Study on optical confinement of ridge waveguide heterostructure for laser diode applications

Abstract

The ridge waveguide laser diode is theoretically analyzed and experimentally fabricated in this thesis. The waveguide properties are investigated by using the effective refractive index approximation. The optical confinement, defined as the fraction of the optical power containing in the waveguiding layers, is obtained by this technique. The analyses of the fundamental transverse heterostructures of DH, LOC and SCH are carried out and consequuently yields the optimal values of active, waveguiding and cladding layer thickness; such values providing the single transverse mode. In order to obtain the single lateral mode, the optimal values of residual upper-cladding layer thickness (t) and ridge width (w) are determined by analyzing the effect of cladding layer thickness. The experimental fabrication of ridge waveguide laser with GaAs/AlGaAs DH structure and an 0.2 micron GaAs active layer is demonstrated by the Liquid Phase Epitaxy (LPE) technique. The ridge width of 4 micron and residual thickness of 0.35 micron are established by wet-chemically etching and thereby provide the difference of 0.002 lateral index step for single-spot beam profile (TE00). The threshold current ranging from 120 to 150 mA and the differential quantum efficiency ranging from 2.5 to 3.6% were achieved from the fabricated chips with 500-600 micron cavity length.