KARLSRUHE, Germany — Mixing nanoparticles of
high-purity quartz glass with small amounts of liquid
polymer, researchers have developed a new process using
glass for additive manufacturing techniques.
Once the mixture is complete, the Karlsruhe Institute
of Technology (KIT) researchers then cure it with light
at specific points through a process called stereolithography.
The material, which remains a liquid, is then washed
out in a solvent bath, leaving only the desired cured
structure. The polymer still mixed in this glass structure
is subsequently removed by heating.
“The shape initially resembles that of a pound cake;
it is still unstable, and therefore the glass is sintered in a
final step — in other words, heated so that the glass particles are fused,” said group leader Bastian Rapp.
3D-printing techniques have primarily been used on
polymers or metals. In instances where glass has been
processed into structures, Rapp said, the surface tends to
be rough and the material is porous and contains voids.
“We present a new method, an innovation in materi-
als processing in which the material of the piece manu-
factured is high-purity quartz glass with the respective
chemical and physical properties,” said Rapp.
The glass structures made by the KIT scientists show
resolutions in the range of a few micrometers. However,
Rapp said the structures may have dimensions in the
range of a few centimeters.
Future applications include biological and medical
technologies where very small analytical systems could
be made out of miniaturized glass tubes. In addition, 3D-
shaped microstructures of glass could be employed in a
variety of optical areas, from eyeglasses meeting special
requirements to lenses in laptop cameras. Data technology is another possible future application of 3D-printed
“The next plus one generation of computers will use
light, which requires complicated processor structures;
3D-technology could be used, for instance, to make
small, complex structures out of a large number of very
small optical components of different orientations,” said
The KIT research has been published in the journal
Nature (doi: 10.1038/nature22061).
New technique uses stereolithography for the additive manufacturing of glass
Complicated high-precision structures made of glass
can be manufactured in a 3D-printing process
developed at KIT.
WARSAW, Poland — An innovative fiber laser that generates ultrashort high-energy pulses in an optical fiber
could soon shorten the time of processing materials in
industrial laser machines.
Optical scientists at the Laser Centre of the Institute of
Physical Chemistry of the Polish Academy of Sciences
(IPC PAS) and the Faculty of Physics of the University
of Warsaw have forced an optical fiber laser to generate
ultrashort high-energy pulses. The method they used was
once considered by experts as impossible to achieve.
The new laser is devoid of any mechanically sensitive
external parts, which makes it appealing for future industrial laser applications.
“Fiber lasers can be built so that all the processes im-
portant for the generation and shaping of the ultrashort
pulses take place in the fiber itself,” said Yuriy Ste-
panenko from the IPC PAS. “Such devices, without any
external mechanically sensitive components, operate in a
very stable manner and are ideal for working in difficult
Laser action in the fiber leads to the generation of a
continuous light beam. The release of energy in the short-
est possible pulses is more favorable since it signifies a
great increase of power. Pulses are generated in fiber
lasers by a system known as a saturable absorber. When
the light intensity is low, the absorber blocks light, when
it is high, it lets it through. In femtosecond pulses, the
light intensity is much greater than in a continuous beam,
and the parameters of the absorber can be adjusted so that
it only lets through pulses.
“Up to now, graphene sheets, among others, have been
used as the saturable absorbers, in a form of a thin layer
deposited on the tip of the fiber,” said Jan Szczepanek, a
Ph.D. student from the faculty of physics of the Univer-
sity of Warsaw. “But the diameters of optical fibers are in
the order of single microns. Even a little energy cramped
in such a small cross section has a significant density per
unit area, affecting the lifetime of the materials. There-
fore, if an attempt was made to increase the power of the
femtosecond pulses, the graphene on the tip of the con-
nector was destroyed. Other absorbers, such as carbon
nanotubes, may also undergo degradation.”
In order to generate higher-energy femtosecond pulses in
the optical fiber, the Warsaw physicists decided to improve
saturable absorbers of a different type, not functioning be-
cause of the unique properties of materials but because of
the clever use of optical phenomena, such as nonlinear ef-
fects causing a change in the refractive index of glass.
At the input of a nonlinear artificial saturable absorber,
the linearly polarized light is divided into beams with
low and high intensity. The medium of the absorber can
be chosen for both light beams to experience a slightly
different refractive index. As a result, the plane of polarization starts to rotate. At the output of the absorber there
is a polarization filter that only lets through waves oscillating perpendicularly to the plane of polarization of the
incoming light. When the laser is operating in continuous
mode, an optical path difference does not occur, the polarization does not change and the output filter blocks the
light. At a high-enough intensity, typical for femtosecond pulses, the rotation of polarization causes the pulse
to pass through the polarizer.
For the saturable absorber with polarization rotation
to work, the fiber must have different refractive indices in different directions (making it birefringent) and
both indices also should be stable. The problem is that in
ordinary optical fibers birefringence occurs accidentally.
Lasers built in this manner are extremely sensitive to
external factors. In turn, birefringence of the polariza-tion-preserving fibers is so large that the light propagates
in them in only one direction and the construction of
artificial saturable absorbers becomes physically impossible.
“Birefringent optical fibers retaining the polarization
state of the light entering them are already in produc-
tion in the world. We are the first to demonstrate how
they can be used to construct a saturable absorber,” said
Szczepanek. “We cut the optical fiber into segments of
an appropriate length and then reconnect them, rotat-
ing each successive segment 90 degrees in relation to its
“Rotation means that if in one segment a pulse with,
shall we say, vertical polarization, travels slowly, in
the next it will run faster and catch up with the second
pulse, polarized perpendicularly,” said Stepanenko. “A
simple procedure has therefore allowed us to eliminate
the main obstacle on the road to increasing the energy —
that is, the great difference in velocities between pulses
of different polarities, so typical for all polarization-
The more rotated segments there are, the better the
quality of the pulses generated in the fiber. In the laser
built in the Warsaw laboratory, the saturable absorber
consisted of a fiber with a length of approximately
3 meters, divided into three segments, and a filtering po-
larizer. The potential number of rotated segments can be
increased up to a dozen or so.
The laser produces high-quality femtosecond pulses,
and their energy can be up to 1000 times larger than
typical for lasers with material absorbers. In comparison
to the devices with artificial absorbers, the laser made
by Warsaw scientists has a much simpler construction,
therefore its reliability is significantly greater.
Their research findings have been published in the
journal Optics Letters ( doi.org/10.1364/OL.42.000575).
Ultrashort high-energy pulses show promise for faster materials processing
Jan Szczepanek, a Ph.D. student from the faculty
of physics of the University of Warsaw, with the
innovative fiber laser.