Browsing by Subject "Tapering"
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Item Open Access CO2 laser glass processing for high power fiber laser applications(Bilkent University, 2016-01) Şimşek, BartuHigh power lasers have been extensively used in industry, military, astrophysics and medicine for decades. Thanks to developments in optical ber technology in terms of transmittance, heat resistance, robustness, stability and power endurance, ber lasers have recently become more favourable compared to conventional laser types such as gas and solid state lasers. Furthermore, high power ber lasers possess advantageous features like compactness, robustness, all- ber and alignment-free operation. Besides advances in high power ber lasers, the structure and power endurance of the critical components as well as their integration quality have been improved. CO2 laser is one the most e ective source in glass processing of optical bers since it provides stable and homogeneous radiation resulting in a clean process. We have tailored optical bers to attain low-loss, high quality, mechanically stable integration points by using CO2 laser radiation. Moreover, we have produced high power ber laser components such as end-cap and ball lens for manipulating the ber laser output beam. By tapering the optical bers, we have fabricated pump and signal combiners which have mode eld adapting properties. The 7x1 pump combiner was integrated to the high power ber laser system developed in our laboratory. Pump source limited power handling capacity of this pump combiner was measured as 850 Wwith an overall e ciency of 98%. In addition, the same pump combiner was adapted to a high power ber laser system which was built by using an in-house fabricated active ber. Finally, we have fabricated a 3x1 laser combiner to combine two in-house ber lasers with an output power of 1 kW and 690 W at 1080 nm wavelength. The maximum combined power was measured as 893 W by using two ports of this combiner with a launched power of approximately 500 W from each of them. The overall e ciency of the combiner was calculated as 93%. On the whole, we have performed successful glass processing by using CO2 laser radiation. As a consequence of optimized, high quality tapering and splicing of optical bers, we have fabricated critical components for high power ber lasers such as end-cap, ball lens, pump and laser combiners.Item Open Access Development of multicore and tapered chalcogenide fibers for supercontinuum generation(Bilkent University, 2016-12) Saleh, Abba UsmanThe dramatic spectral broadening of an electromagnetic radiation as it propagates through a nonlinear medium is called Supercontinuum generation. Supercontinuum generation is indeed regarded as one of the prominent phenomenon in nonlinear optics and photonics with burgeoning applications in various fields such as spectroscopy, early cancer diagnostics, gas sensing, food quality control, uorescence microscopy e.t.c. Supercontinuum generation in optical fibers is however associated with three fundamental challenges: minimization of input power threshold, maximization of output power as well as output spectrum of a supercontinuum. Two unique fabrication approaches namely "Direct tapering" and "Multicore fibers" were proposed to address the aforementioned challenges. Chalcogenide nanowires were fabricated via direct tapering of chalcogenide glasses, and spectral broadening with extremely low peak power of 2 W was demonstrated. Multicore array of chalcogenide step index fibers were also fabricated using a new method. The fabricated step index fiber has a diameter 1.35 m which was engineered to have a zero dispersion wavelength (ZDW) around 1100 nm with a pump of center wavelength at 1550 nm .Using split step Fourier method, it was shown that the fiber possesses a great potential for severe spectral broadening. Supercontinuum generation with the as drawn fiber, encountered challenges as well as proposed solutions were demonstrated and discussed.Item Open Access Dynamic integration and network structure of the EMU sovereign bond markets(Springer, 2019) Şensoy, Ahmet; Nguyen, D. K.; Rostom, A.; Hacıhasanoğlu, E.In this paper, we propose a novel concept of correlation-based stable networks to empirically investigate the dynamic integration and network structure of the European Monetary Union (EMU) sovereign bond markets. The obtained results uncover a high degree of market integration between sample markets over the period preceding the recent financial crises, while segmentation is found afterwards. The stable network analysis shows, for its part, the existence of two different network structures before and after the onset of the European debt crisis, where the in-crisis network structure is characterized by two groups of countries with respect to their fiscal performance. In particular, Belgium is the unique vertex connecting the two groups, making it the channel for shock transmission in the event of worsening debt crisis in the EMU.