JPS54138452A - Photo attenuator - Google Patents

Abstract

PURPOSE:To constitute a variable attenuator from the point of zero attenuation by means of a simple jig only, by providing a member to warp the optical fiber. CONSTITUTION:Nylon coated 1/2 optical fiber 3 is wound around an elastic body 4 about 5 turns, and pressures 7, 8 are applied from the outside of holders 5, 6, then the optical fiber is deformed into an elliptical form. As the deformation proceeds, the output of the light entering from an end face 1 and emitting from an end face 2 will be decreased. When the number of openings of an optical fiber of which refractive index is n1 and n2 at core 10 and clad layer 11 respectively is supposed to be a, the value of a may be expressed as a=(n<2>1-n2)<1/2>, and the maximum propagation angle thetaM is determined in the relation of sinthetaM=a. The light propagated at angle theta becomes theta1 (theta1>thetaM) at the bent part of the fiber, being unable to be propagating light. The light entering at angle theta3 as beam 13 is transformed into light of angle theta2 inside the core. Because theta2>theta3, the light becomes high order mode light, being liable to be lost. Thus, a variable attenuator may be consitituted easily from the point of zero attenuation.