Yavuz Ozturk

A magnetic non-reciprocal isolator for broadband terahertz operation

A Faraday isolator is an electromagnetic non-reciprocal device, a key element in photonics. It is required to shield electromagnetic sources against the effect of back-reflected light, as well as to limit the detrimental effect of back-propagating spontaneous emissions. A common isolator variant, the circulator, is widely used to obtain a complete separation between forward- and backward-propagating waves, thus enabling the realization of a desired transfer function in reflection only. Here we demonstrate a non-reciprocal terahertz Faraday isolator, operating on a bandwidth exceeding one decade of frequency, a necessary requirement to achieve isolation with the (few-cycle) pulses generated by broadband sources. The exploited medium allows a broadband rotation, up to 194°/T, obtained using a SrFe12O19 terahertz-transparent permanent magnet. This in turn enables the design of a stand-alone complete terahertz isolator without resorting to an external magnetic field bias, as opposed to all the optical isolators realized so far.

Terahertz Faraday rotation in a magnetic liquid: High magneto-optical figure of merit and broadband operation in a ferrofluid

We report on the demonstration of a high figure of merit (FOM) Faraday rotation in a liquid in the terahertz (THz) regime. Using a ferrofluid, a high broadband rotation (11 mrad/mm) is experimentally demonstrated in the frequency range of 0.2–0.9 THz at room temperature. Given the low absorption of the liquid, a high magneto-optical figure of merit (5-16 rad.cm/T) is obtained.

Skirting terahertz waves in a photo-excited nanoslit structure

Terahertz fields can be dramatically enhanced as they propagate through nanometer-sized slits. The enhancement is mediated by a significant accumulation of the induced surface charges on the surrounding metal. This enhancement is shown here to be dynamically modulated while the nanoslits are gradually shunted using a copropagating optical beam. The terahertz fields are found to skirt the nanoscale photo-excited region underneath the slits, scattering to the far field and rigorously mapping the near field.

Cerium-Doped Yttrium Iron Garnet Thin Films Prepared by Sol-Gel Process: Synthesis, Characterization, and Magnetic Properties

We studied here synthesis, characterization, and magnetic properties of YIG (yttrium-iron-garnet, Y3Fe5O12) and Ce-doped YIG (CexY3−xFe5O12) thin films prepared by using a sol–gel technique for magneto-optical applications. Pure YIG and Ce-doped YIG films were deposited on a glass and Si (100) substrates out of a solution prepared from Ce, Y, and Fe-based precursors, solvent, and chelating agent at low temperature using the sol-gel technique. Prior to coating process, solution characteristics that influence the intended thin film structure were determined using turbidimeter, pH meter, and rheometer machines. Film thickness was monitored with varying sol-gel solution’s properties and spin coating’s process parameters. Since we mainly want to improve the magnetic properties of our films, an optimum sol-gel solution containing cerium, yttrium, and iron precursors were found, and a garnet phase was formed after annealing at temperatures between 700 and 1,000° C for 2 h in air. The thermal, structural, and microstructural properties of the films were characterized using DTA/TG, XRD, and SEM-EDS. The magnetic properties of the films produced by doping with Ce with an optimal process conditions were investigated through VSM device. The films include micro and nanosize CeO2 regions because of using partially dissolved Ce precursor in the solution. Our preliminary study revealed that a significant improvement in magnetic properties of polycrystalline YIG thin films have been achieved through the substitution of Ce.

Terahertz magnetic modulator based on magnetically clustered nanoparticles

Random orientation of liquid-suspended magnetic nanoparticles (Ferrofluids) gives rise to a zero net magnetic orientation. An external magnetic field tends to align these nanoparticles into clusters, leading to a strong linear dichroism on a propagating wave. Using 10 nm-sized Fe3O4, we experimentally realize a polarization-sensitive magnetic modulator operating at terahertz wavelengths. We reached a modulation depth of 66% using a field as low as 35 mT. The proposed concept offers a solution towards fundamental terahertz magnetic modulators.

Synergetic effect of antimony trioxide on the flame retardant and mechanical properties of polymer composites for consumer electronics applications

Nowadays polymers are used in wide range applications of industries. Parts of the electronic devices composed of polymer materials can be easily ignited because they are susceptible to flame. In this study, it was aimed to produce flame retardant nanocomposite materials by reinforcing halogen-free inorganic additives and to use in components of electronic devices. Within this scope, halogen-free nano sized milled huntite/hydromagnesite and antimony trioxide nanoparticles were reinforced in polymer matrix. The composites reinforced in various ratios were produced using a twin screw extruder. These samples were obtained by the method of injection molding from the extruded granules for the flame retardant test. Structural, morphological, thermal, mechanical and flame retardancy properties of samples were characterized by XRD, SEM, FTIR, DTA-TG, mechanical and flame retardant measurement. It is found that the inorganic reinforcement minerals improved the flame retardant properties and thermal stability of polymer nanocomposites depending on the amount of additives. The huntite/hydromagnesite and antimony trioxide effectively reduce the flammability of the ABS composites utilizing synergism by achieving UL94/V-0 classification.

Effect of pH and annealing temperature on the structural and magnetic properties of cerium-substituted yttrium iron garnet powders produced by the sol-gel method

Abstract Cerium substituted yttrium iron garnet (Ce0.2Y2.8Fe5O12; Ce-YIG) nanoparticles were produced via the sol-gel method from solutions of Ce-, Y- and Fe-based precursors, a solvent and a chelating agent. The solutions were dried at 200°C and heat treated at temperatures between 800 °C and 1400°C for 3 h in air. The effects of pH and annealing temperature on the structure, phase formation, magnetic properties and crystallite size were investigated. A cubic YIG phase was obtained for the sample annealed at 1400 °C. The presented results showed that the pH value of the starting solution affects the crystal size and consequently, the saturation magnetization.

Sub-wavelength terahertz beam profiling of a THz source via an all-optical knife-edge technique

Terahertz technologies recently emerged as outstanding candidates for a variety of applications in such sectors as security, biomedical, pharmaceutical, aero spatial, etc. Imaging the terahertz field, however, still remains a challenge, particularly when sub-wavelength resolutions are involved. Here we demonstrate an all-optical technique for the terahertz near-field imaging directly at the source plane. A thin layer (<100 nm-thickness) of photo carriers is induced on the surface of the terahertz generation crystal, which acts as an all-optical, virtual blade for terahertz near-field imaging via a knife-edge technique. Remarkably, and in spite of the fact that the proposed approach does not require any mechanical probe, such as tips or apertures, we are able to demonstrate the imaging of a terahertz source with deeply sub-wavelength features (<30 μm) directly in its emission plane.

Polarization-sensitive magnetic field induced modulation of broadband THz pulses in liquid

We demonstrate broadband THz modulation in liquid under the applications of suitable magnetic fields. 65% modulation has been obtained using 50mT. The modulation is polarization sensitive and achieved thanks to a magnetic-induced medium anisotropy.

OLED TV İçin Yarım Köprü LLC Rezonans Dönüştürücü Güvenilirlik Analizi

Bu calismada 65’’ ekran AMOLED TV icin yarim kopru LLC rezonant DC-DC donusturucu tasarimi gerceklestirilmistir. Yapilan tasarimin ana amaci, optimum guvenilirlik duzeyinin elde edilerek uygun MTBF (Mean-time between failure – ariza yapana kadar ortalama omur suresi) suresine ulasabilmektir. Tasarlanan guc kartinin ve kritik devre bilesenlerinin termal, EMC ve elektriksel testlerini kapsayan guvenilirlik testleri gerceklestirilmistir. Ayrica farkli anahtarlama frekanslarinda devrenin calisma karakteristigini incelemek amaciyla PSIM programi kullanilarak benzetim analizleri gerceklestirilmistir. Tum bu benzetim ve deneysel calismalar sonucunda 120.215 saat MTBF degeri ile on yilin uzerinde ust duzey guvenilirlik elde edilmistir.