Power budget improvement of symmetric 40-Gb/s DML-based TWDM-PON system

We propose a symmetric 40-Gb/s time and wavelength division multiplexed passive optical network (TWDM-PON) system with directly modulated laser (DML) as both downstream and upstream transmitters. A single bi-pass delay interferometer (DI), deployed in the optical line terminal (OLT), is used to mitigate multiple channels' signal distortions induced by laser chirp and fiber chromatic dispersion. With the help of the DI, we successfully demonstrate error-free transmission with the aggregate capacity of 40 Gb/s over different transmission distance. And in back-to-back case, by using a 0.2-nm free spectrum range (FSR) DI, ~11 dB optical power budget improvement is achieved at a bit error ratio of 1e-3. Owing to this high power budget, the maximum reach can be extended to 50 km for 1024 splits, 75 km for 256 splits, and 100 km for 64 splits. Meanwhile, the impacts of FSR of DI and laser wavelength shift on system performance are investigated in terms of receiver sensitivity. It is shown that, our system can achieve more than 43-dB power budget and support ± 2.5-GHz wavelength shift when the FSR is less than 0.2 nm.