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One hundred thousand times improvement in silicon’s nonlinearity



Increase Si's nonlinearity 100,000 times

The light scattering intensity in the Mie silicon resonator as a function of the excitation intensity with resonator dimensions is 1

00, 170 and 190 nm. The solid red lines show the corresponding linear responses. Credit: Osaka University

A team of researchers led by Osaka University and National Taiwan University has created a system of nanoscale silicon resonators that can act as logic gates for light pulses. This work could lead to the next generation of silicon-based computer microprocessors that bridge the gap between electronic and optical signals.


Silicon is one of the most abundant elements on our planet – and the basis for all modern computers. That means, from smartphones to mainframe computers, all computation takes place based on electrical signals passed through silicon transistors. Creating switches and logic gates from the electronic signals is very easy, since the voltage can control the current in the other conductors. However, data on the internet is mainly sent as light pulses over fiber optic cables. The ability to control both data and logic entirely with light on silicon could result in devices much faster.

The challenge is that the light particles, called photons, barely interact with each other, so the pulses cannot switch on or off each other to perform logical tasks. Nonlinear optics is the field of study aimed at finding materials in which light beams interact in some way. Unfortunately, the nonlinearity of monocrystalline silicon is extremely weak, so in the past one had to use very powerful lasers.

Now, scientists at Osaka University and National Taiwan University have increased silicon nonlinearity 100,000 times by creating a nano optical resonator, so that the optical switches can work. by using low power laser continuously. They accomplished this by fabricating microscopic resonators out of silicon blocks less than 200 nm in size. Laser light with a wavelength of 592 nm can become trapped inside and rapidly heat blocks, based on the Mie resonance principle. “Mie resonances occur when the size of a nanoparticle matches multiples of the wavelength of light,” says author Yusuke Nagasaki.

Increase Si's nonlinearity 100,000 times

Demonstration of optical switch with controlled light (wavelength 592 nm). The intensity of the signal light (543 nm) is switched by turning ON or OFF the controlled lamp. Credit: Osaka University

With a nanobloc in a heat-induced hot state, a second laser pulse at 543 nm can pass through with virtually no scattering, which does not happen when the first laser turns off. Blocks can cool with relaxation times measured in nanoseconds. This large and fast nonlinearity leads to potential applications for the nano-scale all-GHz control. “Silicon is expected to remain the material of choice for optical integrated circuits and optical devices,” said senior author Junichi Takahara.

Current work allows optical switches to take up much less space than previous efforts. This advancement paves the way for direct on-chip integration as well as hyper-resolution imaging.


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More information:
Yi-Shiou Duh et al., Massive photothermal nonlinearity in a silicon nanostructure, Nature Communications (Year 2020). DOI: 10.1038 / s41467-020-17846-6

Provided by Osaka University

Quote: One hundred thousand-fold improvement in silicon’s nonlinearity (2020, Nov. 4) retrieved November 4, 2020 from https://phys.org/news/2020-11-thousand-fold-nonlinearity -silicon.html

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