Membrane-Based Broadband Semiconductor Light Sources for Optical Coherence Tomography

Optical coherence tomography (OCT) has experienced tremendous progress over the last three decades and has nowadays become a standard optical imaging modality in the field of biomedicine. High-resolution, multi-dimensional imaging including information about depth is provided in real-time for clinical in-vivo applications even while the field is rapidly growing pushed by continuous technological advance.

The scope of the thesis is to advance OCT technology along two main avenues:
i) more versatile membrane-based sources for visible wavelength range;
ii) development of polarization sensitive OCT (PS-OCT) as an advanced technique providing information of birefringence.

For the first path several membrane external-cavity surface-emitting lasers (MECSELs) were demonstrated targeting operation at difficult wavelength ranges, i.e., the red and near-infrared spectral range, and broad-band tuning, an essential feature for OCT. Main results including tunable emission were successfully demonstrated yet full scale implementation into OCT set-ups would require more advanced engineering to stabilize the operation for wavelength tuning.

Broad-emitting MECSEL structures were presented based on novel design structures, including the incorporation of quantum dots in the gain region, as well as using two different quantum well types in the same active region. Also, the characterization of a novel design criterion to mitigate undesired spectral effects inherent in MECSELs is presented.

For the PS-OCT the impact of changes in temperature of a setup was characterized using a technique to obtain depth information from a measured set of interference fringes using reference signals with known distances. This approach has never been carried out for fiber-based polarization-sensitive systems, which are known to be highly sensitive to dispersion changes. This study can contribute to further development of this approach to image birefringence. In addition to this, a novel approach is proposed to demonstrate super-luminescence operation based on the membrane emitting platform. As in the case of MECSEL, this allows to surpass the limitations of carrier injection that edge emitting laser devices are facing when operating at short wavelength ranges.