Visible Light Communications (VLC) receivers adapted to be used in high transmission rates will eventually use either, high aperture lenses or non-linear optical elements capable of converting light arriving to the receiver into an electric signal. The high aperture lens case, reveals a challenge from an optical designers point-of-view. As a matter of fact, the lens must collect a wide aperture intensity flux using a limited aperture as its use is intended to portable devices. This last also limits both, lens thickness and its focal length. Here, we show a first design to be adapted to a VLC receiver that take these constraints into account. This paper describes a method to design catadioptric and monolithic lenses to be used as an optical collector of light entering from a near point light source as a spherical fan L with a wide acceptance angle α◦ and high efficiency. These lenses can be mass produced and therefore one can find many practical applications in VLC equipped devices. We show a first design for a near light source without magnification, and second one with a detector’s magnification in a meridional section. We utilize rigorous geometric optics, vector analysis and ordinary differential equations.
We developed a home-made sample-holder unit used for 2D nano-positioning with millimeter travelling ranges. For each
displacement axis, the system includes a long range travelling stage and a piezoelectric actuator for accurate positioning.
Specific electronics is integrated according to metrological considerations, enhancing the repeatability performances.
The aim of this work is to demonstrate that near-field microscopy at the scale of a chip is possible. We chose here to
characterize highly integrated optical structures. For this purpose, the sample-holder is integrated into an Atomic Force
Microscope in order to perform optical imaging. To demonstrate the overall performances, a millimeter scale optical
images have been realized.
Ultraviolet single mode laser light is proposed by frequency quadrupling the output of a Nd:YLF laser with two successive frequency doubling stages. For a simple linear cavity laser configuration investigated at 1312 nm, we have obtained an intracavity power of 310 W for 16 W of absorbed pump power (λp ~ 806 nm). Up to 10 mW tunable single-frequency laser (λ2ω=656-658 nm) is observed. This has been achieved by intracavity second-harmonic generation of a diode-pumped Nd:YLiF4 linear laser oscillating on the σ-polarized 4F3/2-4I13/2 transition (λω ~1314 nm) with a β-Barium Borate (BBO) crystal. We also report the experimental measurement of the red-uv conversion efficiency according to the waist size in the BBO crystal. Obtained value is compared to those given by the Boyd-Kleinman theory.
Ultraviolet single mode laser light is proposed by frequency quadrupling the output of a Nd:YLF laser with two successive frequency doubling stages. For a simple linear cavity laser configuration investigated at 1312 nm, we have optained an intracavity power of 310 W for 16 W of absorbed pump power (λp ~ 806 nm). Up to 10 mW tunable single-frequency laser (λ2W = 656 - 658 nm) is observed. This has been achieved by intracavity second-harmonic generation of a diode-pumped Nd:YLiF4 linear laser oscillating on the σ-polarized 4F3/2-4I13/2 transition (λw ~ 1314 nm) with a β-Barium Borate (BBO) crystal. We also report the experimental measurement of the red-uv conversion efficiency according to the waist size in the BBO crystal. Optained value is compared to those given by the Boyd-Kleinman theory.
We show how a Fabry Perot interferometer could be used to determine the gravitational axis of the earth g with an
high sensitivity. Our method lie g axis to an optical beat frequency value between two lasers. The principle is
described and a budget error is presented. The sensitivity of the sensor is estimated to be below of 85 nrad/MHz.
This method could be used as a high sensitivity and absolute tilt sensor or even as a seismometer. This sensor is
dedicated to the french watt balance project as described in this paper.
One of the most promising projects for the new definition of the kilogram is the watt balance. It uses a two-mode
procedure: static mode and dynamic mode. One of the key points is to control the velocity, the yaw and the pitch of a
moving coil during the dynamic mode. We have developed a specific method based on the use of a homemade double
pass heterodyne interferometer, a two-level translation stage, and a home-made high frequency phase shifting electronic
circuit. This system will replace the commercial heterodyne system (laser head and interferometer) used at present time
which is limited in power and has polarization limitations. In this paper, we propose a novel and specific heterodyne
interferometer able to ensure all previous demands to control the displacements of the moving coil in order to reduce the
velocity noise. The laser source is powerful enough to ensure multiple measurements axis. The laser is frequency
stabilized on iodine atomic transition around &lgr;=532 nm to ensure traceability. All the polarization defaults of the
classical heterodyne interferometer have been minimized in order to reduce non-linearity effects. The most original point
is that the reference beam is locked on an external electronic reference, which allows to be less sensitive to vibration and
polarization defects of optical components from the laser head to the vacuum enclosure where the interferometer is placed.
We propose an alternative design to the wavemeters based on scanning Michelson interferometers. Using realistic
experimental parameters, we show that a relative accuracy of one part in 6x10-8 can be reached with a
displacement of the target mirror of only 360 &mgr;m. This improvment becomes possible thanks to the significant
advances in polarimetry that permit measurement of the ellipsometric parameters &psgr; and &Dgr; with an accuracy of
0.07° with readily-available commercial equipment. This leads to an interpolation rate of &lgr;/10000. The proposed method has been setup and the chief parameters limiting its accuracy are determined.
KEYWORDS: Actuators, Near field, Interferometers, Control systems, Mirrors, Heterodyning, Near field optics, Phase shifts, Electronic circuits, Optoelectronics
We report on a new high accuracy home-made sample holder for near field characterization of millimeter long wave guiding structures (Y junction, Multi Modes Interference coupler). The principle of near field characterization is based on an atomic force microscopy tip that is brought to the surface of the sample (in the near field zone) in order to coupled out a small amount of the light confined inside the wave guiding structures. Due to the size of the components, scans as long as a few millimeters are required to get an entire optical mapping of the structure [1]. With the commonly available equipments such a scan is performed by acquiring step by step more than 100 images for a 2 mm scan. The overlapping of the different images is time consuming and unsatisfactory unless a numerical stitching procedure based on topographical details is used. Effective refractive indexes are typically determined with a precision of 10-3 which could be further improved by increasing the millimeter scan resolution. The reason why successive images do not overlap is mainly due to the mechanical system supporting the sample. Actually, the nonlinearity of the actuator and the thermal expansion of the mechanical part prevent us to reach nanometric scale of repeatability on the positioning for micrometric range of displacements. In order to enable long range scans with nanometric repeatability and accuracy, we develop a specific mechanical system controlled by a heterodyne interferometric apparatus and a home-made high frequency electronic board [2]. The position of the sample is measured in real time with a resolution of 0.3 nm. The servo-loop allows to control the position of the sample with a repeatability of 1 nm (1σ) for a displacement of 1 mm. Furthermore our method is insensitive to the nonlinearity of the actuator.
This paper presents a positioning control system based on an optical heterodyne interferometric technique associated to a home-made high frequency electronic board. This system aims to control the translation of a mechanical stage with a quantified step as low as 0.258 574 970 5 (5) nm. Intrinsic relative uncertainty is very low. Hence the method is suitable for long displacement range, even millimeters long. Experimental results show the reliability of the method.
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