WO2001005084A1 - Systeme et procede de demultiplexage asymetrique optique dans le domaine terahertz - Google Patents

Systeme et procede de demultiplexage asymetrique optique dans le domaine terahertz Download PDF

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Publication number
WO2001005084A1
WO2001005084A1 PCT/US2000/018763 US0018763W WO0105084A1 WO 2001005084 A1 WO2001005084 A1 WO 2001005084A1 US 0018763 W US0018763 W US 0018763W WO 0105084 A1 WO0105084 A1 WO 0105084A1
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Prior art keywords
optical
nle
demultiplexer
pulses
data
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PCT/US2000/018763
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English (en)
Inventor
Paul R. Prucnal
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Prucnal Paul R
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Priority to AU59260/00A priority Critical patent/AU5926000A/en
Publication of WO2001005084A1 publication Critical patent/WO2001005084A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/08—Time-division multiplex systems
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/3515—All-optical modulation, gating, switching, e.g. control of a light beam by another light beam
    • G02F1/3517—All-optical modulation, gating, switching, e.g. control of a light beam by another light beam using an interferometer
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0005—Switch and router aspects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0005—Switch and router aspects
    • H04Q2011/0037—Operation
    • H04Q2011/0041—Optical control

Definitions

  • the present invention relates generally to ultrafast optical switching and more specifically to an optical demultiplexer capable of selecting individual pulses from a time- division multiplexed input pulse train having data rate in the terabit per second range, and a corresponding method for optical demultiplexing.
  • OTDM optical time-division multiplexed
  • the demultiplexing switch must have sufficient bandwidth to permit sampling of data in the time slot and must perform a sampling operation every frame. Because such demultiplexers are the only components of the network that operate at rates corresponding to the optical system's aggregate bandwidth, they are also the components that primarily limit the achievable signal throughput. The same observation also holds in the case of optical packet switching networks, where data along with routing information is encoded in optical packets, which flow through multiple communication nodes before reaching their ultimate destination. The network has a higher capacity if the optical packets are temporally compressed. However, in such networks an optical demultiplexer is required to read individual bits of information within the packet, thus limiting the achievable throughput of the packet-switched network.
  • Ultrafast Nonlinear Interferometer developed at MIT Lincoln Labs, which is an all-optical OTDM switch using a semiconductor optical amplifier (SOA) as a nonlinear element in a single-arm interferometer.
  • SOA semiconductor optical amplifier
  • the UNI has a long birefringent fiber used to separate orthogonally polarized components of data pulses in time using accurately timed control pulses. While the UNI approach is capable of providing very high data throughput, its integratability and thus practicality are limited by the long length of birefringent fiber needed to induce the polarization walk-off.
  • Another examples are provided by different existing embodiments of the Terahertz
  • Optical Asymmetric Demultiplexer developed at Princeton University, which is a versatile, high performance all optical switch.
  • TOAD Optical Asymmetric Demultiplexer
  • the reader is directed, for example, to U.S. Pat. Nos. 5,917,979; 5,841,560; 5,825,519; 5,493,433; 5,073,980 and 5,060,305 for further detail.
  • the disclosure of the above patents is incorporated herein for all purposes. While the above and other references disclose significant advances in the field of optical switching, alternative approaches that may take advantage of currently developed technologies would be beneficial in certain practical applications.
  • Another object of this invention is to provide a novel optical demultiplexer system and method for operation in the terabit per second range. Another object is to provide an optical demultiplexer that can be compact and generally compatible with integrated semiconductor elements.
  • An optical demultiplexer in a preferred embodiment has a coupler connected to a first optical path that has a first reflecting nonlinear optical element (NLE), which responds to a control pulse to induce a phase shift in an optical data signal propagating therethrough.
  • NLE nonlinear optical element
  • a second optical path is connected to the coupler, which includes a similar reflecting NLE.
  • Optical pulses provided at an input port of the coupler propagate concurrently through both optical paths and, when reflected, experience at the coupler either constructive or destructive interference dependent on the state of the first and second NLE.
  • a control input induces a first control pulse in the first optical path and a second control pulse in the second optical path, the second control pulse delayed a time ⁇ t from the first control pulse, so that a data pulse propagating through the first path is phase delayed by 180 degrees by the first NLE but experiences no additional phase delay in the second NLE.
  • an optical pulse in a high data rate optical pulse train can be selected, and forwarded to an output port of the device.
  • the reflecting NLEs are implemented either as integrated components, or alternatively using reflective mirrors separate from the NLE. Different schemes for providing the control input are also disclosed.
  • an optical demultiplexer comprising: a first optical path having a first nonlinear optical element (NLE) and a reflective mirror; a second optical path having a second NLE and reflective mirror, where the first and second NLE responsive to an optical control pulse to induce a phase shift in an optical data pulse propagating through them.
  • the demultiplexer also comprises an optical coupler having an input port for concurrently coupling a train of optical data pulses onto the first and second optical paths, the coupler being responsive to in-phase data pulses reflected from the first and second optical paths to provide an output data pulse on a first output terminal, and to phase-offset data pulses reflected from the first and second optical paths to provide an output data pulse on a second output terminal.
  • the demultiplexer also comprises a control circuit providing optical control pulses with predetermined timing to the first and second NLE to direct output data pulses to a select output terminal.
  • a control circuit providing optical control pulses with predetermined timing to the first and second NLE to direct output data pulses to a select output terminal.
  • an optical demultiplexer comprising a coupler concurrently coupling a train of input optical data pulses to one end of a first and a second optical paths; a first non-linear optical element (NLE) and an associated mirror at an opposite end of the first optical path and a second NLE and an associated mirror at an opposite end of the second optical path; and a control circuit providing control signals that cause changes in the optical properties of the first NLE in a predetermined timing relationship to changes in the optical properties of the second NLE to direct in-phase optical pulses reflected from the first and the second optical paths to a select output terminal.
  • NLE non-linear optical element
  • a method for optical demultiplexing comprising the steps of providing an input optical data pulse train comprising time-division multiplexed signals from a plurality of channels; passing the input optical data pulse train concurrently through one end of a first and second optical paths, each path having at an opposite end a non-linear optical element (NLE) and an associated reflecting mirror; applying an optical control pulse in a predetermined timing relationship to each NLE to cause reflected optical data pulses propagating through the first and second optical paths to interfere constructively; and directing optical pulses resulting from the constructive interference to a select output terminal.
  • NLE non-linear optical element
  • Fig. 1 is a schematic diagram illustrating one embodiment of an optical demultiplexer system in accordance with the present invention
  • FIG. 2 is a waveform diagram helpful in understanding the operation of the demultiplexer in accordance with the present invention
  • FIGs. 3, 4 and 5 are schematic block diagrams of different embodiments of the demultiplexer system in accordance with the present invention.
  • the Michelson Terahertz Optical Asymmetric Demultiplexer (TOAD) in accordance with the present invention is an optically-controlled optical switch that is capable of demultiplexing data from a terabit per second optical data stream.
  • the Michelson TOAD in a specific embodiment splits an input optical data pulse from an input module 10 into two separate paths (C) and (D) using a 3-dB coupler 20.
  • coupler 20 has an input port A and two ports C and D connected to the corresponding optical paths.
  • each optical path has at another end a Nonlinear Element (NLE) and a mirror, which reflect the optical data pulse back to the 3- dB coupler 20.
  • NLE Nonlinear Element
  • the NLE and the mirror of each optical path can be combined into a reflecting NLE 30 and 40, respectively.
  • a control pulse is injected into each of the reflecting NLE's 30, 40 either through a coupler along the optical path, as illustrated in the embodiment of Fig. 1, or through a second input at the NLE, as illustrated in Figs. 3 and 4.
  • the control pulse from a source generally designated as clock 50 is injected through couplers 35, 45 along the optical paths C and D.
  • couplers 35 and 45 are 90/10 couplers, which permit the use of strong control pulses.
  • coupler used in a particular application is a design choice that depends on the relative strength of the data and clock signals.
  • the selection of 90/10 coupler in the specific embodiment shown in Figs. 1 and 5 reflects the concern that data signals are typically relatively weak, and it is desirable to avoid any attenuation.
  • other choices, such as 60/40 are possible in alternative embodiments.
  • NLEs 30, 40 used in accordance with this invention exhibit an optical non-linearity with an extremely fast rise time and may have a relatively slow fall time.
  • the rise time must be less in duration than the bit time slot of an incoming data train and the fall time must be less than the frame time, so as enable the NLE in each optical path to be prepared for a next bit time slot in a next frame.
  • the relaxation time of the non-linearity of NLE 30, 40 does not have to be smaller than the bit period, which is the case in many prior art optical switch configurations.
  • NLE 30 and 40 may be any optical device that exhibits a rapid change in an optical non-linearity in response to an applied energy pulse.
  • the optical non-linearity may be evidenced by a change in refractive index, attenuation, or other optical phenomenon.
  • a gating pulse is applied from clock 50 to the optical switch via couplers 35, 45.
  • the control pulse injected in the NLE causes a very fast response - preferably a change in the index of refraction of the material - and the NLE then relaxes back into its original state, typically at a slower rate.
  • an optical time domain-multiplexed (OTDM) signal train is applied to the optical demultiplexer via an OTDM input 10.
  • the signal is split in coupler 20 and propagates concurrently in optical paths C and D until it is reflected by the mirror of the reflecting NLEs 30, 40.
  • the optical data pulses recombine at the 3-dB coupler 20.
  • the lengths of the optical paths are calibrated in advance.
  • the calibration may be such that when the pulses recombine in coupler 20, constructive interference occurs at input port A and destructive interference occurs at port B. Alternatively, the calibration may result in constructive interference that occurs at port B and destructive interference at port A.
  • the interferometer may be balanced so that output pulses can come out from either port A or port B, depending on the desired configuration.
  • the data pulses can then be switched to the other port if a control pulse is applied to change the state of the reflecting NLE on only one optical path, so that the pulse on this path experiences an additional 180° phase shift.
  • Figs. 1, 3, 4 and 5 reflect one type of calibration of the interferometer, where constructive interference normally occurs at the input port.
  • the demultiplexed output may coincide with the input port, and in order to recover the output signal, another coupler can be used to separate it from the input signal.
  • the Michelson TOAD in accordance with the present invention performs fast demultiplexing of the desired channel by using the rapid response time of the NLE.
  • a mode-locked laser can be used to provide both the data and the control pulses.
  • data and control pulses may be provided using different lasers. It should be apparent that where different lasers are used, it would be necessary to synchronize their operation, so that data pulses corresponding to a desired channel can be selectively extracted from the input data train. Details of such synchronization should be apparent to one of skill in the art and will therefore not be discussed in further detail. The reader is directed to for such details, for example, to the disclosure of the above-identified patents incorporated by reference.
  • a pulse is split in a 50/50 coupler 55 and injected into both reflecting NLEs of the Michelson TOAD. It should be apparent that the strength of the provided control signal depends on the NLE and in practice would be selected to trigger the non-linearity of the NLE.
  • the relative arrival time of the two control pulses into each optical path is offset by a time ⁇ t. As illustrated in Fig. 1 , in a preferred embodiment the difference in arrival time (which may be due to the different length of the optical paths, to temperature or other properties of the optical paths) can be tuned externally using a tunable delay line (TDL) 60.
  • TDL tunable delay line
  • Figure 2 shows how the difference in arrival time can switch out the desired channel in time.
  • all the pulses experience the same phase shift at the NLEs 30, 40, regardless of whether the NLEs are in the relaxed state or the excited state.
  • experiencing the same phase shift in the NLEs in the two optical paths causes the recombined pulse to exit from the input port A.
  • the pulse within the time window ⁇ t (solid pulse) in Fig. 2 experiences different properties of the NLE at the two optical paths, however.
  • the time slot ⁇ t can be made arbitrarily small (subject to practical limitations) by decreasing the difference in path lengths, and therefore the arrival times, of the control pulse.
  • the time slot to be switched can also be tuned very easily and rapidly to difference channels using devices, such as the fast TDL 60.
  • control pulse can also be injected into the NLEs in both optical paths directly through a second port.
  • Fig. 3 where li e reference numerals designate like elements.
  • the control pulse can be injected through the back of the NLE, as shown in Fig. 4.
  • Different embodiments are possible dependent on the structure and the properties of the NLE, the availability of a second input port. In practical applications the selection of the type of NLE and the way in which control pulses are injected in it would be determined by considerations including how well the structure integrates, on its cost, performance, etc.
  • Figure 5 shows an alternative embodiment of the present invention in which the NLEs 30, 40 can be physically separated from the mirrors 32, 42.
  • separating the elements may be a more cost-effective approach. It should be noted, however, that it also effectively extends the transit time across the NLE to include the separation distance between the NLE and the mirror, and therefore acts to reduce the achievable throughput of the device.
  • the setup With the NLE separated from the mirror, the setup also allows the possibility of injecting the control pulse from the same input as the data, as the difference in arrival time at the NLE is determined by their relative position in each optical path.
  • the reader is directed to the Mach-Zehnder TOAD configuration disclosed, for example, in U.S. Pat. No. 5,825,519.
  • control pulses having orthogonal polarization with respect to the data pulse it may be necessary to filter out control pulses from the output.
  • control pulses having different wavelength, compared with the data pulses and use a corresponding filter to remove the control data wavelengths from the output data stream.
  • such filter can be positioned between port B of the coupler 20 and the demultiplexed output 70.
  • the Michelson TOAD of the present invention can use an interferometer based on free space optics with discrete components, fiber optics with discrete components, or integrated optics combining optical waveguides and nonlinear elements on the same substrate, as known in the art.
  • the discrete components consist of optical fiber cables, optical couplers, polarizers, polarization splitters, optical filters, and a mode-locked laser that provides the control pulses.
  • the reflecting NLE can be made from a semiconductor optical amplifier (SOA) with one reflecting surface, a saturable Bragg reflector (SBR), or other reflecting nonlinear devices.
  • the NLE is implemented using vertical cavity surface emitting laser(s) (VCSEL).
  • another approach to building a Michelson TOAD is to integrate the optical waveguides, using either semiconductor materials, Lithium Niobate, or glass (SiO 2 ) as the substrate.
  • the active components preferably can be fabricated on the same surface with the optical waveguides.
  • the most common semiconductor material used is InGaAsP, where enabling technologies such as re-growth, tapered waveguide, and Twin Waveguide allows both the passive components and the active components to be fabricated on the same chip.
  • glass waveguides employ a hybrid implementation that uses both discrete and integrated components where slots are left opened in the waveguides for the insertion of the nonlinear element.
  • Michelson TOAD to be realized as ultrafast optical demultiplexer that can be monolithically integrated and compactly packaged.
  • Various techniques are envisioned for use in accordance with the principles of the present invention, dependent on the specific practical application.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
  • Optical Communication System (AREA)

Abstract

La présente invention concerne un démultiplexeur optique comportant un coupleur (20) connecté au premier chemin optique ayant un premier élément optique non linéaire (NLE) réflecteur qui répond à une impulsion de commande afin d'induire un décalage de phase de 180 degrés dans un signal de données optiques qui se propage à travers cet élément. Un second chemin optique est connecté au coupleur, qui comprend un second NLE réflecteur similaire. Des impulsions optiques disponibles à un port d'entrée du coupleur se propagent à travers les deux chemins optiques et, lorsqu'elles sont réfléchies, connaissent des interférences, soit constructives soit destructives, en fonction de l'état des NLE. Une entrée de commande (50) génère une première impulsion de commande dans le premier chemin optique et une seconde impulsion de commande dans le second chemin optique, la seconde impulsion de commande étant décalée d'un temps (delta t) par rapport à la première impulsion de commande, de façon qu'une impulsion de données (10) se propageant à travers le premier chemin subit un décalage de phase de 180 degrés par le premier NLE, mais ne connaît pas de décalage de phase supplémentaire dans le second NLE. Dans certains modes de réalisation, les NLE réflecteurs sont mis en place soit sous forme de composants intégrés, soit par utilisation de miroirs réflecteurs séparés du NLE. Cette invention concerne également différents plans relatifs à l'entrée de commande.
PCT/US2000/018763 1999-07-08 2000-07-10 Systeme et procede de demultiplexage asymetrique optique dans le domaine terahertz WO2001005084A1 (fr)

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US60/142,892 1999-07-08

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002076000A1 (fr) * 2001-03-19 2002-09-26 General Instrument Corporation Demultiplexeur de paquets de donnees tout-optique a intervalle de temps accordable
EP1298827A2 (fr) * 2001-09-27 2003-04-02 Fujitsu Limited Système de traitement de signal optique

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US5493433A (en) * 1994-03-02 1996-02-20 Trustees Of Princeton University Terahertz optical asymmetric demultiplexer
US5625727A (en) * 1995-03-15 1997-04-29 U.S. Philips Corporation Unit for modulating an optical pulse series in conformity with a data signal
US5701327A (en) * 1996-04-30 1997-12-23 Lucent Technologies Inc. Saturable Bragg reflector structure and process for fabricating the same
US5742415A (en) * 1993-10-11 1998-04-21 British Telecommunications Public Limited Company Optical switching device
US5825519A (en) * 1996-09-27 1998-10-20 Princeton University Optical mach-zehnder time division demultiplexer
US5848205A (en) * 1996-01-30 1998-12-08 Alcatel N.V. Polarization independent non-linear optical mirror
US5912913A (en) * 1995-12-27 1999-06-15 Hitachi, Ltd. Vertical cavity surface emitting laser, optical transmitter-receiver module using the laser, and parallel processing system using the laser
US5999293A (en) * 1995-01-19 1999-12-07 British Telecommunications Public Limited Company Optical switch
US6097529A (en) * 1997-12-17 2000-08-01 Electronics And Telecommunications Research Institute Apparatus for enhancing extinction ratio in optical NRZ-to-RZ converting system, and optical modulation system therefor

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5742415A (en) * 1993-10-11 1998-04-21 British Telecommunications Public Limited Company Optical switching device
US5493433A (en) * 1994-03-02 1996-02-20 Trustees Of Princeton University Terahertz optical asymmetric demultiplexer
US5999293A (en) * 1995-01-19 1999-12-07 British Telecommunications Public Limited Company Optical switch
US5625727A (en) * 1995-03-15 1997-04-29 U.S. Philips Corporation Unit for modulating an optical pulse series in conformity with a data signal
US5912913A (en) * 1995-12-27 1999-06-15 Hitachi, Ltd. Vertical cavity surface emitting laser, optical transmitter-receiver module using the laser, and parallel processing system using the laser
US5848205A (en) * 1996-01-30 1998-12-08 Alcatel N.V. Polarization independent non-linear optical mirror
US5701327A (en) * 1996-04-30 1997-12-23 Lucent Technologies Inc. Saturable Bragg reflector structure and process for fabricating the same
US5825519A (en) * 1996-09-27 1998-10-20 Princeton University Optical mach-zehnder time division demultiplexer
US6097529A (en) * 1997-12-17 2000-08-01 Electronics And Telecommunications Research Institute Apparatus for enhancing extinction ratio in optical NRZ-to-RZ converting system, and optical modulation system therefor

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002076000A1 (fr) * 2001-03-19 2002-09-26 General Instrument Corporation Demultiplexeur de paquets de donnees tout-optique a intervalle de temps accordable
US6650800B2 (en) 2001-03-19 2003-11-18 General Instrument Corporation Time slot tunable all-optical packet data demultiplexer
EP1298827A2 (fr) * 2001-09-27 2003-04-02 Fujitsu Limited Système de traitement de signal optique
EP1298827A3 (fr) * 2001-09-27 2004-09-22 Fujitsu Limited Système de traitement de signal optique

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