The present paper describes a novel systematic solution to the problem of controlling the chromatic dispersion and dispersion slope in photonic crystal fibers (PCFs), using a structurally-simple PCF with a defected-core. By adjusting the size of the central air-hole defect we can successfully design an ultra-flattened PCF with low confinement losses, as well as small effective mode area. The design strategy is based on the mutual cancellation between the waveguide and the material dispersions of the PCF, by varying the size of the central defected region in the core. The verification of the ultra-flattened chromatic dispersion property of the proposed PCF is ensured with an accurate full-vector finite element method with anisotropic perfectly matched layers. The ultra-flattened dispersion feature, as well as the low confinement losses and the small effective mode area are the main advantages of the proposed PCF structure, making it suitable as a chromatic dispersion controller dispersion compensator, or as candidate for nonlinear optical applications.

We propose and numerically investigate the operation of a novel class of polarization-independent splitters based on the photonic crystal fiber (PCF) technology. The proposed polarization-independent feature of the PCF splitter is realized by uniformly distributed elliptically-shaped air-holes in the cladding of a dual-core PCF. The design procedure follows a rigorous synthesis protocol based on exact equations for describing the wavelength de-coupling mechanism, and on full-vectorial finite element as well as beam propagation methods for optical characterization of PCFs. The compact de-coupling lengths as well as the low cross-talk over appreciable optical bandwidths are the main advantages of the proposed PCF splitter. The proposed device can be employed in reconfigurable optical communication systems for performing wavelength de-multiplexing operation, especially for fiber-to-the-home applications, as well as the emerging passive optical network applications.

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Abstract:The present paper describes a novel systematic solution to the challenging task of realizing photonic crystal fibers (PCFs) with flat chromatic dispersion, low leakage losses, and large mode area, mainly for applications as information carriers in wide-band high speed optical transmission systems. The proposed design strategy is based on the existence of an artificially-defected air-hole ring in the cladding and on the modulation of the refractive index of the core by assembling additional defected air-holes in the central core region of the fiber. The validation of the proposed design is carried out by adopting an efficient full-vectorial finite element method with perfectly matched layers for accurate characterization of PCFs. The remarkable flat chromatic dispersion as well as the large mode area and the low leakage losses are the main advantages of the proposed PCF structure, making it an ideal candidate for performing wavelength division multiplexing operation in reconfigurable optical transmission systems or as an information delivering platform in high speed optical communication systems. Typical characteristics of the newly proposed PCF are: flattened chromatic dispersion of 6.3±0.5 ps/km/nm in the S+C+L telecommunication band, and effective mode area as large as 100 μm 2 in the same wavelength range. We additionally provide numerical data about the performance of the proposed PCF in splicing mode as well as during macrobending operation and we give qualitative information regarding the sensitivity of the proposed transmission platform to structural disorders of the design parameters. A. Ferrando, E. Silvestre, P. Andres, J. J. Miret, and M. V. Andres, "Designing the properties of dispersionflattened photonic crystal fibers," Opt. Express 9, 687-697 (2001), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-9-13-687. 10. T. Yamamoto, H. Kubota, S. Kawanishi, M. Tanaka, and S. Yamaguchi, "Supercontinuum generation at 1.55 μm in a dispersion-flattened polarization-maintaining photonic crystal fiber," Opt. Express 11, 1537-1540 (2003), http://www.opticsinfobase.org/abstract.cfm?URI=oe-11-13-1537. 11. K. Saitoh and M. Koshiba, "Highly nonlinear dispersion-flattened photonic crystal fibers for supercontinuum generation in a telecommunication window," Opt. Express 12, 2027-2032 (2004), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-10-2027. 12. K. Saitoh, N. Florous, and M. Koshiba, "Ultra-flattened chromatic dispersion controllability using a defected-core photonic crystal fiber with low confinement losses," Opt. ©2005 Optical Society of America

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