Ultra-short pulse laser with low threshold value mode locking

Abstract

The invention relates to a low-threshold mode-locked ultrashort pulse laser, which comprises a pumping source, a pumping protector, a polarization-maintaining optical fiber beam splitter, an optical fiber oscillator and an optical fiber amplifier, and is characterized in that pump light emitted by the pumping source is transmitted to the optical fiber oscillator and the optical fiber amplifier through the polarization-maintaining optical fiber beam splitter; the optical fiber oscillator outputs ultra-short pulse laser based on dissipation soliton mode locking, the pulse laser is transmitted to the optical fiber amplifier to be amplified, an escape pump light multiplexing technology is adopted, so that population inversion of gain optical fibers of the optical fiber oscillator is distributed more evenly in the axial direction, and the ultra-short pulse laser solves the problems caused by high pump power and improves the laser efficiency. The pump light threshold value of the mode-locked fiber laser is reduced, and the stability and reliability of the laser are improved.

Description

Technical Field

[0001] The invention relates to the field of lasers, and in particular to an ultrashort pulse laser with low threshold mode locking. Background Art

[0002] In the application of ultrashort pulse lasers, high requirements are placed on 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] To maintain steady state, a mode-locked laser must ensure that the pulse parameters (pulse energy, pulse duration, chirp, spectral bandwidth, etc.) remain constant after each round trip, even though these parameters may undergo significant changes during the round trip. This means that the various effects that affect the circulating pulse (such as laser gain, propagation loss, nonlinear effects, and dispersion) must reach a state of equilibrium so that they can 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 the art 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 an ultrashort pulse laser with low threshold mode locking, comprising a pump source, a pump protector, a polarization-maintaining fiber beam splitter and 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, 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 grating and an isolator, and the first polarization-maintaining wavelength division multiplexer converts the polarization-maintaining light into a wavelength division multiplexer. The pump light output by the fiber splitter is coupled into the fiber oscillator, and 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 reflector, and the fiber reflector reflects the pump light that is not completely absorbed by the first gain fiber 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, and 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 amplification again and then outputs it through the fiber collimator.

[0008] In one of the embodiments, a collimator is further arranged between the semiconductor saturable absorber and the polarization-maintaining beam splitter coupler.

[0009] In one embodiment, the semiconductor saturable absorber mirror and the collimator 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 grating to laser light is ≥99%.

[0011] In one embodiment, the polarization-maintaining fiber beam splitter splits the pump light output by 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 grating has a filtering effect on the laser.

[0016] In one embodiment, the second fiber grating has high transmission for pump light and high reflection for 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, wherein a second polarization-maintaining wavelength division multiplexer splits the escaped pump light and the transmitted laser, transmits the laser to a first fiber grating, and transmits the escaped pump light to a fiber reflector, and the fiber reflector is used to reflect the received remaining pump light back to the second polarization-maintaining wavelength division multiplexer, and then this part of the pump light is transmitted to the first gain fiber again and absorbed, and the pump light reflected by the fiber reflector is reused, so that the first gain fiber population inversion is more evenly distributed along the axial direction, and this even population inversion distribution helps the laser to operate at a low pump threshold, therefore, the ultrashort pulse laser of the present invention has a lower pump light threshold, which can not only avoid damage to the optical fiber device due to excessively high pump power, but also effectively prevent the occurrence of multiple pulses during the mode-locking process, thereby maintaining the stability of the mode-locking 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] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0021] In addition, 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 the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0022] like Figure 1As shown, this embodiment provides an ultrashort pulse laser with low threshold mode locking, 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 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 comprises a semiconductor saturable absorber 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, wherein the isolator 10 is used to prevent the laser of the fiber amplifier 200 from being reflected back to the fiber oscillator 100. 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, and the fiber circulator 16 transmits the pulse 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 also connected to the fiber reflector 8, and the fiber reflector 8 reflects the pump light that is not completely absorbed by the first gain fiber 6 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, and the fiber circulator 16 transmits the mode-locked pulse 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 amplification again and then outputs it through the fiber collimator 17. The present embodiment provides a low-threshold mode-locked ultrashort pulse laser, wherein the second polarization-maintaining wavelength division multiplexer 7 splits the escaped pump light and the transmitted laser light, transmits the laser light to the first fiber grating 9, and transmits the escaped pump light to the fiber reflector 8. The fiber reflector 8 reflects the received remaining pump light 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 population inversion of the first gain fiber 6 is more evenly distributed along the axial direction. This even population inversion distribution helps the laser to operate at a low pump threshold. Therefore, the ultrashort pulse laser of the present invention has a lower pump light threshold, which can not only avoid damage to the optical fiber device due to excessively high pump power, but also effectively prevent the occurrence of multiple pulses during the mode-locking process, maintain the stability of the mode-locking state, and improve the stability and reliability of the laser.

[0023] In one of the embodiments, a collimator 2 is further provided between the semiconductor saturable absorber mirror 1 and the polarization-maintaining beam splitter coupler 4. The laser spot formed on the semiconductor saturable absorber mirror 1 by the optical fiber output laser in the optical fiber oscillator 100 after passing through the collimator 2 is relatively large, and the laser power density is maintained below the damage threshold of the semiconductor saturable absorber mirror 1, thereby avoiding damage to the semiconductor saturable absorber mirror 1 and ensuring the long-term stable operation of the laser.

[0024] In one of the embodiments, the semiconductor saturable absorber mirror 1 and the collimator 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 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 split in a 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, transmits the laser to the first fiber grating 9, transmits the escaped pump light to the fiber reflector 8, and the fiber reflector 8 reflects the remaining pump light to the polarization-maintaining wavelength division multiplexer 7, and then returns 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 of the embodiments, 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 state 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 grating 14 has high transmittance to the pump light and high reflectivity to the laser. The fiber amplifier 200 amplifies the laser through the second gain fiber 15 and then reflects it through the second fiber grating 14. The laser is amplified again through the second gain fiber 15 and then collimated by the fiber collimator 17 for 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 above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention, and any figure mark in the claims should not be regarded as limiting the claims involved.

[0034] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood 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, and is characterized in that: The fiber oscillator (100) comprises a semiconductor saturable absorber (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); the first polarization-maintaining wavelength division multiplexer (5) couples the pump light output by the polarization-maintaining optical fiber beam splitter (13) into the fiber oscillator; the fiber circulator (16) transmits the pulse laser output by the fiber oscillator (100) to the fiber amplifier (200) through the fiber circulator (16), amplifies the pulse laser and then outputs the pulse laser through the fiber collimator (17); The second polarization-maintaining wavelength division multiplexer (7) is also 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) comprises a second optical fiber grating (14) and a second gain optical fiber (15); 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 an optical fiber collimator (17).

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

3. The low-threshold mode-locked ultrashort pulse laser according to claim 1, characterized in that: The semiconductor saturable absorber mirror (1) and the collimator mirror (2) are coaxially packaged, and the semiconductor saturable absorber 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 optical 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 optical fiber oscillator (100) and the optical 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 passage 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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