Paul Schiopu

The EDFA performance with gain versus pump power

In this paper, we analyze gain versus pump power for EDFA. The Runge-Kutta method with fourth-order accuracy is the method used to calculate the input pump power and gain for EDFA. In addition, we compare the theoretical results with experimental characterization for gain versus pump power. Also, we present the analytical method to determine the EDFA gain as a function of input pump power.

Reduced Base Fuzzy Logic Controller for Robot Actuators

The paper proposes an innovative type of fuzzy logic controller for robot actuators, building upon the current state of the art fuzzy architectures and various observations from work with Fuzzy Logic and Extenics Theory. This leads to a modified fuzzy controller, with a significantly simpler rule base, which shows comparable results. The effect is achieved by taking advantage of the rule base makeup of a regular linear fuzzy controller. Some slight modification is needed to the controller architecture, which is explained in detail. The rationality and validity of the proposed model are demonstrated through simulation in the Matlab/Simulink environment. The results show that the proposed new controller architecture obtains remarkable results, while having the advantage of increased simplicity in design and setting of parameters. Throughout the paper, opportunities for further improvement and research are highlighted and discussed.

Development of SAW filters based on GaPO 4

The results of research into Surface Acoustic Wave — SAW — devices have been recognized for their efficiency and versatility in the electrical signals processing [1], [3]. Actual progress in the industrial application of piezoelectric materials such as Lithium Niobate (LiNbO<inf>3</inf>), Langasite (LGS), Lanthanum-Gallium Silicate La<inf>3</inf>Ga<inf>5</inf>SiO<inf>14</inf> and Gallium Orthophosphate (GaPO<inf>4</inf>), allows the manufacturing of devices with performances, which overcome the limits obtained with quartz crystals [2]. The single crystal materials have a long term high stability — near to infinite — and moreover, some of these have an excellent behavior with temperature variation, as is the case of GaPO<inf>4</inf> [4]. Today, GaPO<inf>4</inf> with its properties is by far the best suited piezoelectric material to be used in sensor applications for machine monitoring and pressure measurements, at high temperatures. SAW microdevices based on GaPO<inf>4</inf> operate at temperatures of up to 800°C. We have developed five SAW filters based on GaPO<inf>4</inf>. The paper describes the steps to solve the problems regarding the use of GaPO<inf>4</inf> substrates for the development of SAW filters. In the 3rd chapter of the paper are given some experimental results obtained with Network Analyzer.

White light interferometry applications in nanometrology

Precise three-dimensional (3D) information is demanded by many new industries such as: semiconductor, photonics, MEMS, communications, microprocessing etc. [1, 2]. The problem is to select the proper measurement methods for material characteristics in the measurement field, from the point of view of the measurement accuracy and errors that can appear [1, 4, 3, 5]. There are several optical 3D measurements approaches, e.g.: triangulation, grating projection with phase shift, moiré with phase shift, confocal and (white light) interferometry (WLI) [2, 3]. They can measures: surface profile, roughness, step height, microstructure, and other surface parameters. The white light interferometers allows generally surface profiling with high accuracy with no phase ambiguity errors, making them more suitable for profiling stepped or discontinuous surfaces. WLI technique to determine the thickness of thin coating on reflective materials is very effective. One of the first techniques to utilize the short coherence of the white light source was the scanning interference microscope. There are on the market a variety of scanning white light interferometers. Measurement calibration is done using the short coherence feature of white light. Some of the presented applications in nanometrology are thin films thickness measurements of: carbons films on glass, metallic films on Silicon, ablated small holes diameter, and profiles of micro / nanostructure.

Evaluation method for the dynamics of an erbium-doped fiber laser

We propose a simple method for integration by numerical computations of the atomic rate equations for three-level systems and the laser amplifier equations. We calculate the gain coefficient in erbium-doped fiber considering the effects of pump on the system dynamics. Described the atomic rate equations for three-level system and the dynamics Maxwell-Bloch equations for erbium-doped fiber laser amplifier is presented.

Grating light valve based on high reflectance micro-beams: Design by simulation

In this paper are presented the results of grating light valve (GLV) structure simulation using Coventorware software in order to maximize the intensity of diffracted light in the ±1 diffraction orders. Was simulated a GLV element which consists from 6 high reflective micro-beams suspended above a silicon substrate and which are ellectrostatically actuated. By simulation are optimized the length, width and thicknesses of the micro-beam and the space between micro-beams to obtaining a deflection of »/4 at moderate value of applied voltage.

Recent developments in surface acoustic wave sensors

Surface Acoustic Wave sensors - SAW have been recognized for their efficiency and versatility in the electrical signals processing. The majority of results reported till the present, regarding SAW sensors, have been used Rayleigh SAW, on the principle of delay line. Reflexive delay line can be used for passive sensing and remote control. In the paper is presented a short introduction regarding the actual level of SAW devices development and their applications. A comparative study in connection with diversity of piezoelectric materials used for SAW devices manufacturing, (Quartz, LiNbO3, LGS with emphasis on GaPO4) evidence the advantages of GaPO4. The development directions of SAW sensor devices are shown: telecommunication, RFID SAW systems, SAW devices for remote monitoring, SAW sensors for early cancer diagnostics. Some applications of SAW sensor devices with GAPO4 are presented in the directions: remote monitoring and identification of gas. Some conclusions regarding trends in the development of SAW sensor devices are presented in the end of the work.

p-NiO/ITO transparent heterojunction — Preparation and characterization

The paper presents the preparation of a transparent heterojunction on glass substrate consisting of p type NiO and n type ITO transparent oxidic semiconductors. NiO layer as a p type semiconductor and transparent layer was obtained by thermal oxidation at 430 oC of 50 nm metallic Ni films deposited by DC sputtering. Spectrophotometrical measurements used to investigate optical properties revealed a transmittance higher than 70% for NiO and 90% for ITO in the spectral range of 300-900 nm. The obtained p-NiO/n-ITO heterojunction exposed to ultraviolet radiation (λ ~ 240 nm) shows a good sensibility due to wide band gap of the layers.

Modeling distributed Bragg reflectors with superlattice materials for UV range

Development of vertical cavity surface emitting lasers (VCSEL) is currently experiencing exponential growth. The main problem in achieving these lasers is the Bragg reflector that requires a large number of layers pairs with high contrast to obtain a high reflectivity DBR. But by increasing the number of layers and with the increase of contrast crack formation occurs due to the lattice mismatch between the different nitride compounds while keeping a large Refractive index contrast. By introducing a layer of superllatice (AlN)n/(GaN)n as one layer in the DBR pairs reduces lattice mismatch between the layers. Modeling was done using the self-consistent eight-band kp Schrödinger-Poisson solver. The refractive indices of these SLs were finally estimated for the design of an optimized high reflective Bragg mirror at 450 nm.

Comparative study of GaPO 4 , langasite, and LiNbO 3 properties with application in Surface Acoustic Waves microdevices

The results of research into Surface Acoustic Wave — SAW — devices have been recognized for their efficiency and versatility in the electrical signals processing. Actual progress in the industrial application of piezoelectric materials such as Lithium Niobate (LiNbO3), Langasite (LGS), Lanthanum-Gallium Silicate La3Ga5SiO14 and Gallium Orthophosphate (GaPO4), allows the manufacturing of devices with performances, which overcome the limits obtained with quartz crystals. One of the most important applications of SAW microdevices is passively, wirelessly interrogating systems. Today, GaPO4 with its properties is by far the best suited piezoelectric material to be used in sensor applications for machine monitoring and pressure measurements, at high temperatures. SAW microdevices based on GaPO4 operate at temperatures of up to 800°C. In this paper is presented a short introduction regarding the actual level of SAW microdevices development. We discuss our investigations as a comparative study of GaPO4, Langasite, and LiNbO3, regarding their properties. Each has unique strengths and weaknesses giving advantages in different applications. Conclusions regarding trends in the development of SAW sensor devices with novel materials are presented in the end of the work.