Optical path testing device and optical path testing method

An optical path testing device comprising:

• a laser light source;
• a branching unit that divides output light from the laser light source into a probe optical path and a local optical path;
• a modulator that modulates input light of the probe optical path to generate modulated light and converts the modulated light into probe light including pulsed light;
• an interference device that receives signal light emitted from one end of an optical fiber when the probe light enters into the one end and generates a beat signal by causing the signal light and input light of the local optical path to interfere with each other;
• an optical reception unit that acquires backscattered light in the optical fiber on a basis of the beat signal;
• and
• a signal analysis unit that analyzes a loss distribution on a basis of a signal of the optical reception unit, wherein:
• the modulator generates the modulated light by performing, on the output light,
• a first modulation in which a plurality of modulations based on at least two or more different first frequencies is sequentially performed for a duration of an optical frequency output from the laser light source, and
• a second modulation in which modulation is performed based on a second frequency that changes by a predetermined amount of change for each period of the pulsed light;
• and
• the signal analysis unit
• generates an analysis signal by averaging the backscattered light in each different frequency band included in the beat signal between the different frequency bands, and
• acquires the loss distribution by analyzing an intensity of the backscattered light included in the analysis signal.