Convolutional encoding is successfully applied to an experimental system of direct-detection optical orthogonal frequency-division multiplexing(OFDM) signal transmission over fiber.In this experiment,the 2 Gb/s QPSK optical OFDM is generated and transmitted over 200 km single mode fiber.The performance of bit error rate is greatly improved compared with the optical transmission system without convolutional encoding,performance of the system BER is greatly improved and about 1 dBm optical power may be saved ...