In this paper we report on the optimization and control of key layer properties of visible vertical cavity surface emitting laser (VCSEL) for emission at wavelengths around 650 mn by means of an optical real-time sensor allowing for both spectroscopic reflectance and reflectance anisotropy measurements. In contrast to conventional ex-situ characterization the in-situ sensor yields information on properties like thickness, composition and doping for all buried layers, especially the lower distributed Bragg reflector which has a strong influence on the final device performance. Using in-situ sensor-based optimization of the growth process 650 run VCSEL devices with a record-high continuous-wave output power of 3 mw at room temperature have been fabricated. (C) 2002 Elsevier Science B.V. All rights reserved.