Researchers have developed a new shrinking technique that enables the creation of tiny 3D photonic devices capable of manipulating visible light. The method, named implosion carving (ImpCarv), creates vacancies within a material before shrinking it to nearly 1/2,000 of its original volume, producing nanoscale structures with highly detailed features.

The Massachusetts Institute of Technology (MIT) team fabricated devices in various complex shapes, including helices and butterfly wing-inspired designs. The breakthrough could support future optical computing systems and other technologies that rely on controlling light at extremely small scales. “We envision ImpCarv as a scalable and cost-effective platform for fabricating nanoprecise 3D metastructures,” said the team in their research paper.

Laser vacancy fabrication

Photonic devices, which manipulate and transmit light, could serve as energy-efficient alternatives to semiconductor chips in future optical computing systems. However, existing manufacturing methods have struggled to achieve the 100-nanometer resolution needed to guide visible light, which has wavelengths ranging from 380 to 750 nanometers.

Two-photon lithography can create 3D nanoscale structures using light, but its resolution remains above 100 nanometers. Electron-beam lithography can produce smaller features on silicon chips, though it is limited to flat, two-dimensional structures.

To overcome these limitations, MIT researchers developed a method called “implosion carving,” based on the earlier concept of implosion fabrication. The technique uses a laser to create tiny vacancies within a hydrogel by exciting a photosensitizing dye that generates reactive oxygen species. These reactive molecules cut the hydrogel’s chemical bonds, forming precisely targeted voids with different optical properties from the surrounding material, MIT News reported.

After the vacancy pattern is formed, the hydrogel is shrunk through a two-step process involving ion soaking and supercritical drying. The material contracts more than tenfold in each dimension, reducing its volume by roughly 2,000 times while preserving nanoscale features.

Tiny optical networks

To demonstrate the flexibility of their technique, the researchers created several complex 3D structures, including a helix and a design inspired by a butterfly wing. Some of these structures were too thin and had aspect ratios too high to be fabricated using conventional two-photon lithography methods.

The team also developed a photonic device capable of performing a simple digit-classification task commonly used to evaluate neural networks. In the demonstration, the device received an input digit, such as 1 or 5, and illuminated a specific output location corresponding to the detected number, according to the press release .

The device functioned through carefully patterned vacancies distributed throughout the hydrogel structure. As light passed through multiple patterned layers, the vacancies diffracted the incoming light, allowing the output to depend on the shape of the digit entered into the system. Researchers described the setup as a purely optical system capable of performing optical computing.

According to the team, the technology allows material properties to be controlled at millions of tiny locations, creating complex design challenges that can be addressed using deep-learning algorithms to optimize optical system performance.

The researchers now plan to apply the same principles to optical devices that can classify cells flowing through microfluidic systems, potentially enabling the detection of rare circulating tumor cells in blood samples. The method could also support high-throughput imaging and the fabrication of 3D nanofluidic devices.