Quality factor and finesse optimization in buried InGaAsP/InP ring resonators

Quality factor and finesse of buried In1-xGaxAsyP1-y/ InP ring resonators have been optimized in this paper by a very general modelling technique. Limiting effect of propagation loss within the ring has been investigated using a three-dimensional (3D) highly accurate complex mode solver based on mode matching method to analyze bending loss dependence on ring radius and wavelength. Coupling between straight input/output (I/O) bus waveguides and ring resonator has been studied by 3D Beam Propagation Method (BPM), deriving coupling loss and coupling coefficient for a large range of ring radius and bus waveguides-ring distance values (for both polarizations). Ring resonator has been modelled by the transfer-matrix approach, while finesse and quality factor dependence on radius has been estimated for two resonator architectures (including one or two I/O bus waveguides) and for quasi-TE and quasi-TM modes. Guiding structure has been optimized to enhance resonator performance. The modelling approach has been validated by comparing results obtained by our algorithm with experimental data reported in literature. Influence of rejection (at resonance wavelength) at through port on quality factor and finesse has been widely discussed. A quality factor larger than 8×105 has been predicted for the ring resonator employing only one I/O bus waveguide and having a radius of 400 μm. This resonator exhibits a rejection of -8 dB at through port.