A low-threshold mode-locked ultrashort pulse laser

Abstract

The present invention relates to a low-threshold mode-locked ultrashort pulse laser, comprising a pump source, a pump protector, a polarization-maintaining fiber beam splitter, a fiber oscillator, and a fiber amplifier. Pump light emitted by the pump source is transmitted to the fiber oscillator and the fiber amplifier respectively through the polarization-maintaining fiber beam splitter. The fiber oscillator outputs ultrashort pulse laser based on dissipative soliton mode-locking. The pulse laser is transmitted to the fiber amplifier for amplification. The escaped pump light multiplexing technology is adopted to make the fiber oscillator gain fiber population inversion more uniformly distributed along the axial direction. The ultrashort pulse laser of the present invention solves the problem caused by high pump power, reduces the pump light threshold of the mode-locked fiber laser, and improves the stability and reliability of the laser.

Description

Technical Field

[0001] The present invention relates to the field of lasers, and in particular to a low-threshold mode-locked ultrashort pulse laser. Background Art

[0002] In the application of ultrashort pulse lasers, there are high requirements for the long-term stability of the laser system. In order to ensure the stability of the laser system, the mode-locked state and key components in the laser system must remain stable and damage-free for a long time.

[0003] Maintaining steady-state in a mode-locked laser requires that the pulse parameters (pulse energy, pulse duration, chirp, spectral bandwidth, etc.) remain constant after each complete round trip, even though these parameters may undergo significant changes during the round trip. This means that the various effects influencing the circulating pulse (such as laser gain, propagation losses, nonlinear effects, and dispersion) must reach a state of equilibrium so that they cancel each other out after each complete round trip, thereby maintaining stable pulse parameters.

[0004] However, when the pump light power is high, it is easy to cause multiple pulses and damage to the components in the oscillator, which will bring challenges to the long-term stable operation of the laser.

[0005] Therefore, there is an urgent need in this field to propose an ultrashort pulse laser that can operate stably under low pump power conditions. Summary of the Invention

[0006] Based on this, in order to solve the above problems, the present invention provides a low-threshold mode-locked ultrashort pulse laser, which adopts the escaped pump light multiplexing technology to solve the problems caused by high pump power, greatly reduce the pump light threshold of the mode-locked fiber laser, and improve the stability and reliability of the laser.

[0007] To achieve the above-mentioned object, the present invention provides a low-threshold mode-locked ultrashort pulse laser, comprising a pump source, a pump protector, a polarization-maintaining fiber beam splitter, a fiber oscillator, and a fiber amplifier, wherein the pump light emitted by the pump source is transmitted to the fiber oscillator and the fiber amplifier respectively through the polarization-maintaining fiber beam splitter, the fiber oscillator outputs ultrashort pulse laser based on dissipative soliton mode locking, and the pulse laser is transmitted to the fiber amplifier for amplification, the fiber oscillator comprises a semiconductor saturable absorber mirror, a polarization-maintaining optical coupler, a first polarization-maintaining wavelength division multiplexer, a first gain fiber, a second polarization-maintaining wavelength division multiplexer, a first fiber Bragg grating and an isolator, the first polarization-maintaining wavelength division multiplexer being optically connected in sequence. The pump light output by the polarization-maintaining fiber beam splitter is coupled into the fiber oscillator. The fiber circulator transmits the pulse laser output by the fiber oscillator to the fiber amplifier through the fiber circulator for amplification and then outputs it through the fiber collimator. The second polarization-maintaining wavelength division multiplexer is also connected to a fiber retroreflector. The fiber retroreflector reflects the pump light that is not completely absorbed by the first gain fiber back to the second polarization-maintaining wavelength division multiplexer, and then is absorbed by the first gain fiber again. The fiber amplifier includes a second fiber grating and a second gain fiber. The fiber circulator transmits the mode-locked pulse laser to the second gain fiber for amplification, and then reflects it back to the second gain fiber through the second fiber grating for further amplification and then outputs it through the fiber collimator.

[0008] In one embodiment, a collimating mirror is further provided between the semiconductor saturable absorber mirror and the polarization-maintaining optical coupler.

[0009] In one embodiment, the semiconductor saturable absorber mirror and the collimating mirror are coaxially packaged, and the semiconductor saturable absorber mirror is mounted on a one-dimensional linear motor.

[0010] In one embodiment, the reflectivity of the first fiber Bragg grating to laser light is ≥99%.

[0011] In one embodiment, the polarization-maintaining fiber beam splitter splits the pump light output from the pump source into a beam ratio of 3:7 and transmits the beams to the fiber oscillator and the fiber amplifier respectively.

[0012] In one embodiment, the length of the first gain fiber is a preset value, so that a portion of the pump light is allowed to escape from the end of the first gain fiber during a single pass of the pump light through the first gain fiber.

[0013] In one embodiment, the semiconductor saturable absorber mirror is bonded to metal for heat dissipation.

[0014] In one embodiment, the polarization-maintaining optical coupler is further connected to a photodiode.

[0015] In one embodiment, the first fiber Bragg grating has a filtering effect on the laser light.

[0016] In one embodiment, the second fiber Bragg grating has high transmittance to the pump light and high reflectivity to the laser light.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides a low-threshold mode-locked ultrashort pulse laser. A second polarization-maintaining wavelength division multiplexer splits the escaped pump light and the transmitted laser light, transmits the laser light to a first fiber grating, and transmits the escaped pump light to a fiber retroreflector. The fiber retroreflector reflects the remaining received pump light back to the second polarization-maintaining wavelength division multiplexer. This portion of the pump light is then transmitted to the first gain fiber and absorbed. The pump light reflected by the fiber retroreflector is reused, making the population inversion distribution of the first gain fiber more uniform along the axial direction. This uniform population inversion distribution helps the laser operate at a low pump threshold. Therefore, the ultrashort pulse laser of the present invention has a low pump light threshold, which not only prevents damage to optical fiber components due to excessively high pump power, but also effectively prevents the occurrence of multiple pulses during the mode-locking process, thereby maintaining the stability of the mode-locked state. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic structural diagram of a low-threshold mode-locked ultrashort pulse laser according to the present invention. DETAILED DESCRIPTION

[0020] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0021] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0022] like Figure 1As shown, this embodiment provides a low-threshold mode-locked ultrashort pulse laser, including a pump source 11, a pump protector 12, a polarization-maintaining fiber beam splitter 13, a fiber oscillator 100, and a fiber amplifier 200. The pump light emitted by the pump source 11 is transmitted to the fiber oscillator 100 and the fiber amplifier 200 respectively through the polarization-maintaining fiber beam splitter 13. The fiber oscillator 100 outputs picosecond pulse laser based on dissipative soliton mode locking, and the pulse laser is transmitted to the fiber amplifier 200 for amplification. The fiber oscillator 100 includes a semiconductor saturable absorber mirror 1, a polarization-maintaining optical coupler 4, a first polarization-maintaining wavelength division multiplexer 5, a first gain fiber 6, a second polarization-maintaining wavelength division multiplexer 7, a first fiber grating 9, and an isolator 10, which are optically connected in sequence. The isolator 10 is used to prevent the laser of the fiber amplifier 200 from being reflected back to the fiber oscillator. The first polarization-maintaining wavelength division multiplexer 5 couples the pump light output by the polarization-maintaining fiber beam splitter 13 into the fiber oscillator 100. The fiber circulator 16 transmits the pulsed laser output by the fiber oscillator 100 to the fiber amplifier 200 through the fiber circulator 16 for amplification and then outputs it through the fiber collimator 17. The second polarization-maintaining wavelength division multiplexer 7 is further connected to the fiber retroreflector 8. The fiber retroreflector 8 reflects the pump light that is not completely absorbed by the first gain fiber 6 back to the second polarization-maintaining wavelength division multiplexer 7, and then is absorbed by the first gain fiber 6 again. The fiber amplifier 200 includes a second fiber grating 14 and a second gain fiber 15. The fiber circulator 16 transmits the mode-locked pulsed laser to the second gain fiber 15 for amplification, and then reflects it back to the second gain fiber 15 through the second fiber grating 14 for further amplification and then outputs it through the fiber collimator 17. This embodiment provides a low-threshold mode-locked ultrashort pulse laser, in which the second polarization-maintaining wavelength division multiplexer 7 splits the escaped pump light and the transmitted laser, transmits the laser to the first fiber grating 9, and transmits the escaped pump light to the fiber reflector 8. The function of the fiber reflector 8 is to reflect the remaining pump light received back to the second polarization-maintaining wavelength division multiplexer 7, and then this part of the pump light is transmitted to the first gain fiber 6 again and absorbed. The pump light reflected by the fiber reflector 8 is reused and then absorbed by the first gain fiber (6) again, so that the particle number inversion of the first gain fiber 6 is more uniformly distributed along the axial direction. This uniform particle number inversion distribution helps the laser operate at a low pump threshold. Therefore, the ultrashort pulse laser of the present invention has a lower pump light threshold, which not only avoids damage to the optical fiber device due to excessive pump power, but also effectively prevents the occurrence of multiple pulses during the mode-locking process, maintains the stability of the mode-locking state, and improves the stability and reliability of the laser.

[0023] In one embodiment, a collimator 2 is further provided between the semiconductor saturable absorber mirror 1 and the polarization-maintaining optical coupler 4. The laser light outputted from the optical fiber in the fiber oscillator 100 forms a larger laser spot on the semiconductor saturable absorber mirror 1 after passing through the collimator 2. The laser power density is maintained below the damage threshold of the semiconductor saturable absorber mirror 1, thereby preventing damage to the semiconductor saturable absorber mirror 1 and ensuring long-term stable operation of the laser.

[0024] In one embodiment, the semiconductor saturable absorber mirror 1 and the collimating mirror 2 are coaxially packaged, and the semiconductor saturable absorber mirror 1 is mounted on a one-dimensional linear motor, so that the semiconductor saturable absorber mirror 1 has the function of replacing bad points, thereby ensuring the long-term reliability of the fiber laser.

[0025] In one embodiment, the reflectivity of the first fiber grating 9 to laser light is ≥99%, so that a relatively high power density is maintained in the fiber oscillator 100, and the oscillator produces a relatively strong nonlinear effect at low pump power, thereby achieving mode locking at low pump power.

[0026] In one embodiment, the polarization-maintaining fiber splitter 13 splits the pump light output by the pump source 11 into a beam splitting ratio of 3:7 and transmits the beams to the fiber oscillator 100 and the fiber amplifier 200 respectively. The portion transmitted to the fiber amplifier 200 is used to provide pump energy for the second gain fiber 15.

[0027] In one embodiment, the length of the first gain fiber 6 is a preset value, so that a portion of the pump light is allowed to escape from the end of the first gain fiber 6 during a single pass of the pump light through the first gain fiber 6. The second polarization-maintaining wavelength division multiplexer 7 splits the escaped pump light and the transmitted laser beam, transmits the laser to the first fiber grating 9, and transmits the escaped pump light to the fiber reflector 8. The fiber reflector 8 reflects the remaining pump light back to the polarization-maintaining wavelength division multiplexer 7, and then returns it to the first gain fiber 6 to be absorbed, so that the population inversion of the first gain fiber 6 is more evenly distributed along the axial direction, ensuring that the laser operates in a low pump threshold state.

[0028] In one embodiment, the semiconductor saturable absorber mirror 1 is bonded to metal for heat dissipation to avoid thermal damage to the device.

[0029] In one embodiment, the polarization-maintaining optical coupler 4 is further connected to a photodiode 3 for monitoring the operating status of the laser.

[0030] In one embodiment, the first fiber grating 9 has a filtering effect on the laser, so that the laser operates in a dissipative soliton mode-locking mechanism.

[0031] In one embodiment, the second fiber Bragg grating 14 has high transmittance for pump light and high reflection for laser light. The fiber amplifier 200 amplifies the laser light through the second gain fiber 15, reflects the laser light through the second fiber Bragg grating 14, amplifies the laser light again through the second gain fiber 15, and collimates the laser light through the fiber collimator 17 before output.

[0032] In one embodiment, the first gain fiber 6 and the second gain fiber 15 are polarization-maintaining ytterbium-doped fibers.

[0033] It should be noted that it is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from all perspectives, the embodiments should be regarded as illustrative and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the foregoing description. It is intended that all changes that fall within the meaning and range of equivalents of the claims be included in the present invention, and any reference signs in the claims should not be construed as limiting the claims to which they relate.

[0034] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A low-threshold mode-locked ultrashort pulse laser, comprising a pump source (11), a pump protector (12), a polarization-maintaining fiber beam splitter (13), a fiber oscillator (100), and a fiber amplifier (200), wherein: The pump light emitted by the pump source (11) is transmitted to the fiber oscillator (100) and the fiber amplifier (200) respectively through the polarization-maintaining fiber beam splitter (13). The fiber oscillator (100) outputs ultrashort pulse laser based on dissipative soliton mode locking. The pulse laser is transmitted to the fiber amplifier (200) for amplification. The invention is characterized in that: The fiber oscillator (100) comprises a semiconductor saturable absorber mirror (1), a polarization-maintaining optical coupler (4), a first polarization-maintaining wavelength division multiplexer (5), a first gain fiber (6), a second polarization-maintaining wavelength division multiplexer (7), a first fiber grating (9) and an isolator (10) which are optically connected in sequence. The first polarization-maintaining wavelength division multiplexer (5) couples the pump light output by the polarization-maintaining optical fiber splitter (13) into the fiber oscillator. The fiber circulator (16) transmits the pulsed laser output by the fiber oscillator (100) to the fiber amplifier (200) through the fiber circulator (16) for amplification and then passes through the fiber collimator (17). output; the second polarization-maintaining wavelength division multiplexer (7) is further connected to an optical fiber reflector (8), and the optical fiber reflector reflects the pump light that is not completely absorbed by the first gain optical fiber (6) back to the second polarization-maintaining wavelength division multiplexer (7), and then is absorbed by the first gain optical fiber (6) again; the optical fiber amplifier (200) includes a second optical fiber grating (14) and a second gain optical fiber (15), and the optical fiber circulator (16) transmits the mode-locked pulse laser to the second gain optical fiber (15), amplifies it, reflects it back to the second gain optical fiber (15), amplifies it again, and then outputs it through the optical fiber collimator (17).

2. The low-threshold mode-locked ultrashort pulse laser according to claim 1, characterized in that: A collimating mirror (2) is further provided between the semiconductor saturable absorber mirror (1) and the polarization-maintaining optical splitter coupler (4).

3. The low-threshold mode-locked ultrashort pulse laser according to claim 2, characterized in that: The semiconductor saturable absorption mirror (1) and the collimating mirror (2) are coaxially packaged, and the semiconductor saturable absorption mirror (1) is installed on a one-dimensional linear motor.

4. The low-threshold mode-locked ultrashort pulse laser according to claim 1, characterized in that: The reflectivity of the first optical fiber grating (9) to laser light is ≥99%.

5. The low-threshold mode-locked ultrashort pulse laser according to claim 1, characterized in that: The polarization-maintaining fiber beam splitter (13) splits the pump light output by the pump source (11) in a ratio of 3:7 and transmits the split light to the fiber oscillator (100) and the fiber amplifier (200) respectively.

6. The low-threshold mode-locked ultrashort pulse laser according to claim 1, characterized in that: The length of the first gain optical fiber (6) is a preset value, so that a portion of the pump light is allowed to escape from the end of the first gain optical fiber (6) during a single pass of the pump light through the first gain optical fiber (6).

7. The low-threshold mode-locked ultrashort pulse laser according to claim 1, characterized in that: The semiconductor saturable absorber mirror (1) is bonded to metal for heat dissipation.

8. The low-threshold mode-locked ultrashort pulse laser according to claim 1, characterized in that: The polarization-maintaining optical coupler (4) is also connected to a photodiode (3).

9. The low-threshold mode-locked ultrashort pulse laser according to claim 1, characterized in that: The first fiber grating (9) has a filtering effect on the laser.

10. The low-threshold mode-locked ultrashort pulse laser according to claim 1, characterized in that: The second optical fiber grating (14) has high transmission for pump light and high reflection for laser light.

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