JEOS:RP - Journal of the European Optical Society Rapid publications
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Rotating vortex imaging implemented by a quantized spiral phase modulation
Get PDFWe demonstrate both theoretically and experimentally that a spiral mask with a finite number of discrete phase levels allows a defocusing induced rotation of the point spread function in the vortex imaging. Two experimental configurations based on a spiral phase modulation of light and a spiral filtering of the spatial spectrum are studied in a unified theoretical treatment. The rotating point spread functions are analyzed in detail for imaging realized by the vortex lens and the 4-f system used in the spiral phase contrast microscopy. The theoretical results are verified by experiments using a spatial light modulator. The method is applicable to a precise focusing and optical imaging allowing depth estimation from diffracted rotation. Apart from implementation simplicity, the main advantages of the method are high energy efficiency, a possibility to operate with either complex amplitude or spatial spectrum of light and variability allowing a simple control of number of lobes of the point spread function
Method of lines solution to the transient SBS equations for nanosecond Stokes pulses
Get PDFThe spectral and temporal evolution of distributed sensing based on stimulated Brillouin scattering (SBS) in optical fibers for severalnanosecondStokes pulses is demonstrated by using the method of lines (MOL) solution of the transient SBS equations. A superbee fluxlimiter is utilized to avoid numerical damping and dispersion that would otherwise be brought on by the approximation of spatial derivativesassociated with the partial differential equations (PDEs). In order to increase computational efficiency, an approach is adopted wherebythe sparse PDE Jacobian matrix integrator option of the ODE solver(s) is employed. Simulation examples of SBS-based sensing for fiberscontaining sections with different Brillouin frequencies are presented. To the best of our knowledge, this MOL solution is proposed for thefirst time for modeling of the transient SBS equations for nanosecond Stokes pulses with different waveforms in a SBS based fiber opticsensor
Polishing of optical media by dielectric barrier discharge inert gas plasma at atmospheric pressure
Get PDFIn this paper, surface smoothing of optical glasses, glass ceramic and sapphire using a low-power dielectric barrier discharge inert gas plasma at atmospheric pressure is presented. For this low temperature treatment method, no vacuum devices or chemicals are required. It is shown that by such plasma treatment the micro roughness and waviness of the investigated polished surfaces were significantly decreased, resulting in a decrease in surface scattering. Further, plasma polishing of lapped fused silica is introduced. Based on simulation results, a plasma physical process is suggested to be the underlying mechanism for initialising the observed smoothing effect
Methods in reducing surface reflected glint for shipborne above-water remote sensing
Get PDFSurface reflected glint is a curse for ocean color remote sensing from above-water platforms. In calibrated above-water shipborne radiometry,there are several surface reflected glint correction approaches widely implemented. These approaches were developed using radiativetransfer simulations and/or field measurements in different water types, sea states, and cloud conditions. To date no particular surfacereflected glint correction approach has been prescribed in ocean optics standard protocols. Without synoptic inherent optical propertiesto accurately determine apparent optical properties, glint correction is therefore rather qualitative or subjective. There is need to fullytake inventory of uncertainties resulting from such differences. We look at different methods that have been implemented in calibratedshipborne radiometry and how surface reflected glint is corrected for using these available approaches. Field measurements are utilized toassess how the correction approaches perform under clear and overcast skies, we also elucidate on aspects for further improvements
Theoretical demonstration of highly efficient cw THz generation by using composite photonic-structure elements
Get PDFWe theoretically propose one-dimensional composite photonic structures for high-resolution THz spectroanalysis. We compare the performance of two GaAs/AlAs composite photonic-structure devices, one with usual 1/4-wavelength layers of distributed Bragg reflectors (DBRs), and the other with the designed DBRs. The device with designed DBRs shows the optical-to-terahertz conversion efficiency up to 10^-5 and wide frequency tunability ranging from sub-THz to 3 THz. We found that the composite photonic structure allows us to control photonic modes with a high degree of freedom by flexible structure designs. This device achieve a cw THz source with a highly narrow bandwidth operating at room temperature
Invisibility cloaking based on geometrical optics for visible light
Get PDFOptical cloaking has been one of unattainable dreams and just a subject in fiction until recently. Several different approaches to cloaking have been proposed and demonstrated: stealth technology, active camouflage and transformation optics. The last one would be the most formal approach modifying electromagnetic field around an object to be cloaked with metamaterials. While cloaking based on transformation optics, though valid only at single frequency, is experimentally demonstrated in microwave region, its operation in visible spectrum is still distant from realisation mainly owing to difficulty in fabricating metamaterial structure whose elements are much smaller than wavelength of light. Here we show that achromatic optical cloaking in visible spectrum is possible with the mere principle based on geometrical optics. In combining a pair of polarising beam splitters and right-angled prisms, rays of light to be obstructed by an object can make a detour to an observer, while unobstructed rays go straight through two polarising beam splitters. What is observed eventually through the device is simply background image as if nothing exists in between
Wavelength-dependent nonlinear optical loop mirror for simultaneous amplitude noise reduction at two wavelengths
Get PDFWe propose and study analytically and numerically a polarisation-imbalanced Nonlinear Optical Loop Mirror (NOLM) scheme exhibitinga wavelength-dependent nonlinear characteristic. The device includes a symmetric coupler, an isotropic (or, in practice, twisted nonpolarisation-maintaining) fibre loop and a section of high birefringence (HiBi) fibre to break the polarisation symmetry. Thanks to thewavelength-dependent phase shift of the HiBi fibre, wavelength-dependent switching is obtained. For proper orientation of the HiBi fibrein the loop plane and using linear input polarisation at 45° with respect to its birefringence axes, the NOLM switching power varies withwavelength, whereas its zero low-power transmission and 100% maximal transmission are constant. Through slight adjustments of the HiBifibre birefringence, which can be realised mechanically or thermally, the ratio between switching powers at two particular wavelengthscan be readily adjusted. We show numerically that this scheme can be applied to simultaneous amplitude regeneration of two wavelengthchannels exhibiting uneven power levels
Design of nanofibres for efficient stimulated Raman scattering in the evanescent field
Get PDFNanofibres can be produced with diameters smaller than the wavelength of the light they guide. In this regime, the guided mode presents a strong evanescent field well adapted to the excitation of “evanescent nonlinearitiesâ€. We theoretically investigate such an evanescent nonlinearity: the Raman interaction between the evanescent field and a liquid surrounding the nanofibre. Our calculations demonstrate that the Raman conversion is obtained with nanofibre lengths an order of magnitude lower than those required for liquid core photonic crystal fibres
Influence of interfaces reflectivity for central thickness measurement of a contact lens by low coherence interferometry
Get PDFThis paper evaluates quantitatively the relative interfaces reflectivity of a soft contact lens set in air or in water by a low coherence interferometric method. The sensitivity of the set-up is then measured and the minimum reflectivity is estimated to be as low as 0.02%. Measurement of the central thickness of the lens, even when it is immersed in water, is then possible using a new supercontinuum source
Optical security device for document protection using plasmon resonant transmission through a thin corrugated metallic film embedded in a plastic foil
Get PDFThe well known resonant or extraordinary transmission through an undulated metallic thin film embedded in a dielectric layer using the Plasmon modes excitation under normal incidence is industrially exploited for document protection applications. While the effect is very spectrally sensitive to the incidence angle in collinear incidence since it leads to a transmission peak separation in two peaks, it is very tolerant in conical incidence (incidence angle in the plan normal to the grating direction). This property is used to create color transmission effects by playing with the sample rotation in the two directions to enhance the contrast of such effect. Theoretical approach, modeling and experimental demonstration in the visible range on a flexible plastic foil are presented for a see-through window implemented in document security