Researchers demonstrate 40-channel optical communication link

A silicon-based device could help meet the ever-growing need to move more data faster

WASHINGTON — Researchers have demonstrated a silicon-based optical communications link that combines two multiplexing technologies to create 40 optical data channels capable of simultaneously moving data. The new chip-scale optical interconnect can transmit approximately 400 GB of data per second, equivalent to approximately 100,000 streaming movies. It could improve data-intensive Internet applications, from video streaming services to high-capacity transactions for the stock market.

Caption: Researchers have designed and optimized a modal multiplexer that transforms each of the 10 wavelengths into four new beams, each with different shapes. This quadrupling of data capacity creates 40 channels.

Image credit: Kiyoul Yang, Stanford University

“As demands to transfer more information over the Internet continue to grow, we need new technologies to push data rates further,” said Peter Delfyett, who led the University of Central Florida. College of Optics and Photonics (CREOL) Research Team. “Because optical interconnects can move more data than their electronic counterparts, our work could enable better and faster data processing in the data centers that form the backbone of the Internet.”

A group of multi-institutional researchers describes the new optical communication link in the Optica Publishing Group Optical Letters magazine. It achieves 40 channels by combining a frequency comb light source based on a new photonic crystal resonator developed by the National Institute of Standards and Technology (NIST) with an optimized mode division multiplexer designed by Stanford University researchers. Each channel can be used to carry information just as different stereo channels, or frequencies, carry different music stations.

“We show that these new frequency combs can be used in fully integrated optical interconnects,” said Chinmay Shirpurkar, co-first author of the paper. “All photonic components were fabricated from a silicon-based material, demonstrating the potential for fabricating optical information processing devices from low-cost, easy-to-fabricate optical interconnects.”

In addition to improving data transmission over the Internet, the new technology could also be used to make faster optical computers that could provide the high levels of computing power needed for artificial intelligence, machine learning, large-scale emulation and other applications.

Using multiple dimensions of light

The new work involved research teams led by Firooz Aflatouni from University of PennsylvaniaScott B. Papp of NIST, Jelena Vuckovic of Stanford University and Delfyett of CREOL. It is part of the DARPA Photonics in the Package for Extreme Scalability (PIPES) program, which aims to use light to dramatically improve the digital connectivity of packaged integrated circuits using microcomb-based light sources.

Caption: Researchers have demonstrated a silicon-based optical communications link that combines two multiplexing technologies to create 40 optical data channels. The ring-shaped photonic crystal resonator (left) has a nanopattern inside (right) that splits a selected resonance mode for comb generation. Images taken with a scanning electron microscope

Image credit: Su-Peng Yu, NIST

The researchers created the optical link using tantalum pentoxide (Ta2O5) waveguides on a silicon substrate fabricated in a ring with nanoscale oscillation on the inner wall. The resulting photonic crystal micro-ring resonator transforms a laser input into ten different wavelengths. They also designed and optimized a modal multiplexer that transforms each wavelength into four new beams, each with different shapes. Adding this spatial dimension quadruples the data capacity, creating the 40 channels.

After data is encoded on each beam shape and each beam color, the light is recombined into a single beam and transmitted to its destination. At the final destination, wavelengths and beam shapes are separated so that each channel can be received and detected independently, without interference from other transmitted channels.

“An advantage of our link is that the photonic crystal resonator allows for easier soliton generation and a flatter comb spectrum than those demonstrated with conventional ring resonators,” said NIST co-first author Jizhao Zang. “These features are beneficial for optical data links.”

Better performance with inverted design

To optimize the modal split multiplexer, the researchers used a computational nanophotonic design approach called photonic inverse design. This method provides a more efficient way to explore a full range of possible designs while providing smaller footprints, better efficiency, and new functionality.

“The photonic inverse design approach makes our link highly customizable to meet specific application needs,” said co-first author Kiyoul Yang of Stanford University.

Tests of the new device matched the simulations well and showed that the channels exhibited low crosstalk of less than -20 dB. Using less than -10 dBm of received optical receive power, the link performed error-free data transmission in 34 of 40 channels using a PRBS31 model, a standard used for stress testing high-speed circuits.

Researchers are now working to further improve the device by incorporating photonic crystal micro-ring resonators that produce more wavelengths or by using more complex beam shapes. Commercialization of these devices would require full integration of a transmitter and receiver chip with high bandwidth, low power consumption and small footprint. This could enable the next generation of optical interconnects for use in data center networks.

The open source code of the photonic optimization software used in the article is available at https://github.com/stanfordnqp/spins-b.

Article: C. Shirpurkar, J. Zang, KY Yang, D. Carlson, SP Yu, E. Lucas, SV Pericherla, J. Yang, M. Guidry, D. Lukin, GH Ahn, J. Lu, L. Trask, F. Aflatouni, J. Vuĉkovic, SB Papp, PJ Delfyett, “Photonic crystal resonators for inversely designed multidimensional optical interconnects”, Opt. Lett., 47, 12 (2022).

DO I: 10.1364/OL.461272

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