U. PITTSBURGH (US) — Researchers have demonstrated a physical basis for terahertz bandwidth that could make smartphones and laptops 1,000 times faster than current communication technologies.
Many products today rely on the function of light or, more specifically, on applying information to a light wave. Up until now, research on electronic and optical devices with materials that are the basis of radio, TV, and computers have generally relied on nonlinear optical effects, producing devices with bandwidths limited to the gigahertz (GHz) frequency region. Hertz stands for cycles per second of a periodic phenomenon, in this case 1 billion cycles.
In a paper published in Nature Photonics, Hrvoje Petek, professor of physics and chemistry at the University of Pittsburgh, details his success in generating a frequency comb—dividing a single color of light into a series of evenly spaced spectral lines for a variety of uses—that spans a more than 100 terahertz bandwidth by exciting a coherent collective of atomic motions in a semiconductor silicon crystal.
Terahertz bandwidth (one trillion cycles per second) is the portion of the electromagnetic spectrum between infrared and microwave light.
“The ability to modulate light with such a bandwidth could increase the amount of information carried by more than 1,000 times when compared to the volume carried with today’s technologies,” Petek says. “Needless to say, this has been a long-awaited discovery in the field.”
To investigate the optical properties of a silicon crystal, Petek and his team investigated the change in reflectivity after excitation with an intense laser pulse.
Following the excitation, the team observed that the amount of reflected light oscillates at 15.6 THz, the highest mechanical frequency of atoms within a silicon lattice. This oscillation caused additional change in the absorption and reflection of light, multiplying the fundamental oscillation frequency by up to seven times to generate the comb of frequencies extending beyond 100 THz. Petek and his team were able to observe the production of such a comb of frequencies from a crystalline solid for the first time.
“Although we expected to see the oscillation at 15.6 THz, we did not realize that its excitation could change the properties of silicon in such dramatic fashion,” says Petek. “The discovery was both the result of developing unique instrumentation and incisive analysis by the team members.”
Petek notes the team’s achievements are the result of developing experimental and theoretical tools to better understand how electrons and atoms interact in solids under intense optical excitation and of the invested interest by Pitt’s Dietrich School in advanced instrumentation and laboratory infrastructure.
The team is currently investigating the coherent oscillation of electrons, which could further extend the ability of harnessing light-matter interactions from the terahertz- to petahertz-frequency range. Petahertz is a unit of measure for very fast frequencies (1 quadrillion hertz).
This research was funded by a grant from the National Science Foundation.
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