DQPSK based Hybrid VCSEL-SMF-FSO Link for Gigabit PON

Hybridization of wireless and wired optical communications is a predominant solution to make best use of both these meritorious technologies. In this paper, we have designed a Differential Quadrature Phase-Shift Keying (DQPSK) based hybrid Single Mode Fiber (SMF)- Free Space Optics (FSO) link with Vertical Cavity Surface Emitting Laser (VSCEL) as a source of light for gigabit Passive Optical Network (PON) applications. The VCSEL is used as an optical source which makes the system cost-effective and less vulnerable to atmospheric turbulences. We have used 80:20 splitting ratio beyond SMF link of 20 km to transmit the 80% power fraction through free space and the remaining 20% for direct reception by the PIN photodetector. The transmitter section includes DQPSK modulator to provide better spectral efficiency and tolerance to dispersion. The receiver section employs optical amplifiers to diminish the effect of noise and increase the link range. The performance of the system is examined w.r.t. Qfactor and BER with regards to four different data rates viz. 1.25 Gbit/s, 2.5Gbit/s, 5Gbit/s, and 10 Gbit/s, under clear, rainy, and snowy weather constrains. The largest FSO link length is also calculated for each case. The analysis unveil that the proposed model yields better satisfactory results of up to 1.7 km, 1 km, and 0.7 km under clear, rain, and snow weather conditions, respectively.