Measurement device for measuring temperature or distortion of an optical fiber, method of adjusting measurement device, and measurement method for measuring temperature of distortion of an optical fiber

A measurement method for causing a processor to execute a process, the measurement method comprising executing on the processor the steps of:

• splitting light from a laser light source into two split lights;
• shifting, by a phase modulator, a frequency of one of the two split lights by an adjusted frequency shift amount by driving the phase modulator with a modulation signal of a sawtooth wave;
• modulating an intensity of the one of the two split lights and generating probe light having two frequency components;
• generating pump light by pulsing the other of the two split lights;
• detecting, when the probe light is incident from one end side of an optical fiber to be measured and the pump light is incident from the other end side of the optical fiber, a light intensity of light emitted from the other end side of the optical fiber;
• and
• measuring, based on the light intensity, a temperature or a distortion of the optical fiber,
• wherein a frequency of a lower frequency component out of the two frequency components is a frequency at which Brillouin gain occurs by interaction with the pump light, and a frequency of a higher frequency component out of the two frequency components is a frequency at which Brillouin loss occurs by the interaction with the pump light, and
• the adjusted frequency shift amount, used in the splitting of the light from the laser light source, is obtained by executing on the processor the steps of:
• setting an initial frequency shift amount of the frequency of the one of the two split lights so as to prevent the two frequency components of the probe light from simultaneously receiving a gain by the Brillouin gain and a loss by the Brillouin loss;
• acquiring the light intensity each time a frequency of a modulation signal is changed in the modulating the intensity of the one of the two split lights and the generating the probe light;
• obtaining a shape of a Brillouin gain spectrum based on a relationship between the frequency of the modulation signal and the light intensity;
• obtaining a Brillouin frequency shift based on the initial frequency shift amount and a peak frequency, and the peak frequency is obtained from the relationship between the frequency of the modulation signal and the light intensity;
• and
• adjusting the initial frequency shift amount such that a relationship between the light intensity and one of the temperature and the distortion of the optical fiber becomes a predetermined relationship within a predetermined range based on the shape of the Brillouin gain spectrum and the Brillouin frequency shift to provide the adjusted frequency shift amount.

A measurement device comprising:

• a splitter configured to split light from a laser light source into first and second split lights;
• an optical frequency shifter configured with a phase modulator, the phase modulator being configured to receive the first split light and shift a frequency of the first split light by an adjusted frequency shift amount by driving the phase modulator with a modulation signal of a sawtooth wave so as to provide shifted first split light;
• a first optical modulator configured to receive the shifted first split light to modulate an intensity thereof and to generate probe light having two frequency components;
• a second optical modulator configured to receive the second split light to generate pump light by pulsing the second split light;
• an optical detector configured to detect, when the probe light is incident from one end side of an optical fiber to be measured and the pump light is incident from the other end side of the optical fiber, a light intensity of light emitted from the other end side of the optical fiber;
• and
• a processor configured to be programmed to measure, based on the light intensity, a temperature or a distortion of the optical fiber,
• wherein a frequency of a lower frequency component out of the two frequency components is a frequency at which Brillouin gain occurs by interaction with the pump light, and a frequency of a higher frequency component out of the two frequency components is a frequency at which Brillouin loss occurs by the interaction with the pump light,
• the adjusted frequency shift amount in the optical frequency shifter is set so as to prevent the two frequency components of the probe light from simultaneously receiving a gain by the Brillouin gain and a loss by the Brillouin loss,
• the light intensity is acquired by the optical detector each time a frequency of a modulation signal of the first optical modulator is changed,
• a Brillouin gain spectrum and a Brillouin frequency shift are obtained based on a relationship between the frequency of the modulation signal and the light intensity,
• the adjusted frequency shift amount is obtained based on the Brillouin gain spectrum and the Brillouin frequency shift, and
• the adjusted frequency shift amount is set such that a relationship between the light intensity of the light emitted from the other end side of the optical fiber and the temperature or the distortion of the optical fiber satisfies a predetermined function.

A measurement method for causing a processor to execute a process, the measurement method comprising executing on the processor the steps of:

• splitting light from a laser light source into first and second split lights;
• receiving the first split light and shifting, by a phase modulator, a frequency of the first split light by an adjusted frequency shift amount by driving the phase modulator with a modulation signal of a sawtooth wave so as to provide shifted first split light;
• receiving, by a first optical modulator, the shifted first split light to modulate an intensity thereof and to generate probe light having two frequency components;
• receiving, by a second optical modulator, the second split light to generate pump light by pulsing the second split light;
• detecting, when the probe light is incident from one end side of an optical fiber to be measured and the pump light is incident from the other end side of the optical fiber, a light intensity of light emitted from the other end side of the optical fiber;
• and
• measuring, based on the light intensity, a temperature or a distortion of the optical fiber,
• wherein a frequency of a lower frequency component out of the two frequency components is a frequency at which Brillouin gain occurs by interaction with the pump light, and a frequency of a higher frequency component out of the two frequency components is a frequency at which Brillouin loss occurs by the interaction with the pump light,
• the adjusted frequency shift amount is set so as to prevent the two frequency components of the probe light from simultaneously receiving a gain by the Brillouin gain and a loss by the Brillouin loss,
• the light intensity is acquired each time a frequency of a modulation signal of the first optical modulator is changed,
• a Brillouin gain spectrum and a Brillouin frequency shift are obtained based on a relationship between the frequency of the modulation signal and the light intensity,
• the adjusted frequency shift amount is obtained based on the Brillouin gain spectrum and the Brillouin frequency shift, and
• the adjusted frequency shift amount is set such that a relationship between the light intensity of the light emitted from the other end side of the optical fiber and the temperature or the distortion of the optical fiber satisfies a predetermined function.