Raman fiber laser with highly non-linear fiber

This paper demonstrates the power performance of an asymmetrical distributed feedback Raman fiber laser (DF-RFL) employing 2 km of highly nonlinear fiber (HNLF). The forward-pumped architecture exhibited better threshold condition and higher output power alongside a broader spectral profile compared to a DF-RFL utilizing a standard transmission fiber. This experimental layout could offer better insight on flatter broadband gain compared to conventional DF-RFL

MEH-PPV film thickness influenced fluorescent quenching of tip-coated plastic optical fiber sensors

The performance of plastic optical fiber sensors in detecting nitro aromatic explosives 1,4-dinitrobenzene (DNB) have been investigated by fluorescence spectroscopy and analyzed by using fluorescence quenching technique. The plastic optical fiber utilized is 90 degrees cut tip and dip-coated with conjugated polymer MEH-PPV poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] thin films for detection conjugants. The thicknesses of the MEH-PPV coating were varied to improvise the sensitivity whilst slowly reducing the fluorescence intensity. It was shown that fluorescence intensity from thinner film decreased by (82% in 40 s) in the presence of DNB signifying an improvement of 28% reduction with time 13 s less than that of the thicker film

Tunable ultra-long random distributed feedback fiber laser

A 72 km open-ended symmetrical tunable random distributed feedback fiber laser (RDB-FL) with different pumping schemes is presented in this study. The random distributed feedback was contributed by Rayleigh scattering in the single-mode fiber while distributed gain was provided by the effect of stimulated Raman scattering. The pumping schemes tested with the configuration was outward and inward pumping, where these would be backward and forward pumping in a non-symmetrical configuration of a fiber laser, respectively. The tuning range was also varied in conjunction with the different pumping schemes to determine the optimum performance. Random lasing in the RDB-FL was achieved by utilizing multiple scattering in the disordered gain medium to achieve resonance. With pump power limited to 1.5 W, the best threshold was measured as low as 1.4 W while the highest total output power was at 8 mW. In outward pumping configuration, the wavelengths that are within the maximum Raman gain (1555-1565 nm) show the best peak powers and total output power with a narrow linewidth, as low as 0.25 nm

Synthesis, optical and magnetic behavior of (BiFeO3)1−x(α-Fe2O3)x nanocomposites

(BiFeO3)1−x(α-Fe2O3)x nanocomposites were synthesized from dried gels of BiFeO3 and α-Fe2O3. Samples with x = (0.00 (BiFeO3), 0.25, 0.50 and 1.00 (α-Fe2O3)) were studied using X-rays diffractions (XRD), UV–vis spectroscopy, photoluminescence spectroscopy (PL), electron spin resonance (ESR) and vibrating sample magnetometer (VSM). Amounts of α-Fe2O3 phase were 23 and 35% for samples x = 0.25 and 0.50, respectively. Microstrain of BiFeO3 phase tended to decrease with increasing α-Fe2O3. Optical band gap reduced from 2.42 eV for BiFeO3 to 2.35 eV for sample x = 0.25 and then increased to 2.56 eV for sample x = 0.50. From PL, intensity of near band emission peak of BiFeO3 increased with increasing α-Fe2O3 content. From ESR and VSM, the g-value and magnetization saturation were enhanced with embedding of α-Fe2O3 into BiFeO3

Dinitrobenzene sensing utilizing chitosan-based thin films optical fluorescence sensors via linear and nonlinear excitation

We presented here the findings of linear and nonlinear excitation of an optical fluorescence sensor enhanced with chitosan-based thin films coated on tapered optical fiber for detecting of dinitrobenzene solution compound. The absorbance peak of linear excitation at 441.2 nm shows a small shift to from 540.8 nm to 541.3 nm when 0.003g/ml dinitrobenzene was diluted in acetone. Time resolved fluorescence resulting in decreasing of fluorescence intensities was recorded for both linear and nonlinear excitation. Both showed an agreement of quenching of fluorescence up to 30% of its initial fluorescence due to the free electron transfer from chitosan thin film to the dinitrobenzene. Nonlinear excitation gives more rapid time-resolved florescence after 4 minutes compared to 6 minutes in linear excitation

Reflectivity variation in asymmetric random distributed feedback Raman fiber laser

This paper demonstrates and discusses the effect of reflectivity on the intracavity power development and spectral profile of a 41.1 km asymmetric (half-opened cavity) random distributed feedback fiber laser with different pumping schemes. The laser cavity is confined by a fiber Bragg grating and the Rayleigh feedback amplified by Raman scattering effect that serves as virtual random distributed mirrors. The laser performance was observed by integrating a variety of power couplers while employing forward and backward pumping schemes. Forward pumping exhibits greater susceptibility to reflectivity variation compared to backward pumping. Meanwhile, higher reflectivity produced better threshold conditions but at the expense of lower saturation power. A power-saturated laser also manifested a broader spectrum than a laser conducted outside the saturation regime. These research findings will be beneficial in understanding the role of reflectivity and pumping configurations in enhancing asymmetric random distributed feedback fiber laser

Nonlinear optical characterization of phosphate glasses based on ZnO using the Z-scan technique

The nonlinear optical properties of a phosphate vitreous system [(ZnO)x − (MgO)30−x − (P2O5)70], where x = 8, 10, 15, 18, and 20 mol% synthesized through the melt-quenching technique have been investigated by using the Z-scan technique. In the experiment, a continuous-wave laser with a wavelength of 405 nm was utilized to determine the sign and value of the nonlinear refractive (NLR) index and the absorption coefficient with closed and opened apertures of the Z-scan setup. The NLR index was found to increase with the ZnO concentration in the glass samples by an order of 10−10 cm2centerdotW−1. The real and imaginary parts of the third-order nonlinear susceptibility were calculated by referring to the NLR index (n2) and absorption coefficient (β) of the samples. The value of the third-order nonlinear susceptibility was presented by nonlinear refractive or absorptive behavior of phosphate glasses for proper utilization in nonlinear optical devices. Based on the measurement, the positive sign of the NLR index shows a self-focusing phenomenon. The figures of merit for each sample were calculated to judge the potential of phosphate glasses for application in optical switching

Photothermal imaging using non-contact photopyroelectric method

Photothermal imaging is a non-destructive and contactless technique for testing and monitoring defect of materials. This work is demonstrated thermal images for film sample of Al, Cu, Ni, and Cu with artificial defect with sampling area of 10 mm × 12 mm (21 × 25 pixels), 10 mm × 14 mm (21 × 29 pixels), 10 mm × 14 mm (21 × 29 pixels), 10 mm × 10 mm (21 × 21 pixels) respectively, acquired by raster scanning with the step size of 500 µm at fixed frequency modulation of 6 Hz and lock in detection in the range of 50 to 500 mV depending of studied material. The thermal image of defect sample is successfully acquired by introducing artificial defect onto the sample of Cu film. The thermal signal is obtained by taking transmission measurement which is defined by the ratio of intensity with sample to without sample. This paper also involves a photopyroelectric non-contact configuration for thermal diffusivity of the Al, Cu, and Ni film samples. Normalization procedure was used to wipe out the amount of photopyroelectric cell media parameter that should usually known before the sample’s thermal diffusivity could be decided. In this case, sample Al, Cu, and Ni were nearly to literature values but therefore justified the suggested model, the thermal diffusivity acquired

Time-temperature profiles effect on thermoluminescence glow curve formation of germanium doped optical fibres

The development of optical fibres technology grows in response to seeking a radiation detector with better thermoluminescence (TL) performance. Concerning the dosimetric characterization study by previous researchers, this research work has widened the exploration to optimize the time-temperature profile (TTP) in connection with the glow curve formation of the optical fibres. Two forms of germanium (Ge) doped optical fibres, namely cylindrical optical fibre (CF) and flat optical fibre (FF) were fabricated, and the TTP were investigated prior to commissioning the optical fibres for fieldwork. CF and FF were irradiated to the dose of 2 Gy using a 6 MV linear accelerator. Various TTP profiles, including preheat temperature, preheat time, acquisition temperature rate, and acquisition time were varied to determine the best thermal profile for the CF and FF based on the glow curve formations. Out of 4 parameters, an increase in preheat temperatures ranging from 40 to 120 °C caused a significant variation in the glow curve formation, thus possibly giving rise to different TL signals of the optical fibres. The maximum glow peak temperature of CF and FF was unvarying when different preheat temperatures employed. These findings support the conceptual idea that manipulating the optical fibres’ readout system can alter the glow curve formation. Thus, an optimized TTP will provide the correct glow curve configuration for kinetic parameter analysis

Structure tuned, high transmission 180° waveguide bend in 2-D planar photonic crystal

We present a high transmission, small bending radius, 180° waveguide bend based on triangular lattice air holes two-dimensional (2-D) planar photonic crystal. The desired high transmission is achieved by altering the waveguide structure at the bending region. Drop hole defects are introduced at the bending region to guide the incoming electromagnetic wave. Simulation results based on the 2-D finite difference time domain method show that normalized transmission as high as 99.4% is achieved at 1550 nm optical wavelength and it is >94% for nearly the entire optical C-band. In addition, the small bending radius enhances the suitability of our design to be used in ultra-compact photonic integrated circuits