High-order modes of photonic wires excited by the Cherenkov emission of solitons

Abstract

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.

Mode structure in continuum generation

“…The fibre used is typically multimoded at the pump and fundamental mode GVD zero wavelengths, however reports of higher order mode behaviour in the produced continuum are limited [7]- [12] and these other studies use very different fibre structures from our study. Third harmonic generation [7], four wave mixing [11] and Cherenkov radiation coupling [12] have been proposed as mechanisms to produce the mode generation.…”

“…Third harmonic generation [7], four wave mixing [11] and Cherenkov radiation coupling [12] have been proposed as mechanisms to produce the mode generation. Previous reports used structure data acquired by filtering out portions of the spectrum and imaging these with a camera.…”

Nonlinear optics in photonic nanowires

“…9 [9,55]. This Cherenkov emission has been used to excite high-order modes of photonic nanowires [56] and as a mechanism for parametric amplification [57].…”

Supercontinuum generation in a microstructured optical fiber by picosecond self Q-switched mode-locked Nd:GdVO4 laser

“…When the femtosecond laser is launched into the nonlinear MFs, various nonlinear optical effects including self-phase modulation (SPM), modulation instability (MI), higher-order soliton breakup, self-frequency shift by stimulated Raman scattering (SRS), and four-wave mixing (FWM), etc., will be induced to cause spectral broadening [5][6][7][8][9] or optical frequency conversion [3,4,[10][11][12][13]. The anti-Stokes emission from MFs can be efficiently generated by modifying the air holes and controlling the bire-fringent [3,4,10].…”

“…The anti-Stokes emission from MFs can be efficiently generated by modifying the air holes and controlling the bire-fringent [3,4,10]. Besides, the Cherenkov emission is ideally suited for selective coupling into the high order guided modes in MFs that are both experimentally and numerically demonstrated [11]. Through the mode control, the switching between the regime of broadband emission generation and the regime of isolated spectral components are experimentally observed [12].…”