Quasi-periodic layering of linear/nonlinear materials in hollow core Bragg fiber for all-optical diode action

Abstract

A novel approach to achieving an inline all-optical diode action is presented using a quasi-periodic arrangement of titanium dioxide and polydiacetylene 9-BCMU in cladding region of hollow core Bragg fiber structure. The proposed quasi-periodicity is based on Fibonacci sequences. The reflectance formula and power transmission are derived using the transfer matrix method, and their spectra are plotted for two different Fibonacci sequences. The quasi-periodicity of the structures enables the formation of multiple photonic bandgaps. An optical asymmetry is introduced at both ends of the fiber by splicing two combinations of Bragg fibers. The all-optical diode action is investigated and simulated under two conditions: both spliced Bragg fibers have identical Fibonacci sequences (symmetric combination) and different Fibonacci sequences (asymmetric combination). In the symmetric structure, light propagation is reciprocal for both ends, while the asymmetric structure exhibits non-reciprocal propagation with significantly reduced backward light 92 % less at the output compared to forward propagation. The proposed structure demonstrates a high transmitted contrast over 97 % and exhibits a nonlinear response with increasing incident light intensity at a specific wavelength (λ = 1735 nm). Furthermore, by adjusting the refractive index of the fiber core, the all-optical diode action remains nearly constant. This suggests that the proposed structure can serve as a stable inline all-optical diode in higher wavelength regions with a variable core index.