Beyond resonance shift: decoupling tunability and performance in semiconductor and superconducting defect photonic crystals.

This work presents a unified multi-parameter framework for evaluating tunable one-dimensional defect photonic crystals based on semiconductor (STO) and superconducting (SC) active layers. Unlike conventional approaches that rely solely on resonance shift, the proposed methodology incorporates spectral linewidth, quality factor stability, and a newly introduced trade-off index (TI) to quantify tuning efficiency under external fields. Using a transfer matrix method (TMM), the optical response of both structures is analyzed under electric (STO) and magnetic (SC) control in the terahertz regime. The results reveal fundamentally different tuning mechanisms governed by material physics: the STO structure exhibits moderate electro-refractive tuning with stable spectral characteristics, while the SC structure demonstrates significantly enhanced tunability due to strong magneto-optical response, accompanied by Q-factor degradation. Despite operating in distinct spectral regions (∼160µm for STO and ∼745-810µm for SC), the comparative analysis confirms that performance differences arise primarily from intrinsic material-dependent refractive index modulation rather than wavelength scaling. The SC-based structure achieves a substantial enhancement in performance metrics, including ∼51× improvement in figure of merit and ∼143× increase in the proposed trade-off index. Field-distribution analysis further confirms stronger electromagnetic confinement within the superconducting defect layer, explaining the observed linewidth reduction. The presented framework provides a physically meaningful approach for evaluating tunable photonic devices and offers new insights into balancing tunability and spectral stability in advanced terahertz photonic systems.