A 1-mum ultrafast fiber laser with adjustable repetition rate based on mamyshev pulse shaping technique

Abstract

The application provides a 1-micron ultrafast fiber laser with adjustable repetition frequency based on Mamyshev pulse shaping technology. The device comprises a seed source, a first-stage preamplifier, a first-stage main amplifier, a first-stage stretcher, a bias filter, a second-stage preamplifier, a second-stage stretcher, a second-stage main amplifier, a third-stage stretcher and a pulse compressor, and has 10 parts in total. The application can adjust the repetition frequency of the laser within a wide range, and can reduce the time and economic cost caused by replacing different repetition frequency lasers in industrial production and scientific research. The application can continuously adjust the output pulse width within a certain range by controlling the SPM induced spectral broadening and fine-tuning the pulse compressor, and can expand the versatility of the fixed frequency ultrafast laser.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lasers. BACKGROUND

[0002] SPM: self-phase modulation.

[0003] Gain Switch: gain switch.

[0004] Pulse picker: pulse picker.

[0005] EOM: electro-optic modulator.

[0006] AOM: acousto-optic modulator.

[0007] ASE: amplified spontaneous emission.

[0008] With the advantages of high peak, narrow pulse width, compact structure, easy maintenance, etc., ultrafast fiber lasers have wide application prospects in the fields of laser processing, biomedical treatment, scientific research, etc., and have always been the research focus of people. However, the repetition rates of lasers required by different application scenarios are different. In order to reduce the cost of replacing lasers and improve the efficiency of production and scientific research, many researchers are committed to developing ultrafast fiber lasers with a large range of adjustable repetition rates.

[0009] Ultrafast fiber lasers are mainly composed of three parts: laser seed source, fiber amplifier and pulse compressor. As the mainstream laser seed source, although the passively mode-locked fiber laser can realize femtosecond-level pulse output, it is difficult to achieve flexible adjustment of the repetition rate. If a semiconductor laser based on Gain Switch technology is used as a laser seed source, although flexible adjustment of the repetition rate can be achieved, the generated pulses cannot reach femtosecond level, which is difficult to meet the wide range of application requirements.

[0010] Currently, there is no published device and scheme of an ultrafast fiber laser with adjustable repetition rate using Mamyshev pulse shaping technology with a Gain Switch semiconductor laser as a laser seed source.

[0011] Traditional ultrafast fiber lasers need to rely on Pulse picker, EOM, AOM and other devices to achieve repetition rate adjustment. However, after adding the above-mentioned devices to the laser, in addition to affecting the working stability of the laser, the range of repetition rate adjustment that can be achieved is also very limited, far from reaching the level of flexible adjustment.

[0012] In addition, there is also a scheme in the prior art that uses a Gain Switch semiconductor laser as a seed source, supplemented by a multi-stage fiber amplifier, to realize a repetition frequency adjustable ultrafast fiber laser. However, since the pulse compression of the Gain Switch semiconductor laser is poor, the pulse produced by this scheme is at most several picoseconds, which is difficult to meet the application requirement of femtosecond level.

[0013] The repetition frequency adjustable ultrafast fiber laser realized by means of a Pulse picker, an EOM, an AOM and the like has the following shortcomings:

[0014] 1) The additional devices such as a Pulse picker, an AOM and an EOM connected inside the ultrafast fiber laser will reduce the working stability of the laser.

[0015] 2) The chopping by means of a Pulse picker, an AOM and an EOM can only realize proportional reduction of the repetition frequency of the laser, and the adjustment range and flexibility are greatly limited.

[0016] The repetition frequency adjustable ultrafast laser realized by using a Gain Switch semiconductor laser and a multi-stage fiber amplifier has the following shortcomings:

[0017] 1) The narrowest pulse output by the Gain Switch semiconductor laser is at most several picoseconds, and the compression is poor, which is difficult to meet the application requirement of femtosecond level. SUMMARY

[0018] The present application mainly solves the following problems:

[0019] 1) The problem of limited adjustment range of the repetition frequency of the repetition frequency adjustable ultrafast fiber laser is solved. A Gain Switch semiconductor laser with adjustable repetition frequency is selected as a laser seed source, which provides a wide space for the repetition frequency adjustment of the ultrafast fiber laser.

[0020] 2) The problem of poor stability of the repetition frequency adjustable ultrafast fiber laser is solved. The feature that the SPM induced spectral broadening has no direct correlation with the pulse repetition frequency is fully utilized, and the Mamyshev pulse shaping technology is used to shape the pulse spectrum at different repetition frequencies into the same shape, thereby ensuring the operation stability of the laser at different repetition frequencies.

[0021] 3) solve the problem that the output pulse of Gain Switch semiconductor laser cannot be compressed to femtosecond level. The high coherent component in the output pulse of Gain Switch semiconductor laser is obtained by using SPM induced spectral broadening and bias filter, and the pulse compression problem is fundamentally solved by using the optimization effect of Mamyshev pulse shaping technology on the coherence of laser pulse. Then, the pulse spectrum and time domain shape are controlled by using the combination of fiber amplifier and passive fiber, and the compressibility of the pulse is further improved, so that the pulse width can be compressed to femtosecond level.

[0022] The 1μm ultrafast fiber laser device with adjustable repetition frequency based on Mamyshev pulse shaping technology is shown in the figure. Figure 1 The device includes seed source, first stage preamplifier, first stage main amplifier, first stage stretcher, bias filter, second stage preamplifier, second stage stretcher, second stage main amplifier, third stage stretcher and pulse compressor, a total of 10 parts.

[0023] The specific devices used in the device will be described in detail below.

[0024] In the figure, 101 is a Gain Switch semiconductor laser, which can be a Gain Switch semiconductor laser with narrow spectrum and pulse width of about 60 picoseconds. The function is to generate a micro-watt level 1μm laser pulse as a seed.

[0025] In the figure, 201 is a first laser diode, which can be a semiconductor laser diode with a center wavelength of 915nm or 976nm. The tail fiber and the optical fiber can be fused by a fiber fusion machine. The function of the first laser diode is to provide energy for pumping the first single-mode ytterbium-doped fiber.

[0026] In the figure, 301 is a first wavelength division multiplexer. The pump input fiber is fused with the output fiber of the first laser diode. The signal input fiber is fused with the output fiber of the Gain Switch semiconductor laser. The output fiber is fused with the first single-mode ytterbium-doped fiber. The function of the first wavelength division multiplexer is to guide the light output by the first laser diode and the Gain Switch semiconductor laser into the first single-mode ytterbium-doped fiber.

[0027] In the figure, 401 is a first single-mode ytterbium-doped fiber, which can be a single-clad ytterbium-doped fiber. The function is to absorb pump light, generate laser gain, and amplify 1μm laser pulse.

[0028] In the figure, 501 is a fiber filter, whose filter center wavelength is consistent with the Gain Switch semiconductor laser, and the filter bandwidth is 2 nm. Its input fiber is fused with the first single-mode ytterbium-doped fiber. Its output fiber is fused with the input fiber of the first fiber isolator. The function of the fiber filter is to filter out the amplified 1 μm laser and filter out the ASE generated in the amplification process.

[0029] In the figure, 601 is the first fiber isolator. Its input fiber is fused with the output fiber of the fiber filter. Its output fiber is fused with the signal input fiber of the first pump combiner. The function of the first fiber isolator is to prevent reverse light from damaging the previous stage device.

[0030] In the figure, 202 is the second laser diode, which can be selected as a semiconductor laser diode with a center wavelength of 915 nm or 976 nm, and the output fiber can be fused by a fiber fusion machine. The function of the second laser diode is to provide energy to pump the first large-mode-area ytterbium-doped fiber.

[0031] In the figure, 701 is the first pump combiner, which can be selected as a (2+1) x 1 pump combiner. Its pump input fiber is fused with the output fiber of the second laser diode. Its signal input fiber is fused with the output fiber of the second fiber isolator. Its output fiber is fused with the first large-mode-area ytterbium-doped fiber. The function of the pump combiner is to guide the light output from the second laser diode and the first fiber isolator into the first large-mode-area ytterbium-doped fiber.

[0032] In the figure, 801 is the first large-mode-area ytterbium-doped fiber, which can be selected as a double-clad ytterbium-doped fiber. Its function is to absorb pump light, generate laser gain, and amplify 1 μm laser pulses.

[0033] In the figure, 602 is the second fiber isolator, whose input fiber is fused with the first large-mode-area ytterbium-doped fiber. Its output fiber is fused with the first passive fiber. The function of the second fiber isolator is to prevent reverse light from damaging the previous stage device.

[0034] In the figure, 901 is the first passive fiber, which can be selected as a high nonlinear fiber with a small dispersion amount. Its function is to induce SPM effect and broaden the spectrum of 1 μm laser pulses.

[0035] In the figure, 1001 is a bias filter, which can be selected as a tunable filter or a fiber Bragg grating. Its filter center wavelength is 1-2 nm different from the Gain Switch semiconductor laser, and the filter bandwidth is less than 0.5 nm. Its input fiber is fused with the first passive fiber. Its output fiber is fused with the signal input fiber of the second wavelength division multiplexer. The function of the bias filter is to filter out the new spectral components generated by spectral broadening.

[0036] In the figure, 203 is the third laser diode, which can be a semiconductor laser diode with a center wavelength of 915 nm or 976 nm. The pigtail of the third laser diode can be fused with an optical fiber by an optical fiber fusion splicer. The third laser diode provides energy to pump the second single-mode ytterbium-doped fiber.

[0037] In the figure, 302 is the second wavelength division multiplexer. The pump input fiber of the second wavelength division multiplexer is fused with the output fiber of the third laser diode. The signal input fiber of the second wavelength division multiplexer is fused with the output fiber of the offset filter. The output fiber of the second wavelength division multiplexer is fused with the second single-mode ytterbium-doped fiber. The second wavelength division multiplexer guides the light output by the third laser diode and the offset filter into the second single-mode ytterbium-doped fiber.

[0038] In the figure, 402 is the second single-mode ytterbium-doped fiber, which can be a single-clad ytterbium-doped fiber. The second single-mode ytterbium-doped fiber absorbs pump light to generate laser gain and amplify the 1 μm laser pulse.

[0039] In the figure, 603 is the third fiber isolator. The input fiber of the third fiber isolator is fused with the second single-mode ytterbium-doped fiber. The output fiber of the third fiber isolator is fused with the second passive fiber. The third fiber isolator prevents backward light from damaging the previous-stage device.

[0040] In the figure, 902 is the second passive fiber, which can be a high-nonlinear fiber with a small dispersion. The second passive fiber induces SPM effect to broaden the spectrum of the 1 μm laser pulse.

[0041] In the figure, 204 is the fourth laser diode, which can be a semiconductor laser diode with a center wavelength of 915 nm or 976 nm. The pigtail of the fourth laser diode can be fused with an optical fiber by an optical fiber fusion splicer. The fourth laser diode provides energy to pump the second large-mode-area ytterbium-doped fiber.

[0042] In the figure, 702 is the second pump combiner, which can be a (2+1)×1 pump combiner. The pump input fiber of the second pump combiner is fused with the output fiber of the fourth laser diode. The signal input fiber of the second pump combiner is fused with the second passive fiber. The output fiber of the second pump combiner is fused with the second large-mode-area ytterbium-doped fiber. The second pump combiner guides the light output by the fourth laser diode and the second passive fiber into the second large-mode-area ytterbium-doped fiber.

[0043] In the figure, 802 is the second large-mode-area ytterbium-doped fiber, which can be a double-clad ytterbium-doped fiber. The second large-mode-area ytterbium-doped fiber absorbs pump light to generate laser gain and amplify the 1 μm laser pulse.

[0044] In the figure, 604 is the fourth fiber isolator. The input fiber of the fourth fiber isolator is fused with the second large-mode-area ytterbium-doped fiber. The output fiber of the fourth fiber isolator is fused with the third passive fiber. The fourth fiber isolator prevents backward light from damaging the previous-stage device.

[0045] In the figure, 903 is a third passive optical fiber, which can be a high nonlinear optical fiber with a small amount of dispersion, and its function is to induce SPM effect to broaden the spectrum of 1-micron laser pulse.

[0046] In the figure, 1101 is a pulse compressor, which can use a pair of diffraction gratings or a pair of prisms. The function of the pulse compressor is to compensate for intra-pulse dispersion and compress the width of 1-micron laser pulse.

[0047] According to the above description, the composition and function of each part in the dashed box in the figure are summarized as follows.

[0048] The seed source includes a Gain Switch semiconductor laser (101). Its function is to generate a micro-watt level 1-micron laser pulse as a seed.

[0049] The first-stage pre-amplifier includes a first laser diode (201), a first wavelength division multiplexer (301), a first single-mode ytterbium-doped optical fiber (401), a fiber filter (501), and a first fiber isolator (601). Its function is to amplify the power of 1-micron laser pulse to the milliwatt level.

[0050] The first-stage main amplifier includes a second laser diode (202), a first pump combiner (701), a first large-mode-area ytterbium-doped optical fiber (801), and a second fiber isolator (602). Its function is to amplify the power of 1-micron laser pulse to the watt level.

[0051] The first-stage stretcher includes a first passive optical fiber (901). Its function is to induce SPM to broaden the spectrum of 1-micron laser pulse, so that the spectral edges pass through the bias filter (1001).

[0052] The function of the bias filter (1001) is to filter out the new spectral components generated after the spectrum of 1-micron laser pulse is broadened.

[0053] The second-stage pre-amplifier includes a third laser diode (203), a second wavelength division multiplexer (302), a second single-mode ytterbium-doped optical fiber (402), and a third fiber isolator (603). Its function is to re-amplify the power of 1-micron laser pulse after bias filtering to the milliwatt level.

[0054] The second-stage stretcher includes a second passive optical fiber (902). Its function is to induce SPM to pre-broaden the spectrum of 1-micron laser pulse after bias filtering.

[0055] The second-stage main amplifier includes a fourth laser diode (204), a second pump combiner (702), a second large-mode-area ytterbium-doped optical fiber (802), and a fourth fiber isolator (604). Its function is to continue to boost the power of 1-micron laser pulse to the watt level.

[0056] The third stage stretcher contains a third passive fiber (903). Its function is to induce SPM, greatly stretching the spectrum of 1-micron laser pulses.

[0057] The function of the pulse compressor (1101) is to provide dispersion compensation, compressing the pulse width of 1-micron laser pulses to the femtosecond level.

[0058] The 1-micron ultrafast fiber laser with adjustable repetition rate designed in the present application can adjust the repetition rate of the laser within a wide range, and can reduce the time and economic cost of replacing different repetition rate lasers in industrial production and scientific research.

[0059] The 1-micron ultrafast fiber laser with adjustable repetition rate designed in the present application can continuously adjust the output pulse width within a certain range by controlling the SPM-induced spectral stretching and fine-tuning the pulse compressor, which can expand the versatility of fixed-frequency ultrafast lasers. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 Device schematic diagram of the 1-micron ultrafast fiber laser with adjustable repetition rate based on Mamyshev pulse shaping technology DETAILED DESCRIPTION

[0061] (1) The Gain Switch semiconductor laser (101) is used as the seed source in the device, which generates 1-micron laser pulses with a pulse width of picosecond level and a power of microwatt level. Compared with the passive mode-locked fiber laser with fixed repetition rate, the Gain Switch semiconductor laser can quickly adjust the repetition rate according to specific needs, improving the overall flexibility of the system.

[0062] (2) The Mamyshev pulse shaping technology used in the laser is mainly reflected in the first pre-amplifier, the first main amplifier, the first stretcher, and the bias filter. The 1 μm laser pulse generated by the Gain Switch semiconductor laser (101) is amplified by two-stage amplifier to improve the power, and then the SPM is induced in the first passive fiber (901) of the first stretcher, which leads to the rapid spectral broadening of the pulse. In this process, the components with higher intensity and stronger coherence within the pulse are broadened more, and are more likely to pass through the bias filter (1001). Therefore, after the filtering effect of the bias filter (1001), the coherence of the obtained shaped pulse will be greatly improved compared with the seed source, and the proportion of the linear chirp that can be compressed within the pulse will also be significantly improved. The above-mentioned device for shaping the pulse by using SPM-induced spectral broadening and bias filtering is also called Mamyshev regenerator, which is a classic case of pulse processing using Mamyshev pulse shaping technology. Since the intensity of SPM-induced spectral broadening is not directly related to the pulse repetition frequency, by adjusting the repetition frequency of the Gain Switch semiconductor laser (101), the output power of the first laser diode (201) and the second laser diode (202) can be changed to make the pulse spectrum passing through the bias filter (1001) consistent, that is, the 1 μm laser pulse with different repetition frequencies can achieve consistent shaping effect through Mamyshev pulse shaping, and then achieve the goal of stable operation of the laser at different repetition frequencies.

[0063] (3) After the Mamyshev pulse shaping processing, the power of the 1 μm laser pulse is significantly reduced, and the pulse width is still in the picosecond level. Therefore, it is necessary to further broaden the spectrum while improving the power of the 1 μm laser pulse, so that the pulse can be compressed to the femtosecond level by the pulse compressor (1101). The device used to achieve this step is the second pre-amplifier, the second stretcher, the second main amplifier, and the third stretcher. The 1 μm laser pulse output by the bias filter (1001) will be pre-spectrally broadened by the second pre-amplifier and the second stretcher, and then be spectrally broadened by the second main amplifier and the third stretcher. According to the spectral width and pulse width of the 1 μm laser pulse, the pulse compressor (1101) is adjusted for dispersion compensation, and a femtosecond-level 1 μm laser pulse is obtained. In this process, by controlling the output power of the third laser diode (203) and the fourth laser diode (204), the SPM-induced spectral broadening can be adjusted, and then the pulse width output by the pulse compressor (1101) can be changed, realizing the real-time adjustment of the pulse width.

Claims

1. A 1μm ultrafast fiber laser with tunable repetition rate based on Mamyshev pulse shaping technology, characterized in that: It consists of 10 parts: seed source, first-stage preamplifier, first-stage main amplifier, first-stage stretcher, bias filter, second-stage preamplifier, second-stage stretcher, second-stage main amplifier, third-stage stretcher, and pulse compressor. The seed source includes a Gain Switch semiconductor laser (101); Its function is to generate microwatt-level 1μm laser pulses as seeds; The first-stage preamplifier includes a first laser diode (201), a first wavelength division multiplexer (301), a first single-mode ytterbium-doped fiber (401), a fiber filter (501), and a first fiber isolator (601); Its function is to amplify the power of a 1μm laser pulse to the milliwatt level; The first-stage main amplifier includes a second laser diode (202), a first pump combiner (701), a first large-mode-field ytterbium-doped fiber (801), and a second fiber isolator (602); Its function is to amplify the power of a 1μm laser pulse to the watt level; The first-stage stretcher includes a first passive fiber (901); its function is to induce SPM, stretch the spectrum of the 1μm laser pulse, and allow its spectral edges to pass through the bias filter (1001). The function of the bias filter (1001) is to filter out the new spectral components generated after the 1μm laser pulse undergoes spectral broadening; The second-stage preamplifier includes a third laser diode (203), a second wavelength division multiplexer (302), a second single-mode ytterbium-doped fiber (402), and a third fiber isolator (603); its function is to amplify the power of the 1μm laser pulse after bias filtering back to the milliwatt level. The second-stage stretcher includes a second passive optical fiber (902); Its function is to trigger SPM to pre-broaden the spectrum of the 1μm laser pulse after bias filtering; The second-stage main amplifier includes a fourth laser diode (204), a second pump combiner (702), a second large-mode-field ytterbium-doped fiber (802), and a fourth fiber isolator (604), which boosts the power of 1μm laser pulses to the watt level. The third-stage stretcher contains a third passive fiber (903) that induces SPM and stretches the 1μm laser pulse spectrum; The pulse compressor (1101) compresses the pulse width of a 1μm laser pulse to the femtosecond level.

2. The 1μm ultrafast fiber laser with tunable repetition rate based on Mamyshev pulse shaping technology according to claim 1, characterized in that: Gain Switch semiconductor lasers are selected, featuring narrow spectrum and a pulse width of 60 picoseconds.

3. The 1μm ultrafast fiber laser with tunable repetition rate based on Mamyshev pulse shaping technology according to claim 1, characterized in that: The first laser diode is a semiconductor laser diode with a center wavelength of 915nm or 976nm. Its pigtail and optical fiber are fused together by an optical fiber fusion splicer. The first single-mode ytterbium-doped optical fiber is then pumped.

4. A 1μm ultrafast fiber laser with tunable repetition rate based on Mamyshev pulse shaping technology according to claim 1, characterized in that: The first wavelength division multiplexer; its pump input fiber is fused to the output fiber of the first laser diode; its signal input fiber is fused to the output fiber of the Gain Switch semiconductor laser. Its output fiber is fused to the first single-mode ytterbium-doped fiber; the function of the first wavelength division multiplexer is to guide the light output from the first laser diode and the Gain Switch semiconductor laser into the first single-mode ytterbium-doped fiber.

5. A 1μm ultrafast fiber laser with tunable repetition rate based on Mamyshev pulse shaping technology according to claim 1, characterized in that: The first single-mode ytterbium-doped fiber uses a single-clad ytterbium-doped fiber to absorb pump light, generate laser gain, and amplify 1μm laser pulses.

6. A 1μm ultrafast fiber laser with tunable repetition rate based on Mamyshev pulse shaping technology according to claim 1, characterized in that: The fiber optic filter has the same center wavelength as the Gain Switch semiconductor laser and a filtering bandwidth of 2nm. Its input fiber is fused to the first single-mode ytterbium-doped fiber; its output fiber is fused to the input fiber of the first fiber isolator.

7. A 1μm ultrafast fiber laser with tunable repetition rate based on Mamyshev pulse shaping technology according to claim 1, characterized in that: The first fiber optic isolator has its input fiber optic cable fused to the output fiber optic cable of the fiber optic filter; its output fiber optic cable is fused to the signal input fiber optic cable of the first pump combiner; the function of the first fiber optic isolator is to prevent reverse light from damaging the preceding components.

8. A 1μm ultrafast fiber laser with tunable repetition rate based on Mamyshev pulse shaping technology according to claim 1, characterized in that: The second laser diode is a semiconductor laser diode with a center wavelength of 915nm or 976nm. Its output fiber can be spliced ​​by a fiber optic fusion splicer. The function of the second laser diode is to provide energy to pump the first large mode field ytterbium-doped fiber.

9. A 1μm ultrafast fiber laser with tunable repetition rate based on Mamyshev pulse shaping technology according to claim 1, characterized in that: The first pump combiner can be a (2+1)×1 pump combiner; its pump input fiber is fused to the output fiber of the second laser diode; its signal input fiber is fused to the output fiber of the second fiber isolator. Its output fiber is fused to the first large-mode-field ytterbium-doped fiber; the function of the pump combiner is to guide the light output from the second laser diode and the first fiber isolator into the first large-mode-field ytterbium-doped fiber.

10. A 1μm ultrafast fiber laser with tunable repetition rate based on Mamyshev pulse shaping technology according to claim 1, characterized in that: The bias filter is a tunable filter or a fiber Bragg grating, with a filter center wavelength that differs from that of the Gain Switch semiconductor laser by 1 to 2 nm and a filter bandwidth of less than 0.5 nm. Its input optical fiber is fused to the first passive optical fiber; Its output fiber is fused to the signal input fiber of the second peak multiplexer; the bias filter is used to filter out the new spectral components generated by spectral broadening.

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