Birefringence Loss Research Articles

Polarization and leakage properties of rectangular lattice photonic crystal fibres with doped cores

Based on the analysis of birefringence and leakage properties in rectangular lattice photonic crystal fibres (RLPCFs), we present a simple technique of improving the optical properties of the fibres by the introduction of a doped core. The advantage of a doped core is firstly investigated by the comparison of the mode profiles of RLPCFs with a pure silica core, an additional air-hole in the core and a down-doped silica core. The influence of doping level on that of birefringence and leakage losses of the fibres is also explored. Our numerical simulation indicates, for PCFs with a anisotropic cladding, increased birefringence and reduced leakage losses can be obtained by a down-doped core. The proposed technique also has the merit of enlarging the mode field without the reduction of birefringence, therefore, coupling light to the fibre will become easier.

IR Laser and Heat‐induced Changes in Annulus Fibrosus Collagen Structure

The purpose of this study was to characterize essential changes in the structure of annulus fibrosus (AF) after hydrothermal and infrared (IR) laser treatment and to correlate these results with alterations in tissue state. Polarization-sensitive optical coherence tomography imaging was used to measure collagen birefringence in AF. Differential scanning calorimetry was used as a complementary technique, providing detailed information on thermodynamic processes in the tissue. Birefringence, peak of the denaturation endotherm, and the enthalpy of denaturation (DeltaHm) were determined before and after hydrothermal heat treatment (85 degrees C for 15 min) and non-ablative Er:glass fiber laser exposures on AF in the whole disk (vertebrae-disk-vertebrae complex). Our data have demonstrated quantitative differences between results of laser and hydrothermal heating. Birefringence did not disappear and DeltaHm did not change after treatment in the water bath, but loss of birefringence and a decrease in the enthalpy did occur after laser exposure. These results could be explained by the photomechanical effect of laser irradiation. We suggest that thermo-mechanical stress played a dominant role in the disruption of the collagen network of AF under non-homogeneous laser heating.

Accurate Analysis of Photonic Crystal Fibers by Means of the Fast-Fourier-Based Mode Solver

The recently proposed full-vectorial fast-Fourier-transform-based mode solver is applied to the rigorous analysis of arbitrarily shaped index-guiding photonic crystal fibers. The inclusion of perfectly matched layers absorbing boundary conditions into the formulation makes it possible to obtain an accurate description of the fundamental characteristics of these devices such as chromatic dispersion, modal birefringence, and confinement losses. Obtained results are in close agreement with those previously published in bibliography using other full-vectorial numerical approaches such as the biorthonormal-basis method, the cluster multiple-scattering method, and the finite-element methods

Thermally Induced Birefringence Compensation in High Average Power Nd:YAG Laser

Efficient compensation of thermally induced birefringence with thermal lensing in a rod geometry Nd:YAG laser amplifier was achieved by an in-cavity 90° polarization rotator with three sets of image relaying optics between the laser rods. The measured birefringence loss per transit was 2.8% for pumping power of 580 W per rod. A nearly diffraction limited output beam of 38 W was observed.

Measurement of Mueller matrix for an optical fiber system with birefringence and polarization-dependent loss or gain

In an optical fiber system with both birefringence and polarization-dependent loss or gain (PDL/G), a set of input polarization states and their corresponding outputs are deduced to fulfill some general relationships in Stokes space, by considering the fact that the Mueller matrix of such an optical fiber system meets Lorentz transformation. Then, it can be proven that the minimum number of input polarization states is three for an explicit determination of such a Mueller matrix and no independent input parameter is redundant. Based on the theoretical findings, a general and simple approach is proposed to measure the Mueller matrix. The requirements regarding the choices of three inputs are presented for achieving optimum measurement stability and accuracy. Experimental results on an optical fiber system, formed by two 10-km long single-mode fibers with an optical isolator in between, show excellent agreement with the theory.

High pressure phase transition kinetics of maize starch

In this paper, the impact of high hydrostatic pressure, temperature and time on the gelatinization of maize starch is reported. Starch transition has been assessed by microscopic inspections of the granule’s loss in birefringence which occurs during the first stage of gelatinization in consequence of the water uptake. Experiments have been carried out under combined pressure–temperature treatments in the range of 0.1–650 MPa and 30–75 °C. The rate of gelatinization has been determined by an interpolating model and isokineticity lines were plotted in pressure–temperature diagrams. Pressure higher than 300 MPa is necessary to reduce significantly the onset temperature of gelatinization. At those pressures, the isokineticity lines are bended to the left, indicating that the phase transition in birefringence is occurring at lower temperatures. At 30 °C, maize starch was gelatinized completely after 30 min at 650 MPa.

Clinical diagnosis of potentially treatable early articular cartilage degeneration using optical coherence tomography

A series of bench to operating room studies was conducted to determine whether it is feasible to use optical coherence tomography (OCT) clinically to diagnose potentially reversible early cartilage degeneration. A human cadaver study was performed to confirm the reproducibility of OCT imaging and grading based on identification of changes to cartilage OCT form birefringence using a polarized OCT system approved for clinical use. Segregation of grossly normal appearing human articular cartilage into two groups based on the presence or absence of OCT form birefringence showed that cartilage without OCT form birefringence had reduced ability to increase proteoglycan synthetic activity in response to the anabolic growth factor IGF-1. The bench data further show that IGF-1 insensitivity in cartilage without OCT form birefringence was reversible. To show clinical feasibility, OCT was then used arthroscopically in 19 human subjects. Clinical results confirmed that differences to OCT form birefringence observed in ex vivo study were detectable during arthroscopic surgery. More prevalent loss of cartilage OCT form birefringence was observed in cartilage of human subjects in groups more likely to have cartilage degeneration. This series of integrated bench to bedside studies demonstrates translational feasibility to use OCT for clinical studies on whether human cartilage degeneration can be diagnosed early enough for intervention that may delay or prevent the onset of osteoarthritis.

Cowpea cooking characteristics as affected by micronisation temperature: a study of the physicochemical and functional properties of starch

AbstractBechuana white cowpeas were micronised to three temperatures (130, 153 and 170 °C). Cooking properties of the cowpea seeds and the role of starch‐related properties were studied. In all cases, micronisation significantly reduced the cooking time and thus the time required for the cowpea seeds to attain a suitably soft texture. This was attributed in part to the significant improvement in rate of water absorption during cooking and starch pre‐gelatinisation, as evidenced by loss of birefringence and increased susceptibility of the cowpea starch to α‐amylase digestion. However, micronisation to 170 °C resulted in a severe deterioration in pasting properties of the cowpea flour, possibly due to starch depolymerisation and/or amylose‐associated crosslinking. Owing to these changes, cowpea seeds micronised to 170 °C required a longer cooking time than the other two micronised samples. Flour prepared from cowpea seeds micronised to 170 °C may have limited starch functionality. Copyright © 2006 Society of Chemical Industry

The effects of pulse energy variations on the dimensions of microscopic thermal treatment zones in nonablative fractional resurfacing

We examined the effects of pulse energy variations on the dimensions of microscopic thermal injury zones (MTZs) created on human skin ex vivo and in vivo using nonablative fractional resurfacing. A Fraxel SR laser system emitting at 1,550 nm provided an array of microscopic spots at variable densities. Pulse energies ranging from 4.5 to 40 mJ were tested on human abdominal skin ex vivo and in vivo. Tissue sections were stained with hematoxylin and eosin (H&E) or nitro blue tetrazolium chloride (NBTC) and MTZ dimensions were determined. Ex vivo and in vivo results were compared. Dosimetry analyses were made for the surface treatment coverage calculation as a function of pulse energy and collagen coagulation based on H&E stain or cell necrotic zone based on NBTC stain. Each MTZ was identified by histological detection of a distinct region of loss of tissue birefringence and hyalinization, representing collagen denaturation and cell necrosis within the irradiated field immediately, 1, 3, and 7 days after treatment. At high pulse energies, the MTZ depth could exceed 1 mm and width approached 200 microm as assessed by H&E. NBTC staining revealed viable interlesional tissue. In general, no statistically significant difference was found between in vivo and ex vivo depth and width measurements. The Fraxel SR laser system delivers pulses across a wide range of density and energy levels. We determined that increases in pulse energy led to increases in MTZ depth and width without compromising the structure or viability of interlesional tissue.

Map of spatial-dispersion induced birefringence losses in single-crystal silicon

We report measurements of the birefringence-induced losses in silicon single crystals for [001] and [111] crystallographic orientation and for different doping levels. These results are compatible with the so-called spatial-dispersion-induced birefringence in cubic crystals. These angular maps have been used to fix some tolerances for the next generation of optics in the Virgo gravitational-wave detector.

Relationships Between Birefringence of Constituent Fibers and Properties of Thermally Bonded Nonwovens

AbstractSummary: Three‐dimensional nonwoven fabrics have been produced using a newly developed air‐laid web forming and through‐air thermal‐bonding process directly from commercial PP/polyester (sheath/core) bi‐component staple fibers. Following the previous study on the morphology and structure of constituent fibers, this paper reports the breaking force and abrasion resistance of the fabrics. Results indicate that the relationships between both the breaking strength and abrasion resistance of the samples, and the thermal‐bonding process conditions are similar to each other. The appropriate thermal‐bonding temperature and dwell time are critical for achieving fabrics with high breaking strength and abrasion resistance. Such relationships are inconsistent with those between the tensile strength of the constituent fiber reflected by the birefringence and the thermal‐bonding process conditions. The birefringence of the constituent fiber appears to decrease with increasing thermal‐bonding temperature and dwell time. These results provide evidence that both the breaking force and abrasion resistance for the thermally bonded nonwoven fabrics are governed not only by the mechanical properties of constituent fibers, but also by the bonding properties between the fibers.Abrasion mass loss and breaking force of fabric and birefringence of constituent fiber for the thermally bonded nonwoven samples as functions of the dwell time.magnified imageAbrasion mass loss and breaking force of fabric and birefringence of constituent fiber for the thermally bonded nonwoven samples as functions of the dwell time.

Study of Protein Detection and Ultrastructure of Brazilian Rice Starch during Alkaline Extraction

AbstractAlkaline extraction of Brazilian rice starch was studied. UV/Vis and fluorescence spectroscopy were employed as an innovative way for protein detection during the extraction. Moreover, the results were compared to the traditional biuret colorimetric test. In parallel, the ultrastructure of starch was monitored by small angle X‐ray scattering (SAXS) during every extraction step. A progressive reduction of the granules organization was observed, which was also detected by the loss of birefringence under polarized light. The external integrity of starch granules after complete removal of proteins was maintained, as verified by scanning electron microscopy (SEM). The size of the granules, determined by the Mie scattering method varied between 3 and 8 µm.

Mechanism of starch gelatinization and polymer leaching during microwave heating

The objective of this study was to investigate the process of gelatinization, granule swelling, and polymer leaching following microwave heating of wheat starch suspensions. Polymer leaching was investigated as a function of heating rate, final temperature and starch concentration. Different heating rates were achieved by changing the mass of the starch slurry heated in the microwave oven and the temperature study was conducted on samples of same weight heated to different final temperatures. The total soluble carbohydrate and amylose content in the supernatant was measured. Granule swelling and leaching of polymers occurred only after complete loss of granule birefringence presenting evidence of an asynchronous process of gelatinization compared to conduction modes of heating. The amount of soluble carbohydrate and amylose in the supernatant increased with the increase in temperature and the amylose leached into supernatant decreased with increasing heating rates.

Bouts of Passive Stretching after Immobilization of the Rat Soleus Muscle Increase Collagen Macromolecular Organization and Muscle Fiber Area

This study evaluated the effect of short bouts of stretching on the soleus muscle after immobilization, by measuring the birefringence of the intramuscular connective tissue (ICT) and the muscle fiber area. Thirty rats were divided into five groups: the left soleus was immobilized in the shortened position; after immobilization the animals remained free; after immobilization, the soleus was stretched daily (10 stretches of 60 sec followed by 30 sec rest); after immobilization, the soleus was stretched 3 times a week; control. Immobilization caused a loss of birefringence of the ICT and of muscle fiber area and only daily stretching increased both compared with the control (p < 0.01). In conclusion, short daily bouts of stretching after immobilization induced molecular reorganization of the collagen bundles and muscle fiber hypertrophy in the rat soleus.

Histological evidence for the role of mechanical stress in modulating thermal denaturation of collagen

The hyperthermia and thermal denaturation literatures reveal a time-temperature equivalency when heating cells or connective tissues: thermal damage increases with increasing temperature (for the same duration) and increases with increasing duration (for the same temperature). Recent findings conversely suggest that increasing the mechanical loading on a tissue during heating decreases the thermal damage (for a given temperature and duration of heating). Surprisingly, however, there are few histological correlates of such damage. In this paper, we show that progressive light microscopic changes - swelling of collagen bands, thickening of collagen-rich layers, hyalinization, and loss of birefringence approximately - correlate very well with both increased heating times and decreased mechanical loading. Increased mechanical stress is thus thermally protective and should be considered in the design of clinical procedures that use heating to treat diseases or injuries.

Design of defect-core in highly birefringent photonic crystal fibers with anisotropic claddings

The influence of defect-core on the birefringence and confinement losses of rectangular-lattice photonic crystal fibers are investigated numerically by applying the multipole method. Numerical results illustrate that the birefringence in such fibers is determined not only by the arrangement of air holes in the cladding but also the shape of the core. It is found that asymmetry of the core represented by its rectangular shape implies a higher effective index of the mode that is parallel with the longer side of the rectangle, whereas the anisotropic rectangular-lattice cladding gives rise to just the opposite effect and thus the resulting birefringence can be controlled by a proper combinations of both mechanisms. In particular, effect of the asymmetry of the core on the birefringence is dominant for shorter wavelength. Increased birefringence and reduced confinement loss can be achieved, if we form the core by the omission of several air holes in a row to reduce its negative effect on the birefringence. On the other hand, when asymmetry is increased in the other direction, a negative birefringence at shorter wavelength can be achieved. This occurs due to the fact that asymmetry of the core at higher frequencies overcomes the effect of the asymmetric cladding. As a result, its possible to achieve zero birefringence in anisotropic cladding photonic crystal fiber with an asymmetric core.

Effect of dye doping in poly(vinyl alcohol) waveguides

Dye-doped poly(vinyl alcohol) (PVA) waveguides have been fabricated and characterized. The waveguiding parameters of PVA film, for example the refractive index, thickness, birefringence, polarization conversion and propagation losses, were evaluated using the various concentration of dyes in polymeric solution. It has been shown that the dyes can affect the basic waveguiding parameters considerably. However, birefringence in PVA waveguides remains unaffected irrespective of any dyes and any concentration of dye used.

Calculation of three-dimensional thermal-gradient-induced stress birefringence in slab lasers

The thermal-gradient-induced stress birefringence and depolarization losses were reported previously for a Yb:YAG slab in which the plane-strain approximation applied. In this paper we present analyses of these phenomena applying a full three-dimensional treatment of deposited pump power and cooling in a Yb:YAG slab. We treat both straight-through and zigzag propagation and the cases of the slab length along the crystalline [1 1 1] and [1 1 0] axes. We also describe the losses in a slab with undoped Brewster ends and pump edges.

Effect of hydrothermal treatment on the physical and rheological properties of maize starches

Standard maize (SMS) and waxy maize starch (WMS) were hydrothermally treated at their residual moisture level (∼12%) by Instantaneous Controlled Pressure Drop process in order to obtain pre-gelatinised starches in a single step. The effects of two parameters of this process, namely the steam pressure level and processing time, on the structural and rheological properties of the native maize starches were described. The occurrence of partial gelatinization for DIC treated starches was clearly attested by the increase of the median volume diameter in cold water, the decrease of the gelatinization enthalpy and a loss of birefringence under polarized light. This was more prominent for the highest pressure and longest time: 2.7–3 bar for 200–300 s. Sensitivity of starches to the process was also dependent on their origin, SMS being more affected than WMS.

Optical birefringence and polarization dependent loss of square- and rectangular-lattice holey fibers with elliptical air holes: numerical analysis

Polarization dependent leakage loss as well as optical birefringence for the fundamental mode in square- and rectangular-lattice holey fibers with elliptical air holes are studied numerically based on the full-vector finite element method for the first time. It is shown that high birefringence in the order of 10-2 and large polarization dependent loss required for single-polarization single-mode transmission are both achievable by using the proposed structure.