Electro-optic synchronization of two tunable semiconductor slotted lasers for wider tuning range application

The recent advancements of swept-source optical coherence tomography (SS-OCT) calls for a compact widely tunable swept-source that can emit single mode, and narrow linewidth radiation over a 70-100 nm wavelength tuning range. However, the gain bandwidth of the laser material critically limits the wider tuning range of the device. Moreover, to ensure the single-mode operation, the mirror sections of the laser should be designed with a specific free spectral range (FSR) which further limits achieving wider tuning range of the device. These limitations drive the laser manufacturer to opt for external filters which restricts the speed of operation of the device. In this work, we have discussed an alternative approach of increasing the tuning range of the device without adding further complexities in the laser design by employing the method of electro-optic synchronization. Two tunable semiconductor lasers with different epitaxial structures and central wavelengths have been electrically synchronized and their outputs have been coupled optically. The tuning range of these lasers partially overlaps with each other for a smooth transition of the laser emission. Two multi-section semiconductor lasers with a central wavelength of 830 nm and 862 nm respectively, and with a tuning range of 40 nm, have been fabricated using standard UV optical lithography to be utilized in this approach. Initial electro-optic characterization of the lasers shows single mode emission with high SMSR throughout the tuning range.