Nonuniform output characteristics of laser diode with wet-etched spot-size converter

We study the output characteristics of spot-size converter (SSC) integrated buried heterostructure (BH) laser diode (LD) by forming SSC with wet etching process. SSC-LD shows large chip-to-chip variation in threshold current(Ith) and slope efficiency (eta(slope)) compared to LD without SSC. Ith and eta(slope) are closely related with each other so that the front facet eta(slope) increases while the rear facet eta(slope) decreases with Ith. Far-field angle is also found to be proportional to the front facet eta(slope). The trends observed are explained clearly by a unidirectional loss occurring when photons travel from the front to rear facet.