Title

Fabrication of a deoxyribonucleic acid polymer ridge waveguide electro-optic modulator by nanoimprint lithography

Date of Award

2014

Degree Name

Ph.D. in Electro-Optics

Department

Department of Electro-Optics and Photonics

Advisor/Chair

Advisor: Andrew Sarangan

Abstract

The purpose of this dissertation is to develop the nanoimprint lithography (NIL) technique for direct patterning of the deoxyribonucleic acid biopolymer DNA-CTMA. The Mach Zehnder modulator was chosen as the test device to demonstrate the NIL patterning technique for DNA-CTMA as well as the unique optical and electrical properties of the DNA-CTMA as a cladding material for poled electro-optic polymers. Towards this goal, a DNA-CTMA clad inverted ridge waveguide is demonstrated at 633 nm and 1550 nm, the structure of which is patterned directly in the DNA-CTMA cladding by NIL. Additionally, EO modulation is demonstrated in a slab waveguide structure with DNA-CTMA cladding and SEO110 EO polymer core.Marine-derived deoxyribonucleic acid biopolymer (DNA-CTMA) is a green, nontoxic, low cost optical polymer material derived from waste products of the salmon fishing industry. It exhibits low optical loss at 1550 nm, forms a thin flexible film, is compatible with existing poled polymer technologies, increases the poling efficiency when used as a low resistivity cladding layer, and is thermally stable to 200 oC. Due to chemical incompatibility with the photoresists and the associated solvents, NIL has been developed for patterning the DNA biopolymer cladding to form an inverted ridge waveguide for the basis of the Mach Zehnder modulator.While DNA-CTMA presents significant advantages over other commonly used cladding materials for the 1550 nm wavelength range, one of the commonly used bands for optical communications, the mechanical properties and environmental susceptibility of the material poses significant fabrication challenges. A study of the effects of optical and mechanical effects of environmental humidity exposure are presented for the DNA-CTMA and SEO110 polymers used in the inverted ridge waveguide. While the soft, flexible nature of the DNA-CTMA is desirable for certain applications, this presents a challenge in producing a clean polished window for optical coupling. Incompatibility with standard polishing techniques has led to the study of focused ion-beam milling (FIB) as a technique for polishing the DNA-CTMA film edge.This dissertation presents a demonstration at 633 nm and 1550 nm of an inverted ridge waveguide patterned by NIL in the DNA-CTMA cladding. Optical modulation in a slab waveguide structure consisting of the same polymer layers as the inverted ridge waveguide is also demonstrated, which together with waveguiding in an inverted ridge waveguide presents the case for the DNA-CTMA clad Mach Zehnder modulator. In this dissertation the FIB polishing technique for DNA-CTMA is demonstrated as a means to overcome the challenges of mechanically polishing the DNA-CTMA polymer. A study of the optical and mechanical effects of environmental exposure for DNA-CTMA and SEO110 is presented along with an analysis polymer film stresses as a result of fabrication processes and environmental exposures. This dissertation represents a significant advancement in fabrication techniques for DNA-CTMA thin films with the development of NIL for DNA-CTMA and is a significant step towards fully patterned DNA-CTMA EO waveguide devices.

Keywords

Biopolymers, Ion bombardment, Thin films Design and construction, Electrical Engineering, Nanotechnology, Optics, Physics, Polymers, Nanoimprint Lithography, DNA, Biopolymer, Mach Zehnder, Modulator, Electro-Optic Polymer, Waveguide

Rights Statement

Copyright 2014, author

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