WDM switch using OADM and control method thereof

Details WDM switch using OADM and control method thereof WDM switch using OADM and control method thereof

2002-09-03

2004-08-17

Healy, Brian M. (Department: 2874)

Optical waveguides

With optical coupler

C385S016000, C385S017000, C385S024000, C385S042000, C385S031000, C385S009000, C385S010000, C398S079000, C398S082000, C398S083000, C398S048000, C398S045000

Reexamination Certificate

active

06778721

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wavelength division multiplexing (WDM) system, and more particularly to a WDM switch which includes an optical add/drop multiplexer (OADM) and control method thereof.
2. Background of the Related Art
In an optical communication network, a wavelength division multiplexing (WDM) system transmits a plurality of optical signals simultaneously using various wavelengths. This enables the communication network to operate efficiently and at very high speed. Thus networks of this type are suitable for many broadband applications.
When an optical path having a specific wavelength is terminated at a specific node of an optical communication network employing a WDM system, the node should drop the wavelength. Moreover, if it is necessary to setup an optical path at the specific node using a new wavelength, the node uses a wavelength which will not bring about wave collision with signals transmitted on an optical path to another node. This is usually accomplished by having the node add the wavelength to other wavelengths which are passing by the specific node.
There are two kinds of mechanisms for adding/dropping a specific wavelength in a WDM system. The first mechanism operates based on the diffraction grating principle that diffraction/reflection varies in accordance with wavelength. The second mechanism operates by filtering a wavelength using a dichroic filter. At least one embodiment of the present invention includes an optical add/drop multiplexer (OADM) which operates in accordance with the first mechanism, for instance, an coupler-type OADM.
FIG. 1
is a diagram which illustrates a grating used in a coupler-type OADM according to a related art. In this circuit, when an UV (ultraviolet) beam is irradiated on a fusion-type coupler
10
including a photosensitive material through a phase mask, interference patterns are generated so that gratings
30
are formed in the coupler
10
by a photosensitive effect. Such a method of forming gratings in a coupler-type OADM can be applied to an optical waveguide-type coupler as well. As an alternative to the aforementioned technique, etching can be used to form the gratings in an optical waveguide-type coupler.
FIG. 2
is a diagram of a coupler-type OADM according to a related art. In this circuit, when optical signals are input into an input port
50
of an optical waveguide-type coupler
10
, an optical signal having a specific wavelength is dropped from the input optical signals by a grating
45
formed at the optical waveguide type coupler
10
with a predetermined period so as to be outputted through a drop port
55
. Moreover, when an optical signal having a specific wavelength is inputted to an add port
65
of the optical waveguide type coupler
40
, the coupler type OADM according to the related art adds the optical signal having the specific wavelength to an optical signal passing the optical waveguide type coupler
40
by the grating
45
, so as to output the added optical signals through an output port
60
.
An output wavelength (drop wavelength) of the drop port
55
and an input wavelength (add wavelength) of the add port
65
in the coupler-type OADM are determined by the following Formula 1:
&lgr;
1
=2
n
eff
&Lgr;
1
  [1]
where &lgr;
1
, n
eff
, and &Lgr;
1
indicate an input/output wavelength (drop/add wavelength), an effective refractive index, and a grating period respectively.
FIGS.
3
(
a
)-(
e
) are graphs of optical signals having wavelengths dropped/added in a coupler-type OADM according to a related art. In these figures, an optical signal &lgr;
1
(FIG.
3
(
b
)), suitable for satisfying the condition of Formula 1 among optical signals &lgr;
1
, &lgr;
2
&lgr;
3
, . . . , &lgr;
n
(FIG.
3
(
a
)) input into an input port
50
, is dropped so as to be output to a drop port
55
. The rest of the optical signals (FIG.
3
(
c
)) except optical signal &lgr;
1
pass through an optical waveguide-type coupler
40
. Once the optical signal &lgr;
1
(FIG.
3
(
d
)) having a wavelength suitable for satisfying the condition of Formula 1 is input into an add port
65
, the input optical signal &lgr;
1
(FIG.
3
(
d
)) is added to an optical signal passing through the optical waveguide-type coupler so as to be output to an output port
60
(FIG.
3
(
e
)).
One drawback of the related art is that the grating of the coupler-type OADM cannot be eliminated and still function as intended. Thus, if a function of dropping/adding an optical signal of a specific wavelength is unnecessary, additional manual work is required to remove the coupler-type OADM or the output of the drop port must be returned back to the input of the add port. Because manual work is required to modify or eliminate the coupler-type OADM, it is very difficult to operate this device by remote control. In addition, the coupler-type OADM fails to be flexible to network variation, and thus has poor adaptability when the structure of WDM network frequently varies due to rapid increases in the amount of data.
SUMMARY OF THE INVENTION
An object of the invention is provide a wavelength division multiplexing (WDM) system that substantially obviates one or more problems and/or disadvantages of the related art.
Another object of the present invention is to provide an OADM in a WDM system which freely forms/eliminates a grating of an optical waveguide-type coupler constituting the OADM.
Another object of the present invention is to provide an OADM in a WDM system which is suitable for being remotely controlled.
A further object of the present invention is to provide an OADM in a WDM system which drops/adds a plurality of channels simultaneously, by connecting a plurality of remotely controllable 1-channel OADMs in series.
Another object of the present invention is to provide a WDM switching system and method which connects different WDM networks by controlling a WDM switch which includes a multi-channel OADM.
These and other objects and advantages of the present invention are achieved by providing a WDM switching system which includes: a plurality of multi-channel OADMs connected in parallel and having drop and add ports which can be connected to cross with each other, and switching unit for switching a corresponding channel in accordance with an operation control signal for each channel, wherein each of the multi-channel OADMs has drop and add ports.
In another aspect of the present invention, a multi-channel OADM in a WDM system includes a plurality of 1-channel OADMs connected in series, each of the 1-channel OADMs dropping or adding different channels from an input WDM optical signal in accordance with operation control signals for the channels, respectively.
In a further aspect of the present invention, a 1-channel OADM in a WDM system includes first and second conductors arranged periodically so as to have a pair of different polarities, an optical waveguide-type coupler dropping or adding an optical signal of a specific channel by an electric field generated from the first and second conductors, a power supply unit supplying the second conductor with a power, and a switch placed between the second conductor and power supply unit to control a power supply of the second conductor, so as to control generation and termination of the electric field in accordance with an operation control signal.
In a further aspect of the present invention, a method of controlling a 1-channel OADM in a WDM system includes checking whether a drop/add operation is demanded or not, forming an electric field at an optical waveguide-type coupler if the drop/add operation is demanded, and carrying out the drop/add operation of a channel by the formed electric field.
In another aspect of the present invention, a method of controlling a multi-channel OADM in a WDM system includes checking channels to be dropped/added, outputting operation control signals for activating OADMs of channels to be dropped/added, activating the OADMs which receive the operation control signals for activation, a

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