Voltage tunable SiGe photodetector: A novel tool for crypted optical communications through wavelength mixing

A novel tandem SiGe-Si device is demonstrated which, based on different photoresponses in two back-to-back diodes, exhibits a voltage tunable spectral responsivity. This feature, in conjunction with a wavelength dependence in the current direction, allows the efficient decryption of a signal when substantial noise is added to distinct carrier frequencies. Time dependent encryption schemes are also possible via a modulated voltage bias. (C) 1997 American Institute of Physics.