Optical signal transfer device

An optical signal transfer device which transfers a signal between a base unit and a rotary unit rotatable around a rotary axis and supported on the base unit, the device comprising:

• a transmitter system provided in one of the base unit and the rotary unit to transmit a signal;
• and
• a receiver system provided in the other of the base unit and the rotary unit to receive the signal from the transmitter system, wherein:
• the receiver system comprises n light receiving portions which are rotated around the rotary axis relative to the transmitter system on a single plane orthogonal to the rotary axis by a relative rotation of the base unit and the rotary unit and form a single ring-like light receiving area, and a light reception controller which processes an electric signal output from each of the light receiving portions, the n being a natural number;
• the transmitter system comprises a light emitting portion, an emission controller which drives the light emitting portion in accordance with a transmit signal, and an optical guide which guides a light beam from the light emitting portion to a light emitting area provided in an area opposing the light receiving area;
• the opposing area is an area in a ring-like form around the rotary axis opposing the light receiving area and is equally divided into n areas in a circumferential direction;
• and
• the optical guide guides the light beam to at least one of the n divided areas as the light emitting area, so that at least one of the n light receiving portions is to face the light emitting area irrespective of a rotary position of each of the light receiving portions relative to the transmitter system.