U.S. patent application number 09/793290 was filed with the patent office on 2001-11-29 for configurable wavelength routing device.
Invention is credited to Tedesco, James M..
Application Number | 20010046350 09/793290 |
Document ID | / |
Family ID | 27391905 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046350 |
Kind Code |
A1 |
Tedesco, James M. |
November 29, 2001 |
Configurable Wavelength routing device
Abstract
A dispersive optical element and positionable micromirrors are
deployed to implement a configurable wavelength routing device for
add/drop and other applications. Input light is dispersed and
imaged onto a focal plane where there is disposed an array of light
redirection elements operative to decenter wavelengths on a
selective basis. In the preferred embodiment, the dispersive
optical element is a grating or grating/prism featuring a high
degree of dispersion allowing the input and return paths to be
parallel and counter-propagating, both for a compact size and to
facilitate a lateral shifting in a localized area. The inputs and
outputs may be implemented in conjunction with optical fibers, with
a lens being used to collimate light prior to illumination of the
grating. A focusing lens is preferably used to form a nominally
telecentric image of the dispersed spectrum at the image plane. A
control mechanism is provided to locate individual mirrors of the
array in one of at least two positions, to effectuate the selective
wavelength routing. In the preferred embodiment, the mirrors are 90
degree V-mirrors, translatable within the plane of the telecentric
image, such that in one position, a common port is coupled to an
express port and whereas, in another position, a common port is
placed in communication with an add/drop port.
Inventors: |
Tedesco, James M.; (Livonia,
MI) |
Correspondence
Address: |
John G. Posa
Gifford, Krass, Groh et al.
Suite 400
280 N. Old Woodward Ave.
Birmingham
MI
48009
US
|
Family ID: |
27391905 |
Appl. No.: |
09/793290 |
Filed: |
February 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60184893 |
Feb 25, 2000 |
|
|
|
60203963 |
May 12, 2000 |
|
|
|
Current U.S.
Class: |
385/37 ;
385/24 |
Current CPC
Class: |
G02B 6/29395 20130101;
G02B 6/29383 20130101; G02B 6/29313 20130101; G02B 6/29311
20130101 |
Class at
Publication: |
385/37 ;
385/24 |
International
Class: |
G02B 006/34; G02B
006/293 |
Claims
I claim:
1. A configurable wavelength routing device, comprising: a light
input; a light output; a dispersive optical element supported to
receive the light from the input and disperse the light into a
dispersed spectrum; a lens to form a telecentric image of the
dispersed spectrum at an image plane; an array of reflectors
disposed at the image plane; and a controller for positioning the
reflectors to return particular wavelengths of the telecentric
image to the light output.
2. The configurable wavelength routing device of claim 1, wherein
the dispersive optical element is a grating.
3. The configurable wavelength routing device of claim 1, wherein
the controller for operating the reflectors includes an
electronically addressable micro electromechanical system
(MEMS).
4. The configurable wavelength routing device of claim 1, wherein
the controller is operative to position individual reflectors in at
least one of two positions, such that light from similarly
positioned reflectors are delivered to one of two outputs,
respectively.
5. The configurable wavelength routing device of claim 4, wherein
the same dispersive optical element is used to recombine the light
from the similarly positioned reflectors to one of two outputs
laterally displaced on opposite sides of the input.
6. The configurable wavelength routing device of claim 4, wherein
one of the outputs functions as an express port and the other
functions as a drop/add port.
7. The configurable wavelength routing device of claim 1, wherein
the reflectors are controllable between: a first position wherein
they are V-shaped, and a second position, wherein one side of the V
is folded down substantially parallel to the image plane to return
selected wavelengths to the light input.
8. The configurable wavelength routing device of claim 1, wherein
the reflectors are W-shaped and controllable between: a first
position wherein selected wavelengths are routed to an add/drop
port, and a second position, wherein non-selected wavelengths
communicate with an add/drop port.
9. An optical add/drop module, comprising: a common port; an
express port; a drop/add port; a dispersive optical element
operative to receive light and output a dispersed spectrum; a lens
to form a telecentric image of the dispersed spectrum at an image
plane; an array of reflectors disposed at the image plane; and
apparatus for controlling the reflectors to: a) divert wavelengths
contained in the telecentric image of the light received through
the common to the drop/add port while permitting remaining
wavelengths to pass through the express port, or b) insert
wavelengths entering through the drop/add port into the telecentric
image of light received through the express port and output the
merged spectrum through the common port.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of U.S. provisional
application Serial Nos. 60/184,893, filed Feb. 25, 2000, and
60/203,963, filed May 12, 2000, the entire contents of both
applications are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention related generally to optical communications
and, in particular, to a configurable wavelength routing device
finding utility in various applications including use as an optical
add/drop module (OADM) in a dense wavelength division multiplexing
(DWDM) system.
BACKGROUND OF THE INVENTION
[0003] Optical telecommunications over optical fibers is now the
preferred mode of high-bandwidth data transmission in comparison to
copper wire, particularly over long distances. Such systems use
lasers modulated in amplitude by the data to be transmitted. The
signals are coupled into an optical fiber for detection and
demodulation at the other end of the link. The existing
infrastructure of long-haul optical fiber is rapidly becoming taxed
to its bandwidth capacity. Laying more fiber to carry additional
bandwidth is an extremely expensive proposition.
[0004] Dense wavelength-division multiplexing (DWDM) has emerged as
a more cost-effective solution. The idea is to force existing
fibers to carry more bandwidth by combining signals from multiple
lasers operating at different wavelengths onto a single fiber. Key
components of DWDM systems include the optical multiplexers and
demultiplexers, the latter often being the former operated in
reverse. The multiplexers take optical signals at different
wavelengths propagating on different fibers and combine them onto a
single fiber. The demultiplexers take several wavelengths
propagating on a common fiber and separate them onto different
fibers.
[0005] Another important component in a DWDM system is the add/drop
module, or OADM. The OADM is used to drop or pick-off wavelengths
to carry local node traffic to businesses or other destinations for
optical or electro-optical conversion. The OADM is also used to
re-insert wavelengths, typically carrying new data, back into the
DWDM fiber(s). These functions are illustrated schematically in
FIG. 1.
[0006] As shown in FIGS. 2A and 2B, existing OADMs utilize passive
components to define a fixed wavelength or a set of wavelengths to
be dropped or added. FIG. 2A shows a single-wavelength schematic,
having a fixed fiber Bragg grating to drop and add .lambda..sub.i,
whereas FIG. 2B illustrates a multiple wavelength schematic to add
and drop two fixed wavelengths, .lambda..sub.i and .lambda..sub.j.
FIG. 3 depicts a wavelength-configurable system including input
wavelength multiplexers and output demultiplexers on the other side
of a fiber-optic crossbar switch. A network control function is
used to dictate which channels are dropped and added according to
the switch settings.
[0007] Although configurations of the type just described have been
in use for some time, they are inflexible and/or expensive due to
the discrete nature of the components involved. As such, systems
based on these concepts tend to be expensive to implement and
maintain. Accordingly, there remains a need for a more flexible,
easier to implement OADM for use in DWDM and other
applications.
SUMMARY OF THE INVENTION
[0008] This invention utilizes a dispersive optical element and
positionable micromirrors to implement a configurable wavelength
routing device for add/drop and other applications. Broadly, input
light is dispersed and imaged onto a focal plane where there is
disposed an array of light redirection elements operative to
decenter wavelength images on a selective basis. In the preferred
embodiment, the decentered wavelengths are returned through the
same grating and directed to points shifted laterally with respect
to the input so as to implement wavelength routing or add/drop
functions.
[0009] In the preferred embodiment, the dispersive optical element
is a grating or grating/prism featuring a high degree of dispersion
allowing the input and return paths to be parallel and
counter-propagating, both for a compact size and to facilitate a
lateral shifting in a localized area. The inputs and outputs may be
implemented in conjunction with optical fibers, in which case a
lens is used to collimate light for a illumination through the
grating, and to focus return beams to respective inputs or outputs,
as the case may be. A focusing lens is preferably spaced
approximately one focal length from the output of the dispersing
element, so as to form a nominally telecentric image of the
dispersed spectrum; that is, with the primary rays being incident
substantially perpendicular to the image plane at all wavelengths
of interest.
[0010] An array of reflectors is positioned at the focal plane, and
a control mechanism is provided to locate individual mirrors of the
array in one of at least two positions, to effectuate the selective
wavelength routing. In the preferred embodiment, the mirrors are 90
degree V-mirrors, translatable within the plane of the telecentric
image, such that in one position, a common port is coupled to an
express port and whereas, in another position, a common port is
placed in communication with an add/drop port.
[0011] Various alternative configurations of the reflector array
are described in detail. Although a unitary V-shaped mirror element
is used in the array, one side of the mirror may also fold down to
permit a direct reflection, thereby creating a direct coupling
between common and express ports. In such a configuration, the
device functions as a two-port module, as opposed to a three-port
module, such that one or more circulators may desirably be added to
isolate wavelength paths.
[0012] According to a different embodiment, a multi-position "W"
mirror array may be used at the spectral image plane, such that, in
one position, input wavelengths are coupled to an express port,
whereas, in a shifted position, input and add/drop ports are placed
in communication. Further alternative embodiments include the use
of N-position mirrors, which may be tilted and/or translated to
realize an N-port routing capability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a simplified schematic of an optical add/drop
module (OADM) for wavelength routing in a multi-node network;
[0014] FIG. 2A is a schematic of a single-wavelength OADM using
passive components to define a fixed wavelength;
[0015] FIG. 2B is a schematic of a multiple-wavelength prior-art
OADM also utilizing passive components;.
[0016] FIG. 3 is a drawing of an existing configurable OADM
utilizing a wavelength multiplexer and demultiplexer in conjunction
with an array of 2.times.2 fiber switches;
[0017] FIG. 4A is a top view of an optical configuration used to
introduce concepts according t o the invention;
[0018] FIG. 4B is a side-view of the configuration of FIG. 4A;
[0019] FIG. 5A shows how an object decentered in a plane
perpendicular to dispersion may be used to image a point decentered
by an equal amount opposite the lens axis;
[0020] FIG. 5B is an end view of the arrangement of FIG. 5A;
[0021] FIG. 6 is a drawing which shows how a V-mirror according to
the invention may be used to convert a point in a dispersed
spectral image into a decentered virtual object for the return
path;
[0022] FIG. 7A is a schematic drawing showing how a V-mirror array
may be employed by the invention to implement a
wavelength-configurable router as a 3-port device;
[0023] FIG. 7B is a side view of the configuration of FIG. 7A,
showing a V-mirror in position A routing its common port to port
A;
[0024] FIG. 7C is a similar side view drawing showing a V-mirror in
position B routing its common port to port B;
[0025] FIG. 8 is an end view drawing illustrating an array of
V-mirrors at the spectral image plane configured to route some
common-port wavelengths to port A and others to port B, according
to the configurations of FIG. 7;
[0026] FIG. 9 is a functional block diagram of the 3-port device of
FIGS. 7 and 8 which shows how the common port may be coupled by
wavelengths to one of two other ports according to the
invention;
[0027] FIG. 10 illustrates a comprehensive system according to the
invention, implementing both drop and add functions by cascading
two of the 3-port devices of FIGS. 7 and 8;
[0028] FIG. 11 is a schematic illustration which shows how a
V-mirror is used in two positions to decenter a common port image
in two different directions for routing to two different output
ports according to FIG. 7;
[0029] FIG. 12 illustrates an alternative micro-mirror
configuration for a two-port device having a direct
retro-reflection express position and a fold-down add/drop
position;
[0030] FIG. 13A is a drawing of a 2-port configuration using an
array of mirrors of the type shown in FIG. 12, showing a mirror
element in an add/drop position;
[0031] FIG. 13B shows the 2-port configuration of FIG. 13A with a
mirror element of the type shown in FIG. 12 tilted to the express
position;
[0032] FIG. 14 is a simplified functional block diagram of the
2-port configuration of FIGS. 13A and 13B;
[0033] FIG. 15 is a schematic illustration of a complete add/drop
system using a single two-port device of the type shown in FIGS. 12
through 14 in conjunction with two circulators;
[0034] FIG. 16A is a drawing which illustrates mirror
configurations for a one-into-four router;
[0035] FIG. 16B is a drawing which shows the fiber positions
addressed by the mirror positions of FIG. 16A;
[0036] FIG. 17A is a schematic drawing of a further alternative
embodiment of the invention allowing the implementation of a full
4-port add/drop device through the use of a two-position "W" mirror
array at the spectral image plane, with no additional circulators
or cascaded gratings required, with the W-mirror shown in the
express position; and
[0037] FIG. 17B is a drawing of the configuration of FIG. 17A, with
the position of the W-mirror at the add/drop position.
DETAILED DESCRIPTION OF THE INVENTION
[0038] Having introduced and discussed certain prior-art
configurations with references to FIGS. 1 through 3, the reader's
attention is directed to FIGS. 4A and 4B, which will be used to
introduce a novel wavelength routing system according to the
invention. FIG. 4A is a top-view of the arrangement, wherein an
input fiber 402 carrying multiple wavelengths is collimated by
element 404 and dispersed by element 406 into spectrum 408. A
telecentric imaging lens 410 is used to focus the spectrum at focal
plane 412. A reflective surface such as a flat mirror is placed at
focal plane 412, which is operative to retro reflect the dispersed
wavelength bundle back along its original path and into input fiber
402, as enabled by the telecentric nature of the image.
[0039] FIG. 4B is a side-view illustration of the configuration of
FIG. 4A, keeping in mind that the dispersed spectrum lies along a
line into the paper. Dispersive element 406 preferably includes a
holographically derived grating 420 sandwiched between optical
blocks 422 and 422', enabling incident and exit paths to lie on
parallel paths, as shown. However, it must be understood that such
a compact dispersive element need not be used according to the
invention, in that the incident and exit paths need not be
parallel, and a reflective as opposed to transmissive grating may
alternatively be used.
[0040] Having introduced the concept of retro reflecting the
dispersed wavelength bundle at the telecentric image back along its
original path to an input fiber, reference is now made to FIGS. 5A
and 5B, which illustrate the concept of decentering as used
advantageously by this invention. As shown in FIG. 5A, an object
502 decentered from the lens axis 510 will image to a point
decentered by an equal amount opposite the lens axis as shown in
the end-view of FIG. 5B. Accordingly, light delivered in the
position of the object 502 may be received in a decentered
collection fiber 512 at the image plane.
[0041] According to this invention, the concepts of retro
reflection and decentering are used to convert a point in the
dispersed spectral image into a decentered virtual object for the
return path, as depicted in FIG. 6. In place of a flat mirror, a 90
degree V-mirror element 600 is positioned with respect to each
wavelength position of interest relative to lens axis 602. A
centered light bundle from the grating and lens along the lens axis
602 is now decentered using the V-mirror, for a return along path
610 emanating from virtual image 612. Again, although a 90 degree
V-mirror element is used to force decentering along a parallel
counter-propagating path, other beam redirection configurations may
alternatively be used to cause decentering according to the
invention, perhaps with the addition of other optical elements.
[0042] The mirror array is preferably fabricated utilizing micro
mechanical (MEMS) technology, wherein electronically addressable
micro actuators are used to manipulate micro mirrors on a selective
basis. A preferred decenter of 250 microns is used on each side of
the optical axis so as to be compatible with industry standard
V-groove fiber mounting components. A multi-element focusing lens
may alternative be used to achieve resolution, throughput and
cross-talk specifications compatible with 50 GHz DWDM channel
spacings.
[0043] FIGS. 7A and 7B illustrate the use of a V-mirror array in
implementing a wavelength-configurable 3-port router according to
the invention. FIG. 7A is a topview of the arrangement, whereas
FIG. 7B is a side-view. The configurations of FIGS. 7A and 7B are
similar to those of FIGS. 4A and 4B, except that the planar
retro-reflector has been replaced with the V-mirror array 702. As
such, instead of retro reflecting all wavelengths back into the
input fiber 704, the use of a V-mirror decenters the returns on a
selective basis. Additionally, by translating the array in the
focal plane, wavelengths may be arbitrarily routed with respect to
multiple fibers positioned at decentered locations on a selective
basis. In FIG. 7B, for example, with the V-mirror in position A, a
wavelength from centered input fiber 704 will be reimaged to fiber
A, whereas, as shown in FIG. 7C, with the V-mirror element in
position B, a particular wavelength is reimaged to fiber B.
[0044] FIG. 8 is an end-view of FIG. 7 which illustrates the
concept of multiple differently-routed wavelengths according to the
invention. The centered common fiber is shown on the right, with
decentered fibers B and A above and below, respectively. With
dispersion occurring from the left to the right in this drawing,
with the V-mirror elements in the A positions, decentered virtual
images are shown at the top, whereas, with the mirror elements in
position B, a the corresponding wavelengths are shown along the
bottom of the diagram. Wavelengths corresponding to mirror elements
in position A are routed to decentered fiber A just below the
common fiber, and wavelengths corresponding to mirror elements in
position B are routed to decentered fiber B just above the common
fiber.
[0045] FIG. 9 illustrates the embodiment of FIGS. 7 and 8 in the
form of a functional block diagram. Broadly, a common port 902 is
used to couple wavelengths to either of two other ports selected by
the movement of the mirror elements, in either direction. Such a
device may therefore be thought of as a wavelength-configurable
three-port splitter/combiner.
[0046] FIG. 10 is a drawing which illustrates how a device
according to the invention as shown in FIGS. 7 and 8 may be
configurable for use in both drop/add modes, as well as cascaded to
form a complete optical add/drop module (OADM). A drop function is
shown at the left generally at 1002, wherein a plurality of
wavelengths .lambda..sub.1, .lambda..sub.2, .lambda..sub.3, . . .
.lambda..sub.11, are carried on a common fiber 1004, and wherein
.lambda..sub.i, . . . .lambda..sub.j are dropped at position A. The
remaining wavelengths proceed through along express path 1006 at
position B under network control 1010, which commands the mirror
element positions. An add function is implemented generally at
1020, wherein the express wavelengths at position B are input to
module 1022, and wavelengths .lambda..sub.i, . . . .lambda..sub.j
are added at position A under separate network control 1030. A full
set of wavelengths are then output along common path 1032.
[0047] By way of a review, FIG. 11 is a close-up view of reflectors
according to the invention operated with respect to the preferred
embodiment. Light associated with the common port is returned from
a real centered image generated by the grating and lens. With the
V-reflector in the express position, a decentered virtual image is
developed in alignment with the express port, whereas, with the
reflector in the add/drop position, a decentered virtual image is
generated with respect to the add/drop port.
[0048] FIG. 12 illustrates an alternative embodiment of the
invention, wherein instead of a unitary V-mirror, one side of the
reflector folds down into the express position from the add/drop
position, thereby coupling the express bundles to the input fiber.
Thus, the module now functions as a two-port device.
[0049] FIG. 13A is a side view drawing of the 2-port embodiment
introduced in FIG. 12, showing a mirror element in the add/drop
position. The mirror is tilted to the add/drop position such that
the decentered path to and from the tilted mirror is coupled to the
add/drop fiber, as shown. FIG. 13B is a similar side view of this
2-port configuration showing a mirror element in the express
position, wherein the center path to and from the untilted mirror
is retro reflected to the same centered fiber.
[0050] The overall concept of the modified 2-port device according
to the alternative embodiment of FIGS. 12 and 13 is depicted
functionally in FIG. 14. With the mirror untilted or planar with
respect to the image plane, express wavelengths are looped back out
through a common/express port, whereas, with certain of the mirrors
selectively tilted, add/drop wavelengths are routed out of, or
into, the add/drop port.
[0051] Given that this alternative embodiment functions as a
two-port device, circulators may be added to implement a complete
4-port add/drop module, as shown in FIG. 15. Wavelengths received
through an input/common port are fed to circulator 1502. Express
wavelengths from this group are retroreflected from the untilted
mirrors back to the common/express fiber of the 2-port device, and
then output through port 3 of the circulator 1502 due to their
reverse direction of propagation. Input wavelengths routed to the
add/drop fiber of the 2-port device by tilted mirror elements are
routed to the drop port due to their direction of propagation.
These same dropped wavelengths may be added with different signal
traffic back onto the Output/Express port by sending them to the
circulator Add port, where they are routed by the circulator to the
decentered add/drop fiber of the 2-port device, and imaged to the
centered common/express fiber by the same tilted mirror
elements.
[0052] Although the modified alternative embodiment of the OADM
just described may be more expensive as a stand-alone drop-only or
add-only unit, due to the fact that at least one circulator is
needed to isolate common/express wavelengths, the modified version
does offer certain advantages. For one, only one pass is made
through the grating/mirror module, thereby potentially affording a
lower insertion loss. Indeed, only one grating/mirror module is
required to implement a complete OADM, though two circulators are
required in a robust configuration. The alternative system also
features a simpler mirror/actuation structure, in that a single
tilting flat mirror as opposed to a translating V-mirror may be
used at each wavelength position.
[0053] In addition, although the devices just described are used to
route input wavelengths to either of two ports, the invention may
be extended to N output ports, though a trade off exists in terms
of complexity and wavelength resolution. Broadly, the two-position
mirror may be replaced with an N-position mirror, with the
additional position decentering the reflected image further away
from the optical axis. More than one surface must be actuated for
each wavelength, and/or the actuation must be carried out in more
than one dimension. The approach may be extended to arbitrarily
couple a wavelength between any two ports.
[0054] FIGS. 16A and 16B illustrate the extension of the invention
to a one-into-four router. As shown in FIG. 16A, a small tilting
and rotational mirror 1602 is supported relative to the real image
of the common path, and may be tilted in either direction with
respect to fiber positions A and B, or translated and tilted in
either direction for fiber positions C and D. The relationship
between the common input and the add/drop positions is shown in
FIG. 16B. The addressing motion is therefore multi-dimensional,
with a single actuated element in each wavelength. Note, that the
larger decenterers move the mirrors further from the spectral
focus, thereby potentially reducing the achievable level of
resolution as the number of ports grows. Further extensions of this
embodiment include alternative mirror/fiber configurations, and
additional ports.
[0055] As yet a further alternative and perhaps preferred
embodiment of the invention, a translatable unitary "W" mirror
array may be used at the spectral image plane, as shown
schematically in FIGS. 17A and 17B. The express position of a
mirror element is shown in FIG. 17A, wherein wavelengths received
over the input port are routed back out the output port. In the
add/drop position of FIG. 17B, however, the "W" mirror has been
moved upwardly in the drawing, such that input wavelengths are
routed out a separate drop port, and add wavelengths are reinserted
into the output port. This configuration has the advantage of
providing a full 4-port add/drop router using a single dispersive
module without the use of expensive circulators, while still
requiring only two different lateral mirror positions as per the
3-port device. The only added complexity is in the fabrication of a
more complicated mirror element.
* * * * *