Abstract: In a light attenuator or its attenuating method, a nonlinear optical material and an aperture section are placed respectively on a same optical axis, between a receiving optical finder and a sending optical fiber. The nonlinear optical material receives and refracts an input light outputted from the receiving optical fiber. The aperture section has an aperture, receives the light having passed through the nonlinear optical material, and outputs constant output light to the sending optical fiber by only allowing only a part of the light to be outputted from the aperture.

Abstract: In a light attenuator or its attenuating method, a nonlinear optical material and an aperture section are placed respectively on a same optical axis, between a receiving optical fiber and a sending optical fiber. The nonlinear optical material receives and refracts an input light outputted from the receiving optical fiber. The aperture section has an aperture, receives the light having passed through the nonlinear optical material, and outputs constant output light to the sending optical fiber by only allowing a part of the light to be outputted from the aperture. Then, for obtaining the wishful output light with constant strength no depending upon the input light, these parameters of the quadratic nonlinear refractive index n2 and the thickness t of the nonlinear optical material; the distance L between nonlinear optical material and aperture section; and the diameter Ø of the aperture, are set most appropriately.