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UCSD Jacobs School of Engineering

Electrical Engineers at UC San Diego Demonstrate Revolutionary Photonic Technology

Team Achieves World Record for Wavelength Translation

San Diego, CA, March 28, 2006 -- Until now much of the investment on equipment to generate, transport and detect signals traveling through optical fiber has revolved around 1.55 micron (infrared) as the standard wavelength for telecommunications. Yet many critical new applications rely on other wavelengths (colors) for optical transmission that hitherto could not be generated, carried or received by today's standard equipment. Now, researchers at the University of California, San Diego (UCSD) have demonstrated a way to build on the dominant infrastructure rather than replace it -- by "translating" optical signals between the current infrared standard and a wide range of other bands of light.

Stojan Radic
UCSD Electrical and Computer Engineering
professor Stojan Radic in the new
Calit2 Photonics Laboratory 

At the Optical Fiber Conference (OFC) in Anaheim, CA, earlier this month, the team from UCSD's Jacobs School of Engineering announced that they successfully used a parametric process in photonic crystal fiber to change the wavelengths of modulated optical channels from 1.55 micron (1550 nanometers) infrared to a visible light signal at half a micron   -- a record 1 micron difference. The researchers measured a difference in frequency between the infrared starting point and the visible-light end point of 375 terahertz (THz), a factor of ten greater than previously achieved.

"This work demonstrates a revolutionary technology for new applications that include airborne and submarine communications, standoff spectroscopy and remote sensing," said Stojan Radic, a professor of Electrical and Computer Engineering (ECE) in the Jacobs School and leader of the UCSD team. "The parametric band translator means that mature telecom technology can be applied to any other wavelength, permitting development of new applications at various bands without requiring huge investment in new infrastructure to replace what already exists."


Calit2 Photonics Laboratory at UCSD

Located on the 6th floor of Atkinson Hall, the Calit2
Photonics Laboratory is one of the first and largest labs
to get up and running since the insitute’s new building
opened last October. Four faculty members based in
the Jacobs School’s Electrical and Computer Engineering
department—Stojan Radic, Shaya Fainman, Joseph Ford
and George Papen—and their graduate students
collaborate in the lab. Currently, the researchers are
participating in four core projects that focus on high-
capacity and unconventional networking research:

Universal Band Translator
This project explores new architectures for distant band
translation and casting (see companion news release).
The lab uses its parametric testbed to explore the
feasibility of frequency translation of standard
communication band over very large spectral ranges,
ranging from ultraviolet to far-infrared. The technology
expected to emerge from this work will leverage the
standard telecommunication infrastructure across any
other optical band, opening new applications in
communications, spectroscopy and sensing.

Electronic Dispersion and ISI Mitigation 
Researchers in the Photonics Lab explore qualitatively
new, electronics technologies for penalty removal in
terrestrial and datacom networks. The group has
demonstrated a world record in transmitting 10-gigabit-
per-second wave division multiplexing (WDM) channels
over more than 600 kilometers of high-dispersion fiber.
The new transmission architecture holds a promise of
dramatically reducing the cost of existing high-capacity
networks, and, more importantly, the first practical
datacom distribution over large distances and high
data rates. 

Ultrawideband WDM Transmission
Conventional transmission utilizes the conventional
transmission window in the 1.5- to 1.6-micron
(1500-1600nm) range, and is limited by excessive
fiber loss outside this band. A new class of fibers
offers considerably wider spectral range, and
potentially could be extended from 1 to 2 microns (or 150
terahertz). The project investigates new means for
ultrawideband division multiplexing, signal
generation, amplification and reception, which could
eventually increase the transmission capacity through
a single fiber one-hundredfold.

Ultrafast and Coherent Signal Processing
The Photonics Lab operates one of the most
advanced parametric testbeds capable of ultra-
fast signal processing, band conversion and quantum-
limited amplification. Parametric interaction in
high-confinement fibers is used to perform packet-
and bit-level signal processing for optical routing,
line protection and ultrafast pattern recognition
applications. In contrast to conventional approaches,
the new technology offers a new, transparent layer
that is inherently rate-independent.

In the UCSD tests, information was encoded into 1.55 micron light, the standard because that is where the glass fiber is most transparent and efficient for transmission, offering tremendous bandwidth up to 12,000 gigahertz. Using a nonlinear optical process, the signal was recreated in a very different 0.5 micron green light and received by a standard visible-light detector. "Other researchers have shown the ability to create new colors of light via nonlinear processes and to move data signals between nearly identical wavelengths," said Radic. "In this case we showed that the wavelengths can be very different and still carry the same high-speed data signal. We completed data recovery with zero errors, even though the new color was very different from the starting color."

Researchers also reported the first multiple channel mapping over the same spectral range, thus demonstrating arbitrary capacity mapping across the entire visible band.

"This is an amazing accomplishment, and Professor Radic never ceases to amaze me with his ambition and vision of what is possible," said Larry Smarr, a professor of computer science and engineering in the Jacobs School and director of the California Institute for Telecommunications and Information Technology (Calit2), which is supporting Radic's work through the institute's new Photonics Lab at UCSD. "This experiment is precisely the type of cutting-edge research that we expect will be a hallmark of the projects enabled as more and more faculty move into the new lab." (For more on the Calit2 Photonics Lab, see box at left.)

The ability to translate signals for transport through the fiber transmission window has dramatic implications for equipment manufacturers and users. Telecom and fiber-optic companies have built generations of lasers, detectors, amplifiers and sophisticated signaling devices around 1.55 micron infrared as the standard. But other wavelengths of light may be better suited for a variety of applications. 
Unfortunately, most technologies developed for 1.55 microns are not available for other parts of the spectral range. Complex, fast phase or amplitude modulation is rarely possible outside of this band, and fast 1.55 micron receivers are superior to those in any other band. There is also no equivalent of the erbium-doped fiber amplifier.

Critical new applications exist outside the standard telecommunication bandwidth. Free-space communication requires mid- and far-infrared bands. Undersea communication uses visible wavelengths, and general sensing applications can occupy any band from ultraviolet to infrared. "Unfortunately," explained Radic, "the development of these new, band-specific technologies would necessarily multiply enormous investments already made in fiber telecommunications."

The paper presented at OFC was co-authored by Radic and fellow ECE professors Shaya Fainman and Joseph Ford, their graduate students, and Bell Labs scientist Colin McKinstrie.* 

Typical measured spectrum in visible
band with the output coupling
According to Radic, the 375 THz parametric translation paves the way for further work on a "universal band translator" (UBT), now under development at UCSD and Calit2. The project's goal is to extend the 1.55 micron technology across the entire optical spectrum, thereby leveraging the enormous investment in telecom so signals can move across any spectral window or application.

Professor Radic and his colleagues have used their extensive experience in parametric fiber technology to pursue the translator concept. The team holds a record in parametric amplification, and it was the first to demonstrate 40-gigabit-per-second, bit-level optical switching and multicasting in parametric fiber.

As it currently stands, the UCSD translator architecture allows for arbitrary band mapping from half a micron to five microns. More demonstrations are planned for the testbed in the newly-built Calit2 Photonics Laboratory.

The translator work is currently funded by the Defense Advanced Research Projects Agency, Lockheed Martin Corporation and the National Science Foundation.

* "375 THz Parametric Translation of Modulated Signal from 1550nm to Visible Band," Rui Jiang, Robert Saperstein, Nikola Alic, Maziar Nezhad, Colin J. McKinstrie, Joseph Ford, Yeshaiahu Fainman and Stojan Radic (all UCSD Electrical and Computer Engineering except Bell Labs' McKinstrie). Postdeadline paper accepted at OFCNFOEC 2006, March 5-10, 2006.

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