Abstract

The oscillation mode properties of multiple-stripe gain-guided phased-array GaAIAs laser diodes are investigated in cw operating conditions. Both longitudinal mode spectra and spatial mode patterns of the laser arrays are measured. With a simple collecting optics arrangement and in certain operating temperature and driving current conditions, a single longitudinal mode (with intensity ratios as high as 70 to 1) and a single spatial lobe are observed from an otherwise multimode multi-lobe laser output. The effects of operating temperature and current on the single-mode oscillation are investigated, and the results show that the single mode can be controlled over certain current and temperature ranges. The use of various collecting optics such as microscope objectives and GRIN lenses is explored, and in each case a different mode intensity ratio is obtained. It is also found that insertion of a quarterwave plate between the laser array and collecting lens spoils the single-mode oscillation, which suggests that optical feedback due to the collecting lens may be responsible for the single-mode occurrence. The details of these mode control investigations are described.

© 1987 Optical Society of America