Double-clad fiber with step Gaussian compound refractive index distribution

Abstract

The invention provides a double-clad fiber with step and gauss composite refractive index distribution, and belongs to the technical field of fibers. An existing step-type double-clad fiber is larger in light beam fundamental mode light filed deviation when the fiber is bent; an existing gauss type double-clad fiber is smaller in mode field area. The double-clad fiber with step and gauss composite refractive index distribution is characterized in that distribution of a fiber core refractive index is divided into two areas, a round 0-R0 area in the range of a fiber core radius R1 is a step area, R0 is the radius of the step area, and R0 is less than R1, in the step area, distribution of the fiber core refractive index is a step type, and the fiber core refractive index is the maximum value n1; an annular R0-R1 area in the range of the fiber core radius R1 is a gauss area, in the gauss area, distribution of the fiber core refractive index is a gauss type, and a fiber core refractive index n'1 is determined by the following formula (please see the formula in the instruction), in the formula, r is a variable of the fiber core radius, R0 is less than r, r is less than R1, and n2 is the inner-clad refractive index of the double-clad fiber. The performance of the fiber is optimized comprehensively.

Description

Technical field [0001] The invention relates to a step-gauss composite refractive index distribution double-clad optical fiber, which has a large mode field area, and when the optical fiber is bent, the mode field deviation is small, and is suitable for high-power gain and transmission optical fibers, belonging to optical fibers Technical field. Background technique [0002] The double-clad fiber is composed of core 1, inner cladding 2, outer cladding 3, and protective layer 4 from the inside to the outside. figure 1 As shown, the core 1 and the outer cladding 3 are circular, and the radius of the core 1 is R 1 The inner cladding layer 2 generally adopts a special-shaped structure, and its cross-sectional shape includes ellipse, rectangle, quincunx, D-shape and hexagon, etc., usually rectangular, such as square, at this time, the inner cladding layer 2 radius R 2 Refers to the radius of the inscribed circle of the square. The refractive index of core 1, inner cladding layer 2, an...

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Problems solved by technology

However, when the step-type double-clad fiber is bent, the light field of the beam fundamental mode shifts greatly, such as Figure 4 As shown, the optical power loss including the pump light is large, so the light energy loss of the gain beam or transmission beam is large

Although the optical field shift of the fundamental mode of the beam is small when the Gaussian double-clad fiber is bent, such as Figure 5 As shown, however, the Gaussian double-clad fiber has a small mode field area. When working at high power, the power density will become very large. This will cause damage to the fiber easily, and cause nonlinearities such as multiple wavelengths. effect, reducing beam quality

If the mode field area of ​​the Gaussian double-clad fiber is increased by increasing the core diameter, it will be accompanied by the multi-mode of the light mode, which will seriously reduce the beam quality.

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