Device and a method for distinguishing faults employed in an optical transmission system

A method for distinguishing a fault for establishing whether fault exists in an optical fiber cable and in another optical system, said method comprising the steps of:

• introducing a test pulse light for detecting a fault position into said optical fiber cable via an optical coupler, whereby said test pulse light is used for detecting a fault position and different from a communication light for transmitting data;
• receiving said test pulse light reflected by an optical filter disposed in front of said another optical system, and whereby detecting an intensity of said reflected test pulse light and a reflecting position, wherein said optical filter reflects only said test pulse light;
• comparing said detected intensity and reflecting position with a beforehand measured intensity and reflecting position about said test pulse light reflected by said optical filter at normal state in said optical transmission system;
• judging that a fault exists in said optical fiber cable and determining a position of said fault, as a result of said comparison, when variation occurs in at least one of said intensity and reflecting position;
• and
• judging that a fault does not exist in said optical fiber cable, as a result of said comparison, when variation does not occur in both said intensity and reflecting position.

A method for distinguishing a fault among an optical fiber cable, branching optical fibers and optical receivers employed in an optical transmission system, said method comprising the steps of:

• introducing respectively test pulse lights for detecting a fault position into said branching optical fiber cables via an optical divider, whereby said test pulse lights are used for detecting fault positions and different from a communication light for transmitting data;
• receiving said test pulse lights reflected by respective optical filters disposed immediately in front of said optical receivers, and whereby detecting intensities of said reflected test pulse lights and reflecting positions, wherein said optical filters reflect only said test pulse lights;
• comparing said detected intensities and reflecting positions with beforehand measured intensities and reflecting positions about said test pulse lights reflected respectively by said optical filters at normal state in said optical transmission system;
• judging that a fault exists in said optical fiber cable and determining a position of said fault, as a result of said comparison, when variation occurs in at least one of said intensities and reflecting positions;
• and
• judging that a fault does not exist in said optical fiber cable, as a result of said comparison, when variation does not occurs in neither of said intensities and reflecting positions.