Buried heterostructure laser with vertically-integrated Mach-Zehnder interferometer for Vernier-effect-based wide wavelength tuning

A widely tuneable laser is presented that utilises a vertically-integrated Mach-Zehnder interferometer (VMZ) as a wavelength-selective filter inside the resonator. Among the different design configurations this paper focuses on the ´separate waveguide´ design that features large confinement factors in the active and tuning region. Calculations show that a tuning range of 80 nm and a side-mode-suppression-ratio (SMSR) of more than 30 dB are feasible for this design. According to the model calculations, corresponding VMZ lasers with different interferometer lengths have been fabricated and analysed with respect to the filter characteristics. The resulting emission spectra show that the filter is well suited to select individually any of the Fabry-Pe´rot modes out of the gain-limited longitudinal mode spectrum of the resonator. Moreover, a double-VMZ laser is shown that comprises two different interferometers combining the filtering properties of both interferometers. First tuning experiments confirm the Vernier-effect-based tuning mechanism.