Optical demultiplexer architecture

Details Optical demultiplexer architecture Optical demultiplexer architecture

2000-04-27

2002-06-04

Spyrou, Cassandra (Department: 2872)

Optical waveguides

With optical coupler

Plural

C385S039000, C385S043000, C385S015000, C359S199200, C359S199200

Reexamination Certificate

active

06400861

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to optical filter architectures, and in particular to multiplexer and demultiplexer architectures for wave division multiplex optical signals.
BACKGROUND OF THE INVENTION
Wave division multiplexed optical networks can utilise fused fibre coupler based wavelength multiplexers and demultiplexers. A fused fibre coupler
1
is shown in
FIG. 1
a,
and as is known this has complementary sinusoidal frequency responses at its two output ports as shown in
FIG. 1
b.
In the example shown in
FIG. 1
, channels or bands having wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
, and &lgr;
4
entering the fused coupler input port X are split on exiting the fused coupler
1
between its output ports Y and Z. The frequency response corresponding to port Y is shown in solid line in
FIG. 1
b
and it can be seen that attenuation is at a minimum at wavelengths &lgr;
1
and &lgr;
3
, and at a maximum at wavelengths &lgr;
2
and &lgr;
4
. Channels corresponding to wavelengths &lgr;
1
and &lgr;
3
are therefore passed out at port Y while channels corresponding to wavelengths &lgr;
2
and &lgr;
4
are not passed. The frequency response through port Z is shown in dashed line in
FIG. 1
b
and is such that only channels corresponding to wavelengths &lgr;
2
and &lgr;
4
pass out of port Z. Fused fibre couplers and equivalent devices are used as sinusoidal filters. Fused fibre couplers are symmetrical as is known such that wavelengths fed into the Y port for example, can be split between the W and X ports in the same way that wavelengths through port X can be split between the Y and Z ports as described above.
FIG. 2
shows a typical fused coupler based wavelength demultiplexer structure
10
utilising a number of fused coupler elements or sinusoidal filters
11
a-o
arranged in a tree and branch structure or architecture. These arrangements rely on a series of channels having equally spaced wavelengths. In the example shown, a 16 channel demultiplexer comprises 15 fused coupler filter elements
11
a-o
arranged in a tree and branch structure. Each fused coupler filter element
11
a-o
is designed to pass half the channels entering its X port to its Y port, and the other half of the incoming channels to its Z port. The fused couplers filter elements
11
a-o
are arranged to have a pass band (ie minimum attenuation) corresponding to the lowest of the channel wavelengths entering their input ports (X). As discussed above in connection with
FIG. 1
, the filter elements
11
a-o
are arranged to split the incoming wavelengths or channels between their two output ports Y and Z. The sinusoidal frequency response of the filters
11
a-o
are arranged such that they may pass more than one of the wavelengths of the channel series. This is described in more detail with reference to
FIG. 3
below which shows the demultiplexing stages of channel
1
by the filter series F, which comprises filter elements
11
a,
11
b,
11
c
and
11
d.
FIG. 3
a
shows the frequency response of fused coupler or filter element
11
a.
It can be seen that at the Y port, minimum attenuation is centred about wavelengths corresponding to channels
1
,
3
,
5
,
7
,
9
,
11
,
13
,
15
. These channels are then passed to the input port X of filter element
11
b
which has a sinusoidal frequency response shown in
FIG. 3
b
and has a period double that of filter element
11
a.
It can be seen therefore that of the channels passed to input port X of filter
11
b,
channels
1
,
5
,
9
,
13
are passed to output port Y of filter
11
b.
These channels are then fed to the input port X of filter element
11
c,
the frequency response of which is shown in
FIG. 3
c.
Filter element
11
c
has a period double that of filter
11
b,
and hence quadruple that of filter
11
a.
It can be seen from
FIG. 3
c
that only channels
1
and
9
will be passed to output port Y of filter element
11
c.
These are then fed to the input port X of filter element
11
d
which has a period 8 times that of filter element
11
a,
and its frequency response is shown in
FIG. 3
d.
As can be seen, only channel
1
will be passed to output port Y of filter element
11
d.
It can be appreciated therefore that all channels
1
-
16
can be demultiplexed through various filter element series (e.g. F) as shown in
FIGS. 2 and 3
. Similarly, multiplexers can be constructed by a similar process as is known.
A major disadvantage with this type of demultiplexer is the high cost of fabrication. This is particularly significant in the deployment of wave division multiplex optical networks in the metro and access arenas.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved or at least alternative demultiplexer for use in wave division multiplexed optical networks.
In this specification the words multiplexer and demultiplexer are used interchangeably.
In a first aspect the present invention provides an apparatus or structure arranged to filter a predetermined range and number of wavelengths comprising:
a tree and branch filter architecture having a plurality of filters, each having a frequency response such that said filter passes a first set of wavelengths to a first output port and a second set of wavelengths to a second output port;
wherein at least two filters have the same frequency responses, and wherein each of said same frequency response filters are arranged to pass different wavelength sets.
Preferably said filters are sinusoidal filters.
Preferably said filters are fused fibre couplers.
Preferably said apparatus comprises a number
(n) of filter stages and wherein each stage has filters with a maximum of two different frequency responses.
Preferably said minimum attenuated wavelengths of the two frequency responses are:
(
T
1
+T
2
+ . . . +T
n
)/
n
and (
T
n+1
+T
n+2
+ . . . +T
2n
)/
n,
each having a period of 2
(n−1)
T.
In a second aspect the present invention provides a demultiplexer comprising:
a plurality of devices each having at least one input port and two output ports, the frequency responses of the output ports of each device being complimentary in wavelength;
wherein the devices are connected in a tree and branch architecture to demultiplex a predetermined range and number of wavelengths;
and wherein at least two of the devices have the same frequency responses.
Preferably the devices are fused fibre couplers.
Preferably the demultiplexer comprises a number of stages and wherein each stage has devices with a maximum of two different frequency responses.
In a third aspect the present invention provides an apparatus arranged to multiplex or demultiplex a predetermined range and number of wavelengths comprising:
a plurality of devices each having at least one input port and two output ports, the output ports of each device having a periodic and complimentary series of minimum attenuation wavelength peaks;
wherein the devices are arranged such that each multiplexes or demultiplexer a unique series of wavelengths;
and wherein the apparatus comprises at least one device having a series of minimum attenuation wavelength peaks which do not correspond to the unique series of wavelengths the device is arranged to multiplex or demultiplex.
Preferably the devices are fused fibre couplers.
Preferably the demultiplexer comprises a number of stages and each stage has devices with a maximum of two different frequency responses.
Preferably each device in the last stage is replaced with a bi-directional module to enable said apparatus to simultaneously multiplexes and demultiplexes said wavelengths.
Preferably each said module comprises a four port device having the same frequency response as the device in the first stage, and two devices having the same two responses as the replaced devices.
In a fourth aspect the present invention provides an optical network or network segment comprising an apparatus or structure arranged to filter a predetermined range and number of wavelengths comprising:
a tree and branch filter architecture having a plura

Affiliated with

Also associated with

Rating

Optical demultiplexer architecture does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical demultiplexer architecture, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical demultiplexer architecture will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2949269