Light guide sensor, and method of forming light guide sensor

A method of forming a detecting portion of a light guide sensor, the light guide sensor comprising a flexible light guide member elongated in a longitudinal direction, the light guide member having a core which guides light radiated from a light source and a cladding surrounding the core, at least one detecting portion being formed in the cladding and disposed at a detection position of a measurement target;

• and a light receiving unit which receives the light guided by the light guide member, the method comprising:
• forming a first opening by deforming at least part of the cladding into a recessed shape resulting in the cladding having a first thickness at the first opening in a thickness direction perpendicular to the longitudinal direction such that the cladding having the first thickness is sufficient so as to not transmit light at the detection position of the detecting portion;
• and
• forming a second opening deformed into a recessed shape, the second opening being deformed in the cladding having the first thickness and within a width of the first opening, the width being in a direction perpendicular to the thickness direction, the second opening one of exposing the core or resulting in a second thickness of cladding sufficient so as to transmit the light from the core.