Browsing by Author "Ortaç, Bülend"

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Open Access
130 nJ 77 fs dissipative soliton fiber laser
(OSA, 2010) Baumgartl, M.; Ortaç, Bülend; Lecaplain, C.; Hideur, A.; Limpert J.; Tünnermann, A.
We report on ultrashort high-energy pulse generation from an all-normal-dispersion fiber oscillator. The watt-level laser directly emits chirped pulses with a duration of 1ps and 163nJ of pulse energy. These can be compressed to 77fs. © 2010 Optical Society of America.
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
All-fiber all-normal-dispersion femtosecond laser with a nonlinear multimodal interference-based saturable absorber
(OSA - The Optical Society, 2018) Teğin, Uğur; Ortaç, Bülend
In this Letter, we demonstrate, to the best of our knowledge, the first all-fiber all-normal-dispersion ytterbium-doped oscillator with a nonlinear multimodal interference-based saturable absorber capable of generating ultrashort dissipative soliton pulses. Additional to functioning as a saturable absorber, the use of multimode fiber segments between single-mode fibers also ensures the bandpass filtering via multimode interference reimaging necessary to obtain dissipative soliton mode locking. The oscillator generates dissipative soliton pulses at 1030 nm with 5.8 mW average power, 5 ps duration, and 44.25 MHz repetition rate. Pulses are dechirped to 276 fs via an external grating compressor. All-fiber cavity design ensures high stability, and ∼70 dB sideband suppression is measured in the radio frequency spectrum. Numerical simulations are performed to investigate cavity dynamics, and obtained results are well matched with experimental observations. The proposed cavity presents an alternative approach to achieve all-fiber dissipative soliton mode locking with a simple and low-cost design.
Open Access
All-fiber all-normal-dispersion femtosecond laser with nonlinear multimodal interference-based saturable absorber
(Institute of Electrical and Electronics Engineers Inc., 2019) Teğin, Uğur; Ortaç, Bülend
Chong et al. demonstrated a stable passively mode-locked all-normal-dispersion fiber laser and pulse generation is attributed to the strong spectral filtering of chirped pulses, dissipative soliton pulses [1]. In the following years, with very-large-mode-area fibers the energy and power scalability of the dissipative soliton pulses is demonstrated. Recently, multimodal interactions are subject to device studies with various configurations. Nazemosadat et al. theoretically proposed a short graded-index multimode fiber segment in between single mode fiber as a saturable absorber [2]. On the other hand, with similar device structure an all-fiber bandpass filter is later presented both numerically and experimentally [3].
Open Access
An all-fiber ultra-low numerical aperture high power fiber MOPA system with an output power above 500 W
(Institute of Electrical and Electronics Engineers Inc., 2019) Midilli, Yakup; Ortaç, Bülend
Optical fiber technology has been developed dramatically in the last two decades. Especially, the invention of the Large Mode Area (LMA) fibers has made a great impact, and consequently the power scale of the fiber lasers started to increase exponentially [1]. However, at a certain point this increase has been saturated due to the non-linear effects such as Stimulated Raman Scattering (SRS) and Thermal Modal Instability (TMI). Therefore, a new approach has been proposed to mitigate these so called problems by decreasing the numerical aperture (NA) of the LMA active fiber so that it behaves like an intrinsically single mode fiber. In the literature, an active fiber having ultra-low (<; 0.04) NA, is proposed [2, 3] in 2009; and finally, the highest power, which is 4.3 kW, was demonstrated in 2017 [4]. However, all of these works based on free space orientation. In this letter, we demonstrate all-fiber and monolithic version of the high power low NA fiber laser system based on an Yb-doped active fiber having 26 μm/410 μm core/cladding diameters respectively with a NA of 0.032 which has also been verified experimentally.
Open Access
Cascaded Raman scattering based high power octave-spanning supercontinuum generation in graded-index multimode fibers
(Nature Publishing Group, 2018) Teğin, Uğur; Ortaç, Bülend
A new method to generate multi-watt-level, octave-spanning, spectrally flat supercontinua stemmed from cascaded Raman scattering in graded-index multimode fibers is reported. Formation dynamics of supercontinua are investigated by studying the effect of fiber length and core size. High power handling capacity of the graded-index multimode fibers is demonstrated by power scaling experiments. Pump pulse repetition rate is scaled from kHz to MHz while pump pulse peak power remains same and ~4 W supercontinuum is achieved with 2 MHz pump repetition rate. To the best of our knowledge, this is the highest average power and repetition supercontinuum source ever reported based on a graded-index multimode silica fiber. Spatial properties of the generated supercontinua are measured and Gaussian-like beam profiles obtained for different wavelength ranges. Numerical simulations are performed to investigate underlying nonlinear dynamics in details and well-aligned with experimental observations.
Open Access
Clinical evaluation of DIAGNOVIR SARS-CoV-2 ultra-rapid antigen test performance compared to PCR-based testing
(Nature Publishing Group, 2023-03-17) Seymen, Ali Aytaç; Gulten, E.; Ozgur, E.; Ortaç, Bülend; Akdemir, İ.; Cinar, G.; Saricaoglu, E.M.; Guney-Esken, G.; Akkus, E.; Can, F.; Karahan, Z. C.; Azap, A.; Tuncay, E.
Coronavirus Disease-19 (COVID-19) is a highly contagious infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The development of rapid antigen tests has contributed to easing the burden on healthcare and lifting restrictions by detecting infected individuals to help prevent further transmission of the virus. We developed a state-of-art rapid antigen testing system, named DIAGNOVIR, based on immune-fluorescence analysis, which can process and give the results in a minute. In our study, we assessed the performance of the DIAGNOVIR and compared the results with those of the qRT-PCR test. Our results demonstrated that the sensitivity and specificity of the DIAGNOVIR were 94% and 99.2%, respectively, with a 100% sensitivity and 96.97% specificity, among asymptomatic patients. In addition, DIAGNOVIR can detect SARS‑CoV‑2 with 100% sensitivity up to 5 days after symptom onset. We observed that the DIAGNOVIR Rapid Antigen Test’s limit of detection (LoD) was not significantly affected by the SARS‑CoV‑2 variants including Wuhan, alpha (B1.1.7), beta (B.1.351), delta (B.1.617.2) and omicron (B.1.1.529) variants, and LoD was calculated as 8 × 102, 6.81 × 101.5, 3.2 × 101.5, 1 × 103, and 1 × 103.5 TCID50/mL, respectively. Our results indicated that DIAGNOVIR can detect all SARS-CoV-2 variants in just seconds with higher sensitivity and specificity lower testing costs and decreased turnover time.
Open Access
CO2 polishing of femtosecond laser micromachined microfluidic channels
(Optical Society of America, 2016) Serhatlıoğlu, Murat; Ortaç, Bülend; Elbuken, C.; Bıyıklı, Necmi; Solmaz, Mehmet E.
The CO2 polishing of femtosecond laser micromachined channels is studied. The surface quality before and after polishing is observed with naked eye and optical microscope. The method improves imaging of microspheres.
Open Access
A combinatorial buffered oxide etching method for high-power cladding light stripper
(Institute of Electrical and Electronics Engineers Inc., 2019) Yapar-Yıldırım, Elif; Karatutlu, Ali; Balk, Ekin Teslime; Midilli, Yakup; Ortaç, Bülend
High-power fiber lasers have been applied in many areas due to their advantages such as high beam quality, compact structure, flexibility and high efficiency. However, the absorption of the pump light is limited and a residual pumped light keeps propagating in the cladding. This residual pumped light affects the beam quality and can damage the whole system. Therefore, an efficient removal of excess high-power cladding light is critical for the safe operation of the high-power fiber lasers and high beam quality [1]. Adding a new structure to the cladding of the fiber leading to interrupt total internal reflection in the clad and scatter away the unwanted pump light is the generalized approach for a cladding light stripper (CLS) device fabrication. Also, it is important to scatter all the unwanted light uniformly along the CLS. Etching the fiber for surface damage and recoating the fiber [2] are two general methods for stripping the cladding light [3-5].
Open Access
Combined method for the fabrication of high-power cladding light stripper using a buffered oxide etchant
(OSA - The Optical Society, 2019-08) Yıldırım, Elif Yapar; Karatutlu, Ali; Balk, Ekin Teslime; Midilli, Yakup; Ortaç, Bülend
Cladding light strippers (CLSs) are vital and one of the critical components for high-power fiber laser applications. In this study, we show the first studies of the formation mechanisms and optimum conditions of a CLS device using a buffered oxide etchant by a combined method of stain (wet) etching and vapor-phase etching. This high-power CLS was shown to result in a stripping performance of ∼17.2 dB∼17.2 dB at the launched power of 333 W (pump limited). The thermal imaging demonstrates that the maximum temperature reached when operating the device at maximum launched power was ∼75°C∼75°C. The atomic force microscopy (AFM) results show that the combined method yields crystal-like structures with the height in microscales, whereas other conventional methods give only nanoscale roughness. The method also preserves the diameter of the CLS device close to the bare fiber with about 10 μm tapering leads to a high surface area to strip unwanted light, which is good for heat dissipation. The combined method possesses the outcome of two methods, including both the crystal-like structures and nanosized hillocks, resulting in high-power stripping performance and robustness.
Open Access
Cucurbit[7]uril-capped hybrid conjugated oligomer-gold nanoparticles for combined photodynamic-photothermal therapy and cellular imaging
(ACS, 2020) Özkan, Melis; Tunç, İ.; Midilli, Y.; Ortaç, Bülend; Tuncel, Dönüş
Herein, hybrid nanoparticles composed of a redemitting conjugated oligomer (COL) and gold nanoparticles (Au-NPs) were prepared through a one-pot synthetic method in which the oligomer acts as a reducing agent as well as a matrix to wrap the newly formed Au nanoparticles. These hybrid nanoparticles(COL-Au-NPs) exhibited photodynamic and photothermal activity against both Gram-positive and Gram-negative bacterial strains. They were also proven to possess high photostability and thermal reversibility. Dark cytotoxicity of COL-Au-NPs toward pathogens and mammalian breast cancer cells (MCF-7) reduced significantly upon complexation with cucurbit[7]uril while preserving their light-induced cytotoxic activity when irradiated with a 915 nm laser for photothermal therapy and white light for photodynamic therapy, respectively. Furthermore, these nanoparticles have cellular imaging capability because of their intrinsic fluorescence characteristics and can be used in image-guided therapy.
Open Access
Demonstration of a novel cladding light stripper fabrication method based on poly (Chloro-P-Xylene) polymer material
(IEEE, 2021-09-30) Midilli, Yakup; Liman, Görkem; Demirel, Gökhan; Ortaç, Bülend
Cladding light stripper (CLS) is a key component for high power fiber laser systems to remove the unwanted light sources out of the system effectively. If they cannot be removed out of the system, the quality of the laser beam is affected severely. For that purpose, the fabrication of CLS has been investigated for years based on two main approaches. One of them is etching method [1] , [2] and the other one is the coating method [3] , [4] . The CLS fabrication based on the recoated polymer has a problem of power scaling whereas the other one is more fragile since the fiber is deformed even though they are more capable of handling power. However, in this work we present a new method to coat a special polymer material on top of the fiber with Chemical Vapor Deposition (CVD) method with a high precision level in the range of nm scale.
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
Double ring firing single optical fiber deflector
(Institute of Electrical and Electronics Engineers Inc., 2019) Seymen, A. A.; Uzcengiz-Şimşek, Elif; Ӧzgür, E.; Ortaç, Bülend
We report a novel fabrication method of double ring firing single optical fiber deflector. The fiber deflector is fabricated as a convergent cone having two different cone angles, by conventional mechanical polishing. The two-angled conical fiber deflector geometry is formed in a single fiber tip, deflecting incoming laser light into two distinct circular rings. Two cone angles provide two deflection angles due to total internal reflection and refraction of the incoming laser light. We achieved two deflected circular beams at 60° and 85° with the cone angles of 56° and 72° at one single fiber deflector. The laser power is evenly split between two conical areas. The fabrication process of the fiber deflector does not involve any splicing or arc discharge process; thus, it is convenient, effective, and high-throughput.
Open Access
Effects of gamma radiation on Yb-doped Al–P–silicate optical fibers
(Springer, 2022-09) Kendir Tekgül, Esra; Midilli, Yakup; Çamiçi, Hüseyin Can; Yapar Yıldırım, Elif; Karatutlu, Ali; Ortaç, Bülend
Ytterbium (Yb)-doped optical fibers are mainly used in the fiber laser resonator and amplifier systems. These systems have been widely utilized for applications in air and space, the defense industry, and the medical field. Particularly for the applications yielding operation in harsh environments consisting of radiation, it is essential to determine the radiation hardness of the Yb-doped optical fibers and their long-term performance in such environments. This study analyzed the optical properties of four different Yb-doped aluminophosphosilicate fibers before and after gamma irradiation. For each fiber, the effect of different total dose values including 0.5, 1, 10, and 50 kGy were determined at different operation wavelengths, such as 495 nm, 590 nm, 685 nm, and 730 nm, using radiation-induced attenuation (RIA) analysing curves. The total dose values of 10 kGy and 50 kGy were studied to demonstrate the results under extreme environmental conditions such as large hadron colliders (LHCs). Our findings reveal that the formation of radiation-induced color centers (e.g. AlOHC, POHC, and NBOHC) are highly dependent on the Yb-concentration, the amount of excess alumina (Al22O33) compared to the phosphorous pentoxide (P22O55), total irradiation dose and wavelength at which the respective RIA is recorded.
Open Access
Enhanced light scattering with energy downshifting using 16 nm indium nitride nanoparticles for improved thin-film a-Si N-i-P solar cells
(Electrochemical Society Inc., 2015-05) Chowdhury F.I.; İslam, K.; Alkış, Sabri; Ortaç, Bülend; Alevli, Mustafa; Dietz, N.; Okyay, Ali Kemal; Nayfeh, A.
In this work the effect of Indium nitride (InN) nanoparticles (NPs) on the performance of a-Si: H solar cells has been investigated. The average Jsc of InN NPs coated cells was found 6.76 mA/cm2 which is 16.69% higher than the average Jsc of the reference cell which was 5.79 mA/cm2. Average efficiency of InN NPs coated cells showed 14.16% increase from 3.32% to 3.79%. Peak EQE has increased from 44.8% at 500 nm to 51.67% at 510 nm and peak IQE has increased from 51.70% at 510 nm to 68.38% at 500 nm for InN NPs coated cell. Further study shows that EQE change is larger between 510 nm-700 nm compared to IQE change indicting a surface scattering mechanism that reduces the reflectivity. However, between 400 nm-510 nm IQE change is larger than EQE change which indicates that energy downshifting mechanism is dominating. So overall performance enhancement can be attributed to the scattering and photoluminescence properties of InN NPs that enhances absorption inside a-Si: H solar cells. © The Electrochemical Society.
Open Access
Erratum: Specialty optical fiber modeling, fabrication, and characterization feature issue
(Optica, 2022) Ortaç, Bülend; Jain, Deepak; Jha, Rajan; Hu, Jonathan; Ung, Bora
Two articles [1,2] appearing in the “Specialty optical fiber modeling, fabrication, and characterization” feature issue should have been labeled as invited.
Open Access
Fabrication of biaxial polarization-maintaining optical fiber with ultra-low bending-dependent polarization extinction ratio deterioration
(Academic Press, 2022-02-07) Karatutlu, Ali; Yapar Yıldırım, Elif; Midilli, Yakup; Akçimen, Samet; Ortaç, Bülend; Kendir, Esra
Different applications, including interferometers, gyroscopes, and frequency combs, require a single polarized light transmission by maintaining this property against the environmental perturbation. As a new type of polarization-maintaining (PM) fiber, a biaxial PM fiber was fabricated over 30 dB of high polarization extinction ratio (PER) values among two orthogonal axes over a fiber length of 110 m. The PM fiber was manufactured with a combination of an elliptical core and Panda-type geometries. The PER values were demonstrated to be preserved at harsh temperature conditions from −55 °C to +85 °C. The bending loss measurements indicate the biaxial PM fiber has ultra-low bending dependent PER deterioration (<0.5 %) at various bending diameters from 12 mm to 5 mm. The biaxial PM property was also confirmed by the group beat length measurements and found to be less than 1.5 mm at 1550 nm. The optical time-domain reflectometer (OTDR) measurements show that the optical loss of the biaxial PM fiber was below 1.5 dB/km over 3 km length. The mode-field diameter (MFD) and the numerical aperture (NA) values were also reported along two polarized axes. This novel PM fiber offers a single solution for the elliptical and Panda-type PM fibers utilized for integrated fiber-based sensors and instruments.
Open Access
Femtosecond microjoule-Class ytterbium fiber lasers
(Optical Society of America, 2011) Lecaplain, C.; Ortaç, Bülend; Machinet G.; Boullet J.; Baumgartl, M.; Schreiber, T.; Cormier, E.; Hideur, A.
We report the generation of 830 nJ energy from a mode-locked all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. After external compression, 550 fs pulses with 1.2 MW peak power are demonstrated. © 2011 OSA.
Open Access
Generation of soliton molecules with independently evolving phase in a mode-locked fiber laser
(Optical Society of America, 2010) Ortaç, Bülend; Zaviyalov, A.; Nielsen, C.K.; Egorov, O.; Iliew, R.; Limpert, J.; Lederer, F.; Tünnermann, A.
We report the experimental generation of two-soliton molecules in an ytterbium-doped fiber laser. These molecules exhibit an independently evolving phase and are characterized by a regular spectral modulation pattern with a modulation depth of 80%. © 2010 Optical Society of America.