UCLA Builds Terasample Per Second Digitizer

UCLA researchers said that they have developed digitizer technology that captures a signal 50 times faster than any instrument commercially available. Part of the challenge of incorporating high-speed electrical signals into viable applications has been the ability to effectively digitize and then analyze those analog signals. Test and measurement instrument vendors have incorporated silicon germanium chips and similar technologies into their instruments to get their digitizers and oscilloscopes into the multiple gigahertz/gigasamples per second range. Now professor Bahram Jalali and graduate researcher Yan Han at UCLA's Henry Samueli School of Engineering and Applied Science say they have been able to capture and digitize an electrical signal at the rate of 1 trillion times per second. They unveiled their terasample per second single-shot digitizer at the 2005 American Physical Society's March meeting at the Los Angeles Convention Center.

Using light to slow down electrical pulses, ultra-fast waveforms can be digitized at picosecond intervals, or one-millionth of one-millionth of a second, the researchers said. But they don't have their eyes set on faster consumer gadgets or PC buses; they envision the technology's as a countermeasure against a so-called microwave "e-bomb."

Theoretically, a burst of high power electromagnetic energy could be created and directed at an electronics system; the resulting ultra-fast burst of charge burns it out, much like lightning can destroy objects in its path, the researchers explained. Such a weapon theoretically could damage computer networks and destroy wireless communication equipment and radar systems.

"As electronic devices become smaller and faster, they also become more susceptible to outside interference," Jalali said in a statement. "In order to make equipment more robust, to shield it from electromagnetic attacks, you first have to understand what kind of signals you're dealing with.

Because the pulses we're talking about are one-time events and are extremely fast, their capture and analysis eludes conventional digitizers," he said. "That's exactly what our technique allows."

That technique is the culmination of eight years of research, funded by the Defense Advanced Research Project Agency (DARPA), according to the researchers.

Using Light to Slow Down Electricity – So to Speak

To capture the pulses in question, the team at UCLA uses an optical time-dilation processor followed by a conventional electronic digitizer. The time-dilator takes the ultra-fast event and slows it down so the digitizer can capture the signal. Although the processor's input and output are electrical, the actual time manipulation is done in the optical domain, according to the researchers.

"Imagine you have a flat rubber band and you draw an arrow on it. The arrow's length reflects the duration of the event," Jalali explained. "When you stretch the rubber band, the arrow is elongated, meaning that the event now occurs over a longer time -- in other words, the event is slowed down in time.

"With our technique, a laser pulse is the rubber band," he continued. "An optical modulator writes the ultra-fast waveform onto the optical pulse. The composite signal is then slowed down in a dispersive optical device, such as a chain of optical resonators made on a silicon chip. A photo detector then converts everything to the electrical domain and gives a slowed-down copy of the original electrical waveform."

The team at UCLA also has shown that the resulting time-elasticity can be used to perform time compression and time reversal, capabilities that have application in advanced radar systems.

UCLA's approach has other significant ramifications for areas of research such as particle physics, among others, the researchers say. For example, the technique also will allow physicists to capture the smashing of particles, and by analyzing that instant, peer into the very fundamental building blocks of nature on the smallest scale.

RadiaBeam Technologies LLC of Los Angeles already has entered into licensing negotiations with UCLA for the patents that led to the breakthrough. The company plans to commercialize the technology and produce a laboratory tool for high-energy physics research, according to Salime Boucher, president of RadiaBeam.

"We see a market for this breakthrough with research laboratories involved in ultra-fast phenomena and transient events, as well as for future applications by engineering and technology companies in the communication, chemical engineering and life science sectors," Boucher said in a statement.


A research prototype already is in development for space applications.

"Direct digitization of signals in the 10GHZ to 100GHz band and beyond offers incredible opportunities for new applications in communications, spectroscopy and radar," George C. Valley, senior scientist at the Aerospace Corp., said in a statement. The company is researching the time stretch analog to digital converter (ADC) for potential space applications.

"Besides breaking the terasample-per-second rate barrier, the results reported by Jalali's group at UCLA beat other photonic ADC technologies by about a factor of 10 in the key figure of merit, bit rate times number of quantization levels," Valley said.

All of the necessary optical components, including pulsed lasers, optical modulators, amplifiers and dispersive elements have already been made using silicon, the researchers said. The recent advances in silicon photonics make it possible to integrate the entire digitizer on a silicon chip.