Optical fiber-based microdevices: from salinity sensors to nanolithography probes

Abstract

Optical fibers are the backbone of optical communications, connecting the world of internet across continents. Besides its optical signal carrier application, optical fibers can be a low-cost, compact base platform for microsystems in sensing and actuation applications. In this thesis, it is presented the demonstration of various fiber-based elements for applications in sensing and nanolithography, with micro and nanoscale fabrication processes adding added functionality to telecom grade standard optical fibers. The first part of this work explores the development of highly sensitive salinity sensors. Salinity is a key property and indicator of water quality having a great impact on biodiversity and human health with an ever-increasing demand for real-time and in-situ monitoring of salinity in environmental and industrial applications. The demonstrated sensors are based on optical fibers and consist on Fabry-Pérot optical cavities formed by optimized processes that include chemical etching and fusion splicing, on which microfluidic channels are milled by focused ion beam. Several configurations are developed and their performance compared, including a special configuration that makes use of Vernier-effect for the simultaneous measurement of salinity and temperature with high sensitivity. The interrogation of the devices is carried out by spectral measurements using a broadband light source and sensitivities to salinity up to 80 nm/M are obtained. The second part focuses on the development of a photolithography system based on optical fiber probes as an alternative to high resolution conventional lithography methods such as optical projection lithography and electron beam lithography. Classically, there is a trade-off between resolution and cost in lithographic systems, where high resolution lithography systems can cost up to tens or hundreds of millions of dollars. A low-cost lithography system with highresolution can greatly benefit applications such as energy generation and desalination, which require the patterning of nanostructures in large areas. The developed optical fiber probe consists on an optical diffractive element, a photon sieve, milled onto the tip of an UV-Visible single mode fiber by focused ion beam. Two different applications are demonstrated, 1D scans and optical nanostencils, with features as small as 160 nm being obtained in the photoresist coated substrates.

Date of Award	Jul 2018
Original language	American English
Supervisor	JAIME Viegas (Supervisor)