A somewhat more complex but often more efficient method is to translate the baseband signal onto an electrical subcarrier prior to intensity modulation of the source, This is done using standard amplitude - modulation (AM), frequency- modulation (FM), or phase-modulation (PM) techniques11. No matter which method is implemented, one must pay careful attention to signal impairments ill the optical source. These include harmonic distortions, intermodulation products, relative intensity noise (RIN) in the laser, and laser clipping.12