Optical power limiting amplifier

In an optical amplifier comprising:

• an optical waveguide doped with a rare earth and capable of producing stimulated emission of light within a predetermined band of wavelengths and within a predetermined power range and when pumped with light of wavelength .lambda. p, said waveguide having an input end and an output end;
• means for introducing pump light at a wavelength .lambda. p into at least one of said input end and said output end;
• and
• coupling means for coupling input signals at a predetermined wavelength in said band and at different power levels into said input end of said waveguide, said waveguide providing gain for said signals depending upon the amount of
• pumping light power along the length of said waveguide wherein the improvement comprises differential loss inducing means intermediate said input end and said output end and spaced from both said input end and said output end which causes a loss for said signals of said predetermined wavelength which is greater by a predetermined amount than the loss for light at said pumping wavelength .lambda. p, said predetermined amount and the spacing of said loss inducing means from said input end and said output and being selected to cause amplification of said input signals of lower power than other said input signals and in said power range greater than amplification of said other said input signals of greater than power than said input signals of lower power and in said power range by an amount which produces output signals corresponding to said input signals which are of a substantially constant output power at said output end when the dynamic power range of said input signals introduced into said input end is at least 15 dB.