Optically induced mode conversion in graded-index fibers using ultra-short laser pulses

Hellwig T, Walbaum T, Fallnich C

Abstract

We propose the use of graded-index few- mode fibers for mode-conversion by long-period grat- ings (LPG) transiently written by ultrashort laser pulses using the optical Kerr effect. The mode interaction is studied by numerically solving the multi-mode coupled nonlinear Schrödinger equations. We present highly ef- ficient conversion of the LP 01 - into the LP 11 -mode pre- serving the pulse shape in contrast to previous results in step-index fibers. Furthermore, mode conversion us- ing different wavelengths for inducing and probing the LPG is shown. Due to the flat phase-matching curve of the examined modes in the graded-index fiber, mode- conversion can be observed for probe center wavelengths of 1100nm up to 1800nm with a write beam centered around 1030nm. Therefore, a complete separation of the probe from the write beam should be possible as well as the application of optically induced guided mode conver- sion for all optical modulation across a broad wavelength range.