Laser Pulses In Optical Fiber Research Articles

Emergence of polynomial external potentials in solitonic hierarchies: Applications to the nonisospectral LPDE model

Inspired by the work of Akira Hasegawa, recently published in Optik 279 (2023) 170769, we set ourselves the task of explaining in detail how external nonstationary polynomial potentials appear in the nonisospectral NLSE hierarchy. We consider possible applications for observing solitonic regimes of propagation of ultrashort laser pulses in optical fibers. Our main goal is pedagogical, and our central point is the detailed derivation of new equations resulting from the application of the concept of nonautonomous solitons. It is revealed that complex potentials arise as polynomial series of the fourth degree of the spatial coordinate Uext(x,t)=α0(t)+α1(t)x+α2(t)x2+α3(t)x3+α4(t)x4, if the derivative of the spectral parameter is also expanded into a polynomial series of the spectral parameter up to the second order Λt(t)=λ0t+λ1(t)Λ+λ2(t)Λ2. It is predicted that new fourth-order nonlinear models arise if and only if the NLSE operator, the mKdV complex operator, and the fourth-order LPDE operators are connected by the extended Hirota constraint. We focus on exact analytical solutions and basic dynamic regimes of formation and interaction of new phase-modulated nonautonomous solitons of the nonisospectral LPDE model with fourth-order and time-dependent polynomial potentials.

Helical plasma filaments from the self-channeling of intense femtosecond laser pulses in optical fibers: publisher's note.

This publisher's note contains a correction to Opt. Lett.47, 1 (2022)10.1364/OL.445321.

Helical plasma filaments from the self-channeling of intense femtosecond laser pulses in optical fibers.

We experimentally and numerically study the ignition of helical-shaped plasma filaments in standard optical fibers. Femtosecond pulses with megawatt peak power with proper off-axis and tilted coupling in the fiber core produce plasma skew rays. These last for distances as long as 1000 wavelengths thanks to a combination of linear waveguiding and the self-channeling effect. Peculiar is the case of graded-index multimode fibers; here the spatial self-imaging places constraints on the helix pitch. These results may find applications for fabricating fibers with helical-shaped core micro-structuration as well as for designing laser components and three-dimensional optical memories.

Spatial distribution of the electric field of laser pulses in optical fibers having a gradient profile of the refractive index. Linear case

The aim of the present research is to investigate the spatiotemporal regime of propagation of three-dimensional optical pulses in fibers with spatial dependence of the refractive index. An exact analytical solution of the linearized equation is found. Numerical simulations are conducted of the solutions obtained.

Efficient generation of all-fiber femtosecond pulses at 1.7 μ m via soliton self-frequency shift

Soliton self-frequency shift (SSFS) is a nonlinear effect that generates wavelength-shifted laser pulses in optical fibers. Based on SSFS, we report the generation of ultrashort pulses emitting at 1.7-μm band in a common dispersion shifted fiber (DSF) pumped by an ultrafast Er-doped fiber laser. Through optimizing the DSF length, sub-200 fs pulses in the range from 1.70 to 1.74 μm have been achieved with >76% conversion efficiency. The maximum output power is 26.8 mW and the single pulse energy is up to 0.7 nJ. Numerically, simulations have been carried out to map the SSFS pulse evolution in DSF. The simulation results are in a good agreement with the experiment results, giving the feasibility of this method.

THIRD ORDER NONLINEAR EFFECT NEAR A DEGENERATE BAND EDGE

We describe the properties of a 1D anisotropic periodic structure, designed to have a band edge with fourth order degeneracy, called a degenerate band edge (DBE). A giant field resonance at the transmission peak frequency closest to this band edge has been verified by rigorous numerical calculation and is supported by experimental evidence. Simulations are presented of the consequences of a χ3 nonlinear index change at a DBE resonant frequency which can provide all-optical switching and transmission self-limiting.

Intra-pulse Raman frequency shift versus conventional Stokes generation of diode laser pulses in optical fibers

We report experimental observations of stimulated Raman scattering in a standard fiber using a directly modulated DFB semiconductor laser amplified by two erbium-doped fibers. The laser pulse width was variably controlled on a nanosecond-scale; the laser emission was separated into two distinct regimes: an initial transient peak regime, followed by a quasi steady-state plateau regime. The transient leading part of the pump pulse containing fast amplitude modulation generated a broadband Raman-induced spectral shift through the modulation instability and subsequent intra-pulse Raman frequency shift. The plateau regime amplified the conventional Stokes shifted emission expected from the peaks of the gain distribution. The output signal spectrum at the end of a 9.13 km length of fiber for the transient part extends from 1550 nm to 1700 nm for a pump pulse peak power of 65 W. We found that the Raman-induced spectral shift is measurable about 8 W for every fiber length examined, 0.6 km, 4.46 km, and 9.13 km. All spectral components of the broadband scattering appear to be generated in the initial kilometer of the fiber span. The Stokes shifted light generation threshold was higher than the threshold for the intra-pulse Raman-induced broadened spectra. This fact enables the nonlinear spectral filtering of pulses from directly modulated semiconductor lasers.

Experimental demonstration of the Fermi-Pasta-Ulam recurrence in a modulationally unstable optical wave.

Through a detailed spectral analysis of the propagation of square-shaped laser pulses in optical fibers, we provide the experimental demonstration of the Fermi-Pasta-Ulam recurrence phenomenon in modulationally unstable optical waves ruled by the nonlinear Schrödinger equation.

Temporal interference of coherent laser pulses in optical fibers

We report on collective effects for the train of optical pulses when a reproduction of the periodical pulse train occurs at some distance in dispersive medium. The reproduction of the initial temporal distribution can be treated as a temporal analog of the spatial Talbot effect. In experiment with a multimode fiber, the group of seven pulses lost its temporal shape converting in one broad pulse at the distance of 1200 m, while continuous train of pulse preserved its temporal structure.