CN118151374A - Superlattice design method, structure and application based on Archimedes spiral line - Google Patents
Superlattice design method, structure and application based on Archimedes spiral line Download PDFInfo
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- 238000000034 method Methods 0.000 title claims description 26
- 238000013461 design Methods 0.000 title claims description 18
- 239000013078 crystal Substances 0.000 claims abstract description 30
- 230000010287 polarization Effects 0.000 claims description 25
- 239000000758 substrate Substances 0.000 claims description 3
- ORUCDOXAKFCOJF-UHFFFAOYSA-N [O-2].[Mg+2].[Li+] Chemical compound [O-2].[Mg+2].[Li+] ORUCDOXAKFCOJF-UHFFFAOYSA-N 0.000 claims description 2
- 230000001419 dependent effect Effects 0.000 claims description 2
- 230000003287 optical effect Effects 0.000 abstract description 10
- 230000004044 response Effects 0.000 abstract description 6
- 238000004891 communication Methods 0.000 abstract description 3
- 230000006835 compression Effects 0.000 abstract description 2
- 238000007906 compression Methods 0.000 abstract description 2
- 238000006243 chemical reaction Methods 0.000 description 37
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 13
- 238000005516 engineering process Methods 0.000 description 4
- 230000000737 periodic effect Effects 0.000 description 4
- 239000010409 thin film Substances 0.000 description 4
- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical compound CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 description 2
- QBLDFAIABQKINO-UHFFFAOYSA-N barium borate Chemical compound [Ba+2].[O-]B=O.[O-]B=O QBLDFAIABQKINO-UHFFFAOYSA-N 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 229910013641 LiNbO 3 Inorganic materials 0.000 description 1
- 229910003327 LiNbO3 Inorganic materials 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000012938 design process Methods 0.000 description 1
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- 239000010408 film Substances 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- GCICAPWZNUIIDV-UHFFFAOYSA-N lithium magnesium Chemical compound [Li].[Mg] GCICAPWZNUIIDV-UHFFFAOYSA-N 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 239000007777 multifunctional material Substances 0.000 description 1
- 238000012634 optical imaging Methods 0.000 description 1
- 230000005693 optoelectronics Effects 0.000 description 1
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- 230000009467 reduction Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
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Abstract
Compared with a superlattice structure with uniform period and a linearly chirped superlattice structure, the superlattice structure based on the Archimedes spiral can realize larger broadband frequency multiplication under the condition of the same crystal length, has obviously more excellent response flatness, and has huge application potential in ultrashort pulse compression, frequency-tunable lasers and optical communication.
Description
Technical Field
The invention belongs to the technical field of nonlinear optics, and particularly relates to a superlattice design method based on an Archimedes spiral, a superlattice structure and application thereof in frequency multiplication.
Background
Broadband frequency conversion is one of nonlinear optical important branches, and has unique significance in the fields of laser technology, optical communication, optical imaging and the like. Second order nonlinear frequency conversion encompasses frequency multiplication, sum frequency, difference frequency, parametric down-conversion, parametric oscillation, etc., which have been successfully implemented in a variety of nonlinear crystals such as lithium niobate (LiNbO 3), lithium tantalate (LiTaO 3), barium metaborate (BBO) crystals. Lithium niobate is used as a multifunctional material, has excellent characteristics of a wide wavelength window (350 nm-5 μm), an electro-optical effect, a nonlinear optical effect, an acousto-optic effect and the like, is often called as optical silicon, and is widely applied in the field of photonics. At present, with the increasing demands for miniaturized and integrated broadband variable frequency equipment, compared with bulk single crystals, the thin film lithium niobate has low loss, small size and easy high integration, and the thin film lithium niobate optical waveguide prepared by micro-nano processing can remarkably reduce the size of a device and improve nonlinear interaction efficiency. Phase matching is a necessary condition to achieve a higher nonlinear frequency conversion. At present, several phase matching methods, quasi-phase matching (QPM), birefringent Phase Matching (BPM), mode Phase Matching (MPM) and the like have been developed on thin film lithium niobate; wherein, quasi-phase matching is to enhance nonlinear frequency change effect by periodically changing the polarization direction of the crystal. In China, min Naiben team of Nanjing university grows lithium niobate crystal with periodic domain as early as 1970 and verifies the quasi-phase matching principle for the first time. With the development of integrated photonics, wu Xiao is equal to 2022, and wideband frequency multiplication is realized on a lithium niobate film by adopting a quasi-phase matching technology through designing a chirp period. These studies all show that frequency doubling can be effectively achieved by designing the superlattice structure using quasi-phase matching techniques.
Up to now, superlattice structures may be generally categorized as periodic and aperiodic superlattice structures. For a uniform period superlattice structure, higher conversion efficiency but too narrow a bandwidth may be obtained, while a linearly chirped superlattice structure may obtain a larger bandwidth but reduced conversion efficiency.
In summary, in the process of generating wideband frequency multiplication in an optical waveguide with a superlattice structure, the conversion efficiency and the bandwidth are very important performance indexes. The product of the conversion efficiency and the frequency doubling bandwidth is a fixed value due to the group velocity mismatch between the interacting waves. On the one hand, realizing efficient frequency conversion by utilizing the superlattice structure will necessarily lead to a very narrow frequency multiplication bandwidth, usually only on the order of nanometers; on the other hand, when ultra-wide frequency multiplication bandwidth is realized by utilizing the superlattice structure, the frequency multiplication conversion efficiency is also very low. Therefore, how to balance the conversion efficiency and bandwidth has been the subject of research.
In addition, the flatness of the frequency doubling conversion efficiency curve is also another important index for measuring the frequency doubling of the broadband. The flatter the frequency doubling conversion efficiency curve, the less the frequency doubling signal is distorted. Therefore, how to suppress fluctuation in frequency multiplication conversion efficiency and to obtain better flatness is also one of the subjects of interest to researchers.
Disclosure of Invention
Aiming at the problems, the invention aims to provide a superlattice design method, structure and application based on an Archimedes spiral line, so as to solve the problems of over-narrow bandwidth and poor curve response flatness in downstream technology.
In order to achieve the above purpose, the technical scheme adopted by the invention comprises the following steps:
A superlattice design method based on an Archimedes spiral line comprises the following steps:
S1, determining a nonlinear crystal, setting the working wavelength and the environment temperature of the nonlinear crystal, and respectively calculating the working wavelength and the temperature of the nonlinear crystal to obtain a fundamental frequency wave refractive index and a frequency multiplication wave refractive index through SELLMEIER equations;
S2, determining the geometric parameters of the ridge waveguide, calculating the effective refractive index of the fundamental frequency wave and the effective refractive index of the frequency doubling wave obtained in the step S1 and the geometric parameters of the ridge waveguide through a finite element method, and substituting the effective refractive index of the fundamental frequency wave and the effective refractive index of the frequency doubling wave into a polarization period formula to calculate to obtain a polarization period range;
S3, calculating a plurality of superlattice unit widths Λ through the formula (1), and sequentially arranging all the superlattice unit widths along the y-axis direction to obtain a superlattice;
Λ＝Λ0+βθsinθ#(1)
Where Λ 0 denotes the initial superlattice cell width, its polarization period range, which is derived from S2, is according to 7:3 the width of the 8 th polarization period after the proportion division; beta represents the pitch of the archimedes' spiral; θ represents the rotation angle of the archimedes spiral in the rectangular coordinate system, corresponding to the arrangement position of each superlattice unit on the ridge waveguide.
Preferably, the nonlinear crystal in the S1 is a Z-cut Mgo:LN frequency doubling crystal, the SELLMEIER equation is a temperature-related SELLMEIER equation doped with 5mol% of magnesium oxide lithium niobate, the operating wavelength of the nonlinear crystal is in a range of 1538-1562 nm, and the ambient temperature is 22 ℃.
Preferably, the polarization period formula adopts a type 0 quasi-phase matching method.
Preferably, the ridge waveguide geometry parameters in S2 include ridge waveguide thickness h=0.6-0.7, and waveguide width w=1.45-1.8.
Preferably, the ridge waveguide geometry parameters in S2 include ridge waveguide thickness h=0.7 um, substrate thickness h1=0.35 um, and waveguide width w=1.8 um.
Preferably, the effective refractive index of the fundamental frequency wave in S2 is 1.951-1.946, the effective refractive index of the frequency doubling wave is 2.112-2.109, and the polarization period is 4.779-4.798.
Preferably, the initial superlattice cell width Λ 0 takes on a value of 4.793 μm and the pitch β of the archimedes spiral takes on a value of 0.003; dividing the arrangement position theta of the superlattice unit width on the ridge waveguide into theta 1 and theta 2,θ1, wherein the value range is 0-pi, and a value is taken every delta theta 1; the value range of theta 2 is pi-2 pi, and a value is taken every delta theta 2.
Preferably, Δθ 1＝0.012,Δθ2 =0.009.
The superlattice structure is a superlattice, and is designed by the superlattice design method based on the Archimedes spiral.
The application discloses an application of a superlattice structure based on an Archimedes spiral line in a broadband frequency multiplier.
Compared with the prior art, the invention has the advantages that:
Compared with a superlattice structure with uniform period and a linearly chirped superlattice structure, the superlattice structure based on the Archimedes spiral can realize larger broadband frequency multiplication under the condition of the same crystal length, has obviously more excellent response flatness, and has huge application potential in ultrashort pulse compression, frequency-tunable lasers and optical communication.
Drawings
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate the invention and together with the description serve to explain, without limitation, the invention. In the drawings:
FIG. 1 is a schematic view of a Z-cut Mgo:LN waveguide of the invention;
FIG. 2 is a graph of the effective refractive index and calculated polarization period of the fundamental and frequency multiplied waves of the present invention;
FIG. 3 is a block diagram of a nonlinear arrangement of superlattice cells based on an Archimedes spiral function in accordance with the invention;
FIG. 4 is a graph showing the comparison of G 2 at different values of β according to the present invention;
FIG. 5 is a graph showing the comparison of G 2 at different values of Δθ according to the present invention;
FIG. 6 is a graph showing the variation of the highest conversion efficiency and the average conversion efficiency with the length of the waveguide in the scan band according to the present invention;
FIG. 7 is a graph of bandwidth as a function of waveguide length for the present invention;
fig. 8 is a graph of a comparison of a uniformly periodic superlattice structure, a linearly chirped superlattice structure, and a G 2 based on an archimedes spiral superlattice structure.
Detailed Description
Exemplary embodiments of the present application will be described hereinafter with reference to the accompanying drawings. In the interest of clarity and conciseness, not all features of an actual embodiment are described in the specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions may be made to achieve the developers' specific goals, and that these decisions may vary from one implementation to another.
It should be noted here that, in order to avoid obscuring the present application due to unnecessary details, only the device structures closely related to the solution according to the present application are shown in the drawings, and other details not greatly related to the present application are omitted.
It is to be understood that the application is not limited to the described embodiments, as a result of the following description with reference to the drawings. In this context, embodiments may be combined with each other, features replaced or borrowed between different embodiments, one or more features omitted in one embodiment, where possible.
Example 1
The embodiment discloses a superlattice structure based on an archimedes spiral, which is designed by the following steps:
S1, determining a nonlinear crystal, setting the working wavelength and the environment temperature of the nonlinear crystal, and respectively calculating the working wavelength and the temperature of the nonlinear crystal to obtain a fundamental frequency wave refractive index and a frequency multiplication wave refractive index through SELLMEIER equations;
the nonlinear crystal disclosed in the embodiment is a Z-cut Mgo LN frequency doubling crystal, the SELLMEIER mol% magnesium oxide-doped lithium niobate SELLMEIER equation, the working wavelength of the nonlinear crystal is 1538-1562 nm, and the ambient temperature is 22 ℃.
Wherein, SELLMEIER mol percent of doped magnesium lithium niobate is shown in the equation (Gayer O,Sacks Z,Galun E,et al.Temperature and wavelength dependent refractive index equations for MgO-doped congruent and stoichiometric LiNbO3[J].Applied Physics B,2008,91:343-348.)
S2, determining the geometric parameters of the ridge waveguide, calculating the effective refractive index of the fundamental frequency wave and the effective refractive index of the frequency doubling wave obtained in the step S1 and the geometric parameters of the ridge waveguide through a finite element method, and substituting the effective refractive index of the fundamental frequency wave and the effective refractive index of the frequency doubling wave into a polarization period formula to calculate to obtain a polarization period range;
Referring to fig. 1, the ridge waveguide geometry parameters include ridge waveguide thickness h=0.7 um, substrate thickness h1=0.35 um, waveguide width w=1.8 um, and the effective refractive index range of fundamental frequency wave is 1.951-1.946 and the effective refractive index range of frequency multiplication wave is 2.112-2.109 calculated by comsol software finite element method, and the calculated polarization period range is 4.779-4.798, referring to fig. 2.
Wherein, the polarization period formula is (Meyn J P,Fejer M M.Tunable ultraviolet radiation by second-harmonic generation in periodically poled lithium tantalate[J].Optics letters,1997,22(16):1214-1216.),0, and the quasi-phase matching method is (Vazimali M G,Fathpour S.Applications of thin-film lithium niobate in nonlinear integrated photonics[J].Advanced Photonics,2022,4(3):034001-034001.)
S3, calculating a plurality of superlattice unit widths Λ through the formula (1), and sequentially arranging all the superlattice unit widths along the y-axis direction to obtain a superlattice, and referring to FIG. 3;
Λ＝Λ0+βθsinθ#(1)
Where Λ 0 denotes the initial superlattice cell width, its polarization period range, which is derived from S2, is according to 7:3 the width of the 8 th polarization period after the proportion division; beta represents the pitch of the archimedes' spiral; θ represents the rotation angle of the archimedes spiral in the rectangular coordinate system, corresponding to the arrangement position of each superlattice unit on the ridge waveguide.
The value of Λ 0 disclosed in this example is 4.793 μm, and the value of β is 0.003; the superlattice structure has the total length of 3mm, and is divided into two sections, wherein θ is divided into two sections of θ 1 and θ 2 (respectively corresponding to the two sections), the value range of θ 1 is 0-pi, one value is taken at intervals of Δθ 1, the value range of Δθ 1＝0.012;θ2 is pi-2pi, and the value of every Δθ is taken at intervals of Δθ 2
Take a value, Δθ 2 =0.009. Scanning the fundamental frequency band 1525-1575 nm, and obtaining the bandwidth range of the structure in the band through numerical calculation. Refer to fig. 4.
Example 2
This embodiment differs from embodiment 1 in that β=0.002. Scanning the fundamental frequency band 1525-1575 nm, and obtaining the bandwidth range of the structure in the band through numerical calculation. Refer to fig. 4.
Example 3
This embodiment differs from embodiment 1 in that β=0.004. Scanning the fundamental frequency band 1525-1575 nm, and obtaining the bandwidth range of the structure in the band through numerical calculation. Refer to fig. 4.
It can be seen from examples 1-3 that the other parameters remain unchanged, and when β=0.002, the variation range of the obtained superlattice unit is far smaller than the polarization period range of the design band, and the bandwidth is narrowed; when β=0.004, the obtained superlattice unit variation range is far larger than the period range of the design band, and the bandwidth is narrowed. Therefore, when β is changed only, most wavelengths are caused to generate serious phase mismatch, so that the conversion bandwidth is affected. When β=0.003, the bandwidth is maximum and the center wavelength range remains large conversion efficiency all the time.
Example 4
The difference between this embodiment and embodiment 1 is that Δθ 1＝0.015,Δθ2 =0.008, the variation range of the polarization period corresponds to the width range of the superlattice structure unit, and the bandwidth range of this structure in this band is obtained by scanning the fundamental frequency band 1525-1575 nm and calculating the value. Refer to fig. 5.
Example 5
The difference between this embodiment and embodiment 1 is that Δθ 1＝0.009,Δθ2 =0.01, the polarization period variation range corresponds to the superlattice structure unit width range, and the bandwidth range of this structure in this band is obtained by scanning the fundamental frequency band 1525-1575 nm and calculating the value. Refer to fig. 5.
It can be seen from examples 1,4 and 5 that the other parameters remain unchanged, and that only the values of Δθ 1 and Δθ 2 are changed, i.e. the values of θ are changed by different superlattice unit arrangement positions, so that the distribution of the number of superlattice units in two segments is unbalanced, resulting in a reduction of the central wavelength shift bandwidth. When Δθ 1＝0.012,Δθ2 =0.009, the bandwidth range is located at the band center and is widest.
Example 6
Conversion bandwidths were calculated using matlab software for the archimedes spiral-based superlattice structure of example 1, scanning fundamental bands 1525-1575 nm, the highest conversion efficiency and average conversion efficiency over the structure length, as a function of length, see fig. 6. The crystal length is respectively set to be 1-5 mm, eta (max) represents the highest conversion efficiency, eta (avg) represents the average conversion efficiency, the superlattice unit number is increased along with the increase of the crystal length, the phase mismatch quantity of certain wavelengths can be continuously accumulated, both eta (max) and eta (avg) are led to be in a descending trend, and the conversion efficiency is rapidly reduced. Variation of bandwidth ratio with structural length referring to fig. 7, the crystal lengths are set to 1 to 5mm, respectively, and the maximum bandwidth of 31nm is obtained at 3mm, and the maximum conversion bandwidth can be obtained only when the range and number of superlattice units are balanced with the crystal length, so that the crystal length needs to be considered in the design process.
The conversion efficiency formula is shown in (Gu B Y,Dong B Z,Zhang Y,et al.Enhanced harmonic generation in aperiodic optical superlattices[J].Applied physics letters,1999,75(15):2175-2177.)
The average conversion efficiency in the scanning wavelength range is shown as formula (2), Ση i Δs is the frequency multiplication efficiency bandwidth product (EFP), that is, the frequency multiplication efficiency in the scanning frequency range, and S is the scanning wavelength range.
Comparative example
The bandwidths of the uniformly periodic superlattice structure, the linearly chirped superlattice structure, and the archimedes spiral-based superlattice structure of example 1 were compared. Uniform period superlattice structure see (Miller G D,Batchko R G,Tulloch W M,et al.42％-efficient single-pass cw second-harmonic generation in periodically poled lithium niobate[J].Optics letters,1997,22(24):1834-1836.), linearly chirped superlattice structure see (Wu X,Zhang L,Hao Z,et al.Broadband second-harmonic generation in step-chirped periodically poled lithium niobate waveguides[J].Optics Letters,2022,47(7):1574-1577.).
The total length of the three structures is 3mm. The uniform-period superlattice structure polarization period Λ=4.793 μm. The polarization period Λ 1 = 4.779 μm, ΔΛ=0.001 μm of the linearly chirped superlattice structure is divided into 20 segments, Λ 20 = 4.798 μm, and 31 repetition periods per segment. Based on the initial unit width lambda 0 =4.793 mu m of the Archimedes spiral superlattice structure, the Archimedes spiral superlattice structure is divided into two sections, beta=0.003, theta 1 takes a value range of 0-pi, delta theta 1＝0.012,θ2 takes a value every delta theta, and delta theta 2 =0.009. Referring to fig. 8, it can be seen that the conversion bandwidth based on the archimedes spiral superlattice structure is at most 31nm, the conversion efficiency of the uniform period superlattice center wavelength position is highest, but the bandwidth is only 10nm, while the conversion efficiency of the linearly chirped superlattice is reduced, the bandwidth is 11nm, it is obvious that the increase of the bandwidth is at the expense of the conversion efficiency, and the conversion efficiency is measured by using the G 2 value because the conversion efficiency is proportional to the G 2 by introducing the concept of the response flatness as an index for measuring the conversion efficiency and the bandwidth, see (Gao S,Yang C,Jin G.Flat broad-band wavelength conversion based on sinusoidally chirped optical superlattices in lithium niobate[J].IEEE Photonics Technology Letters,2004,16(2):557-559.). The response flatness based on the archimedes spiral superlattice structure is significantly better than that of the other two structures, namely only 0.065, and the table 1 is referred to.
Wherein G 2 can be used to measure the conversion bandwidth, see (Wu X,Zhang L,Hao Z,et al.Broadband second-harmonic generation in step-chirped periodically poled lithium niobate waveguides[J].Optics Letters,2022,47(7):1574-1577.).
TABLE 1 three superlattice structural Performance parameters
| Structure name | Conversion bandwidth (nm) | Response flatness |
| Uniform period superlattice structure | 10 | 0.116 |
| Linear chirped superlattice structure | 11 | 0.079 |
| Superlattice structure based on Archimedes spiral | 31 | 0.065 |
The above description is merely illustrative of various embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily think about variations or substitutions within the scope of the present application, and the application is intended to be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (10)
1. The superlattice design method based on the Archimedes spiral is characterized by comprising the following steps of:
S1, determining a nonlinear crystal, setting the working wavelength and the environment temperature of the nonlinear crystal, and respectively calculating the working wavelength and the temperature of the nonlinear crystal to obtain a fundamental frequency wave refractive index and a frequency multiplication wave refractive index through SELLMEIER equations;
S2, determining the geometric parameters of the ridge waveguide, calculating the effective refractive index of the fundamental frequency wave and the effective refractive index of the frequency doubling wave obtained in the step S1 and the geometric parameters of the ridge waveguide through a finite element method, and substituting the effective refractive index of the fundamental frequency wave and the effective refractive index of the frequency doubling wave into a polarization period formula to calculate to obtain a polarization period range;
S3, calculating a plurality of superlattice unit widths Λ through the formula (1), and sequentially arranging all the superlattice unit widths along the y-axis direction to obtain a superlattice;
Λ＝Λ0+βθsinθ#(1)
Where Λ 0 denotes the initial superlattice cell width, its polarization period range, which is derived from S2, is according to 7:3 the width of the 8 th polarization period after the proportion division; beta represents the pitch of the archimedes' spiral; θ represents the rotation angle of the archimedes spiral in the rectangular coordinate system, corresponding to the arrangement position of each superlattice unit on the ridge waveguide.
2. The superlattice design method based on archimedes spiral line as recited in claim 1, wherein the nonlinear crystal in S1 is a Z-cut Mgo: LN frequency doubling crystal, SELLMEIER equation is a temperature-dependent SELLMEIER equation doped with 5mol% of lithium magnesium oxide niobate, the operating wavelength of the nonlinear crystal ranges from 1538 nm to 1562nm, and the ambient temperature is 22 ℃.
3. The archimedes spiral-based superlattice design method as defined in claim 1, wherein said polarization period formula employs a type 0 quasi-phase matching method.
4. A superlattice design method based on archimedes spiral as in claim 2, wherein said ridge waveguide geometry parameters in S2 include ridge waveguide thickness h = 0.6-0.7 and waveguide width w = 1.45-1.8.
5. The archimedean spiral-based superlattice design method of claim 4, wherein the ridge waveguide geometry parameters in S2 include ridge waveguide thickness h=0.7 um, substrate thickness h1=0.35 um, and waveguide width w=1.8 um.
6. The archimedes spiral-based superlattice design method as recited in claim 5, wherein said S2 has an effective refractive index of 1.951-1.946 for fundamental waves, an effective refractive index of 2.112-2.109 for frequency doubling waves, and a polarization period of 4.779-4.798.
7. A superlattice design method based on an archimedes spiral as recited in any one of claims 1-6, wherein said initial superlattice cell width Λ 0 takes on a value of 4.793 μm and the pitch β of the archimedes spiral takes on a value of 0.003.
Dividing the arrangement position theta of the superlattice unit width on the ridge waveguide into theta 1 and theta 2,θ1, wherein the value range is 0-pi, and a value is taken every delta theta 1; the value range of theta 2 is pi-2 pi, and a value is taken every delta theta 2.
8. A superlattice design method based on archimedes spiral as recited in claim 7, wherein Δθ 1＝0.012,Δθ2 =0.009.
9. A superlattice structure based on an archimedes spiral, characterized in that the superlattice structure is a superlattice, and is designed by the superlattice design method based on an archimedes spiral as defined in any one of claims 1 to 8.
10. Use of a superlattice structure based on archimedes' spiral obtained by a design method as defined in any one of claims 1-9 in a wideband frequency multiplier.
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