Transmission apparatus using a plastic fiber

A transmission apparatus using a plastic fiber, comprising:

• i) a plastic fiber, which is provided with a core containing a polymethyl methacrylate as a principal constituent, and
• ii) a semiconductor light emitting device, which produces light to be propagated through the plastic fiber,
• wherein the semiconductor light emitting device is a device, which produces light having wavelengths falling within the range of 630 nm to 680 nm, and
• the transmission apparatus further comprises a temperature adjusting system, which comprises:
• a) heating means for heating the semiconductor light emitting device,
• b) temperature detecting means for detecting the temperature of the semiconductor light emitting device and feeding out a temperature detection signal, which represents the temperature of the semiconductor light emitting device, and
• c) a control circuit for controlling actuation of the heating means in accordance with the temperature detection signal, which is received from the temperature detecting means, in order to set the temperature of the semiconductor light emitting device at a predetermined target value that is lower than the highest temperature assumed to occur under an environment, in which the semiconductor light emitting device is located.