From trendy gadgets to large industrial robots, minuscule electronic microchips power the many smart machines we use in our daily lives. Replacing electrons with light to create photonic circuits, however, could bring these chips to new heights.
Not only can high-speed, high-bandwidth photonic circuits lead to faster and more efficient optical computers, but they can also be used for other purposes like biosensing and quantum computing. Miniaturizing photonic circuits like traditional chips means shrinking a basic photonic component: waveguides, also known as the ‘wires’ of photonic circuitry that transmit light from one location to the next.
To replace the current bulky waveguides, researchers at A*STAR led by study first author Lu Ding, a Scientist at the Institute of Materials Research and Engineering (IMRE), designed a subwavelength nanochain waveguide capable of transmitting infrared light with low losses at a smaller footprint. Notably, while their nanochains are less bulky than conventional waveguides, they can still be manufactured using standard silicon fabrication techniques.
“A nanochain waveguide consists of a chain of identical silicon nanoparticles specially engineered to resonate at a particular frequency of light and guide the light,” explained Thomas Ang, a Scientist at A*STAR’s Institute of High Performance Computing (IHPC) who performed simulations for this study.
Despite their promise, the previous proof-of-concept nanochain waveguide tested by the group were inefficient light transmitters at wavelengths 960 nm and 720 nm, with propagation losses between 5.5 and 34 dB/mm due to large material losses, respectively. “To avoid material absorption in silicon, we redesigned the nanochains to operate using near infrared light at a wavelength of about 1550 nm, which silicon is more efficient at transmitting,” Lu and Ang added.
When the team tested the new nanochain waveguide, they found that the propagation loss had been reduced to between 0.1 and 0.3 dB/mm—far lower than their previous prototypes, and comparable to conventional single mode silicon waveguides. The team also introduced raindrop-shaped optical couplers that shunt light into narrower nanoparticles, further reducing the losses associated with inserting or extracting light from the nanochain waveguide.
Moreover, the nanochain waveguides showed a ‘slow light’ effect—where light pulses pass through the waveguide at only three percent of light’s speed in vacuum. “The slow light in a nanochain waveguide leads to strong light-matter interactions, which has potential applications for better light control in optical communications, quantum photonics or biosensing platforms,” said Lu.
Having demonstrated the capabilities of silicon nanoparticle chains as efficient waveguides, the team hopes to expand their functionalities moving forward. Further modifying the structure and arrangement of the nanoparticles could enable the waveguides to control the polarization, propagation direction and other optical features of light signals, making them versatile and powerful components for integrated photonics.
The A*STAR researchers contributing to this work are from the Institute of Materials Research and Engineering (IMRE) and the Institute of High Performance Computing (IHPC).
