Scopus İndeksli Yayınlar Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395

Browse

Now showing 1 - 3 of 3

PERFORMANCE EVALUATIONS OF SINGLE MODE OPTICAL RECEIVER FOR DEGRADED VISUAL FIELD AND PHOTONIC LANTERN BASED COHERENT DETECTION
(Abdullah Gül Üniversitesi, 2016) ORAN, ABDULLAH
Imaging at degraded visual environments is one of the biggest challenges in today’s imaging technologies. Especially military and commercial rotary wing aviation is suffering from impaired visual field in sandy, dusty, marine and snowy environments. For example, during landing the rotor churns up the particles and creates dense clouds of highly scattering medium, which limits the vision of the pilot and may result in an uncontrolled landing. The vision in such environments is limited because of the high ratio of scattered photons over the ballistic photons that have the image information. In this thesis, we propose to use optical spatial filtering (OSF) method in order to eliminate the scattered photons and mainly collect the ballistic photons at the receiver. OSF is widely used in microscopy; to the best of our knowledge this thesis will be the first application of OSF for macroscopic imaging. Our experimental results show that most of the scattered photons are eliminated using the spatial filtering in a highly scattering degraded visual field. The results are compared with a standard broad area photo detector which shows the effectiveness of spatial filtering. Free space optical systems have applications in different areas such as laser ranging, three-dimensional imaging, weather predictions and optical wireless communication. Some applications require very high performance free space optical systems that are not available today. The need of systems with higher performance and lower size, weight and power (SWaP) is the biggest research motivation of free space optical systems. Between various detection techniques, vi coherent optical detection comes forward for applications that require high sensitivity and bandwidth. Coherent detection based LIDAR systems have the potential to provide quantum noise limited performance. However coherent systems suffer from poor free space to fiber collection efficiency due to the single mode detection characteristics and small size of the optical fiber. In order to overcome this problem, photonic lantern is introduced to effectively collect the multimode beam coming from free space and convert it to a number of single mode fibers. The photonic lantern consists of a multimode fiber to a number of single-mode fibers. The collection efficiency enhancement of photonic lanterns have been investigated, however there is no study on the signal to noise ratio –performance- improvement on the photonic lantern based free space coherent systems. In this thesis; the effect of random distribution of the optical power in the 19-port photonic lantern will be investigated mathematically. The photonic lantern based coherent detection system performance will also be simulated by using the MATLAB software. The output of this thesis may open the path to experimental demonstration and maybe even to a prototype.
Centella asiatica extract containing bilayered electrospun wound dressing
(Abdullah Gül Üniversitesi, 2019) KOÇ, NURAY
Innovative and bioactive wound dressings prepared by electrospinning mimicking the native structure of the extracellular matrix (ECM) have gained significant interest as an alternative to conventional wound care applications. In this study, bilayered wound dressing material was produced by sequential electrospinning of quaternized poly(4- vinyl pyridine) (upper layer) on the Centella Asiatica (CA) extract containing electrospun poly(D, L-lactide-co-glycolide) (PLGA)/poly(3-hydroxybutyrate-co-3- hydroxy valerate) (PHBV) blend membrane (lower layer). Scanning electron microscopy (SEM) was utilized to show a uniform and bead-free fiber structure of electrospun membranes. The average diameter of CA extract containing electrospun PLGA/PHBV blend membrane was calculated 0.471±0.11 µm, whereas the average fiber diameter of electrospun poly(Q-VP) membranes was in the range of 0.460±0.057 µm. Chemical, thermal, mechanical properties, and adsorption capacity of electrospun membranes, as well as the cumulative release of CA from the electrospun PLGA/PHBV membrane, were investigated. Viability, adhesion, and attachment of human fibroblast cells on the electrospun membranes on pre-set days were evaluated by the colorimetric CellTiter 96® Aqueous One Solution Cell Proliferation Assay (MTS assay) and SEM. Results revealed that CA loaded bilayered electrospun wound dressing showed promoted attachment and proliferation of fibroblasts. Hence, it can be concluded that CA extract containing bilayered electrospun wound dressing prepared in this study has a promising potential for wound healing applications.
Phase noise filtering effects of mode-locked lasers
(Abdullah Gül Üniversitesi, 2018) MBONDE, HAMIDU
The subject of Mode-Locked Lasers has experienced a massive growth over the last two decades. Previously meant as the source of ultra-short optical pulses, its concepts have recently expanded to be applicable in areas beyond Optics such as Biomedical[1], Micro-machining[2], Sensing[3] and RF/Microwaves communication[4]. In particular this thesis focuses on application of Mode-Locked Lasers in RF/Microwave communications. One of the common problems with RF communication systems is signal integrity. Due to the nature of oscillation systems that are used to produce RF signals there is always an inevitable amount of undesirable signal associated with main signal being generated. These spurious (noise) signals have significant effect on the efficient performance of particular RF system. Low noisy RF signals are highly desirable and have many applications in high speed communication, RADAR and electronic warfare. Therefore it is critical to have an efficient means of producing low noise RF signals. Generating RF signals by Optical means has emerged as a major solution to this problem. Various methods for optically generating lower noise RF signals of high frequency have been developed such as frequency stabilized mode-locked lasers[5], phase locked loop based oscillators[6] and optoelectronic oscillators[7]. In this thesis a novel approach to this problem is presented, instead of generating lower noise signals a unique method of efficiently filtering the noise of RF signal using Mode-Locked Laser is explained. The first two chapters give brief introduction to mode-locked lasers and phase noise in oscillator, the concepts which will be used throughout this thesis. Then the experimental setups of the proposed system with the results obtained are presented in Chapter 3. Furthermore, theoretical study and analysis of limitations of this method is presented in ii Chapter 4. This includes analysis of these limitations as well as supporting simulations results. Phase noise is frequency domain term which in time domain is referred to as jitters. For various applications it is necessary to determine total jitters value of the system in order to estimate its bit error rates and other performance features. Chapter 5 of this thesis is dedicated to introducing jitter concept and a numerical method of converting a phase noise spectrum into jitter Probability Density Function (PDF).Together with the MATLAB code for aforementioned simulation a special GUI (Graphical User Interface) has been developed for the purpose of converting any given phase noise spectrum into its corresponding jitter PDF. The last chapter gives some concluding remarks and look at the possible futures of this work.

Browse

Browsing Scopus İndeksli Yayınlar Koleksiyonu by Publisher "Abdullah Gül Üniversitesi"