Ultrashort pulses (picoseconds or less), are characterized by a high peak intensity that usually leads to nonlinear interactions. Recently ultrashort pulses with orbital angular momentum have attracted great attention due to their wide field of applications, from super-resolution microcopy, optical tweezers and ultra-fast optical communications to quantum computing and astrophysics. A principal challenge here is the development of robust and effective methods for OAM generation. At the moment few techniques are known to obtain OAM beams in the free space arrangement cylindrical lenses, spiral phase plates or computer-generated holograms have been used. All those techniques imply that pulse is passing through an optical component and thus obtain dispersive broadening. We propose here a method and a device allowing formation of ultrashort optical vortices from an incident ultrashort pulse without its broadening or compensating the pulse chirp acquired previously. Potentially method and device will allow obtain ultrashort vortices shorter than incident pulse. Case study is presented based on spatio-temporal numerical simulation and analytical modeling.
Microstructured fibers have recently become popular due to their numerous applications for fiber lasers,1 super-continuum generationi2 and pulse reshaping.3 One of the most important properties of such fibers that is taken into account is its dispersion. Fine tuning of the dispersion (i.e. dispersion management) is one of the crucial peculiarities of the photonic crystal fibers (PCFs)4 that are particular case of the microstructured fibers.
During last years, there have been presented various designs of the PCFs possessing specially-designed dispersion shapes. 5-7 However, no universal technique exists which would allow tuning the PCF dispersion without using optimization methods.
In our work, we investigate the sensitivity of the PCF dispersion as respect to variation of its basic parameters. This knowledge allows fine-tuning the position of local maximum of the PCF dispersion while maintaining other properties unchanged.
The work is organized as follows. In the first section we discuss the dispersion computation method that is suitable for the global sensitivity analysis. The second section presents the global sensitivity analysis for this specific case. We also discuss there possible selection of the variable parameters.
We have investigated ultrashort parabolic pulse formation via passive nonlinear reshaping in normal dispersive optical fibers at 1550 nm. It was investigated parabolic pulse formation in the transient-state regime and in the steady-state regime. Numerical simulations have been made based on generalized nonlinear Schrödinger equation taking into account high-order dispersion terms and high order nonlinear terms. It was examined the applicability of different commercially available fibers for parabolic pulse formation at 1550 nm. It was found that small amount of positive second-order dispersion and quite sufficient third-order dispersion can restrict strongly the formation of parabolic pulses at 1550 nm. The most suitable fiber for pulse reshaping has been found.