Optical amplifier evaluation method and optical amplifier evaluation instrument

An optical amplifier evaluation method for an optical amplifier evaluation instrument, said instrument comprising:

• a rectangular spectrum light source for providing high-level light output having a flat characteristic at an output level in an arbitrary wavelength range of an optical signal and a rectangular spectrum shape over a wide band;
• a first optical modulator for pulse-modulating output light of said rectangular spectrum light source and causing an on/off state of an optical signal to exist in a time domain in any constant period;
• a second optical modulator for performing on/off pulse operation in the same period as said first optical modulator in synchronization therewith, thereby providing a sampling window in a time domain for extracting and suppressing an optical signal;
• a modulation signal generation section for controlling said first optical modulator and said second optical modulator;
• a light intensity measuring instrument having an optical signal passage band width (Δνn) for measuring the optical intensity for each frequency;
• and
• a measured optical amplifier formed of an optical fiber comprising a rare earth element,
• said method comprising the steps of:
• executing pulse strength modulation for an optical signal output from said rectangular spectrum light source in a sufficiently shorter period than the atomic lifetime at an upper level determined by an amplification medium of said measured optical amplifier or the carrier lifetime and feeding a pulse generated accordingly into said measured optical amplifier;
• controlling the phase of said second optical modulator, synchronizing the sampling window with a time domain in which an optical pulse signal exists, and measuring post-amplified signal light power (Pout—n) of output light of said measured optical amplifier for each frequency component contained in said rectangular spectrum light source;
• synchronizing the sampling window with a time domain in which an optical pulse signal does not exist and measuring amplified spontaneous emission power (PASE—n) of output light of said measured optical amplifier for each frequency component contained in said rectangular spectrum light source;
• and
• computing a noise figure of said measured optical amplifier, (NFn), with respect to each of the wavelengths according to NF n = P ASE ⁢ ⁢ _ ⁢ ⁢ n hv n ⁢ G n ⁢ Δ ⁢ ⁢ v n + 1 G n ( 1 )
• wherein a Planck's constant is (h), each frequency component contained in said rectangular spectrum light source undergoing the pulse modulation is (νn), the gain of said measured optical amplifier at each frequency is (Gn), the optical signal light passage band width of said light intensity measuring instrument when the amplified spontaneous emission power (PASE—n) is measured is (Δνn), and the sampling wavelength in a level flat portion of said rectangular spectrum light source is n=1 to m.