A method for improving the coupling efficiency and working bandwidth of a grating coupler

Abstract

The present invention discloses a method for improving the coupling efficiency and working bandwidth of a grating coupler, comprising the following steps: S1: A metasurface structure is composed of two-dimensional structural units and a uniform medium. The incident light is irradiated onto the metasurface structure with a fixed angle of the optical fiber. S2: A phase mutation is introduced through the two-dimensional structural units to cause the incident light to generate a deflection angle θ i ; S3: The light deflected by the metasurface is incident on the light receiving port of the grating coupler at an angle θ i . By utilizing the diffraction effect of the grating, the propagation direction of the light field is changed, so that the light of the external optical fiber is coupled into the waveguide. The present invention uses the metasurface structure to adjust the incident light so that the angles of different wavelengths of the incident light on the light receiving port of the grating all satisfy the optimal coupling angle of the grating, thereby improving the coupling efficiency and working bandwidth of the grating.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technologies, and particularly to a method for improving the coupling efficiency and working bandwidth of a grating coupler. Background Art

[0002] In the big data era, traditional electrical interconnections can no longer meet the ever-expanding demand for data transmission due to the physical characteristics of electrons. Optical signal transmission, with its advantages of fast transmission speed, low loss, and working bandwidth greater than that of electrical transmission, has officially become a new generation of information transmission method. Silicon-based integrated chips play an important role in integrated optical communication systems with their unique advantages. In addition, an optical fiber coupler is an important optical component for coupling optical signals in an optical fiber into a silicon-based chip for transmission, playing the role of a bridge for optical signals to transmit between two media. The grating coupler has been widely concerned by all sectors due to its advantages such as no need for polishing, no strict space limitation, large alignment tolerance, relatively simple processing requirements, relatively flexible system design, strong compatibility with CMOS process, and suitability for large-scale integration. With the continuous in-depth research work and the increasing maturity of the fabrication process technology, the characteristics such as the coupling efficiency, working wavelength, and polarization mode of the grating coupler will be continuously improved. It can be expected that high-efficiency, large-bandwidth, and vertical-coupling grating couplers will develop rapidly and tend to be mature along the direction of practical application, becoming an indispensable key unit in the field of silicon-based photon integration.

[0003] Metasurfaces can achieve arbitrary regulation of electromagnetic waves. By designing and arranging unit structures, a phase mutation is introduced on the surface of a homogeneous medium, thereby realizing the regulation of the optical field so that incident light within a certain bandwidth can be emitted at a desired angle. These gradient-phase metasurfaces are very thin on the optical scale, so light will not propagate inside the structure for a long time. Therefore, they are less affected by scattering and phase mutation problems, and metasurfaces provide greater flexibility for the propagation of light and the wavefront. In addition, the metasurface structure adopts mature processing technologies such as standard lithography, electron beam lithography, and etching, which are compatible with the CMOS process and are easy to integrate on a chip. Therefore, combining the optical field regulation of the metasurface structure with a silicon-based integrated chip can provide new ideas for improving the coupling efficiency, increasing the optical bandwidth, reducing polarization sensitivity, etc., and promoting the further development of optical communication.

[0004] Chinese Patent CN113835155 realizes the coupling between free - space light and a grating coupler on a photonic chip using a grating coupler and a metalens. However, it does not involve the content of using a metasurface structure to improve the coupling efficiency and optical bandwidth between an optical fiber and a grating coupler. Due to the limitation of diffraction conditions, its coupling spectral line is parabolic, and generally the 1dB bandwidth is only about dozens of nanometers, which has a great restrictive effect on the optical transmission capacity. In addition, at a specific wavelength, the grating coupler only has high - efficiency coupling characteristics for light incident at a certain angle, and the high - efficiency coupling angle of the same grating coupler changes with the wavelength. Therefore, different working wavelengths require corresponding incident angles to achieve high - efficiency light coupling. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a method for improving the coupling efficiency and working bandwidth of a grating coupler.

[0006] To achieve the above - mentioned purpose, the technical solution adopted by the present invention is as follows: A method for improving the coupling efficiency and working bandwidth of a grating coupler, comprising the following steps: S1: A metasurface structure is composed of two - dimensional structural units and a homogeneous medium. The optical fiber is incident at a fixed angle, and the incident light is irradiated onto the metasurface structure. S2: A phase mutation is introduced through the two - dimensional structural units to cause the incident light to generate a deflection angle θ i ; S3: The light deflected by the metasurface is incident on the light - receiving port of the grating coupler at an angle θ i . Utilizing the diffraction effect of the grating, the propagation direction of the light field is changed, so that the light from the external optical fiber is coupled into the waveguide.

[0007] In a preferred embodiment of the present invention, the two - dimensional structural unit in step S1 is an I - shaped two - dimensional structural unit.

[0008] In a preferred embodiment of the present invention, in step S1, the incident light is perpendicularly incident on the metasurface structure from air.

[0009] In a preferred embodiment of the present invention, in step S2, the deflection angle where λ is the wavelength and p is the period of the metasurface structure composed of two - dimensional structural units.

[0010] In a preferred embodiment of the present invention, the two - dimensional structural unit can satisfy a uniform distribution of phase from 0 to 2π at different wavelengths.

[0011] The present invention also provides a grating coupler structure, comprising a single - mode optical fiber, a grating coupler, and a strip - shaped waveguide. It is characterized in that it further comprises a metasurface structure composed of two - dimensional structural units and a homogeneous medium, which can introduce different phase mutations through the two - dimensional structural units to realize the regulation of the incident light and generate a deflection angle.

[0012] The present invention solves the defects existing in the background art, and the present invention has the following beneficial effects:

[0013] The present invention uses a metasurface structure to adjust the incident light so that the angles of different wavelengths of the incident light reaching the grating light-receiving port all satisfy the optimal coupling angle of the grating, eliminating the problem of limited working bandwidth caused by the wave vector mismatch between the optical fiber and the waveguide, and can also achieve the problem of incident at the optimal incident angle by adjusting the metasurface unit structure, so that the grating coupler has the optimal incident angle for different incident lights, making the matching between the optical fiber wave vector and the wave vector in the waveguide, and obtaining the optimal coupling efficiency. Since each wavelength has the maximum coupling efficiency, the working bandwidth can also be increased accordingly. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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 for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings;

[0015] Figure 1 is a schematic diagram of the grating coupling structure of the preferred embodiment of the present invention;

[0016] Figure 2 is a schematic diagram of the metasurface structure unit in the grating coupler of the preferred embodiment of the present invention;

[0017] Figure 3 is a schematic diagram of the principle of the grating coupler of the preferred embodiment of the present invention;

[0018] Figure 4 is a schematic diagram of the working process of the preferred embodiment of the present invention;

[0019] Figure 5 is a schematic diagram of the grating coupling structure of the preferred embodiment of the present invention;

[0020] In the figure: S101, optical fiber; S102, two-dimensional structure unit; S103, uniform medium; S104, grating coupler; S105, waveguide; 6,; 7,; 8,; 9,; 10,; 11,; 12,; 13,; 14,; 15,; 16,; 17,; 18,; 19,; 20,. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. In the description of the present invention, the mention of "embodiment", "one embodiment" or "other embodiments" means that the specific features, structures or characteristics described in conjunction with the embodiments are included in at least some embodiments, but not necessarily all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0022] It should be noted that the metasurface in the present invention, that is, a two-dimensional metamaterial, is an artificial microstructure array composed of meta-units on the sub-wavelength scale. Through the effective artificial construction of the electromagnetic characteristics and spatial arrangement order of the meta-units, the metasurface can flexibly manipulate the light field in multiple dimensions on the sub-wavelength spatial scale with a unique geometric configuration of ultra-thin and planar integration.

[0023] Anomalous refraction: Different from the fact that the ratio of the sines of the incident angle and the refraction angle is a constant in the traditional Snell's law, the refraction angle at any angle can be achieved by adjusting the metasurface.

[0024] As Figure 4 shown, a method for improving the coupling efficiency and working bandwidth of a grating coupler includes the following steps: a metasurface structure is composed of two-dimensional structural units and a homogeneous medium, the optical fiber is incident at a fixed angle, the incident light is irradiated on the metasurface structure, and a phase mutation is introduced through the two-dimensional structural units to cause the incident light to generate a deflection angle θ i ; the light deflected by the metasurface is incident on the light receiving port of the grating coupler at an angle θ i , and by using the diffraction effect of the grating, the propagation direction of the light field is changed, so that the light of the external optical fiber is coupled into the waveguide.

[0025] A grating coupler structure adapted to the above method includes a single-mode optical fiber, a grating coupler, and a strip waveguide, and further includes a metasurface structure capable of achieving anomalous refraction composed of two-dimensional structural units and a homogeneous medium, which can introduce different phase mutations through the two-dimensional structural units to realize the regulation of the incident light and generate a deflection angle.

[0026] Embodiment 1

[0027] As Figure 1Shown is a grating coupler structure that uses a metasurface to achieve grating coupling efficiency and operating bandwidth. This structure consists of a single-mode fiber (S101), a two-dimensional structural unit (S102), and a homogeneous medium (S103) that form a metasurface structure capable of achieving anomalous refraction, a grating coupler (S104), and a strip waveguide (S105). The fiber (S101) perpendicular to the metasurface irradiates light onto the metasurface composed of the two-dimensional structural unit (S102) and the homogeneous medium (S103). By adjusting the relevant parameters of the structural unit shown in Figure 2 such as the crossing angle α of the two "I" shapes, the rotation angle β of the small unit, the widths w1, w2 of the "I" shapes, and the lengths L1, L2, a set of unit structures is selected to form a period P of the metasurface structure, so that it can satisfy the uniform distribution of the phase from 0 to 2π at different wavelengths of λ1 to λ n .

[0028] According to the generalized Snell's law, when light is incident perpendicularly from air onto the metasurface device, the metasurface device uses the structural unit to introduce different phase mutations to regulate the incident light, so that it generates a deflection angle of The light deflected by the metasurface is incident on the grating coupler (S104) at a certain angle θ i . Using the diffraction effect of the grating, the propagation direction of the light field is changed, so that the light from the external fiber is coupled into the waveguide (S105).

[0029] As shown in Figure 3 , for the grating coupler (S104) with a uniform period Λ, in the k space, it provides the reciprocal lattice vector for the wave vector with an incident angle of θ g to compensate for the mismatch between the wave vector in the fiber (S101) and the wave vector in the waveguide (S105). The tilt angle of the incident light from the fiber is Finding the metasurface structural unit that satisfies θ i = θ g can make the grating coupler have the best incident angle for different incident lights, so that the matching between the fiber wave vector and the wave vector in the waveguide is achieved, and the best coupling efficiency is obtained. Since each wavelength has the maximum coupling efficiency, the operating bandwidth can also be increased accordingly.

[0030] Embodiment 2

[0031] On the premise that the designed superscalar structure is insensitive to the polarization of the TE / TM mode, the structure shown in Figure 5 is adopted. Below the metasurfaces of two completely perpendicular grating couplers, waves of both the TE and TM modes can be coupled into the waveguide, thereby improving the coupling efficiency.

[0032] Based on the inspiration of the ideal embodiments of the present invention, through the above description, relevant personnel can make various changes and modifications completely within the scope without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A method for improving the coupling efficiency and working bandwidth of a grating coupler, characterized in that, The following steps are involved: S1: The metasurface structure is composed of a two-dimensional structural unit and a uniform medium. The optical fiber is incident at a fixed angle to irradiate the incident light onto the metasurface structure. The two-dimensional structural unit is an I-shaped two-dimensional structural unit. S2: Introducing phase mutation through two-dimensional structural units, so that the incident light produces a deflection angle θi. The deflection angle θi=arcsin(1-λ / p), where λ is the wavelength and p is the period of the metasurface structure composed of two-dimensional structural units. The two-dimensional structural units can satisfy the uniform distribution of phase 0 to 2π at different wavelengths. S3: The light deflected by the metasurface is incident on the light receiving port of the grating coupler at an angle θi, and the diffraction effect of the grating is used to change the propagation direction of the light field, so that the light from the external optical fiber is coupled to the waveguide.

2. A method for improving the coupling efficiency and working bandwidth of a grating coupler according to claim 1, characterized in that: In step S1, the incident light is incident vertically from the air onto the metasurface structure.

3. A method for improving the coupling efficiency and working bandwidth of a grating coupler according to claim 1, characterized in that: The grating coupler also includes: a metasurface structure capable of achieving abnormal deflection composed of a two-dimensional structural unit and a uniform medium, which can introduce different phase mutations through the two-dimensional structural unit to achieve regulation of the incident light to produce a deflection angle.

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