New type of optical fiber data transmission system using AO mode space frequency modulator and LED

Statuses acquired from automatic controlled machines are required to be transmitted without any disturbance. Statuses can be transmitted through SSB data lines and optical fibers are more effective than metal lines. This paper describes a short distance single-mode optical fiber SSB data transmission system, which is constructed using an AO mode space frequency modulator, in which an edge-emitting LED is used as a light source. The system is constructed by combining LED space frequency modulation with LED direct intensity modulation to increase the size of information. Twelve channels of SSB data in the frequency range of 72 kHz to 120 kHz are transmitted by the square-wave frequency modulation scheme through an AO mode space frequency modulator. Three channels of SSB data in the frequency range of 12 kHz to 24 kHz are transmitted by the narrow-band frequency modulation scheme through a direct intensity modulator using an LED. The output frequency responses for the 0th and 1st order beams from the AO mode space frequency modulator used together with the LED were flat over the frequency range of DC to 3.5 MHz when a squarewave frequency modulation (SWFM) was accomplished. An FM signal at it carrier frequency of 350 kHz is applied to the current source which drives the LED. When 12 channels of SSB data modulated the carrier at a frequency of 2.5 MHz and 3 channel of SSB data modulated the carrier at a frequency of 350 kHz, respectively, the obtained SWFM signal and FM signal were respectively transmitted over a distance of 10 km through single-mode optical fibers