Mid-infrared conventional solitons and soliton molecules are generated in a polarization-maintaining erbium-doped fluoride fiber oscillator, where a semiconductor saturable absorber is used as the mode locker and a polarization beam splitter is employed for getting linearly polarized output pulses. By rotating the half-wave plate in front of the polarization beam splitter to change the output coupling ratio, the system is switchable between conventional solitons and soliton molecules. conventional solitons with a pulse duration of 120 ps, a maximum average power of 248 mW, and a repetition rate of 44.5 MHz are obtained when the oscillator operates in the single-pulse mode-locked state. By decreasing the output coupling ratio, the operating regime of the oscillator switches to the soliton-molecule mode-locked state, in which soliton-triplets equally distributed at a repetition rate of 44.5 MHz with a signal-to-noise ratio of 78 dB and a temporal separation of 60 ps are obtained. Our work offers a scheme to realize switchable operations between the conventional soliton and the soliton molecule in the mid-infrared polarization-maintaining mode-locked fiber laser.
We have successfully demonstrated a high-power erbium-doped fluoride glass fiber laser operating at 2.94 μm. The system achieved continuous operation with an output power of 7.1 W at 2.94 μm. The all-fiber Fabry–Perot laser cavity was constructed using an 11.5 m, 7 mol. % Er3+ :ZBLAN fiber with two fiber Bragg gratings (FBG) having reflectivities of 99.7% and 29.2%. These fiber Bragg gratings were inscribed using a 513 nm femtosecond (fs) laser direct-writing technique. To prevent deterioration at high output powers, an endcap was fused at the output fiber end. The system operated at 2.94 μm exhibited an overall slope efficiency of 20.5% in relation to the launched pump power at 980 nm, and demonstrated a single-mode output beam quality with M2 < 1.2.
In this paper, we demonstrate a synchronously pumped 3.5 μm mode-locked fiber laser based on the cross-phase modulation effect. The fiber laser delivered pulses with a central wavelength of 3541.8 nm, 3 dB spectral bandwidth of 5.1 nm, pulse repetition rate of 18.63 MHz, average output power of 50 mW, and signal-to-noise ratio of 68 dB. The Fourier transform limit pulse width is 2.6 ps, estimated by the hyperbolic secant curve.
In this paper, a high power Tm3+-doped fiber laser (TDFL) based on a monolithic master oscillator power amplifier (MOPA) system with the center wavelength is 1940 nm is demonstrated. The maximum laser power was measured to be 200 W with a slope efficiency of 56.2% at the 793 nm pump power of 368.6 W. Power stability of the laser output over 60 min is measured to be ~0.12%, which indicate a relatively stable laser operation of the TDFL. The output power is limited by the available pump power for the lack of amplified spontaneous emission, parasitic oscillation or self-pulsing effects even at the maximum output power level, showing further power scaling should be possible with increase the pump power.
An ultra-flat and ultra-broadband supercontinuum (SC) is demonstrated in a 4-m photonic crystal fiber (PCF) pumped by an Yb-doped all-fiber noise-like pulses (NLP) laser. The Yb-doped fiber laser is seeded by a SESAM mode-locked fiber laser, and amplified by cascaded fiber amplifiers, with its center wavelength, repetition frequency and the average noise-like bunch duration of 1064.52 nm, 50.18 MHz, 9.14 ps, respectively. Pumped by this NLP laser, the SC source has a 3 dB bandwidth and a 7 dB bandwidth (ignore the pump residue) of 1440 nm and 1790 nm at the maximum average output power of 6.94 W. To the best of our knowledge, this flatness is significantly prominent for the performance of PCF-based SC sources.
In this paper, we drew a 500 m-long PCF taper directly on the industry drawing tower. The fiber taper has a uniform
cross-section structure with OD from 170 μm to 70 μm, and demonstrates very good beam quality. The optical
attenuation of PCF taper was measured. The optical attenuation is ~5 dB/km near 1200 nm, but the water absorption
peak around 1400 nm and the attenuation beyond 1600 nm are still large. The zero dispersion wavelength (ZDW) was
calculated to be ~1090 nm at the taper input end, and shifted to ~870 nm at the taper output end. The PCF taper was
pumped with a picosecond laser source at wavelength of 1064 nm, and generated 200 mW output power of SC covering
from ~450 nm to 1600 nm.
Raman fiber amplifier (RFA) can be used for amplifying signals in all wavelength bands. To obtain flat Raman gain in considered wavelength range, we can use either more fiber amplifiers for different wave bands or more pump sources combined with appropriate pump powers at appropriate wavelengths. However, appropriate wavelengths and powers make the communication system complex and not easily controlled. Because of its ultra-wide band single mode operation, flexible structure design, their realization of high nonlinearity and overall controlled dispersion properties, photonic crystal fiber (PCF) is recognized as a novel class of fibers and a promising new kind of Raman gain medium. The larger nonlinear coefficient could be obtained by reducing mode area through its air hole microstructure region, thus leading to a greatly improved Raman gain coefficient. In this paper, we have modeled and simulated Raman gain properties of PCFs. Appropriate pump wavelengths and output powers are used as the multi-pump for PCFRAs. Through tuning the pump wavelengths and their output powers we can obtain the gain bandwidth of 40nm (from 1530nm to 1570nm) and the gain value is 14dB with ±0.5dB ripple.
Rod-type photonic crystal fibers (PCFs) bring enormous advantages in Q-switched fiber laser with high pulse energy, short pulse width and good beam quality for its large mode area and short fiber length. In this paper, an acoustic-optic Q-switched photonic crystal fiber laser was investigated by using a 1m-long Yb-doped large mode area rod-type photonic crystal fiber as gain medium. A maximum pulse energy of 0.78 mJ (21.7 KW peak power) and the shortest pulse width of 20 ns were obtained at low repetition rates. A maximum 1033.6 nm average power of 14.5 W was demonstrated at 65 KHz with a slope efficiency of 56%. Further improvements would be obtained by optimizing the experiment configuration so as to achieve shorter pulse width and higher pulse energy.
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