“Negative” absorption and “negative” emission in nonlinear optics

Лев Абрамович Ривлин

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

Jan Peřina

Yoshinobu Maeda, Masatoshi Migitaka

An all-optical switch which has a negative amplification of the optical signal was demonstrated in an erbium-doped fiber. The dependence of the negative nonlinear absorption effect on the modulation degree of the incident laser was investigated and we obtained the negative amplification degree of -3 for a fiber length of 6 m at room temperature. It has been confirmed that the mechanism of the effect can be explained by calculating the rate equations based on an analytical model for a five-level system of the Er3+ ion. It is suggested that the effect was due to stimulated emission from the 4 S 3/2 level to the 4 I 13/2 level.

Pierre Meystre, Murray Sargent

Yoshinobu Maeda, Takao Sakakibara, M. Migitaka

The dependence of the negative nonlinear absorption effect on both modulation degree and modulation frequency of an incident laser was investigated in erbium-doped fibers at 77 K. Negative input-output characteristics were obtained at modulation frequencies of 10 to 250 kHz for fiber lengths above 2 m. The maximum ratio of the transmitted modulation degree to the incident one was approximately -2 for a fiber length of 4 m. It is suggested that emissions induced in the fiber can contribute to the negative nonlinear absorption effect because they propagate with low loss.