Optical: systems and elements – Optical amplifier – Correction of deleterious effects
Reexamination Certificate
2000-04-14
2001-12-04
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Correction of deleterious effects
C359S341400
Reexamination Certificate
active
06327076
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical amplifier equipment used for wavelangth division multiplexing (WDM) optical communication, and more particularly, relates to optical amplifier equipment for WDM optical communication which has a high degree of flatness in a gain of a signal light of each wavelength.
2. Description of Related Art
A WDM optical communication system which wavelength-division-multiplexes a plurality of signal lights with mutually different wavelengths and optically communicates them is widely used, since it can increase the communication capacity. In the WDM optical communication system, optical amplifier equipment is also applied for the purpose of extending the communication distance or the like.
As the optical amplifier equipment, for example, erbium doped fiber optical amplifier equipment (EDFA) is well known, in which an erbium doped optical fiber to which erbium is doped is used as the optical fiber to be an amplifying medium. Optical fiber amplifier equipment is normally configured by a pumping light source which outputs pumping light and a WDM which wavelength-division-multiplexes the pumping light with the signal light and which puts them into an amplifying optical fiber, besides an optical fiber to be an amplifying medium.
As conventional optical amplifier equipment for WDM optical communication, for example, optical fiber amplifier equipment is well known, which is configured by a two-stage optical fiber amplifier using pumping light with a wavelength of the 980 nm band at the front stage and using pumping light with a wavelength of the 1480 nm band at the rear stage for simultaneously attaining low noise and high power. A description will be given by taking such a configuration as an example. In order to finally flatten the gain for each signal light of the wavelength-division-multiplexed signal light (hereafter, referred to simply as “WDM light”) outputted from the optical fiber amplifier equipment, a gain equalizer is arranged between a front stage optical fiber amplifier and a rear stage optical fiber amplifier.
The gain equalizer is an optical part having a wavelength characteristic of loss which is the reverse of the wavelength characteristic of gain of the optical fiber amplifier. Therefore, the branched output light is received by a monitor PD, and by controlling a pumping light source so that the output light may be constant, the control is performed so that the gain of the optical fiber amplifier may be kept constant.
However, since the wavelength characteristic of the gain of the optical fiber amplifier changes depending on the gain value, the optimized gain flatness can be established only at one point of a certain gain value. Therefore, there is a probability that the gain flatness may not be kept when the loss of an optical part configuring the optical fiber amplifier changes with the environmental temperature.
That is, even if the wavelength characteristic of the gain of an optical fiber amplifier is flattened through the total of the wavelength band of the signal light at a certain specific gain value, for example, a gain of +10 dB, the gain for light with a short wavelength may relatively be higher than that for light with a long wavelength, or the reverse thereof may occur. In any case, the gain is different depending on the wavelength, and the flatness cannot be kept.
Such a fact does not matter when the optical amplification is performed by a gain at which the flatness is previously compensated, for example, in the case where the optical amplifying control is performed so that the optical output level of the amplified signal light may be kept constant, but it may occur when the optical input level of the inputted signal light is lowered and a higher gain is required for still keeping the optical output level constant.
As one means for avoiding the above described problem, it is also considered to control the optical input level of signal light inputted into the optical fiber amplifier equipment so that the optical output level may be a certain constant value and it may be a gain at which the flatness of the gain of the optical fiber amplifier can be attained.
However, even if the control is performed so that the optical input level of such signal light may be a specified value, it is difficult to keep the flatness of the gain of the optical fiber amplifier, for example, because of the loss fluctuation of the optical part itself configuring the amplifier which is caused by the change of the ambient temperature of the optical fiber amplifier, or various other factors. Finally, it is difficult to keep the flatness of the optical output level of each signal light in the amplified WDM light.
SUMMARY OF THE INVENTION
It is an object of the optical amplifier equipment for WDM optical communication of the present invention to prevent the degradation of the gain flatness caused by the change of the ambient temperature of the optical amplifier equipment or the like which is worrisome in the case where an optical fiber amplifier is applied to the WDM optical communication as it is, and to make it possible to perform the optical amplification in the state where the gain uniformity is kept in each signal light.
The Optical amplifier equipment for WDM optical communication of the present invention has, as the basic configuration, an optical amplifier which optically amplifies the inputted WDM light and outputs the amplified signal light, and a control circuit of an optical branching unit and an optical output level detector and an optical amplifier, which optically branches part of the amplified signal light and monitors the light and controls the gain of the optical amplifier and controls the optical output level of the amplified signal light so that it may be constant.
In addition to the above described configuration, on the input side of a first optical amplifier, a WDM which wavelength-division-multiplexes two following quasi-signal lights is arranged, and a first quasi-signal light and a second signal light which have wavelengths different from the wavelength of the signal light and have mutually different wavelengths are wavelength-division-multiplexed with the above described WDM light to be inputted into the first optical amplifier. On the output side of the optical amplifier, an wavelength division multiplexer is arranged, and the configuration is made such that a first amplified quasi-signal light (hereafter, referred to as “first post-amplification quasi-signal light”) and a second amplified quasi-signal light (hereafter, referred to as “second post-amplification quasi-signal light”) are taken out from among the amplified signal light respectively.
The optical output levels of the first and second branched post-amplification quasi-signal lights are detected, and the gain of the optical amplification imposed on the optical amplifier is controlled so that the levels of both may be approximately the same or may be within the previously determined range. That is, the ratio of the set optical output levels is controlled so that the output level to the optical input level of the inputted WDM light may be constant. Preferably, in order that the quasi-signal light is transmitted in the same direction as the signal light, a quasi-signal WDM should be arranged on the input side of the optical amplifier, and the WDM should be arranged on the output side. However, it is also possible to make the quasi-signal light travel in the opposite direction of the direction of the signal light.
The wavelengths of the first and second quasi-signal lights should basically be different from the wavelength of the original signal light, and the wavelengths of both should mutually be different. However, in the case where all wavelengths of the original signal light are close and the wavelength band occupied by the total of the WDM light is narrow, as for the wavelengths of the first and second quasi-signal lights, one quasi-signal light should have a wavelength shorter than that of the wavelength ba
Hellner Mark
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
LandOfFree
Optical amplifier equipment for WDM optical communication does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical amplifier equipment for WDM optical communication, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical amplifier equipment for WDM optical communication will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2583588