Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-07-15
2001-09-25
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06295147
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
This invention relates to a wavelength multiplexing transmission apparatus and a wavelength demultiplexing reception apparatus suitable for use with wavelength multiplex transmission of a high density.
2) Description of the Related Art
In recent years, a demand for increase in capacity of a transmission apparatus has been and is progressively increasing as the information society advances progressively. Particularly, increase of the speed in electronics (an increase in transmission speed of an electric signal) is getting difficult after the speed exceeds 10 Gb/s, and it is anticipated significantly to achieve an increase in capacity by an increase in speed on an optical signal level, particularly, by signal transmission to which a wavelength multiplex system is applied.
As a wavelength multiplex system, narrow-band wavelength multiplexing in the 1.55 &mgr;m band which provides a wavelength with which the loss of an optical fiber is lowest is considered promising and has already been put into practical use. Further, since this wavelength band coincides with an application wavelength band of an optical amplifier for which an optical fiber doped with erbium is used and also the loss of a wave combiner/separator provided for performing wavelength multiplexing or wavelength demultiplexing can be compensated for by the optical amplifier, wavelength multiplexing of such a large number of waves that is not conventionally available can be performed.
However, in a transmission apparatus which adopts such a wavelength multiplex system as described above, when wavelength arrangement of the wavelengths of a plurality of transmission optical signals (transmission lights) is performed in a narrow band and in a high density in the 1.55 &mgr;m band, small variations occur with the wavelengths of the transmission light signals by various causes, and also where a small wavelength variation occurs with some transmission light in this manner, the signal of the channel may not be transmitted successfully or may have an influence on the optical signal of a wavelength of an adjacent channel and bring about crosstalk with the adjacent channel.
In such an instance, a communication error may possibly occur not only with the channel with which the wavelength variation occurs but also with the channel with which the crosstalk occurs.
Accordingly, a transmission apparatus which performs high density wavelength multiplexing or wavelength demultiplexing described above not only has a subject to be solved in that wavelengths of transmission light sources must be stabilized, but also has another subject in that, should wavelength displacement occur, crosstalk with another channel must be prevented.
Further, while some optical signal transmission apparatus include a temperature stabilization circuit or a like circuit for a light source in order to secure stability of the temperature, where the stability of a thermistor which monitors the environment temperature of the light source is not sufficiently high, there is a subject in that it must be taken into consideration that a variation may occur because of deterioration of the thermistor as time passes. On the other hand, also there is another subject in that care must be taken of deterioration of a transmission light source itself which outputs an optical wavelength as time passes.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a wavelength multiplexing transmission apparatus and a wavelength demultiplexing reception apparatus wherein a variation of a wavelength of a transmission light source is detected to prevent that such variation causes crosstalk with another channel.
In order to attain the object described above, according to an aspect of the present invention, there is provided a wavelength multiplexing transmission apparatus, comprising a plurality of optical signal outputting sections for outputting optical signals having different wavelengths from each other, and a wavelength multiplexing section for wavelength multiplexing the optical signals outputted from the optical signal outputting sections and sending out a resulting optical signal, each of the optical signal outputting sections including a transmission light source and a wavelength filter.
The transmission light source is driven by an electric signal for outputting an optical signal of a predetermined wavelength, and the wavelength filter is capable of passing therethrough and sending out only an optical signal of the predetermined wavelength to be outputted from the transmission light source to prevent a wavelength drift of the optical signal outputted from the transmission light source.
Accordingly, with the wavelength multiplexing transmission apparatus, since, in each of the optical signal outputting sections, the transmission light source is driven by an electric signal to output an optical signal of the predetermined wavelength and the wavelength filter can pass therethrough and send out only the predetermined wavelength to be outputted from the transmission light source to prevent a wavelength drift of the optical signal outputted from the transmission light source, any optical wavelength displaced out of a pertaining predetermined normal range is attenuated by the pertaining wavelength filter and is not transmitted as a wavelength multiplex signal. Consequently, the wavelength multiplex transmission apparatus is advantageous in that crosstalk with another channel can be prevented.
The wavelength multiplexing transmission apparatus may be constructed such that each of the optical signal outputting sections further includes a first abnormal condition detecting section for supervising a level of the optical signal sent out from the wavelength filter and detecting an abnormal condition when the level is lower than a first threshold level set in advance.
The wavelength multiplexing transmission apparatus having the construction just described is advantageous in that, since the first abnormal condition detecting section in each of the optical signal outputting sections supervises a level of the optical signal sent out from the wavelength filter, by discriminating whether or not the level of the optical signal is lower than the first threshold level set in advance, an abnormal condition of the light source wavelength can be detected.
The wavelength multiplexing transmission apparatus may be constructed such that each of the optical signal outputting sections further includes a second abnormal condition detecting section for detecting an abnormal condition of an output level of the optical signal outputted from the transmission light source, and a third abnormal condition detecting section for detecting an abnormal condition of a wavelength of the optical signal outputted from the transmission light source when an abnormal condition is detected by the first abnormal condition detecting section and a normal condition is detected by the second abnormal condition detecting section.
The wavelength multiplexing transmission apparatus having the construction just described is advantageous in that, since, in each of the optical signal outputting sections, the second abnormal condition detecting section detects an abnormal condition of an output level of the optical signal outputted from the transmission light source and the third abnormal condition detecting section supervises results of detection of the first abnormal condition detecting section and the second abnormal condition detecting section, not only an abnormal condition of the light source but also a wavelength displacement can be detected.
According to another aspect of the present invention, there is provided a wavelength multiplexing transmission apparatus, comprising a plurality of optical signal outputting sections for outputting optical signals having wavelengths different from each other, and a wavelength multiplexing section for wavelength multiplexing the optical signals outputted from the optical signal outputting sections and sending out a resulti
Kawasaki Yumiko
Okano Satoru
Tsuda Takashi
Yamane Kazuo
Chan Jason
Fujitsu Limited
Nguyen Chau M.
Staas & Halsey , LLP
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