Optical Sources and Transmitters

To construct an optical communications system one requires a source of optical power and a means for modulating that source. A suitable source for an optical fiber communications system must have certain characteristics which include the following: emission at a wavelength within a window of low fiber transmission loss, efficient conversion of prime power to light coupled into the fiber, high reliability, ease of modulation, adequate modulation speed capability, sufficient ruggedness, ease of coupling the source output into the fiber, adequately low noise, adequately high linearity of modulation, sufficiently narrow spectral width (range of wavelengths in the emitted light), and other more subtle requirements. No source can provide ideal characteristics, but the requirements above eliminate many candidate sources either because they are totally impractical for the fiber system application or they are clearly inferior to other alternatives. (Obviously all of these requirements must be met at an acceptable cost if the source and the system are to be practical.)