Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Tightly focused laser light generates nonlinear effects and rainbow of color

21.05.2004


Physicists at Lehigh University achieve supercontinuum generation in nonlinear fibers

Two physicists at Lehigh University have produced a rainbow of visible and invisible colors by focusing laser light in a specially designed optical fiber that confines light in a glass core whose diameter is 40 times smaller than that of a human hair.

Jean Toulouse, professor of physics, and Iavor Veltchev, research associate in Lehigh’s Center for Optical Technologies (COT), are among the few scientists in the world to achieve and study the phenomenon, which is called "supercontinuum generation in nonlinear fibers."



The phenomenon can be observed in a new class of optical fibers, called photonic crystal fibers. PCFs consist of a tiny solid glass core surrounded by a cladding, or casing, that contains air holes along the length of the fiber.

When Toulouse and Veltchev run a demonstration in their lab, incoming infrared (IR) light waves, which are invisible to the human eye, are converted to visible lightwaves. As the IR light propagates, or spreads, through a 1-meter-long fiber, the light appears, first orange, then yellow and finally green.

IR and UV light of varying wavelengths are also generated at both ends of the visible spectrum.

The visible lightwaves emerge from the fiber as white light, which contains all the colors of the spectrum. The colors are dispersed by the precisely spaced grooves of a diffraction grating, in the same way that water droplets create a rainbow.

Potential uses for supercontinuum generation in nonlinear fiber optics range from medical applications, including non-invasive imaging of live tissues, to all-optical networks, in which light waves, not electronics, perform switching, routing, amplifying and other functions.

Nonlinear optical effects are the main focus of the COT’s All-Optical Network research thrust, which Toulouse directs. Toulouse receives funding from the National Science Foundation.

Supercontinuum generation is not observed in conventional optical fibers, Toulouse says, because their optical intensity (the optical power per unit area) is too low. In the new fibers, the light is confined in a much smaller core and the optical intensity is much greater. This modifies the optical properties of the medium (the fiber), creating new, nonlinear optical effects.

Linear optical effects occur when the optical intensity of light is not great enough to alter the properties of the medium (especially the speed at which the light propagates) through which the light is passing.

Nonlinear effects occur when the light’s optical intensity alters the properties of the medium, which, in turn, affects the manner in which the light itself propagates. The increased intensity, says Veltchev, also causes a corresponding increase in the refraction, or bending, of the light wave by the medium.

Nonlinear effects cause different parts of a wave to move at different velocities and distort the light’s periodic sinusoidal pattern. These effects generate new wavelengths and result in what Toulouse calls an "avalanche effect" - as more wavelengths are generated, more distortion results, leading to yet more wavelengths.

"What we see in the nonlinear regime," says Toulouse, "is that if we send light in at one wavelength, we generate many other wavelengths" - thus achieving supercontinuum generation in nonlinear fiber optics.

The high optical intensity necessary for supercontinuum generation is achieved by the tight confinement of the incoming light wave in the extremely small core of the fiber, says Toulouse.

Toulouse and Veltchev begin their demonstration by using lenses to steer and focus the incident, or incoming, lightwaves with a wavelength (the distance between two adjacent crests of the wave) of approximately 800 nanometers (1 nm is one one-billionth of a meter). At 800 nm, the lightwaves fall within the infrared range and are not visible.

The incident lightwave, being powerful enough, creates nonlinear effects inside the glass fiber, generating new light waves with longer and shorter wavelengths (visible and multi-colored). This is caused by two factors. First, the light waves are confined to a solid glass core inside the optical fiber that measures only 2.5 microns in diameter. (A micron is one one-millionth of a meter; 2.5 microns is roughly one-fourtieth the thickness of a typical human hair.) By contrast, the core of a typical optical fiber, measures 10 microns in diameter. And a typical laser beam has a diameter of about 2 millimeters, almost 1,000 times greater than the diameter of the Lehigh researchers’ new optical fiber core.

The optical intensity (power transmitted per unit area) in the core of these new fibers, says Toulouse, is thus almost 1 million times greater than the intensity in the core of a typical laser, given that the area of a circle equals p times the radius squared.

The creation of nonlinear effects is also triggered by air holes in the cladding around the fiber core. The holes force the light to remain confined inside the narrow glass core, Toulouse says, because "light hates to be in air when it can be in a medium where it travels more slowly."

The tight confinement of light inside the new PCFs forces the waves to propagate coherently (with a well-defined initial-phase relationship), thus producing the full spectrum of visible colors.

The optical fiber used by Toulouse and Veltchev costs up to several thousand dollars per meter, and is manufactured by only five companies in the world, several of which have ties to the COT.

Toulouse has contacts with other researchers who have achieved supercontinuum generation in nonlinear fibers. In 2002, he spent six months studying the nonlinear effects of new types of optical fibers at the University of Bath in England, with the very people who invented PCFs in 1992.

Veltchev has a Ph.D. in physics from the Free University of Amsterdam (The Netherlands) and will soon join the Fox Chase Cancer Research Center near Philadelphia on a project utilizing laser radiation in cancer treatment.

Kurt Pfitzer | EurekAlert!
Further information:
http://www.lehigh.edu/

More articles from Physics and Astronomy:

nachricht The taming of the light screw
22.03.2019 | Max-Planck-Institut für Struktur und Dynamik der Materie

nachricht Magnetic micro-boats
21.03.2019 | Max-Planck-Institut für Polymerforschung

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: The taming of the light screw

DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.

The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...

Im Focus: Magnetic micro-boats

Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.

The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...

Im Focus: Self-healing coating made of corn starch makes small scratches disappear through heat

Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.

Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...

Im Focus: Stellar cartography

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.

A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...

Im Focus: Heading towards a tsunami of light

Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.

"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Modelica Conference with 330 visitors from 21 countries at OTH Regensburg

11.03.2019 | Event News

Selection Completed: 580 Young Scientists from 88 Countries at the Lindau Nobel Laureate Meeting

01.03.2019 | Event News

LightMAT 2019 – 3rd International Conference on Light Materials – Science and Technology

28.02.2019 | Event News

 
Latest News

Solving the efficiency of Gram-negative bacteria

22.03.2019 | Life Sciences

Bacteria bide their time when antibiotics attack

22.03.2019 | Life Sciences

Open source software helps researchers extract key insights from huge sensor datasets

22.03.2019 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>