Natural carbon powder has been used as a precursor to prepare two main types of sensitising agents of nitrogen-doped carbon nanoparticles (N-CNPs) and nitrogen-doped graphene quantum dots coupled to nanosheets (N-GQDs-NSs) by using simple treatments of chemical oxidation and centrifugation separation. Characterization based on FTIR, XPS, XRD, Raman spectroscopy, FE-SEM, HR-TEM, AFM, UV-Vis and FL, revealed successful doping carbon nanoparticle with nitrogen with an average plane dimension of 50 nm and relatively smooth surface. The versatility of the prepared samples as sensitising agents was developed and established by exploiting its ability for detection of volatile organic compounds via simple optical fibre based sensing configuration. The comparative experimental studies on the proposed sensor performance indicate fast response achieved at a few tens of seconds and excellent repeatability in exposure to the methanol vapour. The low limit of detection of 4.3, 4.9 and 10.5 ppm was obtained in exposure to the methanol, ethanol and propanol vapours, respectively, in the atmosphere condition. This study gives insights into the chemical/physical mechanism of an enhanced economic optical fibre based gas sensor and illustrates it for diverse sensing applications, especially for chemical vapour remote detection and future air quality monitoring.

No abstract

Multi-wavelength erbium-doped fiber laser (EDFL) is demonstrated using a piece of a bismuth-based erbium-doped fiber (Bi-EDF) in a simple ring resonator. The proposed EDFL is able to generate up to 17 lines with a constant channel spacing of 0.41 nm at 1615.5 nm region using only a piece of 215 cm long of Bi-EDF as both linear and nonlinear gain medium. However, the number of lines reduces to two with the use of 49 cm long of Bi-EDF. The multi-wavelength generation is due to oscillating Bi-EDF laser lines which interacts each other to create new photons at other frequency via four-wave mixing process. The multi-wavelength EDFL is stable at room temperature and also compact due to use of only a very short length of gain medium.

No abstract

Carboxyl-functionalized molybdenum disulfide (COOH-MoS2) nanosheets were prepared through a facile low-temperature hydrothermal method. The phase transformation of metallic-1T to 2H-semiconductor COOH-MoS2 nanosheets was conducted through introducing Au thin film on the unclad optical fiber as a sensing layer in a low temperature. The developed structure successfully refined the loss of the semiconducting properties and poor adhesion of COOH-MoS2 on the unclad polymer optical fiber, which provided limited semiconductor potential as the sensing layers on the optical fiber surfaces. The sensing performance of the as-prepared structure was tested for quantitative detection of three different volatile organic carbons (VOCs) of ethanol, propanol, and methanol gases as well as cross-sensitivity to relative humidity. The operating principle was based on intensity variation of the evanescent wave in the sensing region. The response of the proposed sensing system shows maximum response and better linearity (R 2 = 0.999) to methanol at room temperature. Finally, the comparative experimental cross-sensitivity to relative humidity and methanol was also studied to evaluate the potential of sensing range.