阅读说明：本技术 一种pt对称耦合微腔和磁微腔复合结构及其应用 (PT symmetrical coupling microcavity and magnetic microcavity composite structure and application thereof ) 是由 黄琦涛 方云团 于 2021-07-14 设计创作，主要内容包括：本发明提供了一种PT对称耦合微腔和磁微腔复合结构,整体为左右对称结构,包括设置在左右两侧的P层以及设置在中间的G层和L层,P层、G层及L层两两之间间隔设置；所述P层为耦合棱镜,G层和L层均为由具有磁光效应的介质层形成的耦合微腔,其中G层为增益介质层,而L层则为损耗介质层。此结构处于PT对称的极点状态时,具有极大的透射率,其透射率数值高达数千,能够将输入的弱光放大数千倍后透射出去,并且透射率大小还受所施加磁场的磁感应强度线性调控；可用于对光强或光信号的放大功能,或者用于通过弱磁场信号对强光场的信号调制功能。(The invention provides a PT symmetrical coupling microcavity and magnetic microcavity composite structure, which is integrally of a bilateral symmetrical structure and comprises P layers arranged on the left side and the right side, and a G layer and an L layer arranged in the middle, wherein the P layer, the G layer and the L layer are arranged at intervals; the P layer is a coupling prism, the G layer and the L layer are both coupling micro-cavities formed by medium layers with magneto-optical effects, wherein the G layer is a gain medium layer, and the L layer is a loss medium layer. When the structure is in a PT symmetrical pole state, the structure has extremely high transmissivity, the transmissivity value is up to thousands, input weak light can be amplified by thousands of times and then transmitted out, and the transmissivity is linearly regulated and controlled by the magnetic induction intensity of an applied magnetic field; the device can be used for the amplification function of light intensity or light signals or the signal modulation function of strong light fields through weak magnetic field signals.)

1. A PT symmetrical coupling microcavity and magnetism microcavity composite structure which characterized in that: the whole structure is symmetrical and comprises P layers arranged at two sides and a G layer and an L layer arranged in the middle, wherein the P layer, the G layer and the L layer are arranged at intervals; the P layer is a coupling prism, the G layer and the L layer are both coupling micro-cavities formed by medium layers with magneto-optical effects, wherein the G layer is a gain medium layer, and the L layer is a loss medium layer.

2. The PT symmetrically-coupled microcavity and magnetic microcavity composite structure of claim 1, wherein: the G layer and the L layer are made of InSb and are prepared by doping quantum wells.

3. The PT symmetrically-coupled microcavity and magnetic microcavity composite structure of claim 1, wherein: a layer is arranged between the P layer and the G layer, between the G layer and the L layer and between the L layer and the P layer for separation, and the A layer is an air layer.

4. The PT symmetrically-coupled microcavity and magnetic microcavity composite structure of claim 1, wherein: in use, the G and L layers are subjected to a y-direction magnetic field, and the composite structure operates with PT symmetric pole states.

5. The PT symmetrically-coupled microcavity and magnetic microcavity composite structure of claim 4, wherein: dielectric tensor ε of G layer_GAnd the dielectric tensor ε of the L layer_LThe expression of (a) is:

where i τ is a set imaginary number, i is an imaginary unit, ε₁、ε₂And ε₃The expression of (a) is:

where ω is the angular frequency of the incident wave, ε_∞Is a high frequency limiting dielectric constant, omega_pFor the frequency of the plasma to be,is the electron rotation frequency controlled by the magnetic induction B, e is the electron charge, gamma is the electron impact frequency, m^*＝0.014m_eIs the effective mass of an electron, m_eIs electron mass,. epsilon_phIs the phonon damping rate, omega_tAnd ω_lTransverse and longitudinal optical phonon frequencies, gamma, respectively_phIs the phonon damping rate.

6. The PT symmetrically-coupled microcavity and magnetic microcavity composite structure of claim 5, wherein: the distance d between the P layer and the G layer or the L layer_A1600nm, G layer width d_GWidth d of L layer_L1500nm, distance d between G and L layers_A2The section of the P layer is an isosceles right triangle with the length of 300 nm.

7. The PT symmetrically-coupled microcavity and magnetic microcavity composite structure of claim 6, wherein: τ 0.7742, lightwave frequency 29.6989 THz.

8. Use of the PT symmetrically coupled microcavity and magnetic microcavity composite structure of any one of claims 1-7 as an optical triode for signal amplification, wherein: and amplifying the light intensity or light signals based on the amplification effect of the PT symmetrical coupling microcavity and the magnetic microcavity composite structure in the pole state.

9. Use of the PT symmetrically coupled microcavity and magnetic microcavity composite structure as claimed in any one of claims 1-7 for applying signal modulation to an optical field, wherein: based on the characteristic that the transmissivity of the PT symmetrical coupling microcavity and magnetic microcavity composite structure is regulated and controlled by a magnetic field in a pole state, signal modulation is applied to an output optical field through a magnetic field signal.

10. The use of claim 9 to apply a signal modulation to an optical field, wherein: the fluctuation range of the magnetic field signal is selected in a linear change interval of the transmissivity along with the magnetic field.

Technical Field

The invention belongs to the field of optical devices, and particularly relates to a PT symmetrical coupling microcavity and magnetic microcavity composite structure and application thereof.

Background

In the field of optical communications today, there is an increasing demand for optical devices with special functions, such as all-optical diodes, optical buffers, optical resonators, optical memories, etc.; these optical components are designed similarly to the functions of electronic components and are usually realized by optical effects of specific materials. Although there are many optical devices like the above-mentioned electronic components, the research on the optical triode still has little success because it is difficult to find a mechanism for controlling a strong signal by a weak signal in the optical field.

In order to realize an optical triode, in the prior art, researchers try to construct a graphene optical mechanical system which is formed by coupling a graphene nano mechanical oscillator and a microwave cavity, wherein signal amplification is realized by adjusting the power intensity of a pumping field; researchers also design all-optical triodes by utilizing the cross gain modulation of two reflection-type semiconductor amplifiers based on a cascade wavelength converter; researchers also realize phototriodes in lithium niobate superlattices by using an electric induction secondary cascade method. However, the above implementation mechanisms of the phototriode involve optical nonlinear processes, which results in increased design complexity and limited power amplification.

The optical PT (critical-Time) symmetric structure with specific distribution of gain and loss media has unique advantages in optical device design, and can be described by a symmetric state, a symmetric defect state, and a critical point of transition from the symmetric state to the symmetric defect state, i.e. a singular point, and shows special properties at the singular point. In addition to the singularity, in the defect state of the PT symmetric structure, there are some discrete poles where two eigenvalues of the scattering matrix of the structure are reciprocal and they correspond to the excited amplification mode and the coherent perfect absorption mode, respectively, however, the research on the state of the pole is less, especially the research and application of using the characteristics of the PT symmetric structure at the pole in the aspect of enhancing the optical effect are lacked.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a PT symmetrical coupling microcavity and magnetic microcavity composite structure, which realizes the control and amplification functions of an optical triode under the condition of avoiding an optical nonlinear process.

The present invention achieves the above technical objects by the following technical means.

A PT symmetrical coupling microcavity and magnetic microcavity composite structure is a bilateral symmetrical structure integrally and comprises P layers arranged on the left side and the right side, a G layer and an L layer arranged in the middle, wherein the P layer, the G layer and the L layer are arranged at intervals; the P layer is a coupling prism, the G layer and the L layer are both coupling micro-cavities formed by medium layers with magneto-optical effects, wherein the G layer is a gain medium layer, and the L layer is a loss medium layer.

Further, the G layer and the L layer are made of InSb and prepared by doping quantum wells.

Furthermore, A layers are arranged between the P layer and the G layer, between the G layer and the L layer and between the L layer and the P layer for separation, and the A layers are air layers.

Further, in use, the G and L layers are subjected to a y-direction magnetic field, and the composite structure operates with PT symmetric pole states.

Further, the dielectric tensor ε of the G layer_GAnd the dielectric tensor ε of the L layer_LThe expression of (a) is:

where i τ is a set imaginary number, i is an imaginary unit, ε₁、ε₂And ε₃The expression of (a) is:

where ω is the angular frequency of the incident wave, ε_∞Is a high frequency limiting dielectric constant, omega_pFor the frequency of the plasma to be,for electrons controlled by magnetic induction BRevolution frequency, e is electron charge, γ is electron impact frequency, m^*＝0.014m_eIs the effective mass of an electron, m_eIs electron mass,. epsilon_phIs the phonon damping rate, omega_tAnd ω_lTransverse and longitudinal optical phonon frequencies, gamma, respectively_phIs the phonon damping rate.

Further, the distance d between the P layer and the G layer or the L layer_A1600nm, G layer width d_GWidth d of L layer_L1500nm, distance d between G and L layers_A2The section of the P layer is an isosceles right triangle with the length of 300 nm.

Further, τ is 0.7742, and the lightwave frequency is 29.6989 THz.

The PT symmetrical coupling microcavity and magnetic microcavity composite structure is applied to optical triode signal amplification: and amplifying the light intensity or light signals based on the amplification effect of the PT symmetrical coupling microcavity and the magnetic microcavity composite structure in the pole state.

The application of the PT symmetrical coupling microcavity and magnetic microcavity composite structure in applying signal modulation to an optical field is as follows: based on the characteristic that the transmissivity of the PT symmetrical coupling microcavity and magnetic microcavity composite structure is regulated and controlled by a magnetic field in a pole state, signal modulation is applied to an output optical field through a magnetic field signal.

Further, the fluctuation range of the magnetic field signal is selected within a linear variation interval of the transmissivity along with the magnetic field.

The invention has the beneficial effects that:

(1) the invention provides a novel PT symmetrical coupling microcavity and magnetic microcavity composite structure, which has extremely high transmissivity when in a PT symmetrical pole state, the transmissivity value is up to thousands, input weak light can be amplified by thousands of times and then transmitted out, and the transmissivity is linearly regulated and controlled by the magnetic induction intensity of an applied magnetic field.

(2) The novel structure of the invention can be used as an optical triode to realize the amplification function of light intensity or light signals.

(3) The transmissivity of the structure of the invention has the characteristic of being linearly regulated and controlled by a magnetic field, so the structure can also be used for applying signal modulation to an optical field, and because the structure of the invention has great transmissivity, a strong optical field with very large amplitude can be output, and in contrast, a magnetic field signal for modulation is a weak signal, so the function of modulating the strong signal by the weak signal is realized.

(4) In the current optical field, there is no relevant research on the characteristics and applications of PT symmetric pole states, because PT symmetric pole modes are often isolated and static, and are not combined with other optical effects, which makes it difficult to produce wide application. The invention innovatively breaks through the technical prejudice, successfully utilizes the unusual amplification effect of the PT symmetrical structure in the pole state, and realizes the function of weak control and strong control in signals.

Drawings

FIG. 1 is a structural diagram of a composite structure of PT symmetrical coupling microcavity and magnetic microcavity in accordance with the present invention;

FIG. 2 is a structural operating state diagram of the present invention;

fig. 3 is a transmission spectrum of the inventive structure at τ 0;

fig. 4 is a transmission spectrum of the inventive structure at τ 0.5;

fig. 5 is a transmission spectrum of the inventive structure at τ 0.7;

fig. 6 is a transmission spectrum at τ 0.7742 for the inventive structure;

FIG. 7 is a graph of the change in transmission with magnetic induction for a structure according to the present invention;

FIG. 8 is a schematic diagram of the fluctuation range of the magnetic field signal selected on the in-phase modulation side;

FIG. 9 is a graph of simulation results of magnetic field signal versus transmittance in-phase modulation;

FIG. 10 is a schematic diagram showing the fluctuation range of the magnetic field signal selected on the anti-phase modulation side;

fig. 11 is a graph showing simulation results of the inverse modulation of transmittance by the magnetic field signal.

Detailed Description

Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

One, structure model

The PT symmetrical coupling micro-cavity and magnetic micro-cavity composite structure is constructed based on PT symmetry, wherein the weak magnetic light effect of a material is combined with the pole state of the PT symmetrical structure, so that an unusual amplification effect is generated.

The PT symmetric composite structure of the present invention as shown in fig. 1 and 2 is a bilateral symmetric structure as a whole, and includes P layers disposed on the left and right sides, and G and L layers disposed between the two P layers, wherein the two P layers are symmetric, the G layer is symmetric with the L layer, and a layer a is disposed between the P layer and the G layer, between the G layer and the L layer, and between the L layer and the P layer as a partition. The P layer is a coupling prism, the cross section of the P layer is triangular, and the P layer is parallel to the adjacent surface between the G layer and the L layer; the G layer and the L layer are both coupled microcavities formed by dielectric layers, wherein the G layer is a gain dielectric layer, the L layer is a loss dielectric layer, both are made of semiconductor material InSb (indium antimonide) and are prepared by doping quantum wells, and the specific preparation methods of the gain dielectric layer and the loss dielectric layer belong to the prior art and are not described in detail in the invention; InSb is an optical material with magneto-optical effect, and the G layer and the L layer can be made of other optical materials with similar magneto-optical effect; the layer A is an air layer and plays a role of spacing.

As shown in fig. 2, in practical use, a y-direction (a direction perpendicular to the paper surface of fig. 2) magnetic field is applied to the G layer and the L layer, and the structure of the present invention is ensured to work in a PT symmetric pole state, so that the structure of the present invention can obtain a very large transmittance, the transmittance value of which is as high as thousands, and the transmittance is linearly controlled by the magnetic induction intensity of the applied magnetic field. The specific effect is that when weak light waves are incident into the structure from the P layer on one side, and the incident direction is vertical to the surface of the prism, the P layer on the other side transmits the strong light waves due to the amplification effect generated by the extremely high transmissivity of the structure.

Second, the working principle of the structure

1) InSb material properties:

the InSb adopted by the G layer and the L layer in the structure of the invention has a magneto-optical effect, and when a magnetic field is applied to the InSb along the y direction, the dielectric constant of the InSb is tensor, and the InSb can be written as follows:

wherein i is an imaginary unit, ε₁、ε₂And ε₃The expression of (a) is:

where ω is the angular frequency of the incident wave, ε_∞Is a high frequency limiting dielectric constant, omega_pFor the frequency of the plasma to be,is the electron rotation frequency controlled by the magnetic induction B, e is the electron charge, gamma is the electron impact frequency, m^*＝0.014m_eIs the effective mass of an electron, m_eIs electron mass,. epsilon_phThe expression is the phonon damping rate as follows:

in the formula of omega_tAnd ω_lTransverse and longitudinal optical phonon frequencies, gamma, respectively_phIs the phonon damping rate.

As can be seen from the equations (1) to (4), ε₂Modulated by an externally applied magnetic field inWhen the incident surface is an xz plane and the incident light is an H-polarized wave, the electric displacement and the electric field vector are both in the xz plane, ε₃No influence is caused on the transmission result; gamma and omega_pThe values for the temperature dependent Drude model parameters can be determined by fitting the values of the reflectance and transmittance spectra, a particular method being known in the art, and some of the results are shown in table 1:

table 1: temperature dependent Drude model parameters gamma and omega_p

Temperature (K)	ωp/2π(THz)	γ(THz)	B(T)
				180	0.35±0.05	1.05±0.05	0.18
220	0.8±0.02	1.19±0.03	0.18
				260	1.45±0.02	1.5±0.05	0.165
295	2.11±0.03	1.65±0.05	0.15

2) The dielectric tensor of the G layer and the L layer of the invention:

based on the InSb dielectric tensor formula (1), for research convenience, the imaginary numbers i tau which are conjugated with each other are respectively added at the main diagonal elements of the dielectric tensor to represent the dielectric tensor epsilon of the gain layer of the G layer in the structure of the invention_GAnd the dielectric tensor ε of the depletion layer of the L layer_L：

3) The structural state analysis of the invention:

for the mode field evolution in the gain layer and the loss layer, a coupling model theory is adopted for analysis, and specifically, the following equation is established:

wherein a is₁And a₂Field amplitude, ω, of the gain and loss layers, respectively₀Is the resonant frequency of the two microcavities, the G layer and the L layer; g and v are gain coefficient and loss coefficient respectively, and v is-g under the condition of meeting PT symmetry, and the specific numerical value is related to tau; k is the coupling coefficient. The light wave transmitted in the structure of the invention is a simple monochromatic harmonic wave in a specific formWherein ω is₁The eigenfrequency of the structure of the invention is as follows:

further, it is obtained from equations (8) and (9):

and solving the following solution according to v ═ g:

equation (11) determines the state of the structure of the present invention when k>g is, ω₁There are two real solutions, indicating that the structure of the invention is in the PT symmetric state; when k is g, it is the critical point from PT symmetrical state to PT symmetrical defect state; when k is<g is then omega₁There are two complex solutions that represent the inventive structure in a PT symmetry break-away state. The PT symmetrical broken state has some discrete poles, and the invention forms special pole effect based on PT symmetrical coupling microcavity under the modulation of magnetic field signal.

Third, specific embodiments

1) Structural and environmental parameter settings

As shown in fig. 2, to verify the effect of the structure of the present invention through simulation, the parameters in the structure of the present invention are set as follows:

d_A1＝600nm，d_G＝d_L＝1500nm，d_A2300nm, wherein d_A1Is the distance between P layer and G layer or P layer and L layer, d_GIs the width of the G layer, d_LIs the width of the L layer, d_A2The distance between the G layer and the L layer; the section of the P-layer coupling prism is an isosceles right triangle, and the acute angle theta of the P-layer coupling prism is pi/4; and let the high frequency limiting dielectric constant ε_∞15.6, transverse optical phonon frequency ω_t5.90THz,/2 π ═ 5.90THz, longitudinal optical phonon frequency ω_l5.54THz,/2 π, phonon damping rate γ_ph3.77 THz; the temperature is selected to be room temperature 295K and magnetic induction intensity B is 0.15T, so that the plasma frequency omega is_p2 pi 2.11THz, electronThe collision frequency γ is 1.65 THz.

2) Determining the value of parameter tau at pole state

The change condition of the transmission spectrum of the structure along with the set tau is analyzed and calculated by a transmission matrix method, and the result is shown in figures 3-6, wherein the abscissa in the figures is the light wave frequency, and the ordinate is the transmissivity of the structure; where τ shown in fig. 3 is 0, there are two peaks with a peak value of 1 in the transmission spectrum, corresponding to two real solutions of equation (11); as shown in fig. 3 to 5, as τ increases, two peaks in the transmission spectrum tend to merge, because the gain coefficient g is related to τ, so as τ increases, g also increases, and thus the two real solutions of equation (11) tend to approach; then continuing to increase tau until k < g, the two peaks are completely merged, the structure enters a PT symmetrical defect state, and a plurality of poles exist in the state; as shown in fig. 6, when τ is 0.7742, the transmittance is increased to 2252 at 29.6989THz, which is the pole state of the structure of the present invention, and in this state, the transmittance is very sensitive to the influence of magnetic induction.

3) Effect testing

The transmittance of the structure of the present invention was measured by adjusting the magnetic induction B, setting τ to 0.7742 and the light wave frequency to 29.6989THz, and the result is shown in fig. 7, where the abscissa represents the magnetic induction B and the ordinate represents the transmittance of the structure, where the transmittance peak reaches 6000.

Fourth, practical application

1) Signal amplification application of optical triode

The structure of the invention can amplify and transmit light waves injected from a P layer on one side from a P layer on the other side, the amplification factor is equal to the transmissivity of the structure, and the amplification factor is extremely large, and the specific numerical value reaches thousands of times; therefore, the optical triode is formed, and the functions of light intensity amplification or light signal amplification are realized.

2) Application of signal modulation to optical field

As shown in fig. 7, in the structure of the present invention, in the pole state, the transmittance is very sensitive to the influence of the magnetic field, and the variation curve of the transmittance with the magnetic induction includes a linear variation region on both sides of the peak, and the slope of the curve on the left side of the peak is positive, and the slope of the curve on the right side of the peak is negative. As described in the background art, most of the existing optical triodes involve optical nonlinear processes, and the nonlinearity increases the complexity of the design, so that linear change regions on the left and right sides of the peak value can be selected in the invention to realize the function of applying signal modulation to the optical field by using the magnetic field signal.

Respectively selecting an input signal B which is 2.5+0.45sin (t) and an input signal B which is 3.8+0.4sin (t) to carry out simulation test; the magnetic induction variation range of the input signal B ═ 2.5+0.45sin (t) corresponds to the gray area in fig. 8, the test result is shown in fig. 9, the upper half of fig. 9 is the input magnetic induction waveform, and the lower half is the output transmittance waveform, and it can be seen from fig. 9 that the magnetic field signal is modulated in phase onto the transmittance. The magnetic induction variation range of the input signal B ═ 3.8+0.4sin (t) corresponds to the gray area in fig. 10, and the test result is shown in fig. 11, and it can be seen from fig. 11 that the magnetic field signal is inversely modulated to the transmittance.

In practical use, the amplitude of incident light is ensured to be constant, so that the structure of the invention provides a strong light field outwards through the transmission amplification effect, under the condition, the linear regulation and control effect of the magnetic field on the transmissivity is utilized, the change of the transmissivity directly acts on the amplitude of transmitted light, namely, the amplitude of the transmitted light synchronously fluctuates along with the change of the magnetic induction intensity, and thus, a magnetic field signal is modulated on the strong light field at the same frequency; meanwhile, as can be seen from fig. 9 or fig. 11, the fluctuation amplitude of the magnetic field signal is within 0.5T, and the transmission rate fluctuation amplitude is more than 1000, so that the structure of the invention realizes the function of applying same-frequency modulation to the strong optical field through the weak magnetic field signal.

Furthermore, because the magnetic field can be generated by current and the magnetic induction intensity changes with the current, the magnetic field signal actually reflects an electric signal, and meanwhile, the optical field signal can also be photoelectrically converted into an electric signal, but compared with a weak current signal corresponding to a weak magnetic field signal, the strong optical field signal output by the structure of the invention is converted into a strong current signal, thereby realizing another weak control function similar to the traditional transistor.

In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.

The present invention is not limited to the above-described embodiments, and any obvious modifications, substitutions or alterations can be made by those skilled in the art without departing from the spirit of the present invention.