Measuring method and measuring apparatus for coherent crosstalk light

A measuring apparatus for measuring coherent crosstalk light generated by multiple reflection of light between a plurality of reflection points existing within an object of measurement, comprising:

• a light source section which generates a measurement light in which the frequency of a light emitted from a laser light source operating under single longitudinal mode oscillation is modulated to a sawtooth wave shape at a variable period;
• an optical output port for irradiating the measurement light generated by said light source section into one end of an optical path which passes through the inside of said object of measurement;
• an optical input port to which the light emitted from the other end of the optical path of said object of measurement is applied;
• a light receiving section which receives the light from said optical input port using an optical receiver and converts the light to an electrical signal, and then applies the electrical signal to a frequency filter, and extracts a beat component of a frequency which corresponds to half the difference between the maximum value and minimum value of the optical frequency of said measurement light;
• a modulation period control section which controls the modulation period of the measurement light generated by said light source section so that the power of the beat component extracted by said light receiving section becomes a local maximum;
• and
• a measuring section which measures whether or not coherent crosstalk light is generated in said object of measurement, based on the power of the beat component which has become the local maximum due to control of the modulation period by said modulation period control section.