All-optical nonlinear feedback devices derived from the negative nonlinearabsorption effect in erbium-yttrium aluminum garnet crystals

All-optical nonlinear feedback devices derived from the negative nonlinear absorption effect in erbium-yttrium aluminum garnet crystals were demonstra ted using a feedback ring resonator and an erbium-doped fiber amplifier. Th e output modulation degree depends on the dosage of erbium and the amplifie r gain. The maximum value was 83% when the input modulation degree was 55%. The inverted output signal was amplified by approximately ten times as lar ge as the input signal. The output modulation degree increased abruptly at an amplifier gain of more than 25 dB when it has feedback. The device was c haracterized by the property that optical signals for 1.53 mu m light can b e inverted and amplified. (C) 2000 American Institute of Physics. [S0003-69 51(00)03624-X].