JEOS:RP - Journal of the European Optical Society Rapid publications
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Single-pixel imaging with deterministic complex-valued sensing matrices
Full text linkIn this paper, complex deterministic sensing matrices are explored to sample the signals in the single pixel imaging (SPI). A new analysissynthesis scheme is proposed to realize the complex deterministic sensing matrix for the DMD-based SPI. The analysis process divides the complex sensing matrix into real sensing matrix and imaginary sensing matrix, and multiple imaging is performed with these sensing matrices. After synthesizing the real and imaginary measurements, the final image of complex deterministic sensing matrix is reconstructed. The performance of deterministic sensing matrix is investigated through simulation and experiment. Compared with the random sensing matrix, the deterministic sensing matrix gives more favorable reconstructed images
Electromagnetic field intensity distribution along focal region of a metallic circular reflector covered with a plasma layer
Full text linkTheoretical analyses has been carried out to study the deviation of the electromagnetic field intensity distribution in the focal region of a long metallic circular reflector that contains a uniform cold collisional plasma layer on its surface. The electromagnetic field intensity expressions along the focal region have been obtained using Maslov’s method. Maslov’s method is systematic procedure, which combines the simplicity of ray optics and the generality of transform methods. The derived analytical field expressions in the focal region have been solved numerically. The reflected and transmitted field intensity distributions from the plasma layer along the focal point were examined. The effects of some physical parameters such as the plasma frequency, the thickness of plasma layer and the effective collision frequency on the transmitted field intensity distribution along the focal region are studied. The results are found to be in a good agreement with results obtained using Kirchhoff’s approximation
Enhancements on multi-exposure LASCA to reveal information of speed distribution
Full text linkLaser Speckle Contrast Analysis (LASCA) has been proven to be a highly useful tool for the full-field determination of the blood perfusion of a variety of tissues. Some of the major advantages of this technique are its relatively high spatial and temporal resolution as well as its good or excellent accordance to Doppler systems. However, traditionally it is only able to report a single characteristic speed regarding to the actual range of interest. This might be misleading if multiple characteristic speeds are present (e. g. tremor and perfusion in skin) or if several kinds of tissues are mixed (e. g. parenchyma and vessels in brain). Here we present two relatively simple extensions of LASCA for these problems. The application of multiple autocorrelation functions (combined with the usage of multiple exposure times) can help in the separation of multiple characteristic speeds. We also present a useful method for the separation of information those originate from a mixture of different tissues. The latter method can be also implemented to single-exposure systems
Refractive index sensing setup based on a taper and an intrinsic micro Fabry-Perot interferometer
Full text linkIn this work, a refractive index sensor setup based on a biconically tapered fiber (BTF) concatenated to an intrinsic all-fiber micro Fabry-Perot interferometer (MFPI) is presented. Here, the power of the MFPI spectral fringes decreases as the refractive index interacts with theevanescent field of the BTF segment. Furthermore, it is demonstrated that the RI sensitivity can be enhanced by bending the BTF segment.Finally, it is shown that by using this sensing arrangement, at ~1.53 µm wavelength, it is possible to detect refractive index changeswithin the measurement range of 1.3 to 1.7 RIU, with a sensitivity of 39.92 dB/RIU and a RI resolution of 2.5 x 10􀀀^-3 RIU with a curvature of C = 18.02 m^-􀀀1
Modification of optical properties of seawater exposed to oil contaminants based on excitation-emission spectra
Full text linkThe optical behaviour of seawater exposed to a residual amount of oil pollution is presented and a comparison of the fluorescence spectra of oil dissolved in both n-hexane and seawater is discussed based on excitation-emission spectra.Crude oil extracted from the southern part of the Baltic Sea was used to characterise petroleum properties after contact with seawater. The wavelength-independent fluorescence maximum for natural seawater and seawater artificially polluted with oil were determined. Moreover, the specific excitation-emission peaks for natural seawater and polluted water were analysed to identify the natural organic matter composition. It was found that fluorescence spectra identification is a promising method to detect even an extremely low concentration of petroleum residues directly in the seawater. In addition, alien substances disturbing the fluorescence signatures of natural organic substances in a marine environment is also discussed.Â
Design of an efficient terahertz wave source from a GaP waveguide embedded in a silicon slot waveguide
Full text linkHere, we propose an efficient scheme for terahertz (THz) wave generation on the basis of difference frequency mixing (DFM) using a GaP ridge waveguide embedded in a silicon slot waveguide. Phase matching in the DFM process, between the nonlinear polarisation wave induced by two near-infrared pumps and the generated THz wave in the low-refractive-index slot waveguide, was achieved by utilising the modal birefringence of the fundamental transverse electric- and transverse magnetic-like modes at telecom wavelengths in the GaP ridge waveguide. The effective cross-sectional area of the THz wave in the waveguide was small, 220 μm2 at 2.26 THz, resulting in a photon conversion efficiency of 5.7x10-2%. The THz output power approached the multi-W level using the proposed waveguide structure
Optical path difference evaluation of laser-soldered optical components
Full text linkWe present Solderjet Bumping, a laser-based soldering process, as an all inorganic joining technique for optical materials and mechanical support structures. The adhesive-free bonding process enables the low-stress assembly of fragile and sensitive components for advanced optical systems. Our process addresses high demanding applications, e.g. under high energetic radiation (short wavelengths of 280 nm and below and/or high intensities), for vacuum operation, and for harsh environmental conditions. Laser-based soldering allows the low stress assembly of aligned sub-cells as key components for high quality optical systems. The evaluation of the optical path difference in fused silica and the radiation resistant LAK9G15 glass components after soldering and environmental testing shows the potential of the technique
Exploring the impact of rotating rectangular plasmonic nano-hole arrays on the transmission spectra and its application as a plasmonic sensor
Full text linkPlasmonic nano-structures play a significant role in most recent photonic devices and applications. In this paper, we investigate the optical transmission spectra of rotatable periodic nano-metric apertures with different dimensions. This investigation includes monitoring the modification of both the transmission resonance wavelengths and peak transmittance at different dimensions and orientations of the nano-holes. The obtained results provide better insight to the interaction of light with periodic plasmonic nano-hole arrays. We find that nano-holes dimension/orientation can totally suppress an optical transmission, tune its resonance wavelengths, and change its peak values. Furthermore, we present the surface plasmonic resonance sensing as an application for the reported nano-hole array
Comparison of two-color methods based on wavelength and adjacent pulse repetition interval length
Full text linkThis paper describes the characteristics of a two-color method based on the adjacent pulse repetition interval length (APRIL), which functions as a length unit for femtosecond optical frequency combs (FOFCs), and compares the results to the wavelength-based two-color method. The wavelength-based two-color method can eliminate the inhomogeneous disturbance of effects caused by the phase refractive index; therefore, the APRIL-based two-color method can eliminate the air turbulence of errors induced by the group refractive index. Our numerical analysis of the APRIL-based two-color method will contribute to the pulse-laser-based two-color method, which secures traceability to the definition of the meter via APRIL
Energy efficiency of a new trifocal intraocular lens
Full text linkThe light distribution among the far, intermediate and near foci of a new trifocal intraocular lens (IOL) is experimentally determined, as a function of the pupil size, from image analysis. The concept of focus energy efficiency is introduced because, in addition to the theoretical diffraction efficiency of the focus, it accounts for other factors that are naturally presented in the human eye such as the level of spherical aberration (SA) upon the IOL, light scattering at the diffractive steps or the depth of focus. The trifocal IOL is tested in-vitro in two eye models: the aberration-free ISO model, and a so called modified-ISO one that uses an artificial cornea with positive spherical SA in instead. The SA upon the IOL is measured with a Hartmann-Shack sensor and compared to the values of theoretical eye models. The results show, for large pupils, a notorious reduction of the energy efficiency of the far and near foci of the trifocal IOL due to two facts: the level of SA upon the IOL is larger than the value the lens is able to compensate for and there is significant light scattering at the diffractive steps. On the other hand, the energy efficiency of the intermediate focus for small pupils is enhanced by the contribution of the extended depth of focus of the near and far foci. Thus, while IOLs manufacturers tend to provide just the theoretical diffraction efficiency of the foci to show which would be the performance of the lens in terms of light distribution among the foci, our results put into evidence that this is better described by using the energy efficiency of the foci