A repetition frequency tunable femtosecond fiber laser based on bandpass filter

Abstract

The application discloses a repeated frequency codeable femtosecond fiber laser based on a band-pass filter, which comprises a pulse shaping and femtosecond pulse generating system and a pulse sequence editing system. The pulse shaping and femtosecond pulse generating system comprises a gain-switched semiconductor seed source, a first non-polarization isolator, a first core amplifier, a first cladding amplifier, a first non-polarization passive spectrum widening fiber, a first non-polarization band-stop filter, a second cladding amplifier, a second non-polarization passive spectrum widening fiber, a first fiber collimator and a pulse compressor which are sequentially connected. The pulse sequence editing system comprises a pulse sequence plotter and a seed source signal triggering device which are sequentially connected. The application uses a gain-switched semiconductor picosecond laser as a seed source, uses passive fiber nonlinear effects to realize the separation of coherent components and incoherent components in the frequency domain and the time domain, and finally obtains a pulse with a pulse width less than 200 fs after spectrum widening, amplification and compression. The whole is easy to realize industrialization.

Description

Technical Field

[0001] This invention discloses a repetition frequency coded femtosecond fiber laser based on a bandpass filter. Background Technology

[0002] Ultrashort pulses refer to pulses with durations on the order of 10⁻⁹ to 10⁻¹² seconds, possessing excellent characteristics such as high energy concentration, high temporal resolution, and high spatial resolution. They are currently widely used in fields such as laser processing, material microstructure analysis, nonlinear microscopy, and high-precision laser detection. In industrial applications, the search for robust, durable, and compact light sources has never ceased. In this process, fiber lasers have become increasingly popular due to their excellent stability, high beam quality, flexible transmission characteristics, and large surface area-to-volume ratio for easy heat dissipation.

[0003] Typically, fiber lasers generate ultrashort pulses using either real saturable absorbers (such as semiconductors, graphite, or carbon nanotubes) or artificial saturable absorbers (such as nonlinear polarization rotation or nonlinear fiber ring mirrors). These methods produce pulses with excellent pulse contrast and signal-to-noise ratio, while different mode-locking schemes offer varying characteristics in terms of stability and lifetime. However, a common feature of these schemes is that the laser's repetition rate is fixed to a basic repetition rate determined by the cavity length, typically within the range of 10-100 MHz. This limitation of the repetition rate for seed laser sources obviously imposes certain restrictions on applications requiring synchronized laser pulse output with external components. Summary of the Invention

[0004] The purpose of this invention is to design a repetition frequency coded femtosecond fiber laser based on a bandpass filter. This invention uses a DFB laser diode to generate pulses with durations as low as picoseconds and a simple device to generate highly stable femtosecond pulses. At the same time, it retains the characteristic of arbitrary tunable repetition frequency of gain-switching semiconductor seed source pulses and combines the compact design and heat dissipation-free characteristics of fiber lasers. It can serve as a true on-demand output femtosecond laser.

[0005] To enable the above-mentioned design to be realized, the present invention adopts the following technical solution:

[0006] A repetition frequency coded femtosecond fiber laser based on a bandpass filter includes: a pulse shaping and femtosecond pulse generation system and a pulse sequence editing system.

[0007] The pulse shaping and femtosecond pulse generation system includes a gain-switching semiconductor seed source, a first non-polarization-maintaining isolator, a first fiber core amplifier, a first cladding amplifier, a first non-polarization-maintaining passive spectral broadening fiber, a first non-polarization-maintaining band-stop filter, a second cladding amplifier, a second non-polarization-maintaining passive spectral broadening fiber, a first fiber collimator, and a pulse compressor, connected in sequence.

[0008] The pulse sequence editing system includes a pulse sequence plotter and a seed source signal triggering device connected in sequence;

[0009] The seed source signal triggering device is a signal generator. The signal generator is connected to a gain-switching semiconductor seed source;

[0010] Furthermore, the first fiber core amplifier includes a first pump source, a first non-polarization-maintaining wavelength division multiplexer, a first non-polarization-maintaining gain fiber, a first non-polarization-maintaining bandpass filter, and a second non-polarization-maintaining isolator.

[0011] Furthermore, the first cladding amplifier includes a first non-polarization-maintaining combiner, a second non-polarization-maintaining gain fiber, a third non-polarization-maintaining isolator, and a second non-polarization-maintaining bandpass filter connected in sequence; the second pump source is connected to the first non-polarization-maintaining combiner.

[0012] Furthermore, the second cladding amplifier includes a second non-polarization-maintaining combiner and a third non-polarization-maintaining gain fiber connected in sequence; the third pump source is connected to the second non-polarization-maintaining combiner.

[0013] Furthermore, the pulse compressor comprises a pair of diffraction gratings and a first total reflection mirror connected in sequence;

[0014] Furthermore, the pulse sequence editing system relies on the pulse sequence editing system to complete the editing of arbitrary pulse sequences.

[0015] Preferably, the first pump source, the second pump source, and the third pump source are semiconductor lasers, solid-state lasers, gas lasers, fiber lasers, or Raman lasers, the laser type is a continuous laser or a pulsed laser, and the output fiber is a single-mode fiber or a multimode fiber.

[0016] Preferably, the pumping methods of the first pump source, the second pump source, and the third pump source are one of the following: single-end pumping of the fiber core, double-end pumping of the fiber core, single-end pumping of the cladding, and double-end pumping of the cladding.

[0017] Preferably, the first polarization-maintaining gain fiber and the second polarization-maintaining gain fiber are silica fibers or photonic crystal fibers doped with rare earth ions, wherein the doped rare earth elements are one or more of rare earth elements such as ytterbium (Yb), erbium (Er), thulium (Tm), and praseodymium (Pr).

[0018] Compared with the prior art, the present invention has the following beneficial effects.

[0019] 1. This invention uses a gain-switched semiconductor picosecond laser as a seed source and uses passive fiber nonlinear effects to separate the pulse coherent components and incoherent components in the frequency and time domains. A band-stop filter is used to filter the incoherent components remaining at the center wavelength. After spectral broadening, amplification and compression, a pulse with a pulse width of less than 200 fs is finally obtained.

[0020] 2. This invention innovatively employs center band-stop filtering to address the spectral evolution caused by self-phase modulation effect. This simple structure solves the problem of mismatch between filter bandwidth and signal spectrum during laser repetition frequency tuning, while simultaneously improving pulse coherence and achieving stable output of femtosecond pulses.

[0021] 3. The present invention is simple in design, compact in structure, and easy to industrialize. Attached Figure Description

[0022] Figure 1 A schematic diagram of a repetition frequency coded femtosecond fiber laser based on a bandpass filter, provided for implementation of the present invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0024] like Figure 1 As shown, this embodiment of the invention provides a repetition frequency coded femtosecond fiber laser based on a bandpass filter, including a pulse shaping and femtosecond pulse generation system and a pulse sequence editing system;

[0025] The pulse shaping and femtosecond pulse generation system includes a gain-switching semiconductor seed source 1, a first non-polarization-maintaining isolator 2, a first fiber core amplifier, a first cladding amplifier, a first non-polarization-maintaining passive spectral broadening fiber 13, a first non-polarization-maintaining band-stop filter 14, a second cladding amplifier, a second non-polarization-maintaining passive spectral broadening fiber 18, a first fiber collimator 19, and a pulse compressor, connected in sequence.

[0026] The pulse sequence editing system includes a pulse sequence plotter 23 and a seed source signal triggering device connected in sequence;

[0027] The seed source signal triggering device is a signal generator 22. The signal generator 22 is connected to the gain-switching semiconductor seed source 1;

[0028] Furthermore, the first fiber core amplifier includes a first pump source 3, a first non-polarization-maintaining wavelength division multiplexer 4, a first non-polarization-maintaining gain fiber 5, a first non-polarization-maintaining bandpass filter 6, and a second non-polarization-maintaining isolator 7.

[0029] Furthermore, the first cladding amplifier includes a first non-polarization-maintaining combiner 9, a second non-polarization-maintaining gain fiber 10, a third non-polarization-maintaining isolator 11, and a second non-polarization-maintaining bandpass filter 12 connected in sequence; the second pump source 8 is connected to the first non-polarization-maintaining combiner 9.

[0030] Furthermore, the second cladding amplifier includes a second non-polarization-maintaining combiner 16 and a third non-polarization-maintaining gain fiber 17 connected in sequence; the third pump source 15 is connected to the second non-polarization-maintaining combiner 16.

[0031] Furthermore, the pulse compressor comprises a diffraction grating pair 20 and a first total reflection mirror 21 connected in sequence;

[0032] Furthermore, the pulse sequence editing system relies on a pulse sequence editing system to complete the editing of arbitrary pulse sequences.

[0033] Furthermore, the picosecond pulses output from the gain-switching semiconductor seed source 1 are amplified by the core amplifier (3-7) and the first cladding amplifier (8-12) and then injected into the passive spectral broadening fiber 13. Under the nonlinear self-phase modulation effect, the coherent and incoherent components of the pulses in the passive spectral broadening fiber 13 are separated in the frequency domain. These components are then separated and shaped by the first non-polarization-maintaining band-stop filter 14. The output pulses are amplified again by the second cladding amplifier (15-17) and then spectrally broadened by the second non-polarization-maintaining passive spectral broadening fiber 18. The broadened pulses are then collimated by the first fiber collimator 19 and compressed into femtosecond pulses by the pulse compressors (20, 21). In addition, the desired pulse sequence, pre-drawn using the pulse sequence plotter 23, is stored in the seed source signal triggering device (signal generator 22) and connected to the seed source's external trigger interface. Simultaneously, the seed source is switched from internal trigger mode to external trigger mode, enabling arbitrary editing of the pulse sequence output.

[0034] This invention proposes a repetition-frequency coded femtosecond fiber laser based on a bandpass filter. The device uses a DFB laser diode to generate picosecond pulses, which are then shaped and compressed to produce femtosecond pulses. This system enables wide-range frequency sweep output and arbitrary pulse coding output. This is achieved by using band-stop filtering to address the spectral evolution caused by self-phase modulation, thus resolving the mismatch between the filter bandwidth and the signal spectrum during laser repetition-frequency tuning with the simplest structure. It also improves pulse coherence, achieving stable femtosecond pulse output. Furthermore, it combines the compact design and heat dissipation-free characteristics of fiber lasers, making it a true on-demand femtosecond laser with promising applications in the field of tunable femtosecond lasers.

Claims

1. A repetition frequency coded femtosecond fiber laser based on a bandpass filter, characterized in that, include: Pulse shaping and femtosecond pulse generation system, pulse sequence editing system; The pulse shaping and femtosecond pulse generation system includes a gain-switching semiconductor seed source, a first non-polarization-maintaining isolator, a first fiber core amplifier, a first cladding amplifier, a first non-polarization-maintaining passive spectral broadening fiber, a first non-polarization-maintaining band-stop filter, a second cladding amplifier, a second non-polarization-maintaining passive spectral broadening fiber, a first fiber collimator, and a pulse compressor, connected in sequence. The pulse sequence editing system includes a pulse sequence plotter and a seed source signal triggering device connected in sequence; The seed source signal triggering device is a signal generator; the signal generator is connected to the gain-switching semiconductor seed source. The picosecond pulse of the output pulse from the gain-switching semiconductor seed source is amplified by the core amplifier and the first cladding amplifier and then injected into the passive spectral broadening fiber. Under the nonlinear self-phase modulation effect, the coherent and incoherent components of the passive spectral broadening fiber pulse are separated in the frequency domain. The first non-polarization-maintaining band-stop filter separates and shapes the pulse. The output pulse is amplified again by the second cladding amplifier and then spectrally broadened by the second non-polarization-maintaining passive spectral broadening fiber. The broadened pulse is collimated by the first fiber collimating lens and then compressed into a femtosecond pulse output by the pulse compressor.

2. The repetition frequency coded femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that, The first fiber core amplifier includes a first pump source, a first non-polarization-maintaining wavelength division multiplexer, a first non-polarization-maintaining gain fiber, a first non-polarization-maintaining bandpass filter, and a second non-polarization-maintaining isolator.

3. A repetition frequency coded femtosecond fiber laser based on a bandpass filter according to claim 2, characterized in that, The first cladding amplifier includes a first non-polarization-maintaining combiner, a second non-polarization-maintaining gain fiber, a third non-polarization-maintaining isolator, and a second non-polarization-maintaining bandpass filter connected in sequence; the second pump source is connected to the first non-polarization-maintaining combiner.

4. A repetition frequency coded femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that, The second cladding amplifier includes a second non-polarization-maintaining combiner and a third non-polarization-maintaining gain fiber connected in sequence; a third pump source is connected to the second non-polarization-maintaining combiner.

5. A repetition frequency coded femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that, The pulse compressor comprises a pair of diffraction gratings and a first total reflection mirror connected in sequence.

6. A repetition frequency coded femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that, The pulse sequence editing system relies on a pulse sequence editing system to complete the editing of any pulse sequence.

7. A repetition frequency coded femtosecond fiber laser based on a bandpass filter according to claim 2, characterized in that, The first, second, and third pump sources are semiconductor lasers, solid-state lasers, gas lasers, fiber lasers, or Raman lasers. The laser type is a continuous laser or a pulsed laser, and the output fiber is a single-mode fiber or a multimode fiber.

8. A repetition frequency coded femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that, The pumping methods of the first, second, and third pump sources are one of the following: single-end pumping of the fiber core, double-end pumping of the fiber core, single-end pumping of the cladding, and double-end pumping of the cladding.

9. A repetition frequency coded femtosecond fiber laser based on a bandpass filter according to claim 3, characterized in that, The first non-polarization-maintaining gain fiber and the second non-polarization-maintaining gain fiber are rare-earth ion-doped silica fibers or photonic crystal fibers, wherein the doped rare-earth elements are one or more of ytterbium, erbium, thulium, and praseodymium.

10. A repetition frequency coded femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that, The required pulse sequence is pre-drawn using a pulse sequence plotter and stored in the seed source signal triggering device. This device is then connected to the seed source's external triggering interface. Simultaneously, the seed source is switched from internal triggering mode to external triggering mode, allowing for arbitrary editing of the pulse sequence output.

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