1 Metro-Access and Short Range Systems, Department of Photonics Engineering, Technical University of Denmark2 Department of Photonics Engineering, Technical University of Denmark3 Nanophotonic Devices, Department of Photonics Engineering, Technical University of Denmark
This thesis expands the state-of-the-art on the detection of high speed wireless signals using optics. Signal detection at speeds over 1 Gbps at carrier Radio Frequency (RF) ranging from 5 GHz to 100 GHz have been achieved by applying novel concepts on optical digital coherent receivers. This achievement has satisfied the requirements on transmission robustness and high capacity of next generation hybrid optical fibre-wireless networks. One important contribution of this thesis is the novel concept of photonic downconversion with free-running pulsed laser source for phase modulated Radio-over-Fiber (RoF) links. This scheme operates without high frequency electronics at the digital coherent receiver for the detection of high bitrate wireless signals. Based on this concept, I have experimentally demonstrated the recovery of up to 3.2 Gbps 16-QAM signal modulated at 40 GHz RF carrier. At that time, it was the highest bitrate reported of a wireless signal, with complex modulation format, detected using photonic means. I have developed an analytical model to support the experimental results and performed a linearity characterization to establish engineering design rules for this type of links. The results confirmed that this configuration provides high linear end-to-end transmission links and is capable of transparent transport of high spectral efficient modulation formats. Furthermore, this thesis introduces a novel approach for the generation and detection of high speed wireless signals in mm-wave frequencies at carrier frequencies exceeding 60 GHz, using photonic baseband technologies. For signal generation, high spectral-efficient optical modulation technologies are used together with optical heterodyning. In the detection side, the mm-wave signal is modulated in the optical domain and received using digital coherent detection. The experimental demonstration tested the generation and detection in the 60 GHz and 75-110 GHz bands of signals with capacity up to 40 Gbps. Those results reported the highest bitrate at mm-wave frequencies for signal generation and detection using photonic methods at the time of the writing of this thesis. In conclusion, the results presented in this thesis demonstrate the feasibility of photonic technologies for the generation, distribution and detection of high speed wireless signals. Furthermore, it opens the prospects for next generation hybrid wireless-wired access networks providing ultra-high capacities.