U.S. patent application number 09/119562 was filed with the patent office on 2002-05-30 for optical communication system.
Invention is credited to HUBER, DAVID R..
Application Number | 20020063929 09/119562 |
Document ID | / |
Family ID | 22385075 |
Filed Date | 2002-05-30 |
United States Patent
Application |
20020063929 |
Kind Code |
A1 |
HUBER, DAVID R. |
May 30, 2002 |
OPTICAL COMMUNICATION SYSTEM
Abstract
Apparatuses and methods are disclosed for use in optical
communication systems. An optical system of the present invention
includes an optical transmitter, an optical receiver, and an
optical processing node optically connecting the transmitter and
the receiver. The optical processing node includes at least one
waveband selector configured to selectively pass at least one
optical waveband of information including a plurality of
information carrying wavelengths from the transmitter to the
receiver. In an embodiment, the optical processing node includes a
switch configured to separate an optical signal into optical
wavebands of information and selectively pass the optical wavebands
to the receiver without separating the plurality of information
carrying wavelengths into individual wavelengths. In an embodiment
of the optical transmission system, a plurality of nodes containing
optical transmitters, receivers, and/or switching equipment are
interconnected using optical processing nodes to form the network.
The assignment of wavelengths to information and to destination can
be performed at the client system interface with the optical
network to provide for wavelength and waveband management without
wavelength conversion.
Inventors: |
HUBER, DAVID R.; (GLENWOOD,
MD) |
Correspondence
Address: |
CORVIS CORPORATION
INTELLECTUAL PROPERTY DEPARTMENT
7015 ALBERT EINSTEIN DRIVE
COLUMBIA
MD
210469400
|
Family ID: |
22385075 |
Appl. No.: |
09/119562 |
Filed: |
July 21, 1998 |
Current U.S.
Class: |
398/140 ;
398/6 |
Current CPC
Class: |
H04Q 11/0005 20130101;
H04J 14/0213 20130101; H04Q 2011/0016 20130101; H04Q 2011/0075
20130101; H04J 14/021 20130101; H04Q 2011/0022 20130101; H04Q
2011/0015 20130101; H04Q 2011/0035 20130101; H04J 14/02
20130101 |
Class at
Publication: |
359/154 ;
359/110 |
International
Class: |
H04B 010/08; H04J
014/02; H04B 010/00 |
Claims
What is claimed is:
1. An optical transmission system comprising: at least one optical
transmitter configured to transmit information via at least one
information carrying wavelength; at least one optical receiver
configured to receive the information transmitted via the at least
one information carrying wavelength; and, at least one optical
processing node including at least one waveband selector
configurable to selectively pass and substantially prevent the
passage of at least one optical waveband comprised of a plurality
of information carrying wavelengths from at least one of said at
least one transmitters to at least one of said at least one
receivers.
2. The optical transmission system of claim 1, wherein said at
least one waveband selector is configured to selectively pass and
substantially prevent the passage of said at least one optical
waveband without separating said plurality of information carrying
wavelengths into individual information carrying wavelengths.
3. The optical transmission system of claim 1, wherein each of said
at least one waveband selectors is configured to only selectively
pass and substantially prevent the passage of optical
wavebands.
4. The optical transmission system of claim 1, wherein said at
least one optical processing node includes an optical switch having
input ports corresponding to said at least one transmitter and
output ports corresponding to said at least one receiver and said
information carrying wavelengths are switched from said input ports
to said output ports in said at least one optical waveband by said
at least one waveband selector.
5. The optical transmission system of claim 4 wherein said switch
includes a waveband demultiplexer corresponding to each input port
and configured to receive and separate an optical signal containing
the at least one information carrying wavelength into separate
optical wavebands signals, an optical splitter in optical
communication with and corresponding to each of the separated
waveband signals from each of said optical demultiplexers, each of
said optical splitters configured to split the separated waveband
signals into a number of split waveband signals corresponding to
each output port, at least one said waveband selectors being
positioned to receive each split waveband signal and configurable
to pass and to substantially prevent the passage of the split
waveband signal to said corresponding output port, and an optical
combiner corresponding to each output port and configured to
receive the split waveband signals from each of said waveband
selectors corresponding to said output port and provide a combined
optical waveband signal to said output port.
6. The optical transmission system of claim 5 wherein at least one
said waveband selectors includes a doped optical fiber configured
to allow an optical waveband to pass through the fiber in one mode
and to substantially prevent the passage of the optical waveband
through the fiber in another mode.
7. The optical transmission system of claim 6 wherein doped optical
fiber includes an erbium doped fiber coupled to an optical energy
pump source, the erbium fiber being configured to substantially
prevent the passage of the optical waveband signal when said fiber
is not pumped with optical energy from said optical energy pump
source and to allow said optical waveband signal to substantially
pass through the fiber when pumped with optical energy from said
pump source.
8. The optical transmission system of claim 7 wherein said optical
energy pump source is configured to control the intensity of the
optical waveband passing through the fiber by varying the optical
energy pumped into the erbium doped fiber.
9. The optical transmission system of claim 5 wherein at least one
of said waveband selectors is selected from the group consisting of
doped fiber, mechanical, electro-optic, liquid crystal switches,
semiconductor, and combinations thereof, in which said switch can
be operated to pass at least one waveband in one mode and
substantially prevent the passage of said at least one waveband in
another mode.
10. The optical transmission system of claim 1, wherein said at
least one optical processing node includes an optical add/drop
device containing said at least one waveband selector to
selectively add an optical waveband to be transmitted to said at
least one receiver and to selectively drop an optical waveband
transmitted by said at least one transmitter.
11. The optical transmission system of claim 1, wherein said at
least one optical processing node includes ports selected from the
group consisting of add devices, drop devices and combinations
thereof.
12. The optical transmission system of claim 1, wherein said at
least one optical processing node includes a demultiplexer
configured to receive the information carrying wavelengths from
said at least one transmitter and distribute the information
carrying wavelengths in optical wavebands to at least one of said
at least one receivers.
13. The optical transmission system of claim 1, wherein said at
least one optical processing node includes a multiplexer configured
to receive optical wavebands passed by said at least one waveband
selector and provide a multiple optical waveband signal to said at
least one receiver.
14. The optical transmission system of claim 1 wherein said at
least one waveband selector includes transmissive and reflective
waveband selectors selected from the group consisting of optical
filters, Bragg gratings, gates, switches and combinations
thereof.
15. The optical transmission system of claim 1 wherein said at
least one waveband selector includes an optical waveguide
configured to provide for the formation of an optical grating
therein.
16. The optical transmission system of claim 1 wherein said at
least one waveband selector includes a permanent Bragg grating
selected from the group consisting of transmissive and reflective
operated permanent gratings.
17. The optical transmission system of claim 1 wherein said at
least one waveband selector includes a tunable grating.
18. The optical transmission system of claim 17 wherein said
tunable grating is selected from the group consisting of
mechanically, thermally, optically, and electronically tunable
gratings, and combinations thereof.
19. The optical transmission system of claim 1 wherein said at
least one waveband selector includes an optical circulator having a
first port optically connected to said at least one transmitter, a
second port optically connected between said first port and a
reflective grating configured to reflect said at least one waveband
and a third port optically connected to pass a reflected waveband
from said reflective grating to said at least one receiver.
20. The optical transmission system of claim 1 wherein said at
least one waveband selector includes an optical circulator having a
first port optically connected to said at least one transmitter, a
second port optically connected to said first port and a
transmissive grating configured to transmit said at least one
waveband from said second port to said at least one receiver.
21. The optical transmission system of claim 1 wherein: said at
least one optical receiver includes a plurality of optical
receivers; said at least one optical transmitter includes a
plurality of optical transmitters; and, said optical processing
node includes a switch optically connecting said transmitters and
said receivers and configured to pass optical wavebands of
information from said transmitters to said receivers.
22. The optical transmission system of claim 1 wherein said optical
processing node is configurable to provide any of one or more
wavebands from any of said at least one transmitters to any of said
at least one receivers.
23. The optical transmission system of claim 1, further comprising:
a demultiplexer corresponding to each of said at least one
transmitters and configured to receive and separate the plurality
of individual information carrying wavelength signals; and, a
plurality of wavelength converters optically connecting said
demultiplexer and said at least one waveband selector and
configured to convert the plurality of information carrying
wavelength signals from said demultiplexer into information
carrying wavelengths within said at least one waveband.
24. The optical transmission system of claim 1 wherein said at
least one transmitter includes at least one modulated laser for
providing at least one of said information carrying wavelengths and
said receiver includes a plurality of photodiodes corresponding to
said plurality of information carrying wavelengths in said at least
one optical waveband.
25. The optical transmission system of claim 1 wherein said at
least one waveband selector comprises an in fiber Bragg grating
configured to selectively pass said optical waveband including said
plurality of information carrying wavelengths.
26. A method of passing information to a destination comprising:
producing an optical signal comprised of a plurality of information
carrying wavelengths; transmitting the optical signal; and, passing
only a selected optical waveband of the optical signal including
more than one of the plurality of information carrying wavelengths
to a destination without separating the individual information
carrying wavelengths.
27. The method of claim 26 further comprising separating the
information carrying wavelengths from the waveband at the
destination into individual information carrying optical
wavelengths; and, reproducing the information contained in the
information carrying wavelengths in electronic form.
28. The method of claim 27 wherein said passing includes providing
a Bragg grating to selectively reflect or transmit the optical
waveband of information to the destination.
29. A method of passing information from an origin to a destination
comprising: assigning a waveband comprised of a band of wavelengths
to at least one destination; providing an optical processing node
containing a waveband selector configured to pass the waveband of
information to the at least one destination without separating the
individual information carrying wavelengths in the waveband;
producing an optical signal including a plurality of information
carrying wavelengths within the assigned waveband; transmitting the
optical signal to the optical a processing node; and, passing the
optical signal through waveband selector in the optical processing
node to selectively pass the assigned waveband of information to
the at least one destination without separating the individual
wavelengths.
30. The method of claim 29 wherein said passing includes providing
a pumped erbium doped fiber in the waveband selector to selectively
pass assigned wavebands to the at least one destination.
31. The method of claim 29 wherein said passing includes providing
at least one grating selected from the group consisting of
reflective and transmissive gratings and combinations thereof in
the waveband selector to selectively pass assigned wavebands to the
at least one destination.
32. An optical switch comprising: at least one input port; at least
one output port; and, at least one waveband selector providing
optical communication between said at least one input port and said
at least one output port, wherein said at least one waveband
selector is configurable to pass or substantially prevent the
passage of information in at least one optical waveband between
said at least one input port and said at least one output port, and
at least one of said at least one optical wavebands includes a
plurality of information carrying wavelengths.
33. The method of claim 32 wherein said at least one waveband
selector is configured to information carrying wavelengths only as
a part of said at least one optical waveband.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
BACKGROUND OF THE INVENTION
[0003] The present invention is directed generally to network,
transmission and communication systems. More particularly, the
invention relates to optical information network, transmission and
communication systems and optical components, such as cross connect
switches, add/drop devices, demultiplexers, and multiplexers, for
use therein.
[0004] The development of digital technology has provided
electronic access to a vast amount of information. The increased
access to information has fueled an increasing desire to quickly
obtain and process the information. This desire has, in turn,
placed ever increasing demands for faster and higher capacity
electronic information processing equipment (computers) and
transmission networks and systems linking the processing equipment
(i.e., telephone lines, cable television (CATV) systems, local,
wide and metropolitan area networks (LAN, WAN, and MAN)).
[0005] In response to these demands, many transmission systems in
use today either have been or will be converted from electrical to
optical networks. Optical transmission systems provide
substantially larger information transmission bandwidths than
electrical systems, which provides for increased information
transmission capacities.
[0006] Early optical transmission systems were developed as space
division multiplex (SDM) systems. In early SDM systems, one signal
was transmitted as a single optical wavelength in each waveguide,
i.e., fiber optic strand. A number of waveguides were clustered to
form a fiber optic cable that provided for the transmission of a
plurality of signals in spaced relationship.
[0007] As transmission capacity demands increased, optical
transmission and receiving equipment was developed that provided
for time division multiplexed (TDM) transmission of a plurality of
distinct optical signals in a single waveguide. Optical TDM systems
are generally analogous to electrical TDM systems in that the
signals are transmitted on a common line, but spaced in time. The
transmission of the signals is in a known sequence allows the
plurality of distinct signals to be separated after
transmission.
[0008] A problem with TDM transmission is the transmission
bandwidth in the waveguide increases with each additional
multiplexed signal. For example, information can be transmitted
through a waveguide via a first series of optical signals separated
in time by an interval .DELTA.t. Additional information can also be
transmitted over the same waveguide using a second series of
optical signals during the time interval .DELTA.t by merely
offsetting the transmission of the first and second series of
signals in time. While an optical signal in each series is only
transmitted through the waveguide every .DELTA.t interval, two
signals, or n signals in the general case, are passing through the
waveguide during each interval. Therefore, the overall transmission
rate in TDM systems increases directly with the number of signals
transmitted.
[0009] Signal transmission rates in fiber optic waveguides are
generally limited by the interactions between the optical signal
(i.e., light pulse) and microstructural features of the waveguide
material. As the transmission rate is increased, signal dispersion
in the fiber and other transmission effects deleterious to signal
quality begin to occur as a result of the interactions.
[0010] Optical signals are typically transmitted in wavelengths
that minimize dispersion in the fiber. For example, older optical
systems are commonly operated around 1310 nm and employ SMF-28
fiber manufactured by Corning, or its equivalent, which has minimum
dispersion at or near 1310 nm. Another type of fiber, known as
dispersion shifted fiber, has its minimum dispersion at or near
1550 nm. A third type of fiber sold by Corning as LS fiber and by
Lucent Technology as TrueWave has its minimum dispersion at or near
1550 nm. In addition to having different minimum dispersion
wavelengths, each fiber has varying immunity to other signal
degradation mechanisms, such as four wave mixing, at increased
transmission rates.
[0011] The transmission rates at which the signal quality begins to
degrade are substantially lower (<40 Gbps) than the capacity of
the transmission and receiving equipment. Therefore, TDM systems,
which increase capacity by increasing transmission rates, generally
have only a limited potential for further increasing the capacity
of optical transmission systems.
[0012] The development of wavelength division multiplex (WDM)
transmission systems has provided a way to increase the capacity of
optical systems without encountering the waveguide limitations
present in TDM systems. In a WDM system, a plurality of optical
signals including information carrying wavelengths are combined to
produce a multiple wavelength signal that is transmitted through
the system to a receiver. After the multiple wavelength signal is
received, the information carrying wavelengths are separated from
the multiple wavelength signal and provided to a corresponding
plurality of destinations. Unlike TDM systems, only one WDM signal
is transmitted during a time interval .DELTA.t, although each WDM
signal contains a plurality of signals including information
carrying wavelengths.
[0013] Also unlike TDM systems, the waveguide material does not
realistically limit the information bandwidth that can be placed on
a single optical fiber in a WDM system. One skilled in the art can
also appreciate that the number of wavelengths that can be used to
transmit information over a single waveguide is currently limited
by the complexity of the transmission and receiving equipment
required to generate, transmit, receive, and separate the multiple
wavelength signal.
[0014] Currently, many optical transmission systems must convert
the optical signal to an electrical signal during transmission to
perform transmission functions, such as signal amplification and
switching. The optical to electrical conversion, and vice versa,
substantially limits the overall transmission speed of the network,
and increases transmission losses in the network. Thus, it has been
an industry goal to develop optical amplifiers and optical
cross-connect switches to provide for high speed, all optical
transmission systems.
[0015] The development of optical fiber amplifiers produced by
doping the optical fiber with Erbium ions (Er.sup.3+) or other
elements has allowed for the elimination of electrical amplifiers
and the requisite time delay and costs associated with signal
conversion. In addition to simplifying and decreasing the cost of
the equipment required to amplify a signal, optical fiber
amplifiers have proven effective for amplifying a plurality of
wavelengths without a commensurate increase in the complexity of
the amplifier as additional wavelengths are included in the WDM
signal.
[0016] Unlike optical amplifiers, optical cross-connect switches
greatly increase in complexity as the number of waveguides entering
and exiting the switch and the number of wavelengths per waveguide
increases. As a result, the expansion of all optical systems has
been somewhat inhibited by the lack of simple, efficient, and
economically attractive optical cross-connect switching
systems.
[0017] A number of optical cross-connect switches are based on one
or more 1.times.2 signal splitters or 2.times.2 signal couplers
used in conjunction with one or more wavelength filters, such as
described in U.S. Pat. No. 5,446,809 issued to Fritz et al. The
complexity of these types of switch increases not only with the
number of inputs and outputs in the switch, but also with the
number of wavelengths being switched. For example, if a 2.times.2
switch is provided to switch two eight wavelength WDM input signals
to two output signals, the switch would have to include 32 gratings
to allow all wavelengths to be switched. However, if a 4.times.4
switch is provided to switch four sixteen wavelength WDM input
signals to four output signals, 256 gratings will be required. In
addition, the flexibility of the switch is limited because
additional gratings or filters must be added to each waveguide
connecting each input to each output of the switch for every
wavelength that is to be switched.
[0018] Another complication is that different signals entering a
switch at different input ports will often times be carried by the
same wavelengths. The use of common wavelengths frequently occurs
because optical signals are generally transmitted using a
relatively narrow range of wavelengths that have been established
by optical standards committees with the goal of minimizing
transmission losses in a waveguide and allowing equipment
standardization in the industry.
[0019] If two signals on a common wavelength from different inputs
are switched to the same waveguide, both signals will be destroyed.
The switch, therefore, must be designed to prevent the inadvertent
destruction of signals transmitted to the switch on a common
wavelength.
[0020] Switches can be provided that "block" the switching of
certain wavelengths to prevent destruction of two signals on a
common wavelength. Switches can also be provided with wavelength
converters that are used to change the wavelength of a signal, in
lieu of blocking the signal, to prevent the destruction of the
signal. U.S. Pat. No. 5,627,925 issued to Alferness et al.
discloses an example of a switch that includes wavelength
converters to provide a nonblocking switch. As expected, the use of
wavelength converters adds a further degree of complexity to the
design and function of optical cross-connect switches.
[0021] An alternative to adding wavelength converters to provide a
nonblocking switch is to limit the wavelengths used in the system.
For example, U.S. Pat. No. 4,821,255 issued to Kobrinski discloses
an optical system employing transmission systems that transmit data
at a different wavelength to each destination receiving system,
i.e., N wavelengths for N receiving systems. In this manner, the
optical system does not require a nonblocking switch and the
assignment of a specific wavelength to each receiving system allows
for a passive optical connection ("hard wire") between a
transmission demultiplexer and a receiving multiplexer.
[0022] In addition, the same N wavelengths can be transmitted by
each transmitting system if the receiving system is coordinated to
receive a different wavelength from each transmitting system.
Wavelength coordination eliminates the need for wavelength
converters and allows the same transmitters and receivers to be
used in the system.
[0023] A difficulty with passive switching systems is that the
streamlined nature renders the switch somewhat inflexible. For
example, a specified wavelength is used to transmit signals between
a transmission system and a receiving system. Therefore, it may be
difficult to transmit multiple signals from one transmitting system
to one receiving system at any one time. It is presumably possible
to assign additional wavelengths to each of N transmitter/receiver
combinations; however, for each wavelength added to each system,
either N.sup.2 hard wire connections must be made.
[0024] The problem of signal blockage can also be addressed by
designing a system having excess transmission capacity. This would
provide more available wavelengths than is required to meet current
transmission requirements. However, in view of the continued
expansion of communication networks the excess capacity may only be
short term; therefore the ability to upgrade a system remains a
desired feature of a switch.
[0025] Similarly, other optical components, such as add/drop
devices, demultiplexers and multiplexers, used in optical
processing nodes between the transmitter and receivers increase in
complexity and cost as additional channels are added to the system.
In addition, these components most likely have to be replaced when
a system is reconfigured or additional channels are to be added to
the system.
[0026] The continued advancement and development of communication
systems is limited, at least in part, by the constraints placed
upon optical systems by the current technology involved in optical
processing systems. The elimination or reduction of these
constraints is a primary concern of industry as the pace of
communications continues to accelerate.
[0027] Accordingly, there is a need for optical systems and optical
components that allow for increased network capacity and
flexibility. One aspect of which is to reduce the complexity of the
equipment and increase the efficiency of the transmission
system.
BRIEF SUMMARY OF THE INVENTION
[0028] The apparatuses and methods of the present invention address
the above needs and concerns for improved optical switches and
systems. An optical transmission system of the present invention
includes one or more optical signal transmitters and optical signal
receivers optically communicating via one or more intermediate
optical processing nodes. Each optical transmitter includes one or
more optical sources, such as modulated lasers, and is configured
to transmit information via one or more information carrying
wavelengths. Each optical receiver is configured to receive one or
more of the information carrying wavelengths using one or more
various detection techniques, such as direct detection using
optical wavelength filters and photodiodes, or indirect detection
using coherent detectors.
[0029] The intermediate optical processing nodes include optical
switches, add and/or drop devices including at least one waveband
selector configured to pass and substantially prevent the passage
of optical wavebands that include a plurality of information
carrying wavelengths from the transmitter to the receiver. The
optical processing nodes provide for information management and
processing in wavebands, instead of separating individual
information carrying wavelengths from the signal and individually
processing each wavelength. In this manner, high capacity
processing of the information can be achieved without the prior
complexities involved with increasing capacity. The processing of
pluralities of individual wavelengths further provides for
accommodating varying numbers and distributions of individual
information carrying wavelengths in the system without having to
reconfigure or replace system components.
[0030] In an embodiment of the present invention, the optical
processing node includes a switch providing cross connections
between a plurality of transmitters and receivers. Optical signals
including one or more information carrying wavelengths are
transmitted to optical switch input ports and are distributed to
optical switch output ports by splitting and/or waveband
demultiplexing the optical signals depending upon the type of
waveband selector used in the switch.
[0031] Waveband selectors include at least one switch, gate, or
filter, such as an erbium or mechanical switch, a Bragg grating, or
a Mach-Zehnder or Fabry-Perot filter. The waveband selectors are
generally configured to pass one or more optical wavebands from the
input port to the output port in one mode and/or to substantially
prevent the passage the optical wavebands in another mode. A signal
is generally considered to be substantially prevented from passage,
if the signal is sufficiently attenuated such that a remnant of the
attenuated signal passing through the waveband selector does not
destroy signals that have been selectively passed through the
optical processing node. For example, a 40 dB attenuation of a
signal will generally be sufficient to prevent cross-talk
interference between remnant signals and signals passing through
the optical processing node.
[0032] In an embodiment, each input signal is waveband
demultiplexed to separate the input signal into waveband signals.
Each waveband signal is then split and each split waveband signal
passed through a switch to a respective output port. In an
embodiment, an erbium doped fiber is used as the switch in the
waveband selector to pass, as well as to controllably amplify or
attenuate, the split waveband signal to the output port when
supplied with optical pump power. In the absence of pump power, the
erbium fiber absorbs the waveband signal, which substantially
prevents the passage of the signal. One or more optical combiners
are provided at the output ports to combine split waveband signal
from the waveband selector passing optical wavebands from the input
ports.
[0033] The optical signal at each input port can also be
demultiplexed according to a known destination of each waveband
signal and the waveband signal is passed to the output port
corresponding to the destination. The optical signals can be
transmitted to the switch in wavelengths that are unique to the
signal destination to avoid the use of wavelength converters in the
optical system.
[0034] Bragg gratings, either reflective or transmissive, can be
included in the waveband selector to switch any number of
wavebands. The Bragg gratings of the present invention include one
grating produced to reflect an entire waveband or a series of
gratings operated in concert that piecewise correspond to the
waveband. In an embodiment, tunable permanent Bragg gratings can be
provided corresponding to each of the wavebands to allow for
dynamic reconfiguration of the switch.
[0035] In addition, the optical processing node can include
transient gratings to provide for additional reconfiguration of the
processing node. Transient grating can be formed in the waveguide
either by induction using a coupled circuit or via a writing
circuit integrated with the transmission fiber.
[0036] In an embodiment of the optical transmission system,
pluralities of nodes are interconnected to form a network. The
nodes may contain optical transmitters, receivers, add and/or drop
devices/ports, and/or switching equipment depending upon whether
the node is an origination and/or a destination node, and whether
it is a terminal or an intermediate node. In an embodiment, the
network management system is provisioned to assign wavelengths to
information that can be transmitted to destination nodes in a
manner to obviate the need for wavelength conversion at the optical
switch. Wavelength assignment can be static or dynamically
performed via a network management system, for example, at the
client system interface with the optical network. The optical
switches cross connecting the nodes and add and/or drop ports are
configured to respectively switch and add/drop the information
carrying wavelengths in wavebands without separately switching the
individual wavelengths.
[0037] Accordingly, the present invention addresses the
aforementioned problems and provides apparatuses and methods to
increase the efficiency and capacity of optical communication
systems. These advantages and others will become apparent from the
following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Embodiments of the present invention will now be described,
by way of example only, with reference to the accompanying Figures
wherein like members bear like reference numerals and wherein:
[0039] FIGS. 1-4 depict optical communication systems of the
present invention;
[0040] FIGS. 5-8(b) depicts waveband selectors of the present
invention;
[0041] FIGS. 9-11 depict transient grating waveband selectors of
the present invention; and,
[0042] FIGS. 12-13 depict multi-node optical communication networks
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0043] The operation of optical systems 10 of the present invention
will be described generally with reference to the drawings for the
purpose of illustrating embodiments only and not for purposes of
limiting the same.
[0044] Generally, the optical system 10 includes at least one
optical transmitter 12 and at least one optical receiver 14, as
shown in FIG. 1. Each transmitter 12 is configured to transmit
information via one or more information carrying wavelengths
18.sub.i,k contained in at least one waveband 16.sub.1,i to the
receivers 14. Each receiver 14 is configured to receive the
information carried via one or more of the information carrying
wavelengths 18.sub.i,k. As used herein, the term "information"
should be broadly construed to include any type of data,
instructions, or signals that can be optically transmitted.
[0045] As shown in FIG. 1, the system 10 further includes at least
one intermediate optical processing node 20, such as an optical
switch 22. The transmitter 12 is configured to transmit an optical
signal 24 containing one or more information carrying wavelengths
18; along signal transmission waveguide, i.e., fiber, 26 to the
switch 22 via input port 28. The optical processing node 20
includes one or more waveband selectors, or selective element, 30
that are configured to pass and/or substantially prevent the
passage of information in wavebands 16.sub.i to the receiver 14 via
output ports 32. Because the information is being manipulated in
wavebands, the individual information carrying wavelengths 18.sub.j
within the waveband 16.sub.i do not have to be separated in
individual wavelengths to be managed and processed. Also, the
individual wavelengths 18.sub.j within the waveband 16.sub.i be
varied in the system 10 without affecting the configuration of the
optical processing node 20. Wavelengths 18.sub.j in the original
signal 24 but not within the waveband 16.sub.i are prevented from
passing through to the receivers 14.
[0046] In the present invention, optical signals 24 can be produced
including a number of wavebands 16, each of which may contain one
or more information carrying wavelengths in a continuous band of
wavelengths or a plurality of wavelength bands. For example, a
waveband 16 can be defined as having a continuous range of
.about.200 GHz containing 20 different information carrying
wavelengths 18.sub.1-20 spaced apart on a 10 GHz grid. The
bandwidth of each waveband can be uniformly or variably sized
depending upon the network capacity requirements. Likewise, the
bandwidth of the waveband is not restricted, but can be varied to
accommodate varying numbers of wavelengths.
[0047] Generally, systems 10 of the present invention are
configured so that the optical processing nodes do not separate and
process individual information carrying wavelengths during
transmission from the transmitter to the receiver. Instead, optical
processing nodes 20 are configured to process the information in
wavebands that may include any number of individual information
carrying wavelengths. The processing of information in wavebands
decreases the complexity involved in processing large numbers of
channels, while increasing the flexibility of optical components
deployed in the transmission path between transmitters and
receivers. The bandwidth and number of information carrying
wavelengths within a waveband in a network can be statically or
dynamically allocated depending upon the information traffic flow
in a given network segment.
[0048] FIG. 2 shows a more general arrangement of the system 10,
which includes a plurality of transmitter 12.sub.n optically
connected via the switch 22 to a plurality of receiver 14.sub.m.
Analogous to FIG. 1, each transmitter 12.sub.n transmits an optical
signal 24.sub.n which includes one or more wavelengths 18.sub.n,j
through a waveguide 26.sub.n to an input port 28.sub.n of the
switch 22. It will be appreciated that each transmitter may include
one or more sources to transmit and one or more wavelength signals.
Likewise, each receiver may include one or more detectors for
receiving the signals.
[0049] An optical distributor 34.sub.n, such as a demultiplexer 36
and/or a splitter 38, is provided in the input port 28.sub.n to
distribute the signal 24.sub.n to the waveband selectors
30.sub.n,m. An optical combiner 40.sub.m, such as a wavelength
division multiplexer 42 or a coupler 44, is generally included to
combine the wavelengths 18.sub.m,k in waveband 16.sub.m,i emerging
from the waveband selectors 30.sub.n,m and provide a modified
signal 24'.sub.m. The modified signal 24'.sub.m exits the switch
through the output port 32.sub.m and passes along waveguide 26 to
the receiver 14.sub.m.
[0050] For convenience and clarity, FIG. 2 shows only a waveband
selector 30 connecting input port 28.sub.1 to output port 32.sub.1.
However, it should be understood that the switch 22 will generally
include at least one waveband selector 30 between each input port
28 and each output port 32. It is also noted that in some networks
it is not necessary that corresponding input and output ports, e.g.
28.sub.1 and 32.sub.1, be connected to loop a signal back to its
point of transmission. In addition, reference numeral subscripts
are generally not used in the remainder of the description to
simplify the nomenclature.
[0051] Transmitters 12 used in the system 10 can include one or
more optical emitters and sources that provide continuous wave
and/or pulsed beams, such as one or more modulated lasers as is
known in the art. The transmitter 12 may also include narrow band
incoherent sources such as described in U.S. Pat. Nos. 5,191,586
and 5,268,910 issued to Huber or other optical sources for
producing optical signals. Information can be directly or
indirectly, e.g., externally, modulated, or alternatively
upconverted, onto an optical wavelength, and the information itself
may be a time division multiplexed signal.
[0052] The transmitter 12 can also be used to provide multiple
information carrying wavelengths using techniques such as described
in U.S. Pat. No. 5,400,166. Multiple information carrying
wavelengths can be placed on a single carrier from the transmitter
12 using techniques, such as subcarrier modulation (SCM). SCM
techniques are described in U.S. Pat. Nos. 5,101,450, 5,134,509,
and 5,301,058 issued to Olshansky, 4,989,200 issued to Olshansky et
al., 5,432,632 issued to Watanabe and 5,596,436 issued to Sargis et
al.
[0053] The transmitters 12 may be coupled to an external electrical
network or part of an optical-electrical-optical (O/E/O) signal
regenerator within an optical network. One skilled in the art will
appreciate that the selection of the transmitter 12 and the number
of information carrying wavelengths will depend upon the desired
information transfer rates for a particular transmitter/receiver
system at the respective nodes. While the present invention
provides the ability to substantially upgrade the transfer rate for
the node, it does not require that older, slower nodes be upgraded
upon implementation of the present invention.
[0054] Consistent with the discussion regarding the transmitter 12,
the receiver 14 and transmission fiber 26 does not have to be
upgraded to be compatible with the present invention. In the
present invention, the capabilities of the receiving system can be
taken in account when establishing wavebands to be transmitted to a
particular receiver 14.
[0055] As shown in FIG. 3, the receiver 14 will generally be used
to separate the individual information carrying wavelengths
18.sub.i,k in each waveband 16.sub.i contained in the modified
signal 24' and convert the information to one or more electrical
signals. The receiver may include a number of a wavelength filters,
such as Bragg gratings or demultiplexers, in combination with an
optical to electrical converter (O/E), such as a photodiode, to
provide for direct detection of the individual wavelengths. The
receiver 14 may also provide for indirect detection of the
individual wavelengths, such as by using coherent detector
arrangements.
[0056] Referring to FIG. 4, the system 10 may include other types
of intermediate processing nodes 20, such as add and/or drop
devices. The other intermediate processing nodes can be employed to
selectively modify the wavebands in the signal 24' and pass a
further modified signal 24" to successive switches 22 and to the
receivers 14. The subsequent switches 22 between other intermediate
processing nodes 20 and the receivers 14 can be used to further
process the signal 24" to produce a further modified signal 24"'
which may include waveband subset 16.sub.i1. The optical add and/or
drop devices/ports can be embodied as a 2.times.2 switch that can
provide for 100% programmable add/drop capability or by employing
directional devices, such as couplers and/or circulators, with or
without waveband selectors 30 to provide varying degrees of
programmability, as will be further discussed.
[0057] The receiver 14 can also be used to further distribute the
signal 24"' as a part of an O/E/O signal regenerator. One skilled
in the art will appreciate that in an O/E/O regenerator the optical
wavelengths received by the receiver 14 do not necessarily have to
correspond to the optical wavelengths at which the information is
further transmitted.
[0058] Waveband selectors 30 generally include at least one filter,
gate, and/or switch configured to pass and/or substantially prevent
the passage of at least one waveband 16 received from the inlet
port 28 to the outlet port 32. A signal is generally considered to
be substantially prevented from passage, if the signal is
sufficiently attenuated such that a remnant of the attenuated
signal that passes through the waveband selector does not destroy
signals that have been selectively passed through the optical
processing node 20. For example, a 40 dB attenuation of a signal
will generally be sufficient to prevent cross-talk interference
between remnant signals and signals being selectively passed
through the optical processing node 20.
[0059] In an embodiment shown in FIG. 5, the switch 22 includes a
waveband demultiplexer 36 and an optical signal splitter 38 coupled
via a doped optical fiber 46 to the multiplexer 42 at the output
port 32. When an optical signal is to be passed to the output port
32, the doped fiber is supplied with energy from the switch pump 48
to overcome the absorption of the doped fiber 46. The amount of
energy supplied by the pump 48 can be controlled to selectively
amplify or attenuate a signal being passed through the waveband
selector 30. In the absence of optical pump energy, the doped fiber
46 will absorb the optical signal, thereby substantially preventing
the passage of that portion of the signal to the outlet port 32. In
the embodiment of FIG. 5, the wavebands can be switched to any
number of output ports including one to one switching and one to
many broadcasting.
[0060] The dopant in the doped optical fiber 46 can be erbium or
any other dopant including other rare earth elements that can
render the fiber transmissive in one state and substantially less
transmissive in another state. The selection of a dopant in the
doped fiber will depend upon the information carrying wavelengths
that are to be switched in the system. Also, mechanical,
electro-optic, liquid crystal, semiconductor, and other types of
switches along with gratings, filters and gates, can be substituted
for or used in combination with doped fiber 46 to achieve desired
characteristics in the switch 22.
[0061] The waveband selector 30 may include reflective (.gtoreq.50%
reflectance) and/or transmissive (.ltoreq.50% reflectance)
selective elements that can be used to pass, either reflect or
transmit, any of the wavebands 16 that comprise the signal 24. The
waveband selector 30 may employ Mach-Zehnder filters, Fabry-Perot
filters, and Bragg gratings to perform the waveband selection.
[0062] As shown in FIGS. 6 and 7, waveband selectors 130 and 230,
respectively, can include a plurality of in-fiber reflective Bragg
gratings 50 (FIG. 5) and/or transmissive Bragg gratings 52 (FIG. 6)
to pass selected wavebands to the output ports 32. Each grating, 50
and 52, can be provided to pass selected wavebands to output ports
32. Alternatively, the waveband selector 30 may include a series of
multiple Bragg gratings that provide for piecewise coverage of the
waveband. In the case of a multiple grating waveband selector, some
separation of the wavelengths in the waveband will occur between
gratings, but the multiple gratings are collectively operated to
pass or substantially prevent the passage of the waveband. The
multiple grating selector can be tuned to individual idler gaps or
telescoped to one or more common idler gaps to decrease the idler
gap bandwidth.
[0063] The number of gratings in FIGS. 6 and 7 is shown as being
equal to the number of wavebands 16 being switched. However, the
number of selectors provided in the switch does not necessarily
have to correspond to number of wavebands 16 currently in the
system. For example, the configurations shown in FIGS. 5-11 may
also be suitable for use in add/drop multiplexers, as well as
demultiplexers or multiplexers, in which any number of wavebands
can be processed.
[0064] It may also be advantageous to provide sub-wavebands within
the wavebands 16 of varying size that can be received, divided into
the sub-wavebands, and the sub-wavebands can further transmitted to
other receivers within the system. The waveband selectors 30 can
also be used to pass multiple wavebands to reduce the number of
components in the system 10. In addition, the wavebands 16 can be
selected to overlap to allow one or more wavelengths 18 to be
transmitted in multiple wavebands 16.
[0065] As shown in FIG. 6(a), a waveband selector 130 can include a
three port circulator 54 used in conjunction with the plurality of
reflective Bragg gratings 50 using a configuration similar those
discussed in U.S. Pat. Nos. 5,283,686 and 5,579,143 issued to
Huber, and 5,608,825 issued to Ip. In FIG. 6(b), a waveband
selector 230 employs transmissive gratings 52 to transmit selected
wavebands to the output ports 32 and reflect the remaining
wavebands. An optical isolator 56 can be incorporated to prevent
reflected wavebands from propagating back to the input ports 28.
One skilled in the art will appreciate that directional couplers
and other directional devices can be substituted for the optical
circulators with appropriate circuit modifications.
[0066] The optical processing node 20 may include a wavelength
converter 58 to provide for switching one of more of the
wavelengths in the transmitted signal 24. In FIG. 6(a), the
wavelength converter 58 is shown before the waveband selector 30;
however, the wavelength converter 58 may also be positioned after
the waveband selector 30 and operated accordingly.
[0067] Similarly in FIG. 7, a waveband selector 330 can be used
with one or more directional devices, such as a circulator or a
coupler, with either reflective or transmissive waveband gratings,
50.sub.i or 52.sub.i, to select wavebands. It will be appreciated
that the selector 330 can be employed as an add and/or drop
device/port, as well as a filter or in a demultiplexer or
multiplexer in the system 10.
[0068] The optical distributor 34 associated with the input port 28
can be embodied as an optical splitter to split the signal 24 and
distribute a portion of the entire signal 24 to each of the output
ports 32. As shown in FIG. 8(a), the optical distributor 34 can be
embodied as a circulator 54 to provide the entire signal to each
waveband selector 430. Wavelengths within waveband of the selector
230 are transmitted to the output port 32, while the remaining
wavelengths are reflected by the transmissive gratings and
circulated to successive ports.
[0069] Likewise, optical couplers can serve as the distributor 34
to provide the entire signal to waveband selector 530 (FIG. 8(b)).
One skilled in the art will appreciate that directional devices,
such as multiple three port circulators and/or coupler, can be
cascaded in various other configurations equivalent to those shown
in FIGS. 8(a)&(b). The gratings, 50 or 52, could be prepared
having a reflectivity and transmittance of less than 100%, to allow
a portion of signal to be transmitted and reflected.
[0070] The fiber Bragg gratings 50 and 52 used in the switch 22 can
be permanently and/or transiently produced. Embodiments of the
present invention incorporate fixed and/or tunable permanent Bragg
gratings, 50 and 52 as the waveband selectors 30. The permanent
gratings used in the present invention can be prepared by
conventional methods, such as by using ultraviolet (UV) light to
irradiate a GeO.sub.2 doped fiber core. Such methods are discussed
in U.S. Pat. Nos. 4,725,110 issued to Glenn et al., 5,218,655 and
5,636,304 issued to Mizrahi et al., which are incorporated herein
by reference, and related patents.
[0071] The permanent gratings can be tuned to provide for
reflectance of a waveband in one mode and transmittance in another
mode. Tuning of the grating properties can be accomplished
mechanically (stretching), thermally, or optically, such as
discussed in U.S. Pat. Nos. 5,007,705, 5,159,601, and 5,579,143,
and by M. Janos et al., Electronics Letters, v32, n3, pp. 245-6,
electronically, or in some other appropriate manner.
[0072] A limitation of tunable permanent gratings is that a portion
of the wavelength band can not be used to transfer signals. The
unused portion of the wavelength band, called an "idler" gap, is
necessary to provide each permanent grating with a gap in the
wavelength spectrum in which the grating will not affect a signal
encountering the grating.
[0073] Transient reflective or transmissive gratings, 50.sup.T and
52.sup.T, respectively, could also be used in the waveband selector
30. Transient gratings can be used to reduce or eliminate the need
for idler gaps in the transmission wavelengths and provide
increased flexibility in the wavelength selectivity of the switch
22.
[0074] Transient gratings, either 50.sup.T or 52.sup.T, can be
formed in a portion of the fiber in which the refractive index of
the fiber can be transiently varied to produce a grating. In an
embodiment, the fiber portion is doped with Erbium, other rare
earth elements, such as Yb and Pr, and/or other dopants that can be
used to vary the refractive index of the fiber to produce a
grating. In another embodiment, the transient grating can be formed
in a fiber section that contains a permanent grating to provide a
combined performance grating and/or to establish a default grating
in the absence of the transient grating.
[0075] As shown in FIGS. 9-11, transient gratings can be written by
introducing a grating writing beam either directly into the
transmission fiber or by coupling the writing beam into the
transmission fiber. One or more transient grating writing lasers
60.sub.i are used to introduce a transient grating writing beam
into the doped portion of the signal waveguide 26. In a waveband
selector 630 shown in FIG. 9, the writing beam is split into two
paths and introduced into the transmission fiber 26 via ports 62. A
plurality of narrow wavelength reflective gratings 64.sub.i are
positioned in one of the writing beam paths to control the position
of the standing wave in the waveguide 26 by introducing a time
delay on the wavelengths of the writing beam. Narrow wavelength
reflective or transmissive gratings, 64.sub.i or 66.sub.i, can also
be used to remove the writing beam from the transmission fiber
26.
[0076] As shown in FIG. 10, the writing beam can also be reflected
back upon itself using spaced narrow wavelength reflective gratings
64.sub.i, to form a standing wave and produce a transient gratings
50.sup.T in waveband selector 730. The grating writing lasers
60.sub.i can be operated in conjunction with modulators 68 and
pulsing switches 70 to control the coherence of the writing lasers
60.sub.i and the resulting transient gratings 50.sup.T.sub.i. A
waveband selector 830, shown in FIG. 11, can also be configured
with a reflector 72 in a coupled fiber to establish a standing wave
by reflecting the writing beam back upon itself to form the
standing wave in a manner similar to that described with respect to
FIG. 10.
[0077] Single wavelength continuous writing beam arrangements have
been used for signal identification and pattern recognition as
discussed by Wey et al., "Fiber Devices for Signal Processing",
1997 Conference on Lasers and Electro-Optics, Baltimore, Md. Also,
U.S. Pat. No. 5,218,651 issued to Faco et al., which is
incorporated herein by reference, describes two beam methods for
producing a transient Bragg grating in a fiber.
[0078] In systems 10 of the present invention, the switch 22 can be
used to optically connect a transmitter and a receiver (FIG. 1) in
a 1.times.1 configuration or a plurality of nodes 100 in an
n.times.m configuration (FIGS. 12-13). In a 1.times.1
configuration, the switch 22 can be useful for dropping wavebands
or for varying the waveband characteristics (gain trimming) of the
signal.
[0079] The nodes 100 used in the system 10 may contain various
system components including optical transmitters, receivers, and/or
other processing equipment, such as switches depending upon whether
the node is an origination (transmitting signals) and/or a
destination (receiving signals) node, and whether it is a terminal
node. The system 10 may further include other optical transmission
equipment, such as optical amplifiers 74, and other optical
processing nodes 20, such as optical add/drop multiplexers, between
the switches and the nodes 100 as may be useful in a given
system.
[0080] The 4.times.4 switch arrangement shown in FIG. 12 is
representative of a north-south-east-west communication system. One
skilled in the art will appreciate that the nodes/switch
arrangements can be varied to accommodate various network
configurations. For example, a 3.times.3 arrangement is shown in
FIG. 13. The arrangements in FIGS. 12 and 13 show the cross
connections of the switches 22, but do not show the waveband
selectors within the switches 22.
[0081] The flow of communication traffic between the nodes can take
place using a variety of optical waveband hierarchies. In an
embodiment, the optical wavebands are established and wavelengths
assigned based on both the signal origination node and the signal
destination node to avoid the need for wavelength conversion in the
optical network.
[0082] For example, the spectrum of wavelengths used with each
receiver can be divided into wavebands and the destination
wavebands assigned to transmitters. The assignment may be static or
dynamically controlled at the network management level so no
overlap occurs in the wavebands assigned to each transmitter from
the various receivers. Dynamic control of the waveband assignment
provides flexibility in the wavelength management in the system 10
and can be performed at various points in the system, such as at
the client system, e.g., SONET, SDH, ATM, IP interface with the
optical network.
[0083] Waveband hierarchies in which the origination and
destination nodes are paired are particularly useful in
communication systems in which a signal is being sent from the
origin to one destination, such as in telephone communication
systems. In addition, the present invention can also accommodate
the necessary protection systems to provide multiple paths to the
same destination by proper allocation of the wavelengths.
[0084] In a multiple destination system, such as a cable television
system, it may be more appropriate for the wavebands to be
determined based solely on the origination node of the signal.
Waveband selectors can be included in the switches 22 to pass
signals corresponding to a particular source to any number of
destination nodes. The switch 22 can provide further control over
the distribution of signals by passing broadcast signals to a
distribution segment only upon a subscriber's request. The CATV
provider, in response to a programming request, can centrally
control the switch to deliver the signal to the requester. In the
absence of an express request by a subscriber the signal would not
be broadcast to the segment. The limited availability of the signal
on a segment may discourage pirating of programming signals.
[0085] Switches 22 of the present invention can also be used for
remote switching and routing of communication traffic in the event
of a fault in the system. For example, in FIG. 12 if a signal were
to travel from node A to node C, the typical path would be through
the switch connected between nodes A and C. However, if a fault
occurs in the line from the switch to node C, it may be desirable
to route traffic from node A through node D to node C. Upon
detection of the fault, the network management system could
reconfigure the switches 22 in the system 10 to reroute the traffic
or switch to a previously configured protection route.
[0086] As can be seen, the present invention provides for
flexibility in optical transmission systems. In addition, the
present invention provides for increased transmission capacity
without the commensurate increase in complexity that was present in
the prior art systems.
[0087] Those of ordinary skill in the art will appreciate that
numerous modifications and variations that can be made to specific
aspects of the present invention without departing from the scope
of the present invention. It is intended that the foregoing
specification and the following claims cover such modifications and
variations.
* * * * *