Large optical cavity waveguides for high-power diode laser applications

Properties of different Large Optical Cavity (LOC) based high-power diode laser structures with an a 1 mum wide Al0.3Ga0.7As step-index waveguide are discussed. One key parameter is the. position of the double quantum well (DQW) being either located centered or off-centered. By employing Near-field Scanning Optical Microscopy (NSOM) in emission mode with excitation wavelengths close to the laser emission wavelength of 808 nm we visualize the effect of the waveguide design on (i) the number of guided modes and (ii) the spatial profile of, both fundamental and higher order modes. Detailed analysis shows that the data depend distinctly on the spatial position of the DQW and the respective changes in mode structure. By changing the excitation photon energies towards very high values of 2.8 eV (442 nm) surface excitation is realized where the waveguiding effect becomes less effective. We demonstrate the ability to map the DQW location within the waveguide by its specific absorption properties and to verify its off-centered position. Thus the NSOM technique provides a sensitive tool for nondestructive analysis of diode laser structures including its waveguide mode properties.