Optical: systems and elements – Optical amplifier – Correction of deleterious effects
Reexamination Certificate
1999-11-24
2001-09-18
Tarcza, Thomas H. (Department: 3662)
Optical: systems and elements
Optical amplifier
Correction of deleterious effects
C359S341430
Reexamination Certificate
active
06292291
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C § 119 from an application entitled Optical Fiber Amplifier Having Constant Output Power For Each Channel And Amplifying Method Thereof earlier filed in the Korean Industrial Property Office on Nov. 24, 1998, and there duly assigned Ser. No. 98-50473 by that Office.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber amplifier having constant output power for each channel and an amplifying method thereof.
2. Description of the Related Art
In an optical transmission system, an erbium doped fiber amplifier (EDFA) directly amplifies an optical signal that has been weakened during transmission without converting the optical signal into an electrical signal, thus remarkably extending the transmission distance. U.S. Pat. No. 5,768,012 to Raymond Zanoni et al. entitled Apparatus And Method For The High-Power Pumping Of Fiber Optic Amplifiers and U.S. Pat. No. 5,673,129 to Victor Mizrahi entitled WDM Optical Communication Systems With Wavelength Stabilized Optical Selectors are examples of known optical amplifiers.
Wavelength division multiplexing (WDM) optical fiber amplifiers can be generally classified into two groups; automatic gain control (AGC) optical fiber amplifiers in which the gain for each channel is maintained to be constant, and automatic level control (ALC) optical fiber amplifiers in which the output power level for each channel is maintained to be constant.
An AGC optical fiber amplifier can compensate a loss generated in a transmission path because the gain for each channel is maintained at a constant level according to a variation in the power levels of all input signals. In other words, the power level of a signal amplified by an amplifier gradually decreases while passing through the transmission path, and then restored to its original level after passing through the AGC optical fiber amplifier having the same level of the gain as that of the transmission loss. However, the performance of a general optical amplifier used as the transmission path slowly degraded with passing of time and a loss between amplifiers sharply increases. Also, a loss at a certain block of the transmission may abruptly increase due to a temporary problem. In the case of employing the AGC optical fiber amplifier in a transmission path having the above-described characteristics, the power level of a light signal gradually decreases with an increase in the transmission distance due to deterioration of the transmission path or a temporary problem thereof. Repetition of this phenomenon may considerably reduce the power level of a light signal which is input to a final input port compared to an initially set power level of the light signal. Accordingly, in the case where light signals are received in the input port with less than the minimum requirement of reception sensitivity, many en-or signals may be produced.
FIG. 1A
shows a change in the signal power level on a transmission path using the AGC optical fiber amplifier, in which ‘
100
’ denotes an ideal output power level and ‘
101
’ denotes an actual output power level. Referring to
FIG. 1A
, while the gain of the AGC optical fiber amplifier is maintained at a constant value according to the transmission distance, the output power levels are not constant.
An ALC optical fiber amplifier can suppress deterioration in the performance of a transmission system due to deterioration in the performance of a transmission path or an increased loss of a certain block of the transmission path, because the output power level is maintained at a constant level while the gain for each channel varies according to a variation in the power level of an input signal.
FIG. 1B
shows a change in the signal power level on a transmission path using the ALC optical fiber amplifier, in which ‘
102
’ denotes an ideal output power level and ‘
103
’ denotes an actual output power level. Referring to
FIG. 1B
, while the gain of the ALC optical fiber amplifier is varied according to the transmission distance, the output power levels are maintained at a constant level. In order to maintain the output level for each channel at a constant level, the ALC optical fiber amplifier must receive channel add/drop information from the outside.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide an optical fiber amplifier for a constant output level for each channel, which confers different loss characteristics on input light signals according to channels, obtains channel information by comparing a plurality of lossy channels, and amplifies the light signals according to the channel information.
Accordingly, to achieve the above objective, there is provided an optical fiber amplifier having constant output power for each channel including a first measuring unit for dividing an input light signal into a first light signal and a second light signal, sub-dividing the first light signal into a plurality of light signals and converting the plurality of light signals into electrical signals to output the electrical signals, an optical fiber amplifying unit for amplifying the second light signal according to a predetermined amplification control value, a second measuring unit for converting a light signal of a predetermined wavelength band, output from the optical fiber amplifying unit, into an electrical signal, and an output power controller for controlling the predetermined amplification control value according to a plurality of output values of the first measuring unit and an output value of the second measuring unit, so that the power level of the optical fiber amplifying unit is maintained at a constant level.
According to another aspect of the present invention, there is provided an amplifying method for constant output power for each channel including the steps of (a) dividing an input light signal into two signals and amplifying one of the two divided signals according to a predetermined amplification control value, (b) measuring ASE (amplified spontaneous emission) intensity in a predetermined wavelength band from the amplified light signal, (c) sub-dividing the other signal divided in step (a) into a plurality of light signals and inducing different losses to the sub-divided light signals according to wavelengths, and (d) comparing the power levels of the loss-induced light signals of step (c) and controlling the predetermined amplification control value of step (a) so that the ASE intensity measured in step (b) is maintained at a constant level if the compared power levels of the light signals are substantially different. Additionally, the predetermined amplification control value of step (a) is controlled so that the ASE intensity measured in step (b) is increased if the compared power levels of the light signals are substantially the same.
REFERENCES:
patent: 5673129 (1997-09-01), Mizrahi
patent: 5768012 (1998-06-01), Zanoni et al.
patent: 5808785 (1998-09-01), Nakabayashi
patent: 5808788 (1998-09-01), Park et al.
patent: 5812710 (1998-09-01), Sugaya
patent: 5822112 (1998-10-01), Itou et al.
patent: 5907429 (1999-05-01), Sugata
patent: 5912760 (1999-06-01), Sugiya
patent: 5995274 (1999-11-01), Sugaya et al.
patent: 5995275 (1999-11-01), Sugaya
patent: 6038062 (2000-03-01), Kosaka
patent: 6064515 (2000-05-01), Yang
patent: 6067187 (2000-05-01), Onaka et al.
patent: 6108123 (2000-08-01), Kinoshita
patent: 2317044 (1998-11-01), None
patent: 2317044-A (1998-11-01), None
Hwang Seong-taek
Jung Rae-sung
Kim Sung-Jun
Yoon Soo-young
Bushnell , Esq. Robert E.
Hughes Deandra
Samsung Electronics Co,. Ltd.
Tarcza Thomas H.
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