JEOS:RP - Journal of the European Optical Society Rapid publications
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Marine bubble detection using optical-flow techniques
Get PDFBubble detection and quantification is of high relevance for the observation of gas and fluid seeps within the marine environment. The presented work suggests and successfully investigates the application of an image processing strategy based on the optical flow concept followed by a customised thresholding and a new segmentation approach. Both are applicable for laboratory conditions and in situ video sequences, as shown for a deep-sea methane vent
Early days of coherence theory and the first Rochester conference on coherence
Get PDFThe terms coherence and correlations seem to have entered the optics vocabulary about the beginning of the twentieth century, many years after Maxwell discovered that light was an electromagnetic phenomenon. Prior to that time there were only a few investigations, which have a bearing on this subject. The first one was made by a distinguished French optical scientist E. Verdet who around 1865 asked a question which is equivalent to the following: If sunlight illuminates directly two pinholes in an opaque screen, how close must the pinholes be, so that the light which emerges from them can form interference fringes on superposition? He estimated the distance to be about 1/50 millimeter. In modern language this small distance is the diameter of the area of coherence formed by sunlight on the surface of the earth
Low-loss amorphous silicon waveguides grown by PECVD on indium tin oxide
Get PDFLow-loss hydrogenated amorphous silicon (α-Si:H) waveguides were realized by plasma enhanced chemical vapour deposition (PECVD) on a transparent conductive oxide (TCO) layer which is intended to provide the buried contact for the application of an external bias in active devices, e.g. switches and modulators. In particular we propose a technological solution to overcome both the strong reduction in optical transmittance due to the very high extinction coefficient of metal contacts and, at the same time, the optical scattering induced by the texturization effect induced in α-Si:H films grown on TCO. The very high optical propagation losses were minimized by depositing a spin-on-glass (SOG) layer between the α-Si:H core-layer and the TCO bottom contact. In this case, propagation losses of 2.5 dB/cm at 1550 nm were measured. All the fabricated samples were optically characterized and the surface roughness was accurately measured using a mechanical profilometer. We observed that, for an α-Si:H core-layer directly deposited on the TCO contact, the surface roughness is of the order of 100 nm leading to totally opaque waveguides. The experimental performances have been compared to those obtained through calculations using an optical simulation package. The results are found to be in agreement with the experimental data
Quantum theory of coherence and nonlinear optics
Get PDFWe review the beginning stage of quantum theory of coherence and research at the Palacky University in quantum and nonlinear optics related to quantum state reconstruction, generalized superposition of signal and quantum noise, quantum Zeno effect, nonlinear optical couplers and parametric down-conversion
Electro-optical modulating multistack device based on the CMOS-compatible technology of amorphous silicon
Get PDFIn this paper we report results on a field-effect induced light modulation at λ = 1.55 um in a high-index-contrast waveguide based on a multisilicon-on-insulator (MSOI) platform. The device is realized with the hydrogenated amorphous silicon (α-Si:H) technology and it is suitable for monolithic integration in a CMOS Integrated Circuit. The device exploits the free carrier optical absorption electrically induced in the semiconductor core waveguide. The dynamic behaviour of the device was experimentally and theoretically analyzed in presence of a visible illumination showing a link between the photogeneration and the free carriers provided by doped α-Si:H layers.
The core waveguide contains several thin dielectric films of amorphous silicon carbonitride (α-SiCN) embedded along its thickness highly enhancing the absorbing action of the modulator held in the on-state
A Gaussian transition of an optical speckle field studied by the minimal spanning tree method
Get PDFWe propose to study the Gaussian transition of an optical speckle field using the Minimal Spanning Tree method. We perform an analysis of the spatial intensity distribution and show that the maxima of intensity evolve from a cluster distribution in the strongly non Gaussian regime, to a gradient distribution around the transition and then approach the random distribution area when we tend to the Gaussian regime. In the generated minimal spanning trees, we observe that the standard deviation of the edges length exhibits a maximum around the Gaussian transition when about 4 correlation cells of the surface roughness are illuminated
Scanning deflectometric form measurement avoiding path-dependent angle measurement errors
Get PDFFor the highly accurate topography measurement of nearly flat optical surfaces, scanning deflectometric methods are capable of achieving nanometer accuracy. In these systems, an autocollimator is typically used as the deflectometric sensor and a pentaprism is applied for the scanning process. When ultimate accuracy is desired, a drawback of these systems is that the autocollimator output signal often depends slightly on the optical path length, resulting in topography errors during scanning. Here, we present a new deflectometric method which separates the angle measurement from the scanning process and, thereby, avoids possible errors due to different optical path lengths. In contrast to conventional deflectometry, the new technique achieves an almost exact autocollimation by appropriately tilting the specimen during scanning. The tilt angle necessary to achieve autocollimation complies with the deflectometric angle determined in conventional deflectometry. The tilt angle is measured with an additional autocollimator at a fixed distance without errors due to different optical path lengths. The separation of angle measurement and the scanning process enable both tasks to be optimized independently. This opens up new possibilities of reducing lateral resolution by facilitating smaller apertures and of assessing topographies with larger curvatures. The concept was tested successfully by a demonstrator setup. The first measurements on a test specimen agree with results obtained with the established Extended Shear Angle Difference (ESAD) technique at the one nanometer level
Energy scalable terahertz-wave parametric oscillator using surface-emitted configuration
Get PDFWe experimentally demonstrated the scalability of the terahertz-wave parametric oscillator by using a pump beam with a wide aperture and a high pulse energy. Terahertz-wave absorption by the LiNbO3 crystal in the oscillator is substantially suppressed by employing a surface-emitting cavity configuration. We also improved the conversion efficiency by increasing the parametric interaction in the noncollinear phase-matching geometry. A pump depletion of 54% and a conversion efficiency of 0.9 × 10-6 are achieved. A maximum terahertz output of 382 nJ/pulse was achieved at 1.46 THz using a 8.0-mm-diameter pump beam with a pulse energy of 465 mJ/pulse
Advances in lasers and optical micro-nano-systems
Get PDFLasers represent a well consolidated technology: nevertheless, research in this field remains very active and productive, in both basic and applied directions. At the moment significant attention is given to those sources that bring together high power and compactness. Such high power lasers find important applications for material treatments and such applications are presented by Ehsani et al and Saiedeh Saghafi et al, in the treatment of dielectric thin films (Alteration of optical and morphological properties of polycarbonate illuminated by visible/IR laser beams) or of biological tissues like pistachio seeds (Investigating the effects of laser beams (532 and 660 nm) in annihilation of pistachio mould fungus using spectrophotometry analysis). In particular the latter paper show how laser sources can find very important applications in new domains, preserving goods and food without the need for preservatives or pesticides by simply sterilizing them using light.
Optical Micro and Nano Systems presents a new domain for exploration. In this framework this special issue is very attractive, because it assembles papers reporting new results in three directions: new techniques for monitoring integrated micro- and nano-systems, new integrated systems and novel high performance metamaterial configurations. Integrated micro-components can be monitored and controlled using reflectance measurements as presented by Piombini et al (Toward the reflectance measurement of micro components). Speckle formation during laser beam reflection can also be a very sophisticated tool for detecting ultra-precise displacements, as presented by Filter et al (High resolution displacement detection with speckles : accuracy limits in linear displacement speckle metrology). Three dimensional integrated optical structures is indeed a big challenge and a peculiarity of photonics, they can be formed through traditional holography or using more sophisticated and novel technologies. Thus, special manipulation of the writing-reading optical beam can push holography toward storages at higher data densities, as presented by Norihiko Ishii et al (Wavefront compensation method using novel index in holographic data storage). Along a similar direction Furlan et al describe a very innovative technique for producing optical traps using novel Devil micro-lenses (Volumetric multiple optical traps produced by Devil’s lenses). Vynnyk et al presented an interesting application of electron microscopy for monitoring sub-micrometric structures in 3D configurations (3D-measurement with the stereo scanning electron microscope on sub-micrometer structure). Finally, S. Rao et al present two interesting papers on integrated structures compatible with silicon technology: one describes the realisation of low-loss waveguides using amorphous silicon, a relatively novel material with many applications in very different domains (Low-loss amorphous silicon waveguides grown by PECVD on indium tin oxide), and one on the realisation of a electrically drivable device with affective compatibility with CMOS technology (Electro-optical modulating multistack device based on the CMOS-compatible technology of amorphous silicon). We hope that this special issue of the Journal of the European Optical Society will reflect the interest of the European Scientific Community toward these fundamental and applied topics and will demonstrate to readers some of the actual directions of research. We express our full appreciation to the authors that participated to this initiative which acts only as a primer for the vast amount of work now being undertaken in laser physics and applications in micro- and nano-systems.
We would like to give a special thank to the paper reviewers for their important role in the paper selection process and all the journal staff for their very professional support, dedication and energy, which made this special issue feasible
Simulation and analysis of exotic non-specular phenomena
Get PDFWhen coupled modes are excited in a multilayered structure, the profile of the reflected beam presents exotic characteristics like unexpectedly large lateral shifts or beam enlargment. These results are surprising because they are not accounted for by classical approaches (Artmann's formula or Tamir's description of the reflected beam's profile). Studying such situations requires reliable numerical tools - that is why our programmes are published with this paper. Such tools can be used to understand the behaviour of any multi-layered structure