RESUMO
Kerr beam cleaning in graded-index multimode fiber has been investigated in experiments with sub-nanosecond pulses and in experiments with femtosecond pulses at wavelengths where the dispersion is normal. We report a theoretical and experimental study of this effect with femtosecond pulses and anomalous dispersion. In this regime, only weak beam cleaning is observed experimentally, along with strong temporal evolution of the pulse. Numerical simulations exhibit the qualitative trends of the experiments.
RESUMO
We study theoretically the generation of photon pairs with controlled spectral correlations via the four-wave mixing process in graded-index multimode optical fibers (GIMFs). We show that the quantum correlations of the generated photons in GIMFs can be preserved over a wide spectral range for a tunable pump source. Therefore, GIMFs can be utilized as quantum-state-preserving tunable sources of photons. In particular, we have shown that it is possible to generate factorable two-photon states, which allow for heralding of pure-state single photons without the need for narrowband spectral post filtering. We also elaborate on the possibility of simultaneously generating correlated and uncorrelated photon pairs in the same optical fiber.
RESUMO
A short piece of commercial-grade SMF-28 optical fiber is pumped with a 680 ps high-peak power green laser. Red Stokes and blue anti-Stokes beams are generated spontaneously from vacuum noise in different modes in the fiber via intermodal four-wave mixing. Detailed experimental and theoretical analyses are performed and are in reasonable agreement. The large spectral shifts from the pump protect the Stokes and anti-Stokes from contamination by spontaneous Raman scattering noise. This work highlights the predictive power and limitations of a theoretical model to explain the experimental results for a process that relies on the amplification of quantum vacuum energy over more than 11 orders of magnitude.