RU2223522C2 - Single-mode single-polarization light guide - Google Patents

Abstract

FIELD: fiber optics, fiber-optical communication lines, design of fiber-optical gyroscopes and fiber pickups of physical quantities. SUBSTANCE: given light guide includes light guiding conductor, reflecting sheath, two bars loading protective sheath and polymer coat. Relation Λ of difference of refractive indices of material of protective sheath and material of reflecting sheath n_k-n_sh correspondingly to difference of refractive indices of material of light guiding conductor and protective sheath n_c-n_k correspondingly assumes value in range 0,5≤Λ≤2 with 3,5•10³≤n_c-n_sh≤7,5•10^-3. Ratio of radius τ of reflecting sheath to radius ρ of light guiding conductor is selected in range 1,5≤τ/ρ≤2,5. Loading bars are fabricated from material with refractive index equal to refractive index n_p.sh of protective sheath of light guide and are placed at distance Δ from light guiding conductor which satisfies condition ρ≤Δ≤2ρ. This approach secures aperture angle 90^°≤α≤100^° of loading bars when viewed from center of light guiding conductor. EFFECT: enlarged width of spectral window of fiber polarizing mode filter and reduced loss of conductive polarization mode. 6 dwg, 4 tbl

Description

 The invention relates to the field of fiber optics and can be used in fiber communication lines, as well as when creating fiber optic gyroscopes and other fiber sensors of physical quantities.

 A known design of a single-mode fiber waveguide, in which there is a unipolar mode of operation with an elliptical loading sheath [1]. The light guide core of the fiber is surrounded by a loading sheath, and around the loading sheath an additional sheath is formed with a reduced refractive index with respect to pure quartz glass, of which the outer protective sheath of the fiber consists. Due to the mechanical stresses created in the light guide by the elliptical loading sheath, linear birefringence arises in it due to the photoelastic effect. A feature of the fiber design is that in the direction of the y axis, an additional sheath consisting of a material with a low refractive index touches the light guide core and therefore, in this direction, the two polarization modes of the fiber due to induced birefringence in the light guide core have a different cut-off wavelength. Due to this, and also due to the W-profile of the fiber in the y direction, which leads to an increase in the steepness of the spectral loss characteristics of the two polarization modes, a spectral window is formed in which the unipolar mode of operation of the fiber is observed. A disadvantage of the known fiber design is that the spectral window of the unipolarization mode is not wide enough.

 Also known is the design of a unipolarizing optical fiber [2], which contains a light guide core, a reflective sheath with a low refractive index, which in turn is surrounded by an elliptical loading sheath, which creates mechanical stresses in the light guide vein and a reflective sheath. As a result, two different W profiles are obtained in the direction of the y axis for two polarization modes. The W profile is designed in such a way that one polarization mode propagates practically without loss, and the second mode is not channelized at all. This is done with the aim of expanding the spectral window of the unipolarized mode of operation of the fiber. A disadvantage of the known fiber design is that the limiting birefringence induced in the light guide and the reflective sheath by an elliptical loading sheath is lower than the birefringence that can be obtained using circular loading rods (PANDA fibers). From the magnitude of the birefringence induced in the light guide conductor and the reflective sheath, the width of the spectral window of the unipolarizing fiber operating mode also depends.

 The closest in technical essence to the design of the unipolarizing optical fiber proposed by the present invention is the design of a single-mode fiber optical fiber with a large linear birefringence of the PANDA type, considered in [3]. A single-mode fiber contains a light guide core, a reflective sheath, two circular loading rods, an external protective quartz sheath, and a protective-hardening polymer coating. The light guide consists of quartz glass doped with germanium. The reflective cladding is made of quartz glass doped with fluorine, and therefore has a lower refractive index compared to the refractive index of pure silica glass, which makes up the outer protective cladding of the fiber. The loading rods are made of quartz glass doped with boron oxide. The addition of boron oxide to quartz glass lowers the refractive index of quartz glass and increases its coefficient of thermal linear expansion. Due to the difference in the coefficients of thermal linear expansion of the materials of the loading rods and the rest of the material of the fiber, in the light guide there are mechanical, stretching the region of the fiber, located between the loading voltage rods. Due to the photoelastic effect, linear birefringence occurs in the light guide vein. Due to the birefringence, the material of the light guide conductor has a different refractive index for the polarization modes propagating in the fiber. As a result of this, the cutoff wavelengths of the two polarization modes have different meanings, and therefore there is a spectral window in the fiber in which one polarization mode experiences strong attenuation, and the second propagates with sufficiently small losses of optical power. Thus, in this spectral window, the fiber acts as a mode polarizing filter.

при n_К-n_об<<1, n_ж-n_К<<1,
где n_К - показатель преломления материала защитной оболочки;
n_об - показатель преломления материала отражающей оболочки;
n_ж - показатель преломления материала световедущей жилы.The main disadvantage of the known fiber design is the insufficient width of the spectral window in which the fiber acts as a polarization mode filter and the relatively large losses of the conducted polarization mode. The width of the spectral window is not determined by the magnitude of the dip in the refractive index of the material of the reflective shell with respect to the refractive index of the material of the protective shell, but mainly depends on the value of the parameter Λ, which is expressed as follows:

when n _K -n _about << 1, n _w -n _K << 1,
where n _K is the refractive index of the material of the protective shell;
n _about - the refractive index of the material of the reflective shell;
n _W is the refractive index of the light guide core material.

 The aim of the present invention is to increase the width of the spectral window of the fiber mode polarizing filter and reducing the loss of the conducted polarization mode.

This object is achieved in that the ratio Λ difference between the refractive and reflective materials protective shells indices n _K -n _about a difference in refractive index light-guiding core materials and containment n _x -n _K selected in the range 0,5≤Λ≤2, wherein 3 , 5 • 10 ^-3 ≤n _w -n _about ≤7.5 • 10 ^-3 , and the ratio of the radius of the reflecting shell τ to the radius of the light guide core ρ is chosen in the range of 1.5≤τ / ρ≤2.5, and the loading rods made of a material with a refractive index equal to the refractive index n _{K of the} protective sheath of the fiber, and they are burnt at a distance Δ from the light guide core, which satisfies the condition ρ≤Δ≤2ρ, while providing an opening angle of the loading rods when observing from the center of the light guide core 90 ^o ≤α≤100 ^o .

The maximum possible extension of the spectral window operation odnopolyarizatsionnogo fiber (fiber polarization mode filter) is achieved by selecting a more optimal parameter values Λ, Δ, τ / ρ, n _x -n provided _for more effective conjugation odnopolyarizatsionnogo fiber with other fiber optic components of both communication links and fiber sensors of physical quantities. The invention is illustrated by drawings. In FIG. 1 shows the construction of an initial preform for a PANDA fiber having a W profile of the distribution of the refractive index. Figure 2 shows the spectral loss curves of two polarization modes and the principle of determining the width of the spectral window of the unipolar mode of operation of the fiber. In FIG. Figure 3 shows W profiles for two polarization modes in the case of creating mechanical stresses only in the light guide conductor, as well as in the light guide conductor and reflective sheath at the same time. Figure 4 shows the design of the unipolarized fiber "PANDA". Figure 5 shows the central part of the construction of a single-polarized fiber "PANDA" with the designation of the main geometric parameters of the structure. Figure 6 shows the stress distribution profiles in the light guide core and the reflective sheath of the fiber and the corresponding W-profiles for two polarization modes at different distances Δ of the loading rods to the light guide core.

 The cross-sectional design of a unipolarizing fiber is shown in FIG. 1. The light guide contains a light guide core 1, a reflective sheath 2, load rods 3, an external protective quartz sheath 4 and a polymer protective and reinforcing coating 5.

,
где U - параметр моды, характеризующий поперечный раскрыв ее поля и имеющий смысл поперечного волнового числа моды,

, а

. Поскольку параметр U во многих случаях можно выразить через параметры световода и длину волны излучения, из приведенного выше условия отсечки можно определить длину волны, при которой происходит переход основной моды в режим отсечки.The light guide is made as follows [2]. Initially, the initial blank for a unipolarized fiber is manufactured. The workpiece is made by the method of internal paraphase deposition (MCVD - method). The initial billet contains a light guide core 1 (Fig. 1), a reflecting cladding 2 with a low refractive index and a protective quartz cladding 3. A feature of a fiber with a low refractive index of the reflecting cladding 4 is that even a basic lower mode begins to undergo cutoff at a certain radiation wavelength , i.e. as it propagates along the axis of the fiber, it begins to flow from the core region into the protective sheath. Optical fibers with a reduced refractive index of the material of the reflecting cladding are conventionally called optical fibers with a W-profile of the distribution of the refractive index. The condition determining the cutoff wavelength of the main lowest mode in the W fiber is expressed as follows:

,
where U is the mode parameter characterizing the transverse opening of its field and having the meaning of the transverse wave number of the mode,

, a

. Since the parameter U in many cases can be expressed in terms of the parameters of the fiber and the wavelength of the radiation, from the above cutoff condition, we can determine the wavelength at which the main mode transitions to the cutoff mode.

Поэтому условие отсечки основной моды в этом случае имеет вид:

Определяя из этого условия V_1отс, соответствующее данному Λ, можно вычислить искомую длину волны отсечки основной моды:

Предположим теперь, что световедущая жила W-световода является анизотропной, то есть она обладает линейным двулучепреломлением В. Данная величина показывает разность показателей преломления световедущей жилы для двух поляризационных мод. На фиг.2 показаны спектральные кривые затухания 7, 8 низших y-поляризационной и x-поляризационной мод, соответственно. Из-за вырождения длин волн отсечки мод возникает некое спектральное окно, в котором по мере распространения излучения вдоль оси световода y-поляризационная мода практически полностью вытекает из области сердцевины, а х-поляризационная мода не испытывает потерь оптической мощности. Ширина такого спектрального окна, в котором W-световод является однополяризационным, определяется по уровню допустимого затухания х-поляризационной моды, например, 1 дБ/км, и по уровню желательной величины затухания y-поляризационной моды, например, 40 дБ/км. Из фиг. 2 видно, что ширина спектрального рабочего окна световода определяется разностью длин волн отсечки двух поляризационных мод и крутизной их спектральных характеристик затухания. При Λ>0,5 ширина спектрального окна определяется разностью длин волн отсечки, а при Λ<0,5 - уже, в основном, крутизной спектральных характеристик затухания поляризационных мод.Consider for example the profile depicted in figure 3. In this case, the parameter U for a sufficiently large value of τ / ρ can be approximately expressed as:

Therefore, the cutoff condition of the main mode in this case has the form:

Determining from this condition V _1otc corresponding to this Λ, we can calculate the desired cutoff wavelength of the main mode:

Suppose now that the light guide core of the W fiber is anisotropic, i.e., it has a linear birefringence B. This value shows the difference in the refractive indices of the light guide core for the two polarization modes. Figure 2 shows the spectral attenuation curves of 7, 8 of the lower y-polarization and x-polarization modes, respectively. Due to the degeneration of the cutoff wavelengths, a certain spectral window appears in which, as the radiation propagates along the axis of the fiber, the y-polarization mode almost completely leaves the core region, and the x-polarization mode does not experience optical power loss. The width of such a spectral window in which the W-waveguide is single-polarized is determined by the level of allowable attenuation of the x-polarization mode, for example, 1 dB / km, and by the level of the desired attenuation of the y-polarization mode, for example, 40 dB / km. From FIG. Figure 2 shows that the width of the spectral working window of the fiber is determined by the difference in the cut-off wavelengths of the two polarization modes and the steepness of their spectral attenuation characteristics. For Λ> 0.5, the width of the spectral window is determined by the difference in the cut-off wavelengths, and for Λ <0.5 it is mainly determined by the steepness of the spectral characteristics of the attenuation of polarization modes.

где n_К - показатель преломления чистого кварцевого стекла, n_ж - показатель преломления материала световедущей жилы для х-поляризационной моды,
n_об ^х - показатель преломления материала отражающей оболочки для х-поляризационной моды,
В - величина двулучепреломления в световоде.The difference in the cut-off wavelengths of two polarization modes of a W-fiber with an anisotropic light guide core is determined by the following relation:

where n _K is the refractive index of pure quartz glass, n _W is the refractive index of the material of the light guide core for the x-polarization mode,
n _about ^x is the refractive index of the material of the reflective shell for the x-polarization mode,
In - the magnitude of birefringence in the fiber.

Для профилей, изображенных на фиг.3 в случае большой величины отношения τ/ρ, эти условия запишутся в следующем виде:

В таблице 1 приведены расчетные данные по разности длин волн отсечки поляризационных мод в W-световоде с анизотропной световедущей жилой с различными параметрами световода при В=5•10^-4, ρ=2,5 мкм, τ/ρ≥2,5. На фиг.3 показан график распределения показателя преломления 5 W-световода с анизотропной световедущей жилой. Пунктирной линией показан уровень показателя преломления для х-поляризационной моды, а пунктирной линией с точками - уровень показателя преломления для y-поляризационной моды. Разность этих уровней показателя преломления определяется величиной модового двулучепреломления В, наведенного в световедущей жиле.The normalized cutoff frequency for the x- and y-polarization modes V _{UTS UTS} ^x and V ^y respectively determined by the conditions:

For the profiles shown in figure 3 in the case of a large value of the ratio τ / ρ, these conditions are written in the following form:

Table 1 shows the calculated data on the difference in the cutoff wavelengths of the polarization modes in a W-fiber with an anisotropic light guide core with different parameters of the fiber at B = 5 • 10 ^-4 , ρ = 2.5 μm, τ / ρ≥2.5. Figure 3 shows a graph of the distribution of the refractive index 5 of a W-fiber with an anisotropic light guide core. The dashed line shows the level of the refractive index for the x-polarization mode, and the dashed line with points shows the level of the refractive index for the y-polarization mode. The difference in these refractive index levels is determined by the magnitude of the mode birefringence B induced in the light guide.

Since at ρ = 2.5 • 10 ^-6 m for various parameters of the W fiber, the spectral window of the unipolarizing fiber is located in different places of the spectrum, by changing ρ, the cut-off wavelengths can be brought to a certain region of the spectrum. In this case, the difference between the cutoff wavelengths of the two polarization modes will also depend strongly on ρ. Table 1 shows the calculation data for the cutoff wavelengths Δλ ^0.825 for the cutoff wavelength of the x-polarization mode equal to 0.825 μm for various parameters of the W fiber.

 It should be noted that at τ / ρ≤2.5, the calculated cutoff wavelengths are corrected, since in this case the value of the mode parameter U begins to be affected by the jump in the refractive index at r = τ, which we neglected above. However, in our chosen wavelength range, these corrections can be neglected.

В таблице 2 приведены расчетные данные для Δλ и Δλ^0.825 при тех же параметрах W-световода, что и раньше с той лишь разницей, что анизотропия теперь, помимо световедущей жилы, наводится и в отражающей оболочке. Пунктирной линией 8 (фиг.3) показан уровень показателя преломления в световедущей жиле и отражающей оболочке световода для х-поляризационной моды, а пунктирной линией с точками 9 - уровень показателя преломления для у-поляризационной моды.The difference in the wavelengths of the cutoff of the polarization modes can be increased if anisotropy is created not only in the light guide conductor, but also in the reflective sheath. In this case, the relations determining the difference in the wavelengths of the cutoff of the polarization modes take on the following form:

Table 2 shows the calculated data for Δλ and Δλ ^0.825 for the same W-fiber parameters as before, with the only difference being that anisotropy is now, in addition to the light guide core, also induced in the reflective sheath. The dashed line 8 (Fig. 3) shows the level of refraction in the light guide and the reflective sheath of the fiber for the x-polarization mode, and the dashed line with points 9 shows the level of refractive index for the y-polarization mode.

 Unipolarizing optical fibers are necessary for constructing high-precision fiber-optic gyroscopes in which they can be used both for winding multilayer multi-turn sensitive coils with a fiber length of ~ 1000 m, and for use as a polarizer installed in the optical input-output circuit of the radiation of a gyroscope ring interferometer. In this case, the requirements for a unipolarizing optical fiber for the sensitive coil of the gyroscope and for the optical fiber used as a polarizer differ significantly. A unipolarizing fiber for a sensitive coil should have small losses of the canalized polarization mode and a relatively small coefficient of polarization extinction per meter of fiber, since the necessary extinction coefficient in such a fiber can be achieved due to its large length. On the contrary, in a unipolarized fiber for the polarizer, relatively large losses of the conducted polarization mode are allowed, since its manufacture requires shorter fiber lengths (1-2 m), but the coefficient of polarization extinction by one meter should be much larger than in the case of a fiber for sensitive gyro coil. Table 3 shows the optimal values of the W-fiber parameters for the sensitive coil of the gyroscope and for the fiber polarizer.

где d_з ^исх - диаметр исходной заготовки W-световода,
d_ст - диаметр нагружающих стержней,
d_заг ^Р - диаметр заготовки "PANDA",
α - угол раскрыва отверстий для нагружающих стержней при наблюдении из центра световедущей жилы исходной заготовки,
R_ж - радиус световедущей жилы в исходной заготовке W-световода,
Δ - расстояние отверстий для нагружающих стержней до световедущей жилы,
h_п - глубина и ширина пазов, прорезанных в исходной заготовке.Anisotropy in the light guide conductor and in the reflective sheath is created using loading rods located on both sides of the light guide conductor and the reflective sheath of the W fiber. The manufacturing technology of an anisotropic fiber of the PANDA type is described in [2]. Initially, two semicircular grooves with a width and depth of ~ 1 mm are cut from the two diametrically opposite sides in the initial blank (the diameter of the initial blank is approximately 12 mm). Then, the initial billet is placed inside the supporting quartz tube and spawned with it on a thermomechanical billet manufacturing machine (“jacketing” operation) so that two through holes are formed along the entire length of the billet formed by two grooves cut in the initial billet. Then these two through holes are etched with hydrofluoric acid to the desired diameter. Two loading rods are inserted into the etched openings and the PANDA fiber is pulled from the preform thus obtained. In the manufacture of blanks for the fiber "PANDA" the following ratios are used:

where d _z ^ref - the diameter of the original billet W-fiber,
d _article - the diameter of the loading rods,
d _zag ^P - the diameter of the workpiece "PANDA",
α is the opening angle of the holes for the loading rods when observing from the center of the light guide core of the original billet,
R _W is the radius of the light guide core in the original billet W-fiber,
Δ is the distance of the holes for the loading rods to the light guide core,
h _p - the depth and width of the grooves cut in the original workpiece.

 In FIG. Figure 4 shows the design of a transverse fiber of the PANDA type. The light guide comprises a light guide core 10, a reflective sheath with a reduced refractive index with respect to quartz glass 11, loading rods of circular shape 12, an external protective quartz sheath made of pure quartz glass 13, and a polymer protective reinforcing coating 14. The loading rods are made of a material with a high coefficient thermal expansion than the rest of the fiber material. The material of the loading rods should have the same refractive index as the quartz glass of the fiber sheath, since otherwise along the x axis the W profile of the fiber will differ from the W profile of the fiber along the y axis.

It is believed that the main mode of a fiber [4] with a W profile of the refractive index experiences a cutoff if
∫ (n ² -n $\genfrac{}{}{0ex}{}{\text{2}}{\text{K}}$ ) dS <0.

Here, integration is carried out over the entire cross-sectional area of the fiber, with n being the refractive index of the material over the fiber cross-section, and n _{K being} the refractive index of pure quartz glass. However, experimental data show that the cutoff of the fundamental mode of the W fiber occurs even in the case of a positive value of the above integral. The issue of cutting off the main mode of a W fiber must first of all be connected with the ratio of the radius of the reflecting cladding with a reduced refractive index to the radius of the light guide core. This condition, apparently, is valid for sufficiently large values of the ratio of the radii of the reflecting cladding and the light guide core. For sufficiently small values of this ratio (τ / ρ ~ 1.5), the main mode of the W fiber experiences attenuation, and for large values of the ratio τ / ρ (~ 2.5), the main mode experiences cutoff.

 The use of loading rods with a low refractive index in PANDA single-polarized optical fibers leads to the fact that the integral takes a negative value in the direction of the fiber cross section in the x axis direction, which means that the channelized x-polarization mode most likely experiences attenuation, since the ratio of the radii the cladding with a low refractive index and the light guide conductor in the x axis direction in the known PANDA fiber design is greater than 10. The loss of the canalized x-polarization mode in this case have a very large dependence on the bending of the fiber. This is confirmed by experimental data, which show that the spectral loss curves of the x-polarization mode shift to a shorter wavelength range, but the position of the spectral loss curve of the y-polarization mode remains practically unchanged, that is, the bend of the PANDA single-polarized fiber with loading rods with a reduced refractive index with respect to the refractive index of pure quartz glass leads to a narrowing of the spectral window in which the optical fiber conducts only one oyanie polarization.

 The loading rods are also manufactured by the MCVD method of manufacturing quartz glass blanks with the addition of boron oxide and germanium oxide. The correct ratio of boron and germanium oxides makes it possible to obtain a refractive index equal to the refractive index of the silica glass of the protective shell. When the fiber is drawn from the workpiece during the solidification of the material of the loading rods in the region located between them, powerful regular tensile mechanical stresses arise and, due to the photoelastic effect, linear birefringence arises in it.

где Δα - разность коэффициентов температурного расширения материала нагружающих стержней и защитной оболочки,
ΔT - разность между температурой в печи установки вытяжки световодов и комнатной,
α - угол раскрыва нагружающих стержней при наблюдении из центра световедущей жилы.In FIG. 5 shows an enlarged view of the area between the loading rods. In this area there is a light guide core of the fiber and a reflective sheath. Here ρ is the radius of the light guide core, τ is the radius of the reflecting shell, Δ is the distance of the loading rods to the light guide core, d _article is the diameter of the loading rods. The magnitude of birefringence B in the region between the loading rods is proportional to:

where Δα is the difference between the coefficients of thermal expansion of the material of the loading rods and the protective sheath,
ΔT is the difference between the temperature in the furnace installation of the extraction of optical fibers and room,
α is the opening angle of the loading rods when observed from the center of the light guide core.

To understand the mechanism of operation of the unipolarized mode of operation of the fiber, it is necessary to consider the distribution profiles of the refractive index taking into account the mechanical stresses generated by the loading rods for two polarization modes along the axis near the cross section of the fiber. When choosing the parameters of the fiber "PANDA" Δ≤ρ and α = 90 ^o mechanical stresses have a profile of 15 (Fig.6) and are concentrated mainly in the light guide core of the fiber. Therefore, the distribution profile of the refractive index of the W fiber for the x-polarization mode is 16, and for the y-polarization mode it is 17. The profiles for the two polarization modes are the same in the protective and reflective shells, and in the light guide the level of refractive index for the y-polarization modes below the level of refractive index for the x-polarization mode by the value of mode birefringence B.

 When the loading rods are located at a distance Δ = 2ρ from the light guide core, the mechanical stresses along the y axis are concentrated in the light guide core and the reflective cladding and the distribution profiles of the refractive index for the x- and y-polarization modes are described by curves 19 and 20, respectively. At Δ≤0.5ρ, excess losses of the canalized polarization mode of microbending nature occur in the light guide conductor. Microbends of the light guide core can form when the fusion surface of round holes in a workpiece with loading rods approaches, on which air microbubbles can form. Therefore, for monopolarized optical fibers of sensitive coils, it is advisable to arrange the loading rods at a distance Δ = 2ρ to ensure small losses of optical power of the canalized polarization mode in the optical fiber. But with an increase in the Δ parameter, the birefringence in the light guide and the reflective sheath also decreases, which leads to a narrowing of the spectral window of the unipolar mode of operation of a short length of the fiber, but due to the large length of the fiber it can be significantly expanded with minimal loss of the canalized polarization mode.

For a fiber polarizer based on relatively short segments of a unipolarizing fiber, it is necessary to achieve the maximum width of the spectral working window of a unipolarizing fiber. The width of the spectral window of a unipolarizing fiber can be increased by forming a profile of the refractive index distribution with the parameter τ / ρ = 2.5 in the W fiber by approaching the loading rods to the light guide core by a distance Δ = 0.5ρ and ensuring the opening angle of the loading rods α = 100 ^o . Selecting 2.5 provides a sufficiently large difference in the normalized frequency V _{UTS UTS} ^x and V ^y of the greater steepness V _ots depending on the parameter Λ. The approach of the loading rods to a distance Δ = 0.75ρ significantly increases the mode birefringence of B in the light guide conductor both by decreasing the Δ parameter and by increasing the diameter of the loading rods. Increasing the angle of aperture to α = 100 ^o provide for mechanical stress not only in the light-guiding core, but also in the reflective shell that will provide an increase in the difference of the normalized frequency V ^x -V _{UTS UTS} ^y, which determines the difference between the cutoff wavelengths of the two polarization modes W- optical fiber.

 Table 4 shows the optimal geometric cross-sectional parameters of the PANDA W-fiber for single-polarized optical fibers of sensitive gyro coils and fiber polarizers.

Sources of information
1. JR Simpson et all. "A single polarization fiber" J. Lightwave Technology vol. LT-1, 1983, pp. 370-373.

 2. M. J. Messerly, J.R. Onstott, R.C. Mikkelson. "A Broad-Band Single Polarization optical Fiber" J. of Lightwave Technology, vol. 9, 7, 1991, pp. 817-820.

 3. A.M. Kurbatov. "Single-mode single-polarized optical fiber for a polarizing mode filter" RF Patent 2040493, application 4529325 dated 04/09/1990. Date of registration in the State Register of Inventions 07/25/1995

 4. I.M. Skinner (link in article [2]).

Claims (1)

A single-mode unipolarizing optical fiber containing a light guide core, a reflective sheath with a refractive index lower than that of pure quartz glass, two circular loading rods, an outer protective sheath made of pure quartz glass, and a polymer protective and reinforcing coating, characterized in that the ratio

refractive index difference of the material and of the containment shell material reflective _of n _K -n to the difference in refractive index light-guiding core material and containment n _x -n _K selected in the range 0,5≤

≤2, with 3.5 · 10 ³ ≤ n _w -n _rev ≤ 7.5 · 10 ^-3 , and the ratio of the radius of the reflecting shell τ to the radius of the light guide core ρ is chosen in the range of 1.5≤τ / ρ≤2, 5, wherein the loading rods are made of a material with a refractive index equal to the refractive index n _{K of} the fiber sheath, and they are placed at a distance Δ from the light guide core, which satisfies the condition 0.5 ρ≤Δ≤ρ, while providing an opening angle of the loading rods when observed from the center of the light guide, 90 ° ≤α≤100 °.

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