Line coding in fiber optic communication

In an optic fiber communication system, signal in a digital form is applied at the input of an optical fiber. Some specific formats are used for this. This is a very important process in the design of fiber optic communication system and there exist three basic formats for this. These formats employ two-level binary line codes. These codes are non-return-to-zero (NRZ), return-to-zero (RZ) and phase encoded (PE) or optical Manchester code. In NRZ codes, a transmitted data bit occupies the full bit period. Here code requires minimum bandwidth and the average input power transmitted to the receiver entirely depends on the data pattern. RZ codes use pulse width with less than a full bit period and each data bit can be encoded as two optical line code bits. Both full width and half width data pulses are present in phase encoded format. The main feature of this code is that the transition occurs at the center of each bit period. Generation and decoding of the Manchester code is relatively easy and simple.