In this Letter,the loss and gain characteristics of an unconventional InxGa1-xAs/GaAs asymmetrical step well structure consisting of variable indium contents of InxGal-xAs materials are measured and analyzed for the first time,to the best of our knowledge.This special well structure is formed based on the indium-rich effect from the material growth process.The loss and gain are obtained by optical pumping and photoluminescence (PL) spectrum measurement at dual facets of an edge-emitting device.Unlike conventional quasi-rectangle wells,the asymmetrical step well may lead to a hybrid strain configuration containing both compressive and tensile strains and,thus,special loss and gain characteristics.The results will be very helpful in the development of multiple wavelength InGaAs-based semiconductor lasers.