Method and apparatus for testing transmission lines normally propagating optical signals

A method of measuring respective parameters of a first optical signal (S1) and a second optical signal (S2) propagating concurrently in opposite directions in an optical transmission path (16, 16/1, . . . , 16/9) between two network elements (10, 14/1, . . . , 14/9), at least one (14/1, . . . , 14/9) of the network elements being operative to transmit the first optical signal (S1) only if it continues to receive the second optical signal (S2), the method comprising the steps of:

• temporarily connecting first and second connector means (22, 24) of a portable test instrument into the optical transmission path in series therewith, and using the portable test instrument to propagate at least said second optical signal (S2) towards said at least one (14) of the network elements, and measure the parameter for each of the first optical signal (S1) and the second optical signal (S2)
• wherein the portable test instrument comprises coupler means (32) having first and second ports (28,30) connected to the first and second connector means, respectively, so that a path therebetween within the coupler means completes the optical transmission path, a third port (34) for outputting a portion of each optical signal received via the second port (30) and a fourth port (36) for outputting a portion of each optical signal received via the first port (28) and detection means (38, 42, 44) coupled to the third and fourth ports for converting the optical signal portions into corresponding electrical signals.

A portable test instrument for measuring respective parameters of a first optical signal (S1) and a second optical signal (S2) propagating concurrently in opposite directions in an optical transmission path in a passive optical network (16, 16/1, . . . , 16/9) between an optical line terminal (10) and an optical network terminal (14/1, . . . , 14/9), the optical network terminal (14/1, . . . , 14/9) being operative to transmit the first optical signal (S1) only if it continues to receive the second optical signal (S2) from the optical line terminal (10), the portable test instrument comprising first and second connector means (22, 24) for temporarily connecting the portable test instrument into the optical transmission path in series therewith, and propagating and measuring means (32, 38, 46) connected between the first and second connector means for propagating at least said second optical signal (S2) towards said optical network terminal (14), the propagating and measuring means (32, 38, 46) being operable to measure the parameter for each of the first optical signal (S1) and the second optical signal (S2)

• wherein the propagating and measuring means comprises coupler means (32) having first and second ports (28,30) connected to the first and second connector means, respectively, so that a path therebetween within the coupler means completes the optical transmission path, a third port (34) for outputting a portion of each optical signal received via the second port (30) and a fourth port (36) for outputting a portion of each optical signal received via the first port (28) and detection means (38, 42, 44) coupled to the third and fourth ports for converting the optical signal portions into corresponding electrical signals.