Tunable Superlattice p-i-n Photodetectors: Characteristics, Theory, and Applications

We report on extended measurements and theory on the recently developed monolithic wavelength demultiplexer consisting of voltage tunable superlattice p-i-n photodetectors in a waveguide configuration. This includes a reduced wavelength spacing, an investigation of the polarization dependence of the crosstalk and bit-error-rate measurements for various crosstalk levels. We show that the device is able to demultiplex and detect two optical signals with a wavelength separation of 20 nm directly into different electrical channels at a data rate of 1 Gbit/s and with a crosstalk attenuation varying between 20 and 28 dB, depending on the polarization. The minimum acceptable crosstalk attenuation at a data rate of 100 Mbits/s is determined to be 10 dB. The feasibility of using the device as a polarization angle sensor for linearly polarized light is also demonstrated. The paper includes a theory for the emission of photogenerated carriers out of the quantum wells since this is potentially a speed limiting mechanism in these detectors. We show that a theory of thermally assisted tunneling by polar optical phonon interaction is able to predict emission times consistent with the observed temporal response.