JEOS:RP - Journal of the European Optical Society Rapid publications
Not a member yet
545 research outputs found
Sort by
A novel back-side light-trapping structure for thin silicon solar cells
Get PDFDecreasing silicon consumption is one of the most important ways of reducing the cost of solar cells. High-quality light trapping provides the possibility of making thinner silicon solar cells without sacrificing optical efficiency. In this work we introduce an advanced bi-periodic back-side structure with promising light-trapping properties. The structure combines high coupling efficiency of light to oblique travelling modes with the ability of keeping the light within the solar cell for multiple reflections between the front and the rear side. We have done numerical simulations of light trapping for normal incidence in our structure, and we show that our structure with real materials holds the potential to exceed the light trapping of an ideal Lambertian surface. We also investigate the behaviour of our light-trapping structure as a function of angle and state of polarization, and compare it to Lambertian behaviour
An efficient scattering model for PEC and penetrable nanowires on a dielectric substrate
Get PDFAn efficient forward scattering model, based on the Method of
Auxiliary Sources, is formulated for perfectly electrically conducting
(PEC) and penetrable nanowires on dielectric substrates. The accuracy of the model is investigated parametrically, with emphasis on future application in an inverse scattering scheme. The model is tested on families of PEC and silver nanowires on silicon substrate
Optical fibre long period grating spectral actuators utilizing ferrofluids as outclading overlayers
Get PDFResults are presented on the spectral tuning of optical fibre long period gratings utilizing water and oil based ferrofluids as outclading overlayers, under static magnetic field stimulus. Two approaches are adopted for modifying the ambient refractive index at the position of the long period grating. In the first approach, a water based ferrofluid is controllably translated along the length of the grating via a magnetic field. Changes as high as 7.5nm and 6.5dB are monitored in the wavelength and strength, respectively, of the attenuation bands of the grating. The repeatable performance of this device for repetitive forward and backward translation verifies that no ferrofluidic residue is left on the fibre, due to silanization cladding functionalisation. In the second approach, the refractive index of an oil based ferrofluidic overlayer is modified through the magneto-optical effect. For an applied static magnetic field in the order of 400 Gauss the strength of the attenuation band of the grating is modified by more than 10% while its spectral position remains unaffected. Accordingly for the implementation of the last approach, the magnetically induced refractive index changes of ferrofluids of different solution concentrations are studied by employing diffraction efficiency measurements
Tunable Raman fiber laser induced by Rayleigh backscattering in an ultra-long cavity
Get PDFWe report an ultra-long Raman laser with a 46 km fiber length that behaved as a Rayleigh back-scattering–based optical feedback. The laser was tunable from 1550 nm to 1571 nm (3 dB bandwidth) with the insertion of an optical grating filter. Evaluations on the spectral evolution and power development were also performed from the results obtained. In fact, it was discovered that the spectral broadening effect between the modeless spectra resembled the same process that happens in a typical fiber cavity that has high reflectors at each cavity end. In addition, the output power showed a square-root development with respect to the input power
Reduction of global interference in functional multidistance near-infrared spectroscopy using empirical mode decomposition and recursive least squares: a Monte Carlo study
Get PDFFunctional near-infrared spectroscopy (fNIRS) is a sensitive technique that has the potential to detect haemodynamic changes during the performance of specific activation tasks. However, in real situations, fNIRS recordings are often corrupted by physiological phenomena, especially by cardiac contraction, breathing and blood pressure fluctuations, and these forms of interference can severely limit the utility of fNIRS. We present a novel fNIRS enhancement based on the multidistance fNIRS method with short-distance and long-distance optode pairs. With this method empirical mode decomposition (EMD) is applied to decompose the superficial haemodynamic changes, derived from the short-distance fNIRS measurements, into a series of intrinsic mode functions (IMFs). By utilizing the weighting parameters for the IMFs, we perform an estimation for global interference in the desired haemodynamic changes, derived from the long-distance fNIRS measurements. We recover the evoked brain activity by minimizing least squares between the desired haemodynamic changes and the estimated global interference. To accelerate the computation, we adopt the recursive least squares (RLS) to decrease the computation complexity due to the matrix inversion. Monte Carlo simulations based on a five-layered slab model of a human adult head was implemented to evaluate our methodology. The results demonstrate that the EMD-RLS method can effectively remove contamination from the evoked brain activity
Loss optimization in double fishnet metamaterials at telecommunication wavelengths
Get PDFA hole shape optimization study was made for a double fishnet metamaterial producing a negative index of refraction within 1.4 - 1.5 μm. It is found that within these wavelengths, elliptical holes offer lower losses as compared to rectangular ones and theoretically produce the best figure of merit (FOM) of approximately 6
Diffractive shaping of excimer-laser beams for pulsed laser deposition
Get PDFWe present a beam-shaping system for a pulsed laser deposition setup. This system is based on two diffractive beam-splitter gratings and is able to produce 2*2-mm2 flat-top distributions of UV light with a fluence of 3 J/cm2 on the target some 30 cm behind the system. We have applied the setup to deposit ferromagnetic Ni-Mn-Ga films
Monocular multi-view stereo imaging system
Get PDFIn this study, we present a single-camera, multi-view stereo imaging system for capturing three-dimensional (3D) information. First, we design a monocular, multi-view stereo imaging device composed of a fisheye lens, and planar mirrors placed around the lens. The fisheye lens has a wide view-angle. The captured image includes a centered region of direct observation and surrounding regions of mirrored observations. These regions can be considered as images captured by multiple cameras at different positions and orientations. Therefore, the proposed device is equivalent to a synchronous multiple-cameras configuration, in which all the cameras share the same physical characteristics.
In addition, we show how to place the mirrors in order to maximize the common view-angles, which is an important design consideration. Then, after calibrating the projection function of the fisheye lens, we obtain the positions and orientations of the virtual cameras from the external parameters. We also develop two multi-baseline stereo algorithms for the 3D measurement system.
The first algorithm transforms the captured image to perspective images, and uses the traditional method to perform stereo determination. The second algorithm directly uses the original captured image along with an analysis of the epipolar geometry.
Experimental results show that our system is more effective than traditional stereo methods that use a stereo pair, and it can achieve robust 3D reconstruction
Microfiber loop resonator based temperature sensor
Get PDFA microfiber loop resonator (MLR) is fabricated by coiling a microfiber which is fabricated using a flame heating technique, into itself. A temperature response on a comb spectrum of a fabricated MLR, which is embedded in a low refractive index polymer, is investigated. The spacing of the transmission comb spectrum of the MLR is observed to be unchanged with the temperature. However, the extinction ratio of the spectrum is observed to be linearly decreased with the temperature. The slope of the extinction ratio reduction against temperature was about 0.043dB/oC. The dependence of the extinction ratio on temperature is due to the change in the material’s refractive index
Spectral properties for 1D multilayer systems and application to super resolution
Get PDFThe spectral properties of one-dimensional multilayer structures for the two polarizations TE and TM are investigated and a physical explanation for the large spatial transmission band that can be obtained with this kind of system is given together with a discussion of the correlated super resolution effect. A designing approach to build 1D metal-dielectric multilayer structures that have super resolution is also suggeste