Fiber- and FSO-Protected Connections for Long-Reach TWDM Access Architecture With Fault Protection

In this paper, we propose a long-reach star-ring-based timeand wavelength-divisionmultiplexing passive optical network (TWDM-PON) by using fiberand free space optical (FSO)-protected architecture against fiber breakpoint. Here, the new fiber-based and FSO-based optical network unit (ONU) modules are designed in the PON system to achieve the self-protected operation. Thus, the adjacent ONU is linked to produce the fiberor FSO-based reconnections. Thus, 4 × 10 Gbit/s downstream and 10 Gbit/s upstream signals can be reached through 70 km fiber transmission and a length of free space link without signal amplification and dispersion compensation. Moreover, the relationships of splitter ratio and FSO link length in the proposed TWDM access network are also analyzed and discussed.