Bandwidth Improvement Using Adaptive Loading Scheme in Optical Direct-Detection OFDM

In current metro and access optical networks, the frequency band beyond the bandwidth of the electro-optical components is always deprecated due to the fading frequency response. On the other hand, an orthogonal frequency division multiplexing (OFDM) system is managed on individual subcarrier and can adapt to the varied channel frequency response by optimally allocating different modulation formats and powers across different subcarriers. Therefore, to reuse the commercial low bandwidth components in high speed networks, we design modified OFDM signals, which are with adaptive power and bit allocation, to improve the bandwidth utilization and maximize the data rate. We successfully transmit 16-GHz optical OFDM signals over a 20-km standard single mode fiber link with a 10-GHz commercial Mach-Zehnder (MZ) intensity modulator and direct detection. Eleven modulation formats are used for bit loading and the maximum data rate can reach 88.8 Gb/s. The modulation bandwidth utilization of the MZ modulator is increased by 60%.