Tunable four-wave mixing enabled by a self-phase modulation of chirped pulses.

We experimentally demonstrate how a concatenation of the standard and microstructure fiber segments permits adjusting the four-wave mixing sideband position over a large spectral range by varying the chirp of an input pulsed pump at a fixed wavelength in the presence of a self-phase modulation. The blue- and redshifted sidebands can stand aside over ∼200 nm and ∼450 nm from the pump, respectively, which agrees well with the numerical simulations. We validate our approach by showing the feasibility of CARS imaging.

Continuous spatial self-cleaning in GRIN multimode fiber for self-referenced multiplex CARS imaging.

We demonstrate how spatial beam self-cleaning and supercontinuum generation in graded-index multimode optical fibers can be directly applied in multiplex coherent anti-Stokes Raman Scattering (M-CARS) spectroscopy. Although supercontinuum generation causes pump depletion mainly in the center of the beam, the partial recovery of the pump brightness due to self-cleaning may enable self-referenced M-CARS, with no additional delay lines to synchronize pump and Stokes waves. As a proof-of-principle, we report examples of imaging of single chemical compounds and polystyrene beads. The new scheme paves the way towards simpler M-CARS systems based on multimode fiber sources.

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.

Frequency-resolved spatial beam mapping in multimode fibers: application to mid-infrared supercontinuum generation.

We present a new, to the best of our knowledge, spatial-spectral mapping technique permitting measurement of the beam intensity at the output of a graded-index multimode fiber (GIMF) with sub-nanometric spectral resolution. We apply this method to visualize the fine structure of the beam shape of a sideband generated at 1870 nm by geometric parametric instability (GPI) in a GIMF. After spatial-spectral characterization, we amplify the GPI sideband with a thulium-doped fiber amplifier to obtain a microjoule-scale picosecond pump whose spectrum is finally broadened in a segment of InF3 optical fiber to achieve a supercontinuum ranging from 1.7 up to 3.4 µm.

Spatial beam self-cleaning and supercontinuum generation with Yb-doped multimode graded-index fiber taper based on accelerating self-imaging and dissipative landscape.

We experimentally demonstrate spatial beam self-cleaning and supercontinuum generation in a tapered Ytterbium-doped multimode optical fiber with parabolic core refractive index profile when 1064 nm pulsed beams propagate from wider (122 µm) into smaller (37 µm) diameter. In the passive mode, increasing the input beam peak power above 20 kW leads to a bell-shaped output beam profile. In the active configuration, gain from the pump laser diode permits to combine beam self-cleaning with supercontinuum generation between 520-2600 nm. By taper cut-back, we observed that the dissipative landscape, i.e., a non-monotonic variation of the average beam power along the MMF, leads to modal transitions of self-cleaned beams along the taper length.

Spatially dispersive amplification in a 12-core fiber and femtosecond pulse synthesis by coherent spectral combining.

A compact scheme is demonstrated for amplification and synthesis of ultrashort pulses by fiber amplifiers. Femtosecond pulses are split in 12 different spectral bands which are amplified separately in the 12 cores of a multicore ytterbium doped fiber. Combining the amplifier outputs together with the intensity and phase management of the spectral bands lead to short pulse synthesis with adjustable pulse shape. The scheme gave an x 92 enhancement in amplified power before the onset of nonlinear effects by comparison with standard stretcher free amplification in a single core fiber.

Spatially dispersive scheme for transmission and synthesis of femtosecond pulses through a multicore fiber.

A new scheme is presented for fiber transmission of ultrashort laser pulses. A dispersive device divides the input pulses into spatially separated spectral components which are individually launched in the different channels of a multicore fiber before being recombined at the output by a second dispersive device. The parallel transmission of narrow spectral bands avoids self-phase modulation and could be appropriate to deliver high peak power pulses. Phase management of the spectral bands by an active element offers recovery of the seed pulse duration at the fiber output as well as pulse shaping capabilities. Both are reported in a proof of concept experiment using 190 fs input pulses and a 5 cores polarization maintaining fiber. Extension of the concept to femtosecond pulses amplification is suggested.

Compact direct space-to-time pulse shaping with a phase-only spatial light modulator.

A very compact and innovative pulse shaper is proposed and demonstrated. The standard architecture for pulse shaping that is composed of diffraction gratings associated with an amplitude-phase spatial light modulator (SLM) is replaced by a single phase-only SLM. It acts as a pulse stretcher and as an amplitude and phase modulator at the same time. Preliminary experiments demonstrate the accurate control of amplitude and phase of shaped pulses.

Rainbow Archimedean spiral emission from optical fibres.

We demonstrate a new practical approach for generating multicolour spiral-shaped beams. It makes use of a standard silica optical fibre, combined with a tilted input laser beam. The resulting breaking of the fibre axial symmetry leads to the propagation of a helical beam. The associated output far-field has a spiral shape, independently of the input laser power value. Whereas, with a high-power near-infrared femtosecond laser, a visible supercontinuum spiral emission is generated. With appropriate control of the input laser coupling conditions, the colours of the spiral spatially self-organize in a rainbow distribution. Our method is independent of the laser source wavelength and polarization. Therefore, standard optical fibres may be used for generating spiral beams in many applications, ranging from communications to optical tweezers and quantum optics.