Note: Descriptions are shown in the official language in which they were submitted.
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
COll2PRESSrON-TUNED GRATINGBASED
OPTICAL ADD/riROP MULTIPLEXEIt
Cross References To Related Applications
'S This is a continuation-in-part o.f US Patent Application, Serial No. 09/S
19,220
a:
entitled "Compression-Tmaed Bragg Grating Based Iteconfiguxable wavelength
Channel Addl:Drop Multiplexes", :Czled March 6, 2000 {CC-0204), which is
hereby
incozporated herein by reference in its entirety.
2b3 Technicalh'ield.
The present inventi.an relates to optical add/drop multiplexes devices, and
more partioularly, an optical addldrop multiplexes. {O.ADNI] using a. iarge
diametex
waveguide for dynamically adding and dropping optical signals from a. "~tflM
optical,
signal,
l'5
Baclrground Art
The telecommunications Indus°'.ry is undergoing dramatic changes
with,
increased competition, relentless bandwidth, demand, and a migration toward a
more
data-centric network architeatuxe. First generation point-to-point wave
division
a o multiplex systems have eased the traffio bot~lenecl~ in the backbone
portion of a
networlc. As a new cross-connect architecture moves the technology closer to
ihew
subscriber side of the network, operators are challenged to provide services
at fh.e
opti.aal .layer, calling for more flexible n.etlvorlcs that can switch and
reroute
wavelengths. This is placing great emphasis and demand for wavelength agile
devices, of which compression-tuned grating devices could play a majox xole.
The need to provide services "ju.st in time" by allocation of wavelengths, and
.furth.er migration ofthe optical layer from the high-capacity bacltbone
portion to the
local loop, is driving the transformation of the network toward an all
optie~.l nel."~~orlc
in which basic network requixem,ents wilt be performed. in the optical Iayer,
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
The optical, naetwork is a natural evolution of point-to-point dense
wavelength
division multiplaxin.g (D~7trDM) iTansport to a more dynasn.ie, nexible, and
intelligent
netwvorlting architecture to improve service delivery tuna. The main element
of the
optical network is the wavelength (channel), which will be provisioned,
configured,
.s, routed., and managed in the optical domain. Xntell.igent optical
networking will be first
deployed as an "opaque" network in which periodic optical-electrical
convexsi.on will
be required to monitor and isolate signal impairments, Longex xange, the
optical
netwoxlc will evolve to a "transparent" optical network in which a signal is
transported
from its source to a destination totally within the optical domain.
io A key elean.ent of the emerging optical z~.etvvoxlc is an optical add/drop
multiplexes (OADM), An OADM will drop oz add specific wavelength channels
without affecting tla.e ilrrough channels, nixed OADMs can simplify the
networlc and
readily allow cost-effective DWDM migration from simple point-to-point
topologies
to tzxed mufti-point configyxations. True dynamic OADM, in which
reconfiguration
r15: i.s done in the optical domain without optical-electrical conversion,
vcrould allow
dynamically xeconfigurable, mufti-point DWDM optical networks. This
dynamically
xeeonfigurable mufti-point architecture is slated to be the next major please
in network
evolution, with true OADM an enabling network element for this arcllitecturo,
One known comrnezcially is a fixed all-optical OADM that couples fixed
a o optical clia~mel filters, usually fiber Bragg gratings, to passive optical
routing and
branching components such as couplers and circulators. The fiber Bragg
gratings are
not tuned to filter different wavelengths.
A tunable gratiog/ei..rculator approach for dynamically reconfigurable OADM
has also been pursued in the prior art by thermal or strain tuning the
gzating. These
2s, dynamic or programmable all-optical OADM designs are based on tunable
gratings.
But thermal tuniaag is slow and difficult to maintain and control wavelength
to the
tolerances required in cun~ent DWDM systems that feature sub-manometer channel
spacing, Strain tuning approaches, in vYhioh, the fiber grating is
mechanically
stretched, loave also proved difficult to maintain and control and tune
wavelengths due
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
to ~.ber attachment challenges and slight mechanical creep that cause errors
anal
slippage. The reliability of a fiber. being lteld under tension for extended
periods of
tithe is questionable and controversial for use in the industry.
Ball, in United States Patent No, 6,020,986, shows an addldrop module haying
a. circulator 16, an array of tunable fiber Bragg gratings, a piezoelectric
device and a
controller, which is incorporated here:tn by reference. strain is applied by
coupling
the piezoelectric device to each Ether Bxagg grating, and adjusting the
current applied
to each piezoel.ectri.e device from the controller. The wavelength, o~ the
grating trtay
be adjusted ("tuned") i.n th.e manometer range for gratings having a
wavelength of
a.o. about 1540 manometers. However, SaII does not disclose how the
piezoelectric
device is physi.cal.l,y coupled to the fiber Bragg gratings to apply strain..
See also
United States Patent No. 5,579,143, issued to Huber, and United States latent
No.
5,748,349, issued to Mizxahi, which disclose OA.DM systems having tenable
optical
filters, v~rllzch axe incorporated herein by reference.
z5 Moreover, the grating/circulator approach for OADM has emerged as a. viable
rztethod over otl.~er OAAM techniques such as optical switches and arrayed
vVaveguide
devices, which are broadband in nature, Combinations of switches and
wavelength.
rttultiplexers achieve wavelength selection but suffer fram other performance
problems such as high optical losses and high cost.
ao Despite intense efforts, dynamic OADMs of such types remain elusive due to
inherent performance issues, particularly drift and reliability, tlaz~a
thermal or tension
grating tuning approaches. T, he inadequacy of thermal and tension-based
grating
tuning methods to control and maintain wavelength to tight tolerances would
require
some sort of in-line signal diagnostic, such as a wavelengtl monitoring device
or
s, speci:rttm. aualy~ex, to provide feedbacle and referencing for closed loop
control of the
grating v~avelengtla,
Summary of the Invention
fn accordance with an embodiment of the present invention, an optical drop
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
filter includes a compression-tuned optical device, The compression tuned
optical
device includes an optical waveguide, which has an inner care disposed within
an
outer cladding and a grating disposed within the inner core. The grating
reflectd a
fixst reflection wavelength of light baclc along the inner core and propagates
the
remainirr,ycvaYelengths of light through the grating. The optical waveguide
includes a
pair of opposing surfaces. The optical waveguide also includes a compressing
devzce
that compresses tile optical waveguide fox compressing the opposing surfaces
towards
each other to tttn.e the grating and change th.e reflection wavelength of
light reflected
baclt along the inner core. The drop f lter also includes an optical directing
device for
~.o providing an input optical sig~.ial to the compression-tuned optical
device.. The input
optical signal has a plurality of optical channels cantered at spaced
wavelengths. The
compression-tuned optical device removes an optical charnel from the input
opti,eal
signal.
In accordance wiill another embodiment of the pxesent invezation, an optical
add ~rlter includes a compression-tuned optical device, which has an optical
rnaveguide, The optical waveg~iide includes an inner core disposed within an
outer
cladding and a grating disposed within the inner core. The grating reflects a
first
reflection. wavelength. of light back along the um.er core and propagates the
remaining
wavelengths of light through the grating, The optical waveguide includes a.
pair of
a o opposing surfaces. A compressing device compresses the opposing stufaces
of the
optical waveguide to tune the grating and change the refiection wavelength of
Iight
reflected baelc along the innex core. An optical directing device is optically
connected
to the compression-tuned optical device for combining an input optical signal
and an
added optical Channel. The input optical signal has a phu-ali,ty of optical
channels
z s centered at spaced wavelengths, The compression-tuned optical device
provides the
optical channel to be combined with the input optical signal to provide a
combined
output signal,
In aecorda~.ZCe with another embodiment of fihe present invention, an optical
addldrop multipiexer includes a compression-tuned optical device that has an
optical
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
waveguide. The optical waveguide includes an inner core disposed within an
outer
elad.ding and a grating disposed within the innez core. The grating reflects a
first
reflection wavelength of light back along the inner core and propagates the
retxiailiing
wavelengths of light through, the grating. The optical waveguide includes a
pair of
opposing surfaces, A compressing device compresses the optical waveguide to
compress the opposing surfaces towards each other to tune the grating and to
change
the reflection wavelength. of light reflected back along the inner core, An
optical
directing device is ogtically connected to the compzession-tuned optical
device for
combining an input optical signal and an added optical cha~tnel, The input
optical
so signal has a plurality of optical channels centered at spaced wavelengths.
The
compression-tuned optical device provides the optical channel to be combined
with
the input optical signal to provide a combim.ed output signal.
In. accordance with another embodiment of tine present invention, a.
compression-tuned optical addldrop module includes a compression device for
a.s providing a compzession force applied along an axis of compression. A
grating
compression unit having a grating along the a~ezs of compression is responsive
to the
optical inpui. signal, and fiazther responsive to the compression force, for
providing a
grating compression unit optical signal having tla.e selected wavelength of
the channel
to be added to or dropped from. the input signal.
z o The foregoing and other objects, features and advantages of the present
invention will become more apparent in light ortlxe following detailed
description of
exen~plaxy embodiments ~thareof, as illustrated in the accompanying drawing.
Brief Description of t)xe Drawings
z5 hTG. 1 is a. side view of a tunable grating unit of a tunable optical
filter and a.
block diagram of a positionallforce feedbaelc control circuit in accordance
with the
present invention;
FIG. 2 is a side view of a grating element pf a tunable optical filter in
accordance with the present invention;
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
FIG. 3 is a block diagram of a tunable drop filter in accordance with the
present invention;
FIG. 4 is a block diagraan of another embodiment of a tunable drop alter in
accordance ~arith the present invention;
FIG. 5 is a block diagram of a tunable add filter inn accordance with the
present
invention;
1~'IG. b is a bloclc diagram of another embodiment of a tunable add filter in
accordance with the present invention;
FIG, 7 is a. bloelc dia~am of another embodiment of a tunable add filter in
y o accordance urith the present invention,
FIG. 8 is a block diagram of at~toyer embodiment of a ttu~able add filter.in
accordance with the present invention;
FIG. 9 is a block diagram of a reconiiguxable optical addJc~rop multiplexer
(ROADlI~ in accordance with the present invention;
15 FIG. 10 is a bloclc diagram. of.a~~other ~mbodirnel~t of a reconfi,gurable
optical
addldrop multiplexer (ROAD1VI) in accordance with the present invention;
FIG, 11 is a. block diagram of another embodiment of a reconhgurabl.e optical
addldrop multiplexer (1~OAI7M~ in accordance with the present invention;
FIG. 12 is a block diagram of another embodiment of a reconhgurable optical
2 o addldrop multiplexez (ROADM) in accordance with the present zn.vention,
and
FIG, 13 is a block diagram of another embodiment of a recoufigurable optical
addldrop ~n.ultiplexer (ROADM) in accordance with the present invention.
Detailed. Descrigtion of the Invention
25 FIGS. 3 and 4 show respective embodiments of tunable drop filters 80, 90
that
filter or drop at least one wavelength band ox optical el,lannel of light,
which is
cantered at a respective channel wavelength, from a'VSrDM optical input signal
11,
FIGS, 5 - 8 show respective embodiments of tunable add f Iters 100,110,120,130
that
add or combine at least one optical channel, to a WDM optical input signal 11,
As
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
sho~m in FTGs. 9 -13, tha tunable drop and add filters 80,90,100,110,120,130
may be
combined in a number ways to provide a reconfiguxable optical add/drop
multiplexer
(ROADM~ 140,150,160,170,180.
Referring to FIGs. 1 and 2, each of the tunable drop filters, add filter and
ROADMs shown in Figs. 3 - 13 include at least one ttu able Bragg grating unit
10,
optically coupled to a pork of an optical directing device 12,13 (see Figs. 3 -
6), such
as a 3 or 4 port circulator, or optical coupler 15. The grating unit x 0 tunes
a grating
element 14, which is a bulls or large diameter optical waveguide, having an
outer
cladding 18 and an inner core 16 disposed therein, having a single mode. The
grating
an element 14 has an outer diameter of at least .3 mrxi and comprises silica.
glass (SiOz)
having the appropriate dopants, as is lcnown, to allow light 11 to propagate
along the
inner core 16, The grating element (laxge diameter optical waveguide) may be
formed
by using fiber Braying techniques now lcnow or later developed that provido
the
resultant desired dimensions for the core and the outer dimensions discussed
hereinbafore, similar to that disclosed in co-pending US Patent Application,
Serial
No. 091455,868 entitled "Large Diameter Optical V~l'aveguide, Grating, a~ad
Laser".
The grating element n~.ay then, be etched, grounded or machined to form a
"dogbone"
shape, as will be described in greatex detail hereiafter. A pair of fibers ox
"pigtails" I7
W ay be attached to the ends of the brating element 14 by Icnovvv techniques,
such as
z o epoxy or glass fusion)
Alternatively, floe optical grating element 14 may be formed by heating,
collapsing and fusing a glass capi,ll.ary tube to a fzber (not Shown) by a
laser, filament,
flame, ete,, as is described in copending US Patent Application, Serial. No.
091455,865, entitled "Tube-Encased. Fiber fixating", which is incorporated
herein by
~ s reference. Other techniques may be used foz collapsing and fusing the
tubes to the
fiber, such as is discussed in US Patent No. 5,745,626, entitled "Method For
And
Encapsulation. Of An Optical Tiber", to Duclc et al,, andlor US Patent No.
4,915,467ø
entitled "Method of Malrixag Fibax Coupler Having Tntegral Precision
Connection
'Wells", to Berkey, ~.~hich are incoipoxated herein by reference to the extent
necessary
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
to understand the present invention, or other techniques, Alternatively, other
techniques may be used to fuse the lzber to the tube, such as using a high
temperature
glass solder, e.g., a silica solder (powder or solid), such that the fiber,
the tube and the
solder all become fused to each other, or using laser weldin~fusing or other
fusing
tBChniques.
The grating element 14 includes a reflective element 20, such as a Bra.gg
grating, is vvri ten (embedded or imprinted) into the inner core 16 of the
grating
element 14. Th.e Bragg grating 20 reflects back a portion the input light 11
as
indicated by a line 22 having a predetermined wavelength band of light
centered at a
~. o reflection ~tea~srelength ?a,, a~.d passes the remaining wavelengths of
the incident light
1.3 (within a. predetermined wavelength zange), as indicated by a line 24, The
grating
20, as is 1{nown, is a periodic or aperiodic variation in th.e effective
refractive index
an.dlor effective optical absorption coefficient of an optical waveguide, such
as that
desczibed in US patan.t No. 4,725,110 and 4,507,950, entitled "Method for
Impressing
is GratingS'9Vithin Fiber Optics", to Glenn et al; and US patent No.
5,3$8,173, entitled
"Method and Apparatus for Forming Aperiodic Gratings in Optical. Fibers", to
Glenn,
wluch are hereby incorporated by reference to the extent necessary to
u~~derstvt$ the
presentinvention.
Txowever, any wavelength-itmable grating ox reflective element 20 embedd.ed,,
s o written, etched, imprinted, or otherwise formed in the inner core 16 may
be used if
desired, As used laexein, th.e term "grating" 'means any of such zeflective
dements.
Further, the reflective element (or grating) 20 lnay be used in reflection
and/or
transmission of light.
Other materials and dimensions fox the optical grating element 14 may be used
2 s if desired. For example, the grating element 14 may be made of any glass,
e.g., silica,
phosphate glass, or other glasses, or made of glass and plastic, or solely
plastic,
Tlxe grating element 14 is axially compressed by a compression; d.eviee or
housing 30, similar to that described in US Patent Application, Sezial y'o.
09/707,084,
entitled "Compression-Tuned Bragg Grating Based Laser" (GiDRA. Docket No. CC-
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
0129D), Une end of the grating elexnent 14 is pressed against a seat 32 in one
end 34
of the housing 30. Th.e housing also has a pair of arms (or sides) 36, which.
guide a.
movable bloel~, 3. The block 38 has a seat 40 that presses against the other
end of the
grating element 14, The axial and faces of the grating element 14 andlor the
seats on
mating surfaces 32,40 rnay be plated with a material that reduces stresses or
enhances
the mating of the grating element 14 with the seat on the mating surfaces, The
ends of
the housing 30 and tloe block 38 have a bone 42 drilled through them to allow
the fiber
41 to pass therethtough. Instead of the recessed seats 32,40, the end 34 of
fine housing
30 and th.e bloclc 38 may provide a planar surface for engaging flush with
fine
2o respective ends of the grating element 14.
The housing 30 may be assembled suclz that a. pre-strain or no pre-stain
exists
on the ,grating element 14 prior to applying any outside forces.
Atyctuator 44, such as a piezoelectzic actuator, engages the n~ovcable bloels
38, which causes the bloclz to rza.ove as indicated by arrows 46, Accordingly,
the PZT
a5 actuator 44 provides a predetermined amount of force to the mooring block
38 to
compress the grating element 14, and thereby tune the grating 20 to desired a
reflection wavelela.gCh., In response to control signal generated by a
displacement
control circuit or contxol.ler 60 via conductor 52, the PzT actuator 44 is
energized to
provide the appropriate compression force necessary to tune the grating
element to the
z o d.esized l3xagg reflection wavelength of the grating 20, The control
circuit 50 adjusts
the expansion anal retraction of the actuator 44 in response to an input
command 54
and a displacement sensor 56 that provides feedback representative of the
strain or
eornpression of the grating element 14 to form anon-optical closed-loop
control
eoniiguration. In other words, light 11 propagating through the network or
device is
z5 not used to provide feedback for the timing of the grating 20.
In one embodiment, the displacement sensor S6 includes a pear ofcapacitive
elements S8 and a displacement sensor circuit 59, sirniIar to that disclosed
in co-
pending US Patent Application, Serial No, 09!519,802 entitled, "Tamable
Optical
Structure Featuring Feedback Control", filed March 6, 2000, which is
incorporated by
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
reference in its entirety, As shown. in rrCr. 1, each capacitive element S8 is
generally
tubular having an ~umttlar capacitive end surface 60, The capacitive eleznents
58 are
mounted to respective ends of the grating element 14 at b2 such tlta~ the
capacitive
surfaces 60 are spaced a predetermined distance apart, fox example,
approximately 1 -
2 microns, Other spacings may be used i.~ desired. The capacitive elements 58
may
be bonded or secured using an epoxy or other adhesive compomtd, or fused to
grating
element 14 using a. COZ laser ox other heating element. The capaeitive
surfaces 60 are
coated with a metallic coating, such as gold, to form. a pair of annular
capacitive
plates 64, The change in capacitmce depends on the change in the spacing
between
xo the capacitive plates.
~leatrodes 66 are attached to the capacitive plates b4 to connect the
capacitor
to the displacement sensor circuit 59. The sensor circuit 59 measures the
capaei.tance
between the capacitive plates 64; and provides a sensed signal 67, indicative
of the
measured capacitance, to the displacement controller 50, As the grating
elern.ent 14 is
za strained, the gap between the parallel capacitive plates 64 will vary,
thereby causing
the capacitance to cla.aan.ge correspondingly. Specifically as the grating is
compressed,
the gap between the capaeitive plates 64 is reduced, resulting in an increase
in
capacitutce, The change in capacitance is inversely proportional to the change
in the
reflection wavelength 1y, ofthe grating 20, Since the capacitive elemenfis 58
are
z o directly eaxln.ected to the grating element 14, the capacitive elements
are passive anal
will not slip. One skilled in the art ~twould be able to implement vvitllout
undue
experinaentation, the sensor electronics circuit 59 to measure the change in
eapao.iCance beivycen the two capacitive plates 64.
In the operation of the grating unit 10, the controller SO receives the
as wavelength input signal 54, wluch represents fhe desired reflection
wavelength to tune
the grating unit, In response to the input signal 54 and the sensed signal 67,
which is
representative of the present resection wavelength of the grating 20, the
controller 50
provides a conlxol signal S2 to the actuator 44 to increase or decrease the
compression
force applied to the grating element 14 to set the desired reflection
wavelength of the
zo
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
grating 20, The change in applied force to the grating element 14 changes the
spacing
between the ends of the grating 20, and therefore, the spacing between the
capacitive
plates 64, As described above, the change in spacing of the capacitive plates
64
changes the capacitance th.exebetween provided to the sensor circuit 59, Wlueh
provides displacement feedbacl~ to the controller 50. While the sensor circuit
59 and.
th.e conixoller 50 has been. shown as two separate components, one v~ould
recognize
that th.e functions of these components may be combined into a single
component.
One example of a closed loop actuator 44 that may be used is Model, No, CM
(controller) and DPT-C-M (for a cylindrical actuator) made by Queensgate, Zne.
of
1 o N,'Y'.
Although the invention has been described with respect to using a capacitor 56
to measure the gap dist~co, it should be understood by those slralled in the
art that
other gap sensing techniques may be used, such as inductive, optical,
magnetic,
microwave, time-of flight based gap sensors. Moreover,1he scope of the
invention is
also intended to .include measuring or sensing a force applied on or about the
compzessive element, and feeding it beak to control the compression tuning of
the
optical structure. While the erro.bodiment of the present invention described
hereinbefore includes means to provide feedback of the displacement of a
grating
element 20, one should recognize tlyt the grating units may be accurately and
z a repeatably compressed and thus may oporate in art open loog mode.
Alternatively, instead of using a. piezoelectric actuator drl, the grating
element
1.4 may be compressed by ataother actuator, such as a solenoid, pnemnatic
force
actuator, or any other device that is capable of directly or indirectly
applying an axial
compressive force on the grating element 14. p'urrher, a stepper motor or
other type
a s of motor whose rotation or position can be co~ixolled may be used to
compress the
grating eleznenfi, A mechanical linkage connects the motor, e.g" a screw
drive, linear
actuator, gears, andlor a cam, to the movable block 38 (or piston), which
cause the
bloclt to move as indicated by arrows d.6, similar to that described in
pending U.S.
Patent Application Serial No, 09/751,589 entitled "Wide Range Tunable Optical
11
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
I~lter", fried Decembez 29, 2000 (CC-0274A); and U,S. Patent Application
Serial I~o.
091752,332 entitled "Actuator Mechanism for Tuning an Optical Device", filed
Deeembez 29, 2000. (CC-0322), which are incorporated herein by reference, The
stepper motor may be a high resolution stepper motor driven in a microstepping
mode, s11C1a aS that described in the aforementioned US Patent No, 5,469,520,
"Compression Tuned l~ber Grating", to Mozey et al, (e.g., a Melles Griot
NANOMOVER), incorporated herei7,a by reference.
As shown in. FIG. 2, the grating eler.~.ent 14 may have a "dogbone" shape
having a. narrow central section 70 and larger outer sections 72.
.Advantageously, the
zo dofbone shape provides increased sensitivity in converting force applied by
the
actuator 44 to assure accurate tuning of the grating 20. Th,e narrow section
70 may
leave an outer diameter d2 of about 0.8-1 nvaa, and a length L2 of about 5-20
tnyn, The
large sections 72 each have a diameter d3 of about 2-3 mm an,d a length L3 of
about 2
- 5 nnm, The overall length Ll is about I O-30 mm and flee mufti-component
grating
~.s has a length Lg of about 5-20 mm, Other lengths and diameters of the
sections 70,72
may be used, Other dimensions and lengths for the grating element 14 and the
multi-
companelat grating may be used,
An inner transition region 74 of the large sections 72 may be a sharp vertical
oz angled edge or may be ewwed. A curved geometry lzas less stress risers than
a
x o sharp edge and tlms may reduce the likelihood of breakage. Also, the large
sections 72
may have the outer fluted sections 76 at tine eza~.s.
We have fallnd that such a dimension change between the dimension d3 of the
large section 72 and the dimension d2 of the n.arxow section 70 provides
increased
force to grating wav~elelagth shift sensitivity (or gain or scale factor) by
strain
2s amplification. Also, tho dimensions provided herein for the dogbone are
easily
scalable to provide the desired amoiuat of sensitivity.
Tloe dimensions and geometties for any of the embodiments described herein
are merely for, illustrative purposes and, as such, any other dimensions may
be used if
12
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
desired., depending on th.e appli.eatiarm, site, performance, manufacturing
zequirements, or other. factors, in view of the teachings herein,
The grating element 14 m.ay have tapered (or beveled or angled) outer eoxners
or edges 76 to provide a seat fox ilme grating element 14 to mate v~ritb.
housing 30 and
moving bloclc 38 atmd%or to adjust the force angles on the grating element, or
for other
reasons. The angle ofthe bel~eled cornets 76 is set to aclmiewe the desired
fwmction. 1n
addition, one or both of the axial ends of the grating eleramt 14 vrhere the
fiber 4I
attaches may have an outer tapered (or fluted, conical, or apple) axial
section 78,
11 or the grating element 14 formed by collapsing a tube onto a fiber, the
Bragg
1 o grating may be written in the fiber before or after the capillary tube is
encased axou~d
and fused to the fiber, such as is discussed in copending US Patent
Application, Serial,
No. a9/45~5,865, entitled "Tubo-Encased Fiber Grating", filed Deeernber 6,
1999
(CiDRA Docket No. CC-0078B), whi.clm is incorporated herein by reference, If
the
grating 20 is written in the fiber after tb.e Tube is encased. around the
grating, tlme
is grating naay be written through the tribe into the ~.ber by any desired
teehn.ique, such
as is described in oopmding US Patent Application, Serial No, 09/205,845,
entitled
"Method aid Apparatus For Forming A T~.'~e-Encased l3ragg Crrating", filed
Deeembez 4,1998, (CiDRA Docltet No, CC-0130) which is incorporated herein by
reference,
x o While the tunable grating units I O are actively tuned to provide a.
reconfig~.uabl,e optical addldrop multiplexes (ROADM), one v~till appreciate
and
recognize tlae present invention contemplates substituting the tunable gzating
units
with athermal grating units, rwhieh passively tune the grating element 14 to
.mai.ntain
the reflection wavelength of the grating 20 over a predetermined temperature
xaimge to
2 s provide a fixed optical addldzop multiplexes (k'OAD1V.17, The athezrnal
grating unit is
similar to that disclosed in US Patent Application Serial No. 09/699,940
e~.ltitled
"Temperature Compensated Optical Device" filed October 30, 2000 (CC-0234A),
~cxrhich is incorporated herein by reference. The invention also contemplates
that soma
or all the grating units may be substituted for the atllermal grating units.
13
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
Refezzing to rrG. 3, the tunable drop i~lter 30 includes a plurality of
tunable
Hragg grating .nits 10, optically coupled in series to a port of an optical
directing
device 12, such as a. 3-port circulator, At least ono grating unit 10 is
actuated to
compzess a respective grating element 14, and therefore, tune a respective
grating 20
to reflect die desired optical channels) to be dropped from the optical input
signal 1 I,
while the other grating units 10 axe tanned or parlced to pass tile remaining
channels of
the input signal 11.
Zn the operation of the drop filter 80, a first port 81 ofthe circulator 12
receives the input signal 11, having optical channels centered at wavelengths
At,~, , , .
to ~, that is transmitted through optical fiber 82. The input signal 11 may
originate
from a light source or tapped off an optical neCwoxlc (not shown). The
circulatax 12
directs the input signal 11 in a clockwise direction to a second port 83 o,f,
the
circulator. The input signal 11 exits the second porC 83 and propagates
through
optical fiber 85 to grating elements 14 ofthe grating units 10,
r s A select number of gratuzg elements 10 are tuned to reflect corresponding
optical charnels of the input signal 1 I, effectively dropping the
corresponding optical
channel frotta the input signal 11, Tile retxiaining optical grating units 10
are tuned or
parked. to pass the remaining optical channels of the input signal 11, to
provide an
optical signal 86 that does not include the dropped optical channels. for
example, as
2 o shown in rTG. 3, a pair of grating ututs 10 are respectively tuned to
reflect an optical
signal. having optical chmnels centered at wawelengtlZS >~,~, while the
remaining
gating units I O are pazlced or tuned to pass th.e remaining channels centered
at
wavelengths A1,7~, . . . 7~,r. The grating units 10 may be parked by tuning
the grating
units suab that the f.lter function of the grating 20 is parlted between
optical ehannel.s,
25 parlced outside of the range of optical channels of the input signal 11, or
parked ~t the
same wavelength of the grating of another grating unit, which is tined to
reflect an
optical signal.
z~
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
Tlle reflected optical channels propagate back to the second pozt 83 of the
circulator 12, Which then directs the reflected channels to a third port 87 of
the
circulator and through optical fiber 88 to provide a drop optical signal 89.
Fig. A. illustzates another embodiment of a tunable drop filter 90, The
tunable
drop Filter 90 includes a plurality of tunable Bragg grating units 10,
optically coupled
in series to a port of an optical directing device 12, such as a 3-port
circulator. At
least one grating unit I O is actuated to compress a respective grating
element 14, and
therefore, ttuze a respecti~te grating 14 to pass the desired optical,
channels) to be
dropped from the optical input signal I 1, while the other grating units are
tuned to
refl.eet the remaining optical channels of the input signal,
u~ the operation of the drop filter 90, a first port 91 of the circulator 12
receives the input siglal 11, having optical channels centered at wavelengths
A1,A2, ...
)~, that is transmitted through optical fiber 92. The input signal 11 may
originate
from a light source or tapped off an optical networlc {not. shown). The
circulator. 12
i5 directs the input signal 1 I in a. counter-cloelo~rise dareei~ion to a
second part 93 of the
circulator. Tla.e input signal 11 exits the second port 93 atad propagates
through
optical fiber 94 to grating elements 14 of the grating units 10.
Each of the grating elements 14 are tuned or parked to pass corresponding
optical channels of the input signal 11, effectively dropping the
corresponding optical
a o channels from the input signal, A select numbez of optical grating waits
are tuned to
zeflect the remaining optical chay.~.nels of the input signal 11 to provide an
optical
signal 98, which does net include the dropped optical channels. Fox example as
shown in FIC. 4, each of th,e gr. acing ututs 10 are respectively tuned or
parked to pass
~.u. optical signal 95 having a optical channels centered at wavelengths
1,2,3, while a
2 s select number of grating units are tuned to reflect the remaiiri.ng
channels centezad at
~vavelengtlls A1,3~, ... ~.
The reflected optical channels centered at ~z,>u propagate back fio the second
port 93 of the circulator 12, which then directs the zefleeted channels to a
third port 96
of the circulator and tlrrough optical (ibex 97 to provide an output optical
signal 98.
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
Refernng to Fig. S, the tunable add filter 100 includes a plurality of tunable
Bragg grating units 10 optically coupled in sez~es to a port of an optical
direct~yig
device 13, such as a 3-port circulator. At least one grating unit I O is
actuated to
compress a respective grating element 14, and therefore, tune a respective
grating 20
to reflect the desired optical, channel.(s) to be added to the optical input
signal 11,
while the other grating units are tuned to pass the optical channels of the
input siyal.
rn the operation of the add filter 100, a first port 101 of the circulator 13
receives the optical signal 102 to be added to the input signal 1 I. The added
signal
102 has, for example, a single optical channel centered at wavelei~gtl~ l~
that is
z:o transmitted thxough optical fiber 103. The circulator 13 directs the added
optical
signal 102 in a cloclcwise direction to a second port 104 of the circulator,
The added
optical sig~lal 102 exits the second port 104 and propagates tluough. optical
fiber 105
to grating elements 14 of the grating units 10. At least one grating element
14 is
timed to reflect tile added. signal 102 to be combined yyitl~ the input signal
I 1. The
input light 11, having optical channels centered at rwavelengthS 7~t,~~ . , ,
~.r, are
transmitted to the grativg el,etnents 14 ofthe grating units 10 through
optical fibex
106. The grating elements 14 are tined or parked to pass the optical channels
of tlae
input signal 11 and combine with, tla,e added optical signal 102 to provide an
optical.
signal I09 having optical channels centered at wavelengths ?~i,Aa, ... ~y,
4 a The coxubined optical light propagates ba.ek to the second port 104 ofthe
circulator I3, which tlZen directs the combined optical light to a third port
107 of the
eixculator 7.3 ao.d thxough optical fiber 108 to provide the output signal
109, having
optical channels centered at wavelengths ~1,~2, , .. 7~.
While the add Biter 100 of I~IG. 5 adds a single channel to the inp~.t light
11,
2 s one skilled in the art will appreciate and recognize that more than onE
optical signal
may be added provided tlm add filter has a concesponding number of gratiu,g
units 10,
or a single grating unit that has sufficient bandwidth to reflect adjacent
optical
eltat~nels to be added.
is
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
Fig. 6 i.l.lusiraces anotla.ex embodiment of a. tunable add alter 110. The
tunable
add filter 110 includes a plurality of tmiable Bragg grating units 10,
optically coupled
in series to a port of an optical directing device 13, such as a 3-port
circulator, The
gratiy~g units 10 are actuated to compress respective grating elements 1d, and
therefore, tune or pa~rlt gratings 20 to pass the desired optical channels) to
be added to
the optical input signal I I, while the outer grating units 10 are tuned to
reflect and
combine the channels of the input signal 11.,
?n the operation of the add filter 110, a first port 1 I 1 of the circulator
13
receives th.e input si.ga~al 11, having optical channels centered at
wavelengths 7~~,h3, ...
?o ?~.1, that is lxmsxnitted through optical fiber 112. Tho input signal 11
may originate
from a light source or tapped off an optical network (not shown). The
circulator 13
directs the input signal I 1 in a counter-clockwise direction to a second port
I 13 of th.e
circulator. The input signal 11 exits the second port I I3 and propagates
through
optical i'iber I 14 to the grating elements 14 of the grating units 10. A
select nurxiber
zs of grating elements 14 axe tuned to zeflect the optical channels of the
iyaput signal 11
centered at wavelengths A1,3~, . , , I~,a of the gratings 20 to be combixted
vVith an optical
added signal I 15. The added signal 11.5, having an opiical chmnel centered at
wavelength ~, are tTmsmitted to the grating elements Id of the grating units I
O
through optical fiber 116. Each grating trait 10 is tuned or parked to pass
the optical
2 o clzazu~.el(s) of the added signal 1 I5, which is then combined with the
optical i~aput
signal 1I to provide a combined optical signal having optical channels
centered at
~lo~r ." ~ljy.
The combined optical. signal propagates baclc to the second port 113 of the
circulator I.3, Which thezz directs the combined optical 1ig11t to a third
port I I7 of the
25 circulator 13 and thzough optical fiber I18 to provide the output signal
119, having
optical channels centered at wavelengths A~,')~, .., >~,
Referring to Pig. 7, the tuz~.able add filter 120 is similar to the tunable
add filter
o~ FIG. 5, and therefore, like eorflponents have the same reference number,
Tlae
tunable add filter 120 includes a plurality of tunable Bragg grating units 10
optically
z~
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
coupled in series to a port of an optical directing device 13, such as a 3-
port circulator
At least one grating unit I 0 is actuated to compress a respective grating
element I4,
and therefore, tune a respective grating 20 to reflect the desired optical
clza~mel(s) to
be added to the optical input signal 11, while the other gxatuig units 10 are
tuned or
parlced to pass the reznai.ning optical, ch annels of fihe input signal 11; ,
Zn the operation of the add filter I20, a first port I01 of the circulator 13
receives the added optical signal lOZ to be added to the input signal 11. The
added
signal 102 may, for example, include a plurality ofoptical channels centered
at
wavelengths ~1,A2, . . . '~,,~, any of which that maybe added to the input
signal 11. The
a a added signal 102 is transmitted through optical fiber 103 to th,e
circulator 13, ~Wh.icli.
then directs the added optical signal 102 in a clockwise direction to a second
port 104
of the. circulator. The added optical signal 102 exits the second port 104 and
propagates thro~,gh optical fiber 105 to grating elements 14 ofthe gzating
units 10, At
least one grating element 1~. is tuned to reflect at least one optical channel
of the
a.5 added signal 102. For example, one grating unit 10 may be tuned to reflect
an optical
channel centered at wavelength 7~ to pzovide a filtered added signal 109. The
other
grating elements are toyed or parked to pass the rem.ainiog optical charutels
of the
added optical signal 102.
The filtexed added signal propagates baclc to the second port 104 of the
z o circulator 13, which then directs the combined optical light to a. third
port 10? of the
cixculator 13 and through optioal fiber 108 to provide the filtered added
signal 109.
The output signal 109 is then transmitted to an irZput port of an optical
co~.pler 12I .
The input signal I l, having optical channels centEred at wavelengths 7~i,A3,
. .. fir, are
transmitted to a second input port of the optical coupler 121. The aptieal
coupler 121.
as combines the filtered added signal 109 and the input signal 11 and provides
a.
combined optical signal 122 at are output. port orthe coupler, wherein the
combined
output signal 122 includes a. plurality of channels centered at wavelengths
AI,Az, ...
?fir.
ze
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
Wbile the add filter 120 of FIG. 7 adds a single channel. to the input light
11,
one skilled in tlae art will appreciate and recognize that more thin on,e.
optical signal
may be added prowi.ded the add filter has a. corresponding yaumber of gxating
units 10,
or a single grating unit that h.as sufficient bandwidth to reflect adjacent
optical
channels to be added.
Referni.o.g to b'ig. $, the tunable add filter 130 is similar io the tunable
add filter
110 of FrG. 6, amd therefore, lilce components have tl.~.e same reference
number. The
t~.nabl.e add filter 130 includos a plurality of tunable Hragg grating units
10 optically
coupled in series to a porC of an optical directing device 131, such as an
optical
xo coupler, Each of the grating units 10 are actuated to compress respective
grating
elements 14, and therefore, tune or park gratings 20 to pass the desired
optical
channels) to be added to the optical input signal 11.
Tn the operation of the add filter 110, tile added signal 115 may, for
example,
include a plurality of optical channels centered at waYelengths At,7~, , , .
l~, any of
zs which that may be added to the input signal 11. The added signal 115 is
traansmitted
to the grating elern.eots 14 of the dating units 10 through optical fiber 116.
Each
grating unit 10 is tuned or parlced to pass a selected opfiieal ela.anxlel(s)
ofthe added
signal 115 to be added to the input signal 11. For example, each, grating unit
10 may
be tined to pass an optical channel at wavelength ~ to provide a filtered
added signal
a.o 132, The filtered added signal 132 is then transmiti~ed to an input port
of an optical
coupler 131 through optical fiber 114. The optical coupler 13I combines the
filtered
added signal. 132 and the input signal 11 and provides a combil~ed optical
signal 133
at m output port of the optical ooupler 131, wherein the combined output
signal 133
includes a. plurality of channels centered at wavelengths At,A2, . . . ~.
2 s V~hile the add filter 130 of 1~TCr. 8 adds a single channel to the input
light 11,
one skilled in the a~ will appreciate and recognize that .more than one
optical signal
may be added.
FIG, 9 illustrates a reconfigurable optical addJdrop multiplexer (RO.AnIVI)
140
that effectively combines the tunable drop filter $0 of FTG. 3 and the tunable
add f.~ll:er
19
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
100 of FIG, 5, rYvhexein a single series of grating units 10 are. used to both
drop a
selected optical channel and add a. selected optical channel, as discussed
hereinbefore,
Components similax to the drop filter 80 of FIG. 3, the add filter 100 of FIG,
5 and the
ROADM 140 of FIG. 9 have the same reference number.
As shown in FIG. 9, a pair of grating units 10 are tuned to reflect optical
channels centered at wavelen gths ~z,~, w'hi'le the other gratings units are
tuned to pass
the remaining channels centered at wavelengths hl,lt, , , , ?~,,.
Consequently, fine
ROAbM 140 drops optical channels centered at ~rave1e7,1gt11S 7~,~, and adds
the
added optical signal 102 having a ehal~nel centered at wavelengths 1~~. The
output
yo signal 109, therefore, includes optical channels centered at ~1,A2,?~y, .
..1~,1.
FIG. 10 illustrates a recon~gurable optical add/drop multxplexer (RO.A.DM)
150 that effectively combines the tunable drop filter 80 of J~IG. 3 and the
tunable add
filter 110 of FIG, 6, ryherein the add alter 110 is optically connected in
series with the
drop fl.ter 80, Tloe drop at~d add filters 80,110 .functions substantially the
same, as
~.s disoussed hereinbefore, Components suxailar to the drop filter 80 of FIG.
3, the add
filter 110 of FIG. 6 and the RO.ADM 150 of FIG. 10 have the same reference
number.
As shown in FIG. 10, a pair of grating units 10 of the drop filter 80 axe
tuned
to reflect optical channels centered afi wavelengths >~,~, while the other
gratings traits
are tuned to pass the rem.ainung chaJUtel.s eenCered at wavelengths l~l,~, ...
>~. The
2 o grating units 10 of the add alter 110 axe tuned to pass the added signal
115, haying an
optical channel centred a.t A2. Consequently, the ROA.DM 150 drops opti.eaJ,
channels centered at Wavelengths 1~2,h~, anal adds the added optical signal
115 lyving
a eJ2aru.~el, centered at wavelengths ~. The output signal 119, therefore,
includes
optical ahanne.ls centered at A~,~2,~, , , , )~.
2s FIG. 11 illustxates a reeanfi.gyable optical add/drop mulhplexer (ROAb~vI)
160 that effectively combines the tunable drop filter 90 of FIG. 4 and the
tunable add
filter 100 oflllG, 5, whexein the add alter 100 zs optically connected in
series with the
drop filter 90. The drop and add filters 90,100 functions substantially the
same, as
zo
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
discussed hsreinbefore. Components similar to the drop fzlter 90 of FIG. ~,
the add
filter 100 of FIG, 5 and the. ROADM 160 of FIG. 1 I have the. same reference
number.
As shown in FIG, 10, each of the grating units 10 of the drop filter 90 are
tuned to pass optical eh.annels centered at wavelengths l~a,~, while the other
gratings
units are tensed to reflect the remaining channels centered at wavelengths
?,1,~, , , , )~,
The grating units 10 of the add filter x 00 are tuned to reflect the added
signal 102,
having an optics). ch.almel centered at ~2. Consequently, the ROADM I60 drops
optical chama.els centered at wavel.exyths ~,~, and adds fine added optical.
signal 102
having a channel centered at wavelengths 7~2: The output signal 108,
therefore,
to includes optical channels centered at ~~,?~,1~, ... )~.
FTG, 12 illustrates a reconfigurable optical add/drop rnultiple~er (ROA:DM)
170 that effectively ootr~biues the tunable drop filter 90 of FTG, 4 and the
tunable add
filter 110 of FTG. 6, wherein the add f leer 110 is optically connected in
series with the
drop filter 90. The drop au.d add f lters 90,110 functions substantially the
same, as
is discussed hereiabefore. ComponEnts similar to the drop filter 90 ofFIG. 4,
the add
filter I I O of FIG, 6 and the ROA>aM, I70 of FIG, 12 have the same refesenee
number.
As shown in FIG. 12, each of the grating units 1.0 of the drop alter 90 are
tuned to pass optical channels centered at wavelengths 1~,>~, while the other
gratings
units are tuned to reflect the remaining channels centered at wavelengths
t~1,7~, , , , ?~,~.
a a Each, of th,e grating units 10 of the add filter 110 are tuned to pass the
added signal
115, having an optical channel centered at ~2, while the other gratings units
are i~.nec~
to reflect the remaining channels centered at wavelengths A1,7~., , . , )~
Consequently,
the ROADM 170 drops optics) chu~.nels centered at wavelengths ~2,?<3, and adds
the
added optical signal 1 I5 having a chaxu~el centered at wavelengths >1Z, The
output
2s signal 119, therefore, includes optical c)tannels centered at ~l,~z,~, ...
~,
FTG. 13 illustrates a reconfigurable optical add/drop multiplea:ar (ROADM)
170 is substantial.l.y similar to the RO.ADM I60 of FIG, 22, which effectively
combines the tunable drop filter 90 of FTG, 4 and the tunable add .filter I l
O of FIG. 6.
Effectively, the ItOADM l3.as substituted the pair of 3.port circulators 12,
13 with a
21
CA 02402309 2002-09-05
WO 01/67137 PCT/USO1/07165
single 4-port eircul,ator 181, The ROADM 180 of FIG. 13 operates substantially
the
same as the ROA17M 170 of FIG. 12, as discussed hereinbefore. Components
similar
to th,e drop filtex 90 of FTG. 4, the add filter 110 of FZG. 6 an,d floe ROADM
170 of
FIG, 12 have the sane reference number.
Itz addition to the above embodiments of an ROADM, the present invention
also contemplates other ROADM eonfzguxations by optically connecting in series
in
various combinations of any one of the tunable drop filters 80,90 of FIGS. 3
and 4
respectively, with any one oftha tunable add filters 120,1,30 of FIGS. 7 and 8
respectively.
a. o While the grating units 10 are interconnected to a 4-port circulator, one
will
appreciate that it is within the scope of the present invention that any other
optical
directing device or means may be substituted for the cizculator 1.2,13, such
as an
optical eouplex, op~cal sputter or frog space.
The dimensions and geornetries for any of the embodiments described herein
s5 are merely for illustrative purposes md, as much, any other dimensions may
be used
if desired, depending on the application, size, performance, manufacturing
zequirements, or oilier factors, in view of the teachings herein.,
Ii should be understood that, unless stated otherwise hexean, any of the
features, characteristics, alternatives or modifieatzons described regarding a
particular
2 o embodiment herein may also be applied, used, or incorpoxated, with any
other
embodi,rn.en,t described herein. Also, the drawings herein are not draw. to
scale.
Altloough the invention has been described seed illustrated ~rith respect to
e:cemplary embodiments thereof tl~e foregoing and various other additions and
omissions may be made therei~i ~,vithout departing from the spirit and scope
of th.e
z s present invention.
2Z
