In the automotive industry it is necessary to automatically inspect Ball Grid Arrays (BGAs) components. As BGAs are surface-mounted devices that are soldered on a Printed Circuit Board (PCB), they have soldered balls fixed on their bottom. In order for such a device to work properly, it is important that these balls do not create „bridges” between them when they are soldered to the PCB. In order to verify this aspect in the industry, X-ray imaging is utilized for the inspection of BGA components. The aim of this work is to assess the capability of Optical Coherence Tomography (OCT) to perform the inspection of solder bridges, as well as to try to image the integrated circuits located inside a BGA component. A second aim is to compare the performances of OCT and X-ray imaging for such purposes. We utilized an industrial X-ray system and an in-house developed SS-OCT system working at 1310 nm, the latter characterized by an axial resolution of 15 μm. Five BGA components were inspected and the obtained images were utilized to perform the proposed comparison. While using OCT one cannot penetrate the upper layers of the BGAs, proof-of-concept 3D OCT images were obtained from the bottom of the investigated components. Therefore, X-ray imaging remains to be utilized for the inspection of components after they are soldered on the PCB, whereas OCT is only able to inspect smaller unsoldered components. However, OCT proves to be a viable method to cover the existing gap in the process because it can inspect the surface of the solder balls before entering the production area. While the industrial X-ray imaging used for this research is not able to inspect individual BGA components, OCT can perform this task. Therefore, using OCT could prevent supplying defect components to be soldered on the PCB.
Polygon mirror (PM)-based laser scanners are the fastest opto-mechanical scanning system. One of their most common applications is in optical micrometers for industrial applications. The aim of the present work is to study experimentally such a system from the point of view of the non-linearity of their scanning function. In this respect, we built upon the developed opto-mechanical analysis and design of PM scanning heads. Thus, testing measurements are performed regarding both the dimension and the position of the object to be measured, which is positioned between the two lenses (i.e., achromatic doublets) of a telescope positioned after the PM and preceding the system’s photodetector (PD). The measuring method is discussed, and its errors are pointed out in obtaining the object’s dimension on the direction of the scanning velocity (of the beam that sweeps the space between the telescope’s lenses perpendicular on their optical axis), using the time interval when the PD receives no laser signal because of the obscuration by the object to be measured. The energy received by the PD with the rotation of the PM is measured for objects of different diameters placed between the lenses of the telescope at different positions with regard the optical axis of the lenses.
The aim of this study is to compare the advantages and limitations of two optical methods, namely Optical Coherence Tomography (OCT) and microscopy for minute investigation of the structure of Aloe Vera leaves. Microscopy has the advantage of a higher resolution, but the disadvantage that the object under investigation is completely damaged (as the leaf must be peeled off). On the contrary, an advantage of OCT is that it is non-invasive with the potential added benefit of on-site measurements (if portable). Depending on the OCT method used, different resolution values are achievable. In principle, Time Domain (TD) OCT can achieve lateral resolutions similar to microscopy but the method is slow for depth investigations. Spectrometer-based and Swept Source (SS) OCT trade lateral resolution for speed of acquisition. In order to acquire sufficient axial range A-scans, low numerical aperture interface optics is used, that exhibits lower transversal resolution. The main limitation of the spectrometer based and swept source OCT is therefore the achievable lateral resolution, which might not be good enough to reveal the detailed structure of noteworthy parts of leaves, for example, their stomata. The present study experimentally compares Aloe Vera data obtained using an optical microscope at different magnifications, and an in-house SS-OCT system with a 1310 nm center wavelength. For gathering additional information, an analysis of the normalized A-scan OCT images was also performed. This reveals additional parts of the leaf structure, while it still falls short of what can be obtained by using conventional microscopy.
New ways of employing optics at the micro and nanometer scale are of interest. This study analyses the most common two micro-mirror shapes (i.e., spherical and parabolic) that can be used for on-chip communication - in conjunction with fiber optics/waveguides. The classical conic sections that can be used for micro-mirrors are described and a technological approach to design and manufacture such devices is presented. Finally an optimization of the parabolic micro-mirror is achieved. Other micro-mirror shapes (e.g., elliptical and hyperbolic) can be approached and compared using the same procedure. The large area of applications of such micro-mirrors includes intra- or inter-chips communications, as well as free-space optics used for various optical systems: micro-optics, optical amplifiers, lasers, and wavelength converters.
We present our efforts in establishing a Research Pole in Photonics in the future Arad-Timisoara metropolitan area projected to unite two major cities of Western Romania. Research objectives and related training activities of various institutions and groups that are involved are presented in their evolution during the last decade. The multi-disciplinary consortium consists principally of two universities, UAVA (Aurel Vlaicu University of Arad) and UMF (Victor Babes Medicine and Pharmacy University of Timisoara), but also of the Arad County Emergency University Hospital and several innovative SMEs, such as Bioclinica S.A. (the largest array of medical analysis labs in the region) and Inteliform S.R.L. (a competitive SME focused on mechatronics and mechanical engineering). A brief survey of the individual and joint projects of these institutions is presented, together with their teaching activities at graduate and undergraduate level. The research Pole collaborates in R&D, training and education in biomedical imaging with universities in USA and Europe. Collaborative activities, mainly on Optical Coherence Tomography (OCT) projects are presented in a multidisciplinary approach that includes optomechatronics, precision mechanics and optics, dentistry, medicine, and biology.
We present our experience regarding the establishing of an interdisciplinary group with Optics as one of its main topic at the Aurel Vlaicu University of Arad (UAVA) – linked with the improvement through research of our educational activities. The 3OM Group (in Opto-Mechatronics, Optical Metrology, and Optics and Mechanics) is described in its evolution from optomechanics to photonics, the latter with a focus on OCT (Optical Coherence Tomography) – with the national and the international collaborations established, with universities from Romania, Europe and USA. While the research directions of the 3OM Group are presented, they are linked with the educational components implemented in the various subjects we teach, for both undergraduate and graduate students, both in Mechanical and in Electrical Engineering. The main effort is to integrate education and research, to move teaching beyond the classical aspects to put the stress on hands-on-experiments, as well as on research-based activities – even with undergraduates. The main goals of this approach are to obtain an early orientation towards innovation and discovery, with a taste for novelties and with a clear focus on international standards. While this account is only one of many, it offers our experience in passing through the difficulties of developing both research and education in Optics in a young university in an emergent economy in Eastern Europe.
High-end biomedical applications, such as Optical Coherence Tomography (OCT) or Confocal Microscopy (CM) require both precision and speed. The latter is essential in OCT by example to achieve in vivo, real time imaging – with video rate imaging capability. An essential element of this effort to achieve such speeds in OCT by example is the optomechatronic system used for lateral scanning. It usually consists of a dual axis double galvanometer-based scanner (GS). However, GSs are used in a larger variety of applications in biomedical imaging – not only in lateral scanning. Due to the importance of the topic, we have approached different aspects of GSs technology, including scanning and control functions, duty cycle optimization, and minimization of artifacts. The paper proposes a Model-based Predictive Control (MPC) structure for driving the GSs in order to achieve either an improved precision or a higher speed. The predictive control solution was tested for different types of input signals. Reasons for choosing the objective function and the predictive horizons are discussed. The GS was characterized by a second order mathematical model (MM), with the values of the parameters identified experimentally. Simulations were carried out using Matlab Simulink. The control results achieved are compared with the Proportional Integrative Derivative controller with Lags (PID-L1). The conclusions support the proposed control solution and its implementation in applications.
The paper presents an insight into our current researches on galvanometer-based scanners (GSs). A brief overview is first performed on the state-of-the-art, as well as on some of our contributions to optimize the scanning and the command functions of this most used scanning device. Considerations on the use of GSs in high-end biomedical imaging applications such as Optical Coherence Tomography (OCT) are made, with a focus towards obtaining the best possible duty cycles and artifact-free OCT images when using GSs for lateral scanning, as studied in our previous works. The scope of our present study is to obtain the mathematical model of a GS system (motor and controller included) in order to optimize the command functions of the device and to support the development of some more advanced control
structures. The study is centered on the mathematical and experimental modeling of GSs. Thus, the results of an
experimental identification made on a classical multi-parameter mathematical model proposed for such a system are
presented. The experiments are carried out in different operating regimes, and the specific characteristic parameters of
the GS are determined. Using these parameters obtained experimentally, we carry out simulations in Mathlab Simulink
to validate the theoretical model. With the indentified model, an extended control solution is proposed. We point out the match between the theory and the results of the simulations and of the testing for different types of input signals, such as triangular, sinusoidal, and sawtooth with different duty cycles.
KEYWORDS: Scanners, Polygon scanners, Mirrors, Medical imaging, Optical coherence tomography, Promethium, Real time imaging, Signal attenuation, 3D modeling, Prisms
We discuss and demonstrate the optimal scanning functions of a galvanometer-based scanner (GS) from an optomechanical
point of view. Triangular versus sawtooth and sinusoidal scanning functions are reviewed briefly. From this
discussion, we focus on triangular functions with linear active portions and as fast as possible non-linear stop-and-turn
portions, necessary to obtain an as high as possible duty cycle. We have studied analytically the performances of these
return portions for various sinusoidal, parabolic and higher order polynomial equations. Contrary to what is pointed out
in the literature, where linear + sinusoidal scanning function was considered best, we demonstrated that actually the
linear + parabolic function provides the highest duty cycle (i.e. time efficiency of the scanning process).
The second part of the study approaches the command function, given by the input voltage of the GS that has to provide
the optimal scanning function discussed above. This command function is considered in relationship with the active
torque that drives the device. This torque is studied with regard to the constructive parameters of the device (moment of
inertia, damping coefficient and elastic coefficient of the torsion springs), and to the imposed parameters of the scanning
regime (scan frequency, amplitude, velocity and duty cycle). Especially the trade-off that can be done between the
various - and contradictory - requirements one has for the device is of interest. The main one is between the duty cycle
and the maximum value of the command voltage, in order to minimize the maximum input electrical signal for the
device with a minimum loss in what concerns the scan efficiency. Thus, this modeling of the active torque can show the
practical limits of the duty cycle, after the study concerning the scanning function has demonstrated its theoretical
limitations.
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