EP1329047A1 - Systeme et procede destines a la communication optique multiplexee par repartition de code - Google Patents

Systeme et procede destines a la communication optique multiplexee par repartition de code

Info

Publication number
EP1329047A1
EP1329047A1 EP01977299A EP01977299A EP1329047A1 EP 1329047 A1 EP1329047 A1 EP 1329047A1 EP 01977299 A EP01977299 A EP 01977299A EP 01977299 A EP01977299 A EP 01977299A EP 1329047 A1 EP1329047 A1 EP 1329047A1
Authority
EP
European Patent Office
Prior art keywords
signal
code
data
optical
receiver
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP01977299A
Other languages
German (de)
English (en)
Inventor
Michael Tseytlin
Isaac Shpantzer
Yaakov Achiam
Aviv Salamon
Israel Smilanski
Charles Sciabarra
Peter Feldmann
Alper Demir
Peter Kinget
Nagendra Krishnapura
Jaijeet Roychowdhury
Jacob Khurgin
Joseph Schwarzwalder
Olga Ritterbush
Gioulang Li (Eric)
Pak Shing Cho
Yehouda Meiman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Celight Inc
Original Assignee
Celight Inc
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 Celight Inc filed Critical Celight Inc
Publication of EP1329047A1 publication Critical patent/EP1329047A1/fr
Withdrawn legal-status Critical Current

Links

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
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H04B10/505—Laser transmitters using external modulation
    • H04B10/5057—Laser transmitters using external modulation using a feedback signal generated by analysing the optical output
    • H04B10/50577—Laser transmitters using external modulation using a feedback signal generated by analysing the optical output to control the phase of the modulating signal
    • 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
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/2569—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to polarisation mode dispersion [PMD]
    • 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
    • H04B10/505—Laser transmitters using external modulation
    • 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
    • H04B10/505—Laser transmitters using external modulation
    • H04B10/5051—Laser transmitters using external modulation using a series, i.e. cascade, combination of modulators
    • 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
    • H04B10/505—Laser transmitters using external modulation
    • H04B10/5057—Laser transmitters using external modulation using a feedback signal generated by analysing the optical output
    • H04B10/50572—Laser transmitters using external modulation using a feedback signal generated by analysing the optical output to control the modulating signal amplitude including amplitude distortion
    • 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
    • H04B10/508—Pulse generation, e.g. generation of solitons
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/10—Code generation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/005—Optical Code Multiplex

Definitions

  • Polarization mode dispersion arises in optical fiber when circular symmetry is broken by the presence of an elliptical core or by noncircularly symmetric stresses.
  • the loss of circular symmetry results in the difference in the group velocities associated with the two polarization modes of the fiber.
  • the main effect of the PMD is the splitting of the narrow-band pulse into two orthogonally polarized pulses (dual imaging) that propagate through the fiber with the different group velocities.
  • SOP states of polarization
  • the present invention is directed to a spreader calibration unit which ensures that each of the pulse spreaders has proper modulation.
  • the optical detection circuit includes a polarization beam splitter which splits the information signal into first and second orthogonal polarization components, a first optical phase detector that receives the first orthogonal polarization component and a reference signal as inputs, and outputs in-phase and quadrature components of the first orthogonal polarization component, a second optical phase detector which receives the second orthogonal polarization component and the same reference signal as inputs, and outputs in-phase and quadrature components of the second orthogonal polarization component, and a symbol synchronizer circuit that receives the in-phase and quadrature components of the first and second orthogonal polarization components of the information signal, and outputs at least one timing signal to synchronize symbol boundaries of said data-modulated codewords in said optical phase detectors.
  • the present invention is directed to a PSP-based PMD compensator, to compensate for PMD caused by the fiber and its environment over a long distance run, without the use of a repeater.
  • the receiver restores a transmitted signal's polarization by aligning the SOP of the received signal with the SOP of the signal launched into the fiber.
  • the transmitter selects the optimal SOP to launch the optical signal into the fiber by aligning the SOP with the principal state of polarization (PSP) axes of the fiber.
  • PSP principal state of polarization
  • the SOP transmitted along the PSP axes exhibits the least frequency dependence that minimizes the coupling of the propagating signal.
  • Fig. 2a is a block diagram of a simplex optical communication system in accordance with a preferred embodiment of the present invention
  • Fig. 2b is a block diagram of one-half of a duplex optical communication system in accordance with a preferred embodiment of the present invention
  • Fig. 6 is a block diagram of a second embodiment of a spreader calibrator
  • Fig. 7 is a block diagram of the transmitter-side optical phase detector in a preferred embodiment of the present invention.
  • Fig. 12 is a block diagram of the symbol synchronizer in a preferred embodiment of the present invention.
  • Fig. 13a is a graph of the average symbol energy as a function of the symbol time
  • Fig. 13b is a plot of the average symbol-to-symbol energy difference as a function of the symbol time
  • Fig. 14c is a flow diagram of a PMD controller for compensating the receiver and the transmitter of Fig. 14a;
  • each receiver module 267 includes a receiver 260 and preferably also incorporates a receiver-end polarization mode distortion (PMD) compensation 285.
  • PMD receiver-end polarization mode distortion
  • Each channel 240 is characterized by a different wavelength, ⁇ / , where the index, /, runs from 1 to N. In a preferred embodiment, N is equal to 40 thereby giving each channel a bandwidth of about 100 GHz.
  • Each channel 240 is capable of carrying K codes 280 and each code 280 carries a data stream.
  • a transmitter (Tx) 250 creates the K codes, modulates each code 280 with a data stream, and combines the /(data modulated codes into an optical channel signal 245 before passing the optical signal 245 to the multiplexer 210.
  • Each channel 240 also includes a receiver (Rx) 260 that recovers the / data streams from the Demux 230.
  • Fig. 3 is a block diagram of a transmitter 250 configured to create a code division multiplexed signal in accordance one embodiment of the present invention.
  • Coherent pulsed light source 310 generates a linearly polarized monochromatic light beam characterized by wavelength, ⁇ ,-.
  • the coherent pulsed light source 310 comprises a continuous wave laser 311 that generates a coherent monochromatic light beam.
  • the light beam is directed into an intensity modulator 312.
  • the intensity modulator 312 is, in turn, controlled by a pulse generator 313.
  • the coherent light source 310 is a mode-locked laser that directly generates a similar pulse stream.
  • Fig. 4 is a block diagram of a preferred embodiment of the pulse spreader 330.
  • a portion of the pulsed light beam 318 is directed to the spreader calibration unit 335 while the code beam 322 is split by a 1 :P splitter 410, P representing the number of code bits (referred to a "chip") in each code word.
  • the code beam is split into P - 16 split beams, however, any number of split beams may be used and is within the scope of the invention.
  • Fig. 4 shows the modification of only one of the P split beams and it is understood that the remaining split beams are directed to structures identical to the chip modulators 450 of Fig. 4.
  • Each of the P split beams is passed through a delay 420 that delays the split beam by a predetermined amount.
  • the delay 420 is a multiple of T/P where Tis the symbol period and P is the number of split beams or chips.
  • the delay 420 may be a calibrated length of waveguide such as an optical fiber or a semiconductor waveguide.
  • combiner 440 combines each of the delayed-and-now-chip-modulated split beams into a single code beam 332. A portion of the code beam 332 exiting the combiner 440 is directed to the spreader calibration unit 335.
  • the selection of the orthogonal code sets may be from any one of the orthogonal code sets known to one of skill in the signal processing arts.
  • the modulation consists of phase shifts given by the following equation:
  • Processor 560 measures the amplitude a kp and the phase ⁇ kp -2 ⁇ f( ⁇ kp - ⁇ p ) and commands the spreader calibration unit 335, for the k-th pulse spreader, to maintain a kp and ⁇ kp -2 ⁇ f ⁇ kp at the required value given, for example, by equation 1.
  • the phase detector 650 determines the amplitude product of, and the phase difference between, the selected imprinted code beam 612 and the gated reference beam 632.
  • the amplitude product and phase difference are passed to a processor 660 that determines the offset that should be applied by the (kp)-th chip modulation circuit.
  • Fig. 7 presents a block diagram of the optical phase detector 550, 650, seen in Figs. 5 and 6.
  • the optical phase detector receives two optical beams 705, 701 and generates two electrical signals 795, 791 corresponding to the in-phase and quadrature components of the multiplication of 705 by the complex conjugate of 701.
  • One of the two beams, designated as A in Fig. 7, is referred to as a signal beam.
  • Data Modulator Fig. 8 is a block diagram of a preferred embodiment of a data modulator 340 in accordance with the present invention.
  • the imprinted code beam 332 from pulse spreader 330 enters the data modulator 340 through a power splitter 810.
  • the power splitter 810 splits the imprinted code beam 332 into two beams, designated as H and V.
  • the H and V beams are each directed into separate 1 :2 splitters 820a, 820b, although a 1 :4 splitter may be used instead.
  • the splitter 820a splits the H beam into H1 and H2 components and directs one of these (H2 in Fig. 8), into a 90° phase shifter 825a.
  • the splitter 820b splits the V beam into V1 and V2 components and directs one (V2 in Fig. 8) into a 90° phase shifter 825b.
  • Each of the four component beams are directed into a separate modulator 830a, 830b, 830c, 830d where the data stream 370 is modulated on the four component beams.
  • the data stream DATAy k includes data to be encoded on the H and V polarizations of a single code word, depending on the index 'j'.
  • Control signals from a power balancer 345 ensure that the intensity of each data-modulated component beam is comparable to that of the others and ensures the orthogonality of the in-phase and quadrature components of the constellation.
  • the power balancer may have inputs into one or both of the phase shifters 825a, 825b and the data modulators 830a, 830b, 830c, 830d.
  • Fig. 10 is a block diagram of one embodiment of the receiver unit 930 seen in Fig. 9a.
  • This unit 930 employs homodyne detection.
  • a split beam signal 925 is directed into a polarizing beam splitter 1010 of the optical detection circuitry 1090.
  • the polarizing beam splitter 1010 splits the split beam 925 into its first and second orthogonal polarization components, designated as H and V in Fig. 10.
  • the signal from the clock distribution unit 1295 controls the sample & hold unit in each gate 1210, 1215 and determines the sampling instance of the input analog signals 1775, 1777 by each gate 1210, 1215.
  • the analog-to-digital converter converts the analog sampled signal to digital format.
  • the symbol synchronizer 1040 receives the in- phase and quadrature components of the first and second orthogonal polarization components of split beam signal 925, and outputs a timing signal 1242 to help synchronize the symbol boundaries of the data-modulated codewords in the optical phase detectors 1030a, 1030b.
  • Fig 14c presents a flow diagram 1480 describing the operation of the PMD controller Rx/Tx module to control both the receiver PMD compensator 1476 and the transmitter SOP compensator 1472, in a system such as that seen in Fig. 14a.
  • the receiver SOPs are adjusted to conform the new candidate Tx SOP so as to preserve the TX/RX SOP alignment. This is done by adjusting the receiver PMD compensator in a manner complementary to the adjusment made to the transmitter compensator. In effect then, a rotation of the Tx compensator 1472 to a new candidate SOP is followed by a "counter-rotation" of the Rx compensator 1476.
  • the Tx SOPs preferably are adjusted on some predetermined basis that is known to the receiver so as to allow the Rx SOPs to be changed each time a new Tx candidate SOP is tried.
  • step 1490 a check is made to determine whether all the candidate Tx SOPs have been evaluated. If it is determined in step 1490 that additional candidate Tx SOPs remain, these are tried. If, on the other hand, it is determined in step 1490 that there are no further candidate Tx SOPs, controls flows to step 1492.
  • step 1492 the transmitter and receiver compensators 1472, 1476, respectively, are adjusted based on the states corresponding to the optimum metric.
  • the final TX/RX SOP adjustment takes place to align the TX SOP with the PSP axes.
  • the above-described procedure is repeated to track the polarization changes occuring in the fiber. Preferably, this is done on a continuous basis.
  • the candidate PSP list can be limited to the subset of the original list situated around the current PSP axes during the tracking. This limitation is based on the assumption that the small variations in the fiber polarization transformation matrix will lead to small variations of the PSP orientation.

Abstract

Un système de communication optique (2a) constitue une famille de codes optiques orthogonaux modulés par un train de données. Pour former les codes orthogonaux, un train d'impulsions espacées uniformément est créé au moyen d'un circuit étalant les impulsions et les impulsions sont modulées en amplitude et/ou en phase pour former une famille de mots de codes optiques orthogonaux, qui représentant chacun un symbole. Un circuit d'étalonnage de l'étaleur est utilisé pour assurer la synchronisation et la modulation précises. Chaque mot de code est ensuite modulé par un nombre prédéterminé de bits utiles. Le plan de modulation des données divise un mot de code en constituants H et V puis traite les constituants avant la modulation avec les données qui est suivie par la recombinaison avec un combineur de faisceaux de polarisation. Le mot de code modulé par les données est ensuite envoyé, en même temps que d'autres, au récepteur. Le signal reçu est détecté et démodulé au moyen d'une unité de synchronisation des symboles qui définit le début et la fin des mots de code. Un compensateur (275) de la distorsion en mode de polarisation situé au niveau du récepteur coopère avec un état du compensateur de polarisation situé au niveau de l'émetteur pour atténuer la distorsion de polarisation dans la fibre.
EP01977299A 2000-09-26 2001-09-26 Systeme et procede destines a la communication optique multiplexee par repartition de code Withdrawn EP1329047A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US23493000P 2000-09-26 2000-09-26
US234930P 2000-09-26
PCT/US2001/030607 WO2002027994A1 (fr) 2000-09-26 2001-09-26 Systeme et procede destines a la communication optique multiplexee par repartition de code

Publications (1)

Publication Number Publication Date
EP1329047A1 true EP1329047A1 (fr) 2003-07-23

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EP01977299A Withdrawn EP1329047A1 (fr) 2000-09-26 2001-09-26 Systeme et procede destines a la communication optique multiplexee par repartition de code

Country Status (4)

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EP (1) EP1329047A1 (fr)
JP (1) JP2004511128A (fr)
AU (1) AU2001296430A1 (fr)
WO (1) WO2002027994A1 (fr)

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WO2002027994A1 (fr) 2002-04-04
AU2001296430A1 (en) 2002-04-08
JP2004511128A (ja) 2004-04-08

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