CN112666650B

CN112666650B - Large cross section single mode optical fiber

Info

Publication number: CN112666650B
Application number: CN202011606142.4A
Authority: CN
Inventors: 余学才; 秦宗; 郭甜; 李陈
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2020-12-30
Filing date: 2020-12-30
Publication date: 2022-07-22
Anticipated expiration: 2040-12-30
Also published as: CN112666650A

Abstract

The invention discloses a large-cross-section single-mode optical fiber, which comprises a core layer structure and a cladding layer structure, wherein the core layer structure comprises two lightly doped SiO fibers with unequal radiuses and semicircular cross sections₂The planes of the diameters of the two core layers are attached to each other, and the circle centers of the cross sections are superposed; the cladding structure is wrapped at the periphery of the core layer structure, the cross section of the outer edge of the cladding structure is circular, the circle center of the cladding structure coincides with that of the cross section of the core layer, and the cladding structure is heavily doped SiO₂And (4) forming. The optical fiber core layer has larger sectional area, and is beneficial to transmitting high-power single-mode light.

Description

Large cross section single mode optical fiber

Technical Field

The invention belongs to the field of optical fiber communication, and particularly relates to an optical fiber with a large cross-sectional area.

Background

With the rapid development of optical fiber technology, it is increasingly applied in the fields of optical fiber communication, laser processing, high-power weaponry, etc. With the increasing demand for optical power transmitted in optical fiber, the common single mode optical fiber also faces many problems. As the power transmitted in the optical fiber is higher and higher, nonlinear effects such as stimulated raman scattering and stimulated brillouin scattering, etc., which generally reduce the efficiency of laser transmission, and the transmitted high optical power may damage the optical fiber. There are large cross-section multimode commercial fibers available but there is a lack of large cross-section single mode fibers.

In recent years, as researchers have continuously searched, designed and manufactured, various new single mode optical fibers having a large mode field cross section have been proposed in succession, and among them, single mode photonic crystal fibers have been intensively studied. The optical fiber has the advantages of realizing large-mode-field single-mode transmission, and having the characteristics of high birefringence, low limiting loss, adjustable chromatic dispersion and the like. However, the structure of the photonic crystal fiber with a large mode field area is very complex, which brings many problems to the process technology, so that the manufacturing cost is high, and the photonic crystal fiber cannot be widely used. In addition to photonic crystal fibers, the lobed fiber is considered to be another effective way to achieve ultra-large mode field single mode operation. The optical fiber is periodically composed of a high-refractive-index fiber core and a fan-shaped segmented cladding with high and low refractive indexes alternately distributed. By such a leakage structure, low loss transmission of the fundamental mode and high order mode suppression capability can be maintained, and good beam quality can be maintained while obtaining a large mode field condition. However, these optical fibers have a fatal disadvantage that they are difficult to manufacture in terms of process, so that the manufacturing cost is greatly increased and they cannot be widely used.

Fig. 1 and 2 show two common fiber configurations: FIG. 1 shows a conventional single mode optical fiber with a small core radius, large mode loss, and low nonlinear threshold; FIG. 2 is a single mode photonic crystal fiber, which is complex to fabricate.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a single-mode optical fiber which is large in sectional area and relatively easy to prepare.

The invention is realized by the following technical scheme: the large-cross-section single-mode optical fiber comprises a core layer structure and a cladding layer structure, wherein the core layer structure comprises two lightly doped SiO layers with unequal radiuses and semicircular cross sections₂The planes of the diameters of the two core layers are attached to each other, and the circle centers of the cross sections of the two core layers are superposed; the cladding structure is wrapped at the periphery of the core layer structure, the cross section of the outer edge of the cladding structure is circular, the circle center of the cladding structure coincides with that of the cross section of the core layer, and the cladding structure is heavily doped SiO₂And (4) forming.

Furthermore, the doping of the core layer structure is Ge or P, and the doping of the cladding layer structure is B or F.

The invention has the beneficial effects that: compared with the traditional optical fiber, the large-cross-section single-mode optical fiber has the following advantages: (1) the sectional area of the optical fiber core layer is larger; (2) compared with special optical fibers such as photonic crystals and the like, the preparation process is easy to realize, and the preparation cost is relatively low; (3) compared with the common optical fiber, the optical fiber has the advantages that the core layer of the optical fiber is larger, the mode is bound more, and the loss is smaller; (4) by adjusting the ratio of the radius R and the radius R of the two semicircles of the core layer, a high-order mode is inhibited; (5) the invention can realize high-efficiency coupling of the transmission mode and the ridge type optical waveguide due to the special geometrical structure of the ridge type optical waveguide.

Drawings

FIG. 1 is a cross-sectional view of a conventional optical fiber;

FIG. 2 is a cross-sectional view of a photonic crystal fiber;

FIG. 3 is a cross-sectional view of a large cross-section single mode optical fiber of the present invention;

FIG. 4 is a cross-sectional view of a ridge optical waveguide;

FIG. 5 shows the calculation results of the fundamental modes of the large-cross-section single-mode fiber and the common multimode fiber.

Detailed Description

The technical scheme of the invention is further explained by combining the attached drawings.

As shown in FIG. 3, the large cross-section single mode fiber of the present invention comprises a core structure and a cladding structure, wherein the core structure comprises two lightly doped SiO fibers with unequal radii and semicircular cross-section₂The planes of the diameters of the two core layers are attached to each other, and the circle centers of the cross sections of the two core layers are superposed; the cladding structure is wrapped at the periphery of the core structure, the cross section of the outer edge of the cladding structure is circular, the circle center of the cladding structure is coincident with that of the cross section of the core structure, and the cladding structure is heavily doped SiO₂And (4) forming.

Furthermore, the doping of the core layer structure is Ge or P, and the doping of the cladding layer structure is B or F. The purpose of the light and heavy doping is to form a core cladding structure, so that light transmitted in the core cladding structure propagates in a form similar to total reflection; in addition, the lightly doped core layer has lower optical loss.

The manufacturing process comprises the following steps: the invention relates to a large-cross-section single-mode optical fiber, belonging to a medium-special optical fiber, which is prepared by firstly manufacturing a die similar to a core layer, then melting the preform, simultaneously carrying out light doping, and drawing through the die to form two light-doped SiO fibers with different radiuses₂A semicircular core layer; and finally, preparing a cladding layer on the prepared core layer in a sleeve mode. The structure shown in fig. 3 is finally formed.

By adjusting the radius of the two semicircles in the core layer, the size of the base mode light spot can be changed, and single-mode transmission with a large cross-sectional area can be realized. Numerical simulation shows that the radii of the two semicircles are different, the effective refractive indexes of the core layers are different, the number of modes excited in the optical fiber is different, and when the radii are adjusted to appropriate values, a high-order mode is cut off and only a fundamental mode exists.

The working principle of the invention is as follows: the laser output from the laser and other optical fibers via the optical amplifier is coupled into the large-cross-section single-mode optical fiber of the invention, because the core layer area of the optical fiber is large, the nonlinear threshold value is high, and the nonlinear effect is not easy to cause (the nonlinear effect is only when the power on the cross section of the optical fiber exceeds the nonlinear power threshold value, the larger the core layer area is, the lower the optical power density per unit area is, and therefore, the larger the cross-sectional area is, the less the nonlinear effect is, compared with the small-area core layer), the optical power can be accommodated. Due to the special structure of the core layer, the input circular light spot can generate mode derivation during transmission in the optical fiber, and the circular light spot is derived into a quasi-rectangular light spot. By adjusting the geometry of the core layer, the optical fiber of the present invention supports only fundamental mode transmission.

The implementation principle of the invention is further explained as follows:

the present invention is derived from the ridge waveguide shown in fig. 4, and the ridge waveguide shown in fig. 4(a) can obtain the condition of single-mode transmission by adjusting the height of the ridge and the thickness of the slab, which has been proved in the previous work; due to the manufacturing process, the perfectly vertical side walls of the ridge type optical waveguide are difficult to etch. Thus, the semicircular ridge light wave shown in fig. 4(b) is reported on the basis of considering the process, and single-mode transmission can be realized by adjusting the thickness of the flat plate and the radius of the semicircular ridge in the structure, so that the present invention can also realize large-cross-section single-mode transmission. Because the structure of the optical fiber is complex, the mode analysis is complex by adopting a mathematical physical model analysis method of the circularly symmetric optical fiber, and in order to represent the mode of the optical fiber more intuitively, the invention adopts a numerical calculation method to calculate the effective refractive index of 1550nm laser in the fundamental mode of the optical fiber with different sizes, as shown in table 1.

TABLE 1 different sized optical fibers and their fundamental mode effective refractive indices

The fundamental mode of the large cross-section fiber of different sizes and the fundamental mode spot of a normal multimode fiber (core diameter 60 μm) are shown in fig. 5. Wherein, fig. 5(a) is a large-cross-section fiber fundamental mode spot with R/R10 μm/30 μm 0.3; FIG. 5(b) shows the first-order mode spot of large-cross-section fiber with R/R10 μm/30 μm 0.3; FIG. 5(c) shows a large cross-section fundamental mode spot of an optical fiber with R/R of 20 μm/30 μm of 0.66; FIG. 5(d) shows the fundamental mode spot of the large cross-section fiber with R/R20 μm/40 μm 0.5; FIG. 5(e) shows a large cross-section fundamental mode spot of an optical fiber with R/R20 μm/50 μm 0.4; FIG. 5(f) shows the first-order mode spot of large-cross-section fiber with R/R20 μm/50 μm 0.4; FIG. 5(g) shows the fundamental mode spot size and its size of a conventional multimode optical fiber (core diameter: 60 μm), which is smaller than that of (a). Therefore, numerical simulation analysis shows that when the value of R/R is less than 2.5 and proper values of R and R are taken, the large-cross-section single-mode fiber provided by the invention can transmit a large-area fundamental mode, and in addition, the fiber can be used as a spot size converter and can be directly coupled with a ridge waveguide, so that the coupling efficiency is improved.

It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.

Claims

1. The large-cross-section single-mode optical fiber is characterized by comprising a core layer structure and a cladding layer structure, wherein the core layer structure comprises two lightly doped SiO fibers with unequal radiuses and semicircular cross sections₂The planes of the diameters of the two core layers are attached to each other, and the circle centers of the cross sections are superposed; the cladding structure is wrapped at the periphery of the core layer structure, the cross section of the outer edge of the cladding structure is circular, the circle center of the cladding structure coincides with that of the cross section of the core layer, and the cladding structure is heavily doped SiO₂And (4) forming.

2. The large cross-section single mode optical fiber of claim 1, wherein the doping of the core structure is Ge or P and the doping of the cladding structure is B or F.