Running your finger along the rim of a wineglass produces a haunting, clear tone—a beautiful demonstration of resonance, as mechanical energy excites the glass to ‘sing’ at its natural frequency. A wineglass ‘orchestra’ can even be made by filling the glasses with different amounts of water to modify their frequencies and produce different notes.
Instead of resonating with sound, scientists are designing materials at the nanoscale that resonate with light, also known as optical resonators. Current optical resonators such as gratings or photonic crystals use regular spacings between nanostructures to resonate with the desired wavelength of light.
“Optical resonators can trap large amounts of light energy in a very small volume, allowing us to build compact devices that manipulate light on the nanoscale—nanophotonics—or even replace electrical signals with light—optoelectronics,” said Arseniy Kuznetsov, a Principal Scientist at A*STAR’s Institute of Materials Research and Engineering (IMRE) who led the study.
To build a more sensitive and effective optical resonator, Kuznetsov’s team turned to silicon, which changes its refractive index when pumped with visible light energy. The goal? To develop a compact optical resonator that can be switched on and off quickly and efficiently using light input alone.
Together with colleagues from A*STAR’s Institute of Microelectronics (IME), Kuznetsov’s team designed and fabricated a chain of silicon nanoblocks, with both the dimensions of the blocks and the spacing between blocks optimized for infrared resonance.
“Our one-dimensional nanoparticle chain resonator is composed of a series of silicon nanoantennas (resonant nanoparticles) embedded in silicon dioxide cladding,” he explained. “Under optical excitation, the silicon nanoantenna absorbs light and the refractive index of silicon is modified by the photo-generated free carriers.”
Their experiments confirmed that the nanochain resonated with the correct wavelength of infrared light, and that a short visible laser pulse could indeed shift the resonance enough to prevent the original infrared wavelength from resonating inside the nanochain.
“The collective nature of the nanochain resonance makes it extremely sensitive to any induced changes, which allowed us to switch the device on and off by light alone, using far less laser power compared to competing designs,” Kuznetsov said. “The low power also prevented the device from accumulating heat, allowing it to be switched on and off within nanoseconds.”
The researchers are now investigating if their highly sensitive silicon nanochain resonator can be used to sense biological molecules such as DNA or proteins. “We are also hoping to develop compact modulator devices based on the nanochain for use in optical communications and optoelectronics,” he added.
The A*STAR-affiliated researchers contributing to this work are from the Institute of Materials Research and Engineering (IMRE) and the Institute of Microelectronics (IME).