Researchers develop ultrafast oscilloscope on a chip

Nov 06, 2008 By Bill Steele
In the ultrafast optical oscilloscope developed at Cornell, light from a broadband laser is passed through a length of optical fiber that spreads it into a pulse whose wavelength varies with time; and mixed with an optical signal -- also passed through a delay to match -- whose intensity varies with time. The readout is a new pulse whose spectrum matches the original waveform. The technique can display waveforms stretching over just a few picoseconds with a resolution of a few femtoseconds.

( -- As photonics -- using beams of light in place of electricity for communications and computing -- becomes more common, engineers need new tools for troubleshooting. Now researchers at Cornell have created a way to plot the waveform of an ultrashort-lived optical signal with a resolution of less than a trillionth of a second.

Several current methods can measure such brief waveforms by averaging many repeating events, but the new method -- using an "ultrafast optical oscilloscope" -- can catch those frustrating events that happen only once in a while, the Cornell researchers said.

"We can make measurements of very short optical phenomena. The signal can be very weak, and it doesn't have to be repetitive," said Alexander Gaeta, Cornell professor of applied and engineering physics. Applications include analyzing intermittent glitches in fiber-optic communications and observing such fast-moving events as chemical reactions or laser fusion, he said.

The device is described in the Nov. 6 issue of the journal Nature (455: 7218) by Gaeta and colleagues including Michal Lipson, associate professor of electrical and computer engineering, and postdoctoral researcher Mark Foster.

The innovation converts "time to frequency" using a process called four-wave mixing, in which two beams of light, referred to as the signal and the pump, are combined in a narrow channel -- in this case a silicon waveguide on a chip, 300-by-750 nanometers in cross section. The narrow space forces the two beams to exchange energy, and a copy of the signal at a new wavelength emerges. The wavelength of the copy depends on the wavelength of the pump, and for this application the wavelength of the pump changes linearly in time.

The pump pulse is generated by a laser that outputs a broad band of wavelengths, and sent through a 50-meter length of optical fiber. Each wavelength of light travels at a slightly different speed in the fiber, so the pump pulse stretches into a stream in which wavelength varies continuously over time. In the four-wave mixing chip the stream is combined with the waveform to be analyzed, which varies in intensity over time. What emerges is a pulse in which each tiny moment of the input waveform is represented by a different wavelength of light, and the intensity, or brightness, of the light at that wavelength corresponds to the intensity of the input wave at that moment.

The result is fed into a spectrometer, which produces a graph of the intensity of light at each wavelength, and that graph corresponds to the original temporal waveform.

Lipson's research group is developing a dispersive waveguide on a chip that will replace the 50 meters of fiber, as well as a spectrometer on a chip, Gaeta said, so that the entire device eventually can be fabricated on a single chip.

The work is supported by the Defense Advanced Research Projects Agency, the National Science Foundation and the New York Office of Science, Technology and Academic Research.

Provided by Cornell University

Explore further: What's fair?: New theory on income inequality

Related Stories

A conversation with astronomer Dimitri Mawet

May 18, 2015

Associate Professor of Astronomy Dimitri Mawet has joined Caltech from the Paranal Observatory in Chile, where he was a staff astronomer for the Very Large Telescope. After earning his PhD at the University ...

The trillion-frame-per-second camera

Apr 29, 2015

When a crystal lattice is excited by a laser pulse, waves of jostling atoms can travel through the material at close to one sixth the speed of light, or approximately 28,000 miles/second. Scientists now have ...

Building a more versatile frequency comb

Feb 17, 2015

Frequency combs are the rulers of light. By counting a wavelength's many oscillations, they measure distance and time with extraordinary precision and speed.

Recommended for you

What's fair?: New theory on income inequality

9 hours ago

The increasing inequality in income and wealth in recent years, together with excessive pay packages of CEOs in the U.S. and abroad, is of growing concern, especially to policy makers. Income inequality was ...

Scientists one step closer to mimicking gamma-ray bursts

15 hours ago

Using ever more energetic lasers, Lawrence Livermore researchers have produced a record high number of electron-positron pairs, opening exciting opportunities to study extreme astrophysical processes, such ...

On-demand X-rays at synchrotron light sources

May 26, 2015

Consumers are now in the era of "on-demand" entertainment, in which they have access to the books, music and movies they want thanks to the internet. Likewise, scientists who use synchrotron light sources ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.