All-fiber column vector laser

Abstract

The utility model discloses an all-fiber column vector laser which comprises a pumping source 10, the pumping source 10 and a polarization-maintaining coupler 15 are jointly connected into a wavelength division multiplexer 11, the wavelength division multiplexer 11 couples a light source into an ytterbium-doped fiber 12, the ytterbium-doped fiber 12 is connected with a polarization-maintaining long-period fiber bragg grating 13, the polarization-maintaining long-period fiber bragg grating 13 is connected with a polarization-maintaining few-mode fiber bragg grating 14, and the polarization-maintaining few-mode fiber bragg grating 14 is connected with a polarization-maintaining few-mode fiber bragg grating 14. The polarization-maintaining few-mode fiber bragg grating 14 is connected to the polarization-maintaining few-mode coupler 16, the polarization-maintaining few-mode coupler 16 divides an optical path into two paths, one path is connected to the first end of the polarization-maintaining few-mode polarization beam combiner 17, and the other path enters the second end of the polarization-maintaining few-mode polarization beam combiner 17 through the fiber stretcher 18. The cylindrical vector laser solves the problems that the optical structure of the cylindrical vector laser is unstable, the purity of the generated cylindrical vector is low, and the conversion efficiency of the vector light beam is low, and has wide application prospects in the fields of advanced laser manufacturing, material processing, nonlinear optics and the like.

Description

Technical Field

[0001] The invention relates to the field of laser technology, in particular to an optical fiber laser in the field of laser technology. Background Art

[0002] For ease of understanding, the professional terms involved in the present invention are as follows:

[0003] PMF: Polarization Maintaining Fiber

[0004] PM-YDF: Polarization Maintaining Ytterbium-Doped Fiber

[0005] PM-WDM: Polarization Maintaining Wavelength Division Multiplexer PM-FMFBG: Polarization Maintaining Few-Mode Fiber Bragg Grating

[0006] PM-LPFG: Polarization Maintaining Long Period Fiber Grating PM-FMC: Polarization Maintaining Few-Mode Coupler

[0007] PM-FMPBC: Polarization Maintaining Few-Mode Polarization Beam Combiner

[0008] HOM: High-Order Mode

[0009] FMF: Few Mode Fiber

[0010] SMF: Single Mode Fiber

[0011] FM-FBG: Few-Mode Fiber Bragg Grating

[0012] MSC: Mode Selective Coupler

[0013] FM-LPFG: Few-Mode Long Period Fiber Grating

[0014] CVB: Cylindrical Vector Beam

[0015] MDM: Mode Division Multiplexing

[0016] Higher-order modes (HOMs) in optical fibers have attracted widespread attention due to their unique spatial intensity and polarization distribution characteristics. Unlike ordinary polarized beams, cylindrical vector light refers to a beam whose polarization direction on the cross section has a cylindrical symmetric distribution, and its transverse light intensity distribution is annular, which can generally be divided into angular and radial polarized light. The special polarization and amplitude characteristics of cylindrical vector light allow it to be used in many fields, such as particle manipulation, material processing, plasma excitation, optical storage, super-resolution microscopy, optical communications, and other fields.

[0017] Since few-mode fiber (FMF) can support more transmission modes and can bear larger communication capacity, it has better application prospects than single-mode fiber (SMF) in the field of MDM technology. Different devices using FMF to stimulate high-order modes in optical fibers have been studied, including single few-mode fiber Bragg grating (FM-FBG), mode selective coupler (MSC) and few-mode long-period fiber grating (FM-LPFG). Most of the work on CVB generation focuses on direct conversion to generate CVB output, while there are few reports on fiber lasers that generate CVB based on the mode superposition principle.

[0018] Chinese patent CN103424870B proposes to use an adjustable beam expander, an outward reflector, a birefringent crystal cone, an inward reflector component and a reflector to form a device for generating a cylindrical vector beam. This device has complex device parameter settings, unstable structure, and low purity of the cylindrical vector beam, which cannot meet the needs of actual applications.

[0019] Chinese patent CN1588169A proposes an adjustable vector beam shaping system to generate a cylindrical vector beam. The necessary condition for this method is that the system incident beam needs to be a special form of a rotating vector polarized beam, such as a radially polarized beam or an angularly polarized beam. However, the generation of radially polarized beams and angularly polarized beams also belongs to the category of rotating vector polarized beam generation, and it is impossible to realize the conversion of non-rotating vector polarized beams into rotating vector polarized beams. This essentially determines that the conversion process of an incoherent incident beam into a rotating vector polarized beam cannot be realized, and objectively it is difficult to generate a cylindrical vector beam.

[0020] Chinese patent CN102544999A proposes an all-fiber column vector laser, which mostly uses the misaligned fusion coupling of single-mode fiber and few-mode fiber to achieve the conversion from fundamental mode to first-order mode. The mode conversion efficiency is low, and the phase mismatch brings large intracavity loss. At the same time, in order to suppress the output of the fundamental mode beam to ensure the output purity of the first-order mode, a high-reflectivity output mirror is used, which is difficult to achieve the optimal output coupling ratio and limits the output power. This method has the disadvantages of high pump light power requirements, difficult to control misalignment accuracy, complex experimental equipment and uncertain structure.

[0021] Chinese patent CN108539567A proposes a 2μm band tunable random fiber laser based on a phase-shift grating. Although it uses a phase-shift grating to form a randomly distributed optical feedback and uses thulium-doped fiber as a gain medium to achieve the output of a 2μm band random laser, the 2μm band random laser is not a cylindrical vector light.

[0022] U.S. Patent US2010303402A1 proposes a phase-engineered optical fiber that produces a cylindrical polarized light beam. The optical fibers are relatively expensive, and they expand and contract with time and temperature. This method has the disadvantages of high parameter requirements and unstable structure.

[0023] U.S. Patent US2013177273A1 proposes a method for generating cylindrical vector beams based on multi-core optical fibers. The working principle is based on maintaining the birefringence characteristics of the polarization elliptical magnetic core. This method has the disadvantages of complex design and unstable structure.

[0024] U.S. Patent US7599069B2 proposes using passive phase-stabilized optical devices to generate cylindrical vector beams. This method has the disadvantages of complex structure, high system positioning requirements due to the use of optical coherence principles, difficulty in obtaining the required diffraction optical elements, and low polarization degree of the vector beam. Summary of the invention

[0025] In order to solve the problems of unstable optical structure, low purity of column vector and low vector beam conversion efficiency of column vector laser, the utility model proposes an all-fiber column vector laser with the advantages of stable optical structure, high purity of column vector beam and high laser conversion efficiency.

[0026] The technical solution of this utility model:

[0027] An all-fiber column vector laser comprises a pump source 10. The pump source 10 and a polarization-maintaining coupler 15 are connected to a wavelength division multiplexer 11. The wavelength division multiplexer 11 couples the light source into an ytterbium-doped fiber 12. The ytterbium-doped fiber 12 is connected to a polarization-maintaining long-period fiber grating 13. The polarization-maintaining long-period fiber grating 13 is connected to a polarization-maintaining few-mode fiber Bragg grating 14. The polarization-maintaining few-mode fiber Bragg grating 14 is connected to a polarization-maintaining few-mode coupler 16. The polarization-maintaining few-mode coupler 16 divides an optical path into two paths. One path is connected to the first end of a polarization-maintaining few-mode polarization combiner 17, and the other path passes through a fiber stretcher 18 and enters the second end of the polarization-maintaining few-mode polarization combiner 17.

[0028] The third end of the polarization-maintaining few-mode polarization combiner 17 is connected to the collimator 19 , the collimator 19 is connected to the polarizer 20 , and the output light of the polarizer 20 is monitored and displayed by a charge coupled device 21 .

[0029] The pump source 10 is a laser diode with a wavelength of 976 nm; the wavelength division multiplexer 11 is a 980 / 1060 nm polarization-maintaining wavelength division multiplexer.

[0030] The polarization-maintaining coupler 15 is connected end to end to form a total reflector with a reflectivity of 100%. The polarization-maintaining long-period fiber grating 13 is used for mode conversion. The polarization-maintaining few-mode fiber Bragg grating 14 is used as a partial reflector and an output cavity mirror. The polarization-maintaining coupler 15 and the polarization-maintaining few-mode fiber Bragg grating 14 form a resonant cavity.

[0031] The polarization-maintaining few-mode coupler 16 divides the power of port O equivalently; the polarization-maintaining few-mode polarization combiner 17 serves as a mode superposition device; the fiber stretcher 18 consists of two cylinders for fixing the optical fiber and a micrometer, which is used to adjust the phase shift of the linear mode.

[0032] The laser cavity between the polarization-maintaining coupler 15 and the polarization-maintaining long-period fiber grating 13 operates in the fundamental mode, and the laser cavity between the polarization-maintaining long-period fiber grating 13 and the polarization-maintaining few-mode fiber Bragg grating 14 operates in the first-order mode.

[0033] The light incident from the ytterbium-doped optical fiber 12 to the polarization-maintaining long-period fiber grating 13 excites a first-order mode near the resonance wavelength; after the generated first-order mode reaches the polarization-maintaining few-mode fiber Bragg grating 14, a part of it is output to enter the mode superposition unit, and the other part is reflected back into the cavity, and then converted into the fundamental mode by the polarization-maintaining long-period fiber grating 13, and oscillates in the resonant cavity.

[0034] Polarization-maintaining long-period fiber grating 13 converts fundamental mode into LP x 11a At port O, the power is equivalently divided into two paths. One path is input from the ① end of the polarization-maintaining few-mode polarization combiner 17, and the mode is LP. x 11aThe other path is adjusted for phase shift by the fiber stretcher and input from the second end of the polarization-maintaining few-mode polarization combiner 17. The mode is LP. y 11a , after the modes are superimposed by the polarization-maintaining few-mode polarization combiner 17, the radial polarization mode is output at port ③.

[0035] Compared with the prior art, the advantages of the utility model are as follows:

[0036] (1) The device of the present invention has the advantages of stable structure, high column vector beam purity and high efficiency, and can meet the needs of practical applications. The mode conversion efficiency can reach 95%, and the final angular polarization and radial polarization column vector purities are 95.6% and 96.1%, respectively.

[0037] (2) The device of the present invention is simple to connect, easy to prepare and put into practical use. The device of the present invention is not affected by external factors, has a stable structure, is easy to implement, can improve production efficiency, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0039] The above features and advantages of the present invention can be better understood after reading the detailed description of the embodiments of the present disclosure in conjunction with the following drawings. In the drawings, the components are not necessarily drawn to scale, and components with similar related properties or features may have the same or similar reference numerals.

[0040] Figure 1 It is a schematic diagram of an all-fiber laser device for generating a cylindrical vector beam provided by the present invention.

[0041] The invention comprises: an amplifier unit 100, a functional structure unit 200, a mode superposition unit 300 and a beam monitoring unit 400. The amplifier unit 100 comprises a pump source 10, a wavelength division multiplexer 11 and an ytterbium-doped optical fiber 12; the functional structure unit 200 comprises a resonant cavity composed of a 3dB polarization-maintaining coupler 15 and a polarization-maintaining few-mode fiber Bragg grating 14, and a polarization-maintaining long-period fiber grating 13; the mode superposition unit 30 comprises a 50:50 polarization-maintaining few-mode coupler 16, a polarization-maintaining few-mode polarization combiner 17 and a fiber stretcher 18; and the beam monitoring unit 400 comprises a collimator 19, a polarizer 20 and a charge coupled device 21. DETAILED DESCRIPTION

[0042] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The aspects described below in conjunction with the accompanying drawings and specific embodiments are only exemplary and should not be construed as limiting the protection scope of the present invention in any way.

[0043] The present invention proposes an all-fiber cylindrical vector laser, which is characterized by comprising: an amplifier unit 100, a functional structure unit 200, a mode superposition unit 300 and a beam monitoring unit 400.

[0044] The amplifier unit 100 is used to provide laser generation and amplification;

[0045] The functional structure unit 200 is used to phase modulate the light beam to satisfy a certain phase relationship;

[0046] The mode superposition unit 300 is used to perform mode superposition on the light beam to generate a target light beam;

[0047] The light beam monitoring unit 400 is used to adjust the phase of the light beam to obtain a cylindrical vector light beam with a preset polarization distribution, and monitor and display it through an optical device.

[0048] The amplifier unit 100 includes: a pump source 10, a wavelength division multiplexer 11, and an ytterbium-doped optical fiber 12; the functional structure unit 200 includes: a resonant cavity, a mode conversion device; the mode superposition unit 300 includes: a coupler 16, a polarization combiner 17 and a fiber stretcher 18; the beam monitoring unit includes a collimator 19, a polarizer 20 and a charge coupled device 21.

[0049] The following is a description of the feasible structures of each unit in the embodiment of the present invention (refer to Figure 1 )

[0050] The amplifier unit 100 includes a pump source 10, a wavelength division multiplexer 11, and an ytterbium-doped optical fiber 12; the pump source 10 is a laser diode with a wavelength of 976nm; the wavelength division multiplexer 11 is a 980 / 1060nm polarization-maintaining wavelength division multiplexer (PM-WDM), and the wavelength division multiplexer 11 is used to better couple the light source into the optical fiber and reduce transmission loss; the ytterbium-doped optical fiber 12 is used as a gain medium.

[0051] The functional structure unit 200 includes a resonant cavity composed of a 3dB polarization-maintaining coupler 15 and a polarization-maintaining few-mode fiber Bragg grating 14, and a polarization-maintaining long-period fiber grating 13; the 3dB coupler 15 is connected end to end to form a total reflector with a reflectivity of 100%; the polarization-maintaining few-mode fiber Bragg grating 14 is written on the polarization-maintaining fiber as a partial reflector, used as an output cavity mirror, and performs mode selection and spectrum filtering at the same time. The polarization-maintaining long-period fiber grating 13 is used as a mode conversion device. The laser cavity between the total reflection mirror and the polarization-maintaining long-period fiber Bragg grating 13 operates in the fundamental mode, and the laser cavity between the polarization-maintaining long-period fiber Bragg grating 13 and the polarization-maintaining few-mode fiber Bragg grating 14 operates in the first-order mode. The fundamental mode is amplified by the amplifier unit 100 and incident on the polarization-maintaining long-period fiber Bragg grating 13, and the first-order mode is excited efficiently and selectively near the resonance wavelength; the generated first-order mode reaches the polarization-maintaining few-mode fiber Bragg grating 14, a part of which is output into the mode superposition unit, and the other part is reflected back into the cavity, and then converted into the fundamental mode by the polarization-maintaining long-period fiber Bragg grating 13, and oscillates in the resonant cavity.

[0052] The mode superposition unit 300 includes a 50:50 polarization-maintaining few-mode coupler 16, a polarization-maintaining few-mode polarization combiner 17, and a fiber stretcher 18; the polarization-maintaining few-mode coupler 16 divides the port O power equivalently, the polarization-maintaining few-mode polarization combiner 17 serves as a mode superposition device, and the fiber stretcher 18 consists of two cylinders for fixing the optical fiber and a micrometer for adjusting the phase shift of the linear mode. The polarization-maintaining long-period fiber grating 13 converts the fundamental mode into the LP x 11a , after the power is equivalently divided at port O, it is divided into two paths. One path is input from the ① end of the polarization-maintaining few-mode polarization combiner 17, and the mode is LP x 11a The other path is adjusted for phase shift by the fiber stretcher and input from the second end of the polarization-maintaining few-mode polarization combiner 17. The mode is LP. y 11a , after the PM-FMPBC polarization-maintaining few-mode polarization combiner 17 modes are superimposed, the radial polarization mode is output at port ③.

[0053] The beam monitoring unit 400 includes a collimator 19 , a polarizer 20 and a charge coupled device 21 .

[0054] The edge of the light beam cannot pass through completely due to phase reasons, thereby narrowing the light beam. In such a resonant cavity, the light beam is narrowed again and again and amplified again and again under the action of the ytterbium-doped optical fiber 12, and finally a balance between gain and loss is achieved.

[0055] In the example of the present invention, the mode conversion efficiency can reach 95%, and the vector purity of the angular polarization and radial polarization columns finally obtained are 95.6% and 96.1% respectively.

[0056] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0057] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be apparent to those skilled in the art, and the universal principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein, but should be granted the widest scope consistent with the principles and novel features disclosed herein.

[0058] The above description is only a preferred example of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An all-fiber cylindrical vector laser, comprising a pump source (10), characterized in that: The pump source (10) and the polarization-maintaining coupler (15) are connected to a wavelength division multiplexer (11) together. The wavelength division multiplexer (11) couples the light source into an ytterbium-doped optical fiber (12). The ytterbium-doped optical fiber (12) is connected to a polarization-maintaining long-period optical fiber grating (13). The polarization-maintaining long-period optical fiber grating (13) is connected to a polarization-maintaining few-mode optical fiber Bragg grating (14). The polarization-maintaining few-mode optical fiber Bragg grating (14) is connected to a polarization-maintaining few-mode coupler (16). The polarization-maintaining few-mode coupler (16) divides the optical path into two paths. One path is connected to the first end of a polarization-maintaining few-mode polarization combiner (17), and the other path passes through an optical fiber stretcher (18) and enters the second end of the polarization-maintaining few-mode polarization combiner (17).

2. The all-fiber cylindrical vector laser according to claim 1, characterized in that: The third end of the polarization-maintaining few-mode polarization beam combiner (17) is connected to a collimator (19), the collimator (19) is connected to a polarizer (20), and a charge coupled device (21) is used to monitor and display the output light of the polarizer (20).

3. The all-fiber cylindrical vector laser according to claim 2, characterized in that : The pump source (10) is a laser diode with a wavelength of 976nm; the wavelength division multiplexer (11) is a 980 / 1060nm polarization-maintaining wavelength division multiplexer.

4. The all-fiber cylindrical vector laser according to any one of claims 1 to 3, characterized in that: The polarization-maintaining coupler (15) is connected end to end to form a total reflection mirror with a reflectivity of 100%. The polarization-maintaining long-period fiber grating (13) is used for mode conversion. The polarization-maintaining few-mode fiber Bragg grating (14) is used as a partial reflection mirror and an output cavity mirror. The polarization-maintaining coupler (15) and the polarization-maintaining few-mode fiber Bragg grating (14) form a resonant cavity.

5. The all-fiber cylindrical vector laser according to claim 4, characterized in that: The polarization-maintaining few-mode coupler (16) divides the power of port O equivalently; the polarization-maintaining few-mode polarization combiner (17) serves as a mode superposition device; and the optical fiber stretcher (18) is composed of two cylinders for fixing the optical fiber and a micrometer, and is used to adjust the phase shift of the linear mode.

6. The all-fiber cylindrical vector laser according to claim 5, characterized in that: The laser cavity between the polarization-maintaining coupler (15) and the polarization-maintaining long-period fiber grating (13) operates in the fundamental mode, and the laser cavity between the polarization-maintaining long-period fiber grating (13) and the polarization-maintaining few-mode fiber Bragg grating (14) operates in the first-order mode.

7. The all-fiber cylindrical vector laser according to claim 6, characterized in that: Light incident from an ytterbium-doped optical fiber (12) to a polarization-maintaining long-period optical fiber grating (13) excites a first-order mode near a resonance wavelength; after the generated first-order mode reaches a polarization-maintaining few-mode optical fiber Bragg grating (14), a portion of the first-order mode is output to enter a mode superposition unit, and the other portion is reflected back into the cavity, and then converted into a fundamental mode by the polarization-maintaining long-period optical fiber grating (13), and oscillates in the resonance cavity.

8. The all-fiber cylindrical vector laser according to claim 7, characterized in that: Polarization-maintaining long-period fiber grating (13) converts the fundamental mode into LP x 11a At port O, the power is equivalently divided into two paths. One path is input from the ① end of the polarization-maintaining few-mode polarization combiner (17), and the mode is LP. x 11a The other path is adjusted for phase shift by a fiber stretcher and input from the second end of the polarization-maintaining few-mode polarization combiner (17). The mode is LP. y 11a , after mode superposition by the polarization-maintaining few-mode polarization combiner (17), a radial polarization mode is output at port ③.

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