Optical fibers made solely of water can sense minute forces

Researchers at Technion Israel Institute of Technology (Haifa, Israel) have created something unusual in the field of photonics—an optical fiber that is entirely liquid. The water-based fiber, which can be longer than a millimeter while having a diameter of only around 5 μm, could be useful in sensing minute forces. In particular, the researchers say that, in comparison to microelectromechanical-systems (MEMS) sensing devices, the microelectrocapillary-systems (MECS) fiber is a million times softer, greatly improving its sensitivity.

The creation and sustaining of such an optical fiber is based on a phenomenon that has been known for more than a century, but has never before been used for guiding light. If an electric potential difference is applied between two water reservoirs, a thin water thread can arise that connects the two reservoirs. The weight of the water thread is supported by dielectric and interfacial tensions. To create a water fiber, the researchers start with an adiabatically tapered glass input fiber coupler and a ball-lens-to-fiber output coupler, each placed in a small water reservoir. Applying a 3 kV voltage across the two couplers causes the water fiber to form. In one example, input light at a 770 nm wavelength is transmitted at a 54% efficiency through a 0.83-mm-long water fiber. The diameter of the fiber could be made as small as 1.6 μm for a 46-μm-long water fiber. Light waves in the fiber were observed to couple with capillary (mechanical) waves, potentially enabling nonlinear optical as well as lab-on-a-chip devices. Reference: M. L. Douvidzon et al., arXiv:1609.03362v1 (Sept. 12, 2016).