Liquid sensor and method for manufacturing optical waveguide

A liquid sensor configured to detect a state of a liquid, the liquid sensor comprising:

• a light emitting element;
• an optical waveguide;
• a light receiving element configured to receive light that was emitted by the light emitting element and passed through the optical waveguide;
• and
• a detection circuit configured to detect output of the light receiving element, wherein the optical waveguide includes:
• a first pillar portion,
• a first metal plate embedded in the first pillar portion,
• a second pillar portion provided at a position opposing the first pillar portion, and
• a second metal plate embedded in the second pillar portion,
• the first pillar portion includes a first end surface that faces the light emitting element,
• the first metal plate includes a first reflecting portion that is tilted relative to the first end surface and is configured to reflect the light toward the second pillar portion,
• the second pillar portion includes a second end surface that faces the light receiving element,
• the second metal plate includes a second reflecting portion that is tilted relative to the second end surface and is configured to reflect the light from the first metal plate toward the light receiving element, and
• a space for the liquid is formed between a portion of the first pillar portion in which the first metal plate is embedded and a portion of the second pillar portion in which the second metal plate is embedded.