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

Abstract

We propose the use of graded-index few-mode fibers for mode-conversion by long-period gratings (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 efficient conversion of the LP01-into the LP11-mode preserving the pulse shape in contrast to previous results in step-index fibers. Furthermore, mode conversion using 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 1100 nm up to 1800 nm with a write beam centered around 1030 nm. Therefore, a complete separation of the probe from the write beam should be possible as well as the application of optically induced guided mode conversion for all optical modulation across a broad wavelength range.

Experimental realization of femtosecond transverse mode conversion using optically induced transient long-period gratings

“…In numerical studies of femtosecond mode-conversion scenarios a conversion efficiency of about 77% for identical probe and pump pulse lengths as used in our experiments, and more than 90% for longer pump than probe pulses, have already been demonstrated [9,12]. In order to get a better understanding why the experimentally observed mode-conversion efficiency differed from the numerical results the involved ultrashort pulses were studied in more detail: It was identified that the intensity auto-correlation of the pulses in use for the experiments revealed significant and unavoidable energy in a structure surrounding the 400 fs pulse up to delays of about 5 ps.…”

“…We will therefore continue to use numerical simulations parallel to experiments for the identification of the best suited nonlinear platform for all-optical mode switching. Currently we are eliminating the possible cross-talk of pump and probe beam originating from nonlinear polarization rotation by exploiting a dichroic setup that we already numerically studied elsewhere [12,15].…”

Spatiotemporal mode-locking in multimode fiber lasers

“…Recent years have seen increased interest in linear and nonlinear wave propagation in multiple transverse modes, particularly in multimode (MM) optical fibers (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16) and largely in anticipation of spatial division multiplexing (17) for telecommunications and as a platform for new fiber laser sources. The presence of disorder (through random linear mode coupling) also connects MM fibers to the field of random lasers and, more broadly, to the optical properties of complex media (18)(19)(20)(21).…”

Visible‐Wavelength Spatiotemporal Mode‐Locked Fiber Laser Delivering 9 ps, 4 nJ Pulses at 635 nm

“…So far, the complex spatiotemporal profiles and the additional spatial degree of freedom induced by the implementation of multimode fibers have attracted intensive attention, as the STML multimode fiber lasers have not only fueled the development of ever‐evolving optical telecommunication systems and high‐power applications, [ 1 ] but also contributed to the specific scientific research based on multimode nonlinear fiber optics. [ 2–11 ] It is worth pointing out that STML in multimode fiber lasers have been first found by L. G. Wright et al. in 2017, [ 12–14 ] but the experimental demonstrations are mostly limited to the near‐infrared spectral region.…”