Transmission enhancement in photonic crystal T-junction waveguides using defect engineering

This paper investigates transmission optimization in photonic crystal T-junction waveguides using defect engineering. Six modified junction structures are analyzed using the finite-difference time-domain (FDTD) method. The optical transmission characteristics are evaluated through normalized transmission spectra, and several quantitative performance metrics including insertion loss, transmission enhancement factor, effective transmission bandwidth, and average transmission are introduced for systematic comparison. The results show that the optimized configuration significantly improves the transmission efficiency of the junction. In particular, the peak transmission increases from approximately 0.15 in the reference structure to about 0.42 in the optimized design, corresponding to a reduction of insertion loss from 8.24 dB to 3.77 dB. In addition, the optimized structure exhibits a broader transmission bandwidth and higher average transmission across the operating frequency range. Field distribution analysis reveals that the improved performance originates from enhanced mode matching and reduced scattering at the junction interface. These results demonstrate that defect engineering provides an effective approach for improving power transmission in photonic crystal waveguide junctions and may be useful for integrated photonic circuits.