Effect of elongation deformation on power losses in polymer optical fibers

We investigate the effect of fiber elongation on power loss as rays propagate along deformed polymer optical fibers (POFs). Variations in core diameter, incident angle, stress and strain distributions, and necking of the POFs during fiber elongation are studied. The power losses in the deformed POFs are analyzed both experimentally and numerically. Theoretical analysis based on an elastic-plastic finite-element model and a planar waveguide assumption is proposed. It is found that fiber elongation significantly affects the power loss in POFs, particularly at higher values of elongation. Good agreement between the measured results and the results simulated from the proposed model is obtained. The maximum difference is less than 5%. Results indicate that the proposed theoretical analysis based on an elastic-plastic finite-element model and a planar waveguide assumption is feasible to predict the power loss variation introduced by elongated deformations. A curve-fitted equation is also proposed to estimate the power loss of POFs under different fiber elongation conditions.     

On confocal Raman spectroscopy of semicrystalline polymers: the effect of optical scattering

A series of semicrystalline polymers has been prepared through morphological control. Each of these has an identical refractive index but a different, well-defined, scattering behavior. From existing geometrical optical theories of confocal Raman spectroscopy, these materials should behave identically. Initially, the extent of scattering in each system was assessed quantitatively, from the near-infrared through the visible wavelength range, by UV/visible spectroscopy. The effect of optical scattering on the variation of intensity of the Raman scattered radiation with subsurface position was then examined in all four materials; the effect of surface roughness was also considered in the highest clarity system. Where surface effects are removed through careful sample preparation and the materials are interrogated using identical optical systems to mitigate against the impact of refractive index mismatch and other optical effects, the Raman response is strongly affected by the scattering characteristics of each material. A simple empirical relationship has been determined that adequately described all our specimens.     

Simple method of measuring scattering losses in optical fibers

A simple method of measuring the scattering losses of optical fibers was developed. The method permits the measurement of the scattering-loss spectra by use of photon counting. Measurement is based on right-angle scattering, which is dominated by Rayleigh scattering, a material-intrinsic loss. A reference fiber for which the scattering loss is known is used to cancel out the unknown factors that are dependent on the optical setup. The scattering-loss measurement was demonstrated by use of two different low-loss fibers and was found to agree with predetermined figures to within 10% over the wavelength range 0.44-1.0 mum. Finally, the method was applied to a new high-numerical-aperture optical fiber to find its material scattering loss.     

Effect of metal coating on the optical losses in heated optical fibers

The effect of heating in air on the optical losses in metal-coated fibers has been studied. Two fibers were drawn from the same silica preform and coated by different metals (copper and aluminum). Dependences of a change in the optical losses on the temperature were measured in a 20–400°C range at a 50°C step. The optical losses of metal-coated fibers heated to temperatures below 300°C change mostly due to the microbending contribution. At temperatures above 300°C, the main contribution to increasing optical losses is due to the absorption on OH groups. It is established for the first time that the contribution to optical losses due to the OH groups is much more pronounced in Al-coated fibers than in Cu-coated ones. In addition, the Al-coated fibers exhibit growth in the optical losses above 300°C due the absorption on molecular hydrogen.     

Light scattering losses of high reflection dielectric multilayer optical devices

Light scattering losses from dielectric multilayer are becoming increasingly important for designing high precision performance optical devices. In this paper, we applied the bi-directional reflectance distribution function of optical multilayer and analyzed the total reflectance scattering losses based on both the completely correlated and non-correlated interface models to compare with a high reflection 17-layer optical multilayer deposited on roughness of 2.8 nm substrates. The experimental result supports the completely correlated interface model as firstly the wavelength dependence is in good agreement with the phase change of the calculated result and secondly the calculated scattering intensity of the completely correlated interface scattering model is approximately the same as that of the measured scattering spectrum, while the intensity using the non-correlated interface scattering model is significantly higher than the measured result in the high transmission ranges and lower in the main band of the high reflection range.     

Effect of heterophase inclusions on the optical losses in high-purity IR optical materials

Using a tungstate-tellurite glass and high-purity zinc sulfide—promising IR optical materials—as test systems, we have developed an approach for evaluating the limits of the sensitivity of optical losses to the presence of heterophase impurity inclusions and second-phase inclusions differing in chemical nature and size. We have calculated the volume fraction of disperse phases and concentration of inclusions which ensure optical losses in these materials below a predetermined level.     

Effects of light scattering in optical coatings on energy losses in LED devices

The effect of light scattering in phosphor-containing optical coatings on energy losses in chip-on-board LED devices is considered. The energy losses have been evaluated by numerical simulation with the refractive index of the coating material (n = 1.4–1.8) and the average radius of dispersed phosphor particles (R = 5–50 μm) being the variable parameters. It is established that the energy losses most significantly depend on the level of total internal reflection at the coating/air interface. In the LED device configuration studied, the optimum refractive index of the coating material is n = 1.4. It is also found that, in order to reduce the energy losses related to light scattering on phosphor particles, it is expedient to use phosphors with coarse particles (R = 50 μm).     

Modal field deformation and transition losses in UV side-written optical fibers

The asymmetry of the UV-induced refractive-index profile in photosensitive optical fibers causes a deformation of the modal fields, resulting in transition losses between UV-exposed and unexposed fiber sections up to 0.1 dB for UV-induced index changes of the order of 相似文献   

Quadrefringence of optical vortices in a uniaxial crystal

The splitting of a single optical vortex into four separate ones in a singular beam is theoretically and experimentally described for the propagation of obliquely incident light in a uniaxial crystal. We also find the condition under which the generated vortices in each of the four individual beams propagate independently without changing their structure and have different locations in all beams for any crystal lengths.     

Effect of scattering on nonlinear optical scanning microscopy imaging of highly scattering media

The intensity of two-photon excited fluorescence (TPF) generated by ultrashort laser pulses was measured as a function of the depth of a focal point inside highly scattering media. The purpose was to investigate the spatial location of TPF in a scattering medium. Owing to the scattering, the intensity of the incident beam as well as the generated TPF signal was attenuated exponentially as the focal point was scanned into the medium. As the scattering strength of the medium was increased, the TPF was not confined to the focal region and had a wider distribution. These observations show that the scattering will result in the degradation of the ability of optical depth sectioning of nonlinear optical scanning microscopy.     

Toward the description of uniaxial deformation of metals

Effectiveness of using the endochronic theory of plasticity for describing unidimensional deformation processes under cyclic loading is investigated. A method is developed for determining parameters of the equations of state which depend on the amplitude of plastic deformation and length of strain path. A sufficiently good agreement is shown between calculated and experimental data in describing the kinetics of the stress-strain state of specimens of steels 316 and 45 subjected to variable loads.Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev Polytechnic Institute. Translated from Problemy Prochnosti, No. 11, pp. 65–69, November, 1989.     

Influence of voids on the stress distribution and deformation behaviour of epoxies under uniaxial deformation

A zero-order model is presented, which allows calculation of the stress distribution in porous epoxies by taking into account the interaction between randomly distributed voids. These results demonstrate that the mean value of the stress concentration factor increases with the volume fraction of voids. This leads to a decrease in sample yield strength. However, the generation of a porous morphology also creates a considerable number of regions where the stress is completely released. The theoretical predictions are in good agreement with experimental results obtained with macroporous epoxies, which were prepared based on the chemically induced phase separation technique, and tested under uniaxial compression.     

Tunable phase-only optical filters with a uniaxial crystal

A novel method of fabricating phase-only optical filters that is based on the properties of a uniaxial crystal is proposed. With these optical filters, the phase differences are tunable among the different filter zones. Many focal patterns can be obtained if these optical filters are placed in front of a lens; furthermore, these optical filters can also be used to make up for the distortions in fabrications in which they were used only as untunable optical filters.     

A generalized model for the uniaxial isothermal deformation of a viscoelastic body

Summary Using the notion of a fractional derivative we formulate a new model for a uniaxial deformation of a visco-elastic body. The basic assumption is that all derivatives ₍₎ with respect to time of the stress depend (with specified weighting factor) on all derivatives ₍₎ with respect to time of the strain (multiplied with another weighting factor), for 01. In this respect our model is a generalization of the Zener model, i.e., it is a Zener fractional model with infinitely many terms. The relation between stress and strain is given in explicit form. For two specific choices of parameters the behavior of the model under suddenly applied stress (creep) and suddenly applied strain (stress relaxation) are examined.     

Constitutive model for large strain deformation of semicrystalline polymers

A constitutive model for large strain deformation of semicrystalline polymers has been formulated to predict the complex elasto-viscoelastic-viscoplastic material response. The general form of this model can be represented by three parallel rheological components corresponding to each of the modes of deformation. It will be shown that such a configuration is well suited to the mechanical nature of polymers as observed in recent studies. The constitutive stress-strain-time relationships are drawn from continuum mechanics which are more suitable than simple linear expressions from rheology. The result is a large strain, fully three-dimensional constitutive model, derived from a thermodynamic basis. The proposed model can be fit to macroscopic experimental data and is highly suited to numerical analysis. The paper reviews the literature relevant to constitutive representation of semicrystalline polymers, provides conclusion and validation of the most suitable form of constitutive model and presents the relevant constitutive mathematics.     

Propagation of the Airy beam along the optical axis of a uniaxial medium

We investigate the propagation of an Airy beam along the optical axis of a uniaxial medium, and we find that the propagation property of the Airy beam is determined by the ordinary refractive index of uniaxial crystals and is independent of the ratio of the extraordinary to ordinary refractive index. We also know that the polarization state of linearly polarized Airy beams changes gradually during the propagation. This shows that the propagation properties of the Airy beam in uniaxial crystals along the optical axis is distinctly different from that orthogonal to the optical axis.     

Features of the deformation of sintered iron in uniaxial tension

The stress — strain relation of the solid phase of sintered iron is calculated for materials with a porosity of 1–30. The deforming stress is calculated with allowance for features of the deformation of the specimens and stress redistribution over their volume connected with transformation of the pore structure in tension. Porosity is determined to have an effect on the curve which describes the strain-hardening of the solid phase. The nature of the effect is discussed in connection with a change which occurs in the stress state in active volumes of materials with different porosities. The laws that determine the dependence of the uniform strain on porosity are also discussed.Translated from Problemy Prochnosti, No. 11, pp. 12–18, November, 1993.