Optical amplifier for collectively amplifying optical signals having a plurality of multiplexed wavelengths

An optical amplifier comprising:

• an erbium doped fiber having three cross section layers of glass materials which are doped with erbium;
• and
• three light sources for generating excitation lights in a 1.48 .mu.m band, a 0.5 .mu.m band and a 0.98 .mu.m band, respectively, and for emitting the excitation lights to the erbium doped fiber,
• wherein an innermost layer of said three cross section layers is located at a center of the erbium doped fiber, a second layer is located near a middle of mode field diameters for said 0.5 .mu.m and 0.98 .mu.m bands, and a third layer is located near a middle of mode field diameters for said 0.98 .mu.m band and said 1.48 .mu.m band.

An optical amplifier comprising:

• an optical fiber including first and second cross section layers with the second cross section layer surrounding the first cross section layer, the first and second cross section layers both being made of glass doped with a rare earth element and having different emission cross section characteristics;
• and
• first and second light sources providing excitation lights in first and second wavelength bands, respectively, to the optical fiber, so that a plurality of different wavelengths included in a wavelength division multiplexed (WDM) signal travelling through the optical fiber are collectively amplified,
• wherein the first cross section layer is doped with erbium and germanium, and the second cross section layer is doped with erbium and aluminum.

An optical amplifier comprising:

• an optical fiber including first and second cross section layers with the second cross section layer surrounding the first cross section layer, the first and second cross section layers both being made of glass doped with a rare earth element and having different emission cross section characteristics;
• first and second light sources providing excitation lights in first and second wavelength bands, respectively, to the optical fiber, so that a plurality of different wavelengths included in a wavelength division multiplexed (WDM) signal travelling through the optical fiber are collectively amplified;
• and
• a circuit controlling powers of the excitation lights in the first and second wavelength bands.

An optical amplifier comprising:

• an optical fiber including first and second cross section layers with the second cross section layer surrounding the first cross section layer, the first and second cross section layers both being made of glass doped with a rare earth element and having different emission cross section characteristics;
• and
• first and second light sources providing excitation lights in first and second wavelength bands, respectively, to the optical fiber, so that a plurality of different wavelengths included in a wavelength division multiplexed (WDM) signal travelling through the optical fiber are collectively amplified,
• wherein the wavelength bands of the excitation lights are a 1.48 .mu.m band and a 0.98 .mu.m band, respectively, and a cutoff wavelength of the optical fiber is 0.98 .mu.m or shorter.

An optical amplifier comprising:

• an optical fiber including first and second cross section layers with the second cross section layer surrounding the first cross section layer, the first and second cross section layers both being made of glass doped with a rare earth element and having different emission cross section characteristics;
• and
• first and second light sources providing excitation lights in first and second wavelength bands, respectively, to the optical fiber, so that a plurality of different wavelengths included in a wavelength division multiplexed (WDM) signal travelling through the optical fiber are collectively amplified,
• wherein the first cross section layer is formed of GeO.sub.2 --SiO.sub.2 glass, and the second cross section layer is formed of Al.sub.2 O.sub.3 --SiO.sub.2 glass.

An optical amplifier comprising:

• an optical fiber including first and second cross section layers with the second cross section layer surrounding the first cross section layer, the first and second cross section layers both being made of class doped with a rare earth element and having different emission cross section characteristics;
• and
• first and second light sources providing excitation lights in first and second wavelength bands, respectively, to the optical fiber, so that a plurality of different wavelengths included in a wavelength division multiplexed (WDM) signal travelling through the optical fiber are collectively amplified,
• wherein the first cross section layer is formed of GeO.sub.2 --Al.sub.2 O.sub.3 --Si glass, and the second cross section layer is formed of Al.sub.2 O.sub.3 --SiO.sub.2 glass.

An optical amplifier comprising:

• an optical fiber having first, second and third concentrically arranged cross section layers of glass materials which are each doped with a rare earth element, the second layer concentrically arranged around the first layer, and the third layer concentrically arranged around the second layer;
• and
• first, second and third light sources providing excitation lights in first, second and third bands, respectively, to the optical fiber so that a plurality of different wavelengths included in a wavelength division multiplexed (WDM) signal travelling through the optical fiber are collectively amplified, wherein
• the first layer is at a position corresponding to a mode field diameter of the first band so that the first layer is excited by excitation light in the first band to a higher degree than by excitation lights in the second and third bands,
• the second layer is at a position corresponding to a mode field diameter of the second band so that the second layer is excited by excitation light in the second band to a higher degree than by excitation lights in the first and third bands, and
• the third layer is at a position corresponding to a mode field diameter of the third band so that the third layer is excited by excitation light in the third band to a higher degree than by excitation lights in the first and second bands.

An optical amplifier comprising:

• an optical fiber having first and second concentrically arranged cross section layers of glass materials which are each doped with a rare earth element, the second layer concentrically arranged around the first layer;
• and
• first and second light sources providing excitation lights in first and second bands, respectively, to the optical fiber so that a plurality of different wavelengths included in a wavelength division multiplexed (WDM) signal travelling through the optical fiber are collectively amplified, wherein
• the first layer is at a position corresponding to a mode field diameter of the first band so that the first layer is excited by excitation light in the first band to a higher degree than by excitation light in the second band, and
• the second layer is at a position corresponding to a mode field diameter of the second band so that the second layer is excited by excitation light in the second band to a higher degree than by excitation light in the first band.