Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-10-29
2002-10-22
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S341430
Reexamination Certificate
active
06469814
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for detecting channel information; and, more particularly, the present invention relates to an apparatus and a method for monitoring channel status and detecting location and a number of working channels from a wavelength division multiplexed (WDM) signal without demultiplexing the WDM signals by using a wavelength selective detector (herein, in the WDM signal, a wavelength means a channel).
2. Description of the Prior Art
A status of an individual channel is an important factor in terms of management, maintenance and monitoring performance of network. Switching and recovering operations should be rapidly performed in accordance with a channel status when there is an error in optical network, since a lot of information are transmitted through transmission channel at a high speed (e.g., 10 Gbps or more than 10 Gbps). Thus, the status information for each channel should be monitored rapidly, correctly, simply, and in an economical way.
In a wavelength division multiplexed optical transmission system and an optical transport network, presence of individual channel cannot be identified without demultiplexing the wavelength division multiplexed signal, since lots of channels, each channel having a different wavelength, are transmitted as mixed.
FIG. 1
is a diagram illustrating a WDM channel detector in accordance with a conventional method. The WDM channel detector comprises an optical multiplexer
11
, an optical amplifier
12
, an optical coupler
13
, an optical demultiplexer
14
, a photo detector
15
and a signal processor
16
.
Optical signals, each of which has a different wavelength, are multiplexed by the optical multiplexer
11
. The multiplexed optical signals are divided into individual channel at the optical demultiplexer
14
. Thereafter, it is determined that the channel is presented or not on the basis of the divided signals. Thus, there existed disadvantages that lots of optical elements, such as the optical demultiplexer
14
and the photo detectors
15
(D
1
to Dn), are needed, thereby additional loss of optical power resulted from use of the demultiplexer
14
is caused. Such a conventional WDM. channel detector is described in U.S. Pat. No. 5,617,234 issued to M. Koga, entitled of “Multiwavelength simultaneous monitoring circuit employing arrayed-waveguide grating”.
FIG. 2
is a diagram illustrating another conventional WDM channel detector. The WDM detector comprises an optical multiplexer
21
, an optical amplifier
22
, an optical coupler
23
, a variable optical filter
24
, a waveform counter
25
and an optical detector
27
.
The waveform counter
25
detects presence and location of working channels from wavelength division multiplexed optical signals scanned through a tunable optical filter
24
and optical-to-electrical converted through a photo detector
27
. An article by C. Konishi, “Dynamic gain controlled erbium doped fiber amplifier repeater for WDM network”,
OFC'
97
Paper TuE
1, pp18-19, 1997, shows an example of method for checking the presence of channel by using the tunable optical filter
24
without demultiplexing the WDM signals such as shown in FIG.
2
. Even though the optical demultiplexer
14
is not used in Konishi's method contrary to the above mentioned U.S. Pat. No. 5,617,234, there are demerits that the tunable optical filter
24
such as an expensive Acousto Optic Tunable Filter(AOTF) is necessarily needed, and that a detection speed is restricted due to scanning of the tunable optical filter
24
. Moreover, there is a disadvantage in Konishi's method that processing of signal in a tunable optical filter controller
26
and a waveform counter
25
is relatively complicated.
SUMMARY OF INVENTION
Therefore, it is an object of the present invention to provide an apparatus and a method for detecting channel information from wavelength division multiplexed signals without demultiplexing the wavelength division multiplexed signals.
It is another object of the present invention to provide an apparatus and a method for detecting channel information from wavelength division multiplexed signals without using complicated and expensive devices.
It is still another object of the present invention to provide an apparatus and a method for more rapidly detecting channel information from wavelength division multiplexed signals without delay due to scanning.
In accordance with one embodiment of the present invention, there is provided an apparatus for detecting channel information in each channel from wavelength division multiplexed (WDM) optical signals each having a different wavelength, comprising: a pre-processor for pre-processing WDM optical signals and outputting a portion of the WDM optical signals; a photo detector for converting the WDM optical signal from said pre-processor into a first electrical signal having a constant value regardless of wavelengths of the WDM optical signal; a wavelength selective photo detector for converting the WDM optical signal from said pre-processor into a second electrical signal having a different value in response to the wavelength of the distributed optical signal; a lookup table for storing the wavelengths, a number of channels and optical power per channel; normalization part for normalizing the second electrical signal with respect to the first electrical signal; channel number detector for detecting a number of channels using the optical power per channel and power of the first electrical signal; and channel location detector for detecting channel locations by using normalized electrical signals and electrical power values stored in said lookup table.
In accordance with another embodiment of the present invention, there is provided a method for detecting channel information from wavelength division multiplexed optical signals each having a different wavelength, comprising the steps of: a) storing wavelengths to be used as channls, a number of channel, an optical power per a channel and electrical power values, each of the electrical power value corresponding to a channel combination specifying location of working channel in a lookup table; b) pre-processing WDM optical signals and outputting a portion of the WDM optical signals; c) converting pre-processed WDM optical signal into a first electrical signal having a constant value regardless of wavelengths of the WDM optical signal; d) converting the pre-processed WDM optical signal into a second electrical signal having a different value in response to the wavelength of the WDM optical signal; e) normalizing the second electrical signal with respect to the first electrical signal; f) detecting a number of channels using the optical power per channel and power of the first electrical signal; and g) detecting channel location by using normalized electrical signals and electrical power values stored in the lookup table.
In accordance with still another embodiment of the present invention, there is provided a computer-readable recording medium, tangibly embodying a program of instruction executable by the machine to perform a method for detecting channel information from wavelength division multiplexed signals each having a different wavelength, said programs of the instruction running in a data processing machine, the method comprising the steps of: a) storing wavelengths to be used as channels, a number of channel, electrical power values for one channel (almost all the same) and each electrical power corresponding to a channel combination specifying location of working channel in a lookup table; b) pre-processing WDM optical signals and outputting a portion of the WDM optical signals; c) converting the WDM optical signal pre-processed into a first electrical signal having a constant value regardless of wavelengths of the WDM optical signal; d) converting the WDM optical signal pre-processed into a second electrical signal having a different value in response to the wavelength of the WDM optical signal; e) normalizing the
Park Chang Soo
Seo Wan Seok
Yun Byung Ho
Blakely & Sokoloff, Taylor & Zafman
Electronics and Telecommunications Research Institute
Pascal Leslie
Phan Hanh
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