Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2000-07-07
2003-04-08
Spyrou, Cassandra (Department: 2872)
Optical waveguides
With optical coupler
Plural
C385S032000, C385S042000, C385S043000, C385S045000, C359S199200, C359S199200
Reexamination Certificate
active
06546164
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to wavelength selective devices. In particular, the present invention relates to dense wavelength division multiplexers (DWDMs).
2. The Prior Art
Background
With the growing use of the Internet, users are accessing a wider variety of data, such as streaming voice and video, and as a result are placing greater demands on the existing Internet backbone. As a consequence, traditional coaxial cable, which forms the backbone of the Internet, can no longer support these increased demands. Thus, current information systems are continually being expanded to meet increasing bandwidth demands.
One viable alternative to the traditional coaxial backbone is optical fiber because of its potential for greatly increased bandwidth. Various methods have been proposed to maximize the bandwidth of optical systems.
One such system is disclosed in U.S. Pat. No. 5,809,190 (the '190 patent) to the present inventor. Therein, a Dense Wavelength-Division Multiplexer (DWDM) is disclosed which utilizes a Fused-Biconical Taper (FBT) technique.
FIG. 1
shows a prior art diagram of a 1×N DWDM
100
according to the '190 patent. As used herein, the symbol N indicates the number of channels that are used by a DWDM to multiplex or demultiplex a given input provided by an input fiber. The number N is equal to 2
m
wherein m represents the number of times a DWDM performs signal divisions for the given input signal prior to their being demultiplexed at a receiving end.
Accordingly, the prior art DWDM is known as a m-stage DWDM in which MWDM
111
is a first stage Wavelength Division Multiplexer (WDM) having a window spacing of &Dgr;&lgr;. Likewise, MWDMs
121
and
122
are a pair of second stage WDMs, each having a window spacing 2&Dgr;&lgr;. MWDMs
131
,
133
, and
134
are a plurality of third stage WDMs, each having a window spacing of 4&Dgr;&lgr;.
Each of the WDMs in
FIG. 1
has a window with a center wavelength which varies with its sequence in the DWDM. Each stage in the DWDM
100
may be designated as
1
m
1
,
1
m
2
, . . . , and
1
m(2
m−1
), representing a m-th stage WDM of the DWDM. Regarding window spacing, the window spacing of a m-th stage MWDM is 2
m−1
&Dgr;&lgr;, which is twice as large as a window spacing demonstrated by a m−1 stage MWDM, yet one half of the size of the window spacing of a m+1 stage MWDM. The number of stages m may be from be from 1 to n, where n=(logN/log2), forming a plurality of MWDMs,
1
n
1
,
1
n
2
, . . . ,
1
n(N/2).
Each channel of the DWDM
100
has only one window with a characteristic central wavelength corresponding to a particular center wavelength originating from the first stage WDMs. For example, in
FIG. 1
, each of the windows included in channel pathways
111
-
131
and
111
-
132
has a center wavelength identical to a center wavelength in corresponding window of the channel
121
. Likewise, each of the windows in the channel pathways
111
-
133
and
111
-
134
has a center wavelength identical to a center wavelength in a corresponding window of the channel
122
.
Referring still to
FIG. 1
, the operation of the DWDM
100
as a demultiplexer may now be shown. A lightwave signal having wavelengths &lgr;
1
-&lgr;
N
are provided by fiber
10
to MWDM
111
. Wavelength series &lgr;
1
, &lgr;
3
, . . . , &lgr;
N−1
is transmitted to WDM
121
, and wavelength series &lgr;
2
, &lgr;
4
, . . . , &lgr;
N
is transmitted to WDM
122
.
FIGS. 2A and 2B
show representative spectral distributions of the wavelength series where N=8.
Referring back to
FIG. 1
, after demultiplexing by subsequent stages, the light signals are demultiplexed into N individual channels and distributed to N individual fibers
11
,
12
, . . . ,
1
N.
Referring now to
FIGS. 3A-3E
, detailed embodiments of the DWDM of the '190 patent are shown.
FIG. 3A
is a logic diagram of a 1×4 DWDM according to the '190 patent, also known as a 4-channel DWDM. The first stage MWDM
311
is cascadedly connected to two second stage MWDMs
321
and
322
. For demultiplexing purposes, a lightwave input having wavelengths &lgr;
1
-&lgr;
4
are input on fiber
30
, and outputs &lgr;
1
, &lgr;
2
, &lgr;
3
, and &lgr;
4
are provided on fibers
31
,
32
,
33
, and
34
, respectively. For multiplexing purposes, the inputs and outputs are reversed.
FIGS. 3C
,
3
D, and
3
E show the respective insertion loss of the MWDMs
311
,
321
, and
322
wherein &Dgr;&lgr; is the window spacing and &dgr;&lgr; is the window bandwidth. The dash curve and the solid curve in
FIG. 3C
indicates respectively the insertion loss in channels
30
-
321
and
30
-
322
. The dash curve and the solid curve in
FIG. 3D
indicates respectively the insertion loss in channels
34
-
311
and
34
-
311
. The dash curve and the solid curve in
FIG. 3E
indicates respectively the insertion loss in channels
33
-
311
and
33
-
311
.
FIG. 3B
shows an actual physical structure of the '190 DWDM according to the '190 patent. The first stage MWDM
311
is cascadedly connected to two second stage MWDMs
321
and
322
, and the DWDM of the '190 patent in housed in a container
35
having a length L and a width W.
As is appreciated by those of ordinary skill in the art, the length and width of container
35
is dictated by the radius R about which the optical fibers of the DWDM of
FIG. 3B
may be bent. As a consequence, the DWDM of the '190 patent suffers from certain disadvantages. While satisfactory for the purposes intended in terms of performance, the DWDM of the '190 patent suffers from size disadvantages. Due to the fused-biconical technique used in the DWMs of the '190 patent, the minimum radius about which fibers can be bent is approximately 35 mm. Thus, the minimum finished size of a DWDM according to the'190 patent has a length L of approximately 100 mm and a width W of approximately 50 mm.
Given the need to upgrade communications system as discussed above, there is an apparent need to fabricate a DWDM which is smaller in size than DWDMs of the prior art.
BRIEF DESCRIPTION OF THE INVENTION
The invention satisfies the above needs. The present invention relates to wavelength selective devices. In particular, the present invention relates to dense wavelength division multiplexers (DWDMs).
A miniature dense wavelength division multiplexer (DWDM) is disclosed.
In a first aspect of the present invention, a plurality of multi-window wavelength multiplexers (MWDMs) are cascaded and optically coupled to form a tree, and each of the MWDMs forming the tree comprises a microbend coupler.
In a second aspect of the present invention, the forming of the MWDM tree is characterized by the absence of the bending of optical fibers external to said microbend couplers.
A method for forming a DWDM is disclosed, which comprises providing a plurality of multi-window wavelength multiplexers (MWDMs) cascaded and optically coupled to form a tree, wherein each of the MWDMs of the tree comprises a microbend coupler.
Additional aspects of the present invention are disclosed wherein the DWDM formed by the present invention measures approximately 100 mm×50 mm, and as little as 50 mm×20 mm.
REFERENCES:
patent: 5138676 (1992-08-01), Stowe et al.
patent: 5809190 (1998-09-01), Chen
patent: 6314219 (2001-11-01), Zhang et al.
Assaf Fayez
Finisar Corporation
Fish & Richardson P.C.
Spyrou Cassandra
LandOfFree
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