Next Generation Free-space Optical System by System Design Optimization and Performance Enhancement

Free Space Optical (FSO) system is being realized as an alternative means to compensate and/or replace the traditional optical communication in many applications where the flber cable is not available. New generation FSO systems in which the optical signal after transmission over free-space is directly coupled into a single mode flber have attracted consid- erable interest recently due to its remarkable advantages. This paper introduces the concept of FSO technology and reviews our recent achievements on development and demonstration of new generation free-space optical systems. The other aspects on the system design optimization and performance improvement are also clarifled in this paper. Light-wave communication has become an attractive means for broadband access networks. Re- cently, free-space optical (FSO) communication is receiving considerable attention to provide broad- band communications due to its remarkable advantages including ∞exibility, easy-to-install, and license-free. FSO systems can be categorized into 2 broad groups, i.e., conventional FSO based- systems, and new generation FSO based-systems. Conventional FSO systems operate at 800nm wavelength band, and need to use O/E and E/O conversions before emitting/coupling optical sig- nals from/into an optical flber. They have been used for data transmission but due to power and bandwidth limitation of optical devices in this wavelength band, they are not possible to operate above 2.5Gbps (1). The use of 0.8"m wavelength optical devices also makes it incompatible with current high capacity optical flber systems. Because of this, it is not being considered as a suitable and practical solution for very high-speed communications. New generation FSO technology has been developed in order to overcome the limitations of con- ventional FSO systems (2). Unlike conventional FSO systems, in the new generation FSO systems the necessity of converting signal from electrical to optical and vice versa before transmitting or receiving through free-space is eliminated. In this conflguration, the signal is emitted directly to the free-space from the flber termination point and at the receiving end focused directly into the flber core. Therefore, a protocol and data rate transparent FSO link is achieved. In this paper, we review our recent achievements on development of new generation FSO systems and introduce some experimentally evaluated results. Some prospects on system design optimization and performance enhancement will also be pointed out.