CN103728691A - Gain fiber with step and gauss composite ion doping concentration distribution - Google Patents

Abstract

The invention provides a gain fiber with step and gauss composite ion doping concentration distribution, and belongs to the technical field of fiber lasers. In gain light output, fundamental mode optical power ratio is not high in the prior art. The gain fiber with step and gauss composite ion doping concentration distribution is a large-core-diameter multimode fiber and is of a double-cladding structure, and rare earth ions are doped in a fiber core doping radius R'1. The gain fiber is characterized in that distribution of ion doping concentration N 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 R'1, in the step area, distribution of the ion doping concentration N is a step type, and the ion doping concentration N is the maximum value Nmax; an annular R0-R'1 area in the fiber core radius R1 is a gauss area, in the gauss area, distribution of the ion doping concentration N is a gauss type, the ion doping concentration N is determined by the following formula (please see the formula in the instruction), and in the formula, r is the radius of the gain fiber.

Description

The compound doping ion concentration distribution of step Gauss gain fibre

Technical field

The present invention relates to the compound doping ion concentration distribution of a kind of step Gauss gain fibre, belong to Fiber laser technology field.

Background technology

Gain fibre is as wavelength shifter, image intensifer, fiber laser etc.; have double clad structure, optical fiber is from inner fibre core 1, inner cladding 2, surrounding layer 3, the protective seam 4 of being outwards followed successively by, as shown in Figure 1; fibre core 1, surrounding layer 3 are circular, and the radius of fibre core 1 is fiber core radius R ₁, the general polymorphic structure that adopts of inner cladding 2, its cross sectional shape has ellipse, rectangle, quincunx, D shape and hexagon etc., conventional rectangle, as square, now, inner cladding 2 radius Rs ₂the square inscribed circle radius of making a comment or criticism, rectangle inner cladding 2 can make laser-conversion efficiency bring up to 50%.The refractive index of fibre core 1, inner cladding 2, surrounding layer 3 is followed successively by n ₁, n ₂, n ₃, and n ₁>n ₂>n ₃.Fibre core 1 adulterate radius R ' ₁interior doping with rare-earth ions, doping radius R ' ₁be less than fiber core radius R ₁.Pumping source is two or four high-power semiconductor lasers, pump light enters inner cladding 2 from doubly clad optical fiber two ends, interface multiple total reflection by inner cladding 2 with surrounding layer 3, pass through fibre core 1, for doping ion provides pump energy, obtain gain light, simple optical fiber has been realized the gain light single mode continuous wave output of 1000W.

As the gain fibre of power device, in order to meet the requirement of high power work state, be typically designed to a kind of large core diameter multimode optical fiber, due to mode competition, in the light that makes to gain, contain high-order mode.The CONCENTRATION DISTRIBUTION of doping ion in fibre core 1 is generally step change type, as shown in Figure 2, namely doping radius R ' ₁in, the ion concentration of adulterating everywhere N is an identical doping ion concentration maximal value N _max.Therefore, in gain of light process, be rendered as the form that basic mode, high-order mode gain simultaneously and export, gain light quality is not high; Also waste pump energy simultaneously.In order to address this problem, there is in the prior art a kind of parabolic type doping ion concentration distribution scheme, as shown in Figure 3, doping radius R ' ₁in, the increase that doping ion concentration N starts from center O with fiber radius r, from doping ion concentration maximal value N _maxalong para-curve, successively decrease, when fiber radius r reach doping radius R ' ₁time, doping ion concentration N is decremented to zero.According to this scheme, the high-order mode gain that is in neighboring area, mould field is inhibited.But, at doping ion concentration maximal value N _maxunder identical prerequisite, the basic mode gain that is in mode field center region also decreases with respect to step change type.Moreover monolateral para-curve, without flex point, is a complete convex curve, doping ion concentration N fails the increase that starts from center O with fiber radius r and fast quick depletion does not reach best to the inhibition of high-order mode gain.

Summary of the invention

In order to improve the basic mode gain of large core diameter multimode gain fiber, suppress high-order mode gain, improve gain light quality, we have invented the compound doping ion concentration distribution of a kind of step Gauss gain fibre.

The present invention's the compound doping ion concentration distribution of step Gauss gain fibre is a kind of large core diameter multimode optical fiber, has double clad structure, fibre core 1 adulterate radius R ' ₁interior doping with rare-earth ions, is characterized in that, as shown in Figure 4, its distribution of doping ion concentration N is divided into two regions, fiber core radius R ₁0～R in scope ₀border circular areas is step district, R ₀for step district radius, R ₀<R' ₁, the ion concentration of adulterating in step district N is distributed as step change type, and doping ion concentration N is maximal value N _max; Fiber core radius R ₁r in scope ₀～R' ₁circle ring area is Gauss district, and the ion concentration of adulterating in Gauss district N is distributed as Gaussian, and doping ion concentration N is determined by following formula:

$N\left(r\right)=N_{\max }\&CenterDot;\exp [-\frac{1}{2}{\left(\frac{r-R_0}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000447297230000011.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;}-R_0}\right)}^2],$

In formula: the fiber radius that r is described gain fibre.

Effect of the present invention is, because the value of the ion concentration N that adulterates in the step district of fibre core 1 is maximal value N everywhere _max, therefore, basic mode gain has the high-gain level of existing step change type gain fibre.And the ion concentration of adulterating in Gauss district N is along with the increase starting from center O with fiber radius r, N is from maximal value N for doping ion concentration _maxalong Gaussian curve, successively decrease, when fiber radius r reach doping radius R ' ₁time, doping ion concentration N is decremented to zero, and Gaussian curve has flex point compared with para-curve, along with the increase of fiber radius r, doping ion concentration N rate of decline is accelerated, and high-order mode obtains more efficiently inhibition.In gain light, the basic mode ratio of luminous power increases, and effectively avoids the pulse strenching and the nonlinear effect that produce because of mode competition, homogenize the distribution of luminous power at fibre core 1, output beam quality and output power are all improved.

Accompanying drawing explanation

Fig. 1 is doubly clad optical fiber structure cross sectional representation.Fig. 2 is existing step change type doping ion concentration distribution figure.Fig. 3 is existing parabolic type doping ion concentration distribution figure.Fig. 4 the present invention's the compound doping ion concentration distribution of step Gauss gain fibre doping ion concentration distribution figure, this figure is simultaneously as Figure of abstract.

Embodiment

The present invention's the compound doping ion concentration distribution of step Gauss gain fibre is a kind of large core diameter multimode optical fiber, has double clad structure, fibre core 1 adulterate radius R ' ₁interior doping with rare-earth ions, as shown in Figure 4, its distribution of doping ion concentration N is divided into two regions, fiber core radius R ₁0～R in scope ₀border circular areas is step district, R ₀for step district radius, R ₀<R' ₁, and step district radius R ₀with doping radius R ' ₁physical relationship be: R ₀=0.5～0.7R' ₁, the ion concentration of adulterating in step district N is distributed as step change type, and doping ion concentration N is maximal value N _max; Fiber core radius R ₁r in scope ₀～R' ₁circle ring area is Gauss district, and the ion concentration of adulterating in Gauss district N is distributed as Gaussian, and doping ion concentration N is determined by following formula:

$N\left(r\right)=N_{\max }\&CenterDot;\exp [-\frac{1}{2}{\left(\frac{r-R_0}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000447297230000011.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;}-R_0}\right)}^2],$

In formula: the fiber radius that r is described gain fibre.

Doping ion is Yb ³⁺, output wavelength is 1.064 μ m.R ₀=0.7R' ₁，R' ₁=15μm。The index distribution of gain fibre is step change type.By numerical evaluation, obtain under the prerequisite of the relative gain coefficient maximum of basic mode, it is maximum that the relative rejection coefficient of high-order mode reaches, as 0.2088, and under similarity condition, the relative rejection coefficient of high-order mode of parabolic type doping concentration distribution gain fibre only has 0.1418.

Claims (2)

1. the compound doping ion concentration distribution of a step Gauss gain fibre, for the large core diameter multimode optical fiber of one, has double clad structure, fibre core (1) doping radius R ' ₁interior doping with rare-earth ions, is characterized in that, its distribution of doping ion concentration N is divided into two regions, fiber core radius R ₁0～R in scope ₀border circular areas is step district, R ₀for step district radius, R ₀<R' ₁, the ion concentration of adulterating in step district N is distributed as step change type, and doping ion concentration N is maximal value N _max; Fiber core radius R ₁r in scope ₀～R' ₁circle ring area is Gauss district, and the ion concentration of adulterating in Gauss district N is distributed as Gaussian, and doping ion concentration N is determined by following formula:

$N\left(r\right)=N_{\max }\&CenterDot;\exp [-\frac{1}{2}{\left(\frac{r-R_0}{R_1^{\&prime;}-R_0}\right)}^2],$

In formula: the fiber radius that r is described gain fibre.

2. the compound doping ion concentration distribution of step Gauss according to claim 1 gain fibre, is characterized in that, step district radius R ₀with doping radius R ' ₁physical relationship be: R ₀=0.5～0.7R' ₁.

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