Researchers have developed a new platform for all-optical computing, meaning computations done solely with beams of light. Most computation right now uses hard materials such as metal wires, semiconductors, and photodiodes to couple electronics to light. All-optical computing removes the rigid components and controls light with light.
These platforms rely on so-called nonlinear materials that change their refractive index in response to the intensity of light. When light is shone through these materials, the refractive index in the path of the beam increases, generating its own light-made waveguide. Currently, most nonlinear materials require high-powered lasers or are permanently changed by the transmission of light. Here, researchers developed a fundamentally new material that uses reversible swelling and contracting in a hydrogel under low laser power to change the refractive index.
The hydrogel is composed of a polymer network that is swollen with water, like a sponge, and a small number of light-responsive molecules known as spiropy-ran (which is similar to the molecule used to tint transition lenses). When light is shone through the gel, the area under the light contracts a small amount, concentrating the polymer and changing the refractive index. When the light is turned off, the gel returns to its original state.
When multiple beams are shone through the material, they interact and affect each other, even at large distances. Beam A could inhibit Beam B, Beam B could inhibit Beam A, both could cancel each other out, or both could go through — creating an optical logic gate.
Photoresponsive materials can be designed that reversibly switch their optical, chemical, and physical properties in the presence of light. Those changes can also be used to create channels of light, or self-trapped beams, that can guide and manipulate light.