The effective refractive index of the active region of 1.3 μm edge-emitting tilted wave lasers based on InAs/InGaAs self-assembled quantum dots by the analysis of the far-field pattern is investigated. The obtained values of 3.485 and 3.487 in the operating lasers and in the cold waveguides, respectively, are well comparable with the refractive index of bulk InAs at corresponding wavelength.
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.