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Silicon (Si) and silicon nitride (Si3N4) have become the dominant photonic integrated circuit (PIC) material platforms, due to their low-cost, wafer-scale production of high-performance circuits. However, novel materials can offer additional functionalities that cannot be easily accessed in Si and Si3N4, such as light emission. Tellurium oxide (TeO2) is a novel material of interest because of its large linear and non-linear refractive indices, low material losses and large rare-earth dopant solubility, with applications including compact low-loss waveguides and on-chip light sources and amplifiers. This thesis investigates the post-processing integration of TeO2 devices onto standardized Si and Si3N4 chips to incorporate TeO2 material advantages into high-performance PICs. Chapter 1 introduces the state-of-the-art functionality for various integrated photonic materials as well as methods for integrating multiple materials onto single chips. Chapter 2 presents the development of a high-quality TeO2 thin film fabrication process by reactive RF sputtering, with material refractive indices of 2.07 and optical propagation losses of <0.1 dB/cm at 1550 nm. Chapter 3 investigates a conformally coated TeO2-Si3N4 waveguide platform capable of large TeO2 optical confinement and tight bending radii, characterizing fiber-chip edge couplers down to ~5 dB/facet, waveguide propagation losses of <0.5 dB/cm, directional couplers with 100% cross-over ratio, and microresonators with internal Q factors of 7.3 × 105. In Chapter 4 a spectroscopic study of TeO2:Er3+-coated Si3N4 waveguide amplifiers was undertaken, with internal net gains of up to 1.4 dB/cm in a 2.2-cm-long waveguide and 5 dB total in a 6.7-cm-long sample demonstrated, predicted to reach >10 dB could 150 mW of pump power be launched based on a developed rate-equation model. Chapter 5 demonstrates TeO2-coated microtrench resonators coupled to silicon waveguides, with internal Q factors of up to 2.1×105 and investigates environmental sensing metrics of devices. Chapter 6 summarizes the thesis and provides avenues for future work. / Thesis / Doctor of Philosophy (PhD)

<p>In this Thesis I report on my work done in replicating the Pound-Drever-Hall (PDH) laser stabilization technique as well as applications of PDH to microring resonators and generated Optical Frequency Combs (OFC). These works have been broken down into three sections. First, I replicated the PDH method with a continuous wave (CW) laser along with a Fabry-Pérot Cavity (FPC). Second, I applied the same technique to a 25 GHz Free Spectral Range (FSR) microring resonator fabricated in Silicon Nitride. Third, I applied the PDH technique to a high Quality Factor (Q) high Free Spectral Range (FSR) microring resonator in preparation to lock the repetition rate of two soliton combs beat together. The last experiment was for an application towards a compact optical clock system; such systems will have a wide impact on the infrastructure of our navigation and communication structures in use today.</p>

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The integration of high-quality (Q)-factor 3-D filters with highly efficient antennas is addressed in this dissertation. Integration of filters and antennas into inseparable units eliminates the transitions between the otherwise separate structures resulting in more compact and efficient systems. The compact, highly efficient integrated 3-D filter/antenna systems, enabled by the techniques developed herein, allow for the realization of integrated RF front ends with significantly- reduced form factors. Integration of cavity filters with slot antennas in a single planar substrate is first demonstrated. Due to the high Q factor of cavity resonators, the efficiency of the integrated filter/antenna system is found to be the same as that of a reference filter with the same filtering characteristics. This means a near 100% efficient slot antenna is achieved within this integrated filter/antenna system. To further reduce the footprint of the integrated systems, vertically integrated filter/antenna systems are developed. We then demonstrate the integration of cavity filters with aperture antenna structures which enable larger bandwidths compared with slot antennas. The enhanced bandwidths are made possible through the excitation and radiation of surface waves. To obtain omnidirectional radiation patterns , we integrate cavity filters with monopole antennas. Finally, the integration of filters with patch antennas is addressed. Unlike the other filter/antenna integration examples presented, in which the antenna is utilized as an equivalent load, the patch antenna provides an additional pole in the filtering function. The presented techniques in this dissertation can be applied for filter/antenna integration in all microwave, and millimeter-wave frequency regions

Numerous techniques exist for measuring temperature using passive devices such as SAW filters. However, SAW filters have a significant limitation regarding high temperature environments exceeding 1000⁰C [1]. There are several applications for a high temperature sensor in this range, most notably heat flux or temperature in turbine engines. For these environments, an alternative to SAW filters is to use a passive resonator. The resonate frequency will vary depending on the environment temperature. Understanding how the frequency changes with temperature will allow us to determine the environmental temperature. In order for this approach to work, it is necessary to induce resonance in the device and measure the resonance frequency. However, the extreme high temperature makes wired connections impractical, therefore wireless interrogation is necessary. To be practical a system of wireless interrogation of up to 20cm is desired.

The resonance frequency of a silicon nitride (SiN) nano-electromechanical systems (MEMS/NEMS) can be measured precisely due to their large quality factor that is associated to low thermomechanical fluctuations. While these properties enable the fabrication of high performance sensors, their use will eventually raise questions regarding their long-term stability, notably for calibration purposes. The long-term frequency stability and aging of SiN are less studied than the short-term fluctuations such as thermomechanical noise. Long-term aging studies exist for quartz clocks as well as MEMS silicon clocks and accelerometers, but not for SiN resonators with high quality factors. Thus, in this work we conduct the aging study of SiN membranes fabricated by our lab, by constantly tracking changes of the resonance frequency of the device over a long period. The evolution of the frequency drift is tracked, by optical interrogation, continuously for 135 days with a digital phase locked loop (PLL). Our device is placed in a cell under high vacuum to suppress air damping on our resonating membrane. Furthermore, due to its high sensitivity to temperature changes, our silicon nitride resonator and vacuum chamber are placed in an air bath providing a stable temperature (within 0.5 K over 135 days in the present case). To compensate further the frequency drifts induced by temperature changes, a multimeter measures the resistance of a calibrated thermistor placed inside the vacuum environment. The measured frequency drift for the aging periods of 135 days was of 300 parts per million (ppm) and was consistent with previously reported double logarithmic models for quartz oscillators. The initial stage of negative frequency drift, in our aging data, is consistent with the behaviour expected from the desorption of water due to the transition from ambient air environment to high vacuum. We review models explaining how water adsorption/desorption impacts our membrane's frequency by (1) inducing chemical reaction stresses (most important effect), (2) through the contribution of the water surface tension stress (non-negligible effect), and (3) through mass loading from water molecules (weakest effect). After this initial negative trend, the membrane frequency drift inverts and increases almost linearly, in a fashion consistent with loss of mass from desorption of other chemical species. To identify these chemical species, X-ray photoelectron spectroscopy measurements were conducted on a reference membrane stored in an ambient setting and on our membrane placed under vacuum during our aging studies. The aged membrane, compared to its reference counterpart, contained substantially less alkaline ion contaminants (i.e., sodium, calcium and potassium), most likely due to desorption of these species during the aging measurement, and to the increase in adsorption occurring on the reference membrane concurrently. We therefore hypothesize that trapped negative charges, which is a typical phenomenon within dielectric materials such as SiN, might progressively attract positive ion contaminants over time when the device is exposed to ambient air.

The electromagnetic spectrum is becoming increasingly congested due to the rapid development of wireless and mobile communication in recent decades. New, compact and efficient passband filters with multi-functions and good performance are highly demanded in current and future wireless systems. This has also driven considerable technological advances in reconfigurable/tunable filter and filtering antenna designs. In light of this scenario, the objectives of this thesis are to design, fabricate and measure efficient, compact, multi-standard, and reconfigurable/tunable microstrip resonator filters and study the integration of the resonators with patch antennas. As a passive design, a compact dual-band filter is implemented to cover 2.5 to 2.6 GHz and 3.4 to 3.7 GHz for 4G and 5G, respectively. Another design is also presented with the advantages of a wide passband of more than 1 GHz. Conversely, new and compact reconfigurable filters are designed using varactor and PIN diodes for 4G and 5G. The proposed filters are tunable in the range from 2.5 to 3.8 GHz. The bandwidth is adjustable between 40 and 140 MHz with return losses between 17 to 30 dB and insertion loss of around 1 dB. Also, the thesis investigates the design of cascaded and differentially-fed filtering antenna structures. The cascaded designs operate at 2.4 and 6.5 GHz and have a relatively wide-band bandwidth of more than 1.2 GHz and a fractional bandwidth of more than 40%. For the differentially-fed structures, good performance is achieved at the 3.5 GHz with a high realized gain of more than 7.5 dBi is observed. / European Union Horizon 2020 Research and Innovation Programme (Marie Skłodowska-Curie Actions) under grant agreement H2020-MSCA-ITN-2016 SECRET-722424.

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