9-shaped hybrid mode-locked fiber laser

Abstract

The utility model belongs to the technical field of lasers, and discloses a 9-shaped hybrid mode-locked fiber laser, which comprises a pumping source, a 2 * 2 polarization-maintaining fiber coupler, a nonlinear amplification loop mirror loop connected with a first side of the polarization-maintaining fiber coupler, and a chirp fiber Bragg grating connected with a second side of the polarization-maintaining fiber coupler, the polarization maintaining optical fiber coupler is located at the connecting position of the nonlinear amplification annular mirror loop and a linear arm of the laser resonant cavity and used for coupling laser of the nonlinear amplification annular mirror loop to the linear arm, and after being reflected by the chirp fiber bragg grating, the laser is output to the nonlinear amplification annular mirror loop through the chirp fiber bragg grating. And then the laser on the linear arm is split into two beams of light which are transmitted clockwise and anticlockwise in a loop of the nonlinear amplification annular mirror. According to the utility model, two passive mode locking technologies are combined, rapid and stable mode locking can be realized, the operation state is slightly influenced by the environment, the signal-to-noise ratio of output laser pulses can be improved, and ultra-short pulses with narrower pulse width can be realized.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of laser, especially relates to a 9-shaped hybrid mode-locked fiber laser. BACKGROUND

[0002] Passive mode-locked technology is an important means to generate fiber super-short pulses, and the saturable absorber is the core component of the passive mode-locked fiber laser, which is usually divided into real saturable absorber and virtual saturable absorber. The real saturable absorber mainly includes semiconductor saturable absorber mirror, graphene, carbon nanotube and other materials; the virtual saturable absorber mainly adopts nonlinear polarization rotation and nonlinear amplifying ring mirror technology.

[0003] In recent years, with the rapid development of two-dimensional materials and the continuous progress of saturable absorber preparation technology, the real saturable absorber made of new nanomaterials has been widely used in mode-locked fiber lasers. The real saturable absorber has good self-starting mode-locked characteristics and wide wavelength coverage, and has become a relatively mature saturable absorption device. However, the damage threshold of the real saturable absorber is usually low, and the performance is easy to degrade or even lose lock after long time running, so it needs to be replaced regularly to maintain the performance of the laser. Therefore, simply relying on the real saturable absorber to build a mode-locked fiber laser will increase the difficulty of later maintenance and is difficult to improve the pulse energy.

[0004] In contrast, the virtual saturable absorber has a high damage threshold and flexible structure design, making it an optimal solution for mode-locked fiber lasers in achieving high-power, high-energy and ultra-short pulse output. Especially the 9-shaped fiber laser based on nonlinear amplifying ring mirror mode-locked has attracted much attention due to its compact structure, high damage threshold and good stability, but the non-reciprocal phase shifter in the 9-shaped fiber laser usually provides a fixed phase shift difference, which makes it difficult to solve the self-starting problem of the laser. Therefore, further improving the performance of the 9-shaped fiber laser is of great significance to the development of ultrafast fiber lasers.

[0005] At present, most of the ultrafast fiber lasers use a single real saturable absorber or a single virtual saturable absorber to achieve ultrafast laser output. The mode-locked state of the real saturable absorber is less affected by the environment, and has good self-starting performance, but its damage threshold is usually low, and its performance is easy to degrade or even lose lock after long time running. The virtual saturable absorber has a high damage threshold and flexible structure design, and has high integration, but its self-starting performance and pulse stability are poor. In addition, since the whole fiber laser adopts a full polarization maintaining structure, the adjustable freedom is not high. UTILITY MODEL CONTENT

[0006] The utility model discloses a 9-shaped hybrid mode-locked fiber laser which overcomes the deficiency of single mode-locked technology.

[0007] The utility model provides a 9-shaped hybrid mode-locked fiber laser, including pump source and 2*2 polarization maintaining fiber coupler, with the first side connection of 2*2 polarization maintaining fiber coupler nonlinear amplification annular mirror loop, and with the second side connection of 2*2 polarization maintaining fiber coupler chirped fiber bragg grating,

[0008] 2*2 polarization maintaining fiber coupler is in the connecting position of nonlinear amplification annular mirror loop and the linear arm of laser resonant cavity, is used for coupling laser of nonlinear amplification annular mirror loop to linear arm, after reflection through chirped fiber bragg grating, again the laser on the linear arm is split into two beams of light clockwise and counterclockwise transmission in nonlinear amplification annular mirror loop.

[0009] Further, the nonlinear amplification annular mirror loop is a loop formed by the 2*2 polarization maintaining fiber coupler, the doped fiber, the wavelength division multiplexer, the real saturable absorber mode-locked device and the non-reciprocal phase shifter connected in sequence; wherein,

[0010] The first end of the wavelength division multiplexer is connected with the pump source, and the pump light generated by the pump source is coupled into the laser resonant cavity.

[0011] The doped fiber is connected with the first end of the 2*2 polarization maintaining fiber coupler, and the doped fiber generates laser signal light by excitation of the pump light.

[0012] The 2*2 polarization maintaining fiber coupler is used for coupling the clockwise propagating light and the counterclockwise propagating light in the nonlinear amplification annular mirror loop.

[0013] The non-reciprocal phase shifter is used for providing a fixed linear phase difference for the clockwise propagating light and the counterclockwise propagating light in the nonlinear amplification annular mirror loop.

[0014] The real saturable absorber mode-locked device is used for maintaining the self-starting and stable mode-locking of the fiber laser.

[0015] Further, the doped fiber is a polarization maintaining doped fiber, the wavelength division multiplexer is a polarization maintaining wavelength division multiplexer, and the non-reciprocal phase shifter is a polarization maintaining non-reciprocal phase shifter.

[0016] Further, the doped fiber is a gain fiber, and the gain fiber is arranged close to the 2*2 polarization maintaining fiber coupler.

[0017] Further, the real saturable absorber device comprises two jumper heads and a thin film between the two jumper heads.

[0018] Further, the thin film is a semiconductor saturable absorber mirror, graphene or carbon nanotube.

[0019] Further, the 2x2 polarization maintaining fiber coupler is a tunable 2x2 polarization maintaining fiber coupler.

[0020] Further, the 2x2 polarization maintaining fiber coupler divides the light into two paths in the nonlinear amplification ring mirror loop, the two paths of light are clockwise propagating light and counterclockwise propagating light respectively, and the two paths of light interfere at the 2x2 polarization maintaining fiber coupler, part of the light continues to transmit along the linear arm, is reflected by the chirped fiber Bragg grating back to the 2x2 polarization maintaining fiber coupler to be divided into two beams of light propagating in opposite directions into the nonlinear amplification ring mirror loop; another part of the light is transmitted out of the 2x2 polarization maintaining fiber coupler as the output of the laser.

[0021] Further, the linear arm of the laser resonant cavity is formed by connecting the third end of the 2x2 polarization maintaining fiber coupler and the chirped fiber Bragg grating; the chirped fiber Bragg grating is used for reflecting the laser beam and performing dispersion compensation to balance the dispersion in the laser resonant cavity.

[0022] Further, the dispersion parameter of the chirped fiber Bragg grating can be selected to compensate for the overall dispersion in the laser resonant cavity.

[0023] Compared with the prior art, the utility model has the beneficial effects of:

[0024] (1) The optical fiber laser provided by the utility model combines two passive mode locking technologies, can realize fast and stable mode locking, has small environmental influence on the running state, can improve the signal-to-noise ratio of the output laser pulse, realize narrower pulse width of the ultrashort pulse, and has the characteristics of compact optical path structure and high integration degree.

[0025] (2) The utility model utilizes the tunable 2x2 polarization maintaining fiber coupler, can realize real-time adjustment of the transmittance of the optical fiber laser and the modulation depth of the virtual saturable absorber, so that the optical fiber laser can better perform the nonlinear amplification ring mirror loop under different parameter configurations, enriches the adjustment degree of freedom of the optical fiber laser, and greatly improves the application compatibility of the optical fiber laser. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical scheme in the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and all other drawings obtained by those skilled in the art without creative effort based on the embodiments of the present application shall fall within the scope of the present application.

[0027] Figure 1 A structure schematic diagram of the 9-shaped hybrid mode-locked fiber laser provided by the present application is shown in the figure.

[0028] The meanings of the various reference signs in the drawings are as follows:

[0029] 1-pump source, 2-wavelength division multiplexer, 3-real saturable absorber mode-locked device, 4-nonreciprocal phase shifter, 5-doped fiber, 6-2x2 polarization maintaining fiber coupler, 7-chirped fiber Bragg grating. DETAILED DESCRIPTION

[0030] The technical scheme in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort shall fall within the scope of the present application.

[0031] For the 9-shaped fiber laser, the optical signal is input from a certain input port of the coupler, and the power is distributed by the coupler to enter the loop and be divided into two opposite transmission optical fields. The total phase shift amount of the two opposite transmission optical fields is 总 = φ NL + φ L , wherein φ L is the nonreciprocal linear phase shift amount, and φ NL is the nonlinear phase shift amount accumulated under high-power pulse induction. Due to the asymmetric amplification experienced by the opposite transmission pulses in the nonlinear amplification ring mirror loop and the bias phase shift provided by the nonreciprocal phase shifter, the nonlinear phase shifts accumulated by the opposite transmission pulses in the nonlinear amplification ring mirror are different. Compared with the two wings of the pulse, the energy of the central part of the pulse is higher, and the nonlinear phase shift difference is more. If interference occurs at the coupler, part of the energy of the incident optical field is reflected, and part of the energy is transmitted. The central part of the pulse has a higher transmission rate, and the two wings have a lower transmission rate. Therefore, the nonlinear amplification ring mirror is equivalent to a saturable absorber, and the laser can realize stable mode-locked operation.

[0032] This invention, based on practical needs, combines different mode-locking methods to design a figure-9 style mode-locked fiber laser with mode-locking assisted by a real saturable absorber and a nonlinear amplifying ring mirror. This invention introduces a hybrid mode-locking method combining a real saturable absorber and a nonlinear amplifying ring mirror, along with a tunable 2×2 polarization-maintaining fiber coupler, facilitating real-time adjustment of the transmittance of the nonlinear amplifying ring mirror loop and the modulation depth of the virtual saturable absorber. This solves the problem of poor self-starting performance in figure-9 style fiber lasers, enhances the self-starting capability of mode-locking, achieves rapid mode-locking, and further improves the signal-to-noise ratio of the output ultrashort laser pulse, reducing its output width, thereby improving the overall stability of the mode-locked fiber laser. This invention combines two passive mode-locking technologies, fully leveraging their respective advantages to form a superior hybrid mode-locking method.

[0033] Please see Figure 1 The present invention provides a figure-9 hybrid mode-locked fiber laser, comprising a pump source 1, a 2×2 polarization-maintaining fiber coupler 6, a nonlinear amplifying ring mirror loop connected to the first side of the polarization-maintaining fiber coupler 6, and a chirped fiber Bragg grating 7 connected to the second side of the polarization-maintaining fiber coupler 6.

[0034] The 2×2 polarization-maintaining fiber coupler 6 is located at the connection position between the nonlinear amplifying ring mirror loop and the linear arm of the laser resonant cavity. It is used to couple the laser from the nonlinear amplifying ring mirror loop to the linear arm. After being reflected by the chirped fiber Bragg grating 7, the laser on the linear arm is split into two beams that propagate clockwise and counterclockwise within the nonlinear amplifying ring mirror loop.

[0035] The nonlinear amplification ring mirror loop is formed by sequentially connecting a 2×2 polarization-maintaining fiber coupler 6, a doped fiber 5, a wavelength division multiplexer 2, a real saturable absorber mode-locking device 3, and a non-reciprocal phase shifter 4.

[0036] The first end of the wavelength division multiplexer 2 is connected to the pump source 1, coupling the pump light generated by the pump source 1 into the laser resonant cavity. The second end of the wavelength division multiplexer 2 is connected to the doped fiber 5, and the third end of the wavelength division multiplexer 2 is connected to the real saturable absorber mode-locking device 3. The wavelength division multiplexer 2 is used for combining the pump light and the signal light.

[0037] The doped fiber 5 is connected to the first end of the 2×2 polarization-maintaining fiber coupler 6, and the doped fiber 5 is excited by the pump light to generate laser signal light.

[0038] The 2×2 polarization-maintaining fiber coupler 6 is used to couple clockwise and counterclockwise propagating light in the nonlinear amplifying ring mirror loop.

[0039] The non-reciprocal phase shifter 4 is used to provide a fixed linear phase difference for the clockwise and counterclockwise propagating light in the nonlinear amplification ring mirror loop. In this embodiment, the fixed linear phase difference provided is π / 2; in other embodiments, it can also be selected according to specific needs.

[0040] The real saturable absorber mode-locked device 3 is used to maintain the self-starting and stable mode-locking of the fiber laser.

[0041] The linear arm of the laser resonant cavity is formed by connecting the third end of the 2x2 polarization maintaining fiber coupler 6 with the chirped fiber Bragg grating 7; the chirped fiber Bragg grating 7 serves as a cavity mirror for reflecting the laser beam and performs dispersion compensation to balance the dispersion in the laser resonant cavity.

[0042] In this embodiment, the nonlinear amplification ring mirror loop uses all polarization maintaining fiber devices: the doped optical fiber 5 is a polarization maintaining doped optical fiber, the wavelength division multiplexer 2 is a polarization maintaining wavelength division multiplexer, and the non-reciprocal phase shifter 4 is a polarization maintaining non-reciprocal phase shifter. All polarization maintaining fiber devices are less affected by the environment, further ensuring the environmental adaptability and reliability of the laser.

[0043] In this embodiment, the 2x2 polarization maintaining fiber coupler uses a tunable 2x2 polarization maintaining fiber coupler, which can realize real-time adjustment of the transmittance of the fiber laser and the modulation depth of the virtual saturable absorber, so that it can better perform the nonlinear amplification ring mirror loop under different parameter configurations, enrich the adjustment freedom of the fiber laser, and greatly improve the application compatibility of the fiber laser.

[0044] In this embodiment, the real saturable absorber mode-locked device 3 includes two jumper heads and a thin film between the two jumper heads, and the thin film includes but is not limited to a semiconductor saturable absorber mirror, graphene, or carbon nanotubes, and other materials that have a nonlinear response to light.

[0045] The real saturable absorber mode-locked device 3 is arranged in the nonlinear amplification ring mirror loop, the formation of the mode-locked pulse is dominated by the nonlinear amplification ring mirror, and the real saturable absorber mode-locked device 3 maintains self-starting and stable mode-locking of the fiber laser. The 2*2 polarization maintaining fiber coupler 6 divides the light into two paths for propagation in the nonlinear amplification ring mirror loop, the two paths of light are clockwise propagation light and counterclockwise propagation light respectively, and the two paths of light interfere at the 2*2 polarization maintaining fiber coupler 6, part of the light continues to transmit along the linear arm, is reflected by the chirped fiber Bragg grating 7 back to the 2*2 polarization maintaining fiber coupler 6, is divided into two beams of light with opposite propagation directions again, and enters the nonlinear amplification ring mirror loop; the other part of the light is transmitted out of the 2*2 polarization maintaining fiber coupler 6 and is used as the output of laser. The 9-shaped fiber laser provided by the utility model has the advantages of the nonlinear amplification ring mode-locking and the real saturable absorber mode-locking, can improve the mode-locking stability of the system, and has self-starting capability.

[0046] In the embodiment, the doped fiber 5 can be a gain fiber with different doping elements according to requirements. In addition, in the nonlinear amplification ring mirror loop, the doped fiber 5 is arranged close to the 2*2 polarization maintaining fiber coupler 6; this is to make the nonlinear phase shifts accumulated by the two paths of light in the nonlinear amplification ring mirror loop different, and more conducive to mode-locking.

[0047] In the embodiment, the chirped fiber Bragg grating 7 can select a dispersion parameter according to requirements to compensate for the overall dispersion in the laser resonant cavity.

[0048] After the two beams of light transmitted clockwise and counterclockwise pass through the polarization non-reciprocal phase shifter 4, a non-reciprocal linear phase shift difference is generated between the two beams of light. Further, the two beams of light transmitted clockwise and counterclockwise pass through the saturable absorption process after passing through the real saturable absorber mode-locked device 3 and continue to propagate clockwise and counterclockwise along the nonlinear amplification ring mirror loop, which will help the nonlinear accumulation of the nonlinear amplification ring mirror. Subsequently, the two beams of light transmitted clockwise and counterclockwise return to the tunable 2*2 polarization maintaining fiber coupler 6 and interfere, part of the light continues to transmit along the linear arm, the chirped fiber Bragg grating 7 generates dispersion opposite to the pre-fiber after the dispersion compensation, and the signal pulse is compressed and reflected back to the tunable 2*2 polarization maintaining fiber coupler 6, and the two beams of light with opposite propagation directions enter the nonlinear amplification ring mirror loop again to continue the above process; the other part of the light is transmitted out of the tunable 2*2 polarization maintaining fiber coupler 6 and is used as the output of laser.

[0049] The utility model discloses according to concrete demand, the different mode of combining use of locking, can give full play to respective superiority, forms better mixed mode of locking. From the above, the utility model discloses a kind of 9-shaped mixed mode of locking fiber laser by introducing real saturable absorber and the combination of nonlinear amplification ring mirror mode of locking technology, to further enhance the self-starting ability of mode locking, the signal-to-noise ratio of super-short pulse, reduce its output width, to improve the overall stability of mode locking fiber laser.Simultaneously still introduce tunable 2×2 polarization maintaining fiber coupler, further enrich the degree of freedom of fiber laser, can real-time adjust the transmissivity and modulation depth of nonlinear amplification ring mirror loop, so that it can better perform in nonlinear amplification ring mirror loop under different parameter configuration, can greatly improve the application compatibility of fiber laser.

[0050] The above describes a 9-shaped mixed mode of locking fiber laser in detail, and the principle and implementation of the utility model are described by applying specific examples; the above examples are only used to help understand the core idea of the utility model; meanwhile, for those skilled in the art, according to the idea of the utility model, the specific implementation and application range will be changed, and the above description should not be understood as a limitation of the utility model.

Claims

1. A figure-9 hybrid mode-locked fiber laser, characterized in that, It includes a pump source and a 2×2 polarization-maintaining fiber coupler, a nonlinear amplifying ring mirror loop connected to the first side of the 2×2 polarization-maintaining fiber coupler, and a chirped fiber Bragg grating connected to the second side of the 2×2 polarization-maintaining fiber coupler. The 2×2 polarization-maintaining fiber coupler is located at the connection position between the nonlinear amplifying ring mirror loop and the linear arm of the laser resonant cavity. It is used to couple the laser from the nonlinear amplifying ring mirror loop to the linear arm. After being reflected by the chirped fiber Bragg grating, the laser on the linear arm is split into two beams that propagate clockwise and counterclockwise within the nonlinear amplifying ring mirror loop.

2. The figure-9 hybrid mode-locked fiber laser according to claim 1, characterized in that, The nonlinear amplifying ring mirror loop is formed by sequentially connecting the 2×2 polarization-maintaining fiber coupler, doped fiber, wavelength division multiplexer, real saturable absorber mode-locking device, and non-reciprocal phase shifter; wherein... The first end of the wavelength division multiplexer is connected to the pump source, and the pump light generated by the pump source is coupled into the laser resonant cavity. The second end of the wavelength division multiplexer is connected to the doped fiber. The third end of the wavelength division multiplexer is connected to the real saturable absorber mode-locking device. The doped fiber is connected to the first end of the 2×2 polarization-maintaining fiber coupler, and the doped fiber is excited by the pump light to generate laser signal light. The 2×2 polarization-maintaining fiber coupler is used to couple clockwise and counterclockwise propagating light in the nonlinear amplifying ring mirror loop. The non-reciprocal phase shifter is used to provide a fixed linear phase difference between clockwise and counterclockwise propagating light in the nonlinear amplifying ring mirror loop; The real saturable absorber mode-locking device is used to maintain the self-starting and stable mode-locking of the fiber laser.

3. The figure-9 hybrid mode-locked fiber laser according to claim 2, characterized in that, The doped fiber is a polarization-maintaining doped fiber, the wavelength division multiplexer is a polarization-maintaining wavelength division multiplexer, and the non-reciprocal phase shifter is a polarization-maintaining non-reciprocal phase shifter.

4. The figure-9 hybrid mode-locked fiber laser according to claim 3, characterized in that, The doped fiber is a gain fiber, and the gain fiber is positioned close to the 2×2 polarization-maintaining fiber coupler.

5. The figure-9 hybrid mode-locked fiber laser according to claim 2, characterized in that, The real saturable absorber device includes two jumper heads and a thin film located between the two jumper heads.

6. The figure-9 hybrid mode-locked fiber laser according to claim 5, characterized in that, The thin film is a semiconductor saturable absorber mirror, graphene, or carbon nanotubes.

7. The figure-9 hybrid mode-locked fiber laser according to claim 1, characterized in that, The 2×2 polarization-maintaining fiber coupler is a tunable 2×2 polarization-maintaining fiber coupler.

8. The figure-9 hybrid mode-locked fiber laser according to claim 1, characterized in that, The 2×2 polarization-maintaining fiber coupler splits the light into two paths that propagate in the nonlinear amplifying ring mirror loop. The two paths propagate clockwise and counterclockwise, respectively. When the two paths return to the 2×2 polarization-maintaining fiber coupler, they interfere. One portion of the light continues to propagate along the linear arm, is reflected by the chirped fiber Bragg grating, and is reflected back to the 2×2 polarization-maintaining fiber coupler, where it is split into two beams with opposite propagation directions and enters the nonlinear amplifying ring mirror loop again. The other portion of the light is transmitted through the 2×2 polarization-maintaining fiber coupler as the laser output.

9. The figure-9 hybrid mode-locked fiber laser according to claim 1, characterized in that, The linear arm of the laser resonant cavity is formed by connecting the third end of the 2×2 polarization-maintaining fiber coupler to the chirped fiber Bragg grating; the chirped fiber Bragg grating is used to reflect the laser beam and perform dispersion compensation to balance the dispersion within the laser resonant cavity.

10. The figure-9 hybrid mode-locked fiber laser according to claim 1, characterized in that, The dispersion parameters of the chirped fiber Bragg grating can be selected to compensate for the overall dispersion within the laser resonant cavity.

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