Browsing by Subject "Optical fibers"

Now showing 1 - 20 of 22

Open Access
915 nm pumped 1018 nm Yb-doped all-fiber high power fiber laser system
(Institute of Electrical and Electronics Engineers Inc., 2019) Midilli, Yakup; Efunbajo, O. Benjamin; Şimşek, Bartu; Ortaç, Bülend
Fibers lasers have attracted great attention in the last decades and the power scaling has reached tens of kW levels. Especially with the tandem pump configuration, pumping the active medium with a pump laser light instead of a diode laser, has made a breakthrough and so many research has been conducted about 1018 nm fiber laser systems [1]. Decreasing the quantum defect, the slope efficiency could be increased up to 90 % levels; on the other hand, due to the emission cross section of the Ytterbium (Yb), to operate the laser in the 1018 nm wavelength region is very challenging because of the presence of the ASE about the 1030 nm region. However, in the literature by using 976 nm pump diodes multi-hundred watts level 1018 nm fiber lasers could be demonstrated [2, 3].
Open Access
CO2 laser polishing of conical shaped optical fiber deflectors
(Springer Verlag, 2017-06) Şimşek, E. U.; Şimşek, B.; Ortaç, B.
A novel method for polishing conical shaped optical fiber deflectors by modulated CO2 laser exposure is reported. The conical shaped fiber deflector geometry was first formed with rough mechanical polishing, then it was exposed to modulated CO2 laser operating with wavelength at 10.6 µm to achieve fine polish surfaces. The motivation of this work is to demonstrate that the modulated CO2 laser exposure approach allows a fiber surface roughness at a nanometer scale without modifying the conical shape of the fiber deflector. The average surface roughness of mechanically polished fiber deflectors with 30 and 9 µm lapping films was smoothed down to 20.4 and 4.07 nm, respectively, after CO2 laser polishing process. By combining mechanical and laser polishing techniques, fabrication of conical shaped optical fiber deflectors takes less time and it becomes laborer independent and easy to apply. © 2017, Springer-Verlag Berlin Heidelberg.
Open Access
Demonstration of an all-fiber ultra-low numerical aperture ytterbium-doped large mode area fiber in a master oscillator power amplifier configuration above 1 kW power level
(IEEE, 2020) Midilli, Yakup; Ortaç, Bülend
We demonstrate an all-fiber ultra-low numerical aperture high power fiber laser system operating in the continuous-wave regime at a central wavelength of 1080 nm. A special Ytterbium-doped fiber preform has been designed and fabricated by using modified chemical vapor deposition technique with the deposition percentages of 0.03mol% of Yb2O3, 1.8mol% of Al2O3, and 2.1mol% of P2O5. Then it has been drawn to obtain an active fiber having core/cladding diameters of 26 μm/410 μm respectively. The numerical aperture of the fiber has been first predicted as 0.034 from refractive index profile of the preform. Afterward, this number has been verified with a simple test setup by altering the bending diameter of the fiber and the excitation conditions of it. To test the high power performance, a laser system has been constructed in a master oscillator power amplifier configuration, and ~ 80 W seed signal power is amplified to 1.05 kW. The quality of the laser output beam has been measured in terms of M 2 value along both x and y coordinates as 1.11 and 1.16 respectively.
Open Access
Development of high-beam quality high power Ytterbium-doped fiber lasers
(2022-01) Midilli, Yakup
High power fiber laser (HPFL) systems have drawn considerable interest for the last decades in health, industry, and especially defense applications due to their compactness, robustness, and high directionality. In this respect, the defense industry is currently in high demand for HPFL systems in the naval, air force, and ground operations. As an example, they have been implemented to the battleship, armored vehicles, and most currently to the drones. Outstanding features of these systems allow us to utilize them in various applications; however, this great demand brings some shortcomings. For example, power scaling of highpower fiber lasers has been impeded by non-linear interactions such as Stimulated Raman Scattering (SRS) and Transverse Mode instability (TMI). Regarding these non-linear interactions, I have built high-power fiber laser oscillators and amplifier systems based on both commercial and homemade selffabricated Ytterbium (Yb)-doped large mode area active (LMA) fibers. Amplifier systems have been built based on the Master Oscillator Power Amplifier (MOPA) configuration, and the average power reaches up to 1 kW power level. Besides, the fiber oscillator system has been built with a power level up to 2 kW power level and M2 value of 1.2, the beam quality parameter of the fiber laser system. To understand and investigate the TMI effect on the fiber laser system and the fiber itself, I have intended to observe the intensity change of the probe lasers and the color center formation inside a homemade active fiber in the presence of TMI. Then, I have rebuilt the system to eliminate the TMI effect and repeated the same experiments to ensure that the TMI effect was responsible for the difference. For that purpose, I have installed a fiber laser system whose fiber has been coiled in a large bending diameter to ensure the existence of the TMI effect. I have utilized two different probe lasers with 645 nm and 520 nm central wavelengths, respectively. I have coupled these probe lasers to the fiber laser system via freespace arrangements. Afterward, I have repeated the same experiment only with the 520 nm probe laser ensuring the absence of the TMI effect by rebuilding the laser structure. Finally, I have taken data about the intensity change of the probe lasers for both cases and compared them. Having benefited from the experience of these studies, to suppress the SRS and TMI, I have fabricated a new type of generation Yb-doped LMA active fiber having an ultra-low numerical aperture (NA) around 0.034. Then I have built a monolithic MOPA system based on this fiber with a 1 m bending diameter. In addition, I have obtained 1 kW maximum power with a diffraction-limited beam quality with an M2 value of 1.16. Additionally, I have studied the side-pump combining technique, which is one of the mitigation methods for TMI. It allows us to pump the active fiber from both sides, thus decreasing the thermal load on fiber. Finally, I have studied the side pump combiner on both homemade self-fabricated Photonic Crystal Fiber (PCF) and ultra-low NA active fiber in a (1 + 1) x 1 pumping configuration with 95% and 89% pump coupling e ciencies, respectively.
Open Access
Distributed strain sensing by frequency-selective fading in phase-OTDR
(IEEE, 2024-10-29) Yıldız, Muhammed Kaan; Uyar, Faruk; Kartaloğlu, Tolga; Özbay, Ekmel; Özdür, İbrahim
We demonstrate a novel approach using frequency-selective fading in phase-OTDR systems to measure dynamic strain on a fiber optic cable. We present the measurements of 200 Hz, 0.03 με strain at 2 kHz interrogation frequency. CLEO 2024 © Optica Publishing Group 2024 © 2024 The Author(s)
Open Access
Engineering particle trajectories in microfluidic flows using speckle light fields
(SPIE, 2014) Volpe, G.; Volpe, Giovanni; Gigan, S.
Optical tweezers have been widely used in physics, chemistry and biology to manipulate and trap microscopic and nanoscopic objects. Current optical trapping techniques rely on carefully engineered setups to manipulate nanoscopic and microscopic objects at the focus of a laser beam. Since the quality of the trapping is strongly dependent on the focus quality, these systems have to be very carefully aligned and optimized, thus limiting their practical applicability in complex environments. One major challenge for current optical manipulation techniques is the light scattering occurring in optically complex media, such as biological tissues, turbid liquids and rough surfaces, which give rise to apparently random light fields known as speckles. Here, we discuss an experimental implementation to perform optical manipulation based on speckles. In particular, we show how to take advantage of the statistical properties of speckle patterns in order to realize a setup based on a multimode optical fiber to perform basic optical manipulation tasks such as trapping, guiding and sorting. We anticipate that the simplicity of these "speckle optical tweezers" will greatly broaden the perspectives of optical manipulation for real-life applications. © 2014 SPIE.
Open Access
An examination of the effect of polarization on the radiation losses of bent optical fibres
(Kluwer Academic Publishers, 1993) Altintas, A.; Tanyer, S. G.
It has long been recognized that the bending losses in weakly guiding optical fibres are independent of the polarization for large bend radius. Here, we show this fact using the volume equivalent current method. The procedure is then applied to a helically bent fibre and it is shown that the radiation from the helical fibre is also independent of the polarization as long as the fibre is weakly guiding.
Open Access
Fabrication of polarization-maintaining optical fiber with ultra-low bending-dependent polarization extinction ratio deterioration
(2023-02) Akçimen, Samet
Polarization-Maintaining Optical Fiber (PM) is a unique-designed fiber that pre-serves and utilizes the polarization state of the light transmission that is launched into it. With this aspect, our biaxial PM fiber is adequate for different applications, including interferometers, fiber optic gyroscopes (FOGs), telecommunication, and all-PM fiber lasers by maintaining single polarized light transmission against the environmental perturbation. A biaxial PM fiber, which was found to possess high polarization extinction ratio (PER) values over 30 dB among two orthogonal axes, is composed of the unique geometry that is the combination of elliptical core and Panda-type PM fibers. Even under environmental temperature conditions, from -55 °C to +85 °C, the PER values were obtained to be maintained. During the bending dependent PER measurements, it was observed that the PER values at relatively small diameters from 12 mm to 5 mm were not altered compared to the biaxial PM fibers not bent. PER deterioration was determined as 0.5%. We measured the group beat lengths which were 1.40 mm for one axes and 1.45 mm for the other at 1550 nm to confirm the biaxial PM property. The optical loss of the biaxial PM fiber was measured with an optical time-domain reflectometer (OTDR) and the loss was found to be below 1.5 dB/km for over 3 km of fiber length. Along two polarized axes, the mode field diameter (MFD) and the numerical aperture (NA) values were also determined. This novel PM fiber addresses a need for the Panda and elliptical core type (PM) fibers which are essential for integrated fiber based sensors and instruments, such as fiber optic gyroscopes.
Open Access
Femtosecond laser fabrication of fiber based optofluidic platform for flow cytometry applications
(SPIE, 2017) Serhatlioglu, Murat; Elbuken, Çağlar; Ortac, Bülend; Solmaz, Mehmet E.
Miniaturized optofluidic platforms play an important role in bio-analysis, detection and diagnostic applications. The advantages of such miniaturized devices are extremely low sample requirement, low cost development and rapid analysis capabilities. Fused silica is advantageous for optofluidic systems due to properties such as being chemically inert, mechanically stable, and optically transparent to a wide spectrum of light. As a three dimensional manufacturing method, femtosecond laser scanning followed by chemical etching shows great potential to fabricate glass based optofluidic chips. In this study, we demonstrate fabrication of all-fiber based, optofluidic flow cytometer in fused silica glass by femtosecond laser machining. 3D particle focusing was achieved through a straightforward planar chip design with two separately fabricated fused silica glass slides thermally bonded together. Bioparticles in a fluid stream encounter with optical interrogation region specifically designed to allocate 405nm single mode fiber laser source and two multi-mode collection fibers for forward scattering (FSC) and side scattering (SSC) signals detection. Detected signal data collected with oscilloscope and post processed with MATLAB script file. We were able to count number of events over 4000events/sec, and achieve size distribution for 5.95μm monodisperse polystyrene beads using FSC and SSC signals. Our platform shows promise for optical and fluidic miniaturization of flow cytometry systems. © 2017 SPIE.
Open Access
High power supercontinuum generation in graded-index multimode fibers
(Institute of Electrical and Electronics Engineers Inc., 2019) Teğin, Uğur; Ortaç, Bülend
Over the years, supercontinuum generation in fibers are studied extensively. Photonic crystal fiber technology detailed these studies by allowing the change of dispersion parameter. Nowadays, multimode fibers attracted huge attention by enabling spatiotemporal nonlinearities and multimodal interactions. Recently, with graded-index multimode fibers, researchers reported new nonlinear dynamics such as cascaded Raman scattering [1], spatiotemporal instability [2,3], self-beam cleaning [4], multimode solitons [5].
Open Access
High-speed 1.55 μm operation of low-temperature-grown GaAs-based resonant-cavity-enhanced p-i-n photodiodes
(American Institute of Physics, 2004) Butun, B.; Bıyıklı, Necmi; Kimukin, I.; Aytur, O.; Özbay, Ekmel; Postigo, P. A.; Silveira, J. P.; Alija, A. R.
The 1.55 μm high-speed operation of GaAs-based p-i-n photodiodes was demonstrated and their design, growth and fabrication were discussed. A resonant-cavity-detector structure was used to selectively enhance the photoresponse at 1.55 μm. The bottom mirror of the resonant cavity was formed by a highly reflecting 15-pair GaAs/AlAs Bragg mirror and molecular-beam epitaxy was used for wafer growth. It was found that the fabricated devices exhibited a resonance of around 1548 nm and an enhancement factor of 7.5 was achieved when compared to the efficiency of a single-pass detector.
Open Access
An integrated femtosecond timing distribution system for XFELS
(Massachusetts Institute of Technology, 2006) Kim, J.; Burnham, J.; Chen, J.; Kartner, F. X.; İlday, Fatih Ömer; Ludwig, F.; Schlarb, H.; Winter, A.; Ferianis, M.; Cheever, D.
Tightly synchronized lasers and RF-systems with timing jitter in the few femtoseconds range are necessary sub-systems for future X-ray free electron laser facilities. In this paper, we present an optical-microwave phase detector that is capable of extracting an RF-signal from an optical pulse stream without amplitude-to-phase conversion. Extraction of a microwave signal with 3 fs timing jitter (from 1 Hz to 10 MHz) from an optical pulse stream is demonstrated. Scaling of this component to subfemtosecond resolution is discussed. Together with low noise mode-locked lasers, timing-stabilized optical fiber links and compact optical cross-correlators, a flexible femtosecond timing distribution system with potentially sub-10 fs precision over distances of a few kilometers can be constructed. Experimental results on both synchronized RF and laser sources will be presented.
Open Access
Investigation of AlGaN buffer layers on sapphire grown by MOVPE
(SPIE, 2004) Van Gemmern, P.; Dikme, Y.; Bıyıklı, Necmi; Kalisch, H.; Özbay, Ekmel; Jansen, R. H.; Heuken, M.
In this work, AlGaN layers were grown on sapphire by metal-organic vapor phase epitaxy (MOVPE) on (0001)-oriented sapphire substrates, with the intention to investigate the effect of varying Al/MO and V/III ratios on the Al incorporation into the AlGaN layers. The parameters Al/MO and V/III describe the proportions of source material inside the reactor. With the help of optical transmission measurements, characteristic cut-off wavelengths of the Al xGa(1-x)N layers were determined. These wavelengths were used to calculate the Al content x of the layers, leading to values between 26.6% and 52.1%. Using the two process parameters Al/MO and V/III as input and the Al content of the AlGaN layers as a response variable, the experimental results were further investigated with the help of the software STATGRAPHICS. An estimated response surface for the variable x was generated. It was found that the Al incorporation is only tunable within a wide range for high V/III ratios of about 900. For constant Al/MO ratios and varying V/III ratios, two different growth characteristics were observed at high and low Al/MO values. This behavior is ascribed to the superposition of two oppositional effects.
Open Access
Kilometer-long ordered nanophotonic devices by preform-to-fiber fabrication
(Institute of Electrical and Electronics Engineers, 2006) Bayındır, Mehmet; Abouraddy, A.F.; Shapira O.; Viens J.; Saygin-Hinczewski, D.; Sorin, F.; Arnold, J.; Joannopoulos, J. D.; Fink, Y.
A preform-to-flber approach to the fabrication of functional fiber-based devices by thermal drawing in the viscous state is presented. A macroscopic preform rod containing metallic, semiconducting, and insulating constituents in a variety of geometries and close contact produces kilometer-long novel nanostructured fibers and fiber devices. We first review the material selection criteria and then describe metal-semiconductor-metal photosensitive and thermally sensitive fibers. These flexible, lightweight, and low-cost functional fibers may pave the way for new types of fiber sensors, such as thermal sensing fabrics, artificial skin, and large-area optoelectronic screens. Next, the preform-to-fiber approach is used to fabricate spectrally tunable photodetectors that integrate a photosensitive core and a nanostructured photonic crystal structure containing a resonant cavity. An integrated, self-monitoring optical-transmission waveguide is then described that incorporates optical transport and thermal monitoring. This fiber allows one to predict power-transmission failure, which is of paramount importance if high-power optical transmission fines are to be operated safely and reliably in medical, industrial and defense applications. A hybrid electron-photon fiber consisting of a hollow core (for optical transport by means of a photonic bandgap) and metallic wires (for electron transport) is described that may be used for transporting atoms and molecules by radiation pressure. Finally, a solid microstructured fiber fabricated with a highly nonlinear chalcogenide glass enables the generation of supercontinuum light at near-infrared wavelengths.
Open Access
Nonlinearity engineering of mode-locked fiber lasers: Similariton and soliton-similariton lasers
(IEEE, 2011) İlday F. Ömer; Öktem, Bülent; Ülgüdür, Coşkun
Fiber lasers are attractive with their simplicity, high powers and low cost. However, propagation of short pulses in optical fiber leads to nonlinear effects, which limit the technical performance. These effects drive rich dynamics, which is interesting from a fundamental perspective. The nonlinear waves community has unraveled the fascinating world of solitons and similaritons through experiments in fibers. This paper overviews the recent development of the soliton-similariton laser. The original similariton laser was the first to work with nonlinear effects, rather than minimizing or compensating them. In the soliton-similariton laser, the propagation is strongly nonlinear everywhere. © 2011 IEEE.
Open Access
Optical resolution photoacoustic imaging of multiple probes via single fiber laser with independently adjustable parameters
(OSA, 2017) Yavaş, S.; Kipergil, E. A.; Uluç, N.; Demirkıran, A.; Kayıkçıoğlu, T.; Salman, H. S.; Karamuk, Şöhret Görkem; Ünlü, M. B.; İlday, Fatih Ömer
Photoacoustic microscopy (PAM) is a promising imaging modality that combines optical and ultrasound imaging. It combines the advantages of high ultrasonic spatial resolution and high optical contrast. When a short laser pulse illuminates the tissue, absorbed light leads to an acoustic emission via thermoelastic expansion. The laser system needs to generate short enough pulses, i.e., several nanoseconds, to create photoacoustic signals with high efficiency and emit wavelengths in the visible range to excite tissue chromophores in their absorption peaks. To increase penetration depth of imaging, it is also desirable to utilize a wavelength in the NIR range, from 600 to 1200 nm, where biological tissues are relatively transparent.
Open Access
Passive polarization filtering in negative curvature hollow-core fibers
(SPIE - International Society for Optical Engineering, 2023-10-05) Siddiqui, Muhammad Zain; Akosman, A. E.; Ordu, Mustafa; Yin, Shizhuo; Guo, Ruyon
A novel negative curvature hollow-core fiber (NCF) design is proposed capable of spectral and polarization filtering in the near-infrared region. The designed six-tube silica-based NCF contains nest elements in the form of suspended tubes radially anchored with a pole to the outer cladding in the vertical direction. In contrast, standard nested cladding elements without any suspension are used through the horizontal axis. This fiber configuration introduces an asymmetry in the core, which helps maintain the orthogonal X and Y polarization states in the fiber core. Pole anchors in vertically positioned tubes only give rise to the spectral filtering confinement loss profile for a vertically polarized state. Based on the geometrical optimization of the fiber, we achieved an improved birefringence on the order of 10-5 with filtered wavelength losses below 0.01 dB/km in the wavelength range of 1.4 µm to 1.7 µm. The operational bandwidth, polarization extinction ratio, filtered wavelengths, birefringence, and modulation depth loss can be tuned by optimizing the fiber parameters, including outer tube thickness, nest tube diameter, and pole dimensions. This proposed fiber design with selective transmission spectrums has untapped potential sensing capabilities in hollow-core negative curvature fibers. © 2023 SPIE. All rights reserved.
Open Access
Plasmonics: merging photonics and electronics at nanoscale dimensions
((AAAS) American Association for the Advancement of Science, 2006) Özbay, Ekmel
Electronic circuits provide us with the ability to control the transport and storage of electrons. However, the performance of electronic circuits is now becoming rather limited when digital information needs to be sent from one point to another. Photonics offers an effective solution to this problem by implementing optical communication systems based on optical fibers and photonic circuits. Unfortunately, the micrometer-scale bulky components of photonics have limited the integration of these components into electronic chips, which are now measured in nanometers. Surface plasmon-based circuits, which merge electronics and photonics at the nanoscale, may offer a solution to this size-compatibility problem. Here we review the current status and future prospects of plasmonics in various applications including plasmonic chips, light generation, and nanolithography.
Open Access
Subnetwork partitioning and section restoration in translucent optical networks
(SPIE, 2003) Karasan, Ezhan; Arısoylu, M.
We discuss the problem of designing translucent optical networks composed of restorable, transparent subnetworks interconnected via transponders. We formulate the problem of designing restorable subnetworks in translucent networks as an Integer Linear Programming (ILP) problem, where the subnetworks are determined subject to the constraints that each subnetwork satisfies size limitations and it is 2-connected. A greedy heuristic algorithm for the same problem is also proposed for planar network topologies. We propose section restoration for translucent networks where failed connections are rerouted inside the subnetwork which contains the failed link. The network design problem of determining working and restoration capacities with section restoration is formulated as an ILP problem. Numerical results show that section restoration generates fiber costs which are close to those with the path restoration technique for the mesh topologies used in this study. It is also shown that the number of transponders with the translucent optical network is substantially reduced compared to opaque networks.
Open Access
Tapered nanoscale chalcogenide fibers directly drawn from bulk glasses as optical couplers for high-index resonators
(OSA - The Optical Society, 2017) Aktaş, O.; Bayındır, Mehmet
We report production of air-clad tapered chalcogenide fibers by directly drawing bulk glasses between cleaved tips of tapered silica fibers. Exploiting these tapered fibers with nanoscale waists as evanescent optical couplers, we demonstrate phase-matched coupling of light into on-chip whispering gallery mode chalcogenide microresonators with coupling efficiencies as high as 95%. To the best of our knowledge, this is the first-time demonstration of critical coupling into high-index microresonators by using high-index tapered fibers. The tapered chalcogenide fibers can also be utilized as optical couplers for microresonators made of various high-index materials, as well as for nonlinear optical applications.