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).
