How to launch 1 W into single-mode fiber from a single 1.48-mu m flared resonator

The operation of 1.48-mum flared resonators is thoroughly studied, both exp erimentally and theoretically: the accurate determination of threshold cond ition as a function of geometrical and material parameters, the study of em ission spectra and astigmatism variations as a function of optical power le vel allow us to better understand the way these devices operate. The origin of modal distortion is then analyzed, and an original solution is proposed to increase the single-transverse-mode power at high il lection level: it is shown that implanting the multiple-quantum-well active layer with proton s efficiently enhances the filtering capability of the overall structure, a nd particularly that of the ridge waveguide, by bringing additional lateral absorption losses. The explanation of the filtering mechanism is successfu lly confirmed by simulations using the beam-propagation method. This techni que finally allowed more than 1.3 W of continuous wave (CW) diffraction-lim ited power at 6 A. Low-modal-gain structures were then realized to reduce m odal optical absorption in the implanted structures with a view to maintain ing a high external efficiency and a reduced vertical divergence. Finally, a three-lens coupling system was designed and the effects of optical feedba ck minimized so as to obtain a very high coupling efficiency: with an impro ved laser design, 1.12 W of CW power were then coupled into single-mode fib er at 6.6 A, which represents 65% of the power emitted by the laser chip.