A bidirectional coupler and its usage method

Abstract

The present invention discloses a bidirectional coupler and its use method, relating to the field of information optoelectronics. The bidirectional coupler comprises a boron nitride film and a graphene film, which is interlaced with the boron nitride film to form a coupling region. The bidirectional coupler can couple light waves in two directions using a single structure.

Description

Technical Field

[0001] The present invention relates to the field of information optoelectronic technology, and in particular to a bidirectional coupler and a method for using the same. Background Art

[0002] When a light wave (electromagnetic wave) is incident on the interface between metal and dielectric, the free electrons on the metal surface oscillate collectively. The electromagnetic wave couples with the free electrons on the metal surface to form a near-field electromagnetic wave that propagates along the metal surface. If the oscillation frequency of the electrons is consistent with the frequency of the incident light wave, resonance will occur. In the resonant state, the energy of the electromagnetic field is effectively converted into the collective vibration energy of the free electrons on the metal surface. At this time, a special electromagnetic mode is formed: the electromagnetic field is confined to a very small range on the metal surface and is enhanced. This phenomenon is called surface plasmon polaritons (SPP).

[0003] Due to their unique electromagnetic properties, such as high localization, field enhancement, and subwavelength transmission, surface plasmons have been intensively studied and widely applied. However, because metals behave as perfect conductors at microwave frequencies, surface plasmons cannot naturally exist in this frequency band. Consequently, artificial surface plasmons, which emerge in the microwave band at the interfaces of specially designed artificial electromagnetic materials, have been gradually studied and promoted. Because they possess properties similar to those of surface plasmons, artificial surface plasmon technology has important applications in devices such as antennas, sensors, and waveguides.

[0004] In recent years, the excitation and propagation of surface plasmons have been a hot topic in research, and the design of simple and efficient surface plasmon couplers is a pressing issue. However, most surface plasmon couplers employ unidirectional coupling, meaning they can only couple lightwaves in one direction within a single structure. However, unidirectional coupling suffers from limited design freedom and significant corner losses, severely limiting its practical application and requiring urgent solutions. Summary of the Invention

[0005] In view of the defects existing in the prior art, the first aspect of the present invention provides a bidirectional coupler, which can realize light wave coupling in two directions on the same structure.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A bidirectional coupler comprising:

[0008] Boron nitride thin films;

[0009] The graphene film is arranged alternately with the boron nitride film to form a coupling region.

[0010] In some embodiments,

[0011] The length of the coupling region satisfies: Lc=π / |N effect-graphene -N effect-hBN |, where Lc is the length of the coupling region, N effect-graphene is the effective refractive index of graphene surface plasmons, N effect-hBN is the effective refractive index of the BN surface phonon polaritons.

[0012] In some embodiments, the distance between the boron nitride film and the graphene film is 50 nm.

[0013] In some embodiments, the boron nitride film has a thickness of 50 nm.

[0014] In some embodiments, the boron nitride films and graphene films are spaced apart vertically and arranged horizontally and staggered left and right.

[0015] In some embodiments, the graphene film is a single-layer graphene.

[0016] A first aspect of the present invention provides a method for using a bidirectional coupler, which can achieve light wave coupling in two directions on the same structure.

[0017] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0018] According to the above-mentioned method for using a bidirectional coupler, the method includes the following steps:

[0019] Using mid- and far-infrared light to generate surface plasmon waves on a graphene film and surface phonon waves on a boron nitride film;

[0020] The surface plasmon wave and the surface phonon polariton wave are coupled.

[0021] In some embodiments, the present invention further comprises:

[0022] Based on the wavelength of mid- and far-infrared light and the dielectric constants of graphene and boron nitride, the effective refractive index of graphene surface plasmons and boron nitride surface phonon polaritons are calculated respectively;

[0023] According to the formula: Lc=π / |N effect-graphene -N effect-hBN |Set the length of the coupling region Lc, where N effect-graphene is the effective refractive index of graphene surface plasmons, N effect-hBN is the effective refractive index of the BN surface phonon polaritons.

[0024] In some embodiments, mid- and far-infrared light in the wavelength range of 6.22 μm-7.3 μm is used to couple the surface plasmon waves and the surface phonon polariton waves in the same direction.

[0025] In some embodiments, mid- and far-infrared light with a wavelength range of 12.05 μm-12.82 μm is used to cause the surface plasmon waves and the surface phonon polariton waves to be back-coupled.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] The bidirectional coupler of the present invention comprises graphene and boron nitride films. By staggering the graphene and boron nitride films to form a coupling region, and selecting different wavelengths of incident light waves, the same structure can achieve bidirectional light wave coupling. Compared to the existing unidirectional coupling method, this offers greater design flexibility, allowing the propagation direction to be changed according to actual conditions, effectively avoiding bending losses caused by cornering. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic structural diagram of a bidirectional coupler according to an embodiment of the present invention;

[0029] Figure 2 1 is a diagram of the electric field distribution of the coupler when the lasing wavelength is 6.4 μm in an embodiment of the present invention;

[0030] Figure 3 1 is a diagram of the electric field distribution of the coupler when the lasing wavelength is 6.5 μm in an embodiment of the present invention;

[0031] Figure 4 1 is a diagram of the electric field distribution of the coupler when the lasing wavelength is 12.3 μm in an embodiment of the present invention;

[0032] Figure 5 4 is a flow chart of a method for using a bidirectional coupler according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The following is a further detailed description of the technical solutions of the present invention (including preferred technical solutions) by means of the accompanying drawings and by listing some optional embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] In the description of this application, it should be noted that the terms "upper" and "lower" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0035] Furthermore, in this application, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

[0036] See also Figure 1 As shown, an embodiment of the present invention discloses a bidirectional coupler, which includes a boron nitride film and a graphene film.

[0037] The graphene film and the boron nitride film are arranged alternately to form a coupling region. The boron nitride film and the graphene film are arranged alternately up and down and horizontally left and right. Figure 1 What is shown in FIG is that the boron nitride film is located above the graphene film. Of course, the graphene film can also be arranged above the boron nitride film.

[0038] It is worth noting that the graphene surface can transmit surface plasmon waves, and its operating wavelength is mainly in the mid-to-far infrared band (greater than 3μm). When the mid-to-far infrared light is coupled to the surface plasmons of graphene, the wavelength of the surface plasmon waves can be reduced to tens to hundreds of nanometers.

[0039] In practice, grating structures are typically used to compensate for wavevector mismatch, effectively coupling free-space infrared light to graphene surface plasmon waves. Boron nitride surfaces support the transmission of mid-infrared surface phonon polaritons, formed by the collective oscillation of boron nitride phonon vibrations and infrared photons. These waves, similar to graphene surface plasmon waves, can significantly reduce the wavelength of the transmitted wave. The coupling mechanism is also similar to that of graphene. However, because the dielectric constant is negative in the wavelength ranges I (6.22μm-7.3μm) and II (12.05μm-12.82μm), surface phonon polaritons can be supported in these two wavelength ranges.

[0040] Generally speaking, a suitable length of the coupling region can improve the coupling efficiency. A length of the coupling region that is too long or too short is not conducive to coupling. In some preferred embodiments, the length of the coupling region is determined according to the effective refractive index of the graphene surface plasmon and the boron nitride surface phonon polaritons. The effective refractive indices of the graphene surface plasmon and the boron nitride surface phonon polaritons can be calculated by the wavelength of the incident light wave and the dielectric constant of the two-dimensional material (graphene, boron nitride), respectively. Specifically, in this embodiment, the length of the coupling region satisfies: Lc = π / |N effect-graphene -N effect-hBN |, where Lc is the length of the coupling region, N effect-graphene is the effective refractive index of graphene surface plasmons, N effect-hBN is the effective refractive index of the BN surface phonon polaritons.

[0041] The graphene film can be selected from graphene or monolayer graphene as needed, and the thickness of the boron nitride film can also be reasonably selected as needed, for example, 50 nm. Different sizes result in different effective refractive indices, thereby causing different coupling lengths between the two. In addition, the spacing between the boron nitride film and the graphene film cannot be too far, as too far will also lead to a decrease in coupling efficiency. The coupling efficiency can be determined by simulation calculation. In this embodiment, a spacing of 50 nm can obtain a relatively suitable coupling efficiency.

[0042] The following example uses a single-layer graphene and a boron nitride film with a thickness t of 50 nm and a distance g of 50 nm between the two as an example:

[0043] When the wavelength of the incident light wave is 6.4 μm, N effect-graphene =16.245μm, N effect-hBN =47.56μm, the length of the coupling region can be calculated: Lc=102nm.

[0044] When the wavelength of the incident light wave is 6.5 μm, N effect-graphene =29.02μm, N effect-hBN=15.98μm, the length of the coupling region can be calculated: Lc=250nm.

[0045] Figure 2 and Figure 3 The electric field distribution diagram of the coupler when the lasing wavelength is 6.4μm and 6.5μm respectively is given in the figure. It can be seen that the graphene surface plasmons are coupled to the surface phonon polaritons on the boron nitride surface from left to right.

[0046] When the wavelength of the incident light wave is in interval II 12.05μm-12.82μm. Here, taking the laser wavelength of 12.3μm as an example, the length of the coupling region Lc=93nm can be calculated in the same way. Figure 4 The electric field distribution diagram of the coupler at this wavelength is given. It can be seen that the surface plasmons on graphene are coupled to the surface phonon polaritons on boron nitride, and their transmission directions are opposite.

[0047] In summary, the bidirectional coupler of the present invention comprises graphene and boron nitride films. By staggering the graphene and boron nitride films to form a coupling region, and selecting different wavelengths of incident light waves, bidirectional light wave coupling can be achieved within the same structure. Compared to the existing unidirectional coupling method, this offers greater design flexibility, allowing the propagation direction to be changed according to actual conditions, effectively avoiding bending losses caused by cornering.

[0048] See also Figure 5 As shown, an embodiment of the present invention further discloses a method for using the bidirectional coupler, which includes the following steps:

[0049] S1. Use mid- and far-infrared light to generate surface plasmon waves on a graphene film, and surface phonon waves on a boron nitride film.

[0050] Specifically, step S1 includes:

[0051] S11. Calculate the effective refractive index of graphene surface plasmons and boron nitride surface phonon polaritons based on the wavelength of mid- and far-infrared light and the dielectric constants of graphene and boron nitride, respectively.

[0052] S12. According to the formula: Lc=π / |N effect-graphene -N effect-hBN |Set the length of the coupling region Lc, where N effect-graphene is the effective refractive index of graphene surface plasmons, N effect-hBN is the effective refractive index of the BN surface phonon polaritons.

[0053] S2. Couple the surface plasmon wave and the surface phonon polariton wave.

[0054] In some embodiments, mid- and far-infrared light in the wavelength range of 6.22 μm-7.3 μm is used to couple the surface plasmon waves and the surface phonon polariton waves in the same direction.

[0055] In some embodiments, mid- and far-infrared light with a wavelength range of 12.05 μm-12.82 μm is used to cause the surface plasmon waves and the surface phonon polariton waves to be back-coupled.

[0056] In some embodiments, the distance between the boron nitride film and the graphene film is 50 nm.

[0057] In some embodiments, the boron nitride film has a thickness of 50 nm.

[0058] In some embodiments, the boron nitride films and graphene films are spaced apart vertically and arranged horizontally and staggered left and right.

[0059] In some embodiments, the graphene film is a single-layer graphene.

[0060] In summary, the bidirectional coupler of the present invention achieves bidirectional light wave coupling on the same structure by staggering graphene and boron nitride films to form a coupling region and selecting different ranges of incident light wavelengths. Compared with the unidirectional coupling method in the prior art, it offers greater design freedom, allowing the propagation direction to be changed according to actual conditions, effectively avoiding bending losses caused by corners.

[0061] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A bidirectional coupler, characterized in that: include: Boron nitride thin films; A graphene film, which is alternately arranged with the boron nitride film to form a coupling region; The length of the coupling region satisfies: ,in, is the length of the coupling region, is the effective refractive index of graphene surface plasmons, is the effective refractive index of the BN surface phonon polaritons; The boron nitride film and the graphene film are arranged in an upper and lower interval and horizontally staggered manner, so that when using mid-to-far infrared light in the wavelength range of 6.22μm-7.3μm, the surface plasmon wave formed on the graphene film and the surface phonon polariton wave formed on the boron nitride film are coupled in the same direction, and when using mid-to-far infrared light in the wavelength range of 12.05μm-12.82μm, the surface plasmon wave and the surface phonon polariton wave are coupled in opposite directions.

2. A bidirectional coupler according to claim 1, characterized in that: The distance between the boron nitride film and the graphene film is 50 nm.

3. The bidirectional coupler according to claim 1, wherein: The thickness of the boron nitride film is 50 nm.

4. The bidirectional coupler according to claim 1, wherein: The graphene film is a single-layer graphene.

5. The method for using a bidirectional coupler according to claim 1, wherein: The method comprises the following steps: Using mid- and far-infrared light to generate surface plasmon waves on a graphene film and surface phonon waves on a boron nitride film; The surface plasmon wave and the surface phonon polariton wave are coupled.

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