New All-Optical Computing Platform Could Revolutionize Future of Computation

The future of computation looks bright, and this can be said in the literal sense.

SEAS researchers have developed a new platform for all-optical computing, meaning computations done solely with beams of light. Image Credit: Harvard SEAS.

Working with scientists from McMaster University and the University of Pittsburgh, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have created a novel platform for all-optical computing, in other words, computations performed solely using light beams.

Most computation right now uses hard materials such as metal wires, semiconductors and photodiodes to couple electronics to light. The idea behind all-optical computing is to remove those rigid components and control light with light. Imagine, for example, an entirely soft, circuitry-free robot driven by light from the sun.

Amos Meeks, Study Co-First Author and Graduate Student, Harvard SEAS

These platforms word based on what are called non-linear materials that alter their refractive index depending on the intensity of light. Upon shining light through these materials, there is an increase in the refractive index in the path of the beam, producing its own, light-made waveguide. At present, a majority of the non-linear materials need high-powered lasers or are altered permanently due to light transmission.

In this study, fundamentally new material was created by the researchers. This material changes the refractive index by making use of reversible swelling and contracting in a hydrogel under low laser power.

The hydrogel is made of a polymer network that tends to swell in the presence of water, similar to a sponge, and fewer light-responsive molecules called spiropyran (analogous to the molecule employed for tinting of transition lenses).

Upon shining light through the gel, there is a slight contraction of the area under the light. This leads to the concentration of the polymer and change in the refractive index. Upon turning the light off, the gel is restored to its original state.

If multiple beams are shone through the material, they tend to interact and have an impact on each other, even at huge distances. Beam B could be inhibited by Beam A, Beam A could be inhibited by Beam A, both could pass through, or both could cancel each other out—forming an optical logic gate.

Though they are separated, the beams still see each other and change as a result. We can imagine, in the long term, designing computing operations using this intelligent responsiveness.

Kalaichelvi Saravanamuttu, Study Co-Senior Author and Associate Professor of Chemistry and Chemical Biology, McMaster University

Not only can we design photoresponsive materials that reversibly switch their optical, chemical and physical properties in the presence of light, but we can use those changes to create channels of light, or self-trapped beams, that can guide and manipulate light,” stated Derek Morim, co-author of the study, who is a graduate student in Saravanamuttu’s lab.

Materials science is changing. Self-regulated, adaptive materials capable of optimizing their own properties in response to environment replace static, energy-inefficient, externally regulated analogs. Our reversibly responsive material that controls light at exceptionally small intensities is yet another demonstration of this promising technological revolution.

Joanna Aizenberg, Study Co-Senior Author and Amy Smith Berylson Professor of Materials Science, Harvard SEAS

This study was published in the Proceedings of the National Academy of Sciences. The co-authors of the study are Ankita Shastri, Andy Tran, Anna V. Shneidman, Victor V. Yashin, Fariha Mahmood, and Anna C. Balazs.

The study was partially supported by the U.S. Army Research Office under Award W911NF-17-1-0351 and by the Natural Sciences and Engineering Research Council, Canadian Foundation for Innovation.


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