Light Propagation Path Research Articles

Anisotropic waveguide theory for electrically tunable distributed feedback laser from dye-doped holographic polymer dispersed liquid crystal

Anisotropic waveguide theory is developed for electrically tunable distributed feedback (DFB) laser from dye-doped holographic polymer dispersed liquid crystal (HPDLC) grating. The period grating structure, optical anisotropy of the liquid crystal (LC) and practical light propagation path in the HPDLC have been considered. The emitted lasing wavelength is deduced on basis of the dielectric anisotropy of the LC, transverse-magnetic (TM) light wave propagation in the core layer and DFB laser theory. An experimental method to determine the tilt angle of the LC and the lasing behaviours under different electric fields are used to verify the validity of the anisotropic numerical analysis. The results show that a more accurate agreement between the theoretical calculations and the experimental data is achieved. The anisotropic numerical analysis presented here is very useful when designing and optimising tunable lasers for optical communications and integrated optics.

A fast surface reconstruction method for fluorescence molecular tomography based on cross-beam edge back projection

An accurate surface reconstruction method is important to fluorescence molecular tomography (FMT) for it provides boundary information of the domain occupied by the image object which is essential to modeling light propagation in free space and inside the object. In this paper, a method based on cross-beam edge back projection (CEBP) is proposed to achieve fast and three-dimensional (3D) surface reconstruction for FMT. This method consists of a cost effective and easy-to-implement setup; it back-projects the edge of an image object of all projection angles along the actual light propagation path to perform 3D surface reconstruction. Simulation studies and experiments were performed to compare the reconstruction accuracy and computational cost of the CEBP based method and the conventional radon transform (RT) based method. Results demonstrate that the CEBP based method significantly accelerates surface reconstruction compared with the RT based method while keeping similar accuracy.

Comparison Between Elementary- and Middle-school Students' Conceptions of the Propagation Path of Light and the Consistency of Those Conceptions

Comparison Between Elementary- and Middle-school Students' Conceptions of the Propagation Path of Light and the Consistency of Those Conceptions

Validation of luminescent source reconstruction using single-view spectrally resolved bioluminescence images

We characterize the capabilities and limitations of the Living Image Software 3D Analysis package (Xenogen, Alameda, California) in the reconstruction of calibrated light sources. Sources shallower than the mean free path of light propagation suffered reconstruction inaccuracy. For sources deeper than the mean free path, the average error in depth and intensity reconstruction was less than 4% and 12%, respectively, for homogeneous tissue. The reconstruction of luminescent beads implanted within an optically heterogeneous mouse abdomen proved less accurate. The ability to distinguish multiple sources decreased with increasing source depth. A number of factors influence the accuracy of light source reconstruction.

Non-invasive glucose sensing with near-infrared spectroscopy enhanced by optical measurement conditions reproduction technique

Non-invasive glucose sensing utilizing near-infrared spectroscopy (NIRS) has been a focusing topic in biomedical optics applications. However, different probing locations and contact pressures between the probe and skin cause variations in the light propagation paths within tissue, making it very hard to obtain stable near-infrared spectra concerning body content. This paper proposes one possible solution to the reproduction of light propagation within tissue for near-infrared non-invasive glucose sensing systems by introducing the optical measurement conditions reproduction technique. Results of experiments on glucose concentrations within human body through application of our proposed system show a RMSEP value of 15–20 mg/dL and a correlation coefficient greater than 0.8.

Revised Kubelka–Munk theory I Theory and application

Using a statistical analysis of light propagation in media, we propose a revision to Kubelka-Munk (K-M) theory by taking into account the effect of scattering on the path length of light propagation (path variation). This leads to new relationships between the K-M scattering S and absorbing K coefficients and the intrinsic scattering s and absorbing a coefficients of a material that indicate that the S and K coefficients depend non-linearly on both a and s. The additivity law that bridges K-M S and K coefficients of a composite medium, such as dye-dispersed paper (dyed paper) and those of its material components (dye and paper), is also revised. It is further shown that experimental findings on dyed paper that the original K-M theory failed to explain can be clearly understood and accommodated by the new K-M theoretical framework (two-flux approach). Numerical simulations with the revised theory on model ink, paper, and dyed paper have been carried out.

Conducting Polymer Nanowires and Nanodots Made with Soft Lithography

The conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT-PSS) was patterned by micromolding in capillaries (MIMIC), in the form of nanowires on a glass or a Si wafer. The periods of the molded nanowires were 833 or 278 nm. By applying force on top of the stamp during MIMIC, the height of these nanowires could be changed. An alternative method of preparing structured surfaces is the liquid embossing technique, used to pattern polymers deposited from dispersion. Nanowires (278 nm) and 2-D nanodots on semiconducting polymer (poly(3-(2‘-methoxy-5‘-octyphenyl) thiophene)) POMeOPT were also achieved by another soft lithography techniquesoft-embossing. The possibility to pattern both semiconducting and metallic conjugated polymers from aqueous solutions or organic solvents on a submicron level makes it possible to use these materials in flexible optoelectronic devices where light propagation and electronic paths are defined by patterning.

Fluorescence Confocal Polarizing Microscopy: Imaging Liquid Crystal Director Fields in Three Dimensions

Conventional polarizing microscopy allows only information from two dimensions, on account of optical integration along the path of light propagation. Real three-dimensional imaging of orientational order has now become possible with fluorescence confocal polarizing microscopy. This technique provides a useful tool in the visualization of director fields in liquid crystal cells, as schematically shown in the picture, and will be of great potential in the study of director distributions in defect structures of anisotropic fluids.

Gas flow visualization by means of sheared beam interferometry: sensitivity, maximum measurable gradient of the density fluctuation, and integrated density estimation

A technique for visualizing the density distribution of a gas flow using sheared beam interferometry was analyzed. The interference pattern which arises in the shearing interferometer encodes information about the gradient of the line integral of the density fluctuation along the propagation path of the light. While this method of flow visualization has been previously used, the sensitivity and dynamic range of this technique have not been analyzed. It is also shown that it is possible to obtain quantitative information about the integral of the density fluctuations along the path of light propagation using shearing interferometry. This paper presents the theoretical aspects of this technique, and provides an analysis of the sensitivity and maximum measurable gradient of the line integral of the density fluctuation. Representative results from a laboratory experiment conducted on a shear-layer gas flow are shown.

Recent developments of optical fiber sensors for automotive use

Abstract Optical fiber sensing technologies are expected to apply for many future electronic control systems in automobiles, because of their inherent outstanding features, such as high noise immunity, high heat resistance, and flexible light propagation paths which can be applied to measure the movements and directions of the mobiles. In this paper, two typical applications of fiber sensing technologies in automobiles are described in detail. The combustion flame detector is one of the typical applications of a fiber spectroscopic technology which utilizes the feature of high noise and heat resistibility and remote sensibility. Measurement of engine combustion conditions, such as the detonation, the combustion initiation, and the air-fuel ratio, have been demonstrated in an experimental fiber sensing method. Fiber interferometers, such as a fiber gyroscope, have great possibilities in future mobile applications because they are applicable to many kinds of measurements for movements and physical variables...

Adaptive correction of images

An analysis is made of the problem of improving the quality of an image of a coherent extended object formed by an optical system after transmission through the atmosphere. The problem is tackled by adaptive correction. The correction is carried out in accordance with a phase conjugacy algorithm and information on the distribution of turbulent inhomogeneities of the medium (atmosphere) in the propagation path of light is deduced from measurements of the phase of the field of a reference source. Characteristics of an optical adaptive correction system, such as the optical transfer function and resolution, are considered.

Improvement in the quantum efficiency of silicon photodetectors at near IR wavelengths by edge illumination

The concept of illuminating a silicon photodetector along an edge to increase the light propagation path through the depletion region and thus to increase quantum efficiency at near IR wavelengths is introduced. Quantum efficiency measurements using both a GaAlAs laser and a He–Ne laser are included. These measurements show an improvement in quantum efficiency at λ = 0.83 μm for edge illumination over normal incidence of 75% for a photodiode and of 142% for a MOS capacitor photosensor.