Abstract
In-line Fabry–Perot cavities manufactured by a new technique using electric arc fusion of NIR laser microdrilled optical fiber flat tips were studied herein for refractive index sensing. Sensors were produced by creating an initial hole on the tip of a standard single-mode telecommunication optical fiber using a Q-switched Nd:YAG laser. Laser ablation and plasma formation processes created 5 to 10 micron cavities. Then, a standard splicing machine was used to fuse the microdrilled fiber with another one, thus creating cavities with lengths around 100 micrometers. This length has been proven to be necessary to obtain an interferometric signal with good fringe visibility when illuminating it in the C-band. Then, the sensing tip of the fiber, with the resulting air cavity, was submitted to several cleaves to enhance the signal and, therefore, its response as a sensor, with final lengths between tens of centimeters for the longest and hundreds of microns for the shortest. The experimental results were analyzed via two signal analysis techniques, fringe visibility and fast Fourier transform, for comparison purposes. In absolute values, the obtained sensitivities varied between 0.31 nm−1/RIU and about 8 nm−1/RIU using the latter method and between about 34 dB/RIU and 54 dB/RIU when analyzing the fringe visibility.
Highlights
Fiber-based Fabry–Perot (FP) interferometers share the advantages of all types of optical fiber sensors: low-cost manufacture, immunity to electromagnetic interference, compact size, and high sensitivity
Due to the reduced with L1 = 105 μm corresponding spectral the reflected signal obtained from the optical spectrum analyzer (OSA) has a complex structure and shows irregular fringe spacing value of L2, the reflected signal obtained from the OSA has a complex structure and shows irregular due to the three surfaces
In this paper we presented a method for manufacturing in-line fiber Fabry–Perot cavities based on microstructured optical fiber flat tips
Summary
Fiber-based Fabry–Perot (FP) interferometers share the advantages of all types of optical fiber sensors: low-cost manufacture, immunity to electromagnetic interference, compact size, and high sensitivity. While fiber-based extrinsic cavities rely on externally coupled elements to create interference (i.e., the cavity is external to the fiber), for intrinsic sensors the interferometric cavity is created within the fiber (Figure 1). In an intrinsic FP sensor, the fiber contains the resonant cavity, Photonics 2019, 6, 109; doi:10.3390/photonics6040109 www.mdpi.com/journal/photonics found in the literature, using a few basic principles: creating the cavity on the tip of a fiber and fusing it with another fiber, relying on the creation of microscopic air bubbles embedded in the fiber’s axis [7,8] or air bubbles attached at the end of the fiber or between two fibers, using a glass tube [9,10], or from a photonic bandgap fiber and a polymer [11]. All of them are created with the aid of a fusion
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