Enhanced second harmonic generation in Kolakoski-based multilayers using LiTaO₃: A comparative study with periodic and other aperiodic structures

We introduce a new class of one dimensional aperiodic photonic crystals based on the Kolakoski sequence, designed for the efficient generation of significantly enhanced forward and backward second harmonic (SH) signals. The proposed structure consists of alternating air and nonlinear LiTaO₃ layers, where each nonlinear layer comprises a pair of 180° antiparallel poled crystals. Using the nonlinear transfer matrix method, we compute the conversion efficiencies for both forward and backward SH waves at various generation stages. Our numerical results demonstrate that the Kolakoski based multilayers outperform conventional periodic structures by at least one order of magnitude, achieving maximum forward SH conversion efficiencies of approximately 1.0×{10}⁻²% and 6.0×{10}⁻³% at N=85 and N=63, respectively. Beyond efficiency, we conduct a comprehensive analysis of fabrication tolerance, angular dependence, and material loss, revealing that the Kolakoski structure exhibits superior robustness compared to periodic and other aperiodic arrangements such as Fibonacci and Thue Morse. This work confirms that the inherent periodicity breaking in Kolakoski multilayers leads to strong field localization and resonant enhancement, enabling efficient SH generation even under non ideal conditions. Given its high performance and practical resilience, the proposed Kolakoski based LiTaO₃ platform represents a promising candidate for integrated nonlinear optical devices, including multi wavelength and high power frequency converters.