Method for inhibiting SBS effect of laser MOPA amplification system of thulium-doped fiber laser

Abstract

The application provides a method for inhibiting SBS effect of a laser MOPA amplification system of a thulium-doped fiber laser, which comprises arranging a rectangular spectrum shaper between a master oscillator and a power amplifier, wherein the rectangular spectrum shaper is configured to adjust a Gaussian spectrum of laser pulses emitted by the master oscillator into a rectangular spectrum and then output to the power amplifier; and further comprising using a backward pumping mode and a fiber with a higher doping density. The application can effectively inhibit SBS effect by arranging the rectangular spectrum shaper, first shaping the Gaussian spectrum of seed laser into a rectangular spectrum, and then entering the power amplifier; using the backward pumping mode can reduce waste of pumping energy, improve energy pumping efficiency, and reduce the influence of SBS effect; and using the fiber with a higher doping density can further absorb pumping light in a shorter length, so that the optimal fiber length Lout is smaller, the interaction length of signal light and Stokes signal is reduced, and SBS effect is effectively inhibited.

Description

Technical Field

[0001] This invention relates to the field of fiber laser technology, and more specifically to a method for suppressing the SBS effect in a laser MOPA amplification system of a thulium-doped fiber laser. Background Technology

[0002] Thulium-doped fiber lasers can emit laser light at a wavelength of 2000 nm, which has a wide range of applications due to its mid-infrared range. However, the output power of thulium-doped fiber lasers is relatively low, so it is necessary to amplify the laser light emitted by thulium-doped fiber lasers to increase the laser power and obtain high-energy laser light to meet the needs of laser applications.

[0003] The most efficient amplification system currently used to amplify the laser light from thulium-doped fiber lasers is the MOPA (Master Oscillator and Power Amplifier) ​​structure. For example... Figure 1 As shown, the existing laser MOPA amplification system consists of two parts: a master oscillator based on a modulated pulse seed source, which includes a seed laser; and a power amplifier, which includes thulium-doped fiber (TDF) and diode pumping. The TDF also serves as the gain medium, and the diode pumps are positioned in both the forward and backward directions of the TDF, employing a bidirectional pumping method. The master oscillator and the power amplifier are isolated by an optical isolator. The laser MOPA amplification system offers advantages such as flexible time characteristics and high conversion efficiency.

[0004] For applications requiring high pulse peak power, thulium-doped fiber lasers are an ideal light source. Laser MOPA amplification systems can significantly increase laser output power; however, while improving output power, these systems are limited by several factors, one of which is stimulated Brillouin scattering (SBS). The SBS effect is a nonlinear effect, and compared to continuous-wave fiber lasers, pulsed fiber lasers have higher peak power, thus making them more susceptible to nonlinear effects.

[0005] The SBS effect converts a significant portion of the signal light in the amplifier into backward-propagating Stokes light. This backward-propagating Stokes light is amplified in the active fiber, consuming the inverted particle number and affecting the conversion efficiency of the forward output, thus reducing the laser amplification effect and hindering laser amplification. Simultaneously, the laser MOPA amplification system also amplifies the backward-propagating light, potentially damaging the pump and seed laser in the amplifier's preamplifier stage. Therefore, suppressing or even eliminating the SBS effect during laser amplification becomes a crucial issue that must be considered when improving laser amplification power. Summary of the Invention

[0006] To address at least one of the above technical problems, the present invention provides a method for suppressing the SBS effect in a laser MOPA amplification system of a thulium-doped fiber laser.

[0007] A method for suppressing the SBS effect in a laser MOPA amplification system of a thulium-doped fiber laser includes setting a rectangular spectral shaper between a master oscillator and a power amplifier. The rectangular spectral shaper is configured to adjust the Gaussian spectrum of the laser pulse emitted by the master oscillator into a rectangular spectrum before outputting it to the power amplifier.

[0008] Preferably, the rectangular spectral shaper includes an even number of phase modulators, which are connected in series between the main oscillator and the power amplifier.

[0009] In any of the above embodiments, the rectangular spectral shaper further includes a controller configured to be connected to an even number of phase modulators respectively.

[0010] In any of the above embodiments, the controller is preferably configured to generate a continuous sinusoidal signal to drive and control an even number of phase modulators respectively, thereby enhancing the intensity of weak spectral lines, and thus adjusting the Gaussian spectrum of the laser pulse emitted by the master oscillator into a rectangular spectrum output after passing through an even number of phase modulators.

[0011] In any of the above schemes, the rectangular spectrum shaper first modulates the seed laser, and after the modulated spectrum is checked by a spectrometer to see if it meets the requirements of a rectangular spectrum, the rectangular spectrum shaper is then set between the main oscillator and the power amplifier.

[0012] Preferably, in any of the above embodiments, an optical isolator is provided between the rectangular spectral shaper and the main oscillator.

[0013] Preferably, in any of the above embodiments, the method further includes a backward pumping method.

[0014] Preferably, in any of the above schemes, the method further includes using thulium-doped optical fiber with a high doping density.

[0015] Accordingly, the present invention also provides a laser MOPA amplification system for thulium-doped fiber lasers that suppresses the SBS effect, including a master oscillator and a power amplifier, and further including a rectangular spectrum shaper. The rectangular spectrum shaper is disposed between the master oscillator and the power amplifier and is configured to adjust the Gaussian spectrum of the laser pulse emitted by the master oscillator into a rectangular spectrum before outputting it to the power amplifier.

[0016] Preferably, the rectangular spectral shaper includes an even number of phase modulators, which are connected in series between the main oscillator and the power amplifier.

[0017] In any of the above embodiments, the rectangular spectral shaper further includes a controller configured to be connected to an even number of phase modulators respectively.

[0018] In any of the above embodiments, the controller is preferably configured to generate a continuous sinusoidal signal to drive and control an even number of phase modulators respectively, thereby enhancing the intensity of weak spectral lines, and thus adjusting the Gaussian spectrum of the laser pulse emitted by the master oscillator into a rectangular spectrum output after passing through an even number of phase modulators.

[0019] Preferably, in any of the above embodiments, the laser MOPA amplification system further includes an optical isolator, which is disposed between the rectangular spectral shaper and the master oscillator.

[0020] In any of the above embodiments, the laser MOPA amplification system further includes a thulium-doped fiber with a high doping density as a gain medium, and the thulium-doped fiber is disposed after the rectangular spectral shaper.

[0021] Preferably, in any of the above embodiments, the laser MOPA amplification system further includes a diode pump, which is disposed after the gain medium and employs a backward pumping method.

[0022] The method for suppressing the SBS effect in a laser MOPA amplification system of a thulium-doped fiber laser of the present invention has the following beneficial effects:

[0023] 1. By setting a rectangular spectrum shaper, the Gaussian spectrum emitted by the seed laser is first shaped into a rectangular spectrum before entering the power amplifier, which can effectively suppress the SBS effect.

[0024] 2. By adopting a backward pumping method, the waste of pumping energy is reduced, the energy pumping efficiency is improved, and the impact of the SBS effect is reduced;

[0025] 3. By using optical fibers with higher doping density, pump light can be fully absorbed with a shorter length, resulting in a smaller optimal fiber length (Lout). This reduces the interaction length between the signal light and the Stokes signal, thereby effectively suppressing the SBS effect. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of an existing laser MOPA amplification system.

[0027] Figure 2 This is a schematic diagram of a preferred embodiment of a laser MOPA amplification system corresponding to the method of the present invention for suppressing the SBS effect in a laser MOPA amplification system for thulium-doped fiber lasers.

[0028] Figure 3 This is a schematic diagram of a preferred embodiment of a rectangular spectral shaper for a laser MOPA amplification system, corresponding to the method for suppressing the SBS effect in a laser MOPA amplification system for thulium-doped fiber lasers according to the present invention. Detailed Implementation

[0029] To better understand the present invention, the present invention will be described in detail below with reference to specific embodiments.

[0030] Example 1

[0031] A method for suppressing the SBS effect in a laser MOPA amplification system of a thulium-doped fiber laser includes setting a rectangular spectral shaper between a master oscillator and a power amplifier. The rectangular spectral shaper is configured to adjust the Gaussian spectrum of the laser pulse emitted by the master oscillator into a rectangular spectrum before outputting it to the power amplifier.

[0032] Preferably, in this embodiment, the rectangular spectrum shaper includes an even number of phase modulators, which are connected in series between the main oscillator and the power amplifier. The rectangular spectrum shaper also includes a controller configured to be connected to each of the even number of phase modulators; the controller is further configured to generate a continuous sinusoidal signal to drive and control each of the even number of phase modulators, enhancing the intensity of weak spectral lines, thereby adjusting the Gaussian spectrum of the laser pulse emitted by the main oscillator into a rectangular spectrum output after passing through the even number of phase modulators.

[0033] It should be noted that by shaping the Gaussian spectrum emitted by the master oscillator into a rectangular spectrum, the spectrum can be broadened, the maximum peak value of the spectrum can be reduced, and the optical power spectral density can be lowered, thereby keeping the optical power spectral density below the threshold for triggering the SBS effect and avoiding its activation. Furthermore, because the Gaussian spectrum is shaped into a rectangular spectrum, after the laser signal passes through the power amplifier but before its use, the rectangular spectrum can be restored to a Gaussian spectrum using another shaping device.

[0034] In this embodiment, preferably, the rectangular spectrum shaper first modulates the seed laser, and after the modulated spectrum is checked by a spectrometer to meet the requirements of a rectangular spectrum, the rectangular spectrum shaper is then set between the main oscillator and the power amplifier.

[0035] By setting a rectangular spectrum shaper, the Gaussian spectrum emitted by the seed laser is first shaped into a rectangular spectrum before entering the power amplifier. The rectangular spectrum has a strong ability to suppress the SBS effect.

[0036] In this embodiment, preferably, an optical isolator is also provided between the rectangular spectral shaper and the main oscillator to limit the unidirectional propagation of the seed laser.

[0037] In this embodiment, preferably, the method further includes backward pumping. The signal power under forward pumping is higher than that under backward pumping almost across the entire fiber segment. Therefore, forward pumping causes more signal energy to be transferred to the Stokes wave, wasting pump energy. Therefore, backward pumping reduces pump energy waste, improves energy pumping efficiency, and reduces the impact of the SBS effect.

[0038] In this embodiment, preferably, the method further includes using thulium-doped fiber with a high doping density. Using fiber with a high doping density allows for sufficient absorption of pump light over a shorter length, reducing the optimal fiber length (Lout) and decreasing the interaction length between the signal light and the Stokes signal, thereby effectively suppressing the SBS effect. It should be noted that the standard for doping density is generally: a particle number of 10-1. 26 / m 3 The doping density is measured in orders of magnitude higher than this; anything above this level is considered high doping density. However, please note that this is a relative range, not an absolute standard. In practice, it is necessary to consider factors such as the material properties and purity of the optical fiber.

[0039] Example 2

[0040] Corresponding to Example 1, the present invention also provides a laser MOPA amplification system for thulium-doped fiber lasers that suppresses the SBS effect, such as... Figure 2As shown, it includes a master oscillator 10 and a power amplifier 20, and also includes a rectangular spectrum shaper 40. The rectangular spectrum shaper 40 is disposed between the master oscillator 10 and the power amplifier 20, and is configured to adjust the Gaussian spectrum of the laser pulse emitted by the master oscillator 10 into a rectangular spectrum before outputting it to the power amplifier 20.

[0041] In this embodiment, preferably, the rectangular spectrum shaper 40 includes an even number of phase modulators, which are connected in series between the main oscillator 10 and the power amplifier 20.

[0042] like Figure 3 As shown, the rectangular spectrum shaper 40 includes two phase modulators as an example, one of which is numbered 401 and the other 402. Phase modulators 401 and 402 are connected in series and positioned between the main oscillator 10 and the power amplifier 20. The rectangular spectrum shaper 40 also includes a controller 403, which is configured to be connected to each phase modulator. The controller 403 is also configured to generate a continuous sinusoidal signal to drive each phase modulator, enhancing the intensity of weak spectral lines, thereby adjusting the Gaussian spectrum of the laser pulse emitted by the main oscillator 10 into a rectangular spectrum output after passing through an even number of phase modulators. It should be noted that since the main oscillator 10 emits Gaussian spectral lines with the highest intensity at the center and a symmetrical decrease on both sides, and a single phase modulator only acts on one side of the spectral line, it is necessary to set up phase modulators in pairs to act on the spectral lines on both sides, shaping the Gaussian spectral lines into rectangular spectral lines. Due to the limitations of phase modulator functionality, when a pair of phase modulators cannot meet the spectral line shaping requirements, phase modulators can be added in pairs. Before connecting the rectangular spectral shaper 40 to the laser MOPA amplification system, the rectangular spectral shaper 40 first modulates the seed laser 401. After the modulated spectrum is checked by a spectrometer and found to meet the rectangular spectral requirements, the rectangular spectral shaper 40 is then positioned between the main oscillator 10 and the power amplifier 20.

[0043] In this embodiment, preferably, the laser MOPA amplification system further includes an optical isolator 30, which is disposed between the rectangular spectral shaper 40 and the master oscillator 10.

[0044] In this embodiment, preferably, the laser MOPA amplification system further includes a thulium-doped fiber 201 with a high doping density as a gain medium, and the thulium-doped fiber 201 is disposed after the rectangular spectral shaper 40.

[0045] In this embodiment, preferably, the laser MOPA amplification system further includes a diode pump 202, which is disposed after the gain medium, i.e., the thulium-doped fiber 201, and adopts a backward pumping method.

[0046] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the foregoing embodiments have described the present invention in detail, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, and these substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A method of suppressing SBS effect in a laser MOPA amplification system of a thulium-doped fiber laser, characterized in that: The method comprises arranging a rectangular spectrum shaper between the master oscillator and the power amplifier, the rectangular spectrum shaper being configured to adjust a Gaussian spectrum of laser pulses emitted by the master oscillator into a rectangular spectrum before outputting to the power amplifier. The rectangular spectrum shaper comprises an even number of phase modulators arranged in series between the master oscillator and the power amplifier. The rectangular spectrum shaper further comprises a controller configured to be connected to the even number of phase modulators respectively, and the controller is further configured to generate a continuous sinusoidal signal to drive and control the even number of phase modulators respectively, to enhance the intensity of weak spectral lines, so that the Gaussian spectrum of laser pulses emitted by the master oscillator is adjusted into a rectangular spectrum after passing through the even number of phase modulators.

2. The method of suppressing SBS effect in a laser MOPA amplification system of a thulium-doped fiber laser as claimed in claim 1, wherein: The rectangular spectrum shaper is first arranged to modulate the seed laser, and the modulated spectrum is checked by a spectrometer to meet the requirement of rectangular spectrum, and then the rectangular spectrum shaper is arranged between the master oscillator and the power amplifier.

3. The method of suppressing SBS effect in a laser MOPA amplification system of a thulium-doped fiber laser as claimed in claim 1, wherein: The method further comprises using a backward pumping mode.

4. The method of suppressing SBS effect in a laser MOPA amplification system of a thulium-doped fiber laser as claimed in claim 1, wherein: The method further comprises using a thulium-doped fiber with a high doping density.

5. A laser MOPA amplification system of a thulium-doped fiber laser for suppressing SBS effect, comprising a master oscillator and a power amplifier, characterized in that: The method further comprises a rectangular spectrum shaper arranged between the master oscillator and the power amplifier, and configured to adjust a Gaussian spectrum of laser pulses emitted by the master oscillator into a rectangular spectrum before outputting to the power amplifier. The rectangular spectrum shaper comprises an even number of phase modulators arranged in series between the master oscillator and the power amplifier. The rectangular spectrum shaper further comprises a controller configured to be connected to the even number of phase modulators respectively, and the controller is further configured to generate a continuous sinusoidal signal to drive and control the even number of phase modulators respectively, to enhance the intensity of weak spectral lines, so that the Gaussian spectrum of laser pulses emitted by the master oscillator is adjusted into a rectangular spectrum after passing through the even number of phase modulators.

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