Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-04-21
2001-05-15
Negash, Kinfe-Michael (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S337000, C359S341430
Reexamination Certificate
active
06233078
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photo signal amplification transmission system for amplifying a photo signal (multi-wavelength signal) constituted of plural multiplexed signals having different wavelengths which are transmitted through an optical fiber cable, and particularly to a control over an amplitude in accordance with the number of multiplexed wavelengths.
2. Description of the Prior Art
As is well known, when a photo signal is transmitted over a long distance by using an optical fiber cable, a failure occurs on a receiving side even if output power is. too low or too high. Therefore, an optimum output power is required.
Therefore, in the long-distance transmission of the photo signal by means of the optical fiber cable, in general a relay amplifying device is installed at each relay point, so that amplification is performed to obtain the optimum output power.
FIG. 1
is a block diagram showing a conventional photo signal amplification transmission system.
In
FIG. 1
, numeral
31
denotes a WDM (wavelength division multiplex) photo coupler for combining an input signal from IN and an activating laser beam;
32
denotes an erbium doped fiber (EDF) for amplifying a photo signal when an activating light is injected;
33
denotes an output monitoring photo coupler;
34
denotes an activating laser beam source (referred to as the activating LD);
35
denotes an automatic output power control (APC) circuit; and
36
denotes an output monitoring photo detector(PD).
In the conventional photo signal amplification transmission system, for example at a relay point, as shown in
FIG. 1
, the EDF
32
and the activating LD
34
constitute an optical fiber amplifier. An output level is monitored by the output monitoring photo coupler
33
. The monitored output level is compared with a predetermined optimum value (fixed value). Then, the activating LD
34
is feedback-controlled by the APC
35
in such a manner that the output level reaches the optimum value.
In the conventional photo signal amplification transmission system, since the output power is generally controlled to reach the predetermined optimum value (fixed value), a problem occurs when the photo signal (multi-wavelength signal) constituted of plural multiplexed signals having different wavelengths is transmitted.
Specifically, in the conventional system, even the multi-wavelength signal is controlled as one signal in such a manner that it reaches the predetermined fixed value. Therefore, in the case of one wavelength (one signal), the output power is largely varied in accordance with the number of multiplexed wavelengths.
For example, as the number of multiplexed wavelengths is increased, the light output power for one wavelength is decreased. Therefore, when multiple signals (wavelengths) are multiplexed, the light output power for one wavelength is weakened to a degree to which a dynamic range of a receiver cannot be followed. As a result, an error in transmission of the photo signal or another problem arises.
SUMMARY OF THE INVENTION
Wherefore, an object of the invention is to provide a photo signal amplification transmission system in which a light output power is controlled in accordance with the number of multiplexed wavelengths and finally a light power of each signal received by a receiver can be optimized.
To attain this and other objects, the invention provides a photo signal amplification transmission system in which at a transmission end a photo signal to be transmitted via an optical fiber cable is amplified to a desired level before transmitted, wherein when the photo signal to be transmitted is a multi-wavelength signal constituted of plural multiplexed signals having different wavelengths, an amplifying means is controlled in accordance with the number of wavelengths, and the photo signal is batch-amplified to the desired level in accordance with the number of wavelengths before transmitted.
The invention also provides a photo signal amplification transmission system in which at a relay point a photo signal transmitted via an optical fiber cable is amplified to a desired level before transmitted, wherein the photo signal amplification transmission system is provided with a wavelength number information management section which receives and transmits wavelength number information, when the transmitted photo signal is a multi-wavelength signal constituted of plural multiplexed signals having different wavelengths, an amplifying means is controlled in accordance with the number of wavelengths which is obtained by the wavelength number information management section, and the photo signal is batch-amplified to the desired level in accordance with the number of wavelengths before transmitted.
The invention further provides a photo signal amplification transmission system in which at a receiving end a photo signal transmitted via an optical fiber cable is amplified to a desired level, wherein the photo signal amplification transmission system is provided with a means for receiving wavelength number information, when the transmitted photo signal is a multi-wavelength signal constituted of plural multiplexed signals having different wavelengths, an amplifying means is controlled in accordance with the number of wavelengths which is obtained by the means, and the photo signal is batch-amplified to the desired level in accordance with the number of wavelengths.
Also, the wavelength number information management section at the relay point separates and receives a wavelength number information signal which is transmitted while being multiplexed on a main signal by using a wavelength different from the wavelength of the photo signal (main signal) transmitted from the transmission end via the optical fiber cable. The wavelength number information, signal is multiplexed onto the main signal which has been amplified by the amplifying means by using the wavelength different from the wavelength of the main signal, before transmitted.
Also, the means for receiving the wavelength number information at the receiving end separates and receives a wavelength number information signal which is transmitted while being multiplexed on the main signal by using a wavelength different from the wavelength of the photo signal (main signal) transmitted from the transmission end or the relay point via the optical fiber cable.
Also, the amplifying means is provided with an activating laser beam source, a WDM photo coupler for combining an activating light from the activating laser beam source with the multi-wavelength signal and an erbium doped fiber.
Further the amplifying means is controlled in accordance with the number of wavelengths by monitoring the amplified output and transmitting the wavelength number information to an APC circuit for feedback-controlling an activating laser beam source.
In the photo signal amplification transmission system according to the invention, the information of the number of multiplexed wavelengths is managed as aforementioned. By transmitting the information together with the main signal, the multi-wavelength signal is amplified in accordance with the number of wavelengths by a transmission photo amplifier, a relay photo amplifier and a receiving photo amplifier.
Finally, a light power for each signal received by the receiver can be optimized. Therefore, a receiver with a narrow dynamic range can be used.
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Harano Hiroshi
Maruyama Naoki
NEC Corporation
Negash Kinfe-Michael
Scully Scott Murphy & Presser
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