Active Passive Monolithic Platforms in Si3N4 Technology
Jinfeng Mu is a PhD student in the research group Optical Sciences (OS). His supervisor is prof.dr. S.M. García Blanco from the Faculty of Science and Technology.
In the last decade, great efforts have been directed towards the development of “generic” photonic platforms that will enable the “foundry” concept and the scaling of the manufacturing of PICs. To achieve more diverse functionalities on a photonic chip, the combination of different material platforms is extremely important. This is generally carried out by either hybrid integration, heterogeneous integration or monolithic integration.
Recently, tremendous progress has been made on applications using silicon nitride (Si3N4) photonics in microwave photonics, non-linear optics, and sensing fields benefiting from these outstanding optical properties, i.e., wide transparency window (~400 nm to 2.4 µm) and low-loss feature (~0.1 dB/cm in C-band). The integration of active devices such as lasers, amplifiers, and modulators in the Si3N4 platform is significant to realize diverse functionalities.
The goal of this thesis is to develop generic integrated platforms and building blocks that enable various active-passive photonic applications based on the Si3N4 platform. In this thesis, a generic integration technology as well as building blocks that enable the integration of active functionalities into Si3N4 platform are designed, fabricated and experimentally demonstrated. Two materials, the SU-8 polymer and amorphous aluminium oxide (Al2O3) have been used in the demonstrations. In particular, Er3+ doped Al2O3 has been utilized to demonstrate an active-passive application, i.e., optically pumped integrated Al2O3:Er3+-Si3N4 amplifiers.
Chapter 2 of this thesis presents the development of building blocks based on the passive Si3N4 platform, including MMI multi/demultiplexers, ring resonator, and loop mirrors. These building blocks are needed for the realization of integrated active-passive devices.
In Chapter 3, hybrid and monolithic integration technologies were studied to integrate polymers onto the Si3N4 platform. Hybrid integration based on flip-chip bonding was environmentally demonstrated and showed robust optical coupling between the polymer and Si3N4 waveguides after several thermal shock cycles according to the international standard (IEC 60512-11-4: 2002). The monolithic integration of polymer onto the Si3N4 platform was also demonstrated by employing thickness-tapered Si3N4 waveguides, with low-loss, ultra-broadband, and ultra-high fabrication tolerant optical coupling features.
Chapter 4 developed the integration of rare-earth-ion doped materials on the Si3N4 platform based on the knowledge of Chapter 3. We proposed an innovative double-layer photonic platform that combines the outstanding optical features of Si3N4 and the properties of rare-earth-ion doped Al2O3, enabling the realization of various active-passive integrations on the Si3N4 platform by scalable monolithic integration. Such optical coupling solution was further tested for active-passive integration between Al2O3:Er3+ and Si3N4. The technologies developed in this chapter provide a promising way towards the realization of active functionalities on the Si3N4 platform by scalable monolithic integration and show great potential for the realization of low-cost, mass-produced integrated amplifiers and lasers.
Chapter 5 introduces the first integrated optical Al2O3:Er3+ amplifier on the Si3N4 platform with a high net gain (i.e., from Si3N4 input-Si3N4 output waveguide, circa 18 dB) based on the developed double-layer platform. We proposed an improved approach to characterize the optical gain considering all on-chip losses. This approach was experimentally demonstrated and showed good agreement with commonly used gain characterization method based on signal enhancement. Furthermore, the proposed method gave us further insight into the methodology based on signal-enhancement, letting to an improved more robust signal-enhancement method that takes into consideration potential waveguide imperfections.
