阅读说明：本技术 一种保偏色散补偿微结构光纤 (Polarization-maintaining dispersion compensation microstructure optical fiber ) 是由 王伟 周凡迪 杨骐豪 李正然 杨慢 王彦 龚琳 于 2019-11-29 设计创作，主要内容包括：一种保偏色散补偿微结构光纤,该微结构光纤由石英作为基底材料,所述微结构光纤包括内纤芯区域和由内至外依次呈正六边形排列包裹在内纤芯区域外层的内包层空气孔、外纤芯区域和外包层空气孔,所述内纤芯区域是由中心空气孔与周围石英共同组成的C<Sub>6v</Sub>对称性结构,所述外纤芯区域是由空气孔与周围石英共同组成的C<Sub>6v</Sub>对称性结构,且所述中心空气孔与外纤芯区域空气孔内均填充有液晶。本发明有效的解决了在色散补偿过程中,要补偿的偏振方向一旦确定就无法改变的技术问题,而且采用该技术方案,最终在1550nm的通信波长处获得的结果为：对x偏振模式得到的负色散为-16040.3ps/(nm·km),对y偏振模式得到的负色散为-12354.2ps/(nm·km)。(The micro-structure optical fiber comprises an inner fiber core area, and an inner cladding air hole, an outer fiber core area and an outer cladding air hole which are sequentially arranged in a regular hexagon from inside to outside and wrapped on the outer layer of the inner fiber core area, wherein the inner fiber core area is a C-shaped micro-structure optical fiber consisting of a central air hole and surrounding quartz 6v The symmetric structure, the outer fiber core region is C composed of air holes and surrounding quartz 6v And the central air hole and the air holes of the outer fiber core area are both filled with liquid crystals. The invention effectively solves the technical problem that the polarization direction to be compensated can not be changed once being determined in the dispersion compensation process, and by adopting the technical scheme, the final result obtained at the 1550nm communication wavelength is as follows: the negative dispersion obtained for the x-polarization mode was-16040.3 ps/(nm · km), and the negative dispersion obtained for the y-polarization mode was-12354.2 ps/(nm · km).)

1. A polarization-maintaining dispersion compensating micro-structured fiber, which uses quartz as a substrate material, is characterized in that: the micro-structure optical fiber comprises an inner fiber core area, and an inner cladding air hole, an outer fiber core area and an outer cladding air hole which are sequentially arranged in a regular hexagon from inside to outside and wrap the outer layer of the inner fiber core area, wherein the inner fiber core area is C consisting of a central air hole and surrounding quartz_6vThe symmetric structure, the outer fiber core region is C composed of air holes and surrounding quartz_6vAnd the central air hole and the air holes of the outer fiber core area are both filled with liquid crystals.

2. The polarization maintaining dispersion compensating microstructured optical fiber of claim 1, wherein: the pitch Lambda of the air holes is 1.27-1.29 mu m.

3. A polarization-maintaining dispersion compensating microstructured optical fiber according to claim 1 or 2, wherein: the inner cladding air holes are formed by two layers of air holes which are arranged in a regular hexagon, and the number of the air holes is respectively 6 and 12; the air holes of the outer cladding are formed by two layers of air holes which are arranged in a regular hexagon, and the number of the air holes is respectively 24 and 30.

4. The polarization maintaining dispersion compensating microstructured optical fiber of claim 2, wherein: diameter d of the central air hole₁Is 0.76 lambda-0.78 lambda.

5. A polarization-maintaining dispersion compensating microstructured optical fiber according to claim 2 or 4, wherein: the air holes in the outer fiber core area are formed by a layer of air holes which are arranged in a regular hexagon, the number of the air holes is 18, and the diameter d of each air hole₃Is 0.59Λ～0.61Λ。

6. A polarization maintaining dispersion compensating microstructured optical fiber according to claim 3, wherein: the air holes of the inner cladding and the outer cladding have the same size, and the diameter d of the hole₂Is 0.91 lambda-0.93 lambda.

7. The polarization maintaining dispersion compensating microstructured optical fiber of claim 1, wherein: the liquid crystal is E7 liquid crystal.

Technical Field

The invention relates to the field of optical fiber communication, in particular to a polarization-maintaining dispersion compensation microstructure optical fiber.

Background

With the rapid development of the high-speed optical communication field, the photonic crystal fiber is widely applied due to the advantage of flexible parameter design. The traditional circularly symmetric single-mode fiber can simultaneously transmit two orthogonal linear polarization modes, if the fiber is uniform and perfectly symmetric in the transmission direction, the two orthogonal linear polarization modes can be transmitted forwards at the same speed and the polarization modes can not be changed, but perfect circular symmetry cannot be realized in the actual fiber drawing process, and crosstalk can occur in the transmission process of the two polarization modes, so that the signal transmission quality is seriously influenced. The polarization-maintaining photonic crystal fiber eliminates the influence of stress on the polarization state of incident light in the drawing process by generating a strong birefringence effect, can effectively reduce polarization coupling, and keeps the linear polarization of optical signals. Meanwhile, in order to solve the problem of chromatic dispersion in the transmission process, chromatic dispersion compensation needs to be performed on the polarization maintaining fiber. If the polarization maintaining fiber is compensated by using the conventional dispersion compensating fiber, since the conventional dispersion compensating fiber does not have the polarization maintaining characteristic, mode coupling occurs between two polarization directions to cause crosstalk, and the polarization state of light cannot be maintained. Therefore, a dispersion compensating fiber having polarization maintaining characteristics is undoubtedly an effective solution to the above-mentioned problems: the optical fiber not only can compensate the positive dispersion accumulated in the transmission process, but also has good polarization maintaining capability to the transmission mode. The problem of signal broadening caused by dispersion is avoided, and the problem of crosstalk caused by polarization mode coupling is solved. Therefore, the dispersion compensation fiber with the polarization maintaining characteristic has good application prospect in high-speed optical communication.

Microstructured optical fiber designTherefore, the characteristics of polarization maintaining and dispersion compensation can be well realized simultaneously. For the existing microstructure fiber, the common technical scheme for realizing the polarization-maintaining dispersion compensation fiber is as follows: (1) neglecting one air hole in the center of the silicon dioxide material with the air holes arranged in a regular hexagon to form a solid area, wherein the solid area forms an inner core area; the outer core is formed by decreasing the diameter of an air hole in a certain layer to increase the average refractive index of the layer. The coaxial double-core optical fiber structure is formed by the method. (2) The geometric structure of the inner fiber core and the adjacent area, such as the size and the shape of an air hole adjacent to the inner fiber core, is designed to reduce the symmetry of the inner fiber core, so that the transmission mode of the inner fiber core generates structural birefringence, and the optical fiber (the inner fiber core) has polarization-maintaining characteristics. (3) For the outer core, there are two cases: the symmetry of the outer core is not changed, so that the outer core still has C_6vSymmetry, no birefringence in the outer core region; or the geometry of the outer core and adjacent regions may be designed to reduce symmetry (e.g., change the size, shape, etc. of the outer core air holes) such that birefringence is induced in the outer core region. (4) Structural parameters of the outer fiber core are reasonably optimized, so that a certain or two polarization mode refractive index variation curves of the outer fiber core and a certain or two polarization mode refractive index variation curves of the inner fiber core are intersected at 1550nm, and therefore energy coupling of the inner fiber core and the outer fiber core is generated, further, sudden change of the inner fiber core mode refractive index along with wavelength variation is caused, large negative dispersion is generated, and the dispersion compensation effect in one direction or two orthogonal directions is realized.

By utilizing the technical scheme, von Korea printing and the like design a polarization-maintaining dispersion compensation optical fiber, and the technical scheme is as follows: (1) on a silica material having a regular hexagonal arrangement of air holes, ignoring the central air hole forms a solid region which forms the inner core. And reducing the diameter of the air hole of the third layer to form an outer fiber core to form a coaxial dual-core structure. (2) The diameter of 2 air holes in the x direction of the first layer of air holes adjacent to the inner fiber core is reduced, the symmetry of the inner fiber core area is reduced, and the inner fiber core mode is generated to be as high as 2.36 multiplied by 10^-2The birefringence of (2) provides the optical fiber with polarization maintaining properties. (3) The diameter of the air holes in the outer core region is adjusted so that the modal index of refraction varies with wavelengthThe refractive index variation curve of the inner fiber core mode along with the wavelength is intersected at 1550nm, so that the inner fiber core mode and the outer fiber core mode are coupled at 1550nm, the refractive index variation curve of the inner fiber core mode along with the wavelength is suddenly changed, and large negative dispersion with the value of-7740 ps/(nm-km) is formed. (Feng Chaoyao, Wang Shenxian, a novel high birefringent photonic crystal fiber characterization [ J ]]Optical communications research, 2014,40(1):41-44.)

The key of the scheme for realizing the polarization-maintaining dispersion compensation microstructure optical fiber is that the geometric symmetry of the optical fiber is reduced by changing the geometric structure of a fiber core area in the optical fiber (changing the size and the shape of an air hole or performing operations such as compression and the like), so that the optical fiber generates structural birefringence and has the polarization-maintaining characteristic; by changing the geometric structure of the outer fiber core region, the mode coupling effect of a certain polarization direction or two polarization directions of the outer fiber core and a certain polarization direction or two polarization directions of the inner fiber core is utilized to form large negative dispersion of the inner fiber core, so that the optical fiber has the dispersion compensation characteristic. The above-mentioned scheme has the disadvantage that once the polarization-maintaining dispersion compensation microstructure optical fiber structure is determined, the polarization direction capable of compensating the dispersion of the polarization-maintaining optical fiber is also fixed, and cannot be dynamically adjusted, and the requirement of variable polarization direction of dispersion compensation cannot be met.

Disclosure of Invention

In view of the above-mentioned shortcomings, the present invention provides a polarization-maintaining dispersion-compensating microstructure optical fiber, which can change and control the polarization direction of dispersion compensation by changing the liquid crystal molecule deflection direction.

The technical scheme adopted by the invention is as follows:

the invention provides a polarization-maintaining dispersion compensation micro-structural optical fiber which comprises an inner fiber core area, and an inner cladding air hole, an outer fiber core area and an outer cladding air hole which are sequentially arranged in a regular hexagon from inside to outside and wrapped on the outer layer of the inner fiber core area, wherein the inner fiber core area is C composed of a central air hole and surrounding quartz_6vThe symmetric structure, the outer fiber core region is C composed of air holes and surrounding quartz_6vSymmetrical structure, and the central air hole and the outerLiquid crystal is filled in the air holes of the fiber core area.

The pitch Lambda of the air holes is 1.27-1.29 mu m.

The inner cladding air holes are formed by two layers of air holes which are arranged in a regular hexagon, and the number of the air holes is respectively 6 and 12; the air holes of the outer cladding are formed by two layers of air holes which are arranged in a regular hexagon, and the number of the air holes is respectively 24 and 30.

Diameter d of the central air hole₁Is 0.76 lambda-0.78 lambda.

The air holes in the outer fiber core area are formed by a layer of air holes which are arranged in a regular hexagon, the number of the air holes is 18, and the diameter d of each air hole₃Is 0.59 lambda-0.61 lambda.

The air holes of the inner cladding and the outer cladding have the same size, and the diameter d of the hole₂Is 0.91 lambda-0.93 lambda.

The liquid crystal is E7 liquid crystal.

Compared with the prior art, the invention has the following beneficial effects:

the polarization maintaining dispersion compensating micro structure fiber consists of inner and outer fiber core areas and inner and outer air holes. Using the characteristic of liquid crystal molecules being rotatable and C of the optical fiber_6vThe symmetry realizes the technical effects that the liquid crystal direction deflects, the structure (symmetry) of a fiber core area in the optical fiber is changed, the positions of refractive indexes of two polarization modes are interchanged along with the position of a wavelength change curve, and the numerical value is unchanged; meanwhile, as the inner fiber core area is filled with liquid crystal, the absolute value of the slope of the mode refractive index curve of the inner fiber core area is increased, namely the curve is steep; the technical effects that the liquid crystal direction is deflected, the structure (symmetry) of the outer fiber core area of the optical fiber is changed, the positions of refractive indexes of two polarization modes are interchanged along with the position of a wavelength change curve, and the numerical offset is reduced are achieved by utilizing the modes of arranging air holes in the outer fiber core area, reducing the diameter of the air holes and filling liquid crystal; finally, the liquid crystal molecules are controlled to deflect in two directions of 0 degrees and 90 degrees, so that the polarization-maintaining dispersion compensation optical fiber for respectively realizing dispersion compensation in an x polarization mode or a y polarization mode is obtained. Therefore, the technical problem that the polarization direction to be compensated cannot be changed once being determined in the dispersion compensation process is effectively solved. Practice ofFor example, with this technical solution, the final result obtained at the 1550nm communication wavelength is: producing a 1.376 × 10 core region in the inner core region^-1The birefringence of (2) was 7.344 × 10 in the outer core region at a liquid crystal angle of 0 DEG^-3When the liquid crystal angle is 90 degrees, 5.068X 10 is generated in the outer core region^-3Birefringence of (d); the negative dispersion obtained for the x-polarization mode was-16040.3 ps/(nm · km), and the negative dispersion obtained for the y-polarization mode was-12354.2 ps/(nm · km).

Drawings

FIG. 1 is a schematic structural diagram of an embodiment of a polarization-maintaining dispersion compensating microstructured optical fiber according to the present invention;

FIG. 2 is a graph of the effective refractive index for the x-polarization mode of the inner and outer core regions at 0 and the y-polarization mode of the inner and outer core regions at 90 for liquid crystal;

FIG. 3 is a plot of the effective index for the y-polarization mode of the inner and outer core regions at 0 for liquid crystal and the x-polarization mode of the inner and outer core regions at 90 for liquid crystal;

FIG. 4 is a graph of the x-polarization mode dispersion at 0 for liquid crystal and the y-polarization mode dispersion at 90 for liquid crystal.

Detailed Description

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Referring to fig. 1, a specific structure of an embodiment of a polarization-maintaining dispersion compensating microstructured optical fiber according to the present invention is shown. The microstructure optical fiber comprises an inner fiber core area 1, an inner cladding air hole 2, an outer fiber core area 3, an outer cladding air hole 4, liquid crystal 5 and a quartz substrate material 6. The optical fiber takes the central air hole 11 as the center, and the optical fiber structure sequentially comprises an inner fiber core area 1, an inner cladding air hole 2, an outer fiber core area 3 and an outer cladding air hole 4 from inside to outside.

All air holes in the microstructure optical fiber are arranged in a regular hexagon to form a five-layer optical fiber structure, the hole pitch Lambda of every two air holes is set to be 1.27-1.29 mu m, and in the embodiment, the hole pitch Lambda is 1.28 mu m; the inner core region 1 is C composed of a central air hole 11 and a quartz substrate material 6 around the hole_6vSymmetrical construction, diameter d of the central air hole 11₁Set at 0.76-0.78 Λ, the diameter d of the central air hole 11 in this embodiment₁Is 0.77 Λ, and the central air hole 11 is filled with the liquid crystal 5; the inner cladding air holes 2 are arranged in a regular hexagon and are positioned on a first layer and a second layer of the inner fiber, wherein the number of the holes of the first layer is 6, the number of the holes of the second layer is 12, and the diameter d of the inner cladding air holes 2₂All are 0.91-0.93 Λ, in this embodiment, the diameter d of the inner cladding air hole 2₂Is 0.917 Λ; the outer fiber core region 3 is C composed of 18 outer fiber core air holes 31 arranged in a regular hexagon manner in the third layer of the optical fiber and quartz substrate material 6 around the holes_6vSymmetrical structure, and each outer core region air hole 31 is filled with liquid crystal 5 and has reduced aperture size, and the diameter d of the outer core region air hole 31₃Set to 0.59-0.61 Λ, the diameter d of the outer core region air holes 31 in this embodiment₃Is 0.6 lambda; the outer cladding air holes 4 are positioned at the fourth layer and the fifth layer of the optical fiber, wherein the number of the holes at the fourth layer is 24, the number of the holes at the fifth layer is 30, and the diameter of the outer cladding air holes 4 is the same as that of the inner cladding air holes 2.

In the present invention, since the liquid crystal 5 is filled in the central air hole 11 of the inner core region 1 and the air hole 31 of the outer core region 3, the symmetry of the two regions can be reduced, high birefringence can be generated, and both core regions have polarization maintaining characteristics. The scheme also reduces the diameter of the air hole 31 in the outer fiber core area, increases the energy leakage degree in the core, increases the energy coupling strength of each core for forming a supermode, and is used for reducing the deviation of the refractive index curve of the outer fiber core area 3 after the liquid crystal 5 rotates and reducing the movement of the coupling wavelength. Filling the liquid crystal 5 in the central air hole 11 can increase the absolute value of the slope of the modal index curve of the inner core region 1, ensuring that the modal index curve of the outer core region 3 moves after the liquid crystal 5 rotates, but the coupling wavelength shift is small.

The invention has the following action principle: the central air hole 11 and the quartz substrate material 6 around the hole are C_6vSymmetrical structures, which are used as the inner fiber core area 1 together, have no double refraction; liquid crystal 5 is filled in the central air hole 11 of the inner core region 1 in order to reduce the symmetry of the inner core region 1 to C_2vBirefringence is generated in the inner core region 1 having no birefringence, so that the optical fiber has polarization maintaining characteristics; further, filling the central air hole 11 with a high-refractive-index dopant such as the liquid crystal 5 increases the absolute value of the slope of the mode refractive index curve of the inner core region 1. When the liquid crystal molecules are 0 °, the major axis of the liquid crystal 5 coincides with the x-axis direction of the optical fiber (the direction in which two holes farthest from each other are connected to each other), and the minor axis coincides with the y-axis direction of the optical fiber. When the liquid crystal molecules are deflected by 90 degrees from 0 degrees, the long axis of the liquid crystal 5 is consistent with the y-axis direction of the optical fiber (the perpendicular bisector direction of the connecting line of the two holes with the farthest distance of the regular hexagon), and the short axis is consistent with the x-axis direction of the optical fiber. Although the difference exists between the x-direction and the y-direction of the inner core region, namely, the x-direction axis corresponds to two air holes in the direction of the line of two holes which are farthest away from the regular hexagon, and the y-direction axis corresponds to quartz between adjacent air holes in the direction of the perpendicular bisector of the line. But since the central air hole 11 is circular, has infinite dimensional symmetry, and is provided with C_6vThe remaining quartz region after the symmetrical air hole segmentation also has C_6vHas a symmetry of C in the liquid crystal molecules in the central air hole 11_2vThe symmetry of (A), the combined structure of the three has C_2vI.e. the inner core region 1 has C after filling with liquid crystal 5_2vThe angle of the rotational symmetry and the angle of the axial symmetry are both 180 degrees, and the rotation angle of the liquid crystal 5 is half of the angle of the symmetry axis each time, so that the structure (symmetry) of the inner fiber core region 1 can be changed when the liquid crystal 5 rotates from 0 degree to 90 degrees (or changes from 90 degrees to 0 degrees), and the refractive indexes of the two polarization modes are interchanged along with the position of the wavelength change curve, but the numerical value is not changed.

Air hole 31 and quartz substrate around the holeThe material 6, which together serves as the outer core region 3, has C_6vSymmetry, no birefringence. The outer core region 3 uses 18 air holes 31 while reducing the hole diameters of the 18 air holes 31, and fills the liquid crystal 5 therein so that the directions of the liquid crystal molecules at 0 ° and 90 ° are made to coincide with the directions of the liquid crystal molecules in the central air hole 11 of the inner core region 1. Because the outer fiber core area 3 does not have infinite symmetry of the central circular air hole 11, and there is a difference between the x direction and the y direction, after the liquid crystal 5 rotates in the direction, the positions of the refractive index curves of the two polarization modes of the outer fiber core area 3 are interchanged, but the value is changed, so that the actual coupling point is far away from the target coupling point. Therefore, 18 air holes 31 are arranged in the fourth layer, so that the outer fiber core area 3 is consistent with the integral structure of the optical fiber; meanwhile, the 18 air holes 31 of the outer core region 3 are filled with the liquid crystal 5, so that the average refractive index of the outer core region 3 is improved, the coupling with the inner core region 1 is facilitated, the birefringence is generated in the outer core region 3, and the outer core region 3 also has the polarization-maintaining characteristic; since the refractive index of the liquid crystal 5 is higher than that of quartz, each region filled with the liquid crystal 5 transmits a mode, and thus the mode of the outer core region 3 is actually a supermode generated by mutual coupling between 18 liquid crystal region modes. After the diameters of the 18 air holes 31 are reduced, the core diameter of each liquid crystal core is reduced, the energy leakage degree in the core is increased, and the energy coupling strength of the supermode formed by each core is increased. The outer fiber core area 3 does not lack air holes, so that the completeness of the optical fiber structure is guaranteed, and the super-mode coupling strength of the outer fiber core area 3 can be enhanced. On the basis of the above two points, the directions of the liquid crystal molecules at 0 ° and 90 ° are made to coincide with the directions of the liquid crystal molecules in the central air hole 11 of the inner core region 1, and the influence of other multi-factors on the shift of the refractive index profile can be minimized to control the shift of the refractive index profile. Therefore, by providing 18 air holes 31 and a reduced hole diameter in the outer core region 3 and filling liquid crystal, the movement of the liquid crystal after turning the refractive index curves due to the difference in the x and y directions of the optical fiber after rotating is reduced in both structural symmetry and mode coupling. The liquid crystal 5 direction deflection is achieved, the structure (symmetry) of the fiber core region 3 outside the optical fiber is changed, the refractive indexes of the two polarization modes are interchanged along with the position of a wavelength change curve, and the numerical value can be reducedThe technical effect of the offset.

In the above scheme, after the liquid crystal 5 is filled in the inner core region 1, the absolute value of the slope of the mode refractive index curve is increased, that is, the curve is steeper, and meanwhile, after the liquid crystal is rotated, the mode refractive index curve of the outer core region 3 moves less, so that it is ensured that after the liquid crystal 5 is rotated, the movement of the coupling wavelength from the x polarization state to the y polarization state (or from the y polarization state to the x polarization state) of the inner core region and the outer core region is smaller.

By reasonably adjusting the refractive index of each polarization mode, when the liquid crystal 5 is at 0 DEG, the refractive index curves of the x polarization mode in the inner fiber core area and the outer fiber core area are intersected at 1550 nm; when the liquid crystal 5 is at 90 degrees, the y polarization mode refractive index curves of the inner fiber core area and the outer fiber core area are intersected near 1550nm, and mode energy coupling of the inner fiber core area and the outer fiber core area is generated, so that sudden change of the x polarization mode or the y polarization mode refractive index along with a wavelength change curve is caused, large negative dispersion is generated, dispersion compensation is realized, and the technical effect of changing the optical fiber dispersion compensation polarization direction is achieved.

Referring to fig. 2, when the angle of the liquid crystal 5 is 0 °, the x-polarization mode of the inner and outer core regions is energy-coupled at 1550nm, which generates large negative dispersion at that wavelength; when the angle of the liquid crystal 5 is 90 degrees, the y polarization modes of the inner fiber core area and the outer fiber core area are subjected to energy coupling at 1562nm, the coupling point is near 1550nm, and large negative dispersion can be generated at 1550 nm. Referring to fig. 3, at an angle of 0 ° of the liquid crystal 5, the y-polarization modes of the inner and outer core regions are not coupled around 1550 nm. Similarly, at an angle of 90 ° for the liquid crystal 5, the x-polarization modes of the inner and outer core regions are not coupled around 1550 nm. When the angle of the liquid crystal 5 is changed from 0 degrees to 90 degrees (or 90 degrees to 0 degrees), the polarization mode of the optical fiber dispersion compensation of the scheme is changed from the x polarization mode to the y polarization mode (or from the y polarization mode to the x polarization mode), thereby realizing the technical effect of changing the polarization direction of the optical fiber dispersion compensation.

The central air hole 11 of the inner core region 1 of the present invention is circular, has infinite symmetry, and is provided with C_6vThe remaining quartz region after the symmetrical air hole segmentation also has C_6vHas a symmetry of C in the liquid crystal molecules in the central air hole 11_2vThe symmetry of (1), so the combination of the threeThe structure has C_2vThe symmetry angle of (1) is 180 °, and since the rotation angle of the liquid crystal 5 is half of the symmetry axis angle each time, the liquid crystal 5 rotates from 0 ° to 90 ° (or from 90 ° to 0 °), and the refractive indices of the two polarization modes are interchanged with the wavelength variation curve, but the values are unchanged. So n in FIG. 2₁The curves are the x-polarization mode index curve for 0 deg. of liquid crystal 5 in the inner core region and the y-polarization mode index curve for 90 deg. of liquid crystal 5. Because the outer fiber core region 3 does not have the infinite symmetry of the central air hole 11 of the inner fiber core region, after the liquid crystal 5 rotates, the refractive index curves of the two polarization modes can shift, so that the actual coupling point is far away from the target coupling point. The invention arranges 18 air holes 31 in the outer fiber core area 3, reduces the diameter and fills the liquid crystal 5, and reduces the movement of the liquid crystal after two refractive index curves are turned over due to the difference of the optical fibers in the x and y directions after the liquid crystal rotates from the two aspects of structural symmetry and mode coupling. Meanwhile, the slope of the mode refractive index curve of the inner core region 1 is increased because the central air hole 11 is filled with the liquid crystal 5, and it is ensured that the mode refractive index curve of the outer core region 3 is shifted but the coupling wavelength is shifted less after the liquid crystal 5 is rotated. Still as can be seen from fig. 2, due to the design of the present embodiment, the refractive index value shift amount of the outer core region 3 after the liquid crystal 5 is rotated is controlled to a small range.

Referring to FIG. 4, dispersion value curves of the x-polarization mode of the liquid crystal 5 at 0 ℃ and the y-polarization mode of the liquid crystal at 90 ℃ are shown, the x-polarization mode of the inner and outer core regions at an angle of 0 ℃ of the liquid crystal 5 is energy-coupled at 1550nm to obtain negative dispersion of-16040.3 ps/(nm. km) at 1550nm, the y-polarization mode of the inner and outer core regions at an angle of 90 ℃ of the liquid crystal 5 is energy-coupled at 1562nm, and a large negative dispersion value of-12354.2 ps/(nm. km) still exists at 1550 nm.

This scheme produces 1.376 × 10 in the inner core region 1^-1Birefringence of (d); when the angle of the liquid crystal 5 is 0 °, 7.344 × 10 is generated in the outer core region 3^-3Birefringence of (d); when the angle of the liquid crystal 5 is 90 °, 5.068 × 10 is generated in the outer core region 3^-3Birefringence of (c).

The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solution of the present invention by those skilled in the art should fall within the protection scope defined by the claims of the present invention without departing from the spirit of the present invention.