Patent ID: 7114395

Claim:
A vibration detector comprising: a diaphragm which vibrates upon reception of vibration; and an optical waveguide which extends along a direction of a flat plane of said diaphragm and equipped with said diaphragm to vibrate integrally with said diaphragm, wherein: in accordance with deformation of said optical waveguide caused by vibration of said diaphragm, a leak light quantity of light entered from one end of said optical waveguide and leaked to an outside of said optical waveguide changes and a light propagation quantity of the light propagated to the other end of said optical waveguide changes; a displacement of said diaphragm caused by the vibration is detected by detecting a change in the light propagation quantity of said optical waveguide; in accordance with the deformation of said optical waveguide caused by vibration of said diaphragm, a material density of a deformed portion of said optical waveguide changes to thereby change a refractive index of the deformed portion; and the leak light quantity of light from said optical waveguide changes with a change in the refractive index, wherein a refractive index of said optical waveguide is set irregularly so that the leak light quantity of light from said optical waveguide changes with the deformation of said optical waveguide.