Optical amplifier and optical transmission system

Optical amplifying unit (100) having an amplification wavelength band above 1570 nm, comprising:

• an input (101) for the input of optical signals,
• an output (102) for the output of said optical signals,
• at least an erbium-doped active fiber (103a, 103b) having a first end optically coupled to said input (101) and a second end optically coupled to said output (102), for the amplification of said optical signals,
• a pump source (104, 106) for generating a pump radiation adapted to excite erbium, and
• an optical coupler (105, 107) optically coupling said pump source (104) to said at least an active fibre (103),
• characterized in that said pump source has an emission wavelength greater than 1400 nm and lower than 1470 nm.

Optical amplifying unit (100) having an amplification wavelength band above 1570 nm, comprising:

• an input (101) for the input of optical signals,
• an output (102) for the output of said optical signals,
• at least an active fiber (103a, 103b) having a core doped with erbium and aluminum and having a first end optically coupled to said input (101) and a second end optically coupled to said output (102), for the amplification of said optical signals,
• a pump source (104, 106) for generating a pump radiation at a wavelength between 1400 nm and 1480 nm for exciting erbium, and
• an optical coupler (105, 107) optically coupling said pump source (104) to said at least an active fibre (103),
• characterized in that the Al concentration in the core of said active fiber is comprised between 1% and 6% weight molar concentration.

Optical amplifying unit (100) having an amplification wavelength band above 1570 nm, comprising:

• an input (101) for the input of optical signals,
• an output (102) for the output of said optical signals,
• at least an active fiber (103a, 103b) having a core doped with erbium and aluminum and having a first end optically coupled to said input (101) and a second end optically coupled to said output (102), for the amplification of said optical signals,
• a pump source (104, 106) for generating a pump radiation at a wavelength between 1400 nm and 1480 nm for exciting erbium, and
• an optical coupler (105, 107) optically coupling said pump source (104) to said at least an active fibre (103),
• characterized in that Al concentration in the core of said active fiber has a numeric aperture NA comprised between 0.25 and 0.32.