Silicon photonics (SiP) has evolved into a mature platform for cost-effective low power compact integrated photonic microsystems for many applications. There is a looming capacity crunch for telecommunications infrastructure to overcome the data-hungry future, driven by streaming and the exponential increase in data traffic from consumer-driven products. To increase data capacity, researchers are now looking at the wavelength window of the thulium-doped fiber amplifier (TDFA), centered near 2 µm as an attractive new transmission window for optical communications, motivated by the demonstrations of low loss, low nonlinearity, and high bandwidth transmission. Large-scale implementation of SiP telecommunication infrastructure will require light sources (lasers) and amplifiers to generate signals and boost transmitted and/or received signals, respectively. Silicon (Si) and silicon nitride (Si3N4) have become the leading photonic integrated circuit (PIC) material platforms, due to their low-cost and wafer-scale production of high-performance circuits. Silicon does however have a number of limitations as a photonic material, including that it is not an ideal light-emitting/amplifying material. This proposed research pertains to the fabrication of on-chip silicon and silicon nitride lasers and amplifiers to be used in a newly accessible optical communications window of the TDFA band, which is a significant step towards compact PICs for the telecommunication networks. Tellurium oxide (TeO2) is an interesting host material due to its large linear and non-linear refractive indices, low material losses and large rare-earth dopant solubility showing good performance for compact low-loss waveguides and on-chip light sources and amplifiers. Chapter 1 provides an overview of silicon photonics in the context of particularly rare earth lasers and amplifiers, operating at extended wavelengths enabled by the Thulium doped fiber amplifier. Chapter 2 presents a theoretical performance of waveguides and microresonators as the efficient structure for laser and amplifiers applications designed for optimized use in Erbium and Thulium doped fiber amplifier wavelength bands. Then spectroscopic study thulium (Tm3+) has been studied as the rare earth element for Thulium doped fiber amplifier wavelength bands. Chapter 3 presents an experimental study of TeO2:Tm3+ coated Si3N4 waveguide amplifiers with internal net gains of up to 15 dB total in a 5-cm long spiral waveguide. Chapter 4 provides a study of TeO2:Tm3+ -coated Si3N4 waveguide lasers with up to 16 mW double-sided on-chip output power. Chapter 5 presents an experimental study of low loss and high-quality factor silicon microring resonators coated with TeO2 for active, passive, and nonlinear applications. Chapter 6 represents the first demonstration of an integrated rare-earth silicon laser, with high performance, including single-mode emission, a lasing threshold of 4 mW, and bidirectional on-chip output powers of around 1 mW. Further results with a different design are presented showing lasers with more than 2 mW of double-sided on-chip output power, threshold pump powers of < 1 mW and lasing at wavelengths over a range of > 100 nm. Importantly, a simple, low-cost design was used which is compatible with silicon photonics foundry processes and enables wafer scale integration of such lasers in SiP PICs using robust materials. Chapter 7 summarizes the thesis and provides paths for future work. / Dissertation / Doctor of Engineering (DEng)

This thesis presents studies of novel terahertz photonic devices, including photoconductive optoelectronic devices and guided-wave components, aimed at the development of next-generation terahertz systems. In chapter 2, a scalable interdigitated THz transmitter is designed to increase the output power and compared with a conventional 50 μm coplanar transmitter. In chapter 3, we compare four different receivers with different antenna geometries in terms of bandwidth and sensitivity. Then we describe a photoconductive near-field detector with a subwavelength aperture and its system integration and characterization. In chapter 4, a parallel metal plate waveguide is designed with an integrated step inside the waveguide that can couple to higher order TM modes efficiently from the TEM mode. In this chapter, we also experimentally and numerically study a 2-dimensionally tapered parallel plate waveguide, by which a free-space THz beam can be focused into a deep subwavelength-scale volume. In chapter 5, a parallel thin dielectric film waveguide is used to explore the guiding mechanism of an antiresonant optical reflection waveguide. Cylindrical silica single capillaries and a microstructured capillary, which guide in a similar way, are characterized in terms of mode profiles and attenuation. In chapter 6, we study oblique transmission through freestanding thin nickel films, which are perforated with periodic conical hole arrays. Surface modes can be supported by both metallic surfaces with different nonlinear dispersion curves, which results in spectral interferences in a near-field region when the surface modes couple out of the waveguide into free space.

La realización de esta tesis doctoral permitió confirmar la combinación exitosa de la configuración de láseres guiados y las propiedades espectroscópicas de los dobles tungstatos de potasio y tierra rara para ser usados en la fabricación de dispositivos de óptica integrada. Mediante crecimiento epitaxial en fase líquida (LPE) de capas monocristalinas de KY1-x-yGdxLuy(WO4)2 activadas con Er3+ y Tm3+ se fabricaron guías de onda planas. Usando la composición KY0.58Gd0.22Lu0.17Tm0.03(WO4)2 se demostró por primera vez un láser guiado en los regímenes continuo y pulsado (Q-switch) con emisión a 1.84 m. Combinando técnicas de fotolitografía UV, Ar-ion milling y LPE, se fabricaron guías de onda acanaladas de dos tipos: superficiales y soterradas. Mediante esta novedosa combinación, se demostró por primera vez un láser guiado de Tm3+ con emisión a 1.84 m sin la necesidad de añadir espejos a la guía acanalada soterrada. / The successful combination of the advantages of the waveguide laser geometry and the spectroscopic properties of monoclinic double tungstates was confirmed in this work by the realization of planar and channel waveguide lasers activated with Tm3+. Planar waveguides activated with Er3+ and Tm3+ were fabricated by Liquid Phase Epitaxial growth (LPE) of KY1-x-yGdxLuy(WO4)2 single crystalline layers over KY (WO4)2 substrates. CW and Q-switch laser operation at 1.84 m were, for the first time, demonstrated using the lattice matched composition KY0.58Gd0.22Lu0.17Tm0.03(WO4)2 . Surface channel waveguides were fabricated by structuring the surface of the Er3+ and Tm3+-doped planar waveguides by means of standard UV-photolithography and Ar-ion milling. Buried channel waveguides were fabricated by a novel combination of LPE of the activated layers after structuring of the surface of the KY (WO4)2 substrates by Ar-ion milling. Mirrorles waveguide laser in CW regime was demonstrated using these buried channel waveguides.