Method and system for detecting trouble in two-way single-fiber optical transmission

A system for detecting trouble occurring in a single-fiber two-way optical transmission system containing first and second optical terminal stations connected to each other through at least one two-way single optical fiber, each of the first and second optical terminal stations comprising:

• abnormality detecting means for detecting a first abnormality in a first optical signal received at said each optical terminal station;
• notice transmitting means for transmitting from each said optical terminal station to the other optical terminal station a first notice that each said optical terminal station will stop transmission of second optical signals when the first abnormality is detected by the abnormality detecting means of the optical terminal station;
• transmission stopping means for stopping the transmission of second optical signals after transmission of the first notice by the notice transmitting means;
• said abnormality detecting means being able to detect a second abnormality in a third optical signal received at said each optical terminal station after the stopping of the transmission of the second optical signals.

Terminal equipment used in an optical terminal station in a single-fiber two-way optical transmission system which contains the optical terminal station, another optical terminal station, and at least one two-way single optical fiber connecting the terminal equipment with said other optical terminal station, comprising:

• abnormality detecting means for detecting a first abnormality in a first optical signal received at said terminal equipment;
• first notice transmitting means for transmitting from said terminal equipment to said other optical terminal station a first notice that said optical terminal station will stop transmission of second optical signals when the first abnormality is detected by the abnormality detecting means;
• transmission stopping means for stopping the transmission of the second optical signals after the transmission of the first notice by the first notice transmitting means;
• said abnormality detecting means being able to detect a second abnormality in a third optical signal received at said terminal equipment after the stopping of the transmission of the second optical signals.