Laser ablation fabrication of ap-NiO/n-Si heterojunction for broadband and self-powered UV-Visible-NIR photodetection.

We report on the optoelectronic characteristics ofp-NiO/n-Si heterojunction photodiode for broadband photodetection, fabricated by depositing ap-type NiO thin film onto a commercialn-type silicon substrate using pulsed laser deposition (PLD) technique. The structural properties of the PLD-grownp-NiO material were analysed by means of x-ray diffraction and x-ray photoelectron spectroscopy, confirming its crystalline nature and revealing the presence of Ni vacancies, respectively. Hall measurements confirmed thep-type semiconducting nature of the NiO thin film having a carrier concentration of 8.4 × 1016cm-3. The current-voltage (I-V) characteristics of thep-NiO/n-Si heterojunction photodevice were investigated under different wavelengths ranging from UV to NIR. The self-bias properties under different illuminations of light were also explored systematically. Under self-bias condition, the photodiode exhibits excellent responsivities of 12.5 mA W-1, 24.6 mA W-1and 30.8 mA W-1with illumination under 365 nm, 485 nm, and 850 nm light, respectively. In addition, the time dependency of the photoresponse of the fabricated photodevice has also been investigated and discussed thoroughly.

Enhancement of light harvesting efficiency of perovskite solar cells by using one-dimensional photonic crystals.

We present methyl-ammonium lead iodide perovskite solar cells coupled with one-dimensional photonic crystals (PCs) to achieve enhancement in light harvesting and photocurrent efficiencies. The introduction of PCs as a light reflection layer in the solar cells attributes to the increase in light harvesting efficiency and photocurrent density, which can be tuned by controlling the PC parameters such as the number of layers and layer thickness. Another important feature of the design is the introduction of a thin Au/Ag layer on top, which lets through more than 70% sunlight incident on it into the device, protects the hole transporting layer, and also helps in containing the light reflected from the PC layer into the device for further harvesting. The effects of layer thickness of the perovskite, hole transporting, and metallic contact layers on solar absorption enhancement and photocurrent density are also studied to achieve high power conversion efficiencies. We propose the optimum structural parameters of the considered solar cell structures, which provide the required guidance and also give further opportunities in the design of organo-metal halide perovskite solar cells coupled with PC structures.

Gold-aluminum-based surface plasmon resonance sensor with a high quality factor and figure of merit for the detection of hemoglobin.

A gold (Au) and aluminum (Al)-based surface plasmon resonance (SPR) sensor, with a high-quality factor and figure of merit, for the detection of hemoglobin concentration in human blood is proposed. The sensing performance of a bimetallic Au grating over an Al film-based sensor depends on the thickness of the Al film. The sensor's performance is closely analyzed in terms of well-defined performance parameters: sensitivity, FWHM, and depth of SPR dips in order to optimize the thickness of Al film. With optimized thickness, we could achieve quality factor and figure of merit values of 286.2 RIU-1 and 0.97 deg-1, respectively. Al is chemically unstable, and, to address the oxidation problem, we analyzed the sensor with an ultrathin protective Au layer between the Au grating and Al film. We show that the introduction of an ultrathin Au layer gives stability to the sensor without much affecting the performance of the sensor. The obtained values of quality factor and figure of merit of the proposed sensor are 245.2 RIU-1 and 0.86 deg-1, respectively. We also discuss the potential of hemoglobin detection of the proposed sensor in the near-infrared region. Reported sensitivity of the sensor is 0.62°/dgL-1.

Sensitivity enhancement of a conventional gold grating assisted surface plasmon resonance sensor by using a bimetallic configuration.

A surface plasmon resonance (SPR)-based refractive index sensor using a silver grating fabricated over the gold film is proposed. The performance of the sensor has been evaluated on the basis of sensitivity, full width half maximum (FWHM), and dip strength of the reflection spectrum. Rigorous coupled wave analysis has been utilized to study the effect of grating parameters on sensing performance. Our systematic analysis exhibits that inappropriate grating parameters may lead to poor performance of the sensor. Sensitivity of the conventional gold grating (grating engraved in gold) assisted SPR sensor is obtained to be 321°/RIU. Further, we have shown that sensitivity and FWHM could be improved by using a bimetallic structure that consists of a silver grating on a thin gold film and thereby increases the quality factor. Sensitivity of the proposed structure is 346°/RIU with a quality factor more than 97.46 RIU-1.

Design optimization of two concatenated long period waveguide grating devices for an application specific target spectrum.

We propose a global optimization method to optimize the parameters of two concatenated long period waveguide gratings (LPWGs) for generating a desired target spectrum. The design consists of two concatenated LPWGs with different grating periods inscribed in the guiding films of a four-layer planar waveguide with finite over cladding. We have used the transfer matrix method to compute the modes of the structure and the coupled mode theory to compute the spectrum of the device. The adaptive particle swarm optimization method has been used to optimize the parameters of LPWGs to generate symmetric as well as asymmetric target spectra. Two concatenated gratings of different lengths and periods have been used to generate the target spectra. To demonstrate the method of optimization we have designed a variety of wavelength filters including a rectangular shape rejection band filter, asymmetric band rejection filters, band rejection filters for flattening the amplified spontaneous emission (ASE) spectrum of an erbium doped fiber amplifier (EDFA), and a gain equalization filter for an erbium doped waveguide amplifier (EDWA) in the C-band. Seven parameters of the proposed LPWG structure have been optimized to achieve the desired spectra. We have obtained an ASE flattening with ±0.8 dB peak-to-peak ripple in case of the EDFA and gain flattening with ±0.4 dB peak-to-peak ripple in case of an EDWA. The study would be useful in the design of wavelength filters for specific applications.

Long-period-grating in a trench assisted planar optical waveguide.

We present long-period-grating in a planar optical waveguide that contains a low-index trench in the cladding region. The effect of the trench on transmission spectrum of the grating has been studied. The waveguide structure has been analyzed by the transfer matrix method and the output spectrum of the grating has been calculated by the coupled mode theory. Our numerical results show that position, strength, and width of the trench significantly affect the transmission spectrum of the grating. In particular, we show the appearance of triple resonance between a set of coupled modes and obtain an ultrawide band rejection in the output spectrum. We numerically demonstrate applications of the proposed structure in wideband rejection filters, refractive index sensors, and gain equalization of erbium-doped waveguide amplifiers.

Large-effective-area dispersion-compensating fiber design based on dual-core microstructure.

We present a microstructure-based dual-core dispersion-compensating fiber (DCF) design for dispersion compensation in long-haul optical communication links. The design has been conceptualized by combining the all-solid dual-core DCF and dispersion-compensating photonic crystal fiber. The fiber design has been analyzed numerically by using a full vectorial finite difference time domain method. We propose a fiber design for narrowband as well as broadband dispersion compensation. In the narrowband DCF design, the fiber exhibits very large negative dispersion of around -42,000 ps nm(-1) km(-1) and a large mode area of 67 µm(2). The effects of varying different structural parameters on the dispersion characteristics as well as on the trade-off between full width at half-maximum and dispersion have been investigated. For broadband DCF design, a dispersion value between -860 ps nm(-1)km(-1) and -200 ps nm(-1) km(-1) is obtained for the entire spectral range of the C band.

Birefringence analysis of segmented cladding fiber.

We present a full-vectorial modal analysis of a segmented cladding fiber (SCF). The analysis is based on the H-field vectorial finite element method (VFEM) employing polar mesh geometry. Using this method, we have analyzed the circular SCF and the elliptical SCF. We have found that the birefringence of the circular SCF is very small (1.0×10(-8)). Birefringence of a highly elliptical SCF can be altered to some extent by the number of segments and duty cycle of segmentation in the segmented cladding. However, the change is not profound. The analysis shows that the circular SCF possesses low birefringence and that the segmented cladding does not add any significant birefringence in an elliptical fiber. This result strongly indicates that small deviations in the segmented cladding parameters arising from fabrication process do not significantly affect the birefringence of the fiber.

Poor Outcomes after Recidivism in Living Donor Liver Transplantation for Alcohol-Related Liver Disease.

BACKGROUND: Recidivism in patients who underwent liver transplantation for alcohol-related liver disease (ALD) is shown to be associated with poor survival in some studies. METHODS: Living donor liver transplantation (LDLT) recipients for ALD with at least 2 years of follow-up and history of significant alcohol relapse were included. The recipients underwent LDLT from June 2010 to December 2016, and data were analyzed until June 2019. The cohort had a median follow-up of 54 (33-78 IQR) months. Recidivism (significant alcohol intake) was defined as >21 units per week. RESULTS: A total of 27 of 463 (5.8%) LDLT recipients (all men), aged 43.5 ± 9.6 years, had significant alcohol intake. A liver biopsy was performed on demand in 14 patients (in the presence of raised levels of liver enzymes or jaundice). The histological diagnoses in these patients were as follows: alcoholic hepatitis in 7 (50%), alcoholic hepatitis and acute cellular rejection or chronic rejection in 4 (28.5%), cirrhosis in 2 (14.2%), and acute cellular rejection and cirrhosis in 1 (7.1%) patient. Four of 5 patients with a biopsy diagnosis of acute or chronic rejection were noncompliant with immunosuppression. Six of these patients died. The mortality after 1 year of transplant was significantly more in patients with recidivism. CONCLUSION: Recidivism was associated with significant morbidity and mortality after liver transplantation.

Large-mode-area leaky optical fiber fabricated by MCVD.

A large-mode-area single-mode optical fiber based on leaky-mode filtering was prepared by a modified chemical vapor deposition (MCVD) technique. The fiber has a leaky cladding that discriminates the fundamental mode from higher-order modes. A preliminary version has a 25 µm core diameter and 0.11 numerical aperture. A Gaussian-like mode with 22 µm mode field diameter was observed after 3 m propagation, in agreement with modeling.

Good outcome of living donor liver transplantation for severe alcoholic hepatitis not responding to medical management: A single center experience of 39 patients.

INTRODUCTION: There are limited data on outcomes of living donor liver transplantation (LDLT) for patients with severe alcoholic hepatitis. METHODS: The study included LDLT recipients for severe alcoholic hepatitis (n = 39) who did not improve with medical treatment and compared their outcomes with patients who underwent LDLT for alcoholic liver disease (n = 461). The diagnosis of severe alcoholic hepatitis was based on both clinical and explants data. No patients had psychiatric contraindications for liver transplant and all had good family support. The data are shown as number, mean (SD), or median (25-75 interquartile range). RESULTS: All transplant recipients were males, aged 42 ± 8 years. The patients with alcoholic hepatitis were abstinent for a duration of 4 ± 1.8 months at the time of LDLT. All patients underwent LDLT with a graft to recipient weight ratio of 0.95 ± 0.17. The post-transplant ICU and hospital stay were 5.4 ± 1.3 and 17.6 ± 8.4 days, respectively. When patients with alcoholic hepatitis (n = 39) were compared to patients who underwent LDLT for alcoholic liver disease without alcoholic hepatitis (n = 461), patients with alcoholic hepatitis were significantly younger (43.2 ± 8.5 vs. 48.2 ± 9.1 years, p = 0.001) and had higher Child's (10.9 ± 1.5 vs. 9.8 ± 1.8) and MELD scores (22.1 ± 4.5 vs. 18.4 ± 5.9, p = 0.000). Post-operative infections were also significantly more common in the alcoholic hepatitis group (71.7% vs. 51.6%, p = 0.018). Fungal infections developed in 23% of alcoholic hepatitis patients as compared to 14% in the rest of the alcoholic patients (p = 0.247). Six recipients (15.7%) died at a median follow-up of 28 (6-37) months due to infections, and five (12.8%) patients had relapse of alcohol drinking. Survival was not different between the two groups. CONCLUSION: Living donor liver transplantation can be successfully performed with good survival for patients with severe alcoholic hepatitis.

Lower relapse rates with good post-transplant outcome in alcoholic liver disease: Experience from a living donor liver transplant center.

INTRODUCTION: Post-transplant relapse is a major factor influencing the long-term outcome in alcoholic liver disease (ALD) patients. AIMS: The aim of this study was to evaluate the relapse rates following living donor liver transplantation (LDLT) in patients with ALD in the Indian context with strong family support. METHODS: Of 458 patients who underwent LDLT for ALD, 408 were included in the study. Post-transplant relapse was determined by information provided by the patient and/or family by means of outpatient and e-mail questionnaire, supported by clinical/biochemical parameters/liver histopathology. RESULTS: All except one were males, with a mean age of 46.9 ± 8.5 years. The overall rate of relapse was 9.5 % at 34.7 months (interquartile range (IQR) 15-57.6), lower than that reported in the literature from the West. The relapse rate was higher in patients with a shorter duration of pre-transplant abstinence (17.4 % and 15.4 % for recipients with pre-transplant abstinence of <3 and <6 months, respectively, p < 0.05). The overall survival was 88.5 % at 3 years. Of 39 patients with relapse, 16 (41 %) were occasional drinkers, 14 (35.8 %) were moderate drinkers, and 9 (23 %) were heavy drinkers. All the heavy drinkers presented with features of graft dysfunction. CONCLUSIONS: Good results can be obtained following LDLT for ALD, with significantly lower relapse rates in our setup as compared to the West.

Long-period gratings in planar optical waveguides.

We present a theoretical analysis of light propagation in a four-layer planar waveguide that consists of a long-period grating (LPG) having a period of the order of 100 microm. By means of the coupled-mode theory, we show that such a structure is capable of coupling light from the fundamental guided mode to the cladding modes at specific wavelengths (resonance wavelengths) and thus results in sharp rejection bands in the transmission spectrum of the waveguide. Our numerical results show that the resonance wavelengths as well as the transmission spectrum can be significantly changed with the waveguide and grating parameters. A waveguide-based LPG should provide a useful approach to the design of a wide range of integrated-optic devices, including wavelength-tunable filters, switches, and environmental sensors.

Holey optical fiber with circularly distributed holes analyzed by the radial effective-index method.

We analyze a holey fiber that consists of a circular distribution of air holes by the radial effective-index method. By this method, we show that the holey fiber is a leaky structure and its extended single-mode operation is governed by the differential leakage loss between the first two modes of the fiber. The effects of the hole size and the hole separation on the leakage losses of the first two modes are calculated. The leakage loss of the fundamental mode of the fiber is found to be comparable to that of a conventional holey fiber that has a hexagonal distribution of air holes.