JEOS:RP - Journal of the European Optical Society Rapid publications
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Polarization sensitivity of optical resonant dipole antennas
Get PDFThe polarization sensitivity of optical resonant dipole antennas is investigated numerically using the Green's tensor technique. The electric field-intensity in the feed-gap of the antenna is calculated as function of the polarization of the incident field. A simple analytical model is proposed that matches the numerical data very well. While a very strong polarization sensitivity can be achieved for specific wavelengths, our results also indicate that there are situations where the antenna is not sensitive at all to the polarization. The role played by different plasmon resonances in the system is illustrated
Synchronisation of spatiotemporal complex states by incoherent coupling
Get PDFSynchronisation of spatiotemporal continuous disorder is realised in a Liquid Crystal Light Valve single feedback system with an incoherent, unidirectional master-slave-coupling scheme as excellent model system for synchronisation. Thus, complex states disordered in space and time were completely synchronised by using identical systems as master and slave. Thereby the impeding role of system differences is demonstrated in comparison to former experiments. A novel imaging method is introduced, in which the synchronisation process and effects like a time lag can be more easily characterised
Experimental demonstration of singular-optical colouring of regularly scattered white light
Get PDFExperimental interference modelling of the effects of colouring of a beam traversing a light-scattering medium is presented. It is shown that the result of colouring of the beam at the output of the medium depends on the magnitudes of the phase delays of the singly forward scattered partial signals. The colouring mechanism has for the first time experimentally been illustrated for a forward propagating beam through a light-scattering medium. This is showed in video-fragments of the interferograms recorded within the zero interference fringe with a gradual change of the path difference of the interfering polychromatic wave trains. Spectral investigation of the effects of colouring has been carried out using a solution of liquid crystal in a polymer matrix. The amplitude ratio of the non-scattered and the singly forward scattered interfering components significantly affects the colour intensity. It has further been established that the spectral content of the illuminating beam strongly influences the colour of the resulting radiation
Experimental demonstration of distance measurement with a femtosecond frequency comb laser
Get PDFWe experimentally demonstrate that a stabilized femtosecond frequency comb can be applied as a tool for distance measurement in an interferometric scheme. A proof of principle of this method, as proposed by Ye, is provided by measuring a displacement of about 15 cm in air and comparing it to a reference value from a calibrated laser interferometer. The experiment shows that the new scheme easily achieves an accuracy better than one optical fringe
Design concepts for broadband high-efficiency DOEs
Get PDFSeveral design-concepts are presented for so-called efficiency achromatized diffractive optical elements (EA-DOEs) possessing diffraction efficiency larger than 97% over a broad spectral range. We start with tracing two different methods for surface relief profiles well known from the literature: common depth and multilayer EA-DOEs. Successively we present the following new approaches together with design parameters and performance properties: 1) gradient-index EA DOEs, 2) sub-wavelength EA-DOEs, and 3) a so-called cut-and-paste strategy. All designs are based on scalar assumptions and certain necessary dispersion relations of two different materials. The scalar assumption is no real limitation as the minimum zone width of our main application, the correction of chromatic aberrations, is 50 -100 times the wavelength. From aforementioned relations, design parameters as profile heights are derived and the resulting diffraction efficiency can be deduced. Additionally it turns out that the necessary dispersion relation concerning the sub-wavelength EA-DOE is the same as for the common depth EA-DOE. Moreover, for the multilayer EA-DOE we were able to show that if the dispersion relations of the materials can be accurately described by a second order Cauchy series, the efficiency becomes generic and will be the same regardless of which materials are chosen. By proper choice of the materials, all types of EA-DOEs yield thicknesses of 10 - 30 µm which is more than ten times larger than for conventional DOEs. Due to the small refractive index difference of GRIN materials, such EA-DOEs exhibit thicknesses of 90 µm and more. Therefore, it is advisable to look for material combinations which yield thicknesses as small as possible
Nano-meter scale heterogeneous III-V semiconductor-silicon photonic integration
Get PDFIt is pointed out that the fully recognised and ever growing need for a combination of photonic and electronic functionalities could be made fully effective by the heterogeneous integration of active III-V semiconductor/passive silicon photonics and silicon microelectronics. It is shown that the inevitable scaling down to nano-meter range of photonic integration requested by the necessary matching to microelectronics is made possible by the heterogeneous association of IIIV semiconductor and silicon membranes including high index contrast and nano-meter scale structuring. It is emphasized that these membrane photonic nanostructures can be considered as the absolute must on the track to the ultimate confinement of photons which is highly desired in the prospect of the development of Micro-Nano-Photonic devices and systems. Examples of devices and systems along this approach are presented (micro-laser/micro-guide integration, active devices with very low threshold,...)
Semiconductor microcavities for enhanced nonlinear optics interactions
Get PDFSemiconductor microcavities offer a unique way to enhance nonlinear optical processes through light confinement in space and time. In this article we review two different nonlinear optics semiconductor-based applications that benefit from the microcavity setting. Firstly, we discuss a difference frequency generation scheme in a GaAs microdisk. Secondly, we show how a recently demonstrated source of counter-propagating twin photons can display an appreciable performance improvement when combined with a vertical cavity
Fourier transformed picosecond synchronously pumped optical parametric oscillator without spectral filtering element
Get PDFAn optical parametric oscillator for the infrared region pumped by a picosecond Ti:Sapphire laser is demonstrated. Fourier transform limited pulses of 15 and 10 ps, for signal and idler wavelengths respectively, have been obtained using a periodically poled stoechiometric lithium tantalate nonlinear crystal, without any spectral filtering. A complete experimental study of the influence of the cavity length detuning on the spectral and temporal dynamic of the output radiation is discussed
Interference or not: analysis of the Young’s experiment for a single cycle pulse: erratum
Get PDFIn the paper published in the J. Europ. Opt. Soc. Rap. Public. 1, 06016 (2006), the model that has been used to describe the spectral distribution of the field followed by the diffraction calculations does not lead to a pulse with a “single†cycle but to a pulse of several cycles. In this paper, we present a discussion on the subject and implications in the interpretation of the results
Towards a new concept for high sensitivity Compton scatter emission imaging
Get PDFA new efficient scheme for imaging gamma-emitting objects is advocated in this work. It is elaborated on the recent idea of collecting data, using a detector equipped with a parallel-hole collimator, from Compton scattered photons to reconstruct an object in three-dimensions. This paper examines a working mode without collimation, which should increase its sensitivity and field of view. To simplify the otherwise complex mathematical formulation, we choose to discuss the image formation process in two-dimensions, which can be implemented with a slit collimator. Comparison with the standard collimated case, via the analysis of the shapes of the respective point spread functions (PSF), shows marked improvements and numerical simulation results, obtained using a brain phantom, support the viability and attractiveness of this new imaging modality