THEORETICAL INVESTIGATION ON QUANTUM-WELL LASERS WITH EXTREMELY LOW VERTICAL BEAM DIVERGENCE AND LOW-THRESHOLD CURRENT

A specially designed quantum well laser for achieving extremely low ve rtical beam divergence was reported and theoretically investigated. Th e laser structure was characterized by two low index layers inserted b etween the waveguide layers and the cladding layers. The additional la yers were intended to achieve wide optical spread in the cladding laye rs and strong confinement in the active region. This enabled significa nt reduction of beam divergence with no sacrifice in threshold current density. The numerical results showed that lasers with extremely low vertical beam divergence from 20 degrees down to 11 degrees and thresh old current density of less than 131 A/cm(2) can be easily achieved by optimization of the structure parameters. Influences of individual ke y structure parameters on beam divergence and threshold current densit y are analyzed. Attention is also paid to the minimum cladding layer t hicknesses needed to maintain low threshold current densities and low internal loss. The near and far field patterns are given and discussed . (C) 1998 American Institute of Physics.