All-optical switching due to state-filling in quantum dots

We report all-optical switching due to state-filling in quantum dots (QDs) within a Mach-Zehnder Interferometric (MZI) switch. The MZI was fabricated using InGaAsP/InP waveguides containing a single layer of InAs/InP QDs. A 1530-1570 nm probe beam is switched by optical excitation of one MZI-arm from the top. By exciting below the InGaAsP bandgap, we prove that the refractive index nonlinearity is only due to the QDs. The switching efficiency is 2 rad/(microW absorbed power). Probe wavelength insensitivity was obtained using a broad distribution of QDs.Comment: 12 page

Polarization switching studies in ferroelectric glycine phosphite single crystals

Glycine Phosphite [NH3CH2COOH3PO3], abbreviated as GPI, undergoes a para-ferroelectric phase transition from the monoclinic symmetry P2(1)/a to P2(1) at 224.7 K. We report here a systematic study of the polarization switching process in this crystal. Growth of these crystals from aqueous solution has been undertaken employing both solvent evaporation and slow cooling methods. Hysteresis loop measurements along the polar b-axis yielded a spontaneous polarization value of 0.5 muC/cm(2) and a coercive field of 2.5 kV/cm. Conventional Merz technique was employed for polarization switching studies, wherein bipolar square pulses were applied to the sample to induce domain reversal. The transient switching pulse that flows through the sample on application of the field was recorded. The maximum switching time required for domain switching was measured both as a function of electric field and temperature. The experimentally observed switching curves were fitted with the model based on the Pulvari-Kuebler theory of nucleation and growth of domains. From the experimental data, the values of mobility and activation field were obtained. It was observed that switching process in this crystal is predominantly governed by the forward growth of domain walls in the high field region. However, switching process in GPI crystal was found to be slower than that found in other glycine based ferroelectric crystals

Growth and characterization of ferroelectric glycine phosphite single crystals

Single crystals of a recent ferroelectric material, glycine phosphite were grown from aqueous solution employing the techniques of slow cooling and controlled evaporation. Powder X-ray diffraction studies as well as thermal analysis were carried out on the grown crystals. The morphology of the crystal has been determined using contact and optical goniometry. The mechanical hardness of the crystal was evaluated by Vickers indentation method. Thickness dependence of the dielectric properties has been investigated and the results can be interpreted in terms of a surface layer of lower dielectric constant

Potassium titanyl phosphate and its isomorphs: Growth, properties, and applications

Potassium titanyl phosphate (KTP) and its isomorphs have received enormous attention in the last 2 decades. In particular, KTP assumes importance due to its large nonlinear optic and electrooptic coefficients together with the broad thermal and angular acceptance for second harmonic generation. This article provides an overview of the material aspects, structural, physical, and chemical properties and device feasibility of the KTP family of crystals. Some of the current areas of research and development along with their significance in understanding the physical properties as well as device applications are addressed. Optical waveguide fabrication processes and characteristics with their relevance to the present-day technology are highlighted. Studies performed so far have enabled us to understand the fundamental aspects of these materials and what needs to be pursued vigorously is the exploitation of their device applications to the maximum extent

Risk factors of pneumonia among elderly with robust Poisson regression-A study on mimic III data

Introduction and Aim:Pneumonia is a common and serious illness among the elderly. Early identification of the risk factors for pneumonia is essential for improving the survival outcomes among elderly. The present study aimed to identify an optimal regression approach to determine the risk factors for pneumonia among elderly patients.Materials and Methods:The present study utilized data from the Medical Information Mart for Intensive Care (MIMIC III) to evaluate the use of alternative generalized linear models to identify the risk factors for pneumonia. The regression model with the smallest AIC, BIC and SE was considered as the appropriate regression model for the data. Robust Poisson model was considered the best fit for the current data as it had the lowest AIC, BIC and standard error compared to other regression models. Results:Variables such as BMI, renal failure, hypertension, diabetes and asthmawere identified as the significant risk factors for pneumonia. The risk of pneumonia was found to be significantly higher in the underweight category of BMI [RRadj=1.70; 95% CI=1.38, 2.08]; diabetic patients [RRadj=1.29; 95% CI=1.03, 1.61); asthmatic patients [RRadj=1.35; 95% CI=1.15, 1.58] and patients with renal failure [RRadj=1.16; 95% CI= 1.05, 1.29]. Conclusion:Among various binary regression models, Poisson regression with robust variance (sandwich Poisson regression) provided unbiased estimates of the relationship. In the present study, variables such as BMI, renal failure, diabetics, hypertension and asthma were identified as the significant risk factors for pneumonia in the elderly using robust Poisson regression

Photoluminescence studies on gray tracked KTiOPO4 single crystals

The photochromic, electrochromic and x-ray irradiation damages (commonly called the gray tracks) produced in KTiOPO4 single crystals have been studied using photoluminescence (PL) spectroscopy. Gray tracks were produced in this material by exposure to high laser powers (similar to MW/cm(2)), application of electric fields (similar to kV), and exposure to x rays (30 kV). The PL spectra recorded for such gray tracked samples at 4.2 K, exhibited a luminescence band in the 1-1.8 eV range with a peak at 1.41 eV. Temperature and excitation intensity dependence of PL peaks were carried out to probe the exact nature of the broad emission band in the gray tracked samples. The observed photoluminescence is attributed to transitions in the Ti3+ levels, created on irradiation. The microscopic effects produced in the crystal by electric field, optical field, and x rays are similar, as can be concluded from the similarity of PL spectra as well as their intensity and temperature dependences. (C) 1999 American Institute of Physics. [S0021-8979(99)04512-0]

Thermal properties of glycine phosphite across ferroelectric phase transition: A photopyroelectric study

A photopyroelectric measurement of the thermal parameters of glycine phosphite (GPI) single crystals across the ferroelectric phase transition temperature has been carried out. The thermal parameters—thermal diffusivity $(\alpha)$, thermal effusivity (e), thermal conductivity (K), and heat capacity $(c_p)$-of GPI single crystals are reported. The para-ferroelectric phase transition is reflected in these thermal parameters as anomalies at the transition point. The anisotropy in thermal wave propagation is established by measuring thermal conductivity along the a, b, and c crystal axes. The anomalous variations in the thermal parameters across the phase transition temperature reveal an order–disorder type transition at 224 K in this crystal

Ultrasonic investigation of elastic properties and a phase transition in ferroelectric glycine phosphite NH3CH2COOH3PO3NH_3CH_2COOH_3PO_3 single crystals

A detailed ultrasonic study of the elastic properties of glycine phosphite single crystals has been carried out at room temperature as well as across the ferroelectric phase-transition temperature. All 13 elastic stiffness moduli of this monoclinic crystal at room temperature have been determined by measuring the velocities of ultrasonic waves of different polarizations, propagating along different symmetry directions using the pulse echo overlap technique. The anisotropy in elastic wave propagation is established employing polar plots of the phase velocity surfaces in the ab, ac, and bc planes. Variation of selected mode velocities with temperature establishes the reported ferroelectric phase transition in this crystal at 224 K