Wide bandwidth and flat multiwavelength Brillouin-erbium fiber laser.

A wide bandwidth and flat multiwavelength Brillouin-erbium fiber laser is demonstrated experimentally. In the proposed laser setup, the combination of a Brillouin mirror with feedback and a ring cavity with four-wave mixing assistance is realized. The efficiency of Brillouin Stokes lines generation is enhanced by the feedback-based Brillouin mirror structure. The effect of four-wave mixing in highly nonlinear fiber increases the generation of Brillouin Stokes lines in a wider bandwidth. The laser lines over 16 nm bandwidth (i.e 200 channels) within 4.65 dB power difference are obtained. The generated laser lines span from 1534 to 1550 nm with wavelength spacing of 0.08 nm and optical signal-to-noise ratio of at least 15 dB. The laser can also be freely tuned over 32 nm and is stable with power fluctuations of 0.7 dB over 1 hour duration.

Modified plastic optical fiber with CNT and graphene oxide nanostructured coatings for ethanol liquid sensing.

A high sensitivity and simple ethanol sensor based on an un-cladded multimode plastic optical fiber (UCPOF) coated with carbon nanotubes (CNTs) for the detection of different concentrations of ethanol in de-ionized water is developed and demonstrated. The UCPOF probe is fabricated by chemically removing the fiber cladding and integrated with CNT as a sensing layer. The effect of surface morphology on the sensor performance is investigated by characterizing another UCPOF coated with GO nanomaterial. The developed fibers are coated with CNTs and GO using drop casting technique. Energy dispersive X-ray spectroscopy (EDX), atomic-force microscopy (AFM) and scanning electron microscope (SEM) are used to investigate the element and morphology of the synthesized nanomaterials. The experimental results indicated that the absorbance spectrum of the CNT-based UCPOF sensor increases linearly with a higher sensitivity of 0.68/vol% and magnitude change of 95.4% as compared to 0.19/vol% and 56.3%, respectively, for the GO-based sensor. The UCPOF coated with CNT exhibits faster response and recovery than that of GO. The sensor shows high selectivity to ethanol amongst a range of diluted organic VOCs. The superior sensing performance of the developed fiber sensor indicates its high efficiency for ethanol detection in various industrial applications.

Room temperature ammonia sensing using tapered multimode fiber coated with polyaniline nanofibers.

We demonstrate an ammonia sensor composed of a tapered multimode fiber coated with polyaniline nanofibers that operates at room temperature (26°C). The optical properties of the polyaniline layer changes when it is exposed to ammonia, leading to a change in the absorption of evanescent field. The fiber sensor was tested by exposing it to ammonia at different concentrations and the absorbance is measured using a spectrophotometer system. Measured response and recovery times are about 2.27 minutes and 9.73 minutes, respectively. The sensor sensitivity can be controlled by adjusting the tapered fiber diameter and the highest sensitivity is achieved when the diameter is reduced to 20 µm.

20 GHz spacing multi-wavelength generation of Brillouin-Raman fiber laser in a hybrid linear cavity.

We demonstrate a tunable multi-wavelength Brillouin-Raman fiber laser with 20 GHz wavelength spacing. The setup is arranged in a linear cavity by employing 7.2 and 11 km dispersion compensating fibers (DCF) in addition to a 30 cm Bismuth-oxide erbium doped fiber. In this experiment, for the purpose of increasing the Stokes lines, it is necessary to optimize Raman pump power and Brillouin pump power together with its corresponding wavelengths. At the specific Brillouin pump wavelength, it is found that the longer length of 11 km DCF with optimized parameters results in larger number of Stokes combs and optical signal to noise ratios (OSNRs). In this case, a total of 195 Brillouin Stokes combs are produced across 28 nm bandwidth at Brillouin pump power of -2 dBm and Raman pump power of 1000 mW. In addition, all Brillouin Stokes signals exhibit an average OSNR of 26 dB.

Multi-wavelength Brillouin-Raman fiber laser utilizing enhanced nonlinear amplifying loop mirror design.

We demonstrate a single-spacing, multi-wavelength Brillouin-Raman fiber laser utilizing an enhanced cavity of nonlinear amplifying loop mirror. In this structure, the optimization of multi-wavelength lasing is done with proper adjustments of coupling ratio and Brillouin pump power. When setting the Raman pump power to 300 mW, up to 28 channels with an average 17 dB optical signal-to-noise ratio are achieved. In this case, the Brillouin pump power is maintained at -2.6 dBm when the splitting ratio and Brillouin pump wavelength are fixed at 99/1 and 1555 nm, correspondingly. Our achievements present high numbers of Stokes channels with an acceptable optical signal-to-noise ratio at low pump power operation.

In situ Raman spectroscopy of H2 interaction with WO3 films.

It is well known that WO(3) interacts efficiently with H(2) gas in the presence of noble metals (such as Pd, Pt and Au) at elevated temperatures, changing its optical behaviors; and that its crystallinity plays an important role in these interactions. For the first time, we investigated the in situ Raman spectra changes of WO(3) films of different crystal phases, while incorporating Pd catalysts, at elevated temperatures in the presence of H(2). The Pd/WO(3) films were prepared using RF sputtering and subsequently annealed at 300, 400 and 500 °C in air in order to alter the dominant crystal phase. The films were then characterized using SEM, XRD, XPS, and both UV-VIS and Raman spectroscopy. In order to fundamentally study the process, the measurements were conducted when films were interacting with 1% H(2) in synthetic air at elevated sample temperatures (20, 60, 100 and 140 °C). We suggest that the changes of Raman spectra under such conditions to be mainly a function of the crystal phase, transforming from monoclinic to a mix phase of monoclinic and orthorhombic achieved via increasing the annealing temperature. The as-deposited sample consistently shows similar Raman spectra responses at different operating conditions upon H(2) exposure. However, increasing the annealing temperature to 500 °C tunes the optimum H(2) response operating temperature to 60 °C.