Repetition Frequency Detuning in Mode-Locked Lasers with Integrated S-Bend Waveguide

We present the integration of an S-bend waveguide into the cavity of a mode-locked diode laser to tune its repetition frequency for use in terahertz time-domain spectroscopy applications. The mode-locked diode laser, featuring a facet-to-facet 6-mm-long straight ridge waveguide, emits light at a wavelength of around 830 nm and operates at a repetition frequency of 6.3 GHz. By incorporating an S-bend into the cavity, the optical path length can be modified, enabling a variation of up to 12 MHz in the repetition frequency. Furthermore, this approach supports the co-integration of two lasers on a single chip, each with a distinct repetition rate but operating under identical environmental and driving conditions, offering a robust and compact two-laser solution for asynchronous optical sampling.