CN106908895B - An all-solid-state broadband dispersion-compensated index-guided microstructured fiber - Google Patents

Abstract

An all-solid-state broadband dispersion-compensated refractive index-guided microstructure optical fiber comprises inner and outer core cylinders, cladding cylinders and a base material, wherein the base material is pure silica, and the inner core cylinder is germanium-doped pure silica Rod, the outer core cylinder is a layer of fluorine- or boron-doped pure quartz rods closely arranged in a regular hexagon; the cladding cylinder is a fluorine- or boron-doped pure quartz rod closely arranged in a regular hexagon; the inner core The refractive index of the cylinder is greater than the refractive index of the base material, the refractive index of the base material is greater than the refractive index of the outer core cylinder, the refractive index of the outer core cylinder is greater than the refractive index of the cladding cylinder; the diameter of the cladding cylinder is the same and larger than that of the outer core Cylinder diameter, the inner core cylinder diameter is larger than the outer core cylinder diameter; the column spacing of all cylinders is equal. The invention is easy to prepare and easy to couple with the traditional optical fiber, can perform broadband dispersion compensation for the accumulated dispersion in the high-speed dense wavelength division multiplexing optical fiber communication transmission process, and provide an effective transmission medium for the optical fiber communication system.

Description

An all-solid-state broadband dispersion-compensated index-guided microstructured fiber

technical field

The invention belongs to the technical field of optical fibers, and particularly relates to a microstructure optical fiber.

Background technique

In modern optical fiber communication systems, especially high-speed dense wavelength-division multiplexing optical fiber communication systems, the accumulated dispersion during transmission becomes the main limitation for such systems. Therefore, broadband dispersion compensation for high-speed dense wavelength division multiplexing optical fiber communication systems has become a research hotspot.

With the continuous understanding of the theoretical research and preparation technology of microstructured fibers (also known as photonic crystal fibers), it has been found that by adjusting the microstructure design of the fiber, the dispersion properties of the fiber can be greatly adjusted, such as the dispersion flatness of the fiber, dispersion compensation characteristics, etc.

At present, the research on dispersion-compensated microstructured fibers mainly focuses on hollow-core, all-solid bandgap and air-hole-quartz structure index-guided microstructured fibers. However, the bandgap optical fiber limits the light guide window and is not suitable as a transmission medium; the microstructure optical fiber with air hole-quartz structure is not easy to couple with the traditional optical fiber, and the air hole in the cladding is easy to be caused by the high temperature during the drawing process. Disadvantages such as collapse or deformation occur.

Since the all-solid index-guided microstructure fiber is composed of medium columns with different refractive indices instead of air holes, it is suitable for transmission media and has the advantages of easy coupling with traditional optical fibers and easy preparation, which can effectively solve the above-mentioned hollow, all-solid Problems with bandgap and air hole-quartz structure index-guided microstructured fibers. At present, some researchers have carried out research on the all-solid index-guided microstructured fiber, but they mainly study its dispersion flattening characteristics and large mode area characteristics. This type of optical fiber can effectively transmit signals in optical fiber communication, but does not have dispersion compensation characteristics, and cannot compensate for the accumulated dispersion in the transmission process of optical fiber communication.

At present, no researchers have studied the dispersion compensation characteristics of all-solid index-guided microstructured fibers, and only two reports have been found that are closely related to all-solid dispersion-compensated microstructured fibers. First, Gautam Prabhakar et al. designed a local all-solid dispersion-compensated refractive index-guided microstructure fiber. Although the fiber has single-point dispersion compensation characteristics or broadband dispersion compensation characteristics, the fiber still contains two layers of circular air holes. Coupling with traditional optical fibers, the air holes in the cladding are prone to collapse or deformation due to excessive temperature during the drawing process. Second, He Fengliang et al. designed an all-solid dispersion compensation bandgap microstructure fiber. Although the fiber has the characteristics of multiple zero dispersion points and negative dispersion compensation, the fiber is a bandgap fiber, which limits the light guide window and is not suitable for as a transmission medium.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an all-solid-state broadband that is easy to prepare, easy to couple with traditional optical fibers, can perform broadband dispersion compensation for the accumulated dispersion in the transmission process of high-speed dense wavelength division multiplexing optical fiber communication, and can provide an effective transmission medium for optical fiber communication systems. Dispersion-compensated index-guided microstructured fibers.

The invention includes inner and outer layer core cylinders, cladding cylinders and base material, wherein the base material is pure quartz, the inner core cylinder is pure quartz rod doped with germanium, and the outer core cylinder is a layer according to a regular hexagon. Closely arranged fluorine- or boron-doped pure silica rods; cladding cylinders are fluorine- or boron-doped pure silica rods closely arranged according to regular hexagons; the refractive index of the inner core cylinder is greater than that of the base material, and the refractive index of the base material is The refractive index of the outer core cylinder is greater than that of the outer core cylinder, and the refractive index of the outer core cylinder is greater than the refractive index of the cladding cylinder; the diameters of all cladding cylinders are the same and larger than the diameter of the outer core cylinder, and the inner core cylinder diameter is greater than that of the outer core Cylinder diameter; all cylinders are equally spaced.

The base material has a refractive index of 1.45;

The refractive index of the inner core cylinder is 1.45-1.485;

The refractive index of the outer core cylinder is 1.44-1.45;

The refractive index of the cladding cylinder is 1.425-1.44;

The diameter of the inner layer core cylinder is 1.2-2.0 μm;

The diameter of the outer core cylinder is 0.43-0.59 μm;

The diameter of the cladding cylinder is 0.8-1.8 μm;

The column spacing of all the columns is 1.8-2.4 μm.

The total number of the cladding layers is 6 layers, there are three layers between the inner layer core and the outer layer core, and there are three layers outside the outer layer core.

Compared with the prior art, the present invention has the following advantages:

1. The optical fiber is a double-layer core structure, and a large negative dispersion value is obtained by using the coupling mechanism between the inner core and the outer core mode.

2. By designing appropriate refractive index and diameter of inner and outer core cylinders, refractive index and diameter of cladding cylinders, and column spacing, broadband dispersion compensation characteristics can be obtained.

3. The all-solid structure reduces the complexity of the fiber-forming process, is easy to prepare, and is easy to couple with traditional optical fibers.

4. The refractive index-guided microstructure fiber does not limit the light guide window and can be used as an effective transmission medium.

Description of drawings

FIG. 1 is a schematic cross-sectional view of the structure of the present invention.

FIG. 2 is a refractive index distribution diagram of Example 1 of the present invention.

3 is a graph showing the change of the effective refractive index of the fundamental mode with wavelength and the mode field distribution diagram of the fundamental mode at different wavelengths according to Embodiment 1 of the present invention.

FIG. 4 is a graph showing the relationship between dispersion value and wavelength in Example 1 of the present invention.

5 is a graph showing the relationship between the kappa value and the wavelength in Example 1 of the present invention.

FIG. 6 is a residual dispersion curve diagram of Example 1 of the present invention.

In the figure: 1-inner core cylinder, 2-outer core cylinder, 3-cladding cylinder, 4-base material, 5-column spacing between cylinders, 6-refractive index of inner core cylinder, 7- The refractive index of the outer core cylinder, 8- The refractive index of the cladding cylinder.

Detailed ways

Example 1

In the schematic diagram of the all-solid-state broadband dispersion-compensated refractive index-guided microstructure fiber shown in FIG. 1 , the base material 4 is pure silica, the inner core cylinder 1 is a germanium-doped pure silica rod, and the outer core cylinder 2 is a The layers are fluorine-doped pure quartz rods closely arranged in a regular hexagon; the cladding cylinder 3 is a fluorine-doped pure quartz rod closely arranged according to a regular hexagon; The diameter of the core cylinder is 0.51 μm, the diameter of the inner core cylinder is 1.6 μm, and the column spacing of all cylinders is equal, which is 2.1 μm; the total number of cladding layers is 6, between the inner core and the outer core. There are three layers, and there are three layers outside the outer core; as shown in Figure 2, the refractive index n ₀ of the base material is 1.45, the refractive index n ₁ of the inner core cylinder is 1.48, and the refractive index n ₂ of the outer core cylinder is 1.445 , the cladding cylindrical refractive index n ₃ is 1.43.

The cylindrical refractive index of the inner core and the outer core are both greater than the refractive index of the cladding cylinder, forming a microstructure fiber based on total internal reflection light guide. The refractive index and diameter of the cladding cylinder, as well as the column spacing, can flexibly adjust the dispersion characteristics. The multipole method is used for theoretical calculation to obtain the effective refractive index change of the fundamental mode of the optical fiber according to the present invention with wavelength and the mode field distribution of the fundamental mode at different wavelengths. As shown in Figure 3. It can be seen from the figure that at a certain wavelength, the refractive index changes abruptly, and this wavelength is called the phase matching wavelength λ _p . When the wavelength is less than the phase matching wavelength, the fundamental mode propagates in the inner core, and the effective refractive index of the inner core fundamental mode is greater than the effective refractive index of the outer core high-order mode; when the wavelength is equal to the phase matching wavelength, the inner core fundamental mode and The effective refractive indices of the high-order modes of the outer core are equal, so that the two are coupled, that is, the fundamental mode of the inner core is converted into the outer core to propagate, and the higher-order modes of the outer core are converted to propagate in the inner core. When the wavelength is greater than the phase matching wavelength, the energy of the fundamental mode of the inner core is gradually coupled to the outer core, and the effective refractive index of the fundamental mode of the outer core is greater than the effective refractive index of the high-order mode of the inner core.

Since the dispersion of optical fiber varies with wavelength, in order to meet the needs of broadband dispersion compensation, it is necessary to consider the compensation of dispersion and dispersion slope at the same time. In order to consider the factors of dispersion and dispersion slope at the same time, a new parameter kappa (K) is defined. , whose expression is K=D/D _slope . It represents the device's ability to simultaneously compensate for fiber dispersion and dispersion slope. In order to achieve ideal broadband dispersion compensation, it is generally required that the kappa value of the dispersion compensating fiber is close to or equal to that of the fiber being compensated.

As shown in Figure 4 and Figure 5, it can be seen from the figures that at the phase matching wavelength, the dispersion value changes abruptly. And before the phase matching wavelength, the dispersion value has a negative dispersion value and a negative dispersion slope, which meets the needs of broadband dispersion compensation. In the range of 1500nm～1600nm, the dispersion value varies within -220ps/nm·km～-163ps/nm·km, the Kappa value of the optical fiber of the present invention is very close to that of the standard single-mode fiber, and at 1538nm It is equal to the two kappa values at 1578nm, and has good broadband dispersion compensation characteristics.

As shown in Figure 6, it can be seen from the figure that in the range of 1500nm to 1600nm, after the optical fiber of the present invention compensates 10.69 times the standard single-mode fiber, the residual dispersion is nearly zero and flat, which further shows that the optical fiber of the present invention has good Broadband dispersion compensation characteristics.

Example 2

The base material is pure quartz, the inner core cylinder is a germanium-doped pure quartz rod, the outer core cylinder is a layer of boron-doped pure quartz rods closely arranged in a regular hexagon; the cladding cylinder is a regular hexagonal close Arranged boron-doped pure quartz rods; all cladding cylinders have the same diameter, 1.0 μm, the outer core cylinder diameter is 0.43 μm, the inner core cylinder diameter is 2.0 μm, and the column spacing of all cylinders is equal, all is 1.8μm; the total number of cladding layers is 6, there are three layers between the inner core and the outer core, and there are three layers outside the outer core; the refractive index n ₀ of the base material is 1.45, and the inner core is cylindrical The refractive index _n1 is 1.46, the outer core cylindrical refractive index _n2 is 1.44, and the cladding cylindrical refractive index _n3 is 1.425.

The above-mentioned embodiments are only to describe the preferred embodiments of the present invention, and do not limit the scope of the present invention. On the premise of not departing from the design spirit of the present invention, those of ordinary skill in the art can Such deformations and improvements shall fall within the protection scope determined by the claims of the present invention.

Claims (2)

1. an all-solid-state broadband dispersion compensation refractive index guided microstructure optical fiber, it comprises inner and outer layer core cylinder, cladding cylinder and base material, it is characterized in that: described base material is pure quartz, inner layer core The cylinder is a germanium-doped pure quartz rod, the outer core cylinder is a layer of fluorine- or boron-doped pure quartz rods closely arranged in a regular hexagon; the cladding cylinder is a fluorine- or boron-doped pure quartz rod closely arranged in a regular hexagon. Quartz rod; the refractive index of the inner core cylinder is greater than the refractive index of the base material, the refractive index of the base material is greater than the refractive index of the outer core cylinder, and the refractive index of the outer core cylinder is greater than the refractive index of the cladding cylinder; the diameter of all cladding cylinders The same and larger than the outer core cylinder diameter, the inner core cylinder diameter is larger than the outer core cylinder diameter; the column spacing of all cylinders is equal; The refractive index of the optical fiber base material is 1.45; the refractive index of the inner core cylinder of the optical fiber is in the range of 1.45 to 1.485; the refractive index of the outer core cylinder of the optical fiber is in the range of 1.44 to 1.45; the refractive index of the optical fiber cladding cylinder The rate range is 1.425-1.44; the diameter of the inner core cylinder of the optical fiber is 1.2-2.0 μm; the diameter of the outer core cylinder of the optical fiber is 0.4-0.59 μm; the diameter of the fiber cladding cylinder is 0.8-1.8 μm ; The column spacing of all the above cylinders is 1.8 ~ 2.4μm; The cylindrical refractive index of the inner core and the outer core are both greater than the refractive index of the cladding cylinder, forming a microstructure optical fiber based on total internal reflection light guide. By flexibly setting the refractive index and diameter of the inner and outer core cylinders, The refractive index and diameter of the cladding cylinder, as well as the column spacing, can flexibly adjust the dispersion characteristics; When the wavelength is less than the phase matching wavelength, the fundamental mode propagates in the inner core, and the effective refractive index of the inner core fundamental mode is greater than the effective refractive index of the outer core high-order mode; when the wavelength is equal to the phase matching wavelength, the inner core fundamental mode and The effective refractive index of the high-order mode of the outer core is equal, so that the fundamental mode of the inner core and the high-order mode of the outer core are coupled, that is, the fundamental mode of the inner core is converted to propagate in the outer core, and the high-order mode of the outer core is converted to propagate in the inner core, When the wavelength is greater than the phase matching wavelength, the energy of the fundamental mode of the inner core is gradually coupled to the outer core, and the effective refractive index of the fundamental mode of the outer core is greater than the effective refractive index of the high-order mode of the inner core; Since the dispersion of the fiber varies with wavelength, in order to meet the needs of broadband dispersion compensation, it is necessary to consider the simultaneous compensation of dispersion and dispersion slope, in order to consider the factors of dispersion and dispersion slope at the same time; before the phase matching wavelength, the dispersion value has a negative dispersion value and negative dispersion slope, to meet the needs of broadband dispersion compensation, in the wavelength range of 1500nm ~ 1600nm, the dispersion value changes within -220ps/nm·km ~ -163ps/nm·km, the Kappa value of the fiber is close to the standard single The Kappa value of the mode fiber, and the Kappa value of the fiber at 1538nm and 1578nm is equal to that of the standard single-mode fiber, which has good broadband dispersion compensation characteristics. 2. The all-solid-state broadband dispersion-compensated refractive index-guided microstructure optical fiber according to claim 1, wherein the total number of layers of the optical fiber cladding is 6 layers, between the inner core and the outer core There are three layers, and there are three layers outside the outer core.

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