Enhancement of optical nonlinearity for short wavelength (/spl sim/1.5 /spl mu/m) intersubband transitions by n-doped InGaAs/AlAsSb MQW

Summary form only given. For the application of ultrafast optical devices in future OTDM or WDM network, the intersubband transition (ISBT) provides attractive features such as large optical nonlinearity with ultrafast response. The material system available for achieving ISBT at optical communication wavelength is, however, limited. Although the ISBT at 1.5 /spl mu/m have been reported in In/sub 0.53/Ga/sub 0.47/As/AlAs, the large lattice mismatch makes it difficult to grow, and the electron leakage into the X valley of the barriers reduces the absorption. Alternatively, GaN/AlN and InGaAs/AlAsSb have attracted attention because of their large /spl Delta/E/sub 0/, reduced electron leakage, and the design flexibility of the lattice-matched system. ISBT by use of InGaAs/AlAsSb has been recently observed by our group at 1.5 /spl mu/m. However, its optical nonlinearity has not yet been reported. We show that the InGaAs/AlAsSb exhibits a larger nonlinearity than GaN due to the large dephasing time (T/sub 2/) stemming from the small effective mass (m/sub e/*) and LO phonon energy (/spl planck//spl omega//sub LO/), and that the conduction band nonparabolicity plays only a minor role.