Fabrication of Mid-Infrared Porous Anodic Alumina Optical Microcavities via Aluminum Anodization

This study reports the production of mid-infrared (MIR) porous anodic alumina (PAA)-based microcavities with tunable optical quality. The spectral position of the cavity resonance peak (λ_C), along with its intensity (I_R) and Q-factor, varies depending on the geometric positioning of the cavity layer within the multilayer stack of alternating low- and high-porosity layers, as well as the type of cavity produced-either by high voltage (Cv_H-type) or low voltage (Cv_L-type) pulses. In most cases, PAA microcavities with Cv_H-type cavity layers exhibited superior light confinement properties compared to those with Cv_L-type cavities. Additionally, shifting the cavity layer from the center toward the edges of the multilayer stack enhanced the intensity of the resonance peak. For PAA microcavities with Cv_H-type cavity layers, the highest intensity (I_R = 53%) and the largest Q-factor (Q = 31) were recorded at λ_C of around 5.1 µm. The anodization approach used in this study demonstrates significant potential for designing PAA-based microcavities with high optical performance in the MIR spectral region, especially with further refinement of electrochemical parameters. These findings pave the way for the development of new photonic materials specifically tailored for the MIR spectral range, broadening their applications in various optoelectronic and sensing technologies.