Enhanced Ultrafast Nonlinear Optics With Microstructure Fibers And Photonic Crystals

摘要

A broad class of nonlinear-optical phenomena enhanced in microstructure and photonic-crystal fibers has been studied both experimentally and theoretically as a part of this project. Hollow-core photonic crystal fibers capable of transporting sub-100-fs pulses of Ti: sapphire laser radiation in one of their transmission peaks centered around 800 nm have been designed and demonstrated. These fibers are shown to enhance self-phase modulation of submicrojoule 100-fs Ti: sapphire laser pulses, allowing a spectral bandwidth of 35 nm to be achieved with an 8-cm PCF sample. Two cascaded hollow-core photonic-crystal fibers with slightly shifted, but still overlapping transmission peaks are shown to function as an optical diode for ultrashort laser pulses. Submicrojoule 100-fs Ti: sapphire laser pulses with a spectrum falling within the passband of one of the fibers, but outside the passband of the second fiber, experience spectral broadening due to self-phase modulation in the first fiber. A part of this selfphase- modulation-broadened spectrum is then transmitted through the second fiber. Identical short pulses propagating in the opposite direction are blocked by the second fiber with a shifted passband. A forward-to-backward signal ratio exceeding 40 is achieved with the created photonic-crystal fiber diode for 0.9- J, 100-fs pulses of 800- nm Ti: sapphire laser radiation. Self-phase-modulation-induced spectral broadening of laser pulses in air-guided modes of hollow photonic-crystal fibers (PCFs) is shown to allow the creation of fiber-optic limiters for high- intensity ultrashort laser pulses. The performance of PCF limiters is analyzed in terms of elementary theory of self-phase modulation. Experiments performed with 100-fs microjoule pulses of 800-nm Ti: sapphire laser radiation demonstrate the potential of hollow PCFs as limiters for 10-MW ultrashort laser pulses and show different PCF modes.