CN106707408A - Graded index fiber based on ring-structure fiber core - Google Patents

Abstract

The invention relates to a graded refractive index optical fiber based on a ring-shaped core. The fiber core of the optical fiber adopts a ring structure; the refractive index distribution mode of the ring-shaped core adopts a graded type.

Description

A Gradient Index Fiber Based on Ring Structure Core

technical field

The present invention relates to the technical field of optical fibers for optical communication applications, and more specifically, to a graded-index optical fiber based on a ring-shaped core.

Background technique

As a cheap and efficient optical waveguide, optical fiber has been widely used in the field of communication, but the limited channel capacity of optical fiber itself restricts the development of the entire optical fiber communication system.

At present, the use of multiplexing technology is the core solution to increase the capacity of Fiber Channel, but the current development trend of the capacity of commercial optical fiber communication systems cannot meet people's needs; part of the reason is that the traditional multiplexing technology has been perfected after years of research , unable to bring a breakthrough improvement to the channel capacity. In order to further improve the communication capacity, the prior art proposes a space-division multiplexing scheme, which relies on few-mode fibers to multiplex a small number of beam modes in the few-mode fibers; this multiplexing scheme is due to the relatively large number of multiplexing modes. Less, the algorithm is relatively simple. In order to increase the number of multiplexed channels, multiplexing schemes based on multi-core optical fibers or multimode optical fibers have appeared in the prior art; however, the crosstalk of channels in these schemes is particularly serious, and the solution to these crosstalks is very dependent on chip algorithms; at the same time, The multipath effect brought by multi-mode also restricts the expansion of communication capacity.

Therefore, the existing technology proposes to use the orbital angular momentum mode in the optical fiber as the base mode for multiplexing. In the prior art, the optical fiber generally used for the transmission of the orbital angular momentum mode is a step ring optical fiber. This optical fiber matches the orbital angle The shape of the momentum mode can group the modes in the fiber into two groups, thus reducing the difficulty of the algorithm. However, this core structure has a strong spin-orbit angular momentum coupling effect, which leads to a more complicated polarization state in it. In addition, since the orbital angular momentum is easily disturbed, this kind of fiber core cannot guarantee the long-distance stable transmission of specific mode groups.

Contents of the invention

The problem to be solved by the present invention is to provide a graded-refractive-index optical fiber based on a ring-shaped core for stable long-distance transmission.

The technical scheme that the present invention proposes for realizing the above object is as follows:

Based on the graded-refractive-index optical fiber with a ring-shaped core, the fiber core of the optical fiber adopts a ring structure; the refractive index distribution mode of the ring-shaped core adopts a graded type.

In the above scheme, the core of the optical fiber adopts a ring structure, which limits the radial divergence of the optical modes transmitted in the core, and simplifies the coupling in the mode group; wherein, the refractive index distribution mode of the core adopts a gradient type, which improves The degeneracy of the modes in the same mode group reduces the spin-orbital angular momentum coupling of the transmission mode; eliminates the influence of the refractive index boundary, reduces the spin-orbital angular momentum coupling effect of the mode in the core, and makes the orbital angular momentum The polarization state of the mode is closer to left-handed circular or right-handed circular polarization, which is more conducive to the synthesis and decomposition of free space; the graded-index optical fiber transmits data in the form of mode groups, which effectively reduces the coupling standard between mode groups and improves the mode The distance of group transmission realizes stable, long-distance, and relatively simple algorithm communication.

Preferably, the inner diameter of the annular structure fiber core is 1um-30um, and the ring width is 1um-5um.

Preferably, the core of the annular structure is doped with silicon dioxide; the inner diameter of the core of the annular structure is filled with air or is doped with silicon dioxide.

Preferably, the graded refractive index distribution of the fiber core satisfies the following formula:

Among them, r is the radial coordinate of the polar coordinates with the center of the core as the origin, R is the distance from half the core ring width of the ring structure to the fiber core, w ₁ represents the width of half the core ring width of the ring structure, and w ₂ represents The width of half the ring width of the annular structure core, n _core is the refractive index of the inner diameter of the annular structure core, n _cladding indicates the refractive index of the outer diameter of the annular structure core, n _max is the maximum value of the ring structure core refractive index; Δ ₁ and _Δz are respectively:

Preferably, grooves with low refractive index are opened on the outer surface of the annular structure core. Strengthen the restriction on the mode in the fiber core and improve the transmission efficiency of the mode.

Compared with prior art, the beneficial effect of the present invention is:

The graded-index optical fiber based on the annular structure core proposed by the present invention, the core of the optical fiber adopts an annular structure, which limits the radial divergence of the optical modes transmitted in the core, and simplifies the coupling in the mode group; in the annular The inside and outside of the structural fiber core are doped with materials. At the same time, the refractive index of the material inside and outside the core can be adjusted. Among them, the refractive index distribution of the fiber core adopts a gradient type, which improves the degeneracy of the modes in the same mode group and reduces The spin-orbit angular momentum coupling of the transmission mode eliminates the influence of the refractive index boundary, reduces the spin-orbit angular momentum coupling effect of the mode in the fiber core, improves the transmission distance of the mode group, and realizes stability, long distance, and relatively fast algorithm. Simple communication.

Description of drawings

Fig. 1(a) is a schematic structural diagram of an optical fiber of the present invention.

Figure 1(b) is a graph of the refractive index distribution on the cross-sectional diameter line.

detailed description

The accompanying drawings are for illustrative purposes only and cannot be construed as limiting the patent;

In order to better illustrate this embodiment, some parts in the drawings will be omitted, enlarged or reduced, and do not represent the size of the actual product;

For those skilled in the art, it is understandable that some well-known structures and descriptions thereof may be omitted in the drawings.

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

A graded-index optical fiber based on a ring-shaped core, its structural schematic diagram is shown in Figure 1: Figure 1 (a) is a cross-sectional view of the optical fiber, and Figure 1 (b) is a refractive index profile on the cross-sectional diameter line, where , the structure of Fig. 1(a) is as follows: 1 is the outer interface of the fiber cladding, 2 is the outer diameter of the annular structure core, 3 is the position of the maximum refractive index inside the fiber core, and 4 is the inner diameter of the annular structure core; The refractive index distribution diagram shown in 1(b) corresponds to the cross-section of the optical fiber in Figure 1(a), and the refractive index between the outer diameter 2 of the core and the outer interface 1 of the fiber cladding is zero; the ring-shaped core The refractive index at the outer diameter 2 is n _cladding , and the refractive index at the inner diameter 4 of the annular structure core is n _core ; the refractive index is reached at 3 places between the outer diameter 2 of the annular structure core and the inner diameter 4 of the annular structure core. The maximum value n _max , wherein, the distance from the 3 places to the center of the fiber is the radius R; the distance w ₂ between the outer diameters of the annular structure core 2 to 3 is half of the ring width of the annular structure core, and the inner diameter of the core ring is The distance w ₁ between 4 and 3 is half of the core ring width of the ring structure.

In this embodiment, the inner diameter of the core of the ring structure is 1um-30um, and the ring width is 1um-5um; wherein, the core of the ring structure is doped with silica; the inner diameter of the core of the ring structure is Air-filled or doped with silica.

Wherein, in this embodiment, the graded refractive index distribution of the fiber core satisfies the following formula:

Among them, r is the radial coordinate of the polar coordinates with the center of the core as the origin, R is the distance from half the core ring width of the ring structure to the fiber core, w ₁ represents the width of half the core ring width of the ring structure, and w ₂ represents Half the ring width of the ring structure core, n _core is the refractive index at the inner diameter of the ring structure core, n _cladding is the refractive index at the outer diameter of the ring structure core, and n _max is the maximum value of the ring structure core refractive index ; Δ ₁ and Δ ₂ are:

In this embodiment, the core of the optical fiber adopts a ring structure to limit the radial divergence of the optical modes transmitted in the core, so that the radial order of the mode is one. Except for the two fundamental modes, the mode group The number of modes in the model is controlled to four, and they are sorted from low-order modes to high-order modes; the four modes in the mode group are degenerated, and the mode isolation between the mode groups is relatively high, which simplifies the coupling within the mode group.

At the same time, in this embodiment, the inner diameter and outer diameter of the ring-shaped core are doped with materials, and the number of mode groups and the effective refractive index difference between the mode groups can be adjusted by controlling the structural size and refractive index parameters of the ring fiber. ; At the same time, a low-refractive-index groove is added outside the core of the annular structure to strengthen the confinement of the mode in the core.

The refractive index distribution of the fiber core adopts a gradual change type, and the transmission is based on the orbital angular momentum mode; the degeneracy of the modes in the same mode group is improved, and the spin-orbital angular momentum coupling of the transmission mode is reduced; the influence of the refractive index boundary is eliminated. The spin-orbital angular momentum coupling effect of the mode in the core is reduced, so that the polarization state of the orbital angular momentum mode is closer to left-handed circular or right-handed circular polarization, which is more conducive to the synthesis and decomposition of free space; Data transmission in the form of mode groups effectively reduces the coupling standard between mode groups, improves the transmission distance of mode groups, and realizes stable, long-distance, and simpler algorithm communication.

Apparently, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the implementation of the present invention. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. All modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (5)

1. a kind of graded index fiber based on loop configuration fibre core, it is characterised in that：The fibre core of optical fiber uses ring junction Structure；The index distribution mode of the fibre core of the loop configuration uses gradation type.

2. the graded index fiber based on loop configuration fibre core according to claim 1, it is characterised in that：The ring The internal diameter of shape structure fibre core is 1um~30um, and ring width is 1um~5um.

3. the graded index fiber based on loop configuration fibre core according to claim 1, it is characterised in that：The ring The fibre core of shape structure is doped with silica；Air is filled in the internal diameter of the fibre core of the loop configuration or doped with titanium dioxide Silicon.

4. the graded index fiber based on loop configuration fibre core according to claim 1, it is characterised in that：The fibre The gradation type index distribution of core meets below equation：

$n\left(r\right)=\left\{\begin{array}{cc}{n}_{core}& r<R-w_1\\ n_{max}\sqrt{1-2_{\mathrm{\&Delta;}1}{\left(\right(R-r)/w_1)}^{\mathrm{\&alpha;}}}& R-w_1<r<R\\ n_{max}\sqrt{1-2_{\mathrm{\&Delta;}2}{\left(\right(r-R)/w_2)}^{\mathrm{\&alpha;}}}& R<r<R+w_2\\ n_{cladding}& R+w_2<r\end{array}\right.;$

Wherein, r is the polar radial coordinate with the fibre core center of circle as origin, and R is the half of loop configuration fibre core ring width to fibre The distance of core, w₁Represent the width of loop configuration fibre core ring width half, w₂The width of loop configuration fibre core ring width half is represented, n_coreIt is the refractive index of loop configuration fibre core inner radius, n_claddingRepresent the refractive index of loop configuration fibre core outer radius, n_maxIt is ring The maximum of shape structure fiber core refractive index；Δ₁With Δ₂It is respectively：

${\mathrm{\&Delta;}}_1=\frac{{n_{\max }}^2-{n_{core}}^2}{2*n_{max}},{\mathrm{\&Delta;}}_2=\frac{{n_{\max }}^2-{n_{cladding}}^2}{2*n_{max}}.$

5. the graded index fiber based on loop configuration fibre core according to claims 1 to 4, it is characterised in that：Institute The low groove of refractive index is offered on the outer surface of the loop configuration fibre core stated.