An optical antenna based on the low sidelobe characteristics of surface plasmons

Abstract

The present invention discloses an optical antenna based on the low sidelobe characteristics of surface plasmons, belonging to the field of antennas. The antenna structure of the invention includes a silicon-based substrate at the bottom layer, a buried oxide layer of silicon dioxide in the middle layer, and an optical antenna composed of two gold thin film strips at the top layer. The present invention uses an optical plasmonic slot waveguide to transmit guided waves, in which the change in the slot width is used to generate a periodic modulation of the electric field amplitude to achieve the migration of spatial frequency, so as to radiate the fundamental harmonic into free space. At the same time, a bias is superimposed on the basis of the periodically changing slot width to further control the width of the slot along the transmission direction, so that the radiation aperture of the antenna meets the low sidelobe design amplitude. The present invention has the characteristics of simple structure, convenient processing and easy large-scale integration, and can be used in lidar and high-speed optical communication systems.

Description

Technical Field

[0001] The present invention belongs to the technical fields of optical communication and optical antenna, and particularly relates to an optical antenna based on the low sidelobe characteristics of surface plasmons, which is applicable to lidar and high-speed optical communication systems. Background Art

[0002] Photonic integrated circuits can implement various complex optical systems at low cost and high performance, and can achieve specific applications, such as imaging, ranging, communication, etc. on a chip the size of a fingernail. In these applications, optical antennas are essential components, which can effectively convert the guided mode in the optical waveguide and the radiation mode in free space. Most of the current research on optical antennas focuses on how to direct the guided wave into free space. Among them, dielectric grating antennas are the most widely used type of antenna in optics, but they generally have a large size and it is difficult to control the radiation field in free space.

[0003] With the progress of micro-nano processing technology and the rapid development of photonic integration technology, the integration level of chips is getting higher and higher, and new requirements are also put forward for the performance of antennas. First of all, the antenna must have a compact structural size for large-scale integration. The directivity of the antenna is another important parameter. A high-directivity antenna means that it can detect a farther distance and link with the receiving antenna more effectively. Finally, the low sidelobes of the antenna reduce unnecessary coupling, which is beneficial to the further integration of photonic circuits. In order to reduce the interference of the antenna to other components in the photonic integrated circuit during operation, the sidelobe level of the antenna should be as small as possible.

[0004] The present invention is precisely proposed for the key technical problems such as low sidelobes and high gain of optical antennas. Summary of the Invention

[0005] The purpose of the present invention is to: aiming at the above key problems, propose a surface plasmon optical antenna to achieve higher directivity and lower sidelobe level.

[0006] In order to achieve the above object of the invention, the present invention adopts the following technical solution: an optical antenna based on the low sidelobe characteristics of surface plasmons, the antenna comprising: a silicon-based substrate layer 101, a buried silicon dioxide layer 102, and a metal thin film antenna layer 103;

[0007] The lowermost layer is a silicon-based substrate layer 101 with a thickness of 500 μm; the buried silicon dioxide layer 102 is located on the upper surface of the silicon-based substrate layer with a thickness of 1 μm; the metal thin film antenna layer 103 is located on the upper surface of the buried silicon dioxide layer; the metal thin film antenna layer is composed of two symmetric gold strip bands, the width and thickness of the gold strip bands are 350 nm and 100 nm respectively, and there is a gap between the two gold strip bands, and this gap supports the surface plasmon slot mode;

[0008] The width W(y) of the gap between two gold strip lines varies along the transmission direction and satisfies the following formula:

[0009] W(y) = 2 * [a0 + b0 * y^2 + (a n + b n * y + c n * y^2) * cos(2 * π * y / p)]

[0010] where a0 = 0.17 μm, b0 = 0.0009 μm -1 , a n = 0.0089 μm, b n = 0.0085, c n = 0.008 μm -1 , p = 0.9 μm.

[0011] Furthermore, the length of the gap between the two gold strip lines is 12.6 μm.

[0012] The beneficial effects of the present invention are as follows: Utilizing the plasmonic effect to reduce the antenna size, coupling energy into free space with only a single-layer metal structure through the periodic variation of the guided wave field amplitude, and controlling the amplitude of the antenna aperture radiation field to satisfy the Chebyshev distribution by the gap width between strips at different positions in the propagation direction, thereby achieving a low sidelobe level. Description of the Drawings

[0013] Figure 1 It is a schematic structural diagram of the optical antenna with low sidelobe characteristics based on plasmonics described in Embodiment 1.

[0014] Figure 2 It is the mode field distribution diagram of the plasmonic slot waveguide described in Embodiment 1.

[0015] Figure 3 It is the curve of the normalized propagation constant and electric field strength of the plasmonic slot waveguide varying with the gap width described in Embodiment 1.

[0016] Figure 4 It is the amplitude distribution diagram of the aperture field with Chebyshev characteristics of the optical antenna with low sidelobe characteristics based on plasmonics described in Embodiment 1.

[0017] Figure 5 It is the H-plane radiation pattern of the optical antenna with low sidelobe characteristics based on plasmonics described in Embodiment 1.

[0018] Figure 6 It is a schematic diagram of an amplitude-modulated leaky wave antenna based on periodic perforations. Detailed Embodiments

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings.

[0020] Example 1 Design of a Low Sidelobe Optical Antenna

[0021] An optical antenna based on plasmon with low sidelobe characteristics in this embodiment is designed to operate in the optical communication band with a wavelength of 1550 nm. As Figure 1 shown, the bottom silicon layer 101 and the silicon dioxide layer 102 form a basic silicon dioxide wafer, and on the silicon dioxide layer is an optical antenna composed of two gold thin film strips symmetrically distributed along the y-axis. The thickness of the gold thin film strip is 100 nm, and the width is 350 nm and remains constant. The input end of the antenna is a plasmonic gap waveguide composed of two gold thin film strips with a length of 3 μm and a constant gap width of 358 nm. This waveguide supports the plasmonic slot mode as Figure 2 shown. Most of the energy of this mode is confined in the gap between the two gold strips. The propagation constant of the mode hardly changes with the gap width, while the electric field amplitude varies with the gap width as Figure 3 shown. In the radiation part of the antenna, the change in the gap width between the two gold thin film strips along the transmission direction satisfies the expression: W(y) = 2 * [a0 + b0 * y^2 + (a n + b n * y + c n * y^2) * cos(2 * π * y / p)], where a0 = 0.17 μm, b0 = 0.0009 μm -1 , a n = 0.0089 μm, b n = 0.0085, c n = 0.008 μm -1 , p = 0.9 μm. The length of this part is 12.6 μm, corresponding to 14 cycles. When the antenna operates, the electric field amplitude in the plasmonic waveguide is periodically modulated to achieve the migration of spatial frequency, thereby radiating the first harmonic into free space. The radiation angle of the antenna is determined by the parameter p. The gap width between the two gold thin film strips is adjusted by the coefficients a0, b0, a n , b n and c n . For the first ten cycles, the aperture amplitude is adjusted, and the target sidelobe level is -25 dB. Different radiation intensities are obtained in each radiation cycle of the antenna to satisfy the designed Chebyshev distribution as Figure 4 shown. Figure 5 The H-plane radiation pattern of the antenna described in this example is given. It can be seen that the sidelobe levels in the upper half radiation space are all below -22 dB, and the directivity coefficient of the antenna is as high as 15.8 dBi.

[0022] Figure 6 An amplitude-modulated leaky-wave antenna based on periodic via holes is presented. A similar uniform sinusoidal amplitude modulation is constructed using metallized vias to achieve radiation in the millimeter-wave band. The sidelobe levels of the antenna under different structural parameters are between -13.3 dB and -8.3 dB, and the maximum gain achieved is 15 dBi. In contrast, the present invention proposes to achieve the required amplitude modulation with a plasmonic slot waveguide in the optical band. The planar single-layer structure does not require via holes. Moreover, the leakage rate is regulated by the width of the slot in each period to achieve a Chebyshev amplitude distribution, achieving a sidelobe level below -22 dB and a high directivity coefficient of 15.8 dBi.

Claims

1. An optical antenna based on the low sidelobe characteristic of surface plasmons, the antenna comprising: Silicon-based substrate layer, buried oxide layer of silicon dioxide, metal thin film antenna layer; The bottom layer is a silicon-based substrate layer with a thickness of 500 μm; The buried oxide layer of silicon dioxide is located on the upper surface of the silicon-based substrate layer with a thickness of 1 μm; the metal thin film antenna layer is located on the upper surface of the buried oxide layer of silicon dioxide; the metal thin film antenna layer is composed of two symmetric gold strips, and the width and thickness of the gold strips are 350 nm and 100 nm respectively. There is a gap between the two gold strips, and this gap supports the plasmonic slot mode; The width W(y) of the gap between the two gold strips varies along the transmission direction and satisfies the following formula: W(y) = 2 * [a0 + b0 * y^2 + (a n + b n * y + c n * y^2) * cos(2 * π * y / p)] Among them, a0 = 0.17μm, b0 = 0.0009μm -1 , a n = 0.0089μm, b n = 0.0085, c n = 0.008μm -1 , p = 0.9μm.

2. The optical antenna with low sidelobe characteristics based on surface plasmons as claimed in claim 1, wherein The length of the gap between the two gold strips is 12.6 μm.

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