Bidirectional electrostatic tunable MEMS VCSELs

This thesis deals with the design and characterization of robust high­speed MEMS VCSELs. These lasers are predominantly used as swept light sources in optical coherence tomography, an imaging modality mainly used within ophthalmology. Due to the lasers’ high
sweep rate, they allow imaging of the whole eye without motion blur caused by involuntary eye movement. This allows for clear depiction of the eye leading to a more accurate diagnosis. A result of the thesis is the predicted reduction in optoelectromechanical noise resulting from the use of a robust 2D photonic crystal instead of a high contrast grating conventionally used as the movable mirror in the optical cavity. The increased mechanical stability of the photonic crystal elevates the resonant frequency of higher­order mechanical modes, reducing the risk of unwanted excitation of higher­order modes by a broadband signal. This leads to a possible reduction of the dynamic laser linewidth, resulting in a longer imaging depth. The thesis also presents a bidirectional electromechanical model. A fabricated bidirectional electromechanical laser experimentally supports the model. The bidirectional electromechanical device allows for linear wavelength tuning, as well as paving a way to actuate ultra­stiff MEMS close to the instability points without the need to amplify the driving signal. The bidirectional laser demonstrates a fractional bandwidth of 3.44% around a
center wavelength of 1585 nm at a drive frequency of 2.73 MHz. Finally, the dissertation presents a new application area for MEMS VCSELs, namely ultrashort pulse generation, enabled by the highly coherent ultra­fast and broad­banded bidirectional electromechanical laser coupled together with a semiconductor optical amplifier and a highly dispersive medium.