An ultra-narrow bandwidth dual-notch filter

Abstract

The application discloses a kind of ultra-narrow bandwidth double trap wave filters, comprising: upper periodic nanorod layer (1), substrate layer (2) and lower periodic nanorod layer (3);The upper periodic nanorod layer (1) is attached to the upper surface of the substrate layer (2), and the lower periodic nanorod layer (3) is attached to the lower surface of the substrate layer (2);In the upper periodic nanorod layer (1) and lower periodic nanorod layer (3), two nanorods are a unit, and are arranged in the same periodic manner.This trap wave filter structure is compact, easy to prepare, and has a low manufacturing cost, and also has two wavelength stop bands, and the stop band bandwidth is very narrow, uses all-dielectric materials, avoids ohmic loss, and is simple in structure and low in cost.

Description

Technical Field

[0001] This invention belongs to the field of optical communication technology, specifically relating to an ultra-narrow bandwidth dual notch filter. Background Technology

[0002] With the advancement of science and technology, especially the rapid development of optical communication technology, there is a growing demand for highly integrated optical communication devices, leading to increasingly smaller individual components. Notch filters can pass most wavelengths almost without loss while attenuating a specific wavelength. These devices have wide applications in image processing, data transmission, seismology, biomedical engineering, Raman spectroscopy, and laser protective coatings.

[0003] Traditional notch filters are composed of multiple thin layers, making them costly, difficult, and complex to manufacture. The traditional method for fabricating notch filters is to stack high-refractive-index and low-refractive-index dielectric films to create a layered design with refractive index differences. The stopband width depends on the thickness of the high-refractive-index and low-refractive-index layers and their refractive index ratio. Furthermore, the stopband bandwidth is controlled by selecting a relatively small refractive index difference between the two materials. However, in actual fabrication, distinguishing between high-refractive-index and low-refractive-index materials with similar refractive indices, and precisely controlling their thicknesses to achieve the desired notch filter performance, are challenging problems. Additionally, existing narrowband notch filters have relatively wide bandwidths, severely limiting their application in the communications field. Summary of the Invention

[0004] In order to solve the technical problems existing in the background art, the present invention aims to provide an ultra-narrow bandwidth dual notch filter based on periodic all-dielectric bilayer nanorods. This notch filter has a compact structure, is easy to fabricate, has low manufacturing cost, and has two wavelength stopbands with very narrow stopband bandwidth.

[0005] To solve the technical problem, the technical solution of the present invention is as follows:

[0006] An ultra-narrow bandwidth dual notch filter includes: an upper periodic nanorod layer, a substrate layer, and a lower periodic nanorod layer; the upper periodic nanorod layer is attached to the upper surface of the substrate layer, and the lower periodic nanorod layer is attached to the lower surface of the substrate layer.

[0007] Furthermore, in the upper and lower periodic nanorod layers, two nanorods form a unit and are arranged in the same periodic manner.

[0008] Furthermore, the nanorods in both the upper and lower periodic nanorod layers are made of dielectric silicon material.

[0009] Furthermore, the substrate layer is made of silicon dioxide.

[0010] Furthermore, the nanorods in the upper and lower periodic nanorod layers are spaced apart.

[0011] During operation, light waves enter the device through input terminal I. The upper and lower periodic nanorod layers generate Fabry-Pérot continuous domain bound states for the light, confining the energy within the silicon nanolayer. Transmitted light exits from the transmitted light wave output terminal O1, and reflected light exits from the reflection port O2.

[0012] Compared with the prior art, the advantages of the present invention are as follows:

[0013] This invention discloses an ultra-narrow bandwidth dual notch filter based on periodic all-dielectric bilayer nanorods. This notch filter has a compact structure, is easy to fabricate, and has low manufacturing cost. It also has two wavelength stopbands with very narrow stopband bandwidth. By using all-dielectric materials, ohmic loss is avoided, and the structure is simple and low-cost. Attached Figure Description

[0014] Figure 1 This is a schematic front view of the dual notch filter structure in the embodiment.

[0015] Figure 2 This is a side view schematic diagram of the dual notch filter structure in the embodiment;

[0016] Figure 3 This is a schematic diagram of the transmission spectrum of the dual notch filter in the embodiment;

[0017] Figure 4 This is a schematic diagram of the transmission spectrum of valley 1 of the dual notch filter in the embodiment;

[0018] Figure 5 This is a schematic diagram of the transmission spectrum of valley 2 of the dual notch filter in the embodiment;

[0019] Figure 6 This is a schematic diagram of the electric field intensity distribution in valley 1 of the dual notch filter in the embodiment.

[0020] Figure label:

[0021] 1. Upper nanorod layer; 2. Base layer; 3. Lower nanorod layer; I. ​​Light wave incident end; O1. Transmitted light wave output end; O2. Reflected light wave output end. Detailed Implementation

[0022] The specific implementation of the present invention is described below with reference to embodiments:

[0023] It should be noted that the structures, proportions, sizes, etc. shown in this specification are only used to complement the content disclosed in the specification for those skilled in the art to understand and read, and are not intended to limit the conditions under which the present invention can be implemented. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0024] Furthermore, the terms such as "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity of description and are not intended to limit the scope of the invention. Any changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0025] Example 1:

[0026] An ultra-narrowband dual-notch filter based on periodic all-dielectric bilayer nanorods includes a base layer 2, an upper nanorod 1, and a lower nanorod 3. The upper and lower nanorods have the same structure. Two nanorods form a unit and are arranged periodically.

[0027] The substrate layer 2 is silicon dioxide.

[0028] The upper nanorod 1 is directly attached to the upper surface of the substrate layer 2 and is made of dielectric silicon material.

[0029] The lower nanorods 3 are directly attached to the lower surface of the substrate layer 2 and are made of dielectric silicon material.

[0030] The width of the substrate layer 2 is 50 μm. TE mode light is incident orthogonally through the upper periodic structure, passes through the cavity formed by nanorods, and the transmitted light is output from the lower periodic structure, while the reflected light is output from the input end.

[0031] When this filter operates, it is mainly based on optically continuous bound states, which theoretically have a very large radiation quality factor Q. However, in practice, due to structural asymmetry, material absorption dispersion, and structural size defects, continuous bound states may collapse into leakage resonances with finite Q factors. This resonance mode is called a quasi-continuous bound state.

[0032] Based on the different physical mechanisms underlying the generation of continuous-domain bound states, optics primarily classifies them into two categories: symmetry-protected continuous-domain bound states and incidental continuous-domain bound states. Symmetry-protected continuous-domain bound states depend on structural symmetry; under conditions that introduce defects or perturbations that disrupt structural symmetry, the symmetry-protected continuous-domain bound state collapses into a quasi-continuous-domain bound state with a high Q value. The other type of continuous-domain bound state belongs to coupled resonances and can be further divided into two types: the Friedrich–Wintgen continuous-domain bound state formed by interference between two different resonances in the same cavity, and the Fabry–Pérot continuous-domain bound state based on two identical resonances of two interacting cavities coupled through a single radiation channel.

[0033] The two-layer periodic structure confines the incident light wave, thereby exciting bound states in the Fabry–Pérot continuous domain. The physical mechanism of this bound state generation can be explained using temporal coupled-mode theory: a closed resonant cavity can form resonant modes with spatiotemporal dynamics, whose expressions share a common time factor e. iwt The energy excited by the bound modes in this field plays a decisive role in the magnitude of the field amplitude, which is denoted by 'a'. For ease of description, two additional assumptions need to be made regarding the resonant cavity: firstly, there are no energy exchange ports; secondly, the system is closed and there is no energy loss. The amplitude of this dynamic field is then subjected to time differentiation:

[0034]

[0035] Where Ω corresponds to the frequency matrix, it can be written as:

[0036]

[0037] Where: ω 01 and ω 02 These are the resonant frequencies of the modes. The magnitude of K represents the degree of coupling between modes. In this case, since the upper and lower layer structures are identical, we have ω. 01 =ω 02 =ω. Suppose that the incident wave I from the port resonates with the system's resonant cavity, and the resonant cavity also radiates energy to the port. At this time, the energy inside the cavity will decay, and let the decay rate be Γ.

[0038] At this point, the dynamic expression of the system can be expressed as:

[0039]

[0040] Where D represents the coupling coefficient matrix, and the attenuation rate Γ is a second-order matrix:

[0041]

[0042] Where γ represents the energy dissipation of the mode, and is the damping rate of a single resonance. This is the phase difference between the round trip of the electromagnetic waves within the resonant cavity. For such a system, its Hamiltonian matrix H can be written as:

[0043]

[0044] By solving for the eigenvalues ​​of the Hamiltonian matrix H, we have:

[0045]

[0046] When the phase difference of an electromagnetic wave during one round trip within the resonant cavity is an integer multiple of 2π, it corresponds to It is an integer multiple of π. Therefore, the phase difference of electromagnetic waves in the resonant cavity can be changed by adjusting the thickness of the substrate. When the phase matching condition is met, the Fabry–Pérot continuous domain bound state with eigenfrequency ω+k can be obtained.

[0047] When a plane electromagnetic wave enters the filter device, it oscillates in the resonant cavity composed of nanorods. When the thickness of the substrate changes, the symmetry protection is disrupted, mode leakage occurs, and a quasi-continuous domain bound state is formed, thereby realizing an ultra-narrow double notch filter.

[0048] This dual notch filter uses all-dielectric materials, avoiding ohmic losses, and is simple to construct and low in cost.

[0049] Example 2:

[0050] Reference Figure 1 and Figure 2 An ultra-narrow bandwidth dual-notch filter based on a periodically structured all-dielectric bilayer nanorod includes an upper periodic nanorod layer 1, a substrate layer 2, and a lower periodic nanorod layer 3. The upper periodic nanorod layer 1 and the lower periodic nanorod layer 3 are arranged in the same periodic pattern. For a single periodic unit, the center-to-center spacing between the two nanorods in the upper periodic nanorod layer 1 is 465 nm, the width of the substrate layer 2 is 1000 nm, and the center-to-center spacing between the two nanorods in the lower periodic nanorod layer 3 is 465 nm. This embodiment uses 50 periodic units.

[0051] The upper periodic nanorod layer 1 is a dielectric silicon nanorod. In this example, the refractive index of silicon is 3.45, the diameter of the silicon nanorod is 300 nm, and the length is 50 μm.

[0052] The substrate 2 is silicon dioxide. In this example, the silicon dioxide has a refractive index of 1.45, a thickness of 700 nm, and a length and width of 50 μm.

[0053] The lower periodic nanorod layer 2 is a dielectric silicon nanorod. In this example, the refractive index of silicon is 3.45, the diameter of the silicon nanorod is 300 nm, and the length is 50 μm.

[0054] The upper periodic nanorod layer 1 is directly adhered to the upper surface of the substrate layer 2.

[0055] The lower periodic nanorod layer 2 is directly adhered to the lower surface of the substrate layer 2.

[0056] When the filter is in operation, light waves enter the device through input terminal I. The upper periodic nanorod layer 1 and the lower periodic nanorod layer 2 generate Fabry-Pérot continuous domain bound states for the light. The energy is then confined within the silicon nanolayers. Figure 6 The electric field distribution at 1310.12 nm in this case is shown, and it is clear that the electric field energy is basically confined within the structure. Transmitted light exits from the transmitted light wave output port O1, and reflected light exits from the reflected light port O2.

[0057] refer to Figure 4 The transmission spectrum of this case shows two very distinct valley lines, namely Valley 1 and Valley 2. The center wavelength of Valley 1 is located at 1310.12 nm, and the center wavelength of Valley 2 is located at 1330.92 nm. Figure 4 The transmission spectrum of Valley 1 shows that its linewidth is 0.02 nm. Figure 5 The transmission spectrum of Valley 2 shows that its linewidth is 0.11 nm.

[0058] from Figure 3 The transmission spectrum clearly shows that, except for the valley line spectrum, the transmittance of the other spectra is greater than 95%. This indicates that the double notch filter has excellent filtering capabilities and is a high-performance filter.

[0059] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

[0060] Many other changes and modifications can be made without departing from the concept and scope of this invention. It should be understood that this invention is not limited to the specific embodiments, and the scope of this invention is defined by the appended claims.

Claims

1. An ultra-narrow bandwidth dual notch filter, characterized in that, include: The substrate consists of an upper periodic nanorod layer (1), a base layer (2), and a lower periodic nanorod layer (3). The upper periodic nanorod layer (1) is attached to the upper surface of the base layer (2), and the lower periodic nanorod layer (3) is attached to the lower surface of the base layer (2). The upper periodic nanorod layer (1) and the lower periodic nanorod layer (3) have the same periodic arrangement and are each composed of multiple periodic units. Within a single periodic unit, the center-to-center distance between two adjacent nanorods in the upper periodic nanorod layer (1) is 465 nm, the center-to-center distance between two adjacent nanorods in the lower periodic nanorod layer (3) is 465 nm, and the width of the base layer (2) is 1000 nm. Both the upper periodic nanorod layer (1) and the lower periodic nanorod layer (3) are made of dielectric silicon material with a refractive index of 3.

45. The silicon nanorods have a diameter of 300 nm and a length of 50 μm; the substrate layer (2) is made of silicon dioxide material with a refractive index of 1.45, a thickness of 700 nm, and a length and width of 50 μm; the number of periodic units is 50; in the working state, light waves enter from the input end (I), and the upper periodic nanorod layer (1) and the lower periodic nanorod layer (3) generate Fabry-Pérot continuous domain bound states for the light, confining the electric field energy within the silicon nanorod layer, thereby forming two notch valleys with center wavelengths of 1310.12 nm and 1330.92 nm respectively in the transmission spectrum, wherein the linewidth of the first notch valley is 0.02 nm and the linewidth of the second notch valley is 0.11 nm, and the transmittance of the other bands is greater than 95% except for the bands corresponding to the notch valleys.

2. The ultra-narrow bandwidth dual-notch filter of claim 1, wherein, In the upper periodic nanorod layer (1) and the lower periodic nanorod layer (3), two nanorods form a unit and are arranged in the same periodic manner.

3. The ultra-narrow bandwidth dual notch filter according to claim 1, characterized in that, The nanorods in both the upper periodic nanorod layer (1) and the lower periodic nanorod layer (3) are made of dielectric silicon material.

4. The ultra-narrow bandwidth dual-notch filter of claim 1, wherein, The substrate layer (2) is made of silicon dioxide.

5. The ultra-narrow bandwidth dual notch filter according to claim 1, characterized in that, The nanorods in the upper periodic nanorod layer (1) and the lower periodic nanorod layer (3) are all spaced apart.

6. The ultra-narrow bandwidth dual notch filter according to claim 1, characterized in that, When in operation, light waves enter the device from the input terminal I. The upper periodic nanorod layer (1) and the lower periodic nanorod layer (2) generate Fabry-Pérot continuous domain bound states for the light, and the energy is confined within the silicon nanolayer. The transmitted light is emitted from the transmitted light wave output terminal O1, and the reflected light wave is emitted from the reflection port O2.

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