Packaging for grating-based WDM router

Details Packaging for grating-based WDM router Packaging for grating-based WDM router

2000-05-25

2002-04-23

Spyrou, Cassandra (Department: 2872)

Optical waveguides

With optical coupler

Input/output coupler

C385S052000, C385S037000, C385S056000, C359S566000, C359S199200

Reexamination Certificate

active

06377728

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to wavelength division multiplexers and demultiplexers in optical communications networks and systems, and more particularly to their packaging.
BACKGROUND OF THE INVENTION
Fiber optic communication systems are becoming increasingly popular for data transmission due to their high speed and high data capacity capabilities. Wavelength division multiplexing is used in such fiber optic communication systems to transfer a relatively large amount of data at a high speed. In wavelength division multiplexing, multiple information-carrying signals, each signal comprising light of a specific restricted wavelength range, may be transmitted along the same optical fiber.
In this document, these individual information-carrying lights are referred to as either “signals” or “channels.” The totality of multiple combined signals in a wavelength-division multiplexed optical fiber, optical line or optical system, wherein each signal is of a different wavelength range, is herein referred to as a “composite optical signal.”
The term “wavelength,” denoted by the Greek letter &lgr; (lambda) is used herein in two senses. In the first usage, this term is used according to its common meaning to refer to the actual physical length comprising one fall period of electromagnetic oscillation of a light ray or light beam. In its second usage, the term “wavelength” is used synonymously with the terms “signal” or “channel.” Although each information-carrying channel actually comprises light of a certain range of physical Wavelengths, for simplicity, a single channel is referred to as a single wavelength, &lgr;, and a plurality of n such channels are referred to as “n wavelengths” denoted &lgr;
1
-&lgr;
n
. Used in this sense, the term “wavelength” may be understood to refer to “the channel nominally comprised of light of a range of physical wavelengths centered at the particular wavelength, &lgr;.”
A crucial feature of fiber optic networks is the separation of the composite optical signal into its component wavelengths or channels, typically by a wavelength division multiplexer. This separation must occur to allow for the exchange of signals between loops within optical communications networks. The exchange typically occurs at connector points, or points where two or more loops intersect for the purpose of exchanging wavelengths.
FIG. 1
a
schematically illustrates one form of an add/drop system, which typically exists at connector points for the management of the channel exchanges. The exchanging of data signals involves the exchanging of matching wavelengths from two different loops within an optical network. In other words, each composite optical signal drops a channel to the other loop while simultaneously adding the matching channel from the other loop.
A wavelength division multiplexer (WDM) typically performs separation of a composite optical signal into component channels in an add/drop system. Used in its reverse sense, the same WDM can combine different channels, of different wavelengths, into a single composite optical signal. In the first instance, this WDM is strictly utilized as a de-multiplexer and, in the second instance, it is utilized as a multiplexer. However, the term “multiplexer” is typically used to refer to such an apparatus, regardless of the “direction” in which it is utilized.
FIG. 1
a
illustrates add/drop systems
218
and
219
utilizing wavelength division multiplexers
220
and
230
. A composite optical signal from Loop
110
(&lgr;
1
-&lgr;
n
) enters its add/drop system
218
at node A (
240
). The composite optical signal is separated into its component channels by the WDM
220
. Each channel is then outputted to its own path
250
-
1
through
250
-n. For example, &lgr;
1
would travel along path
250
-
1
, &lgr;
2
would travel along path
250
-
2
, etc. In the same manner, the composite optical signal from Loop
150
(&lgr;
1
′-&lgr;
n
′) enters its add/drop system
219
via node C (
270
). The signal is separated into its component channels by the WDM
230
. Each channel is then outputted via its own path
280
-
1
through
280
-n. For example, &lgr;
1
′ would travel along path
280
-
1
, &lgr;
2
′ would travel along path
280
-
2
, etc.
In the performance of an add/drop function, for example, &lgr;
1
is transferred from path
250
-
1
to path
280
-
1
. It is combined with the others of Loop
150
's channels into a single new composite optical signal by the WDM
230
. The new signal is then returned to Loop
150
via node D
290
. At the same time, &lgr;
1
′ is transferred from path
280
-
1
to path
250
-
1
. It is combined with the others of Loop
110
's channels into a single new composite optical signal by the WDM
220
. This new signal is then returned to Loop
110
via node B (
260
). In this manner, from Loop
110
's frame of reference, channel &lgr;
1
of its own signal is dropped to Loop
150
while channel &lgr;
1
′ of the signal from Loop
150
is added to form part of its new signal. This is the add/drop function.
FIG. 1
b
illustrates a second form by which add/drop systems
218
and
219
may be configured. In
FIG. 1
b,
each WDM is optically coupled to a first plurality of paths through which channels are outputted and to a second plurality of paths through which signals are inputted. For instance, the paths
250
-
1
,
250
-
2
, . . . ,
250
-n are utilized to output signals comprising wavelengths &lgr;
1
, &lgr;
2
, . . . , &lgr;
n
, respectively, from the WDM
220
and the paths
251
-
1
,
251
-
2
, . . . ,
251
-n are utilized to input signals comprising such wavelengths to the WDM
220
. Likewise, as shown in
FIG. 1
b
, the paths
280
-
1
,
280
-
2
, . . . ,
280
-n are utilized to output signals &lgr;
1
′, &lgr;
2
′, . . . , &lgr;′
n
(comprising the physical wavelengths &lgr;
1
, &lgr;
2
, . . . , &lgr;
n
) respectively, from the WDM
230
and the paths
281
-
1
,
281
-
2
, . . . ,
281
-n are utilized to input signals comprising such wavelengths to the WDM
230
.
FIGS. 2
a
and
2
b
illustrate a top view and side view, respectively, of a prior-art grating-based WDM. In the WDM
200
, a concave reflection-type holographic grating
202
is disposed upon a substrate plate or block
201
comprised of a material with low thermal expansion. The grating
202
, which comprises a portion of a spherical surface
206
centered at point
210
, receives a wavelength-division multiplexed composite optical signal
211
input to the WDM
200
from an input fiber
204
. The composite optical signal
211
is comprised of a plurality of individual channels, &lgr;
1
, &lgr;
2
, . . . . The concave grating
202
diffracts, reflects, focuses and spatially disperses each of these individual channels according to its respective wavelength such that each channel is directed to exactly one of a plurality of output fibers
209
a
-
209
b.
For instance, referring to
FIG. 2
a,
if input signal
201
is comprised of two channels, namely channel &lgr;
1
(
207
a
) and channel &lgr;
2
(
207
b
), with &lgr;
1
<&lgr;
2
, then, upon back-diffraction from grating
202
, the &lgr;
1
channel (
207
a
) and the &lgr;
2
channel (
207
b
) are focused onto the end of fiber
209
a
and fiber
209
b,
respectively.
The input fiber
204
and the plurality of output fibers
209
a
-
209
c
are disposed within an array
205
of fibers. The end faces of the fibers in array
205
are disposed along or parallel to a plane
208
which makes an angle of 60° with the line
203
that is normal to the grating
202
at the center of the grating
202
. With this disposition, the grating
202
diffracts light according to the Littrow configuration, in which the angles of incidence and diffraction are approximately equal.
FIG. 2
b
shows a side view of the prior art apparatus taken parallel to the fiber
204
.
FIG. 2
b
shows that the fibers are directed towards the grating vertex and are at an angle to the grating dispersion plane
215
. The input fiber
204
and the ou

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