The nanoimprint lithography (NIL) of functional materials is a powerful approach to develop low-cost photonic devices with high optical performance. Supported by the US Air Force STTR Program, researchers at aBeam Technologies, the Molecular Foundry (a DOE-funded user facility for nanoscience at Lawrence Berkeley National Laboratory) and NanoOptic Devices have collaborated. They demonstrate a novel approach to fabricate low-cost, printable photonic integrated devices that work in the visible wavelength range.

Simplification

The devices are printed directly onto a functional NIL resist and their optical properties (transparency and refractive index) are tuned by post-annealing. “We wanted to simplify the fabrication of photonic devices as much as possible by printing them onto a functional material in one single step, thereby avoiding any etching steps,” says Christophe Peroz.

High refractive index

The method combines the advantages of top-down (NIL) and bottom-up (sol-gel chemistry) approaches. After annealing at high temperatures, the photonic structures shrink and reach a refractive index up to 2.1. “Conventional lithography is very challenging for high refractive index materials, particularly at few nanometer resolution, but now we have shown that it can be easy” said lead author Carlos Pina-Hernandez.

Complex devices

The printed structures on the top of a waveguide core are used to create planar lightwave circuits. To demonstrate the practicality of this process, elementary optical structures like multi-mode ridge waveguides, light splitters and more complex devices like digital planar holograms (DPH) are fabricated. Printable wavelength demultiplexer-on-chips were also created and their performance was comparable to current devices fabricated by standard and more expensive technologies.

The road is open

This work demonstrates the high potential of nanoimprint technology for fabricating novel photonic devices at low-cost and high throughput. According to the Molecular Foundry’s Stefano Cabrini, “Direct nanoimprinting of functional materials is just beginning and I have no doubt that a lot of applications will emerge in the near future.”

More information about the research can be found in the journal Nanotechnology.

Further reading

UV curing prints photonic nanodevices (Mar 2013)
Nanoimprint lithography: anisotropic remastering reduces feature size (June 2012)