New Approach to Creating Flexible Waveguides

Creating flexible optical waveguides has long been a challenge, as it requires the self-contradicting task of shaping a highly soft material into thin and long structures that are also self-sustaining.

A new fabrication technique developed by researchers from Iowa State University alleviates this challenge by reconciling the conflicting requirements and creating structures capable of standing upright on their own.

Researchers in Iowa have developed a new approach to creating flexible optical waveguides. Images courtesy of Iowa State University.

Polydimethylsiloxane (PDMS) was used as the waveguide material, which in the traditional method of replica molding proves difficult as it is too soft to cast into self-sustaining waveguides. The fabrication is further complicated with the demand of de-molding of the completed structure. This process has been particularly detrimental to thin and long structures.

The researchers’ new approach employs direct drawing, which eliminates the need for de-molding. To increase self-sustainability of the PDMS structure, in situ thermal hardening was also incorporated into the drawing process.

With this extra treatment, the completed PDMS waveguides were able to stand upright on their own in the form of vertical micropillars. They are 800 to 2400 µm in height and 25 µm or less in diameter, leading to aspect ratios exceeding 100. The researchers said that the height and aspect ratio are unprecedented for structures made of soft materials like PDMS.

The structures can now be bent with a distant nasal wind, prompting the researchers to turn them into wind sensors, in which the air flow velocity is estimated through the increase in the waveguide’s bending loss.

New PDMS waveguide structures can be used as wind sensors.

The PDMS waveguides for this purpose were drawn with shiny silver-coated microspheres that can be left to cap the tips of the waveguides. The resulting wind sensors exhibited high sensitivity to both constant and time-varying airflows.

The researchers expect that their direct drawing-based PDMS shaping technique and the resulting microstructure with self-aligned microsphere capping will enhance materials-based microtechnology.

The work was published in Nature Communications.

For more information, visit www.iastate.edu.