RU2401813C1 - Photonic-crystal fibre production method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing photonic-crystal fibre relates to production of optical fibre based on nanotechnology used in fibre-optic communication systems and optoelectronics. The photonic-crystal structure is obtained by exposing a fibre workpiece made from a homogeneous chemical substance, mainly silicon dioxide, to streams of slow neutrons with a strictly predetermined absorption depth in order to change isotopic composition of the workpiece and attain the required optical properties. The workpiece is exposed using a special centralised apparatus consisting of several irradiators, the number of which is equal to the number of rods in the photonic-crystal fibres lying on the diametre of the workpiece at distances from each other corresponding to the position of the rods in the fibre. The irradiators form beams of slow neutrons with strictly predetermined parametres.

EFFECT: simplification of the technological process and more accurate production of separate elements of the photonic-crystal fibre, which has significant effect on quality characteristics of the fibre.

6 dwg

Description

The invention relates to the field of nanotechnology, intended for the production of optical fiber (S) used for various purposes, including information transfer, modern optics, laser physics, photonics.

Photonic crystalline fibers are a new type of optical waveguides, the unique properties of which are determined by the special structure of the cladding in the form of a photonic crystal lattice.

It should be noted the following known methods for the production of PCF [1, 2].

The first method is intended for the manufacture of only PCF and consists of three operations, namely:

1) the manufacture of PCF blanks from glass (fiber base) by fusion together with the base of the central quartz rod (future core) and the surrounding quartz rods of smaller diameter (future shell);

2) the manufacture of the PCF preform from the workpiece by pulling it from the crucible;

3) the manufacture of PCF from the preform by stretching the photonic crystal fiber in a special exhaust tower.

The second method is intended for the manufacture of various optical fibers by neutron irradiation of a glass blank after drawing from a crucible.

The fundamental difference between the first method and the claimed one is that in the proposed method there is no first stage, i.e. fusion of the base of the PCF blank from glass with quartz rods. The first stage of the production of PCF described above solves the complex technological problem of simultaneously ensuring strict periodicity of the photonic structure of the OB shell and the constancy of the ratio of the diameter of the rods to the period of the photonic crystal lattice of the PCF. This operation in the inventive method is combined with the manufacture of the PCF preform by irradiating the workpiece with a neutron flux after drawing it from the crucible. Due to the fact that the PCF core and shell rods can have diameters of the order of several nanometers, the PCF properties are very sensitive to small changes in their structure. This is reflected primarily in the energy loss in the fiber. The formation of the core and the shell by irradiation of the base of a silicon dioxide preform with a neutron beam will allow avoiding distortions in the sizes of the diameters of the rods and the distances between them. In addition, in the first method, the relative difference in the refractive indices Δn between the fiber base and the rods is provided by a combination of different materials (SiO ₂ , Si) or by alloying with chemical elements that increase the value of the coefficient n. In the inventive method, the Δn value is achieved by increasing the concentration of heavy silicon isotopes in the glass for the irradiated areas of the workpiece.

Thus, the disadvantages of the first method include the complexity of manufacturing the PCF and the difficulty of ensuring geometric relationships between the elements of the OM due to repeated heating and stretching of the fiber preform.

In addition, in the inventive method, the preform is directly obtained from a homogeneous preform (mainly silicon dioxide) by drawing from a crucible followed by irradiation with neutrons, which is more economical. The accuracy of manufacturing the diameters of individual fiber elements is ensured by modern nuclear technologies due to the high resolution of neutron energy provided by modern monochromators of neutron sources. Therefore, the inventive method will provide more accurate compliance with the size and proportions of the structure of the PCF, which will reduce energy loss in the fiber.

The second method for the fabrication of optical elements can be used for the production of a wide class of optical fibers by irradiating with a neutron flux certain sections of a uniform glass preform obtained by the operation of pulling from a crucible. As a result, changes in the isotopic composition of silicon in the glass occur, which are manifested in an increase in the percentage of heavier isotopes in the irradiated layers of the preform, and, consequently, in the light refractive index n.

The main differences of the second method from the claimed are in the irradiation scheme, in the irradiated areas and the exposure parameters of the workpiece. In the second method, neutron fluxes act only on the central part (core) of the workpiece wound on a special coil. Such an irradiation scheme does not allow the formation of shell rods and ensure the required manufacturing accuracy of the periodic PCF structure. In addition, the intensity of the neutron flux and the irradiation time do not correspond to the task of fabricating the PCF.

Thus, the main disadvantage of the second method is its unsuitability for obtaining PCF. Using this method, it is possible to produce an optical fiber of only a simple structure, consisting of a central part (core) and a sheath. The inventive method offers an irradiation scheme consisting of several irradiators, each of which forms with the help of a neutron beam a specific rod in the shell and the core of the OM. In this case, uniform irradiation of the workpiece from all sides and obtaining a photonic crystal structure of the fiber is guaranteed. In addition, the claimed method proposes to irradiate a heated preform as it is drawn out of the crucible, which simplifies the process.

Closest to the technical nature of the claimed invention is the second method, which is taken as a prototype.

The essence of the claimed invention lies in the fact that they use a preform of a homogeneous chemical substance, mainly silicon dioxide, and act along the entire length of the preform with a neutron flux with a given absorption depth in the process of pulling out of the crucible using a special centered installation consisting of several irradiators, the number of which is equal to the number of rods in the PCF, which are located along the diameter of the workpiece at distances from each other, corresponding to the position of the rods in the fiber, and which form a beam slow neutrons and with the following parameters: a diameter of the irradiated spot on the workpiece for each illuminator d≤0,01 mm; the value of the resolution of neutron energy ΔE≤10 ^-7 eV; the magnitude of the integral neutron flux f ₀ ≥10 ²² neutrons / cm ² .

The technical result of the claimed invention is to simplify and reduce the cost of production of PCF, increase the accuracy of manufacturing the geometric dimensions of the fiber, improve the quality characteristics, including reducing energy losses.

The novelty of the claimed invention lies in the formation of the internal structure of the PCF from the same material (mainly silicon dioxide) by neutron irradiation. The necessary difference in the refractive indices of the rods and the base of the fiber is achieved by increasing the concentration of heavier silicon isotopes in the glass. As a result, the core and the shell are simultaneously formed in the form of a two-dimensional photonic crystal (FC), which provides a physical mechanism of the retention of light in the fiber that is different from the usual OB.

The invention is illustrated by the following drawings:

figure 1 shows the structure of the PCF, where 1 is the shell of the PCF, 2 is the solid core of the shell, 3 is the core of the PCF, 4 is the distance between the centers of the rods (Λ); 5 - the distance between the centers of the core and the rod (Λ ¹ ); 6 - d diameter of the rod; 7 - d ^{1 the} diameter of the core;

figure 2 shows the installation of the fiber hood using a special tower [1], consisting of a core blank (preform) in the centering cartridge - 8, an electric furnace - 9, a laser micrometer for controlling the diameter of OB - 10, the primary coating device - 11, curing devices using UV radiation - 12, receiving device - 13;

figure 3 shows a diagram of the irradiation of the workpiece using the method of manufacturing an optical fiber, taken as a prototype [2], which consists of a shell OV - 14, core OV - 15, neutron flux - 16;

Fig. 4a shows an irradiation scheme for a PCF preform, which consists of a crucible - 17, a PCF preform - 18, a centered system - 19, neutron irradiators - 20, a rack for fixing a centered system with irradiators - 21, a laser micrometer - 10, a receiving device - 22;

on figb presents the dimensions of the irradiated spot on the workpiece PCF: neutron flux - 16; spot width d - 23, spot height h - 24;

figure 5 shows the cross-sectional structure of the irradiated PCF blank in the form of a hexagon, where 1 is the PCF cladding, 2 is the shell rods, 3 is the core, 16 is the neutron beam, 25 is the distance l ₁ , 26 is the distance l ₂ ;

, 28 - энергия

, 29 - энергия Е_р, 30 - ширина резонансного пика поглощения нейтронов Г_γ.figure 6 presents the dependence of the absorption cross section on the neutron energy σ _n = f (E _n ), where 27 is the energy

, 28 - energy

, 29 - energy E _p , 30 - width of the resonant peak of neutron absorption Г _γ .

In a photonic crystal, dielectric particles (rods) form a lattice with distances between them comparable with the wavelength of visible light (Figure 1). In such a lattice, the refractive index n varies according to the periodic law [3].

It is known that when crossing the interface between regions with different n, part of the light passes, part is reflected, but there is a spectral region in which the greatest reflection occurs. For wavelengths satisfying the Bragg reflection condition, namely:

,

,

where Λ is the lattice constant of the PC,

λ is the wavelength of the incident light,

θ is the angle of incidence between the wave vector and the FK planes,

maximum reflection coefficient.

The mirror effect is created due to the difference in the refractive indices of n, for example, silicon rods (Si n = 1.45) and a glass base of glass (SiO ₂ n = 1.44) for λ = 1.55 μm.

, то отраженные волны интерферируют (гасят друг друга) и свет не распространяется в ФК. В этом случае диаметры стержней одинаковы (d=d¹) и постоянная фотонно-кристаллической решетки не изменяется (Λ=Λ¹). Если в решетке ФК создать дефект, то волна из запрещенного диапазона будет двигаться вдоль него. Дефектом можно считать изменение расстояния Λ¹ (5) между центральным стержнем и стержнями оболочки (в этом случае d=d¹) или разницу в их диаметрах (d<d¹). Поэтому свет будет распространяться вдоль сердцевины, в то время как в остальной части волокна (оболочке) света не будет.Thus, if the path difference of two waves reflected from neighboring planes formed by the FC rods is

, then the reflected waves interfere (cancel each other out) and the light does not propagate in the photonic crystal. In this case, the diameters of the rods are the same (d = d ¹ ) and the photonic crystal lattice constant does not change (Λ = Λ ¹ ). If a defect is created in the FC lattice, then the wave from the forbidden range will move along it. A defect can be considered a change in the distance Λ ¹ (5) between the central rod and the shell rods (in this case d = d ¹ ) or the difference in their diameters (d <d ¹ ). Therefore, light will propagate along the core, while there will be no light in the rest of the fiber (sheath).

The main advantages of the FCW are the ability to provide:

1) single-mode operation for all wavelengths of the used range;

2) changes over a wide area of the spot area of the main mode;

3) a constant value of the dispersion coefficient.

In the solid-state PCF, considered in the application for the invention, the retention of light is provided due to total internal reflection and the effect of the forbidden zone for the propagation of light formed in the photonic crystal of the shell.

An industrial method of manufacturing solid-state PCF is illustrated in figure 2.

The technology of the claimed invention is based on the fact that substances with different concentrations of heavy isotopes of individual elements have different refractive indices of light.

The required value of the refractive indices can be achieved by irradiating a neutron flux of certain layers of the workpiece and increasing the concentration of heavy isotopes in them. The possibility of using neutrons for the fabrication of OM is explained by their properties and features of nuclear reactions that occur during irradiation. A method of manufacturing a standard optical fiber, taken as a prototype, is based on the high penetration of neutrons (figure 3). When neutrons interact with the nuclei of the chemical elements of the irradiated substance, excited composite nuclei are formed, which decay as a result of nuclear reactions [4]. In the inventive method, slow neutrons with energy E _n in the range of 0.1-1 eV are used, for which two types of nuclear reactions are characteristic: elastic scattering and radiation capture (absorption).

Elastic scattering reaction: a neutron as a result of a collision with a nucleus loses energy, speed and slows down. Neutron energy loss depends on the thickness of the layer and the properties of the substance in which the deceleration is carried out.

Absorption reaction: as a result of a collision, a neutron is captured by a nucleus and a lighter isotope of a chemical element turns into a heavier one.

In the inventive method, both nuclear reactions are used, each of which is characterized by a probability σ, called the reaction cross section (σ _n is the absorption cross section, σ _p is the scattering cross section). These parameters of nuclear reactions depend on the properties of matter and the energy of neutrons. They are determined on the basis of graphs σ _n = f (E _n ), σ _p = f (E _n ) obtained experimentally. The sequence of nuclear reactions during irradiation of the workpiece (scattering, then absorption) determines the need to use a horizontal irradiation scheme (figa, b).

The manufacturing process of PCF by the claimed method is divided into two stages:

1) drawing from a crucible (17) heated to 2000 ° C billet of silicon dioxide (18);

2) irradiation of the workpiece with neutron beams (16) to form the central rod (3) and shell rods (2).

The irradiation scheme consists of a centered system (19) with neutron irradiators (20), which is mounted on a special rack (21). The number of irradiators is determined by the number of simultaneously formed rods, including the core. Their placement inside the facility (19) depends on the location of the structural elements inside the PCF. The diameter of the finished fiber is controlled by a laser micrometer (10). The obtained PCF is wound into the coil of the receiving device (22). The parameters of the irradiated portion of the preform, which is affected by neutrons for a time t from one irradiator, while the fiber passes through the facility (19), have dimensions: width d (24) and height h (25).

The cross-sectional structure of the irradiated PCF preform in the form of a hexagon with a central rod (core) is shown in FIG. Neutron beams (16) penetrate the base of the shell (1) and are absorbed in certain places corresponding to the location of the core (3) and the rods (2) of the shell.

(27) уменьшается до значения

(28), которое соответствует началу резонанса поглощения нейтронов. В результате происходит реакция радиационного захвата нейтронов. На фиг.6 представлена типичная зависимость сечения поглощения большинства химических элементов от энергии резонансных нейтронов σ_n=f(Е_н) [4].Thus, the neutrons in the workpiece fly a distance l ₁ (25) or l ₂ (26), slow down, lose energy due to the elastic scattering reaction. Beam neutron energy

(27) decreases to

(28), which corresponds to the beginning of the neutron absorption resonance. As a result, the reaction of radiation capture of neutrons occurs. Figure 6 presents a typical dependence of the absorption cross section of most chemical elements on the energy of resonant neutrons σ _n = f (E _n ) [4].

The difference between the values of the cross sections at the base of the resonance peak and in its center for the resonance energy E _p (29) is several tens of thousands of barns (1 bar = 10 ^-24 cm ² ). This allows us to represent the dependence in Fig.6 in the form of a delta pulse with E _p >> G _γ (30), where G _γ is the energy width of the resonance peak.

к значению

. Следовательно, изменяя величину

, можно добиться формирования необходимой структуры фотонного кристалла оболочки с дефектом ФКВ, например, за счет разницы в параметре решетки Λ¹ (5).So, flying a distance of l ₁ or l ₂ in the preform (depending on the rod being formed), neutrons begin to be rapidly absorbed by the nuclei of the substance, increasing the concentration of heavier isotopes of silicon in the glass. The closer the rod is to the outer boundary of the shell (1), the smaller the deceleration distance l, the closer the initial energy is

to value

. Therefore, changing the value

, it is possible to achieve the formation of the necessary structure of the photonic crystal of the shell with a PCF defect, for example, due to the difference in the lattice parameter Λ ¹ (5).

The dimensions of the irradiated spot in width d (23) are determined by the diameters of the rods, and in height h (24), they are determined by the value of the integrated irradiation Ф _о and the fiber drawing speed V.

The accuracy of the manufacture of FC rods depends on the neutron resolution in energy ΔЕ _n . Modern neutron sources have monochromators, allowing to achieve ΔЕ _n <10 ^-7 eV. The value of the integral flux is determined by the required concentration of heavy silicon isotopes in the glass for the formed PCF rods, which, in turn, depends on the required value Δn of the relative difference in the refractive indices of light in the rods and the PCF base.

The possibility of manufacturing FKV proposed in the application method will consider a specific example.

The calculations are based on a photonic crystal fiber produced by foreign and domestic companies such as Coming, Blaze Photonics (UK), TEGS (RF) [1].

To characterize nuclear reactions upon irradiation with resonant neutrons, it is necessary to know the absorption cross section σ _n and the scattering cross section σ _{p of} neutrons. The main calculated parameters of neutron sources are the integral neutron flux Ф _о = φt (φ is the neutron flux intensity, t is the irradiation time), and the neutron energy resolution is ΔЕ _n .

So, the value of the resonance absorption cross section can be estimated by the Breit-Wigner formula [4]:

where G _n = 0.001 eV is the neutron width characterizing the probability of a scattering reaction;

G = 0.1 eV is the total energy width characterizing the probability of decay of a compound nucleus;

см - длина волны нейтрона.

cm is the neutron wavelength.

For resonant neutrons with E _p = 1 eV, the wavelength is λ _o = 4.5 · 10 ^-10 cm. From here, after substituting into formula (1), we obtain: σ _n = 25434 barn.

The neutron absorption depth l _n must correspond to the diameter of the formed rod, for example, d = 8 μm [1].

The average value of l _{n is} calculated by the following formula [4]:

where K = 5.04 · 10 ²² at / cm ³ - the number of silicon atoms in one cm ³ .

The obtained value l _n = 7.83 · 10 ^-6 cm indicates the possibility of the formation of rods using resonant neutrons.

To obtain the effect of the forbidden zone in a photonic crystal, the main thing is that all the rods are of the same diameter. This means that all irradiators must guarantee the same value of resonant energy (29), which is achieved using modern monochromators with high energy resolution of neutrons.

, которая зависит от расстояний l₁=36 мкм, l₂=34 мкм, взятых в качестве примера. Эти расстояния можно выразить следующим образом:At the next stage of calculations, it is necessary to estimate the value of the deceleration

, which depends on the distances l ₁ = 36 microns, l ₂ = 34 microns, taken as an example. These distances can be expressed as follows:

- средняя длина замедления после одного столкновения нейтрона с ядром вещества;Where

- the average length of the deceleration after one collision of a neutron with the nucleus of a substance;

- среднее число столкновений нейтрона с ядрами вещества в процессе замедления;

- the average number of collisions of a neutron with nuclei of a substance in the process of deceleration;

A = 28 is the mass number of the silicon core.

эВ, l₁=36 мкм получим следующие цифры: l_p=11,67 см; n^ст=0,0003085; ΔE=0,000022036 эВ.So, for σ _p = 1.7 barn [2],

eV, l ₁ = 36 μm, we obtain the following numbers: l _p = 11.67 cm; n ^st = 0,0003085; ΔE = 0.000022036 eV.

For a distance l ₂ = 34 μm, we have the following numbers: n ^st = 0,0002913; ΔE = 0.00002087 eV.

Based on the above calculations, we can conclude that the initial neutron energies for the formation of rods located at distances from each other of the order of 2 μm should differ in the sixth decimal place. This requires the resolution of the monochromator of the neutron source is not worse than ΔE _n = 10 ^-7 eV.

The magnitude of the integral neutron flux φt, which determines the concentration of heavy isotopes achieved as a result of irradiation, can be calculated by the following formula [2]:

where N _0i is the concentration of the jth isotope of silicon;

K is the number of silicon atoms in 1 cm ³ ;

K _i is the relative content of the i-th isotope in the initial mixture;

σ _n is the absorption cross section (barn);

φ is the magnitude of the neutron flux intensity (neutr. / cm ² s);

t is the exposure time (s).

The value of N _oj in the irradiated regions of the preform should be sufficient so that the relative difference in the refractive indices of the light of the irradiated and unirradiated regions ensures the properties of the photonic crystal.

So, the concentration of heavier isotopes can be taken equal to:

where m is a number characterizing the increase in the initial concentration of the j-th isotope obtained from the i-th isotope as a result of irradiation.

If we take m = 4, then after substituting into formula (6), we obtain Ф _о = φt = 0.04 · 10 ¹⁷ neutrons / cm ² . For a neutron source with an intensity of φ = 10 ¹⁸ neutrons / cm ² · s, the time t of irradiation of the preform portion with an area corresponding to the size of the irradiator spot (d · h) should be equal to 0.004 s.

For a neutron source with φ = 10 ¹⁷ neutrons / cm ² · s, the irradiation time increases (t = 0.04 s).

If the concentration of isotopes is increased to m = 3, the integral flux will be an order of magnitude greater than the previous case, namely: at φ = 10 ¹⁸ neutrons / cm ² · s, the time t will be 0.04 s; at φ = 10 ¹⁷ neutrons / cm ² · s we get t = 0.4 s.

The next important parameter of the workpiece irradiation scheme is the size of the irradiated spot (width d and height h). As already noted, the width should correspond to the diameter of the formed rods and, therefore, should be less than 10 microns [1]. The choice of height is determined by the fiber drawing speed V and the irradiation time t. It is known that the speed of pulling from the crucible has a value of (1-10) m / s [1]. Hence, for t = 0.004 s and V = 1 m / s, the height should be equal to h = 0.4 cm.

If the time increases by an order of magnitude t = 0.04 s and the speed remains the same, we obtain the value h = 4 cm.

Hence, with increasing irradiation time or drawing speed, the required height h increases.

At the last stage of the calculations, we evaluate how the refractive index of the irradiated sections of the PCF preform changes if the concentration of heavy isotopes increases by 10 ^-3 · K · K _i . To do this, we use the Lorentz-Lorentz formula [5], which characterizes molecular refraction, namely:

where K is the number of atoms of the substance in 1 cm ³ ,

a is the magnitude of the polarizability of the molecule of the substance,

n is the refractive index of the substance.

The expression of the Lorentz-Lorentz equation for silicon dioxide (n = 1.44) has the form:

where a ₂₈ is the polarizability of the isotope ²⁸ Si,

K ₂₈ = 0.9218 is the natural concentration of the ²⁸ Si isotope in glass,

K ₂₉ = 0.0471 - the natural concentration of the ²⁹ Si isotope in glass,

K ₃₀ = 0.0312 - the natural concentration of the ³⁰ Si isotope in glass.

Coefficients Δa and Δa ¹ show the relative change in the polarizability of various silicon isotopes. It is known that the value of a is directly proportional to the size of the molecules of the substance [6]. The absorption cross sections σ _{n are} directly proportional to the sizes of the nuclei of silicon isotopes [4]. With an increase in the number of neutrons in the isotope nucleus, the size of the nucleus first increases ( ²⁹ Si), then decreases ( ³⁰ Si). Therefore, the coefficients Δa and Δa ¹ have different values.

After transforming equation (9) we get:

0.26355 = 1.12877B,

- постоянный коэффициент в уравнении молекулярной рефракции (9).Where

is a constant coefficient in the molecular refraction equation (9).

To draw up a similar equation for the irradiated areas of the workpiece, it is necessary to calculate:

1) the number of ²⁸ Si isotopes converted as a result of a nuclear reaction into ²⁹ Si isotopes;

2) the number of ²⁹ Si isotopes that transferred as a result of a nuclear reaction into ³⁰ Si isotopes;

3) the number of ³⁰ Si isotopes converted as a result of a nuclear reaction into ³¹ Si isotopes.

After neutron irradiation of the silicon dioxide preform, the Lorentz-Lorentz equation takes the form:

where K ¹ = 10 ^-3 is a coefficient characterizing the degree of transition of one isotope to another;

n _x is the refractive index of light after irradiation with neutrons.

After substituting the values of the corresponding coefficients, we obtain:

Hence, n _x = 1,4487≈1,45.

The relative difference in the refractive indices Δn of the irradiated and unirradiated parts of the workpiece will be:

The obtained value of the relative difference in the refractive indices of light is sufficient to realize the physical properties of the PCF [3].

Calculations of the relative difference in refractive indices for m = 4 (formula (7)) given in the prototype [2] indicate that the Δn value was an order of magnitude smaller (Δn = 0,0002), which complicates the implementation of the properties of the PCF. Therefore, the value of the integrated flux Ф _о provided for in the prototype is insufficient for the manufacture of PCF.

Thus, a comparison of the proposed method for the manufacture of PCF with the prototype allows us to draw the following conclusions:

1) using one irradiator used in the prototype, it is impossible to form several rods of a photonic crystal structure, which requires several irradiators with different values of neutron energy;

2) for the formation of PCF rods, the workpiece should be accessible to irradiators from all sides, which cannot be provided in the workpiece wound on a coil, as in the prototype;

3) the accuracy of manufacturing dimensions of the PCF in the claimed method is higher than in the prototype for two reasons:

a) provides for the use of neutron sources with a resolution of energy significantly higher than in the prototype;

b) the irradiation scheme of the workpiece in the prototype occurs in a twisted form, which prevents the penetration of neutrons into the given surface of the workpiece;

4) adopted in the prototype, the percentage increase in heavy isotopes of silicon (10 ^-4 · 100%) as a result of neutron irradiation is insufficient for PCF [1, 3]. In the inventive method, the irradiation parameters are calculated for the number 10 ^-3 · 100%, which allows to provide a sufficient relative difference in the refractive indices of the rods and the base of the PCF.

Description of the manufacturing method of PCF on a specific example

In an application for an invention, a manufacturing method consists of the following steps:

1) the molten preform mainly from silicon dioxide (18) with a natural content of silicon isotopes (92.18% Si ²⁸ O ₂ ) flows from the crucible (17) Figa;

2) gradually cooling in air and hardening, the billet with a diameter of D = 87 μm enters the centered system (19), on which neutron irradiators are installed (20);

irradiators are located along the inner diameter of the system (19) in the form of irradiating gaps consisting of several irradiators;

the diameter of the irradiated spot from one irradiator is 0.008 mm;

the dimensions of the irradiation slots correspond to the size of the irradiated spot on the PCF blank d × h, for example, 8 μm × 40 μm (Fig. 4b);

for the considered example of PCF (Figure 5), consisting of a core with a diameter of d ¹ = 8 μm and six rods with diameters of d = 1 μm, the system (19) should have 7 irradiating slits: the first slot (for core formation) consists of 5 irradiators (40 μm / 8 μm), located one above the other to create an irradiated spot on the workpiece with dimensions of 8 μm × 40 μm, and six identical slits (for forming shell rods), each of which consists of 40 irradiators (40 μm / 1 μm) also located one above the other to create an irradiated spot on the workpiece with 1 microns × 40 microns;

for the formation of the internal PCF structure with the parameters: a) the distance between the core and the shell rods (l ₁ -l ₂ -d) = 4.5 μm, b) the size of the PCF lattice Λ = 9 μm, c) the distance from the edge of the workpiece to the edge of the core l ₁ = 34 μm, g) the distance from the edge of the workpiece to the edge of the rod l ₂ = 39.5 μm, d) diameters d = 1 μm, d ¹ = 8 μm, the resolution of the neutron energy ΔE _n = 10 ^-7 eV is required eV and integral neutron flux Ф _о = 10 ²² neutrons / cm ² ;

3) slow neutrons from irradiating gaps with energy E _p + ΔE penetrate into the workpiece, lose energy and slow down (in contrast to thermal neutrons, which immediately enter the absorption reaction);

flying distance: a) l ₁ = 34 microns (neutrons with energy E _p + ΔE, where ΔE = 2.087 · 10 ^-5 eV for the formation of the rod) or b) l ₂ = 39.5 microns (neutrons with energy E _p + ΔE where ΔЕ = 2.204 · 10 ^-5 eV for core formation), the neutron energy is reduced to a resonance value (E _p = 1 eV), which allows them to enter the absorption reaction;

as a result, in volumes at the neutron penetration depth equal to l ₁ or l ₂ , the process of compaction of the substance begins by increasing the concentration of heavy isotopes of silicon in the glass (mainly Si ²⁹ ) and the formation of core and rods;

the process of densification (neutron absorption by the nuclei of silicon atoms) ends at a distance of (l ₁ + d ¹ ) or (l ₂ + d);

4) the process of irradiation of the workpiece with neutrons occurs as it is pulled out of the crucible, which is carried out at a speed of V = 0.1 m / s (when irradiated with thermal neutrons, the workpiece is stationary and fixed in a special installation);

the drawing speed is controlled by the results of measurements of the size of the structural elements of the PCF using a laser micrometer (10);

the manufacturing process of PCF in the receiving device (22) ends after winding the fiber into a coil.

As a result of the manufacture of PCF as described above:

a) increases the accuracy of the manufacture of structural elements of PCF (in the prototype, the accuracy of the manufacture of optical fiber is ± 0.1 μm, in the claimed method, the manufacturing accuracy is ± 5 nm);

b) the purity of the starting material is ensured (the absence of internal mechanical stresses and defects, impurities, roughness in the interface between the core and the rods with the shell base);

c) the above-mentioned qualitative changes in the internal structure of the PCF significantly improve the characteristics of the PCF, reduce energy losses and dispersion distortions in the fiber.

Information sources

1. Nanotechnology in electronics. Edited by Yu.A. Chaplygin. - M.: “Technosphere”, 2005.

2. Zhuravleva L.M., Plekhanov V.G. A method of manufacturing an optical fiber. Patent for invention No. 2302381 (prototype).

3. Slepov N.N. Photonic crystal fiber is already a reality. New types of optical fibers and their application. Electronics: Science, Technology, Business; 5/2004.

4. Mukhin K.N. Experimental nuclear physics. - S-P, M., Krasnodar, "Doe", 2008.

5. Landsberg G.V. Optics. - M .: Fizmatlit, 2006.

Claims (1)

A method of manufacturing a photonic crystal fiber (PCF) by pulling a preform from a homogeneous chemical substance, mainly silicon dioxide, and exposing the entire length of the preform to a neutron flux with a given absorption depth, characterized in that the preform is irradiated in the process of drawing from the crucible using a special centered installation consisting of several irradiators, the number of which is equal to the number of rods in the PCF, which are located along the diameter of the workpiece at distances from each other, corresponding x the position of the rods in the fiber, and which form slow neutron beams with the following parameters: diameter of the irradiated spot on the workpiece for each irradiator d≤0.01 mm; the value of resolution in neutron energy ΔE _n ≤10 ^-7 eV; the magnitude of the integral neutron flux f ₀ ≥10 ²² neutrons / cm ² .

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