Etched optical fiber sensors and devices

Masoud Vaziri, Purdue University

Abstract

This thesis is concerned with the fabrication and characterization of etched fiber sensors and devices with multimode and two-mode fibers. Novel corrugation structures are formed on fiber cladding. Standard integrated circuit technology is used to delineate the desired patterns and the structures are etched onto the fiber cladding by chemical etching. Etched multimode fiber sensors are used to measure strain. The etched two-mode fibers are used as modal couplers. The operating principles and experimental results of these sensors and couplers are presented. Asymmetrically etched multimode fiber intensity sensors are developed and tested as strain sensors. The sensitivity of these sensors depends on the asymmetry of the etched structures and the number of etched sections. Existing structural analysis programs based on a finite element method are used to analyze the structural deformation of fiber sensors under tensile stress. The calculations show that lateral bends are induced on fibers when they are stretched. To relate the lateral bending to the optical attenuation, a ray tracing technique is then employed to investigate the dependence of the attenuation on the structural deformation. Based on the structural analysis and the ray tracing study, parameters affecting the sensitivity have been studied. Also reported is a novel technique to measure the intermodal beat length of two-mode fibers in an optical fiber Fabry-Perot configuration. The technique is based on measuring the change in relative phase difference between the fiber cavity modes as a function of the cavity length. Using this technique, we can study mode coupling in two-mode fibers. A compact two-mode modal coupler with etched fibers is also presented. In the theoretical study, we examine mode coupling due to periodic fiber bends. A simple model is developed to predict the magnitude of the bends as a function of the etching depth and the contour of the deformed fiber. Mode coupling due to these bends is determined by a new and accurate procedure. We also developed a polarization insensitive mode stripper which is useful for all two-mode fiber devices. Finally, a second technique based on Fabry-Perot fiber cavities for characterizing the modal couplers is also presented.

Degree

Ph.D.

Advisors

Chen, Purdue University.

Subject Area

Electrical engineering

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