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

TL;DR

This paper demonstrates a novel method for transverse mode conversion in optical fibers using transient gratings induced by femtosecond laser pulses, enabling efficient optical switching with significantly reduced pulse energies.

Contribution

It introduces a new experimental approach for mode conversion utilizing optically induced transient gratings with low pulse energy requirements.

Findings

Successful experimental realization of mode conversion.

Reduced pulse energy requirement to 120 nJ.

Numerical simulations agree with experimental results.

Abstract

We present the experimental realization of transverse mode conversion in an optical fiber via an optically induced long-period grating. The transient gratings are generated by femtosecond laser pulses, exploiting the Kerr effect to translate intensity patterns emerging from multimode interference into a spatial refractive index modulation. Since these modulations exist only while the pump beam is present, they can be used for optical switching of transverse modes. As only a localized part of the grating was written at a time and the probe beam was co-propagating with the pump beam the required pulse energies could be reduced to 120\,nJ which is about a factor of 600 lower than in previous quasi-continuous-wave experiments. Accompanying numerical simulations allow a better understanding of the involved effects and show excellent agreement to the experimental results.