Abstract: The present invention relates to fiber lasers for long wavelength band. More particularly, the invention relates to an Erbium-doped fiber laser for long wavelength band for lowering lasing threshold and improving the output efficiency by injecting conventional band backward Amplified Spontaneous Emission (ASE) for the design of a laser which lases in 1580 nm band.

Abstract: The present invention is to provide an optical fiber amplifier for clamping and equalizing gain in optical communication systems comprising: a gain clamping amplifier unit for clamping the gain, so as to make input signals have the same output power for each channel by applying a compensating signal; a second isolator for passing the input signal light from said gain clamping amplifier unit and isolating the light coming from the opposite direction; a gain equalizing filter for equalizing the output gain spectrum from the input signal from said second isolator; and a post-amplifier unit for amplifying the signal from said gain equalizing filter. Thus, the optical fiber amplifier is capable of clamping gain automatically by maintaining the same population inversion, and capable of maintaining the same gain equalization for the wide signal gain band to achieve the high transmission capacity, in cases that the number of channel varies in the input signal, while providing a high output signal power.