Negative amplification of optical signal derived from negative nonlinear absorption effect in Er-doped fibers
Yoshinobu Maeda, Takao Sakakibara, Masatoshi Migitaka
A reversion of optical signal is observed in a 470 ppm Er-doped fiber with more than 2 m in length, and the negative nonlinear absorption (NNA) effect is confirmed. The negative amplification, which is the ratio of modulation indexes between the transmitted and input lights, is confirmed, and the maximum negative amplification of −2.9 is obtained. It is found from the measurements the room (300 K) and liquid nitrogen temperatures (77 K) that the negative effect is larger at room temperature than at liquid nitrogen temperature. The NNA effect is observed in the wavelength range from 784 to 792 nm and with incident laser power intensities ranging from 3 mW/cm2 to 14 mW/cm2. The NNA effect is observed for the modulation frequency up to 1 MHz, and for high frequency the transmitted waveform becomes asymmetric. The polarization dependence of the effect is also confirmed. The mechanism of the NNA effect is considered mainly due to the enhanced absorption caused by the spontaneous emission in the excited three-level system. Since the emission light can be propagated in the fiber with very low loss, the NNA effect can be effectively generated causing the negative amplification of the optical signal. © 1998 Scripta Technica. Electron Comm Jpn Pt 2, 80(7): 8–17, 1997
Electronics and Communications in Japan (Part II Electronics)•Jul 1, 1997•0 citations