Fiber optics has emerged as the leading technology for high-speed and reliable internet connectivity. It leverages the transmission of data through pulses of light that bounce off the walls of fiber cables, allowing signals to travel longer distances with minimal loss. However, dispersion, which refers to signal degradation in optical fibers, remains a challenge in fiber data transmission. Dispersion compensation methods have been developed to address this issue, with on-chip devices showing promise in extending signal reach. Researchers from the Photonics Devices and Systems Group at Singapore University of Technology and Design (SUTD), led by Associate Professor Dawn Tan, aimed to bridge the gap in on-chip dispersion compensation for high-speed data.
The research team focused on gratings, as they possess advantageous transmission and phase properties, making them ideal for integrated dispersive devices. Drawing on their expertise in grating design, the team developed a groundbreaking dispersive device using silicon nitride, which was compatible with complementary metal-oxide semiconductor (CMOS) technology. Their device fulfilled three key criteria: high dispersion, low data loss, and a small form factor suitable for on-chip integration.
Existing dispersive devices with high dispersion often suffer from high data loss, while those with low data loss lack the necessary dispersion. The researchers addressed this challenge by designing two types of grating devices: a single grating device (SGD) with a pitch of 434 nanometers and an overlaid grating device (OGD) with two gratings having dissimilar pitches of 434 and 440 nanometers. Both devices exhibited similar transmission spectra, generating a slow-light effect that resulted in high dispersion while minimizing data loss.
In their study, both SGD and OGD demonstrated effective dispersion compensation for long fiber distances of up to 20 kilometers with minimal loss. Additionally, the devices significantly improved error correction performance, reducing bit error rates by nine orders of magnitude. The OGD, in particular, offered a range of dispersion values suitable for dynamic dispersion compensation, which can simplify dispersion compensation systems and mitigate temperature or fiber stress effects on data transmission.
The integration of SGD and OGD into commercial transceivers, either within the transmitter or receiver chips, proved feasible and advantageous. These devices are compatible with CMOS manufacturing processes, enabling wider fiber reach and higher data rates.
Associate Professor Tan intends to collaborate with industry partners to commercialize these novel grating devices, preferably with transceiver manufacturers to enhance their chip performance through integrated dispersion compensation. Future research will focus on further improving dispersion performance, exploring supported data rates and fiber distances, refining device mechanisms, developing new grating designs, and exploring additional applications for gratings.