CN215833643U

CN215833643U - Multi-channel photonic filter based on binary Rudin-Shapiro photonic crystal pair

Info

Publication number: CN215833643U
Application number: CN202122339152.2U
Authority: CN
Inventors: 刘芳华
Original assignee: Hubei University of Science and Technology
Current assignee: Hubei University of Science and Technology
Priority date: 2021-09-26
Filing date: 2021-09-26
Publication date: 2022-02-15
Anticipated expiration: 2031-09-26

Abstract

The utility model provides a multi-channel photonic filter based on a binary Rudin-Shapiro photonic crystal pair, and belongs to the technical field of optics. The multi-channel photonic filter comprises two binary RS photonic crystals which are symmetrically distributed, wherein each binary RS photonic crystal comprises a plurality of first dielectric layers H and a plurality of second dielectric layers L, and the structure of the multi-channel photonic filter is represented as HHHLHHLHHLHHLHHH; the first dielectric layer and the second dielectric layer are respectively two uniform dielectric sheets with different refractive indexes; the first dielectric layer and the second dielectric layer have a thickness of 1/4 a of the respective optical wavelength. The utility model can be used for multi-channel photonic filters. Compared with RS photonic crystals, the filtering channel in the photonic crystal pair has better selectivity on frequency.

Description

Multi-channel photonic filter based on binary Rudin-Shapiro photonic crystal pair

Technical Field

The utility model belongs to the technical field of optics, and relates to a multi-channel photonic filter based on a binary Rudin-Shapiro photonic crystal pair.

Background

Dielectric sheets with different refractive indexes are arranged periodically in space to form one-dimensional, two-dimensional or three-dimensional photonic crystals. Photonic crystals have band structures, which can be used for total transmission and total reflection of light waves. The band gap of the photonic crystal with defects has defects, and the defect mode is also a transmission mode. The defects can enhance the electric field locality, thereby improving the resonant output of the light waves. The transmission of the defect mode is extremely large and the reflection is extremely small.

The quasi-periodic photonic crystal also has an energy band structure with an order between that of the periodic photonic crystal and that of the aperiodic photonic crystal. The presence of a natural defect layer in a quasi-periodic photonic crystal is often used to obtain defect mode output. In addition, the number of defect modes in the quasi-periodic photonic crystal expands rapidly with the increase of the ordinal number of the crystal, and the defect modes have self-similar characteristics, so the phenomenon is called optical fractal effect, and the corresponding resonance mode is called optical fractal. The optical fractal effect can be applied to electric field localization, reflection enhancement, lasers, filters, and the like.

In particular, filters can be classified into four types, a band pass, a band stop, a low pass, and a high pass, according to the amplitude-frequency characteristics. In the wavelength division multiplexing technology, multiple channels need to be filtered, and thus a multi-channel filter is used. The traditional optical wavelength division multiplexer realizes the separation of channels by regulating and controlling the spatial period of the fiber grating. The rise of artificial photonic crystals fills a new design concept for the design of multi-channel filters.

Mathematically, a binary ludin-sharp (RS) sequence is a quasi-periodic sequence, and the corresponding RS photonic crystal is a quasi-periodic photonic crystal. In an RS photonic crystal, there are a series of transmission modes, corresponding to optically fractal states. When the optical fractal state is applied to a multi-channel optical filter, the number of channels can be expanded through the serial number of the RS sequence, and the positions of the channels can be flexibly regulated and controlled through the incident angle of light waves. However, in the photonic crystal of RS, the resonance of the defect mode is weak, and the width of the resonance peak is too large, i.e., the frequency selectivity of each channel is poor. In order to improve the frequency selectivity of the channel, two RS photonic crystals can be considered to be arranged in sequence along the same axis to form an RS photonic crystal pair. The whole structure is symmetrical about a central origin, and the structure is similar to a distributed feedback bragg grating. The structure has stronger frequency selectivity to light waves.

SUMMERY OF THE UTILITY MODEL

The present invention is directed to provide a multi-channel photonic filter based on a binary Rudin-Shapiro photonic crystal pair, and the technical problem to be solved by the present invention is how to make a composite structure applicable to the multi-channel photonic filter.

The purpose of the utility model can be realized by the following technical scheme: a multi-channel photonic filter based on a binary Rudin-Shapiro photonic crystal pair is characterized by comprising two binary RS photonic crystals which are symmetrically distributed, wherein each binary RS photonic crystal comprises a plurality of first dielectric layers H and a plurality of second dielectric layers L, the structure of the multi-channel photonic filter is represented as HHHLHHLHHLHHLHHH, the first dielectric layers and the second dielectric layers are respectively two uniform dielectric sheets with different refractive indexes, and the thicknesses of the first dielectric layers and the second dielectric layers are 1/4 of respective optical wavelengths.

Further, the first dielectric layer is made of lead telluride which is a high-refractive-index material, and the second dielectric layer is made of cryolite which is a low-refractive-index material.

Further, the central wavelength of the filtering channel of the multi-channel photonic filter is regulated and controlled by the size of the incident angle.

Furthermore, the number of the filtering channels of the multi-channel photonic filter is regulated and controlled by the size of the incident angle.

Two dielectric sheets H and L with different refractive indexes are sequentially arranged according to a binary Rudin-Shapiro (RS: ludin-Xiapino) sequence to form two RS photonic crystals. And compounding the two RS photonic crystals to form an RS photonic crystal pair which is symmetrical about an origin, wherein the structure is similar to a distributed feedback Bragg grating.

Optical fractal states of multi-wavelength resonance exist in the RS photonic crystal pair and correspond to a series of transmission modes; the frequency selectivity of the transmission mode in the RS photonic crystal pair is stronger than that of a single RS photonic crystal. These optical sub-morphologies can be used in multi-channel photonic filters; the number of channels can be expanded by increasing the serial number of the RS sequence, and the central wavelength of the channel can be flexibly regulated and controlled by changing the size of the incident angle. In addition, by changing the incidence angle, the conversion between the multichannel filter and the band-pass filter in the RS photonic crystal and the channel expansion of the multichannel filter can be realized.

Drawings

Fig. 1 is a schematic diagram of the structure of an RS photonic crystal pair with the number N-3.

FIG. 2 is a schematic diagram of the structure of RS photonic crystals with different numbers.

Fig. 3 shows transmission spectra corresponding to RS photonic crystal pairs of different numbers (where N is 2, 3, and 4 in the RS photonic crystal pairs corresponding to the graphs (a), (b), and (c)).

Fig. 4 shows transmission spectra corresponding to RS photonic crystals of different numbers (where N is 2, 3, and 4 in the RS photonic crystals corresponding to the graphs (a), (b), and (c)).

Fig. 5(a) is a transmission spectrum corresponding to an incident angle θ of 0 °, 30 °, and 60 ° in an RS photonic crystal pair with N of 3; fig. 5(b) is a transmission spectrum corresponding to an incident angle θ of 82 ° and 88 ° in the RS photonic crystal pair with N ═ 3.

Fig. 6 is a graph of transmission in parameter space as a function of angle of incidence and normalized frequency (RS photonic crystal pair with N-3).

Fig. 7 shows the variation of the center wavelength of the first transmission peak from left to right of fig. 6 with the incidence angle (N-3 RS photonic crystal pair).

In the figure, H, a first dielectric layer; l, a second dielectric layer.

Detailed Description

The following are specific embodiments of the present invention and are further described with reference to the drawings, but the present invention is not limited to these embodiments.

Fig. 1 shows a schematic structure diagram of a binary Rudin-Shapiro (RS: ludin-xiapino) photonic crystal pair with sequence number N ═ 3. The RS photonic crystal pair can be represented as: HHHLHHLHHLHHLHHH, wherein the letters H, L denote two homogeneous dielectric sheets with different high and low refractive indices, respectively. An RS photon with the index N-3 can be expressed as: HHHLHHLH. Therefore, two RS photonic crystals in the RS photonic crystal pair are symmetrically distributed about the origin, and the structure is similar to a distributed feedback Bragg grating.

In the RS photonic crystal pair, H is a high-refractive-index material lead telluride, and the refractive index of the material is n_H4.1 as the ratio; l is cryolite of low refractive index material with refractive index n_L1.35. Both H and L have a thickness of 1/4 optical wavelengths, i.e., H has a thickness d_H＝λ₀/4/n_H0.0945 μm (μm denotes μm), where λ₀1.55 μm as the center wavelength and L as the thickness d_L＝λ₀/4/n_L0.287 μm. Incident light is transverse magnetic wave and is incident from the left side, symbol I_iFor incident light, I_rTo reflect light, I_tTo transmit light, θ is the angle of incidence.

Mathematically, the iteration rule for a binary RS sequence is: s₀＝H，S₁＝HH，S₂＝HHHL，S₃＝HHHLHHLH，……，S_N＝S_N-1(HH → HHHL, HL → HHLH, LH → LLHL, LL → LLLH), … …, wherein N (N ═ 0, 1, 2, 3, … …) denotes the sequence number, S ═ S_NThe Nth item representing the sequence, HH → HHHL representing S_N-1HH in (1) is replaced by HHHL. Fig. 2 shows RS photonic crystal structures with numbers N ═ 0, 1, 2, and 3, respectively. In the corresponding RS photonic crystal, the letters H, L denote two kinds of uniform dielectric sheets having different refractive indices, respectively.

In quasi-photonic crystals, there is an optical fractal effect. The multi-channel filter can be obtained by utilizing the optical fractal effect, and the filtering channel can be expanded. When the transverse magnetic wave is vertically incident, fig. 3(a) shows the transmission spectrum corresponding to the RS photonic crystal pair with N ═ 2. The ordinate T represents the transmittance, and the abscissa (ω - ω)₀)/ω_gapDenotes a normalized angular frequency, where ω is 2 π c/λ, ω₀＝2πc/λ₀And ω_gap＝4ω₀arcsin│(n_H-n_L)/(n_H+n_L)|²And/pi respectively represents incident light angular frequency, incident light central angular frequency and angular frequency band gap, c is light speed in vacuum, and arcsin is an inverse sine function. It can be seen that between the two dotted lines of normalized frequency, the number of transmission peaks is 1, and therefore the filtering in this intervalThe number of wave channels is 1. Fig. 3(b) shows a transmission spectrum corresponding to an RS photonic crystal pair with N ═ 3, where the number of transmission peaks between two virtual lines is 3 and the number of filter channels in this interval is 3. Fig. 3(c) shows the transmission spectrum corresponding to the RS photonic crystal pair with N-4, where the number of transmission peaks between two dotted lines is 5, and the number of filter channels in the interval is 5.

Relative to the RS photonic crystal, the optical fractal state in the RS photonic crystal pair has stronger selectivity to frequency, i.e. the transmission peak becomes steeper and narrower. In addition, in the RS photonic crystal pair, along with the increase of the sequence number N, the selectivity of the optical fractal state to the frequency is better, which is shown in that the transmission peak is steeper and narrower.

The optical fractal state has a self-similar characteristic with which the number of filtering channels can be extended. For clarity of comparison, the number of filter channels of RS photonic crystal pairs with different numbers N in the frequency range between the two dashed lines is given in table 1. The conditions given in the table are: the light waves are incident vertically and the normalized frequency interval is between the two dashed lines in fig. 3. As can be seen from the table, the number of filter channels increases rapidly with increasing sequence number N, and this effect can be used to expand the number of filter channels. TABLE 1 number of channels of the RS photonic crystal pair of different sequence numbers in the frequency range between the two dotted lines

FIG. 4 shows the transmission spectra corresponding to RS photonic crystals with different numbers. Fig. 4(a) is the transmission spectrum of an RS photonic crystal with N-2, and it can be seen that between the two dashed lines, there is no formant; fig. 4(b) is a transmission spectrum of an RS photonic crystal with N-3, with the number of formants between two dashed lines being 1; fig. 4(c) is a transmission spectrum of an RS photonic crystal with N-4, and the number of formants between two dotted lines is 2. Comparing the corresponding transmission spectra of the RS photonic crystal pair in fig. 3 shows that: the same serial number N, in the transmission spectrum between two dotted lines, the number of the resonance peaks of the RS photonic crystal is less, and the resonance peaks are wider, namely the frequency selectivity is poorer.

In table 2, the number of filter channels corresponding to RS photonic crystals with different numbers N is given. The light waves are incident perpendicularly and the chosen normalized frequency interval is the section between the two dashed lines in fig. 4. As can be seen from the table, as the sequence number N increases, the number of filtering channels increases; but the number of filter channels is reduced compared with the RS photonic crystal pair with the same serial number N.

TABLE 2 number of channels of filtering channel in RS photonic crystal of different sequence number within frequency range between two dotted lines

In the above, it can be seen that: when N is 3, the light wave is vertically incident, in the RS photonic crystal pair, the number of filter channels is 3 in the range of normalized frequency interval [ -0.5,0.5 ]. The incident angle of the light wave is changed, so that the center frequency of each filtering channel is regulated. When a light wave is incident on the RS photonic crystal pair of N-3, fig. 5(a) shows transmission spectra corresponding to incident angles θ of 0 °, 30 °, and 60 °, respectively. It can be seen that the number of filter channels in the interval-0.5, 0.5 remains constant despite the variation in the angle of incidence. The transmission spectrum shifts overall to the right with increasing angle of incidence. For this purpose, the center frequency of the filter channel can be changed by adjusting the magnitude of the incident angle.

As the angle increases, fig. 5(b) shows transmission spectra corresponding to incident angles θ of 82 ° and 88 °, respectively. It can be seen that when the entrance angle increases to θ, 82 °, the resonant peaks in the middle dashed box begin to degenerate, and adjacent transmission peaks overlap, which is useful for bandpass filters. Continuing to increase the angle of incidence to θ 88 °, the number of formants increases to 5, and it is seen that splitting of the resonance states occurs, which can be used for channel spreading. Therefore, by changing the magnitude of the incident angle, not only the center wavelength of the channel can be changed, but also the multi-channel filter can be changed to a band-pass filter, and in addition, the number of channels can be expanded.

Keeping the index N equal to 3, fig. 6 shows the transmission of a parametric spatial light wave when the light wave is incident on the photonic crystal pair structure. The parameter space consists of the angle of incidence and the normalized frequency. It can be seen that between the white dotted lines, at an incident angle θ <60 °, there are 3 transmission peaks; when the incident angle increases, the transmittance shifts rightward as a whole, that is, the center frequency corresponding to the transmission peak increases and the wavelength decreases. Therefore, the central frequency of the filtering channel can be regulated and controlled by changing the incidence angle. As the incident angle gradually increases, the transmission peak starts to degenerate around θ 80 °; continuing to increase the angle of incidence, the transmission peak again splits as the angle of incidence approaches 90 °. This effect can be used for switching between a multi-channel filter and a band-pass filter, and for spreading the channel.

The first transmission peak between the two dashed lines in FIG. 6 is denoted as P₁With the corresponding center wavelength denoted as λ_p1。

FIG. 7 shows the first transmission peak P in the middle of FIG. 6₁Central wavelength λ of_p1As a function of the angle of incidence theta. It can be seen that as the angle of incidence increases, the center wavelength of the transmittance gradually decreases, i.e., a blue shift occurs; when θ rises from 0 ° to 60 °, the center wavelength λ_p1Reduced from 1.7271 μm to 1.6306 μm; the transmission ratio is always kept constant, T_p1＝1。

In summary, there is an optical fractal in a binary RS photonic crystal pair, corresponding to different transmission modes. Compared with the RS photonic crystal, the number of the transmission modes in the RS photonic crystal pair is increased, and the frequency selectivity of the transmission modes is better. The transmission modes can be used for multi-channel photon filtering, the number of filtering channels can be expanded by increasing sequence numbers, and the center frequency of each filtering channel can be flexibly regulated and controlled by changing the incidence angle. In addition, by changing the incidence angle, the conversion between the multichannel filter and the band-pass filter in the RS photonic crystal and the channel expansion of the multichannel filter can be realized.

The specific embodiments described herein are merely illustrative of the spirit of the utility model. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the utility model as defined in the appended claims.

Claims

1. A multi-channel photonic filter based on a binary Rudin-Shapiro photonic crystal pair is characterized by comprising two binary RS photonic crystals which are symmetrically distributed, wherein each binary RS photonic crystal comprises a plurality of first dielectric layers H and a plurality of second dielectric layers L, the structure of the multi-channel photonic filter is represented as HHHLHHLHHLHHLHHH, the first dielectric layers and the second dielectric layers are respectively uniform dielectric sheets with different refractive indexes of high and low, and the thicknesses of the first dielectric layers and the second dielectric layers are 1/4 of the optical wavelength of each dielectric layer.

2. The dual Rudin-Shapiro photonic crystal pair-based multi-channel photonic filter of claim 1, wherein the first dielectric layer is a high refractive index material of lead telluride, and the second dielectric layer is a low refractive index material of cryolite.

3. The dual Rudin-Shapiro photonic crystal pair-based multi-channel photonic filter as claimed in claim 1 or 2, wherein the central wavelength of the filtering channel of the multi-channel photonic filter is controlled by the size of the incident angle.

4. The dual Rudin-Shapiro photonic crystal pair-based multi-channel photonic filter as claimed in claim 1 or 2, wherein the number of filtering channels of the multi-channel photonic filter is regulated by the size of the incident angle.