Optical waveguide having core partially formed in S-shape, and position sensor and optical circuit board including the same

An optical waveguide comprising:

• a linear core serving as an optical path;
• and
• upper and lower cladding layers holding the core therebetween,
• wherein the core is partially formed in an S-shape,
• wherein the S-shaped portion includes a first curved portion upstream as seen in the direction of light propagation, and a second curved portion downstream as seen in the direction of light propagation and curved in a direction opposite to the first curved portion,
• wherein the first curved portion and the second curved portion are connected to each other via a straight portion having a length in a range of from 0 mm to 30 mm,
• wherein one of the width of the exit of the first curved portion and the width of the entrance of the second curved portion is smaller than the width of a core portion upstream of the S-shaped portion, and
• wherein all of the first curved portion, the second curved portion, the straight portion and the core portion upstream of the S-shaped portion are formed of a same material.