Physics and application of four-wave mixing in semiconductor optical amplifiers

This thesis investigates the physical mechanisms responsible for four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs), and their application to quantum-well spectroscopy and all-optical signal processing. A microscopic theory of polarization-resolved FWM is developed, and the corresponding polarization selection rules are derived. It is then shown how these results can be used to study basic carrier dynamics in semiconductor active layers. Finally, a wavelength conversion device and a new class of all-optical logic gates, based on FWM in SOAs, are presented and characterized. The first part of the thesis is devoted to several experimental and theoretical investigations of carrier transport dynamics in multiquantum-well SOAs, and of their relation to the FWM nonlinearity of these devices. A polarization-resolved FWM configuration is used to study interwell carrier transport in a SOA consisting of alternating pairs of tensile and compressively strained quantum wells. A similar structure with interwell coupling provided by resonant tunneling is then investigated theoretically; it is shown how FWM can be used to excite coherent electric-dipole oscillations in this device, leading to efficient generation of TeraHertz radiation. Finally, a novel wavelength-resolved FWM technique is demonstrated to directly study the capture of carriers in quantum wells. The second part of the thesis focuses on the application of FWM to all-optical signal processing for WDM communication systems. A wavelength conversion device based on FWM in a long (1.5 mm) SOA is developed, and used to demonstrate error-free conversion of 10 Gbit/sec data over a record 30 nm wavelength span. Other configurations for wavelength conversion by FWM are then proposed and demonstrated, including: a dual-pump configuration for polarization insensitive operation; a self-pumped FWM converter, based on a fiber-Bragg-grating coupled diode laser; and a device based on injection-locked FWM in this same laser, characterized by a large resonance peak in its conversion efficiency. Finally, the last chapter is devoted to a novel class of all-optical logic gates, based on FWM, designed to operate on bytes of information encoded in wavelength ("byte-wide WDM").