Characterization of polymeric channel waveguides

Abstract

Optical waveguides and devices using polymeric materials are attracting considerable interest because of their potential applications in optical communications, optical interconnections, and integrated optics. This thesis focuses on the fabrication and the characterization of SU-8 2000 polymeric material. The normalized parameters are highlighted to solve the results of step-index planar waveguides numerically. To facilitate the analysis of rectangular waveguides, an accurate explicit numerical formula is derived for the calculation of the effective refractive index. The formula is used in the subsequent studies. The optical properties of the polymer, including absorption spectrum, refractive index, birefringence, and thermo-optic coefficient are investigated. The study reveals the polymer is high refractive index, low birefringence, high temperature dependence of refractive index, and low absorption in the near infrared wavelength region. The thermal analysis of the polymer is studied next. It is shown that the polymer can withstand high temperature processing steps, such as standard printed board manufacturing, soldering, and thermal stress processes. The fabrication of SU-8 2000 polymeric channel waveguides using direct ultraviolet photolithography is proposed. Different channel widths are fabricated with different structure configurations. It is found that the propagation losses of optical waveguide with NOA 61 polymer as overcladding layer and SiO2 as buffering layer are lower than other's structure configurations. Properties of the optical waveguide, such as near-field intensity pattern and mode intensity profile, are characterized, and there is an excellent agreement between measured data and theory. The surface morphologies and the propagation losses of the waveguide are studied thoroughly. It is shown that vertical and fairly smooth sidewalls are obtained and the propagation losses are < 1 dB/cm at 800 and 1310nm wavelengths. As to the application, a Y-branch power splitter is demonstrated. It is found that the splitting ratio is ~50:50 and the excess split loss at the apex is ~ 0.5 dB. The combination of direct photolithography technique and used of the polymer can provide a simple, rapid, and controllable process, and has the potential of low cost, high yield, and large area patterning.

Date of Award	2 Oct 2003
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yue Bun Edwin PUN (Supervisor)