Reliability of lightwave communication systems using optical amplifiers along the transmission path from transmitter to receiver depends heavily on the reliability of such optical amplifiers. Optical amplifiers find extensive use in lightwave communication systems for boosting lightwave signal power sufficiently high to enable transmission over relatively long distances. Optical amplifiers are attractive alternatives to other amplifier forms because they amplify lightwave signals in their photonic form without conversion into a corresponding electrical signal. Each such optical amplifier is pumped, either optically or electrically, to provide signal amplification. While fiber structures and semiconductor structures have been used to realize these amplifiers, optically pumped, doped fiber amplifiers appear to be most widely accepted for use in fiber lightwave systems for a number of reasons. An optical fiber realization causes the amplifier to be readily matchable to, and integrable with, the fiber transmission media. In addition, the fiber-based optical amplifier provides polarization-independent gain, a broad and well-defined gain spectrum, and resistance to intersymbol interference for multi-channel wavelength-division-multiplexed systems.
At its inception, the fiber-based optical amplifier such as the rare-earth doped optical fiber amplifier had been optically pumped by a single light source. Light from the single source, such as a laser operating at the appropriate pump wavelength, is coupled into the doped fiber to create an appropriate amplifying medium via inversion of the rare-earth ions. Hence, this type of optical amplifier is only as reliable as its pump laser. When the pump laser fails, the entire optical amplifier fails. Dual port pumping, that is, pumping from the input and output ports of the optical amplifier mitigates this problem to some degree when separate lasers pump the different ports. But, when either pump laser in the dual port scheme fails, the pump power through that port of the amplifier is undeniably lost.
An aging pump laser may provide insufficient optical power to produce the required amount of amplification for the doped optical fiber amplifier. If the laser malfunctions, amplification may be interrupted until the pump laser is replaced or repaired. When the pump laser fails, the amplifier fails.
There is no known technique or apparatus for removing this interdependence between the operational reliability of the amplifier and the operational reliability of its pump laser. No techniques or apparatus are known to have been proposed for providing uninterrupted amplification from an optically pumped optical amplifier regardless of the operational status of its pump laser. Moreover, there has been no technique or apparatus proposed for insuring that pump power continues to be delivered to one or more pump ports of the amplifier in spite of pump laser failures.