An all-fiber, diode-pumped, continuous-wave Tm3+-doped fiber laser operated at a wavelength of 1.94 μm was developed. 37.4 W of output power with a slope efficiency as high as 57% with respect to absorbed pump power at 790 nm was demonstrated. The laser output beam quality factor M2 was measured to be ~1.2. The output beam was very stable with power fluctuations <1% measured over 1 hour. The laser system is to be implemented as a scalpel for surgery of soft biological tissues.
Ultrafast all-fiber oscillators are currently one of the most rapidly developing laser technologies. Many advantages like: environmental stability, low sensitivity to misalignment, excellent beam quality (intrinsic single transverse mode operation), high energy and an excellent active medium efficiency make them the lasers of choice for a variety of applications. In this paper the designs of all-fiber all-normal dispersion femtosecond lasers are described. Due to large positive chirp, the pulses inside the cavity are highly stretched in time and they can achieve higher energies with the same peak power as shorter pulses. High insensitivity to mechanical perturbations or temperature drift is another highly valued property of presented configurations. Two of reported lasers are extremely stable due to the fact that their cavities are built entirely of polarization maintaining fibers and optical elements. We used highly Yb3+ ions doped fibers as an active medium pumped by a fiber coupled 976 nm laser diode. The central wavelength of our laser oscillators was 1030 nm. Three methods of passive mode-locking in all-fiber cavities were studied. In particular, the designs with Nonlinear Polarization Evolution (NPE), Nonlinear Optical Loop Mirror (NOLM) and Nonlinear Amplifying Loop Mirror (NALM) as artificial saturable absorbers were investigated. The most attention was paid to all-PM-fiber configurations. We present two self-starting, high energy, all-fiber configurations: one delivering pulses with energy of 4.3 nJ and dechirped pulse duration of 150 fs based on the NALM and another with a 6.8 nJ, 390 fs pulses in configuration with the NOLM. The influence of different artificial saturable absorber on output pulse characteristics were studied and analyzed.
The issue of temporal pulse distortion occurring during amplification process in a 2-stage, fiber amplifier, operating in
the eye-safe spectral region, is discussed. The amplifier was built in a Master Oscillator Power Amplifier (MOPA)
configuration and seeded by a distributed feedback (DFB) laser providing nanosecond pulses at a repetition rate of 20
kHz. It operated at a wavelength of 1549.13 nm and generated over 200 mW of output power with a slope efficiency of
up to 28%. The comparison between the calculated and measured results on saturation-induced pulse shape deformation,
for ~300-ns pulses, is presented. The analyzed pulse shapes embraced rectangle, Gaussian, triangle and "M" letter.
We demonstrate broadband supercontinuum (SC) generation in a single-mode fluoride (ZBLAN) fiber pumped by
1.55 μm nanosecond pulses amplified in a cascade of fiber amplifiers. The recorded spectrum spread from ~ 900 nm to
3600 nm. The total output power was measured to be 0.66 W in entire spectral band. Over 65% of this power
corresponded to wavelengths longer than 1.65 μm. The SC spectrum was generated in two steps: first the ~1 ns pulses
were broken in a single-mode silica fiber (SMF) into a train of shorter sub-pulses leading to initial spectrum extension
(from ~1.4 to 2.2 μm) and then the spectrum was further broadened into a ZBLAN fiber. The performance of the SC
source is described.
A splicing procedure of erbium doped fiber with standard SMF-28e is discussed in the paper. The optical loss of 0.12 dB
at 1300 nm wavelength was obtained. The active power monitoring method was adopted in the splicing process.
Furthermore, the shape deformation of the octagonal, double clad fiber is reported. In addition, end-cap fabrication and
angled fiber cleaving is discussed in the paper. Splicing and end-cap fabrication was performed with the use of filament
ε Broadband and spectrally flat supercontinuum (SC) generation in standard single-mode passive and Tm-doped fibers
pumped by 1.55 μm pulses in the anomalous dispersion region is presented. Initial results on SC generation in a singlemode
fluoride fiber are also presented. Using only a piece of commercially available SMF-28 as a nonlinear medium, the
SC covering the spectral range from ~1.3 μm to 2.5 μm with the mean power of 1.71 W and a 5 dB spectral flatness of
640 nm is reported. When pumping a piece of Tm-doped fiber, the spectrum spreading from ~1.4 μm to 2.65 μm with its
significant part located over 1.8 μm wavelength was recorded. SC generated in a fluoride fiber spread from ~0.9 μm to
3.2 μm with the average power of 0.85 W (out of which, over 0.1 W was located beyond 2.4 μm) was achieved. εε
The paper presents a current state of the project aiming to develop a compact and mobile pulsed laser source, operated in
“eye-safe” spectral region (1.5 μm). It will be a high power, all-fiber system generating nanosecond pulses with
repetition rate ranging from tens to hundreds kHz and built in Master Oscillator Power Amplifier (MOPA) configuration.
First amplifying cascade of the system has been developed. Distributed Feedback (DFB) laser diode with home-built
supply and pulse control system was used as a master oscillator. It can generate rectangular laser pulses with
independently changeable repetition rate (10 – 200 kHz) and pulse width (20 – 300 ns). The system provides over 34 dB
optical gain. In addition, simulations of amplification laser radiation in the active fiber for different input pulse energies
in relation to saturation energy were presented. Furthermore theoretical and experimental optimization of an active fiber
length was done. In the first elaborated stage of amplifier 18,1 % slope efficiency was obtained.
Pulsed thulium-doped silica fiber laser operating at a wavelength of 1994.8 nm was developed. The laser was fast gain-switched
by 1.55-μm radiation generated from a fiber amplifier system seeded by a directly modulated distributed
feedback semiconductor laser. The Tm-doped fiber laser delivered stable nanosecond pulses at a repetition rate ranging
from 50 kHz to 300 kHz. The maximum average output power as high as 1.08 W with a slope efficiency of 49% for the
repetition rate of 100 kHz was reported. The shortest stable pulses recorded had a width of (20-25) ns and the energy of
<15 μJ. The laser system was developed in all-fiber architecture, thus providing robustness, compactness, high
insensitivity to atmospheric conditions (dust, vibrations, humidity).
The 1.5 μm pulsed 3-stage all-fiber MOPA source seeded by a directly modulated DFB laser was developed. It operated
at the repetition rate ranging from 400 kHz to 2 MHz and delivered up to 6.5 μJ in 1-ns pulse. The total signal gain of up
to 57 dB and the maximum average output power of over 2.8 W (at 2 MHz) were demonstrated when the total pump
power of the MOPA was 10.64 W. The amplified pulses were very stable and did not reveal either duration and shape
change in relation to input pulses generated by the seed.