All-optical wavelength conversion of 21.4-Gb/s QPSK signals using intersubband transition in InGaAs/AlAsSb coupled double quantum wells

We have demonstrated format-free wavelength conversion using cross-phase modulation associated with intersubband transition (ISBT) in a quantum wells waveguide. The waveguide functions as an all-optical phase modulator and a TM-polarized-QPSK launched signal that excites ISBT is converted to a cross-polarized TE-signal immune to ISBT absorption.