Erbium-doped waveguide amplifiers in polycrystalline Al2O3
Carlos Osornio Martinez is a PhD student in the department the Integrated Optical Systems group. (Co)Promotors are prof.dr. S.M. Garcia Blanco and dr. L. Chang from the faculty of Science & Technology, University of Twente.
This thesis investigates the development of high-performance on-chip optical amplifiers based on erbium-doped polycrystalline aluminium oxide (Al2O3:Er3+), aiming to overcome the scalability and integration limitation of traditional erbium-doped fiber amplifiers. The research addresses the growing need for compact, energy-efficient optical amplifiers that can be seamlessly integrated with passive photonic components in data centers, metro-access networks, and emerging LiDAR and quantum systems.
The first objective was to establish a CMOS-compatible material platform by engineering polycrystalline Al2O3:Er3+ thin films with low propagation losses and high optical gain. Through reactive co-sputtering, high-quality films were fabricated and characterized, demonstrating background losses below 0.1 dB/cm and erbium concentrations in the range of 1.5 – 3.9 ×1020 ion/cm3. Spectroscopic analysis confirmed the suitability for optical amplification, and these properties were used for waveguide design and device fabrication (Chapter 2).
To evaluate amplification performance, a series of spiral waveguide amplifiers were fabricated and tested. Optimized waveguide geometries and pump-signal configurations enabled internal net gain values exceeding 33 dB and gain per unit length of >3 dB/cm, validating the platform’s amplification potential (Chapter 3). Coupling strategies were refined through the use of conformal LPCVD SiO2 cladding, significantly reducing coupling losses and enabling external (fiber-to-fiber) gain exceeding 14 dB, with on-chip output powers above 100 mW (Chapter 4). Furthermore, by packaging an amplifier, straightforward characterization and thermal control were enabled, demonstrating over 24 dB of external gain and useful performance up to 95°C (Chapter 5).
This work further explores the monolithic integration of Al2O3:Er3+ amplifiers with passive silicon nitride waveguides (Chapter 6). Integrated wavelength-division multiplexers enabled full pump and signal routing on-chip, while maintaining broadband amplification (~80 nm bandwidth) and fiber-to-fiber noise figures of 3.2 dB. The successful integration demonstrated that high-performance active-passive photonic circuits can be realized using standard wafer-scale processes.
To validate performance under real-world constraints, the developed amplifiers were deployed in a metro-access wavelength-division multiplexed network testbed. The packaged amplifier successfully enabled 800 Gbps per-channel transmission with dynamic add/drop functionality and low optical signal-to-noise penalties (Chapter 7). These experiments confirmed that the platform satisfies key system-level requirements such as optical signal-to-noise ratio margin, scalability, and thermal stability.
The results presented in this thesis establish polycrystalline Al2O3:Er3+ as a competitive and scalable solution for integrated optical amplification. The technology developed in this thesis is currently being commercialized through Aluvia Photonics, underscoring its maturity and relevance for industrial deployment.
