Diffraction-arrested soliton self-frequency shift of few-cycle laser pulses in a photonic-crystal fiber

The balance between diffraction and index-step guiding in photonic-crystal fibers is controlled by modifying the fiber structure, leading to different wavelength dependences of the effective mode area S-eff(lambda) and providing a mechanism to control nonlinear-optical phenomena. In optical fibers with a steep S-eff(lambda) profile, the guided mode of the light field tends to become much less compact with an increase in radiation wavelength, slowing down the Raman-induced soliton self-frequency shift of an ultrashort laser pulse. A 100-nm reduction of the soliton self-frequency shift is demonstrated for 6-fs input laser pulses.