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

: Hellwig, T.; Schnack, M.; Walbaum, T.; Dobner, S.; Fallnich, C.

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Optics Express 22 (2014), Nr.21, S.24951-24958
ISSN: 1094-4087
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer IOF ()

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.