CN110850516A

CN110850516A - Adjustable second harmonic excitation structure and method based on artificial SPP waveguide

Info

Publication number: CN110850516A
Application number: CN201911158003.7A
Authority: CN
Inventors: 崔铁军; 高欣欣; 张婧婧; 张浩驰; 马骞
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2019-11-22
Filing date: 2019-11-22
Publication date: 2020-02-28

Abstract

The invention provides an adjustable second harmonic excitation structure and method based on an artificial SPP waveguide, which mainly comprise a dielectric substrate, an artificial SPP structure and two varactors, and realize the forward/reverse second harmonic excitation with maximum efficiency under the condition of forward/reverse phase matching by regulating and controlling the dispersion curve of a unit structure. The invention has the beneficial effects that: the invention introduces the variable capacitance diode into the artificial SPP waveguide, so that the waveguide not only has the characteristic of electric field enhancement but also has the characteristic of nonlinearity, and the maximum second harmonic of forward propagation and backward propagation can be excited by adjusting the voltage loaded on the variable capacitance diode.

Description

Adjustable second harmonic excitation structure and method based on artificial SPP waveguide

Technical Field

The invention relates to an adjustable second harmonic excitation structure and method based on an artificial SPP waveguide, and belongs to the field of communication and novel artificial electromagnetic materials.

Background

Surface Plasmon Polaritons (SPPs) are generated by the oscillatory coupling of an external electromagnetic field and metal electrons at an optical frequency. It is a surface electromagnetic wave propagating along the metal and dielectric interface, with slow wave characteristics, resulting in stronger field-confining capability. However, SPPs cannot propagate in the microwave band due to the electrically conductive nature of metals. In 2004, the professor j.b. pandry demonstrated a structure in the form of a two-dimensional array of through holes, which made it possible to bind electromagnetic waves to the surface of the structure, forming surface waves similar to SPPs, i.e. artificial SPPs. In order to facilitate application of the surface plasmon polariton structure to an integrated circuit, a trot army topic group of the university of southeast has been proposed in 2013. In recent years, transmission line structures based on artificial SPPs have been studied, and compared with conventional microstrip lines, it has advantages of low bending loss, interference resistance, low crosstalk, and miniaturization.

Due to the field enhancement effect of SPPs, nonlinear effects based on artificial SPP structures have gained widespread attention. In 2011, professor d.r.smith proposed loading a nonlinear device at the gap of the split ring resonator to improve the generation of the second harmonic, but the nonlinear waveguide described above is not easy to integrate. Thereafter, fets and varactors are introduced into the one-dimensional artificial SPP waveguide to excite the forward second harmonic, however, the transmission of the excited second harmonic is unidirectional in these cases, which limits some potential applications.

Disclosure of Invention

The technical problem is as follows: in order to realize the generation of dynamically adjustable second harmonic, the invention provides a technical method for realizing the forward/reverse second harmonic with the maximum conversion efficiency by loading an active device in an artificial SPP waveguide under the condition of forward/reverse phase matching.

The technical scheme is as follows: the transmission line plane of the invention takes a dielectric substrate as a carrier and consists of an artificial SPP waveguide and a variable capacitance diode. The varactors loaded in the special split ring structure unit are different, two varactors above the structure (c)₁) Is linear, and the varactor (c) under the structure₂) Is non-linear. Under the condition that the parameters of the split resonant ring structure are not changed, the dispersion characteristic of the artificial SPP structural unit is determined by the capacitance value of the variable capacitance diode, so that forward phase matching and reverse phase matching can be realized, and the second harmonic of the maximum conversion efficiency is generated.

Has the advantages that: compared with the prior art, the invention has the advantages that:

1. the invention can realize the generation of the nonlinear second harmonic only by loading the active device on the artificial SPP waveguide, has simple operation, saves space and is convenient for miniaturization.

2. The invention changes the dispersion characteristic of the artificial SPP waveguide by adjusting the capacitance value of the active device, realizes the forward and reverse phase matching in the same frequency band, and further excites the forward and reverse second harmonics with the maximum efficiency.

3. The invention can realize the generation of forward and reverse second harmonics by adjusting the bias voltage on the variable capacitance diode under the condition of the same artificial SPP waveguide, and can be better applied to integrated circuits, communication systems and nonlinear SPP systems.

Drawings

Fig. 1 is a schematic diagram of a unit structure of a nonlinear artificial SPP waveguide and a dispersion curve thereof, wherein fig. 1(a) is a geometric unit structure of a loading varactor, and fig. 1(b) and fig. 1(c) are dispersion curves corresponding to different capacitance values;

FIG. 2 shows the forward and reverse phase matching conditions for second harmonic excitation in a nonlinear artificial SPP waveguide, where FIG. 2(a) shows second harmonic generation (k) under forward phase matching conditions_2ω＝2k_ω,n_2ω＝n_ω) FIG. 2(b) shows second harmonic generation (k) under reverse phase matching conditions_2ω＝-2k_ω,n_2ω＝n_ω) Wherein n is_ω，n_2ωRefractive indices of a fundamental mode and a high-order mode, respectively;

fig. 3 is a diagram of forward and reverse phase matched second harmonic generation at different bias voltages, where fig. 3(a) is the conversion efficiency of the forward second harmonic and fig. 3(b) is the conversion efficiency of the reverse second harmonic.

Detailed Description

The technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

The invention utilizes the field enhancement effect of the artificial SPPs, uses the introduced variable capacitance diode as a nonlinear device, and further realizes the generation of the forward/reverse second harmonic with the maximum efficiency under the condition of forward/reverse phase matching by adjusting the bias voltage loaded on the variable capacitance diode.

The unit structure of the nonlinear artificial SPP waveguide is shown in fig. 1 (a). The unit period p is 2mm, the width h is 5mm, the a is 0.2mm, the b is 0.5mm, the d is 1.5mm, the e is 1.9mm, the g is 0.5mm, the p is 2.7mm, the w is 0.3mm, the i is 1.8mm, the j is 1.5mm, the dielectric constant of the dielectric substrate F4B is 2.65, the thickness is 0.813mm, and the loss tangent angle is 0.001. Intrinsic simulation by commercial software CST really gets its dispersion curve as shown in fig. 1(b) and fig. 1(c), and by changing the capacitance of the varactor, it is possible to change the direction of the group velocity in the higher order mode (the direction of the group velocity is consistent with the direction of electromagnetic energy propagation) at the same frequency. When c is going to₁0.27pF and c₂When 0.032pF, the phase matching condition in the forward direction is k_ω＝206.85m^-1(f_F＝5GHz)and k_2ω＝413.7m^-1(f _SH10 GHz). Change the capacitance value of the varactor when c₁0.11pF and c₂The inverse phase matching condition is k at 0.063pF_ω＝183.58m^-1(f_F＝5GHz)and k_2ω＝367.16m^-1(f _SH10 GHz). In addition, the forward and reverse phase matching can be realized in a range of a little bit frequency band.

As shown in fig. 3(a) and 3(b), the second harmonic generation efficiency is highest at the phase matching frequency. The conversion efficiency can be obtained

In the formula I_2ωAnd I_ωIs the energy density of the second harmonic and fundamental wave, l is the length of the nonlinear region, d_effFor effective nonlinear polarizability, n_ωAnd λ_ωIs the refractive index and wavelength at the fundamental wave, u and epsilon₀Δ k is the phase mismatch for propagation velocity and dielectric constant in free space. As can be seen from the equation, when the other parameters are constant values, the conversion efficiency of the second harmonic is only related to Δ k, and thus the conversion efficiency of the second harmonic is as shown in fig. 3.

Claims

1. The utility model provides an adjustable second harmonic arouses structure based on artifical SPP waveguide which characterized in that: the structure comprises a unit structure, wherein the unit structure is composed of a dielectric substrate, an open resonator ring structure and two variable capacitance diodes of different types.

2. The adjustable second harmonic excitation method based on the artificial SPP waveguide as claimed in claim 1, wherein: the SPP structure is designed and the capacitance value loaded on the SPP structure is changed, and the corresponding phase constants under the fundamental mode and the high-order mode have a positive phase matching relation and a reverse phase matching relation, namely k_2ω＝2k_ω，k_2ω＝-2k_ωWherein k is_ω，k_2ωCorresponding to the phase constants of the fundamental and higher order modes, respectively.

3. The adjustable second harmonic excitation method based on the artificial SPP waveguide as claimed in claim 2, wherein: based on the field enhancement characteristic of the artificial SPP and the introduced nonlinear varactor device, forward and reverse second harmonic signals with the maximum conversion efficiency are excited in the artificial SPP waveguide under the condition of forward and reverse phase matching by adjusting the voltage loaded on the varactor diode.