Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Utility Patent
1998-03-13
2001-01-02
Pascal, Leslie (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S341430, C359S199200
Utility Patent
active
06169615
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a wavelength division multiplex optical transmission apparatus in which a plurality of optical signals having different wavelengths are processed by wavelength division multiplexing, and are transmitted to an optical transmission line.
(2) Description of the Related Art
In the optical transmission technical field, an attempt has conventionally been made to process by wavelength division multiplexing (WDM) and transmit a plurality of optical signals having different wavelengths &lgr;1 to &lgr;n (where n: natural number more than or equal to 2) corresponding to the number of channels, thereby making an effective use of a band in one optical transmission line (optical fiber). In particular, in recent years, as the number of channels for the optical transmission has been increased, the WDM technique has become greatly important. Thus, active research and development have progressed on various types of WDM units (wavelength division multiplex optical transmission apparatuses).
Under the current circumstances, among the various types of WDM units described above, the most dominant type is a WDM unit in which, for example, a WDM coupler is used to process by the wavelength division multiplexing the plurality of optical signals having the different wavelengths &lgr;1 to &lgr;n, and a concurrent optical amplification is subsequently made to the optical signals with the wavelengths &lgr;1 to &lgr;n to desired optical signal levels so as to output the optical signals to the optical transmission line, thereby transmitting all the optical signals with the wavelengths &lgr;1 to &lgr;n to an opposite side.
However, in such a wavelength division multiplex optical transmission apparatus, the concurrent optical amplification is made though distances for which the optical signals with the wavelengths &lgr;1 to &lgr;n can be transmitted may be varied for the wavelengths &lgr;1 to &lgr;n depending upon states (such as loss) of the optical transmission line. Hence, according to another optical signal with a wavelength providing a short transmission distance, a higher optical output level must be provided for an optical signal with the wavelength which can ensure a sufficiently long transmission distance even at a low send optical output level. Therefore, an increase in power consumption of the transmission apparatus results in a significantly high transmission cost.
Further, in general, the optical signal is amplified by using an optical amplification fiber such as erbium-doped fiber, and launching, together with a transmit optical signal, an excitation optical signal having desired power into the optical amplification fiber. For example, as shown in
FIG. 48
, there is a complicated correlation between an amplification factor (signal net gain) and incident excitation light power at a time of optical amplification. Thus, under the present circumstances, it is substantially impossible to adjust the optical output level of the optical signal after the optical amplification according to the transmission distance of each of the wavelengths &lgr;1 to &lgr;n.
That is, when only the send optical output level is varied, the variation causes a variation in optical amplification factor, thereby varying the optical output level after the optical amplification. Consequently, the optical signals with the wavelengths &lgr;1 to &lgr;n cannot have optical output levels suitable for the transmission distances of the wavelengths &lgr;1 to &lgr;n. Accordingly, it is impossible to employ a simple method of adjusting the optical output level after the amplification by using an optical attenuator or the like.
SUMMARY OF THE INVENTION
In view of the foregoing problems, it is an object of the present invention to provide a wavelength division multiplex optical transmission apparatus in which it is possible to adjust, for wavelengths, send optical output levels of optical signals having a plurality of different wavelengths, to be transmitted after wavelength division multiplexing so as to transmit, for the wavelengths, the optical signals at optimal optical output levels.
According to the present invention, for achieving the above-mentioned object, there is provided a wavelength division multiplex optical transmission apparatus in which a plurality of optical signals having different wavelengths are processed by wavelength division multiplexing, and are transmitted through an optical transmission line. The apparatus includes an optical sending system having a plurality of optical sending sections to generate and transmit the optical signals having the different wavelengths, a plurality of optical amplifying sections to amplify the optical signals with the wavelengths from the optical sending sections, and a wavelength division multiplexing section to process by the wavelength division multiplexing and output to the optical transmission line the optical signals amplified in the optical amplifying sections, and an optical receiving system having a wavelength division demultiplexing section to demultiplex the wavelength division multiplexed optical signals transmitted through the optical transmission line into the optical signals with the wavelengths, and a plurality of optical receiving sections to receive the optical signals demultiplexed in the wavelength division demultiplexing section. Concurrently, an optical output level control section is mounted to control, for the wavelengths, optical output levels of the optical signals output to the optical transmission line through the wavelength division multiplexing section by individually varying amplification factors of the optical amplifying sections in the optical sending system.
Further, there is provided a wavelength division multiplex optical transmission apparatus in which a plurality of optical signals having different wavelengths are processed by wavelength division multiplexing, and are transmitted through an optical transmission line. The apparatus includes an optical sending system having a plurality of optical sending sections to generate and transmit the optical signals having the different wavelengths, and a wavelength division multiplexing section to process by the wavelength division multiplexing and output to the optical transmission line the optical signals with the wavelengths from the optical sending sections. Concurrently, an optical output level adjusting section is mounted to control, for the wavelengths, optical output levels of the optical signals with the wavelengths, sent to the optical transmission line before the wavelength division multiplexing by the wavelength division multiplexing section in the optical sending system.
Here, the optical output level adjusting section may include a plurality of optical amplifying sections interposed between the optical sending sections and the wavelength division multiplexing section to amplify the optical signals with the wavelengths from the optical sending sections, and an optical output level control section to control, for the wavelengths, optical output levels of the optical signals output to the optical transmission line through the wavelength division multiplexing section by individually varying amplification factors in the optical amplifying sections.
Thus, according the wavelength division multiplex optical transmission apparatus of the present invention, the optical output level control section controls, for the wavelengths, the optical output levels of the optical signals to the optical transmission line (that is, adjusts, for the wavelengths, the optical output levels of the optical signals with the wavelengths before the wavelength division multiplexing) by individually varying the amplification factors in the plurality of optical amplifying sections to respectively amplify the optical signals with the plurality of wavelengths, to be transmitted after the wavelength division multiplexing in the optical sending system. Therefore, it is possible to transmit the respective optical signals at the optical output le
Fujitsu Limited
Helfgott & Karas P.C.
Pascal Leslie
Phan Hanh
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