US Patent 7869686 - Optical fiber amplifier using quantum dots

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Doped fibers are used in optical communications to amplify signals without requiring optoelectric conversion. This patent from Alcatel-Lucent teaches a doped optical fiber including quantum dots having a size chosen to select a wavelength for optical pumping and improve the effectiveness of amplification. Claim 1 reads:

1. An amplifying optical fiber comprising a core and a cladding, wherein the core comprises:

a monomode core comprising a dopant and quantum dots, and propagating an optical signal; and

a multimode core surrounding the monomode core, and receiving a pumping signal, wherein the dopant is provided for coupling with the pumping signal to amplify the optical signal, and the quantum dots are used for selecting a wavelength of the pumping signal, and wherein a diameter of the quantum dots is in a range between 2 nm and 5 nm.