阅读说明：本技术 一种可实现相干吸收激光点的pt对称康托尔光子晶体结构 (PT symmetrical Kantol photonic crystal structure capable of realizing coherent absorption of laser spot ) 是由 赵东 于 2021-09-06 设计创作，主要内容包括：本发明公开了一种可实现相干完美吸收激光点的PT对称康托尔光子晶体结构,两种折射率不同的均匀电介质薄片满足序列序号N=3的康托尔光子晶体排列,康托尔序列的迭代规则：S-(0)=A,S-(1)=ABA,S-(2)=ABABBBABA,S-(3)=S-(2)(3B)～(2)S-(2),……,S-(N)=S-(N-1)(3B)～(N-1)S-(N-1),……,调制电介质薄片中材料的折射率,使整个结构的材料折射率满足PT对称条件：n(z)=n*(??z)；调控光波入射角的大小和PT对称康托尔光子晶体中增益损耗系数的大小,可以得到不同波长的相干完美吸收激光点。可将相干完美吸收激光点用于制作激光器,激光器的工作波长可以通过增益-损耗因子来灵活地调控。该结构具有提高光放大倍数和缩减结构尺寸等优点。(The invention discloses a PT symmetrical Kantol photonic crystal structure capable of realizing coherent perfect laser point absorption, wherein two uniform dielectric sheets with different refractive indexes meet the Kantol photonic crystal arrangement with the sequence number N =3, and the iteration rule of the Kantol sequence is as follows: s 0 =A，S 1 =ABA，S 2 =ABABBBABA，S 3 =S 2 (3B) 2 S 2 ，……，S N =S N‑1 (3B) N‑1 S N‑1 … …, the refractive index of the material in the dielectric sheet is modulated so that the refractive index of the material throughout the structure satisfies the PT symmetry condition: n (z) = n x (-z); the coherent perfect absorption laser points with different wavelengths can be obtained by regulating the light wave incident angle and the gain loss coefficient in the PT symmetrical Cortotel photonic crystal. Can perfectly suck the coherenceThe laser receiving point is used for manufacturing a laser, and the working wavelength of the laser can be flexibly regulated and controlled through a gain-loss factor. The structure has the advantages of improving the light amplification factor, reducing the size of the structure and the like.)

1. A PT symmetrical Kantol photonic crystal structure capable of realizing coherent absorption of laser points is characterized in that two uniform dielectric sheets with different refractive indexes meet the Kantol photonic crystal arrangement with the sequence number N =3, and the iteration rule of the Kantol sequence is as follows:

S₀=A，S₁=ABA，S₂ = ABABBBABA， S₃ = S₂(3B)²S₂，……，S_N = S_N-1(3B)^N-1S_N-1… …, where the sequence number of the N (N =0, 1, 2, 3, … …) sequence, S_NThe nth entry of the sequence is denoted 3B for three B: BBB (3B)²Represents 9B: BBBBBBBBB (3B)^N-1Is represented by 3 ^N-1B, respectively;

letters A, B denote two uniform dielectric sheets, respectively, of different refractive indices;

the incident light of the PT symmetrical Kantol photonic crystal structure is transverse magnetic wave, and the incident angle isθ；

And modulating the refractive index of the material in the dielectric thin sheet to ensure that the refractive index of the material of the whole structure meets PT symmetry condition: n (z) = n x (-z), where x represents complex conjugation;

expressing the refractive index as n (z) = n_r(z)+in_i(z) wherein n_r(z) denotes the real part of the refractive index, n_i(z) denotes the imaginary refractive index, i denotes the imaginary unit;

when the structure satisfies PT symmetry, the real part of the refractive index is distributed in even symmetry about the point 0, and the imaginary part is distributed in odd symmetry about the point 0;

the coherent perfect absorption laser points with different wavelengths can be obtained by regulating the light wave incident angle and the gain loss coefficient in the PT symmetrical Cortotel photonic crystal.

2. The PT symmetric Cortol photonic crystal structure of claim 1,

the matrix material of A is lead telluride, and the refractive index is n_a= 4.1; the matrix material of B is cryolite with refractive index n_b=1.35。

3. The PT symmetric Cortol photonic crystal structure of claim 1,

a andthe thickness of the B dielectric sheets is 1/4 optical wavelength, that is, the thickness of A is d_a=λ₀/4/n_a=0.0945 μm, where λ₀=1.55 μm as center wavelength and B has a thickness d_b=λ₀/4/n_b=0.287μm。

4. The PT symmetric constor photonic crystal structure of claim 1, wherein the PT symmetric constor photonic crystal structure is characterized byθIs from 0 to 90 degrees.

Technical Field

The invention belongs to the technical field of all-optical communication systems, and relates to a PT symmetrical Kantol photonic crystal structure capable of realizing coherent perfect laser point absorption.

Background

Lasers are widely used in the current technical fields, for example, in all-optical communication, semiconductor lasers are mostly used as light sources at an emitting end; in a link of optical fiber communication, an optical fiber amplifier is needed for relaying signals; in the medical field, wavelength-variable optical fiber lasers are required.

The core component of the laser is an optical amplifier, and a common optical amplifier is a semiconductor optical amplifier. The dielectric medium doped with impurities pumps electrons on a ground state to an excited state under the action of pumping light, so that the ion number inversion is realized. The medium for realizing the ion number reversal is called an activated medium, and the activated medium is stimulated to emit, so that the amplification of the signal is realized. And coating a reflecting layer on the end face of the optical amplifier, wherein one end of the reflecting layer is coated with a total reflection film, and the other end of the reflecting layer is coated with a semi-reflection film. When the light intensity exceeds a threshold value, the laser is excited to emit laser. The pump light is actually the energy needed to provide gain to the dielectric, and there are places where electrical pumping is used.

Conventionally, gain is considered useful, while loss is not only useless but also detrimental, so loss should be minimized in optical systems. Recent non-hermite optical studies have shown that losses in dielectrics can also induce many unusual optical properties, such as optical directional stealth, phase jump in reflection coefficient, and anderson's local area.

When there is gain and loss (or only gain, or only loss) in the dielectric, the system exchanges energy with the outside world, and the system is non-hermitian. The refractive index of the dielectric at this time can be written as n=n_r +in_iWherein n is_rIs the real part of the refractive index, n_iThe letter i represents an imaginary unit of an imaginary number, which is the imaginary part of the refractive index. The real and imaginary parts of the refractive index are modulated so as to spatially satisfy the condition: n (z) = n x (-z), where z is a spatial position coordinate, the structure is said to satisfy Parity-time (PT) symmetry. Research shows that in the photonic crystal satisfying PT symmetry, a coherent-perfect-absorption-laser-point (CPA-LP) can be obtained, and the reflectivity and the transmissivity of the point are both maximum values, so that the CPA-LP can be applied to optical amplifiers and lasers. The optical amplifier has more requirements on the number of dielectric layers, has higher manufacturing difficulty and is not easy to reduce the structure size.

Compared with a periodic photonic crystal, the quasi-periodic photonic crystal (also called quasi-photonic crystal) has more defect cavities and transmission films, and the defect cavities have stronger locality to an electric field, namely stronger resonance. The laser is stimulated to emit by utilizing the resonance of the resonant cavity, so that the combination of PT symmetry and quasi-photonic crystal can be considered, and the light amplification laser spot with higher intensity can be realized; or to downsize the device for the same magnification power.

Disclosure of Invention

The invention aims to provide a PT symmetrical Kantol photonic crystal structure capable of realizing coherent perfect absorption of a laser spot.

The technical scheme of the invention is as follows:

a PT symmetrical Kantol photonic crystal structure capable of realizing coherent perfect laser point absorption is disclosed, wherein two uniform dielectric thin sheets with different refractive indexes meet the Kantol photonic crystal arrangement with the sequence number N =3, and the iteration rule of the Kantol sequence is as follows:

S₀=A，S₁=ABA，S₂ = ABABBBABA，S₃ = S₂(3B)²S₂，……，S_N = S_N-1(3B)^N-1S_N-1… …, where the sequence number of the N (N =0, 1, 2, 3, … …) sequence, S_NThe nth entry of the sequence is denoted 3B for three B: BBB (3B)²Represents 9B: BBBBBBBBB (3B)^N-1Is represented by 3 ^N-1B, respectively;

letters A, B denote two uniform dielectric sheets, respectively, of different refractive indices;

the incident light of PT symmetrical Kantol photonic crystal structure is transverse magnetic wave, and the incident angle isθ；

And modulating the refractive index of the material in the dielectric thin sheet to ensure that the refractive index of the material of the whole structure meets PT symmetry condition: n (z) = n x (-z), where x represents complex conjugation;

expressing the refractive index as n (z) = n_r(z)+in_i(z) wherein n_r(z) denotes the real part of the refractive index, n_i(z) denotes the imaginary refractive index, i denotes the imaginary unit;

when the structure satisfies PT symmetry, the real part of the refractive index is distributed in even symmetry about the point 0, and the imaginary part is distributed in odd symmetry about the point 0;

the coherent perfect absorption laser points with different wavelengths can be obtained by regulating the light wave incident angle and the gain loss coefficient in the PT symmetrical Cortotel photonic crystal.

Further, the matrix material of A is lead telluride, and the refractive index is n_a= 4.1; the matrix material of B is cryolite with refractive index n_b=1.35。

Further, the dielectric sheets A and B both had a thickness of 1/4 optical wavelengths, i.e., A had a thickness d_a=λ₀/4/n_a=0.0945 μm, where λ₀=1.55 μm as center wavelength and B has a thickness d_b=λ₀/4/n_b=0.287μm。

Further, the aboveθIs adjustable within the range from 0 degrees to 90 degrees.

The invention has the characteristics and beneficial effects that: according to the technical scheme, the refractive index of a material in a Kangtorr (Cantor) photonic crystal with the sequence number N =3 is modulated, so that PT symmetry is met; the size of the incident angle of the light is changed, so that a laser point meeting a specific wavelength is found. The incident angle and the wavelength corresponding to the laser point can be flexibly regulated and controlled through the gain-loss coefficient of the material.

Typical optical amplifiers have a magnification of 10²-10³The amplification factor of the photonic crystal amplifier can be as high as 10⁴-10⁵。

In addition, the size of the amplifier is only in the micron order, and the system structure of optical amplification is greatly simplified.

Drawings

FIG. 1 is a Cantor sequence photonic crystal structure satisfying PT symmetry according to the present invention;

FIG. 2 (a) is a graph of transmission as a function of incident angle and normalized frequency; (b) is the angle of incidenceθTransmission spectrum corresponding to 30.45 °; (c) the change relation of the reflectivity along with the incident angle and the normalized frequency is obtained; (d) is the angle of incidenceθA corresponding reflection spectrum at =30.45 °; gain-loss factor q = 0.01;

fig. 3 (a) is a graph of transmission as a function of incident angle and normalized frequency for a gain-loss factor q = 0.02;

(b) the positions of CAP-LPs corresponding to different q values in the parameter space;

(c) the variation relation of the incidence angle corresponding to the CAP-LP with q;

(d) the normalized frequency corresponding to CAP-LP varies with q.

Detailed Description

The principles and features of this invention are described below in conjunction with examples and figures, which are set forth to illustrate the invention and are not intended to limit the scope of the invention.

Referring to fig. 1, mathematically, the iteration rule for the kantor (Cantor) sequence is: s₀=A，S₁=ABA，S₂ = ABABBBABA, S₃ = S₂(3B)²S₂，……，S_N = S_N-1(3B)^N-1S_N-1… …, where the sequence number of the N (N =0, 1, 2, 3, … …) sequence, S_NThe Nth term representing the sequence; (3B) represents 3B, (3B)^N-1Is represented by 3 ^N-1And B. The letters A, B in the corresponding Cantor photonic crystal respectively represent two homogeneous dielectric flakes having different refractive indices. The photonic structure of the Cantor photonic crystal with the sequence number N =3 is given in FIG. 1. Wherein, the matrix material of A is lead telluride, the refractive index is n_a= 4.1; the matrix material of B is cryolite with refractive index n_b= 1.35. Incident light is transverse magnetic wave and is incident from the left side at an incident angle ofθ. Dielectric sheets A and B are both 1/4 optical wavelengths thick, i.e. A has a thickness d_a=λ₀/4/n_a=0.0945 μm (μm represents micrometers), where λ₀=1.55 μm as center wavelength and B has a thickness d_b=λ₀/4/n_b=0.287 μm. And modulating the refractive index of the material in the dielectric thin sheet to ensure that the refractive index of the material in the whole structure meets PT symmetry condition: n (z) = n x (-z), where x represents complex conjugation. The refractive index can be expressed as n (z) = n_r(z)+in_i(z) wherein n_r(z) denotes the real part of the refractive index, n_i(z) denotes an imaginary refractive index, and i denotes an imaginary unit. When the structure satisfies PT symmetry, the real part of the refractive index is distributed in even symmetry with respect to the 0 point, and the imaginary part is distributed in odd symmetry with respect to the 0 point.

The imaginary part of the index of refraction represents gain or loss, and when the imaginary part is positive, represents loss; when the imaginary part is negative, a gain is represented. The loss can be realized by doping metal ions such as iron ions, and the gain is obtained by nonlinear two-wave mixing.

The real part of the refractive index in this patent represents the refractive index n of the dielectric matrix material_r(z)=n_aOr n_r(z)=n_bThe imaginary part represents the gain or loss, and its absolute value is called the gain-loss factor, denoted as q = | n_i(z)|。

Referring to fig. 2, the transmittance T of a PT symmetric Cantor photonic crystal with number N =3 is given in fig. 2 (a) by changing the incident angle and wavelength of a light wave. For the sake of contrast, the transmission T is logarithmically logarithmized₁₀(T). The gain-loss factor is then q = 0.01. The ordinate unit Degree represents degrees "°"; abscissa (A)ω−ω ₀)/ω _gapRepresents a normalized angular frequency, whereinω=2πc/λ、ω ₀ =2πc/λ₀Andω _gap= 4ω₀arcsin│[n _a −n _b )/[n _a +n _b ]｜²and/pi respectively represents incident light angular frequency, incident light central angular frequency and angular frequency band gap, c is light speed in vacuum, and arcsin is an inverse sine function. It can be seen that in the parameter space there is a point of maximum transmission, also called coherent perfect absorption laser spot (CPA-LP), abbreviated LP. The position coordinate of LP is [ [ solution ] ]θ=30.45°，(ω−ω ₀)/ω _gap=0.474]Transmittance at this point is T_LP=3.23×10⁴。

To more visually represent LP in transmittance, FIG. 2 (b) shows when the incident angle isθThe corresponding transmission spectrum when =30.45 °, the other parameters being unchanged.θ=30.45 ° is exactly the angle of incidence for LP. By varying the wavelength of the incident light, the normalized frequency is correspondingly varied and the transmittance is a function of the normalized frequency. It can be seen that there is a very large transmission peak in the transmission spectrum, marked by the symbol, whose transmission is precisely thatT_LP=3.23×10⁴。

To verify the point [, ]θ=30.45°，(ω−ω ₀)/ω _gap=0.474]For coherent perfect absorption of the laser spot, the reflectivity R of the light wave in the parameter space is given in fig. 2 (c). log (log)₁₀(R) represents the logarithm of the reflectance. It can be seen that, as the angle of incidence and the normalized frequency vary, there is also an extremum point in the parameter space for the reflectivity R, which is located exactly in [ 2 ]θ=30.45°，(ω−ω ₀)/ω _gap=0.474]. Therefore, this point is both the transmittance and reflectance maxima, and is therefore the CAP-LP. The value of the reflectivity at that point is R_LP=1.03×10⁵。

To more visually illustrate the LP corresponding to reflectivity in the parameter space, FIG. 2 (d) shows the LP when the incident angle isθThe corresponding reflection spectrum when =30.45 °, the other parameters were unchanged.θ=30.45 ° is exactly the angle of incidence for LP. By varying the incident light wavelength, the normalized frequency is correspondingly varied and the reflectivity is a function of the normalized frequency. It can be seen that there is a very large transmission peak in the reflectance spectrum, denoted by the symbol, whose reflectance is exactly R_LP=1.03×10⁵。

Referring to fig. 3, the gain-loss factor q is changed such that q =0.02, the position of the LP in the parameter space will change. Fig. 3 (a) shows the transmittance of the light wave corresponding to the photonic crystal at this time. It can be seen that there is also a transmission maximum point, i.e., CPA-LP, in the parameter space. The position coordinate of LP is [ [ solution ] ]θ=46.2°，(ω−ω ₀)/ω _gap=0.604]Transmittance at this point is T_LP=7.16×10³。

When q varies in the interval [0.01, 0.04], CAP-LP appears in the parameter space by varying the magnitude of the incident angle, as shown in fig. 3 (b). It can be seen that as q increases, LP gradually moves to the upper right. FIG. 3 (c) and FIG. 3 (d) show the angle of incidence and normalized frequency versus q for LP, respectively. It can be seen that the incident angle and normalized frequency for LP increase with increasing q. Thus, when the LP in the device is applied to a laser, the wavelength of the laser can be changed by changing the gain-loss factor.

In summary, CAP-LP can be achieved in PT symmetric Cantor photonic crystals. CAP-LP is the maximum point of reflectivity and transmissivity. The position of the CAP-LP in the parameter space consisting of the angle of incidence and the normalized frequency is a function of the gain-loss factor, and therefore, when the CAP-LP is used to fabricate a laser, the operating wavelength of the laser can be flexibly tuned by the gain-loss factor.

The specific embodiment is as follows: (the implementation of the method is described in detail with reference to the figures, respectively, and if necessary an example of the use of the method can be provided, the more detailed the part is the better)

As shown in fig. 2 (a), when the gain-loss factor is q =0.01, the CAP-LP corresponds to an incident angle of q £ LPθ=30.45 °, normalized frequency of: (ω−ω ₀)/ω _gap=0.474, reflectance R_LP=1.03×10⁵Transmittance of T_LP=3.23×10⁴. And normalizing the frequency (ω−ω ₀)/ω _gap=0.474 corresponding to a wavelength λ =1.1749 μm, i.e. when the angle of incidence satisfiesθAnd when the angle is =30.45 degrees, the photonic crystal is excited to emit laser, and the output wavelength of the laser is lambda =1.1749 μm.

If the output wavelength of the laser is to be changed, this can be achieved by changing the gain-loss factor q, as shown in fig. 3 (a). For example, when the gain-loss factor is increased to q =0.02, the corresponding CAP-LP position is [ ]θ=46.2°，(ω−ω ₀)/ω _gap=0.604]And aω−ω ₀)/ω _gap=0.604 for a laser wavelength λ =1.1018 μm, i.e. as long as the angle of incidence is changed to beθBy =46.2 °, a laser beam with an excitation wavelength λ =1.1018 μm can be obtained.