Described is an optical fiber control signal transmission system in which multifrequency control signals used as parallel control signals are transmitted from the sender to the receiver through the optical fiber. In accordance with the multiplexing of up to 8 sinewave signals at 65kHz, 110kHz, 210kHz, 310kHz, 410kHz, 510kHz, 610kHz, and 710kHz, 8-bit multifrequency signals are formed, and then combined together by the mixer. The multifrequency signals are fed to the squarewave FM modulator to modulate them by squarewave frequency modulation (SWFM) scheme. The SWFM signal is fed to the LED to accomplish optical intensity modulation (IM). The multifrequency signals which are transmitted through the GI mode optical fiber in a distance of up to 2km are detected using a set of bandpass filters and F/V converters.
Based on the concept of the multifrequency control signal generation and the SWFM-IM modulation scheme, the optical fiber control signal transmission system has a capability to transmit the SWFM-IM signal over a distance of 2km with a group delay time of less than 100μs.