A Phase Modulation Method Based on Phonon Polaritons

Abstract

The present invention relates to a phase modulation method based on phonon polaritons, which is applied to a phase modulation device. The phase modulation method includes: using scattered light or infrared light as incident light to irradiate the metal antenna to excite molybdenum oxide phonon polaritons derived from the molybdenum oxide layer; adjusting the chemical doping time of the graphene strip to control the carrier concentration of the graphene strip; adjusting the dispersion of the hybridization mode of graphene plasmons and the molybdenum oxide phonon polaritons to change the phase velocity of the hybridization mode of the molybdenum oxide phonon polaritons transmitted to the graphene strip region, so as to realize the phase modulation of the molybdenum oxide phonon polaritons; the graphene plasmons are generated by irradiating the graphene strip with incident light. The phase modulation method of the present invention is based on the phase modulation device described in the present invention, and realizes the continuous dynamic control of the transmission phase of molybdenum oxide phonon polaritons by changing the carrier concentration of the graphene strip.

Description

Technical Field

[0001] The present invention relates to the technical field of mid-infrared laser phase modulation, and particularly to a phase modulation method based on phonon polaritons. Background Art

[0002] Optical modulation is an important manipulation in photon and optoelectronic research. Among them, the modulation of light amplitude and phase is particularly important, and it has wide applications in wavefront control, transformation optics, phase arrays, modulators, and sensors. Traditional optical modulators include silicon (Si)-based and lithium niobate (LiNbO3) modulators. Among them, in integrated silicon photonics, it is realized by using the free carrier plasma dispersion effect. The change in the density of electrons and holes will cause changes in the refractive index and absorption of silicon, thereby achieving the modulation effect. However, these effects usually require millimeter-sized devices, which often limit the modulation efficiency and increase the modulation energy consumption. The LiNbO3 material has extremely excellent electro-optic properties and is very suitable as the basic material for electro-optic modulators, and can simultaneously achieve ultra-fast modulation, low-voltage operation, and low light loss requirements of the modulator. However, due to the limitations of processing and preparation techniques, its electro-optic efficiency is reduced, the size is increased, the overlap between the electric field and the light field is reduced, and it is not conducive to the transmission of microwave signals, resulting in the fact that lithium niobate electro-optic modulators have always been difficult to be integrated on a chip. With the increasing demand for information processing, the development of small-sized, high-efficiency, fast, low-light-loss, and broadband optical modulators has gradually become inevitable.

[0003] Compared with traditional bulk materials, two-dimensional van der Waals layered materials have shown unique advantages in light control due to their atomic layer thickness, wide spectral response range, strong light-matter interaction, flexible regulation methods, and highly compatible integration, thus attracting extensive attention. Surface plasmon polaritons and phonon polaritons have broad application prospects in the research of photons and optoelectronics due to their advantages of being able to highly localize the optical wavelength in free space, having mid-infrared and terahertz working frequency bands, and being able to stably exist at room temperature. In particular, graphene can actively regulate its plasmon characteristics through chemical doping and electrical regulation; α-MoO3 supports phonon polaritons that propagate anisotropically in the plane, and it has a long lifetime. However, surface plasmon polaritons have high Ohmic losses and relatively short lifetimes, and phonon polaritons are difficult to regulate due to being limited by the inherent lattice structure of the material. Therefore, how to overcome the above defects and achieve phase modulation of phonon polaritons is an urgent problem to be solved. Summary of the Invention

[0004] The object of the present invention is to provide a phase modulation method based on phonon polaritons, which can realize continuous dynamic regulation of the transmission phase of phonon polaritons.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] The present invention provides a phase modulation method based on phonon polaritons, which is applied to a phase modulation device. The phase adjustment device includes: a base layer, a molybdenum oxide layer, a graphene strip, and a metal antenna; the molybdenum oxide layer is disposed on the base layer, and the graphene strip and the metal antenna are disposed on the molybdenum oxide layer; a set distance is provided between the metal antenna and the graphene strip;

[0007] The phase modulation method includes:

[0008] Using scattered light or infrared light as incident light to irradiate the metal antenna to excite the molybdenum oxide layer to derive molybdenum oxide phonon polaritons;

[0009] By adjusting the chemical doping time of the graphene strip, the carrier concentration of the graphene strip is regulated; to adjust the dispersion of the hybridization mode of graphene plasmons and the molybdenum oxide phonon polaritons, and change the phase velocity of the hybridization mode of the molybdenum oxide phonon polaritons transmitted to the graphene strip region, so as to achieve phase modulation of the molybdenum oxide phonon polaritons; the graphene plasmons are generated by irradiating the graphene strip with incident light.

[0010] Optionally, the material of the base layer is a metal material, an inorganic dielectric material, or an organic polymer material.

[0011] Optionally, the planar geometric size of the molybdenum oxide layer is 10um - 500um, and the thickness of the molybdenum oxide layer is 50nm - 5um.

[0012] Optionally, the planar geometric size of the graphene strip is 5nm - 100um.

[0013] Optionally, the planar geometric size of the metal antenna is 5nm - 30um, and the thickness of the metal antenna is 5nm - 5um.

[0014] Optionally, the material of the metal antenna is one of iron, aluminum, copper, gold, silver, platinum, and steel.

[0015] Optionally, the set distance is 5nm - 10um.

[0016] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0017] The present invention provides a phase modulation method based on phonon polaritons. The method is applied to a phase modulation device, and the phase adjustment device includes: a base layer, a molybdenum oxide layer, a graphene strip, and a metal antenna; the molybdenum oxide layer is disposed on the base layer, and the graphene strip and the metal antenna are disposed on the molybdenum oxide layer; a set distance is provided between the metal antenna and the graphene strip; the phase modulation method includes: using scattered light or infrared light as incident light to irradiate the metal antenna to excite the molybdenum oxide layer to derive molybdenum oxide phonon polaritons; by adjusting the chemical doping time of the graphene strip, controlling the carrier concentration of the graphene strip; to adjust the dispersion of the hybridization mode of graphene plasmons and the molybdenum oxide phonon polaritons, and change the phase velocity of the hybridization mode of the molybdenum oxide phonon polaritons transmitted to the graphene strip region, so as to realize the phase modulation of the molybdenum oxide phonon polaritons; the graphene plasmons are generated by irradiating the graphene strip with incident light. The phase modulation method of the present invention is based on the phase modulation device of the present invention, and realizes continuous dynamic control of the transmission phase of the molybdenum oxide phonon polaritons by changing the carrier concentration of the graphene strip. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings without creative efforts.

[0019] Figure 1 It is a schematic structural diagram of the phase modulation device of the present invention;

[0020] Figure 2 It is an atomic force microscope image corresponding to the optical photograph of the phase modulation device;

[0021] Figure 3 It is the phase change of the molybdenum oxide phonon polaritons excited by the metal antenna on the left side of the graphene strip with different Fermi levels transmitted to the right side of the graphene strip and the corresponding real-space simulation image;

[0022] Figure 4 It is an experimental image of the phase change of the molybdenum oxide phonon polaritons at different Fermi levels of the graphene strip and different incident light frequencies;

[0023] Figure 5 It represents the relationship between different Fermi levels of the graphene strip and different incident wave numbers and phase offsets;

[0024] Figure 6The phase difference between the phase of the phonon polaritons excited by the metal antenna on the left side and transmitted to the right side of the graphene strip and the transmission phase without the graphene strip as a function of the Fermi level of the graphene strip for different incident light frequencies.

[0025] Symbol description:

[0026] Substrate layer - 1, molybdenum oxide layer - 2, graphene strip - 3, metal antenna - 4, mid-infrared scattering type scanning near-field optical microscope - 5, chemically doped molecular adsorption layer - 6. Specific implementation manner

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to 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 of 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.

[0028] The object of the present invention is to provide a phase modulation method based on phonon polaritons, which can realize continuous dynamic regulation of the transmission phase of phonon polaritons.

[0029] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0030] A phase modulation method based on phonon polaritons of the present invention is applied to a phase modulation device, such as Figure 1 As shown, the phase adjustment device includes: a substrate layer 1, a molybdenum oxide layer 2, a graphene strip 3 and a metal antenna 4; the molybdenum oxide layer 2 is disposed on the substrate layer 1, and the graphene strip 3 and the metal antenna 4 are disposed on the molybdenum oxide layer 2; a set distance is provided between the metal antenna 4 and the graphene strip 3. Figure 2 Is the atomic force microscope image corresponding to the optical photograph of the phase modulation device. Figure 2 The left rod-shaped structure in [figure] is the metal antenna 4, and the middle strip-shaped structure is the graphene strip 3. The metal antenna and the graphene strip 3 are located on the molybdenum oxide layer 2.

[0031] Specifically, the material of the substrate layer 1 is a flat metal material or an inorganic dielectric material or an organic polymer material. The metal materials include iron, aluminum, copper, gold, silver, platinum, and steel. The inorganic dielectric materials include silicon dioxide, silicon, quartz, sapphire, germanium, aluminum oxide, boron nitride, calcium fluoride, magnesium fluoride, gallium arsenide, and gallium nitride. The organic polymer materials include PET, PMMA, PDMS, and plastics.

[0032] Specifically, the planar geometric size of the molybdenum oxide layer is 10 um - 500 um, and the thickness of the molybdenum oxide layer is 50 nm - 5 um.

[0033] Furthermore, the planar geometric size of the graphene strip is 5 nm - 100 um.

[0034] Specifically, the planar geometric size of the metal antenna is 5 nm - 30 um, and the thickness of the metal antenna is 5 nm - 5 um.

[0035] Preferably, the material of the metal antenna is one of iron, aluminum, copper, gold, silver, platinum, and steel. Among them, the shape of the metal antenna can be rod-shaped, cuboid, ellipsoid, disc, and other structures.

[0036] Preferably, the set distance is 5 nm - 10 um.

[0037] Furthermore, the phase modulation device further includes: a chemically doped molecular adsorption layer 6.

[0038] Furthermore, the phase modulation method includes the following steps:

[0039] S1: Use scattered light or infrared light as the incident light to irradiate the metal antenna 4, and excite the molybdenum oxide layer 2 to generate molybdenum oxide phonon polaritons. Specifically, the metal antenna 4 can be directly irradiated by the scattered light of the tip of the mid-infrared scattering-type scanning near-field optical microscope 5.

[0040] S2: By adjusting the chemical doping time of the graphene strip 3, control the carrier concentration of the graphene strip 3; to adjust the dispersion of the hybridization mode of graphene plasmons and the molybdenum oxide phonon polaritons, and change the phase velocity of the hybridization mode of the molybdenum oxide phonon polaritons transmitted to the region of the graphene strip 3, so as to realize the phase modulation of the molybdenum oxide phonon polaritons; the graphene plasmons are generated by irradiating the graphene strip 3 with incident light.

[0041] Furthermore, in step S1, scan to obtain the near-field image of the molybdenum oxide phonon polaritons transmitted from one side of the graphene strip 3 to the other side of the graphene strip 3, and extract the transmission curve of the molybdenum oxide phonon polaritons on the other side of the graphene strip 3.

[0042] In step S2, adjust the chemical doping time of the graphene strip 3, control the carrier concentration of the graphene strip 3, repeat step S1, and then obtain the near-field image and transmission curve of the molybdenum oxide phonon polaritons at different graphene Fermi levels. Repeat step S2 until the phase modulation of the molybdenum oxide phonon polaritons reaches 2π.

[0043] Figure 3 Indicating at the incident wave number of 893 cm-1 When [conditions], the phase change of the molybdenum oxide phonon polaritons excited by the left metal antenna in the case of graphene strips with different Fermi levels and the corresponding real-space simulation images transmitted to the right side of the graphene strips. Figure 3 a - c successively represent that at the incident wave number of 893 cm -1 Under the condition, when the Fermi energy is 0 eV (a), 0.6 eV (b), and 0.7 eV (c), the phase difference between the phase of the molybdenum oxide phonon polaritons excited by irradiating the left metal antenna 4 and transmitted to the right side of the graphene strip and the phase without the graphene strip 3. Figure 3 d - f represent the results of the real-space simulation images corresponding to experiments 3a - c. Among them, the upper region H represents the simulation image corresponding to the case with the graphene strip, and the lower region K represents the simulation image corresponding to the case without the graphene strip.

[0044] It can be clearly seen from the experimental and simulation results that as the Fermi level of graphene increases, the phase difference between the phase of the molybdenum oxide phonon polaritons transmitted to the right side of the graphene strip and the phase without the graphene strip gradually becomes larger, indicating the effect of the graphene Fermi level on the phase modulation of the molybdenum oxide phonon polaritons.

[0045] Furthermore, under each different graphene Fermi energy condition, the incident light frequency is changed, and step S1 is repeated to obtain the near-field images and transmission curves of the molybdenum oxide phonon polaritons at different frequencies under the same Fermi level condition. Figure 4 The experimental images of the phase change of the molybdenum oxide phonon polaritons at different Fermi levels and different incident light frequencies.

[0046] Figure 4 It represents that when the Fermi levels are 0.2 eV, 0.6 eV, and 0.7 eV in sequence, the corresponding incident light frequencies are 893 cm -1 , 900 cm -1 , 905 cm -1 The phase difference between the phase of the molybdenum oxide phonon polaritons excited by the left metal antenna 3 and transmitted to the right side of the graphene strip 3 and the phase without the graphene strip. The experimental results show that under the same graphene Fermi level condition, for different incident frequencies, the molybdenum oxide phonon polaritons excited by infrared light can all achieve phase modulation, demonstrating a wide-band phase modulation effect.

[0047] As Figure 4 shown, Figure 4 in Figure 4 a, Figure 4 b, Figure 4 c represent that when the graphene Fermi level is 0.2 eV, the incident light frequencies are 893 cm -1 , 900 cm -1 , 905 cm -1The phase difference between when the molybdenum oxide phonon polaritons are transmitted to the right side of the graphene strip and the phase without the graphene strip; similarly, Figure 4 d, Figure 4 e, Figure 4 f shows the phase difference between when the molybdenum oxide phonon polaritons are transmitted to the right side of the graphene strip and the phase without the graphene strip at three different incident light frequencies when the Fermi level of graphene is 0.6 eV; Figure 4 g, Figure 4 h, Figure 4 i shows the phase difference between when the molybdenum oxide phonon polaritons are transmitted to the right side of the graphene strip and the phase without the graphene strip at three different incident light frequencies when the Fermi level of graphene is 0.7 eV.

[0048] Figure 5 Represents the relationship between different Fermi levels and different incident wave numbers and phase shifts. Figure 5 Represents that at incident light frequencies of 893 cm -1 , 900 cm -1 , 905 cm -1 in turn, the transmission curves of the molybdenum oxide phonon polaritons excited by the left metal antenna transmitted to the right side of the graphene strip position in the case of no graphene strip and graphene strips with different Fermi levels.

[0049] Figure 5 a, Figure 5 b, Figure 5 c in turn represent the transmission curves of the molybdenum oxide phonon polaritons excited by the left metal antenna transmitted to the left side of the graphene strip in the case of no graphene strip and graphene strips with different Fermi levels at incident light frequencies of 893 cm -1 , 900 cm -1 , 905 cm -1 in turn. Figure 5 d, Figure 5 e, Figure 5 f in turn represent the transmission curves of the molybdenum oxide phonon polaritons excited by the left metal antenna transmitted through the right side of the graphene strip in the case of no graphene strip and graphene strips with different Fermi levels at incident light frequencies of 893 cm -1 , 900 cm -1 , 905 cm -1 in turn. Figure 6 Represents the change trend of the phase difference between the phase of the molybdenum oxide phonon polaritons excited by the left metal antenna transmitted to the right side of the graphene strip and the transmission phase without the graphene strip with the Fermi level of the graphene strip at incident light frequencies of 893 cm -1 , 900 cm -1 , 905 cm -1 in turn.

[0050] It can be seen from the transmission curve that at the same incident light frequency, as the Fermi energy increases, the phase of the molybdenum oxide phonon polariton remains basically unchanged before it is transmitted to the left side of the graphene strip; when the molybdenum oxide phonon polariton is transmitted to the right side of the graphene strip, due to the modulation of the middle graphene strip, the phase difference between it and the phase without the graphene strip gradually increases, and a similar change trend can be obtained at different incident light frequencies, verifying the effective modulation result of the graphene Fermi level on the phase of the molybdenum oxide phonon polariton.

[0051] In addition, the present invention also provides a method for fabricating and characterizing a phase modulation device for molybdenum oxide phonon polaritons, including the following steps:

[0052] Step 1: Select a substrate material and prepare the substrate. The substrate material can be any flat metal material, inorganic dielectric material, organic polymer material, etc. For example, in some embodiments, the metal material can be selected from iron, aluminum, copper, gold, silver, platinum, and steel. In some embodiments, the inorganic dielectric material can be selected from silicon dioxide, silicon, quartz, sapphire, germanium, aluminum oxide, boron nitride, calcium fluoride, magnesium fluoride, gallium arsenide, and gallium nitride. In some embodiments, the organic polymer material can be selected from PET, PMMA, PDMS, and plastics.

[0053] Step 2: Prepare a molybdenum oxide layer and place the molybdenum oxide on the above-mentioned substrate. The crystal plane orientation of the molybdenum oxide is (010). According to the embodiments of the present invention, the planar geometric size of the molybdenum oxide thin layer is 10 μm - 500 μm, and the thickness is 50 nm - 5 μm.

[0054] Step 3: Prepare a single-layer graphene strip and transfer the graphene strip onto the molybdenum oxide. The planar geometric size of the graphene strip is 5 nm - 100 μm.

[0055] Step 4: Select the material, shape, and size of the antenna, and fabricate a metal antenna on one side of the graphene strip on the molybdenum oxide. The metal antenna material can be selected from iron, aluminum, copper, gold, silver, platinum, and steel. The metal antenna shape can be rod-shaped, cuboid, ellipsoid, or disk; the geometric size of the metal antenna is 5 nm - 30 μm, the thickness is 5 nm - 5 μm, and the distance from the graphene boundary is 5 nm - 10 μm. In this embodiment, a rod-shaped metal antenna is taken as an example.

[0056] Step 5: Select horizontally polarized light to be incident on the metal antenna to excite the molybdenum oxide layer to derive molybdenum oxide phonon polaritons.

[0057] Step 6: Change the chemical doping time of the graphene strip, adjust the graphene carrier concentration, and obtain different degrees of phase modulation results.

[0058] In this specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other.

[0059] Specific examples are used in this article to elaborate on the principles and implementation manners of the present invention. The descriptions of the above embodiments are only used to help understand the method of the present invention and its core idea. At the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation on the present invention.

Claims

1. A phase modulation method based on phonon polaritons, characterized in that The method is applied to a phase modulation device, and the phase adjustment device includes: a base layer, a molybdenum oxide layer, a graphene strip, and a metal antenna; the molybdenum oxide layer is disposed on the base layer, and the graphene strip and the metal antenna are disposed on the molybdenum oxide layer; a set distance is provided between the metal antenna and the graphene strip; The phase modulation method includes: Using scattered light or infrared light as incident light to irradiate the metal antenna to excite the molybdenum oxide layer to generate molybdenum oxide phonon polaritons; By adjusting the chemical doping time of the graphene strip, the carrier concentration of the graphene strip is regulated; to adjust the dispersion of the hybridization mode of the graphene plasmon and the molybdenum oxide phonon polariton, and change the phase velocity of the hybridization mode of the molybdenum oxide phonon polariton transmitted to the graphene strip region, so as to realize the phase modulation of the molybdenum oxide phonon polariton; the graphene plasmon is generated by irradiating the graphene strip with incident light; The material of the base layer is a metal material, an inorganic dielectric material, or an organic polymer material; The set distance is 5 nm - 10 μm.

2. The phase modulation method based on phonon polaritons according to claim 1, characterized in that The planar geometric size of the molybdenum oxide layer is 10 μm - 500 μm, and the thickness of the molybdenum oxide layer is 50 nm - 5 μm.

3. The phase modulation method based on phonon polaritons according to claim 1, characterized in that The planar geometric size of the graphene strip is 5 nm - 100 μm.

4. The phase modulation method based on phonon polaritons according to claim 1, wherein The planar geometric size of the metal antenna is 5 nm - 30 μm, and the thickness of the metal antenna is 5 nm - 5 μm.

5. The phase modulation method based on phonon polaritons according to claim 1, wherein The material of the metal antenna is one of iron, aluminum, copper, gold, silver, platinum, and steel.

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