Marie Freebody, email@example.com
TEL AVIV, Israel – The ability to manipulate matter using lasers is enabling scientists
at Tel Aviv University to develop innovative photonic devices. Dr. Yael Roichman
and colleagues at the university’s school of chemistry have come up with a
novel way of assembling photonic crystals, which they hope will aid the development
of anything from optical microscopes to light-fueled computer technology.
The ultimate goal is to build lab-on-a-chip devices that will
be better able to control light and guide it on paths on the scale of microns. Using
these chips, high-throughput, small-scale experiments could be built, which will
enable biological studies of bacteria and yeast, for example.
“We hope to have our first prototype done within the coming
year,” Roichman said. “I hope the devices we are trying to make will
benefit the entire photonics community by paving the way to new designs. What’s
more, our fabrication process lends itself to integration in larger all-optical
devices based on soft lithography.”
Dr. Yael Roichman is pictured in her laboratory at Tel Aviv University
with her students. Courtesy of Tel Aviv University.
Roichman employs a tool known as holographic optical tweezers
(HOTs) to painstakingly move photonic crystals into place to form larger structures.
HOTs operate by trapping and moving tiny particles within a highly focused laser
beam. If light from the laser is sufficiently focused, it provides an attractive
or repulsive force on the particle, enabling matter to be manipulated on the nanoscale.
Using HOTs to assemble photonic devices was first done by Roichman
during her time at New York University as a postdoctoral student. Now, she is improving
the process so that the quality of the final product is better in two key ways:
The positioning of the building blocks is more accurate, and it is coupled to input
and output fibers in an optimal way.
“What we have achieved is to design a method to fabricate
these materials within the coupling box, putting the coupling optical fibers in
place before we assemble the colloidal particles,” Roichman explained. “This
allows us to assemble the device and position it directly around the input/output
This means that the new material can be fabricated around light
sources such as lasers as well as measuring devices such as power meters and spectrometers.
Until now, this step in the construction involved coupling a device measuring 50
x 50 µm with an accuracy of ±1 µm – a complicated process that must
be done skillfully for the device to work.
In the approach, 2- and 3-D holograms are used: 2-D for first
assembly, and then a sequence of 3-D holograms is projected to guide the particles
into their 3-D positions. Once the 3-D structure is assembled, Roichman shines UV
light onto the fluid to fix the particles within the gel.
To aid construction, the Tel Aviv team has also built a unique
microscope combining HOTs and confocal microscopy. This enables the group to monitor
the fabrication process in real time, ensuring accurate positioning of the particles
and also playing an essential role in optimizing the performance of the devices.
The group is currently working on the design and fabrication of
its first prototype, which it hopes to characterize in the coming year. “I
believe we could use our soft material to make tunable and durable devices,”
Roichman commented. “Ultimately, we plan to apply our technique to make lab-on-a-chip
devices as well as all-optical devices.”