An ultra-narrow linewidth single longitudinal mode thulium-doped fiber laser based on a double-ring composite subcavity

Abstract

An ultra-narrow linewidth single longitudinal mode thulium-doped fiber laser based on a dual-ring composite sub-cavity belongs to the technical field of optical fiber communication, optical fiber devices and instrumentation. It includes 793 nanometer cladding pump, 793 nanometer / 2000 nanometer cladding pump combiner, thulium-doped fiber, fiber circulator, uniform fiber grating, Fabry-Perot fiber grating, 3dB fiber coupler 1, 3dB fiber coupler 2, 3dB fiber coupler 3, squeezed polarization controller, 90 to 10 fiber coupler. The dual-ring composite sub-ring cavity used in the present invention successfully expands the effective longitudinal mode interval of the laser, achieves ultra-narrowband filtering effect, and has outstanding single longitudinal mode selection ability and line width narrowing effect. By changing the polarization state of the laser in the fiber laser cavity and optimizing the design of the laser structure, combined with the filtering function of the fiber grating combination, the stable operation of the single longitudinal mode laser can be achieved.

Description

Technical Field

[0001] The invention relates to an ultra-narrow linewidth single longitudinal mode thulium-doped fiber laser based on a double-ring composite subcavity, belonging to the technical field of optical fiber communication, optical fiber devices and instrumentation. Background Art

[0002] Since the advent of laser in the 1960s, it has been widely used in communication, medical treatment, agriculture, industry, defense and other fields due to its high directivity, high coherence and high brightness. With the increasing maturity of C-band fiber laser technology, the need to broaden the laser wavelength and develop near-infrared laser technology is becoming more and more urgent. Among them, the development of 2μm-band laser lasing using thulium-doped fiber and holmium-doped fiber is an important direction for the development of future optical communication technology.

[0003] Single-frequency fiber laser is an important and rapidly developing branch in the field of fiber laser technology. It has the characteristics of ultra-narrow spectral linewidth and ultra-long coherence, and has important application value in the fields of fiber-optic sensing, coherent laser radar, high-power coherent synthesis, coherent optical communication, optical atomic clocks, gravitational wave detection, etc. In recent years, technical research on the generation of single-frequency fiber lasers has mainly focused on high-gain fiber drawing and laser resonant cavity design. In particular, the optimization design of the resonant cavity can greatly improve the noise performance, linewidth performance, and stability performance of the output laser. Commonly used resonant cavity optimization methods include shortening the laser cavity length and cascading multi-ring sub-ring cavities.

[0004] At present, many near-infrared thulium-doped fiber lasers cannot stably output single longitudinal mode lasers. They can only use fiber gratings to construct distributed Bragg reflection lasers and distributed feedback lasers. By greatly shortening the laser cavity length, the laser longitudinal mode is expanded to achieve the effect of selecting and stably outputting a single longitudinal mode in the laser cavity. But at the same time, the shorter length of the gain fiber also limits the output power of the fiber laser, and it is difficult to improve the optical properties. At the same time, it is difficult to produce two completely identical narrowband fiber gratings with existing processes. This defect also limits the output power of distributed Bragg reflection lasers and distributed feedback lasers. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides an ultra-narrow linewidth single longitudinal mode thulium-doped fiber laser based on a double-ring composite subcavity.

[0006] An ultra-narrow linewidth single longitudinal mode thulium-doped fiber laser based on a double-ring composite subcavity, including a 793-nanometer cladding pump, a 793-nanometer / 2000-nanometer cladding pump combiner, a thulium-doped fiber, a fiber circulator, a uniform fiber grating, a Fabry-Perot fiber grating, a 3dB fiber coupler 1, a 3dB fiber coupler 2, a 3dB fiber coupler 3, a squeezed polarization controller, a 90:10 fiber coupler, a 793-nanometer cladding pump source and a 793-nanometer / 2000-nanometer cladding pump combiner. The first end of the 793 nm / 2000 nm cladding pump combiner is connected to one end of the thulium-doped fiber through the first optical fiber conduit, the other end of the thulium-doped fiber is connected to the first port of the optical fiber circulator through the second optical fiber conduit, the second port of the optical fiber circulator is connected to the uniform optical fiber grating through the third optical fiber conduit, the third port of the optical fiber circulator is connected to the Fabry-Perot optical fiber grating through the fourth optical fiber conduit, and the other end of the Fabry-Perot optical fiber grating is connected to the first port of the 3dB optical fiber coupler through the fifth optical fiber conduit. , one end of the 3dB fiber coupler one is connected to one end of the 3dB fiber coupler two through the sixth fiber optic conduit, the other end of the 3dB fiber coupler two is connected to one end of the 3dB fiber coupler three through the seventh fiber optic conduit, one end of the 3dB fiber coupler three is connected to one end of the 3dB fiber coupler one through the eighth fiber optic conduit, one end of the 3dB fiber coupler three is connected to one end of the 3dB fiber coupler two through the ninth fiber optic conduit, one end of the 3dB fiber coupler one is connected to one end of the squeezed polarization controller through the tenth fiber optic conduit, the other end of the squeezed polarization controller is connected to one end of the 90:10 fiber coupler through the eleventh fiber optic conduit, the other end of the 90:10 fiber coupler through the twelfth fiber optic conduit serves as the output port of the entire fiber laser, one end of the 793 nm / 2000 nm cladding pump combiner is connected to one end of the 90:10 fiber coupler through the thirteenth fiber optic conduit, and the fourteenth fiber optic conduit port of the 90:10 fiber coupler serves as the output port of the entire laser.

[0007] The advantage of the present invention is that the dual-ring composite sub-ring cavity successfully expands the effective longitudinal mode interval of the laser, achieves ultra-narrowband filtering effect, and has outstanding single longitudinal mode selection ability and line width narrowing effect. By changing the polarization state of the laser in the fiber laser cavity and optimizing the design of the laser structure, combined with the filtering function of the fiber grating combination, the stable operation of the single longitudinal mode laser can be achieved. It will play an important role in the fields of fiber nonlinearity, optical measurement, distributed fiber sensing, etc.

[0008] The effects of the present invention are as follows: a uniform fiber grating and a Fabry-Perot fiber grating are used as a coarse selection filter, a 3dB fiber coupler 1, a 3dB fiber coupler 2, and a 3dB fiber coupler 3 form an ultra-narrow bandwidth filter, and a squeezed polarization controller is used to adjust the polarization hole burning effect in the laser cavity to obtain a single longitudinal mode fiber laser with stable output.

[0009] The single longitudinal mode operation of the output laser of the present invention is jointly determined by the laser cavity length, the Fabry-Perot fiber grating and the cavity length of the double-ring composite sub-cavity, the intracavity loss is determined by the transmittance of the double-ring composite sub-cavity, the line width is jointly determined by the uniform fiber grating, the Fabry-Perot fiber grating and the double-ring composite sub-cavity, and the power fluctuation of the output laser is determined by the squeezed polarization controller. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] When considered in conjunction with the accompanying drawings, the present invention can be more completely and better understood and many of the accompanying advantages can be easily known by referring to the detailed description below, but the drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention, as shown in the figure:

[0011] Figure 1 It is a structural diagram of the present invention.

[0012] Figure 2a Output laser spectrum diagram for one of the present invention.

[0013] Figure 2b This is the second output laser spectrum diagram of the present invention.

[0014] Figure 3 This is the beat frequency diagram of the single-wavelength single-longitudinal mode output longitudinal mode of the present invention. DETAILED DESCRIPTION

[0015] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0016] Obviously, many modifications and changes made by those skilled in the art based on the purpose of the present invention belong to the protection scope of the present invention.

[0017] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description, "plurality" means two or more, unless otherwise clearly and specifically defined.

[0018] Unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0019] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art.

[0020] To facilitate understanding of the embodiments, further explanations will be given below, and each embodiment does not constitute a limitation on the embodiments.

[0021] Example 1: Figure 1 , Figure 2a , Figure 2b and Figure 3 As shown, an ultra-narrow linewidth single longitudinal mode thulium-doped fiber laser based on a dual-ring composite subcavity includes a 793 nm cladding pump 01, a 793 nm / 2000 nm cladding pump combiner 02, a thulium-doped fiber 03, a fiber circulator 04, a uniform fiber grating 05, a Fabry-Perot fiber grating 06, a 3dB fiber coupler 1 07, a 3dB fiber coupler 2 08, a 3dB fiber coupler 3 09, a squeezed polarization controller 10, and a 90:10 fiber coupler 11.

[0022] The 793 nm cladding pump source 01 is connected to one end of the 793 nm / 2000 nm cladding pump combiner 02. The other end of the 793 nm / 2000 nm cladding pump combiner 02 is connected to one end of the thulium-doped fiber 03 through the first optical fiber pipe 021. The other end of the thulium-doped fiber 03 is connected to the port 1 of the optical fiber circulator 04 through the second optical fiber pipe 031. The port 2 of the optical fiber circulator 04 is connected to the uniform optical fiber grating 05 through the third optical fiber pipe 041. The 3-port of the device 04 is connected to the Fabry-Perot fiber grating 06 through the fourth fiber optic conduit 042, the other end of the Fabry-Perot fiber grating 06 is connected to the 3dB fiber coupler 1 07 through the fifth fiber optic conduit 061, one end of the 3dB fiber coupler 1 07 is connected to one end of the 3dB fiber coupler 2 08 through the sixth fiber optic conduit 071, the other end of the 3dB fiber coupler 2 08 is connected to one end of the 3dB fiber coupler 3 09 through the seventh fiber optic conduit 081, One end of the 3dB fiber coupler three 09 is connected to one end of the 3dB fiber coupler one 07 through the eighth fiber duct 091, one end of the 3dB fiber coupler three 09 is connected to one end of the 3dB fiber coupler two 08 through the ninth fiber duct 092, one end of the 3dB fiber coupler one 07 is connected to one end of the squeezed polarization controller 10 through the tenth fiber duct 072, the other end of the squeezed polarization controller 10 is connected to one end of the 90:10 fiber coupler 11 through the eleventh fiber duct 101, the other end of the 90:10 fiber coupler 11, the twelfth fiber duct 111 serves as the output port of the entire fiber laser, one end of the 793 nm / 2000 nm cladding pump combiner 02 is connected to one end of the 90:10 fiber coupler 11 through the thirteenth fiber duct 022, connecting the entire fiber laser into a ring cavity loop, and at the same time, the fourteenth fiber duct 111 port of the 90:10 fiber coupler 11 serves as the output port of the entire laser.

[0023] The cavity length of the annular sub-cavity and the coupling ratio of the optical fiber coupler and other structural parameters are optimized to obtain the best single longitudinal mode selection effect.

[0024] The main ring cavity of the fiber laser is composed of: 793 nm / 2000 nm cladding pump combiner 02, first fiber duct 021, thulium-doped fiber 03, second fiber duct 031, fiber circulator 04, fourth fiber duct 042, Fabry-Perot fiber grating 06, 3dB fiber coupler 07, tenth fiber duct 072, squeezed polarization controller 10, eleventh fiber duct 101, 90:10 fiber coupler 11 and thirteenth fiber duct 022. The main ring cavity of the fiber laser is 12.46 m long, and the calculated longitudinal mode spacing is 16.4 MHz. The calculation formula for the longitudinal mode spacing of the ring cavity fiber laser is: Δ = c / nL, Δ is the longitudinal mode spacing, c is the speed of light in vacuum 3×10 8m / s, n is the effective refractive index of single-mode optical fiber 1.468.

[0025] like Figure 2a As shown, the output laser spectrum diagram of the present invention is the output spectrum of the laser operating at a single wavelength after adjusting the squeezing polarization controller.

[0026] like Figure 2b As shown, the output laser spectrum diagram of the present invention is a single-wavelength output stability test spectrum within one hour, and the test time interval is 6 minutes.

[0027] Figure 3 This is the beat frequency diagram of the single-wavelength single-longitudinal mode output longitudinal mode of the present invention. Figure 3 The following is the result of the laser beat frequency in the scanning range of 100MHz. In the scanning range, no obvious beat frequency signal is captured, indicating that the laser operates in a stable single longitudinal mode state.

[0028] The sub-ring cavity can be disassembled into two fiber ring cavities (a first ring cavity and a second ring cavity). The sixth fiber duct 071, 3dB fiber coupler 1 07, the eighth fiber duct 091, 3dB fiber coupler 3 09, the seventh fiber duct 081 and 3dB fiber coupler 2 08 constitute the first ring cavity, and the seventh fiber duct 081, 3dB fiber coupler 2 08, the ninth fiber duct 092 and 3dB fiber coupler 3 09 constitute the second ring cavity.

[0029] The length of the sixth optical fiber conduit 071 is 0.5 m, the length of the seventh optical fiber conduit 081 is 0.5 m, the length of the eighth optical fiber conduit 091 is 0.5 m, and the length of the ninth optical fiber conduit 092 is 0.94 m. The splitting ratio of the 3dB optical fiber coupler 07 is 50:50, the splitting ratio of the 3dB optical fiber coupler 08 is 50:50, and the splitting ratio of the 3dB optical fiber coupler 09 is 50:50.

[0030] The present invention uses uniform fiber gratings and Fabry-Perot fiber gratings to form a coarse filter grating combination; 3dB fiber coupler one, 3dB fiber coupler two, and 3dB fiber coupler three form a double-ring composite sub-ring cavity, and uses the vernier effect to expand the longitudinal mode interval of the laser and narrow the laser line width; a squeeze-type polarization controller can adjust the polarization hole burning effect in the laser cavity to achieve stable lasing of the output laser.

[0031] The present invention uses a combination of uniform fiber grating 05 and Fabry-Perot fiber grating 06 to optimize the filter bandwidth, which helps to obtain a stable single-wavelength laser output with a narrower line width. A squeezed polarization controller 10 is added to the cavity to obtain a more stable laser output by utilizing the polarization hole burning effect.

[0032] As described above, the embodiments of the present invention are described in detail, but it is obvious to those skilled in the art that many variations are possible as long as they do not deviate from the inventive point and effect of the present invention. Therefore, all such variations are also included in the protection scope of the present invention.

Claims

1. An ultra-narrow linewidth single longitudinal mode thulium-doped fiber laser based on a dual-ring composite subcavity, characterized in that , including 793 nm cladding pump, 793 nm / 2000 nm cladding pump combiner, thulium-doped fiber, fiber circulator, uniform fiber Bragg grating, Fabry-Perot fiber Bragg grating, 3dB fiber coupler 1, 3dB fiber coupler 2, 3dB fiber coupler 3, squeezed polarization controller, 90:10 fiber coupler, 793 nm cladding pump source is connected to one end of 793 nm / 2000 nm cladding pump combiner, the other end of 793 nm / 2000 nm cladding pump combiner is connected to one end of thulium-doped fiber through a first fiber optic conduit, the other end of thulium-doped fiber is connected to port 1 of fiber circulator through a second fiber optic conduit, port 2 of fiber circulator is connected to uniform fiber Bragg grating through a third fiber optic conduit, port 3 of fiber circulator is connected to Fabry-Perot fiber Bragg grating through a fourth fiber optic conduit, the other end of Fabry-Perot fiber Bragg grating is connected to 3dB fiber coupler 1 through a fifth fiber optic conduit, and port 4 of 3dB fiber coupler 1 is connected to port 5 of 3dB fiber coupler 1. The end of the 3dB fiber coupler is connected to one end of the 3dB fiber coupler 2 through a sixth fiber duct, the other end of the 3dB fiber coupler 2 is connected to one end of the 3dB fiber coupler 3 through a seventh fiber duct, one end of the 3dB fiber coupler 3 is connected to one end of the 3dB fiber coupler 1 through an eighth fiber duct, one end of the 3dB fiber coupler 3 is connected to one end of the 3dB fiber coupler 2 through a ninth fiber duct, one end of the 3dB fiber coupler 1 is connected to one end of a squeeze-type polarization controller through a tenth fiber duct, the other end of the squeeze-type polarization controller is connected to one end of a 90:10 fiber coupler through an eleventh fiber duct, the other end of the 90:10 fiber coupler, a twelfth fiber duct serves as the output port of the entire fiber laser, one end of the 793 nm / 2000 nm cladding pump combiner is connected to one end of the 90:10 fiber coupler through a thirteenth fiber duct, and the fourteenth fiber duct port of the 90:10 fiber coupler serves as the output port of the entire laser; The main ring cavity is composed of a 793 nm / 2000 nm cladding pumped combiner, a first optical fiber pipeline, a thulium-doped optical fiber, a second optical fiber pipeline, an optical fiber circulator, a fourth optical fiber pipeline, a Fabry-Perot optical fiber grating, a 3 dB optical fiber coupler, a tenth optical fiber pipeline, a squeezed polarization controller, an eleventh optical fiber pipeline, a 90:10 optical fiber coupler and a thirteenth optical fiber pipeline. The main ring cavity of the fiber laser is 12.46 m long, and the calculated longitudinal mode spacing is 16.4 MHz. The calculation formula for the longitudinal mode spacing of the ring cavity fiber laser is: Δ = c / nL, Δ is the longitudinal mode spacing, c is the speed of light in vacuum 3×10 8 m / s, n is the effective refractive index of single-mode optical fiber 1.468; The sub-ring cavity is disassembled into a first ring cavity and a second ring cavity, the sixth optical fiber pipeline, the 3dB optical fiber coupler 1, the eighth optical fiber pipeline, the 3dB optical fiber coupler 3, the seventh optical fiber pipeline and the 3dB optical fiber coupler 2 form the first ring cavity, and the seventh optical fiber pipeline, the 3dB optical fiber coupler 2, the ninth optical fiber pipeline and the 3dB optical fiber coupler 3 form the second ring cavity; The length of the sixth optical fiber conduit is 0.5m, the length of the seventh optical fiber conduit is 0.5m, the length of the eighth optical fiber conduit is 0.5m, the length of the ninth optical fiber conduit is 0.94m, the splitting ratio of the 3dB optical fiber coupler is 50:50, the splitting ratio of the 3dB optical fiber coupler is 50:50, and the splitting ratio of the 3dB optical fiber coupler is 50:50.

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