Slow and Fast Light in Semiconductor Optical Amplifiers for Microwave Photonics Applications

The generation of continuously tunable optical delays and tunable phase shifts is a key element in microwave photonics. Among the targeted applications, one can quote the filtering of microwave signals, the synchronization of optoelectronics oscillators, and the control of optically fed phased array antennas. With these applications in view, large efforts are currently done in order to develop delay lines and phase shifters based on slow and fast light effects. To date, one of the most mature approaches for integration in real field systems is that based on Coherent Population Oscillations (CPO) in Semiconductor Optical Amplifiers (SOAs). This approach offers compactness, continuous tunability of the delay or phase shift through injected current control, and possible high-level parallelism. Slow and fast light capability of semiconductor devices has been first studied in the past decade while bearing in mind the delays, the phase shifts and the bandwidth they can offer. Consequently, in a first section, we present the recent advances in architectures based on slow and fast light in SOAs for microwave photonics applications. After a brief introduction about microwave photonics, we present the physical interpretation of the different architectures proposed in the literature. We point out the underlying physics, common to these architectures, and evidence the advantages and drawbacks of each of them. However, within the scope of integration in a realistic radar system, it is also required to study the impact of these slow and fast light architectures on the performances of the microwave photonics link. In particular, the RF transfer function, the generation of spurious signals by harmonic and intermodulation products, and the intensity noise, have to be studied in order to compute the Spurious FreeDynamic Range (SFDR), a key characteristic in microwave photonics. Consequently, in a second section, we present the tools to simulate and understand the RF transfer function, the generation of spurious signals through harmonic distortion and intermodulation products, and the intensity noise at the output of a SOA. In a third section, we use the models presented in the previous part in order to investigate the dynamic range of a microwave photonics link including an architecture based on slow and fast light in SOAs. We focus on the architecture using a SOA followed by an optical filter. The models are experimentally validated and the influence on the microwave photonics link is discussed. 9