A bidirectional mode-locked fiber laser with reciprocity structure

Abstract

The application provides a bidirectional mode-locked fiber laser with reciprocity structure, a first laser pump source is connected with a first wavelength division multiplexer, the first wavelength division multiplexer is connected with one port of a gain fiber, another port of the gain fiber is connected with a second wavelength division multiplexer, the second wavelength division multiplexer is connected with a second laser pump source, the second wavelength division multiplexer is connected with one end of a first polarization controller, another end of the first polarization controller is connected with an optical coupler, the optical coupler is connected with a thulium-doped quartz optical fiber, another end of the thulium-doped quartz optical fiber is connected with one end of a second polarization controller, and another end of the second polarization controller is connected with the first wavelength division multiplexer to form a loop.The application adopts the reciprocity optical path structure, is simple in structure, can offset the influence of environmental changes such as temperature and vibration on the output performance, and improves the stability of the system; and the thulium-doped fiber is used as a saturable absorber, so that the problems of low damage threshold and short service life of the saturable absorber are solved.

Description

Technical Field

[0001] This invention relates to the field of pulsed laser technology, and more specifically, to a bidirectional mode-locked fiber laser with a reciprocal structure. Background Technology

[0002] Mode-locked fiber lasers, as ultrashort pulse sources, possess advantages such as short pulse duration, high peak power, wide operating spectrum, and good stability. They have wide applications in high-speed optical communication, lidar, optical frequency combs, and nonlinear optics, and are therefore subject to extensive research. Most mode-locked fiber lasers employ a ring cavity structure. Compared to traditional unidirectional mode-locked lasers, bidirectional mode-locked fiber lasers can simultaneously generate ultrashort pulses in both clockwise and counterclockwise directions, thus achieving bidirectional output with different operating wavelengths and pulse durations within the same laser.

[0003] Currently, there are two main methods for achieving bidirectional mode-locking in fiber lasers. One method involves removing the isolator used to isolate back-reflected light within the cavity and utilizing saturable absorbers such as graphene or carbon nanotubes assembled within the cavity to achieve bidirectional mode-locking. However, the saturable absorbers used in this method have low damage thresholds and short lifetimes, which are detrimental to the practical application of lasers. The other method utilizes nonlinear polarization rotation to achieve bidirectional mode-locking, but lasers built using this method are difficult to self-start, complex to debug, and easily affected by external environmental interference, thus limiting their practicality. Summary of the Invention

[0004] Based on the above-mentioned technical problems, this invention proposes a bidirectional mode-locked fiber laser with a reciprocal structure.

[0005] A bidirectional mode-locked fiber laser with a reciprocal structure comprises a first laser pump source, a first wavelength division multiplexer (WDM), a gain fiber, a second WDM, a second laser pump source, a first polarization controller, an optical coupler, a thulium-doped silica fiber, and a second polarization controller. The first laser pump source is connected to port 2a of the first WDM. Port 2b of the first WDM is connected to one port of the gain fiber. The other port of the gain fiber is connected to port 4b of the second WDM. Port 4a of the second WDM is connected to the second laser pump source. Port 4c of the second WDM is connected to one end of the first polarization controller. The other end of the first polarization controller is connected to port 7a of the optical coupler. Port 7b of the optical coupler is connected to the thulium-doped silica fiber. The other end of the thulium-doped silica fiber is connected to one end of the second polarization controller. The thulium-doped silica fiber, as a saturable absorber, has the characteristics of long service life and good system compatibility. The other end of the second polarization controller is connected to port 2c of the first WDM to form a loop.

[0006] Furthermore, the center wavelength of the pump light output from the first laser pump source and the second laser pump source is both 980nm.

[0007] Furthermore, the wavelength division multiplexing range of both the first and second wavelength division multiplexers is 980nm / 1550nm.

[0008] Furthermore, the gain fiber is an erbium-doped silica fiber.

[0009] Furthermore, both the first polarization controller and the second polarization controller are three-ring polarization controllers.

[0010] Furthermore, the pigtails of the first laser pump source, the first wavelength division multiplexer, the second wavelength division multiplexer, the second laser pump source, the first polarization controller, the optical coupler, and the second polarization controller are all single-mode optical fibers.

[0011] Furthermore, the optical coupler is a 2×2 optical coupler, wherein ports 7a and 7b are transmission oscillation ports, and ports 7c and 7d are output ports.

[0012] Beneficial effects: This invention employs a reciprocal optical path structure. The reciprocal structural design can offset the impact of external environmental changes such as temperature and vibration on its output performance, thereby improving the stability of the system. This invention uses thulium-doped optical fiber as a saturable absorber, which has a long service life and better system compatibility, and solves the problems of low damage threshold and short life of saturable absorbers. The bidirectional mode-locked fiber laser proposed in this invention has bidirectional output, a simple structure, and is conducive to the practical application of lasers, making it widely used in the fields of optical communication and optical sensing. Attached Figure Description

[0013] Figure 1 A schematic diagram of a bidirectional mode-locked fiber laser with a reciprocity structure is shown. Figure 2 The spectrum of a clockwise output laser pulse provided in an embodiment of the present invention is shown; Figure 3 The spectrum of a counter-clockwise output laser pulse provided in an embodiment of the present invention is shown; Figure 4 A schematic diagram illustrating the stability of the output laser power of the present invention is shown. In the attached diagram, 1 is the first laser pump source; 2 is the first wavelength division multiplexer; 3 is the gain fiber; 4 is the second wavelength division multiplexer; 5 is the second laser pump source; 6 is the first polarization controller; 7 is the optical coupler; 8 is the thulium-doped silica fiber; and 9 is the second polarization controller. Detailed Implementation

[0014] To enable those skilled in the art to better understand the present invention, the following description will be provided in conjunction with the accompanying drawings of the embodiments of the present invention. Figures 1-4 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0015] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can encompass implementations in sequences other than those illustrated or described herein. Furthermore, the terms "comprising," "having," "configured," "connected," etc., should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of these terms in this invention in conjunction with the specific content of the technical solution.

[0016] like Figures 1-4 The diagram illustrates a bidirectional mode-locked fiber laser with a reciprocal structure, outputting pulse signals in both clockwise and counterclockwise directions. It comprises a first laser pump source 1, a first wavelength division multiplexer 2, a gain fiber 3, a second wavelength division multiplexer 4, a second laser pump source 5, a first polarization controller 6, an optical coupler 7, a thulium-doped silica fiber 8, and a second polarization controller 9. The first laser pump source 1 is connected to port 2a of the first wavelength division multiplexer 2. Port 2b of the first wavelength division multiplexer 2 is connected to one port of the gain fiber 3 (which is erbium-doped silica fiber). The other port of the gain fiber 3 is connected to port 4b of the second wavelength division multiplexer 4. The ports are connected as follows: port 4a of the second wavelength division multiplexer 4 is connected to the second laser pump source 5; port 4c of the second wavelength division multiplexer 4 is connected to one end of the first polarization controller 6; the other end of the first polarization controller 6 is connected to port 7a of the optical coupler 7; port 7b of the optical coupler 7 is connected to the thulium-doped silica fiber 8; and the other end of the thulium-doped silica fiber 8 is connected to one end of the second polarization controller 9. The thulium-doped silica fiber 8, as a saturable absorber, has the characteristics of long service life and good system compatibility. The other end of the second polarization controller 9 is connected to port 2c of the first wavelength division multiplexer 2 to form a loop, constituting a ring cavity.

[0017] It should be noted that the center wavelength of the pump light output from the first laser pump source 1 and the second laser pump source 5 is 980nm. The wavelength division multiplexing range of the first wavelength division multiplexer 2 and the second wavelength division multiplexer 4 is 980nm / 1550nm. The first polarization controller 6 and the second polarization controller 9 are both three-ring polarization controllers. The pigtails of the first laser pump source 1, the first wavelength division multiplexer 2, the second wavelength division multiplexer 4, the second laser pump source 5, the first polarization controller 6, the optical coupler 7, and the second polarization controller 9 are all... The optical fiber is single-mode; the optical coupler 7 is a 2×2 optical coupler 7, where ports 7a and 7b are transmission oscillation ports, and ports 7c and 7d are output ports. The light input from port 7a to the optical coupler 7 is partially output from port 7d, which is the clockwise pulse output terminal, and partially maintains the clockwise laser oscillation in the cavity through port 7b; the light input from port 7b to the optical coupler 7 is partially output from port 7c, which is the counterclockwise pulse output terminal, and partially maintains the counterclockwise laser oscillation in the cavity through port 7a.

[0018] The stroke processes of the clockwise and counterclockwise pulses in this invention are as follows: Clockwise pulse formation process: Light generated by the first laser pump source 1 is injected through port 2a of the first wavelength division multiplexer 2 and output from port 2b of the first wavelength division multiplexer 2. The light output from port 2b of the first wavelength division multiplexer 2 is input through one port of an erbium-doped silica fiber and output from the other port of the erbium-doped silica fiber. The light output from the erbium-doped silica fiber is input through port 4b of the second wavelength division multiplexer 4 and output from port 4c of the second wavelength division multiplexer 4. The light output from port 4c of the second wavelength division multiplexer 4 is input through one end of the second polarization controller 9 and output from the other end of the first polarization controller 6. The light output from 6 is input through port 7a of optical coupler 7, part of it is output through port 7d of optical coupler 7, and the other part is injected into thulium-doped silica fiber 8 through port 7b of optical coupler 7. The light output from the other end of thulium-doped silica fiber 8 is input to one end of the second polarization controller 9, and output from the other end of the second polarization controller 9. The light output from the second polarization controller 9 is connected through port 2c of the first wavelength division multiplexer 22 to form a loop. The light output from port 2b of the first wavelength division multiplexer 22 is amplified by the gain loop of erbium-doped silica fiber to form clockwise laser oscillation, outputting a clockwise mode-locked pulse. The spectrum of the clockwise output laser pulse is as follows: Figure 2 As shown, the output laser pulse is in the 1.5µm band.

[0019] Counterclockwise pulse formation process: Light emitted from the second laser pump source 5 is injected through port 4a of the second wavelength division multiplexer 4. Light output from port 4b of the second wavelength division multiplexer 4 is input through one port of an erbium-doped silica fiber and output from the other port of the erbium-doped silica fiber. Light output from the erbium-doped silica fiber port is input through port 2b of the first wavelength division multiplexer 2 and output from port 2c of the first wavelength division multiplexer 2. Light output from port 2c of the first wavelength division multiplexer 2 is input through one end of the second polarization controller 9 and output from the other end of the second polarization controller 9. Light output from the first polarization controller 6 is transmitted through a thulium-doped silica fiber 8. At the other end, the light output from the thulium-doped silica fiber 8 is input through port 7b of the optical coupler 7. Part of it is output through port 7c of the optical coupler 7, and the other part is output through port 7a of the optical coupler 7 and injected into one end of the first polarization controller 6. The light output from the other end of the first polarization controller 6 is then injected through port 4c of the second wavelength division multiplexer 4 and output through port 4b of the second wavelength division multiplexer 4, forming a loop. The light output from port 4b of the second wavelength division multiplexer 4 is amplified by the gain loop of the erbium-doped silica fiber 3 to form a counterclockwise laser oscillation, outputting a counterclockwise mode-locked pulse. The spectrum of the counterclockwise output laser pulse is as follows: Figure 3 As shown, the output laser pulse is in the 1.5µm band.

[0020] like Figure 4 As shown, the output laser pulse power is recorded every 10 minutes for 2 hours, and the diagram shows that the output laser pulse power has good stability.

[0021] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A bidirectional mode-locked fiber laser with a reciprocity structure, characterized in that, include: The system comprises a first laser pump source, a first wavelength division multiplexer (WDM), a gain fiber, a second WDM, a second laser pump source, a first polarization controller, an optical coupler, a thulium-doped silica fiber, and a second polarization controller. The first laser pump source is connected to port 2a of the first WDM. Port 2b of the first WDM is connected to one port of the gain fiber. The other port of the gain fiber is connected to port 4b of the second WDM. Port 4a of the second WDM is connected to the second laser pump source. Port 4c of the second WDM is connected to one end of the first polarization controller. The other end of the first polarization controller is connected to port 7a of the optical coupler. Port 7b of the optical coupler is connected to the thulium-doped silica fiber. The other end of the thulium-doped silica fiber is connected to one end of the second polarization controller. The other end of the second polarization controller is connected to port 2c of the first WDM, forming a loop.

2. The bidirectional mode-locked fiber laser with reciprocity structure according to claim 1, characterized in that, The center wavelength of the pump light output from the first laser pump source and the second laser pump source is 980nm.

3. The bidirectional mode-locked fiber laser with reciprocity structure according to claim 1, characterized in that, The wavelength division multiplexer for both the first and second wavelength division multiplexers is 980nm / 1550nm.

4. The bidirectional mode-locked fiber laser with reciprocity structure according to claim 1, characterized in that, The gain fiber is an erbium-doped silica fiber.

5. The bidirectional mode-locked fiber laser with a reciprocity structure according to claim 1, characterized in that, Both the first polarization controller and the second polarization controller are three-ring polarization controllers.

6. The bidirectional mode-locked fiber laser with reciprocity structure according to claim 1, characterized in that, The pigtails of the first laser pump source, the first wavelength division multiplexer, the second wavelength division multiplexer, the second laser pump source, the first polarization controller, the optical coupler, and the second polarization controller are all single-mode optical fibers.

7. The bidirectional mode-locked fiber laser with reciprocity structure according to claim 1, characterized in that, The optical coupler is a 2×2 optical coupler, where ports 7a and 7b are transmission oscillation ports, and ports 7c and 7d are output ports.

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