Phase-matched four-wave mixing in higher-order modes of microstructure fibers allows unprecedentedly high efficiencies of anti-Stokes frequency conversion to be achieved for subnanojoule femtosecond laser pulses. 70-fs pulses of 790-nm radiation were used to generate an anti-Stokes component at 520-530 nm in a higher-order mode of a microstructure fiber with a 4.8-microm core. The maximum ratio of the anti-Stokes signal energy to the energy of the pump component in the output spectrum is estimated as 1.7.
Microstructure fibers are shown to provide a high efficiency of generation of mode-separable and frequencyconvertible supercontinuum of a high spectral and spatial quality, offering much promise as sources of broadband radiation for wave-mixing spectroscopy and time-resolved pump-probe measurements, and also for seeding optical parametric amplifiers. The long-wavelength and visible parts of supercontinuum emission generated by 40 fs pulses of 800 nm Ti : sapphire laser radiation in fused-silica microstructure fibers are shown to be spatially separated in microstructure-fiber modes. With an appropriate spectral filtering, bell-shaped modes of the long-wavelength section (∼720-900 nm) of the supercontinuum generated in a microstructure fiber with a small core diameter can be separated from either doughnut-like or bipartite modes of the visible part (∼400-600 nm) of this supercontinuum. This effect can be employed for the spectral slicing of single modes of supercontinuum emission from microstructure fibers. Frequency convertibility of spectrally sliced supercontinuum is demonstrated by experiments on sum-frequency generation in a non-linear crystal.
Existence of very high order guided modes of visible radiation is demonstrated for high-refractive-index-step fused silica submicron waveguide channels in microstructure fibers. Cherenkov emission of solitons produced by femtosecond laser pulses in such photonic wires is ideally suited for selective coupling into the high-order modes, which are extremely difficult to excite with the use of standard beam in-coupling optics.Output field patterns of radiation frequency-converted in smallcore waveguide channels in a microstructure fiber High-order waveguide modes [1] are interesting physical objects, which can serve as powerful tools for particle trapping [2,3], laser manipulation of biological species [4], and efficient multimode-phase-matched nonlinear-optical frequency conversion [5,6]. The number of modes in an optical fiber is controlled [1] by the waveguide parameterwhere k = 2π/λ, λ is the radiation wavelength, a is the fiber core radius,and n co and n cl are the refractive indices of the fiber core and the fiber cladding, respectively. The ratio of the fiber core size to the radiation wavelength and the index profile ∆ are thus the key factors determining the number of guided modes. In standard telecommunication fibers, the index step ∆ is most often low, providing a single-mode regime for the visible and near-infrared light with typical fiber core sizes of a few micrometers. Fiber nanotapers [7] and small-size fused silica waveguide channels in microstructure fibers [8,9] provide the limiting values of index step ∆ for fused silica waveguiding structures, allowing the existence of the maximum number of guided modes for a given a/λ ratio.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.