Near-IR unidirectional absorption in a tunable asymmetric one-dimensional photonic crystal with VO₂ defect layers

In this paper, a dynamically modulated Near-IR asymmetric composite photonic crystal (PC) is proposed, which constitutes by a one-dimensional PC (1-D PC) with vanadium dioxide (VO₂) phase transition defect layers. By combining asymmetric composite PC with VO₂ phase material, which will undergo the semiconductor-metal transition (SMT) under thermal stimulation, to realize the controllable unidirectional multi-channel absorber under temperature control. Based on a relatively simple 1-D stacked thin film model, the model is investigated and optimized in terms of the structure, number of periods, and the thickness of defect layers, with the result of 20 nm for VO₂ defect layers and seven circles for the post-defect period. By using the pre-defect period number of 3, an average absorbance of 0.19 can be achieved when VO₂ is in the semiconductor phase at low temperature. With the rise in temperature, VO₂ transitions to metal phase, where the structure absorption reaches 0.99. In addition, changing the per-defect period number to 5, the average absorption at semiconductor and metal VO₂ is 0.73 and 0.10, respectively. The differential absorption around the SMT enables the tunability of single photonic devices. During the simulation, the effects of electric field and incidence angle on the structure are also analyzed. Meanwhile, the Bruggeman approximation effective medium theory is introduced in this work, and the changes of the absorption during the phase transition from semiconductor to metal in the VO₂ defect layers are also given. These characteristics are applicable to controllable multispectral absorbers, infrared detectors, limiter, and optical switchers.