Very high sensitivity optical modulators based on band filling effect in GaInAs quantum wells

The band-filling effect in a blockaded reservoir and quantum-well electron transfer structure (BRAQWETS) was used to achieve the very low voltage-length product (2.1 V-mm) needed to produce a 180 degrees phase shift in a monolithic Mach-Zehnder interferometer. The high sensitivity, high speed, good linearity, and low chirp of the BRAQWETS modulator make it an attractive device for lightwave applications. The structures used contain five to eight periods of BRAQWETS each with an n-doped electron reservoir and an undoped spacer layer of AlGaInAs (1-eV bandgap), a GaInAs quantum well, and an AlInAs blocking barrier. This waveguide core is surrounded by n-doped cladding layers of AlInAs. The leakage current under bias in this n-i-n structure remains low owing to the large conduction-band discontinuity (0.52 eV) available between AlInAs and GaInAs.<>