Double-core active fiber optical amplifier having a wide-band signal wavelength

A double-core active optical fiber (6) comprising fluorescent doping substances, particularly for use in optical fiber amplifiers for optical telecommunication lines, characterised in that it has two optically coupled cores (11 and 12, 101 and 102) uniformly spaced in a common cladding in which the former (11, 101) is an amplifying core and contains a fluorescent doping substance having a stimulated emission in a wavelength range and is adapted to be connected to an optical fiber carrying a telecommunication signal and luminous pumping energy multiplexed in the same fiber, and the second core (12, 102) is an attenuating core and contains a doping substance having high luminous absorption, the maximum optical coupling of the two cores occurring in a wavelength band comprised within said stimulated emission range of the first core and being different from that of the telecommunication signal.

An optical amplifier for amplifying signals at a plurality of wavelengths throughout a predetermined spectral window comprising:

• a length of active optical waveguide pumpable at a pump wavelength for amplifying said signals, when said signals are passed through said waveguide, in accordance with a gain spectrum which includes a peak;
• and an optical filter coupled to said length the waveguide intermediate its ends and operative to reduce gains at wavelengths in a band within said window which includes the peak wavelength of the gain spectrum whereby the gain throughout the window is substantially constant for all signals at wavelengths within the window.

A fiber optic filter structure comprising an optical fiber having a single-mode core surrounded by cladding material, and at least one light-attenuating light path in said cladding material uniformly spaced from said single-mode core, the propagation constants of said single-mode core and said light-attenuating light path being different at wavelengths except for at least one wavelength λf the spacing between said single-mode core and said at least one light-attenuating light path being sufficiently small that light within a first band of wavelengths centered around λf couples between said single-mode core and said light-attenuating light path, at least a portion of the light within said first band of wavelengths being absorbed in said light-attenuating light path.

A fiber optic amplifier structure comprising an optical fiber having a single-mode gain core doped with active dopant ions capable of producing stimulated emission of light within a predetermined range of wavelengths, said optical fiber further comprising light-attenuating coupling means, the coupling characteristics of said gain core and said coupling means being such that optical power in at least one wavelength band centred around at least one wavelength λf within said predetermined range of wavelengths is selectively coupled and attenuated, while optical power at other wavelengths within said predetermined range of wavelengths remains substantially guided by said gain core.

A fiber optic structure for amplifying optical signals, comprising an optical fiber having a single-mode gain core and a light-attenuating core uniformly spaced within a common cladding, said gain core containing active dopant ions that are capable of producing stimulated emission of light within a predetermined band of wavelengths, the optical characteristics of said cores being such that the propagation constants of said cores are different except for at least one wavelength λf within said predetermined band of wavelengths, the spacing between said cores being sufficiently small that light within a band of wavelengths centered around λf couples between said gain core and said light-attenuating core.

An optical amplifier for amplifying signals at a plurality of wavelengths throughout a predetermined spectral window with a gain which is substantially constant throughout said window comprising:

• a length of active optical waveguide pumpable at a pump wavelength for amplifying said signals at said plurality of wavelengths within said window, when said signals are passed through said waveguide, in accordance with a gain spectrum which is substantially constant except for wavelengths in a band within said window which have a greater gain than other wavelengths in said window;
• a source of pumping energy coupled to said waveguide for pumping said waveguide, said pump wavelength being less than said wavelengths in said band;
• and an optical filter disposed at a least one point along the length of the waveguide intermediate its ends and operative to reduce gains at wavelengths in said band within said window whereby the gain throughout the window is substantially constant for all signals at wavelengths within the window.