Mode-locked fiber laser capable of generating high-order mode as required

Abstract

The invention discloses a mode-locked fiber laser capable of generating a high-order mode as required, which belongs to the technical field of lasers, and comprises an amplification module, a transmission element, a computer, a polarization adjustment element and an output element, and the amplification module, the transmission element and the polarization adjustment element form an annular cavity structure through a single-mode fiber; the amplification module comprises a pumping source, an isolator, a wavelength division multiplexer and an erbium-doped gain fiber which are sequentially connected through a single-mode fiber. According to the mode-locked optical fiber laser capable of generating the high-order mode as required, nonlinear polarization rotation mode locking is achieved by adjusting the optical fiber polarization controller, stable high-energy pulses can be generated, and output of ultrashort pulses can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of lasers, and in particular to a mode-locked fiber laser capable of generating high-order modes on demand. Background Art

[0002] In the spatial dimension of photons, the spatial structure of the light field can be manipulated by spatially distributed phase, polarization and intensity. This special light field is called structured light and can be applied in a wider range of fields. For example, the infinite orthogonal characteristics of the vortex light field and its compatibility with other physical dimensions of photons can achieve sustainable expansion in optical communications. Currently, spatial light modulators (SLMs) are mainly used to shape the light beam through computer-generated phase maps or holograms to achieve structured light output.

[0003] In optical communication systems, fiber lasers have better stability and better beam quality than semiconductor lasers, are more compatible with optical fiber communication systems, and can effectively reduce system complexity and cost.

[0004] In fiber optic sensors, high-order modes enable high discrimination of temperature and strain. However, laser light from conventional lasers oscillates in both high-order modes and fundamental modes. Therefore, it is difficult to customize and prescribe pure high-order modes for specific applications. Summary of the invention

[0005] The purpose of the present invention is to provide a mode-locked fiber laser that can generate high-order modes on demand, generate high-order modes of different modes under the light field shaping action of a spatial light modulator, and realize the generation of high-order mode fiber laser on demand.

[0006] To achieve the above-mentioned purpose, the present invention provides a mode-locked fiber laser that can generate high-order modes on demand, including an amplification module, a transmission element, a computer, a polarization adjustment element and an output element, and the amplification module, the transmission element, and the polarization adjustment element form a ring cavity structure through a single-mode optical fiber, and the amplification module includes a pump source, an isolator, a wavelength division multiplexer, and an erbium-doped gain fiber that are sequentially connected through the single-mode optical fiber.

[0007] Preferably, the transmission element includes a first fiber optic collimator, a filter, a half-wave plate, a polarizer, a spatial light modulator, and a second fiber optic collimator which are arranged in sequence. The other end of the first fiber optic collimator is connected to the erbium-doped gain fiber. The first fiber optic collimator, the filter, the half-wave plate, and the polarizer are all coaxially placed at the same height as the liquid crystal screen of the spatial light modulator.

[0008] Preferably, the pump source is a semiconductor laser, the output wavelength of the semiconductor laser is 980 nm, the actual output power range is 0-470 mW, and the operating wavelength of the isolator is 980 nm.

[0009] Preferably, the wavelength division multiplexer uses an optical fiber device with wavelengths of 980nm and 1550nm multiplexing, the insertion loss is no more than 0.2dB, the erbium-doped gain fiber uses a single-mode fiber, the output laser is in the 1550nm band, and the dispersion coefficient is −21.4ps 2 / km.

[0010] Preferably, the central wavelength of the filter is 1550nm±2.4nm, the spatial light modulator is a silicon-based liquid crystal spatial light modulator, the reflectivity of the silicon-based liquid crystal spatial light modulator is 80%, the high-definition phase display pixel is 1920*1080, the spectral range is 1400-1700nm, and the grayscale level is 256.

[0011] Preferably, the polarization adjustment element includes a fiber polarization controller, a fiber coupler, and a polarization-dependent isolator arranged in sequence, the fiber polarization controller and the polarization-dependent isolator are connected to the fiber coupler through a single-mode optical fiber, and the other end of the fiber polarization controller is connected to a second fiber collimator.

[0012] Preferably, the optical fiber polarization controller adopts a three-paddle optical fiber polarization controller, which includes three rotating paddles, and the three rotating paddles are composed of a quarter wave plate, a half wave plate 2 and a quarter wave plate connected in series in sequence.

[0013] Preferably, the coupling ratio of the output optical power and the intracavity optical power corresponding to the optical fiber coupler is 10:90, 20:80, 30:70, 40:60 or 50:50, the isolation of the polarization-dependent isolator is above 30dB, the insertion loss is less than 0.55dB, and the withstand power is not more than 300mW.

[0014] Preferably, the output element includes a third fiber collimator, a few-mode fiber, a fourth fiber collimator, a lens, and an image sensor which are arranged in sequence, and the other end of the third fiber collimator is connected to the spatial light modulator.

[0015] Preferably, the pump source, isolator, wavelength division multiplexer, erbium-doped gain fiber, fiber polarization controller, fiber coupler, and polarization-dependent isolator are respectively fusion-spliced ​​using a fiber fusion splicer, and the fusion loss is less than 0.2 dB.

[0016] Therefore, the present invention adopts the above-mentioned mode-locked fiber laser that can generate high-order modes on demand, and has the following beneficial effects: a silicon-based liquid crystal spatial light modulator with a higher dynamic range is adopted to generate high-order modes of different modes under the light field shaping effect of the spatial light modulator, so as to realize the generation of high-order mode fiber laser on demand, and realize nonlinear polarization rotation mode locking by adjusting the fiber polarization controller, which can not only generate stable high-energy pulses, but also realize the output of ultrashort pulses.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic structural diagram of a mode-locked fiber laser capable of generating high-order modes on demand according to an embodiment of the present invention; Figure 2 The spot diagrams of different high-order modes of a mode-locked fiber laser capable of generating high-order modes on demand according to an embodiment of the present invention; Figure 3 This is a timing diagram of a mode-locked fiber laser capable of generating high-order modes on demand with a pump power of 45.31 mW according to an embodiment of the present invention; Figure 4 This is a timing diagram of a mode-locked fiber laser capable of generating high-order modes on demand with a pump power of 164.4 mW according to an embodiment of the present invention; Reference numerals 1. Pump source; 2. Isolator; 3. Wavelength division multiplexer; 4. Erbium-doped gain fiber; 5. First fiber collimator; 6. Filter; 7. Half-wave plate 1; 8. Polarizer; 9. Silicon-based liquid crystal spatial light modulator; 10. Second fiber collimator; 11. Polarization controller; 12. Fiber coupler; 13. Polarization-dependent isolator; 14. Third fiber collimator; 15. Few-mode fiber; 16. Fourth fiber collimator; 17. Lens; 18. Image sensor; 19. Computer. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0021] Example like Figure 1-4As shown, the present invention provides a mode-locked fiber laser that can generate high-order modes on demand, including an amplification module, a transmission element, a computer 19, a polarization adjustment element and an output element, and the amplification module, the transmission element, and the polarization adjustment element form a ring cavity structure through a single-mode optical fiber.

[0022] The amplification module includes a pump source 1, an isolator 2, a wavelength division multiplexer 3, and an erbium-doped gain fiber 4 connected in sequence through a single-mode optical fiber. The pump source 1 is a semiconductor laser, and the output wavelength band of the semiconductor laser is 980nm. The actual output power range of the semiconductor laser is 0-470mW. The operating wavelength of the isolator 2 is 980nm, which is used to ensure the unidirectional transmission of the 980nm pump light and to prevent the 1550nm oscillation light from being reflected at the amplification module. The wavelength division multiplexer 3 is used to form an optical circuit, and uses an optical fiber device with wavelengths of 980nm and 1550nm multiplexing, and the insertion loss is not greater than 0.2dB. The erbium-doped gain fiber 4 uses a single-mode optical fiber to achieve population inversion and generate stimulated emission amplification of light. The erbium-doped gain fiber 4 uses Coherent SM-EDF 980HP single-mode optical fiber, which is a highly doped gain fiber with a length of 15m, an output laser in the 1550nm band, and a dispersion coefficient of −21.4ps. 2 / km. The pump source 1 introduces the pump laser into the erbium-doped gain fiber 4 through the isolator 2 and the wavelength division multiplexer 3. After the laser is absorbed by the erbium-doped gain fiber 4, a spontaneous emission laser in the 1550nm band is generated, and then oscillation is formed in the ring cavity, thereby generating laser.

[0023] The transmission element includes a first fiber collimator 5, a filter 6, a half-wave plate 7, a polarizer 8, a spatial light modulator 9, and a second fiber collimator 10, which are arranged in sequence. The other end of the first fiber collimator 5 is connected to the erbium-doped gain fiber 4. The central wavelength of the filter 6 is 1550nm±2.4nm, so the wavelength is locked in the C band and the L band. The spatial light modulator 9 is a silicon-based liquid crystal spatial light modulator. The reflectivity of the silicon-based liquid crystal spatial light modulator is 80%, the high-definition phase display pixel is 1920*1080, the spectral range is 1400-1700nm, and the grayscale level is 256. The multi-phase mask plate is loaded on the spatial light modulator using a checkerboard pattern, and the amplitude and phase of the incident light field can be modulated, and the Gaussian basis transverse mode and the high-order mode correspond to different diffraction gratings, so that the high-order mode and the fundamental transverse mode in the reflected light beam are separated in space.

[0024] The first optical fiber collimator 5, filter 6, half-wave plate 7, and polarizer 8 are all placed coaxially and at the same height as the liquid crystal screen of the spatial light modulator 9. The half-wave plate 7 and polarizer 8 are used to adjust the laser polarization direction to be consistent with the functional direction of the spatial light modulator 9.

[0025] The polarization adjustment element includes a fiber polarization controller 11, a fiber coupler 12, and a polarization-dependent isolator 13 which are arranged in sequence. The fiber polarization controller 11 and the polarization-dependent isolator 13 are connected to the fiber coupler 12 via a single-mode optical fiber. The other end of the fiber polarization controller 11 is connected to the second fiber collimator 10.

[0026] The optical fiber polarization controller 11 adopts a three-paddle optical fiber polarization controller, which is used to change the polarization state in the resonant cavity and realize nonlinear polarization rotation mode locking. The three-paddle optical fiber polarization controller includes three rotating paddles, which are composed of a quarter wave plate, a half wave plate and a quarter wave plate connected in series in sequence. The birefringence is obtained by bending and winding the optical fiber, and the polarization state in the resonant cavity is changed, which is used to control the nonlinear polarization rotation related loss to realize mode locking.

[0027] The output optical power and intracavity optical power coupling ratio of the fiber coupler 12 is 10:90, 20:80, 30:70, 40:60 or 50:50. For example, the fiber coupling ratio of the fiber coupler 12 is 20:80, wherein the 20% end is used as the output end of the laser, and the 80% end is connected to the polarization-dependent isolator 13, and oscillates in the ring resonator to generate laser light.

[0028] The polarization-dependent isolator 13 is used to ensure unidirectional transmission of the light field in the ring cavity, and is combined with the polarization controller 11 to construct an equivalent saturable absorber. The polarization-dependent isolator 13 has an isolation of more than 30 dB, an insertion loss of less than 0.55 dB, and a power handling capacity of no more than 300 mW.

[0029] The output element includes a third fiber collimator 14, a few-mode fiber 15, a fourth fiber collimator 16, a lens 17, and an image sensor 18, which are arranged in sequence. The other end of the third fiber collimator 14 is connected to the spatial light modulator 9. The few-mode fiber 15 can realize the simultaneous transmission of multiple modes without being affected by the distance; the lens 17 can focus the laser and output more concentrated energy; the image sensor 18 is used to capture the intensity distribution of the output light beam after propagating in the few-mode fiber 15.

[0030] The pump source 1, isolator 2, wavelength division multiplexer 3, erbium-doped gain fiber 4, fiber polarization controller 11, fiber coupler 12, and polarization-dependent isolator 13 are respectively spliced ​​by fiber fusion splicers, and the single-mode fiber is a standard G.652 type fiber with the minimum loss in the 1550nm band, and the splicing loss is less than 0.2dB.

[0031] Working principle: After the laser is modulated by the multi-mode mask of the spatial light modulator 9 (SLM), the light beam is divided into two sub-beams, one is the fundamental mode and the other is the high-order mode. The fundamental mode beam is coupled into the ring cavity through the second fiber collimator 10, and the high-order mode beam is coupled into the few-mode fiber 15 through the third fiber collimator 14 for transmission, and is output from the fourth fiber collimator 16. After being focused by the lens 17, the image sensor 18 is used to capture the intensity distribution of the output beam after propagation in the few-mode fiber 15.

[0032] Therefore, the present invention adopts the above-mentioned mode-locked fiber laser that can generate high-order modes on demand, and realizes nonlinear polarization rotation mode locking by adjusting the fiber polarization controller, which can not only generate stable high-energy pulses, but also achieve the output of ultrashort pulses.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A mode-locked fiber laser capable of generating high-order modes on demand, characterized in that: It includes an amplification module, a transmission element, a computer, a polarization adjustment element and an output element, wherein the amplification module, the transmission element and the polarization adjustment element form a ring cavity structure through a single-mode optical fiber, and the amplification module includes a pump source, an isolator, a wavelength division multiplexer and an erbium-doped gain optical fiber which are sequentially connected through the single-mode optical fiber.

2. A mode-locked fiber laser capable of generating high-order modes on demand according to claim 1, characterized in that: The transmission element includes a first fiber collimator, a filter, a half-wave plate, a polarizer, a spatial light modulator, and a second fiber collimator which are arranged in sequence. The other end of the first fiber collimator is connected to the erbium-doped gain fiber. The first fiber collimator, the filter, the half-wave plate, and the polarizer are all coaxially placed at the same height as the liquid crystal screen of the spatial light modulator.

3. A mode-locked fiber laser capable of generating high-order modes on demand according to claim 1, characterized in that: The pump source is a semiconductor laser, the output band of the semiconductor laser is 980nm, the actual output power range is 0-470mW, and the working wavelength of the isolator is 980nm.

4. A mode-locked fiber laser capable of generating high-order modes on demand according to claim 1, characterized in that: The wavelength division multiplexer uses a fiber device with wavelengths of 980nm and 1550nm multiplexing, with an insertion loss of no more than 0.2dB. The erbium-doped gain fiber uses a single-mode fiber, the output laser is in the 1550nm band, and the dispersion coefficient is −21.4ps. 2 / km.

5. The mode-locked fiber laser capable of generating high-order modes on demand according to claim 2, characterized in that: The central wavelength of the filter is 1550nm±2.4nm, the spatial light modulator is a silicon-based liquid crystal spatial light modulator, the reflectivity of the silicon-based liquid crystal spatial light modulator is 80%, the high-definition phase display pixel is 1920*1080, the spectral range is 1400-1700nm, and the grayscale level is 256.

6. The mode-locked fiber laser capable of generating high-order modes on demand according to claim 1, characterized in that: The polarization adjustment element includes a fiber polarization controller, a fiber coupler, and a polarization-dependent isolator which are arranged in sequence. The fiber polarization controller and the polarization-dependent isolator are connected to the fiber coupler through a single-mode optical fiber, and the other end of the fiber polarization controller is connected to a second fiber collimator.

7. A mode-locked fiber laser capable of generating high-order modes on demand according to claim 6, characterized in that: The optical fiber polarization controller adopts a three-paddle optical fiber polarization controller, which includes three rotating paddles. The three rotating paddles are composed of a quarter wave plate, a half wave plate 2 and a quarter wave plate connected in series in sequence.

8. The mode-locked fiber laser capable of generating high-order modes on demand according to claim 6, characterized in that: The corresponding coupling ratio of the output optical power and the intracavity optical power of the optical fiber coupler is 10:90, 20:80, 30:70, 40:60 or 50:50, the isolation of the polarization-dependent isolator is above 30 dB, the insertion loss is less than 0.55 dB, and the withstand power is not more than 300 mW.

9. The mode-locked fiber laser capable of generating high-order modes on demand according to claim 6, characterized in that: The output element comprises a third optical fiber collimator, a few-mode optical fiber, a fourth optical fiber collimator, a lens, and an image sensor which are arranged in sequence. The other end of the third optical fiber collimator is connected to the spatial light modulator.

10. A mode-locked fiber laser capable of generating high-order modes on demand according to claim 9, characterized in that: The pump source, isolator, wavelength division multiplexer, erbium-doped gain fiber, fiber polarization controller, fiber coupler, and polarization-dependent isolator are respectively fusion-spliced ​​by fiber fusion splicers, and the fusion loss is less than 0.2 dB.

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