JEOS:RP - Journal of the European Optical Society Rapid publications
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LiNbO3 acousto-optical and electro-optical micromodulators
Get PDFWe report on acousto-optical (AO) and electro-optical (EO) LiNbO3 modulators with an active length of only 11 µm. The miniature devices are based on photonic crystal (PhC) structures that are controlled by an external effect (DC electric field or Surface Acoustic Waves). Two processes are presented for realizing the PhCs despite the resistance of the material to etching. The first method is based on direct FIB writing and can yield the fabrication of holes with depth of 32 m and diameter of 12 m or less. The second method consists in FIB patterning of a mask which is deposited on the substrate. This process is followed by proton exchange (PE) and reactive ion etching (RIE). Thus, structures with a diameter of 400 nm and an aspect ratio of 3:1 have been fabricated. The methods have been applied to the fabrication of EO and AO micromodulators showing a driving voltage of 13,5 V and a driving electric power of 20 mW respectively. These developments open the way to dense integration of dynamic optical functionalities
Characterization and investigation of NLO properties of electrodeposited polythiophenes
No full textIn this work we study the electronic properties of ClO4- doped polythiophenes and discuss the nonlinear optical properties of these organic compounds galvanostatically electrodeposited on ITO glasses. The investigation on the electronic properties (band gap, flat band potential) was performed by means of a non-destructive optical technique, photocurrent spectroscopy (PCS). The investigation on the nonlinear optical response was carried out by means of second and third harmonic generation measurements. In particular, the effect of the oxidation state of the polymeric films was studied by comparing the NLO response of oxidized and reduced polythiophenes. Reduced polymeric films show higher values of the second (χ) and third (χ) order nonlinear susceptibilities
Liquid level sensing by use of digital formatted optical spectrum spreading technique
Get PDFWe propose a novel technique for optical liquid level sensing. The technique takes advantage of an optical spectrum spreading technique and directly measures liquid level with a digital format. The performance of the sensor does not suffer from changes of environmental variables and system variables. Due to its distinct measurement principle both high resolution and a large measurement range can be achieved simultaneously
Optical spectral signatures of liquids by means of fiber optic technology for product and quality parameter identification
Get PDFAbsorption spectroscopy in the wide 200-1700 nm spectral range is carried out by means of optical fiber instrumentation to achieve a digital mapping of liquids for the prediction of important quality parameters. Extra virgin olive oils from Italy and lubricant oils from turbines with different degrees of degradation were considered as ‘case studies’. The spectral data were processed by means of multivariate analysis so as to obtain a correlation to quality parameters. In practice, the wide range absorption spectra were considered as an optical signature of the liquids from which to extract product quality information. The optical signatures of extra virgin olive oils were used to predict the content of the most important fatty acids. The optical signatures of lubricant oils were used to predict the concentration of the most important parameters for indicating the oil’s degree of degradation, such as TAN, JOAP anti-wear index, and water content
Prospects for poor-man's cloaking with low-contrast all-dielectric optical elements
Get PDFWe discuss the prospects for low-contrast all-dielectric cloaking and offer a simple picture illustrating the basic obstacle for perfect cloaking without materials with an effective double-negative response. However, the same simple picture also gives directions for less perfect designs allowing for planar transmitted fields, but at the prize of phase-slips which can only be eliminated at well-defined frequencies where the phase-slip amounts to a multiple of 2pi. As a particular example, we consider assemblies of all-dielectric Luneburg lenses forming a porous structure allowing for hiding objects inside the pores, independently on the polarization of the incident field. Cloaking must in general be realized with metamaterials realized through sub-wavelength structures, i.e. Lambda\ll lambda with Lambda being the period and lambda the free-space wavelength. Interestingly, cloaking-like operations with Luneburg-lens arrays perform in the opposite limit with Lambda\gg lambda
Metal nanoparticles in strongly confined beams: transmission, reflection and absorption
Get PDFWe investigate the interaction of tightly focused light with the surface-plasmon-polariton resonances of metal nanospheres. In particular, we compute the scattering and absorption ratios as well as transmission and reflection coefficients. Inspired by our previous work in [1], we discuss how well a metal nanoparticle approximates a point-like dipolar radiator. We find that a 100 nm silver nanosphere is very close to such an ideal oscillator. Our results have immediate implications for single nanoparticle
spectroscopy and microscopy as well as plasmonics
Regenerated gratings
Get PDFStrong regenerated gratings with a maximum grating strength exceeding (40-50) dB are fabricated inside an optical fibre by bulk macro thermal processing ~900°C using a UV-laser seeded Bragg grating. Further annealing between 1000 and 1100°C leads to a stabilised grating ~18dB in strength. This suffers no further degradation at 1100°C for the period monitored, over 4 hrs. The potential resolution of this process is demonstrated by regenerating two complex profiles. Phase information is retained between seed and regenerated structures. This opens the way for nano-engineering of materials using thermal processing and seed templates
Marker-free cell discrimination by holographic optical tweezers
Get PDFWe introduce a method for marker-free cell discrimination based on optical tweezers. Cancerous, non-cancerous, and drug-treated cells could be distinguished by measuring the trapping forces using holographic optical tweezers. We present trapping force measurements on different cell lines: normal pre-B lymphocyte cells (BaF3; "normal cells"), their Bcr-Abl transformed counterparts (BaF3-p185; "cancer cells") as a model for chronic myeloid leukaemia (CML) and Imatinib treated BaF3-p185 cells. The results are compared with reference measurements obtained by a commercial flow cytometry system
Nested structures approach in designing an isotropic negative-index material for infrared
Get PDFWe propose a new generic approach for designing isotropic metamaterial with nested cubic structures. As an example, a three-dimensional isotropic unit cell design "Split Cube in Cage" (SCiC) is shown to exhibit an effective negative refractive index on infrared wavelengths. We report on the refractive index reaching -2.3 and the figure of merit as high as 2.7. The structure exhibits potential for application as a building block of isotropic negative-index materials
Comparison of plane mirror vs retroreflector peformance for laser-self-mixing displacement sensors
Get PDFThe behavior of a displacement optical sensor based on the Laser-Self-Mixing effect employing a plane mirror (PT) and a solid corner-cube (CC) as moving target is analyzed. The performances of the sensor are compared in terms of simplification of the optical setup, measurement accuracy and tolerance to angular misalignment of the target. On the basis of the innovative assumption that only the fraction of the laser beam orthogonal to the target plane gives rise to the Self – Mixing modulation, it is demonstrated that the interferometer tolerates small tilt of the plane target (up to approximately 0.7°) only when illuminated by a divergent beam, in which case the displacement measurement becomes affected by a cosine – type error. Instead the corner cube preserves the self-mixing signal over a larger angular range (up to approximately 2°) at the same time preserving high measurement accuracy