1. Designing Dispersion- and Mode-Area-Decreasing Holey Fibers for Soliton Compression M.L.V.Tse, P.Horak, F.Poletti, and D.J.Richardson Optoelectronics Research Centre, University of Southampton, Southampton, SO17 1BJ, United Kingdom. Email: mlt@orc.soton.ac.uk What is a Holey Fiber? Soliton Compression Theory:  Core d Cladding Air holes Conventional Optical Fiber: Holey Fiber: Holey fiber basic parameters: Hole size (d) Hole-to-hole spacing or pitch (  ) Air-filling fraction (d/  ). Advantages: Small cross section  Large nonlinearity Dispersion control Long optical pulses Nonlinear tapered holey fiber Dispersion, Dispersion Slope and Effective Area Contour maps: Abstract Compression of soliton pulses propagating in optical fibers with decreasing dispersion is a well-established technique [1]. Using holey fibers it is possible to decrease dispersion (D) and effective mode area (A eff ) simultaneously, which potentially offers a greater range of variation in soliton compression factors. Moreover, soliton compression in new wavelength ranges below 1.3  m can be achieved in holey fibers. Recently, this has been successfully demonstrated with femtosecond pulses at 1.06  m [2]. Here, we investigate numerically the adiabatic compression of solitons at 1.55  m in holey fibers which exhibit simultaneously decreasing in D and A eff. We identify some of the limitations and propose solutions by carefully selecting paths in contour maps of D and A eff in the (d/ ,  ) grid. Compression factors >10 are achieved for optimum fiber parameters. Contour map for dispersion (ps/nm/km), dispersion slope (ps/nm 2 /km) and effective area (  m 2 ) versus pitch  and d/  for holey fibers of hexagonal geometry at 1.55  m wavelength. Contour map for adiabatic compression factors versus pitch  and d/  for holey fibers of hexagonal geometry at 1.55  m wavelength. (Normalized to the top left corner of the map, which has the largest value of D*A eff ) (green dotted line represents the single mode ‘SM’ and multi-mode ‘MM’ boundary) D= 0 D= 25 D= 50 D= 75 A eff = 70 A eff = 30 A eff = 15 A eff = 7 A eff = 3 D s = 0.05 D s = 0 D s = -0.2 For given fiber parameters and pulse energy, the width of a fundamental soliton is Conclusions We have investigated adiabatic compression of femtosecond solitons in silica holey fibers of decreasing dispersion and effective mode area. These parameters are directly related to the structural design parameters  and d/ . A compression factor of 12 has been obtained for low-loss fibers in the adiabatic regime. A method for minimizing the fiber length required for adiabatic compression in the presence of propagation losses is suggested. References [1] S. V. Chernikov, E. M. Dianov, D. J. Richardson and D. N. Payne, “Soliton pulse compression in dispersion-decreasing fiber,” Opt. Lett. 18, 476 (1993). [2] M. L. V. Tse, P. Horak, J. H. V. Price, F. Poletti, F. He, and D. J. Richardson, “Pulse compression at 1.06  m in dispersion-decreasing holey fibers,” Opt. Lett. 31, 3504 (2006). (1) Adiabatic compression, E sol = constant.  0  D *A eff In tapered holey fibers, ( , d/  )(z)  D *A eff (z) Path 1 D: 25  5 ps/nm/km A eff : 70  7  m 2 Expected compression factor: 50 Limitations: Dispersion slope  ZDW close to soliton Raman SSFS effect Therefore, require paths that have D s ~0 near the end and a smaller A eff ratio Path 2 D: 25  5 ps/nm/km Aeff: 75  30  m 2 Ds~ 0 at fiber end Long fiber, (50 m), no loss Compression factor: 12.5 Numerical simulation agrees with theory Length Considerations Fiber loss  soliton broadening Require short fiber length Trade-off with adiabaticity Optimize length using constant effective gain method Example: Path 2 Not optimizedOptimized Input pulse: 400 fs Simulated spectrum, no Raman effect.Simulated spectrum, D s = 0.