STANFORD, California, May 1, 2023 โ Researchers at Stanford University have developed a light-based computing scheme that uses a photonic integrated circuit to reduce the power needed for cryptocurrency and blockchain applications. Mining cryptocurrencies like Bitcoin, a process of verifying transactions and adding new cryptocurrencies to the blockchain, consumes up to 1% of the world's energy. This energy expenditure is expected to grow as cryptocurrency and blockchain applications become more common.
Cryptocurrencies are digital currencies created using encryption algorithms. These altcoins require a blockchain, a type of digital ledger that records information, such as transactions, in a way that is difficult or impossible to change or hack.
Researchers have developed a new light-based computing scheme called LightHash that reduces the power needed for cryptocurrency and blockchain applications. First author Sunil Pai is pictured in the optical setup used for the new research. Courtesy of LightHash.
"Cryptocurrency mining is currently only accessible to those who have access to deeply discounted power, below $0.05/kWh," said first author Sunil Pai, who conducted the research at Stanford and is now at the quantum computer company PsiQuantum. โOur low-power chips will make it possible for people around the world to participate in mining profitably.โ
The scheme is called LightHash. It uses a photonic integrated circuit to create a photonic blockchain. With further development, the researchers believe that this approach, if implemented on a large scale, could create about a tenfold improvement in power usage compared to the best modern digital electronic processors.
โOur photonic blockchain approach could also be used for applications beyond cryptocurrencies, such as secure data transfer for medical records, smart contracts, and voting,โ Pai said. "This work paves the way for low-power optical computing that can ultimately reduce data center power consumption."
Growing concerns about the large amount of energy required to mine cryptocurrencies have caused some of the most popular cryptocurrencies, such as Ethereum, to switch to unproven and potentially insecure methods to minimize their carbon footprint.
To find a greener approach while maintaining a high level of security, Pai and his colleagues used silicon photonics to reduce the power requirements of cryptocurrency networks. LightHash improves on a scheme the team previously developed called HeavyHash, which is currently used in cryptocurrency networks like Optical Bitcoin and Kaspa.
โThe main motivation for LightHash was HeavyHash's high sensitivity to hardware errors,โ Pai said. "Since analog computers, including photonics, struggle to achieve low error rates, we designed LightHash to maintain all of HeavyHash's security properties, while improving its robustness to errors."
The new scheme creates a photonic blockchain using a photonic integrated circuit, the little metallic rectangle. Courtesy of LightHash.
The secure creation of Bitcoin or the operation of your computer network requires the calculation of a hash function such as SHA256 or HeavyHash to transform the input data into a single output number in a way that is too complex to unravel, which accounts for the most part of Bitcoin's energy usage. In the new work, the researchers modified HeavyHash to work with a co-engineered silicon photonics chip carrying a 6 ร 6 programmable interferometer array. This enabled low-energy optical processing of matrix multiplications, which makes up the bulk of of the calculation in LightHash.
To assess the feasibility of using LightHash for matrix multiplication, the researchers built an optical platform to control and track light propagation by adjusting heating elements and imaging grid points in an infrared camera. They also implemented a bug mitigation algorithm and established feasibility criteria for scaling the technology.
The experimental results achieved with the silicon photonic chip coincided with those obtained using simulated error predictions.
โOur results suggest that LightHash can be feasibly computed at scale using current silicon photonic chip technology,โ Pai said. "Essentially, we've devised a way to use analog optical circuitry to perform multiplications with near-zero power dissipation, but with enough precision to use in a digital encryption scheme."
For LightHash to demonstrate significant advantages over digital equivalents, it must scale up to 64 inputs and outputs. The researchers are also working to further reduce power consumption by designing low-power electromechanical tuning elements and energy-efficient converters to convert optical signals to electrical signals.
They say that because the new chip speeds up matrix multiplication, the most computationally intensive operation for AI applications, it could also help make the training and application of photonic neural networks more energy efficient compared to with conventional digital implementations.
"It will be interesting to see how cryptocurrency technology evolves and to what extent photonics can contribute to the increasingly important role of decentralized ledgers in today's society," Pai said.
The research was published in OPTICAL (www.doi.org/10.1364/OPTICA.476173).
