The evolution of 3D printing nanoscale optical devices

Inversely constructed 3D-patterned mid-infrared metaoptics.

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Caltech is developing a new technology allowing researchers to “evolve” optical devices and print them out using a specialized 3D printer. These devices are built of optical metamaterials, which get their properties from structures as small as nanometers. These technologies may enable cameras and sensors to detect and alter light properties in previously impossible ways at small scales. 

According to the researcher, Faraon has developed optical metamaterials, but this is the first time these materials have been pushed into three dimensions,

He said, “Generally, most of these things are done in a thin material layer. You take a very thin piece of silicon or some other material, and you process that to get your device. However, [the field of] optics lives in a three-dimensional space. We are trying to investigate what is possible if we make three-dimensional structures smaller than the wavelength of light we are trying to control.”

Faraon’s lab has developed tiny devices that can classify incoming infrared light by wavelength and polarisation, determining the direction in which light waves vibrate. These devices might be designed to work with visible light and be small enough to be placed right over a camera’s sensor, directing red light to one pixel, green light to another, and blue light to a third. The same might be done with polarised light, resulting in a camera that can detect surface orientation, a valuable capacity for developing augmented and virtual reality settings.

The devices developed by Faraon’s lab appear organic and chaotic, more akin to the inside of a termite mound than an optics lab. This is because the gadgets are evolved by an algorithm that constantly modifies their design until they perform as expected, much as how breeding may produce a dog that is good at herding sheep. At its core, design software is an iterative process, with each phase in the optimization process making a choice.

Roberts said, “The design software at its core is an iterative process. It has a choice at every step in optimizing the device. After it makes one small change, it figures out how to make another small change, and, by the end, we end up with this funky-looking structure that has a high performance in the target function that we set out in the beginning.”

He adds, “We do not have a rational understanding of these designs, in the sense that these are designs produced via an optimization algorithm. So, you get these shapes that perform a certain function. For example, suppose you want to focus light to a point, so basically what a lens does, and you run our simulation for that function. In that case, you will likely get something similar to a lens. However, the functions we target splitting wavelengths in a certain pattern are complicated. That’s why the shapes that come out are not quite intuitive.”

The researchers used two-photon polymerization (TPP) lithography to transform their designs from a computer model into practical devices. This type of 3D printing uses a laser to selectively harden a liquid resin, allowing structures with features smaller than a micron to be manufactured. Faraon describes the work as a proof of concept. However, more research might produce it using a viable manufacturing approach.

The research was funded by the Defence Advanced Research Projects Agency (DARPA). 

Journal Reference:

  1. Roberts, G., Ballew, C., et al. 3D-patterned inverse-designed mid-infrared metaoptics. Nature Communication. DOI: 10.1038/s41467-023-38258-2
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