Tailoring Properties of Microcavity In-Line Mach-Zehnder Interferometer by the Microcavity Enlargement Using Femtosecond Laser

This paper presents a theoretical analysis and experimental verification of fine-tuning of the spectral response and refractive index sensitivity of microcavity in-line Mach-Zehnder interferometer (mu IMZI). The mu IMZIs were fabricated using femtosecond (fs) laser micromachining in standard single-mode fibers as circular cavities with a diameter of 60 mu m. Next, the structures underwentfs laser postprocessing, which included fabrication of an additional cavity with the same diameter but shifted by 15 mu m or 30 mu m against the center of the initial microcavity. Different depths of the additional structures were investigated. The enlargement of the microcavity allows for tailoring the spectral response, i.e., it shifts the interference pattern by more than 200 nm, with no introduction of any additional losses and distortions in the spectrum. As the additional effect, regardless of the size of the extension, the sensitivity of the enlarged mu IMZI was improved by 32%.