Regarding nano-sciences and nano-technologies there is a permanent confusion between resolution and accuracy. Many sophisticated devices (APM, AFM, SNOM, confocal microscopes) characterized by their resolution, are used to observe at the nano-scale but they are far from being metrological devices, i.e. they do not measure. A metrological instrument must be traceable to the internationally accepted unit: meter in our case. We present an optical setup able to measure in micrometer range with nanometer resolution and ten nanometers accuracy. Its utility for MEMS geometrical parameter is obvious. The setup is working on a passive vibration-isolated table and contains a SIOS laser interferometer which assures the traceability of the measurement, a high resolution translation table, and a long working distance microscope. Few hundred measurements were done to a linear grating to measure the micrometric range pitch with nanometer accuracy. A 2 10-4 relative error was obtained.
Spectroscopy is one of the most important tools for studying the structures of atoms and molecules. Paper underlines the procedures required for the determination of metal contents in tobacco samples. Sampling procedures, sample preparation, and atomic absorption instrumentation requirements are presented. Particular attention is given to the determination of metals as Pb, Cr, Li, Cu, Au, Co using atomic absorption spectroscopy. A dual-beam Atomic Absorption Spectrophotometer was used for the measurements. The concentration of these metals in five different tobacco samples is given.
In this paper we are going to present some results regarding the optical trapping and manipulation of dielectric
microparticles immersed in fluids. The experiments will be done in Mie regime, i.e diameter of the particles is larger
than the laser wavelength. We will report optical trapping of multiple particles and their manipulation by means of
optical tweezers setup. To catch microobjects we will use a Gaussian laser beam and to manipulate them we are going to
calculate diffractive optical elements (DOEs) by iterative algorithm and spherical wave method.
The performance of a novel current-steering logic sense amplifier is verified through simulations in 0.35 &mgr;m CMOS
technology. Because the reading time affects destructively the MRAM cell by thermal dissipation and it also affects the
consumption of power, a new sense amplifier is proposed, one that operates at high frequency, that has a reading time of
the order of ns and a low power consumption. This sense amplifier uses the differential charge of the bit line capacity
where the MTJ resistance determines the gain of the amplifying. The differential amplifying starts when the bit line
voltage reaches a certain threshold. In this way we increase the sensitivity of the device and the two values of the MTJ
resistance will be distinguished in a much shorter time. The output voltage will be stored in a latch structure as the
maximum I minimum voltage level (VDD or gnd).
In so rapidly growing sensing technology, Autonomous Surface Acoustic Waves (SAW) based sensors, offer high
flexibility for modern identification/sensing systems, and represent a new perspective for remote monitoring and
control. This paper gives a presentation of operating principles of wireless SAW sensors with separation in
frequency (frequency domain division-FDD) and separation in time (time domain division-TDD). The design of
interdigitated transducers (IDT), and reflectors on the different types of substrate materials as piezo crystals LiNbO3,
LiTaO3 or quartz in connection with application domains is presented. A comparison between Time Domain
Sampling-TDS and Frequency Domain Sampling-FDS principles of transmitter and receiver, gives evidence of their
advantages and disadvantages. A part of the paper dealt with the measurement results.
The paper presents the implementation of an optical CDMA system with two-dimensional coding using wavelength
channels and time chips to create the codeword. Computer simulations have been performed in order to analyze and
optimize the electronic circuits. The experimental work has been designed in order to investigate and evaluate the
capabilities ofthe implemented optical CDMA system.
Proper calibration of any instrument is vital to an investigator's ability to compare laboratory experiments, as well as to
draw quantitative relations between experimental results and the real objects. Traceability is a term used to certify an
instrument's accuracy relative to a known standard. Because traceability to meter is a very expensive and complicated
process, accurate and traceable calibration of lateral and vertical standards (e.g. 1D and 2D gratings) is a basic
metrological task for nano- and micro- technology. On the other hand laser interferometry is the de facto method to
transfer the meter standard to practical measurement. In this lecture, we describe interferometric vertical and lateral
calibration of a grating used to quantify the parameters necessary for proper translation of AFM data into physically
Small displacements of a microparticle in an optical trap can be measured using back focal plane interferometry. The
position of the particle is evaluated by analyzing the fringes pattern obtained by interference between the light scattered
by the particle and unscaterred light in the back focal plane of the condenser. The fringes positions are detected with a
quadrant photo diode, allowing nanometric precision. In this paper we analyze theoretically some parameters that may
influence the measurements: laser power fluctuations, local fluid viscosity, condenser focal length, particle size.
Between other sensing and identification technologies that of Surface Acoustic Waves, (SAW), is a unique sensing
system. The principal advantage to most SAW systems is that they can use two or three SAW sensors and compare the
measurements between them, providing a good accuracy. We have carried out the design of both piezoelectric substrate
and interdigital transducers, (IDTs), and has tested them in a delay line mode operation. The measurement of changes in
the surface waves characteristics were materialized by applying of a radio frequency electric field to the piezoelectric
crystal by means of IDTs. The finger width of the IDTs was measured by high accuracy optical coherent method. The
results are presented in the work. The potential development of microsensors as an array of four or five miniature
sensors, sensitive to Werent chemicals may be used as mobile chemical detecting units carried by remote control
vehicles to the site chemical contamination.
Ray tracing is one of the methods to design diffractive optical elements. We included this theory to obtain two or four Gaussian beans from one Gaussian beam. The power distribution has been calculated by near field diffraction. First we considered one dimensional case and then the two dimensional case. Calculations are numerically solved using a computer program. The solutions for 1:2 branching are resolved for 1:4 branching in one-dimensional and two-dimensional formulations. The basic model for computing is that a given Gaussian beam is equally divided into two or four beams to produce two or four Gaussian beams with same beamwidth as the incident beam.
One of the most promising implementation of artificial neural networks is optoelectronic implementation. Optical interconnections are useful for neural networks as far as one can take advantage of the special potential of 3D connection through free space. In hardware implementations of neural networks, the weights values will be materialized in a technological process during which various errors may occur, so that the resulting network will use more or less deviated weights. This paper studies several aspects concerning the optical interconnection of artificial neurons. The authors analyze the problems involved by using computer-generated holograms (CGH) for these interconnections and some methods of designing such diffractive elements. The authors also analyze the error sources and the consequences caused by random deviations of the neurons interconnection weights from the accurately computed values. The theoretical considerations are illustrated by designing an auto associative memory built for graphic pattern recognition. Neurons interconnections are to be implemented optically by computer generated holograms (CGH). The network functioning was simulated on computer and the paper presents also the results of simulations on a data set and a CGH layout for neuron interconnections.
The paper presents the calculus of efficiencies in diffracted orders of a concave blazed diffraction grating. The diffraction grating was designed with blazed angles and diffraction spacing variable. We have applied the electromagnetic theory in order to obtain the grating efficiency, which is a sum of all diffracted orders efficiencies. We would expect the sum to be equal to unity. Our result show that this sum is greater than 0.94 and less then unity for some incident angles. The calculation of grating efficiency by means of electromagnetic theory was performed numerically. Our calculations did not take into account of the effect of multiple scattering; that is, light which is scattered from one facet to another before leaving the grating. The various diffracted orders were coupled together by a boundary condition on the surface of the grating. We conclude this groove profile of the grating leads to a better efficiency compared to a typical blazed concave grating.
This paper presents an autoassociative memory built for graphic pattern recognition. The network was designed for the validation of handwritten signatures form bank documents. Neurons interconnections are considered to be implemented optically by computer generated holograms (CGH). The network functioning was simulated on computer and the paper presents the result of simulations on a data set and a CGH layout for neutron interconnections.
A comprehensive analysis of the small-signal direct modulation response, based on quantum well (QW) laser rate equations model is presented. This theoretical model is first analytically analyze din order to estimate the influence of the phenomenological parameters taken into account on the modulation bandwidth. We show theoretically that the leakage current increases the low frequency parasitic-like roll-off effect and degrades the differential gain. Results from modulation measurements of a 5 QW AlInGaAs/InP structure are presented. The measurements are fitted with the theoretical model evaluation and the modulation response figures of merit are deduced. The modulation bandwidth limitation mechanisms are related to the extracted parameters and explained by means of carrier transport effects. Simulation results are used in order to assess the carrier capture/escape time ratio influence and leakage current influence on the modulation response.
In view of the increased need of an effective, practical and unified test set to evalute the modeling capabilities of beam propagation method (BPM) based programs, we prose an incident set of tests to be used for a standard evaluation. The proposed test have been chosen to be simple, easy to implement and enable a fairly good evaluation without the need of any experiment. Interesting aspects of the tests' results and some straightforward, practical criteria to estimate program capabilities and to tune the simulation parameters are presented. A cross-checking between 'Mode Solver' based and BPM based programs is also put into discussion. A paraxial error evaluation method is presented and the transverse mesh influence on the paraxial error is analyzed.
The notorious implication of integrated optics in the nowadays communication systems makes more interesting the development of optical integrated devices and circuits. The evolution of the communication systems was sustained by the integrated optics and it is obvious that the actual interests in the optical communications are also transferred and adapted to integrated optics. The presentation of actual state-of-the-art in this field is a good opportunity both for an evaluation on the above mentioned evolution and for discerning the actual trends and their perspectives. These trends, guided by applicative goals, have to be discussed not only from the theoretical point of view but also from a practical one.
The bistability that we are describing results from designing properly the cavity of a Distributed Bragg Reflector laser realized with an external fiber grating and is based on longitudinal mode competition. The analysis of the output power bistability is done with a simulation of the static behavior of the laser. An accurate and fast computing algorithm has been implemented to solve the steady state rate equations for photon and carrier density. The used model is based on multimode analysis and includes gain saturation.