Signal detection method and optical time-domain reflectometer

A signal detection method comprising:

• generating a first optical signal during a first time period, wherein the first optical signal has a first frequency;
• generating a pulse signal based on the first optical signal;
• outputting the pulse signal to an optical fiber during a second time period, wherein the pulse signal has the first frequency, and wherein the first time period comprises the second time period;
• generating a second optical signal during a third time period, wherein the second optical signal has a second frequency, and wherein a start moment of the third time period is later than a stop moment of the first time period;
• and
• performing coherent detection based on a combination of the second optical signal and a scattered signal from the optical fiber,
• wherein the scattered signal has the first frequency.

An optical time-domain reflectometer (OTDR) comprising:

• a laser configured to:
• output a first optical signal at a first frequency in a first time period, and
• output a second optical signal at a second frequency in a second time period, wherein a start moment of the second time period is later than a stop moment of the first time period;
• an optical fiber configured to output a scattered signal;
• a receiver configured to:
• receive the scattered signal;
• and
• perform coherent detection based on a combination of the second optical signal and the scattered signal, wherein the scattered signal has the first frequency;
• a signal modulation apparatus configured to:
• generate a pulse signal based on the first optical signal;
• and
• output the pulse signal in a third time period;
• a coupler coupled to the laser and configured to:
• pass the first optical signal to the receiver and the signal modulation apparatus;
• and
• pass the second optical signal to the receiver;
• and
• a signal coupling apparatus coupled to the optical fiber and the receiver, wherein the signal coupling apparatus is configured to:
• pass the pulse signal to the optical fiber;
• and
• pass the scattered signal from the optical fiber to the receiver.