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Optical multiaccess networks, and more specifically passive optical networks (PONS) are considered to be one of the most promising technologies for deploying fiber-to-the-building/home/curb (FTTx). PONs are expected to solve the problem of limited bandwidth, the so called "first and last mile problem", that remains the bottleneck between the backbone network and high-speed local area networks (LANs). PONs provide a low-cost solution and a guaranteed quality of service (QoS) to enable new multimedia services. In a PON, multiple users share the fiber infrastructure in a point-to-multipoint (P2MP) network topology. This is in contrast to current access technologies, including DSL, VDSL, and cable, which use a point-to-point (P2P) network topology. The P2MP nature of networks introduces optical path delays which inherently cause the data packets to undergo amplitude, phase, and frequency variations - burst, mode trafic. This consequently creates new challenges for the design of optical receivers. / Optical receivers, and in particular, burst-mode receiver front-ends (BM-RXs) and burst-mode clock and data recovery circuits (BM-CDRs), must adapt to burst-mode traffic, where data bursts originate from various sources and travel different distances. The amplitude and phase of successive packets may therefore vary anywhere between 0--20 dB and --pi to +pi rads. The research objective of this thesis is to design, test, and enhance performance requirements of BM-CDRs for PONs. / We design and experimentally demonstrate a 622/1244 Mb/s BM-CDR with forward error correction (FEC) using Reed-Solomon (R-S(255, 239)) codes for Gigabit PONs (GPONs). We measure a coding gain of approximately 5 dB at bit error ratio (BER) of 10-10. The coding gain obtained verifies the claim of the increased link budget specified by ITU-T G.984.3 standard. / We also develop a novel technique for fast burst-error correction for bursty channels. This is achieved by employing FEC on BM-CDRs with fast phase acquisition time. We demonstrate this with our custom built bit error rate tester/analyzer (BBERT/A). / Finally, we develop a small-signal modeling technique for characterizing photodiodes. This technique is based on the measurement of S 11 parameters. We demonstrate our idea with a 10 GHz 1310/1550 nm InGaAs/InP PIN photodiode.

Vertical cavity surface emitting laser (VCSEL) structures have been grown by both metal-organic chemical vapour deposition (MOCVD) and molecular beam epitaxy (MBE). These incorporate 3 strained InGaAs / GaAs quantum wells placed resonantly in a two wavelength long optical cavity, formed between AlAs / GaAs quarter wave dielectric reflector stacks through which current is injected. The reflection spectra of these stacks is studied in detail; the effects on the laser threshold gain of absorption due to impurities and of errors in growth are investigated. Methods of disruption of the AlAs / GaAs heterointerfaces have been used to reduce the operating voltage. The completed designs use 200A intermediate layers containing 30 or 50% aluminium or a superlattice graded region simpler than that used in previous designs. The effectiveness acceptor dopants; Be in MBE, C and Zn in MOCVD; is studied also. Modulation doping was employed to reduce the effects of optical absorption. Devices were fabricated into mesas by SiC14 reactive ion etching or defined by proton implant isolation. MBE grown devices were resonant at wavelengths in the range 950 to 1059mn with essentially constant (at —1020nm) eihhi transition energies in the wells. A detailed study of the wavelength variation of threshold current density Jth (X)was made. A minimum of 366A.cnr2 was measured at 1018nm in mesa devices. A similar relation is found for ion-implanted devices but the minimum is increased to 535A.cm-2 by incomplete isolation. Gain calculations, including strain effects, are used to explain the Jth(X) variation. Implanted devices offer superior c.w. performance due to reduced thermal and ohmic resistances. The relative offset between the gain spectrum and cavity resonance was examined for c.w. operation. It was found that carrier thermal effects limit the output power rather than shifts in the offset. The bias voltage of MOCVD grown devices is as low as 1.7V and the threshold current is as low as 764A.cm-2. This is higher than for MBE grown devices because of growth thickness errors and non-optimal alignment of the gain spectrum and cavity mode. The uniformity in emission wavelength is ±1% over 80% of a 2 inch diameter wafer, offering suitability for very large uniform arrays.

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This thesis serves to address the main challenges of the terahertz technology, providing new efficient ways of actively manipulating, guiding, and generating THz and sub-THz fields. This is accomplished by taking a truly interdisciplinary approach and exploiting the physics of superconductors, and the electrodynamics of metamaterial and plasmonic structures. Metamaterial arrays made of superconducting films are suggested for manipulating the THz radiations, while superconducting plasmonic waveguides are considered for achieving efficient propagation of THz waves. In addition, metamaterial arrays composed of bimetallic rings that exhibit both plasmonic and thermoelectric properties are investigated as a possible new source of THz radiation and strong magnetic fields. I have demonstrated experimentally, for the first time, that high- and low-critical temperature superconducting metamaterials are able to show sub-radiant resonances of Fano type that can be controlled with temperature. Such metamaterial resonances show vanishing radiation losses, while superconductors have very low Ohmic losses. Thus, these structures offer an efficient way to actively manipulate sub-THz (and THz) fields. I have reported on the first experimental realisation of the extraordinary transmission effect in periodically perforated superconducting films. I have shown that the level of transmission of sub-THz waves through these structures could be controlled with temperature near the superconducting transition point. The latter enabled to identify the role of the plasmonic excitations in the mechanism of extraordinary transmission. I have shown that superconductors below their gap-frequency (several THz for high-temperature superconductors) are similar in behaviour to plasmonic metals at optical frequencies. Geometries of superconducting structures have been identified that support almost dispersionless propagation of plasmonic-like modes with frequencies up to several THz, exhibiting both extreme localisation and very low propagation losses. Finally, I have theoretically demonstrated that metamaterial arrays composed of bimetallic gold-nickel nanorings, when illuminated by ultrafast optical pulses, support transient thermoelectric currents that lead to the generation of magnetic pulses of subpicosecond duration, nanoscale localisation and peak amplitudes of the order of one Tesla. These results could facilitate the study of ultrafast nanoscale magnetic phenomena and have potential use in such applications as material characterisation and magnetic recording.

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Halide perovskites have some unique advantages as optoelectronic materials. Metal halide perovskites have been attracting enormous attention for applications in optoelectronic devices such as photodetectors, light-emitting devices and field-effect transistors. The remarkable semiconducting properties have been intensively investigated in recent years. However, the performance of optoelectronics devices based on the conventional perovskite is limited by the ion migration, the mobility of the carriers and the light absorption in the near infrared region and so on. In a decade, numerous attempts are studied to further breakthrough the limitations using both physical and chemical methods. This dissertation is devoted to overcoming the drawbacks by integrating the state-of-art perovskite with other functional materials and to further deciphering the carrier transport mechanics behind the mixed dimensional heterostructures. Field-effect transistors are the workhorse of modern microelectronics. Proof-of-concept devices have been made, utilizing solution-processed perovskite as transistors. Beyond the Field-effect transistors, photodetectors can be construct with a transistor configuration. In this dissertation, we exploited Au dimers with structural darkness to enhance the light harvesting, and utilize sorted semiconducting single-walled carbon nanotubes to enhance the conductivity of thin-film. At last, we developed a hybrid memtransistor, modulable by multiple physical inputs using hybrid perovskite and conjugated polymer heterojunction channels to realize neuromorphic computing.

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