Slow-light and detected electrode voltage based microwave phase shifting in bulk and quantum-dash semiconductor optical amplifiers

Within the photonics community there has been much recent interest in the use of semiconductor optical amplifiers (SOAs) for implementing microwave photonics (MWP) functions. Phase shifting is one of the most important functions required in MWP. The aim of this work is to investigate tunable microwave phase shifting in SOAs with a primary focus on utilising the field of slow and fast light (SFL) effects. The main phenomena exploited to obtain SFL effects are coherent population oscillations (CPO). Phase shifters based on CPO are demonstrated in a conventional and a reflective SOA (RSOA), both with tensile strained active regions. The performance of the RSOA based phase shifter is enhanced at low frequencies by means of so called „forced‟ CPO (FCPO). The beat signal gain is improved considerably as a result of FCPO thereby improving the noise performance of the phase shifter. An enhancement is also seen in the stability and controllability of the FCPO based phase shifter as a result of the improved signal-to-noise ratio. Numerical models developed by other members of the Optical Communications Research Group (OCRG) to model SFL effects in SOAs are also presented and show good agreement with the experimental data. The FCPO numerical model takes into account the RSOA package and current driver frequency response. In addition to the phase shifters based on SFL effects a microwave phase shifter based on the detected electrode voltage of the QDash device is demonstrated. This novel method for achieving optically and electrically controlled phase shifts also highlights the multifunctional capability of SOAs. Other experimental work presented involves the characterisation of a newly developed and quantum-dash (QDash) SOA which was supplied from Alcatel-Thales laboratories in France. Additionally the author assisted other members of the OCRG in developing a linear pulse characterisation technique to analyse the temporal chirp and power of amplified pulses in SOAs.