Optical amplifier

An optical amplifier comprising:

• light-amplifying means for directly amplifying an inputted optical signal which has been inputted using a stimulated emission phenomena, to generate an amplified optical signal;
• first optical branching means for branching part of said amplified light to output first branching light;
• first light-pass filter means which allows light, of said first branching light, with wavelengths in a predetermined specific band to pass, to output first light with specific wavelengths;
• second optical branching means for branching part of said amplified light to output second branching light;
• second light-pass filter means which allows light, of said second branching light, with wavelengths in a predetermined specific band to pass, to output second light with specific wavelengths;
• second light-sensing means for converting said light with specific wavelengths into a second electrical signal to output said signal;
• an operational amplifying medium for subjecting said first electrical signal and said second electrical signal to a subtracting process to output a differential signal;
• and
• gain control means for controlling a gain of said light-amplifying means on the basis of said differential signal so as to maintain a level of said optical signal at a constant value.

An optical amplifier comprising:

• light-amplifying means for directly amplifying inputted signal light which has been inputted using a stimulated emission phenomena, to generate amplified light;
• amplified signal light-extracting means for removing amplified spontaneous emmission from said amplified light to extract the amplified signal light with the same wavelengths as said inputted signal light;
• level-measuring means for measuring a level of said amplified signal light to optput the level of the amplified signal light;
• and
• gain control means for controlloing a gain of said light-amplifying means so as to maintain an optical output of said amplified light at a constant level on the basis of said level of the amplified signal light,
• wherein said amplified signal light-extracting means comprises a first coupler for receiving said amplified light and for producing first and second outputs based on said amplified light, and a second coupler for recieving said second output of said first coupler and for producing first and second outputs, and
• wherein said level-measuring means comprises a first light sensor for receiving said first output of said first coupler,
• wherein said amplified signal light-extracting means further comprises a first bandpass filter coupled between said first light sensor and said first coupler, and a second bandpass filter for receiving said first output of said second coupler,
• wherein said level-measuring means further comprises a second light sensor coupled to an output of said second bandpass filter, and
• wherein said gain control means comprises an operational amplifier for receiving outputs from said first and second light sensors.