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Afzal M.I.,Gwangju Institute of Science and Technology | Alameh K.,Edith Cowan University | Lee Y.T.,Advanced Photonics Research Institute
IEEE Journal on Selected Topics in Quantum Electronics

We experimentally generate an optical frequency comb with a repetition rate of ∼43 GHz using an all-passive fiber cavity operating in varying normal dispersion regime and pumped by a multimode laser diode. Coupling of four fiber segments with different dispersion coefficients and core diameters along a ring cavity enhances the spectral broadening at a low threshold pump power. Self-induced modulation instability is experienced due to cross phase modulation that results from the interaction of co-propagating optical signals inside the cavity. Stabilization of the two fundamental modes that are phase matched with higher order modes enables the amplification of the weakly modulated stokes and antistokes modes through dissipative four wave mixing, which results in the formation of a frequency comb of constant mode spacing of 0.136 nm. Phase locked frequency modes consisting of ∼250 comb lines covering a spectral range from 966 to 1000 nm centered at 978.512 nm are synthesized and reported for the first time. © 1995-2012 IEEE. Source

Jung G.B.,Korea University | Cho Y.J.,Korea University | Myung Y.,Korea University | Kim H.S.,Korea University | And 3 more authors.
Optics Express

THz emission was observed from the vertically aligned silicon nanowire (Si NW) arrays, upon the excitation using a fs Ti-sapphire laser pulse (800 nm). The Si NWs (length = 0.3 ∼9 μm) were synthesized by the chemical etching of n-type silicon substrates. The THz emission exhibits significant length dependence; the intensity increases sharply up to a length of 3 μm and then almost saturates. Their efficient THz emission is attributed to strong local field enhancement by coherent surface plasmons, with distinctive geometry dependence. © 2010 Optical Society of America. Source

Vukovic D.,Technical University of Denmark | Vukovic D.,University of Sydney | Schroder J.,University of Sydney | Schroder J.,RMIT University | And 7 more authors.
Optics Express

We experimentally demonstrate compensation of nonlinear distortion caused by the Kerr effect in a 3 × 32-Gbaud quadrature phaseshift keying (QPSK) wavelength-division multiplexing (WDM) transmission system. We use optical phase conjugation (OPC) produced by four-wave mixing (FWM) in a 7-mm long silicon nanowire. A clear improvement in Q-factor is shown after 800-km transmission with high span input power when comparing the system with and without the optical phase conjugation module. The influence of OSNR degradation introduced by the silicon nanowire is analysed by comparing transmission systems of three different lengths. This is the first demonstration of nonlinear compensation using a silicon nanowire. © 2015 Optical Society of America. Source

Choi S.-H.,Kyungpook National University | Sohn I.-B.,Advanced Photonics Research Institute | Lee H.,Kyungpook National University
International Journal of Precision Engineering and Manufacturing

A femtosecond laser has been used to produce spatially confined micromachining on mold stainless steel STAVAX. We investigated femtosecond laser-induced line structuring on mold stainless steel STAVAX using the laser scanning mode with various scanning speeds, various fluences and two polarization configurations. The damage threshold fluence of single pulse irradiation (F th) was measured to be about 80 mJ/cm 2. The damage threshold fluence of the scanning mode was approximately identical (0.75 F th~1.25 F th) to that of the single pulse irradiation. However, a fluence of 2.50 F th was necessary to induce continuous line structures for high scanning speeds and a fluence of 1.25 F th was required to induce continuous line structures for low scanning speeds. The width of laser-machined lines increased with the irradiation fluence and decreased with the scanning speed regardless of the polarization configuration. The formation of laser-induced periodic structures (termed "ripple") was examined using various laser parameters. It was clear that the formation of the ripple was governed by the irradiation fluence and the scanning speed of the beam. We were able to produce nano-scale structures in large areas by employing multiple line irradiations with the laser beam. © KSPE and Springer 2012. Source

Jeong T.M.,ASCR Institute of Physics Prague | Jeong T.M.,Advanced Photonics Research Institute | Jeong T.M.,Korea Basic Science Institute | Weber S.,ASCR Institute of Physics Prague | And 4 more authors.
Optics Express

The focusing property of a focal spot of a femtosecond laser pulse is presented under tight focusing conditions (below f-number of 1). The spatial and temporal intensity distributions of a focused electric field are calculated by vector diffraction integrals and coherent superposition method. The validity of the calculation method is examined by comparing the intensity distribution obtained under a high f-number condition to that obtained with the fast Fourier transform method that assumes the scalar paraxial approximation. The spatial and temporal modifications under tight focusing conditions are described for a focused femtosecond laser pulse. The calculation results show that a peak intensity of about 2.5×1024 W/cm2 can be achievable by tightly focusing a 12-fs, 10 PW laser pulse with a f/0.5 parabolic optic. The precise information on intensity distributions of a femtosecond focal spot obtained under a tight focusing condition will be crucial in assessing a focused intensity and in describing the motion of charged particles under an extremely strong electric field in ultra-relativistic and/or relativistic laser matter-interaction studies. © 2015 Optical Society of America. Source

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