Multi-wavelength thulium-doped fiber laser and laser output method

Abstract

A multi-wavelength thulium-doped fiber laser and a laser output method belong to the fields of optical fiber communication and instrumentation. A pump source is connected to the input end of a beam combiner, the output end of the beam combiner is connected to one end of a thulium-doped fiber, the other end of the thulium-doped fiber is connected to port two of a circulator one, port three of the circulator one is connected to one end of a polarization controller two, the other end of the polarization controller two is connected to port one of a fiber coupler one, port three of the optical coupler one is connected to port one of an adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter, and port two of the adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter is connected to port three of the fiber coupler two. The advantage of the present invention is that it is a multi-wavelength thulium-doped fiber laser that is tunable and switchable in the 2μm band. Different modes can be adjusted by the curvature of the filter, solving the technical problems of low extinction ratio of the filter and unswitchable filter spectrum in the fiber laser.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber communication and instrumentation, and relates to a multi-wavelength thulium-doped optical fiber laser and a laser output method. Background Art

[0002] Multi-wavelength fiber thulium-doped fiber lasers can output fiber lasers with multiple wavelengths. They are core light source devices for optical communications and are widely used in wavelength division multiplexing (WDM) and mode division multiplexing (MDM). Traditional multi-wavelength lasers require a large system structure and are relatively costly, making them difficult to integrate. Multi-wavelength fiber lasers have a simpler structure and are easy to integrate. They have good heat dissipation and strong anti-electromagnetic interference capabilities. Only one laser is needed to achieve tunable and switchable multiple wavelengths. In addition, the proposed multi-wavelength thulium-doped fiber laser based on few-mode fiber interferometer has a small size and high pumping efficiency, and introduces multiple mode controls into the multi-wavelength laser. With the development of high-speed, multi-scenario, and long-distance optical communications, combining WDM and MDM technologies is one of the powerful technical solutions for the next generation of ultra-large-capacity optical fiber communications.

[0003] The 2μm band is eye-safe, possesses a low-loss atmospheric window, and boasts an atmospheric transmittance exceeding 80%. This band holds significant potential for application in space optical communications and can effectively expand the communication band. Furthermore, the strong absorption peak of water molecules is at 1.94μm, resulting in shallow penetration into muscle tissue. Lasers in the 2μm band can be used for rapid blood coagulation during surgical procedures, enabling simultaneous vaporization and cutting. Furthermore, lasers in the 2μm band also possess significant research value in areas such as terahertz wave generation, two-photon microscopy, lidar, gas molecule detection, and fiber-optic remote sensing.

[0004] Currently, multi-wavelength thulium-doped fiber lasers have been widely studied. For example, Sagnac rings and Rio filters are used to realize comb filters, or fiber Bragg gratings are used to complete mode selection, and nonlinear polarization rotation or four-wave mixing are used to suppress the competition of multiple wavelengths, thereby generating stable tunable and switchable multi-wavelength output. Among them, the filter is an important device for mode selection. Currently, there are problems with the filter's low extinction ratio and the single filter spectrum that cannot be switched. At present, the internal mode of the fiber cannot be switched when achieving multi-wavelength output in fiber lasers. Summary of the Invention

[0005] The present invention aims to solve the problems in the prior art and provides a multi-wavelength thulium-doped fiber laser and a laser output method.

[0006] A multi-wavelength thulium-doped fiber laser is disclosed. A pump source is connected to an input end of a beam combiner, an output end of the beam combiner is connected to one end of a thulium-doped fiber, the other end of the thulium-doped fiber is connected to port 2 of a first circulator, port 3 of the first circulator is connected to one end of a second polarization controller, the other end of the second polarization controller is connected to port 1 of a first fiber coupler, port 3 of the first optical coupler is connected to port 1 of an adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter, port 2 of the adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter is connected to port 3 of the second fiber coupler, port 1 of the second fiber coupler is connected to port 1 of the first circulator, port 2 of the second fiber coupler is connected to port 1 of the second circulator, port 2 of the second circulator is connected to the other port of the beam combiner, port 3 of the second circulator is connected to one end of the first polarization controller, the other end of the first polarization controller is connected to port 2 of the first fiber coupler, and port 4 of the first fiber coupler is connected to a spectrometer.

[0007] A multi-wavelength thulium-doped fiber laser output method comprises the following steps: using a single-mode-coreless-quadruple-coreless-single-mode fiber SMF-NCF-FMF-NCF-SMF with adjustable curvature to laser more high-order modes by regulating its curvature radius; adopting a SIT A cavity structure to improve the coupling efficiency of the pump power; using two polarization controllers located in two different ring cavities to regulate the polarization states in the two cavities through polarization-dependent loss to achieve stable single-wavelength output.

[0008] The advantages of the present invention are: in the 2μm band, a tunable and switchable multi-wavelength thulium-doped fiber laser, different modes can be adjusted by the curvature of the filter, which solves the technical problems of low extinction ratio of the filter and non-switchable filter spectrum in the fiber laser. The filter used in the laser is a single-mode fiber, a coreless fiber, a four-mode fiber, a coreless fiber, and a single-mode fiber that are normally phase-fused in sequence, without the need for staggered core docking. It is fixed on a displacement adjustment frame, and by changing the curvature at both ends, more high-order modes are emitted, thereby improving the extinction ratio of the filter and realizing switchable adjustment of the filter spectrum. In the improved SIT A cavity structure, two polarization controllers are located in different ring cavities, thereby introducing polarization-dependent loss effects and realizing stable multi-wavelength tunable output. The laser has a novel structure, low cost, and has stable high-slope efficiency, tunable, and switchable laser output performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. As shown in the figure:

[0010] Figure 1 It is a schematic diagram of one structure of the present invention.

[0011] Figure 2 This is a second schematic diagram of the structure of the present invention. DETAILED DESCRIPTION

[0012] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0013] Example 1: Figure 1 and Figure 2 As shown, a multi-wavelength thulium-doped fiber laser output method includes the following steps: using a curvature-adjustable single-mode-coreless-quadruple-coreless-single-mode fiber (SMF-NCF-FMF-NCF-SMF) filter, and adjusting its curvature radius to laser more high-order modes, thereby improving the filter's extinction ratio. This improves the current state of the art, which relies solely on offset welding to increase the extinction ratio, which is prone to high intracavity losses. Furthermore, the improved SITAR cavity structure based on bidirectional pump power amplification technology improves the coupling efficiency of the pump power and introduces the dual-ring laser characteristics of the SITAR cavity. The two polarization controllers used are located in two different ring cavities, and polarization-dependent losses are used to control the polarization states of the two cavities to achieve stable single-wavelength output. This laser will play an important role in WDM communication systems, MDM communication systems, high-precision sensing, space optical communications, and other fields.

[0014] A method for tunable and switchable multi-wavelength thulium-doped fiber laser in the 2μm band. A multi-wavelength thulium-doped fiber laser comprises a pump source 01, a beam combiner 02, a thulium-doped fiber 03, a circulator 04, a polarization controller 05, an optical coupler 06, an adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter 07, an optical coupler 08, a circulator 09, a polarization controller 10, and a spectrometer 11. The adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter 07 comprises a single-mode fiber 12, a displacement platform 13, a coreless fiber 14, a fixed platform 15, a quadruple-mode fiber 16, a fixed platform 17, a coreless fiber 2 18, a displacement platform 2 19, and a single-mode fiber 20.

[0015] The thulium-doped double-clad fiber laser uses cladding pumping technology to pump the thulium-doped gain fiber, which can achieve laser output in the 2μm band.

[0016] The method comprises the following steps: by adjusting polarization controller 1 5 and polarization controller 2 10 in two ring cavities of the laser, a polarization-dependent loss effect is introduced; when the polarization direction in one cavity is parallel to the polarization direction in the other, the wavelength can achieve stable laser output; and since the tunable single-mode-coreless-quadruple-coreless-single-mode filter has a comb spectrum with the same interval, the laser can achieve tunable multi-wavelength output with the same wavelength interval.

[0017] The method further includes the following steps: fixing the fixed platform 15 and the fixed platform 2 17 to remain stationary, and adjusting the curvature of the coreless fiber 14 and the core fiber 2 18 by moving the displacement platform 13 and the displacement platform 2 19, so that more high-order modes are excited.

[0018] By adjusting different curvature parameters, the filter spectrum can be freely switched to output, and the extinction ratio of the filter can be improved, thereby improving the mode coupling efficiency.

[0019] Example 2: Figure 1 and Figure 2 As shown, a multi-wavelength thulium-doped fiber laser includes a pump source, a beam combiner, a thulium-doped fiber, a circulator 1, a circulator 2, a polarization controller 1, a polarization controller 2, an optical coupler 1, an optical coupler 2, an adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter, and a spectrometer; wherein the adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter includes a displacement platform 1, a single-mode fiber, a coreless fiber 1, a quadruple-mode fiber, a coreless fiber 2, a displacement platform 1, and a displacement platform 2.

[0020] The pump source is connected to the input of the beam combiner, the output of the beam combiner is connected to one end of a thulium-doped fiber, the other end of the thulium-doped fiber is connected to port 2 of circulator 1, port 3 of circulator 1 is connected to one end of polarization controller 2, the other end of polarization controller 2 is connected to a port of fiber coupler 1, port 3 of optical coupler 1 is connected to port 1 of a tunable single-mode-coreless-quadruple-coreless-single-mode filter, port 2 of the tunable single-mode-coreless-quadruple-coreless-single-mode filter is connected to port 3 of fiber coupler 2, and port 1 of fiber coupler 2 is connected to port 1 of circulator 1. The other port of the beam combiner is connected to port 2 of circulator 2, port 3 of circulator 2 is connected to one end of polarization controller 1, the other end of polarization controller 1 is connected to port 2 of fiber coupler 1, port 4 of fiber coupler 1 is connected to a spectrometer, and port 2 of fiber coupler 2 is connected to port 1 of circulator 2.

[0021] The adjustable single-mode-coreless-quad-mode-coreless-single-mode filter is made by splicing single-mode fiber, coreless fiber, quad-mode fiber, coreless fiber, and single-mode fiber. Single-mode fiber 1 is fixed on the displacement platform, coreless fiber 1 is placed between displacement platform 1 and fixed platform 1, quad-mode fiber is on fixed platforms 1 and 2, coreless fiber 2 is placed between fixed platform 2 and displacement platform 2, and single-mode fiber 2 is fixed on displacement platform 2.

[0022] Example 3: Figure 1 and Figure 2 As shown, a multi-wavelength thulium-doped fiber laser includes a pump source 01, a beam combiner 02, a thulium-doped fiber 03, a circulator 04, a polarization controller 05, an optical coupler 06, an adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter 07, an optical coupler 08, a circulator 09, a polarization controller 10, and a spectrometer 11, wherein the adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter 07 includes a single-mode fiber 12, a displacement platform 13, a coreless fiber 14, a fixed platform 15, a quadruple-mode fiber 16, a fixed platform 17, a coreless fiber 2 18, a displacement platform 2 19, and a single-mode fiber 20.

[0023] The pump source 01 is connected to the input end of the beam combiner 02, the output end 021 of the beam combiner 02 is connected to one end 031 of the thulium-doped fiber 03, the other end 032 of the thulium-doped fiber 03 is connected to the second port 042 of the circulator 04, the third port 043 of the circulator 04 is connected to one end 051 of the polarization controller 05, the other end 052 of the polarization controller 05 is connected to the first port 061 of the optical fiber coupler 06, the third port 063 of the optical coupler 06 is connected to the first port 071 of the tunable single-mode-coreless-quadruple-coreless-single-mode optical fiber filter 07, the tunable single-mode-coreless-quadruple-coreless-single-mode optical fiber filter 07 Port 2 072 of 7 is connected to port 3 083 of fiber coupler 2 08, port 1 081 of fiber coupler 2 08 is connected to port 1 041 of circulator 1 04, port 2 082 of fiber coupler 2 08 is connected to port 1 091 of circulator 2 09, port 2 092 of circulator 2 09 is connected to another port 022 of combiner 02, port 3 093 of circulator 2 09 is connected to one end 101 of polarization controller 10, the other end 102 of polarization controller 10 is connected to port 2 062 of fiber coupler 1 06, and port 4 064 of fiber coupler 1 06 is connected to spectrometer 11.

[0024] The port 1071 of the adjustable single-mode-coreless-quadruple-coreless-single-mode optical fiber filter 07 is connected to one end 121 of the single-mode optical fiber 12. Through the displacement platform 13, the other end 122 of the single-mode optical fiber 12 is connected to one end 141 of the coreless optical fiber 14, and the other end 142 is connected to one end 161 of the four-mode optical fiber 16. Through the fixed platform 15 and the fixed platform 2 17, the other end 162 of the four-mode optical fiber 16 is connected to one end 181 of the coreless optical fiber 2 18, and the other end 182 is connected to one end 201 of the single-mode optical fiber 2 20. Through the displacement platform 2 19, the other end 202 of the single-mode optical fiber 2 20 is connected to the port 2072 of the adjustable single-mode-coreless-quadruple-coreless-single-mode optical fiber filter 07.

[0025] Device functions: Pump source 01 is a semiconductor laser that emits 793nm laser, beam combiner 02 effectively couples the pump light to the doped double-clad fiber, thulium-doped fiber 03 is a gain fiber, circulator 1 04 and circulator 2 09 are multi-port devices that transmit the incident light to the next port in a determined direction sequence, polarization controller 2 05 and polarization controller 10 control the polarization direction in the laser cavity, optical coupler 1 06 and optical coupler 2 08 split the optical power of the same wavelength, and adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter 07 is used for mode selection and curvature control.

[0026] Switchable function: The curvature of the tunable single-mode-coreless-quadruple-coreless-single-mode fiber filter can be adjusted by moving the displacement platform. As the curvature changes, the higher-order modes in the filter are more excited, and the interference pattern and extinction ratio change accordingly. Therefore, the interference spectrum can be switched to different modes to achieve wavelength switching.

[0027] Tunable function: Due to the use of two polarization controllers, when the polarization direction in one cavity is parallel to the polarization direction in the other cavity, due to the effect of polarization-dependent loss, a single-wavelength laser can be output stably. By adjusting the polarization angle of the polarization controller, a multi-wavelength tunable output function with the same wavelength interval is achieved.

[0028] The first fiber coupler 06 is a 2×2 coupler with a splitting ratio of 50:50, and the second fiber coupler 08 is a 1×2 coupler with a splitting ratio of 50:50.

[0029] Curvature-adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter 07, the length of the coreless fiber 14 and the coreless fiber 2 18 is 1 cm, the length of the quadruple-mode fiber 16 is 1 m, and the curvature radius is adjusted by the displacement platform 13 and the displacement platform 2 19, so that the high-order modes are excited more, which not only improves the extinction ratio of the filter, but also enables the filter to switch to multi-wavelength output.

[0030] Thulium-doped fiber 03 is a double-clad thulium-doped fiber. By introducing a second waveguide structure, the double-clad thulium-doped fiber allows the pump light and signal light to propagate in different waveguide structures, thereby achieving efficient energy conversion. The double-clad thulium-doped fiber 03 is 1.9m long and the double-clad thulium-doped fiber used is SM-TDF-10P / 130M produced by Nufern, USA.

[0031] Polarization controller 2 05 and polarization controller 1 10 adjust the polarization states of the two ring cavities to introduce polarization-dependent loss and achieve stable tunable output.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multi-wavelength thulium-doped fiber laser, characterized in that: The pump source is connected to the input end of the beam combiner, the output end of the beam combiner is connected to one end of the thulium-doped fiber, the other end of the thulium-doped fiber is connected to port 2 of circulator 1, port 3 of circulator 1 is connected to one end of polarization controller 2, the other end of polarization controller 2 is connected to port 1 of fiber coupler 1, port 3 of optical coupler 1 is connected to port 1 of the tunable single-mode-coreless-quadruple-coreless-single-mode fiber filter, port 2 of the tunable single-mode-coreless-quadruple-coreless-single-mode fiber filter is connected to port 3 of fiber coupler 2, port 1 of fiber coupler 2 is connected to port 1 of circulator 1, port 2 of fiber coupler 2 is connected to port 1 of circulator 2, port 2 of circulator 2 is connected to the other port of the beam combiner, port 3 of circulator 2 is connected to one end of polarization controller 1, the other end of polarization controller 1 is connected to port 2 of fiber coupler 1, and port 4 of fiber coupler 1 is connected to the spectrometer.

2. The multi-wavelength thulium-doped fiber laser according to claim 1, characterized in that: Port one of the adjustable single-mode-coreless-quad-mode-coreless-single-mode optical fiber filter is connected to one end of single-mode optical fiber one, passes through displacement platform one, and the other end of single-mode optical fiber one is connected to one end of coreless optical fiber one, and the other end is connected to one end of four-mode optical fiber, passes through fixed platform one and fixed platform two, and the other end of four-mode optical fiber is connected to one end of coreless optical fiber two, and the other end is connected to one end of single-mode optical fiber two, passes through displacement platform two, and the other end of single-mode optical fiber two is connected to port two of the adjustable single-mode-coreless-quad-mode-coreless-single-mode optical fiber filter.

3. The multi-wavelength thulium-doped fiber laser according to claim 1, characterized in that: The first fiber coupler is a 2×2 coupler with a splitting ratio of 50:50, and the second fiber coupler is a 1×2 coupler with a splitting ratio of 50:

50.

4. The multi-wavelength thulium-doped fiber laser according to claim 1, characterized in that: The curvature-adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter, the length of coreless fiber 1 and coreless fiber 2 are 1 cm, the length of the quadruple-mode fiber is 1 m, and the curvature radius is adjusted by displacement platform 1 and displacement platform 2, so that higher-order modes are excited more, which not only improves the extinction ratio of the filter but also enables the filter to switch to multi-wavelength output.

5. The multi-wavelength thulium-doped fiber laser according to claim 1, characterized in that: The length of the double-clad thulium-doped fiber is 1.9 m.

6. The multi-wavelength thulium-doped fiber laser according to claim 1, characterized in that: Polarization controller 2 and polarization controller 1 adjust the polarization states of the two ring cavities to introduce polarization-dependent loss and achieve stable tunable output.

7. The laser output method of a multi-wavelength thulium-doped fiber laser according to claim 1, characterized in that: The method includes the following steps: using a curvature-adjustable single-mode-coreless-quadruple-coreless-single-mode optical fiber SMF-NCF-FMF-NCF-SMF, lasing more high-order modes by adjusting its curvature radius, adopting a sita cavity structure to improve the coupling efficiency of the pump power, using two polarization controllers located in two different ring cavities, and regulating the polarization states in the two cavities through polarization-dependent loss to achieve stable single-wavelength output.

8. The laser output method of a multi-wavelength thulium-doped fiber laser according to claim 7 is tunable and switchable in the 2µm band, wherein the adjustable single-mode-coreless-quadruple-coreless-single-mode fiber filter comprises a single-mode fiber, a displacement platform, a coreless fiber, a fixed platform, a quadruple-mode fiber, a fixed platform, a coreless fiber, a displacement platform, and a single-mode fiber. The thulium-doped double-clad fiber laser uses cladding pumping technology to pump the thulium-doped gain fiber, thereby achieving laser output in the 2µm band.

9. The multi-wavelength thulium-doped fiber laser output method according to claim 8, characterized in that: The method comprises the following steps: polarization-dependent loss is introduced by adjusting polarization controller 1 and polarization controller 2 in two ring cavities of the laser; when the polarization direction in one cavity is parallel to the polarization direction in the other, the wavelength achieves stable laser output; and since the adjustable single-mode-coreless-quadruple-coreless-single-mode filter has a comb spectrum with the same interval, the laser achieves tunable multi-wavelength output with the same wavelength interval.

10. The multi-wavelength thulium-doped fiber laser output method according to claim 9, characterized in that: The method further includes the following steps: fixing the fixed platform 1 and the fixed platform 2, and adjusting the curvature of the coreless fiber 1 and the core fiber 2 by moving the displacement platform 1 and the displacement platform 2, so that more high-order modes are excited; and by adjusting different curvature parameters, the filter spectrum can be freely switched output, and at the same time, the extinction ratio of the filter can be improved, thereby improving the mode coupling efficiency.

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