A continuous fiber laser with annular spot output using a fully polarization-maintaining fiber structure

Abstract

The present invention relates to the technical field of optical fiber lasers, and specifically discloses a continuous optical fiber laser with an annular spot output of a full polarization-maintaining optical fiber structure, comprising a first Bragg optical fiber grating, a first long-period optical fiber grating, a wavelength division multiplexer, a pump source, a gain optical fiber, a second long-period optical fiber grating, a second Bragg optical fiber grating, a polarization combiner and an output end. The present invention utilizes the advantage of polarization-maintaining optical fiber in resisting environmental interference, solves the problems of unstable output power and uneven spot of the current annular spot laser, and effectively improves the practicality of optical fiber lasers with high-order mode output. The present invention can be applied to the fields of industrial laser processing, surface plasma excitation, particle manipulation, microscopic imaging and optical storage.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber lasers, in particular to a continuous optical fiber laser with an annular spot output and a full polarization-maintaining optical fiber structure. Background Art

[0002] Axisymmetric polarized beams are different from conventional uniformly polarized light. Their polarization is symmetrically distributed in the beam cross section, and their intensity is a "donut" with the center at zero. Their mode is the four degenerate vector modes in the fiber LP11 mode. Axisymmetric polarized light mainly includes radial polarized light and angular polarized light. Its symmetrical electric field distribution gives it unique application advantages in the fields of surface plasmon excitation, optical tweezers, particle acceleration, laser processing, etc. Therefore, the method of generating axisymmetric polarized beams has attracted much attention from researchers. However, due to errors in the fiber manufacturing process and crosstalk of the modes within the fiber, the output spot of the actual high-order mode fiber laser is unstable and uneven. To obtain the annular spot, additional devices are required to remove the degeneracy of the LP11 mode.

[0003] At present, there are two main methods for generating cylindrical vector beams: active and passive. The active method mainly generates cylindrical vector beams by using birefringent crystals in the cavity to lose certain polarization states in the beam or by using the superposition of polarization states. The problem with this method is that it requires high precision of the device and has a relatively small range of action. The passive method is to add polarization control devices inside or outside the laser cavity. Its disadvantages are that it is easily affected by environmental interference, has poor stability, and is not very practical. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of poor power stability, uneven output spot and poor practicality of the current high-order mode output fiber laser based on ordinary optical fiber, and designs a ring-shaped spot output continuous fiber laser with a full polarization-maintaining fiber structure.

[0005] To achieve the above object, the present invention provides the following technical solution: a ring-shaped spot output continuous fiber laser with a full polarization-maintaining fiber structure, comprising a first Bragg fiber grating, a first long-period fiber grating, a wavelength division multiplexer, a pump source, a gain fiber, a second long-period fiber grating, a second Bragg fiber grating, a polarization combiner and an output end, wherein the first Bragg fiber grating and the second Bragg fiber grating serve as reflectors of a laser cavity;

[0006] Wherein, the first long period fiber grating and the second long period fiber grating are used to convert the LP01 mode into the LP11 mode;

[0007] Wherein, the pump source is used to generate pump light;

[0008] Among them, the wavelength division multiplexer is used to couple the pump light into the resonant cavity;

[0009] Wherein, the gain fiber is used to absorb the pump light and generate the signal light;

[0010] The polarization beam combiner is used to combine two laser beams with orthogonal polarization states into an annular light spot;

[0011] Wherein, the output end is used to output signal light;

[0012] The first end of the wavelength division multiplexer is connected to the first end of the polarization beam combiner through the first long period fiber grating and the first Bragg fiber grating in sequence, the second end of the wavelength division multiplexer is connected to the second end of the polarization beam combiner through the gain fiber, the second long period fiber grating and the second Bragg fiber grating in sequence, the first end of the wavelength division multiplexer is also connected to the pump source, and the third end of the polarization beam combiner is connected to the output end.

[0013] Preferably, the gain optical fiber is a polarization-maintaining optical fiber, and the polarization-maintaining optical fiber is doped with rare earth elements.

[0014] Preferably, the first fiber Bragg grating and the second fiber Bragg grating are Bragg gratings inscribed on polarization-maintaining optical fibers.

[0015] Preferably, the first long-period fiber grating and the second long-period fiber grating are long-period gratings inscribed on polarization-maintaining optical fibers.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The laser involved in the present invention is an all-fiber structure, which is compact and stable.

[0018] 2. The ring-shaped spot laser state finally synthesized by the laser involved in the present invention is a coherent laser signal; the LP11 mode is stably present in the laser cavity, and a ring-shaped spot with uniform light spot is output; the practicality is strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the device connection structure of the present invention.

[0020] In the figure: 1-first long period fiber grating; 2-first Bragg fiber grating; 3-wavelength division multiplexer; 4-pump source; 5-gain fiber; 6-second long period fiber grating; 7-second Bragg fiber grating; 8-polarization combiner; 9-output end. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] See also Figure 1 The present invention provides a technical solution: a ring-shaped spot output continuous fiber laser with a full polarization-maintaining fiber structure, comprising a first Bragg fiber grating 1, a first long-period fiber grating 2, a wavelength division multiplexer 3, a pump source 4, a gain fiber 5, a second long-period fiber grating 6, a second Bragg fiber grating 7, a polarization combiner 8 and an output end 9, wherein the first Bragg fiber grating 1 and the second Bragg fiber grating 7 are Bragg gratings engraved on a polarization-maintaining fiber and serve as reflectors of a laser cavity; the first long-period fiber grating 2 and the second long-period fiber grating 6 are long-period gratings engraved on a polarization-maintaining fiber and are used to convert an LP01 mode into an LP11 mode; a pump source 4 is used to generate pump light, wherein the pump source 4 is a semiconductor laser with a central wavelength of 976 nm. ; The wavelength division multiplexer 3 is used to couple the pump light into the resonant cavity, wherein the wavelength division multiplexer 3 adopts a 976nm / 1064nm wavelength division multiplexer; the gain fiber 5 is used to absorb the pump light and generate signal light, the polarization combiner 8 is used to synthesize two laser beams with orthogonal polarization states into an annular light spot, and the output end 9 is used to output the signal light. The first end of the wavelength division multiplexer 3 is connected to the first end of the polarization combiner 8 through the first long-period fiber grating 2 and the first Bragg fiber grating 1 in sequence, and the second end of the wavelength division multiplexer 3 is connected to the second end of the polarization combiner 8 through the gain fiber 5, the second long-period fiber grating 6 and the second Bragg fiber grating 7 in sequence. The first end of the wavelength division multiplexer 3 is also connected to the pump source 4, and the third end of the polarization combiner 8 is connected to the output end 9. When in use, the signal light resonating in the cavity is converted from the fundamental mode to the LP11 mode after passing through the first long-period fiber grating 2 and the second long-period fiber grating 6, and forms a two-lobe light spot mode field distribution in the polarization-maintaining fiber. The signal light is partially output on the first Bragg fiber grating 1 and the second Bragg fiber grating 7, and the remaining signal light returns to the laser cavity, and finally continuously oscillates in the laser cavity to form a continuous laser. Since the polarization combiner 8 can synthesize two polarized signal lights into one signal light in orthogonal polarization directions, the output signal lights of the left and right arms are connected to the polarization combiner 8, and a signal light with a complete ring shape can be output. Finally, by cutting the length of the output end 9, the two signal lights in the output port are made into a coherently synthesized signal laser.

[0023] In this embodiment, the gain fiber 5 is a polarization-maintaining fiber, and the polarization-maintaining fiber is doped with rare earth elements, and the rare earth elements include but are not limited to ytterbium, erbium, and thulium.

[0024] The advantages of the present invention are that it utilizes the superior environmental interference resistance of polarization-maintaining optical fiber, the straight cavity mode with left and right dual outputs, and the compact structural characteristics of the all-fiber, so that the LP11 mode exists stably in the laser cavity and ensures the uniform distribution of the output light spot.

[0025] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0026] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A continuous fiber laser with an annular spot output and full polarization-maintaining fiber structure. It is characterized in that include: The first Bragg fiber grating (1); A first long period fiber grating (2); Wavelength division multiplexer (3); Pump source (4); Gain fiber (5); A second long period fiber grating (6); A second Bragg fiber grating (7); Polarization beam combiner (8) and An output end (9), wherein the first Bragg fiber grating (1) and the second Bragg fiber grating (7) serve as reflectors of the laser cavity; Wherein, the first long-period fiber grating (2) and the second long-period fiber grating (6) are used to convert the LP01 mode into the LP11 mode; Wherein, the pump source (4) is used to generate pump light; Wherein, the wavelength division multiplexer (3) is used to couple the pump light into the resonant cavity; Wherein, the gain optical fiber (5) is used to absorb the pump light and generate the signal light; The polarization beam combiner (8) is used to combine two laser beams with orthogonal polarization states into an annular light spot; Wherein, the output end (9) is used to output signal light; The first end of the wavelength division multiplexer (3) is connected to the first end of the polarization beam combiner (8) through the first long-period fiber grating (2) and the first Bragg fiber grating (1) in sequence, the second end of the wavelength division multiplexer (3) is connected to the second end of the polarization beam combiner (8) through the gain fiber (5), the second long-period fiber grating (6) and the second Bragg fiber grating (7) in sequence, the first end of the wavelength division multiplexer (3) is also connected to the pump source (4), and the third end of the polarization beam combiner (8) is connected to the output end (9); Wherein, the first Bragg fiber grating (1) and the second Bragg fiber grating (7) are Bragg gratings inscribed on polarization-maintaining optical fibers; Wherein, the first long-period fiber grating (2) and the second long-period fiber grating (6) are long-period gratings inscribed on polarization-maintaining optical fibers.

2. The annular spot output continuous fiber laser of a full polarization-maintaining fiber structure according to claim 1, Features: The gain optical fiber (5) is a polarization-maintaining optical fiber, and rare earth elements are doped in the polarization-maintaining optical fiber.

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