Browsing by Subject "Nonlinear optics"
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Item Open Access All-chalcogenide core-shell fibers for nonlinear applications(Bilkent University, 2015-11) Türedi, BekirThe extreme spectral broadening phenomenon called as Supercontinuum generation is considered as one of the most striking phenomenon in nonlinear optics. Due to their broad spectra and uniformly distributed power over the spectra supercontinuum sources have found wide range of applications in areas such as spectroscopy, frequency metrology, optical coherence tomography, microscopy and telecommunications. In this thesis, we propose a new method to fabricate multicore fibers made of chalcogenide glasses for the use of high power Supercontinuum generation. We designed and fabricated a new seven-core-structured fiber with chalcogenide core /chalcogenide cladding step-index fiber embedded in polymer matrix. After three successful iterative steps we fabricated seven-core chalcogenide glasses fiber which has diameter around 1.35 μm which is engineered to be approximately zero dispersion. The refractive indices of these two materials at 1550 nm are 2.73 and 2.61; as a result the NA is engineered to 0.8 at this wavelength. The step index structure of the fiber provides the very well-confinement of light to the core of the fibers. This enables the more interaction of light with the highly nonlinear part of the fiber and preserves light to be absorbed by the polymer jacket which has high absorbance at IR region. By using split step Fourier method we showed the potential of our fiber to generate supercontinuum covering from 1 μm to 3.5 μm.Item Open Access Amplitude noise of femtosecond fiber lasers in different modelocking regimes(OSA, 2007) Budunoğlu, İbrahim Levent; İlday, Fatih ÖmerAmplitude noise of femtosecond fiber laser oscillators are characterized in soliton, similariton, stretched-pulse and all-normal GVD regimes of mode-locking. Integrated relative intensity noise as low as 0.023% (1 Hz-100 kHz) is reported.Item Open Access Buried waveguides written deep inside silicon(OSA, 2017) Turnalı, Ahmet; Tokel, Onur; Kesim, Denizhan Koray; Makey, Ghaith; Elahi, Parviz; İlday, Fatih ÖmerSummary form only given. Silicon waveguides are widely used as optical interconnects and they are particularly important for Si-photonics. Si-based devices, along with other optical elements, are entirely fabricated on the top surface of Si wafers. However, further integration of photonic and electronic devices in the same chip requires a new approach. One alternative is to utilize the bulk of the wafer for fabricating photonic elements. Recently, we reported a direct-laser-writing method that exploits nonlinear interactions and can generate subsurface modifications inside silicon without damaging the surface. Using this method, we fabricated several functional optical elements including gratings, lenses, and holograms. In this work, we demonstrate optical waveguides entirely embedded in Si.Item Open Access Characterization of thermally poled germanosilicate thin films(Optical Society of American (OSA), 2004) Ozean, A.; Digonnet, M.J.F.; Kino G.S.; Ay F.; Aydınlı, AtillaWe report measurements of the nonlinearity profile of thermally poled low-loss germanosilicate films deposited on fused-silica substrates by PECVD, of interest as potential electro-optic devices. The profiles of films grown and poled under various conditions all exhibit a sharp peak ∼0.5 μm beneath the anode surface, followed by a weaker pedestal of approximately constant amplitude down to a depth of 13-16 μm, without the sign reversal typical of poled undoped fused silica. These features suggest that during poling, the films significantly slow down the injection of positive ions into the structure. After local optimization, we demonstrate a record peak nonlinear coefficient of ∼1.6 pm/V, approximately twice as strong as the highest reliable value reported in thermally poled fused silica glass, a significant improvement that was qualitatively expected from the presence of Ge. ©2004 Optical Society of America.Item Open Access Computer-generated holograms embedded in bulk silicon with nonlinear laser lithography(IEEE, 2016) Turnalı, Ahmet; Tokel, Onur; Makey, Ghaith; Pavlov, Ihor; İlday, Fatih ÖmerRecently, we have showed a direct laser writing method to form subsurface structures inside silicon by exploiting nonlinear interactions. Here, we demonstrate utilization of this phenomenon to create computer-generated holograms buried in silicon.Item Open Access Dynamic nonlinear optical processes in some oxygen-octahedra ferroelectrics: first principle calculations(Taylor & Francis Inc., 2015) Simsek S.; Koc, H.; Palaz S.; Oltulu, O.; Mamedov, A. M.; Özbay, EkmelThe nonlinear optical properties and electro-optic effects of some oxygen-octahedra ferroelectrics are studied by the density functional theory (DFT) in the local density approximation (LDA) expressions based on first principle calculations without the scissor approximation. We present calculations of the frequency- dependent complex dielectric function and the second harmonic generation response coefficient over a large frequency range in tetragonal and rhombohedral phases. The electronic linear electro-optic susceptibility is also evaluated below the band gap. These results are based on a series of the LDA calculation using DFT. The results for are in agreement with the experiment below the band gap and those for are compared with the experimental data where available. © 2015 Taylor & Francis Group, LLC.Item Open Access Highly efficient wavelength conversion of Q-switched Nd: YAG lasers into a red wavelength(Institute of Electrical and Electronics Engineers, 2006) Figen, Z. G.; Yalabik, A.; Aytür, O.We report a nanosecond upconversion optical parametric oscillator which can convert the output of a Nd:YAG laser at 1064-nm wavelength into 627 nm with high efficiency. This device is based on a single KTiOAsO4 crystal that is simultaneously phase matched for optical parametric generation and sum-frequency generation. Pumped at a wavelength of 1064 nm by a Q-switched Nd:YAG laser in a double-pass configuration, this device produces 14.2-ns-long 5.8-mJ red pulses at a wavelength of 627 nm with 29% energy conversion efficiency. In addition, we developed a theoretical model for this device, whose predictions agree reasonably well with our experimental results. It is possible to scale this device for use with higher energy pump lasers and to shape it into a physically small semi-monolithic configuration.Item Open Access Linear and non-linear optical properties of AgBO3(B=Nb, Ta): First principle study(IEEE, 2013) Şimşek, Şevket; Mamedov, Amirullah M.; Özbay, EkmelThe linear and nonlinear optical properties of ferroelectrics AgBO 3 (B=Ta, Nb) are studied by density functional theory (DFT) in the local density approximation (LDA) expressions based on first principle calculations without the scissor approximation. Specially, we present calculations of the frequency-dependent complex dielectric function ε(ω), and the second harmonic generation response coefficient χ(2)(-2ω,ω,ω) over a large frequency range in rhombohedral phase for the first time. The electronic linear electrooptic susceptibility χ(2)(-ω,ω,0) is also evaluated below the band gap. These results are based on a series of the LDA calculation using DFT. © 2013 IEEE.Item Open Access Multimode pumping of optical parametric oscillators(Institute of Electrical and Electronics Engineers, 1996-02) Marshall, L. R.; Kaz, A.; Aytur, O.Calculations suggest that optical parametric oscillators (OPO's) can be efficiently pumped using multimode, divergent pump sources. The influence of pump beam divergence and mode structure upon OPO performance is measured for both noncritical phase-matching, and OPO's with walkoff. Multimode OPO pumping is shown to be efficient, provided appropriate nonlinear crystals and OPO cavities are employed; the nonlinear crystal must have sufficient angular acceptance to tolerate a divergent pump; the OPO cavity must support modes that match the divergence and spatial intensity characteristics of the pump, For low-order pump modes, the OPO can be made to match the mode of the pump. Higher order pump modes reduce the OPO efficiency, and cause a saturation of efficiency with increasing pump power. The efficiency is degraded in a similar fashion in the presence of walkoff. Multimode pumping is more difficult in longer OPO cavities due to increased buildup time of higher order OPO modes.Item Open Access Nanosecond sum-frequency generating optical parametric oscillator using simultaneous phase matching(Optical Society of American (OSA), 2005) Figen, Z.G.; Aytür O.We report a nanosecond sum-frequency generating optical parametric oscillator based on a single KTiOAsO4 crystal that is simultaneously phase matched for optical parametric generation and sum-frequency generation. Pumped at a wavelength of 1064 nm by a Q-switched Nd:YAG laser, this device produces 10.4-ns-long 8.3 mJ red pulses at a wavelength of 627 nm with 21% energy conversion efficiency. This device provides a simple and efficient method for converting high energy Nd:YAG lasers to a red wavelength. © 2005 Optical Society of America.Item Open Access Nonlinearity-tailored fiber laser technology for low-noise, ultra-wideband tunable femtosecond light generation(OSA - The Optical Society, 2017) Liu, X.; Laegsgaard, J.; Iegorov, R.; Svane, A. S.; Ilday, F. Ö.; Tu, H.; Boppart, S. A.; Turchinovich, D.The emission wavelength of a laser is physically predetermined by the gain medium used. Consequently, arbitrary wavelength generation is a fundamental challenge in the science of light. Present solutions include optical parametric generation, requiring complex optical setups and spectrally sliced supercontinuum, taking advantage of a simpler fiber technology: a fixed-wavelength pump laser pulse is converted into a spectrally very broadband output, from which the required resulting wavelength is then optically filtered. Unfortunately, this process is associated with an inherently poor noise figure, which often precludes many realistic applications of such supercontinuum sources. Here, we show that by adding only one passive optical element—a tapered photonic crystal fiber—to a fixed-wavelength femtosecond laser, one can in a very simple manner resonantly convert the laser emission wavelength into an ultra-wide and continuous range of desired wavelengths, with very low inherent noise, and without mechanical realignment of the laser. This is achieved by exploiting the double interplay of nonlinearity and chirp in the laser source and chirp and phase matching in the tapered fiber. As a first demonstration of this simple and inexpensive technology, we present a femtosecond fiber laser continuously tunable across the entire red–green–blue spectral range.Item Open Access Optical properties of the two-dimensional magnetoexcitons under the influence of the Rashba spin-orbit coupling(SPIE, 2011) Hakioglu, Tuğrul; Liberman, M.A.; Moskalenko, S.A.; Podlesny I.V.The influence of the Rashba spin-orbit coupling on the two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field leads to different results of the Landau quantization in different spin projections. In Landau gauge the unidimensional wave vector describing the free motion in one in-plane direction is the same for both spin projections, whereas the numbers of the Landau quantization levels are different. For electron in s-type conduction band they differ by one, as was established earlier by Rashba1, whereas for heavy holes in p-type valence band influenced by the 2D symmetry of the layer they differ by three. There are two lowest spin-splitted Landau levels for electrons as well as two lowest for holes. They give rise to four lowest energy levels of the 2D magnetoexcitons. It is shown that two of them are dipole-active in band-to-band quantum transitions, one is quadrupole-active and the fourth is forbidden. The optical orientation under the influence of the circularly polarized light leads to optical alignment of the magnetoexcitons with different orbital momentum projections on the direction of the external magnetic field. © 2011 SPIE.Item Open Access Simplified calculations of band-gap renormalization in quantum-wells(Academic Press, 1996) Güven, K.; Tanatar, BilalNon-linear optical properties of photoexcited semiconductor quantum-wells are of interest because of their opto-electronic device application possibilities. Many-body interactions of the optically created electrons and holes lead to the band-gap renormalization which in turn determines the absorption spectra of such systems. We employ a simplified approach to calculate the band-gap renormalization in quantum-well systems by considering the interaction of a single electron-hole pair with the collective excitations (plasmons). This method neglects the exchange-correlation effects but fully accounts for the Coulomb-hole term in the single-particle self-energy. We demonstrate that the density, temperature, and well-width dependence of the band-gap renormalization for GaAs quantum-wells within our model is in good agreement with the experimental results. © 1996 Academic Press Limited.Item Open Access Simultaneous phase matching of optical parametric oscillation and second-harmonic generation in aperiodically poled lithium niobate(Optical Society of American (OSA), 2003) Kartaloğlu, T.; Figen, Z. G.; Aytür, O.We report a simple ad hoc method for designing an aperiodic grating structure to quasi-phase match two arbitrary second-order nonlinear processes simultaneously within the same electric-field-poled crystal. This method also allows the relative strength of the two processes to be adjusted freely, thereby enabling maximization of the overall conversion efficiency. We also report an experiment that is based on an aperiodically poled lithium niobate crystal that was designed by use of our method. In this crystal, parametric oscillation and second-harmonic generation are simultaneously phase matched for upconversion of a femtosecond Ti:sapphire laser to 570 nm. This self-doubling optical parametric oscillator provides an experimental verification of our design method. © 2003 Optical Society of America.Item Open Access Spectrally resolved nonlinear optical properties of doped versus undoped quasi-2D semiconductor nanocrystals: copper and silver doping provokes strong nonlinearity in colloidal CdSe nanoplatelets(American Chemical Society, 2022-01-04) Nawrot, K. C.; Sharma, M.; Cichy, B.; Sharma, A.; Delikanli, Savas; Samoć, M.; Demir, Hilmi Volkan; Nyk, M.Nonlinear optical processes are crucial for emerging applications including multiphoton-excited fluorescence microscopy and optical power limiting. Therefore, searching for materials of high multiphoton absorption cross sections is essential for the development of these techniques. We present synthesis of 4.5 monolayer CdSe nanoplatelets (NPLs) doped with silver and copper ions along with the evaluation of their two-photon absorption (TPA) and three-photon absorption (3PA) cross sections. Doping significantly increases the TPA cross section of each NPL sample, which reaches up to 1.33 × 107 GM for the most absorbing copper-doped ones. We also detected 1–2 orders of magnitude-enhanced 3PA cross sections for the doped NPLs in comparison with their undoped counterparts. As TPA and 3PA peaks appear, in the first and the second biological transmission windows, respectively, doped NPLs are promising candidates for multiphoton fluorescence microscopy as bioimaging agents. Moreover, the strong nonlinear response suggests application as active optoelectronic materials in optical sensors.Item Open Access Sub-50 fs all-fiber Yb-doped laser with anomalous-dispersion photonic crystal fiber(IEEE, 2013) Zhang, Zewang; Cenel, C.; Hamid, R.; İlday, F. ÖmerAn intense research effort has been channelled into improving mode-locked Yb-fiber oscillators in recent years. Despite efforts in all-normal dispersion oscillators, dispersion management is evidently necessary to reach pulse durations below 50 fs. This is implemented most commonly with bulk optical components in Yb-doped fiber lasers. Increased robustness remains a valuable trait, for which all-fiber-integration is highly desirable. Photonic crystal fibers (PCF) with anomalous dispersion have small mode field diameters, enhancing nonlinear effects and usually are birefringent. The first mode-locked laser to incorporate a PCF was reported in 2002 [1]. However, mode-locking was not self-starting owing to the residual birefringence of the PCF Since then, a number of dispersion-managed Yb-doped fiber lasers using PCFs and all-fiber-integrated lasers have been reported. After 10 years, no all-fiber-integrated Yb-fiber laser has been demonstrated to support pulses below 60 fs [2]. © 2013 IEEE.Item 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, MehmetWe 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.Item Open Access The role of semiconductors in the future of optical fibers(Frontiers Research Foundation, 2023-07-21) Ordu, MustafaSemiconductors-core optical fibers have gathered attention for light guidance in the infrared spectrum. Cladded with glasses, fibers can be the ideal medium to transfer the favorable bulk properties of semiconductors into the micro/nano scaled one-dimensional form. The integration of these fibers with optical circuits, lasers and photonic crystals offers a wide variety of applications. In this perspective, the role of semiconductors in the future of optical fibers and their integration with photonic crystal structures are analyzed. The past and present efforts of semiconductor-core fibers are briefly reviewed, and the potential future application areas benefited by semiconductors as fiber materials are discussed.Item Open Access Thermally poled germanosilicate films with high second-order nonlinearity(IEEE, 2005) Özcan, A.; Digonnet, M. J. F.; Kino, G. S.; Ay, Feridun; Aydınlı, AtillaAccurate measurements of the second-order nonlinearity profile of thermally poled low-loss germanosilicate films grown on fused-silica substrates are reported, of interest as potential electro-optic devices. After optimization, we demonstrate a record high nonlinear coefficient d 33 ≈ 1.6 pm/V, a two-fold improvement over highest reported d 33 value in fused silica that we attribute to the presence of germanium.Item Open Access Ultralow-threshold up-converted lasing in oligofluorenes with tailored strong nonlinear absorption(Royal Society of Chemistry, 2015) Guzelturk, B.; Kanibolotsky, A.L.; Orofino-Pena, C.; Laurand, N.; Dawson, M.D.; Skabara P.J.; Demir, Hilmi VolkanNonlinear optical response in organic semiconductors has been an attractive property for many practical applications. For frequency up-converted lasers, to date, conjugated polymers, fluorescent dyes and small organic molecules have been proposed but their performances have been severely limited due to the difficulty in simultaneously achieving strong nonlinear optical response and high performance optical gain. In this work, we show that structurally designed truxene-based star-shaped oligofluorenes exhibit strong structure-property relationships enabling enhanced nonlinear optical response with favorable optical gain performance. As the number of fluorene repeat units in each arm is increased from 3 to 6, these molecules demonstrate a two-photon absorption cross-section as high as 2200 GM, which is comparable to that of linear conjugated polymers. Tailored truxene oligomers with six fluorene units in each arm (T6) show two-photon absorption pumped amplified spontaneous emission with a threshold as low as 2.43 mJ cm-2, which is better than that of the lowest reported threshold in organic semiconductors. Furthermore, we show a frequency up-converted laser using the newly designed and synthesized star-shaped oligomer T6 with a threshold as low as 3.1 mJ cm-2, which is more than an order of magnitude lower than that of any conjugated polymer. Thus, these oligomers with enhanced nonlinear optical properties are highly attractive for bio-integrated applications such as photodynamic therapy and in vivo bio-sensing. © The Royal Society of Chemistry 2015.