TRANSMISSION MODE SELECTOR AND LIGHT TRANSMISSION SYSTEM

PROBLEM TO BE SOLVED: To provide a transmission mode selector that is superior in interchangeability (connectability) with a single-mode optical fiber, and where the transfer characteristics, on the wavelength side shorter than the cut-off wavelength of the single-mode optical fiber is further improved in the wide wavelength region. SOLUTION: The selector includes a first optical fiber 22, having at least two or more main mode orders, including the fundamental mode in an operating wavelength band; and a second optical fiber 23, having at least two or more main mode orders, including a basic mode in the operating wavelength band, and also having a larger numerical aperture than that of the first optical fiber 22. Both sides of the first optical fiber 22 function as input and output ports 21 and 24, respectively for inputting and outputting signal light, and a fused extension part 25, constituted by melting the cladding parts 27 and 29 of the optical fibers 22 and 23, is disposed; and only the signal light of the fundamental mode is selectively output to the output port 24, with respect to the input of the signal light, including at least two or more main modes that include the basic mode to the input port 21. COPYRIGHT: (C)2008,JPO&INPIT