Photonics-Assisted High Data Rate Communications

The escalating demand for higher data rates and wider bandwidths in communication networks is being driven by the emergence of new applications. This growth extends beyond communications to include essential requirements for broad-bandwidth devices in various fields, including radar, sensing, and measuring systems. The increasing bandwidths, in addition to the sampling rate, may pose challenges for the electronic digital-to-analog converter (DACs) and analog-to-digital converters (ADCs) in digital systems. These challenges include the utilization of vast digital signal processing, leading to high-power consumption and increased costs. Photonics-assisted high-data rate communication may offer promising alternatives because photonics devices provide wide bandwidth, low-power consumption, and immunity against electromagnetic interferences. The main purpose of this thesis is to explore new methods to generate and detect high-bandwidth signals by low-bandwidth electronics based on optical signal processing. Those methods should be featured by the extremely small size and low-power consumption. The research in this thesis is divided into four main parts. The first part introduces the concept of generating high-bandwidth signals with higher-spectral efficiency from low-bandwidth DACs with lower-spectral efficiency. The method combines the use of electronics and photonics. By electronics, low-bandwidth sub-DACs are employed to generate signals with wide-bandwidth and low-spectral efficiency through the use of electrical orthogonal sampling with sinc-pulse sequences in N parallel branches. In photonics, higher spectral efficiency can be produced from M branches at different optical powers. The second part proposes a concept for detecting high-bandwidth wireless signals by a low-bandwidth photonics-assisted receiver. The idea is based on down-converting the input high-bandwidth wireless signals into low-bandwidth sub-signals using optical orthogonal sampling. It relies on multiplication rather than switching, which avoids introducing aperture jitter and improves the Q-factor for detection. The third part of this thesis presents a silicon ring modulator-based compact photonic sampler with low-power consumption. The sampler can sample various microwave signals by sinc-pulse sequences. The generation of the sinc-pulse sequence and sampling occur simultaneously within the same optical ring modulator. The proposed sampler can sample high-bandwidth signals with low-bandwidth electronics. The last section of this thesis describes a novel concept for the generation and detection of an optical superchannel. The transmitter system employs a comb source and cascaded optical ring modulators. Each modulator works as a filter, selecting one wavelength from the comb lines, and as a modulator, modulating k time division channels on the chosen wavelength. This process generates a rectangular optical superchannel from all wavelengths together. The transmitter does not require the employment of optical filters or delay lines, making it simple and compact. At the receiver side, an optical ring modulator can be utilized with the local oscillator (LO) to separate the generation of the sinc-pulse sequence from sampling. This is to prevent the suppression of the optical carrier. The concepts outlined in the first to fourth sections can be combined together to generate and detect high-bandwidth signals with low-bandwidth electronics. An extremely compact system with very low-power consumption can be achieved by employing optical ring modulators, resulting in low-cost systems. The proposed system is applicable to various fields, including radar, sensing, instrumentation, communications, and data centers.