GRATING BUILT-IN TYPE OPTICAL COUPLER

摘要

PROBLEM TO BE SOLVED: To make it possible to reduce a cost and to embody not only the multiplex sepn. of signals but a function to add the signals of specific wavelengths as well by forming gratings of a structure uniform in the pitch thereof in a longitudinal direction and specifying a grating length and induced refractive index change to specific values. SOLUTION: The fiber coupler formed with the fiber gratings in the melt extended part of the fiber coupler is formed to the structure uniform in the pitch of the gratings in the longitudinal direction. The grating length is 1.5 mm and the induced refractive index change is 0.001. If the grating length is shorter than 1.5 mm, the ratio at which the light is reflected to a port 2 and returned is low and the ratio at which the light transmits to a port 4 is high. When the grating length is longer than 1.5 mm, the ratio at which the light returns to a port 1 increases. The spectral width returning to the port 2 more widens when the induced refractive index change is larger than 0.001. The reflectivity is lower when the change is made smaller than 0.001.