A fiber-based vertically emitting semiconductor laser at 850 nm

The possibility of wavelength tuning and insertion of intra-cavity control elements makes vertical external cavity surface emitting lasers (VECSEL) a useful tool for telecommunication and spectroscopic applications. Very small cavity lengths are desirable for achieving continuous single mode tuning and the fiber-based VECSEL is a simple device which avoids the complicated post-growth processing involved in the fabrication of a membrane-type laser. We report here on the successful operation of an optically-pumped fiber-based VECSEL in the 850 nm wavelength region. The device comprises a half cavity periodic gain structure made of 15 Al_0.2Ga_0.8As/GaAs quantum wells designed to be at the anti-nodes of the electric field standing wave, with a 30 pairs Al_0.2Ga_0.8As/AlAs distributed Bragg reflector (DBR) as the bottom mirror. The structure is similar to one previously described, used in a macroscopic external cavity geometry. The top mirror of our cavity is a dielectric DBR deposited onto the cleaved end of a single mode fiber whose distance from the semiconductor can be controlled via a piezoelectric actuator to allow for wavelength tuning. The aim of this work is to contribute to the understanding of the operation of this optically pumped fiber-based laser. By comparing the laser performance with the f finesseinesse of an empty cavity with otherwise identical geometry, we are able to conclude that the dominant photon loss mechanism is due to fundamental diffraction limits.