A new method for fabricating low-cost, high-performance waveguides, lasers and modulators in photonic integrated circuits for optical communication networks

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Title: A new method for fabricating low-cost, high-performance waveguides, lasers and modulators in photonic integrated circuits for optical communication networks.The integration of multiple lightwave devices such as lasers and optical modulators into a complex, highly functional configuration on a single chip, known as a photonic integrated circuit (PIC), can dramatically reduce the cost of high-speed optical networking systems supporting the internet and telecommunications, akin to advances in electronics and computing offered by silicon integrated circuits. However, current integration technologies require expensive crystal regrowth processes, face fundamental speed limitations due to the physical properties of the materials now in use, and use electron beam lithography methods (not scalable to mass manufacturing) in order to achieve the small waveguide dimensions needed for optimal performance. This project supports research on a new low-cost waveguide fabrication method that addresses each of these current shortfalls which promises to significantly enhance the integration level and performance of modulators and lasers for the advanced photonic integrated circuits of the future. Such PICs will enable lower cost optical communications systems and increase the deployment of broadband internet to underserved population areas.The specific goals of this research are to develop a unique, new selective waveguide core oxidation process for the AlInGaAs/InP material system used for telecommunication-wavelength photonic devices. A novel oxygen-enhanced wet thermal oxidation process will be optimized for this new material system and the benefits of the resulting low-refractive-index, low dielectric-constant, insulating, interface-passivating, and roughness-smoothing buried oxide layer fully exploited for the fabrication of high-speed electro-absorption modulator (EAM) and laser devices. The process allows the overall waveguide core width to be reduced to single-mode dimensions without the need for e-beam lithography. The low dielectric constant offers reduced parasitic capacitance and strong optical confinement without incurring increased contact resistance, thus reducing the overall RC time constant to achieve high modulation speed devices. The oxide promises to simultaneously dramatically reduce interface roughness and waveguide scattering loss and remediate dry-etch ion damage. The resulting high-index-contrast waveguide structure enables InP-based 1.3 and 1.55 micron telecomm wavelength devices with stable optical spatial mode confinement that can be aggressively curved with low bend loss for optical signal routing and on-chip lasers suitable for densely-packed photonic integrated circuits. Research methods to be used include optimization of oxidation system gas flow dynamics to enhance process control and oxide uniformity; characterization and optimization of oxide insulating properties, refractive index, and thermal conductivity; time-resolved photoluminescence to characterize oxide-semiconductor interface quality; precision angle polishing and focused ion beam milling for inspection of buried-oxide interface roughness; and swept-laser Fabry-Perot transmission resonance waveguide loss measurements. Three targeted oxide-confined AlInGaAs/InP device applications will be explored in collaboration with the Tyndall National Institute in Cork, Ireland: high-speed traveling-wave electro-absorption modulators; high-speed directly-modulated lasers; and compact, curved-resonator on-chip integrated lasers exploiting the low-bend loss properties of the proposed unique oxide-confined waveguiding structure.