Pump coupler for four-clad fiber and fiber laser

Abstract

The invention discloses a pump coupler for a four-clad fiber and a fiber laser, the pump coupler is used for accessing and transmitting a first light beam and pump light, the pump coupler comprises a signal light accessing fiber, a pump fiber and a coupling output fiber, the signal light accessing fiber and the coupling output fiber are both multi-clad passive fibers, and the coupling output fiber is a multi-clad passive fiber. The fiber core diameter of the signal light access fiber is larger than the fiber core diameter of the coupling output fiber and does not exceed the minimum cladding diameter of the coupling output fiber. According to the pump coupler for the four-clad optical fiber and the optical fiber laser, the problem that the size of a composite light spot is limited due to the fact that the tapering proportion is limited in the prior art can be solved.

Description

Technical Field

[0001] The present invention relates to the field of fiber lasers, and in particular, to a pump coupler for four-clad fiber and a fiber laser. Background Art

[0002] In a fiber laser, a composite laser is formed through a power combiner. The power combiner is based on the fused biconical taper of fiber beam combining, integrating multiple identical or different lasers to output a composite beam with a spot-ring shape.

[0003] The power combiner has multiple input fibers and one output fiber. The multiple input fibers are arranged in a circular array around one of them. The output fiber has a core and a waveguide layer, and there is also a dielectric layer between the core and the waveguide layer. The core is used to connect to the input fiber located at the center of the circular array and output a central spot, and the waveguide layer is used to connect to the input fibers located in the outer ring of the circular array and output an annular spot; the dielectric layer separates the core from the waveguide layer to constrain the transmission of the light beams in their respective channels, and the superposition of the central spot and the annular spot forms a composite beam with a spot-ring shape.

[0004] Although the above power combiner can form a composite beam, it belongs to the integration of multiple laser beams by using a beam shaping element to form a composite laser. The beam shaping element not only undertakes the role of transmitting the laser, but also needs to take into account the redistribution and utilization of the laser beam energy, which will inevitably cause additional energy loss, increase the cost of system components, and affect the long-term reliability of the laser.

[0005] Moreover, since the output fiber needs to efficiently couple the light beams from multiple input fibers, its size will be very large. Without using biconical taper, the diameter of the output fiber is about 3 times that of the input fiber in the array formed by the input fibers; if the diameter of the array is reduced by using biconical taper, the diameter of the output fiber can be reduced, and correspondingly, the size of the formed spot can be reduced. However, the biconical taper process is limited by the biconical taper ratio and the brightness of the light itself. If the biconical taper ratio is too large, the light beam of the input fiber will leak. Therefore, the biconical taper process cannot infinitely reduce the diameter of the output fiber, which limits the size of the composite spot, and the minimum size of the composite spot is at the level of 50μm / 150μm or 100μm / 300μm. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a pump coupler for four-clad fiber and a fiber laser, which are used to solve the problem of limiting the size of the composite spot due to the limitation of the biconical taper ratio in the prior art.

[0007] To achieve the above and other related objectives, the present invention provides a pump coupler for a four-clad optical fiber, comprising a signal light access fiber, a pump optical fiber, and a coupled output fiber, for accessing and transmitting a first light beam and pump light. Both the signal light access fiber and the coupled output fiber are multi-clad passive optical fibers, and the core diameter of the signal light access fiber is greater than the core diameter of the coupled output fiber.

[0008] Optionally, the pump coupler adopts an end-pumping structure.

[0009] Optionally, the output end face of the signal light access fiber is fusion-spliced to the input end face of the coupled output fiber, and the core diameter of the signal light access fiber at the fusion-splicing surface position is equal to the minimum cladding diameter of the coupled input fiber at the fusion-splicing surface position.

[0010] Optionally, the signal access optical fiber includes a first core, a first inner cladding, and a first outer cladding with refractive indices decreasing in sequence from inside to outside, and the first core is used for transmitting the first light beam.

[0011] Optionally, the coupled output fiber includes a second core, a guiding layer, a second inner cladding, and a second outer cladding with refractive indices decreasing in sequence from inside to outside. The second core and the guiding layer are used for outputting the first light beam, and the second inner cladding is used for outputting the pump light.

[0012] Optionally, the pump optical fiber is a double-clad passive optical fiber.

[0013] Optionally, the core diameter of the signal light access fiber is 50 - 100 μm, and the core diameter of the coupled output fiber is 14 - 34 μm.

[0014] Optionally, the core diameter of the signal light access fiber is 100 μm, and the core diameter of the coupled output fiber is 34 μm; or, the core diameter of the signal light access fiber is 50 μm, and the core diameter of the coupled output fiber is 34 μm; or, the core diameter of the signal light access fiber is 34 μm, and the core diameter of the coupled output fiber is 14 μm; or, the core diameter of the signal light access fiber is 50 μm, and the core diameter of the coupled output fiber is 14 μm.

[0015] Optionally, the signal light access fiber and the coupled output fiber are respectively fusion-spliced to a three-clad active optical fiber and a four-clad active optical fiber, and the core and cladding structures, refractive index distributions, and diameters of the signal light access fiber and the coupled output fiber are adapted to the corresponding signal optical fiber and gain optical fiber.

[0016] The present invention also provides an optical fiber laser, comprising the pump coupler as described in any one of the above.

[0017] As described above, a pump coupler and a fiber laser for a four-cladding fiber provided by the present invention. The signal fiber forms a first light beam, and the gain fiber forms a second light beam. The pump coupler located between the two is used to transmit the first light beam and the pump light to the gain fiber. At the fusion splicing surface position of the signal light access fiber and the coupled output fiber, the core diameter of the signal light access fiber is larger than that of the coupled output fiber, and the core diameter of the signal light access fiber is less than or equal to the minimum cladding diameter of the coupled output fiber. The minimum cladding of the coupled output fiber replaces its core to access the first light beam. When the first light beam is accessed, its power and beam quality will not attenuate, and the continuously transmitted first light beam and the second light beam formed in the core of the gain fiber can be superimposed to form a small-size composite laser. Description of the Drawings

[0018] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements. Unless otherwise stated, the drawings in the figures do not constitute a scale limitation.

[0019] Figure 1 It is a schematic structural diagram of the pump coupler provided in the embodiment.

[0020] Figure 2 It is a schematic end-face structure diagram of the signal light access fiber provided in the embodiment.

[0021] Figure 3 It is a schematic end-face structure diagram of the coupled output fiber provided in the embodiment.

[0022] Figure 4 It is a schematic diagram of the energy distribution of the composite light beam formed by the fiber laser provided in the embodiment.

[0023] Figure 5 It is a schematic structural diagram of the fiber laser provided in the embodiment. Detailed Description of the Embodiment

[0024] For the convenience of understanding the present invention, the present invention will be described in more detail below with reference to the accompanying drawings and specific embodiments. It should be noted that when an element is expressed as "fixed to" another element, it can be directly on the other element, or there can be one or more intermediate elements therebetween. When an element is expressed as "electrically connected to" another element, it can be directly connected to the other element, or there can be one or more intermediate elements therebetween. The terms "upper", "lower", "inner", "outer", "bottom", etc. used in this specification indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0025] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not used to limit the present invention. The term "and / or" used in this specification includes any and all combinations of one or more of the related listed items.

[0026] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0027] This embodiment first introduces a fiber laser 1 for generating composite laser, as Figure 5 shown, the fiber laser 1 includes a section of signal fiber 11 and a section of gain fiber 21.

[0028] Figure 2 Shown is the cross-sectional structure of the output end face of the signal fiber 11. The signal fiber 11 includes a first core 111, a first inner cladding 112, and a first outer cladding 113 with refractive indices decreasing in sequence from inside to outside. The pump light transmitted in the first inner cladding 112 is absorbed by the first core 111 during the back-and-forth reflection process to form a first light beam I1.

[0029] Figure 3 Shown is the cross-sectional structure of the input end face of the gain fiber 21. The gain fiber 21 includes a second core 211, a guiding layer 2110, a second inner cladding 212, and a second outer cladding 213 with refractive indices decreasing in sequence from inside to outside. The pump light transmitted in the second inner cladding 212 is absorbed by the second core 211 during the back-and-forth reflection process to form a second light beam I2.

[0030] From the structural comparison between the signal optical fiber 11 and the gain optical fiber 21, it can be seen that the gain optical fiber 21 is additionally provided with a guiding layer 2110 between the second core 211 and the second inner cladding 22, and the diameter of the second core 211 is smaller than that of the first core 111.

[0031] In application, the numerical aperture of the guiding layer 2110 matches that of the first core 111, and the first light beam I1 output from the first core 111 enters the guiding layer 2110 and the second core 211 for transmission. The first light beam I1 transmitted in the second core 211 will be gain-amplified into a second light beam I2, while the first light beam I1 transmitted in the guiding layer 2110 is not amplified and still outputs along the guiding layer 2110. Therefore, the light beam output by the fiber amplifier 20 is a laser formed by the superposition of the first light beam I1 and the second light beam I2 (with a higher power relative to I1). Moreover, since the diameter of the first core layer 111 is larger than that of the second core layer 211, the spot diameter formed by the first core layer 111 is larger, and the spot diameter formed by the second core layer 211 is smaller. Also, the diameter size of the second core layer 211 does not limit the diameter of the first core layer, and the diameter sizes of the first core layer 111 and the second core layer 211 can be freely proportioned. In application, to adapt to the requirement of a smaller composite spot size, the diameter of the guiding layer is set to be less than or equal to 100 μm, and the diameter of the second core layer is set to be less than or equal to 34 μm to form a composite laser with a small spot size. For example, the diameter of the first core layer 111 is configured to be 100 μm and the diameter of the second core layer 211 is 34 μm; or the diameter of the first core layer 111 is configured to be 50 μm and the diameter of the second core layer 211 is 34 μm; or the diameter of the first core layer 111 is configured to be 34 μm and the diameter of the second core layer 211 is 14 μm. By different diameter size ratios, different spot sizes can be formed. At the same time, compared with the problems existing in the background technology, the composite spot size formed by the active optical fiber 100 provided in this embodiment is smaller and can be applied to more precise processing scenarios.

[0032] As Figure 4 shown is the schematic diagram of the spot energy distribution of the composite laser. The spot energy form of the output laser presents a convex platform distribution form. Among them, the first light beam I1 forms the platform part in the convex platform, and the second light beam I2 forms the protruding part of the convex platform. Correspondingly, the energy size of the platform part can be controlled by controlling the power of the first light beam I1, and the energy size of the protruding part can be controlled by controlling the power of the second light beam I2, and finally different composite lasers with different energy distributions can be tuned and obtained (as Figure 4 shown). Of course, in some application modes, the power of the second light beam I2 can also be separately controlled to be 0 to form a laser beam independently output by the first light beam I1, or the power of the first light beam I1 can be separately controlled to form a laser beam independently output by the second light beam I2.

[0033] In practical applications, a pump coupler 30 needs to be provided between the signal optical fiber 11 and the gain optical fiber 21, which is used to deliver the first light beam I1 to the second core 211 and the guiding layer 2110 and guide the pump light to the second inner cladding 212.

[0034] As Figure 1 shown, this embodiment provides a pump coupler 30 for a four-cladding optical fiber. The pump coupler 30, as an independently fabricated optical element, is applied to the fiber laser 1 introduced above. To achieve low-loss fusion splicing, the cladding structure, the dimensions of each layer, and the refractive index distribution of the signal light access fiber 31 are the same as those of the signal optical fiber 11, and the cladding structure, the dimensions of each layer, and the refractive index distribution of the coupled output fiber 33 are the same as those of the gain optical fiber 21. The output end face of the signal light access fiber 31 is fusion spliced to the input end face of the coupled output fiber 21, which can be a tapered fusion splicing or a direct fusion splicing without tapering. Among them, the core diameter of the signal light access fiber at the fusion splicing surface is larger than the core diameter of the coupled output fiber and does not exceed the minimum cladding diameter of the coupled output fiber.

[0035] As Figure 2 shown, the signal light access fiber 31 (signal optical fiber 11) also includes a first core 111, a first inner cladding 112, and a first outer cladding 113 with refractive indices decreasing in sequence from inside to outside. The pump light transmitted in the first inner cladding 112 is absorbed and converted into the first light beam I1.

[0036] As Figure 3 shown, the coupled output fiber 33 (gain optical fiber 21) also includes a second core 211, a guiding layer 2110, a second inner cladding 212, and a second outer cladding 213 with refractive indices decreasing in sequence from inside to outside.

[0037] As Figure 1 shown, the pump coupler 30 adopts an end-pumping structure. In the end-pumping structure, the signal light access fiber 31 and multiple pump optical fibers 32 form a fiber beam combination. The diameter of the fiber beam combination is about 1-3 times the diameter of the coupled output fiber 33, and it is impossible to directly fusion splice the fiber beam combination with the coupled output fiber 33. To make the core diameters on both sides of the fusion splicing surface of the signal light access fiber 31 and the coupled output fiber 33 match each other, it is necessary to perform combined beam tapering on the signal light access fiber 31 and the pump light access fiber 32. When designing the tapering ratio, it is necessary to consider both the maximum tapering ratio of the signal light access fiber 31 (serious light leakage occurs when exceeding the tapering upper limit) and whether the pump light Is output by the pump light access fiber 32 can be effectively coupled into the second inner cladding 212' (if the tapering ratio is too small, the core of the pump light access fiber cannot be docked with the second inner cladding 212'); therefore, if the diameter of the second inner cladding 212' is too small, it will be impossible to effectively access the pump light Is.

[0038] After the fiber optic bundle is tapered, on both sides of the fusion joint surface, the signal light access fiber 31' (31' represents the signal light access fiber 31 after tapering) is butt-jointed with the coupled output fiber 33. To meet the transmission conditions (standing wave condition and total reflection condition) in the front and rear stage optical fibers, to ensure as low a fusion loss as possible and to ensure that the pump light Is does not leak out to the outer cladding 223, at the fusion joint surface position of the signal light access fiber 31 and the coupled output fiber 33, the diameter of the first core 111 of the signal light access fiber 31 is less than or equal to the diameter of the guiding layer 2110 of the coupled output fiber 33; to form a composite laser with a smaller size, at the fusion joint surface position, the diameter of the first core 111 of the signal light access fiber 31 is greater than the diameter of the second core 211 of the coupled output fiber 33. Preferably, at the fusion joint surface position, the diameter of the first core 111 of the signal light access fiber 31 is equal to the diameter of the guiding layer 2110 of the coupled output fiber 33 (the guiding layer 2110 can be regarded as the smallest cladding in the multi-cladding structure), and the refractive index of the first core 111 is the same as the refractive index of the guiding layer 2110, which can couple the first light beam I1 into the guiding layer 2110 with high efficiency. Further, at the fusion joint surface, the diameter and refractive index of the first inner cladding 112 and the second inner cladding 212 are the same, which can efficiently access the pump light Is to the second inner cladding 212.

[0039] In summary, for the pump coupler and fiber laser for four-cladding optical fiber of the present invention, the signal optical fiber forms the first light beam, the gain optical fiber forms the second light beam, and the pump coupler located between the two is used to transmit the first light beam and the pump light to the gain optical fiber. At the fusion joint surface position of the signal light access fiber and the coupled output fiber, the core diameter of the signal light access fiber is greater than the core diameter of the coupled output fiber, the core diameter of the signal light access fiber is less than or equal to the diameter of the smallest cladding of the coupled output fiber, and the smallest cladding of the coupled output fiber replaces its core to access the first light beam. When the first light beam is accessed, its power and beam quality will not decay, and the first light beam that continues to be transmitted and the second light beam formed in the core of the gain optical fiber can be superimposed to form a composite laser with a small size. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0040] The above embodiments are only illustrative of the principles and effects of the present invention, and are not used to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A pump coupler for a four-clad optical fiber, comprising a signal light access fiber, a pump optical fiber, and a coupled output fiber, for accessing and transmitting a first light beam and pump light, characterized in that, The signal light access fiber and the coupled output fiber are both multi-clad passive fibers, and the core diameter of the signal light access fiber is larger than that of the coupled output fiber.

2. The pump coupler according to claim 1, characterized in that, The pump coupler adopts an end-pumping structure.

3. The pump coupler according to claim 2, characterized in that, The output end face of the signal light access fiber is fusion-connected to the input end face of the coupled output fiber, and the core diameter of the signal light access fiber at the fusion surface position is equal to the minimum cladding diameter of the coupled input fiber at the fusion surface position.

4. The pump coupler according to claim 1, characterized in that, The signal access fiber includes a first core, a first inner cladding, and a first outer cladding with refractive indices decreasing from inside to outside in sequence, and the first core is used for transmitting the first light beam.

5. The pump coupler according to claim 4, characterized in that, The coupled output fiber includes a second core, a guiding layer, a second inner cladding, and a second outer cladding with refractive indices decreasing from inside to outside in sequence. The second core and the guiding layer are used for outputting the first light beam, and the second inner cladding is used for outputting the pump light.

6. The pump coupler according to claim 1, characterized in that, The pump fiber is a double-clad passive fiber.

7. The pump coupler according to claim 1, characterized in that, The core diameter of the signal light access fiber is 50 - 100 μm, and the core diameter of the coupled output fiber is 14 - 34 μm.

8. The pump coupler according to claim 7, characterized in that, The core diameter of the signal light access fiber is 100 μm, and the core diameter of the coupled output fiber is 34 μm; or, the core diameter of the signal light access fiber is 50 μm, and the core diameter of the coupled output fiber is 34 μm; or, the core diameter of the signal light access fiber is 34 μm, and the core diameter of the coupled output fiber is 14 μm; or, the core diameter of the signal light access fiber is 50 μm, and the core diameter of the coupled output fiber is 14 μm.

9. The pump coupler according to claim 1, characterized in that, The signal light access fiber and the coupled output fiber are respectively fusion-connected to a three-clad active fiber and a four-clad active fiber, and the core and cladding structures, refractive index distributions, and diameters of the signal light access fiber and the coupled output fiber are adapted to the corresponding signal fiber and gain fiber.

10. An optical fiber laser, characterized in that, It includes the pump coupler according to any one of claims 1 - 9.

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