Frequency-resolved spatial beam mapping in multimode fibers: application to mid-infrared supercontinuum generation.

Area of Science:

• Optics and Photonics
• Fiber Optics
• Nonlinear Optics

Background:

• Graded-index multimode fibers (GIMF) are crucial for optical signal transmission.
• Geometric parametric instability (GPI) is a phenomenon that can generate new frequencies in optical fibers.
• Characterizing the spectral and spatial properties of light generated through GPI is essential for understanding and controlling nonlinear optical processes.

Purpose of the Study:

• To introduce a novel spatial-spectral mapping technique for analyzing light in GIMF.
• To visualize the detailed beam shape of a sideband generated by GPI in a GIMF.
• To characterize the spectral broadening of a GPI-generated sideband into a supercontinuum.

Main Methods:

• Development of a spatial-spectral mapping technique with sub-nanometric spectral resolution.
• Application of the technique to visualize the beam structure of a 1870 nm GPI sideband in a GIMF.
• Amplification of the GPI sideband using a thulium-doped fiber amplifier.
• Spectral broadening of the amplified sideband in an InF3 optical fiber to generate a supercontinuum.

Main Results:

• Successful measurement of beam intensity at the GIMF output with sub-nanometric spectral resolution.
• Visualization of the fine structure of the GPI-generated sideband beam shape.
• Generation of a microjoule-scale picosecond pump from the GPI sideband.
• Creation of a supercontinuum spanning from 1.7 to 3.4 µm.

Conclusions:

• The developed spatial-spectral mapping technique provides unprecedented detail in analyzing light in GIMF.
• The technique enables detailed visualization of nonlinear phenomena like GPI sidebands.
• The study demonstrates a pathway to generate broadband supercontinuum light from GPI sidebands in multimode fibers.