Light amplifier

A light amplifier comprising:

• a first light amplifying part which is excited by a first exciting light and amplifies a signal light applied hereto;
• an inverted population generating part which is supplied with a second exciting light having a wavelength different from that of the first exciting light and which generates an inverted population of a level of elements or ions related to amplifying based on said second exciting light and another level not related to amplifying;
• a measuring part which measures an amplified spontaneous emission caused by said inverted population;
• a first control part which controls a control operation so that an intensity of an amplified signal light output from said first light amplifying part is constant;
• and
• a second control part which controls the second exciting light so that a peak wavelength or a given wavelength of said amplified spontaneous emission is constant based on a result of a measurement by said measuring part.

A light amplifier comprising:

• a first light amplifying part which is excited by a first exciting light and amplifies a signal light applied hereto;
• an inverted population generating part which is supplied with a second exciting light having a wavelength different from that of the first exciting light and which generates an inverted population of a level of elements or ions related to amplifying based on said second exciting light and another level not related to amplifying;
• a second light amplifying part which is supplied with the first exciting light and a second exciting light and which has a loop in which an output light of the loop is input hereto as an input light, said second light amplifying part having an attenuator;
• an attenuation control part which controls an amount of attenuation of said attenuator on the basis of the signal light input to said first light amplifying part;
• a first control part which controls an intensity of tile second exciting light on the basis of an amplified spontaneous emission output from said attenuator;
• and
• a second control part which performs a control operation so that an intensity of the signal light output from said first light amplifying part is constant.

A light amplifier comprising:

• a first light amplifying part which is excited by a first exciting light and amplifies a signal light applied hereto;
• an inverted population generating part which is supplied with a second exciting light and generates an inverted population of elements or ions performing a light amplifying operation;
• and
• a first control part which obtains a gain of the signal light by said first light amplifying part and a loss of said second exciting light and which controls an intensity of said first exciting light on the basis of said gain and said loss.

A light amplifier comprising:

• a first light amplifying part which has a variable amplifying medium and is excited by a first exciting light, said first light amplifying part amplifying a signal light applied hereto;
• a first control part which controls a length of said variable amplifying medium of said first light amplifying part on the basis of an intensity of the signal light applied to said first light amplifying part;
• and
• a second control part which controls an intensity of said first exciting light on the basis of an amplified light signal output from said first light amplifying part.

A light amplifier comprising:

• a first light amplifying part which is excited by a first exciting light and amplifies a signal light input hereto:
• a first control part which controls an intensity of said first exciting light so that a gain of the signal light by said first light amplifying part is constant;
• and
• a tenth control part which performs a control operation so that an intensity of an amplified light signal output from said first light amplifying part is constant.