Abstract

Direct amplification of light using semiconductor traveling wave amplifiers (TWAs) is expected to play an important role in future optical communication networks. A TWA is obtained by depositing an antireflection (AR) coating on the semiconductor laser facets. High performances require a reflectivity below 10^-4 and a large bandwidth covering the whole semiconductor laser spectrum (30-40 nm for AlGaAs devices). Today, the control of the coating parameters, especially the refractive index, remains difficult. In particular, for single-layer coatings, which typically use nonstoichimetric materials, this poor control can drastically increase the reflectivity. To alleviate this problem, we are proposing two-layer coatings, using stable stoichimetric materials. In our analysis, we have investigated the sensitivity of a large number of two-layer coatings to the wavelength, refractive indices, and thicknesses of the different layers. The simulation was carried out for both a plane-wave and a guided-wave model. It was found that the AR coatings can be grouped in several classes, depending on the value of the index and the order of the layers. The combination of TiO₂ and MgF₂ exhibits a bandwidth close to 30 nm. However, the tolerance of this coating in the value of the upper layer index is tight. This sensitivity can be reduced at the expense of the bandwidth and the tolerance in the value of the lower layer index by using ZrO₂ and MgF₂.

© 1991 Optical Society of America