‘Plasmonic’ material could bring ultrafast all-optical communications

August 7, 2015

This rendering depicts a new “plasmonic oxide material” that could make possible devices for optical communications that are at least 10 times faster than conventional technologies (credit: Purdue University/Nathaniel Kinsey)

Researchers at Purdue University have created a new “plasmonic oxide material” that could make possible modulator devices for optical communications (fiber optics, used for the Internet and cable television) that are at least 10 times faster than conventional technologies.

The optical material, made of aluminum-doped zinc oxide (AZO) also requires less power than other “all-optical” semiconductor devices. That is essential for the faster operation, which would otherwise generate excessive heat with the increase transmission speed.

The material has been shown to work in the near-infrared range of the spectrum, which is used in optical communications, and it is compatible with the CMOS semiconductor manufacturing process used to construct integrated circuits.

Faster optical transistors replace silicon

The researchers have proposed creating an “all-optical plasmonic modulator using CMOS-compatible materials,” or an optical transistor, which allows for the speedup compared to systems that use silicon chips.

A cycle takes about 350 femtoseconds to complete in the new AZO films, which is roughly 5,000 times faster than crystalline silicon.

The researchers “doped” zinc oxide with aluminum (thus the AZO), meaning the zinc oxide is impregnated with aluminum atoms to alter the material’s optical properties. Doping the zinc oxide causes it to behave like a metal at certain wavelengths and like a dielectric at other wavelengths.

The AZO also makes it possible to “tune” the optical properties of metamaterials.

Findings were detailed in an open-access research paper appearing in July in the journal Optica, published by the Optical Society of America.

The ongoing research is funded by the Air Force Office of Scientific Research, a Marie Curie Outgoing International Fellowship, the National Science Foundation, and the Office of Naval Research.


Abstract of Epsilon-near-zero Al-doped ZnO for ultrafast switching at telecom wavelengths

Transparent conducting oxides have recently gained great attention as CMOS-compatible materials for applications in nanophotonics due to their low optical loss, metal-like behavior, versatile/tailorable optical properties, and established fabrication procedures. In particular, aluminum-doped zinc oxide (AZO) is very attractive because its dielectric per-mittivity can be engineered over a broad range in the near-IR and IR. However, despite all these beneficial features, the slow (>100 ps) electron-hole recombination time typical of these compounds still represents a fundamental limitation impeding ultrafast optical modulation. Here we report the first epsilon-near-zero AZO thin films that simultaneously exhibit ultrafast carrier dynamics (excitation and recombination time below 1 ps) and an outstanding reflectance modulation up to 40% for very low pump fluence levels (<4 mJ∕cm2) at a telecom wavelength of 1.3 μm. The unique properties of the demonstrated AZO thin films are the result of a low-temperature fabrication procedure promoting deep-level defects within the film and an ultrahigh carrier concentration. © 2015 Optical Society of America