Transmission Characterisation of Series Dual Ring Resonators Based on Transmission Matrix Model

In this study, a cascaded two-ring dual waveguide structure is proposed to address the problem of limited free spectral range (FSR) of single-ring micro-ring resonators, and its transmission characteristics are deeply analysed by constructing a transmission matrix model. Based on Maxwell's equations, the optical field coupling process is deduced, the transmission matrix of the cascade network is established, and the effects of coupling coefficients, micro-ring radius and transmission loss on the performance are investigated by numerical simulation. The results show that: the cascade structure can significantly extend the FSR, and when the coupling coefficient is reduced (e.g., k = 0. 54), the transmission spectrum is close to the ‘box’ response, and the crosstalk is reduced; the adjustment of the micro-ring radius (10-30 μm) can achieve the resonance wavelength tuning; and the reduction of the transmission loss (α = 0) can improve the signal quality. This study provides theoretical support for the design of high-performance tunable photonic devices, which have potential applications in dense wavelength division multiplexing systems and high-resolution spectral analysis.