Relating the chirp parameter to the number of quantum wells in GaAs/AlGaAs waveguide modulators

Abstract

For wavelengths near the quantum well absorption edge it is found that fewer quantum wells favor ideal phase modulation in GaAs/AlGaAs waveguide modulators. This is due to the dominance of the linear electro-optic effect over quantum absorption effects in the separate confinement waveguide. For TE polarization, it is found that the chirp parameter varies from 10 at −5 V and λ=0.89 μm in actual devices depending on the number of wells. The data fit estimates from theory. For TM polarization no dependence was observed as expected. For an integrated laser/phase modulator (with different absorption edges) a 4-well structure may be near optimum to maximize the modulation efficiency and to still have low laser threshold current.