Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-12-31
2002-08-27
Mullen, Thomas (Department: 2632)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06441933
ABSTRACT:
BACKGROUND
1. Technical Field
The present invention relates generally to a signal monitoring apparatus for wavelength division multiplexed (hereinafter, referring to WDM) optical telecommunication networks, particularly to an optical channel error monitoring and detecting apparatus capable of effectively operating optical telecommunication networks by maintaining a wavelength, which is allocated to each certain WDM channel, and an optical power in a constant error range as well as extending number of WDM channels. It is performed by using a reference signal having a wide wavelength tunable range and a repeatability to a wavelength such that the monitoring system may monitor and revise the wavelength of each WDM channel and the optical output error.
2. Background
Recently, there has been considerable interest to increase the optical telecommunication capacity by using an optical fiber. Thereby, the WDM is introduced among methods capable of handling multichannel optical signals in an optical fiber. And also there is a great amount of study towards minimizing and revising the problems which affect the adjacent channels according to the errors of the channel wavelength and the optical power.
There are a lot of studies to control each WDM channel wavelength. Recently, research into the prevention of crosstalk by maintaining all channels to have the same optical power has begun by measuring each WDM channel optical output.
FIG. 1
shows a schematic diagram of a general WDM optical transmission terminal which comprises a WDM transmitter module
300
, an optical channel error monitoring and detecting device
100
, and an optical transmitter controller
400
. A WDM optical transmitter
310
is a transmitting module which is comprised of a plurality of optical transmitters
320
having optical wavelengths which are different from each other. Here, each optical transmitter
320
is a laser generator for converting an electrical signal to an optical signal of a specified optical wavelength. And an optical combiner
330
is a directional coupler for transmitting the wavelength multiplexed optical signal to a single optical fiber after the wavelength multiplexed optical output of each optical transmitter
320
. An optical divider
340
divides the optical output of the optical combiner
330
by a constant rate. One of the divided optical outputs is used for a WDM optical telecommunication. The other optical output is connected to the optical channel error monitoring and detecting device
100
and used for an optical channel error monitoring and detecting. The optical channel error monitoring and detecting device
100
transmits monitoring information of the optical channel to the optical transmitter controller
400
. The optical transmitter controller
400
controls each optical transmitter
320
and revises the error by using the monitoring information.
FIG. 2
shows a schematic diagram explaining conventional optical channel error monitoring and detecting of a WDM system. And
FIG. 3
shows an illustration for understanding an optical channel wavelength detection according to the prior art, in which
FIG. 3
relates to the optical channel wavelength detection by using a wavelength tunable laser (hereinafter, referring to WTL)
110
and an optical resonator (filter).
Now the prior art will be explained with reference to
FIG. 2
, and FIG.
3
.
The wavelength tunable laser (WTL)
110
is a laser generator for converting an electric signal to an optical signal of a certain optical wavelength. And the optical wavelength is controlled by an electric signal. An optical divider
120
divides the optical signal generated from the WTL
110
and outputs the divided optical signal with a same rate (1:1) to a pair of outputs. An optical combiner
125
couples the optical signal of each WDM channel and the divided signal from the WTL
110
. The optical fiber
130
shows a transmitting state of the multiplexed WDM optical signal. And an etalon resonator
140
is an optical filter of the resonator type. The etalon resonator
140
passes the optical signal of the WTL
110
whenever the optical wavelength of the WTL
110
matches a resonant frequency.
A photodiode
151
detects a beating signal between the optical signal of the WTL
110
and each WDM channel. And the other optical receiver
152
detects an optical signal of the WTL
110
, when the optical wavelength of the WTL
110
matches to the resonant frequency. A timing comparator
160
detects and compares an arrival time between the detected optical signals from each optical receivers
151
,
152
. And it is ideal that signal detecting time of two optical receivers
151
,
152
are same.
Now it will be explained about the operation of the prior art which uses the WTL
110
and the etalon resonator
140
for controlling the WDM channel wavelength described above, at the same time.
The resonant frequency of the etalon resonator
140
is a standard frequency of each WDM channel signal, in which the optical transmitter for each WDM channel should be transmitted during a stable state.
The optical signal generated from the WTL
110
, is separated into a pair of signals having the same power in the optical divider
120
. One signal of the pair of signals is coupled with each WDM channel signal in the optical fiber
130
. And the other signal is passed through the etalon resonator
140
and generates a standard frequency of the WDM channel, in which each WDM channel optical transmitter is operated in the stable state.
Here, an optical signal of WTL
110
which is passed through the optical divider
120
and inputted to the optical fiber
130
, is coupled with the optical signal of each WDM channel. Accordingly, an optical receiver
151
detects a beating signal when the optical wavelength of each WDM channel signal and the optical wavelength of the WTL
110
are same. And the optical receiver
151
measures frequencies of each WDM channel by using the detected beating signal.
Additionally, the optical signal of the WTL
110
which has passed through the optical divider
120
and applied to the etalon resonator
140
, detects the standard frequency in the optical receiver
152
, by passing the optical signal only whose wavelength is the same as resonant wavelength of the etalon resonator
140
(the resonant wavelength of the etalon resonator
140
is the standard frequency of each WDM channel). Here, the resonant wavelength of etalon resonator
140
is synchronized with the standard frequency of each WDM channel, precisely.
The detecting time from the optical receiver
151
is compared with the detecting time from the optical receiver
152
. And thereby, it is possible to detect an error of the optical wavelength of each WDM channel signal.
The WTL
110
sweeps the wavelength region of WDM channel at a constant cycle, and thereby detects the error.
It is ideal that a signal detecting time of the optical channel detected from the respective optical receivers
151
,
152
, is the same compared to the timings comparator
160
.
For example, a detecting time of the certain optical channel among the WDM channels detected from the optical receiver
151
exists slower or faster than the detecting time of the corresponding reference optical signal of the optical receiver
152
, when an optical wavelength of the optical channel has longer or shorter wavelength than the standard frequency which is resonated from the etalon resonator
140
.
Accordingly, it is possible to revise/complement an error signal of the time difference measured from the timing comparator
160
, by controlling an optical transmitter driving unit for each WDM channel.
The conventional error monitoring and detecting technology of the optical telecommunication system, using the WTL
110
, has problems which limit channel number of the WDM optical telecommunication system according to a wavelength tunable range of the WTL
110
.
For example, in case that the channel spacing is 200 GHz, and the channel number is
16
, a current wavelength tunable range is considerably limited even though the wavel
LG Electronics Inc.
McKenna Long & Aldridge LLP
Mullen Thomas
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