction cannot excite surface plasmons, so it will directly pass through graphene. Part of the TE light passes through the 3-non-metallic grating layer (silicon grating) and is reflected by the 4-metallic grating layer, and the other part of the TE light passes through the graphene and is directly reflected by the 4-metallic grating layer, so the TE light cannot pass through, showing strong reflection. After passing through the 1-substrate, the TM light interacts with the 2-modulation layer (graphene), exciting surface plasmons and generating resonance peaks. However, since the metal covering the 2-modulation layer hinders the propagation of the surface plasmon along the x-direction, part of the electric field energy is reflected back, and the other part of the electric field energy is localized in the graphene below the 3-non-metallic grating layer, exciting localized surface plasmon resonance (LSPR). When it is at the resonance peak wavelength, the electric field energy is absorbed and reflected, showing a trough, which is the "OFF" state of the modulator. When it is far away from the resonance peak wavelength, the ability of graphene to constrain the electric field decreases rapidly, and the TM light passes through the 3-non-metallic grating layer and the 4-metallic grating layer and shows high transmittance, which is the "ON" state of the modulator. When a voltage is applied to the 2-modulation layer, the Fermi level of graphene will change, causing the wavelength and intensity of the resonance peak to change. The localized surface plasmon resonance greatly enhances the interaction between light and graphene, thereby greatly improving the modulation depth and modulation bandwidth of this embodiment. In addition, since the present invention shows strong reflection of TE light, when the incident light is natural light, the structure of this embodiment can achieve the modulation function of high modulation depth and wide modulation bandwidth for the transmitted light.

[0029] Preferably, the modulation layer 2 is graphene, and the graphene can be directly grown or transferred onto the substrate 1, and can be a single layer or multiple layers of graphene, and can be in the shape of a complete piece of graphene or a graphene nanoribbon array.

[0030] Preferably, the material of the non-metallic grating layer 3 is silicon, and is deposited on the modulation layer 2 by a coating process to form a uniform silicon film, and the non-metallic grating layer 3 is formed by an etching process.

[0031] Preferably, the material of the metal grating layer 4 is aluminum, which is uniformly deposited on the upper surface of the non-metal grating layer 3 by a coating process, and is located above the modulation layer 2 in the slit of the non-metal grating layer 3 .

[0032] Preferably, the electrode 5 is deposited on the substrate 1 not covered by the modulation layer 2, and the material of the electrode can be gold, silver, or copper, and the material of the substrate 1 is silicon.

[0033] Preferably, the second electrode 6 is deposited on the top of the modulation layer 2 which is the extension of the non-metal grating layer 3, and the material of the electrode can be gold, silver or copper.

[0034] Preferably, the number of graphene layers is 15, the period of the non-metallic grating layer 3 is P=250 nm, the height H=700 nm, the width W=110 nm, and the thickness H2 of the metal grating layer 4 is H2=50 nm.

[0035] Preferably, a DC bias voltage in a vertical direction is applied to the graphene layer.

[0036] Since natural light can be decomposed into two linearly polarized lights with mutually perpendicular electric field components, the TM linearly polarized light with the electric field component perpendicular to the grid line direction and the TE linearly polarized light with the electric field component parallel to the grid line direction will be discussed separately, and their transmittances are expressed as TM-T and TE-T, respectively.

[0037] like Figure 3 As shown, for TM polarized light incident, when there is no bias voltage (i.e., Ef is 0 eV), the TM light does not show strong resonance characteristics, and the transmittance is above ~0.6;

[0038] When a bias voltage is applied to graphene (i.e., when Ef is 0.1, 0.3, or 1.0 eV in the figure), TM light exhibits a strong resonance characteristic, and the resonance peak varies between 7 and 22 μm. Based on this characteristic, the function of a wide-band modulator can be realized by adjusting the Fermi level of graphene. For example, when the Fermi level Ef=1.0 eV, the transmittance of the resonance peak near a wavelength of 7 μm is close to 0, and the optical modulator is in the "OFF" state; when the Fermi level Ef is 0 eV, 0.1 eV, or 0.3 eV, the TM transmittance near 7 μm is greater than 0.7, and the optical modulator is in the "ON" state. When the Fermi level Ef is set to 0.3 eV, at this time at a resonance wavelength of 7.07 μm, the modulation depth of the TM light can reach a maximum of 99.96% (33.77 dB). Therefore, the structure of this embodiment can realize the modulation function of high modulation depth and wide modulation bandwidth for TM light.

[0039] like Figure 4 As shown in the figure, the transmittance spectra at different Fermi levels when TE light is incident are given. It can be seen that when TE light is incident, regardless of the Fermi level, its transmission intensity is close to zero and reaches more than 60 dB. This characteristic shows that the double-layer metal grating structure can effectively filter out TE light, reduce the strict requirements on the polarization state of the incident light, and realize the modulation function of the structure of this embodiment on the transmitted light when the incident light is natural light.

[0040] Since TE light cannot excite the localized surface plasmon resonance effect, only the effect of TM incident light on the modulator is discussed below. Figure 5As shown, the electric field distribution diagram at the resonance peak (wavelength of 13.5μm) when the Fermi level Ef=0.3 eV under TM incidence is given. It can be seen that the internal electric field is concentrated at the interface between graphene and silicon grating. The metallic aluminum limits the propagation of surface plasmon along the graphene surface and localizes the electromagnetic field near the graphene, which greatly enhances the localized surface plasmon of graphene and its ability to constrain the electromagnetic field.

[0041] like Figure 6 As shown, the electric field distribution diagram far away from the resonance peak (wavelength of 7 μm) is given when the Fermi level Ef = 0.3 eV under TM incidence. It can be seen that the electric field near the graphene is significantly weakened. Due to the enhanced transmission of the silicon grating, a strong electric field energy is formed in the grating slit.

[0042] In the double-layer metal grating proposed in the present invention, there is no need to etch metal aluminum, only silicon etching is required, which greatly reduces the difficulty of the experiment; in order to further investigate the influence of the height of silicon grating etching on the device performance, Figure 7 The transmittance spectra at different Fermi levels when the height of the silicon grating is H1=500 nm. Other structural parameters are: the silicon grating period is P=250nm, the grating width is W=110 nm, and the thickness of the metal aluminum is H2=50 nm. Figure 8 The transmittance spectra at different Fermi levels when the height of the silicon grating is H1=600 nm. Other structural parameters are: the silicon grating period is P=250 nm, the grating width is W=110nm, and the thickness of the metal aluminum is H2=50 nm. Fig. 9 The transmittance spectra at different Fermi levels when the height of the silicon grating is H1=700 nm. Other structural parameters are: the silicon grating period is P=250 nm, the grating width is W=110 nm, and the thickness of the metal aluminum is H2=50nm. Figure 7 , 8 , 9 respectively give the device performance at three different silicon grating heights (H1 is 500 nm, 600 nm, and 700 nm). It can be seen that the modulation depth and modulation bandwidth are almost unaffected by the heights of the silicon gratings, and only the TM absolute transmittance in the "ON" state is affected. For TM linearly polarized light, the modulator can achieve a modulation depth greater than 99.85% (28.10 dB) in the range of 7-12 μm, and a maximum modulation depth of 99.96% (33.77 dB); in the range of 12-22 μm, the modulation depth is greater than 94.57% (12.65 dB).

[0043] The present invention utilizes a silicon-based double-layer metal grating structure to realize multi-layer graphene-enhanced localized surface plasmon resonance under TM conditions, while achieving high reflection of TE light, thereby realizing the function of a transmission light modulator with high modulation depth and wide modulation range. Therefore, the structural design of the broadband transmission infrared light modulator based on graphene plasma proposed in the present invention has the advantages of natural light incident, relatively simple structure and preparation, excellent modulation depth and modulation bandwidth, etc., and has a huge application scenario in chip optical interconnection and optical computing technology.

[0044] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the invention content within the protection scope of the present invention.

Claims

1. A broadband transmission infrared light modulator based on graphene plasma, comprising a substrate (1), characterized in that: The substrate (1) is covered with a modulation layer (2), a non-metallic grating layer (3) is provided on the modulation layer (2) by coating-etching, a metal grating layer (4) is provided on the non-metallic grating layer (3) by coating, an electrode 1 (5) and an electrode 2 (6) are provided on both sides of the substrate (1) by coating, and the modulation layer (2) is graphene; The graphene is directly grown or transferred onto the substrate (1), the graphene is a single layer or multiple layers, and the graphene is in the shape of a complete piece of graphene or a graphene nanoribbon array; The material of the non-metallic grating layer (3) is silicon, and is deposited on the modulation layer (2) by a coating process to form a uniform silicon film, and the non-metallic grating layer (3) is formed by an etching process; The material of the metal grating layer (4) is aluminum, which is uniformly deposited on the upper surface of the non-metal grating layer (3) by using a coating process, and is located above the modulation layer (2) in the slit of the non-metal grating layer (3).

2. The broadband transmissive infrared light modulator based on graphene plasma according to claim 1, characterized in that: The electrode one (5) is deposited on the substrate (1) not covered by the modulation layer (2), and the material of the electrode one is selected from one of gold, silver and copper, and the material of the substrate (1) is silicon.

3. The broadband transmissive infrared light modulator based on graphene plasma according to claim 1, characterized in that: The second electrode (6) is deposited on the modulation layer (2) extending from the non-metal grating layer (3), and the material of the second electrode is selected from one of gold, silver and copper.

4. The broadband transmissive infrared light modulator based on graphene plasma according to claim 1, characterized in that: The number of graphene layers is 15, the period of the non-metallic grating layer (3) is (P) = 250nm, the height (H1) is 700nm, the width (W) is 110nm, and the thickness (H2) of the metal grating layer (4) is 50nm.

5. The broadband transmissive infrared light modulator based on graphene plasma according to claim 1, characterized in that: A DC bias voltage in a vertical direction is applied to the graphene layer.

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