Optical: systems and elements – Optical amplifier – Correction of deleterious effects
Reexamination Certificate
1999-12-17
2001-06-12
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Correction of deleterious effects
C359S341430, C359S199200, C372S006000, C372S034000
Reexamination Certificate
active
06246512
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical amplifier which collectively amplifies signal light having a plurality of wavelengths in a WDM type optical transmission system.
2. Related Background Art
As optical communications are attaining a greater capacity and higher speed, studies and developments concerning wavelength division multiplex (WDM) transmission systems are being made. One of the most important optical devices in the WDM transmission systems is an optical amplifier which collectively amplifies signal light having a plurality of wavelengths. As such an optical amplifier, an optical fiber amplifier (EDFA: Er-Doped Fiber Amplifier) using an amplifying optical fiber (EDF: Er-Doped Fiber) doped with Er (erbium) element has conventionally been employed.
Such an optical amplifier is provided in each repeater in an optical transmission system. As a consequence, if its gain characteristic (gain deviation or gain slope) is inferior, then, even though a certain wavelength of signal light among a plurality of wavelengths may reach a receiving station with sufficient intensity, the intensity of signal light having the other wavelengths may attenuate such that errors in reception of signal light are caused. Therefore, the optical amplifier is designed and manufactured so as to exhibit a favorable gain characteristic in its signal light wavelength band.
Since the gain characteristic of the optical amplifier also changes depending on temperature, however, even when the optical amplifier is designed and manufactured so as to attain a favorable gain characteristic at a certain temperature, its gain characteristic will deteriorate if the temperature in use changes. In order to eliminate such a problem, there are some known techniques have been known for maintaining the gain characteristic of the optical amplifier.
For example, according to the technique disclosed in Japanese Patent Application Laid-Open No. HEI 4-11794, a temperature control device such as Peltier device is employed so as to control the temperature of the amplifying optical fiber or the like constituting the optical amplifier to keep it constant, thereby maintaining the gain characteristic of the optical amplifier. According to the technique disclosed in Japanese Patent Application Laid-Open No. HEI 5-82873, on the other hand, the amplifying optical fiber constituting the optical amplifier is made shorter, so as to reduce the change in gain characteristic with respect to the change in temperature.
SUMMARY OF THE INVENTION
The inventors found out that the above-mentioned conventional examples have their respective problems as follows. Namely, the technique described in Japanese Patent Application Laid-Open No. HEI 4-11794 is problematic in that its power consumption is high due to the use of the temperature control device such as Peltier device. According to a trial calculation, the additional power consumption per Peltier device is about 5 W. For releasing the heat generated thereby, the housing for accommodating the optical amplifier has to be made greater.
Further the inventors found out in the technique described in Japanese Patent Application Laid-Open No. HEI 5-82873 that although the change in absolute value of gain becomes smaller, the wavelength characteristic of gain changes, whereby the transmission characteristic would deteriorate in the WDM transmission in which the gain deviation is required to be smaller and the optical analog transmission in which the gain slope is needed to be smaller.
So, the inventors, in order to eliminate the above-mentioned problems, created the present invention.
It is an object of the present invention to provide an optical amplifier which has a low power consumption and exhibits a minimized change in gain characteristic along with changes in temperature.
The optical amplifier in accordance with the present invention comprises: (1) an optical waveguide for amplifying signal light incident thereon while pumping light is being supplied, and outputting thus amplified signal light; (2) a transmission device, substantially cascaded to the optical waveguide, for transmitting therethrough the signal light with a predetermined transmission characteristic; (3) pumping means for outputting the pumping light and supplying the pumping light to the optical waveguide; (4) temperature detecting means for detecting a temperature of or near the optical waveguide; and (5) control means for controlling the transmission characteristic of the transmission device according to the temperature detected by the temperature detecting means.
The signal light fed into the optical amplifier is outputted by way of the optical waveguide and the transmission device. Here, the optical waveguide amplifies the signal light as the pumping light is supplied thereto by the pumping means, whereas the transmission device transmits therethrough the signal light with the transmission characteristic controlled by the control means. Also, the transmission characteristic of the transmission device is controlled according to the temperature of or near the optical waveguide detected by the temperature detecting means. As a consequence, the optical amplifier has a gain which is the combination of the transmission loss in the transmission device and the gain in the optical waveguide, thereby alleviating the change in total gain caused by changes in temperature.
The optical waveguide may be an optical fiber. In this case, the connection loss with respect to optical fiber lines is low. The optical waveguide may be doped with Er element as a material exhibiting an optically amplifying effect. In this case, signal light in the wavelength band of 1.55 &mgr;m, which is most commonly used for optical communications, is amplified.
The transmission device may be a variable optical attenuator, disposed in front of or within the optical waveguide, having a transmission characteristic with a uniform dependence of transmission loss on wavelength and a variable magnitude of transmission loss. In this case, as temperature changes, the intensity of the whole signal light fed into the optical waveguide changes, thereby improving population inversion in the optical waveguide, and also improving the gain characteristic of the optical amplifier.
The transmission device may be a Fabry-Perot resonator having a variable resonator length and a transmission characteristic corresponding to the resonator length. In this case, the change in gain in the optical waveguide caused by a change in temperature is canceled by the change in transmission characteristic in the Fabry-Perot resonator, whereby the gain characteristic of the optical amplifier is improved.
REFERENCES:
patent: 4906949 (1990-03-01), Pocholle et al.
patent: 6104526 (2000-08-01), Kakui
patent: 4-11794 (1992-01-01), None
patent: 4-99080 (1992-03-01), None
patent: 8-5860 (1996-01-01), None
Hellner Mark
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
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