Electroabsorption Modulator Using Intersubband Transitions in GaN–AlGaN–AlN Step Quantum Wells

We calculate the high-speed modulation properties of an electroabsorption modulator for lambda=1.55 mum based on Stark shifting an intersubband resonance in GaN-AlGaN-AlN step quantum wells. In a realistic simulation assuming an absorption linewidth Gamma=100 meV we obtain an RC-limited electrical f3dB~60 GHz at an applied voltage swing Vpp=2.8 V. We also show that a small negative effective chirp parameter suitable for standard single-mode fiber is obtained and that the absorption is virtually unsaturable. The waveguide is proposed to be based on the plasma effect in order to simultaneously achieve a strong confinement of the optical mode, a low series resistance, and lattice-matched cladding and core waveguide layers. Extrapolated results reflecting the decisive dependence of the high-speed performance on the intersubband absorption linewidth Gamma are also given. At the assumed linewidth the modulation speed versus signal power ratio is on a par with existing lumped interband modulators based on the quantum confined Stark effect