Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Counting the twists in a helical light beam

09.01.2013
New device could contribute to a major increase in the rate of future optical communications
At a time when communication networks are scrambling for ways to transmit more data over limited bandwidth, a type of twisted light wave is gaining new attention. Called an optical vortex or vortex beam, this complex beam resembles a corkscrew, with waves that rotate as they travel.

Now, applied physicists at the Harvard School of Engineering and Applied Sciences (SEAS) have created a new device that enables a conventional optical detector (which would normally only measure the light's intensity) to pick up on that rotation.

The device, described in the journal Nature Communications, has the potential to add capacity to future optical communication networks.

"Sophisticated optical detectors for vortex beams have been developed before, but they have always been complex, expensive, and bulky,” says principal investigator Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS.

In contrast, the new device simply adds a metallic pattern to the window of a commercially available, low-cost photodetector. Each pattern is designed to couple with a particular type of incoming vortex beam by matching its orbital angular momentum—the number of twists per wavelength in an optical vortex.

Sensitive to the beam’s “twistiness,” this new detector can effectively distinguish between different types of vortex beams. Existing communications systems maximize bandwidth by sending many messages simultaneously, each a fraction of a wavelength apart; this is known as wavelength division multiplexing. Vortex beams can add an additional level of multiplexing and therefore should expand the capacity of these systems.

"In recent years, researchers have come to realize that there is a limit to the information transfer rate of about 100 terabits per second per fiber for communication systems that use wavelength division multiplexing to increase the capacity of single-mode optical fibers," explains Capasso. "In the future, this capacity could be greatly increased by using vortex beams transmitted on special multicore or multimode fibers. For a transmission system based on this 'spatial division multiplexing' to provide the extra capacity, special detectors capable of sorting out the type of vortex transmitted will be essential."

The new detector is able to tell one type of vortex beam from another due to its precise nanoscale patterning. When a vortex beam with the correct number of coils per wavelength strikes the gold plating on the detector’s surface, it encounters a holographic interference pattern that has been etched into the gold. This nanoscale patterning allows the light to excite the metal's electrons in exactly the right way to produce a focused electromagnetic wave, known as a surface plasmon. The light component of this wave then shines through a series of perforations in the gold, and lands on the photodetector below.

If the incoming light doesn't match the interference pattern, the plasmon beam fails to focus or converge and is blocked from reaching the detector.
Capasso's research team has demonstrated this process using vortex beams with orbital angular momentum of −1, 0, and 1.

"In principle, an array of many different couplers and detectors could be set up to read data transmitted on a very large number of channels," says lead author Patrice Genevet, a research associate in applied physics at SEAS. “With this approach, we transform detectors that were originally only sensitive to the intensity of light, so that they monitor the twist of the wavefronts. More than just detecting a specific twisted beam, our detectors gather additional information on the phase of the light beam.”

The device's ability to detect and distinguish vortex beams is important for optical communications, but its capabilities may extend beyond what has been demonstrated.

"Using the same holographic approach, the same device patterned in different ways should be able to couple any type of free-space light beam into any type of surface wave," says Genevet.

Coauthors on this work included Jiao Lin, a former postdoctoral fellow in Capasso’s lab (now at the Singapore Institute of Manufacturing Technology), and Harvard graduate student Mikhail A. Kats.

The research was supported by the U.S. Air Force Office of Scientific Research, the U.S. Intelligence Advanced Research Projects Agency, and through research fellowships from the Agency for Science, Technology, and Research in Singapore and the U.S. National Science Foundation (NSF). The researchers also benefited from facilities at Harvard's Center for Nanoscale Systems, a member of the NSF-supported National Nanotechnology Infrastructure Network.

Caroline Perry | EurekAlert!
Further information:
http://www.seas.harvard.edu

More articles from Physics and Astronomy:

nachricht Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

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

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...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

IHP presents the fastest silicon-based transistor in the world

05.12.2016 | Power and Electrical Engineering

InLight study: insights into chemical processes using light

05.12.2016 | Materials Sciences

High-precision magnetic field sensing

05.12.2016 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>