Optical detection sensor

An optical detection sensor comprising:

• a light source,
• a first optical fiber guiding exit light emitted from the light source,
• a second and a third optical fiber receiving reflection light produced in such a way that the exit light is incident upon an object to be measured and thus reflected therefrom, the object being disposed a relative distance away from an end portion of the first optical fiber;
• a first and a second detection element receiving the reflection light that is guided through the second and the third optical fiber, thereby to convert the reflection light into an electric signal;
• and
• an arithmetic processing means computing a displacement quantity of the object to be measured on the basis of a ratio of the electric signals obtained through the conversion in the first and the second detection element;
• wherein the first optical fiber is disposed so that an angle between a longitudinal direction thereof and a normal line to an incident surface of the object to be measured becomes θ;
• wherein the second and the third optical fiber are disposed so as to be in parallel with each other and so that an angle between a longitudinal direction of the second and the third optical fiber and the normal line becomes θ;
• wherein the first optical fiber is disposed symmetrically with the second and the third optical fiber with respect to the normal line;
• and
• wherein the first to the third optical fiber have a dNA/dλ of 4×10−5 or less with respect to a wavelength of the light source.