5-Gb/s optical transmitter based on incoherent-light-injected RSOAs with graceful upgrade capability for WDM PONs

We propose and demonstrate a novel and cost-effective optical transmitter based on incoherent-light-injected reflective semiconductor optical amplifiers (RSOAs) which can be upgraded to higher data rate without discarding the existing low-data-rate transmitter. The transmitter is based on optical time-division multiplexing (OTDM) of return-to-zero modulated RSOAs and thus capable of upgrading the system capacity on an as-needed basis simply by adding RSOAs. By using the proposed transmitter, we experimentally demonstrate a capacity upgrade from 2.5 to 5 Gb/s/channel by using two RSOAs, each operating at 2.5 Gb/s. To the best of our knowledge, this is the highest reported data rate demonstrated using incoherent-light-injected RSOAs. We also demonstrate the performance of the proposed transmitter after 10-km transmission over standard single-mode fiber, and investigate the sensitivity penalty to the power level injected into the RSOAs as well as the optical delay for the OTDM.