Electronics and Communications Engineering Department Swept Laser Source

Abstract

Swept wavelength laser source is currently an essential element for many biomedical and sensing applications especially for Optical Coherence Tomography (OCT). Swept Source OCT (SS-OCT) is fast becoming one of the most successful optical technologies, in the field of disease diagnostics and biomedical imaging. For such applications, the main interest is to have a wide wavelength-tuning range, high speed, miniaturized dimensions and low cost. Miniaturization opens the door to integrate the system on a handheld unit, which may initiate a wide variety of new applications. Various configurations have been proposed for SS-OCT utilizing external optical components, which are bulky, expensive and difficult to align. To overcome these challenges, swept sources based on MEMS technology have recently attracted a great attention. The technology provides miniaturized dimensions, low cost and batch processing. In-plane MEMS components suitable for building a complete integrated SS-OCT head have been reported. The main drawback of swept source based on in-plane MEMS filter is the small tuning range (20 nm - 35 nm), which is not suitable for many OCT applications. In this thesis, we present an SOI-MEMS tunable Fabry-Perot filter with 125 nm tuning range and a free-spectral range (FSR) larger than 130 nm. The SOI-MEMS filter is based on two-silicon-layers Bragg mirrors etched with an 80 μm depth. The SOI-MEMS filter is then used to construct a 100 nm tuning range swept laser source. The tuning of the filter is carried out using a MEMS electrostatic comb-drive actuator attached to the free-Bragg mirror of the filter, in a lithographically self-aligned manner. The presented results represent, to the best of our knowledge, the largest tuning range reported in literature for an in-plane MEMS-based swept laser source.