RESUMEN
A phase sensing system fitted to the control of coherent laser beam array of large cross section is experimented. It is based on the use of a fiber bundle that collects a weak part of the synthetic wavefront, that scales it down (1/40) and that reshapes it in a more compact arrangement (2D to 1D array). Then, the reconfigured beam array can be analyzed by a small footprint system making the large laser beam array easier to phase-lock. The discrete laser array wavefront transmitted by the meter long fiber bundle was stabilized thanks to a multiple arm servo loop. Laser array phase locking was further ensured by random scattering through a diffuser, associated to an alternating projection algorithm. Six fiber laser beams constituting a 110 mm diameter synthetic aperture, were phase-locked with λ/16 accuracy.
RESUMEN
We experimentally demonstrate that spatial beam self-cleaning can be highly efficient when obtained with a few-mode excitation in graded-index multimode optical fibers. By using 160 ps long, highly chirped (6 nm bandwidth at -3dB) optical pulses at 1562 nm, we demonstrate a one-decade reduction of the power threshold for spatial beam self-cleaning, with respect to previous experiments using pulses with laser wavelengths at 1030-1064 nm. Self-cleaned beams remain spatio-temporally stable for more than a decade of their peak power variation. The impact of input pulse temporal duration is also studied.
RESUMEN
We report experimental results, showing that the Kerr beam self-cleaning of many low-order modes in a graded-index multimode fiber can be controlled thanks to optimized wavefront shaping of the coherent excitation beam. Adaptive profiling of the transverse input phase was utilized for channeling the launched power towards a specific low-order fiber mode, by exploiting nonlinear coupling among all guided modes. Experiments were carried out with 7 ps pulses at 1064 nm injected in a five meters long multimode fiber operating in the normal dispersion regime. Optimized Kerr beam self-cleaning of five different LP modes is reported, with a power threshold that increases with the mode order.
RESUMEN
We experimentally demonstrate that Kerr spatial self-cleaning of a pulsed beam can be obtained in an amplifying multimode optical fiber. An input peak power of 500 W only was sufficient to produce a quasi-single-mode emission from the double-clad ytterbium doped multimode fiber (YMMF) with non-parabolic refractive index profile. We compare the self-cleaning behavior observed in the same fiber with loss and with gain. Laser gain introduces new opportunities to achieve spatial self-cleaning of light in multimode fibers at a relatively low power threshold.
RESUMEN
We study a coupled cavity laser configuration where a passively Q-switched Nd:YAG microchip laser is combined with an extended cavity, including a doped multimode fiber. For appropriate coupling levels with the extended cavity, we observed that beam self-cleaning was induced in the multimode fiber thanks to nonlinear modal coupling, leading to a quasi-single mode laser output. In the regime of beam self-cleaning, laser pulse duration was reduced from 525 to 225 ps. We also observed a Q-switched mode-locked operation, where spatial self-cleaning was accompanied by far-detuned nonlinear frequency conversion in the active multimode fiber.
RESUMEN
Passive phase-locking of laser arrays is usually less efficient when the operating point is far above the laser threshold. We investigated the contribution due to the spectral filtering effect induced by the coupled cavities. Experiments carried out on a basic dual-arm laser as well as modeling show that some laser combining losses arise from the spectral filtering whose transmission windows have a non-uniform profile. A simple analytical model of the laser confirms this interpretation.
RESUMEN
A compact multicore ytterbium doped fiber amplifier has been implemented according to the spectral division scheme. It was shown that it allows amplification of pulses with about 40 nm wide spectrum. Compensation of the different spectral bands delay through bending and twist of the multicore ribbon fiber followed by appropriate setting of their phase permitted the synthesis of pulses close to 100 fs duration.
RESUMEN
A new approach is proposed for the adaptive phase-locking of a set of parallel laser beams. It is based on an optical conversion of phase differences in the array into an intensity pattern which feeds an optimization algorithm for iterated adjustments of the phase modulators. A numerical analysis and proof of principle experiment support the method and demonstrate its speed.
RESUMEN
A laser based on a ribbon multicore ytterbium doped fiber where different cores amplified different spectral bands, has been mode-locked with a single saturable absorber mirror. Tunable dual wavelength synchronized picosecond pulses were obtained. Compensation of differential cavity roundtrip times was achieved in the fiber.
RESUMEN
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.
RESUMEN
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.
RESUMEN
We have used a two-channel fiber laser array for the study of cophasing dynamics in a passively locked laser array for coherent combining. Starting from an in-phase laser emission, the array was unbalanced by a short phase perturbation introduced on one arm. The dynamics for recovery of phase locking and recovery of initial power of the laser array have been characterized. Cophasing was found to be quickly restored, in a few cavity rounds, before the gain dynamics brought back the steady-state power.
RESUMEN
We report co-phasing of 49 beams from a multicore fiber based on a spatial light modulator using a simple feedback loop control. A specific fiber of 7x7 Germanium doped cores was fabricated. The power carried by the far field main lobe of the phased array, in the continuous wave regime, amounts to 96% of its theoretical value. Femtoseconde pulses were also phase-locked with the same device configuration.
RESUMEN
We propose a new design of microstructured fiber combining large doped area (500 mum(2)), high rare earth concentration and single mode propagation despite the high core refractive index (n(Si) + 0.01). Actually, original guiding properties, based on a total internal reflection guidance regime modified by coupling between core and resonant cladding modes (close to the ARROW model) ensure single mode propagation. Moreover spectral properties which are largely governed by characteristics of high index cladding rods can be adjusted by properly choosing diameter and refractive index of the rods.
RESUMEN
We report an all solid state laser device producing tunable dual wavelength emission in the near IR region (1060nm, and 1550 nm) by use of an Er/Yb co-doped fiber. Generation of continuous-wave radiation around 630 nm is then demonstrated by extra-cavity sum frequency mixing in a Periodically Poled Lithium Niobate (PPLN) crystal. Quasi phase matching conditions are obtained over 7 nm to generate tunable coherent light in the red spectral range.