Silicon-based passive optical filtering method for photonic crystal nanobeam microcavity

Abstract

A silicon-based passive optical filtering method for a photonic crystal nanobeam microcavity is disclosed, wherein a straight waveguide coupler and a parallel one-dimensional photonic crystal nanobeam microcavity based on a topological structure are prepared on an SOI wafer by electron beam lithography and inductively coupled plasma etching, and then a layer of silicon dioxide is deposited on the exposed top surface of the structure by plasma enhanced chemical vapor deposition, and then an optical signal is injected into one end of the straight waveguide coupler to obtain transmitted light at the other end to achieve optical filtering. The present invention applies an optical topological structure to a passive filter, which not only achieves the filter's high Q value, high extinction ratio (high transmittance), low mode volume and other characteristics, but also greatly reduces the device size and enhances the robustness of the device.

Description

Technical Field

[0001] The present invention relates to a technology in the field of microwave power distribution, and in particular to a silicon-based passive optical filtering method based on a photonic crystal nanobeam microcavity with a one-dimensional topological structure. Background Art

[0002] Silicon-based passive optical filters have been widely used in existing long-distance communication optical networks and data centers, among which optical filters around 1550nm have received intensive research and attention. Improving the Q value of optical filters and reducing transmission losses have become important research directions. Photonic crystal technology with topological microcavity structures utilizes its ultra-small mode volume and strong light-matter interaction characteristics, which can greatly improve the filtering efficiency of devices and is one of the key technologies for building future optical transmission communication networks. Summary of the invention

[0003] In view of the problems that the existing filters based on microcavity coupling are large in size and cannot be highly integrated, and the manufacturing process of photonic crystal filters with reflection cavities is weak in robustness, the present invention proposes a silicon-based passive optical filtering method of photonic crystal nanobeam microcavity, and applies optical topological structure to passive filters, which not only realizes the high Q value, high extinction ratio (high transmittance), low mode volume and other characteristics of the filter, but also greatly reduces the size of the device and enhances the robustness of the device.

[0004] The present invention is achieved through the following technical solutions:

[0005] The invention relates to a silicon-based passive optical filtering method for a photonic crystal nanobeam microcavity. A straight waveguide coupler and a one-dimensional photonic crystal nanobeam microcavity based on a topological structure parallel to the straight waveguide coupler are prepared on an SOI wafer by electron beam lithography (EBL) and inductively coupled plasma (ICP) etching. A layer of silicon dioxide is deposited on the exposed top surface of the structure by plasma enhanced chemical vapor deposition (PECVD). Then, an optical signal is injected into one end of the straight waveguide coupler to obtain transmitted light at the other end. Side coupling is formed between the straight waveguide coupler and the one-dimensional photonic crystal nanobeam microcavity. A topological defect of a nanocavity is formed on the interface between two photonic crystals with different topologies, thereby ensuring that only one mode exists in the photonic band gap thereof, thereby realizing optical filtering.

[0006] Technical Effects

[0007] The present invention achieves a higher quality factor and extinction ratio by constructing a nanobeam microcavity with a compact one-dimensional topological structure. Compared with the traditional FP-type nanobeam microcavity structure, it has strong robustness, significantly reduces the impact of changes in nanobeam size caused by process errors on filtering performance, and ensures that only the TE0 mode exists in the photonic band gap. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a schematic diagram of the three-dimensional structure of the present invention;

[0009] Figure 2 It is a two-dimensional schematic diagram of the xy viewing angle of the present invention;

[0010] Figure 3 A two-dimensional schematic diagram of the defect region of the nanobeam waveguide of the present invention from an xy perspective;

[0011] Figure 4 is an output transmittance diagram of the present invention;

[0012] Figure 5 The center wavelength diagram corresponding to the proportional change of the structural parameters of the present invention;

[0013] Figure 6 The volume diagram of the mode corresponding to the proportional change of the structural parameters of the present invention;

[0014] Figure 7 The figure of quality factor corresponding to the proportional change of the structural parameters of the present invention;

[0015] In the figure: one-dimensional topological photonic crystal microcavity nanobeam 1, straight waveguide coupler 2. DETAILED DESCRIPTION

[0016] like Figure 1 As shown, this embodiment relates to a silicon-based passive optical filtering method of a photonic crystal nanobeam microcavity, by preparing a straight waveguide coupler and a parallel one-dimensional photonic crystal nanobeam microcavity based on a topological structure on an SOI wafer by electron beam lithography (EBL) and inductively coupled plasma (ICP) etching, and then depositing a layer of silicon dioxide with a thickness of 1 μm on the exposed top surface of the structure by plasma enhanced chemical vapor deposition (PECVD), and then injecting an optical signal into one end of the straight waveguide coupler to obtain transmitted light at the other end to achieve optical filtering.

[0017] like Figure 2 As shown, the straight waveguide coupler is a straight waveguide structure, and its width is w=0.875a, where a is the topological structure period.

[0018] like Figure 3 As shown, the one-dimensional photonic crystal nanobeam microcavity is composed of a plurality of microcavity units arranged in a straight line.

[0019] The linear arrangement refers to: large elliptical microcavity units and small elliptical microcavity units symmetrically and alternately arranged on both sides of the central defect area, the short axis lengths of the large elliptical microcavity unit and the small elliptical microcavity unit are d1=0.3a and d2=0.2a respectively, and a is the topological structure period.

[0020] The period numbers of the two topological structures are both 60, and the length of the nanobeam waveguide is 48.4 μm.

[0021] The straight waveguide coupler forms side coupling with the one-dimensional photonic crystal nanobeam microcavity, and forms a topological defect of the nanocavity on the interface between two photonic crystals with different topologies, thereby ensuring that only one mode exists in the photonic band gap.

[0022] The SOI wafer comprises: 220 nanometers thick silicon and 3 μm thick silicon dioxide.

[0023] In this embodiment, the period a of the topological structure is 0.4 μm, the minor axis length of the corresponding large ellipse is 0.12 μm, and the minor axis length of the small ellipse is 0.08 μm; the major axis lengths of the two elliptical structures are both 0.304 μm; the width of the one-dimensional photonic crystal nanobeam waveguide is 0.484 μm.

[0024] Due to the protection of the topological structure, if the parameters such as the length of the major and minor axes of the ellipse in the topological structure, the width of the silicon waveguide and the width of the straight waveguide change slightly, the center frequency of the filter will be slightly red-shifted or blue-shifted, the mode volume will be linearly shifted, the quality factor will be cubically shifted with the change ratio, and the mode will still exist in the center of the device, and the device can still form topological protection. Therefore, the device has a large tolerance and good process robustness.

[0025] Since the zak phase of the topological structures of the two antisymmetric structures can be normalized to 0 and PI, a "zero-point defect" can be introduced at the interface of the two topological structures in the photonic band gap to achieve the filtering effect. A straight waveguide is used to couple the nanobeam waveguide for filtering. After 3D-FDTD simulation, the extinction ratio is ~25dB, the Q value is ~26000, and the mode volume is ~1.10μm 3 The simulation results are shown in Figure 2.

[0026] This embodiment uses 3D finite difference time domain method (3D-FDTD) to simulate the filtering process of the structure, which is a filter of a single one-dimensional photonic crystal nanobeam microcavity based on a topological structure. During the simulation process, the light source is in TE0 mode, a monitor is placed at the output port of the straight waveguide to monitor the output filtering signal, and the transmission spectrum of the corresponding structure is recorded.

[0027] Both the straight waveguide and the nanobeam waveguide are silicon waveguides, and the elliptical etching is silica etching. When performing 3D-FDTD simulation, the background of the entire device area is silica. First, use the optimization in 3D-FDTD to optimize the nanobeam microcavity structure, and then add the straight waveguide. The optimization method is also used to optimize the width of the straight waveguide and the gap between the two waveguides, and finally the optimal solution is obtained.

[0028] This embodiment is insensitive to slight changes in parameters such as the major and minor axes of the ellipse, the width of the silicon waveguide and the width of the straight waveguide in the topological structure, and has strong process robustness and large tolerance. When the above parameters change slightly in proportion, the mode still exists in the center of the device, and the central wavelength shifts linearly.

[0029] like Figure 5 As shown; the device mode volume shifts linearly, as Figure 6 As shown; the device quality factor changes with the proportion of structural parameters as shown Figure 7 shown. Figure 5 , Figure 6 , Figure 7 The horizontal axis ratio in is defined as:

[0030] In this embodiment, the size of a single filter is 50×3 μm. 2 the following.

[0031] The extinction ratio of the filter in this embodiment is 25 dB, the Q value is 26000, and the mode volume is 1.10 μm. 3 .

[0032] Compared with the existing technology, this method ensures that only the TE0 mode exists in the photonic band gap by introducing a microcavity with a topological structure. While ensuring a small volume, a high extinction ratio and a high Q value, the process has strong robustness and a large tolerance.

[0033] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. A silicon-based passive optical filtering method for photonic crystal nanobeam microcavity, characterized in that: A straight waveguide coupler and a parallel one-dimensional photonic crystal nanobeam microcavity based on a topological structure are prepared on an SOI wafer by electron beam lithography and inductively coupled plasma etching. A layer of silicon dioxide is then deposited on the exposed top surface of the structure by plasma enhanced chemical vapor deposition. Then, an optical signal is injected into one end of the straight waveguide coupler and transmitted light is obtained at the other end. Side coupling is formed between the straight waveguide coupler and the one-dimensional photonic crystal nanobeam microcavity, and a topological defect of the nanocavity is formed on the interface between two photonic crystals with different topologies, ensuring that only one mode exists in its photonic band gap, thereby realizing optical filtering.

2. The silicon-based passive optical filtering method of the photonic crystal nanobeam microcavity according to claim 1 is characterized in that: The straight waveguide coupler is a straight waveguide structure, the width of which is w=0.875a, where a is the topological structure period.

3. The silicon-based passive optical filtering method of the photonic crystal nanobeam microcavity according to claim 1 is characterized in that: The one-dimensional photonic crystal nanobeam microcavity is composed of a number of microcavity units arranged in a straight line; The linear arrangement refers to: large elliptical microcavity units and small elliptical microcavity units symmetrically and alternately arranged on both sides of the central defect area.

4. The silicon-based passive optical filtering method of the photonic crystal nanobeam microcavity according to claim 3 is characterized in that: The minor axis lengths of the large elliptical microcavity unit and the small elliptical microcavity unit are d1=0.3a and d2=0.2a respectively, where a is the topological structure period.

5. The silicon-based passive optical filtering method of the photonic crystal nanobeam microcavity according to claim 2 or 3, characterized in that: The period of the topological structure is 60, and the length of the nanobeam waveguide is 48.4 μm.

6. The silicon-based passive optical filtering method of the photonic crystal nanobeam microcavity according to claim 2 or 3, characterized in that: The SOI wafer comprises: 220 nanometers thick silicon and 3 μm thick silicon dioxide; The deposited layer of silicon dioxide has a thickness of 1 μm.

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