Browsing by Subject "Fibers"

Now showing 1 - 20 of 45

Open Access
1 mJ pulse bursts from a Yb-doped fiber amplifier
(Optical Society of America, 2012-07-01) Kalaycıoğlu, Hamit; Eldeniz, Y. B.; Akçalan, Önder; Yavaş, Seydi; Efe, M.; İlday, Fatih Ömer
We demonstrate burst-mode operation of a polarization-maintaining Yb-doped fiber amplifier capable of generating 60 μJ pulses within bursts of 11 pulses with extremely uniform energy distribution facilitated by a novel feedback mechanism shaping the seed of the burst-mode amplifier. The burst energy can be scaled up to 1 mJ, comprising 25 pulses with 40 μJ average individual energy. The amplifier is synchronously pulse pumped to minimize amplified spontaneous emission between the bursts. Pulse propagation is entirely in fiber and fiber-integrated components until the grating compressor, which allows for highly robust operation. The burst repetition rate is set to 1 kHz and spacing between individual pulses is 10 ns. The 40 μJ pulses are externally compressible to a full width at half-maximum of 600 fs. However, due to the substantial pedestal of the compressed pulses, the effective pulse duration is longer, estimated to be 1.2 ps.
Open Access
1018 nm Yb-doped high-power fiber laser pumped by broadband pump sources around 915 nm with output power above 100 W
(OSA - The Optical Society, 2017) Midilli, Y.; Efunbajo, O. B.; Şimşek, B.; Ortaç, B.
We demonstrate a 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources operating in the broad absorption spectrum around 915 nm. In the experiment, two different pump diodes were tested to pump over a wide spectrum ranging from 904 to 924 nm by altering the cooling temperature of the pump diodes. Across this so-called pump wavelength regime having a 20 nm wavelength span, the amplified stimulated emission (ASE) suppression of the resulting laser was generally around 35 dB, showing good suppression ratio. Comparisons to the conventional 976 nm-pumped 1018 nm ytterbium-doped fiber laser were also addressed in this study. Finally, we have tested this system for high power experimentation and obtained 67% maximum optical-to-optical efficiency at an approximately 110 W output power level. To the best of our knowledge, this is the first 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources around 915 nm reported in detail.
Embargo
A machine learning approach for the estimation of photocatalytic activity of ALD ZnO thin films on fabric substrates
(Elsevier, 2024-02-01) Akyıldız, Halil I.; Yiğit, E.; Arat, A. B.; Islam, S.
Research in the field of photocatalytic wastewater treatment is striving to enhance catalyst materials to achieve high-performance systems. A promising approach to this goal has been immobilizing photocatalytic materials on fibrous substrates via atomic layer deposition (ALD). Nevertheless, both the ALD process and the assessment of photocatalytic performance involve a multitude of parameters necessitating thorough investigation. In this study, we employ popular machine-learning algorithms, including Support Vector Regression (SVR) and Artificial Neural Networks (ANN), to predict the photocatalytic activity of ALD-coated textiles. The photocatalytic activity is evaluated through methylene blue and methyl orange degradation tests. Machine learning algorithms are tested and trained using the k-fold cross-validation technique. The findings demonstrate that the ANN and SVR methods utilized in this research can predict catalytic activity with mean absolute percentage errors (MAPE) of 2.35 and 3.25, respectively. This study illuminates that, within the defined range of process parameters, the photocatalytic activity of ALD-coated textiles can be precisely estimated with suitable machine-learning algorithms.
Open Access
All-fiber all-normal dispersion laser with a fiber-based Lyot filter
(Optical Society of America, 2010-04-15) Özgören, K.; Ilday, F. Ö.
We propose the use of a short section of polarization-maintaining fiber as a birefringent medium to construct an all-fiber Lyot filter inside the cavity of a fiber laser. This allows mode-locked operation of an all-fiber all-normal dispersion Yb-fiber oscillator without the use of a bulk bandpass filter and using standard components. Moreover, filter bandwidth and modulation depth is easily controlled by changing the length and splice angle of the polarization-maintaining-fiber section, leading to an adjustable filter. At mode-locked operation, the 30% output fiber port delivers 1nJ pulses that are dechirped to 230 fs duration.
Open Access
All-fiber all-normal dispersion laser with an in-fiber Lyot filter
(Optical Society of America, 2010) Özgören, Kıvanç; İlday, F. Ömer
We propose use of a short PM-fiber section as birefringent medium to construct an all-fiber Lyot filter, with bandwidth adjustable through the PM-fiber length. An all-fiber all-normaldispersion laser is demonstrated using standard components only. © 2009 Optical Society of America.
Open Access
All-fiber high-energy yb-doped fiber amplifier
(IEEE, 2009) Öktem, Bülent; Kalaycioǧlu, Hamit; İlday, F. Ömer
We report a robust, all-fiber amplifier seeded by a fiber oscillator. Seed pulses at 1 MHz repetition rate are amplified up to 3 μJ, delivering 1 μJ-energy, 170 fs-long pulses. Duration reduces to 120 fs at 1 μJ amplifier output. These are the highest peak powers from an integrated fiber source. © 2009 IEEE.
Open Access
All-fiber nonlinearity-and dispersion-managed dissipative soliton nanotube mode-locked laser
(American Institute of Physics, 2015) Zhang Z.; Popa, D.; Wittwer, V. J.; Milana, S.; Hasan, T.; Jiang, Z.; Ferrari, A. C.; Ilday F. Ö.
We report dissipative soliton generation from an Yb-doped all-fiber nonlinearity- and dispersion-managed nanotube mode-locked laser. A simple all-fiber ring cavity exploits a photonic crystal fiber for both nonlinearity enhancement and dispersion compensation. The laser generates stable dissipative solitons with large linear chirp in the net normal dispersion regime. Pulses that are 8.7 ps long are externally compressed to 118 fs, outperforming current nanotube-based Yb-doped fiber laser designs.
Open Access
All-fiber, single-mode spectral beam combining of high power Tm-doped fiber lasers
(OSA, 2015) Yılmaz, S.; Ottenhues, C.; Wysmolek, M.; Theeg, T.; Lamrini, S.; Scholle, K.; Fuhrberg, P.; Sayınç, H.; İlday, Fatih Ömer; Neumann, J.; Overmeyer, L.; Kracht, D.
Signal beam combining of Tm-doped fiber lasers can increase the laser output power while simultaneously maintaining the single mode beam quality. We demonstrate an all-fiber integrated dual-wavelength Tm-doped fiber laser with an output power of 36 W by using the spectral beam combining method. The constituent lasers are operating at the wavelengths 1949 and 1996 nm and an in-house-made WDM is used for combination of these two different wavelengths. All-fiber truly single mode power combining is demonstrated for the first time in this wavelength region.
Open Access
All-fiber-integrated soliton-similariton laser with in-line fiber filter
(Optical Society of America, 2012-08-16) Zhang, Z.; Öktem, B.; Ilday, F. Ö.
We demonstrate an all-fiber-integrated Er-doped fiber laser operating in the soliton-similariton mode-locking regime. In the similariton part of the cavity, a self-similarly evolving parabolic pulse with highly linear chirp propagates in the presence of normal dispersion. Following an in-line fiber-based birefringent filter, the pulse evolves into a soliton in the part of the cavity with anomalous dispersion. The similariton and the soliton pulses are dechirped to 75.5 and 167.2 fs, respectively, outside of the cavity. Mode-locked operation is very robust, owing to the influence of the two similariton and soliton attractors that predominate each half of the laser cavity. The experimental results are supported with numerical simulations, which provide good agreement.
Open Access
Antioxidant α-tocopherol/γ-cyclodextrin–inclusion complex encapsulated poly(lactic acid) electrospun nanofibrous web for food packaging
(John Wiley and Sons Inc., 2017-01) Aytac, Z.; Keskin, N. O. S.; Tekinay, T.; Uyar, Tamer
α-Tocopherol (α-TC) and α-TC/cyclodextrin (CD)–inclusion complex (IC) incorporated electrospun poly(lactic acid) (PLA) nanofibers (NF) were developed via electrospinning (PLA/α-TC–NF and PLA/α-TC/γ-CD–IC–NF). The release of α-TC into 95% ethanol (fatty food simulant) was much greater from PLA/α-TC/γ-CD–IC–NF than from PLA/α-TC–NF because of the solubility increase in α-TC; this was confirmed by a phase-solubility diagram. 2,2-Diphenyl-1-picrylhydrazyl radical-scavenging assay shows that PLA/α-TC–NF and PLA/α-TC/γ-CD–IC–NF had 97% antioxidant activities; this value was expected to be high enough to inhibit lipid oxidation. PLA/α-TC–NF and PLA/α-TC/γ-CD–IC–NF were tested directly on beef with the thiobarbituric acid reactive substance (TBARS) method, and the nanofibers displayed a lower TBARS content than the unpackaged meat sample. Thus, active packaging significantly enhanced the oxidative stability of the meat samples at 4 °C. In conclusion, PLA/α-TC/γ-CD–IC–NF was shown to be promising as an active food-packaging material for prolonging the shelf life of foods.
Open Access
Artificial olfaction inside nanostructured infrared fiber arrays
(IEEE, 2011) Yaman, Mecit; Yıldırım, Adem; Bayındır, Mehmet
Nanostructured hollow core fibers are used to demonstrate a new infrared absorption based artificial nose. The sensor unit of the array is a hollow core Bragg fiber that selectively guides incident blackbody radiation and enhances absorption for enhanced sensitivity. © 2011 IEEE.
Open Access
Balancing gain narrowing with self phase modulation: 100-fs, 800-nJ from an all-fiber-integrated Yb amplifier
(IEEE, 2013) Pavlov, Ihor; Rybak, A.; Cenel, C.; İlday, F. Ömer
There is much progress in Yb-fiber oscillator-amplifier systems, which enable generation of high-repetition-rate, microjoule energies and sub-picosecond pulse widths [1,2]. Given the extremely large total gain factors to reach microjoules starting from nanojoules, which is often in the range of 40-60 dB, due to losses, and the impact of mismatched high-order dispersion as temporal stretching and compression of pulses by large factors (30-40 dB) need to be employed. As a result of these challenges, most of the Yb-fiber amplifiers have resulted in pulse durations of several 100 fs or longer. While pulse durations in this range are suited for some applications, there are many cases where 100-fs or shorter pulses in microjoule range are required. Gain narrowing can be effectively countered by self-phase modulation (SPM) [3] by limiting amplification factor in each stage of amplification and through careful optimization of SPM and inversion level along the gain fiber. The conceptual template is readily present in the evolution of the pulse inside the oscillator cavity, where gain factors are often in the 10-50 range per roundtrip. To the extend that the B-integral and the gain distribution along the amplifier can be kept identical to the oscillator by proper scaling of the chirped pulse width and fiber mode area, the original oscillator can be preserved in arbitrary number of amplification stages. Here, we demonstrate a highly fiber-integrated master-oscillator power-amplifier (MOPA) system, from which - 1 μJ pulses are extracted and externally compressed to 100 fs by arranging amplification in each stage as close as possible to the intra-cavity evolution. To our knowledge, these results are the shortest demonstrated from all-fiber-integrated amplifier at the microjoule level. © 2013 IEEE.
Open Access
Binary coded identification of industrial chemical vapors with an optofluidic nose
(OSA - The Optical Society, 2016) Adamu, A. I.; Ozturk, F. E.; Bayındır, Mehmet
An artificial nose system for the recognition and classification of gas-phase analytes and its application in identifying common industrial gases is reported. The sensing mechanism of the device comprises the measurement of infrared absorption of volatile analytes inside the hollow cores of optofluidic Bragg fibers. An array of six fibers is used, where each fiber targets a different region of the mid-infrared in the range of 2-14 ìm with transmission bandwidths of about 1-3 μm. The quenching in the transmission of each fiber due to the presence of analyte molecules in the hollow core is measured separately and the cross response of the array allows the identification of virtually any volatile organic compound (VOC). The device was used for the identification of seven industrial VOC vapors with high selectivity using a standard blackbody source and an infrared detector. The array response is registered as a unique six digit binary code for each analyte by assigning a threshold value to the fiber transmissions. The developed prototype is a comprehensive and versatile artificial nose that is applicable to a wide range of analytes.
Open Access
Bio-inspired hierarchically structured polymer fibers for anisotropic non-wetting surfaces
(Royal Society of Chemistry, 2017) Yunusa, M.; Ozturk, F. E.; Yildirim, A.; Tuvshindorj, U.; Kanik, M.; Bayındır, Mehmet
We demonstrate a rice leaf-like hierarchically textured polymer fiber array for anisotropic non-wetting surfaces. To provide superhydrophobicity in addition to the anisotropic behavior, fiber surfaces are spray coated with organically modified silica nanoparticles. The resulting micro/nano hierarchically structured fiber surfaces demonstrate anisotropic non-wetting properties. We designed various fiber architectures for droplet transportation, mixing, and guiding exploiting the scalability of the fiber texture during thermal drawing; optional nanoparticle surface modification; and inherent flexibility of the fibers.
Open Access
Bio-insprired optoelectronic digital nose for breath analysis
(2011) Bayındır, Mehmet; Yıldırım, Adem; Yaman, Mecit; Vural, Mert
A novel electronic nose device is presented that can be used in disease diagnostics by exhaled breath analysis. Exhaled breath contains more than a thousand organic compounds that can be analysed to insect various diseases and metabolic activity. The novel device is an electronic nose, based on photonic bandgap fibers that can selectively guide infrared radition inside a hollow core plastic fiber. Instead of a laser line source, a broadband balackbody source is used that exploits the filtering/ guiding properties of the fibers to scan the whole mid-infrared region, making it high selectivity of volatile organic compounds possible. In addition waveguiding inside the fiber enhances the electromagnetic radiation intensity, resulting in improved infrared absorption cross-section. The fiber electronic nose can be integrated and deployed as a portable electronics device to point-of-care institutes.
Open Access
Burst-mode thulium all-fiber laser delivering femtosecond pulses at a 1 GHz intra-burst repetition rate
(Optical Society of America, 2017) Elahı, P.; Kalaycıoğlu, H.; Akçaalan, Ö.; Şenel, Ç.; Ilday, F. Ö.
We report on the development of, to the best of our knowledge, the first ultrafast burst-mode laser system operating at a central wavelength of approximately 2 μm, where water absorption and, consequently, the absorption of most biological tissue is very high. The laser comprises a harmonically mode-locked 1-GHz oscillator, which, in turn, seeds a fiber amplifier chain. The amplifier produces 500 ns long bursts containing 500 pulses with 1 GHz intra-burst and 50 kHz inter-burst repetition rates, respectively, at an average power of 1 W, corresponding to 40 nJ pulse and 20 μJ burst energies, respectively. The entire system is built in an all-fiber architecture and implements dispersion management such that output pulses are delivered directly from a single-mode fiber with a duration of 340 fs without requiring any external compression. This gigahertz-repetition-rate system is intended for ablation-cooled laser material removal in the 2 μm wavelength region, which is interesting for laser surgery due to the exceptionally high tissue absorption at this wavelength.
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
Development of high power Cw Yb-Doped fiber laser system
(2015-01) Özkan, Elif Gül
High-average-power fiber lasers are interesting for many applications, including scientific instrumentation, industrial material processing, imaging, medical and military technologies. Fiber concept has well established them as a very attractive beam delivery system and gain medium for laser applications. Rareearth- doped fibers are one of the most promising solid-state laser concepts for efficient diode-pumped high power continuous wave laser systems. In fiber laser systems, the new generation fiber optical cables are used. Fiber laser systems are preferred due to the ease of usage in the field, high beam quality, low cost and low thermo-optic problems. Fiber laser system has an active medium where the light is amplified all along the fiber. The long active medium leads to reduced heat problems, high absorption rate of the light, high quality beam and less need for optimization of the cavity. We designed and developed a high power fiber laser system for metal processing. Material drilling and cutting, which are significant processes in industry, are performed with the powerful fiber laser systems. The main purpose of this thesis is to develop a laser system which enables fast and accurate cutting process with impressive properties such as compactness, low maintenance problems and so on. The fiber laser resonator was first numerically studied by using software and then various laser parameters and laser architectures were designed. In order to perform the numerical results, we designed a compact high power all-fiber laser cavity. In real world applications, the use of free space components to constitute the cavity leads to environmental instabilities and power loss, which results in a decrease of the fiber laser efficiency. One of the most important advantages of all fiber laser system is to handle environmental factors such as humidity, vibrations. To achieve high power level from the fiber laser systems, it is significant to use powerful pumping systems (high power diode lasers), passive laser cavity components (combiner, FBG) and also double-clad active fiber that operate at high power level. In this study, we used new generation laser cavity components. The pump sources have been analyzed in terms of power and wavelength stabilities. Also, experiments have been performed to keep pump sources at optimum temperature to obtain accurate wavelength to excite ytterbium atoms located in the active media. In order to constitute high power laser system, we integrated all fiber optic components for efficient operation. The laser has stable continuous wave regime in temporal domain due to the cavity design. The output power of the system is about 548 W. The M2 value of the system is less than < 1.7. The operation wavelength of the fiber laser was stabilized with FBG at 1.08 μm. We also demonstrate the capability of our fiber laser system for material processing. We successfully drilled and cut 1.7 mm thickness steel target with lower output power of fiber laser (100 W).
Open Access
Doping management for high-power fiber lasers: 100 W, few-picosecond pulse generation from an all-fiber-integrated amplifier
(Optical Society of America, 2012-07-16) Elahi, P.; Yilmaz, S.; Akçaalan, Ö.; Kalaycioğlu, H.; Öktem, B.; Şenel, Ç.; Ilday, F. Ö.; Eken, K.
Thermal effects, which limit the average power, can be minimized by using low-doped, longer gain fibers, whereas the presence of nonlinear effects requires use of high-doped, shorter fibers to maximize the peak power. We propose the use of varying doping levels along the gain fiber to circumvent these opposing requirements. By analogy to dispersion management and nonlinearity management, we refer to this scheme as doping management. As a practical first implementation, we report on the development of a fiber laser-amplifier system, the last stage of which has a hybrid gain fiber composed of high-doped and low-doped Yb fibers. The amplifier generates 100 W at 100 MHz with pulse energy of 1 μJ. The seed source is a passively mode-locked fiber oscillator operating in the all-normaldispersion regime. The amplifier comprises three stages, which are all-fiber-integrated, delivering 13 ps pulses at full power. By optionally placing a grating compressor after the first stage amplifier, chirp of the seed pulses can be controlled, which allows an extra degree of freedom in the interplay between dispersion and self-phase modulation. This way, the laser delivers 4.5 ps pulses with ∼200 kW peak power directly from fiber, without using external pulse compression.
Open Access
Electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon
(Elsevier, 2017) Topuz, F.; Uyar, T.
The electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon was shown, and the detailed studies were conducted to correlate the fiber morphology with electrospinning process parameters and gelatin concentration in electrospinning solution. Particularly, variations in the applied voltage and the concentration of gelatin led to the transition of fiber shape from round to flat/ribbon. The formation of flat-shaped fibers was attributed to rapid evaporation of the solvent (formic acid) from the fiber matrix with increasing the applied voltage and gelatin concentration. On the other hand, round fibers were due to the steady evaporation of formic acid throughout the cross-section of fibers. WAXS analysis revealed that the loss of triple-helical crystalline structure in gelatin after the electrospinning process. The gelatin fibers were cross-linked through treatment with toluene 2,4-diisocyanate (TDI) in a mixed solution of acetone and pyridine, and XPS confirmed the cross-linking of the fibers over an increased carbon content on the elemental composition of the fiber surface due to the incorporated TDI moieties. Overall, this study focuses on morphological tuning of gelatin electrospun fibers towards a flat/ribbon-like structure by variation of electrospinning parameters and polymer concentration, and thus, the proposed concept can be adapted towards flattened/ribbon-like fibers of other protein-based systems by electrospinning.