Abstract: Methods for optimizing a noise figure of a variable gain hybrid amplifier (HA) which includes a variable gain Raman amplifier with adjustable average gain GR and gain tilt TR and a variable gain lumped amplifier with adjustable average gain GL and gain tilt TL. In various embodiments, the methods include receiving as input a required hybrid amplifier average gain GH value and a required gain tilt TH value and deriving a set of GR, TR, GL and TL values which yield an optimal optimized hybrid amplifier NF and satisfy the conditions GR+GL=GH and that TR+TL is within a specified hybrid amplifier operating tilt range. In some embodiments, the derived TR and TL values satisfy the condition TR+TL=TH.

Abstract: Apparatus and method for gain measurement and control of a Distributed Raman Amplifier (DRA). Various embodiments of the apparatus include a detection unit operative to measure, during operation of the DRA, the optical power of a filtered component of the light entering the DRA from the transmission fiber and a gain calculation and control unit coupled to the detection unit and operative to calculate a signal Raman gain property from the measured optical power. The filtered component may exemplarily be a result of passing the light through a band pass filter, a spectral filter with a given spectral shape or a notch filter. The signal Raman gain property may be an average on-off signal Raman gain, an average net signal Raman gain or a signal Raman gain tilt within a communication band. The apparatus and method may be used to operate the DRA in Automatic Gain Control, i.e. to maintain a required constant signal Raman gain and/or signal Raman gain tilt.

Abstract: Method and apparatus for detecting an opening in a transmission fiber connecting a discrete gain unit to a pump unit of a Remote Optically Pumped Amplifier (ROPA) system. The method comprises measuring an optical power entering the pump unit from the transmission fiber, the optical power being in a selected wavelength range, and establishing that the optical power lacks an ASE noise power component generated by the gain unit. The lack of this component indicates the presence of a break or opening in the transmission fiber, and triggers corrective action whereby pump lasers within the pump unit are shut down or have their power reduced to a safe level.