Designing Dispersion- and Mode-Area-Decreasing Holey Fibers for Soliton Compression
M.L.V.Tse, P.Horak, F.Poletti, and D.J.RichardsonOptoelectronics Research Centre, University of Southampton, Southampton, SO17 1BJ, United Kingdom. Email: [email protected]
What is a Holey Fiber?
Soliton Compression Theory:
Cored
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 (Aeff) 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 Aeff. We identify some of the limitations and propose solutions by carefully selecting paths in contour maps of D and Aeff in the (d/, ) grid. Compression factors >10 are achieved for optimum fiber parameters.
Contour map for dispersion (ps/nm/km), dispersion slope (ps/nm2/km) and effective area (m2) 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*Aeff) (green dotted line represents the single mode ‘SM’ and multi-mode ‘MM’ boundary)
D= 0
D= 25
D= 50
D= 75
Aeff= 70
Aeff= 30
Aeff= 15
Aeff= 7
Aeff= 3
Ds= 0.05
Ds= 0
Ds= -0.2
• For given fiber parameters and pulse energy, the width of a fundamental soliton is
sol
eff
Ecn
DA
22
3
02
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, Esol= constant.
• 0 D *Aeff
• In tapered holey fibers, (, d/)(z) D *Aeff(z)
Path 1
• D: 25 5 ps/nm/km
• Aeff: 70 7 m2
• Expected compression factor: 50
Limitations:
• Dispersion slope ZDW close to soliton
• Raman SSFS effect
• Therefore, require paths that have Ds~0 near the end and a smaller Aeff ratio
Path 2
• D: 25 5 ps/nm/km
• Aeff: 75 30 m2
• 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
constz
A
Az
D
DD
cg
opt
eff
effopteff
2
1
2
122
20
Example: Path 2
Not optimized Optimized
Input pulse: 400 fs
Simulated spectrum, no Raman effect. Simulated spectrum, Ds= 0.