CN111812771A - A solid-core polarization-maintaining high nonlinear photonic crystal fiber and its preparation process - Google Patents

Abstract

The invention discloses a solid-core polarization-maintaining high nonlinear photonic crystal optical fiber and a preparation process thereof. The preparation process takes a quartz capillary rod as the center, and closes stacking multiple circles of quartz capillary tubes from the inside to the outside. The diameter of the quartz capillary rod is Consistent with the outer diameter of the quartz capillary, a regular hexagonal stack is formed; the outer quartz sleeve is sleeved outside the stack, and different sizes are inserted into the gap between the outer wall of the outermost quartz capillary and the inner wall of the outer quartz sleeve. The quartz structure supports the capillary rod to obtain an optical fiber preform; perform optical fiber drawing on the optical fiber preform, and randomly select 1 of the quartz capillaries in one circle from the second circle from the inside to the outside to the second circle from the outside to the inside during the fiber drawing process. One quartz capillary or two symmetrically distributed quartz capillaries are used for independent partial pressure control; the advantage is that the resulting fiber has high nonlinearity, small mode field area, adjustable dispersion, can transmit linearly polarized light, birefringence, and adjustable birefringence .

Description

A solid-core polarization-maintaining high nonlinear photonic crystal fiber and its preparation process

technical field

The invention relates to an optical fiber and a preparation technology thereof, in particular to a solid-core polarization-maintaining high nonlinear photonic crystal optical fiber and a preparation technology thereof.

Background technique

High nonlinear optical fiber is a kind of special optical fiber, which is widely used in the field of nonlinear optical fiber devices. The nonlinear coefficient of the traditional single-mode fiber (SMF-28) is 0.78W ^-1 km ^-1 . By doping the core with high concentration of germanium, the refractive index difference between the core and the cladding is increased, and the fiber is reduced at the same time. Compared with the traditional single-mode fiber, the nonlinear coefficient of the highly nonlinear fiber realized by this method can only be increased by one order of magnitude. High nonlinear photonic crystal fiber, or high nonlinear microstructure fiber, because the light is confined in the core by the periodic micron-scale air hole array of the cladding, the effective refractive index difference between the core and the cladding is far away. higher than the refractive index difference between the core and the cladding obtained by doping the core with modulation materials; due to the increase in the numerical aperture, the highly nonlinear photonic crystal fiber can be designed with a very small core, further reducing the optical The effective mode field area of the mode and the nonlinear coefficient are tens to hundreds of times that of the traditional single-mode fiber; due to the flexibility of the structure, the dispersion of the high nonlinear photonic crystal fiber can be adjusted in a considerable range, and it can be adjusted appropriately The structural parameters of the fiber can obtain relatively flat dispersion characteristics, or the zero dispersion point of the fiber can be blue-shifted to short wavelengths. Highly nonlinear photonic crystal fibers with high nonlinear coefficients and controllable dispersion properties have been widely used in optical communications, supercontinuum light sources, optical coherence tomography, and optical frequency measurement.

On the other hand, polarization-maintaining fibers have been widely used in aerospace, industrial manufacturing, unmanned driving, communications and other fields. In the interferometric fiber optic sensor based on optical coherence detection, the use of polarization-maintaining fiber can ensure that the linear polarization direction remains unchanged, improve the coherent signal-to-noise ratio, and achieve high-precision measurement of physical quantities. At present, polarization-maintaining fibers that can achieve higher birefringence parameters are like the invention patent "a high-birefringence polarization-maintaining fiber" (patent number: ZL201610129210.X) published in China, which includes a core and a cladding, and the core is located in the fiber. At the center of the fiber core, symmetrical stress regions are set in the cladding on both sides of the core, and symmetrical air holes are set in the cladding on the other two sides where the core and the stress region are 90° staggered. Corresponding air holes are arranged to form a polarization-maintaining fiber structure that combines air holes and stress regions, so that the fiber has not only single-mode transmission and general high birefringence fiber characteristics, but also high birefringence characteristics and strong external pressure sensitivity characteristics. It can be suitable for the application of optical fiber communication devices and sensing fields, and further broaden the application field. The high-birefringence PM fiber is a double-stressed, double-sided hole and elliptical core structure design, which can achieve birefringence parameters greater than 10 ^-3 , but the high-birefringence PM fiber cannot meet all application requirements, such as Due to the high nonlinear requirements of optical fibers, the existing problems are: (1) Because of its large internal stress structure, it is easily affected by the external environment when using it for optical transmission; (2) In the case of single mode, the mode field area, dispersion, Parameters such as nonlinear coefficients cannot be adjusted flexibly; (3) it requires three kinds of quartz materials, the cost of doping the stress region is high, and the yield is low; (4) the elliptical core structure is difficult to be used in the wire drawing process in the presence of edge space. It is easy to cause the unevenness of the fiber axis, resulting in increased fiber loss.

Photonic crystal fibers have attracted widespread attention in the field of special fiber applications due to their flexible structural design and wide-ranging parameter adjustment capabilities. Through the special structural design of photonic crystal fibers, the problems of fiber parameter requirements that were difficult to achieve in the past have been well resolved. resolved. At present, the mainstream technology for obtaining high nonlinear fibers is photonic crystal fibers. Therefore, based on the structural design of photonic crystal fibers, optical fibers with both high polarization-maintaining performance and high nonlinearity can theoretically be obtained.

For high nonlinear photonic crystal fibers with polarization-maintaining properties, due to the complex fiber design and fabrication process, it is necessary to introduce an asymmetric design of the fiber core during the preform stacking process. The design solutions that can be found so far include: the Chinese published invention patent application "A high birefringence, high nonlinearity and low confinement loss photonic crystal fiber" (application number: 201510105137.8) and the Chinese published invention patent application "A new type of high double Refraction High Nonlinear Photonic Crystal Fiber" (application number: 201510003347.6). The optical fiber structures of these two schemes are difficult to prepare in practice, and there is only a theoretical possibility: (1) The hollow cores of the microstructured optical fibers in 201510105137.8 are all elliptical. Under the action, the microstructure holes cannot maintain the elliptical state, so the optical fiber of this structure does not have the possibility of actual preparation; (2) The fiber design in 201510003347.6 has a variety of microstructured air holes with different diameters. In the actual fiber preparation , for microstructures with more than three air hole sizes, it is necessary to control the partial pressure one by one, and the preparation is extremely difficult; (3) In 201510003347.6, the fiber core is not in the center of the fiber geometry, and there is a problem that it is difficult to couple with other fibers and optoelectronic devices.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a solid-core polarization-maintaining high nonlinear photonic crystal fiber and a preparation process thereof. The fiber prepared by the preparation process has high nonlinearity, small mode field area, adjustable dispersion, and can transmit linear polarization. Light, birefringence, and adjustable birefringence, the fiber preform can maintain the elliptical state of the solid core fiber core in the high temperature melting state during the preparation process, and the solid core fiber core is located in the geometric center of the fiber.

The technical solution adopted by the present invention to solve the above technical problems is: a solid-core polarization-maintaining high nonlinear photonic crystal fiber, which is characterized in that it comprises an outer cladding in a ring-shaped solid structure sequentially distributed from the outside to the inside, and has periodic air holes. Distributed inner cladding, solid core fiber core located at the geometric center of the optical fiber, the inner cladding contains a plurality of circles of air holes, the air duty ratio of the inner cladding is 70-99%, and each circle on the radial cross-section The center connection line of the air hole forms a hexagon, and one of the air holes in any one of the air holes in the second circle from the inside to the outside to the second circle from the outside to the inside or The diameters of the two symmetrically distributed air holes are smaller or larger than the diameters of all the remaining air holes, so that the mode field shape of the solid core fiber core is elliptical and has high birefringence, and the solid core fiber core has a high birefringence. The length of the long axis of the core is 1 to 10 microns.

The inner cladding layer contains at least three circles of the air holes, the diameter of one of the air holes or two symmetrically distributed air holes in the second circle of the air holes from the inside to the outside Smaller or larger than the pore size of all remaining air holes. In order to maintain the uniformity of the overall structure of the optical fiber, the inner cladding generally contains more than three circles of air holes, and one or two air holes that reduce or expand the aperture are not distributed in the innermost circle of air holes, because this will directly Affects the mode field shape and dispersion curve of the optical mode of the solid core fiber; in special cases, if there are only two air holes in the case, one or two air holes that reduce or expand the aperture are distributed in the first circle from the inside to the outside. 2 turns of the air hole.

The number of the air holes contained in the inner cladding layer is 18-468. Here, the number of air holes contained in the inner cladding is theoretically unlimited, but in order to balance the fiber loss and the overall size of the fiber, the number of air holes can be limited to 18-468.

A preparation process of a solid-core polarization-maintaining high nonlinear photonic crystal fiber is characterized by comprising the following steps:

Step 1: Take a quartz capillary rod as the center, and stack multiple circles of quartz capillary tubes from the inside to the outside to form a stack body with a regular hexagonal radial cross-section; among them, the diameter of the quartz capillary rod is the same as the outer diameter of the quartz capillary tube. Consistently, the outer wall of the quartz capillary rod is in close contact with the outer wall of the adjacent quartz capillary, and the outer walls of the two adjacent quartz capillaries are in close contact;

Step 2: Put a quartz outer sleeve on the stack body, the outer walls of the six quartz capillaries located at the corners of the stack body are close to the inner wall of the quartz outer sleeve, and the outer wall of the outermost quartz capillary in the stack body and the quartz jacket Insert capillary rods with different sizes of quartz structures into the gaps between the inner walls of the tubes to maintain the structural stability of the stack, thus obtaining an optical fiber preform; in general, the inner diameter can be selected to be slightly larger than the diameter of the circumscribed circle of the stack by 100-200 Micron Quartz Outer Sleeve.

Step 3: Perform optical fiber drawing on the optical fiber preform, and control the pressure in the capillary hole of the quartz capillary in the optical fiber preform, the pressure in the space between the quartz capillaries, and the pressure between the quartz capillary and the quartz capillary rod during the optical fiber drawing process. The pressure in the void, the pressure in the void between the quartz capillary and the quartz outer sleeve, and in the second circle from the inside to the outside to the second circle from the outside to the inside, 1 quartz capillary or Two quartz capillaries are symmetrically distributed, and independent partial pressure control is performed on the selected quartz capillary to control the reduction or expansion of the pore size of the capillary hole of the selected quartz capillary. The birefringence parameter realizes the polarization-maintaining function, so that in the final solid-core polarization-maintaining highly nonlinear photonic crystal fiber, the inner cladding with periodic distribution of air holes is formed by melting all the quartz capillaries and all the capillary rods supported by the quartz structure. The air duty ratio is 70-99%, the mode field shape of the solid core fiber core formed by melting the quartz capillary rod is elliptical and has high birefringence, and the long axis length of the solid core fiber core is combined with the fiber drawing speed. It is an outer cladding of annular solid structure formed by melting the quartz outer sleeve with a thickness of 1 to 10 microns.

In the step 1, the inner and outer diameter ratio of the quartz capillary is 70-80%.

In the step 2, the inner and outer diameter ratio of the quartz outer sleeve is 70-90%.

The preparation materials of the quartz capillary rod, the quartz capillary tube, the quartz outer sleeve and the quartz structure supporting capillary rod are the same, which are pure quartz glass (silicon dioxide) or multi-component soft glass. , or a polymer material.

The multi-component soft glass is metal oxide glass, and the polymer material is carbon chain high polymer or heterochain high polymer or element organic high polymer; the metal oxide glass is tellurium oxide, Glass of germanium oxide, lithium oxide, zinc oxide, sulfide, selenide, telluride, fluoride, iodide or phosphide, the carbon chain polymer is polypropylene, polyethylene, polyvinyl chloride, polyethersulfone Resin or polymethyl methacrylate, the hetero-chain high polymer is polyamide, polyimide or polyacrylamide.

In the described step 1, at least three circles of quartz capillaries are stacked closely from the inside to the outside, and in the described step 3, one quartz capillary or two symmetrically distributed quartz capillaries in the second circle of quartz capillaries from the inside to the outside are selected, Perform independent partial pressure control on the selected silica capillary to control the reduction or expansion of the pore diameter of the capillary of the selected silica capillary, that is, the inner cladding layer in the final solid-core polarization-maintaining high nonlinear photonic crystal fiber contains at least three turns For air holes, the diameter of one air hole or two air holes symmetrically distributed in the second circle of air holes from the inside to the outside is smaller or larger than that of all the other air holes.

In the step 1, the number of quartz capillaries that are closely stacked from the inside to the outside is 18 to 468, that is, the number of air holes contained in the inner cladding layer in the final solid-core polarization-maintaining high nonlinear photonic crystal fiber is 18. ~468.

Compared with the prior art, the advantages of the present invention are:

1) The outer cladding of the fiber is used to maintain the overall structure and improve the strength of the fiber; the inner cladding of the fiber reduces the effective refractive index of the inner cladding through periodically distributed air holes, so that the solid core core has a higher refractive index distributed.

2) The air duty ratio of the inner cladding of the optical fiber is 70-99%, which realizes the high nonlinearity of the optical fiber.

3) The length of the long axis of the solid core of the optical fiber is 1-10 microns, which realizes the small mode field area of the optical fiber.

4) The diameter of one or two air holes around the solid core fiber is reduced or enlarged, so that the mode field shape of the solid core fiber core is elliptical, so that the optical fiber can transmit linearly polarized light, and at the same time make the The dispersion of this fiber is tunable.

5) The preparation process of the optical fiber is controlled by active air pressure in the optical fiber preparation process, so that the air duty ratio of the inner cladding can be adjusted within the range of 70-99%; through the active air pressure control in the optical fiber preparation process and the optical fiber preform feeding the optical fiber The parameter of the wire drawing speed can control the length of the long axis of the solid core fiber core within the range of 1 to 10 microns.

6) The preparation process of the optical fiber During the stacking process of the optical fiber preform, all the stacked silica capillaries are of the same size, but in the optical fiber preparation process, the selective pressure technology is used to reduce or expand the capillary hole of a specific silica capillary At the same time, the structural parameters of other regions are maintained unchanged. The parameters that remain unchanged include: air duty ratio, number of air holes, shape of air holes, etc. The capillary holes of the selected specific quartz capillary need to be individually selective. partial pressure to precisely control the long and short axis parameters of the solid core.

7) For the same optical fiber preform, this preparation process can be prepared as a non-polarization-maintaining fiber (unified gas pressure control) or a polarization-maintaining fiber with different birefringence (partial pressure gas pressure control), which is flexible in preparation.

Description of drawings

Fig. 1 is the structural representation of the radial section of the optical fiber preform obtained in the preparation process of the present invention;

2 is a schematic diagram of a radial cross-section of a solid-core polarization-maintaining high nonlinear photonic crystal fiber prepared by the preparation process of Example 1;

3 is a scanning electric field microscope (SEM) of a solid-core polarization-maintaining high nonlinear photonic crystal fiber prepared by the preparation process of Example 1;

4 is a schematic diagram of a radial cross-section of a solid-core polarization-maintaining highly nonlinear photonic crystal fiber prepared by the preparation process of Example 2;

5 is a schematic diagram of a radial cross-section of a solid-core polarization-maintaining highly nonlinear photonic crystal fiber prepared by the preparation process of Example 3;

6 is a schematic diagram of a radial cross-section of a solid-core polarization-maintaining highly nonlinear photonic crystal fiber prepared by the preparation process of Example 4;

7 is a schematic radial cross-sectional view of the theoretical structure of the solid-core highly nonlinear photonic crystal optical fiber prepared by performing optical fiber drawing on the optical fiber preform shown in FIG. 1 without performing independent partial pressure control during the optical fiber drawing process;

8 is a scanning electric field microscope (SEM) of a solid-core highly nonlinear photonic crystal fiber prepared by performing fiber drawing on the optical fiber preform shown in FIG. 1 and without independent partial pressure control during the fiber drawing process;

FIG. 9 is a schematic diagram of the composition and structure of a preparation device used for preparing a solid-core polarization-maintaining high nonlinear photonic crystal fiber by using the preparation process of the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the embodiments of the accompanying drawings.

A solid-core polarization-maintaining highly nonlinear photonic crystal fiber proposed by the present invention, as shown in FIG. 2 , FIG. 4 , FIG. 5 and FIG. 6 , includes an outer cladding 41 , an annular solid structure, and a ring-shaped solid structure sequentially distributed from outside to inside. There is an inner cladding 42 with periodic distribution of air holes, a solid core 43 located in the geometric center of the optical fiber, the inner cladding 42 contains a plurality of circles of air holes 421, and the air duty ratio of the inner cladding 42 is 70-99%, such as the inner cladding 42 The air duty ratio of 42 is set to 80%, and the center connection line of each circle of air holes 421 forms a hexagon in the radial section, and any one of the second circle from the inside to the outside to the second circle from the outside to the inside. The diameter of one air hole 421 in the circle of air holes 421 or two symmetrically distributed air holes 421 is smaller or larger than that of all the other air holes 421, so that the mode field shape of the solid core fiber core 43 is elliptical and has a high Birefringence, the length of the long axis of the solid core 43 is 1-10 micrometers, for example, the length of the long axis of the solid core 43 is 5 micrometers.

A preferred solution is: the inner cladding 42 contains at least three circles of air holes 421 , and the diameter of one air hole 421 or two symmetrically distributed air holes 421 in the second circle of air holes 421 from the inside to the outside is smaller or larger than that of all the other air holes 421 the diameter of the air hole 421. In order to maintain the uniformity of the overall structure of the optical fiber, the inner cladding 42 generally includes more than three air holes 421, and one or two air holes 421 that reduce or expand the aperture are not distributed in the innermost air holes 421. Because this will directly affect the mode field shape and dispersion curve of the optical mode of the solid core fiber core 43; in special cases, if there are only two circles of air holes 421, reduce or expand one or two air holes 421 of the aperture Distributed in the air holes 421 of the second circle from the inside to the outside.

A preferred solution is: the number of air holes 421 included in the inner cladding layer 42 is 18-468. Here, the number of air holes 421 included in the inner cladding 42 is theoretically unlimited, but in order to balance the fiber loss and the overall size of the fiber, the number of air holes 421 can be limited to 18-468. If the inner cladding 42 contains three turns The number of air holes 421 included in the inner cladding layer 42 is 36.

The preparation process of a solid-core polarization-maintaining high nonlinear photonic crystal fiber proposed by the present invention comprises the following steps:

Step 1: As shown in FIG. 1, take a quartz capillary rod 51 as the center, and stack multiple circles of quartz capillary tubes 52 from the inside to the outside to form a stack body with a regular hexagonal radial cross section; The diameter of 51 is consistent with the outer diameter of the quartz capillary 52 , the outer wall of the quartz capillary rod 51 is in close contact with the outer wall of the adjacent quartz capillary 52 , and the outer walls of the two adjacent quartz capillaries 52 are in close contact.

Step 2: As shown in FIG. 1, a quartz outer sleeve 53 is sleeved outside the stack, and the outer walls of the six quartz capillaries 52 located on the corners of the stack are close to the inner wall of the quartz outer sleeve 53, and are at the outermost part of the stack. In the gap between the outer wall of the quartz capillary 52 of the circle and the inner wall of the quartz outer sleeve 53, a quartz structure supporting capillary 54 of different sizes is inserted to maintain the structural stability of the stack, and the optical fiber preform 31 is obtained so far, as shown in Figure 1; In general, a quartz outer sleeve 53 with an inner diameter slightly larger than the circumcircle of the stack body and a diameter of 100-200 microns can be selected.

Step 3: Perform optical fiber drawing on the optical fiber preform 31, and control the pressure in the capillary hole of the quartz capillary 52 in the optical fiber preform 31, the pressure in the space between the quartz capillaries 52, the quartz capillary 52 and the quartz capillary 52 during the optical fiber drawing process. The pressure in the space between the capillary rods 51, the pressure in the space between the quartz capillary 52 and the quartz outer sleeve 53, and arbitrarily select a circle of quartz from the second circle from the inside to the outside to the second circle from the outside to the inside One quartz capillary 52 or two symmetrically distributed quartz capillaries 52 in the capillaries 52 perform independent partial pressure control on the selected quartz capillary 52 to control the reduction or enlargement of the pore size of the capillary pores of the selected quartz capillary 52, thereby realizing a real The shape of the mode field of the core fiber core 43 is changed, a higher birefringence parameter is obtained, and the polarization-maintaining function is realized, so that the final solid-core polarization-maintaining high nonlinear photonic crystal fiber is supported by all the quartz capillaries 52 and all the quartz structures The air duty ratio of the inner cladding layer 42 with the periodic distribution of the air holes 421 formed after the capillary rod 54 is melted is 70-99% (for example, the air duty ratio of the inner cladding layer 42 is 80%). The mode field shape of the formed solid core fiber core 43 is elliptical and has high birefringence, and combined with the fiber drawing speed, the long axis length of the solid core fiber core 43 is 1-10 μm (such as the long axis length of the solid core fiber core 43 ). 5 μm), and the quartz outer sleeve 53 is melted to form the outer cladding 41 of the annular solid structure in the final solid-core polarization-maintaining high nonlinear photonic crystal fiber.

A preferred solution is: in step 1, the inner and outer diameter ratio of the quartz capillary 52 is 70-80%, for example, the inner and outer diameter ratio of the quartz capillary 52 is set to 75%.

A preferred solution is: in step 2, the inner and outer diameter ratio of the quartz outer sleeve 53 is 70-90%, for example, the inner and outer diameter ratio of the quartz outer sleeve 53 is set to 82%.

The preferred solution is: the quartz capillary rod 51, the quartz capillary tube 52, the quartz outer sleeve 53, and the quartz structure supporting capillary rod 54 are made of the same materials, which are pure quartz glass (silicon dioxide), or multi-component soft glass, or are Polymer Materials.

The preferred solution is: the multi-component soft glass is metal oxide glass, the polymer material is carbon chain polymer or heterochain polymer or element organic polymer; the metal oxide glass is tellurium oxide, germanium oxide, oxide Lithium, zinc oxide, sulfide, selenide, telluride, fluoride, iodide or phosphide glass, carbon chain polymer is polypropylene, polyethylene, polyvinyl chloride, polyethersulfone resin or polymethylmethacrylate Ester, heterochain high polymer is polyamide, polyimide or polyacrylamide.

The preferred solution is: in step 1, at least three circles of quartz capillaries 52 are stacked closely from the inside to the outside, and in step 3, one quartz capillary 52 or two symmetrically distributed quartz capillaries 52 in the second circle of quartz capillaries 52 from the inside to the outside are selected. The capillary tube 52 is to perform independent partial pressure control on the selected quartz capillary tube 52 to control the reduction or expansion of the aperture of the capillary hole of the selected quartz capillary tube 52, that is, to obtain the inner cladding layer in the final solid-core polarization-maintaining high nonlinear photonic crystal fiber. 42 includes at least three circles of air holes 421 , and the diameter of one air hole 421 or two symmetrically distributed air holes 421 in the second circle of air holes 421 from the inside to the outside is smaller or larger than that of all the other air holes 421 .

The preferred solution is: in step 1, the number of quartz capillaries 52 that are closely stacked from the inside to the outside is 18 to 468, that is, the air holes contained in the inner cladding 42 in the final solid-core polarization-maintaining high nonlinear photonic crystal fiber are obtained. The number of 421 is 18 to 468. If the inner cladding layer 42 includes three circles of air holes 421 , the number of air holes 421 included in the inner cladding layer 42 is 36.

Example 1:

In the preparation process of a solid-core polarization-maintaining high nonlinear photonic crystal fiber proposed in this embodiment, in step 3, two quartz capillaries 52 symmetrically distributed in the vertical direction in FIG. 1 are selected from the second circle of quartz capillaries 52 from the inside to the outside. Root quartz capillary 52, these two quartz capillaries 52 lead out one air pressure control pipeline independently, independent partial pressure control, when the pressure of independent partial pressure control is less than the pressure in the capillary holes of the remaining quartz capillaries 52, the prepared solid core is The radial section of the theoretical structure of the high nonlinear photonic crystal fiber is shown in Figure 2, and its scanning electric field microscope (SEM) is shown in Figure 3. It can be seen from Figure 3 that due to the two air gaps in the inner cladding 42 The diameter of the hole 421 is reduced, thus making the mode field shape of the solid core 43 elliptical in the vertical direction and having birefringence.

Embodiment 2:

In the preparation process of a solid-core polarization-maintaining high nonlinear photonic crystal fiber proposed in this embodiment, in step 3, two quartz capillaries 52 symmetrically distributed in the vertical direction in FIG. 1 are selected from the second circle of quartz capillaries 52 from the inside to the outside. Root quartz capillary 52, these two quartz capillaries 52 lead out a single air pressure control pipeline, independent partial pressure control, when the pressure of the independent partial pressure control is less than the pressure in the capillary holes of the remaining quartz capillaries 52 and is greater than the independent pressure in the first embodiment. The radial cross section of the theoretical structure of the prepared solid-core polarization-maintaining high nonlinear photonic crystal fiber is shown in Fig. 4 when the pressure is controlled by the pressure.

Embodiment three:

In the preparation process of a solid-core polarization-maintaining high nonlinear photonic crystal fiber proposed in this embodiment, in step 3, the diagonal direction of the regular hexagon in FIG. 1 is selected in the second circle of quartz capillaries 52 from the inside to the outside. Symmetrically distributed two quartz capillaries 52, these two quartz capillaries 52 lead out a single air pressure control pipeline, independent partial pressure control, when the pressure controlled by the independent partial pressure is less than the pressure in the capillary holes of the remaining quartz capillaries 52, prepared The radial cross-section of the theoretical structure of the solid-core polarization-maintaining highly nonlinear photonic crystal fiber is shown in Fig. 5. Selecting different positions of the quartz capillary 52 for independent partial pressure control can obtain fibers with different polarization-maintaining properties.

Embodiment 4:

In the preparation process of a solid-core polarization-maintaining high nonlinear photonic crystal fiber proposed in this embodiment, in step 3, one quartz capillary in the vertical direction in FIG. 1 is selected from the second circle of quartz capillaries 52 from the inside to the outside. The capillary 52, this quartz capillary 52 leads out a single air pressure control pipeline, which is independently controlled by partial pressure. When the pressure controlled by the independent partial pressure is less than the pressure in the capillary holes of the remaining quartz capillaries 52, the prepared solid core polarization maintaining high non-linearity is obtained. The radial section of the theoretical structure of the linear photonic crystal fiber is shown in Fig. 6. Different numbers of quartz capillaries 52 can be selected for independent partial pressure control, and the maximum is less than half of the total number of quartz capillaries 52 in a circle. Generally, it is recommended to select one or two quartz capillaries 52 for independent partial pressure control.

Figure 7 shows the radial cross-section of the theoretical structure of the solid-core highly nonlinear photonic crystal fiber prepared by drawing the optical fiber preform shown in Figure 1 without independent partial pressure control during the fiber drawing process, and Figure 8 The scanning electric field microscope (SEM) of the solid-core highly nonlinear photonic crystal fiber prepared by drawing the fiber preform shown in Figure 1 without independent partial pressure control during the fiber drawing process is given. It can be clearly seen from FIG. 7 and FIG. 8 that the dimensions of the air holes 421 in the inner cladding 42 are all the same, and the shape of the mode field of the solid core fiber core is circular.

Using the preparation process of each of the above embodiments to prepare the solid-core polarization-maintaining high nonlinear photonic crystal fiber, the following preparation device can be used, as shown in FIG. pressure, the pressure in the space between the quartz capillaries, the pressure in the space between the quartz capillary and the quartz capillary rod, the pressure in the space between the quartz capillary and the quartz outer sleeve, and in the second circle from the inside to the outside In the second circle from the outside to the inside, randomly select one quartz capillary or two symmetrically distributed quartz capillaries in one circle of quartz capillaries, and perform independent partial pressure control on the selected quartz capillary to control the diameter of the capillary hole of the selected quartz capillary A reduced or enlarged multi-channel active gas control unit 1, and an optical fiber drawing tower system 2 for performing optical fiber drawing on an optical fiber preform 31, the multi-channel active gas control unit 1 can effectively modulate the capillary of the silica capillary. Aperture, the optical fiber drawing tower system 2 consists of a preform feeding device 21, a high temperature furnace 22, 1 to 5 coating and curing devices 23 (two coating and curing devices 23 are generally used), and optical fiber steering guide wheels 24 2. The main traction system 25, the dancer 26 and the finished optical fiber take-up device 27 with the take-up reel 271 are composed of a main pulling system 25 with a main optical fiber pulling wheel 251 capable of adjusting the drawing speed and the diameter of the bare optical fiber 32, and the preform feeding device 21 provides the optical fiber The preform 31 is fed to the high-temperature furnace 22, and the high-temperature furnace 22 melts the optical fiber preform 31 into a filament to form a bare optical fiber 32, and the coating and curing device 23 makes the surface of the bare optical fiber 32 polymer material and solidifies to form an optical fiber 33 with a coating layer, The optical fiber 33 with the coating layer enters the main pulling system 25 after passing through the optical fiber steering guide wheel 24, and the main fiber pulling wheel 251 in the main pulling system 25 changes the diameter of the optical fiber 33 with the coating layer. The linear photonic crystal fiber 34 and the solid-core polarization-maintaining high nonlinear photonic crystal fiber 34 are collected by the take-up reel 271 in the finished fiber take-up device 27 after passing through the dancer 26 .

Here, the coating and curing device 23 includes an applicator 231 for coating the surface of the bare optical fiber 32 with a high molecular polymer and a curing furnace 232 for curing; Coating of optical fiber 33 with coating layer when the material is UV-curable polymer (such as acrylate or silica gel) or heat-cured polymer (such as polyimide), and the polymer material is acrylate or silica gel The thickness of the layer is 50-150 microns, and when the polymer material is polyimide, the thickness of the coating layer of the optical fiber 33 with the coating layer is 10-20 microns.

As mentioned above, the multi-channel active air control unit 1 adopts the prior art, and the required multi-channel active air control unit 1 can independently control the pressure of 4 or more channels, and the multi-channel active air control unit 1 is used to control the optical fiber preform. The value of the gas pressure of each part in 31 is determined according to the actual situation; the preform feeding device 21 adopts the existing feeding equipment; the high temperature furnace 22, the applicator 231, the curing furnace 232, the optical fiber steering guide wheel 24, the dance wheel 26 all adopt the existing technology; the working temperature of the high temperature furnace 22, the curing temperature of the curing furnace 232 and other required process parameters are all adopted in the existing optical fiber drawing process parameters or adjusted appropriately.

Claims (10)

1. The solid core polarization-maintaining high-nonlinearity photonic crystal fiber is characterized by comprising an outer cladding layer, an inner cladding layer and a solid core fiber core, wherein the outer cladding layer, the inner cladding layer and the solid core fiber core are sequentially distributed from outside to inside and are of an annular solid structure, the inner cladding layer is provided with air holes in a periodic distribution mode, the solid core fiber core is located at the geometric center of the fiber, the inner cladding layer comprises a plurality of circles of air holes, the air duty ratio of the inner cladding layer is 70-99%, the central connecting line of each circle of air holes on the radial cross section forms a hexagon, the aperture of 1 air hole or two symmetrically distributed air holes in any circle of air holes in the second circle from inside to outside is smaller than or larger than the aperture of all the rest air holes, the mode field shape of the solid core fiber core is oval and has high birefringence, and the length of the long axis of the solid core fiber core is 1-10 micrometers.

2. The solid core polarization maintaining nonlinear photonic crystal fiber of claim 1, wherein the inner cladding comprises at least three turns of the air holes, and the aperture of 1 of the air holes in the second turn from inside to outside or two of the symmetrically distributed air holes is smaller or larger than the aperture of all the other air holes.

3. The solid core polarization maintaining nonlinear photonic crystal fiber of claim 2, wherein the inner cladding comprises 18 to 468 air holes.

4. A preparation process of a solid core polarization maintaining nonlinear photonic crystal fiber is characterized by comprising the following steps:

step 1: taking a quartz capillary rod as a center, and closely stacking a plurality of circles of quartz capillary tubes from inside to outside to form a stack body with a regular hexagon radial section; the diameter of the quartz capillary rod is consistent with the outer diameter of the quartz capillary tube, the outer wall of the quartz capillary rod is tightly attached to the outer wall of the quartz capillary tube adjacent to the quartz capillary rod, and the outer walls of the two adjacent quartz capillary tubes are tightly attached to each other;

step 2: sleeving a quartz outer sleeve outside the stack body, wherein the outer walls of six quartz capillaries positioned on corners in the stack body are close to the inner wall of the quartz outer sleeve, and inserting quartz structure supporting capillary rods with different sizes into a gap between the outer wall of the quartz capillary tube on the outermost ring of the stack body and the inner wall of the quartz outer sleeve to maintain the structural stability of the stack body, so as to obtain an optical fiber preform rod;

and step 3: carrying out optical fiber drawing on an optical fiber preform, controlling the pressure in capillary holes of quartz capillary tubes in the optical fiber preform, the pressure in gaps among the quartz capillary tubes, the pressure in gaps between the quartz capillary tubes and a quartz capillary rod and the pressure in gaps between the quartz capillary tubes and a quartz outer sleeve in the optical fiber drawing process, randomly selecting 1 quartz capillary tube in one circle of the quartz capillary tubes or two symmetrically distributed quartz capillary tubes from a second circle from inside to outside to a second circle from outside to inside, and carrying out independent partial pressure control on the selected quartz capillary tubes to control the aperture of capillary holes of the selected quartz capillary tubes to be reduced or enlarged, so that the air duty ratio of an inner cladding layer with air hole periodic distribution formed after all quartz capillary tubes and all quartz structure supporting capillary rods are melted in the finally obtained solid core high-retention nonlinear photonic crystal optical fiber is 70-99 percent, The mode field shape of the solid core fiber core formed by melting the quartz capillary rod is elliptical and has high birefringence, and the long axis length of the solid core fiber core is 1-10 microns by combining the optical fiber drawing speed.

5. The preparation process of the solid core polarization maintaining nonlinear photonic crystal fiber according to claim 4, wherein in the step 1, the inner diameter ratio and the outer diameter ratio of the quartz capillary tube are 70-80%.

6. The process for preparing a solid core polarization maintaining nonlinear photonic crystal fiber according to claim 4, wherein in the step 2, the inner diameter ratio and the outer diameter ratio of the quartz outer sleeve are 70-90%.

7. The process according to claim 4, wherein the quartz capillary rod, the quartz capillary tube, the quartz outer sleeve, and the quartz structure supporting capillary rod are made of the same material, and are made of pure quartz glass, or multi-component soft glass, or polymer material.

8. The process for preparing a solid core polarization maintaining high nonlinear photonic crystal fiber according to claim 7, wherein the multicomponent soft glass is a metal oxide glass, and the polymer material is a carbon chain polymer or a heterochain polymer or an element organic polymer; the metal oxide glass is tellurium oxide, germanium oxide, lithium oxide, zinc oxide, sulfide, selenide, telluride, fluoride, iodide or phosphide glass, the carbon chain high polymer is polypropylene, polyethylene, polyvinyl chloride, polyether sulfone resin or polymethyl methacrylate, and the heterochain high polymer is polyamide, polyimide or polyacrylamide.

9. The process according to claim 4, wherein at least three quartz capillaries are stacked in close contact from inside to outside in the step 1, 1 quartz capillary or two symmetrically distributed quartz capillaries in the second quartz capillary from inside to outside are selected in the step 3, and the selected quartz capillary is independently controlled in partial pressure to control the pore diameter of the selected quartz capillary to decrease or increase, so that the inner cladding of the finally obtained solid core high nonlinear photonic crystal fiber comprises at least three air holes, and the pore diameter of 1 air hole or two symmetrically distributed air holes in the second air hole from inside to outside is smaller than or larger than the pore diameter of all the rest air holes.

10. The process according to claim 4, wherein the number of the silica capillaries stacked in the step 1 from inside to outside is 18 to 468, that is, the number of the air holes contained in the inner cladding of the solid core polarization maintaining nonlinear photonic crystal fiber obtained finally is 18 to 468.

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