A multi-channel filter based on period-multiplying photonic crystals

Abstract

The present invention provides a multi-channel filter based on period multiplication photonic crystal, belonging to the field of optical technology. The arrangement rule of the period multiplication sequence in the multi-channel filter is: S0 = H, S1 = HL, S2 = HLHH, ..., S N =S N‑1 S N‑2 S N‑2 , ..., where N is the number of the periodic doubling sequence, S N represents the Nth term of the periodic multiplication sequence; wherein H is the first dielectric layer, L is the second dielectric layer, the first dielectric layer and the second dielectric layer are two uniform dielectrics with different refractive indices; the thickness of the first dielectric layer and the second dielectric layer is 1 / 4 of the optical wavelength corresponding to their respective refractive indices. The present invention has optical fractal forms of multi-wavelength resonance, corresponding to a series of transmission modes, and these optical fractal forms can be used in multi-channel photon filters.

Description

Technical Field

[0001] The invention belongs to the field of optical technology and relates to a multi-channel filter based on periodic multiplication photonic crystals. Background Art

[0002] Filters can be divided into four types according to their amplitude-frequency characteristics: bandpass, bandstop, low-pass, and high-pass. In wavelength division multiplexing technology, multiple independent channels need to be filtered, which requires the use of multi-channel filters. Traditional optical wavelength division multiplexers achieve channel filtering and separation by regulating the spatial period of fiber gratings. The emergence of artificial photonic crystals provides new options for the design of multi-channel filters.

[0003] Dielectrics with different refractive indices are arranged periodically in space to form one-dimensional, two-dimensional or three-dimensional photonic crystals. Photonic crystals have a band structure, which allows them to fully transmit and fully reflect light waves. In defective photonic crystals, there is a single transmission mode, also called a defect mode, because the defect enhances the localization of the light field, thereby improving the resonance of the light wave. The transmittance of the defect mode is extremely large, while the reflection is extremely small.

[0004] Studies have shown that quasi-periodic photonic crystals also have band structures, and their order is between that of periodic photonic crystals and non-periodic photonic crystals. Therefore, there are multiple natural defect layers in quasi-periodic photonic crystals, which are often used to obtain resonant mode output. In addition, the number and position of defect modes in quasi-periodic photonic crystals can be expanded by increasing the order of the quasi-photonic crystal.

[0005] Mathematically, the period-doubling (PD) sequence is a quasi-periodic sequence, and its corresponding PD photonic crystal is a quasi-periodic photonic crystal. In PD photonic crystals, there are a series of transmission modes. These transmission modes are formed by the resonance of light waves in the defect layer. As the sequence number increases, the number of defect modes expands rapidly, and the defect modes have self-similar characteristics. This phenomenon is called the optical fractal effect, and the corresponding resonance mode is also called the optical fractal form. The optical fractal form can be applied to multi-channel optical filters. The number of channels can be controlled by the sequence number of the PD sequence, and the position of the channel can be flexibly controlled by the incident angle of the light wave. Summary of the invention

[0006] The purpose of the present invention is to provide a multi-channel filter based on periodic multiplication photonic crystals in view of the above-mentioned problems existing in the prior art. The technical problem to be solved by the present invention is to make the multi-layer structure have an optical fractal form with multi-wavelength resonance, which can be used for a multi-channel photonic filter.

[0007] The object of the present invention can be achieved by the following technical scheme: a multi-channel filter based on period multiplication photonic crystal, characterized in that the arrangement rule of PD sequence in the multi-channel filter is: S0 = H, S1 = HL, S2 = HLHH, ..., S N =S N-1 S N-2 S N-2 , ..., where N is the number of the periodic doubling sequence, S N represents the Nth term of the periodic multiplication sequence; wherein H is the first dielectric layer, L is the second dielectric layer, the first dielectric layer and the second dielectric layer are two uniform dielectrics with different refractive indices; the thickness of the first dielectric layer and the second dielectric layer are 1 / 4 of the optical wavelength corresponding to their respective refractive indices.

[0008] Furthermore, the first dielectric layer is made of lead telluride, a material with a high refractive index, and the second dielectric layer is made of cryolite, a material with a low refractive index.

[0009] Furthermore, the number of filter channels of the multi-channel filter increases as the sequence number increases, and the center frequency of each filter channel in the multi-channel filter is adjusted by the incident angle.

[0010] Two dielectric sheets with different refractive indices are arranged in sequence according to the PD sequence to form a PD photonic crystal. There are optical fractals with multi-wavelength resonance in this structure, corresponding to a series of transmission modes. These optical fractals can be used in multi-channel photonic filters. The number of channels can be expanded by increasing the number of PD sequences, and the intermediate frequency length of each channel can be flexibly adjusted by changing the size of the incident angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram of the period multiplication photonic crystal structure.

[0012] Figure 2 1 and 2 are transmission spectra corresponding to PD photonic crystals with different serial numbers, wherein the serial numbers of the PD photonic crystals corresponding to (a), (b), (c) and (d) are N=2, 3, 4 and 5 respectively.

[0013] Figure 3 It is the transmission spectrum of the PD photonic crystal corresponding to different incident angles when serial number N=4.

[0014] Figure 4 (a) When the sequence number N = 4 Figure 3 Transmittance of middle channel 1 varies with incident angle; Figure 4 (b) When the sequence number N = 4 Figure 3 The relationship between the normalized frequency of channel 1 and the incident angle; Figure 4 (c) When the sequence number N = 4 Figure 3Transmittance of middle channel 2 varies with incident angle; Figure 4 (d) When the sequence number N = 4 Figure 3 Normalized frequency of channel 2 as a function of incident angle.

[0015] In the figure, H is the first dielectric layer; L is the second dielectric layer. DETAILED DESCRIPTION

[0016] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0017] Mathematically, the iteration rule of the period-doubling (PD) sequence is: S0 = H, S1 = HL, S2 = HLHH, ..., S N =S N-1 S N-2 S N-2 , ..., where N (N = 0, 1, 2, 3, ...) is the sequence number, S N Indicates the Nth item of the sequence. In the corresponding PD photonic crystal, the letters H and L represent two uniform dielectric sheets with high and low refractive indices, respectively.

[0018] Figure 1 The PD photonic crystal structures with serial numbers N=0, 1, 2 and 3 are given respectively, where H is the high refractive index material lead telluride, whose refractive index is n H =4.1; L is the low refractive index material cryolite, whose refractive index is n L =1.35. The incident light is a transverse magnetic wave, incident vertically from the left. The thickness of H and L is 1 / 4 of the optical wavelength, that is, the thickness of H is d H =λ0 / 4 / n H = 0.0945 μm (μm means micrometer), where λ0 = 1.55 μm is the central wavelength, and the thickness of L is d L =λ0 / 4 / n L =0.287μm.

[0019] In quasi-photonic crystals, there is an optical fractal effect. The optical fractal effect can be used to obtain a multi-channel filter and expand the filter channel. When the transverse magnetic wave is incident vertically, Figure 2 (a) shows the transmission spectrum of the PD photonic crystal with N = 2. The ordinate T represents the transmittance, and the abscissa (ω-ω0) / ω gap represents the normalized angular frequency, where ω = 2πc / λ, ω0 = 2πc / λ0 and ω gap =4ω0arcsin│(n a -n b ) / (n a +nb )| 2 / π represent the incident light angular frequency, the incident light center angular frequency and the angular frequency band gap, respectively, c is the speed of light in a vacuum, and arcsin is the inverse sine function. It can be seen that there is a photon band gap in the normalized frequency interval (-1,1); in the middle of the band gap, that is, between the two dotted lines, the number of transmission peaks is 1. Therefore, the number of filtering channels in this structure is 1. Figure 2 (b) shows the transmission spectrum corresponding to the PD photonic crystal with N=3. In the middle of the band gap, the number of transmission peaks is 2, and the number of filtering channels in this structure is 2. Figure 2 (c) shows the transmission spectrum corresponding to the PD photonic crystal with N=4. Between the two dotted lines, the number of transmission peaks is 6, so the number of filtering channels in this structure is 6. Figure 3 (d) shows the transmission spectrum corresponding to the PD photonic crystal with N=5. The number of transmission peaks in the middle of the band gap is 12, so the number of filtering channels in the structure is 12.

[0020] For a clear comparison, we give the number of filter channels corresponding to PD photonic crystals with different serial numbers N in Table 1. The conditions given in the table are: vertical incidence of light waves, and the normalized frequency interval is (-1,1). It can be seen from the table that as the serial number N increases, the number of filter channels increases rapidly, and this effect can be used to expand the number of filter channels.

[0021] Table 1 Number of filter channels in PD photonic crystals with different serial numbers

[0022]

[0023] It was mentioned in the above content that when N=4 and the light wave is incident vertically, the number of filter channels in the middle of the PD photonic crystal band gap is 6. Here, the size of the light wave incident angle will be changed to adjust the center frequency of each filter channel. When the light wave is incident on the PD photonic crystal with N=3, Figure 4 The transmission spectra corresponding to the incident angles of θ = 0°, 15°, 30° and 45° are given respectively. It can be seen that although the incident angle is changing, the number of filter channels remains unchanged in the middle of the band gap. It is just that as the incident angle increases, the transmission spectrum moves to the right as a whole. For this reason, the center frequency of the filter channel can be changed by adjusting the size of the incident angle. For the convenience of comparison, two specific filter channels are selected for quantitative description, and the positions of the two channels are circled with ellipses, and they are named channel 1 and channel 2 in order from left to right.

[0024] Will Figure 3 The transmittance corresponding to channel 1 is denoted as T1, and the corresponding transmission mode center frequency is denoted as ω1; the transmittance corresponding to channel 2 is denoted as T2, and the corresponding transmission mode center frequency is denoted as ω2.

[0025] Figure 4 (a) shows the relationship between the transmittance T1 of channel 1 and the incident angle θ. It can be seen that as the incident angle increases, the transmittance T1 increases accordingly; when θ increases from = 0° to 60°, the transmittance T1 increases from 0.8054 to 0.9391. Figure 4 (b) shows the relationship between the transmission mode center frequency ω1 of channel 1 and the incident angle. It can be seen that as the incident angle increases, the transmittance ω1 increases accordingly; when θ increases from 0° to 60°, (ω1-ω0) / ω gap Increased from -0.6979 to -0.5535.

[0026] Figure 4 (c) shows the relationship between the transmittance T2 of channel 2 and the incident angle θ. It can be seen that: as the incident angle increases, the transmittance T2 first decreases and then increases; when θ increases from 0° to 60°, the transmittance T2 decreases from 0.8054 to 0.8001, and then increases to 0.8731; it has a minimum value of 0.8001 near θ = 25°. Figure 4 (d) shows the relationship between the transmission mode center frequency ω1 of channel 2 and the incident angle. It can be seen that as the incident angle increases, the transmittance ω2 increases accordingly; when the incident angle θ increases from 0° to 60°, (ω2-ω0) / ω gap Rising from 0.6978 to 0.9051.

[0027] In short, there are optical fractal forms in PD photonic crystals, corresponding to different transmission modes. These transmission films can be used for multi-channel photon filtering. The number of filter channels can be expanded by increasing the sequence number, and the center frequency of each filter channel can be flexibly adjusted by changing the size of the incident angle.

[0028] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A multi-channel filter based on period multiplication photonic crystal, characterized in that: The arrangement rule of the periodic doubling sequence in the multi-channel filter is: S0 = H, S1 = HL, S2 = HLHH, ..., S N =S N-1 S N-2 S N-2 , ..., where N is the number of the periodic doubling sequence, S N represents the Nth term of the periodic multiplication sequence; wherein H is the first dielectric layer, L is the second dielectric layer, the first dielectric layer and the second dielectric layer are two uniform dielectrics with different refractive indices; the thickness of the first dielectric layer and the second dielectric layer are 1 / 4 of the optical wavelength corresponding to their respective refractive indices.

2. A multi-channel filter based on period multiplication photonic crystal according to claim 1, characterized in that: The first dielectric layer is lead telluride, a material with a high refractive index, and the second dielectric layer is cryolite, a material with a low refractive index.

3. A multi-channel filter based on period multiplication photonic crystal according to claim 1 or 2, characterized in that: The number of filter channels of the multi-channel filter increases as the sequence number increases, and the center frequency of each filter channel in the multi-channel filter is adjusted by the incident angle.

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