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WO2002032027A2 - Circuit tout optique d'extraction d'horloge independant du debit binaire et du format - Google Patents

Circuit tout optique d'extraction d'horloge independant du debit binaire et du format Download PDF

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Publication number
WO2002032027A2
WO2002032027A2 PCT/US2001/031000 US0131000W WO0232027A2 WO 2002032027 A2 WO2002032027 A2 WO 2002032027A2 US 0131000 W US0131000 W US 0131000W WO 0232027 A2 WO0232027 A2 WO 0232027A2
Authority
WO
WIPO (PCT)
Prior art keywords
optical
signal
interferometric device
stage
clock
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.)
Ceased
Application number
PCT/US2001/031000
Other languages
English (en)
Other versions
WO2002032027A3 (fr
Inventor
Bharat Dave
Doruk Engin
Kwang Kim
Mohammad Laham
Julio Martinez
Olga Nedzhvetskaya
Jithamithra Sarathy
Ronald Simprini
Boris Stefanov
Tan Thai
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.)
Alphion Corp
Original Assignee
Alphion Corp
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
Priority claimed from US09/848,968 external-priority patent/US6570697B2/en
Priority claimed from US09/849,441 external-priority patent/US6563621B2/en
Application filed by Alphion Corp filed Critical Alphion Corp
Priority to AU2002213010A priority Critical patent/AU2002213010A1/en
Publication of WO2002032027A2 publication Critical patent/WO2002032027A2/fr
Publication of WO2002032027A3 publication Critical patent/WO2002032027A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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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
    • H04B10/29—Repeaters
    • H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
    • H04B10/299—Signal waveform processing, e.g. reshaping or retiming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L7/00—Arrangements for synchronising receiver with transmitter
    • H04L7/0075—Arrangements for synchronising receiver with transmitter with photonic or optical means

Definitions

  • This invention relates to optical communications, and in particular to a method of optical domain clock signal recovery from high-speed data, which is independent of the data format or the optical signal rate.
  • Optical fiber networks are in widespread use due to their ability to support high bandwidth connections.
  • the bandwidth of optical fibers runs into gigabits and even terabits.
  • Optical links can thus carry hundreds of thousands of communications channels multiplexed together.
  • Future optical networking line systems will incorporate service signals at both lOGb/s, 40Gb/s and much higher data rates, along with the associated Forward Error Corrected (FEC) line rate at each nominal bit rate.
  • FEC rates associated with, for example, lOGb/s optical signal transport include the 64/63 coding for lOGb/s Ethernet, the 15/14 encoding of SONET-OC192 FEC, and the strong-FEC rate of 12.25Gb/s.
  • the nodal devices in the optical network must work with any commercially desired line rate, independent of format, whatever that is or may be.
  • one of the fundamental functions these devices must provide is the capability to extract the clock from an arbitrary optical signal.
  • this clock recovery must be done completely in the optical domain.
  • a method and circuit are disclosed for the recovery of the clock signal from an arbitrary optical data signal.
  • the method involves two stages.
  • the first stage consists of a Semiconductor Optical Amplifier - Asymmetric Mach-Zehnder Interferometer, or SOA-AMZI, preprocessor, which is responsible for transforming an incoming NRZ type signal into a pseudo return to zero (“PRZ”) type signal, which has a significant spectral component at the inherent clock rate.
  • SOA-AMZI Semiconductor Optical Amplifier - Asymmetric Mach-Zehnder Interferometer
  • This preprocessing stage is followed by a second stage clock recovery circuit.
  • the second stage is implemented via an SOA-MZI circuit (symmetric in structure, i.e., no phase delay introduction in one of the arms) terminated by two Distributed Feedback (DFB) lasers that go into mutual oscillations triggered by the dominant frequency of the first stage's output signal.
  • the SOA-MZI is tuned to adjust the input phase of the oscillatory signal into the DFBs. This provides the tuning and control of the oscillation frequency of the output clock signal.
  • the SOA gain currents can be adjusted to reshape the clock signal, which is the output of the second stage.
  • Fig. 1 depicts a circuit implementing the method of the present invention
  • Fig. 2 depicts just the second stage of the circuit of Fig. 1
  • Fig. 3 depicts an exemplary semiconductor optical amplifier device used according to the method of the present invention.
  • the fundamental problem of all-optical clock recovery from an arbitrary incoming optical signal is thus the passing of an RZ signal without attenuation, and the generation of a RF spectral component at the line rate for a NRZ signal.
  • an NRZ/PRZ converter is used to generate this latter spectral component by converting the incoming NRZ into a pseudo return to zero, or PRZ signal.
  • optical oscillations can be triggered to obtain a pure line rate optical clock signal.
  • Fig. 1 depicts a preferred embodiment of the two circuit stages needed for all optical clock recovery of an arbitrary NRZ signal.
  • the first stage 150 converts an input signal 100 to PRZ format, where PRZ denotes a "pseudo return to zero" or PRZ data format.
  • PRZ is generated from a standard NRZ format input signal 100 by generating an RZ like pulse each time the NRZ signal transitions, whether from high to low or from low to high, i.e. PRZ has a pulse at each rising edge and at each falling edge of the original signal.
  • a PRZ signal As above, the key property of a PRZ signal is that its RF frequency spectrum has a significant frequency component at the original NRZ signal's clock rate. It is this very property that the method of the invention exploits to recover the clock signal.
  • the actual conversion of an NRZ signal to the PRZ format is the result of the operation of a PRZ generator 150 on an NRZ input.
  • a related patent application under common assignment with the present one, describes in detail a method and circuit for implementing the preprocessor of the first stage 150. That patent application is entitled "FORMAT INSENSITIVE AND BIT RATE INDEPENDENT OPTICAL PREPROCESSOR" by Bharat Dave, et al., filed on May 4, 2001. That disclosure is hereby fully incorporated herein by this reference. The method and circuit described therein will thus be summarily described here for purposes of reference.
  • the PRZ generator forms the first stage 150 of the All Optical Clock
  • AOCR AOCR Recovery
  • This stage consists of a path-delayed Asymmetric Mach-Zehnder Interferometer (AMZI).
  • the AMZI incorporates semiconductor optical amplifiers (SOAs) in each of its arms 105 and 106, respectively, and a phase delay element 107 in one, but not both, of the two arms; hence the asymmetry.
  • SOAs semiconductor optical amplifiers
  • the AMZI is set for destructive interference of the signals in the two paths.
  • the interference of a high bit with its path delayed inverse, i.e. a low bit generates an RZ-like bit at both the leading and falling edges of the original high bit.
  • This latter signal with a bit rate effectively double that of the original NRZ bit rate, is the PRZ signal 110.
  • the preprocessor does not need to know the actual bit rate or format of the input data, it is data rate and format insensitive. Thus the preprocessor has the ability to reshape the PRZ signal as well as adjust its duty cycle.
  • the output 110 of the first stage 150 becomes the input to the second stage 160.
  • the second stage 160 comprises a symmetric Mach-Zehnder Interferometer, where each arm contains a semiconductor optical amplifier 111 and 112, respectively.
  • the principle of clock recovery is based on inducing oscillations between the two lasers DFB1 113 and DFB2 114.
  • the oscillations are triggered by the output of the first stage 110. As described above, this output can be either RZ or PRZ.
  • the current to DFB2 114 is tuned close to its lasing threshold, with DFB1 113 energized so as to be in lasing mode.
  • the trigger pulse 110 induces lasing in DFB2 114.
  • the feedback from DFB2 114 turns off the lasing in DFB1 113 resulting in DFB2 114 itself turning off.
  • the reduced feedback from DFB2 114 now returns DFB1 113 to lasing. In this manner the two lasers mutually stimulate one another in oscillation.
  • pulses from the input 110 are sufficient to lock the oscillation of the DFB lasers at that rate, and, in general, to hold for quite a number of low bits (such as would appear where the original signal 100 had a long run of high bits).
  • the forced triggering by the PRZ/RZ input 110 locks the phase of the oscillations at the original signal ' s 100 clock rate.
  • the interferometer improves the control of the phase input to DFB2 114.
  • the use of the SOA-MZI facilitates the tuning of the oscillation rate by adjusting the input signal phase into DFB2 114. As the phase of the MZI output is tuned, the gain recovery time of DFB2 114 is adjusted. This results in the oscillation rate being altered. In this manner the clock frequency can be tuned to the desired line rate.
  • Using non-linear SOA elements also allows shaping of the output clock with a lesser energy expenditure .
  • the refractive index of each SOA's waveguide can be manipulated, thus altering the phase of the pulse entering DFB2 114.
  • the oscillation rate of the circuit can be altered, and the identical circuit can be tuned to the various bit rates available in the network, thus rendering the system bit rate independent.
  • the use of the SOA-AMZI in the first stage 150 of the clock recovery system allows the input power required by the device to be quite nominal, in the embodiment depicted approximately -lOdBm; thus signal pre-amplification concerns are diminished or avoided.
  • the output power of the clock signal in this embodiment is on the order of OdBm.
  • the laser wavelength of the all-optical clock signal is a function of the wavelength amplification spectrum of the second stage SOAs.
  • the standard carrier frequencies used in optical networks all fall within the SOA amplification spectrum. This wavelength can be anywhere in the amplification window of the SOAs in the second stage 160 SOA-MZI circuit.
  • a wavelength such as 1550 nm may be chosen
  • for the L-band of optical transmission a wavelength such as 1585 nm may be chosen.
  • Multimode Interference (MMI) couplers with a 50:50 splitting ratio make up the couplers of the first stage 102 and 103, respectively, as well as the couplers of the second stage 120 and 125, respectively.
  • MMI Multimode Interference
  • Figures 2 and 2A show the second stage clock recovery circuit in isolation.
  • the input 200 to this stage is the amplified RZ or PRZ signal output from the first stage.
  • the stage comprises a symmetric interferometer, with an SOA 210 and 215, respectively, in each arm.
  • the interferometer has two DFB lasers as termini, DFB1 205, in lasing mode, and DFB2 220 near the lasing threshold. This state of affairs results in an optical cavity that is sensitive to the incoming input signal such that self-pulsating behavior will be triggered by any incoming data pulse.
  • the input signal 200 which has a large, usually far and away dominant, frequency component at the original optical signal's clock rate, thus triggers the DFB lasers 205 and 220 into self pulsating behavior at that frequency, and the feedback between the two lasers results in a pendulum like behavior that maintains the two lasers in a conservative self oscillatory state.
  • This self oscillation is thus maintained for some time, due to the mutual interaction of the lasers, even if the incoming data has numerous "zero" bits in a row (and thus no pulses at all for that interval).
  • the output signal of the second stage 225 is an optical clock signal at the original line rate of the optical input signal 100 in Fig. 1.
  • the clock signal can be "locked” on to after the second stage MZI has been fed ten (10) or more "one" bits from the input signal.
  • the output clock signal 225 can be maintained even during significant periods of no second stage input signal 200, such as in the event of 100 "zero" bits, a statistically very rare occurrence, and under some data formats, (where scrambling is done prior to transmission over a link, and descrambling at the receiving end), quite impossible.
  • the mutual feedback and self oscillation of the two lasers presents a robust structure for extracting a clean optical clock signal as its output 225.
  • Fig. 3 depicts a cross section of an exemplary integrated circuit SOA.
  • Figure 3 depicts a cross section of any of the depicted SOAs taken perpendicular to the direction of optical signal flow in the interferometer arms. Numerous devices of the type depicted in Figure 3 can easily be integrated with the interferometers of the preprocessor, so that the entire circuit can be fabricated on one IC.
  • the device consists of a buried sandwich structure 350 with an active Strained Multiple Quantum Well region 311 sandwiched between two waveguide layers 310 and 312 made of InGaAsP.
  • the ⁇ g of the InGaAsP in layers 310 and 312 is 1.17 ⁇ m.
  • the sandwich structure does not extend laterally along the width of the device, but rather is also surrounded on each side by the InP region 304 in which it is buried.
  • the active Strained MQW layer is used to insure a constant gain and phase characteristic for the SOA, independent of the polarization of the input signal polarization.
  • the SMQW layer is made up of pairs of InGaAsP and InGaAs layers, one disposed on top of the other such that there is strain between layer interfaces, as is known in the art. In a preferred embodiment, there are three such pairs, for a total of six layers.
  • the active region/waveguide sandwich structure 350 is buried in an undoped InP layer 404, and is laterally disposed above an undoped InP layer 303. This latter layer 303 is laterally disposed above an n-type InP layer 302 which is grown on top of a substantially doped n-type InP substrate.
  • the substrate layer 301 has, in a preferred embodiment, a doping of 4-6 x 10 /cm " .
  • the doping of the grown layer 302 is precisely controlled, and in a preferred embodiment is on the order of 5
  • p-type InP region 321 On top of the buried active region/waveguide sandwich structure 350 and the undoped InP layer covering it 304 is a laterally disposed p-type InP region 321. In a preferred embodiment this region will have a doping of 5 x 10 17 /cm "3 . On top of the p-type InP region 321 is a highly doped p+-type InGaAs layer. In a preferred embodiment this latter region will have a doping of 1 x 10 1 /cm "3 .
  • the p-type layers 320 and 321, respectively, have a width equal to that of the active region waveguide sandwich structure, as shown in Fig. 3. As described above, the optical signal path is perpendicular to and heading into the plane of Fig. 3.
  • the entire all-optical clock recovery device can be integrated in one circuit.
  • An exemplary method of effecting this integration is next described.
  • the wafer is patterned to delineate the SOAs, the AMZI and the MZI.
  • the path length difference between the two arms of the AMZI is approximately 1mm.
  • the DFB regions of the second stage of the device are created using either a holographic or a non-contact interference lithographic technique.
  • the periodicity of the grating in a preferred embodiment is approximately 2850A.
  • the grating is of Order 1 and provides optical feedback through second-order diffraction.
  • the undoped InP top cladding layer, the p-type InP layers, and the contact layer are then regrown on the patterned substrate. This step is then followed by photolithography for top-contact metallization.
  • the device is then cleaved and packaged.

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

Abstract

L'invention concerne un procédé et un circuit destinés à la récupération tout optique du signal d'horloge à partir d'un signal de données optique aléatoire. Le procédé comprend deux étapes. Au cours de la première étape, le signal optique est prétraité par conversion d'un signal NRZ en un signal PRZ (retour à zéro aléatoire), ou si le signal optique d'entrée est RZ, par simple amplification de celui-ci. Dans un mode de réalisation préféré, cette étape est mise en oeuvre via un SOA (amplificateur optique semi-conducteur) intégré dans chaque branche d'un dispositif interférométrique asymétrique. La sortie de l'étape de prétraitement est distribuée à une étape de récupération d'horloge, consistant en un interféromètre symétrique captant le signal d'horloge inhérent, au moyen du signal d'entrée de la seconde étape, en vue de déclencher deux sources optiques, de manière qu'elles soient soumises à une auto-oscillation au rythme de l'horloge. Dans un mode de réalisation, la seconde étape est mise en oeuvre via des SOA intégrés dans les branches d'un interféromètre, avec deux lasers DFB (à rétroaction distribuée) comme terminus. La sortie de l'interféromètre est un signal optique d'horloge au rythme de l'horloge de l'entrée originale.
PCT/US2001/031000 2000-10-06 2001-10-04 Circuit tout optique d'extraction d'horloge independant du debit binaire et du format Ceased WO2002032027A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002213010A AU2002213010A1 (en) 2000-10-06 2001-10-04 Bit-rate and format insensitive all-optical clock extraction circuit

Applications Claiming Priority (8)

Application Number Priority Date Filing Date Title
US23829700P 2000-10-06 2000-10-06
US23829800P 2000-10-06 2000-10-06
US60/238,298 2000-10-06
US60/238,297 2000-10-06
US09/848,968 US6570697B2 (en) 2000-10-06 2001-05-04 Format insensitive and bit rate independent optical preprocessor
US09/849,441 2001-05-04
US09/848,968 2001-05-04
US09/849,441 US6563621B2 (en) 2000-10-06 2001-05-04 Bit-rate and format insensitive all-optical clock extraction circuit

Publications (2)

Publication Number Publication Date
WO2002032027A2 true WO2002032027A2 (fr) 2002-04-18
WO2002032027A3 WO2002032027A3 (fr) 2003-02-27

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PCT/US2001/030999 Ceased WO2002032033A2 (fr) 2000-10-06 2001-10-04 Preprocesseur optique independant du debit binaire et insensible au format
PCT/US2001/031000 Ceased WO2002032027A2 (fr) 2000-10-06 2001-10-04 Circuit tout optique d'extraction d'horloge independant du debit binaire et du format

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WO (2) WO2002032033A2 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2390243A (en) * 2002-06-28 2003-12-31 Corning Inc Two-stage interferometric optical regenerator

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5387972A (en) * 1993-03-15 1995-02-07 National Research Council Of Canada Coherent phase and frequency detection using sum-frequency mixing in non-linear waveguides
FR2703547B1 (fr) * 1993-03-29 1995-05-12 Rene Auffret Dispositif optique de récupération du rythme d'un signal code.
GB2320634A (en) * 1996-12-19 1998-06-24 Northern Telecom Ltd Optical sampling by using an interferometer to modulate a pulse train
JPH10178418A (ja) * 1996-12-19 1998-06-30 Fujitsu Ltd 光時分割分離装置及び分離信号切替方法並びに光時分割多重伝送システム
JPH11101922A (ja) * 1997-07-30 1999-04-13 Nec Corp 光タイミングパルス生成方法及び光タイミング回路
DE69834531T2 (de) * 1997-08-27 2007-05-31 Interuniversitair Micro-Elektronica Centrum Vzw Optische Entscheidungsschaltung und dessen Verwendung

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2390243A (en) * 2002-06-28 2003-12-31 Corning Inc Two-stage interferometric optical regenerator
GB2390243B (en) * 2002-06-28 2005-11-02 Corning Inc Optical regenerator
US7057785B2 (en) 2002-06-28 2006-06-06 Corning Incorporated Optical regenerator

Also Published As

Publication number Publication date
AU2002213010A1 (en) 2002-04-22
WO2002032033A3 (fr) 2003-09-25
WO2002032033A2 (fr) 2002-04-18
AU2002213009A1 (en) 2002-04-22
WO2002032027A3 (fr) 2003-02-27

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