Characteristics of Subcarrier Modulation and Its Application in WDM-PONs

We mathematically analyze and experimentally investigate the characteristics of subcarrier-modulated (SCM) light. Our investigation shows that the baseband data are also carried on the optical carrier after subcarrier modulation. This residual data introduce crosstalk when the optical carrier is separated from subcarriers and reused for uplink data modulation. The influence of the residual data carried on the optical carrier is studied in three kinds of upstream transmissions based on wavelength-seeded reflective semiconductor optical amplifiers (RSOAs) for carrier-reuse wavelength-division-multiplexed-passive optical networks (WDM-PONs). Results show that the crosstalk can be significantly suppressed with proper selection of the seeding power and operation conditions of downlink Mach-Zehnder modulator (MZM), including driving voltage and bias voltage.