Materials that switch from one phase to another when illuminated by light with different polarizations could form a platform for ultrafast photonic computing and information storage, say researchers at the University of Oxford, UK. The materials take the form of structures known as hybridized-active-dielectric nanowires, and the researchers say they could become part of a multiwire system for parallelized data storage, communications and computing.
Because different wavelengths of light do not interact with each other, fibre optic cables can transmit light at multiple wavelengths, carrying streams of data in parallel. Different polarizations of light also do not interact with each other, so in principle each polarization could similarly be employed as an independent information channel. This would allow more information to be stored, dramatically increasing information density.
But while wavelength-selective systems for transmitting data are common, polarization-selective alternatives have not been widely explored, explains study lead author June Sang Lee. “Our work shows the first prototype of programmable device using polarizations and it maximizes the density of information processing,” he tells Physics World. Photonics has a huge advantage over electronics in this respect, he adds, since light travels faster than electrons and functions over large bandwidths. “Indeed, the computing density of our device is several orders of magnitude larger than that of conventional electronics.”
Functional nanowires
The new photonic computing processor consists of functional nanowires made of a phase-change material, Ge2Sb2Te5(GST), and silicon, which acts as a dielectric. The researchers connected the nanowires, each of which is 15 µm long and 180 nm wide, to two metal electrodes. This set-up allowed them to measure the electric current through the GST while they illuminated it with light pulses from a 638-nm-wavelength laser.
When illuminated with this light, the phase of the active material switches reversibly from a highly resistive (amorphous) state to a conductive (crystalline) one. The researchers can therefore use the polarization of the incoming light to tune the absorption of light by the active layer.
Ultrathin nanowires could be a boon for error-resistant quantum computing
“The interesting point is that each nanowire shows a selective switching response to a specific polarization direction of optical pulses,” Lee says. “Using this concept, we have implemented the photonic computing processor with multiple nanowires so that multiple polarizations of light can independently interact with different nanowires and perform parallel computing.”
The researchers describe the study, which is published in Science Advances, as early-stage work towards a large-scale photonic computing device. “We would like to scale up such functionality by changing the device configuration or by using integrated photonic circuits,” Lee reveals. “We would also like to further investigate other nanostructures that can exploit the properties of polarization.”
