Photonic analog-to-digital conversion and photonic microwave signal generation
Wong, Jia haur
Date of Issue2012
School of Electrical and Electronic Engineering
Network Technology Research Centre
Driven by the increasing demand for speed and capacity in advanced signal-processing systems such as radar, surveillance, millimeter-wave access networks, and satellite communication, there has been a strong interest in developing analog-to-digital converters (ADC) with high sampling rate and resolution. It is recognized that the jitter-limited accuracy and low sampling rate issues commonly associated with conventional electronic ADCs can be overcome by either optically-sampled ADC or photonic time-stretched ADC (TS-ADC) systems. Besides ADCs, electronic oscillators generating continuous-wave (CW) or/and arbitrary microwave waveforms also play a critical role in the aforementioned systems. The performance-bottlenecks imposed by the electronic circuits, however, restrict the highest frequency that can be generated and the largest bandwidth that can be achieved by the electronic oscillators. Various photonic techniques that exploit the unique and advantageous features of photonic components that include mode-locked lasers have been developed to circumvent the aforementioned restrictions. In this thesis, novel schemes for photonic analog-to-digital (A/D) conversion and photonic microwave signal generation have been reported. In the first part of the thesis, we first demonstrate a 2 Giga samples per second (GS/s) optically-sampled ADC system incorporating complementary dual-output modulation and balanced photodetection, subsequently implementing a linearization process on the digitized data for odd-order harmonics suppression. An effective number of bits (ENOB) of ~ 5.34-bits was obtained for this system. Following this, a photonic TS-ADC system amenable to continuous-time operation based on polarization modulation and balanced photodetection is investigated. Demonstrating with a single channel, we have obtained a sampling rate of 2 GS/s and ENOB of ~ 3.56 bits for this system. We end the first part of the thesis with a demonstration of a technique which enables the generation of a 10x2 GHz time- and wavelength- interleaved pulse-train (TWIPT) with pulsewidth tunability that is suitable for a 20 GS/s optically-sampled ADC adopting the wavelength-division-demultiplexing (WDD) parallel processing approach for increasing the sampling rate of the electronic ADCs. The second part of the thesis is devoted to the development of photonic techniques which can generate frequency-tunable CW microwave signals and linearly-chirped microwave signals with wide chirp tuning range. We first demonstrate two techniques which are able to generate frequency-tunable CW microwave signals with large suppression ratio of unwanted frequency components. In both of these demonstrations, we show the generation of stable tunable microwave signals with the frequencies ranging from 4 GHz to 14 GHz. Subsequently, we demonstrate an approach capable of generating microwave waveforms with tunable centre frequencies and chirp rates covering the negative, zero and positive values. In essence, a chirp rate ranging from ~ −126.7 GHz/ns to ~ +120.8 is obtained in the experiment. It should be emphasized that all the techniques demonstrated in this thesis make use of mode-locked lasers, thus rendering it a common component between the two topics studied here. With this common component, there is a good potential to integrate the techniques presented here on a common platform.
DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics