Method for driving a laser amplifier with minimized distortion

A method for controlling an optical amplifier, said optical amplifier amplifying an input optical beam in accordance with an optical gain which varies as a function of both change in wavelength and a change in power level of the input optical beam, within a range of wavelengths and a range of power levels, respectively, within which the optical amplifier is operable, the relationship between the variation in optical gain with respect to wavelength of the input optical beam within the operable wavelength range defining for a fixed power level of the input optical beam within the operable power level range, a corresponding, fixed characteristic curve and defining for power levels varying throughout the operable power level range respectively corresponding, varying characteristic curves, each fixed characteristic curve defined a corresponding, fixed characteristic peak gain and a respective, fixed characteristic wavelength, said method comprising:

• determining a first reference optical power level of the input optical beam, and thereby a corresponding first reference characteristic curve, below which first reference optical power level a further reduction in the optical power level of the input optical beam does not produce any substantial change in the relationship of the optical gain of the optical amplifier as a function of a change in wavelength of the input optical beam and accordingly of the first reference characteristic curve;
• defining, in accordance with the first reference characteristic curve, a corresponding first reference peak gain and a respective, first reference characteristic wavelength;
• determining a second reference optical power level of the input optical beam, greater than the first reference optical power level, at which the corresponding second reference characteristic curve has a corresponding, second reference peak gain which is lower than the first reference peak gain by approximately three decibels and defines a respective second reference characteristic wavelength;
• limiting the variable optical power level of the input optical beam to a range having a maximum level equal to the second reference optical power level;
• and
• limiting the variable wavelength of the input optical beam to a reference range between the first and second reference wavelengths.