All-optical nonlinear feedback devices derived from the negative nonlinear absorption effect in erbium–yttrium aluminum garnet crystals were demonstrated using a feedback ring resonator and an erbium-doped fiber amplifier. The output modulation degree depends on the dosage of erbium and the amplifier gain. The maximum value was 83% when the input modulation degree was 55%. The inverted output signal was amplified by approximately ten times as large 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 characterized by the property that optical signals for 1.53 μm light can be inverted and amplified.

Topics
Laser materials, Fiber amplifiers, Chemical elements
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