Optical module and optical encoder comprising a dummy light receiving device formed between a light receiving device and a through hole in a sensor substrate

An optical module, comprising:

• a fixed substrate;
• a sensor substrate secured to the fixed substrate and having a through-hole formed therein;
• a light emitting device secured to the fixed substrate at a position in the through-hole;
• a light receiving device provided in the sensor substrate;
• and
• a dummy light receiving device formed between the light receiving device and the through-hole, around the through-hole, and in the sensor substrate,
• wherein the light receiving device and the dummy light receiving device are made of an impurity diffusion layer having a same conductive type as a conductive type of a surface layer of the sensor substrate, and
• wherein the sensor substrate is secured to the fixed substrate via a conductive adhesive layer containing a light absorbing member.