Yoh IMAI and Naoya MATSUDA

Department of Computer Science and Electronics, Kyusyu Institute of Technology, 680-4, Kawazu, Iizuka, Fukuoka, 820 Japan

(Accepted July 22, 1994)

A large change in the refractive index originating in the transition absorption of erbium ions is induced in an Er³⁺-doped fiber. It is shown that the Er³⁺-doped fiber exhibits the nonlinear refractive index of n₂=7.4 × 10^-15 m²/W, which is 10⁵-10⁶ times larger than that caused by the optical Kerr effect in a usual silica fiber at the pumping wavelength of 514.5 nm. The large nonlinear refractive index occurred in a fiber directional coupler fabricated with the Er³⁺-doped fiber optically changes the coupling condition. The coupling ratio changes up to 0.16 by increasing the pumping power up to 0.7 mW.

Key words : nonlinear fiber coupler, nonlinear refractive index, directional coupler, optical switching, optical fiber, optical nonlinear effect, Kramers-Kronig relationship, intensity-dependent refractive index