Tunable liquid crystal asymmetric dual-core photonic crystal fiber mode converter.

In this study, a compact mode converter based on an asymmetric dual-core photonic crystal fiber (ADC-PCF) infiltrated with nematic liquid crystal (NLC) is reported. The full vectorial finite difference method is used to compute the modal characteristics of the studied transverse magnetic (TM) mode. In this investigation, the geometrical and material parameters of the proposed mode converter are studied to achieve high wavelength selectivity with a compact device length. The proposed mode converter has a compact device length of 403.6 µm at λ=1.3µm. In addition, the reported device is simulated under different temperature levels from 15°C to 45°C to show the thermal tunability. Therefore, the proposed design can be used efficiently in integrated photonic circuits.

Mid-infrared optical modulator based on silicon D-shaped photonic crystal fiber with VO2 material.

Recently, photonic crystal fibers (PCFs) have become of significant interest due to their various applications, especially in the mid-infrared (mid-IR) regime. In this work, an optical mid-IR modulator based on silicon D-shaped PCF (Si-D-PCF) with vanadium dioxide (VO2) as a phase changing material (PCM) is presented and analyzed. Thanks to the phase transition of the VO2 material between insulating (ON) and conducting (OFF) states, the modulation process can be attained. The well-known full vectorial finite element method is utilized to numerically analyze the proposed design. Further, the propagation of light through the suggested structure is studied using the 3D finite difference time domain method. The optical losses of the fundamental TM mode supported by the Si-D-PCF structure in both ON and OFF states are investigated. The obtained results reveal that the extinction ratio (ER) of the reported modulator approaches 236 dB, while the insertion loss (IL) is less than 1.3 dB over the studied wavelength range 3-7 µm at a device length (LD) of 0.5 mm. Additionally, the ER of the proposed modulator is higher than 56 dB through the whole studied wavelength range. Therefore, the proposed modulator could be utilized in photonic integrated circuits that require high ER, low IL, and large bandwidth. To the best of the authors' knowledge, this is the first time an infrared optical modulator based on Si-D-PCF with VO2 material has been presented.

Hybrid Si-VO2 modulator with ultra-high extinction ratio based on slot TM mode.

Nowadays, the development of modern optical systems relies on optical device size minimization and operating power reduction. Optical modulator based on silicon on insulator (SOI) platform is a key element in different optical systems. Therefore, the optical modulator with compact size and low insertion loss could improve the optical system efficiency. In this work, a novel compact optical modulator based on hybrid plasmonic/silicon layers is introduced. The full vectorial finite element method (FV-FEM) is used to numerically analyze the proposed design. Vanadium dioxide (VO2) is also utilized as a cap layer to control the modulation process. The insertion loss (IL) and extinction ratio (ER) of the suggested modulator are equal to 2.1 dB/µm and 28 dB/µm, respectively, at the operating wavelength 1.55 µm. Consequently, high figure-of-merit (FoM) =ER/IL = 13.5 is achieved with an optical bandwidth (ER > 3 dB) greater than 1 µm, which is large in comparison to pervious designs.

Expression profiling of Sudanese visceral leishmaniasis patients pre- and post-treatment with sodium stibogluconate.

Visceral leishmaniasis (VL) in Sudan caused by Leishmania donovani is fatal in susceptible individuals if untreated. Treatment with sodium stibogluconate (SSG) leads to post-kala-azar dermal leishmaniasis (PKDL) in 58% of patients. Here, Affymetrix microarrays were used to identify genes differentially expressed in lymph nodes (N=9 paired samples) pre- and post-treatment with SSG. Using the Bioconductor package limma, 438 genes from 28 869 post-quality-control probe sets were differentially expressed (Pnominal ≤.02) post- vs pretreatment. Canonical pathway analysis using Ingenuity Pathway Analysis™ identified "role of nuclear factor of activated T-cell in regulation of immune response" (Pnominal =1.35×10-5 ; PBH-adjusted =4.79×10-3 ), "B-cell development" (Pnominal =2.04×10-4 ; PBH-adjusted =.024), "Fcγ receptor-mediated phagocytosis in macrophages and monocytes" (Pnominal =2.04×10-4 ; PBH-adjusted =.024) and "OX40 signalling" (Pnominal =2.82×10-4 ; PBH-adjusted =.025) as pathways differentially regulated post- vs pretreatment. Major network hub genes included TP53, FN1, MYC, BCL2, JUN, SYK, RUNX2, MMP1 and ACTA2. Top endogenous upstream regulators included IL-7 (P=2.28×10-6 ), TNF (P=4.26×10-6 ), Amyloid Precursor Protein (P=4.23×10-5 ) and SPI1/PI.1 (P=1.17×10-7 ). Top predicted chemical drug regulators included the flavonoid genistein (P=4.56×10-7 ) and the quinoline alkaloid camptothecin (P=5.14×10-5 ). These results contribute to our understanding of immunopathology associated with VL and response to SSG treatment. Further replication could identify novel therapeutic strategies that improve on SSG treatment and reduce the likelihood of progression to PKDL.

Ultra-high tunable liquid crystal-plasmonic photonic crystal fiber polarization filter.

A novel ultra-high tunable photonic crystal fiber (PCF) polarization filter is proposed and analyzed using finite element method. The suggested design has a central hole infiltrated with a nematic liquid crystal (NLC) that offers high tunability with temperature and external electric field. Moreover, the PCF is selectively filled with metal wires into cladding air holes. Results show that the resonance losses and wavelengths are different in x and y polarized directions depending on the rotation angle φ of the NLC. The reported filter of compact device length 0.5 mm can achieve 600 dB / cm resonance losses at φ = 90° for x-polarized mode at communication wavelength of 1300 mm with low losses of 0.00751 dB / cm for y-polarized mode. However, resonance losses of 157.71 dB / cm at φ = 0° can be achieved for y-polarized mode at the same wavelength with low losses of 0.092 dB / cm for x-polarized mode.

Asymmetric dual-core liquid crystal channel-based tunable mode converter.

In this work, a higher order-to-fundamental mode converter is reported and analyzed based on an asymmetric dual channel waveguide (ADC-WG) on silicon. In the reported structure, one of the two waveguides is infiltrated with nematic liquid crystal (NLC) material to add temperature tunability while the other one is a solid BK7 waveguide. The modal characteristics are obtained using the full vectorial finite difference method (FVFDM). In addition, the structural parameters and optical characteristics of the employed materials are investigated to achieve good wavelength selectivity with a short device length (LD). Thus, a compact mode converter that can work at different wavelengths including the telecommunication wavelength i.e., 1.55 µm with LD ~ 482.31 µm and a low crosstalk of - 19.86 dB is presented. To prove the thermal tunability of the suggested mode converter, its operation is tested through a temperature range between 20 and 35 °C and the results show that the mode conversion process is achieved at each temperature with different phase matching wavelengths (λPMW) but with quite similar coupling length (LC). The proposed device can therefore be effectively utilized in integrated photonic circuits.

Efficient MIR crosstalk reduction based on silicon-on-calcium fluoride platform with Ge/Si strip arrays.

Reduction of the crosstalk (CT) between contiguous photonic components is still a big challenge in fabricating high packing density photonic integrated circuits (PICs). Few techniques to accomplish that goal have been offered in recent years but all in the near-IR region. In this paper, we report a design for realizing a highly efficient CT reduction in the MIR regime, for the first time to the best of our knowledge. The reported structure is based on the silicon-on-calcium-fluoride (SOCF) platform with uniform Ge/Si strip arrays. Using Ge strips shows better CT reduction and longer coupling length (Lc) than the conventional Si based devices over a wide bandwidth in the MIR region. The effect of adding a different number of Ge and Si strips with different dimensions between two adjacent Si waveguides on the Lc and hence on the CT is analyzed using both full vectorial finite element method and 3D finite difference time domain method. An increase in the Lc by 4 orders of magnitude and 6.5 times are obtained using Ge and Si strips, respectively, compared to strips-free Si waveguides. Consequently, crosstalk suppression of - 35 dB and - 10 dB for the Ge and Si strips, respectively, is shown. The proposed structure is beneficial for high packing density nanophotonic devices in the MIR regime, such as switches, modulators, splitters, and wavelength division (de)multiplexers, which are important for MIR communication integrated circuits, spectrometers, and sensors.

Leishmania donovani: genetic diversity of isolates from Sudan characterized by PCR-based RAPD.

Drug unresponsiveness in patients with visceral leishmaniasis (VL) is a problem in many endemic areas. This study aimed to determine genetic diversity of Leishmania donovani isolates from a VL endemic area in Sudan as a possible explanation for drug unresponsiveness in some patients. Thirty clinically stibogluconate (SSG)-sensitive isolates were made SSG-unresponsive in vitro by gradually increasing SSG concentrations. The sensitive isolates and their SSG-unresponsive counterparts were typed using mini-circle kDNA and categorized using PCR-RAPD. All the isolates were typed as L. donovani, the resulting PCR-RAPD characterization of the SSG-sensitive isolates gave three distinct primary genotypes while, the SSG-unresponsive isolates showed only a single band. L. donovani isolates from eastern Sudan are diverse; this probably resulted from emergence of new L. donovani strains during epidemics due to the pressure of widespread use of antimonials. In this communication the possible role of isolates diversity in antimonial unresponsiveness and the in vitro changing PCR-RAPD band pattern in SSG-unresponsive strains were discussed.

Treatment-based strategy for the management of post-kala-azar dermal leishmaniasis patients in the Sudan.

UNLABELLED: Post-kala-azar dermal leishmaniasis (PKDL) is a dermatosis that affects more than 50% of successfully treated visceral leishmaniasis (VL) patients in Sudan. PKDL is considered an important reservoir for the parasite and its treatment may help in the control of VL. Currently, treatment is mainly with sodium stibogluconate (SSG), an expensive and fairly toxic drug and without universally in treatment protocols used. A literature review, a consensus of a panel of experts, and unpublished data formed the basis for the development of guidelines for the treatment of PKDL in the Sudan. Six treatment modalities were evaluated. Experts were asked to justify their choices based on their experience regarding of drug safety, efficacy, availability, and cost. The consensus was defined by assigning a categorical rank (first line, second line, third line) to each option. Regarding the use of AmBisome the presence of the drug in the skin was confirmed in smears from PKDL lesions. RECOMMENDATIONS: AmBisome at 2.5 mg/kg/day/20 days or SSG at 20 mg/kg/day/40 days plus four/weekly intradermal injection of alum-precipitated autoclave L. major vaccine are suggested as first- and second-treatment options for PKDL in the Sudan, respectively. SSG at 20 mg/Kg/day/60 or more days can be used if other options are not available.

Blindness following visceral leishmaniasis: a neglected post-kala-azar complication.

Visceral leishmaniasis (VL) is an important cause of morbidity and mortality that affects multiple organs. Post-kala-azar ocular involvement is a serious complication that can manifest as blepharo-conjuctivitis or pan-uveitis. Failure of prompt diagnosis and treatment can result in blindness. We report five cases with pan-uveitis that followed the successful treatment of VL and consequent post-kala-azar dermal leishmaniasis were presented. Two patients lost their sight permanently but the rest were successfully treated. A high index of suspicion and prompt treatment are of paramount importance in order to avoid blindness following post-kala-azar ocular uveitis.

Surrogate markers of subtle renal injury in patients with visceral leishmaniasis.

Sudanese visceral leishmaniasis (VL) is a disease of children that is characterized by fever, hepatosplenomegaly, lymphadenopathy, pancytopenia, and renal injury. Microalbuminuria (MA) and urinary retinol binding protein (urRBP) are useful markers for glomerular and tubular dysfunctions, respectively. We report the prevalence of subtle renal injury in 88 parasitologically confirmed VL patients in a cross-sectional and hospital-based study. Blood and urine were collected before treatment for hematological, biochemical profiles in addition to MA and urRBP measurement using competitive solid phase, sandwich enzyme-linked immune sorbent assay (ELISA), and immunoturbidometry. All the patients had normal serum urea and creatinine levels and no detectable urRBP. However, 40% of the patients had MA detected by ELISA, and 42% were reactive with turbidometry. The sensitivity, specificity, positive and negative predictive values for MA turbidometric technique were calculated as 100%; 96%; 95% and 100%, respectively. In conclusion; subtle renal injury in VL is mainly glomerular. Turbidometry for MA measurement is a simple, inexpensive, sensitive, and specific technique with high predictive values.