At the bottom of the ocean, optical fibers transmit telecommunications and internet data across the world. Waveguides make that feat possible by channeling and amplifying the light - and therefore the data within - over enormous distances.
And the technology goes beyond undersea cables. Waveguiding optics are among the most important advances in photonics since the invention of the laser. They are fundamental to the structure of glass fiber lasers, which are used for high-power national security applications like counter-drone laser systems and missile defense.
Now, researchers at Lawrence Livermore National Laboratory (LLNL) have fabricated a first-of-a-kind all-ceramic waveguide with 3D printing. The work was published in Optics Letters.
"With further development, this crystalline architecture could enable more than a tenfold increase in output power over glass fibers while retaining a compact footprint," said LLNL scientist and author Ross Osborne.
Waveguides exploit the phenomenon of total internal reflection with two regions: a core and a cladding material that surrounds that core. As light travels and bounces through the core, it spreads out. When it hits the cladding, it is reflected back into the core.
Typically, waveguides are made from silica glass. A crystalline ceramic version could tolerate higher power output, improve heat dissipation and suppress instabilities. Until now, methods to fabricate such a waveguide were cumbersome and unreliable, often creating very short or poor-quality waveguides.
LLNL's novel method uses direct ink write printing to address that challenge. The technique squeezes filaments of ytterbium-doped yttrium aluminum garnet within an undoped garnet ceramic matrix.
"We developed a direct ink writing additive-manufacturing technique for fabricating ceramics with highly tailored structures," said Osborne. "The process begins with a nanoparticle paste that is extruded into a three-dimensional shape. The printed structure is then dried, sintered and hot isostatically pressed to produce a transparent ceramic."
The team created three waveguides contained in a single ceramic block and demonstrated high-efficiency laser performance. Because the waveguide core and cladding are fabricated in tandem as a single structure, the approach offers high fabrication yield and minimizes defects at the interface between core and cladding.
The channel waveguide lasers described in the paper were tested in collaboration with the DEVCOM Army Research Laboratory in Maryland. The authors continue to hone the process, and they plan to eventually scale the output power from hundreds of milliwatts to kilowatts. Ultimately, they aim to make the waveguide and its production process commercially viable for high-power applications such as laser machining and national defense.
In addition to funding from the Army, the fundamental capability was developed with Laboratory Directed Research and Development support.
