| dc.description.abstract | Recently, photonic integrated circuits (PICs), especially silicon photonics, have been applied widely in various technologies. Due to their exceptional compatibility with complementary metal-oxide-semiconductor (CMOS) fabrication processes and remarkable integration density, PICs are generally regarded as the cornerstone of next-generation computing solutions. Among all the photonic devices, micro-ring resonators play an important role in PICs, offering optical functionalities such as filtering, modulation, and detection. For micro-ring resonators, the quality factor(Q) is a critical parameter determining performance. Traditionally, the Q factor is limited by waveguide material absorption and scattering loss from the imperfections of the fabrication processes, such as waveguide roughness and sidewall angles. In pursuit of a high Q factor, lightly confining the waveguide mode in the core layer permits the mode field to propagate with significant overlap with the high-quality cladding layer while the effective area of the mode field is much larger than the conventional tightly confined waveguide, in which the mode field is mostly confined in the core layer. In addition, a thin core layer allows a better etching budget with a shallower etching depth. Therefore, low-confined waveguides with a thin core layer serve to minimize both the material loss from the waveguide core and the scattering loss induced by the sidewall roughness. In this thesis, we realize the low-confined Si₃N₄ waveguide with a core layer of 100 nm thickness, enabling a bending radius of less than 1 mm and providing a higher integration density than the millimeter-sized resonators.
To achieve optimal structural design and reduce transmission losses, this paper utilizes the FEMSIM module in RSoft simulation software to investigate the light extinction depth of low-confinement waveguides under different cladding materials. This ensures that the thickness of the insulating layer is sufficient to prevent energy from reaching the silicon substrate. Additionally, through the BeamPROP module in the RSoft simulation software, this paper studies the bending losses of low-confinement ring waveguides under a silicon dioxide cladding layer, aiming to design the optimal radius for the ring waveguide. In experimental investigations, various processing methods are explored to identify the best practices for reducing material absorption and scattering losses in the waveguide. This includes different deposition techniques for silicon nitride film, deposition parameters for the cladding layer, and the impact of thermal annealing.
By integrating and validating various parameters discussed above, we have achieved a high-quality factor, low-loss micro-ring resonator. The quality factor reaches up to 1.2×10⁶, with a reduced transmission loss of 0.22 dB/cm. Moreover, the micro-ring resonator exhibits tunability.
This paper presents a design of low-confinement waveguide and optimal fabrication methods to achieve a high-quality factor, low-loss micro-ring resonator. | en_US |