First pulse of relaxation oscillations that appear after the start of the pumping can be used to realize an efficient pulsed laser based on gain switching. Because there is no need for any additional active optical element this can be very simple and robust technique to produce nanosecond pulses. Together with fiber technology it can produce compact and reliable lasers appropriate for industrial applications such as micro-processing. However, to produce pulses with appropriate peak power and duration, one must carefully design such systems. We report on a numerical model that describes time and spatial dependencies of photon and ion populations which was developed to enable design and optimization of a gainswitched fiber laser. The peak pump power influence on basic output laser pulse parameters is presented in this paper. To confirm theoretical result an experimental setup was built around double clad ytterbium doped fiber laser.
Security, defense and sensing applications often require routing of optical fibers through constrained spaces.
Fibers or fiber cables must frequently be tightly matched or mounted onto structures having arbitrary shapes
or forms, which inevitably leads to requirement for tight fiber bends. In such case macro bend loss presents
one of the major concerns and limitations in practical applicability of optical fibers. Fibers with high bend
tolerance are therefore required in such environments. To date, significant works relating to the
understanding and improvement of bend-loss sensitivity have been carried on for single-mode fibers and
fiber systems. However, in security and defense applications, robust connectivity and installation
reliability issues often favor multimode fiber systems.
This paper presents a highly effective micromachining process that can reform a section of an optical fiber into an allfiber,
complex photonic microstructure. The proposed process utilizes specially designed structure forming fibers that are
reformed into various complex shapes through selective etching. The control over the etching rate of the structureforming
fiber sections is achieved by the introduction of dopants, particularly phosphorus pentoxide, into silica glass
through the standard fiber manufacturing technology. Doping with appropriate dopants and dopant concentrations can be
used to create highly-preferential etchable areas within a fiber cross-section that can be selectively removed upon
exposing the fiber to the etching medium. The doped areas in the fiber cross-section can thus serve as sacrificial layers,
similar to those in the case of silicon MEMS production. Thus, the shaping of fiber devices can be achieved through the
design and fabrication of structure-forming fibers.
Nanoparticle-doped optical fibers are causing significant scientific interest in different application fields. Nanoparticle-doping
of silica glass layers during optical fiber preform fabrication was so far reported by sol-gel and solution doping
processes, by flame hydrolysis spraying and by pulling hollow cylinders from nanoparticle suspensions. A new method
for fabrication of high quality nanoparticle-doped fibers is suggested.
Proposed method is based on "flash vaporization" deposition process, previously reported as method to fabricate rare
earth- and metal ion-doped specialty optical fibers. Experiments were made where SiO2 layers were deposited using
"flash vaporization"-equipped MCVD system, adding vapors carrying metal or oxide nanoparticles into deposition zone.
Analysis of produced preforms confirms presence of nanoparticles in deposited layers, albeit with low deposition rate
due to weak thermophoretic forces acting on very small particles or agglomerations. Based on results, a number of
improvements were suggested and implemented in fabrication process, device design and choice of precursor materials.
"Flash vaporization" method was demonstrated as suitable method for deposition of nanoparticles in silica layers,
permitting in-situ fabrication of complete preforms, providing easy upgrade path for existing MCVD and OVD
deposition systems and allowing simultaneous co-doping by a wide range of other co-dopants.
Rare earth and metal ion doped optical fiber preforms have been produced using a novel flash vaporization method for
precursor delivery  into substrate tube. TEOS and solutions of organometallic compounds, containing lanthanide, Al,
Bi, Fe or Co were used. Use of TEOS and organometallic precursors makes this process similar to aerosol and sol-gel
processes, but glass is laid down in thin layers in MCVD fashion, strongly relying on thermophoretic forces. Preforms
with fully consolidated core layers have been made and were in most cases drawn to fibers. Results of these fibers and
preform glass composition are discussed.