The current paper describes an optoelectronic method for direct monitoring of the axial clamping forces both in static and in dynamic duty. As advantages of this method we can state that it can be applied both to new and refurbished transformers without performing constructive changes or affecting in any way the transformer safety in operation. For monitoring the axial clamping forces for high-voltage (HV) power transformers, we use an optical fiber that we integrate into the laser cavity of a passively mode-locked fiber laser (PMFL). To each axial clamp corresponds a solitonic optical spectrum that is changed at the periodical passing of the fundamental soliton pulse through the sensitive fiber inside the transformer. Moreover, as a specific characteristic, the laser stability is unique for each set of axial clamping forces. Other important advantages of using an optical fiber as compared to the classical approach in which electronic sensors are used consist in the good reliability and insulator properties of the optical fiber, avoiding any risk of fire or damage of the transformer.
In this paper we propose a novel optical method for measuring the circular magnetic field. In practice, many situations may appear in which there are difficulties in measuring the magnetic field, as inside coils, motors etc., where the magnetic field lines are circular or elliptical. The proposed method, applied for measuring the current on high voltage lines, strongly benefits from the advantages that it offers as compared to classical solutions based on the inductive principle. Some of the advantages of optoelectronic and optic measurement methods have a real importance. These advantages consist in: avoiding the use of energy intensive materials (Cu, Fe etc.), reducing the weight of the measuring system, reducing at the minimum the fire danger due to the use of paper-oil insulation in high voltage devices etc. The novelty of our proposed method consists in using the electromagnetic radiation in ultrashort pulses, having a relatively large frequency band and a much improved resistance to external perturbations, for measuring the circular magnetic field generated from the current of high voltage lines, inside power transformers or high power motors.
Until now, very few systematic studies have been made for comparing various photodiode structures in terms of their
performance characteristics. Most of the studies included only few structures, some of them only simulated, without
experimental measurements. Unfortunately, all these studies comprised only a few photodiodes, and in our knowledge there is no extended study to compare all types of CMOS photodiodes, fabricated using various CMOS processes. In this paper we will try to fill in this empty space in this area, in order to provide an easier choice of the most appropriate CMOS photodiode (and thus of the CMOS image sensor) to be used in a certain application, according to the desired characteristics for each situation. We will review some important studies in which essential parameters for the characterization of the CMOS photodiode were evaluated: quantum efficiency, photocurrent and dark current. We consider that this paper will provide a useful reference for choosing the most suitable photodiode and CMOS image sensor for a very large area of applications.
In this paper we present, for a CMOS n-diffusion photodiode, the effects of various doping concentrations on the
behaviour of two of the main parameters that characterize the performance of these devices: the photocurrent (for low
and for high levels of the illumination) and the dark current. We performed simulations aided by T-CAD tools for each
type of layer of the CMOS photodiode structure (substrate, p-epitaxial layer, n-diffusion layer) and evaluated the
behaviour of the photocurrent and dark current in various levels of the doping concentrations of these layers. These
results may be helpful in the process of fabricating these devices, where controlled amounts of impurities may be added to some layers (or their level might be reduced in some other layers), in order to maximize the photocurrent and to minimize the dark current in these structures.
Applications of CMOS image sensors can be found nowadays in an incredibly large range of domains. In this paper
we present a review of the main applications of these devices in the latest years, in domains like medicine, astronomy,
automotive field, digital photography etc. We also highlight the capabilities of these CMOS sensors that constitute
advantages over their competitors, the CCD sensors, and which imposed them for specific applications.
Since the late 1960s when they appeared, CMOS image sensors have evolved a lot. Whereas in the beginning their
performances could not be compared with those of the CCD image sensors, since the late 1990s CMOS sensors became
real competitors of CCDs, both in industrial and scientific fields, due mainly to several important advantages, such as
low power consumption, low voltage operation, high-speed imaging, low cost, integration capability etc.
Prior work on CMOS image sensors reviewed mainly new types and structures, touching only tangentially the range of
applications. Our paper proposes to partially fill this gap, presenting the most recent developments in a large area of
domains of applications, providing the researcher with a quick reference for the state-of-art applications of CMOS image
A method for measuring the timing jitter in a 1550 nm mode-locked fiber laser, with the help of an autocorrelator, has been developed and the error in measuring the value of the jitter has been evaluated. The preliminary results have shown that the fluctuations of the jitter are higher than the medium value of the jitter itself, so we decided to use some amplifiers in the circuit in order to eliminate this problem. The setup was changed by adding a laser diode, with the wavelength of 980 nm, and an erbium fiber. The medium value of the jitter we obtained (from eight measurements) for our setup was 78.8 fs. In order to still improve the measurements, we changed the time constant of the autocorrelator from 1.1 ps to 10 fs. The new medium value we obtained for the timing jitter was 78.33 fs. Finally, we calculated the error in measuring the timing jitter in our setup. We can say that the optical cross correlations present a powerful tool for characterizing the timing jitter in mode-locked fiber lasers.
We simulated several structures of dilute nitride quantum well InGaAsN semiconductor lasers that work at the
wavelength of 1047 nm. InGaAsN is a new semiconductor alloy system having the remarkable property that the
inclusion of only 2% of nitrogen reduces the bandgap by more than 30%. This alloy system can be successfully used for
long wavelength laser systems and high-efficiency multi-junction solar cells. In this paper we compared several
structures of dilute nitride quantum well InGaAsN semiconductor lasers in terms of the electrical properties such as the
threshold current and the slope. By also comparing the optical properties of these structures, and taking into account the
results obtained for the electrical properties, one can choose the structure with the best overall performances for being
used in practical applications.
III-nitride semiconductor materials have received much attention in the past few years, due mainly to their relatively wide band gap and high emission efficiency. We simulated a 462 nm InGaN quantum well semiconductor laser, with different properties (different layer thicknesses, layer dopings and In composition in different layers of the structure) and we compared the results for the fourteen situations that we analyzed. Thus we can choose the best structure, in terms of the laser power and threshold current, to be used in applications.
Today, the CMOS image sensors are being used in an increasing number of applications. A significant
problem for these devices is due to the fact that the production testing is complicated and expensive. This
problem arises from the need to use light sources in order to test the photosensitive elements. As an
alternative solution, we proposed the use of a test performed in the absence of light. In order to evaluate the
quality of the proposed test approach, we performed an analysis of the defects and failure mechanisms in
the photodiode. This is the main contribution of the paper, as until now very little literature was written
concerning this subject, due to the fact that these defects are not well enough understood to enable the
development of a general model.
The paper presents the basic concepts of the optical correlators. In our knowledge, it is the first systematic
presentation of the applications of optical correlators. The main three types of optical correlators: the optical correlator
in incoherent light, the optical correlator in coherent light (VanderLugt) and the joint transform correlator are presented.
The optical correlators are very powerll systems used for image recognition, that perform a correlation between a
bidimensional function which represents a Scene that must be analyzed and another bidimensional function that contains
information about the reference function. This correlation is optically realized by a Fourier transform between the two
functions. The optical Correlators have found a lot of applications for image recognition and target detection in various
fields, such as the military field, robotics, medical field, industry a.s.o. Among the various applications of the optical
correlators we can mention: digital fingerprints identification, credit card security, antique scripts recognition,
determination of the cosmic ships and satellites behavior, amelioration of cancer tests precision, quality control etc.