Optical: systems and elements – Optical amplifier – Correction of deleterious effects
Patent
1998-04-07
1999-09-28
Moskowitz, Nelson
Optical: systems and elements
Optical amplifier
Correction of deleterious effects
359161, 359187, 359341, H01S 306, G02F 139
Patent
active
059597666
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention concerns an optical amplifier device for transmitting composite signals consisting of optical signals with different wavelengths.
Optical amplifiers are used in optical transmission systems, e.g. cable television distribution systems, and serve to amplify optical signals whose signal level is attenuated by optical components, e.g. couplers or glass fibers. Many optical components cause wavelength-dependent attenuation. If an optical transmission system transmits composite signals consisting of optical signals having respectively different wavelengths, the wavelength-dependent attenuation causes optical signals with different levels to be received at the input of the optical amplifier. The amplifiers amplify the different levels of the optical signals within a predetermined range of the optical input power, which causes the wavelength-dependent attenuation to extend to the subscriber, and thus the transmission range is determined by the wavelength that is attenuated most.
The article "Equalization in Amplified WDM Lightwave Transmission Systems" in IEEE Photonics Letters, Vol. 4, No. 8, August 1992, pages 920-922, describes an optical transmission system wherein composite signals consisting of optical signals with respectively different wavelengths are transmitted by a sending unit to a receiving unit via a glass fiber path. To compensate for the wavelength-dependent attenuation and to provide optical signals of the same level at the receiving unit, the optical signals are transmitted by the sending unit via variable optical attenuators with respectively different signal levels. Optical signals whose wavelengths are attenuated more are transmitted at a higher signal level. A monitoring line is required from the receiving unit to the sending unit to adjust the signal level. Because of the different distances and the different number of optical components between the sending unit and the receiving unit in a branched, e.g. tree-shaped distribution network, it is only conditionally possible to adjust the levels of the optical signals in the direction of the transmission so that the same signal levels are produced in all receiving units.
SUMMARY OF THE INVENTION
It is therefore the task of the invention to provide a device whereby the wavelength-dependent attenuations can be compensated for in a more flexible manner.
This task is fulfilled by an optical amplifier device for transmitting composite signals consisting of optical signals with different wavelengths, the optical amplifier device (REG) comprising a variable attenuator, a variable-gain optical amplifier, a coupler, a composite-signal input, a composite-signal output, and a control unit for determining control signals for the variable attenuator and the variable-gain optical amplifier, wherein the composite-signal input is connected to the composite-signal output via a series combination of the variable attenuator, the variable-gain optical amplifier, and the coupler, wherein a portion of the composite signal at the output of the variable-gain optical amplifier is feedable via the coupler to the control unit, and wherein the control signals are determinable in the control unit from the individual levels of the optical signals of the portion of the composite signal.
A particular advantage of the invention is the increase in the transmission range of optical signals with respectively different wavelengths which are collectively transmitted via a glass fiber path, by optically manipulating the wavelength-dependent spectrum with erbium-doped fiber amplifiers.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained in the following by means of a configuration example with the help of FIGS. 1 to 3, wherein:
FIG. 1 is a schematic illustration of a transmission system according to the invention,
FIG. 2 is a schematically illustrated configuration of an amplifier device according to the invention,
FIG. 3 has three diagrams wherein the signal level is drawn above the wavelength in each case.
BEST MODE FOR CARRYING OUT TH
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Chraplyvy et al, IEEE Photonics Tech. Lett., vol. 4, #8, pp. 920-922, Aug. 1992.
Sugaya et al, O & A '95 paper Fc 3, Davas, Switzerland, 4 pages., Jun. 16, 1995.
Nakabayashi et al, Tech Report of IEIce, OCS 94-66, PE 94-89 (1994-11); with Translation, 1994.
Patent Abstract of Japan, vol. 015, No. 480 (P-1284), Dec. 5, 1991 & JP 03 206427 A (Mitsubishi Electric Corp) Sep. 9, 1991.
"Equalization in Amplified WDM Lightwave Transmission Systems" by Chraplyvy et al in IEEE Photonics Technology Letters, vol. 4, No. 8, Aug. 1992, pp. 920-922.
Otterbach Jurgen
Pfeiffer Thomas
Alcatel Alsthom Compagnie Generale d'Electric
Moskowitz Nelson
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