WO2002071658A1 - Source optique agile pouvant etre reglee precisement en longueur d'onde - Google Patents

Source optique agile pouvant etre reglee precisement en longueur d'onde Download PDF

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Publication number
WO2002071658A1
WO2002071658A1 PCT/CA2002/000305 CA0200305W WO02071658A1 WO 2002071658 A1 WO2002071658 A1 WO 2002071658A1 CA 0200305 W CA0200305 W CA 0200305W WO 02071658 A1 WO02071658 A1 WO 02071658A1
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WO
WIPO (PCT)
Prior art keywords
laser
wavelength
optical
frequency
during
Prior art date
Application number
PCT/CA2002/000305
Other languages
English (en)
Inventor
Cedric Don-Carolis
Peter Mcilroy
Edward Ryszard Sokolowski
Original Assignee
Cedric Don-Carolis
Peter Mcilroy
Edward Ryszard Sokolowski
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Cedric Don-Carolis, Peter Mcilroy, Edward Ryszard Sokolowski filed Critical Cedric Don-Carolis
Publication of WO2002071658A1 publication Critical patent/WO2002071658A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/572—Wavelength control
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/03—Arrangements for fault recovery
    • H04B10/032—Arrangements for fault recovery using working and protection systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/08—Time-division multiplex systems

Definitions

  • This invention relates generally to telecommunications networks that have a plurality of nodes interconnected by an optical transmission medium that require the use of such rapidly tuned optical sources to provide data units, frames or packets, such as in optically bursted asynchronous or synchronous wavelength system, where each data unit can be of arbitrary frequency within a set of operational frequencies, for a configurable duration.
  • optical burst data unit (OBDU) is defined,herein as an end-to-end optical channel, or circuit of the same optical frequency from source to destination across an optical network.
  • wavelengths may change frequency in optical telecommunications through wavelength translation to make longer distance connections and/or to avoid wavelength blocking at intermediate nodes.
  • OBDU Optical Burst Data Unit
  • the cyclically repeated transmission of a burst in its appropriate timeslot and wavelength is the basis for a communication channel having a fixed data rate.
  • This communication channel is referred to herein as a ' Waveslot'.
  • the agile action of the transmitter in changing its transmission wavelength from timeslot to timeslot is referred to herein as 'Wavelength Hopping'.
  • Tuning rate is not the only requirement on the laser source devices however. It is necessary to ensure the optical frequency is precisely on the target frequency; typically the ITU optical grid. In general, the lasers can not be set to the grid points with sufficient accuracy over their operating life and conditions using 'open loop' control.
  • Wavelength lockers constructed of detectors and wavelength sensitive optical elements, such as Fabry- Perot etalons, are used to provide feedback signals to ensure the laser output is precisely aligned to the grid. These lockers require sufficient signal, and finite locking times, to operate. While some tunable laser technologies can change from one optical frequency to another in a few nanoseconds the lockers generally require substantially more than 1 microsecond to pull the laser precisely 'on-grid'.
  • Fast optical switching systems may require that transitions from one well-defined optical frequency to another, can be achieved in much less than one microsecond.
  • Limited frequency tuning range also presents a problem, as not all lasers can tune over the full optical bands of interest.
  • This invention provides a method for improving the accuracy for rapidly switched wavelength applications while enabling full range tuning.
  • Such laser sources are useful in optical transmission systems which use dynamic wavelength allocation. Examples are optically packet switched networks, optical MPLS networks, or high speed re-routing in circuit switched systems, or in optically bursted asynchronous or synchronous wavelength systems.
  • An aspect of the present invention is to provide an agile transmitter architecture that provides rapid wavelength tuning for applications where the optical data (the OBDU) is transmitted as in optical asynchronous or synchronous burst mode across different wavelengths using wavelength agile transmitters, of the like herein, to allow all-optical switching of the channels between different signal paths in the optical switch nodes, and time slot by time slot basis using WDM to reduce the probability of blocked connections.
  • Each OBDU has a unique timeslot, and wavelength properties. The cyclically repeated transmission of a burst in its appropriate timeslot and wavelength is the basis for a communication channel having a fixed data rate. This communication channel is referred to herein as an 'OBDU'.
  • Two approaches are discussed: one for cases when the laser cannot be tuned within an allowed switching time, and one which applies when the laser can be tuned sufficiently quickly but requires on-going stabilization.
  • the second approach may be used to improve the performance of the first approach.
  • the first approach in which a single laser cannot tune accurately within the required time, makes use of multiple lasers implemented with an appropriately fast optical switch to select the desired laser, each laser being tuned and locked on the frequency required for the packet it will address during the time the other is (or others are) transmitting.
  • the implementation improves the initial spectral quality and frequency accuracy on switching to a new frequency through: -setting the initial frequency as determined by a set of parameters based on nominal settings in firmware that have been established for the particular laser source type - such as center wavelength, wavelength spacing, wavelength range, wavelength line width (narrow, wide, coarse etc) , wavelength stability, wavelength aging margin etc in a table, - monitoring and adjusting the output quality during the data transmission, -updating the table parameters based on the changes necessary to improve the signal.
  • the second approach is particularly appropriate for rapid cyclical requirements for a particular wavelength, as the conditions for any wavelength may be nominally unchanged from cycle to cycle. If the tunable lasers cover only a fraction of the desired optical band, multiple lasers may be operated in paralleled to provide full coverage of the wavelength band, and combined with a fast optical switch, while being controlled with either of the two control approaches.
  • This invention also applies to the use of such rapidly tuned optical sources to provide data units, frames or packets where each data unit can be of arbitrary frequency within a set of operational frequencies.
  • An aspect of the invention is a mechanism to provide full coverage of an optical spectrum by an agile transmitter unit even in cases where the individual tunable laser sources available cannot cover the entire range of frequencies required. This is achieved in the invention by employing multiple lasers, each covering part of the optical spectrum, can be combined to achieve full coverage of the optical spectrum.
  • Another aspect of the invention is to provide a "hitless" agile transmitter architecture, whereby intermediate frequencies do not disrupt, referred to a “hit” herein, data traffic on these intermediate frequencies on the transmission medium or communications network to which the agile transmitter unit is attached.
  • Another further aspect of the invention is to provide an "isolatable" transmitter architecture, whereby upon failure or errant transmission of frequencies, the agile transmitter unit can be isolated from the transmission medium or communications network to which it is attached.
  • FIG. 1 is a block diagram of an example implementation of the wavelength agile transmitter and data output format according to the present invention.
  • Figure 2 is a block diagram of an example implementation of an efficient multiplexing method for the wavelength agile transmitter.
  • a key aspect of one form of this invention is the use of more than one laser source to cover a given region of the optical spectrum, where the format of the wavelength switching allows the laser sources to be used in sequence.
  • the application will involve packet-like transmission, and the output will be a modulated emission at a stable optical frequency for a period of time, followed by a rapid transition to a modulated output at a different optical frequency (though it could be the same frequency) for a period of time, etc. If the tuning plus locking time to frequency for a laser source is longer than the transition time, but comparable to, while ideally less than, the packet time, then installing multiple sources is useful.
  • the optical switch can be a lithium Niobate (LiNbO 3 ) based switch or a Silicon Optical Amplifier (SOA) based optical switch etc.
  • a suitable switch is in the process of being offered by Trellis, LightCross, Corning, and JDSU etc and is representative of other vendors' optical switch devices.
  • Another option instead of the switch is a fast tunable filter, suitable lithium Niobate based filters for example are available from Dense Optics inc., of Quebec Canada.
  • the second laser may be set to the frequency required for the subsequent OBDU and stabilized.
  • the optical switch inserts the second source, freeing up the first source to be tuned for the next data unit frequency.
  • This process called pipelining, can go on as long as the locking time is less than OBDU length. If the OBDUs are too short for the locker to stabilize the frequency during transmission of one OBDU more lasers can be added, with each tuned to the appropriate packet in the stream.
  • Multiplexing the lasers with an optical switch, rather than a passive star coupler, allows the laser to be 'set up' before the signal is required.
  • Figure 1 shows an example for a system using an external modulator 122, rather than directly modulated tunable lasers to illustrate the full applicability of the invention to all types of tunable lasers, and shows four lasers, 118, within the transmitter unit.
  • the tunable lasers 118 are assumed to only reliably access approximately half of the desired wavelength channels that are required to send the optical burst data units (OBDU) 106, and so two lasers are required to access the entire block of channels.
  • OBDU optical burst data units
  • An OBDU 101 consists of the preamble of bits, 103 that serves as a label or tag containing information which provides nodes on the transmission path the ability to periodically read data contained in the label and compare it with a value configured in the node at the time the connection was set up and contains information that a receiver can use to verify there is no collision with another OBDU or wavelength from another transmitter, and assists in clock recovery, the payload 102 that carries the data traffic, and the tail label or tag, 105, that contains connection management information. Aside from the clock recovery assist information the rest of the information in the head and tail tags does not have to be ahead of the data payload 102, and could even be superimposed on the payload, say by using a sub-carrier or a similar technique.
  • the lasers 118 in figure 1 are assumed to lock within one data unit length, only two laser devices per wavelength range are needed to maintain the data-unit-by-data-unit wavelength agility. Though only two sources of the same wavelength range are shown, since the locker 115 is assumed to lock within one data unit length, more sources of each wavelength channel group could be used if longer locking times are required.
  • the number of wavelength locking systems 115 required depends on the locking times and the numbers of sources 118 required, but can range from one (shared) to two (one for the transmitting channel and one for the channel being set up to the number of sources in the system (one locking system for each tunable source).
  • 110 is the control unit for the agile laser transmitter unit, that is connects to over control lines 113,114,112,111 and 107.
  • the control unit will typically be based around an embedded processor module with processor, volatile and non-volatile RAM and ROM memory, running a multi-tasking operating system or an embedded multi- controller, however programmable logic devices such as filed programmable gate arrays of the suitable speed could also be used.
  • the control unit controls the wavelength locker circuitry, the laser temperature, the laser optical power level, and processes and updates the dynamic data portion of then parameter look up table referred to previously etc
  • the head, payload and tail data from the control unit 110 goes to the external modulator 122 for the OBDU 100 over the data line 107, as shown by 108.
  • the lasers, all four of the lasers in 118, not just the laser that is transmitting the OBDU, 100, are being controlled by control lines 112 from the control unit 110.
  • the optical switch 119 has been switched , 120 appropriately under the control of the control unit 110, over control lines 111.
  • the control unit 110 then switches over to the next laser of the four in 118 to transmit, the OBDU is then switched in 120 by controlling the switch 119 over the control lines 111 as required.
  • the switch 119 is switched 120 to the next laser source to transmit and so on.
  • Multiple transmitters may be multiplexed, as per figure 2, using star couplers 127, as a node "add" device.
  • Star coupling is used to avoid the high costs of wavelength aware multiplexer and de-multiplexer, such as for example, interference filter, array Waveguide, fiber Bragg Grating, Dispersive filter, etc, and possibly optical switches that would otherwise have to be employed, but does not preclude the use of fast Tunable Lithium Niobate hitless filters etc.
  • This is an efficient approach to combining the signals from multiple sources 123, and 134, so the optical streams 124 and 133 from each agile transmitter join with streams from other agile transmitter units 132, to combine onto a single fibre 128.
  • the star coupler device, 127 could be replaced with an optical filter device, either wavelength fixed or agile, for adding the OBDUs from the agile transmitter units to the fiber.
  • the optical filter devices can be configured so that the added OBDUs are at different wavelengths for each optical burst connection. This permits the use of lower optical isolation version of these optical filters components, to be used for cost sensitive applications. Suitable optical filters are made by Corning, and JDSU.
  • An optional optical gain block 129 such as fiber amplifiers, such a EDFAS, or specialized short fiber amplifiers, or silicon optical amplifiers (SOAs), and linear optical amplifiers (LOAs) are supported for adding amplification to individual wavelengths or groups of wavelengths to achieve the required optical system bit error rate performance.
  • Suitable combiners and optical amplifiers are made by Corning, and JDSU.
  • the lookup table used to set the nominal wavelength of a tuneable laser is modified during operation to ensure the targeting algorithm has the most up-to-date values.
  • Accurate operation can be achieved by first finding the appropriate conditions during a 'set up' phase, prior to sending data on the transmission fibre, and then operating the laser open loop each time it starts to send a particular wavelength, based on the previous 'set up' parameter values. Refinement of the wavelength is done during the data transmission itself, with new parameters for the optimum open loop settings replacing the previous ones.
  • This method is particularly applicable to formats in which the wavelengths used cycle repeatedly over a short period of time: each wavelength state will follow the same previous state, reducing any deviation due to patterning, and the rapid repetitive nature ensures little change required due to device drift. Cyclic operation allows additional processing to predict the best start-up operating point given the known operating pattern.
  • the system requests a particular wavelength within a cycle of wavelength requests
  • the transmission to the optical fibre is blocked , for hitless operation, and the laser is operated close to the desired based on values in a look-up table that establish the such parameters as center wavelength, wavelength spacing, wavelength range, wavelength line width (narrow, wide, coarse etc) , wavelength stability, wavelength aging margin etc
  • any tuneable source such as the ones in the first approach, needs an initial set-point from which optimisation occurs, it makes sense to use the method of the second approach to increase the accuracy of the initial value even in the first approach, as it will speed up the process of achieving sufficient accuracy.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)

Abstract

La présente invention concerne un procédé constituant une amélioration des architectures de transmission optique habituelles, permettant la production de paquets de signaux de données à une fréquence optique pouvant être choisie précisément dans le spectre optique cible. La présente invention permet de supprimer les limites rencontrées lorsque l'écran et des circuits de rétroaction n'offrent pas une commande suffisante de la stabilité de longueur d'onde dans le temps requis. La présente invention est notamment caractérisée en ce qu'elle permet de garantir une commande efficace de la fréquence de sortie, même dans le cas de changements rapides de la fréquence de sortie, comme par ex. dans des systèmes à longueurs d'ondes synchrones ou asynchrones à éclatement optique. La présente invention offre deux modes de réalisation, un premier mode de réalisation intervenant lorsque le laser ne peut pas être accordé dans un temps de commutation autorisé, et l'autre mode de réalisation intervenant lorsque le laser peut être accordé suffisamment rapidement mais nécessite une stabilisation continue. Le deuxième mode de réalisation peut être employé pour améliorer les résultats du premier mode de réalisation.
PCT/CA2002/000305 2001-03-07 2002-03-07 Source optique agile pouvant etre reglee precisement en longueur d'onde WO2002071658A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CA2,339,911 2001-03-07
CA 2339911 CA2339911A1 (fr) 2001-03-07 2001-03-07 Source optique de longueur d'onde precise et agile, et utilisation connexe

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WO2002071658A1 true WO2002071658A1 (fr) 2002-09-12

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2483930A (en) * 2010-09-27 2012-03-28 Oclaro Technology Plc Fast wavelength switching
CN112189286A (zh) * 2018-05-21 2021-01-05 谷歌有限责任公司 用于突发模式可调谐激光器的开关电路

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2250394A (en) * 1990-09-14 1992-06-03 Gen Electric Co Plc Optical frequency synthesis
EP0529732A1 (fr) * 1991-08-30 1993-03-03 Koninklijke Philips Electronics N.V. Oscillateur à laser accordable

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2250394A (en) * 1990-09-14 1992-06-03 Gen Electric Co Plc Optical frequency synthesis
EP0529732A1 (fr) * 1991-08-30 1993-03-03 Koninklijke Philips Electronics N.V. Oscillateur à laser accordable

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
ISHIDA O ET AL: "DELAYED SELF-MULTIPLEX LIGHT SOURCE FOR FREQUENCY-AGILE TRANSMITTERS", JOURNAL OF LIGHTWAVE TECHNOLOGY, IEEE. NEW YORK, US, vol. 13, no. 12, 1 December 1995 (1995-12-01), pages 2336 - 2341, XP000585016, ISSN: 0733-8724 *
SHIOZAWA T ET AL: "RAPID WAVELENGTH STABILISING CONTROL FOR FAST LD WAVELENGTH SWITCHING", ELECTRONICS LETTERS, IEE STEVENAGE, GB, vol. 29, no. 15, 22 July 1993 (1993-07-22), pages 1331 - 1332, XP000385658, ISSN: 0013-5194 *
YASUHIKO TADA ET AL: "DESIGN CONSIDERATION ON A DBR-LASER TRANSMITTER FOR FAST FREQUENCY-SWITCHING IN AN OPTICAL FDM CROSS-CONNECT SYSTEM", JOURNAL OF LIGHTWAVE TECHNOLOGY, IEEE. NEW YORK, US, vol. 11, no. 5/6, 1 May 1993 (1993-05-01), pages 813 - 818, XP000396712, ISSN: 0733-8724 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2483930A (en) * 2010-09-27 2012-03-28 Oclaro Technology Plc Fast wavelength switching
CN112189286A (zh) * 2018-05-21 2021-01-05 谷歌有限责任公司 用于突发模式可调谐激光器的开关电路

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Publication number Publication date
CA2339911A1 (fr) 2002-09-07

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