This article investigates the possibilities of gas detection using a tapered optical fiber coated with a graphene oxide layer. Measurement is based on changes in light beam propagation depending on the process of gas absorption to the graphene oxide layer. In this paper, we investigated the light change in a double-clad tapered optical fiber in a wide optical range. We present a special platform constructed for the deposition of additional functional materials that enable the preparation of the sensor module. Our results present differences in light transmission for three different kinds of gasses pure nitrogen, pure hydrogen, and a mixture of propane–butane. Measurements were provided in a wide range of 500 nm–1800 nm to find the most sensitive ages for which we are able to detect mentioned absorption and their interaction with light. Obtained results for pure gasses for which the refractive indices are similar to the air show the greatest changes for the visible range 750 nm–850 nm, and for propane–butane, changes are much visible in the whole investigated range.

This paper investigates the application of a G-Flake graphene oxide (GO) layer as an innovative coating material for optical fibre tapers, enhancing the sensor sensitivity to various volatile liquid vapours. The results confirm that this combination is effective because the formation of a monolayer of adsorbed gas alters light propagation in the tapered optical fibre. These changes are detectable across a broad wavelength spectrum, ranging from visible to infrared. In this study, three volatile liquids – trimethyl phosphate (TMP), 1,4-thioxane (THX), and ammonium hydroxide (NH4OH) – were tested using pure THX and TMP without dilution, while NH4OH was applied as a 25% solution. The gases used in the research simulate chemical warfare agents, such as sulphur mustard and sarin. The authors used the differential method to analyse the results, which revealed the formation of characteristic peak pairs around a wavelength of 795 nm. The peak heights and the distance between them varied over time in response to exposure to the selected vapours. Additionally, the amplitude of the transmitted power changes linearly in the first 30–45 min, with the highest power change rate observed for TMP (0.026 dBm/min at 789.2 nm). The greatest contrast between maximum and minimum power levels was observed for TMP, reaching 4.45 dBm. An approach was presented that demonstrates how a tapered fibre covered with GO can be used as the basis for developing a low-cost gas and vapour sensor.

An intensity-based refractive index (RI) sensor using a laser micromachined side-hole optical fibre (S-H OF) is presented in this paper. To achieve this, a microcavity was cut into a side surface of the S-H OF, providing access to one of the air holes within its structure. The geometrically modified fibre was then connected at both ends to a single-mode fibre for structure investigation in a system containing a supercontinuum laser and an optical signal analyser. In the next step, an immersion liquid was applied to a microcavity for RI values ranging from 1.30 to 1.57 in increments of 0.02. Power loss measurements were conducted for each RI value. Based on the obtained results, it can be concluded that an RI sensor has been successfully developed, which holds potential applications in biochemistry.

This article describes an external refractive index (RI) sensor based on a spectral analysis of the light transmission through a long tapered side-hole optical fiber (S-H OF). A section of the S-H OF was fusion-spliced with SMFs at both ends and connected to a supercontinuum source at the input and an optical spectrum analyzer (OSA) at the output. To investigate the effect of the external RI on the spectral characteristics, immersion liquids with refractive indices in the ranges of 1.32–1.35 and 1.37–1.42, with increments of 0.01, were used. Power loss measurements were carried out for each liquid in two wavelength ranges: 600–1200 nm and 1200–1800 nm. The highest sensitivity obtained in this study was 622 ± 11 nm/RIU in the near-infrared region. This result highlights the suitability of longtapered S-H OFs for spectral-interrogation-based RI sensing, offering a promising yet simpler alternative to more complex interferometric or plasmonic configurations.