CN210720804U

CN210720804U - Ytterbium-doped double-clad optical fiber with gradually-changed inner cladding

Info

Publication number: CN210720804U
Application number: CN201921388760.9U
Authority: CN
Inventors: 李海清; 廖雷; 刘长波
Original assignee: Wuhan Changjin Laser Technology Co ltd
Current assignee: Wuhan Changjin Photonics Technology Co ltd
Priority date: 2019-08-23
Filing date: 2019-08-23
Publication date: 2020-06-09
Anticipated expiration: 2029-08-23

Abstract

The utility model discloses an ytterbium-doped double-clad optical fiber with gradually changed inner cladding, which comprises: the optical fiber comprises a fiber core, an inner cladding, an outer cladding and a protective layer, wherein the inner cladding is coated on the fiber core, the outer cladding is coated on the inner cladding, the protective layer is coated on the outer cladding, and the refractive index of the inner cladding is increased firstly and then reduced along with the increase of the distance from the fiber core. The ytterbium-doped double-clad optical fiber with the gradually changed inner cladding realizes effective convergence of pump light in the inner cladding by changing the structure of the inner cladding, and further improves the power intensive characteristic of the pump light passing through the fiber core, thereby improving the absorption of the effective pump light and reducing the residual cladding pump light.

Description

Ytterbium-doped double-clad optical fiber with gradually-changed inner cladding

Technical Field

The utility model relates to the technical field of optical fiber, concretely relates to ytterbium-doped double-clad optical fiber with gradually changed inner cladding.

Background

In recent years, fiber lasers have been developed rapidly, especially with double claddingSince the invention of the optical fiber, the output power of the optical fiber laser is increased from milliwatt level to ten-thousand watt level. Generally, the core is made of rare earth doped SiO₂The structure is used as a transmission channel of laser, and the single mode is designed for relevant wavelength so as to ensure that the output laser is a fundamental transverse mode. The cladding is made of SiO with transverse size and numerical aperture larger than those of the fiber core and smaller refractive index than that of the fiber core₂The structure is that it is a pump light transmission channel, which is multimode to the pump light.

However, with the technical development of ytterbium-doped double-clad fibers, shortening the length of the ytterbium-doped fiber in the laser is one of the key directions for reducing the cost of the ytterbium-doped fiber laser and further realizing the portability and small volume of the ytterbium-doped fiber laser, and currently, by adjusting the ytterbium-doped concentration of the fiber core, the absorption and conversion efficiency of the fiber core structure to the cladding pumping light is improved, and the adjustment upper limit is reached. Therefore, it is necessary to improve the absorption of the effective pump light by changing the inner cladding structure.

SUMMERY OF THE UTILITY MODEL

The present invention is directed to provide an ytterbium-doped double-clad optical fiber with a gradually changing inner cladding to solve the above problems.

The utility model adopts the technical proposal that: the ytterbium-doped double-clad optical fiber with the gradually changed inner cladding comprises a fiber core, an inner cladding, an outer cladding and a protective layer, wherein the fiber core is coated with the inner cladding, the outer cladding is coated with the protective layer, and the refractive index of the inner cladding is increased firstly and then reduced along with the increase of the distance between the inner cladding and the fiber core.

The utility model has the effects that: the ytterbium-doped double-clad optical fiber with the gradually changed inner cladding realizes effective convergence of pump light in the inner cladding by changing the structure of the inner cladding, and further improves the power intensive characteristic of the pump light passing through the fiber core, thereby improving the absorption of the effective pump light and reducing the residual cladding pump light.

Drawings

Fig. 1 is a schematic structural diagram of an ytterbium-doped double-clad optical fiber with a gradually-changed inner cladding according to the present invention;

fig. 2 is a graph showing the refractive index profile of the ytterbium-doped double-clad optical fiber with a gradually-changed inner cladding according to the present invention.

Detailed Description

The ytterbium-doped double-clad optical fiber with gradually changed inner cladding of the utility model is described below with the accompanying drawings:

as shown in fig. 1, for the utility model provides a pair of ytterbium-doped double-clad optical fiber with gradually changed inner cladding, it includes fiber core 1, inner cladding 2, surrounding layer 3 and protective layer 4, inner cladding 2 cladding in fiber core 1, surrounding layer 3 cladding in inner cladding 2, protective layer 4 cladding in surrounding layer 3.

The refractive index of the inner cladding 2 increases and then decreases with increasing distance from the core 1.

The inner cladding 2 can be made into various shapes, such as circular, square and rectangular, and when the pump light is transmitted in the inner cladding with different shapes, the absorption rates of the fiber core 1 to the pump light are different. The outer cladding 3 is made of a polymer material having a lower refractive index than the inner cladding, thus forming a large-cross-section, large-numerical-aperture optical waveguide between the inner cladding 2 and the outer cladding 3, which allows high-power pump light of large numerical aperture, large cross-section and multiple modes to be coupled into the optical fiber. The protective layer 4 is a hard plastic for protecting the optical fibers. The double-clad fiber is different from the conventional single-mode fiber in that the inner cladding refractive index close to the fiber core is higher than the outer cladding refractive index through the research on the fiber structure design and the selection of a proper material double-clad erbium-ytterbium co-doped fiber amplifier, so that the inner cladding allowing the high-power multimode pump light to be transmitted therein is formed outside the single-mode fiber core. When the pumping light longitudinally propagates along the inner cladding, the pumping light passes through the fiber core for many times, so that rare earth ions are excited to generate a laser effect. The requirement on a pumping source is greatly reduced because the pumping light in the cladding is allowed to transmit in multiple modes, a relatively cheap multimode laser diode can be selected for pumping, and meanwhile, the fiber-entering pumping power and the coupling efficiency are greatly improved because the inner cladding has a large cross-sectional area and a large numerical aperture.

The refractive index profile of the inner cladding 2 is parabolic.

As shown in fig. 2, the refractive index of the inner cladding 2 conforms to the following formula:

wherein n is the refractive index of the inner cladding 2, and r is the distance between the inner cladding 2 and the fiber core 1.

The preparation method of the optical fiber is similar to the traditional optical fiber preparation method, only the content of germanium is increased to control the refractive index of the inner cladding when the inner cladding is deposited, sulfur hexafluoride is firstly introduced to integrally adjust the refractive index of the fiber core when the core layer is deposited, and then the gradient refractive index structure of the inner cladding is formed by controlling the pressure in the tube when the rod is shrunk.

Compared with the traditional optical fiber, the optical fiber is numerically simulated, the mode of the parabolic graded cladding can be bound more than that of the conventional cladding, and for a fiber core model, the graded cladding can enable the fiber core model to be closer to the center of a fiber core; the cladding mode can be made closer to the core, with more energy passing through the core.

The ytterbium-doped double-clad optical fiber with the gradually changed inner cladding realizes effective convergence of pump light in the inner cladding by changing the structure of the inner cladding, and further improves the power intensive characteristic of the pump light passing through the fiber core, thereby improving the absorption of the effective pump light and reducing the residual cladding pump light.

The above description is only for the preferred embodiment of the present invention, and is not intended to limit the present invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. An ytterbium-doped double-clad optical fiber with a gradually-changed inner cladding, comprising: the optical fiber comprises a fiber core, an inner cladding, an outer cladding and a protective layer, wherein the inner cladding is coated on the fiber core, the outer cladding is coated on the inner cladding, the protective layer is coated on the outer cladding, and the refractive index of the inner cladding is increased firstly and then reduced along with the increase of the distance from the fiber core.

2. The inner-clad graded ytterbium-doped double-clad fiber according to claim 1, wherein the refractive index profile of the inner cladding is parabolic.

3. The inner-clad graded ytterbium-doped double-clad fiber according to claim 2, wherein the refractive index of the inner cladding satisfies the following formula:

wherein n is the refractive index of the inner cladding, and r is the distance between the inner cladding and the fiber core.