Vibration detection apparatus and vibration detection method

1. A vibration detection apparatus, comprising:

a ring laser resonator that generates a laser beam propagating a ring-shaped light path;

a fiber Bragg grating which is disposed in the ring laser resonator such that the laser beam enters the grating, and of which transmittance distribution characteristic of transmitted light in a wavelength direction changes in accordance with vibration of an object; and

a detection system that detects the vibration based on the transmitted light through the fiber Bragg grating.

2. The vibration detection apparatus according to claim 1 , wherein the fiber Bragg grating is constituted by a phase shift fiber Bragg grating.

3. The vibration detection apparatus according to claim 2 , wherein the detection system is configured to detect the vibration based on a change of intensity of a longitudinal mode representing a highest intensity of light that is transmitted through the phase shift fiber Bragg grating, out of multiple longitudinal modes generated in the ring laser resonator.

4. The vibration detection apparatus according to claim 3 , wherein the detection system is configured such that, when the transmittance distribution characteristic is shifted in the wavelength direction by a shift amount exceeding a threshold due to an environmental factor other than the vibration, the vibration is detected based on a change of intensity of another longitudinal mode corresponding to the shift amount.

5. The vibration detection apparatus according to claim 1 , further comprising an optical filter that removes components in an unnecessary frequency band from the transmitted light through the fiber Bragg grating.

6. The vibration detection apparatus according to claim 5 , wherein the optical filter is connected to the ring laser resonator via an optical circulator.

7. The vibration detection apparatus according to claim 5 wherein the optical filter is constituted by an apodized fiber Bragg grating.

8. The vibration detection apparatus according to claim 1 , further comprising an optical amplifier that is disposed in the ring laser resonator, and that amplifies the transmitted light through the fiber Bragg grating and allows the light to enter the fiber Bragg grating again, wherein the detection system is configured to detect the vibration based on the transmitted light through the fiber Bragg grating, of which intensity has reached a predetermined intensity by amplifying the transmitted light by the optical amplifier at least once.

9. The vibration detection apparatus according to claim 1 , further comprising an ultrasonic transmission system that applies vibration by an ultrasound wave to the object, wherein the detection system is configured to detect the vibration of the object generated by the ultrasound wave.

10. The vibration detection apparatus according to claim 1 , wherein the detection system is configured to detect the vibration due to acoustic emissions generated in the object.

11. The vibration detection apparatus according to claim 1 , wherein the detection system is configured to detect a defect in the object based on the detected vibration.

12. A vibration detection method, comprising the steps of:

generating a laser beam with a ring laser resonator and propagating the generated laser beam through a ring-shaped light path of the ring laser resonator;

allowing the laser beam to enter a fiber Bragg grating disposed in the ring laser generator such that the laser beam enters the grating, and of which transmittance distribution characteristic of transmitted light in a wavelength direction changes in accordance with vibration of an object; and

detecting the vibration based on the transmitted light through the fiber Bragg grating.