Modeling of an Optical Sensor for Detection of Nanoparticles at 1550 nm
Keywords:
Acetonitrile, infrared, Mach-Zehnderinterferometer, nanoparticles, nanowires, optical fiberapplications.
Abstract:
We study an optical sensor in the infrared region ofthe spectrum based on a Mach-Zehnder interferometerassembled with two single-mode subwavelength diameter silicawires immersed in acetonitrile. We propose to use acetonitrileas the detecting solution, because it has negligible losses in theinfrared wavelengths of 1300 nm and 1550 nm in contrast towater which has very high losses in the infrared. By biomodifyingthe surface of the sensing wire, we can use theoptical sensor to selectively detect nanoparticles. Fornaoparticles with size of 12 nm and index of refraction of 1. 4forming a coating around the sensing wire, the propagationconstant difference at the output of the optical sensor becomes amaximum for a wire diameter of 1. 23 µm. By using a wirelength of 955 µm, a maximum phase shift of radians isobtained at the output of the Mach-Zehnder interferometer. Anoptical sensor using water as the detecting solution at anoperating wavelength of 325 nm will require nanowires withdiameter of 240 nm and length of 68 µm, which is much moredifficult to implement. Effects of wavelength, wire diameter, andspecimen thickness and index on the optical sensor are alsostudied.