MEXICO CITY — A novel method for fabricating poly-dimethylsiloxane (PDMS) waveguides using low-power
laser etching could make it easier and less expensive to
incorporate optical sensing onto lab-on-a-chip devices.
The PDMS waveguides can be easily integrated into lab-on-a-chip devices made of the same material.
Researchers from National Autonomous University of
Mexico created a mold for the waveguides using the laser
beam of a CD/DVD burner to etch a clear sheet of acrylic.
Because low-power laser sources like the ones in CD/
DVD burners typically aren’t absorbed by transparent
materials, the researchers coated the acrylic with highly
absorbent nanocarbon. This created pinpoint areas of intense heat that could be used to etch the material with
The researchers next created PDMS with two different indices of refraction by carefully modifying the mixing and curing conditions of the material. They filled the
etched micromold with PDMS of one refractive index,
cured the material, then placed a layer of PDMS with
a different refractive index on top. After another curing step, the researchers removed the PDMS from the
mold, flipped it and added another layer of PDMS to create a waveguide completely embedded into two slabs of
To verify the reproducibility of the mixing and curing
recipe used to control the optical properties of PDMS,
the researchers measured the refractive index of their
fabricated PDMS layers several times. They also showed
that the optical losses of waveguides made with this technique matched those reported for more complicated fabrication techniques.
“In addition to being low cost, our technique accom-
plishes rapid prototyping of waveguides that can make
it possible to integrate light-based capabilities such as
interferometric devices into lab-on-a-chip devices,” said
researcher Mathieu Hautefeuille. “It is also possible to
fabricate long waveguides with our method, which can be
a great advantage in lab-on-chip devices.”
Using their technique, the researchers fabricated an
8-mm-long, Y-shaped PDMS beamsplitter. Experiments
showed that the beamsplitter could separate a laser beam
into two output arms and that the light could be switched
between each arm by changing the position and angle of
the optical fiber delivering the light.
The researchers believe that their fabrication tech-
nique could be useful for several applications, including
those requiring precision microstructuring. They say that
the technique could be used to etch other polymer materi-
als in addition to PDMS.
“Our new method is compatible with the development
of lab-on-chip platforms where integrated optical wave-
guides can be a great tool for light-based diagnostics or
monitoring applications,” said Hautefeuille.
The researchers are now working to demonstrate that
their method can be used to fabricate more complex in-
tegrated optical devices such as an interferometer that
could serve as an all-PDMS platform for sensing appli-
“Our study shows that short-pulsed lasers are not
strictly necessary to etch transparent polymers and plas-
tics with a micron-scale resolution,” said Hautefeuille.
“The use of a recycled CD/DVD unit further shows that
you might be able to stretch the usage of equipment that
could be starting to look out of date.”
The most common material used to make lab-on-
a-chip devices today is the silicone PDMS because of
its optical, mechanical and chemical properties, its
low cost and the ease with which it can be structured
at the microscale. As these devices become more com-
mon and complex, there may be a need for less-expen-
sive ways to incorporate all-PDMS optical components
such as waveguides to direct light onto and within the
“To the best of our knowledge, this is the first time that
low-power laser etching has been used to microstructure
polymers for optical waveguide fabrication,” said Haute-
feuille. “This study shows that a very inexpensive laser
platform, based on a CD/DVD unit in our case, can com-
pete with high-power lasers for such applications.”
The research was published in Optical Materials Express, a publicaton of OSA, The Optical Society of America (doi: 10.1364/OME.7.001343).
Low-power laser etching may speed lab-on-a-chip fabrication
In the beamsplitter validation test design, separation between the legs with respect to the central input channel is
controlled to vary the output efficiency as it gets closer to the critical angle.
Researchers develop erasable ink for 3D printing
KARLSRUHE, Germany — Direct 3D laser printing
or laser writing uses a computer-controlled focused laser
beam to generate the structures. The process produces
micrometer-sized objects with precisely defined properties.
Researchers from the Karlsruhe Institute of Technology (KIT) have developed a method that actually erases
the ink used for 3D printing, allowing the small structures up to 100 nm to be repeatedly erased and rewritten
if need be. This new development opens up many new 3D
“Developing an ink that can be erased again was one
of the big challenges in direct laser writing,” said profes-
sor Christopher Barner-Kowollik of KIT’s Institute for
Chemical Technology and Polymer Chemistry.
KIT researchers have successfully developed an ink
with reversible bonding, the building blocks of which
can be separated from each other. The printed structure
is simply erased by immersing it into a chemical solvent
and can be rewritten or modified repeatedly.
The process was developed in close cooperation with
professor Martin Wegener’s group at the Institute of
Applied Physics and the Institute of Nanotechnology
of KIT. The physicists developed highly specialized