CN111404012B - Forward zero-dispersion regulation and control method for nanosphere light field - Google Patents

Forward zero-dispersion regulation and control method for nanosphere light field Download PDF

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CN111404012B
CN111404012B CN202010113105.3A CN202010113105A CN111404012B CN 111404012 B CN111404012 B CN 111404012B CN 202010113105 A CN202010113105 A CN 202010113105A CN 111404012 B CN111404012 B CN 111404012B
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gain
optical
nanosphere
optical fiber
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CN111404012A (en
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张允晶
李鹏
窦玉江
何兴理
李灵峰
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Suzhou University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094042—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a fibre laser
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094049—Guiding of the pump light
    • H01S3/094053—Fibre coupled pump, e.g. delivering pump light using a fibre or a fibre bundle
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/169—Nanoparticles, e.g. doped nanoparticles acting as a gain material

Abstract

A forward zero-dispersion regulation and control method of a nanosphere light field is provided, an original light field is assumed to be formed by incident light and an original optical nanosphere, and the method is characterized in that: the gain nanospheres with optical gain characteristics are added into the original optical nanosphere system of the original optical field to serve as optical gain media, the optical gain media are excited in an optical fiber pumping mode to achieve gain, and the gain intensity of the optical gain media is adjusted by adjusting the excitation intensity of optical fiber pumping, so that forward zero scattering of the optical field is achieved. The invention adopts a gain compensation mode, and further realizes the forward scattering regulation and control of the nanosphere light field through the modulation relation between gain and loss. It is characterized in that: firstly, forward zero scattering of an object, which cannot be realized in a passive regulation and control method, is realized; secondly, forward zero scattering of an object can be realized by modulating the gain intensity, and even zero scattering in any direction can be realized; thirdly, the structure is relatively simple, easy to realize, efficient and effectual.

Description

Forward zero-dispersion regulation and control method for nanosphere light field
Technical Field
The invention relates to the technical field of light field regulation, in particular to a method for regulating and controlling forward zero scattering of a nanosphere light field. The method utilizes an active gain method to regulate and control the scattering, thereby achieving the purpose of regulating and controlling the forward zero scattering of the light field.
Background
Scattering refers to the process by which a particle absorbs a portion of the energy of an incident wave and re-radiates it into space. To date, a great deal of research has been devoted to studying the scattering of objects, and the scattering regulation becomes a big focus of research, and can be used in cloak, nano-antenna, medical treatment, sensor, light emitter and photovoltaic devices, and the ultra-low scattering cross section can be used in cloak and non-invasive measurement. Absorbing screens and retroreflective coatings have been applied to antennas, aircraft, and the like. However, the structural complexity, the inherent bandwidth limitation and the suitable object size place high demands on the application.
Due to the limitation of optical theorem, the forward scattering is larger than that in other directions, Kerker proposes the condition that the forward scattering is approximately equal to zero, but the parameter size of an object is required to be far smaller than the wavelength, and the magnetic permeability meets certain conditions. The traditional scattering regulation is divided into the scattering regulation based on a metamaterial structure; scattering regulation based on optical transformation; scattering regulation and control based on a grating structure; scattering regulation based on photonic crystals; scattering regulation based on surrounding high dielectric constant structures; scattering regulation based on plasmonic elements. The six scattering regulation methods all belong to passive regulation methods in the field of light field regulation. The most outstanding problems of such regulation methods are: due to the energy conservation principle, besides the KerKer condition of a magnetic sphere with the characteristic dimension far smaller than the wavelength, the scattering modulation based on a passive system is a regulation target which cannot realize forward zero scattering. In addition, the change of the scattering direction usually needs to change a specific structure, so that the requirement of adjustable flexibility of scattering is difficult to meet, and the regulation effect is poor.
Chinese patent CN106950195A discloses an invention patent application with application number 201710103303.X entitled "programmable optical element based on scattering medium and light field regulation system and method" in 2017, 7, month 14. In order to solve the problems of single function, high cost, poor regulation and control capability and the like of a transmission optical element, the application adopts the following technical scheme: the light source beam expanding module, the modulation module, the scattering medium microscopic module and the detection module are sequentially arranged aiming at the regulated and controlled light field, and the data processing module is arranged between the modulation module and the detection module. The computer controls the spatial light modulator to modulate the input light field circularly, the detector detects the output light field to perform data shaping, the scattering medium optical transmission matrix is measured, and the scattering medium optical transmission matrix is used as a programmable intelligent optical element to realize light field regulation and control by combining methods of optical phase conjugation, phase recovery, speckle reconstruction and the like. Obviously, the technical scheme belongs to an active regulation and control method, but has the following defects: firstly, in order to meet the requirements of scattering regulation and control, the detection precision requirements (including scattering intensity and scattering phase) are high, accurate detection is difficult to be carried out, and particularly, accurate scattering quantity is difficult to detect by adding an input light field, so that accurate regulation and control are difficult to be finally carried out; and secondly, the light source beam expanding module, the modulating module, the scattering medium microscopic module, the detecting module and the data processing module are arranged, so that the structure is complex, and the manufacturing process requirement is high.
In view of this, the invention provides a method for controlling active scattering, which has a simple structure and a better control effect.
Disclosure of Invention
The invention provides a forward zero-scattering regulation and control method of a nanosphere light field, and aims to solve the problems of complex structure and poor regulation and control effect of an active regulation and control method in the prior art.
In order to achieve the purpose, the invention adopts the technical scheme that: a forward zero-dispersion regulation and control method of a nanosphere light field supposes that an original light field is formed by incident light and an original optical nanosphere, and the innovation is as follows:
the gain nanospheres with optical gain characteristics are added into the original optical nanosphere system of the original optical field to serve as optical gain media, the optical gain media are excited in an optical fiber pumping mode to achieve gain, and the gain intensity of the optical gain media is adjusted by adjusting the excitation intensity of optical fiber pumping, so that forward zero scattering of the optical field is achieved.
The relevant content in the above technical solution is explained as follows:
1. in the above scheme, the optical gain medium adopts trivalent erbium ion (Er)3+) Doped silicon material, trivalent erbium ions (Er)3+) Has a doping concentration of 3X 1020-6×1020Number of ions per cubic centimeter, wherein the trivalent erbium ions (Er)3+) Preferably, the doping concentration of (A) is 4X 1020-5×1020Number of ions per cubic centimeter.
2. In the above scheme, the optical fiber pump uses laser as an excitation source, uses an optical fiber as a carrier, and surrounds the optical fiber around the optical gain medium, wherein one end of the optical fiber is used as a laser injection port, and the other end of the optical fiber is used as a laser injection port, and when the laser passes through the optical fiber, the optical gain medium is excited in an optical coupling mode to generate forward gain.
3. In the above scheme, the laser intensities of the gain nanospheres and the optical fiber pump are as follows:
analyzing the original optical nanospheres and the gain nanospheres to be added by a dipole equivalent method, wherein if the forward scattering of the optical field is zero, the polarizability of the added gain nanospheres is as shown in a formula (I):
Figure BDA0002390677680000021
in formula (I):
α2representing the polarizability of the gain nanospheres, which is unknown quantity and has the dimension of coulomb meter2A voltage;
α1representing the polarizability of the original optical nanospheres, which is a known quantity and is measured in coulomb and meter2A voltage;
eta represents the azimuth angle of the incident light direction, which is a known quantity and has a dimension of radian;
gamma represents the pitch angle of incident light, is a known quantity, and has a dimension of radian;
k represents the wave number of incident light, k is 2 pi/lambda, is a known quantity, and has a dimension of meter-1Wherein λ is the wavelength of incident light, which is a known quantity, and the dimension is meter, and the relationship between the wavelength λ and the angular frequency ω is ω ═ 2 π c/λ, and c is the speed of light in vacuum;
d represents the distance between the sphere centers of the original optical nanospheres and the gain nanospheres, which is a known quantity and is measured in meters;
epsilon represents the absolute dielectric constant of the environment, is a known quantity and has a dimension of normal/meter;
e represents the euler constant, e is 2.71828;
i represents an imaginary unit;
the relationship between the dielectric constant and polarizability of nanospheres is known as formula (II):
Figure BDA0002390677680000022
in formula (II):
alpha represents the polarizability of the nanosphere, is a known quantity and is measured in coulomb meter2A voltage;
εrthe relative dielectric constant of the nanosphere is expressed as an unknown quantity and is dimensionless;
r represents the radius of the nanosphere, is a known quantity and is measured in meters;
ε represents the absolute dielectric constant of the environment, and has the same meaning as ε of formula (I);
k represents the wave number of incident light, and has the same meaning as k in formula (I);
substituting the polarizability of the gain nanospheres obtained by the formula (I) into the formula (II) to obtain the dielectric constant epsilon of the gain nanospheresG(ω)；
According to the dielectric constant epsilon of the gain nanosphereG(ω) having a dielectric constant εGThe specific implementation manner of the (omega) gain nanosphere is as follows:
since the gain intensity can be characterized by the equivalent dielectric constant and is expressed by the following formula (III):
Figure BDA0002390677680000031
in formula (III):
εGthe relative dielectric constant of the optical gain medium after being pumped and excited by the optical fiber is known quantity and dimensionless;
εLthe relative dielectric constant of the optical gain medium before the optical fiber pumping excitation is expressed, is a known quantity and is dimensionless;
k represents the laser intensity coefficient transmitted in the optical fiber, is unknown and dimensionless;
γ0the gain bandwidth of the optical gain medium is represented, is a known quantity and has the dimension of radian/second;
ω represents the frequency of the incident light, which is a known quantity in radians/second;
ω0to representThe resonant frequency of the optical gain medium is a known quantity and is measured in radians/second;
i represents an imaginary unit, and has the same meaning as I in the formula (I);
the laser intensity coefficient K transmitted in the optical fiber can be obtained by the formula (III), so that the laser intensity of the excitation source in the optical fiber pump under the condition of forward zero scattering of the optical field can be obtained.
The design concept and the effect of the invention are as follows: in order to solve the problems of complex structure and poor regulation effect of an active regulation method in the prior art, the invention aims at adding a gain nanosphere as an optical gain medium in an original optical nanosphere system of a nanosphere light field, then exciting the optical gain medium by using optical fiber pumping to realize gain, and realizing forward zero scattering of the light field by adjusting the excitation intensity of the optical fiber pumping. The invention adopts a gain compensation mode, and further realizes the forward scattering regulation and control of the nanosphere light field through the modulation relation between gain and loss. Firstly, the most outstanding characteristic of the invention is that the outstanding problem that the forward zero scattering of the object can not be realized in the passive regulation and control method is solved; secondly, the invention can realize the forward zero scattering of the object, even the zero scattering in any direction by modulating the gain intensity; thirdly, the invention has the advantages of relatively simple structure, easy realization, high efficiency and good effect.
The invention realizes the scattering regulation and control of the scattering system by regulating the gain intensity, and can be designed to directly realize the regulation of the gain intensity by regulating the intensity of current or voltage in the future practical application so as to regulate the scattering direction and size. Compared with the traditional passive structure, the structure of the system does not need to be redesigned or new materials are not needed to be reused, and the adjustment characteristic is more convenient. The method can be particularly applied to application of nano circuits, nano medical equipment, low RCS antenna arrays, nondestructive and noninvasive detection and the like.
The necessity of using gain compensation if forward zero scattering of the light field is to be achieved is illustrated below by the object scattering system. In other words, scattering modulation based on passive systems is not able to achieve forward zero scattering of objects.
Assembly of optically bound scattering objectsScattered energy and forward vector scattered intensity (including scalar magnitude and phase), the derivation principle comes from conservation of energy. The object scattering system is shown in FIG. 1, in which the wave vector of the incident wave is KOThe incident electric field and the magnetic field are respectively EiAnd BiScattering by a scatterer to generate a scattering field E at point PsAnd BsThe wave vector scattered by the scatterer is K, the scatterer bounding surface is S, the normal vector of any point of the source boundary is n ', the direction of the observation point is r, and the direction of any point of the source boundary is r'. Assuming that the scattering point P is far from the scatterer, its scattered wave is approximately (equal to) a plane wave.
The extinction cross section of the object and the forward scattering intensity relation are as the following formula (IV):
Figure BDA0002390677680000041
σ in formula (IV)tIs the extinction cross section of the object, f is the forward scattering intensity, including phase and direction, epsiloniIs the polarization direction of the incident field, k0Is the direction of the incident wave. The above relationship establishes the optical theorem for a single scatterer, which can be approximated as a single scatterer for multiple scatterers if the distance between the scatterers is much smaller than the distance of the observation point.
For passive systems, the forward scatter can be approximately equal to zero unless the extinction cross-section is small (kerkerkerr condition). However, objects tend to have large extinction cross-sections and therefore their forward scatter tends to be large.
In the invention, forward zero scattering is realized by adjusting the gain. From electromagnetic theory, the total extinction cross section is the following formula (V):
σt＝σs+σa-|σgequation (V)
In the formula (V), σsIs a scattering cross section, σaTo loss cross section, σgThe resulting scattering and radiation cross-section is the gain. It will be appreciated that for systems with gain, the gain term can be adjusted so that the total extinction cross-section isIs zero. As can be seen from equation (iv), forward scatter can be more easily modulated to zero.
FIG. 2 is a schematic diagram of a gain mechanism-based forward zero scattering modulation, in which the scatterer 1 is a conventional passive object when an incident field E existsiThe forward scattered wave of the scatterer 1 is Es1In order to cancel the forward scattering, the scattering body 2 is added, and the forward wave scattered by the scattering body 2 is Es2So that the total forward scattered field is Es1+Es2. Since there is a phase delay between the scatterer 1 and the scatterer 2 and there is a reduction in amplitude, the total forward scattering cannot be zero if the scatterer 2 is a passive object. Therefore, the scatterer 2 must be an active object, and forward scattering cancellation of both objects must be zero. There are various forms for adding gain to the scatterer 2, and optical gain media can be used for optics, and there are various ways for implementing optical gain media, such as optically pumped gain materials, electrically pumped gain materials, microwave pumped gain materials, etc.
Drawings
FIG. 1 is a diagram of an object scattering system;
FIG. 2 is a schematic diagram of forward zero-scattering regulation based on a gain mechanism;
FIG. 3 is a schematic diagram of the structure of the forward zero-scattering regulation system of the nanosphere light field of the present invention;
FIG. 4 is a diagram of a dual dipole system in accordance with an embodiment of the present invention;
FIG. 5 is a radiation pattern of the gain nanospheres of the embodiment of the present invention at different incident angles;
fig. 6 is a zero-dispersion directional diagram of different directions of the gain nanospheres in the fixed incident direction according to the embodiment of the invention.
In the above drawings: 1. incident light; 2. a primary optical nanosphere; 3. a gain nanosphere; 4. an optical fiber; 5. laser is injected into the port; 6. the laser light exits the port.
Detailed Description
The invention is further described with reference to the following figures and examples:
example (b): forward zero-dispersion regulation and control method for nanosphere light field
As shown in fig. 1, assuming that the original light field is formed by incident light 1 and an original optical nanosphere 2, the forward zero-scattering regulation method of the nanosphere light field is as follows:
the gain nanosphere 3 with optical gain characteristic is added into the original optical nanosphere 2 system of the original optical field as an optical gain medium, the optical gain medium is excited by utilizing an optical fiber pumping mode to realize gain, and the gain intensity of the optical gain medium is adjusted by adjusting the excitation intensity of the optical fiber pumping, so that the forward zero scattering of the optical field is realized.
The optical gain medium adopts trivalent erbium ion (Er)3+) Doped silicon material, trivalent erbium ions (Er)3+) Has a doping concentration of 3X 1020-6×1020Number of ions per cubic centimeter. Wherein, trivalent erbium ion (Er)3+) The preferred doping concentration is 4 x 1020-5×1020Number of ions per cubic centimeter.
The optical fiber pump takes laser as an excitation source, takes an optical fiber 4 as a carrier, and surrounds the optical fiber 4 on the periphery of an optical gain medium, wherein one end of the optical fiber 4 is used as a laser injection port 5, the other end of the optical fiber 4 is used as a laser injection port 6, and when the laser passes through the optical fiber, the optical gain medium is excited in an optical coupling mode to generate forward gain.
The laser intensities of the gain nanospheres 3 and the fiber pump are as follows:
analyzing the original optical nanospheres 2 and the gain nanospheres 3 to be added by a dipole equivalent method, wherein if the forward scattering of the optical field is zero, the polarizability of the added gain nanospheres 3 is as shown in formula (I):
Figure BDA0002390677680000051
in formula (I):
α2representing the polarizability of the gain nanosphere 3, which is unknown quantity and has the dimension of coulomb.m2A voltage;
α1which represents the polarizability of the original optical nanosphere 2, is a known quantity,the dimension is coulomb and meter2A voltage;
eta represents the azimuth angle of the incident light 1 direction, which is a known quantity and has a dimension of radian;
gamma represents the pitch angle of the incident light 1, which is a known quantity and has a dimension of radian;
k represents the wave number of the incident light 1, k is 2 pi/lambda, which is a known quantity in the dimension of meter-1Wherein λ is the wavelength of the incident light 1, which is a known quantity, and the dimension is meter, and the relationship between the wavelength λ and the angular frequency ω is ω ═ 2 π c/λ, and c is the speed of light in vacuum;
d represents the distance between the sphere centers of the original optical nanosphere 2 and the gain nanosphere 3, which is a known quantity and is measured in meters;
ε represents the absolute permittivity of the environment, is a known quantity, and has a dimension of normal/meter (absolute permittivity is an absolute value, and absolute permittivity is used herein as an absolute value and therefore has a dimension);
e represents the euler constant, e is 2.71828;
i represents an imaginary unit;
the relationship between the dielectric constant and polarizability of nanospheres is known as formula (II):
Figure BDA0002390677680000061
in formula (II):
alpha represents the polarizability of the nanosphere, is a known quantity and is measured in coulomb meter2A voltage;
εrthe relative dielectric constant of the nanospheres is unknown and dimensionless (the relative dielectric constant is a relative value and is a numerical value relative to the dielectric constant in vacuum, so that the relative dielectric constant is dimensionless);
r represents the radius of the nanosphere, is a known quantity and is measured in meters;
ε represents the absolute dielectric constant of the environment, and has the same meaning as ε of formula (I);
k represents the wave number of the incident light 1, and has the same meaning as k of formula (I);
the gain obtained by the formula (I)Substituting the polarizability of the nanosphere 3 into the formula (II) to obtain the dielectric constant epsilon of the gain nanosphere 3G(ω)；
According to the dielectric constant epsilon of the gain nanosphere 3G(ω) having a dielectric constant εGThe gain nanosphere 3 of (omega) is realized in the following way:
since the gain intensity can be characterized by the equivalent dielectric constant and is expressed by the following formula (III):
Figure BDA0002390677680000062
in formula (III):
εGthe relative dielectric constant of the optical gain medium after being excited by the optical fiber pump is a known quantity and is dimensionless (the relative dielectric constant is a relative value and is a numerical value relative to the dielectric constant in vacuum, so the relative dielectric constant is dimensionless);
εLthe relative dielectric constant of the optical gain medium before the fiber pump excitation is represented, which is a known quantity and is dimensionless (the relative dielectric constant is a relative value and is a numerical value relative to the dielectric constant in vacuum, so the relative dielectric constant is dimensionless);
k represents the laser intensity coefficient transmitted in the optical fiber 4, is unknown and dimensionless;
γ0the gain bandwidth of the optical gain medium is represented, is a known quantity and has the dimension of radian/second;
ω represents the frequency of the incident light 1, which is a known quantity in radians/sec;
ω0representing the resonant frequency of the optical gain medium, which is a known quantity and has a dimension of radian/second;
i represents an imaginary unit, and has the same meaning as I in the formula (I);
the laser intensity coefficient K transmitted in the optical fiber 4 can be obtained by the formula (III), thereby obtaining the laser intensity of the excitation source in the optical fiber pump under the condition of forward zero dispersion of the optical field. Here, the laser intensity coefficient K is relative to a reference intensity of the laser fiber pump, for example, the reference intensity is 10W, and the laser intensity coefficient K is actual laser output power/10, and the reference intensity needs to be determined according to a specific system in practical application.
The following illustrates the formula (I) of the present invention by taking a dipole system as an example:
fig. 4 is a diagram of a dual dipole system in accordance with an embodiment of the present invention. Taking the dipole system as an example, if the azimuth angle and the pitch angle of the incident field are η and γ, respectively, then the far field specifies the direction (the azimuth angle and the pitch angle are γ, respectively)
Figure BDA0002390677680000071
And θ) is the following formula (VI):
Figure BDA0002390677680000072
p in formula (VI)1,p2Is the dipole moment of the two dipoles,
Figure BDA0002390677680000073
for the green function, r is the position of the observation point, r' is the position of the dipole, assuming that the electric field direction is z-axis polarized, the rest of the letters have the same meaning as above.
From the relationship between dipole moment and incident field, the following formula (VII) is known:
Figure BDA0002390677680000074
in the formula (VII), α1,α2The remaining letters are as defined above for the polarizability of the dipoles.
And the polarizability is related to the material properties of the object, such as the dielectric constant of the object. If the far field is zero, the following formula (VIII) is satisfied between the obtained polarizability according to the formula (VII)
Figure BDA0002390677680000075
In the formula (VIII), A is the following formula (IX), and the other letters have the same meanings as above.
Figure BDA0002390677680000081
In the formula (IX), the letters have the same meanings as above.
Substituting the formula (IX) into the formula (VII) to obtain the formula (I).
The controllability of the forward zero scattering of the optical field after the optical gain medium and the optical fiber pump are adopted in the invention is described as follows:
fig. 5 is a radiation pattern of the gain nanospheres of the embodiment of the invention at different incident angles. As can be seen from fig. 5, the forward zero scattering of the system is achieved with gain nanospheres: a) a radiation pattern at an incident angle of 0 degrees; b) a radiation pattern at an incident angle of 45 degrees; c) radiation pattern at an angle of incidence of 90 degrees.
According to the relation between the dielectric constant and the polarizability of the nanospheres, the dielectric constant of another nanosphere required for realizing forward scattering when the nanosphere is incident at different angles can be calculated. Assuming that the distance between nanospheres is fixed at 1/3 wavelengths, the radius of the nanospheres is 0.1 wavelength, the dielectric constant value of the nanospheres whose scattering patterns are to be manipulated is epsilon1From the above method, it can be seen that the dielectric constants of the gain nanospheres corresponding to the other gain nanospheres in fig. 5 are 0.4436+0.0974i
Figure BDA0002390677680000082
Figure BDA0002390677680000083
It can be seen that the imaginary part of the dielectric constant of the nanospheres required is different for different incidence directions, i.e. the intensity representing the gain is different. According to the formula (III), forward zero scattering can be achieved by controlling the pump intensity, i.e. it is proved that the adjustment and control of the forward zero scattering direction can be achieved by introducing gain.
Fig. 6 is a direction-different zero-dispersion directional diagram of the gain nanospheres under a fixed incident direction according to the embodiment of the invention. It can be seen from fig. 6 that under the same incident direction, by adjusting the gain intensity of one nanosphere, the condition of zero dispersion in different directions is realized. Meanwhile, the reconstruction of the directional diagram is realized.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims (4)

1. A forward scattered radiation regulation and control method of a nanosphere light field assumes that an original light field is formed by incident light (1) and an original optical nanosphere (2), and is characterized in that:
adding a gain nanosphere (3) with optical gain characteristic into an original optical nanosphere (2) system of the original optical field as an optical gain medium, exciting the optical gain medium by using an optical fiber pumping mode to realize gain, and adjusting the gain intensity of the optical gain medium by adjusting the excitation intensity of the optical fiber pumping so as to realize forward zero scattering of the optical field;
the laser intensity of the gain nanosphere (3) and the optical fiber pump is as follows:
analyzing the original optical nanospheres (2) and the gain nanospheres (3) to be added by a dipole equivalent method, wherein if the forward scattering of the optical field is zero, the polarizability of the added gain nanospheres (3) is as shown in formula (I):
Figure FDA0002942487580000011
in formula (I):
α2representing the polarizability of the gain nanosphere (3) as unknown quantity in the dimension of coulomb meter2A voltage;
α1representing the polarizability of the original optical nanosphere (2), which is a known quantity and has a dimension of coulomb and meter2A voltage;
η represents the azimuth angle of the incident light (1) direction, which is a known quantity and has a dimension of radian;
gamma represents the pitch angle of the incident light (1), is a known quantity, and has a dimension of radian;
k represents the wave number of the incident light (1), k is 2 pi/lambda, is a known quantity, and has a dimension of meter-1Wherein λ is the wavelength of the incident light (1), is a known quantity, and has a dimension of meter, and the relationship between the wavelength λ and the angular frequency ω is ω 2 π c/λ, and c is the speed of light in vacuum;
d represents the distance between the sphere centers of the original optical nanosphere (2) and the gain nanosphere (3), which is a known quantity and is measured in meters;
epsilon represents the absolute dielectric constant of the environment, is a known quantity and has a dimension of normal/meter;
e represents the euler constant, e is 2.71828;
i represents an imaginary unit;
the relationship between the dielectric constant and polarizability of nanospheres is known as formula (II):
Figure FDA0002942487580000012
in formula (II):
alpha represents the polarizability of the nanosphere, is a known quantity and is measured in coulomb meter2A voltage;
εrthe relative dielectric constant of the nanosphere is expressed as an unknown quantity and is dimensionless;
r represents the radius of the nanosphere, is a known quantity and is measured in meters;
ε represents the absolute dielectric constant of the environment, and has the same meaning as ε of formula (I);
k represents the wave number of the incident light (1), and has the same meaning as that of k in formula (I);
substituting the polarizability of the gain nanospheres (3) obtained by the formula (I) into the formula (II) to obtain the dielectric constant epsilon of the gain nanospheres (3)G(ω)；
According to the dielectric constant epsilon of the gain nanosphere (3)G(ω) having a dielectric constant εGThe gain nanosphere (3) of (omega) is realized in the following specific way:
since the gain intensity can be characterized by the equivalent dielectric constant and is expressed by the following formula (iii):
Figure FDA0002942487580000021
in formula (III):
εGthe relative dielectric constant of the optical gain medium after being pumped and excited by the optical fiber is known quantity and dimensionless;
εLthe relative dielectric constant of the optical gain medium before the optical fiber pumping excitation is expressed, is a known quantity and is dimensionless;
k represents the intensity coefficient of the laser transmitted in the optical fiber (4), is unknown and dimensionless;
γ0the gain bandwidth of the optical gain medium is represented, is a known quantity and has the dimension of radian/second;
ω represents the frequency of the incident light (1), a known quantity, in radians/second;
ω0representing the resonant frequency of the optical gain medium, which is a known quantity and has a dimension of radian/second;
i represents an imaginary unit, and has the same meaning as I in the formula (I);
the laser intensity coefficient K transmitted in the optical fiber (4) can be obtained by the formula (III), so that the laser intensity of the excitation source in the optical fiber pump under the condition of forward zero scattering of the optical field can be obtained.
2. The method of regulating as claimed in claim 1, wherein: the optical gain medium is made of silicon material doped with trivalent erbium ions, and the doping concentration of the trivalent erbium ions is 3 multiplied by 1020-6×1020Number of ions per cubic centimeter.
3. The method of claim 2, wherein the step of: the doping concentration of the trivalent erbium ions is 4 multiplied by 1020-5×1020Number of ions per cubic centimeter.
4. The method of regulating as claimed in claim 1, wherein: the optical fiber pump uses laser as an excitation source, uses an optical fiber (4) as a carrier, and surrounds the optical fiber (4) on the periphery of an optical gain medium, wherein one end of the optical fiber (4) is used as a laser injection port (5), the other end of the optical fiber is used as a laser injection port (6), and when the laser passes through the optical fiber (4), the optical gain medium is excited in an optical coupling mode to generate forward gain.
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