Optical property of few-mode fiber with non-uniform refractive index for cylindrical vector beam generation

This paper investigates optical properties of few-mode fiber with non-uniform refractive index, namely: the few mode fiber with U-shape refractive index and the two-mode and four-mode few-mode fiber with bent radius. Finite element method is used to analyze the mode distributions based on their non-uniform refractive index. Effective mode control can be achieved through these few mode fibers to achieve vector beam generation. Finally, reflection spectra of a few-mode fiber Bragg grating are calculated theoretically and then measured under different bending conditions. Experimental results are in good accordance with the theoretical ones. These few mode fibers show potential applications in generation of cylindrical vector beam both for optical lasing and sensing systems

Identification and evaluation of the role of the manganese efflux protein in Deinococcus radiodurans

<p>Abstract</p> <p>Background</p> <p><it>Deinococcus radiodurans </it>accumulates high levels of manganese ions, and this is believed to be correlated with the radiation resistance ability of this microorganism. However, the maintenance of manganese ion homeostasis in <it>D. radiodurans </it>remains to be investigated.</p> <p>Results</p> <p>In this study, we identified the manganese efflux protein (MntE) in <it>D. radiodurans</it>. The null mutant of <it>mntE </it>was more sensitive than the wild-type strain to manganese ions, and the growth of the <it>mntE </it>mutant was delayed in manganese-supplemented media. Furthermore, there was a substantial increase in the <it>in vivo </it>concentration of manganese ions. Consistent with these characteristics, the <it>mntE </it>mutant was more resistant to H₂O₂, ultraviolet rays, and γ-radiation. The intracellular protein oxidation (carbonylation) level of the mutant strain was remarkably lower than that of the wild-type strain.</p> <p>Conclusions</p> <p>Our results indicated that <it>dr1236 </it>is indeed a <it>mntE </it>homologue and is indispensable for maintaining manganese homeostasis in <it>D. radiodurans</it>. The data also provide additional evidence for the involvement of intracellular manganese ions in the radiation resistance of <it>D. radiodurans</it>.</p

Identification and evaluation of the role of the manganese efflux protein in Deinococcus radiodurans

<p>Abstract</p> <p>Background</p> <p><it>Deinococcus radiodurans </it>accumulates high levels of manganese ions, and this is believed to be correlated with the radiation resistance ability of this microorganism. However, the maintenance of manganese ion homeostasis in <it>D. radiodurans </it>remains to be investigated.</p> <p>Results</p> <p>In this study, we identified the manganese efflux protein (MntE) in <it>D. radiodurans</it>. The null mutant of <it>mntE </it>was more sensitive than the wild-type strain to manganese ions, and the growth of the <it>mntE </it>mutant was delayed in manganese-supplemented media. Furthermore, there was a substantial increase in the <it>in vivo </it>concentration of manganese ions. Consistent with these characteristics, the <it>mntE </it>mutant was more resistant to H₂O₂, ultraviolet rays, and γ-radiation. The intracellular protein oxidation (carbonylation) level of the mutant strain was remarkably lower than that of the wild-type strain.</p> <p>Conclusions</p> <p>Our results indicated that <it>dr1236 </it>is indeed a <it>mntE </it>homologue and is indispensable for maintaining manganese homeostasis in <it>D. radiodurans</it>. The data also provide additional evidence for the involvement of intracellular manganese ions in the radiation resistance of <it>D. radiodurans</it>.</p

All-fiber fused-type mode selective coupler with high performance and free of pre-tapering

In this paper we propose and demonstrate a novel all-fiber fused-type mode selective coupler (MSC) that capable of converting LP01 mode to LP11 mode with high efficiency and purity. Unlike other coupler fabrication techniques for which single mode fiber (or few mode fiber) must be pre-tapered, the advantage of our proposed coupler is that pre-tapering is not required. Two different fibers of the MSC have the same diameter. We achieve LP11 mode with a high modal purity of > 90% and a coupling efficiency of >20%, with a low insertion loss of about 0.3 dB at the wavelength of 1064 nm

Ultrasensitive refractive index sensor based on graphene coated hollow core fiber

A high-quality nanolayer graphene (NLG) coated hollow core fiber (HCF) platform has been demonstrated for accurate monitoring of refractive index (RI) changes so far mainly operate in liquids but not in air. The NLG with high index is deposited on the outer surface of the HCF, and an enhanced anti-resonant reflecting guidance is formed, which induces sharp periodic lossy dips in the transmission spectrum. A cute experiment conducted interrogating the transmission intensity of the lossy dip demonstrates a high resolution of 2.73×10-6 RIU and a sensitivity of -365.9 dB/RIU, which is two or three times higher than that of intensity-modulated RI sensors reported previously. We believe that this configuration opens research directions for highly sensitive sensing in researches of chemistry, medicine, and biology

A mode-locked fiber laser generating high purity cylindrical vector beams based on a mode selective coupler in a figure-8 cavity

We propose and demonstrate an all-fiber passively mode-locked laser with pulsed cylindrical vector beam output based on a mode selective coupler (MSC) in a figure-8 cavity, The MSC made of a two mode fiber and a standard single mode fiber is used as both the intracavity transverse mode converter and mode splitter. Through adjusting the polarization state in the laser cavity, both radially and azimuthally polarized beams have been obtained with high mode purity which are measured to be > 94%. The mode-locked laser pulses have duration of 17 ns and a repetition rate of 0.66 MHz, operating near a wavelength of 1556.3 nm with a spectral bandwidth of 3.2 nm

An injection-locked single-longitudinal-mode fiber ring laser with cylindrical vector beam emission

We demonstrate a fiber ring laser with narrow bandwidth single-longitudinal-mode cylindrical vector beam (CVB) output at C-band wavelength range for the first time to the best of our knowledge. A step index two-mode fiber Bragg grating is used as a transverse mode selector for CVB generation, while both the injection-locking technique and narrow bandwidth of the fiber Bragg grating lead to single-longitudinal-mode operation. The 3-dB bandwidth of the laser output is measured to be 60 dB. Mode distribution and optical spectra of few-mode fibers with periodic modulated refractive index profile, namely the few-mode fiber Bragg gratings with bent radius, are investigated theoretically and experimentally, which provide a comprehensive exploration of CVB's generation

A 1.0 μm Cylindrical Vector Beam Fiber Ring Laser Based on A Mode Selective Coupler

We propose and demonstrate a continuous-wave all-fiber ring laser generating cylindrical vector beams (CVBs) using a MSC as transverse mode converter and mode splitter. The MSC is fabricated by a novel method free of pre-tapering, achieving LP11 mode with a high purity of > 96% near the wavelength of 1064 nm. The CVB fiber laser operates at a center wavelength of 1053.9 nm, with a 3 dB linewidth of less than 0.04 nm and a signal-to-background ratio of > 60 dB. The laser slope efficiency is > 9%. The radially and azimuthally polarized beams can be switched by adjusting the polarization controllers in the fiber ring cavity, with a high mode purity measured to be > 96%

Solid optical fiber with tunable bandgaps based on curable polymer infiltrated photonic crystal fiber

We demonstrated the realization and characterization of a solid photonic bandgap fiber (SPBF) with a compact size of about 10 mm and a high wavelength sensitivity of up to -4.034 nm/°C by means of fully infiltrating an ultraviolet curable polymer with a high refractive index of 1.515 into air holes of a photonic crystal fiber (PCF). To the best of our knowledge, it was the first time that the SPBF with tunable bandgaps was fabricated in the conventional index-guiding PCF. Compared with conventional fluid filled PBFs, the proposed SPBF can be stable to temperature and other environmental effects and maintain a large extinction ratio of more than 30 dB within a broad wavelength. The splicing between the SPBF and single mode fibers has been solved. Moreover, it is observed that the bandwidth of bandgap (G2) gradually broadens with the increase in temperature

Monitoring the ecological environment of open-pit coalfields in cold zone of Northeast China using Landsat time series images of 2000-2015

Procjena pogoršanja ekološkog okruženja i vegetacije rudnika u Kini zbog prekomjernog vađenja ugljena važna je zbog osjetljivog ekološkog okruženja i niske temperature u hladnim i sušnim područjima. U ovom se istraživanju kao primjeri uzimaju rudnici Haizhou, Gulianhe i Huolinhe s otvorenim jamskim oknom te se predlaže metoda za procjenu njihovog ekološkog okruženja primjenom Landsat vremenske serije slika na temelju varijacija Normalized Difference Vegetation Index-a (NDVI) rudnika s otvorenim jamskim oknom u hladnim i sušnim područjima. Prosječna NDVI vrijednost rudarskog područja izračunavala se svakog mjeseca primjenom podataka Landsat serije slika od 2000 do 2015. Područje nalazišta ugljena pod vegetacijom određeno je u skladu s graničnim vrijednostima NDVI pa su tako izrađeni grafikoni godišnjeg maksimalnog NDVI i područja pod vegetacijom. Prilagodili smo liniju trenda varijacije maksimalne vrijednosti NDVI i područja pod vegetacijom kako bi se smanjio učinak meteoroloških čimbenika na NDVI vrijednosti. Rezultati pokazuju da se poslije zatvaranja jame i čišćenja područja odlaganja, naglo, tijekom zadnjeg desetljeća, povećao NDVI rudnika s otvorenim jamskim otvorom i područja pod vegetacijom, a ekološko okruženje tih rudnika se očito poboljšalo. Rudarske aktivnosti su dovele do naglog opadanja godišnjeg maksimalnog NDVI i područja pod vegetacijom s trajno smrznutim slojem tla, a ekološko okruženje rudnika se nastavlja pogoršavati. Premda četverogodišnji prosječni NDVI ostaje nepromijenjen u dijelovima nalazišta ugljena koji se eksploatiraju, a nemaju trajno smrznuti sloj tla, područje ugljenokopa pod vegetacijom se linearno smanjuje, ukazujući na činjenicu da se ekološko okruženje ugljenokopa pogoršava. Sa stajališta zaštite ekološkog okruženja, rezultati ovog istraživanja čine osnovu za donošenje odluke o otvaranju velikih rudnika s otvorenim jamskim oknom u hladnim i sušnim područjima.Evaluating the deterioration of ecological environment and vegetation of coalfields caused by China’s large-scale coal mining activities is important because of the fragile ecological environment and low temperature in cold and arid areas. This study takes the open coal pits of Haizhou, Gulianhe, and Huolinhe as examples and proposes a method for evaluating their ecological environment using Landsat time series images based on the Normalized Difference Vegetation Index (NDVI) variations of open-pit coalfields in cold and arid zones. The average NDVI value of the mining area each month was calculated using Landsat image data from 2000 to 2015. The vegetation cover area in the coalfields was extracted according to the NDVI threshold, and the scatter plots of the annual maximum NDVI and vegetation cover area were drawn. We fitted the variation trend line of maximum NDVI value and vegetation cover area to reduce the effect of meteorological factors on NDVI values. Results show that after the closure of open pit and reclamation of dump area, the NDVI of open-pit coalfields and vegetation cover area have been increasing rapidly over the last decade, and the ecological environment of these coalfields has obviously improved. The coal mining activities have led to the rapid decline of annual maximum NDVI and vegetation cover area of the coalfields in permafrost zones, and the ecological environment of coalfields continues to deteriorate. Although the quarterly average NDVI remains unchanged in non-permafrost mining coalfields under coal exploitation, the vegetation cover area in the coalfields decreases linearly, indicating that the ecological environment of the coalfields tends to deteriorate. From an ecological environment protection perspective, the results of this study provide a basis for decision making in constructing large-scale open pits in cold and arid zones