Method and otdr apparatus for optical cable defect location with reduced memory requirement

An optical time domain reflectometer (OTDR) system, comprising:

• a transmit circuit operative to generate a transmit signal defining at least one pulse;
• an optical source operative to transmit optical signals at a first location of an optical cable according to the transmitted signal from the transmit circuit;
• an optical sensor operative to receive optical reflections at the first location of the optical cable and to generate a receive signal according to the received optical reflections;
• a receive circuit operative to sample the receive signal at a selectable sample rate and to provide sample data corresponding to the optical reflections received by the optical sensor;
• an electronic memory operative to store the sample data;
• and
• at least one processor operatively coupled with the transmit circuit, the receive circuit, and the electronic memory, the at least one processor operative to:
• provide at least one transmit control signal or value to cause the transmit circuit and the optical source to generate a first optical signal at the first location of the optical cable,
• provide at least one receive control signal or value to cause the receive circuit to sample the receive signal at a first sample rate over a first time range following transmission of the first optical signal to obtain a first set of sample data corresponding to reflections of the first optical signal,
• temporally correlate the first set of sample data with the transmitted first optical signal,
• identify a first time in the first time range corresponding to a suspected defect location of the optical cable based at least partially on the temporal correlation of the first set of sample data with the transmitted first optical signal;
• provide at least one further transmit control signal or value to cause the transmit circuit and the optical source to generate a second optical signal at the first location of the optical cable,
• provide at least one further receive control signal or value to cause the receive circuit to sample the receive signal at a second sample rate over a second time range following transmission of the second optical signal to obtain a second set of sample data corresponding to reflections of the second optical signal, the second time range including the first time, the second time range being less than the first time range, and the second sample rate being greater than the first sample rate,
• temporally correlate the second set of sample data with the transmitted second optical signal, and
• identify at least one defect location of the optical cable based at least partially on the temporal correlation of the second set of sample data with the transmitted second optical signal.

An integrated circuit for an optical time domain reflectometer (OTDR) system, the integrated circuit comprising:

• a transmit circuit operative to generate a transmit signal defining at least one pulse for controlling an optical source to transmit optical signals;
• a receive circuit operative to sample receive signals from an optical sensor receiving optical reflections at a selectable sample rate and to provide sample data corresponding to the optical reflections;
• an electronic memory operative to store the sample data;
• and
• at least one processor operatively coupled with the transmit circuit, the receive circuit, and the electronic memory, the at least one processor operative to:
• provide at least one transmit control signal or value to cause the transmit circuit and the optical source to generate a first optical signal at a first location of an optical cable,
• provide at least one receive control signal or value to cause the receive circuit to sample the receive signal at a first sample rate over a first time range following transmission of the first optical signal to obtain a first set of sample data corresponding to reflections of the first optical signal,
• identify a first time in the first time range corresponding to a suspected defect location of the optical cable based at least partially on a temporal correlation of the first set of sample data with the transmitted first optical signal;
• provide at least one further transmit control signal or value to cause the transmit circuit and the optical source to generate a second optical signal at the first location of the optical cable,
• provide at least one further receive control signal or value to cause the receive circuit to sample the receive signal at a second sample rate over a second time range following transmission of the second optical signal to obtain a second set of sample data corresponding to reflections of the second optical signal, the second time range including the first time, the second time range being less than the first time range, and the second sample rate being greater than the first sample rate, and
• identify at least one defect location of the optical cable based at least partially on the temporal correlation of the second set of sample data with the transmitted second optical signal.