Silicon-based tunable optical filters

This thesis presents the design, the fabrication and the characterization of a new class of silicon-based tunable optical filters. For this purpose a Fabry-Perot structure was chosen and implemented as a thin-film interference filter. The filter layers were configured as a self-supporting square membrane with side lengths of a few hundred microns. The approach presented in this work is primarily intended for use in the near-infrared spectral region. <br>Tunable optical filters are essential components in a wide range of optical systems. They are also used to enable wavelength agility in lasers and add/drop multiplexers, which are used in optical data communication systems. The filter presented in this work is especially designed to meet the requirements that exist in this field of application. <br>Initially, a review of tunable optical filters is provided, which covers miniaturized waveguide and thin-film filters. Additionally, various tuning mechanisms for thin-film filters are highlighted. Recent models of waveguide filters make use of photonic bandgaps, which are modified by changing the optical material properties. This review enables the reader to classify the filter presented in this work with respect to optical performance and to consider its specific advantages and drawbacks. <br>After a brief introduction of the modeling and optical properties of Fabry-Perot etalons, this theory is extended to cover thin-film interference filters. Two approaches are pursued in this thesis. A comprehensive theory for the calculation of spectral characteristics of arbitrary optical multilayer designs is presented, which requires significant numerical effort for evaluation. A new simplified analytical model, which accurately describes the filter’s spectral characteristics close to the filter wavelength, is derived for reasons of flexible design investigation and optimization. This model quantitatively explains the specific difference in tunability for etalons and thin-film filters. <br>Besides the desired optical functionality, fabrication of the optimized design was performed according to the structural stability requirements for the filter device. As the employed materials (amorphous silicon, silicon nitride and silicon dioxide) show mechanical stress, a stress-compensated design was developed, which provides excellent stability with good optical performance. In addition to the actual implementation of the optical layer stack, further features are integrated for achieving tunability. Microsystem technology was employed to realize thin-film resistor structures and improve heating efficiency by configuring the filter as a membrane. An assembly approach was proposed, which is based on a self-aligned micro-optical bench. <br>Characterization of the device was performed with respect to electro-thermal and optical behavior. In the first case the coupling between applied electrical power and the resulting temperature is of special interest. It was found that the achievable temperature depends on membrane size and composition. Maximum temperatures of 450 °C were achieved with an input power of less than 100 mW. The behavior was investigated statically and dynamically. Typical thermal time constants are smaller than 10 ms. <br>The optical parameters of interest include actual filter performance and, more importantly, its tunability. A filter linewidth smaller than 0.4 nm at a wavelength of 1550 nm was achieved. This peak was shift by more than 40 nm by temperature modulation. It was observed that the measurement results are consistent with the theory presented for modeling the filter structure. Towards the end of the thesis, the suitability of different designs for tunable filters is discussed.

Author dc:creator

• Hohlfeld, Dennis

Contributors dc:contributor

• Zappe, Hans

• optische Filter
• thermo-optisch
• wdm
• Mikrosystemtechnik
• silicium-basiert
• optical filter
• thermo-optic
• microsystem technology
• silicon-based

Repository record source_url

https://freidok.uni-freiburg.de/data/1910

OAI identifier oai:identifier

oai:freidok.uni-freiburg.de:1910