Optical fiber modes using stimulated four photon mixing

Stimulated four photon mixing has been used to excite separately all the modes of a ten-mode optical fiber. Photographs were taken and the mode intensities scanned with a moving pinhole. Measured intensities were found to agree well with the intensities calculated for an ideal guide with an abrupt core-cladding interface. In addition a locking effect was observed in which two separate Stokes:anti-Stokes pairs, which normally occur at slightly different frequency shifts from the pump, locked together at the same frequency.