An etched tapered single mode optical fiber (SMF) coated with polyaniline (PANI) nanofibers is developed to detect ammonia (NH3) in low concentrations. The SMF is etched with hydrofluoric acid (HF) and subsequently tapered using a glass processing workstation. The etched tapered SMF is coated with PANI via spray-coating deposition. This SMF modification significantly enhances the interaction of the evanescent field of the light propagating in the core with the PANI-sensing layer. The modified fiber sensor response is investigated by exposing the sensor to different concentrations of NH3 over the C-band wavelengths of 1535–1565 nm. Integrating the modified optical fiber with the nanostructured PANI films produces highly sensitive optical sensor that operates at room temperature. The 50 μm etched tapered SMF coated with PANI produced response, recovery times, and sensitivity of 58 s, 475 s, and 231.5%, respectively, in the C-band range. The limit of detection of the modified fiber sensor was 0.0025%, which is equal to 25 ppm. The developed sensor exhibits good repeatability, reversibility, and selectivity.

This work aims to investigate the integrated ultra-dense wavelength division multiplexing (UDWDM) and polarization division multiplexing (PDM) schemes incorporated in the free space optic (FSO) communication system. Erbium-doped fiber amplifiers (EDFAs) are used as post and pre-amplifiers in the proposed UDWDM–PDM–FSO system to boost the transmission power for increasing the distance. Thirty-two channels are transported over the FSO link to realize the total data transmission of 160 and 320 Gbps with 0.08 and 0.1 nm channel spacing, respectively. Results are also reported with non-return to zero modulation schemes. The performance of the proposed UDWDM–PDM–FSO transmission system is measured in terms of bit error rate (BER) and eye diagrams. The transmission distances are 100 and 87 km under clear weather and have acceptable BERs with 0.08 and 0.1 nm channel spacing, respectively. The weather conditions may worsen due to the increase in atmospheric turbulence. Hence, the transmission distances decrease to 3.93 and 2.6 km for heavy rain weather conditions. The UDWDM–PDM–FSO communication system exhibits an excellent performance due to the use of EDFAs with high achievable maximum distance and good and acceptable BER performance. The UDWDM–PDM–FSO communication system considerably enhances the transmission distance compared with the UDWDM–FSO communication system.

The increased deployment of optical fiber sensors along with the development of internet of things has increased the demand for real-time in situ remote monitoring systems in the optical sensing industry. Etched-tapered single-mode optical fiber (ETSMF) sensors coated with polyaniline nanofiber/graphite nanofiber (PANI/GNF) nanocomposites have been developed for the real-time in situ remote monitoring of NH3. In this investigation, the sensors with a reel of SMF with 3 km length were integrated with Erbium-doped fiber amplifier (EDFA) with 15 dB gain. Modification performed on SMF significantly enhanced the interaction between the PANI/GNF sensing layer and the evanescent wave due to the light that propagates from the core layer. The response of the modified fiber sensor to NH ₃ with different concentrations over the C-band (1535–1565 nm) was investigated. The integration of EDFA into SMF sensors extended the remote monitoring distance. In the C band, the developed sensor showed the response, recovery time, and sensitivity of 59 s, 461 s, and 210, respectively. ETSMF sensors coated with nanocomposite of PANI/GNF exhibit successful remote-sensing performances.

We present surface plasmon resonance-based sensor for arsenite [As(III)] detection using Di-iron trioxide hydrate - multi-walled carbon nanotube (Fe ₂ H ₂ O ₄ -MWCNT) nanocomposite as a sensing layer. The enticing traits of Fe ₂ H ₂ O ₄ -MWCNT having high surface to volume ratio and good affinity toward arsenic have proven to enhance As(III) absorption onto the sensing surface and consequently increase the sensitivity of the sensor. When tested with different concentrations of As(III) within the range of 0.2 ppb to 1 ppb, sensitivity value was obtained at 1.756° ppb ^-1 with Fe ₂ H ₂ O ₄ -MWCNT thickness of 7 nm. The detection limit was achieved at 0.2 ppb which surpassed conventional methods and reported studies on SPR-based sensor for As detection.