A RESEARCH STUDY ON 3-D SOLITON AND PHOTONIC CRYSTAL FIBRE

Physics

We theoretically study broadband super continuum generation in photonic crystal fibers exhibiting two zero dispersion wavelengths and under continuous-wave pumping. We show that when the pump wavelength is located in between the zero-dispersion wavelengths, a wide and uniform spectral broadening is achieved through modulation instability, generation of both blue-shifted and red-shifted dispersive waves and subsequently through soliton self-frequency shift. This super continuum is therefore bounded by these two dispersive waves which allow the control of its bandwidth by a suitable tuning of the fiber dispersion. As a relevant example, we predict that broadband (1050–1600 nm) continuous-wave light can be generated in short lengths of micro structured fibers pumped by use of a 10-W Ytterbium fiber laser. Photonic crystal fibers with three and four zero-dispersion wavelengths are presented through special design of the structural parameters, in which the closing to zero and ultra-flattened dispersion can be obtained. The unique phase-matching properties of the fibers with three and four zero-dispersion wavelengths are analyzed. Variation of the phase-matching wavelengths with the pump wavelengths, pump powers, dispersion properties, and fiber structural parameters is analyzed. The presence of three and four zero-dispersion wavelengths can realize wavelength conversion of optical soliton between two anomalous dispersion regions, generate six phase-matching sidebands through four-wave mixing and create more new photon pairs, which can be used for the study of super continuum generation, optical switches and quantum optics. The effect of initial frequency chirp is investigated numerically to obtain efficient super continuum radiation in photonic crystal fibers (PCFs) with two closely spaced zero-dispersion wavelengths. The positive chirps, instead of zero or negative chirps are recommended because self phase modulation and four-wave mixing can be facilitated by employing positive chirps. In contrast with the complicated and irregular spectrum generated by negative-chirped pulse, the spectrums generated by positive-chirped pulses are wider and much more regular. Moreover, the saturated length of the PCF, corresponding to the maximal spectrum width, can be shortened greatly and the efficiency of frequency conversion is also improved because of initial positive chirps. Nearly all the energy between the zero-dispersion wavelengths can be transferred to the normal dispersion region from the region within the two zero-dispersion wavelengths provided that the initial positive chirp is large enough.

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.