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.
High-power supercontinuum (SC) generation in soft glass fibers is a relatively new research domain and the number of research groups dealing with this topic is still very small. Nevertheless, the results already achieved are very impressive and promising regarding potential applications of SC sources. In this paper I briefly reviewed recent results on highpower SC generation in fluoride fibers achieved at the Institute of Optoelectronics (Military University of Technology, MUT). The works are mainly focused on achieving high spectral flatness as well as very good power distribution towards the long wavelengths, while keeping the output time-averaged power at the level of over 1 W. To this aim, different home-built pump sources (e.g. mode-locked fiber laser and amplifier, gain-switched fiber laser and amplifier) and some selected nonlinear fibers (fluorozirconate, fluoroindate) were used for tests. Such light sources can find applications in a lot of important areas, like stand-off detection, directional countermeasure, and medicine. For these applications, the magnitude of bandwidth, spectral flatness as well as the level of output power together with efficient power distribution towards the mid-IR are very important factors.
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.
High-power mid-infrared (mid-IR) fiber-based supercontinuum (SC) sources are considered a key enabling technology for numerous applications in such important areas as microscopy, spectroscopy, medicine, and military. Most of the applications require robust, high power, sources emitting radiation in the 2-4 μm spectral band. To meet these requirements, a suitable design of SC laser source has to be applied. High-power SC generation in soft glass fibers is a relatively new research domain and the number of research groups dealing with this topic is still very small. Nevertheless, the results already achieved are very impressive and promising regarding practical applications of SC sources. In this paper I briefly reviewed the developments in scaling up the output average power and spectral coverage in the mid-IR region in fluoride fiber-based SC sources that have been achieved recently by my group.
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.
An efficient high-peak-power Ho:YAG hybrid laser resonantly pumped by a 20 W linearly polarized Tm:fiber laser
at the wavelength of 1908 nm was developed. At room temperature a maximum continuous output power of 10.7 W
with a slope efficiency of over 55% with respect to the incident pump power was achieved. In Q-switching regime
an acousto-optic modulators were applied. The research was conducted for normal and Brewster's angle Q-switches
respectively. In CW pumping regime the repetition rate was changed from 500 Hz to 5000 Hz. For the best case, for
5 kHz repetition rate, pulses of 1.6 mJ energy and 123 kW peak-power were achieved at the wavelength of 2090.2 nm
with an M2 ≈ 1.6.
Fiber lasers emitting in the 2 μm wavelength range doped with thulium ions can be used as highly efficient pump
sources for nonlinear converters to generate mid-infrared radiation. For spectroscopic purposes, illumination and
countermeasures, a broad mid-infrared emission spectrum is advantageous. This can be reached by supercontinuum
generation in fibers, e.g. fluoride fibers, which up to now has, however, only been presented with either low
average power, complex Raman-shifted 1.55 μm pump sources or multi-stage amplifier pump schemes. Here we
present recent results of a new actively-mode-locked single-oscillator scheme that can provide the high-repetition
rate sub-ns pump pulses needed for pumping supercontinuum generators. A thulium-doped silica fiber laser is
presented that provides > 11 W of average power CW-mode-locked pulses at 38 MHz repetition rate at ~ 38 ps
pulse width. Upgrading the setup to allow Q-switched mode-locked operation yields mode-locked 40 MHz pulses
arranged in 60 kHz bunched Q-switch envelopes and thus increases further the available peak power. In this
Q-switched mode-locked regime over 5 W of average power has been achieved.
In the paper the method of synthesis, physical and optical properties of 45SiO2 - 8Al2O3 - 15B2O3 - (32 -x) PbO + Na2O
+ K2O + xNd2O3/NdF3, x = (1 - 3% mol) glasses were presented. The transparent and thermally stable aluminosilicate
glasses without any crystallization effect were synthesized. Optimal concentration of neodymium ions in glass host was
established in order to obtain high luminescence. Absorption and luminescence spectra of obtained glasses were
measured. Influence of thermal treatment on level of luminescence was investigated.
In Er:YAG, Er:YSGG and Er:YLF lasers the most important are the three lowest energy levels of Er3+ ion. Transitions
between these levels decide about wavelength of generated laser radiation. In Er:YAG laser these levels are: 4I15/2
(energy: 280 cm-1), 4I13/2 (6710 cm-1), 4I11/2 (10330 cm-1) [1]. Er:YAG has many absorption lines mainly in visual and
near infrared wavelength spectrum. This laser may generate optical radiation at two wavelengths: 1,6 μm and 2,94μm.
For the first one Er:YAG works as a three level quantum system and the for the second one it works as a four level
quantum system. In this case the top laser level is 4I11/2 and the down laser level is 4I13/2. Both the wavelength generated
and the work mode may be selected by dopant concentration.
In lasers such as Er:YAG an analysis of transitions between levels during optical radiation absorption and generation the
Boltzman distribution of energy levels occupation and thermalization effects must be taken into consideration [2].
Authors have developed computer software, which allows analysing transitions dynamics, laser output power/energy and
rod's temperature increase (during pulse generation) which depends on: pump properties, initial temperature, and dopant concentration.
Analysis may be carried on for monopulse generation as well as for pulse generation. This software allows simplifying
Er:YAG laser application designing.
The characteristics of a Q-switched neodymium-doped double-clad fiber laser were presented. Based on the proposed differential equations with suitable boundary and initial conditions, a numerical model was developed to simulate this fiber laser. All the calculations were based on wave-travelling approach. Using this model, pulse duration and the energy of generated pulses can be predicted. In the experiment, pulses with the energy of 0.36mJ (84ns) and 154μJ (48ns) at the repetition rate of 500Hz were achieved for 5 and 3-m long fiber, respectively. The extractable energy was limited due to low energy storage and the fiber-end facet damage. The results obtained numerically agree well with the experimental results.
In this paper we report on a record 1.4 MW peak power, actively Q-switched Er:YAG laser operating at 2.94 μm. As a result of our experiment, at 3 Hz repetition rate, we achieved 91 ns pulses with 137 mJ energy. At higher repetition rate (10 Hz) the laser generated 100 ns pulses with 35 mJ energy. These results, according to our knowledge, are the best that have been ever achieved.
This paper presents a Q-switched Er:YAG laser generating in near infrared range. In this laser system Pockels cell (as an active switch) was applied. For the optimal repetition rate of 10 Hz and maximal pumping energy of 62 J over 15 mJ of the ouptut laser energy was achieved. The pulses generated were characterized by time duration of 115 ns corresponding with 130 kW peak power. Non-linear absorbers allowing to build an effective losses modulator are also discussed.
Problems related to optical activation of high-power fiber lasers are presented in this work. Double-clad fiber lasers with different cross sections of inner clad are discussed. The authors of this study have presented an alternative attempt at analyzing the problems touched upon. In this paper a computer program allowing visualization of the path of the light rays in geometrical optics approximation is presented. This program visualizes a trajectory of the light rays along the fiber and the result is the graphic presentation of distribution of radiation transmitted along the fiber (on cutting plane of the fiber). Circle, stadium and D-shaped clads were considered. The results of the analyses carried out clearly indicate unquestionable superiority of D-shaped and stadium-shaped fibers over fibers with circular cross section, when the efficiency of activation is taken into account.
KEYWORDS: Fiber lasers, Optical fibers, Laser systems engineering, High power fiber lasers, Absorption, Signal attenuation, Mirrors, Optoelectronics, Diodes
In this paper a high-power Nd-doped double-clad fiber laser is presented. We obtained 10 W cw-output power from 20 m long fiber with laser core in 12 μm diameter (NA = 0.12) and pump core in 400 μm diameter (D-shaped, NA = 0.38). Nd-doping concentration has been at 1300 ppm level and attenuation in the laser core has been less than 10 dB/km (for λ = 1100 nm). High power diode laser module operating at λ = 808 nm has been used as a pump unit. This pump ensured 30 W cw output power. As a result, we have built a coherent source of radiation generating 10 W cw output power with 63 percent slope efficiency.
In this article we present a diode pumped fiber laser. An active Q-switched fiber laser system has been elaborated. An active neodymium-doped double-clad optical fiber was used as an active medium. For low repetition rate (20 Hz) we achieved pulses with 211 ns time duration and 12 μJ energy. Applying high repetition (10 kHz) driver of Pockels cell we achieved pulses with 250 ns time duration and 300 μJ energy (for 500 Hz repetition rate). The length of the active fiber was 5 m. The pump source delivered 30 W continuous output power at 808 nm wavelength.
In this paper high power Yb-doped double-clad fiber laser is presented. A Yb3+-silica fiber laser has been cladding pumped at 937 nm by a InGaAs semiconductor laser diode and operated with the slope efficiency of 73 ± 3% with respect to the incident pump power. We obtained 4 W cw-output power when working with 20-m long fiber with laser core in 7 μm diameter (cut-off wavelength - 1 μm) and pump core in 120 x 120 μm (rectangle-shaped, NA = 0.6). Yb-doping concentration has been at the level 3 - 10 • 1019 cm-3 and attenuation in laser core has been 8 - 12 dB/km. The fiber laser operated at 1084 nm.
The state of development of constructions and technology of elements used in high-power fiber laser systems is presented. Laser working conditions related to constructions and new technology limit maximum cw-output power and level of energy (pulse regime). The analysis concerns recent available active dopants used in active optical fiber lasers and methods of its activation. The perspectives of progress of high-power fiber lasers have also been presented.
KEYWORDS: Fiber lasers, Optical fibers, Laser systems engineering, Continuous wave operation, Absorption, Mirrors, High power fiber lasers, Signal attenuation, Optoelectronics
In this paper a high-power Nd-doped double-clad fiber laser is presented. From 20 m long fiber with laser core in 12 μm diameter (NA=0.12) and pump core in 400 μm diameter (D-shaped, NA=0.38) we obtained 10 W cw-output power. Nd-doping concentration has been at the level 1300 ppm and attenuation in the laser core has been less than 10 dB/km (for λ=1100 nm). High power diode laser module operating at λ= 808 nm has been used as a pump unit. This pump ensured 30 W cw output power. As a result we have built a coherent source of radiation generating 10 W cw output power with slope efficiency 63 per cent.
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