WO2017121160A1

WO2017121160A1 - Low-loss radiation-proof birefringent photonic crystal fibre

Info

Publication number: WO2017121160A1
Application number: PCT/CN2016/102805
Authority: WO
Inventors: 罗文勇; 刘志坚; 李伟; 柯一礼; 赵磊; 杜城; 胡福明; 雷琼; 杜琨; 康志文; 但融
Original assignee: 烽火通信科技股份有限公司
Priority date: 2016-01-11
Filing date: 2016-10-21
Publication date: 2017-07-20
Also published as: CN105403952A; CN105403952B

Abstract

A low-loss radiation-proof birefringent photonic crystal fibre, comprising a central fibre core (1). The central fibre core (1) comprises a pure silicon fibre core (11) and a deep fluorine-doped concave inner cladding (12) coating the outside of the pure silicon fibre core (11). An air pore layer (2) and a quartz cladding (3) successively coat the outside of the central fibre core (1) from inside to outside. The outside of the quartz cladding (3) is coated with a coating layer (4). The air pore layer (2) comprises four layers of rings composed of air pores from inside to outside. The first layer of rings is composed of two large air pores (21) and a plurality of small air pores (22). The second, third and fourth layers of rings are all composed of the plurality of small air pores (22). The air pores of the four layers of rings are all arranged in a regular hexagonal manner. All the air pores are connected by means of a quartz connecting wall. The fibre realizes birefringence, and at the same time has low-loss and radiation-proof performances, and satisfies the usage requirements in special environment application occasions, such as aerospace.

Description

Low loss anti-irradiation birefringent photonic crystal fiber

Technical field

The invention relates to the field of photonic crystal fibers, in particular to a low loss radiation resistant birefringent photonic crystal fiber.

Background technique

High-birefringence fibers in communications, sensing, and other fields have a wide range of applications. Optical fiber sensing technology with polarization-maintaining fiber as the core component, especially fiber optic gyro technology and fiber-optic hydrophone technology, has received more attention. The polarization-maintaining fiber has an excellent birefringence effect, so that the difference between the propagation constants of the two orthogonal composition modes HEx11 and HEy11 of the fundamental mode transmitted therein is increased, and the coupling probability of the two orthogonal modes is reduced, thereby The polarization of the transmission line maintains its polarization state well. With the in-depth development of modulation from amplitude modulation to phase or polarization state in the fields of optical communication systems and optical fiber sensing, fiber optic technology has made great progress. The polarization-maintaining capability of polarization-maintaining fibers makes polarization-maintaining fibers useful in many polarization-related applications.

However, since the conventional polarization-maintaining fiber needs to adopt the core layer doping and the stress region is doped with boron, it is sensitive to external environmental interference. One of the most concerned issues of fiber optic gyro devices with conventional polarization-maintaining fibers as their core components is their temperature characteristics. Because when the temperature of the polarization-maintaining fiber changes from high to low or from low to high, since the stress characteristics of the materials in the various regions inside are different, when the temperature changes, stress fluctuations occur between the regions, resulting in stress fluctuations. The characteristics of optical signal transmission in different areas are different. Although people have invented four-pole, eight-pole and other symmetrical winding methods, they still cannot completely avoid this problem. In addition, since the conventional polarization maintaining fiber needs to ensure total reflection in the core layer, it is necessary to incorporate in the core layer. The amount of enthalpy, which also causes attenuation degradation in the irradiation environment, affecting the transmission of optical signals.

In order to solve the above problems, the emerging technology is Photonic Crystal Fibers (PCF). Photonic crystal fibers have many unique and novel physical properties that are difficult or impossible to achieve with conventional quartz single mode fibers (polarization maintaining fibers). By utilizing the flexible characteristics of the photonic crystal fiber, the single-mode transmission of the core layer can be realized by arranging the air holes in the cladding layer, and the special air hole arrangement structure can be used to realize the geometry of the arrangement structure when the optical signal is transmitted in the core layer. Birefringence results in a good birefringence effect. Compared with the conventional polarization-maintaining fiber, the stress region or the non-round core method, the photonic crystal fiber can obtain optical fibers with different mode field area, birefringence size and dispersion characteristics by various methods due to structural flexibility. These potential advantages lay the foundation for the replacement of polarization-maintaining fiber products in terms of transmission characteristics, structure, cost-performance ratio, and operating band expansion.

However, the existing photonic crystal fiber is also limited to the simple replacement of the performance of the conventional polarization maintaining fiber, that is, the arrangement of the air holes realizes a good birefringence effect to replace the birefringence effect of the conventional polarization maintaining fiber. However, there is still a certain limitation on the improvement of the optical fiber loss, and the existing photonic crystal fiber cannot meet the use requirements in special environmental applications such as aerospace, and therefore, it has been delayed. It is suitable for the practical research results of birefringent photonic crystal fiber developed by higher precision fiber optic gyroscope.

Summary of the invention

In view of the defects existing in the prior art, an object of the present invention is to provide a low-loss radiation-resistant birefringent photonic crystal fiber which has good low loss and radiation resistance while achieving birefringence, and can satisfy, for example, Requirements for use in special environmental applications such as aerospace.

In order to achieve the above object, the technical solution adopted by the present invention is: a low loss radiation-resistant birefringent photonic crystal fiber, including a central core, and the outer portion of the central core is internally to externally The outer layer is coated with an air hole layer and a quartz cladding layer, and the outer portion of the quartz cladding layer is coated with a coating layer, wherein the center core comprises a pure silicon core and a deep fluorine-doped outer layer coated on the outer side of the pure silicon core a concave inner cladding; the air hole layer includes a four-layer loop composed of air holes from the inside to the outside: a first layer loop, a second layer loop, a third layer loop, and a fourth layer loop The air hole is divided into a large air hole and a small air hole, and the first layer ring is composed of two large air holes and a plurality of small air holes, and the second layer ring, the third layer ring and the fourth layer ring are both The air holes of the four-layer ring are arranged in a regular hexagon shape, and all the air holes are connected by a quartz connecting wall; when the operating wavelength of the birefringent photonic crystal fiber is 1550 nm, the attenuation reaches 1 dB. Below /km, the crosstalk reaches -25dB/km; at 100krad total irradiation dose, the 1550nm induced loss increase is less than 2dB/km.

Based on the above technical solution, the first layer loop includes two large air holes and four small air holes, and the two large air holes are symmetrically distributed around the center core; the second layer ring is composed of 12 The small air hole is composed; the third layer ring and the fourth layer ring are all composed of 18 small air holes, and the fourth layer ring is arranged with a regular hexagonal hexagonal portion with a gap.

Based on the above technical solution, the small air hole has a radius of 1.2 um to 3.0 um; and the large air hole has a radius of 2.4 um to 4.8 um.

On the basis of the above technical solution, the relative refractive index difference between the pure silicon core and the deep fluorine-doped concave inner cladding is -0.50% to -0.05%; the refractive index of the quartz connecting wall and the pure silicon fiber The cores have equal refractive indices.

On the basis of the above technical solution, the radius of the pure silicon core is 2.0 um to 4.0 um; the radius of the deep fluorine-doped concave inner cladding is 2.5 um to 5.0 um; and the radius of the quartz connecting wall is 2.5 Um ~ 5.0um.

Based on the above technical solution, the quartz cladding has a diameter of 80 um to 135 um; and the coating layer has a diameter of 135 um to 250 um.

Based on the above technical solution, the large air hole and the small air hole adopt a partition The vertical air pressure control is formed by high temperature melting; the control air pressure of the large air hole is larger than the control air pressure of the small air hole.

Based on the above technical solution, the ratio of the control air pressure of the large air hole to the control air pressure of the small air hole is 1.0 to 1.3.

Based on the above technical solution, the coating layer is a single layer coating layer, which is made of a polyimide material and is heat-cured.

On the basis of the above technical solution, the coating layer is a double-layer coating, the Young's modulus of the inner coating layer is 0.2 MPa to 10 MPa, and the Young's modulus of the outer coating layer is 450 MPa to 2000 MPa, and The inner coating and the outer coating are both thermally cured or cured by ultraviolet curing.

The beneficial effects of the invention are:

1. The present invention optimizes the arrangement of the air hole layers of the conventional photonic crystal fiber, and forms a four-layer loop structure composed of air holes, wherein the first layer ring consists of two large air holes and a plurality of small holes. The air hole is composed of a second layer ring, a third layer ring and a fourth layer ring, which are all composed of a plurality of small air holes, and the air holes of the four layer rings are arranged in a regular hexagon shape, which can realize birefringence. At the same time, the light is effectively confined in the core region to realize low-loss optical signal transmission, so that the attenuation of the photonic crystal fiber of the present invention at 1550 nm is controlled within 1 dB/km (decibel/km), and crosstalk can be achieved - 25dB ~ -30dB / km, the beat length can reach 0.5 ~ 4.5mm.

On this basis, the core of the present invention adopts a pure silicon core, which is coated with a deep fluorine-doped concave inner cladding. Compared with the prior art, the pure silicon core avoids the introduction of the "color center" material, can effectively achieve the anti-irradiation characteristics, and the designed deep fluorine-doped concave inner cladding can not only block the immersion of some external pollution, but further The anti-irradiation performance of the optical fiber is ensured, so that the photonic crystal fiber of the present invention has an induced loss increase of 1550 nm of less than 2 dB/km at a total irradiation dose of 100 krad.

In summary, the present invention is optimized by air holes, pure silicon core and deep fluorine doping The design of the concave inner cladding enables the photonic crystal fiber to achieve good birefringence and good low loss and radiation resistance, which can meet the needs of special environmental applications such as aerospace.

2. In the present invention, the radius of the pure silicon core is 2.0 um to 4.0 um, the radius of the concave inner cladding layer is 2.5 um to 5.0 um, and the radius of the quartz connecting wall is 2.5 um to 5.0 um. Under the design of the air hole structure, the photonic crystal fiber can work well under a small bending radius. When the bending radius is 2mm, the crosstalk of the fiber at 1550nm can still reach below -25dB/km, and the additional attenuation is less than 0.5dB. Winding a smaller size fiber optic ring.

3. In the present invention, the outer portion of the quartz cladding is coated with a single layer or a double layer coating layer. In the case of a single-layer coating layer, the coating layer is made of a polyimide material and subjected to heat curing; if it is a double-layer coating layer, the inner coating has a Young's modulus of 0.2 MPa. The material of 10 MPa is coated with a material having a Young's modulus of 450 MPa to 2000 MPa, and the inner coating and the outer coating are both thermally cured or cured by ultraviolet curing. The special coating composition design can make the birefringent photonic crystal fiber have excellent full-temperature performance. In the range of -45 °C to 85 °C, the 1550 nm full-temperature crosstalk variation is less than 0.5 dB, which can be in space. Good work in harsh environments such as nuclear radiation.

4. In the present invention, the diameter of the quartz cladding is 80 um to 135 um, and the diameter of the coating layer is 135 um to 250 um, and birefringent photonic crystal fibers of different diameters can be formed according to different application requirements, and the application range is wide.

DRAWINGS

1 is a schematic structural view of a low-loss radiation-resistant birefringent photonic crystal fiber according to an embodiment of the present invention;

2 is a schematic structural view of an end face of a low-loss radiation-resistant birefringent photonic crystal fiber according to an embodiment of the present invention;

3 is a schematic structural view of a center core and a first layer loop in the embodiment of the present invention;

4 is a schematic view showing a waveguide structure of a pure silicon core in an embodiment of the present invention.

LIST OF REFERENCE NUMERALS: 1-center core, 11-pure silicon core, 12-deep fluorine-doped concave inner cladding; 2-air hole layer, 21-large air hole, 22-small air hole; 3-quartz cladding ; 4 coating layer.

detailed description

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

Referring to FIG. 1 and FIG. 2, an embodiment of the present invention provides a low-loss radiation-resistant birefringent photonic crystal fiber, including a center core 1, and an outer portion of the center core 1 is sequentially covered with air holes from the inside to the outside. Layer 2 and quartz cladding 3, the exterior of the quartz cladding 3 is coated with a single or double coating layer 4. Among them, the central core 1, the air hole layer 2 and the quartz cladding 3 constitute a quartz portion of the optical fiber.

Referring to FIG. 2 and FIG. 3, the central core 1 comprises a pure silicon core 11 and a deep fluorine-doped concave inner cladding 12 coated on the outside of the pure silicon core 11. The deep fluorine-doped concave inner cladding 12 can block The immersion of some external pollution has certain anti-irradiation performance, and can also provide a better design basis for the low loss transmission of photonic crystal fibers. The air hole layer 2 includes four layers of rings composed of air holes from the inside to the outside: a first layer ring, a second layer ring, a third layer ring and a fourth layer ring, the air holes are divided into large The air hole 21 and the small air hole 22 have a radius larger than the radius of the small air hole 22, and the first layer ring is composed of two large air holes 21 and a plurality of small air holes 22, and the second layer ring, The third layer ring and the fourth layer ring are each composed of a plurality of small air holes 22, and the air holes of the four layer rings are arranged in a regular hexagon shape, and all the air holes are connected by a quartz connecting wall.

Specifically, the first layer loop is disposed next to the center core 1, and includes two large air holes 21 and four small air holes 22, and the two large air holes 21 are symmetrically distributed around the center core 1; The layer ring is composed of 12 small air holes 22; the third layer ring and the fourth layer ring are each composed of 18 small air holes 22, and the fourth layer ring is arranged as a regular hexagonal hexagon. There are gaps. The total number of air holes of the four-layer loop is 54, wherein the number of large air holes 21 is two, and the number of small air holes 22 is 52. In this embodiment, the radius r is _small air holes 22 is small 1.2um ~ 3.0um; large radius r of the air hole 21 is _large 2.4um ~ 4.8um.

Referring to FIG. 3 and FIG. 4, it is assumed that the refractive index of the pure silicon core 11 is n _fiber (since it is a pure silicon core, it corresponds to the refractive index value of the pure silicon core quartz), and the radius is r _fiber ; concave inner cladding refractive index is _n-cladding 12, a radius r _packet; provided connecting walls quartz _walls having a refractive index n and radius r _wall.

The relative refractive index difference of the birefringent photonic crystal fiber is calculated as: Δ = (n1 - n2) / (n1 + n2) * 100%, where Δ is the relative refractive index difference. When pure silicon core 11 is calculated when the fluorine doped deep concave inner cladding relative refractive index difference between △ n _{fiber package} 12, the above formula is a value of n2 the refractive index n of pure silica core _fiber 11, taken N1 The value is the deep fluorine-doped concave inner cladding 12 refractive index n _package .

On the basis of this, as shown in FIG. 4, the waveguide structure of the pure silicon core 11 is a refractive index guiding type waveguide structure, and the relative refractive index difference between the pure silicon core 11 and the deep fluorine-doped concave inner cladding layer 12 is Δn. _{The fiber} diameter is -0.50% to -0.05%, and the refractive index n _{wall of the} quartz connecting wall is equal to the refractive index n _{fiber of the} pure silicon core 11, so that the photonic crystal fiber can achieve an excellent birefringence effect around 1550 nm. Meanwhile, pure silica core _fiber 11 has a radius r 2.0um ~ 4.0um, deep fluorine-doped depressed cladding the inner radius r of _{the package} 12 is 2.5um 5.0um, the quartz _{wall of} the connecting wall radius r of ~ 2.5um ~ 5.0um Under the optimized air hole structure design, the photonic crystal fiber can work well under a very small bending radius. When the bending radius is 2mm, the crosstalk of the fiber at 1550nm can still reach below -25dB/km, and the additional attenuation is less than 0.5. dB, which allows for the winding of smaller-sized fiber rings.

In the embodiment of the present invention, the diameter of the quartz cladding layer 3 is 80 um to 135 um, and the diameter of the coating layer 4 is 135 um to 250 um, which can form different diameters according to different application requirements. Refracted photonic crystal fibers.

Further, the large air hole 21 and the small air hole 22 are controlled by a partition independent air pressure and melt-molded at a high temperature. Wherein, the control air pressure P1 of the large air hole 21 is greater than the control air pressure P2 of the small air hole 22, so that the expansion ratio of the central hole formed by the large air hole 21 during the fiber forming process is larger than the outer ring ring composed of the small air hole 22. The expansion ratio. Specifically, the ratio of the control air pressure P1 of the large air hole 21 to the control air pressure P2 of the small air hole 22 is 1.0 to 1.3.

In actual production, when the outer layer of the quartz cladding layer 3 is coated with a single layer of the coating layer 4, the coating layer 4 is made of a polyimide material and thermally cured to obtain a photonic crystal fiber. The working temperature reaches 350 degrees or more. When the outer portion of the quartz cladding layer 3 is coated with the double-layer coating layer 4, the Young's modulus of the inner coating layer of the coating layer 4 is 0.2 MPa to 10 MPa, and the Young's modulus of the outer coating layer of the coating layer 4 The amount of 450 MPa to 2000 MPa, and the inner coating and the outer coating are both heat-cured or UV-cured, so that the obtained photonic crystal fiber has excellent full-temperature performance, in the range of -45 ° C to 85 ° C, The 1550 nm full temperature crosstalk variation is less than 0.5 dB.

When the operating wavelength of the birefringent photonic crystal fiber in the embodiment of the present invention is 1550 nm, the attenuation reaches 1 dB/km or less, and the crosstalk reaches -25 dB/km, which has excellent low loss performance; at a total irradiation dose of 100 krad, 1550 nm The induced loss increase value is less than 2dB/km and has excellent anti-irradiation performance.

The design principle of the low loss radiation resistant birefringent photonic crystal fiber in the present invention is as follows:

Birefringent photonic crystal fibers are designed with a refractive index-guided waveguide structure, which is consistent with the light guiding mechanism of conventional polarization-maintaining fibers, and is a total reflection principle. This requires that the core has a higher refractive index than the cladding. The refractive index-guided implementation of the conventional polarization-maintaining fiber is such that the core is doped with erbium to raise its refractive index, and the cladding is pure quartz, so that the refractive index of the core is higher than the refractive index of the cladding. For the photonic crystal fiber of the present invention, a plurality of air holes are distributed in the cladding, and the air holes will reduce the overall refractive index of the region in which it is located, thereby making the package The effective refractive index of the layer is reduced, so that the core is not doped with erbium, and the refractive index of the core can be made larger than the refractive index of the cladding, thereby achieving total reflection to transmit the optical signal. This will provide the basis for the design of radiation-resistant photonic crystal fibers.

For the radiation resistance of optical fibers, the main anti-irradiation implementation is to avoid introducing materials that cause "color center" defects, such as metal ions such as bismuth and aluminum, in the core of the light guide. Since the photonic crystal fiber is introduced into the air hole by the cladding layer to greatly reduce the effective refractive index of the cladding layer, this creates conditions for combining the characteristics of the anti-irradiation fiber and the photonic crystal fiber. To this end, the core of the photonic crystal fiber of the present invention adopts a pure silicon core 11 and the cladding is arranged in an air hole ring manner, which can realize total reflection light guiding and can effectively realize radiation resistance characteristics (because it is avoided) The introduction of "color center" materials). Of course, in the actual design, it is also necessary to consider the pollution transfer that may be caused to the core when the capillary tube forming the air hole is formed. In this case, it is necessary to design a special barrier layer between the core and the air hole, that is, in the present invention. Deeply doped with fluorine under the inner cladding layer 12, this layer of material can not only block the immersion of some external pollution, but also make the fiber have certain anti-irradiation performance, and can also provide a better design basis for the low loss transmission of photonic crystal fiber.

In the present invention, the surrounding silicon core 11 of the birefringent photonic crystal fiber is symmetrically introduced with two air holes (i.e., large air holes 21) which are inconsistent with other air hole sizes. The size of the two air holes is larger than the size of the other air holes, so that the effective refractive index of the cladding is sufficiently depressed in the region where the air holes are located, so that the mode field of the core transmission direction of the two air holes is compressed. Thereby, the mode of transmission in the core is an elliptical mode field, thereby achieving birefringence. On the basis of this, since the size of the large air hole 21 is different from the size ratio of the surrounding small air holes 22, different birefringence effects are caused, and the light transmission characteristics are also different, and the air hole ring around the core is combined. The number of turns will result in a better design of birefringent photonic crystal fibers.

Based on the above principle, the present invention optimizes the arrangement of air holes, the number of rings, and the like, and forms a four-layer loop composed of air holes, and the air holes of the four layers of rings are all positive six. The edge arrangement can effectively realize the low loss characteristic, and combined with the above-mentioned deep fluorine-doped concave inner cladding 12 design, thereby realizing a birefringent photonic crystal fiber with good low loss and radiation resistance, which satisfies, for example, aerospace. Demand for use in special environmental applications such as aviation.

The low loss radiation-resistant birefringent photonic crystal fiber of the present invention will be specifically described below by means of two embodiments.

Example 1: Five kinds of birefringent photonic crystal fibers treated with ultraviolet light curing using two layers of coating layer 4: fiber 1, fiber 2, fiber 3, fiber 4 and fiber 5, fiber 1, fiber 2, fiber 3, The specific parameters of fiber 4 and fiber 5 are shown in Table 1.

Table 1. Parameter Table of Five Types of Optical Fibers Cured by Ultraviolet Curing

Referring to Table 1, when the coating layer 4 was a double layer, the implementation of five kinds of optical fibers was carried out. It can be seen from the embodiment that when the operating wavelength is 1550 nm, the attenuation is controlled below 1 dB/km, the optimal value can reach 0.5 dB/km, and the crosstalk can reach -25 dB/km to -30 dB/km. It can reach 0.5mm~4.5mm and has excellent low loss performance. When the bending radius is 2mm, the crosstalk of the fiber at 1550nm can still reach -25dB/km, and the additional attenuation is still less than 0.5dB, which has superior bending resistance; Under the total irradiation dose of 100krad, the 1550nm induced loss increase value is less than 2dB/km, which has excellent anti-irradiation performance; in the range of -45°C～85°C, the 1550nm full-temperature crosstalk variation is less than 0.5dB, which is excellent. Full temperature performance.

Example 2: 5 kinds of birefringent photonic crystal fibers treated with a single layer of coating layer 4, which are thermally cured: optical fiber 6, optical fiber 7, optical fiber 8, optical fiber 9 and optical fiber 10, optical fiber 6, optical fiber 7, optical fiber 8, The specific parameters of the optical fiber 9 and the optical fiber 10 are shown in Table 2.

Table 2. Parameter Table of Five Types of Fibers Cured by Single Layer Coating

Referring to Table 2, when the coating layer 4 was a single layer, the implementation of five kinds of optical fibers was also carried out. It can be seen from the embodiment that when the operating wavelength is 1550 nm, the attenuation can still be controlled below 1 dB/km, the optimal value can reach 0.8 dB/km, and the crosstalk can reach -25 dB/km to -30 dB/km. The length of the beat can reach 0.5mm~4.5mm, and it also has excellent low loss performance. When the bending radius is 2mm, the crosstalk of the fiber at 1550nm can still reach -25dB/km, and the additional attenuation is still less than 0.5dB, which is also superior. Bending resistance; under the total irradiation dose of 100krad, the 1550nm induced loss increase value is less than 2dB/km, which also has excellent anti-irradiation performance; in the range of -45°C～85°C, the 1550nm full-temperature crosstalk variation is less than 0.5dB, also has excellent full temperature performance.

The present invention is not limited to the above embodiments, and those skilled in the art can also make several improvements and retouchings without departing from the principles of the present invention. These improvements and retouchings are also considered as protection of the present invention. Within the scope. The contents not described in detail in the present specification belong to the prior art well known to those skilled in the art.

Claims

A low-loss radiation-resistant birefringent photonic crystal fiber comprising a central core (1), the outer core of the central core (1) being sequentially coated with an air hole layer (2) and a quartz cladding layer from inside to outside (3) The outer portion of the quartz cladding (3) is coated with a coating layer (4), characterized in that the central core (1) comprises a pure silicon core (11) and is coated with a pure silicon core (11). ) an outer deep fluorine-doped concave inner cladding (12);

The air hole layer (2) includes four layers of loops composed of air holes from the inside to the outside: a first layer loop, a second layer loop, a third layer loop and a fourth layer loop, the air The hole is divided into a large air hole (21) and a small air hole (22), and the first layer ring is composed of two large air holes (21) and a plurality of small air holes (22), the second layer ring, the third ring The layer loop ring and the fourth layer loop ring are each composed of a plurality of small air holes (22), and the air holes of the four layer loops are arranged in a regular hexagon shape, and all the air holes are connected by a quartz connecting wall;

When the operating wavelength of the birefringent photonic crystal fiber is 1550 nm, the attenuation reaches 1 dB/km or less, and the crosstalk reaches -25 dB/km. Under the total irradiation dose of 100 krad, the 1550 nm induced loss increase value is less than 2 dB/km.
The low loss radiation resistant birefringent photonic crystal fiber according to claim 1, wherein said first layer loop comprises two large air holes (21) and four small air holes (22), 2 The large air holes (21) are symmetrically distributed around the center core (1); the second layer ring is composed of 12 small air holes (22); the third layer ring and the fourth layer ring are all 18 The small air holes (22) are composed, and the hexagons of the regular hexagons arranged in the fourth layer ring are provided with a gap.
A low loss radiation-resistant birefringent photonic crystal fiber according to claim 1, wherein said small air hole (22) has a radius of 1.2 um to 3.0 um; and a radius of said large air hole (21) It is 2.4um to 4.8um.
The low loss radiation resistant birefringent photonic crystal fiber of claim 1 The characteristic is that the relative refractive index difference between the pure silicon core (11) and the deep fluorine-doped concave inner cladding layer (12) is -0.50% to -0.05%; the refractive index and the purity of the quartz connecting wall are pure The refractive indices of the silicon cores (11) are equal.
The low-loss radiation-resistant birefringent photonic crystal fiber according to claim 1, wherein the pure silicon core (11) has a radius of 2.0 um to 4.0 um; and the deep fluorine-doped concave inner cladding The radius of (12) is 2.5 um to 5.0 um; the radius of the quartz connecting wall is 2.5 um to 5.0 um.
A low loss radiation-resistant birefringent photonic crystal fiber according to claim 1, wherein said quartz cladding (3) has a diameter of 80 um to 135 um; and said coating layer (4) has a diameter of 135 um ~250um.
The low-loss radiation-resistant birefringent photonic crystal fiber according to claim 1, wherein the large air hole (21) and the small air hole (22) are controlled by a partition independent air pressure and melted at a high temperature. The control air pressure of the large air hole (21) is greater than the control air pressure of the small air hole (22).
The low loss radiation-resistant birefringent photonic crystal fiber according to claim 7, wherein a ratio of a control air pressure of said large air hole (21) to a control air pressure of said small air hole (22) is 1.0 to 1.3. .
The low loss radiation-resistant birefringent photonic crystal fiber according to any one of claims 1 to 8, wherein the coating layer (4) is a single layer coating using polyimide Material and heat cured.
The low loss radiation-resistant birefringent photonic crystal fiber according to any one of claims 1 to 8, wherein the coating layer (4) is a double-layer coating, and the inner coating of the yang The modulus of the coating is 0.2 MPa to 10 MPa, the Young's modulus of the outer coating layer is 450 MPa to 2000 MPa, and the inner coating layer and the outer coating layer are both thermally cured or cured by ultraviolet curing.