On-chip optical coupling system based on metasurface and coupling method of free-space incident light and on-chip waveguide

Abstract

The disclosure provides a kind of on-chip optical coupling system based on super surface and the coupling method of free space incident light and on-chip waveguide, the on-chip optical coupling system based on super surface includes metal substrate, SiO2 film, super surface coupler and on-chip waveguide.SiO2 film is set on metal substrate, the shape of SiO2 film is fan-shaped;Super surface coupler is set on SiO2 film, super surface coupler is suitable for converting free space incident light into surface plasmon, and inducing surface plasmon to spread to the fan-shaped tip of SiO2 film, and form focused plasmon;One end of on-chip waveguide is coupled with the fan-shaped tip of SiO2 film, to convert focused plasmon into guided wave mode, realize the transmission of TM guided wave mode in on-chip waveguide;Super surface coupler includes a plurality of fan-shaped artificial atoms arranged, the range of corresponding central angle of fan-shaped includes 30°~180°, to realize the collection of free space incident light in larger field of view range.

Description

Technical Field

[0001] At least one embodiment of this disclosure relates to the field of micro-nano optoelectronic integration technology, and more specifically to an on-chip optical coupling system based on metasurfaces and a coupling method for free-space incident light with an on-chip waveguide. Background Technology

[0002] In the post-Moore's Law era, silicon photonics integration technology possesses significant development potential due to its combination of the large scale and high precision of microelectronics with the high speed and low power consumption of photonics. Optical coupling is a key technology for silicon photonic chips. There are two main methods for coupling incident light to the waveguide: fiber-waveguide coupling and free-space light-waveguide coupling. Fiber-waveguide coupling is further divided into end-face horizontal coupling and on-chip vertical coupling. End-face horizontal coupling expands the mode field of the single-mode waveguide at the waveguide end using a mode converter, and at the fiber end, the single-mode fiber is tapered to form a tapered lens fiber, reducing the fiber mode field and achieving efficient coupling between the waveguide and the fiber. This coupling method typically provides high coupling efficiency, large coupling bandwidth, and low polarization sensitivity; however, the fabrication process is complex and requires high precision, generally necessitating exposure processes below 100 nanometers. Traditional vertical couplers based on the principle of grating diffraction employ a surface coupling method where the fiber surface and the grating surface are directly connected. To reduce coupling loss caused by mode mismatch, the grating size needs to be similar to the fiber size, and the incident angle needs to be close to the diffraction angle of the grating, thus limiting the range of receiving angles. The coupling of free-space light to waveguides, whether end-face coupling or vertical coupling, is very inefficient due to mode mismatch. With the continuous development of photonic integration, miniaturization, high integration, and the ability to control free-space light have become key areas for improving the performance of on-chip couplers. However, due to constraints such as wave vector mismatch and mode volume differences, it is difficult to efficiently couple external free-space light to the on-chip optical system and convert it into a guided wave mode.

[0003] For example, patent document CN115079342A, "Surface Plasmon Polariton On-Chip Optical Device Coupling System Based on Geometric Phase Metasurface," describes an on-chip optical coupling device that only allows free-space light within a single field of view to be incident perpendicularly. This results in a very limited receiving field of view and a large focused spot size, and it does not yet achieve efficient conversion from surface plasmon polariton (SPP) waves to in-plane guided wave modes. Another example is patent document CN113687465A, "Surface Plasmon Near-Field Focusing Lens Based on All-Dielectric Metasurface." This patent document describes a surface plasmon near-field focusing lens based on an all-dielectric metasurface that uses a fan-shaped metasurface and a metal substrate to converge SPP to a focal point, increasing lateral constraint and generating a focused spot that breaks the diffraction limit at the lens's focal point. However, this lens suffers from high loss and difficulty in guiding light into the waveguide.

[0004] On-chip couplers in related technologies are generally designed for fiber mode fields. Due to the small size of the waveguide and the difficulty in mode matching between the waveguide and the incident light in free space, the coupling loss is very large. This results in problems such as a small field of view when the incident light in free space is coupled to the waveguide, limited ability to receive incident light in free space, and low coupling efficiency of the on-chip coupler. Summary of the Invention

[0005] To address at least one technical problem mentioned above and in other aspects in the prior art, this disclosure provides an on-chip optical coupling system based on a metasurface and a coupling method between free-space incident light and an on-chip waveguide. This system can collect free-space incident light within a large field of view, expand the field of view for collecting free-space incident light, improve the ability to receive free-space incident light, and improve the coupling efficiency of the on-chip optical coupling system.

[0006] According to a first aspect of this disclosure, an on-chip optical coupling system based on a metasurface is provided, comprising:

[0007] metal substrate;

[0008] A SiO2 thin film is disposed on the metal substrate, and the SiO2 thin film is fan-shaped.

[0009] A metasurface coupler is disposed on the SiO2 thin film. The metasurface coupler is suitable for converting free space incident light into surface plasmons and inducing the surface plasmons to propagate toward the fan-shaped tip of the SiO2 thin film to form focused plasmons.

[0010] An on-chip waveguide, one end of which is coupled to the fan-shaped tip of the SiO2 thin film, to convert the focused plasmon into a guided wave mode and realize the transmission of the guided wave mode within the on-chip waveguide.

[0011] The aforementioned metasurface coupler comprises multiple artificial atoms arranged in a fan shape, with the central angle corresponding to the fan shape being... The range includes 30° to 180° to achieve the collection of the aforementioned free-space incident light over a larger field of view.

[0012] According to embodiments of the present disclosure, the SiO2 thin film has multiple rows of artificial atoms arranged in the radial direction of the fan-shaped structure, and each row of artificial atoms includes multiple columns of artificial atoms arranged in the circumferential direction.

[0013] According to an embodiment of this disclosure, the artificial atom comprises 11 rows and 101 columns, and a total of 1111 artificial atoms are provided.

[0014] According to embodiments of this disclosure, the radius R of the fan-shaped SiO2 thin film is approximately 15 μm, and the angle between two adjacent rows of artificial atoms is... The included angles satisfy the formula:

[0015]

[0016] in, The period represents each of the aforementioned artificial atoms. This represents the distance between the artificial atom in the 6th row of the 11 rows and the fan-shaped tip of the SiO2 thin film.

[0017] According to embodiments of this disclosure, each of the above-mentioned artificial atoms includes a first Ag layer, a first SiO2 layer, and a second Ag layer arranged sequentially from bottom to top;

[0018] Each of the aforementioned artificial atoms is equivalent to a half-wave plate to realize the conversion of the aforementioned free-space incident light into the aforementioned surface plasmons; the aforementioned first Ag layer, first SiO2 layer and second Ag layer are all rectangular in shape, and the perpendicular bisectors of the geometric centers of the aforementioned first Ag layer, first SiO2 layer and second Ag layer coincide with each other.

[0019] According to embodiments of this disclosure, the first Ag layer has a height h1 = 80 nm, a length a1 = P = 300 nm, and a width b1 = P = 300 nm; the first SiO2 layer has a height h2 = 70 nm, a length a2 = P = 300 nm, and a width b2 = P = 300 nm; and the second Ag layer has a height h3 = 30 nm, a length a3 = 215 nm, and a width b3 = 130 nm.

[0020] According to embodiments of this disclosure, the artificial atoms are arranged in the radial and circumferential directions of the fan-shaped structure of the SiO2 thin film.

[0021] In the aforementioned radial direction, the aforementioned artificial atoms satisfy a geometric phase gradient distribution;

[0022] In the aforementioned circumferential direction, the aforementioned angle exists between two adjacent columns of the aforementioned artificial atoms, causing multiple columns of the aforementioned artificial atoms to form a fan-shaped structure, thereby inducing the aforementioned surface plasmons to be transported to the fan-shaped tip of the aforementioned SiO2 thin film and converge to the fan-shaped tip of the aforementioned SiO2 thin film.

[0023] The above geometric phase gradient distribution satisfies:

[0024]

[0025] in, The reflection phase distribution of the above metasurface coupler along the x-axis; The initial phase is a constant. Let be the wave vector of the aforementioned surface plasmons.

[0026] According to an embodiment of the present disclosure, the metal substrate includes an Ag thin film substrate, the Ag thin film substrate is rectangular in shape, and the thickness of the Ag thin film substrate is about 80 nm, so as to ensure that the surface plasmons cannot be transmitted through the Ag thin film substrate.

[0027] According to an embodiment of the present disclosure, the thickness of the SiO2 film is about 70 nm. The SiO2 film is suitable for increasing the lateral confinement of the surface plasmons to improve the efficiency of the surface plasmons converging to the fan-shaped tip of the SiO2 film.

[0028] According to embodiments of this disclosure, the height of the on-chip waveguide includes 750 nm and the width includes 600 nm to ensure the stability of the waveguide mode transmission within the on-chip waveguide.

[0029] According to a second aspect of this disclosure, a coupling method between free-space incident light and an on-chip waveguide is provided, applied to the aforementioned metasurface-based on-chip optical coupling system, the method comprising:

[0030] The above-mentioned metasurface coupler is used to convert free space incident light into surface plasmons, and induces the surface plasmons to propagate to the fan-shaped tip of the SiO2 thin film to form focused plasmons.

[0031] The focused plasmon is coupled using an on-chip waveguide and converted into a guided wave mode to achieve the transmission of the guided wave mode within the on-chip waveguide.

[0032] In this embodiment, one end of the on-chip waveguide is connected to the fan-shaped tip of the SiO2 thin film, and the metasurface coupler comprises multiple artificial atoms arranged in a fan shape, with the central angle corresponding to the fan shape being... The range includes 30° to 180° to achieve the collection of the aforementioned free-space incident light over a larger field of view.

[0033] According to embodiments of this disclosure, the artificial atoms arranged in a fan shape in the metasurface coupler 3 are used to induce the surface plasmons to be transmitted to the fan-shaped tip of the SiO2 thin film, and the surface plasmons are gathered to the fan-shaped tip of the SiO2 thin film.

[0034] According to embodiments of this disclosure, by setting up a metasurface-based on-chip optical coupling system including a metal substrate, a SiO2 thin film, a metasurface coupler, and an on-chip waveguide, free-space incident light is converted into surface plasmons by the metasurface coupler, and the surface plasmons are induced to propagate towards the fan-shaped tip of the SiO2 thin film to form focused plasmons. One end of the on-chip waveguide is coupled to the fan-shaped tip of the SiO2 thin film, and the focused plasmons are converted into guided wave modes by the on-chip waveguide, realizing the transmission of guided wave modes within the on-chip waveguide. This disclosure, based on the metasurface coupler, can collect free-space incident light within a large field of view, expanding the field of view range for collecting free-space incident light, improving the receiving capability of free-space incident light, and improving the coupling efficiency of the on-chip optical coupling system. Attached Figure Description

[0035] The foregoing contents, as well as other objects, features, and advantages of this disclosure, will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0036] Figure 1 This schematic diagram illustrates the working principle of an on-chip optical coupling system based on a metasurface according to an embodiment of the present disclosure;

[0037] Figure 2 A top view of a metasurface-based on-chip optical coupling system according to an embodiment of the present disclosure is shown schematically.

[0038] Figure 3 The diagram illustrates the radial distribution of two adjacent columns of artificial atoms in a fan-shaped SiO2 thin film in an on-chip optical coupling system based on a metasurface according to an embodiment of the present disclosure.

[0039] Figure 4 The diagram schematically illustrates the compositional structure of artificial atoms in a metasurface-based on-chip optical coupling system according to an embodiment of the present disclosure;

[0040] Figure 5 A schematic diagram of an artificial atom with a rotation angle in a metasurface-based on-chip optical coupling system according to an embodiment of the present disclosure is shown.

[0041] Figure 6 A flowchart illustrating a method for coupling free-space incident light with an on-chip waveguide according to an embodiment of the present disclosure is shown schematically.

[0042] Figure 7 The surface optical field E of a metasurface coupler according to an embodiment of the present disclosure is schematically illustrated. z The distribution simulation results are shown in the figure.

[0043] Figure 8 The schematic diagram illustrates the mode field E of a cross-section of an on-chip waveguide according to an embodiment of the present disclosure.z The distribution simulation results are shown in the figure.

[0044] Figure 9 This schematically illustrates the optical field E during the coupling of free-space incident light into an on-chip waveguide using a metasurface-based on-chip optical coupling system according to embodiments of the present disclosure. z The distribution simulation results are shown in the figure; and

[0045] Figure 10 The illustration schematically shows the conversion efficiency of free-space incident light into surface plasmonic laser at different incident angles according to embodiments of the present disclosure.

[0046] The meanings of the reference numerals in the above figures are as follows:

[0047] 1-Metal substrate;

[0048] 2- SiO2 film;

[0049] 3-Metasurface Coupler;

[0050] 31-Artificial Atom;

[0051] 311 - First Ag layer;

[0052] 312 - First SiO2 layer;

[0053] 313 - Second Ag layer;

[0054] 4-On-chip waveguide. Detailed Implementation

[0055] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0056] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0057] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0058] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0059] In related technologies, the coupling of free space light to waveguides, whether end-face coupling or vertical coupling, is very inefficient due to the mode field mismatch problem. Due to the constraints of wave vector mismatch and mode volume differences, it is difficult for external free space light to be efficiently coupled to the on-chip optical system and converted into guided wave modes.

[0060] Current on-chip couplers are generally designed for fiber mode fields. Due to the small size of the waveguide and the difficulty in mode matching between the waveguide and the free space incident light, the coupling loss is very large. There are problems such as small field of view when free space incident light is coupled to the waveguide, limited ability to receive free space incident light, and low coupling efficiency of on-chip couplers.

[0061] In view of this, this disclosure provides an on-chip optical coupling system based on metasurfaces. By setting up an on-chip optical coupling system including a metal substrate, a SiO2 thin film, a metasurface coupler, and an on-chip waveguide, the metasurface coupler converts free-space incident light into surface plasmons and induces these surface plasmons to propagate towards the fan-shaped tip of the SiO2 thin film, forming focused plasmons. One end of the on-chip waveguide is coupled to the fan-shaped tip of the SiO2 thin film, and the focused plasmons are converted into guided wave modes through the on-chip waveguide, realizing the transmission of the guided wave modes within the on-chip waveguide. This disclosure, based on the metasurface coupler, can collect free-space incident light within a large field of view, expanding the field of view for collecting free-space incident light, improving the receiving capability of free-space incident light, and increasing the coupling efficiency of the on-chip optical coupling system.

[0062] Figure 1 This schematic diagram illustrates the working principle of an on-chip optical coupling system based on a metasurface according to an embodiment of the present disclosure; Figure 2 A top view of a metasurface-based on-chip optical coupling system according to an embodiment of the present disclosure is shown schematically.

[0063] According to some embodiments of this disclosure, such as Figure 1and Figure 2 As shown, the above-mentioned on-chip optical coupling system based on metasurfaces includes a metal substrate 1, a SiO2 thin film 2, a metasurface coupler 3, and an on-chip waveguide 4. The SiO2 thin film 2 is disposed on the metal substrate 1, and the shape of the SiO2 thin film 2 is fan-shaped. The metasurface coupler 3 is disposed on the SiO2 thin film 2. The metasurface coupler 3 is suitable for converting free-space incident light into surface plasmons and inducing the surface plasmons to propagate towards the fan-shaped tip of the SiO2 thin film 2 to form focused plasmons. One end of the on-chip waveguide 4 is coupled to the fan-shaped tip of the SiO2 thin film 2 to convert the focused plasmons into guided wave modes, thereby realizing the transmission of the guided wave modes within the on-chip waveguide 4.

[0064] According to some embodiments of this disclosure, such as Figure 1 and Figure 2 As shown, the metasurface coupler 3 includes multiple artificial atoms 31 arranged in a fan shape, with the central angle corresponding to the fan shape being... The range includes 30° to 180° to achieve the collection of free-space incident light with a large field of view.

[0065] According to some embodiments of this disclosure, free-space incident light is converted into surface plasmons by setting a metasurface coupler 3, and the surface plasmons are induced to propagate towards the fan-shaped tip of the SiO2 thin film 2 to form focused plasmons; an on-chip waveguide 4 is set with one end coupled to the fan-shaped tip of the SiO2 thin film 2 to convert the focused plasmons into a guided wave mode, realizing the transmission of the guided wave mode in the on-chip waveguide 4; a metal substrate 1 is set to support the SiO2 thin film 2 and the metasurface coupler 3; it can collect free-space incident light within a large field of view, improve the ability to receive free-space incident light, enhance the ability to control free-space incident light, and improve the conversion efficiency of free-space incident light into surface plasmons, the focusing ability of surface plasmons, and the coupling efficiency of the on-chip optical coupling system.

[0066] According to some embodiments of this disclosure, the waveguide mode can be a transverse magnetic (TM) waveguide mode, which refers to a propagation mode in which the magnetic field component in the waveguide is perpendicular to the propagation direction.

[0067] According to some embodiments of this disclosure, the free-space incident light includes left-handed circularly polarized (LCP) light. In the case of a single dimension, the incident angle of the free-space incident light using the metasurface coupler 3 ranges from -30° to 30°; due to the fan-shaped structure of the metasurface coupler 3, the collection range of the free-space incident light can be extended from one dimension to two dimensions. In the two-dimensional case, such as... Figure 1As shown, the xyz axes form the established three-dimensional coordinate system. The x-axis is parallel to the axis of the on-chip waveguide 4, and the y-axis is perpendicular to the axis of the on-chip waveguide 4. The incident angle of the incident light in free space along the x-axis is... The range and the incident angle of the free space incident light along the y-axis direction The range includes -30° to 30°. As the incident angle increases, the field of view in the x-axis and y-axis directions also increases, which can collect free space incident light within a larger field of view, improve the ability to receive free space incident light, and enhance the ability to control free space incident light.

[0068] According to some embodiments of this disclosure, the metasurface coupler 3 is composed of multiple artificial atoms 31 arranged in a fan shape. Based on the fan-shaped structure formed by the multiple artificial atoms 31, free-space incident light can be converted into surface plasmons, and the surface plasmons are induced to propagate towards the fan-shaped tip of the SiO2 thin film 2 to form focused plasmons. The focused plasmons converge at the fan-shaped tip of the SiO2 thin film 2 to form a focused light spot, which is a light spot that breaks the diffraction limit. Finally, at the connection between one end of the on-chip waveguide 4 and the fan-shaped tip of the SiO2 thin film 2, the focused plasmons are coupled into the on-chip waveguide 4. At this time, the focused plasmons are converted into an in-plane propagating guided wave mode. The guided wave refers to the electromagnetic wave propagating in the on-chip waveguide 4. The energy of the electromagnetic wave is mainly concentrated inside the waveguide structure and propagates along the axial direction of the on-chip waveguide 4. During the propagation of the electromagnetic wave, the electric field and magnetic field components of the electromagnetic wave exhibit a specific distribution pattern on the cross-section of the on-chip waveguide 4. These distribution patterns depend on the geometry, size, and operating frequency of the on-chip waveguide 4. According to some embodiments of this disclosure, the full width at half maximum (FWHM) of the focused spot formed by the convergence of focused plasmons at the fan-shaped tip of the SiO2 thin film 2 is 423.7 nm, which breaks the diffraction limit and improves the coupling efficiency between the focused plasmons and the on-chip waveguide 4.

[0069] According to some embodiments of this disclosure, the diffraction limit refers to the limitation that when an ideal object point is imaged by an optical system, an ideal image point cannot be obtained due to diffraction; instead, a Fraunhofer diffraction image is obtained. A focused spot is a spot that breaks the diffraction limit, meaning that the size of the focused spot is smaller than the diffraction-limited size, and the focused spot can achieve higher resolution.

[0070] According to some embodiments of this disclosure, such as Figure 1 and Figure 2 As shown, the SiO2 thin film 2 has multiple rows of artificial atoms 31 arranged in the radial direction of the fan shape, and each row of artificial atoms 31 includes multiple columns of artificial atoms 31 arranged in the circumferential direction.

[0071] According to some embodiments of this disclosure, the artificial atoms 31 include 11 rows and 101 columns. The artificial atoms 31 are periodically extended into an 11×101 array in the two-dimensional plane of the fan-shaped SiO2 thin film 2, with a period of P, forming a geometric phase metasurface. A total of 1111 artificial atoms 31 are provided.

[0072] According to some embodiments of this disclosure, each artificial atom 31 has a rectangular structure, and the artificial atom 31 can be rotated by a certain angle. It converts circularly polarized light of a certain chirality incident in free space into circularly polarized light of the opposite chirality with a phase change.

[0073] Figure 3 The diagram illustrates the radial distribution of two adjacent columns of artificial atoms in a fan-shaped SiO2 thin film in an on-chip optical coupling system based on a metasurface according to an embodiment of the present disclosure.

[0074] According to some embodiments of this disclosure, such as Figure 3 As shown, the radius R of the fan-shaped SiO2 thin film 2 is approximately 15 μm, and the angle between two adjacent rows of artificial atoms 31 is... included angle It was calculated using the period P of artificial atom 31 along the y-axis, and the included angle was... Satisfying formula (1):

[0075] (1)

[0076] in, The period represents the length and width of each artificial atom 31. ; This represents the distance between the sixth row of artificial atoms 31 in the 11 rows of artificial atoms 31 and the fan-shaped tip of the SiO2 thin film 2.

[0077] According to some embodiments of this disclosure, the total length of each column of artificial atoms 31 arranged in the radial direction of the fan-shaped SiO2 thin film 2 is approximately .

[0078] According to some embodiments of this disclosure, the included angle between two adjacent columns of artificial atoms 31 is set to... This allows adjacent columns of artificial atoms 31 to form a fan-shaped structure, and all 101 columns of artificial atoms 31 to also form a fan-shaped structure. This fan-shaped structure can converge surface plasmons to the fan-shaped tip of the SiO2 thin film 2, improving the convergence efficiency of surface plasmons and reducing the size of the focused spot. This fan-shaped structure allows the incident light source to have a large field of view in both the x-axis and y-axis directions, and the free space incident light can be focused and coupled, expanding the field of view for collecting free space incident light.

[0079] Figure 4 The diagram schematically illustrates the compositional structure of artificial atoms in a metasurface-based on-chip optical coupling system according to an embodiment of the present disclosure.

[0080] According to some embodiments of this disclosure, such as Figure 4 As shown, each artificial atom 31 includes a first Ag layer 311, a first SiO2 layer 312, and a second Ag layer 313 arranged sequentially from bottom to top; each artificial atom 31 is equivalent to a half-wave plate to realize the conversion of free space incident light into surface plasmons; the first Ag layer 311, the first SiO2 layer 312, and the second Ag layer 313 are all rectangular in shape, and the perpendicular bisectors of the geometric centers of the first Ag layer 311, the first SiO2 layer 312, and the second Ag layer 313 coincide with each other.

[0081] According to some embodiments of this disclosure, the length, width, and height of the first Ag layer 311, the first SiO2 layer 312, and the second Ag layer 313 are related to the wavelength of the incident light in free space. The length, width, and height of the first Ag layer 311, the first SiO2 layer 312, and the second Ag layer 313 are also different for free space incident light of different wavelengths.

[0082] According to some optional embodiments of this disclosure, when the wavelength of the free-space incident light is 1064 nm, the height h1 of the first Ag layer is set to 80 nm, the length a1=P=300 nm, and the width b1=P=300 nm; the height h2 of the first SiO2 layer is set to 70 nm, the length a2=P=300 nm, and the width b2=P=300 nm; and the height h3 of the second Ag layer is set to 30 nm, the length a3=215 nm, and the width b3=130 nm. With the size parameters of the artificial atom 31 set, the conversion efficiency of free-space incident light into surface plasmons can be improved, and the coupling efficiency of the on-chip optical coupling system can be improved.

[0083] According to some embodiments of this disclosure, the arrangement of each artificial atom 31 is similar to the three-layer structure of a half-wave plate MIM (Ag / SiO2 / Ag), and each artificial atom 31 can have the properties of a half-wave plate.

[0084] According to some embodiments of this disclosure, such as Figure 1 and Figure 2 As shown, artificial atoms 31 are arranged in the radial and circumferential directions of the fan-shaped SiO2 thin film 2. In the radial direction, the artificial atoms 31 satisfy a geometric phase gradient distribution; in the circumferential direction, there is an angle between adjacent rows of artificial atoms 31. This allows multiple rows of artificial atoms 31 to form a fan-shaped structure, thereby inducing surface plasmons to be transported to and converge at the fan-shaped tip of the SiO2 thin film 2.

[0085] According to some embodiments of this disclosure, the geometric phase gradient distribution in the radial direction satisfies formula (2):

[0086] (2)

[0087] in, The reflection phase distribution of metasurface coupler 3 along the x-axis; The initial phase is a constant. Let be the wave vector of the surface plasmon.

[0088] According to some embodiments of this disclosure, the radial reflection phase distribution matches the surface plasmon wave vector, i.e., satisfies formula (2), based on formula (2) and the rotation angle of the artificial atom 31. Relationship The distribution of the rotation angle of each artificial atom 31 in the x-axis direction can be determined, and the distribution of the rotation angle of each artificial atom 31 satisfies formula (3):

[0089] (3)

[0090] in, This represents the rotational angular distribution of each artificial atom 31 along the x-axis. The reflection phase distribution of metasurface coupler 3 along the x-axis; For ellipticity, when the incident light in free space is left-handed circularly polarized light... When the incident light in free space is right-handed circularly polarized light When the incident light in free space is linearly polarized... .

[0091] According to some embodiments of this disclosure, the rotation angles of the 11 artificial atoms 31 in each column are arranged according to formula (3), and the phase of each artificial atom satisfies the geometric phase gradient distribution of formula (2), thereby causing the propagation of surface plasmons in the radial direction of the fan-shaped SiO2 thin film 2 to exhibit a 0-2 The geometric phase gradient distribution.

[0092] According to some embodiments of this disclosure, the coupling of free-space incident light by the metasurface coupler 3 can be divided into two steps. The first step is to realize the conversion of free-space incident light into surface plasmons. In the first step, the design principle of geometric phase metasurface is mainly adopted. By arranging artificial atoms 31, a 0-2 ohm pattern is achieved in the light propagation direction within the surface of the metasurface coupler 3. The first step involves the geometric phase gradient distribution of the surface plasmons, which completes the conversion of free-space incident light into surface plasmons. The second step is to focus the surface plasmons to form focused plasmons. In this second step, artificial atoms 31 arranged in a fan shape are mainly used. Each column of artificial atoms 31 is rotated circumferentially so that each artificial atom 31 has the same rotation angle in the circumferential direction, thereby forming a fan shape arrangement. This induces the surface plasmons to be transmitted to the fan-shaped tip of the SiO2 film. The SiO2 film at the bottom is used to increase the lateral constraint on the surface plasmons, reduce the loss of the surface plasmons, and improve the focusing efficiency of the surface plasmons to the fan-shaped tip of the SiO2 film. Because this disclosure uses a fan-shaped SiO2 film and fan-shaped artificial atoms 31, the incident light source can have a large field of view in both the x-axis and y-axis directions, and the free-space incident light can be focused and coupled, realizing a large field of view for free-space light and expanding the field of view range for collecting free-space incident light.

[0093] According to some embodiments of this disclosure, the included angle between two adjacent rows of artificial atoms 31 in the metasurface coupler 3 is designed... This ensures that all one-dimensional linear arrays of the metasurface (i.e., all artificial atoms 31 arranged in one-dimensional direction) point to the focal point, enabling the propagation direction of the surface plasmon waves converted from the spatial light waves of the free-space incident light at different positions of the metasurface coupler 3 to point to the center focal point of the SiO2 thin film (i.e., the fan-shaped tip of the SiO2 thin film), and interference enhancement occurs at the focal point.

[0094] Figure 5 A schematic diagram of an artificial atom with a rotation angle in a metasurface-based on-chip optical coupling system according to an embodiment of the present disclosure is shown.

[0095] According to some embodiments of this disclosure, the phase gradient can be generated by rotating the major axis of the artificial atom 31, such as... Figure 5 As shown, a vu coordinate system is established with the geometric center of the second Ag layer of the upper structure of artificial atom 31 as the origin. The uv coordinate system rotates with the rotation of artificial atom 31. The major axis of artificial atom 31 is the v-axis, the minor axis is the u-axis, and the angle between the positive direction of the v-axis and the positive direction of the y-axis in the external xy coordinate system is the rotation angle of artificial atom 31. .

[0096] According to some embodiments of this disclosure, multiple artificial atoms 31 arranged in a fan shape have the same geometric shape, but the spatial orientation of each artificial atom 31 is different, that is, the orientation of the major axis of each artificial atom 31 is different.

[0097] According to some embodiments of the present disclosure, the metal substrate 1 includes an Ag thin film substrate, which is rectangular in shape and has a thickness of about 80 nm to ensure that surface plasmons cannot be transmitted through the Ag thin film substrate.

[0098] According to some embodiments of this disclosure, the SiO2 thin film 2 is suitable for increasing the lateral confinement of surface plasmons to improve the efficiency of surface plasmon convergence to the fan-shaped tip of the SiO2 thin film 2.

[0099] According to some embodiments of this disclosure, the thickness of the SiO2 thin film 2 is approximately 70 nm.

[0100] According to some embodiments of this disclosure, the height of the on-chip waveguide 4 includes 750 nm and the width includes 600 nm to ensure the stability of the waveguide mode transmission within the on-chip waveguide 4, while improving the conversion efficiency of the focused plasmon to the TM waveguide mode.

[0101] According to some embodiments of this disclosure, the height and width of the on-chip waveguide 4 are set according to the dimensions of the fan-shaped SiO2 thin film 2 and the dimensions of the fan-shaped structure of the artificial atoms 31, and the length of the on-chip waveguide 4 is not limited. To reduce losses and ensure compatibility with silicon-based photonic integrated chip materials and processes, the on-chip waveguide 4 is made of a dielectric material, including any one of polymer waveguides, silicon dioxide, silicon nitride, and silicon waveguides.

[0102] According to some alternative embodiments of this disclosure, the on-chip waveguide 4 is a mode-field matched TM-mode silicon dioxide optical waveguide. TM mode refers to a propagation mode in which the longitudinal component of the magnetic field is zero, while the longitudinal component of the electric field is not zero. By employing a mode-field matched TM-mode silicon dioxide optical waveguide, the input focused plasmon can be coupled to the fundamental mode (e.g., TM0 mode) of the silicon dioxide optical waveguide, reducing the transmission loss of the focused plasmon and improving the coupling efficiency of the focused plasmon into the on-chip waveguide 4.

[0103] Figure 6 A flowchart illustrating a method for coupling free-space incident light with an on-chip waveguide according to an embodiment of the present disclosure is shown.

[0104] like Figure 6 As shown, the second aspect of this disclosure also provides a method for coupling free-space incident light with an on-chip waveguide, applied to the above-mentioned on-chip optical coupling system based on metasurfaces. The method for coupling free-space incident light with an on-chip waveguide includes operations S101 to S102.

[0105] In operation S101, the free-space incident light is converted into surface plasmons by the metasurface coupler 3, and the surface plasmons are induced to propagate to the fan-shaped tip of the SiO2 thin film 2 to form focused plasmons.

[0106] In operation S102, the on-chip waveguide 4 is used to couple the focusing plasmon and convert the focusing plasmon into a guided wave mode to realize the transmission of the guided wave mode in the on-chip waveguide 4.

[0107] According to some embodiments of this disclosure, one end of the on-chip waveguide 4 is connected to the fan-shaped tip of the SiO2 thin film 2, and the metasurface coupler 3 includes a plurality of artificial atoms 31 arranged in a fan shape, with the central angle corresponding to the fan shape being... The range includes 30° to 180° to achieve the collection of free-space incident light with a large field of view.

[0108] According to some embodiments of this disclosure, free-space incident light is converted into surface plasmons using a metasurface coupler 3, and the surface plasmons are induced to propagate towards the fan-shaped tip of the SiO2 thin film 2 to form a focused plasmon. The focused plasmon is coupled using an on-chip waveguide 4, and the focused plasmon is converted into a guided wave mode to realize the transmission of the guided wave mode within the on-chip waveguide 4. This can collect free-space incident light within a large field of view, improve the ability to receive free-space incident light, enhance the ability to control free-space incident light, and improve the conversion efficiency of free-space incident light into surface plasmons, the focusing ability of surface plasmons, and the coupling efficiency of the on-chip optical coupling system.

[0109] According to some optional embodiments of this disclosure, the central angle corresponding to the sector is... Approximately 130°. The central angle corresponding to the sector. The angle between the two adjacent columns of artificial atoms 31 is The two satisfy formula (4):

[0110]

[0111] in, The central angle corresponding to the sector-shaped structure; It is the angle between two adjacent columns of artificial atoms 31.

[0112] According to some embodiments of this disclosure, multiple artificial atoms 31 arranged in a fan shape in the metasurface coupler 3 are used to induce surface plasmons to be transported to the fan-shaped tip of the SiO2 thin film 2, and the surface plasmons are gathered to the fan-shaped tip of the SiO2 thin film 2.

[0113] Figure 7 The surface optical field E of a metasurface coupler according to an embodiment of the present disclosure is schematically illustrated. zThe distribution simulation results are shown in the figure. Figure 8 The schematic diagram illustrates the mode field E of a cross-section of an on-chip waveguide according to an embodiment of the present disclosure. z The distribution simulation results are shown in the figure.

[0114] According to some embodiments of this disclosure, simulation experiments were conducted using FDTD simulation software. Left-handed circularly polarized light was used as the free-space incident light. When the left-handed circularly polarized light was perpendicularly incident on the surface of the metasurface coupler 3, i.e. and Both are 0°, and the surface optical field E of the metasurface coupler z The distribution simulation results are as follows Figure 7 As shown, Figure 7 The horizontal axis represents the distance along the x-axis, in units of... The ordinate represents the distance along the y-axis, in units of... The mode field E of the cross section of the on-chip waveguide. z The distribution simulation results are as follows Figure 8 As shown, Figure 8 The horizontal axis represents the distance along the y-axis, in units of... The ordinate represents the distance along the z-axis, in units of... .

[0115] According to some embodiments of this disclosure, the conversion efficiency of free-space incident light incident on the surface of the metasurface coupler 3 and converted into surface plasmons is the ratio of the total energy of the free-space incident light in region S3 to the total energy of the free-space incident light incident on region S4 of the metasurface coupler 3, wherein regions S3 and S4 are as follows: Figure 1 As shown.

[0116] According to some embodiments of this disclosure, the focusing efficiency of surface plasmons converging to the fan-shaped tip of the SiO2 thin film 2 is the ratio of the total energy of the free-space incident light within three times the half-width and height of the focused spot in region S2 to the total energy of the free-space incident light in region S3. Regions S2 and S3 are as follows... Figure 1 As shown.

[0117] According to some embodiments of this disclosure, when left-handed circularly polarized light is incident perpendicularly on the surface of the metasurface coupler 3, i.e. and When both are at 0°, the conversion efficiency of free space incident light incident on the surface of metasurface coupler 3 and converted into surface plasmons is about 38.5% as calculated by FDTD simulation software; the convergence efficiency of surface plasmons converging to the fan-shaped tip of SiO2 thin film 2 is about 51.7%.

[0118] Figure 9This schematically illustrates the optical field E during the coupling of free-space incident light into an on-chip waveguide using a metasurface-based on-chip optical coupling system according to embodiments of the present disclosure. z The distribution simulation results are shown in the figure.

[0119] According to some embodiments of this disclosure, the on-chip waveguide 4 is placed parallel to the x-axis direction, and one end of it is coupled to the fan-shaped tip of the SiO2 thin film. Figure 9 The horizontal axis represents the distance along the x-axis, in units of... The ordinate represents the distance along the y-axis, in units of... .Depend on Figure 9 It can be seen that the metasurface coupler 3 converts free-space incident light into surface plasmons, and then focuses the surface plasmons onto the fan-shaped tip of the SiO2 thin film (i.e., the central focal point of the SiO2 thin film), forming a focused plasmon. The focused plasmon forms a focused spot at the fan-shaped tip of the SiO2 thin film. The focused plasmon is coupled into the on-chip waveguide 4, converted into a guided wave mode, and transmitted. The waveguide coupling efficiency is approximately 55.2% according to simulation. The waveguide coupling efficiency is the ratio of the total energy within three times the half-width and height of the focused spot at section S2 to the total energy of the free-space incident light within the waveguide at section S1.

[0120] According to some embodiments of this disclosure, by Figure 9 It can be seen that when surface plasmons propagate along the direction of gradually decreasing sector cross-sectional area on the SiO2 thin film, the light field energy is continuously concentrated during the propagation process, and finally enters the on-chip waveguide 4 at the sector tip of the SiO2 thin film, transforming into a guided wave mode, thus completing the transformation from surface plasmons to guided wave mode.

[0121] Figure 10 The illustration schematically shows the conversion efficiency of free-space incident light into surface plasmonic laser at different incident angles according to embodiments of the present disclosure.

[0122] According to some embodiments of this disclosure and These represent the incident angles of free-space incident light in the x-axis and y-axis directions onto the metasurface coupler 3, respectively. Figure 10 As shown, when It is 130°. 0° Within the temperature range of -25° to 25°, the conversion efficiency of free-space incident light incident on the surface of metasurface coupler 3 and converted into surface plasmons ranges from 13.9% to 38.5%; when It is 130°. 0° Within the temperature range of -30° to 30°, the conversion efficiency of free-space incident light incident on the surface of metasurface coupler 3 and converted into surface plasmons ranges from 16.8% to 38.5%. Specifically, when It is 130°. 0° At 0°C, the conversion efficiency is approximately 38.5%; when It is 130°. 0° At 15°C, the conversion efficiency is approximately 32.8%; when It is 130°. 0° At 20°C, the conversion efficiency is approximately 21.7%; when It is 130°. 0° At 25°C, the conversion efficiency is approximately 13.9%; when It is 130°. 0° At -15°C, the conversion efficiency is approximately 16.3%; when It is 130°. 0° At -20°C, the conversion efficiency is approximately 14.9%; when It is 130°. 0° At -25°C, the conversion efficiency is approximately 14.3%. It is 130°. 0° At 30°C, the conversion efficiency is approximately 16.8%; when It is 130°. 0° At 25°C, the conversion efficiency is approximately 20.5%; when It is 130°. 0° At 20°C, the conversion efficiency is approximately 22.3%; when It is 130°. 0° At an angle of 15°, the conversion efficiency is approximately 28.8%. Therefore, the conversion efficiency of free-space incident light into surface plasmonic laser is high regardless of the incident angle.

[0123] Those skilled in the art will understand that the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0124] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. An on-chip optical coupling system based on a metasurface, wherein, include: metal substrate; A SiO2 thin film is disposed on the metal substrate, and the SiO2 thin film is fan-shaped. A metasurface coupler is disposed on the SiO2 thin film. The metasurface coupler is suitable for converting free-space incident light into surface plasmons and inducing the surface plasmons to propagate toward the fan-shaped tip of the SiO2 thin film to form focused plasmons. An on-chip waveguide, one end of which is coupled to the fan-shaped tip of the SiO2 thin film to convert the focused plasmon into a guided wave mode, thereby enabling the transmission of the guided wave mode within the on-chip waveguide; The metasurface coupler comprises multiple artificial atoms arranged in a fan shape, wherein the central angle of the fan shape is... The range is 30° to 180° to achieve the collection of free space incident light with a large field of view.

2. The on-chip optical coupling system based on metasurfaces according to claim 1, wherein, The SiO2 thin film has multiple rows of artificial atoms arranged in the radial direction of the fan shape. Each row of artificial atoms includes multiple columns of artificial atoms arranged in the circumferential direction. The artificial atoms include 11 rows and 101 columns.

3. The on-chip optical coupling system based on metasurfaces according to claim 2, wherein, The radius R of the fan-shaped SiO2 thin film is 15 μm, and the angle between two adjacent columns of artificial atoms is... The included angle satisfies the formula: in, The period representing each of the artificial atoms, The distance between the artificial atom in the 6th row of the artificial atom 31 in row 11 and the fan-shaped tip of the SiO2 thin film.

4. The on-chip optical coupling system based on metasurfaces according to any one of claims 3, wherein, Each of the artificial atoms comprises a first Ag layer, a first SiO2 layer, and a second Ag layer arranged sequentially from bottom to top; Each of the artificial atoms is equivalent to a half-wave plate to realize the conversion of the free space incident light into the surface plasmons; the first Ag layer, the first SiO2 layer and the second Ag layer are all rectangular in shape, and the perpendicular bisectors of the geometric centers of the first Ag layer, the first SiO2 layer and the second Ag layer coincide with each other.

5. The on-chip optical coupling system based on metasurfaces according to any one of claims 1-4, wherein, The artificial atoms are arranged in the radial and circumferential directions of the fan-shaped structure of the SiO2 thin film. In the radial direction, the artificial atoms satisfy a geometric phase gradient distribution; In the circumferential direction, there is an angle between two adjacent columns of artificial atoms, so that multiple columns of artificial atoms form a fan-shaped structure to induce the surface plasmons to be transported to the fan-shaped tip of the SiO2 film and converge to the fan-shaped tip of the SiO2 film. Wherein, the geometric phase gradient distribution satisfies: in, The reflection phase distribution of the metasurface coupler along the x-axis; The initial phase is a constant. Let be the wave vector of the surface plasmon.

6. The on-chip optical coupling system based on metasurfaces according to claim 5, wherein, The metal substrate includes an Ag thin film substrate, which is rectangular in shape and has a thickness of 80 nm to ensure that the surface plasmons cannot be transmitted through the Ag thin film substrate.

7. The on-chip optical coupling system based on metasurfaces according to claim 6, wherein, The SiO2 film is suitable for increasing the lateral confinement of the surface plasmons to improve the efficiency of the surface plasmons converging to the fan-shaped tip of the SiO2 film.

8. The on-chip optical coupling system based on metasurface according to claim 7, wherein, The on-chip waveguide has a height of 750 nm and a width of 600 nm to ensure the stability of the waveguide mode transmission within the on-chip waveguide.

9. A coupling method between free-space incident light and an on-chip waveguide, applied to the on-chip optical coupling system based on metasurfaces as described in claims 1-8, wherein, The method includes: The metasurface coupler is used to convert free-space incident light into surface plasmons, and the surface plasmons are induced to propagate toward the fan-shaped tip of the SiO2 thin film to form focused plasmons. The focused plasmon is coupled using an on-chip waveguide and converted into a guided wave mode to achieve the transmission of the guided wave mode within the on-chip waveguide. One end of the on-chip waveguide is connected to the fan-shaped tip of the SiO2 thin film. The metasurface coupler includes multiple artificial atoms arranged in a fan shape, with the central angle corresponding to the fan shape being... The range is 30° to 180° to achieve the collection of free space incident light with a large field of view.

10. The coupling method between free-space incident light and on-chip waveguide according to claim 9, wherein, The surface plasmons are induced to travel to the fan-shaped tip of the SiO2 thin film by multiple artificial atoms arranged in a fan shape in the metasurface coupler, and the surface plasmons are then gathered to the fan-shaped tip of the SiO2 thin film.

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