Current Issue : January - March Volume : 2019 Issue Number : 1 Articles : 5 Articles
Phosphor coated diodes are critical to the lighting industry. Rare-earth doped\nfluoride phosphors are characterized in this work. Spectroscopy and lifetime\nmeasurements of CaF2: Dy3+, LaF3: Eu3+ and Tb3+-doped LaF3 and CaF2 crystals\nwere performed by irradiating the samples with 405 and 375 nm diode\nlasers. Chromaticity diagrams are developed from spectral measurements.\nDy3+-doped CaF2 revealed bright white light emission having peaks at 492,\n570 and 654 nm. The measured color coordinates are x = 0.322 and y = 0.340\nfor Dy3+-doped CaF2 and these values are close to those of sunlight and the\ncoordinated color temperature is 6147 K, under 405 m laser excitation.\nEu3+-doped LaF3 revealed twenty emission peaks in the visible wavelength region.\nThe color coordinates measured for LaF3: Eu3+ are x = 0.283 and y =\n0.293 under 405 nm diode laser excitation and the color temperature is 9557\nK. Eu3+-doped LaF3 provides cool white-light, under 405 nm diode laser excitation.\nTb3+-doped fluoride crystals revealed bright white light under low\npower diode laser excitation. The measured color coordinates for Tb3+-doped\nCaF2 are x = 0.329 and y = 0.558 and the color temperature is 7713 K. The\ncolor coordinates for LaF3: Tb3+ are x = 0.342 and y = 0.365 and the coordinated\ncolor temperature is 5370 K. These values are close to those of sunlight....
A highly sensitive fibre bundle-based reflective optical sensor has been designed and\nfabricated for Tip Clearance measurements in a turbine rig. The sensor offers high spatial and\ntemporal resolution. The sensor probe consists of a single-mode transmitting fibre and two concentric\nrings of receiving multimode fibres that collect reflected light in a differential detection gain\nconfiguration, yielding a highly linear calibration curve for distance measurements. The clearance\nmeasurement range is approximately 2 mm around the central point fixed at 3.2 mm from the probe\ntip, and the sensitivity of the probe is 61.73 ... The fibre bundle has been designed to ensure\nthat the distance security specifications required for the experimental program of the turbine are met.\nThe optical sensor has operated under demanding conditions set by the blade and casing design.\nThe experimental results obtained so far are promising and lead us to think that the optical sensor\nhas great potential for online clearance measurements with high precision....
This paper aims to improve the source tracking efficiency of distributed vibration signals\ngenerated by phase-sensitive optical time-domain reflectometry ..... Considering the two\ndimensions (time and length) of .... signals, the authors saved and processed these signals\nas images after particle filtering. The filtering method could save 0.1% of hard drive space without\nsacrificing the original features of the signals. Then, an integrated feature extraction method was\nproposed to further process the generated image. The method combines three individual extraction\nmethods, namely, texture feature extraction, shape feature extraction and intrinsic feature extraction.\nSubsequently, the signal of each frame image was recognized to track the vibration source. To verify\nthe effect of the proposed method, several experiments were carried out to compare it with popular\nand traditional approaches. The results show that: Hard drive space is greatly conserved by saving\nthe distributed vibration signals as images; the proposed particle filter is a desirable way to screen\nthe vibration signals for monitoring; the integrated feature extraction outperforms the individual\nextraction methods for texture features, shape features and intrinsic features; the proposed method\nhas a better effect than other popular integrated feature extraction methods; and, the signal source\ntracking method has little impact on the positioning accuracy of the vibration source. The research\nfindings provide important insights into the source tracking of ... signals....
Curvature measurement plays an important role in many fields. Aiming to overcome\nshortcomings of the existing optical fiber curvature sensors, such as complicated structure and\ndifficulty in eliminating temperature noise, we proposed and demonstrated a simple optical fiber\ncurvature sensor based on surface plasmon resonance. By etching cladding of the step-index\nmultimode fiber and plating gold film on the bare core, the typical Kretschmann configuration is\nimplemented on fiber, which is used as the bending-sensitive region. With increases in the curvature\nof the optical fiber, the resonance wavelength of the SPR (Surface Plasmon Resonance) dip linear\nred-shifts while the transmittance decreases linearly. In the curvature range between ..... the wavelength sensitivity reached .... and the intensity sensitivity reached ... In addition, with increases in the ambient temperature, the resonance wavelength of the SPR dips\nlinearly blueshifts while the transmittance increases linearly. In the temperature range between 20\nand ..., the wavelength sensitivity is ... and the intensity sensitivity is ... The sensing matrix is built up by combining the aforementioned four sensitivities. By means of\nthe dual modulation method, the cross-interference caused by temperature change is eliminated.\nAdditionally, simultaneous measurement of curvature and temperature is realized....
Free-space optical (FSO) communication requires a line-of-sight connection\nbetween a transmitter and a receiver in which the information signal is modulated\nby an optical carrier that propagates in free space. The FSO channel is\ngreatly affected by weather conditions such as fog, rain, and snow. In the literature,\nseveral adaptive techniques, such as power control (PC), have been\nsuggested to mitigate channel link degradations. In this paper, we investigate\nthe effects of snow and rain attenuation on the bit error rate (BER) of the FSO\nsystem using two types of modulations, the on-off keying (OOK) modulation\nand the pulse-position modulation (16-PPM). The effect of PC on the performance\nof FSO communications is also examined in this study. We evaluated\nthe systemâ??s performance with two types of snow, wet snow and dry\nsnow, as well as with different rain regions. Results show that PC improves\nthe BER of the FSO system; a high rate of improvement is found for wet snow\nand rain. PC has almost no effect with dry snow because of the high attenuation\nand the limitations on transmitted power. The BER for 16-PPM is better\nthan that for OOK modulation....
Loading....