Optical Communications, 2nd Edition

1.1 OPTICAL SYSTEMS

The block diagram of a generic optical communication system is shown in Figure 1.2. The diagram is composed of standard communication blocks, which are endemic to any communication system. A source producing some type of information (waveforms in time, digital systems, etc.) is to be transmitted to some remote destination. This source has its output modulated onto an optical carrier (a carrier frequency in the optical portion of the electromagnetic spectrum). This carrier is then transmitted as an optical light field, or beam, through the optical channel (free space, turbulent atmosphere, fiberoptic waveguide, etc.). At the receiver, the field is optically collected and processed (photodetected), generally in the presence of noise interference, signal distortion, and inherent background radiation (undesired light fields or other electromagnetic radiation). Of course, except for the fact that the transmission is accomplished in the optical range of carrier frequencies, the operations just mentioned describe any communication system using modulated carriers. Nevertheless, the optical system employs devices somewhat uncommon to the standard components of the RF system. These devices have significant differences in their operation and associated characteristics, often requiring variations in design procedures.

Figure 1.2. Optical communication system block diagram. ...