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Photonic integrated circuits (PICs) have significant value in today’s world of research. They enable devices to experience large reductions in size, weight, operation power, and cost (SWAPc), making photonic technology more accessible than ever. The functionality of PICs is greatly enhanced due to the realization of both active and passive devices within a single device structure. This is made possible through hybrid integration, which utilizes various coupling methods to transfer light from an active chip to a passive chip. Hybrid integration technology tremendously expands the capabilities of PICs, leading to a plethora of applications. One significant application is that of narrow linewidth lasers. Narrow linewidth lasers are necessary for many emerging applications including laser spectroscopy, light detection and ranging (LiDAR), optical communication, and other forms of optical measurement. Narrow linewidth lasers have a low phase noise, making them ideal for measurement applications. Achieving narrow linewidth within a semiconductor laser package is of increasing importance due to its smaller form factor, allowing such devices to be employed in a plethora of fields that require a small device footprint. External cavity lasers are usually employed to achieve these characteristics by using hybrid integration to couple light from an active source into a passive waveguide, the external cavity, which greatly extends the incident photon lifetime, thus decreasing linewidth. This passive device structure is highly dependent on micro-ring resonators to couple light to and from the waveguide, making the coupling coefficient an integral parameter to the success of external cavity lasers. The passive device structure in this work utilizes the thermo-optic effect of a passive waveguide within a Mach-Zehnder Interferometer integrated with a racetrack resonator to control how much light couples into a feedback waveguide, thus tuning the linewidth using a thermo-optic heater. This in turn shows the tuning of the ring resonator coupling coefficient. Devices of similar structure have previously been used to create widely tunable lasers and optical switches, but to our knowledge, have not been used to tune laser linewidth in such an application.

The emerging applications of LiDAR, microresonator based frequency comb, and photon pair generation in photonic integrated circuits (PICs) have attracted lots of research interests recently. The single frequency, high power, narrow-linewidth, tunable semiconductor lasers are highly desired for the implementation of these emerging applications in future PICs. In this dissertation, we use the hybrid integration via edge coupling to obtain the integrated diode lasers for future PICs, since the active chip and the passive chip can be fabricated and optimized independently. We demonstrate hybridly integrated narrow-linewidth, tunable diode lasers in the Indium Phosphide/Gallium Arsenide-silicon nitride (InP/GaAs-Si3N4) platform. Silicon nitride photonic integrated circuits, instead of silicon waveguides that suffer from high optical loss near 1 µm, are chosen to build a tunable external cavity for both InP and GaAs gain chips at the same time. Single frequency lasing at 1.55 µm and 1 µm is simultaneously obtained on a single chip with spectral linewidths of 18-kHz and 70-kHz, a side mode suppression ratio of 52 dB and 46 dB, and tuning range of 46 nm and 38 nm, respectively. The resulting dual-band narrow-linewidth diode lasers have potential for use in a variety of novel applications such as integrated difference-frequency generation, quantum photonics, and nonlinear optics. We also demonstrate one potential application of the dual-band diode laser in beam steering. The dual-band diode laser combined with a waveguide surface grating can provide the beam steering by tuning the wavelength of the light signal. However, the output power of the hybridly integrated diode lasers is still limited. Integrated coherent beam combining (CBC) is a promising solution to overcome this limitation. In this dissertation, coherently combined, integrated diode laser systems are experimentally demonstrated through hybrid integration. A chip-scale coherently combined laser system is experimentally demonstrated in the InP-Si3N4 platform through the manipulation of optical feedbacks at different output ports of the coupled laser cavities. Coherent combining of two InP-based reflective semiconductor amplifiers is obtained by use of the cross-coupling provided by an adiabatic 3 dB coupler in silicon nitride, with a combining efficiency of ~92%. The novel system not only realizes the miniaturization of coherent laser beam combining but also provides a chip-scale platform to study the coherent coupling between coupled laser cavities. Besides, the emerging platforms (i.e., gain chips based on semiconductor quantum dots, silicon-carbide-on-insulator and lithium-niobate-on-insulator) have attracted intense interests in recent years. The hybridly integrated diode lasers through edge coupling are demonstrated in these emerging platforms. In addition, we study the Parity-Time (PT) symmetry in the chip-scale hybrid platform. PT symmetric coupled microresonators with judiciously modulated loss and gain have been widely studied to reveal many non-Hermitian features in optical systems. The phase transition at the exceptional points (EPs) is a unique feature of the PT symmetric non-Hermitian systems. In this dissertation, we propose and demonstrate an electrically pumped, hybridly integrated chip-scale non-Hermitian system, where the optical gain, loss and coupling are separately controlled to allow for the PT symmetry breaking and direct access of the EPs. We use the coupled Fabry-Perot resonators through the hybrid integration of two InP active chips with one Si3N4 passive chip to realize the versatile control of the gain and loss. We first demonstrate the PT symmetry breaking and access of the EPs by investigating the spectral and spatial transition processes of the hybrid system induced by the asymmetric gains in the InP active chips. We then control the loss distribution in the Si3N4 passive chip so that the system loss contrast exceeds the coupling coefficient, which leads to the PT symmetry breaking and coherent addition of the two coupled lasers. Our integrated non-Hermitian optical system in the chip-scale hybrid integration platform successfully bridges the non-Hermitian physics and photonic integrated circuits and is able to expand the practical applications of non-Hermitian optical systems to a whole new stage.

Array waveguide gratings (AWG) plays an important role in the field of in-formation and communication technologies through implementation of wavelength division multiplexing(WDM). An AWG consists of an input waveguide, two star cou-plers, and waveguide phase arrays which provides the wavelength dispersion effect along with the output star coupler. In this thesis, I developed and fabricated AWGs and expect to use the WDM inversely to make them compatible to proposed Wave-length Beam Combining(WBC) system by our group on the silicon nitride platform. In essence, the AWG theory is based on the theory of diffraction and interference. Design rules are summarized under the guidance of AWG theory. Mask layouts and routing algorithms are demonstrated. Simulation results are compared with fabri-cated devices. Applications and further improvements of AWG are discussed as well. Due to the limitation of fabrication, only features larger than 0.5um can be resolved in our stepper lithography. Best AWG performance of our fabricated devices can reach the insertion loss of 8 dB with 2 dB non-uniformity. The average channel spac-ing is around 2.8nm. 3 dB channel bandwidth is larger than 1nm with 12.65nm free spectrum range(FSR). Crosstalk is around 19 dB.

In this dissertation, we have explored the use of a highly anisotropic film, porous anodic aluminum oxide (AAO) for electronic and MEMS applications. In the first part, AAO templates integrated with ferromagnetic material were studied for spiral inductors as a magnetic core. In the second part, the applications of AAO as a structure material, a mold for electroforming, and a sacrificial layer for MEMS applications were demonstrated. There is a strong demand for high performance and quality spiral inductors for radio frequency integrated circuits (RFIC). For this purpose, ferromagnetic materials are integrated into the spiral inductors to improve their performance and miniaturize their size. However, spiral inductors with ferromagnetic cores suffer from poor performance at high frequencies due to ferromagnetic resonance effect and eddy current loss occurrence in the layer of ferromagnetic materials. Since AAO templates are self-laminated and patterned, these drawbacks are solved by integration of ferromagnetic materials into the nanopores of AAO templates. By using nickel electroplated AAO templates as a magnetic core, we presented 21% enhancement of inductance value at 5 GHz with a quality factor of 14.48. High precision, high aspect ratio structures are needed for a variety of microelectromechanical systems (MEMS) applications. The most common technology for producing high aspect ratio structures for MEMS is deep reactive ion etching (DRIE). Despite the successes of the DRIE process for MEMS applications, it has several significant shortcomings which limit its adoption for many microstructure applications. The DRIE process is expensive, time consuming, requiring expensive dedicated etching equipment, and primarily useful for etching structures in silicon, making it unlikely to be used for non-silicon applications. Other technologies, such as LIGA and SU-8 are highly specialized, and while they can be used for making simple structures, they are generally not useful for producing MEMS-like structures. Since AAO templates are highly anisotropic and can be prepared at various thicknesses, deep vertical structures with high aspect ratios can be formed by a simple low cost wet etching process. Various types of MEMS structures were fabricated by using this technique.

The accelerating increase in information traffic demands the expansion of optical access network systems that require high-performance optical and photonic components. In short-range communication links, optical interconnects have been widely accepted as a viable approach to solve the problems that copper based electrical interconnects have encountered in keeping up with the surge in the data rate demand over the last decades. Low cost, ease of fabrication, and integration capabilities of low optical-loss polymers make them attractive for integrated photonic applications to support futuristic data communication networks. In addition to passive wave-guiding components, electro-optic (EO) polymers consisting of a polymeric matrix doped with organic nonlinear chromophores have enabled wide-RF-bandwidth and low-power active photonic devices. Beside board level passive and active optical components, on-chip micro- or nano-photonic devices have been made possible by the hybrid integration of EO polymers onto the silicon platform. In recent years, silicon photonics have attracted a significant amount of attentions, because it offers compact device size and the potential of complementary metal–oxide–semiconductor (CMOS) compatible photonic integrated circuits. The combination of silicon photonics and EO polymers can enable miniaturized and high-performance hybrid integrated photonic devices, such as electro-optic modulators, optical interconnects, and microwave photonic sensors. Silicon photonic crystal waveguides (PCWs) exhibit slow-light effects which are beneficial for device miniaturization. Especially, EO polymer filled silicon slotted PCWs further reduce the device size and enhance the device performance by combining the best of these two systems. The potential applications of these silicon-polymer hybrid integrated devices include not only optical interconnects, but also optical sensing and microwave photonics. In this dissertation, the design, fabrication, and characterization of several types of silicon-polymer hybrid photonic devices will be presented, including EO polymer filled silicon PCW modulators for on-chip optical interconnects, antenna-coupled optical modulators for electromagnetic wave detections, and low-loss strip-to-slot PCW mode converters. In addition, some polymer-based devices and silicon-based photonic devices will also be presented, such as traveling wave electro-optic polymer modulators based on domain-inversion directional couplers, and silicon thermo-optic switches based on coupled photonic crystal microcavities. Furthermore, some microwave (or RF) components such as integrated broadband bowtie antennas for microwave photonic applications will be covered. Some on-going work or suggested future work will also be introduced, including in-device pyroelectric poling for EO polymer filled silicon slot PCWs, millimeter- or Terahertz-wave sensors based on EO polymer filled plasmonic slot waveguide, low-loss silicon-polymer hybrid slot photonic crystal waveguides fabricated by CMOS foundry, logic devices based on EO polymer microring resonators, and so on.