Small-scale optical devices capable of using photons for high-speed information processing can be fabricated with unpre­cedented ease and precision using an additive manu­facturing process developed at KAUST. Fiber optics are conventionally produced by drawing thin filaments out of molten silica glass down to micro­scale dimensions. By infusing these fibers with long narrow hollow channels, a new class of optical devices termed “photonic crystal fibers” were introduced. The periodic arrangement of air holes in these photonic crystal fibers act like near-perfect mirrors, allowing trapping and long propa­gation of light in their central core.

“Photonic crystal fibers allow you to confine light in very tight spaces, increasing the optical inter­action,” explains Andrea Bertoncini, a postdoc working with Carlo Liberale. “This enables the fibers to massively reduce the propagation distance needed to realize parti­cular optical functions, like polari­zation control or wavelength splitting.” One way that researchers use to tune the optical properties of photonic crystal fibers is by varying their cross-sectional geometry – changing the size and shape of the hollow tubes, or arranging them into fractal designs. Typically, these patterns are made by performing the drawing process on scaled-up versions of the final fiber. Not all the geo­metries are possible with this method, however, due to the effects of forces such as gravity and surface tension.

To overcome such limi­tations, the group turned to a high-precision three-dimensional printing technology. Using a laser to transform photo­sensitive polymers into transparent solids, the team built up photonic crystal fibers layer by layer. Characterizations revealed that this technique could success­fully replicate the geometrical pattern of several types of micro­structured optical fibers at faster speeds than conventional fabri­cations. Bertoncini explains that the new process also makes it easy to combine multiple photonic units together. They demons­trated this approach by 3D printing a series of photonic crystal fiber segments that split the polarization components of light beams into separated fiber cores. A custom-fabricated tapered connection between the beam splitter and a conventional fiber optic ensured efficient device inte­gration.­

“Photonic crystal fibers offer scientists a type of tuning knob to control light-guiding properties through geometric design,” says Bertoncini. “However, people were not fully exploiting these properties because of the diffi­culties of producing arbitrary hole patterns with conven­tional methods. The surprising thing is that now, with our approach, you can fabricate them. You design the 3D model, you print it, and that's it.” (Source: KAUST)

Reference: A. Bertoncini & C. Liberale: 3D printed waveguides based on photonic crystal fiber designs for complex fiber-end photonic devices, Optica 7, 1487 (2020); DOI: 10.1364/OPTICA.397281

Link: Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology KAUST, Thuwal, Saudi Arabia