INTERSUBBAND ELECTROOPTIC MODULATORS FOR NEAR AND MID INFRARED APPLICATIONS

Optical transitions between conduction subbands of asymmetrical quantu m-well structures can produce large second-order optical nonlinearitie s. In particular, it is possible to engineer asymmetrical quantum-well structures to have very large electro-optic (EO) coefficients. In thi s paper we study three alternative approaches to design and fabricate intersubband EO modulators, i.e. the Stark modulator, the quantum-inte rference (QI) modulator, and the carrier-density (CD) modulator. We sh ow that near a given resonance the Stark modulator has the largest EO coefficient. However, the linear intersubband absorption limits the us ability of this modulator to a very short device length. Far from reso nance we found that the CD and the QI modulators are more efficient. F urthermore, we found that these modulators can be utilized for near-in frared modulation in the 1.3-1.5 mu m spectral range. These modulators are almost unaffected by the linear intersubband absorption so that t heir efficiency can be very high. We present preliminary experimental results that demonstrate the operation of the QI modulator. (C) 1998 A cademic Press Limited.