An optical fiber preform, a mode perturbed optical fiber and a method for manufacturing the same

Abstract

The application provides an optical fiber preform, which comprises a main core rod and a secondary core rod, the main core rod is provided with a core hole in the axial direction, the main core rod is sleeved outside the secondary core rod, and the outer part of the main core rod is sleeved with a cladding layer; the relative refractive index difference of the main core rod is larger than that of the secondary core rod; and the refractive index of the secondary core rod changes periodically in the axial direction after being twisted or changed in diameter. Through twisting or changing the diameter of the secondary core rod, the laser transmission in the core can avoid forming an effective waveguide structure in the fluorine ring outside the secondary core rod due to the change in size or shape of the fluorine ring outside the secondary core rod in the axial direction, the light beam is subjected to periodic disturbance of the refractive index distribution, enters the high refractive index medium for transmission, the Gaussian energy distribution is destroyed to excite high-order modes, and the energy is uniformly dispersed to the periphery from the Gaussian distribution, so that the energy homogenization effect is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical fiber manufacturing, in particular to an optical fiber preform, a mode perturbation optical fiber and a preparation method thereof. BACKGROUND

[0002] The light guiding principle of a common optical fiber waveguide is total internal reflection, and the light beam is bound in the core through total reflection. Due to the large refractive index at the axis of the waveguide, the output laser light field will be distributed in a Gaussian or near-Gaussian shape. In the industrial laser field, such as laser cleaning, laser welding, laser cutting and the like, the over-concentration of the spot energy will cause uneven stress, small effective cleaning area and other adverse effects. Changing the energy distribution of the spot and converting it into a flat-top spot that is uniformly distributed is more conducive to actual processing.

[0003] Currently, the conversion of a Gaussian light beam into a flat-top light beam is mainly solved by the following methods:

[0004] 1) A plurality of aspheric lenses or some diffractive optical devices can be combined to break the Gaussian light beam into a flat-top light beam after the combination of the lenses and devices;

[0005] 2) Different refractive index profiles are designed in the core of the waveguide structure, one of which is a step profile, and the other is a graded flat profile. When the laser propagates in the optical fiber, the Gaussian light beam will be broken into a flat-top light beam due to the inconsistency of the refractive index in the core.

[0006] For the first method, since a continuous high-power laser is required to be moved at any time for industrial production, and the environment and other factors for industrial production are variable, the installation of lenses and diffractive optical device combinations in the laser is prone to instability, which ultimately leads to the failure to stably complete the conversion of the Gaussian light beam, and thus is not suitable for actual industrial production.

[0007] For the second method, the fluorine ring (fluorine-doped layer) outside the core will form a stable waveguide structure when different refractive index profiles are designed in the core, so that the laser will be bound by the fluorine ring to form spot fission when propagating in the optical fiber, resulting in the failure to achieve energy homogenization. SUMMARY

[0008] The present application provides an optical fiber preform, a mode perturbation optical fiber and a preparation method thereof, which solves the problem that the fluorine ring outside the core will form a stable waveguide structure when different refractive index profiles are designed in the core in the prior art, so that the laser will be bound by the fluorine ring to form spot fission when propagating in the optical fiber, resulting in the failure to achieve energy homogenization.

[0009] The technical scheme of the present application is implemented as follows:

[0010] According to one aspect of the present application, there is provided an optical fiber preform, comprising a main core rod and a secondary core rod, the main core rod is provided with a core hole in the axial direction, the main core rod is sleeved outside the secondary core rod, and the outer part of the main core rod is sleeved with a cladding; the relative refractive index difference of the main core rod is greater than that of the secondary core rod; and the refractive index of the secondary core rod changes periodically along the axial direction after being twisted or changed in diameter.

[0011] The present application can avoid the formation of effective waveguide structure in the fluorine ring outside the secondary core rod, and the light beam will be subjected to periodic disturbance of refractive index distribution and be transmitted into the high refractive index medium, so that the Gaussian energy distribution is destroyed to excite high-order modes, so that the energy can be uniformly dispersed to the periphery from the Gaussian distribution, thereby achieving the effect of energy homogenization.

[0012] As a preferred scheme of the present application, the refractive index of the secondary core rod is gradually distributed in a center-low and two-end-high radial section, which is mainly designed to further destroy the waveguide structure in the fluorine ring outside the secondary core rod and improve the effect of energy homogenization.

[0013] As an optional scheme of the present application, the refractive index of the secondary core rod is stepwise distributed in a single-channel or multi-channel radial section, which is also designed to further destroy the waveguide structure in the fluorine ring outside the secondary core rod and improve the effect of energy homogenization.

[0014] As a preferred scheme of the present application, the outer part of the main core rod and the secondary core rod is provided with a fluorine-doped layer, the relative refractive index difference between the fluorine-doped layer of the main core rod and quartz is -0.9% to -1.2%, and the relative refractive index difference between the fluorine-doped layer of the secondary core rod and quartz is -0.26% to -0.42%.

[0015] According to another aspect of the present application, there is provided a preparation method of an optical fiber preform, comprising the following steps:

[0016] S1, depositing core rods in a liner tube to obtain a main core rod and a secondary core rod respectively;

[0017] S2, machining a core hole on the main core rod;

[0018] S3, twisting or changing the diameter of the secondary core rod to make the refractive index of the secondary core rod change periodically along the axial direction;

[0019] S4, sleeving the secondary core rod into the core hole of the main core rod;

[0020] S5, sleeving the cladding sleeve outside the main core rod to obtain an optical fiber preform.

[0021] As a preferred scheme of the present application, the method for twisting the auxiliary core rod in step S3 is:

[0022] S31, fusing a quartz rod at each end of the auxiliary core rod;

[0023] S32, heating and softening the auxiliary core rod;

[0024] S33, driving the quartz rods at both ends of the auxiliary core rod to rotate at different speeds to make the auxiliary core rod in a uniform twisted state.

[0025] The present application drives the quartz rods at both ends of the core rod to rotate at different speeds, which can heat the auxiliary core rod uniformly and make the auxiliary core rod in a uniform twisted state.

[0026] As a preferred scheme of the present application, the auxiliary core rod is polished before the quartz rods are fused, so that the radial cross section of the auxiliary core rod is in a polygonal or asymmetric shape. The polishing can make the auxiliary core rod retain the fluorine-doped layer while having a certain cross-sectional shape. The polygonal or asymmetric auxiliary core rod can further destroy the fundamental mode propagation and improve the energy homogenization effect.

[0027] As a preferred scheme of the present application, the method for changing the diameter of the auxiliary core rod in step S3 is:

[0028] S34, fusing a quartz rod at each end of the auxiliary core rod;

[0029] S35, heating and softening the diameter-changing region of the auxiliary core rod, and controlling the quartz rods at both ends to move at a uniform speed and in opposite directions by a preset distance, so that the diameter of the diameter-changing region changes exponentially along the longitudinal direction;

[0030] S36, sequentially performing the operation of step S35 on the multiple diameter-changing regions arranged at equal intervals on the auxiliary core rod, so that the diameter of the auxiliary core rod changes periodically along the axial direction.

[0031] According to another aspect of the present application, a mode perturbation optical fiber is provided, which is obtained by drawing the above optical fiber preform.

[0032] According to still another aspect of the present application, a mode perturbation optical fiber is provided, which is obtained by drawing the above optical fiber preform through a sleeve-rod drawing process.

[0033] Advantages

[0034] Compared with the prior art, the present application has the following advantages:

[0035] (1) the present application can avoid forming effective waveguide structure in the fluorine ring outside the secondary fiber core rod, the light beam will be subjected to periodic disturbance of refractive index distribution change, enter the high refractive index medium transmission, the Gaussian energy distribution is destroyed to excite high order mode, so that the energy can be uniformly dispersed from the Gaussian shape distribution to the periphery, so as to achieve the effect of energy homogenization; the laser beam can be bound in the core by the main fiber core rod, preventing the laser from leaking into the cladding;

[0036] (2) the present application can further destroy the waveguide structure in the fluorine ring outside the secondary fiber core rod by designing the refractive index of the secondary fiber core rod to be gradually distributed with low center and high ends in the radial section or single channel, multi-channel step distribution, and improve the energy homogenization effect;

[0037] (3) in the process of twisting the secondary fiber core rod, the secondary fiber core rod can retain the fluorine-doped layer while having a certain cross-sectional shape by polishing before fusing the quartz rod, and the polygonal or asymmetric secondary fiber core rod can further destroy the fundamental mode propagation and improve the energy homogenization effect. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description, and obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0039] Figure 1 It is a radial structure schematic diagram of a kind of optical fiber preform in the embodiment 1 of the present application;

[0040] Figure 2 It is the refractive index of the secondary fiber core rod in the embodiment 1 of the present application gradually distributed with low center and high ends in the radial section schematic diagram;

[0041] Figure 3 It is the refractive index of the secondary fiber core rod in the embodiment 1 of the present application single channel or multi-channel step distribution schematic diagram in the radial section;

[0042] Figure 4 It is the device structure schematic diagram of the secondary fiber core rod twisting in the embodiment 1 of the present application using fusion lathe;

[0043] Figure 5 It is the state schematic diagram of the secondary fiber core rod after twisting in the embodiment 1 of the present application;

[0044] Figure 6A schematic diagram of a radial structure of a fiber preform in Embodiment 2 of the present application;

[0045] Figure 7 A schematic diagram of a structure of a sub-core rod after a diameter changing treatment in Embodiment 2 of the present application;

[0046] In the figure: 1, main core rod; 2, sub-core rod; 3, inner cladding; 4, outer cladding; 5, quartz rod; 6, fusion lathe; 7, torch; 8, gradual change region; 9, uniform region. DETAILED DESCRIPTION

[0047] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0048] Embodiment 1

[0049] Referring to Figure 1 the figure, the present embodiment provides a fiber preform, which comprises a main core rod 1 and a sub-core rod 2. The main core rod 1 is provided with a core hole in the axial direction. The main core rod 1 is sleeved outside the sub-core rod 2. The outer part of the main core rod 1 is sleeved with a cladding. The cladding comprises an inner cladding 3 and an outer cladding 4, which are coaxially sleeved. The relative refractive index difference of the main core rod 1 is greater than that of the sub-core rod 2. The refractive index of the sub-core rod 2 after a torsion treatment changes periodically along the axial direction.

[0050] In the present embodiment, the refractive index of the sub-core rod 2 changes periodically along the axial direction after a torsion treatment, which can destroy the fundamental mode and avoid the formation of an effective waveguide structure in the fluorine ring outside the sub-core rod 2, so as to realize mode perturbation of laser transmission and energy homogenization. The main core rod 1 can bind the laser beam in the core to prevent the laser from leaking into the cladding.

[0051] As shown in Figure 2 the figure, as a preferred scheme of the present embodiment, the refractive index of the sub-core rod 2 is gradually changed in a distribution of low in the center and high at both ends in the radial section. The purpose of this design is mainly to further destroy the waveguide structure in the fluorine ring outside the sub-core rod 2 and improve the effect of energy homogenization.

[0052] As shown in Figure 3 the figure, as an optional scheme of the present embodiment, the refractive index of the sub-core rod 2 is stepwisely distributed in a single channel or multiple channels in the radial section. The purpose is also to further destroy the waveguide structure in the fluorine ring outside the sub-core rod 2 and improve the effect of energy homogenization. Figure 3Fig. 1 is a schematic diagram of the distribution of the refractive index of the main core rod 1 in the radial section, Fig. 2 is a schematic diagram of the distribution of the refractive index of the sub core rod 2 in the radial section, wherein (a) is a schematic diagram of the single-channel step distribution of the refractive index of the sub core rod 2 in the radial section, and (b) is a schematic diagram of the double-channel step distribution of the refractive index of the sub core rod 2 in the radial section.

[0053] As a preferred scheme of the present embodiment, the diameter of the main core rod 1 is 25 mm, the outer side of the main core rod 1 and the sub core rod 2 is provided with a fluorine-doped layer, the relative refractive index difference between the fluorine-doped layer of the main core rod 1 and quartz is -0.9% to -1.2%, and the ratio of the diameter of the fluorine-doped layer to the diameter of the main core rod 1 is 12% to 29%; the diameter of the sub core rod 2 is 10 mm, the relative refractive index difference between the fluorine-doped layer of the sub core rod 2 and quartz is -0.26% to -0.42%, and the ratio of the diameter of the fluorine-doped layer to the diameter of the sub core rod 2 is 10% to 32%.

[0054] The present embodiment also provides a preparation method of the optical fiber preform, comprising the following steps:

[0055] S1, depositing the core rods in the liner tube to obtain the main core rod 1 and the sub core rod 2 respectively;

[0056] S2, machining the core hole on the main core rod 1;

[0057] S3, performing the torsion or diameter change treatment on the sub core rod 2 to make the refractive index of the sub core rod 2 periodically change along the axial direction;

[0058] S4, loading the sub core rod 2 into the core hole of the main core rod 1;

[0059] S5, sleeving the cladding on the outside of the main core rod 1 to obtain the optical fiber preform.

[0060] In the present embodiment, the diameter of the core hole is 10.3 mm, which is matched with the outer diameter of the sub core rod 2, the axial line of the core hole is parallel to and does not coincide with the axial line of the main core rod 1, that is, the sub core rod 2 is arranged non-coaxially (radial offset) with the main core rod 1, and the purpose is to further interfere with the propagation of the fundamental mode light beam and improve the energy homogenization effect.

[0061] As a preferred scheme of the present embodiment, the method for performing the torsion treatment on the sub core rod 2 in step S3 is:

[0062] S31, fusing a section of quartz rod 5 to each end of the sub core rod 2;

[0063] S32, softening the sub core rod 2 by heating;

[0064] S33, driving the quartz rods 5 at the two ends of the sub core rod 2 to rotate at different speeds to make the sub core rod 2 in a uniform torsion state.

[0065] As Figure 4As shown, in the implementation process, a section of quartz rod 5 is fused to each end of the secondary fiber core rod 2, the quartz rods 5 at both ends are fixed on the clamps on both sides of the fusion lathe 6, the hydrogen-oxygen flame torch 7 is turned on, the torch 7 is moved to the fusion position of the front end of the secondary fiber core rod 2 and the quartz rod 5, the heating time and temperature are adjusted to the glass softening point, then the rotation speeds of the clamps at both ends of the fusion lathe 6 are adjusted, the rotation speed of the clamp at the left end of the fusion lathe 6 is 157 rad / min, and the rotation speed of the clamp at the right end is 183 rad / min, at this time, the secondary fiber core rod 2 will be twisted due to the differential speed of the clamps at both sides, the torch 7 is moved at a constant speed, the moving speed is 15 mm / min, and the torch 7 is moved to the fusion position of the rear end of the secondary fiber core rod 2 and the quartz rod 5; the torch 7 is moved back and forth 4-6 times, at this time, the whole secondary fiber core rod 2 is in a uniform twisted state, as shown in Figure 5

[0066] In this embodiment, the differential rotation of the quartz rods 5 at both ends of the fiber core rod can uniformly heat the secondary fiber core rod 2, and the secondary fiber core rod 2 is in a uniform twisted state due to the different rotation speeds of the quartz rods 5 at both ends.

[0067] As a preferred scheme of this embodiment, before the quartz rod 5 is fused, the secondary fiber core rod 2 is polished to make the radial cross section of the secondary fiber core rod 2 into a polygonal or asymmetric shape; the polishing can make the secondary fiber core rod 2 retain the fluorine-doped layer while having a certain cross-sectional shape, and the polygonal or asymmetric secondary fiber core rod 2 can further destroy the fundamental mode propagation and improve the energy homogenization effect.

[0068] In this embodiment, the secondary fiber core rod 2 is fixed on a grinding machine, and the radial cross section of the secondary fiber core rod 2 is polished into an octagon (in the implementation process, the cross section can also be polished into other polygons or asymmetric shapes, such as a D shape), and the distance between opposite sides of the octagon is 9.09 mm, and the diagonal distance is 9.82 mm.

[0069] This embodiment also provides a mode perturbation optical fiber, which is obtained after drawing the above optical fiber preform.

[0070] This embodiment also provides a mode perturbation optical fiber, which is obtained after drawing the above optical fiber preform.

[0071] Embodiment 2

[0072] As shown in Figure 6 7 This embodiment provides an optical fiber preform, which is different from the above embodiment 1 in that in this embodiment, the refractive index of the secondary fiber core rod 2 changes periodically along the axial direction after the diameter change treatment.

[0073] ​​In the embodiment, the diameter of the main core rod 1 is 25 mm, the outer side of the main core rod 1 and the outer side of the auxiliary core rod 2 are both provided with a fluorine-doped layer, the relative refractive index difference between the fluorine-doped layer of the main core rod 1 and quartz is -0.9% to -1.2%, and the ratio of the diameter of the fluorine-doped layer to the diameter of the main core rod 1 is 12% to 29%; the diameter of the auxiliary core rod 2 is 8.2 mm, the relative refractive index difference between the fluorine-doped layer of the auxiliary core rod 2 and quartz is -0.26% to -0.42%, and the ratio of the diameter of the fluorine-doped layer to the diameter of the auxiliary core rod 2 is 10% to 32%.

[0074] The embodiment also provides a preparation method of the optical fiber preform, including the following steps:

[0075] In step S3, the method for performing the diameter changing treatment on the auxiliary core rod 2 is as follows:

[0076] S34, a section of quartz rod 5 is fused to each end of the auxiliary core rod 2;

[0077] S35, the diameter changing region of the auxiliary core rod 2 is heated and softened, the quartz rods 5 at the two ends are controlled to move at a constant speed in opposite directions by a preset distance, so that the diameter of the diameter changing region changes in an exponential manner along the longitudinal direction;

[0078] S36, the operation of step S35 is sequentially performed on the multiple diameter changing regions arranged at equal intervals on the auxiliary core rod 2, so that the diameter of the auxiliary core rod 2 changes periodically along the axial direction.

[0079] In the embodiment, the length of the axial diameter gradual change region 8 of the auxiliary core rod 2 is 15±2 mm, the minimum diameter of the gradual change region 8 is 4.2±0.5 mm, and the length of the uniform region 9 between the adjacent two gradual change regions 8 is 10 mm.

[0080] The above merely describes the preferred embodiments of the present application, but should not be used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. An optical fiber preform, characterized by, It includes a main fiber core rod (1) and a secondary fiber core rod (2). The main fiber core rod (1) has a core hole along the axial direction. The main fiber core rod (1) is sleeved on the outside of the secondary fiber core rod (2). The main fiber core rod (1) is covered with a cladding. The relative refractive index difference of the main fiber core rod (1) is greater than that of the secondary fiber core rod (2). The refractive index of the secondary fiber core rod (2) changes periodically along the axial direction by twisting or changing its diameter. The refractive index of the core rod (2) is a gradually changing distribution with a low center and high ends on the radial cross section, or a step distribution with a single channel or multiple channels; both the main fiber core rod (1) and the secondary fiber core rod (2) are provided with fluorine-doped layers on their outer sides. The relative refractive index difference between the fluorine-doped layer of the main fiber core rod (1) and quartz is -0.9% to -1.2%, and the relative refractive index difference between the fluorine-doped layer of the secondary fiber core rod (2) and quartz is -0.26% to -0.42%.

2. A method of producing an optical fiber preform as claimed in claim 1, characterized by, Includes the following steps: S1, core rods are deposited inside the liner to obtain main fiber core rod (1) and secondary fiber core rod (2); S2, core holes are machined on the main core rod (1); S3, the sub-fiber core rod (2) is twisted or its diameter is changed so that the refractive index of the sub-fiber core rod (2) changes periodically along the axial direction; S4, insert the secondary core rod (2) into the core hole of the main core rod (1); S5, the cladding is placed on the outside of the main fiber core rod (1) to obtain the optical fiber preform.

3. A method of making an optical fiber preform according to claim 2, wherein, In step S3, the method for twisting the secondary fiber core rod (2) is as follows: S31, a section of quartz rod (5) is fused to both ends of the secondary fiber core rod (2); S32, the secondary fiber core rod (2) is heated and softened; S33 drives the quartz rods (5) at both ends of the secondary fiber core rod (2) to rotate at a different speed, so that the secondary fiber core rod (2) is in a uniform twisted state.

4. A method of making an optical fiber preform according to claim 3, wherein, Before fusing the quartz rod (5), the secondary fiber core rod (2) is polished so that the radial cross section of the secondary fiber core rod (2) is polygonal or asymmetrical.

5. A method of making an optical fiber preform as claimed in claim 2, wherein, In step S3, the method for changing the diameter of the secondary fiber core rod (2) is as follows: S34, a section of quartz rod (5) is fused to both ends of the secondary fiber core rod (2); S35, the variable diameter region of the secondary fiber core rod (2) is heated and softened, and the quartz rods (5) at both ends are controlled to move in the opposite direction at a uniform speed for a preset distance, so that the diameter of the variable diameter region changes exponentially along the longitudinal direction. S36, the operation of step S35 is performed sequentially on multiple variable diameter zones that are equally spaced on the secondary fiber core rod (2), so that the diameter of the secondary fiber core rod (2) changes periodically along the axial direction.

6. A mode perturbed optical fiber, characterized by, The optical fiber preform described in claim 1 is obtained by drawing the fiber into fibers.

7. A method of making a mode perturbed optical fiber, characterized by, The optical fiber preform described in claim 1 is drawn into a pattern-perturbed optical fiber using a drawing process.

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