Graphic analysis of the effective reflectivity of antireflection-coated films on diode facets

The wavelength dependence of the reflectivity of AR-coated facets and carrier density in relation to peak wavelength of the gain profile have been taken into consideration to study a one-facet AR-coated semiconductor diode laser. A graphic analysis method is developed to study cases in which analytical expressions of the reflectivity curves cannot be extracted. Results show that the upper bound of the carrier density that can be established inside the diode is generally (sometimes to a considerable degree) smaller than that determined by the claimed minimum reflectivity if the spectral width of the reflectivity curve cannot be regarded as infinite. This implies that the effective reflectivity of the AR-coated facet is generally larger than the claimed minimum reflectivity. To increase the effectiveness of AR film, it is essential to maintain tight control of the wavelength at which the reflectivity curve is minimum.