CN2645299Y - Large mode area double cladding optical fiber single-mode laser - Google Patents

Abstract

The utility model relates to a large mode area double cladding optical fiber single-mode laser comprising a double cladding optical fiber raster 1, an outer cladding 2, a large diameter inner cladding 3, a large mode area fiber core 4, a taper-shaped inner cladding 5, a taper-shaped fiber core 6, a single-mode cladding 7, a single-mode fiber core 8, and a single-mode optical fiber raster 9. The outer cladding of a section of a large mode area double cladding optical fiber is removed to form a bare optical fiber to draw an optical fiber made of a taper optical fiber and a single-mode optical fiber; the two ends of the optical fiber are respectively removed to make an optical fiber raster and are capsulated to complete the production of the laser. The incorporated optical fiber laser avoids the connection wastage; the taper-shaped optical fiber is adopted to eliminate the pump light jamming, thereby improving the output stability, realizing single-mode laser, raising coupling efficiency, lowering technical difficulty and cost, and avoiding the supplementary loss caused by the use of lens; the laser chamber lens made of an optical fiber raster has a compact structure; the large mode area fiber core can raise the absorbing efficiency and be connected with other single-mode optical fibers to use conveniently.

Description

Large model area doubly clad optical fiber single-mode laser

Technical field: the utility model belongs to the fiber laser field, relates to the improvement to the high-power double cladding optical fiber laser structure.

Background technology: high-power double cladding optical fiber laser uses doubly clad optical fiber as active medium, doubly clad optical fiber is by the fiber core with single-mold of doping with rare-earth ions, the inner cladding of the outside large-size of fibre core and the surrounding layer of low-refraction are formed, pumping source adopts semiconductor laser usually, its pumping principle be with high-power wide multiple die semiconductor laser or optical fiber output module usually some optical elements high-power laser beam is coupled in the inner cladding in the doubly clad optical fiber, and laser is to be exaggerated transmission at doubly clad optical fiber in fibre core to obtain nearly diffraction limited single-mode laser output, add the front cavity mirror of double color plate as laser between doubly clad optical fiber and pumping source, Effect of Back-Cavity Mirror adopts the natural cleavage plane of doubly clad optical fiber rear end to realize the light feedback.In doubly clad optical fiber, with laser beam different propagation paths is arranged owing to pump beam, the inner cladding diameter is more near the diameter of fiber core with single-mold, the overlapping area of pump beam and laser beam is big more, the effective absorption coefficient of doubly clad optical fiber is big more, and for having the same dopant ion and the fiber core with single-mold of concentration in the doubly clad optical fiber, reducing of inner cladding diameter, adopt Lens Coupling no matter be, still adopt fusion techniques, all strengthen pump light and be coupled into difficulty in the doubly clad optical fiber inner cladding, for the overlapping area that realizes that pump beam and laser beam are higher, pump beam need be compressed, pump light is entered in the inner cladding of doubly clad optical fiber, so that in communication process, absorbed by the single mode fibre core, coupling efficiency is low, perhaps adopt the more optical fiber output pumping source of high power density, but the manufacturing technology difficulty of the pumping source of high power density is big, the cost height, adopt fiber core with single-mold absorptive pumping light simultaneously, the absorption efficiency of fiber core with single-mold is smaller, for obtaining enough gains, just need to increase the use length of doubly clad optical fiber, adopt the pumping source of high power density and the use length that increases doubly clad optical fiber can increase cost exponentially; Need to add other optical element between pumping source and doubly clad optical fiber, focus on coupled lens group and front cavity mirror etc. as collimation, can increase the cavity loss of laser, complex structure and instability also can't realize the high-capacity optical fiber laser of full fiberize structure.

Detailed content of the present utility model: low for solving in the background technology in the double-clad optical fiber laser coupling efficiency of optical fiber and pumping source, it is big to make high power density pump light difficulty, the cost height, the adding optical element can increase the cavity loss of laser again, complex structure and instability, can't realize problems such as full fiberize structure, the purpose of this utility model is design and has prepared a kind of novel high-power large model area doubly clad optical fiber single mode output laser, improved the coupling efficiency of doubly clad optical fiber and pump light, need not to add optical element, compact conformation is simple, has realized full fiberize structure, and cost reduces.

For achieving the above object, the structure of the utility model employing comprises: large model area doubly clad optical fiber: be made up of surrounding layer, major diameter inner cladding, large model area fibre core; The taper doubly clad optical fiber is made up of surrounding layer, taper inner cladding, taper fibre core; Monomode fiber is made up of single mode covering, fiber core with single-mold, doubly clad optical fiber grating, monomode fiber grating, the central shaft of surrounding layer, major diameter inner cladding, large model area fibre core, taper inner cladding, taper fibre core, single mode covering, fiber core with single-mold is located along the same line; Large model area fibre core right side is connected with taper fibre core left side, and the right side of taper fibre core is connected with the left side of fiber core with single-mold, and the right side of major diameter inner cladding is connected with the left side of taper inner cladding, and the right side of taper inner cladding is connected with the left side of single mode covering; Be mounted with successively outward by the lining from the center lateral cross section direction of large model area fibre core: large model area fibre core, major diameter inner cladding, surrounding layer; Be mounted with successively outward by the lining from the center lateral cross section direction of taper fibre core: taper fibre core, taper inner cladding, surrounding layer; Be mounted with successively outward by the lining from the center lateral cross section direction of fiber core with single-mold: fiber core with single-mold, single mode covering, surrounding layer; The doubly clad optical fiber grating is positioned on the position of close large model area fibre core left side input; The monomode fiber grating is positioned on the position of close fiber core with single-mold right side output.

Operation principle of the present utility model is: pump light λ _pEnter the major diameter inner cladding of large model area doubly clad optical fiber, by the doubly clad optical fiber grating on the large model area fibre core, absorb through large model area fibre core quilt rare earth ion wherein repeatedly and produce flashlight, flashlight has a large amount of patterns, flashlight is transferred to forward in the taper fibre core of taper doubly clad optical fiber, the single mode signal light that the taper fibre core only allows to be present in the lowest-order pattern passes through, arrive the fiber core with single-mold of monomode fiber and continue transmission, by the part single mode signal light of returning of the monomode fiber optical grating reflection on the single mode fibre core, part single mode signal light is again oppositely in taper fibre core and the transmission of large model area fibre core, the doubly clad optical fiber grating that arrives on the large model area fibre core is reflected fully, repeat this process repeatedly and both formed single mode signal light light feedback, also have only single mode signal light to obtain gain and amplify, thereby obtain single-mode laser λ at the output of fiber core with single-mold _s

Advantage of the present utility model: because the utility model made the fiber laser that is combined into one by large model area doubly clad optical fiber, conical fiber and monomode fiber, technology is simple, avoided because of connecting the loss that causes between non-integral optical fiber; Because the afterbody at large model area doubly clad optical fiber has used conical fiber, has limited pump light and has passed through, eliminated the interference of pump light to output laser, improve the laser output stability.Owing to used the major diameter inner cladding, improved the coupling efficiency of doubly clad optical fiber and pump light, can use the pumping source of low power density, reduce technical difficulty and cost, avoided using the collimation condenser lens to carry out the pump light coupling, supplementary load loss have been avoided, use fiber grating to replace the resonator mirror of dichroic mirror simultaneously as laser, therefore need not to add other separate optical element, compact conformation is simple, utilize the large model area fibre core in the large model area doubly clad optical fiber, increased the cross-sectional area of original fibre core, make large model area fibre core that bigger absorption efficiency be arranged, reduce the use length of doubly clad optical fiber, further reduced cost, utilized the taper doubly clad optical fiber to realize mode filtering simultaneously, have only the monotype laser of lowest-order to obtain sharp the penetrating of gain amplification realization, guarantee the single mode output of fiber laser.The doubly clad optical fiber of major diameter inner cladding can directly be connected with the output optical fibre of pumping source, has realized full fiberize structure, and the monomode fiber output can connect other monomode fiber transmission laser, and optical fiber can prolong arbitrarily, brings convenience to use.

Description of drawings:

Fig. 1 is the laser cutaway view of the utility model embodiment 1

Fig. 2 a and Fig. 2 b are the utility model fiber grating encapsulation cutaway views

Fig. 3 is the structure cutaway view of the utility model embodiment 2

Embodiment:

Describe the utility model in detail below in conjunction with the drawings and specific embodiments, Fig. 1,2,3 is high power large model area doubly clad optical fiber single-mode laser cutaway view.Device of the present utility model comprises: large model area doubly clad optical fiber: be made up of surrounding layer 2, major diameter inner cladding 3, large model area fibre core 4; The taper doubly clad optical fiber is made up of surrounding layer 2, taper inner cladding 5, taper fibre core 6; Monomode fiber is made up of single mode covering 7, fiber core with single-mold 8, doubly clad optical fiber grating 1, monomode fiber grating 9, pumping source output optical fibre 10, monomode fiber 11, encapsulation sleeve pipe 12, refractive index match coating 13, fiber grating 14.

The preparation method of this device is as follows:

1) chooses one section large model area doubly clad optical fiber, wherein the diameter of large model area fibre core 4 is 45 μ m, large model area fibre core 4 is chosen quartz glass as matrix, be doped with rare earth ion simultaneously, as: neodymium ion or ytterbium ion, doping content is 0.5wt%, or multiple other rare earth ion of codope, the diameter of major diameter inner cladding 3 is 800 μ m, the material of major diameter inner cladding 3 is a quartz glass, mix germanium ion in the large model area fibre core 4, realize that the refringence between large model area fibre core 4 and the major diameter inner cladding 3 is 0.005, promptly numerical aperture is 0.1, the thickness of surrounding layer 2 is 100 μ m, it is 0.45 that major diameter inner cladding 3 forms numerical aperture with surrounding layer 2, and the material of surrounding layer 2 is selected the polymeric material of low-refraction (as n=1.377), the length L of large model area doubly clad optical fiber _LMAFDetermine by following formula: L _LMAF=1/ α _Eff, α _Eff(cm ^-1) be the effective absorption coefficient of large model area doubly clad optical fiber, by formula α _Eff=α _cΓ decision, wherein α _c(cm ^-1) be the absorption coefficient of large model area fibre core 4, by the dopant ion concentration decision of fibre core, the α in the present embodiment _c=1.1cm ^-1Wherein $\mathrm{\Γ}=S_c/S_i,$ S _c, S _iBe respectively the cross-sectional area of large model area fibre core 4 and major diameter inner cladding 3, then L _LMAF=17.5m, our length of choosing large model area doubly clad optical fiber is 20m here.

2) surrounding layer 2 with two meters long optical fibers of large model area doubly clad optical fiber one end soaks in the acid solution of dilution until all being removed, be put into then in the fibre-optical drawing tower, under high temperature (2200 ℃), major diameter inner cladding 3 and large model area fibre core 4 are in molten condition, the diameter of stretching major diameter inner cladding 3 is from 800m to 125m, and drawing out length is L _TaperThe taper doubly clad optical fiber, keeping the constant length that draws out again of diameter 125m of major diameter inner cladding 3 is L _SMFMonomode fiber, on taper doubly clad optical fiber that drawing is finished and monomode fiber, apply the low refractive index polymer material identical again with surrounding layer 2, thickness is 100m.

As shown in Figure 1, for the length L of taper doubly clad optical fiber _TaperThe angle theta that is become with taper fibre core 6 central shafts by the hypotenuse of taper fibre core 6 _TaperDecision, angle theta _TaperBe subjected to guaranteeing that the taper doubly clad optical fiber only allows the restriction of single mode transport condition and no coupling loss condition, require angle theta _TaperClosely may be little, just can avoid lowest-order pattern LP ₀₁With inferior low step mode LP ₀₂Coupling loss, can be by formula: ${\mathrm{\&theta;}}_{\mathrm{Taper}}<{\mathrm{\&theta;}}_{\mathrm{Taper},\max }=\frac{2\&CenterDot;\mathrm{\&pi;}\&CenterDot;a}{{\mathrm{\&beta;}}_{01}-{\mathrm{\&beta;}}_{02}}$ Derive β in the formula ₀₁And β ₀₂Be lowest price pattern LP ₀₁With inferior low step mode LP ₀₂Propagation constant, a is the radius of taper fibre core 6, then taper doubly clad optical fiber length $L_{\mathrm{Taper}}>L_{\mathrm{Taper},\min }=a_1-a_2/\tan \left({\mathrm{\&theta;}}_{\mathrm{Taper},\max }\right),$ A in the formula ₁And a ₂Therefore be respectively the radius of large model area fibre core 4 and fiber core with single-mold 8, when the length of taper doubly clad optical fiber during greater than 5cm, the Mode Coupling loss reduces to negligible degree, the length L of the taper doubly clad optical fiber of our making _TaperBe 3m, satisfy condition fully, the diameter of single mode covering 7 is 125 μ m, the diameter of fiber core with single-mold 8 is 7 μ m, the length of the monomode fiber that forms is 2 meters, this moment, the length of overall optical fibre laser was made up of the long large model area doubly clad optical fiber of 18m, the taper doubly clad optical fiber of 3m length and the monomode fiber of 2m, and the border of taper doubly clad optical fiber is an oblique line, and the taper doubly clad optical fiber also can be with parabolical change of shape.

3) with large model area doubly clad optical fiber apart from input end face 0.5m place, peel the long surrounding layer 2 of 10cm off, after under high pressure mixing the hydrogen enhanced sensitivity, under ultraviolet light (wavelength is 248nm) irradiation, on large model area fibre core 4, produce doubly clad optical fiber grating 1 with mask method, 1 couple of pump light λ of doubly clad optical fiber grating _pHigh permeability (greater than 85%) is to laser λ _sBe all-trans (greater than 99%), apply refractive index match coating 13, encapsulate (a) as Fig. 2 with encapsulation sleeve pipe 12.

4) with monomode fiber apart from output end face 0.5m place, peel the long surrounding layer 2 of 10cm off, under ultraviolet light (248nm) irradiation, on fiber core with single-mold 8, produce monomode fiber grating 9 with mask method, 9 couples of laser λ of monomode fiber grating after under high pressure mixing the hydrogen enhanced sensitivity _sReflectivity is 3-4%, applies refractive index match coating 13 and encapsulates (as Fig. 2 b) with encapsulation sleeve pipe 12,

When 5) using high power large model area doubly clad optical fiber single-mode laser, as shown in Figure 3, the pumping source output optical fibre 10 of same diameter is connected pump light λ with large model area doubly clad optical fiber _pBe coupled into 3 li of major diameter inner claddings, thereby realize full fiberize structure, the output connection monomode fiber 11 at monomode fiber is used for laser transmission.

The inventor provides second embodiment of the present utility model, in Fig. 3, with the monomode fiber grating 9 on the 14 replacement fiber core with single-mold 8 of the fiber grating on monomode fiber 11 fibre cores, it is identical with the method for the 4th step making monomode fiber grating 9 to make fiber grating 14, and the connecting relation of other assembly is identical with first embodiment.

Selected parameter can require to select according to actual design in the foregoing description.

Claims (1)

1, large model area doubly clad optical fiber single-mode laser, it comprises: surrounding layer (2), major diameter inner cladding (3), large model area fibre core (4), single mode covering (7), fiber core with single-mold (8), monomode fiber grating (9), it is characterized in that: also comprise doubly clad optical fiber grating (1), taper inner cladding (5), taper fibre core (6), the central shaft of surrounding layer (2), major diameter inner cladding (3), large model area fibre core (4), taper inner cladding (5), taper fibre core (6), single mode covering (7), fiber core with single-mold (8) is located along the same line; Large model area fibre core (4) right side is connected with taper fibre core (6) left side, the right side of taper fibre core (6) is connected with the left side of fiber core with single-mold (8), the right side of major diameter inner cladding (3) is connected with the left side of taper inner cladding (5), and the right side of taper inner cladding (5) is connected with the left side of single mode covering (7); Be mounted with successively outward by the lining from the center lateral cross section direction of large model area fibre core (4): large model area fibre core (4), major diameter inner cladding (3), surrounding layer (2); Be mounted with successively outward by the lining from the center lateral cross section direction of taper fibre core (6): taper fibre core (6), taper inner cladding (5), surrounding layer (2); Be mounted with successively outward by the lining from the center lateral cross section direction of fiber core with single-mold (8): fiber core with single-mold (8), single mode covering (7), surrounding layer (2); Doubly clad optical fiber grating (1) is positioned on the position of close large model area fibre core (4) left side input; Monomode fiber grating (9) is positioned on the position of close fiber core with single-mold (8) right side output.

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