WASHINGTON — Researchers have developed a new type of optical memory called a programmable photonic latch that is fast and scalable. This fundamental memory unit enables temporary data storage in optical processing systems, offering a high-speed solution for volatile memory using silicon photonics.
The new integrated photonic latch is modeled after a set-reset latch, a basic memory device used in electronic devices to store a single bit by switching between set (1) and reset (0) states based on inputs.
"While optical communications and computing have seen significant progress over the past decades, data storage has been predominantly implemented using electronic memory," said the study's author Farshid Ashtiani from Nokia Bell Labs . "Having a fast optical memory that can be used with optical processing systems, as well as other optical systems used in communications or sensing, would make them more efficient in terms of energy and throughput."
In the Optica Publishing Group journal Optics Express , the researchers describe a proof-of-concept experiment in which they demonstrated the photonic latch using a programmable silicon photonic platform. Features such as optical set and reset, complementary outputs, scalability and compatibility with wavelength division multiplexing (WDM) make this approach promising for faster and more efficient optical processing systems.
"Large language models like ChatGPT rely on massive amounts of simple mathematical operations, such as multiplication and addition, performed iteratively to learn and generate answers," said Ashtiani. "Our memory technology could store and retrieve data for such systems at high speeds, enabling much faster operations. While a commercial optical computer is still a distant goal, our high-speed optical memory technology is a step toward this future."
Advancing integrated optical memory
Optical technologies have been instrumental in advancing communication systems, from long-haul data transmission and data center connectivity to emerging technologies like optical interconnects and computing. However, data storage remains predominantly electronic due to its scalability, compactness and cost-effectiveness. This presents challenges for optical processing systems because transferring optical data to electronic memory — and back — increases energy consumption and introduces latency.
Although there has been extensive research in the area of optical memory, most implementations rely on bulky, costly and energy-intensive setups or specialized materials that are not typically offered in commercially available silicon photonic processes, leading to higher costs and lower yields.
To overcome these challenges, the researchers created an integrated programmable photonic latch based on optical universal logic gates using silicon photonic micro-ring modulators. These devices can be implemented in commercially available silicon photonic chip fabrication processes. They combined two optical universal logic gates to create an optical latch that can hold optical data.
Creating memory that is scalable and fast
Ashtiani says that one key advantage of the new system is its scalability. "Because each memory unit has an independent input light source, it is possible to have several memory units working independently without affecting each other through optical power loss propagation," he said. "The memory units can also be co-designed with the existing silicon photonic systems and be built reliably and with very high yields."
Another advantage is the photonic memory unit's wavelength selectivity, which allows it to work seamlessly with WDM. This is because the unit's micro-ring modulators are designed to operate at specific wavelengths, enabling multi-bit data storage within a single memory unit. Additionally, it enables fast memory response time, measured in tens of picoseconds, outpacing the clock speeds of advanced digital systems and supporting high-speed optical data storage.
To demonstrate this approach to optical memory before making dedicated chips, the researchers used a programmable photonic platform to implement the universal logic gates and the optical latch through experiments and realistic simulations.
The researchers tested the gates under different input scenarios. Even in the presence of random variations, the gates reliably generated the desired outputs. Similarly, the latch also performed all functions — set, reset, hold — accurately in the presence of input power variations.
Next, the researchers would like to pursue several research directions to make the new memory units more practical. This includes scaling the technology to a larger number of memory units and fabricating dedicated photonic memory chips. This, combined with the WDM compatibility, would enable higher on-chip photonic memory density. They would also like to develop a way to use a single manufacturing process to integrate both the photonic memory circuit and the electronics needed to control it.
Paper: F. Ashtiani, "Programmable photonic latch memory," Opt. Express, 33, XXXX (2024).
DOI: https://doi.org/10.1364/OE.536535
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