Patent ID: 6614961
Filing Date: 2003-09-02
Classification: G02B

Abstract:
A method of fabricating a fused-type mode-selective directional coupler in which a mode-coupling ratio between a first mode M1 and a second mode M2 different from the first mode M1 equals a certain value, the method comprising the steps of:preparing mode-coupling graphs including a mode-coupling curve C1 between the first mode M1, and the second mode M2, and mode-coupling curves C2 between the first mode M1 and other modes different from the second mode M2 by use of calculation data for a first optical fiber and a second optical fiber with cladding diameters formed by tapering and etching two identical optical fibers; finding out particular initial cladding diameters D1 of the first optical fiber and D2 of the second optical fiber which enable the mode-coupling curve C1 and the mode-coupling curve C2 to be separated by more than 2 &mgr;m in a mode-coupling region and also enable a difference between a coupler-fabrication line and the mode-coupling curve C1 to be maintained at less than 1.5 &mgr;m in the mode-coupling region from the initial cladding diameters D1 and D2, where the coupler-fabrication line is a straight line from the particular initial cladding diameters toward an origin of the mode-coupling graph: preparing, the first and second optical fibers, each having a core and a cladding, parts of a jacket of each of the first and second optical fibers being removed, the first optical fiber having a cladding diameter of D1 and a normalized frequency of V1, and the second optical fiber having a cladding diameter of D2 and a normalized frequency of V2, said V1 being less than said V2, wherein the first and second optical fibers are prepared by tapering and etching two identical optical fibers; putting in contact the claddings of the first and second optical fibers to form a junction; measuring the mode-coupling ratio between the first mode M1 of the first optical fiber and the second mode M2 of the second optical fiber; extending the first and second optical fibers in longitudinal directions while fusing the junction; and stopping extending the first and second optical fibers when the mode-coupling ratio between the first mode M1 and the second mode M2 reaches the certain value.