Optical waveguides – Accessories – Attenuator
Patent
1999-06-01
2000-10-17
Lee, John D.
Optical waveguides
Accessories
Attenuator
385 32, 385122, 359332, G02B 6122, G02F 137
Patent
active
061343722
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device and method for attenuating light intensity of an optical signal (or a signal wave) which includes a surge component, which is output from an optical amplifier. More specifically, the present invention relates to a light intensity attenuator and attenuating method applied to a communication system using optical signals, in which an optical signal component having an extraordinarily high light intensity (i.e., a pulse-shaped optical surge), which was generated inside or outside the relevant optical signal transmission system, is attenuated (or arrested), and an optical signal component having a desired light intensity is output, thereby preventing components or elements belonging to the light-receiving side of the system from being damaged.
BACKGROUND ART
Practical communication systems using light as a signal such as a wavelength-division multiplexed (WDM) optical communication system are known, and longer-distance communication systems having a larger data capacity have been developed.
Recently, in order to increase the capacity, the wavelength-division multiplexed communication which attracts much attention uses advantageous characteristics of light and information signals transmitted via optical signals having a plurality of wavelengths. On the other hand, the direct optical amplification method using an erbium-doped optical fiber amplifier (EDFA) is also practical and transmission distance has rapidly progressed. However, in the optical communication systems using the EDFA, a pulse-shaped optical signal of high intensity may be generated. Therefore, in order to secure high stability and reliability of the system, it is necessary to protect relevant components such as light-receiving elements from damage due to the pulse-shaped high-intensity optical signal. Similar problems may occur in other electro-optic devices not only in the optical communication system.
Various causes with respect to the generation of the extraordinary pulse-shaped high-intensity optical signal are known, such as: (i) when the optical signal input into the system includes a high-intensity optical signal component, or (ii) when the optical signal is amplified in the system, a secondary high-intensity optical signal component is generated. In the optical communication system performing direct optical amplification using the erbium-doped optical fiber amplifier (EDFA), an extraordinary high-intensity pulse-shaped optical signal component may be included in the optical signal which was amplified using the EDFA (refer to T. Imai, et al., Proceedings of "1992 Optical Amplifier Topical Meeting", Presentation No. PD 12, 1992).
The reason for this phenomenon is that Er.sup.3+ which has been excited to a higher level is stored in the EDFA with a high energy while no optical signal is input (that is, when no optical signal exists) in the EDFA, and that when an optical signal is input into the EDFA under the above situation, the stored high energy is rapidly stimulated and emitted so that the emitted portion is added to the input optical signal as an optical surge. Such an optical surge may damage or degrade a light-receiving element connected to the output side of the EDFA. Therefore, it is preferable that such an optical surge be removed.
A method for removing the above-explained optical surge, and also controlling generation of the optical surge in the optical transmission system including the EDFA is known, in which the optical signal transmitter raises the optical signal during a longer period of the "msec" order or more, so as to gradually emit the energy which was accumulated in the EDFA while no signal was being input (refer to Yoneyama, et al., Proceedings of the spring conference of the IEICE, Presentation No. B-941, p. 4-79, 1993).
Another method is known, which considers that the optical surge is generated due to the emission of energy which was accumulated in the EDFA during a non-signal period. In this method, before a target optical signal to be amplified is input in
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Higuma Kaoru
Ichikawa Junichiro
Minowa Junichiro
Nagata Hirotoshi
Ogata Takaaki
Connelly-Cushwa Michael R.
Lee John D.
NEC Corporation
Sumitomo Osaka Cement Co. Ltd.
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