Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

29.11.2016

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent gradient refractive index (GRIN) micro-optics by electrochemically etching preformed Si micro-structures, like square columns, PSi structures with defined refractive index profiles.


Figure shows how the PSi square GRIN microlens focuses and splits TM and TE polarized light, respectively. TM polarized light is focused to one point and TE polarized light is focused to two different points. The refractive index gradient for the square microlens under the two different polarizations is illustrated using the color map overlaid on the lens (blue is low refractive index, and orange is high refractive index).

Credit: University of Illinois

"The emergence and growth of transformation optics over the past decade has revitalized interest in using GRIN optics to control light propagation," explained Paul Braun, the Ivan Racheff Professor of Materials Science and Engineering at Illinois.

"In this work, we have figured out how to couple the starting shape of the silicon micro-structure and the etch conditions to realize a unique set of desirable optical qualities. For example, these elements exhibit novel polarization-dependent optical functions, including splitting and focusing, expanding the use of porous silicon for a wide range of integrated photonics applications.

"The key is that the optical properties are a function of the etch current," Braun said. "If you change the etch current, you change the refractive index. We also think that the fact that we can create the structures in silicon is important, as silicon is important for photovoltaic, imaging, and integrated optics applications.

"Our demonstration using a three-dimensional, lithographically-defined silicon platform not only displayed the power of GRIN optics, but it also illustrated it in a promising form factor and material for integration within photonic integrated circuits," stated Neil Krueger, a former PhD student in Braun's research group and first author of the paper, "Porous Silicon Gradient Refractive Index Micro-Optics," appearing in Nano Letters.

"The real novelty of our work is that we are doing this in a three-dimensional optical element," added Krueger, who has recently joined Honeywell Aerospace as a Scientist in Advanced Technology. "This gives added control over the behavior of our structures given that light follows curvilinear optical paths in optically inhomogeneous media such as GRIN elements. The birefringent nature of these structures is an added bonus because coupled birefringent/GRIN effects provide an opportunity for a GRIN element to perform distinct, polarization-selective operations."

According to the researchers, PSi was initially studied due to its visible luminescence at room temperature, but more recently, as this and other reports have shown, has proven to be a versatile optical material, as its nanoscale porosity (and thus refractive index) can be modulated during its electrochemical fabrication.

"The beauty of this 3D fabrication process is that it is fast and scalable," commented Weijun Zhou at Dow. "Large scale, nanostructured GRIN components can be readily made to enable a variety of new industry applications such as advanced imaging, microscopy, and beam shaping."

"Because the etching process enables modulation of the refractive index, this approach makes it possible to decouple the optical performance and the physical shape of the optical element," Braun added. "Thus, for example, a lens can be formed without having to conform to the shape that we think of for a lens, opening up new opportunities in the design of integrated silicon optics."

###

Paul Braun is also the director of the Frederick Seitz Materials Research Laboratory at Illinois. In addition to Braun, Krueger, and Zhou, co-authors of the paper include Seung-Kyun Kang, Christian R. Ocier, Glennys Mensing, and John A. Rogers (University of Illinois), Aaron L. Holsteen and Mark L. Brongersma (Stanford University).

Paul Braun | EurekAlert!

More articles from Materials Sciences:

nachricht Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern
20.07.2018 | Princeton University

nachricht Relax, just break it
20.07.2018 | DOE/Argonne National Laboratory

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Future electronic components to be printed like newspapers

A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.

The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

A smart safe rechargeable zinc ion battery based on sol-gel transition electrolytes

20.07.2018 | Power and Electrical Engineering

Reversing cause and effect is no trouble for quantum computers

20.07.2018 | Information Technology

Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern

20.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>