This study introduces constructions of the structural (multiring) doping profile for Large Mode Area fibers, incorporating Tm3+ and Tm3+/Ho3+ layer profiles. The presentation includes a numerical analysis of modal properties and beam shape. The chelate doping technology (CDT) of modified chemical vapour phase deposition (MCVD), known for its low attenuation active preforms fabrication method, was employed in optical fiber manufacturing. The multi-stage deposition in the MCVD-CDT system enables the fabrication of optical preforms with up to 20 layers. Concentrations of lanthanides were optimized to achieve broadband emission in the eye-safe spectral range of 1.55 to 2.10 µm. The fiber construction employed Tm3+ doping design used for a laser construction utilizing the Fabry-Perot resonator for single-mode laser beam generation at a wavelength of 1940 nm, with an M2 value of approximately 1.1.
Acknowledgments: The project was funded by the National Science Centre (Poland) granted on the basis of decision no. UMO-2020/37/B/ST7/03094.
In this paper we describe a compact optoelectronic circuit for spike-free nanosecond pulse generation in semiconductor lasers. The device is designed to work as an injection seeder in high-power fiber lasers built in master oscillator power amplifier architecture. To reduce a significant pulse distortion resulted from relaxation oscillations, a technique called light injection was used. It allows achieving the pulse generation with excellent temporal and spectral properties. Smooth pulses with duration of 1.9ns and narrowband spectrum with a central wavelength of 1550nm have been presented experimentally.
Fiber-based laser sources delivering optical pulses at a wavelength of ~1.5μm have attracted a great interest in recent years mainly due to their unique properties. High efficiency, high output power, eye-safe wavelength and very good output beam quality make them a perfect tool for Free Space Optics communication. The most suitable modulation scheme for long-haul communication is pulse-position modulation mainly due to its high peak-to-average power ratio. In this paper we discuss a potential use of high power fiber laser system built in Master Oscillator Power Amplifier architecture for pulse-position modulated Deep Space Optical Communication. We focus on power scalability, beam quality, laser driver simplicity and temporal deformation of nanosecond laser pulses as well. In summary we shortly compare features of pulse-position modulated fiber laser transmitter with other high power laser sources being used in optical communication.
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.
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).
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.
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
fusion splicer.
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.
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