IMPLEMENTATION OF A HYBRID OPTICAL FIBER-FSO LINK ON WDM SYSTEM FOR BIDIRECTIONAL COMMUNICATION by Divnoor Kaur
Abstract
With the advent of the technology it has become quite easy to transmit and receive the information. Talking about the fiber optics, which offers numerous advantages like secure transmission, accommodation of large bandwidth (20 GHz), and high data rates (10 Gbps). Also, we know that a natural calamity or an emergency situation does not warn before coming. During such a situation it may happen that the optical fiber which is used for the transmission of the information gets damaged, which in turn will break the process of the communication. So, in order to address such a situation a technology known as free space optics (FSO) can be used as an alternative, with which the communication will not be hampered. FSO is a technology which uses light that propagates via atmosphere, to wirelessly transmit the data for telecommunications. FSO technology is simple and offers many advantages like easy installation, low power per transmitted bit, free spectrum license and the ability to transmit high data rates (up to 100 Gbps) over a distance of 1-4 Km. FSO includes a transmitter as well as a receiver in order to provide bidirectional communication. In this, an optical source and a lens is used to transmit the information via free space to the receiving lens for receiving the information. So, by combining the above two technologies that is fiber optics and free space optics, a system can be made which ensures seamless bidirectional communication even in the case of emergencies. The current work is carried out using OptisystemTM which demonstrates bidirectional communication on optical fiber (OF) and FSO system. Eight channels are used each for upstream as well as for downstream at 10 Gbps. To monitor the condition of the optical fiber, a WDM fiber-bragg grating (FBG) sensor is used, which is monitored by using a FBG detector, which includes a rectangular filter, power meter and an optical spectrum analyzer (OSA). In case the optical fiber breaks, the transmission link will quickly be altered from Optical Fiber to FSO ensuring continuity in the communication. Afocal scheme has been implemented in the FSO path which has resulted in the increase of FSO transmission distance from 10 m to 30.15 m. System performance is measured in the terms of BER, Quality factor (Q-factor) and the eye-diagram. A considerable improvement in the terms of BER and eye-diagram has been obtained. The openness of the eye in the eye-diagram indicates a high quality signal transmission. For the signal propagation through the Optical Fiber path, BER of value 10-48 and Q-factor of 14.4589 has been obtained, while for the signal propagation through FSO, BER of value 10-73 and Q factor of value 18.0193 has been achieved. Also, by incorporating Dispersion Compensating Techniques, BER value has been improved from 10-18 to 10-48.
