A hundred thousand times improvement in silicon non-linearity

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

Silicon is among the elements in abundance on our planet and is the basis of all modern computers. That is, from smartphones to mainframes, all calculations occur on the basis of electrical signals flowing through the silicon transistors. Making switches and logic gates from electronic signals is easy, as voltages can control the flow of current in other wires. However, data on the Internet is mainly sent as pulses of light over fiber optic cables. The ability to fully control both data and logic with light on silicon could lead to much faster devices.

The challenge is that particles of light, called photons, barely interact with each other, so the pulses cannot turn each other on or off to perform logical tasks. Non-linear optics is the field of study that works to find materials in which beams of light interact in some way. Unfortunately, the non-linearity of monocrystalline silicon is extremely weak, so in the past it was necessary to use very intense lasers.

Now, scientists from Osaka University and National Taiwan University have increased silicon non-linearity by 100,000 times by creating a nano-optical resonator, so that fully optical switches can be operated using a low-power continuous laser. . They accomplished this by manufacturing tiny resonators from silicon blocks smaller than 200 nm in size. Laser light with a wavelength of 592 nm can get trapped inside and heat the blocks quickly, based on the Mie resonance principle. “A Mie resonance occurs when the size of a nanoparticle is a multiple of the wavelength of light,” says lead author Yusuke Nagasaki.

With a nanoblock in a thermo-optically induced hot state, a second 543 nm laser pulse can pass almost without scattering, which is not the case when the first laser is turned off. The block can cool down with relaxation times measured in nanoseconds. This large and rapid non-linearity leads to potential applications for full optical GHz control at the nanoscale. “Silicon is expected to remain the material of choice for optical integrated circuits and optical devices,” says senior author Junichi Takahara.

Current work allows for optical switches that take up much less space than previous attempts. This advance paves the way for direct-on-chip integration and super-resolution imaging.