Hamed Pourbeyram

Stimulated Raman scattering cascade spanning the wavelength range of 523 to 1750 nm using a graded-index multimode optical fiber

We report on the generation of a Raman cascade spanning the wavelength range of 523 to 1750 nm wavelength range in a standard telecommunication graded-index multimode optical fiber. Despite the highly multimode nature of the pump, the Raman peaks are generated in specific modes of the fiber, confirming substantial beam cleanup during the stimulated Raman scattering process.

Phase matching for spontaneous frequency conversion via four-wave mixing in graded-index multimode optical fibers

A detailed analysis of four-wave mixing (FWM) and its required phase-matching conditions in graded-index multimode optical fibers is presented. The analysis is relevant mainly for spontaneous frequency conversion and photon pair generation via FWM, when the fiber length is of the order of a meter or shorter, and the signal and idler are generated at large frequency separations from the pump. An analytic expression for calculating the phase mismatch occurring as a result of the waveguide dispersion among the pump, signal, and idler beams is derived, and it agrees well with independent numerical analysis. This expression simplifies calculations considerably, as it allows the prediction of the wavelengths of the signal and idler by using only the mode group number of the spatial modes involved in the FWM process and the refractive index profile of the fiber. The scaling of the signal–pump–idler frequency separations with the mode group numbers is explored. The abundance of the configuration degeneracies of the FWM process in graded-index multimode fibers indicates that nearly identical signal and idler frequencies can be obtained for many different pump, signal, and idler spatial mode profile combinations.

Detailed investigation of intermodal four-wave mixing in SMF-28: blue-red generation from green.

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.

Photon pair generation in multimode optical fibers via intermodal phase-matching

A single optical fiber may support the propagation of several spatial modes. It is shown how one could take advantage of intermodal phase matching to engineer a flexible source of photon pairs, in this manner offering a way to produce multiple wavelength-tunable pure single photons.

Nonlinear mode conversion for intermodal four-wave mixing Stokes and anti-Stokes in a multimode fiber

In this paper we study, both experimentally and by theory, a new nonlinear dynamic in multimode optical fiber where intermodal four-wave mixing (IM-FWM) and Kerr-induced nonlinear mode coupling (NLC) are strongly interacting. We show that presence of phase-matched IM-FWM and strong nonlinear mode coupling results in an unprecedented saturable mode conversion in the FWM anti-Stokes beam. We investigate the evolution of modal conversion as a function of fiber length and show that the result of this novel nonlinear dynamic is a controllable, length independent mode conversion. Our theoretical calculations suggest that the converted anti-Stokes beam can also be amplified via IM-FWM. We observe a mode conversion with an efficiency as high as 90 percent.

An analytical approach for calculating the FWM idler and signal wavelengths in a graded index multimode optical fiber

We present a simple yet powerful analytical approach for calculating the four-wave mixing signal and idler wavelengths in a graded-index multimode optical fiber using the core radius, core-cladding index step, and mode group numbers.

Detailed analysis of amplified spontaneous four-wave mixing in a multimode fiber

Detailed theoretical and experimental analyses of the amplified spontaneous FWM in a multimode optical fiber hint at strong non-universality of the third order Kerr nonlinear tensor as a function of its frequency components.