All-fiber ultrafast amplifier at 1.9 μm based on thulium-doped normal dispersion fiber and LMA fiber compressor

Abstract

The duration reduction and the peak power increase of ultrashort pulses generated by all-fiber sources at a wavelength of $$1.9\,\upmu \hbox {m}$$ 1.9 μ m are urgent tasks. Finding an effective and easy way to improve these characteristics of ultrafast lasers can allow a broad implementation of wideband coherent supercontinuum sources in the mid-IR range required for various applications. As an alternative approach to sub-100 fs pulse generation, we present an ultrafast all-fiber amplifier based on a normal-dispersion germanosilicate thulium-doped active fiber and a large-mode-area silica-fiber compressor. The output pulses have the following characteristics: the central wavelength of $$1.9\,\upmu \hbox {m}$$ 1.9 μ m , the repetition rate of 23.8 MHz, the energy per pulse period of 25 nJ, the average power of 600 mW, and a random output polarization. The pulse intensity and phase profiles were measured via the second-harmonic-generation frequency-resolved optical gating technique for a linearly polarized pulse. The linearly polarized pulse has a duration of 71 fs and a peak power of 128.7 kW. The maximum estimated peak power for all polarizations is 220 kW. The dynamics of ultrashort-pulse propagation in the amplifier were analyzed using numerical simulations.

Octave-Spanning Supercontinuum Generation in As2S3-Silica Hybrid Waveguides Pumped by Thulium-Doped Fiber Laser

“…1 shows the schematic of the experimental setup. A home-made all-fiber ultrafast master oscillator power amplifier was used as the pump source (detailed description in [24]). The pump source consists of a thulium-doped fiber laser with hybrid mode-locking [25], a pulse stretcher, an amplifier based on a germanosilicate thulium-doped fiber with normal group velocity dispersion (GVD), and a large mode area fiber compressor.…”

“…Mechanical polarization controllers both in the laser and in the amplifier were used to adjust the pulse generation regime. Thus, with different settings of the polarization controllers, pulses at the amplifier output may be tuned from 65 fs to 1 ps, which is related to the dependence of the nonlinear refractive index on the polarization state of the radiation [26] and, as a consequence, to the different balance of dispersion and nonlinear effects in the amplifier and compressor (see in more detail in [24]). In the experiment, a pulse duration of 78 fs was used along with a maximum pulse energy of 25 nJ and a peak power of 200 kW.…”

“…4a (black). The SC simulation uses the power and phase temporal distributions of the pulse measured by the FROG method at other settings of the laser and amplifier polarization controllers (detailed description of these measurements is given in [24]) and stretched in the time domain to the duration of the measured autocorrelation. The red curve (Fig.…”

“…3b, which can be used in the region from 1 to 3 µm. The pump pulses in the model are in the form of a soliton and have a duration of 65 fs (the shortest duration achievable in a pump source [24]). The maximum power for each waveguide in the simulation was estimated using the effective area of the waveguide mode and the measured damage threshold of As 2 S 3 [42] and is shown by the red curve in Fig.…”

“…The waveguide with a diameter of 1.2 µm are chosen to experimental study the dynamics of changes in the width of the spectrum. All powers used in the simulation can be achieved using the developed pumping system [24].…”