Directional excitation of surface plasmon using multi-mode interference in an aperture.

Plasmonics is a promising technology that can find many applications in nanophotonics and biosensing. Local excitation of surface plasmons with high directionality is required for many of these applications. We demonstrate that by controlling the interference of light in a metal slot with the adjustment of the angle of incidence, it is possible to achieve highly directional surface plasmon excitation. Our numerical analysis of the structure showing a strong directionality of excited surface plasmon is confirmed by near field scanning measurements. The proposed structure can be useful for many applications including excitation of plasmonic waveguides, nanolithography, and optical sensing. To illustrate its usefulness, we experimentally demonstrate that it can be used for highly directional excitation of a dielectric loaded plasmonic waveguide. We also propose a simple structure for surface plasmon interference lithography capable of providing high image contrast using this scheme.

Prevalence of the metabolic syndrome in kidney transplant recipients: A single-center study.

Metabolic syndrome (MS) is characterized by a combination of cardiovascular (CV) risk factors (hypertension, dyslipidemia, obesity, and alterations in glucose homeostasis). Insulin resistance is suggested to be the common pathogenic background. This syndrome is also a risk factor for diabetes and chronic kidney disease. In renal transplant recipients, MS has been shown to be an independent risk factor for chronic allograft dysfunction, graft failure, new-onset diabetes, and CV disease. We performed a cross-sectional study on 106 stable renal transplant recipients to detect MS between January 2013 and August 2013. This syndrome was diagnosed according to the National Cholesterol Education Program-Adult Treatment Panel III criteria. Patients with history of diabetes mellitus were excluded from the study. In this group of patients, 56 (52.8%) had MS. There were 32 males (57.1%) and 24 females (42.9%). The mean age of the MS group was significantly higher than the non-MS group. The mean serum creatinine was higher in the MS group than the non-MS group, but there was no significant difference between them (P >0.05). The calculated glomerular filtration rate was also similar in the two groups (P >0.05). The patients with MS had higher body weight (64.61 ± 14.17 kg vs. 58.76 ± 11.70 kg, P <0.05) and also higher body mass index (BMI) (P <0.05). The prevalence of BMI >25 kg/m2 in the MS group was 75% versus 25% in the non-MS group (P <0.05). Since MS is an important and common risk factor in renal transplant recipients, we have to try to prevent it by educating the patients to control it by modifying their lifestyle. Efforts toward promoting healthy diets, physical activity, and blood pressure control must be undertaken.

Hybrid plasmonic waveguide-based ultra-low insertion loss transverse electric-pass polarizer.

We have designed and experimentally demonstrated an integrated transverse electric (TE)-pass polarizer on silicon-on-insulator platform. The polarizer consists of an asymmetric coupling section where only the transverse magnetic (TM) mode is coupled to the cross-hybrid plasmonic waveguide and attenuated. The TE mode does not couple and passes through the polarizer. The polarizer was fabricated on the silicon-on-insulator platform. The device is 30 µm long, has a high extinction ratio of more than 28 dB over 150 nm bandwidth, and has a good fabrication tolerance. Most important, the proposed polarizer has an ultra-low insertion loss of less than 0.04 dB for the TE mode.

Polarization rotator based on augmented low-index-guiding waveguide on silicon nitride/silicon-on-insulator platform.

Using a newly proposed augmented low-index-guiding scheme with silicon nitride/silicon dual-core waveguide, we have designed, fabricated, and characterized a transverse electric (TE) to transverse magnetic (TM) and TM-to-TE compact polarization rotator. The polarization rotation is realized in an asymmetric directional coupler. The measured peak conversion efficiencies for the TE-to-TM and TM-to-TE rotations are approximately 97%. The measured polarization extinction ratio for the TE-to-TM rotation is greater than 20 dB over 50-nm bandwidth, while for the TM-to-TE rotation it is greater than 15 dB over the C-band.

Compact and broadband polarization beam splitter based on a silicon nitride augmented low-index guiding structure.

We propose a compact polarization beam splitter (PBS) based on a silicon nitride enhanced silicon-on-insulator platform using an augmented low-index guiding (ALIG) waveguide structure. In the ALIG structure, the TM mode is mostly confined in the low-index silicon nitride, while the TE mode is confined in the high-index silicon. Since the two modes are confined in two separate layers, their properties can be controlled independently. The PBS is formed using an asymmetric multimode interference (MMI) section. The TM mode is directed to an output port by the ALIG waveguide, while the TE mode is coupled to the other output port via the multimode interferometer. Such a PBS has a very small footprint, low insertion loss, high polarization extinction ratio, and broadband response.

Compact low loss and broadband hybrid plasmonic directional coupler.

We propose a novel broadband coupler for silicon photonics using a hybrid plasmonic waveguide section. The hybrid plasmonic waveguide is used to create an asymmetric section in the middle of a silicon nanowire waveguide coupler to introduce a phase delay to allow for a 3-dB power coupling ratio over a 150 nm bandwidth around 1.55 µm. The device is very compact (<8.5 µm) and has a low insertion loss (<0.15 dB).

Experimental demonstration of a hybrid plasmonic transverse electric pass polarizer for a silicon-on-insulator platform.

We experimentally demonstrate a transverse electric (TE)-pass polarizer using the recently proposed hybrid plasmonic waveguide. The device consists of a silicon film separated from a chromium layer by a silica spacer. The device was characterized using a tunable laser in the 1.52-1.58 µm wavelength range. For a 30 µm long polarizer, the extinction ratio in this wavelength range varies from 23 to 28 dB and the insertion loss for the TE mode is 2-3 dB. The device is compact; its fabrication is completely compatible with silicon-on-insulator technology, and its performance compares favorably against previously reported silicon-based integrated optic TE-pass polarizers.

Compact and silicon-on-insulator-compatible hybrid plasmonic TE-pass polarizer.

Hybrid plasmonic waveguides consisting of a metal plane separated from a high-index medium by a low-index spacer have recently attracted much interest. Here we show that, by suitably choosing the dimensions and material properties of the hybrid waveguide, a very compact and broadband TE-pass polarizer can be implemented. Finite-difference time-domain simulation indicates that the proposed device can provide large extinction ratio with low insertion loss for the TE mode.

Polarization-independent hybrid plasmonic coupler for a silicon on insulator platform.

Hybrid plasmonic waveguides consisting of a high-index slab separated from a metal plane by a low-index spacer provide an optimal compromise between the loss and confinement for surface plasmon waves in passive medium. In such hybrid structures, because power for the TE and TM modes are concentrated in two different regions of the guide, the characteristics of the two modes can be controlled independently by changing the waveguide dimensions. We propose to use this property to implement a hybrid plasmonic polarization-independent directional coupler for a silicon on insulator platform. We also investigate the effects of variations of wavelength and device dimensions on the performance of the proposed device.

Propagation characteristics of hybrid modes supported by metal-low-high index waveguides and bends.

Hybrid-mode waveguides consisting of a metal surface separated from a high index medium by a low index spacer have attracted much interest recently. Power is concentrated in the low index spacer region for this waveguide. Here we investigate the properties of the hybrid mode in detail and numerically demonstrate the possibility of realizing compact waveguide bends using this wave guiding scheme.

Group velocity inversion in AlGaAs nanowires.

We investigated the dispersion characteristics of submicron sized AlGaAs waveguides. Numerical simulations shows that the tight confinement of the optical waves in such nanowires leads to strong variations of the dispersion characteristics compared to classic, weakly guided waveguides of the same material system. We found numerically that the investigated structure has negative GVD for the TE mode provided the waveguide width is between 670 nm and 280 nm. Experimental data obtained from 300 mum - 1 mm long wires confirms the numerical results.

Preliminary report of a nationwide case-control study for identifying risk factors of tuberculosis following renal transplantation.

BACKGROUND: Tuberculosis (TB) is an important infection encountered posttransplantation, especially among patients in developing countries, where there are high incidences of morbidity and mortality. MATERIALS AND METHODS: One hundred and twenty subjects (1%) from 15 major kidney transplantation centers in Iran from 1984 to 2003 were compared with 440 controls who were matched for operative time, treatment center, and surgical team. RESULTS: Mean ages of research subjects and controls were 38.6 and 36.6 years (P = .04), respectively. The mean duration of pretransplantation hemodialysis was 29 months (range, 2 to 192 months) in research subjects and 20 months (range, 1 to 180 months) in controls (P = .003). Positive past history of tuberculosis was detected in 4 (3.3%) research subjects and in 7 (1.5%) controls (P = .2). Fifty-two research subjects (43.3%) and 241 controls (54.8%) had pretransplantation purified protein derivative of tuberculin less than 5 mm (P = .02). Mean dosages of initial and maintenance immunosuppressive drugs in research subjects and in controls were not significantly different. Sixty research subjects (50%) and 152 controls (34.5%) had rejection prior to diagnosis of TB (P = .03). CONCLUSION: To our knowledge, this is the first study that demonstrates an increased risk of posttransplant TB by prolonged duration of pretransplant hemodialysis and number of posttransplant rejection episodes. Further study is needed to clarify these findings specifically with respect to various immunosuppressive regimens.

Left-handed and right-handed metamaterials composed of split ring resonators and strip wires.

The behavior of two structures composed of split ring resonators (SRRs) and strip wires (SWs) is examined through full wave simulations. It is shown that both structures exhibit a transmission peak in the region where the real parts of the electric permittivity and magnetic permeability are presumed to be negative, a property which is usually assumed to imply a negative index of refraction. However, an analysis of the dispersion characteristics and insertion phase of the two structures shows that the first structure, in which the SRRs and SWs are printed on opposite sides of a dielectric substrate, is a left-handed medium in the passband, whereas the second structure, in which SRRs and SWs are printed on the same side, is a right-handed medium in the passband. Hence the transmission magnitude alone does not provide sufficient evidence of a negative index of refraction. To determine the sign of the index correctly, the insertion phase for propagation through several lengths of the structure or calculations of dispersion diagrams are necessary. The impact of the unit cell size on the "handedness" of the structure is also examined.

Negative group velocity and group delay in left-handed media.

The dynamics of wave propagation in media with negative index of refraction is analyzed through analytical calculations, simulations, and experiments. Using a free space setup, the transmission characteristics of two split ring resonator and strip wire left-handed media (LHM), designed for operation at K -band frequencies (18-26 GHz), are measured. The first LHM, which is 3 unit cells long in the propagation direction, exhibits a maximum negative group delay of -0.9 ns . The second LHM (4 unit cells long) exhibits a maximum negative group delay of -1.2 ns . For both LHM the bandwidth of the negative group delay (and hence the negative group velocity) region was approximately 250 MHz.

Time-domain detection of superluminal group velocity for single microwave pulses

Single microwave pulses centered at 9.68 GHz with 100-MHz (full width at half maximum) bandwidth are used to evanescently tunnel through a one-dimensional photonic crystal. In a direct time-domain measurement, it is observed that the peak of the tunneling wave packets arrives (440+/-20) ps earlier than the companion free space (air) wave packets. Despite this superluminal behavior, Einstein causality is not violated since the earliest parts of the signal, also known as the Sommerfeld forerunner, remain exactly luminal. The frequency of oscillations and the functional form of the Sommerfeld forerunner for any causal medium are derived.