CN111624706B - TM and TE mode forbidden band adjustable hybrid plasmon waveguide Bragg grating and design method thereof - Google Patents

Abstract

The present invention discloses a hybrid plasmonic waveguide Bragg grating with adjustable bandgap in TM and TE modes and a design method thereof. The hybrid plasmonic waveguide Bragg grating is composed of two hybrid plasmonic waveguide structures alternately arranged , the two hybrid plasmonic waveguide structures are centered on the SiO ₂ substrate with a high refractive index material Si with a width of w, and an infinitely wide metal Ag layer is erected on both sides of the SiO ₂ substrate through the support layer ZnO layer. A transition layer Si ₃ N ₄ is filled between the ZnO layer and the metal layer Ag layer, and the width w of the two mixed plasmon waveguide structures is different. The hybrid plasmonic waveguide Bragg grating has a simple structure, high structural integration and is easy to prepare. The width of a specific high-refractive index dielectric layer can be selected according to the desired polarization effect, and the grating unit period and period number can be adjusted appropriately. Dynamic selection of the passband within the specified band can be achieved.

Description

A hybrid plasmonic waveguide Bragg grating with adjustable bandgap in TM and TE modes and its its design method

technical field

The invention relates to a hybrid plasmon waveguide Bragg grating with adjustable band gap in TM and TE modes and a design method thereof, which can be used in technical fields such as optical communication and integrated optics.

Background technique

In recent years, people have developed a variety of nano-optical waveguide structures to meet the high integration requirements in the field of integrated photonic devices, such as photonic crystal waveguides and plasmonic waveguides. Among them, the surface plasmon waveguide has attracted extensive attention because of its scale beyond the diffraction limit and its material properties for optoelectronic integration. However, the loss caused by the metal leads to a small propagation distance of the waveguide mode, which limits the application of surface plasmon waveguides and waveguide devices. Therefore, a hybrid plasmonic waveguide structure that can effectively reduce the loss and increase the transmission distance is proposed. The key point of hybrid plasmonic waveguides (HPWs) is to introduce a low refractive index gap between the metal and the high refractive index medium, so that the waveguide structure can achieve the low loss of the dielectric waveguide and the surface plasmon waveguide. A better trade-off between mode constraint capabilities is achieved. It is for this reason that various integrated photonic devices based on HPWs have been designed, such as surface plasmon nanolenses, efficient optical modulators, polarized beamers, and so on.

Among them, as a wavelength-dependent photonic device Bragg grating, combined with HPWs structure, has attracted many scholars' research for its outstanding filtering characteristics and low loss characteristics. Xiao Jing et al. designed an ultra-compact broadband Bragg grating based on HPSW (Xiao J, Liu J, Zheng Z, et al.Design and analysis of a nanostructuregrating based on a hybrid plasmonic slot waveguide[J]. 2011,13(10):105001.), the Bragg grating can have a transmittance of 75% at a central wavelength of 1550nm and has a superior effective mode area, and has broad application prospects in the direction of highly integrated optoelectronics. The important thing is that an optical device with the characteristics of high integration and high utilization can often realize multiple functions by fine-tuning a certain structure, so it is necessary to study how to solve the forbidden mode on the basis of the original band-pass filter. The question of singularity is very meaningful.

Contents of the invention

The object of the present invention is to solve the above-mentioned problems in the prior art, and propose a hybrid plasmonic waveguide Bragg grating with adjustable bandgap in TM and TE modes and a design method thereof.

The purpose of the present invention will be achieved through the following technical solutions: a hybrid plasmonic waveguide Bragg grating with adjustable bandgap in TM and TE modes, which is composed of two hybrid plasmonic waveguide structures alternately arranged,

The two hybrid plasmonic waveguide structures are centered on the SiO ₂ substrate with a high refractive index material Si with a width of w, and an infinite-width metal Ag layer is erected on both sides of the SiO ₂ substrate through the support layer ZnO layer, and on the support layer A transition layer Si ₃ N ₄ is filled between the ZnO layer and the metal layer Ag layer, and the width w of the two mixed plasmon waveguide structures is different.

Preferably, the number of periods in which the hybrid plasmonic waveguide Bragg gratings are alternately arranged is N, and the number of periods N=10.5.

Preferably, the width of the high refractive index Si layer of the Bragg grating is w, and w takes different values. When the width is w _a , the corresponding hybrid plasmonic waveguide is a; when the width is w _b , the corresponding hybrid The plasmon waveguide is b, and w _a <w _b , the arrangement order of the hybrid plasmon waveguides in the Bragg grating is babab...bab.

Preferably, the period length in the hybrid plasmonic waveguide Bragg grating is Λ=d _B,1 +d _B,2 , and the specific parameter value is determined by the following formula:

Among them, Re(n _eff1 ) and Re(n _eff2 ) are the effective refractive indices of waveguide a and waveguide b respectively; d _B,1 and d _B,2 are the lengths of waveguide a and waveguide b in one period respectively; q is Prague series, take 1.

Preferably, the duty ratios of the two hybrid plasmonic waveguides in one period are both 0.5, that is, d _B,1 =d _B,2 =Λ/2.

The present invention also discloses a design method of a hybrid plasmonic waveguide Bragg grating with adjustable bandgap in TM and TE modes. The design method includes the following steps:

S1: Construction of hybrid plasmonic waveguide structure;

S2: Calculation and mode analysis of the effective refractive index of the hybrid plasmonic waveguide obtained in step S1 under the conditions of the same wavelength and different width w;

S3: Sampling and analyzing the effective refractive index data obtained in step S2 at the same central wavelength and different widths w, select two widths w _a and w _b , and initially obtain the forbidden band width according to the effective refractive index difference. Refractive index and value preliminarily obtain the center of the forbidden band, and ensure that the mixed plasmon mode is excited and confined in the low refractive index layer;

S4: Calculating the effective refractive index at different central wavelengths for w _a and w _b selected in step S3; taking the incident light vertically incident on the Bragg grating as the incident direction condition;

S5: According to the effective refractive index obtained in step S4, the period length Λ of the hybrid plasmonic waveguide Bragg grating structure at a specified central wavelength can be calculated;

S6: According to the selected widths of w _a and w _b in steps S3 and S5, the corresponding hybrid plasmonic waveguide structures a and b are alternately arranged with a period length of d _B,1 =d _B,2 =Λ/2 Construction of hybrid plasmonic waveguide Bragg gratings.

Compared with the prior art, the present invention has the following technical effects: the hybrid plasmonic waveguide Bragg grating has a simple structure, a simple design process, a high degree of structural integration and is easy to prepare, and can be realized according to the desired polarization effect Selecting the width w of a specific high-refractive-index dielectric layer, and properly adjusting the period and number of periods of the grating unit can realize the dynamic selection of the passband within the specified wavelength band, which can be used to realize compact optical polarization filter devices, in optical communications, The field of integrated optics has certain application value. The design method can select the structural parameters of the HPWBG according to the desired filtering and polarization characteristics.

Description of drawings

FIG. 1 is a schematic diagram of the xy-section structure of the hybrid plasmonic waveguide structure of the present invention.

FIG. 2 is a schematic diagram of the xz cross-sectional structure of the hybrid plasmonic waveguide Bragg grating structure of the present invention.

Fig. 3 is a schematic diagram of the real part of the effective refractive index of the TE and TM modes when w changes at the wavelength of 1550nm according to the present invention.

Fig. 4 is a schematic diagram of the imaginary part of the effective refractive index of the TE and TM modes when w changes at the wavelength of 1550nm according to the present invention.

Figure 5 shows the TM and TE modes of the hybrid plasmonic waveguide Bragg grating when the incident light is vertically incident from the air when the widths of the Si widths of the high-refractive-index dielectric layers of the two waveguides of the grating are alternately arranged in the order of bab...ab Transmission spectrum.

Fig. 6 is a graph showing the variation of the real and imaginary parts of the effective refractive index of the TM and TE modes with wavelength when the Si width of the high refractive index material of the present invention is w=200nm.

Fig. 7 is a graph showing the variation of the real and imaginary parts of the effective refractive index of TM and TE modes with wavelength when the width of Si, a high refractive index material of the present invention, is w=350nm.

Fig. 8 shows the TM and TE modes of the hybrid plasmonic waveguide Bragg grating when the incident light is vertically incident from the air when the widths of the Si widths of the high-refractive-index dielectric layers of the two waveguides of the grating are alternately arranged in the order of bab...ab Transmission spectrum.

Fig. 9 is a graph showing the variation of the real and imaginary parts of the effective refractive index of the TM and TE modes with wavelength when the Si width of the high refractive index material of the present invention is w=275nm.

Fig. 10 is a graph showing the variation of the real and imaginary parts of the effective refractive index of TM and TE modes with wavelength when the Si width of the high refractive index material of the present invention is w=600nm.

Detailed ways

Objects, advantages and features of the present invention will be illustrated and explained by the following non-limiting description of preferred embodiments. These embodiments are only typical examples of applying the technical solutions of the present invention, and all technical solutions formed by adopting equivalent replacements or equivalent transformations fall within the protection scope of the present invention.

The present invention discloses a hybrid plasmonic waveguide Bragg grating with adjustable bandgap in TM and TE modes and a design method thereof. The hybrid plasmonic waveguide Bragg grating is composed of two hybrid plasmonic waveguide structures alternately arranged . The two hybrid plasmonic waveguide structures are centered on a sufficiently wide SiO ₂ substrate with a high refractive index material Si with a width w, and an infinite-width metal Ag layer is erected on both sides of the SiO ₂ substrate through the support layer ZnO layer. A transition layer Si ₃ N ₄ is filled between the support layer ZnO layer and the metal layer Ag layer, and the width w of the two mixed plasmon waveguide structures is different.

The number of periods in which the hybrid plasmonic waveguide Bragg gratings are alternately arranged is N, and the number of periods N=10.5. The width of the high refractive index Si layer of the Bragg grating is w, and w takes different values. When the width is w _a , the corresponding hybrid plasmonic waveguide is a; when the width is w _b , the corresponding hybrid plasmonic waveguide The element waveguide is b, and w _a <w _b , the arrangement order of the hybrid plasmon waveguides in the Bragg grating is babab...bab.

The period length in the hybrid plasmonic waveguide Bragg grating is Λ=d _B,1 +d _B,2 , and the specific parameter value is determined by the following formula:

Among them, Re(n _eff1 ) and Re(n _eff2 ) are the effective refractive indices of waveguide a and waveguide b respectively; d _B,1 and d _B,2 are the lengths of waveguide a and waveguide b in one period respectively; q is Prague series, take 1. The duty cycle of the two hybrid plasmonic waveguides in one period is both 0.5, that is, d _B,1 =d _B,2 =Λ/2.

The present invention also discloses a design method of a hybrid plasmonic waveguide Bragg grating with adjustable bandgap in TM and TE modes. The design method includes the following steps:

S1: Construction of hybrid plasmonic waveguide structure;

S2: Calculation and mode analysis of the effective refractive index of the hybrid plasmonic waveguide obtained in step S1 under the conditions of the same wavelength and different width w;

S3: Sampling and analyzing the effective refractive index data obtained in step S2 at the same central wavelength and different widths w, select two widths w _a and w _b , and initially obtain the forbidden band width according to the effective refractive index difference. Refractive index and value preliminarily obtain the center of the forbidden band, and ensure that the mixed plasmon mode is excited and confined in the low refractive index layer;

S4: Calculating the effective refractive index at different central wavelengths for w _a and w _b selected in step S3; taking the incident light vertically incident on the Bragg grating as the incident direction condition;

S5: According to the effective refractive index obtained in step S4, the period length Λ of the hybrid plasmonic waveguide Bragg grating structure at a specified central wavelength can be calculated;

S6: According to the selected widths of w _a and w _b in steps S3 and S5, the corresponding hybrid plasmonic waveguide structures a and b are alternately arranged with a period length of d _B,1 =d _B,2 =Λ/2 Construction of hybrid plasmonic waveguide Bragg gratings.

In this embodiment, the parameters are set as follows: w ₁ =4000nm, w ₂ =200nm, h ₁ =100nm, h ₂ =15nm, h ₃ =450nm, h ₄ =400nm, the selection of w will be detailed in subsequent operations illustrate.

Fig. 2 is a schematic diagram of an xz cross-sectional structure of a hybrid plasmonic waveguide Bragg grating. The hybrid plasmonic waveguide Bragg grating is composed of two hybrid plasmonic waveguides a and b with different high refractive index medium layer Si layer width w arranged alternately for N periods in the order of babab...bab. In this example, the parameters are set as follows: period number N=10.5, that is, the beginning and end of the grating are waveguide b structures, and the period length is Λ=d _B,1 +d _B,2 , and its parameter value is determined by the following formula:

Among them, Re(n _eff1 ) and Re(n _eff2 ) are the effective refractive indices of waveguide a and waveguide b respectively; d _B,1 and d _B,2 are the lengths of waveguide a and waveguide b in one period respectively; q is Prague series, take 1. The specific value of the period length Λ will be described in detail in subsequent operations.

Use the finite element algorithm of Comsol software to conduct pattern analysis on the structure in Figure 1, open the parameter scan, and the width w of the high refractive index dielectric Si layer ranges from 200nm to 600nm, with a step size of 10nm, and calculate the effective structure of the structure at different widths w Refractive index, the calculation result includes the real part and imaginary part of the effective refractive index of the TE and TM modes of the structure with a central wavelength of 1550nm and different widths w.

According to the effective refractive index difference of two waveguides with different width w in Figure 3 and Figure 4 at 1550nm, the forbidden band width is preliminarily estimated. Ratio and value size initially estimate the position of the center of the forbidden band. After actually selecting the data, calculate the period length Λ=2d _B,1 =2d _B,2 , and its parameter value is determined by the following formula:

Among them, Re(n _eff1 ) and Re(n _eff2 ) are the effective refractive indices of waveguide a and waveguide b respectively; d _B,1 and d _B,2 are the lengths of waveguide a and waveguide b in one period respectively; q is Prague series, take 1. The specific value of the period length Λ will be described in detail in subsequent operations.

Example 1: Two kinds of hybrid plasmonic waveguides when the high refractive index layer width w _a =200nm, w _b =350nm, when the wavelength is 1550nm, ΣRe(n _eff )=4.62, Λ=334nm, d _B,1 =d _B,2 =167nm, N=10.5. Figure 5 shows the transmission spectrum relationship between the TM and TE modes of the hybrid plasmonic waveguide Bragg grating when the incident light is vertically incident from air and the high refractive index dielectric layer Si widths of the two kinds of waveguides of the grating are alternately arranged in the order of bab...ab In the figure, the abscissa is the wavelength, and the ordinate is the transmittance. It shows TM mode transmission and TE mode cutoff in the 1250nm～1500nm band, and TE mode transmission and TM mode cutoff in the 1520nm～1600nm band. The 1500nm～1520nm band can As presenting TM, TE dual-mode cut-off. Figure 6 and Figure 7 show the variation of the real and imaginary parts of the effective refractive index of the hybrid plasmonic waveguide with wavelength when w=200nm and w=350nm respectively, the abscissa is the wavelength, and the left ordinate is the real part of the effective refractive index , corresponding to the data of the solid line, and the ordinate on the right is the imaginary part of the effective refractive index, corresponding to the data of the dotted line.

Example 2: Two kinds of hybrid plasmonic waveguides when the high refractive index layer width w _a =275nm, w _b =600nm, when the wavelength is 1550nm, ΣRe(n _eff )=5.15, Λ=300nm, d _B,1 =d _B,2 =150nm, N=10.5, the width of the high refractive index dielectric layer Si of the two types of waveguides of the grating is alternately arranged in the order bab...ab when the incident light is vertically incident on the hybrid plasmonic waveguide Bragg from the air TM and TE mode transmission spectra of the grating.

Specifically: Figure 8 shows the transmission spectrum relationship of a Bragg grating composed of a hybrid plasmonic waveguide, which exhibits TM and TE dual-mode cut-off in the 1500nm-1600nm band, and TE mode cut-off and TM mode transmission in the 1400nm-1500nm band. Figure 9 and Figure 10 respectively show the variation of the real and imaginary parts of the effective refractive index of the hybrid plasmonic waveguide with the wavelength when the width of high refractive index material Si is w=275m and w=600nm, the abscissa is the wavelength, and the left ordinate is the real part of the effective refractive index, corresponding to the data of the solid line, and the ordinate on the right is the imaginary part of the effective refractive index, corresponding to the data of the dotted line.

By changing the width w of the high-refractive-index medium of the two waveguides and properly adjusting the grating length and period number, the dynamic selection of the passband in the specified waveband can be realized, and the position and location of the high-frequency passband and high-frequency forbidden band can be realized. Adjustment and optimization of the transmission spectrum.

There are still many implementations in the present invention, and all technical solutions formed by equivalent transformation or equivalent transformation fall within the protection scope of the present invention.

Claims (4)

1. The utility model provides a TM, TE mode forbidden band adjustable mixes plasmon waveguide Bragg grating which characterized in that:

is formed by alternately arranging two mixed plasmon waveguide structures,

the two mixed plasmon waveguide structures are both in SiO ₂ A high refractive index material Si of width w is placed centrally over the substrate, on SiO ₂ A metal Ag layer is erected on two sides above the substrate through a support layer ZnO layer, and a transition layer Si is filled between the support layer ZnO layer and the metal Ag layer ₃ N ₄ The widths w of the two mixed plasmon waveguide structures are different;

the number of the alternatively arranged periods of the mixed plasmon waveguide Bragg gratings is N, and the number of the periods N =10.5;

the width of the Bragg grating high-refractive-index Si layer is w, and w is different in value when the width is w _a When the width of the corresponding hybrid plasmon waveguide is w, the corresponding hybrid plasmon waveguide is a _b When the corresponding hybrid plasmon waveguide is b, and w _a <w _b The arrangement sequence of the mixed plasmon waveguides in the Bragg grating is babab … … bab.

2. The TM and TE mode bandgap tunable hybrid plasmon waveguide bragg grating of claim 1, wherein: the period length in the hybrid plasmon waveguide Bragg grating is Λ = d _B,1 +d _B,2 The specific parameter value is determined by the following formula:

wherein, re (n) _eff1 ) And Re (n) _eff2 ) Respectively waveguide a and waveThe effective refractive index of the guide b; d _B,1 And d _B,2 The lengths of the waveguide a and the waveguide b in one period respectively; q is the Bragg order and is 1.

3. The hybrid plasmon waveguide bragg grating with adjustable TM and TE mode forbidden bands according to claim 2, wherein: the duty ratio of the two mixed plasmon waveguides in one period is 0.5, namely d _B,1 ＝d _B,2 ＝Λ/2。

4. The design method of the TM and TE mode forbidden band adjustable hybrid plasmon waveguide bragg grating of claim 1, characterized in that: the design method comprises the following steps:

s1: constructing a hybrid plasmon waveguide structure;

s2: calculating the effective refractive index and performing mode analysis on the mixed plasmon waveguide obtained in the step S1 under the conditions of the same wavelength and different widths w;

s3: sampling and analyzing the effective refractive index data with the same central wavelength and different widths w obtained in the step S2, and selecting two widths w _a And w _b Preliminarily obtaining the forbidden band width according to the difference value of the effective refractive indexes, preliminarily obtaining the forbidden band center according to the sum value of the effective refractive indexes, and ensuring that the mixed plasmon mode is excited and limited in the low refractive index layer;

s4: for w selected in step S3 _a 、w _b Calculating the effective refractive index under different central wavelengths; taking the incident light vertically incident into the Bragg grating as an incident direction condition;

s5: according to the effective refractive index obtained in the step S4, the period length Lambda of the mixed plasmon waveguide Bragg grating structure under the specified central wavelength can be calculated;

s6: according to the width w selected in the steps S3 and S5 _a 、w _b Time-corresponding hybrid plasmon waveguide structures a and b with a period length d _B,1 ＝d _B,2 And (5) alternately arranging the (= Lambda/2) to construct a mixed plasmon waveguide Bragg grating.

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