Selectively erbium (Er) doped titanium (Ti) in-diffused optical waveguide amplifiers on lithium niobate (LiNbO3) substrate have been fabricated and characterized in the wavelength regime around λ = 1.53μm using counter-directional pumping at λP = 1.48μm. LiNbO3 waveguide amplifiers are desirable for providing gain in optical circuit chips through integration with other optical elements on a single substrate. A prerequisite for achieving useful gain rests on the optimization of overlap between the incident guided optical signal mode distribution and the evolving emission from excited Er ions. The extent of overlap can be controlled by adjusting fabrication parameters. Fabrication parameters for Er-doped Ti in-diffused waveguide amplifiers of useful optical gain have been optimized by diffusing selective patterns of vacuum-deposited 17nm-thick erbium film at 1100˚C for 100 hours into LiNbO3, and integrating with 7μm-wide single mode straight channel waveguides formed by diffusing 1070Å thick titanium film into the LiNbO3. Small-signal gain characterization was carried out with a -30 dBm of transmitted input signal power at λS=1531nm with counter-directionally launched pump power ranging between 0 to 119mW at λP=1488nm, using TM polarization for both the signal and pump beams. At a maximum launched pump power of 119mW, a signal enhancement of 8.8dBm for 25mm-long erbium doped region, and 11.6dBm for 35mm-long erbium doped region were obtained. The corresponding calculated net gain values are 1.8dB and 2.8dB, for the 25mm-long and 35mm-long Er-doped regions, respectively.

It is well known that thermally evaporated a-As2S3 thin films are prone to oxidation when exposed to an ambient environment. These As2O3 crystals are a major source of scattering loss in sub-micron optical integrated circuits. Magnetron sputtering a-As2S3 not only produces films that have optical properties closer to their equilibrium state, the as-deposited films also show no signs of photo-decomposed As2O3. The TM propagation loss of the as-deposited As2S3-on-Ti:LiNbO3 waveguide is 0.20 plus/minus 0.05 dB/cm, and it is the first low loss hybrid waveguide demonstration. Using the recipe developed for sputtering As2S3, a hybrid Mach-Zehnder interferometer has been fabricated. This allows us to measure the group index of the integrated As2S3 waveguide and use it in the study of the group velocity dispersion in the sputtered film, as both material dispersion and waveguide dispersion may be present in the system. The average group index of the integrated As2S3 waveguide is 2.36 plus/minus 0.01. On-chip optical amplification was achieved through thermal diffusion of erbium into X-cut LiNbO3. The net gain measured for a transverse magnetic propagation mode in an 11 μm wide Er:Ti:LiNbO3 waveguide amplifier is 2.3 dB plus/minus 0.1 dB, and its on-chip gain is 1.2 plus/minus 0.1 dB/cm. The internal gain measured for a transverse electric propagation in an 7 μm wide Er:Ti:LiNbO3 waveguide amplifier is 1.8 dB plus/minus 0.1 dB and is among the highest reported in the literature. These gains were obtained with two 1488 nm lasers at a combined pump power of 182mW. In order to increase further the on-chip gain, we have to improve the mode overlap between the pump and the signal. This can be done by doping erbium into As2S3 film using multi-layer magnetron sputtering. The Rutherford backscattering spectroscopy shows that the doping of Er:As2S3 film with 16 layers of erbium is homogeneous, and Raman spectroscopy confirms no significant amount of Er-S clusters in the sputtered film. The deposition method was used to fabricate an Er:As2S3 waveguide, and the presence of active erbium ions in the waveguide is evident from the green luminescence it emitted when it was pumped by 1488 nm diode laser.

Silicon photonics (SiP) has become a cornerstone technology of the modern age by leveraging the mature fabrication processes and infrastructure of the microelectronics industry for the cost-effective and high-volume production of compact and power-efficient photonic integrated circuits (PICs). The impact that silicon (Si)-based PICs have had on data communications, particularly data center interconnection and optical transceiver technologies, has encouraged SiP chip development and their use in other applications such as artificial intelligence, biomedical sensing and engineering, displays for augmented/virtual reality, free-space communications, light detection and ranging, medical diagnostics, optical spectroscopy, and quantum computing and optics. To expand the functionality and improve the performance of SiP circuits for these surging applications, subwavelength grating (SWG) metamaterials have been thoroughly investigated and implemented in various passive integrated photonic components fabricated on the silicon-on-insulator (SOI) platform. SWG metamaterials are periodic structures composed of two materials with different permittivities that exhibit unnatural properties by using a period shorter than the guided wavelength of light propagating through them. The ability to synthesize the constituent SiP materials without any need to alter standard fabrication procedures enables precise, flexible control over the electromagnetic field and sophisticated selectively over anisotropy, dispersion, polarization, and the mode effective index in these metastructures. This provides significant benefits to SOI devices, such as low loss mode conversion and propagation, greater coupling efficiencies and alignment tolerances for fiber-chip interfaces, ultrabroadband operation in on-chip couplers, and improved sensitivities and limits of detection in integrated photonic sensors. Parallel to the rise of SiP technology is the development of other materials compatible with mature PIC fabrication methods both in the foundry (e.g., silicon nitride (Si3N4)) and outside the foundry (e.g., high-index oxide glasses such as aluminum oxide (Al2O3) and tellurium oxide (TeO2)). Si3N4 offsets the pitfalls of Si as a passive waveguiding material, providing lower scattering and polarization-dependent losses, optical transparency throughout the visible spectrum, increased tolerance to fabrication error, and better handling of high-power optical signals. Meanwhile, Al2O3 and TeO2 both serve as excellent host materials for rare-earth ions, and TeO2 possesses strong nonlinear optical properties. Using a single-step post-fabrication thin film deposition process, these materials can be monolithically integrated onto Si PICs at a wafer scale, enabling the realization of complementary-metal-oxide-semiconductor (CMOS)-compatible, hybrid SiP devices for linear, nonlinear, and active functionalities in integrated optics. While SWG metamaterials have widely impacted the design space and applicability of integrated photonic devices in SOI, they have not yet made their mark in other material systems outside of Si. Furthermore, demonstrations of their capabilities in active processes, including optical amplification, are still missing. In this thesis, we present a process for developing various SWG metamaterial-engineered integrated photonic devices in different material systems both within and beyond SOI. The demonstrations in this thesis emphasize the benefits of SWG metamaterials in these devices and realize their potential for enhancing functionality in applications such as sensing and optical amplification. The objective of the thesis is to highlight the prospects of SWG metamaterial implementation in different media used in integrated optics. This is accomplished by experimentally demonstrating SWG metamaterial waveguides, ring resonators and other components composed of different hybrid core-cladding material systems, including Si-TeO2 and Si3N4-Al2O3. Chapter 1 introduces the background and motivation for integrated optics and SWG metamaterials and provides an overview and comparison of the different materials explored in this work. Chapter 2 presents an initial experimental demonstration of TeO2-coated SOI SWG metamaterial waveguides and mode converters. It also details the design of fishbone-style SWG waveguides aimed at lowering loss and enhancing mode overlap with the active TeO2 cladding material in the hybrid SiP platform. Chapter 3 details an open-access Canadian foundry process for rapid prototyping of Si3N4 PICs, emphasizing the Si3N4 material and waveguide fabrication methods, as well as the design and characterization of various integrated photonic components included in a process design kit. The platform is compared against other Si3N4 foundries, and plans for further development are also discussed. Chapter 4 reports the first demonstration of SWG metamaterial waveguides and ring resonators fabricated using a Si3N4 foundry platform. The measured devices have a propagation loss of ∼1.5 dB/cm, an internal quality factor of 2.11·10^5, and a bulk sensitivity of ∼285 nm/RIU in the C-band, showcasing competitive metrics with conventional Si3N4 waveguides and SWG ring resonators and sensors reported in SOI. Chapter 5 presents work towards an SWG metamaterial-engineered waveguide amplifier. The fabricated device, based in Si3N4 and functionalized by an atomic layer deposited, erbium-doped Al2O3 thin film cladding, exhibited a signal enhancement of ∼8.6 dB, highlighting its potential for on-chip optical amplification. Methods to reduce the loss within the material system are proposed to achieve net gain in future devices. Chapter 6 summarizes the thesis and discusses pathways for optimizing the current devices as well as avenues for exploring new and intriguing materials and devices for future applications in integrated photonics. / Thesis / Doctor of Philosophy (PhD)