Femtosecond fiber laser capable of coding repetition frequency based on band-pass filter

Abstract

The invention discloses a repetition frequency encodable femtosecond fiber laser based on a band-pass filter. The repetition frequency encodable femtosecond fiber laser 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 switch semiconductor seed source, a first non-polarization-maintaining isolator, a first fiber core amplifier, a first cladding amplifier, a first non-polarization-maintaining passive spectrum broadening optical fiber, a first non-polarization-maintaining band elimination filter, a second cladding amplifier and a second non-polarization-maintaining passive spectrum broadening optical fiber which are connected in sequence; a first optical fiber collimating mirror; and a pulse compressor. The pulse sequence editing system comprises a pulse sequence drawing device and a seed source signal triggering device which are connected in sequence; the gain switch semiconductor picosecond laser is used as a seed source, separation of coherent components and incoherent components of pulses in the frequency domain and the time domain is achieved through the passive optical fiber nonlinear effect, the pulses with the pulse width smaller than 200 fs are finally obtained after spectrum broadening, amplification and compression, and industrialization is easy to achieve on the whole.

Description

Technical Field

[0001] The invention discloses a repetition frequency-encodable femtosecond fiber laser based on a bandpass filter. Background Art

[0002] Ultrashort pulses refer to pulses with a duration of 10-9s-10-12s, which have excellent characteristics such as high energy concentration, high temporal resolution, high spatial resolution, etc. At present, they have been widely used in fields such as laser processing, material microstructure processing, nonlinear microscopy, and laser high-precision detection. In industrial environment applications, the exploration of the demand for durable and compact light sources has never stopped. In this process, fiber lasers are favored for their excellent stability, high beam quality, flexible transmission characteristics, large surface area to volume ratio, and easy heat dissipation.

[0003] Usually, the way fiber lasers generate ultrashort pulses is based on real saturable absorbers (such as semiconductors, graphite or carbon nanotubes) or artificial saturable absorbers (such as nonlinear polarization rotation, nonlinear fiber loop mirrors). The pulses obtained by these methods have excellent pulse contrast and signal-to-noise ratio, and different mode-locking schemes also have their own characteristics in terms of stability and life. However, a common feature of these schemes is that the repetition rate of the laser is fixed to the basic repetition rate set by the cavity length, usually in the range of 10-100MHz. This seed laser source with a repetition rate limited to a certain range will obviously cause certain limitations in the application requirements of synchronous output of laser pulses and external collaboration. Summary of the invention

[0004] The purpose of the present invention is to design a repetition rate-encoded femtosecond fiber laser based on a bandpass filter. The present invention uses a DFB laser diode to generate pulses with a duration as low as picoseconds and a simple device to generate high-stability femtosecond pulses. At the same time, the characteristics of the gain-switched semiconductor seed source pulse repetition frequency being arbitrarily tunable are retained and the excellent characteristics of the fiber laser's compact design and no need for heat dissipation are combined. The present invention can be used as a true femtosecond laser that outputs pulses on demand.

[0005] In order to realize the above-mentioned design, the present invention adopts the following technical solutions:

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

[0007] The pulse shaping and femtosecond pulse generating system comprises a gain switch semiconductor seed source, a first non-polarization maintaining isolator, a first core amplifier, a first cladding amplifier, a first non-polarization maintaining passive spectrum broadening fiber, a first non-polarization maintaining band stop filter, a second cladding amplifier, a second non-polarization maintaining passive spectrum broadening fiber, a first fiber collimator, and a pulse compressor which are connected in sequence.

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

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

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

[0011] Further, the first cladding amplifier comprises a first non-polarization-maintaining combiner, a second non-polarization-maintaining gain optical 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] Further, the second cladding amplifier comprises a second non-polarization-maintaining combiner and a third non-polarization-maintaining gain optical fiber connected in sequence; the third pump source is connected to the second non-polarization-maintaining combiner;

[0013] Further, the pulse compressor comprises a diffraction grating pair 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 any pulse sequence.

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

[0016] Preferably, the pumping mode of the first pump source, the second pump source and the third pump source is one of core single-end pumping, core double-end pumping, cladding single-end pumping and cladding double-end pumping.

[0017] Preferably, the first polarization-maintaining gain fiber and the second polarization-maintaining gain fiber are quartz 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. The present invention uses a gain-switched semiconductor picosecond laser as a seed source, uses the nonlinear effect of passive optical fiber to achieve the separation of pulse coherent components and incoherent components in the frequency domain and time domain, and uses a band-stop filter to filter the incoherent components remaining at the central wavelength. After spectral broadening, amplification and compression, a pulse with a pulse width of less than 200fs is finally obtained.

[0020] 2. The present invention innovatively adopts central band-stop filtering for the spectral evolution produced by the self-phase modulation effect, solving the problem of mismatch between the filter bandwidth and the signal spectrum during the laser repetition frequency tuning process with the simplest structure, while improving the coherence of the pulse and achieving stable output of femtosecond pulses.

[0021] 3. The present invention has a simple design, compact structure and is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic structural diagram of a repetition rate encodable femtosecond fiber laser based on a bandpass filter provided for the implementation of the present invention. DETAILED DESCRIPTION

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

[0024] like Figure 1 As shown, an embodiment of the present invention provides a repetition frequency encodable 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 switch semiconductor seed source 1, a first non-polarization maintaining isolator 2, a first core amplifier, a first cladding amplifier, a first non-polarization maintaining passive spectrum broadening fiber 13, a first non-polarization maintaining band stop filter 14, a second cladding amplifier, a second non-polarization maintaining passive spectrum broadening fiber 18, a first fiber collimator 19, and a pulse compressor, which are connected in sequence.

[0026] The pulse sequence editing system includes a pulse sequence plotter 23 and a seed source signal trigger 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 switch semiconductor seed source 1;

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

[0029] Further, the first cladding amplifier comprises 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 which are connected in sequence; the second pump source 8 is connected to the first non-polarization maintaining combiner 9;

[0030] Further, 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] Further, 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 the pulse sequence editing system to complete the editing of any pulse sequence.

[0033] Furthermore, the picosecond pulses of the output pulses of the gain-switched 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 spectrum widening fiber 13. Under the effect of nonlinear self-phase modulation, the coherent components and incoherent components of the pulses in the passive spectrum widening fiber 13 are separated in the frequency domain, separated and pulse-shaped by the first non-polarization-maintaining band-stop filter 14, and the output pulses are amplified again by the second cladding amplifier (15-17) and spectrally widened by the second non-polarization-maintaining passive spectrum widening fiber 18. The widened pulses are collimated by the first fiber collimator 19 and compressed by the pulse compressor (20, 21) to femtosecond pulse output. In addition, the required pulse sequence drawn in advance by the pulse sequence drawer 23 is stored in the seed source signal trigger device (signal generator 22), and connected to the seed source external trigger interface, and the seed source is set from the internal trigger mode to the external trigger mode, so that the output of the arbitrarily edited pulse sequence can be realized.

[0034] The present invention proposes a repetition frequency coded femtosecond fiber laser based on a bandpass filter. The device uses a DFB laser diode to generate a pulse with a duration of picoseconds, and finally generates a pulse with a duration of femtoseconds after pulse shaping and compression. At the same time, this device can achieve a wide range of repetition frequency sweep output and arbitrary pulse coding output, thanks to the use of band-stop filtering for the spectrum evolution generated by the self-phase modulation effect, which solves the problem of mismatch between the filter bandwidth and the signal spectrum during the laser repetition frequency tuning process with the simplest structure, while improving the coherence of the pulse and achieving stable output of femtosecond pulses. In addition, it combines the compact design of the fiber laser and the excellent characteristics of no need for heat dissipation, and can be used as a true femtosecond laser that outputs pulses on demand. It is believed that it will have excellent application prospects in the field of tunable femtosecond lasers.

Claims

1. A repetition rate encodable 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 comprises a gain switch semiconductor seed source, a first non-polarization maintaining isolator, a first core amplifier, a first cladding amplifier, a first non-polarization maintaining passive spectrum broadening fiber, a first non-polarization maintaining band stop filter, a second cladding amplifier, a second non-polarization maintaining passive spectrum 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 trigger device connected in sequence; The seed source signal triggering device is a signal generator; the signal generator is connected to the gain switch semiconductor seed source.

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

3. The repetition rate encodable femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that: The first cladding amplifier comprises a first non-polarization maintaining combiner, a second non-polarization maintaining gain optical fiber, a third non-polarization maintaining isolator and a second non-polarization maintaining bandpass filter which are connected in sequence; and the second pump source is connected to the first non-polarization maintaining combiner.

4. The repetition rate encodable femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that: The second cladding amplifier comprises a second non-polarization maintaining combiner and a third non-polarization maintaining gain optical fiber which are connected in sequence; and the third pump source is connected to the second non-polarization maintaining combiner.

5. The repetition rate encodable femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that: The pulse compressor comprises a diffraction grating pair and a first total reflection mirror connected in sequence.

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

7. The repetition rate encodable femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that: The first pump source, the second pump source and the third pump source are semiconductor lasers, solid lasers, gas lasers, fiber lasers or Raman lasers, the laser type is a continuous laser or a pulsed laser, and the output optical fiber is a single-mode optical fiber or a multi-mode optical fiber.

8. The repetition rate encodable femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that: The pumping mode of the first pump source, the second pump source and the third pump source is one of core single-end pumping, core double-end pumping, cladding single-end pumping and cladding double-end pumping.

9. The repetition rate encodable femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that: The first polarization-maintaining gain optical fiber and the second polarization-maintaining gain optical fiber are quartz optical fibers or photonic crystal optical fibers doped with rare earth ions, wherein the doped rare earth elements are one or more of ytterbium, erbium, thulium and praseodymium.

10. The repetition rate encodable femtosecond fiber laser based on a bandpass filter according to claim 1, characterized in that: The picosecond pulses outputted by the gain-switched semiconductor seed source are amplified by the core amplifier and the first cladding amplifier and then injected into the passive spectrum broadening optical fiber; Under the effect of nonlinear self-phase modulation, the coherent components and incoherent components of the passive spectrum-broadening fiber pulse are separated in the frequency domain, separated and pulse-shaped by the first non-polarization-maintaining band-stop filter, the output pulse is amplified again by the second cladding amplifier and spectrum-broadened again by the second non-polarization-maintaining passive spectrum-broadening fiber, the re-broadened pulse is collimated by the first fiber collimator and compressed by the pulse compressor to a femtosecond pulse output; The required pulse sequence drawn in advance using a pulse sequence plotter is stored in the seed source signal trigger device, and connected to the seed source external trigger interface. At the same time, the seed source is set from the internal trigger mode to the external trigger mode, and the output of the pulse sequence can be edited arbitrarily.

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