Amplified telecommunication system for wavelength-division multiplexing transmissions

An active optical fiber for use in a laser-pumped optical telecommunications amplifier comprising:

• a core;
• at least one main fluorescent dopant in said core;
• and
• at least one secondary dopant in said core, said main dopant and said secondary dopant having relative characteristics such that emission power of the fiber in a predetermined wavelength band includes a main emission peak and a secondary emission peak when optical pumping energy is supplied to the fiber, the emission power at the secondary emission peak not exceeding by more than 1 dB the emission power at all wavelengths between the main emission peak and the secondary emission peak, and wherein the erbium content in the fiber core expressed as an oxide is between 20 and 5000 ppm by mole.

An active optical fiber for use in a laser-pumped optical telecommunications amplifier comprising:

• a core;
• at least one main fluorescent dopant in said core;
• and
• at least one secondary dopant in said core, said main dopant and said secondary dopant having relative characteristics such that emission power of the fiber in a predetermined wavelength band includes a main emission peak and a secondary emission peak when optical pumping energy is supplied to the fiber, the emission power at the secondary emission peak not exceeding by more than 1 dB the emission power at all wavelengths between the main emission peak and the secondary emission peak, and wherein the numerical aperture of the fiber is higher than 0.15.

An active-fiber optical amplifier, comprising:

• at least one length of silica-based active fiber;
• a pump for supplying optical pumping power at a pumping wavelength to said active fiber;
• a coupler coupling said optical pumping power and at least one transmission signal at a transmission wavelength to said active fiber, a predetermined transmission band including said transmission wavelength;
• said active optical fiber having a core doped with at least one main fluorescent dopant and at least one secondary dopant, said main fluorescent dopant and said secondary dopant having relative characteristics such that a maximum gain variation between any and all two different transmission wavelengths in said predetermined transmission band measured at an input power less than or equal to -20 dBm, is lower than 2.5 dB, wherein the predetermined transmission band includes 1535 nm to 1545 nm.

An active-fiber optical amplifier comprising:

• at least one length of silica-based active fiber;
• a pump for supplying optical pumping power at a pumping wavelength to said active fiber;
• a coupler within said active fiber to couple said optical pumping power and at least one transmission signal, at a transmission wavelength included in a predetermined transmission band, to said active fiber;
• said active optical fiber having a core doped with at least one main fluorescent dopant and at least one secondary dopant, said main fluorescent dopant and said secondary dopant having relative characteristics such that a maximum gain variation between two signals at different transmission wavelengths in said predetermined transmission band measured at an input power less than or equal to -20 dBm, is lower than 2.5 dB, wherein said main fluorescent dopant is an oxide of erbium, and wherein said secondary dopant comprises oxides of aluminium, germanium, and lanthanum.

An active fiber optical amplifier, comprising:

• a first silica-based active-fiber;
• a first pump for supplying optical pumping power at a first pumping wavelength to said first active fiber;
• a first coupler for coupling the optical pumping power of said first pump and a first transmission signal at a first transmission wavelength included in a predetermined transmission band to said first active fiber;
• a second silica-based active fiber;
• a second pump for supplying optical pumping power at a second pumping wavelength to said second active fiber;
• a second coupler for coupling the optical pumping power of said second pump and a second transmission signal at a second wavelength included in said predetermined transmission band to said second active fiber;
• wherein at least one of said first active fiber and said second active fiber includes a core doped with a main fluorescent dopant and at least one secondary dopant, said main and secondary dopants having relative characteristics such that a maximum gain variation between any and all two different transmission wavelengths for said first transmission signal and said second transmission signal measured at an input power less than or equal to -20 dBm is lower than 2.5 dB, wherein the predetermined transmission band includes 1535 nm to 1545 nm.

An active fiber optical amplifier comprising:

• at least one length of silica-based active fiber;
• a pump for supplying optical pumping power at a pumping wavelength to said active fiber;
• a coupler within said active fiber to couple said optical pumping power and at least one transmission signal, at a transmission wavelength included in a predetermined transmission band, to said active fiber;
• said active optical fiber having a core doped with at least one main fluorescent dopant and at least one secondary dopant, said main fluorescent dopant and said secondary dopant having relative characteristics such that a maximum gain variation between two signals at different transmission wavelengths in said predetermined transmission band measured at an input power less than or equal to -20 dBm, is lower than 2.5 dB, wherein said predetermined transmission band is between 1525 and 1560 nm, and wherein said main fluorescent dopant is an oxide of erbium and said secondary dopant includes an oxide of aluminium, an oxide of germanium, and an oxide of lanthanum.

A telecommunications system for transmitting optical signals in a predetermined wavelength band from a transmission station to a receiving station, comprising:

• an optical fiber adapted to connect the transmission station and receiving station;
• and
• at least two active-fiber optical amplifiers connected in series along said optical fiber;
• at least one of said optical amplifiers comprising a silica-based active optical fiber having a core doped with at least one main fluorescent dopant and at least one secondary dopant in appropriate amounts such that the receiving station receives signals with an optical signal/noise ratio, measured at a 0.5 nm filter width, greater than or equal to 15 dB for signals of a wavelength included in said predetermined wavelength band, wherein the secondary dopant includes an oxide of lanthanum.

An optical telecommunication method comprising the steps of:

• generating at least one optical signal at a predetermined wavelength in a wavelength band;
• supplying the optical signal to a length of an optical fiber for transmission therein within an optical telecommunication line;
• providing in the length of the optical fiber an active-fiber optical amplifier including an active fiber doped with a main fluorescent dopant and at least one secondary dopant interacting with the main dopant in the active fiber to generate an amplification gain of the optical signal at the predetermined wavelength in the active-fiber optical amplifier, measured at an input power less than or equal to -20 dBm, differing by less than 1.6 dB from the corresponding gain of any and all signals at a different wavelength in the band, wherein the predetermined transmission band includes 1535 nm to 1545 nm;
• amplifying the optical signal at least once in the length of the optical fiber by at least one active-fiber optical amplifier;
• and
• receiving the at least once amplified optical signal through a receiver.