Optical sensing by use of silica nanowires immersed in liquid

Single-mode subwavelength diameter silica nanowires immersed in acetonitrile are investigated for optical sensing in the infrared region of the spectrum. We use acetonitrile as the detecting solution, because it has much lower losses in the infrared spectral range compared to water. By measuring the phase shift at the output of a Mach-Zehnder interferometer assembled with two nanowires, we can detect the presence of a specimen in the solution. Our calculations show that, for nanowire diameters larger than 360 nm, the change in the propagation constant at the output of the optical sensor is higher at a wavelength of 1550 nm compared to a wavelength of 325 nm with water as the detecting solution. The variation of the propagation constant with the molar concentration and the index of refraction of the specimen are also presented.