PUMP WAVELENGTH TUNING OF OPTICAL AMPLIFIERS AND USE OF SAME IN WAVELENGTH DIVISION MULTIPLEXED SYSTEMS

摘要

The variables and parameters previously understood to affect the gain spectrum of an optical amplifier 13 were: (1) the wavelengths to be amplified; (2) the input power levels at those wavelengths; (3) the characteristics of the amplifying medium 20; (4) the insertion loss spectra of the amplifier's components, including any filter(s) used for gain flattening; (5) the pump band chosen to pump the amplifying medium 20; and (6) the total amount of pump power supplied in the chosen pump band. An additional fundamental variable has been identified which can be used to control the gain spectrum of an optical amplifier 13, namely, the center wavelength of the spectrum of the pump's output power within the chosen pump band. Methods and apparatus for using this variable for this purpose are disclosed. For example a, transmission system is disclosed having a transmitter 11 and a receiver 10 connected by an optical fiber 12. A plurality of optical amplifiers 13 are located along the optical fiber 12 to amplify signal channels between the transmitter and receiver. Each of the amplifiers has a pump light source 21, the wavelength of which is such that contributions to differential gain due to pump light wavelength related effects is substantially reduced. Also disclosed is a WDM transmission system having a transmission path including a concatenation of laser diode pumped optical amplifiers 13 wherein the gain spectrum of an amplifier is controlled at least in part by a feedback loop regulating the temperature of its laser diode pump 21. The feedback loop may for instance derive its control signal from a measure of the drive current applied to the pump, of the emission wavelength of the pump, or of the disparity between the power output from the amplifier in one of the multiplexed signal channels and that from at least one other of the channels.