We have proposed and demonstrated the principle of optical decoupling of the AC modulation component in a lossmodulated Vertical Cavity Surface Emitting Laser (VCSEL) using a detuned duo-cavity device. This approach allows the VCSEL power to be modulated without changing the photon density in the active region. Analysis of reflectivity spectra of a Fabri-Perot cavity with absorber shows that at a certain detuning from the resonance wavelength, reflectivity is almost independent of absorption magnitude. At this spectral detuning between the active region cavity and modulator cavity, a feedback-free transmission modulation of the VCSEL output is possible. The use a multiple-double-QW (MDQW) electroabsorption modulator allows absorption swing between 0.2% and 2% per pass. Optical power modulation of transmission with contrasts up to 40% and chirp of less than 0.05 nm at 930 nm was demonstrated with our design. Initial cavity resonance detuning is controlled through growth and was determined to be ideally ~0.7 nm from analysis of stand-alone absorber cavities. Resonance coupling (splitting) was calculated to be less than 0.3 nm in case of matching resonances. Applying bias at the MDQW modulator section allows adjustment of detuning between cavities by changing the top cavity resonance wavelength mainly via Kramers-Kronig relations. The high frequency modulation characteristics can be tuned in this manner to show little or no sign of resonance, in which case the high frequency roll-off of the modulation response is entirely determined by parasitics of the modulator section. We have demonstrated a flat (+/-3db) response up to 20 GHz.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.