WO2001063705A1 - Edfl multiple wavelength laser source - Google Patents
Edfl multiple wavelength laser source Download PDFInfo
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- WO2001063705A1 WO2001063705A1 PCT/US2001/003686 US0103686W WO0163705A1 WO 2001063705 A1 WO2001063705 A1 WO 2001063705A1 US 0103686 W US0103686 W US 0103686W WO 0163705 A1 WO0163705 A1 WO 0163705A1
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- optical
- laser source
- wavelength
- output
- multiple wavelength
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
- H04J14/0278—WDM optical network architectures
- H04J14/0283—WDM ring architectures
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
- H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
- H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
- H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON
- H04J14/0245—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for downstream transmission, e.g. optical line terminal [OLT] to ONU
- H04J14/0246—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for downstream transmission, e.g. optical line terminal [OLT] to ONU using one wavelength per ONU
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
- G02B6/2821—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/0675—Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
- H01S3/2383—Parallel arrangements
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/002—Coherencemultiplexing
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
- H04J14/0201—Add-and-drop multiplexing
- H04J14/0215—Architecture aspects
- H04J14/022—For interconnection of WDM optical networks
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
- H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
- H04J14/0278—WDM optical network architectures
- H04J14/0282—WDM tree architectures
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
- H04J14/0278—WDM optical network architectures
- H04J14/0284—WDM mesh architectures
Definitions
- This invention pertains to optical communications systems, in general, and an optical communications system utilizing a multiple wavelengtli laser source to provide channel synchronization, in particular.
- optical network relates to any network that interconnects a plurality of nodes and conveys information between nodes with optical signals.
- optical communications system refers to any system that utilizes optical signals to convey information between one node and one or more other nodes.
- An optical communications system may include one or more optical networks.
- optical fiber systems relied on time division multiplexing to route traffic through a channel. Time division multiplexed systems add more capacity by time multiplexing signals onto an optical fiber. A disadvantage of time division multiplex systems is that data must be converted from light waves to electronic signals and then back to light. The system complexity is thereby increased.
- Wavelength Digital Multiplexing WDM
- DWDM Dense Wavelength Digital Multiplexing
- WDM and DWDM are being used and/or proposed for use in long-haul telecom network applications for increasing the capacity of existing fiber optic networks.
- WDM and DWDM are being used and/or proposed for use in long-haul telecom network applications for increasing the capacity of existing fiber optic networks.
- the advantage of both WDM and DWDM is that the conversion to electrical signals is not necessary.
- the devices that handle and switch system traffic process light and not electrical signals.
- WDM and DWDM would appear to many to be the solution to optical network limitations.
- WDM plural optical channels are earned over a single fiber optic, with each channel being assigned to a particular wavelength.
- optical amplifiers multiple optical channels are directly amplified simultaneously thereby facilitating the use of WDM systems in long-haul optical networks.
- DWDM is a WDM system in which channel spacing is on the order of one nanometer or less.
- WDM and DWDM expand the capacity of an optical fiber by multiple wavelength channels into a single laser beam. Each wavelength is capable of carrying as much traffic as the original.
- traffic passes from one node of the network to its destination in the form of light waves without conversion to electrical signals.
- DWDM and WDM will permit increase in the capacity of the fiber infrastructure.
- a plurality of optical channels is provided and the optical channels are utilized for coimnunications among a plurality of communications nodes.
- Each optical channel is dete ⁇ nined by at least two of three optical signal characteristics. At least one of the optical signal characteristics is selected from a plurality of predetei nined optical wavelengths, hi accordance with the principles of the invention, the pluralities of multiple optical wavelengths are provided by a multiple wavelength laser source.
- a multiple wavelength laser source is utilized to provide channel synchronization signals for the system.
- the laser source utilizes a plurality of distributed feedback (DFB) lasers.
- the output of each DFB laser is phase modulated, and the phase modulated outputs are multiplexed together and amplified.
- DFB distributed feedback
- a multiple wavelength laser source in accordance with the invention comprises a plurality, m, of erbium doped fiber lasers. Each of the lasers generates optical signals at a predeteiinined one of a plurality, m, of wavelengths.
- a corresponding plurality, m, of gratings is provided. Each of the gratings is selected to conform to one of the desired wavelengths and is coupled to a corresponding one of the lasers.
- a multiplexer is coupled to each of the gratings to multiplex together the outputs to produce a multiplexed multiple wavelength optical output having a plurality, m, of wavelength outputs.
- An Erbium doped fiber amplifier is utilized to amplfy the multiplexed output.
- a method of providing a multiple wavelength laser source comprises providing a plurality, m, of Erbium doped fiber lasers. Each laser generates optical signals at a predeteiinined one of a plurality, m, of wavelengths. Shaping of the optical signals is provided by utilizing fiber gratings. Multiplexing together the shaped optical signals produces a multiplexed multiple wavelength optical output having a plurality, m, of wavelength outputs. Amplification of the multiplexed output is provided with an Erbium doped fiber amplifier.
- FIG. 1 depicts an optical communication system in accordance with the principles of the invention
- FIG. 2 depicts representative optical signal power distribution levels in a portion of the system of FIG. 1;
- FIG. 3 illustrates multiplexing of optical signals in accordance with the principles of the invention;
- FIG. 4 is a block diagram of a system control unit in the system of FIG. 1;
- FIG. 5 is flow chart illustrating channel assignment in accordance with the invention.
- FIG. 6 is illustrates the wavelength multiplexing utilized in the system of FIG. 1;
- FIG. 7 illustrates use of interferometer technology in an embodiment of the invention;
- FIG. 8 illustrates a frequency multiplex/switch layer implementation utilized in an embodiment of the invention
- FIG. 9 illustrates in block diagram fonn a frequency modulator and fi-equency demodulator for use in a system in accordance with the invention
- FIG. 10 illustrates the multiplexing of signals in a second embodiment of the invention in accordance with the principles of the invention
- FIG. 11 illustrates, in simplified fonn, the transmission of data from one network node to a second network node
- FIG. 12 illustrates, in simplified fonn, the transmission of data from the second network node to the first network node of FIG. 11 ;
- FIG. 13 is a block diagram of a network node in accordance with the invention.
- FIG. 14 is a detailed block diagram of a portion of a first optical network processor (ONP) for use with an embodiment of the invention
- FIG. 15 is a detailed block of a second portion of the fust optical network processor useable in conjunction with the optical network processor portion of FIG. 14;
- FIG. 16 is a detailed block diagram of a second optical network processor
- FIG. 17 is a detailed block diagram of a first portion of a third optical network processor for use with the second embodiment of the invention.
- FIG. 18 is a detailed block diagram of a second portion of the third optical network processor useable in conjunction with the optical network processor portion of FIG. 17;
- FIG. 19 is a detailed block diagram of a fourth optical network processor
- FIGs. 20 through 23 depict multiple wavelength laser reference sources
- FIGs. 24 and 25 depict Erbium doped fiber lasers (EDFLs) utilized in the reference sources of FIGs. 20 through 23; and
- EDFLs Erbium doped fiber lasers
- FIG. 26 depicts an optical add/drop (OAD). DETAILED DESCRIPTION
- a system in accordance with one aspect of the invention is able to provide for bandwidtli upgrade to existing optical fiber networks and optical coimnunications systems.
- the number of concuirently available channels is increased over WDM systems by a factor of 10 to 200 pennitting serving up to 20,000 channels simultaneously.
- the number of channels and an occupancy factor detennines the number of users that may be served by a multi-channel coimnunications system.
- the system of the present mvention may be used to provide coimnunications for in excess of 200,000 users concu ⁇ ently.
- FIG. 1 depicts an optical communication system 1000 in accordance with the principles of the invention.
- Optical communication system 1000 includes a Metro Network 1100 coupled to a Long Haul Network 1200 via an optical add/drop module 1203 and optical cross connect module 1205.
- Metro Network 1100 couples one or more local access networks 1301, 1303, 1305 to each other and to Long Haul Network 1200.
- Long Haul Network 1200 interconnects plural Metro Networks 1100.
- Metro Network 1100 For purposes of clarity in the drawings and simplicity in the description, only one Metro Network 1100 is shown. Mefro Networks 1100 are typically located at widespread geographic locations. However, it is not intended to limit applicability of the present invention to airangements in which networks are dispersed geographically. The present invention is applicable to networks that are overlapping in geographic areas or even to networks that are in the same geographic area.
- Metro Network 1100 is, in the illustrative embodiment, depicted as a ring-based metropolitan network system. Metro Networks are intended to provide high bandwidth to end customers directly and/or via local loop access networks. In the illustrative embodiment depicted in FIG. 1 , Metro Network 1100 is depicted as a ring based network having a fiber optic ring 1101. It will be understood by those skilled in the art that the invention is not limited to use in networks that are of a ring based structure. The principles of the invention are equally applicable to other network architecture structures including, not by way of limitation but by way of example, star network stmctures, mesh network structures, and point-to-point stmctures.
- the principles of the present invention are applicable to "long haul” networks. Still further, the principles of the invention are not limited to optical coimnunications systems utilizing only optical fiber for the coimnunications paths. Those skilled in the art will recognize that various other terms may be used to describe or designate the identical or similar networks. For example, the te ⁇ n "long distance network" is also used in place of "long haul network”.
- Each Access Network 1301, 1303, 1305 is coupled to optical fiber ring 1101 of Metro
- optical add/drops in various forms are known to those skilled in the art. hi its simplest form an optical add/drop is a coupler. Optical add/drops are used to add or extract optical signals. In the present mvention, OADs 1307, 1309, 1311 are utilized to inject (add) and retrieve (drop) optical signals into and from optical fiber ring 1101. Both add and drop are bi-directional with respect to optical fiber ring 1101.
- optical signals may be transmitted in or received from either direction, i.e., to the right or to the left in the ring as shown, on optical fiber ring 1101.
- OADs utilized in the embodiment of the invention described herein provide broadband operation.
- An OAD particularly advantageously utilized in the embodiments of the invention is show in FIG. 26 and described in greater detail with respect to FIG. 26.
- Each optical add/drop 1307, 1309, 1311 is, in turn, coupled to an optical fiber amplifier 1313, 1315, 1317.
- Optical fiber amplifiers 1313, 1315, 1317 may be of known design.
- the optical fiber amplifiers 1313, 1315, 1317 are each Erbium-doped amplifiers (EDFAs).
- EDFAs are the latest state-of-the-art solution for broadband amplification of optical signals in optical communication systems. EDFAs are commercially available from various sources. EDFAs overcome propagation losses of the optical signals through the optical fiber and boost the optical signals to necerney receiver levels. EDFAs can be used to amplify WDM and DWDM signals.
- Access network 1301 includes a plurality of access locations or nodes that include a residential complex 1331 and a small office building 1333. Other access locations are not shown for clarity, but it will be understood that more than two access locations may be coupled into access network 1301. Furthennore, it will be understood by those skilled in the art that the various types of access locations or nodes shown are merely representative of the types of end users and are not intended in any way to limit the scope of the invention. The te ⁇ ns "node” and "access location” are used interchangeably herein. Each access location 1331, 1333, 1341, 1343, 1351 has associated with it an optical network processor 1335, 1337, 1345, 1347, 1353.
- Access network 1303 includes user complex 1341 and office buildingl343 along with other locations that are not shown.
- Optical network processors 1345, 1347 are utilized to provide network access functionality for user complex 1341 and office building 1343, respectively.
- Access network 1305 includes large office complex 1351 and a single optical network processor 1353. It will be understood by those skilled hi the art that the number of optical network processors 1335, 137, 1345, 1347, 135 associated with each access network 1301, 1303, 1305 may be more or less than the numbers shown in the drawing Figures.
- any user at any of the locations 1331, 1333, 1341, 1343, 1351 can utilize the coimnunications system shown to access and exchange infonnation with any other user in access networks 1301, 1303, 1305 or any other user coupled to Metro Network 1100 or to any user coupled to long haul network 1200.
- the system of the invention can use any idle channel as a coimnunications channel between any two users or nodes. This is identified as the random connection capability of the coimnunications system of the invention.
- optical reference signals originating at a reference laser source are utilized to provide for channel synchronization and to pe ⁇ nit a significant increase in the number of channels that are available for use in the system.
- an additional ring is provided for the distribution of reference optical signals from a reference laser source.
- the additional ring serves to distribute reference optical signals throughout the Metro Network 1 100 to all access networks 1301, 1303, 1305.
- the reference laser source is, in the illustrative embodiment, co-located with a system control unit 1360.
- the reference optical signals are distributed via a ring network 1370.
- the reference optical signals are coupled to each access network 1301, 1303, 1305 via an optical coupler 1371, 1373, 1375, respectively.
- each coupler 1371, 1373, 1375 is distributed to each optical network processor via an optical amplifier 1381, 1383, 1385.
- optical amplifier 1381, 1383, 1385 an optical amplifier
- the stmcture depicted in the illustrative embodiment of the invention is shown as a ring type distribution, the invention is equally applicable to other distribution stmctures such as, not by way of limitation but by way of example, star, mesh or point-to-point distribution arrangements.
- the distribution stmcture for the reference signals does not have to coirespond to the stmcture of the network.
- the reference laser source utilized in the illustrative embodiment includes a multiple wavelength laser. To assure adequate optical power levels are provided to each node coupled to the access networks 1301, 1303, 1305, a distribution network and power allocation arrangement is provided as shown in FIG. 2.
- System control unit 1360 has co-located therewith a reference laser source 1362.
- Optical reference signals from reference laser source 1362 are coupled to optical fiber ring 1370.
- Additional optical couplers 1372 are shown to indicate that additional access networks may also receive optical reference signals.
- optical amplifiers 1382 are employed to maintain a power level of +10dBm for each wavelength.
- the power level is a +0dBm.
- Optical amplifiers 1381 , 1383, 1385 raise the power level to +13dBm.
- each optical amplifier 1381, 1383, 1385 may be distributed at the access network level to one or more optical network processors, such as optical network processor 1335.
- Optical couplers, such as optical coupler 1384 provide this distribution.
- Optical coupler 1382 couples the output of amplifier 1381 to up to eight optical network processors, such as optical network processor 1335.
- the power level for each wavelength of the reference laser signal at the input to the optical network processor 1335 is maintained at +3dBm.
- a multiple wavelength laser is utilized as reference laser source 1362 to provide a reference optical signals for generation and assignment of optical channels that are dete ⁇ nined from selecting for each channel one wavelength of a plurality of optical wavelengths and one frequency of a plurality of optical modulation frequencies.
- the number of wavelengths that are obtainable from a multiple wavelength laser source is M wavelengths, where M is 32.
- the number of optical modulation frequencies is O, where O is 128.
- Each channel in the system of the illustrative embodiment has a bandwidth of 155 mbs. h other embodiments of the mvention higher or lower speed and bandwidths may be used.
- different numbers of channels, different numbers of wavelengths and different numbers of optical modulation frequencies may be utilized.
- FIG. 3 the functionality of multiplexing and switching channels identified by wavelength and frequency is illustrated.
- frequencies F, through F 0 are multiplexed by multiplexor/demultiplexors 201.
- the frequency-multiplexed wavelengths at the outputs of multiplexors 201 are multiplexed together at wavelength multiplexor/demultiplexor 203.
- the multiplexed optical output of multiplexor/demultiplexor 203 is coupled to optical network 1101.
- the multiplexor/ demultiplexer functions are changed to demultiplexing for received optical signals.
- the optical signals received over optical network 1101 are first wavelength demultiplexed by multiplexor/demultiplexor 203 to wavelengths ⁇ x through ⁇ M .
- FIG. 4 illustrates a system control unit 1360 in block diagram fonn.
- System control unit 1360 In block diagram fonn.
- Optical amplifer 1363 couples wavelength laser 1362 to laser reference ring network 1370.
- a network processing unit 1364 is provided to control and monitor operation of the supply of reference optical signals from multiple wavelength laser 1362 to the reference ring network 1370.
- a wavelength sensing circuit 1366 is coupled to the output of optical amplifier 1363.
- Optical amplifier 1363 provides sensing signals to network processing unit 1364 that pennit network processing unit 1364 to adjust the output level of optical amplifier 1363 and to control multiple wavelength laser 1362.
- Network processing unit 1364 is coupled to network 1100 via an optical network processor 1368, an optical amplifier 1369 and an optical add/drop 1367.
- Network processing unit 1364 receives requests for bandwidth and channel assignments from nodes coupled to the network 1101 and responds with the address of one or more allocated channels. The number of channels allocated to a node depends upon the bandwidth needed for handling the traffic.
- Network processing unit 1364 includes one or more processors and associated memory. The processor units may be commercially available processors. Memory associated with the processor unit or units may be any commercially available memory. Programs stored in memory are utilized to control the operation of network processing unit 1364.
- System control unit 1360 In processing requests for channel assigmnents is shown in FIG. 5.
- System control unit 1360 constantly identifies which channels have been allocated and which channels are idle.
- System control unit 1360 responds dynamically to requests for channels by selecting channels from the idle channels and allocating the channels as needed. When communication between users over a channel is complete, the channel is returned to the designated idle channel pool.
- system control unit 1360 selects an idle channel to achieve maximum isolation with used channels, i.e., the chamiel is selected to have the maximum separation from channels in use.
- the manner in which channels are selected may utilize a selection algoritlim or a weighting selection or other scheme for channel assigmnent.
- a system node that needs to transmit infonnation via the network 1100 transmits a request to system control unit 1360 as indicated at step 501, for a channel.
- the request also identifies the destination node or nodes.
- network processing unit 1364 selects a channel from the pool of idle available channels, as indicated at step 503.
- the chamiel address is assigned.
- the channel address is identified by wavelength and modulation frequency.
- network processing unit 1364 provides the designated channel identity to the transmitting node and to the receiving node.
- Network processing unit 1364 identifies the assigned channel as in use at step 507. Transmission and reception of information occurs at step 509.
- network processing unit 1364 Upon completion of transmission by transmitting node, network processing unit 1364 reclaims the channel and again assigns it to the pool of available channels at step 511. Communication of chamiel assignments to system nodes may be accomplished in any one of a number of conventional channel assigmnent methods. In the illustrative embodiment of the invention, communication of chamiel assignments to nodes from SCU 1360 and from node to SCU 1360 is accomplished by use of dedicated control and communication channels.
- FIG. 6 illustrates the operability of the multiplexing and switching provided in improved network of the invention.
- an optical fiber network such as network 1101 is illustrated as a ring.
- multiple wavelengths optical signals, ⁇ , through ⁇ M are multiplexed together and distributed via reference laser ring network 1370 to network nodes.
- Chart 602 indicates the wavelengths that are available on reference laser ring network 1370.
- a network node, identified as node 603 has requested that a channel be assigned.
- System control unit 1360 allocates a channel. The allocated channel includes wavelength ⁇ z
- a tuned optical wavelength filter 605 is utilized to select the wavelength ⁇ z assigned by the system control unit 1360.
- Filter 605 couples optical channel signals at the wavelengtli ⁇ z over the optical fiber network 1101.
- Chart 604 indicates that the output of the output of node 603 presented to network 1101 is a single wavelength.
- Other nodes likewise transmit different wavelength channels over the network 1 101 as indicated by the additional inputs to optical fiber network 1 101.
- Wavelength chart 606 illustrates that although each node may provide an optical signal at a single wavelength, optical fiber network 1 101 cairies multiple wavelengths.
- System control unit 1360 has infonned node 607 that it is assigned to receive communications from node 603 at wavelength ⁇ z
- a tunable optical wavelength filter 609 is adjusted to select wavelength ⁇ z and provide the signal to a detector 611 that is used to extract information cairied by the optical signals.
- Chart 608 indicates that the output of tunable optical wavelength filter 609 provides a single wavelength output.
- Tunable output wavelength filters 605, 609 may be of a design described in the literature. hi a second embodiment of the invention, advantageous use is made of the properties of optical signals to further enhance the channel capacity of optical communication systems.
- a phase modulated optical signal may be characterized in terms its wavelength ⁇ , its phase ⁇ , and its modulation frequency f.
- the second embodiment of the invention utilizes phase modulated and delayed optical signals and defines each optical chamiel by a wavelength multiplex, a phase delay or coherence multiplex and a frequency multiplex.
- the number of wavelength multiplexed is identified as "M”.
- the number of phase or coherence multiplexed channels is identified as "N”.
- Each chamiel has a bandwidth of 155 mbs.
- higher or lower speed and bandwidths may be used.
- different numbers of channels, different numbers of wavelengths and different numbers of optical modulation frequencies may be utilized.
- the architecture of the second embodiment of the invention is the same as shown FIGs. 1 and 2.
- the system control unit 1360 as shown in Fig. 4 and its operation as set forth with respect to FIG. 5 are substantially the same in the second embodiment.
- the system and method of the second embodiment of the invention utilize a phase multiplex/switch layer, a frequency multiplex/switch layer and a wavelength multiplex layer in addition to the wavelength multiplex/switch layer described in conjunction with FIG. 6.
- the phase multiplex/switch layer makes advantageous use of the fact that a single wavelength optical signal in optical fiber can cany multiple phases. At the transmission end phase separation is provided through delay of the channel with respect to the reference channel.
- phase- multiplexed channel By creating a phase delay that is larger than the coherence length of the laser, multiple phase channels can be multiplexed into a single wavelength. At the receive end, phase recovery is provided. By reversmg the phase delay and interfering with the reference signal, the phase- multiplexed channel can be separated and detected with an interferometer.
- FIG. 7 the manner in which interferometer technology may be utilized to provide phase multiplex/switching is illustrated.
- four phase channels are illustrated. It will be understood by those skilled in the art that the number of phase channels shown in FIG. 7 is merely illustrative and is not to in any way be considered as limiting.
- the transmit end is illustrated at 700 and the receive end is illustrated at 710.
- Interconnecting transmit end 700 and receive end 710 is the optical fiber network 1101.
- Light source 701 generates optical signals. Phase delays Dl, D2, D3, D4 are created as shown at 703 to produce four phase multiplexed data channels.
- the un-delayed optical signal 704 provides a reference that is shown as a shaded in pulse.
- the phase-delayed signals 702 are phase modulated at 705 to encode data onto the signals.
- the phase delayed optical signals appear on the optical network 1101 as shown at 707.
- a phase delay reversal is provided at 709.
- Interferometer techniques 711 are utilized to demodulate and decode the data that was transmitted via the optical signals.
- phase interferometer multiplex/switching portion signals are detected by phase amplitude based interferometer techniques, rather than by intensity based interferometer techniques, to get better sensitivity.
- phase amplitude based interferometer techniques rather than by intensity based interferometer techniques, to get better sensitivity.
- multiple channels are cairied in the same wavelength. Switching between phase channels is done electro-optically within less than 0.1 microsecond to allow for fast packet switching. Channel isolation is enhanced by selection of phase, wavelength and modulation frequency.
- FIG. 8 illustrates the frequency multiplex/switch layer implementation utilized in the invention, h the illustrative embodiment, O optical fiequencies, F, through F 0 , are utilized as earners.
- Modulators 801 produce modulated optical signals at the individual optical carrier frequencies, F, through F 0
- Combiner 803 combines the individual carrier frequencies onto the optical network 1100. As illustrated in spectral chart 804, combiner 803 combines all the carrier frequencies onto the network optical fiber 1101.
- a divider 805 separates the frequency components, Fj through F 0 Demodulators 807 demodulate the optical signals.
- FIG. 9 illustrates in block diagram fonn a modulator 801 and a demodulator 807.
- modulator 801 data 903 to be transmitted is combined in a mixer 905 with an IF signal produced by a RF source 901.
- the resulting RF signal is applied to an RF filter 906 and driver 907 that provides appropriate filtering and driver buffering.
- the particular configuration of RF filter 906 and driver 907 may be selected from any available configuration.
- the output of RF driver 907 is supplied to modulator 909 to modulate an optical signal fiom a light source 91 1.
- the optical signal fiom light so ce 911 is modulated by an RF signal at the modulation frequency coiresponding to the chamiel assigned for coimnunication to the node at which the modulator 801 is located.
- demodulator 807 receives optical signals.
- Demodulator 807 includes a detector circuit 913.
- Detector circuit 913 is set to detect optical signals at the channel frequency designated for coimnunication fi-om the node at which modulator 801 is located.
- the output of detector 913 is coupled to a RF driver filter 915.
- the output of the RF driver 915 is combined with an IF signal provided by RF source 917 in a mixer 919, filtered by filter 921 and provided as recovered data 923.
- the RF source providing the IF signals may be a voltage controlled oscillator.
- the IF signal is provided at the modulation frequency assigned to the particular channel.
- FIG. 10 the functionality of multiplexing and switching channels identified by wavelength, phase and fi-equency is illustrated.
- ⁇ i through ⁇ N of each wavelength, ⁇ , through ⁇ M , frequencies F, through F 0 , are multiplexed by multiplexor/demultiplexors 201.
- the fi-equency multiplexed signals for each of the phases at the outputs of multiplexors 201 are multiplexed together at phase multiplexor/demultiplexors 1021.
- the frequency and phase-multiplexed signals for each wavelength are applied to wavelength multiplexor/demultiplexor 203.
- the multiplexed optical output of multiplexor/demultiplexor 203 is coupled to optical network 1 101.
- the multiplexor/ demultiplexer functions are changed to demultiplexing for received optical signals.
- the optical signals received over optical network 1 101 are first wavelength demultiplexed by multiplexor/demultiplexor 203 to wavelengths ⁇ , through ⁇ M .
- a coiresponding phase multiplexor/demultiplexor 1021 demultiplexes phases and for each phase a multiplexor/demultiplexor 201 demultiplexes the frequencies F, through F 0 .
- Each multiplexor/demultiplexor is bi-directional in that it will switch or multiplex one or more signals into a single stream and that it will demultiplex or switch signals out of a combination stream.
- each channel Since each channel has a unique wavelength, phase and modulation fi-equency con-elation, it can be identified by a unique address that references its wavelength, phase and fi-equency.
- each channel For M wavelengths, N phases, and O modulation fiequencies each channel may be particularly identified by a channel identity in which the wavelength is assigned a number of from 1 to M, each phase is assigned a number of from 1 to N and each modulation fi-equency is assigned a number from 1 to O.
- the chaimel identity for each channel may be refeired to as z y f x ,where "z" is the wavelength number, "y” is the phase number and "x" is the fi-equency number. This chaimel identity is selected for convenience and clarity in description only and is not hi any way h t ended to limit the invention.
- FIGs. 11 and 12 illustrate the exchange of data between two network nodes as represented by optical network processors ONP#l and ONP#50.
- ONP#l request a channel allocation from system control unit 1360.
- System control unit 1360 selects a channel from the idle channels available and allocates the selected channel in response to the request.
- the channel is removed from the grouping of idle channels available.
- an exemplary idle channel identified as channel ⁇ 2 ⁇ g F 4 is selected for transmission of data fiom ONP#l to ONP#50, and the channel identification is provided to both the transmit and receive optical network processors ONP#l and ONP#50. As shown in FIG.
- ONP#l inserts data, D ⁇ X into the designated chamiel ⁇ 2 ⁇ g F 4 .
- ONP#50 receives the modulated signal and extracts the data D ⁇ from chaimel ⁇ 2 ⁇ g F 4 .
- system control unit 1360 Upon completion of the data transmission to ONP#50, system control unit 1360 returns the chaimel assignment of channel ⁇ 2 ⁇ 8 F 4 to the pool of unassigned or idle channels for reassignment.
- the node at which ONP#50 is located may request a channel assigmnent from system control unit 1360.
- System control unit 1360 assigns a channel fonn the pool of available idle channels. In this instance chamiel ⁇ 4 ⁇ 3 F 6 is assigned.
- ONP#50 transmits and ONP#l receives data in the assigned channel.
- the channel is reassigned by system control unit 1360 to the pool of idle channels.
- each network node includes an optical network processor ONP that includes a modulator and a demodulator as described above.
- Each ONP is coupled to the laser reference source 1362 via the laser reference network 1370 as shown in FIG. 1.
- Each ONP is coupled to the optical fiber network 1101 via an optical add/drop OAD and an optical amplifier EDFA.
- OPTICAL NETWORK PROCESSOR FIGs. 14 and 15 depict a transmitter portion and a receiver portion of an optical network processor particularly well adapted for use with the above described first embodiment of the invention.
- FIGs. 16 and 17 depict a transmitter portion and a receiver portion of an optical network processor particularly well adapted for use with the above described second embodiment of the invention.
- Each optical network processor includes a transmit function and a receive function.
- the receive function decodes data from a systems coimnunications chaimel assigned for coimnunications to a node coupled to the optical network processor to control the associated wavelength multiplex/switch, phase multiplex/switch and frequency multiplex/switch.
- the transmit function converts data from an associated node to an assigned system coimnunications channel by controlling the associated wavelength multiplex/switch; phase multiplex/switch and frequency multiplex/switch.
- FIG. 14 a transmitter portion of an optical network processor for use in a first embodiment of the invention is shown.
- Transmitter portion 1400 of an optical network processor includes one or more processors or micro controllers 1401 that provides program control of operation of the optical network processor. For clarity only one processor is shown for each optical network processor, but more than one processor may be used. Transmitter portion 1400 is coupled to laser reference network 1370 and receives signals fi-om the multiple wavelength signals from laser reference source 1360. A polarization controller 1403 under control of micro controller 1401 selects polarization of the received laser signals. The output of polarization controller 1403 is coupled to tunable filter 1407. In an altemate embodiment of the invention, a depolarizer replaces polarization controller 1403.
- Micro controller 1401 receives chamiel allocation info ⁇ nation and utilizes the channels allocation infoirnation to select a wavelength and frequency for its associated node to transmit data.
- Micro controller 1401 via wavelength tuning module 1405 operates tunable filter 1407.
- Wavelength tuning module 1405 selects a wavelength in response to micro controller 1401 providing a wavelength select signal.
- Tunable filler 1407 is tuned to the selected wavelength.
- Tunable filter 1407 thereby selects the wavelength optical signal for transmitting data under control of micro controller 1401.
- the output of tunable filter 1407 is coupled to a Mach-Zehnder interferometer 1413.
- Interferometer 1413 includes two legs coupled at the input to a coupler 1409 and at the output by coupler 1419.
- a first leg includes dc bias module 1412 and a phase modulator 1416.
- a second leg includes dc bias module 1414 and a phase modulator 1418.
- Micro controller 1401 provides quadrature control of interferometer 1413 via bias control module 141 1. Quadrature control ensures stable linear operation of the interferometer 1413.
- Frequency selection is provided via micro controller 1401 controlling voltage-controlled oscillator 1415 that in tum provides a selected modulation frequency to mixer/driver module 1417.
- Mixer/driver module 1417 mixes the modulation frequency output of voltage-controlled oscillator 1415 with Transmit data D ⁇ x .
- the outputs of interferometer 1413 are provided to tunable filter 1421which is tuned by wavelength tuning module 1405 to the wavelength selected by micro confroller 1401.
- the output of tunable filter 1421 is coupled to network 1101.
- coupler 1419 has an output coupled to photo detector 1423.
- the output of photo detector 1423 is coupled to micro controller 1401.
- FIG. 15 depicts optical network processor receive portion 1500.
- Receive portion 1500 of an optical network processor includes a processor or micro controller 1501 that provides program control of operation of the optical network processor.
- Receive portion 1500 is coupled to network 1101 and receives signals fi-om another network node.
- Micro confroller 1501 receives channel assigmnent information from SCU 1360 and utilizes the channel assigmnent to select the wavelength and fi-equency of a channel carrying data for its associated node.
- a polarization controller 1503 under control of micro controller 1501 selects polarization of the received laser signals.
- a depolarizer replaces polarization controller 1503.
- the output of polarization controller 1503 is coupled to tunable filter 1507.
- Micro controller 1501 via wavelength tuning module 1505 operates tunable filter 1507.
- Wavelength tuning module 1505 selects a wavelength in response to micro controller 1501 providing a wavelength select signal.
- Tunable filter 1507 selects the wavelength of a receive chamiel under control of micro controller 1501.
- a coupler 1509 couples the output of tunable filter 1507 to a Mach-Zehnder Interferometer 1513.
- Interferometer 1513 includes two legs. A first leg includes dc bias module 1512 and a phase modulator 1516. A second leg includes dc bias module 1514 and a phase modulator 1518.
- Interferometer 1513 is not used as an interferometer in the receiver. Only the dc bias modules 1512 and 1514 are used in the receive function.
- Phase modulators 1516, 1518 are left unused in this receiver implementation.
- Micro controller 1501 provides quadrature control via bias control module 1511. Frequency selection is provided via micro controller 1501 controlling voltage-controlled oscillator 1515 that in tum provides a selected frequency to mixer/driver module 1517.
- the outputs of interferometer 1513 are applied to coupler 1519.
- the output of coupler 1519 is in tum applied to tunable filter 1521 which is controlled by micro controller 1501 via wavelength tuning module 1505.
- the wavelength-selected output of tunable filter 1521 is in tum applied to detector 1523.
- Detector 1523 provides a quadrature dc output, which is provided to micro controller 1501 for use in controlling bias control circuit 1511.
- An RF output of detector 1523 is provided to amplifier 1525.
- Output of amplifier 1525 is coupled to a second input of mixer/driver 1517.
- An output of mixer/driver 1517 is applied to low pass filter 1529.
- the output of low pass filter 1529 provides data output signals are provided to a network node such as user 1331.
- the design of the optical network processor receive portion and transmit portion share similar basic design components in the implementations shown.
- the transmit portion and receive portions in one embodiment are implemented on two separate chips for full duplex operation.
- a bi-directional, half-duplex design combines both transmit and receive portions in a single integrated optic chip using reflective design.
- Advantages of the second embodiment are that the length of the integrated optic chip is shortened by Vr, cost is reduced; and transmit and receive portions are combined into one design.
- perfonnance of the wavelength filter is greatly enhanced for double pass operation. Sidelobe suppression of 15dB for one pass through the filter increases to 30dB with double pass operation. Still further, the drive voltage of the modulator is reduced 50%.
- a further significant advantage is that integration onto a single chip allows creation of a large sized phase detector.
- FIG. 16 depicts a transceiver 1600 in which a single integrated optic chip 1670 is utilized advantageously.
- Transceiver 1600 is coupled to network 1101 via a circulator 1604.
- Transceiver 1600 is also coupled to laser reference ring 1370 via circulator 1604 and an isolator 1602 interposed in reference laser ring 1370.
- Circulator 1604 is coupled to integrated optic chip 1670 via a polarization controller or scrambler 1603.
- Integrated optic chip 1670 includes a TM polarizer 1651 coupled to a tunable filter 1652.
- Micro confroller 1601 receives transmit and receive channel assignment ii foimation from system control unit 1360 and utilizes the channel assigmnent information to select wavelengths and fi-equencies for transmit or receive functions.
- Micro controller 1601 via a wavelength-tuning module 1605, controls tunable filter 1652.
- a TE polarizer 1653 follows tunable filter 1652 to remove unwanted signals.
- a 2 x 2 coupler 1654 is disposed between TE polarizer 1653 and interferometer 1613,
- Interferometer 1613 includes optical bias modulators 1612, 1614.
- Phase modulators 1616, 1618 follow optical bias modulators 1612, 1614.
- Reflection miirors 1662,1660 are provided on the end of integrated optic chip 1670.
- the operation of the various circuit elements shown hi Fig. 16 is substantially identical to the operation of the elements in FIG. 14 for receive operation and to the elements in FIG. 15 for receive operation. There is a one to one conespondence to the elements of FIGs., 14, 15, and 16 and the operation is identical, except that the interferometer 1613 is foimed as a reflection type interferometer.
- FIG. 17 depicts a transmitter portion 1700 of an optical network processor for use in the above-described second embodiment of the invention.
- Transmitter portion 1700 includes a processor or micro controller 1701 that provides program confrol of operation of fransmitter portion 1700.
- Micro controller 1701 receives channel assignment infoimation fi-om system control unit 1360 and utilizes that infoimation to select wavelength, phase and fi-equency of assigned channels.
- Transmitter portion 1700 is coupled to laser reference network 1370 and receives multiple wavelength signals from laser reference source 1360.
- a polarization controller 1703 under control of micro controller 1701 selects polarization of the reference laser signals.
- the output of polarization confroller 1703 is coupled to tunable filter 1707.
- Micro confroller 1701 via wavelength tuning module 1705 controls tunable filter 1707.
- Wavelength tuning module 1705 selects a wavelength in response to micro confroller 1701 providing a wavelength select signal.
- Tunable filter 1707 selects the wavelength optical signal for transmitting data under control of micro confroller 1701.
- a coupler 1709 couples the output of tunable filter 1707 to phase selector for selecting one out of "N" phases.
- the phase selector includes a 1 x n switch 1771 that is confrolled by micro controller 1701. Each of the N outputs of switch 1771 is coupled to a corresponding phase modulator 1775.
- Micro controller 1701 controlling a voltage-controlled oscillator 1715 provides frequency selection.
- the selected fi-equency output of voltage controlled oscillator 1715 is combined with data to be transmitted D ⁇ x by mixer/driver 1717.
- the data D ⁇ x to be transmitted is received from a user node 1331.
- a filter/switch module 1770 under control of micro controller 1701 provides the output of mixer/driver 1717 to the N phase modulators 1775.
- Each phase modulator 1775 is coupled to a phase delay module 1777.
- the outputs of the phase delay modules are the N phases 1 through N Switch 1779 under control of micro confroller 1701 selects the output phase.
- the output of switch 1779 and the wavelength-selected reference are combined in coupler 1 19 and filtered by tunable wavelength filter 1721.
- Micro controller 1701 via wavelength tuning module 1705, controls tunable filter 1721.
- the output of filter 1721 is the wavelength/fiequency/phase selected optical signals modulated with transmit data and is coupled to optical network 1101. A portion of the output is coupled to a detector 1723 that provides a dc feedback signal to micro controller 1701.
- FIG. 18 depicts optical network processor receive portion 1800 for the above described second embodiment.
- Receive portion 1800 includes a processor or micro confroller 1801 that provides program controlled operation of optical network processor receive portion.
- micro confroller 1801 receives channel assigmnent infoimation fi-om system confrol unit 1360 and utilizes that infoimation to select channel wavelength, phase and frequency to select a desired chamiel for recovery of received data.
- the received data is provided to a node 1331.
- Micro controller 1801 generates wavelength select, phase select and fi-equency select signals.
- the frequency select signals control a voltage-controlled oscillator 1815 to provide a frequency-selected signal to a mixer/ driver circuit 1817.
- the output of mixer/driver 1817 is filtered by filter 1840 to provide output data signals D ⁇ x .
- Receive portion 1800 is coupled to network 1 101 and receives optical signals cany ing data D rx from another node coupled to network 1101.
- a depolarizer 1803 depolarizes the optical signals received via network 1101.
- depolarizer 1803 may be replaced with a polarization confroller controlled by micro controller 1801.
- the output of depolarizer 1803 is coupled to tunable filter 1807.
- Micro controller 1801 via wavelength tuning module 1805 operates tunable filter 1807.
- Wavelength tuning module 1805 selects a wavelength in response to micro controller 1801 and tunes filter 1807 to the selected wavelength.
- Phase selection is accomplished by micro controller 1801 providing phase select signals to control switches 1871 and 1879.
- Switches 1871 and 1879 are used to select one phase delay path from a group of "n" phase delay, where "n” is the number of selectable phases.
- Each phase delay path includes a phase modulator 1875 and a phase delay circuit 1877.
- Micro confroller 1871 via bias confrol 1811 controls phase modulators 1875.
- the output of the selected phase path is coupled via switch 1879 to coupler 1819.
- a phase reference signal is coupled fiom signals received from network 1101 from coupler 1871 to coupler 1919 via optical coimection 1873.
- Coupler 1819 combines the phase reference signal from connection 1873 with the output of phase switch 1879.
- the combined output is applied to wavelength filter 1821 that is tuned to the wavelength selected by micro controller 1801.
- the output of tunable filter 1821 is coupled to detector 1823 that separates an RF signal and a dc servo feedback signal.
- the RF signal is applied to mixer/driver 1817 via pre amplifier 1880. All of the components shown within box 1881 may be fabricated on a single integrated optic chip using reflective design.
- FIG. 19 is a block diagram of a transceiver 1900 in which economies are achieved by utilizing the commonality of receive and transmit portions, 1800, 1700.
- Transceiver 1900 receives data D ⁇ x from a node 1331 and provides data D RX to a node 1331.
- Transceiver 1900 is coupled to optical network 1101 and reference network 1370 by circulator 1940.
- a micro controller 1901 provides program controlled operation of transmit and receive functions.
- micro confroller 1901 provides wavelength, phase and frequency selection to select a desired channel for recoveiy of received data and providing the received data to a node 1331 and for receipt of transmit data from node 1331 for transmission over network 1101.
- Micro controller 1901 generates wavelength select, phase select and frequency select signals for transmit and receive.
- the frequency select signals control a voltage-controlled oscillator 1915a to provide a fi-equency-s elected signal to a mixer/driver circuit 1917a.
- the output of lnixer/driver circuit 1917a is filtered by low pass filter 1940 to provide output data signals D ⁇ .
- Frequency select signals from imcro controller 1901 are used for transmission of data fi-om a node 1331 over network 1101.
- Frequency select signals control voltage controlled oscillator 1915 to select a desired transmit chaimel frequency.
- a mixer/driver 1917 combines the output of voltage-controlled oscillator 1915 and D ⁇ x .
- the modulated frequency signals are applied to filter switch 1970.
- Micro controller 1901 also controls phase and wavelengtli selections. Phase selection is provide by micro controller 1910 providing phase selection signals to a phase control module 1972, bias control signals to bias control circuit 1911 and filter control signals to filter switch 1970. For transmit data, filter switch 1970 is active but bias control 1911 is not.
- Integrated optical chip assembly 1981 provides wavelength selection and phase multiplex selections. Integrated optical chip assembly 1981 utilizes reflective multiplex technology.
- Double pass operation of the integrated optical chip assembly 1981 greatly enhances perfoimance of the wavelength filter operation. Sidelobe suppression is increased, for example, from 15 dB to 30 dB.
- Input signals received from network 1101 via circulator 1940 are applied to depolarizer 1903.
- Outputs of depolarizer 1903 are applied to a TE polarizer 1982.
- Polarizer 1982 is coupled to tunable wavelength filter 1983.
- Tunable f ⁇ lter 1983 is coupled to TM polarizer 1984.
- TM polarizer 1984 is coupled to a phase selection circuit including 2x2 coupler 1909, a 1 x 4 optical switch 1985, bias modulator arcay 1986, phase modulator airay 1987 and phase delay and recovery reflection mirror 1988. In the embodiment shown, selection of four phase channels may be accomplished.
- phase selection circuit may be expanded to more phase channels, but for memeposes of drawing clarity, only a four-phase chamiel selection stmcture is shown.
- micro controller 1901 provides wavelength selection signals to wavelength tuning module 1905.
- Wavelength tuning module 1905 controls tunable filter 1983 to select the wavelength channel for transmit and receive.
- micro controller 1901 controls filter switch 1970 to confrol the phase modulator anay 1987.
- micro controller 1901 controls bias control 1911 to in tum control bias modulator airay 1986.
- filter switch 1970 is used to select a phase and couple the output of mixer/driver 1917 via coupler 1909 through polarizer 1983, wavelength filter 1983, polarizer 1982 to depolarizer 1903 and to network 1101 via circulator 1940.
- optical signals received from network 1101 are coupled via circulator 1940 through depolarizer 1903 to polarizer 1982, tunable filter 1983, polarizer 1984 to the phase selector.
- Bias control module 1911 under control of micro controller 1901 sets the bias to a quadrature point to stabilize the receive phase channel.
- phase selector The output of the phase selector is coupled to detector 1923.
- Detector 1923 provides an RF output to preamplifier 1980.
- Preamplifier 1980 is coupled to mixer/driver 1917, and its output is filtered by low pass filter 1940 to provide output data to node 1331.
- Each laser source may be assembled together to provide a laser reference source useable in the optical networks and optical coimnunication system of the invention.
- Various laser sources may be employed; however, each laser source must have specific characteristics.
- multiple wavelength lasers that have high launch power are desirable.
- the reference provides optical signals for each wavelength channel at levels greater than 10 mw for each wavelength channel.
- Each laser source should desirably meet this requirement. It is also desirable that nonlinear effects such as self phase modulation (SPM), stimulated Brillion scattering (SBS) and four wave mixing be minimized.
- SPM self phase modulation
- SBS stimulated Brillion scattering
- a short coherence length of less than 5mm should be provided for phase multiplex/switching operation.
- wavelength stability is to be controlled within 20 Pico meters. It is desirable that spurious spectral components be minimized between wavelength channels.
- 16 to 32 wavelengths are provided by the reference laser source. The source must be depolarized to remove polarization- wandering effects.
- Embodiments are shown and described that utilize distributed feedback lasers and Erbium Doped Fiber Lasers. High launch power, short coherence length, mmimized SBS/SPM effects and non-linear effects are avoided by the use of Erbium Doped Fiber Lasers (EDFL).
- EDFL Erbium Doped Fiber Lasers
- Spectral width broadening is achieved by phase modulating the nairow line width distributed feedback (DFB) lasers with high fi-equency radio frequencies.
- Stable wavelengths are achieved by active wavelength measurement and control.
- High spectral purity is obtained by use of fiber gratings to remove noise between wavelength channels. At least up to 32 wavelength channels can be implemented in each embodiment.
- DWDM multiplexing is utilized. DWDM multiplexing provides a low loss multiplexing. Fiber coupler arrays can provide the same functionality but with higher loss.
- FIG. 20 depicts one embodiment of a multiple wavelength reference laser source in which multiple distributed feedback (DFB) lasers are used.
- a plurality of DFB lasers 2001 is utilized.
- a separate DFB laser 2001 is used to generate each wavelength i through M .
- DFB lasers There are two limitations on DFB lasers that need to be accoimnodated.
- the output of each DFB laser 2001 typically has a nairow linewidth of less than 50 MHz. This spectral width shown as spike 2002 is too nairow for use in the embodiments of the invention described above.
- the coherence length of each DFB laser 2001 output is too large for application in the embodiments of the present invention.
- Phase modulating the output of each DFB laser 2001 with an RF signal broadens the spectral width of the output and further can reduce the coherence length. In other words, for optimum performance, the laser signals cannot be too coherent and cam ot have too nairow a line width in the above-described embodiments.
- a plurality of phase modulators 2003 is provided. Each phase modulator 2003 is coupled to a coiresponding one of the DFB lasers 2001. Modulation is with an RF signal having multiple frequency components that are selected in the RF range of a veiy low frequency to an upper frequency of 20 GHz. In the embodiment shown, the range is 0.01 to 20.0 GHz.
- Modulation with a multiple component RF signal produces a laser signal having a broad linewidth output of greater than 20 GHz as illustrated by waveform 2004.
- the phase modulation reduces the coherence length.
- the phase modulators produce polarization rotation to depolarize the signals.
- a plurality of fiber gratings 2005 shapes the output spectrum and coherence. More specifically fiber gratings 2005 are utilized to remove the side lobes of the output wavefoims of phase modulators 2003.
- Each modulated DFB laser 2001 output is filtered to remove side lobes by a coiresponding one of the fiber gratings 2005 to shape the modulated laser output spectrum.
- a DWDM multiplexer 2007 is utilized to combine the outputs of each of the DFB lasers 2001.
- the combined output of DWDM multiplexor 2007 is shown as wavefo n 2006.
- An amplifier 2009 is coupled to the output of the DWDM multiplexor and amplifies the multiple wavelength laser output to produce an amplified output shown as wavefonn 2008.
- Amplifier 2009 is an erbium doped fiber amplifier, EDFA.
- FIG. 21 illustrates an altemate embodiment of a Multiple Wavelength Laser.
- the multiple wavelength laser source of FIG. 20 is modified.
- a plurality of DFB lasers 2001 is utilized.
- a separate DFB laser 2001 is used to generate each wavelength , through M .
- each DFB laser 2001 output is too large for application in the embodiments of the present invention.
- phase modulating the output of each DFB laser 2001 with an RF signal broadens the spectral width of the output and further can reduce the coherence length.
- a plurality of phase modulators 2003 is provided. Each phase modulator 2003 is coupled to a coiresponding one of the DFB lasers 2001. Modulation is with an RF signal having multiple frequency components that are selected in the RF range of 0.01 to 20.0 GHz. Modulation with a multiple component RF signal produces a laser signal having a broad linewidth output of greater than 20 GHz as illustrated by waveform 2004.
- phase modulated laser signals at the different wavelengths are each amplified by one of a plurality of EDFA amplifiers 2101 to produce amplified wavefonns 2010 prior to being shaped by fiber gratmgs 2005.
- Each EDFA 2101 is coupled to the output of a coiresponding one of the phase modulators 2003.
- FIG. 22 illustrates a third embodiment of a multiple wavelength laser source that may be used in accordance with the invention.
- a plurality of separate Erbium Doped Fiber Lasers (EDFL) 2201 are used as sources.
- Each EDFL 2201 is designed to have appropriate spectral width and coherence function with a coherence length of less than 5 l n.
- Each EDFL 2201 provides an output at one of a plurality, m, of wavelengths , - m . Wavelength control technology is used with each EDFL 2201 to control emission wavelength.
- Each EDFL 2201 provides a single wavelength output.
- a plurality of fiber gratings 2203 are used to provide output spectrum shaping and coherence function. Each grating 2203 is selected to confonn to one of the wavelengths ,, 2 ,- m .
- a plurality of EDFAs 2205 are coupled to the outputs of gratings 2203, with a one to one coirespondence between each EDFA 2205 and a coiresponding one grating 2203.
- Each EDFA 2205 amplifies a coiresponding grating 2203 output ,, 2 ,- , constructive.
- a DWDM multiplexer 2207 is used to combine the outputs ,, 2 ,- m to produce a multiple wavelength laser output 2211 that contains all the wavelengths , - m .
- phase modulation is not necerney because each EDFL has a broad lme width and the coherence length is not too short.
- fiber gratings 2203 Through selection of appropriate fiber gratings 2203 the desired spectral response is achieved.
- FIG. 23 An alternative EDFL based design for the multiple wavelength laser reference is illustrated in FIG. 23.
- a single EDFA amplifier 2301 is utilized to amplify the combined output.
- a filter 2303 is used to shape the amplified multiplexed output.
- a plurality of separate Erbium Doped Fiber Lasers (EDFL) 2201 are used as sources.
- Each EDFL 2201 is designed to have appropriate spectral width and coherence function with a coherence length of less than 5 mm.
- Each EDFL 2201 provides an output at one of a plurality, m, of wavelengths , - m .
- Wavelength control technology is used with each EDFL 2201 to control emission wavelength.
- Each EDFL 2201 provides a single wavelength output.
- a plurality of fiber gratings 2203 are used to provide output spectrum shaping and coherence function. Each grating 2203 is selected to conform to one of the wavelengths ,, 2 ,- m .
- a DWDM multiplexer 2207 is used to combine the outputs ,, 2 ,- m to produce a multiple wavelength laser output 2211 that contains all the wavelengths , - m .
- An EDFA 2301 is coupled to the outputs of DWDM multiplexer 2207 and amplifies the combined output having all wavelength components ,, 2 ,- m .
- FIGs. 24 and 25 illustrate EDFLs suitable for application to the laser reference sources depicted in FIGs. 22 and 23.
- an erbium-doped fiber 2401 is pumped fi-om a laser pump source 2407 through a WDM 2409.
- Each erbium-doped fiber 2401 is coupled at either end to a fiber grating.
- both gratings 2403 and 2405 are reflecting nairow-band gratings at the same wavelength.
- 25 nairow-band fiber grating 2403 is replaced with a broadband reflecting grating 2501 or alternatively, a mirror.
- WDM 2409 couples the pump source 2407 output to fiber grating 2405.
- An isolator 241 1 is used at the output of the EDFL
- FIG. 26 depicts an optical add/drop 1307 that is utilized to particular advantage in the embodiments of the invention described above.
- FIG. 26 also shows further details of a typical EDFA construction, such as EDFA 1313.
- the design shown is for a reciprocal optical add/drop inserted into optical link network 1101.
- Optical add/drop 1307 utilizes three couplers 2603, 2605, 2607 and two isolators 2609, 2611 all of which are known in the art and are commercially available.
- Optical add/drop 1307 includes a first bi-directional port PI, a second bi-directional port P2 and a third bi-directional port P3.
- Bi-directional ports PI and P2 are connected to optical link network 1101 and bi-directional port P3 is coupled to an optical network processor or coupler via bi-directional amplifier 1313.
- Drop signals from optical link network 1101 are coupled from coupler 2605 to coupler 2607 and to isolator 2611.
- Isolator 2611 couples the optical signals to amplifier 1313.
- Add signals fi-om amplifier 1313 are supplied to isolator 2609. From isolator 2609, the transmit signals are supplied to coupler 2607 which in tum is connected to coupler 2603 and from coupler 2603 to optical link network 1101. A through path couples the couplers 2603 and 2605. Coupler 2607 is utilized to permit the bidirectional drop and add of optical signals.
- Coupler 2607 is chosen such that 50% of the signal is coupled from one path to the other.
- Isolators 2609, 2611 are used to provide directionality for the add and drop paths to the ONP or coupler.
- Amplifier 1331 comprises an EDFA 1313a for amplifying input signals and an EDFA 1313b for amplifying output signals.
- a circulator 1313c having three ports cl, c2, c3 is used to couple both EDFAs 1313a, 1313b to the optical network processor or coupler.
- Drop signals fiom PI are extracted via coupler 2603 and are coupled via coupler 2607 to isolator 2611, amplified by EDFA 1313b, applied to circulator 1313c at its port c2 and extracted from circulator at port c3 which is connected to an optical network processor at port P3.
- Optical signals at port P2 are coupled by coupler 2605 to coupler 2607 and processed as described above.
- Optical signals received at port P3 are provided by circulator 1313c to EDFA 1313and applied to isolator 2609. The output in this add path is applied to coupler 2607 provides 50% of the add signal to each of couplers 2603, 2605.
- the optical add/drop in this embodiment may be characterized as a reciprocal add/drop.
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Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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AU2001264542A AU2001264542A1 (en) | 2000-02-23 | 2001-02-22 | Edfl multiple wavelength laser source |
Applications Claiming Priority (18)
Application Number | Priority Date | Filing Date | Title |
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US51069300A | 2000-02-23 | 2000-02-23 | |
US51156000A | 2000-02-23 | 2000-02-23 | |
US09/511,053 | 2000-02-23 | ||
US09/510,685 | 2000-02-23 | ||
US09/511,053 US6583901B1 (en) | 2000-02-23 | 2000-02-23 | Optical communications system with dynamic channel allocation |
US09/510,693 | 2000-02-23 | ||
US09/511,560 | 2000-02-23 | ||
US09/510,685 US6587239B1 (en) | 2000-02-23 | 2000-02-23 | Optical fiber network having increased channel capacity |
US64448800A | 2000-08-23 | 2000-08-23 | |
US64392600A | 2000-08-23 | 2000-08-23 | |
US64447500A | 2000-08-23 | 2000-08-23 | |
US64443300A | 2000-08-23 | 2000-08-23 | |
US09/644,475 | 2000-08-23 | ||
US09/644,433 | 2000-08-23 | ||
US09/644,488 | 2000-08-23 | ||
US09/643,926 | 2000-08-23 | ||
US09/777,175 US20010015837A1 (en) | 2000-02-23 | 2001-02-05 | EDFL multiple wavelelngth laser source |
US09/777,175 | 2001-02-05 |
Publications (2)
Publication Number | Publication Date |
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WO2001063705A1 true WO2001063705A1 (en) | 2001-08-30 |
WO2001063705A8 WO2001063705A8 (en) | 2001-11-29 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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PCT/US2001/003686 WO2001063705A1 (en) | 2000-02-23 | 2001-02-22 | Edfl multiple wavelength laser source |
Country Status (1)
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WO (1) | WO2001063705A1 (en) |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5550666A (en) * | 1994-06-17 | 1996-08-27 | Lucent Technologies Inc. | Wavelength division multiplexed multi-frequency optical source and broadband incoherent optical source |
US5576881A (en) * | 1995-08-29 | 1996-11-19 | Lucent Technologies Inc. | Multi-frequency optical signal source having reduced distortion and crosstalk |
US6055250A (en) * | 1997-11-07 | 2000-04-25 | Lucent Technologies Inc. | Multifrequency laser having reduced wave mixing |
-
2001
- 2001-02-22 WO PCT/US2001/003686 patent/WO2001063705A1/en active Application Filing
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5550666A (en) * | 1994-06-17 | 1996-08-27 | Lucent Technologies Inc. | Wavelength division multiplexed multi-frequency optical source and broadband incoherent optical source |
US5576881A (en) * | 1995-08-29 | 1996-11-19 | Lucent Technologies Inc. | Multi-frequency optical signal source having reduced distortion and crosstalk |
US6055250A (en) * | 1997-11-07 | 2000-04-25 | Lucent Technologies Inc. | Multifrequency laser having reduced wave mixing |
Also Published As
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WO2001063705A8 (en) | 2001-11-29 |
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