Browsing by Subject "Fiber Optics"

Now showing 1 - 5 of 5

Open Access
83 W, 1 ns, 3.1 MHz all-fiber laser for micromachining
(IEEE, 2011) Özgören, Kıvanç; Öktem, Bülent; Yılmaz, Sinem; İlday, F. Ömer; Pasin, E.; Eken, K.
Fiber lasers are commonly used for various material processing applications. The advantages (such as simplicity of the system, high material removal rate) and disadvantages (larger heat-affected zone, reduced precision) of nanosecond pulses over sub-picosecond pulses are well known. © 2011 IEEE.
Open Access
Development and characterization of a direct detection fiber optic distributed acoustic sensor
(2018-09) Uyar, Faruk
Phase-sensitive optical time domain re ectometer (ø-OTDR) based distributed acoustic sensor (DAS) systems have attracted increasing attention in recent years due to their remarkable advantages in a wide range of industrial and military applications such as health monitoring and security of civil infrastructures, railways, oil and gas pipelines, borders, and so on. They measure vibrations and detect perturbations along a section of fiber. Different approaches have been adopted to realize the ø-OTDR systems and process the data from these sensors. In this thesis, a direct detection DAS based on ø-OTDR architecture with long sensing range and high signal-to-noise ratio (SNR) is demonstrated. Testing and characterization of critical system components is conducted before integrating them into the system. The results of laboratory tests are presented, in which the detected traces are successively analyzed in order to localize and investigate the perturbation events along the test fibers. The field tests are demonstrated with different external events such as digging, walking, and motor vibration. Considering the random nature of Rayleigh backscattered light and fading effect encountered in these tests, a new performance metric, which is Mean SNR, is proposed for assessing and comparing the system performances. Besides, statistical characteristics of the SNR of the vibration events in different distances for both laboratory tests and field tests is experimentally measured. The photon statistics of Rayleigh backscattered signal in a ø-OTDR based fiber sensor in the presence of amplified spontaneous emission noise is theoretically modeled and experimentally demonstrated, as well.
Open Access
Development of a fast fiber based UV-Vis multiwavelength detector for an ultracentrifuge
(2006) Bhattacharyya, S.K.; Maciejewska P.; Börger L.; Stadler, M.; Gülsün, A.M.; Cicek H.B.; Cölfen H.
The advantages of simultaneously detecting multiple wavelengths in ultracentrifugation experiments are obvious, especially for interacting systems. In addition, the detection of the wavelength dependence of turbidity opens up the possibility to obtain independent information on the particle size in addition to the usual sedimentation coefficient distribution for colloidal systems. We therefore made an effort to develop a fast UV/Vis detector, which is able to simultaneously detect the range from 200-800 nm. This is possible by the use of a modern CCD chip based generation of UV-Vis spectrometers, which translates the dispersed white light onto a CCD chip, where each pixel corresponds to a particular wavelength. In addition to the simultaneous detection of a large number of wavelengths in the range 200-800 nm, also with non integer values, these spectrometers are very fast. Current typical spectrum scan times with the necessary scan quality in the ultracentrifuge are in the range of 100 ms but this time can be significantly shortened down to 3 ms for higher light intensities and even down to 10 μs for a new generation of CCD chip based spectrometers. The introduction of a fiber based UV-Vis optics into a preparative XL-80K ultracentrifuge with the associated hardware developments will be described as a first generation prototype. In this study, we use a wavelength dependent optical lens system instead of the necessary but more complex wavelength independent mirror optical system for a first check on possibilities and limitations of the optical system. First examples for biopolymers and latexes will be presented and compared to those obtained in the commercial XL-A ultracentrifuge. Already the fast detection enables completely new possibilities like the determination of a particle size distribution in a few minutes. Multiwavelength detection at constant position in dependence of time will be demonstrated, which is an important mode for the use of speed profiles for very polydisperse samples. Also, the use of radial multiwavelength scans will be demonstrated producing a three dimensional data space for monitoring the sedimentation via radial scans with multiwavelength detection. However, despite the advantages, the current problems with the detector will also be discussed including the main problem that much intensity is lost in the important UV range as a result of fiber coupling and bending. © Springer-Verlag Berlin Heidelberg 2006.
Open Access
Hollow core photonic bandgap fibers for medical applications
(2009) Vural, Mert
The design, fabrication and characterization of photonic band gap (PBG) based optical polymer fibers is discussed. Unlike conventional total internal reflection (TIR) fibers, used primarily in telecommunications, PBG fibers can be made hollow core and can be used to guide infrared radiation of any wavelength, a property known as wavelength scalability. Since the electromagnetic radiation is transmitted in the hollow core of the fiber, the intrinsic absorption of the fiber core as well as the insertion Fresnel losses at front and end faces are avoided, giving rise to extraordinarily high power densities to be delivered. The fiber production line includes material characterization, and the design of nanoscale quarter wavestacks using common thermoplastic polymers (poly ether sulphone and poly ether imide) and chalcogenide glasses (As2S3, As2Se3, Ge15As25Se15Te45). The fiber preform is fabricated using rolling mechanism of thermally evaporated chalcogenide glasses on large area polymers. Subsequently, the fiber preforms are thermally drawn to obtain nano-structured PBG fibers.Two different fibers are designed and produced, signifying wavelength scalability of the overall process, for the widely used holmium (Ho:YAG) and carbon dioxide (CO2) medical lasers. The transmission characteristics of the fibers proved that they can be used to safely deliver 15Wlaser power, along a 3 meter fiber with external diameter of 1.5 mm and hollow core diameter of 0.5 mm, corresponding to a laser power density of 1kW/cm2 with a loss of -10dB/m. The PBG fibers are expected to be widely used in high precision surgical laser for incision, photoablation and coagulation where infrared radiation is the radiation of choice for its superior laser-tissue interaction properties.
Open Access
Miniaturized fiber optic transmission system for magnetic resonance imaging signals
(2005) Memiş, Ömer Gökalp
In conventional Magnetic Resonance Imaging (MRI) instruments, after echo signals are received by an MRI coil, they are transmitted through an ultra low noise transmission system consisting of electrical cables. Although this design proved to be effective over the years, there are recent developments in the MRI technology which require a better, more sophisticated design. One of these emerging technologies is “parallel imaging”, where total size of interconnections is the primary problem, and the other is “interventional MRI”, where safety needs to be improved. The Miniature Fiber Optic Transmission System was developed to serve these needs. The system consists of a receiver MRI coil with passive detuning, a two-stage low-noise preamplifier and a low-noise laser diode connected to a photodetector with fiber optic cable in between. The overall noise figure of the system is measured to be lower than 1 dB which guarantees that total signal-to-noise ratio (SNR) reduction in the images due to optical MRI signal transmission system is less than 15%. Total power consumption is 50mW and the device is switchable by another fiber optic line, which can also control active detuning circuit if it is present. A prototype device was tested in a GE 1.5 Tesla MRI instrument and several images were acquired with a slight SNR drop, due to problems with passive detuning. We believe that this design will significantly reduce the size of parallel imaging arrays and enable placement of internal coils into body cavities without providing any safety hazard to the patient, such as electrical shock or burns.