| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide an optical filter having a new structure and using a long- period grating (LPG) so as to provide in-line band pass filtering for light signals. SOLUTION: In the basic aspect, two LPGs not similar to each other are mounted on an optical fiber transmission line. The first LPG converts the light transmitted in the basic mode or LP01 mode of the optical fiber transmission line into a higher order mode (HOM) of the optical fiber in a wide wavelength range. The signals with converted mode have the mode LPm ,n and then coupled to a second waveguide having different transmission characteristics from those of the first waveguide. The propagation of light in the LPm ,n mode is supported by the second waveguide. The light having the converted mode is transmitted through the second LPG. The signals in a narrow band with selected wavelengths received by the second LPG are again converted into the LP01 mode. The selected narrow band of the LP01 mode efficiently propagates on the rest of the optical fiber transmission line.</p> |
