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US20030035187A1 - Optical receiver, optical receiving method and optical transmission system - Google Patents

Optical receiver, optical receiving method and optical transmission system Download PDF

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Publication number
US20030035187A1
US20030035187A1 US09/802,753 US80275301A US2003035187A1 US 20030035187 A1 US20030035187 A1 US 20030035187A1 US 80275301 A US80275301 A US 80275301A US 2003035187 A1 US2003035187 A1 US 2003035187A1
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optical
optical signal
linear
encoded
decoded
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David Richardson
Periklis Petropoulos
Morten Ibsen
Peh Teh
Ju Lee
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Trumpf Laser UK Ltd
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Assigned to SOUTHAMPTON, UNIVERSITY OF reassignment SOUTHAMPTON, UNIVERSITY OF ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: PETROPOULOS, PERIKLIS, IBSEN, MORTEN, LEE, JU HAN, RICHARDSON, DAVID JOHN, TEH, PEH CHIONG
Publication of US20030035187A1 publication Critical patent/US20030035187A1/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/005—Optical Code Multiplex
    • 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
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
    • G02B6/0208—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response
    • G02B6/02085—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response characterised by the grating profile, e.g. chirped, apodised, tilted, helical
    • 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
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
    • G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
    • G02B6/02152—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating involving moving the fibre or a manufacturing element, stretching of the fibre
    • 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
    • G02F1/3519—All-optical modulation, gating, switching, e.g. control of a light beam by another light beam using an interferometer of Sagnac type, i.e. nonlinear optical loop mirror [NOLM]

Definitions

  • the invention relates to the field of optical telecommunications, more specifically, but not exclusively to optical code division multiple access (OCDMA).
  • OCDMA optical code division multiple access
  • All-optical pattern generation and recognition are two such signal-processing functions that are likely to be required in future high-capacity optical networks. These functions will be needed for example for header recognition in ultra-fast OTDM packet switched networks, and for use within Optical Code Division Multiple Access (OCDMA) systems [ 1 , 2 ].
  • OCDMA is the optical analogue of the CDMA technique that has been applied with such success to the field of mobile communications.
  • CDMA is a spread-spectrum digital transmission technique which allows multiple users of a network to share the same relatively broad transmission bandwidth through the allocation of specific mathematically defined codes which dictate how the individual users use/sample the available spectral bandwidth in order to both send and receive data.
  • DS-CDMA Direct-Sequence
  • FH-CDMA Frequency-Hopping
  • a SSFBG can be defined as a standard fiber grating, i.e. a grating with a rapidly varying refractive index modulation of uniform amplitude and pitch, onto which a slowly varying refractive index modulation has been applied along its length. It can be readily proven that the impulse response of a weakly reflecting SSFBG (reflectivity less than ⁇ 20%) follows precisely the same form as the slowly varying, superstructure refractive index profile [ 5 ].
  • We produce our SSFBGs using a continuous grating writing method which enables us to write fiber Bragg gratings on a grating plane by grating plane basis, and which thereby allows the fabrication of gratings with highly complex refractive index profiles [ 6 ].
  • SSFBGs can thus be designed and fabricated with a wide range of complex tailored impulse response functions with precise amplitude and phase characteristics. Such SSFBGs should find application within a variety of optical pulse processing systems [ 7 , 8 ], including use within both DS-OCDMA code generation and recognition devices and for which precise control of the amplitude and phase of the temporal pulse profile is essential. SSFBG technology represents an attractive means to produce compact, and potentially low-cost components for such applications relative to the more conventional technological approaches and which include: the use of planar lightwave circuits [ 9 ], arrays of discrete fiber gratings [ 10 ], bulk grating based systems incorporating spatial light modulators [ 11 ], and arrays of fiber couplers [ 12 ].
  • FIG. 1 shows the basic principle of pulse encoding and decoding by SSFBG's.
  • the resulting reflected signal represents a coded sequence of distinct, time-spread pulses (the individual pulses that make up the code sequences are commonly known as chips).
  • the individual chip duration, the code sequence, and code length are defined by the SSFBG impulse response, which as discussed above, is given by the SSFBG refractive index profile.
  • the coded pulse sequence is then transmitted along an optical fiber to the decoder/receiver.
  • the decoder operates on the principle of matched filtering, and as such is based upon purely linear optical effects.
  • the matched filtering operation is realized in practice by reflecting the coded pulses from a grating with the spatially reversed superstructure profile of the encoder grating and which thus has the temporally inversed impulse response (phase conjugate frequency response). Consequently the pulse reflected from the decoder grating represents the cross-correlation function between the codes used within the encoder and decoder SSFBGs. In the instance that the codes are matched the reflected pulse represents the autocorrelation function of the encoded pulse sequence.
  • gated detection can be used at the receiver to suppress side lobes caused by fiber dispersion in an OCDMA transmission system.
  • the receiver design is made more complex and optoelectronic and electrical componenents are needed which is a limitation for high bit rate communications.
  • an optical receiver comprising:
  • a non-linear optical element connected to receive the decoded optical signal and enhance the autocorrelation peak relative to the background component by virtue of the autocorrelation peak having an intensity above a non-linear threshold of the non-linear optical element and the background component having an intensity below the non-linear threshold of the non-linear optical element, thereby to enhance the decoded optical signal.
  • This approach provides a simple passive way of improving the reception quality of an optical signal that has been decoded after spread-spectrum encoded transmission.
  • the need for optical gating circuitry [ 21 ] is completely avoided.
  • the advocated approach not only allows intensity discrimination of the decoded autocorrelation peak relative to the background component, but also allows the pulse width of the autocorrelation peak to be reduced (compressed) back down to the pulse width of the optical signal at the transmitter before spread-spectrum encoding, or even to narrower pulse widths if desired.
  • the non-linear optical element in the main embodiments described below is a non-linear optical loop mirror (NOLM).
  • NOLM non-linear optical loop mirror
  • SOA semiconductor optical amplifier
  • any other suitable non-linear component could be used as an alternative, for example a non-linear amplifying loop mirror, a non-linear directional coupler, a semiconductor saturable absorber or a Kerr gate.
  • the decoder may comprise a refractive index modulation induced grating which may be fabricated in an optical fiber or a planar waveguide, for example.
  • the receiver may further comprise a dispersion compensator arranged to compensate for dispersion during transmission of the encoded optical signal.
  • An amplifier is preferably arranged prior to the non-linear optical element and configured to supply the decoded optical signal to the non-linear optical element within a desired power range.
  • the amplifier is preferably an optical amplifier, thereby avoiding optoelectronic components.
  • the decoder is preferably arranged in reflection in combination with a circulator. It could however be arranged in transmission in alternative embodiments.
  • the decoder may be configured to decode a spread-spectrum or OCDMA encoded optical signal. Optical packet switched signals may also be handled.
  • an optical transmission system comprising:
  • an optical transmitter including an encoder for generating encoded optical signals
  • a method of decoding an encoded optical signal comprising:
  • the decoded optical signal is supplied to the non-linear optical element after amplification to ensure that the non-linear optical element performs to a desired specification.
  • NOLM nonlinear optical loop mirror
  • the receiver, system and/or method can also include one or more of the following features:
  • More complex superstructure profiles including amplitude and phase features to shape controllably the individual chip shapes.
  • the apparatus may be reconfigured such that the superstructure grating as above is used in transmission mode rather than reflective mode.
  • the superstructure decoding technique to correlate (provide matched filtering) directly with the output from a modulated optical source.
  • the source can be a directly modulated gain-switch diode, and externally modulated DFB laser, a mode-locked fiber ring laser with external modulation.
  • CDM code division multiplexing
  • CDM we mean not only code-division multiplexing but also include ultrafast packet-switched, or other OTDM networks or transmissions systems.
  • FIG. 1 Basic principle of pulse encoding and decoding by SSFBGs.
  • FIG. 2 Configuration of a 7-chip time spread DS-OCDMA system incorporating a NOLM.
  • the saturated output power from EDFA3 was 15 dBm.
  • the length of DSF in the NOLM was 6.6 km and the dispersion of the DSF was 1.18 ps/nm/km.
  • FIG. 3 Theoretical calculation showing the predicted impact of the NOLM on both the autocorrelation signal reshaping and pedestal rejection as a function of input pulse power; (a) actual pulse shape evolution as a function of increasing input pulse peak power, (b) same data plotted in a log scale.
  • FIG. 4 (a) FWHM of the central autocorrelation feature as a function of input power, (b) corresponding value of the signal contrast defined as the ratio between the peak power of the output pulse to that of the first pedestal lobe, (c) contrast ratio in terms of the measured SHG autocorrelation of the decoded pulse form.
  • FIG. 5 Predicted and measured reflectivity of the NOLM as a function of input peak power.
  • FIG. 6 Experimental and theoretical SHG autocorrelation functions at a peak power of 1.2W both (a) before and (b) after the NOLM.
  • FIG. 7. (a) Experimental setup for the 63-chip, 160 Gchip/s system experiments, (b) two 63-chip bipolar Gold codes and the corresponding spectral profiles of the encoder SSFBGs that were fabricated.
  • FIG. 8 Theoretically predicted, and experimentally observed, response of (a) gratings C 1 and (b) their corresponding conjugates C 1 * after excitation with 2.5 ps pulses. (solid lines: experimental measurements, dashed lines:
  • FIG. 9 The SHG autocorrelations of the central correlation spikes of the decoded pulseforms, (a) prior to the NOLM and (b) directly after the decoder grating for bit-rates of both 1.25 and 2.5 Gbit/s.
  • FIG. 10 Eye diagrams of (a) the input 2.5 ps pulses, (b) the pulses after matched filtering and (c) the matched filtered pulses after nonlinear switching by the NOLM for the data rates of 1.25 GHz and 2.5 GHz, each. (100 ps/div)
  • FIG. 11 Measured BER versus received optical power for single-user operation at 1.25 Gbit/s and 2.5 Gbit/s.
  • FIG. 12 For single-channel operation at 10 Gbit/s, (a) eye diagrams (50 ps/div) and (b) BER versus received optical power.
  • FIG. 13 Eye diagrams for 2-channel operation at 2.5 Gbit/s. (100 ps/div)
  • FIG. 14 Measured BER versus received optical power for 2-channel operation at 1.25 Gbit/s and 2.5 Gbit/s.
  • FIG. 15 Optical packet switching node for a packet-switched optical communication system.
  • NOLM nonlinear optical loop mirror
  • Section II we present the results of a preliminary theoretical study into the pulse-shaping and signal-contrast enhancement effects that can be obtained by incorporating a suitably designed NOLM into a SSFBG based DS-OCDMA system. Calculations are presented for a specific 7-chip, bipolar 160 Gchip/s system based on M-sequence codes, and the results are then compared with experimental data.
  • section III we present the results of detailed system experiments using 63-chip, 160 Gchip/s bipolar coding and decoding SSFBGs in which the noise reduction benefits of using the NOLM within the decoder are more apparent. The performance benefits achieved are then quantified from a system perspective. Both single channel and multi-channel operation are investigated and the cancellation of both intra-channel, and inter-channel interference noise are successfully demonstrated.
  • Section V we describe an optical packet switching receiver incorporating a non-linear element for signal processing.
  • FIG. 2 The configuration for the 7-chip time-spread DS-OCDMA system that we used to first validate the nonlinear, code recognition signature enhancement concept described above is shown in FIG. 2.
  • the system comprised: a 2.5 ps, 10 GHz regeneratively mode locked erbium fiber ring laser (EFRL) with an external 10 GHz ‘pulse selector’; a 7-chip coding SSFBG; a matched 7-chip decoder SSFBG; various low-noise amplifiers to compensate for the system losses; a power amplifier to boost the power of the decoded signal; and a NOLM for nonlinear processing of the matched-filtered signal.
  • EFRL regeneratively mode locked erbium fiber ring laser
  • Short pulses from the laser were launched onto the coding SSFBG resulting in the generation of a code sequence corresponding to the impulse response of the grating.
  • the particular code was bipolar with the required phase-shifts distributed within the grating in accordance with the 7-chip M-sequence code ‘ 0100111 ’.
  • the chip length of the gratings used in our experiments was 6.4 ps, corresponding to a chip rate of 160 Gchip/s.
  • the coded pulse sequence had a total duration of ⁇ 45 ps. The coded pulses were then launched onto the decode grating.
  • the temporal form of the pulses reflected from the decoder grating thus represented the cross-correlation function between the incoming encoded sequence and the decoder grating's impulse response function.
  • the encoder:decoder gratings are well matched then our specific choice of a 7-chip M-sequence ensures a good pattern recognition signature which has the form of a short, chip-length long autocorrelation spike on a relatively low-level broad pedestal.
  • the pedestal has a total duration of twice the code length (i.e. 90 ps).
  • pulse amplitude A is normalized such that
  • ⁇ 1 is the group delay
  • ⁇ 2 is the first order group velocity dispersion (GVD)
  • ⁇ 3 is the second order GVD.
  • ⁇ represents the absorption coefficient of optical power in the fiber and corresponds to 0.25 dB/km
  • ⁇ o is the signal frequency
  • ⁇ n 2 ⁇ ⁇ o c ⁇ ⁇ A eff
  • T R 2 fs has its origin in the delayed Raman response and represents the first-order Raman gain effects. (Note that in fact neither Raman scattering, self-steepening, nor third-order dispersion play a significant role in the evolution of pulses of order the chip length over the ⁇ 6 km propagation lengths considered herein.)
  • the values of the dispersion parameter (D), dispersion slope (dD/d ⁇ ), and nonlinearity coefficient ( ⁇ ) assumed within our calculations were 1.18 ps/nm/km, 0.07 ps/nm 2 /km and 1.55 W ⁇ 1 km ⁇ 1 respectively at the system-operating wavelength of 1558 nm and corresponded to those of a fiber that was available within our laboratories.
  • the fiber length was 6.6 km.
  • FIG. 3 we present the results of our theoretical calculation which show the predicted impact of the NOLM on both the autocorrelation signal reshaping and pedestal rejection as a function of input pulse power.
  • FIG. 3( a ) we plot the pulse shape evolution as a function of increasing input pulse peak power.
  • FIG. 3( b ) is a log scale plot of the same data.
  • the pulse shape of the simple matched filtered decoded signal for the particular 7-chip bipolar pulse sequence used in our experiments is given by the ‘0 W’ pulse form in FIG. 3( a ). (Note that the individual pulse shape at each power is normalized with respect to the peak pulse amplitude). It can be seen that as the decoded signal power is increased the relative height of the ripple features associated with the pedestal decreases and the central autocorrelation feature narrows significantly.
  • FIG. 4( a ) we plot the half width of the central autocorrelation feature as a function of input power. It is seen that optimum compression with compression factors approaching ‘3’ are obtained at a pulse peak power of ⁇ 1.5W. Note that for a peak power of 1.2W the pulse duration is 2.5 ps, essentially the same as that of the input laser pulses.
  • FIG. 4( b ) we plot the corresponding value of the signal contrast which we define as the ratio between the peak power of the output pulse to that of the first pedestal lobe. After simple matched filtering alone, (i.e.
  • this ratio is ⁇ 17 dB. However, this can be increased by as much as 10 dB at a peak power of 1.6W and represents the optimum contrast enhancement in this instance.
  • An 8-9 dB contrast enhancement is achieved at a peak power of 1.2 W.
  • FIG. 4( c ) we quantify the improvement in contrast ratio in terms of the measured SHG autocorrelation of the decoded pulse form, since in practice it is this that we measured directly in our preliminary experiments. A factor of ⁇ 3 reduction in pulse width and a peak contrast ratio enhancement factor of order 10 dB is again predicted. The pulse width contraction and nonlinear filtering result from high order soliton effects within the NOLM [ 19 ].
  • FIG. 5 we plot the predicted reflectivity of the NOLM as a function of input peak power.
  • the NOLM is predicted to transmit ⁇ 12% of the incident decoded pulse power at low intensities, with this percentage increasing to ⁇ 78% at a pulse power of ⁇ 1.8W.
  • FIG. 5 we also plot the experimentally determined reflectivity as a function of incident power.
  • the amplifier used in this particular experiment limited our maximum achievable peak power to 1.2W, which although slightly less than optimum, still allowed for significant switching, pulse shaping and contrast enhancement.
  • the use of longer codes means that interference noise due to temporal overlap of adjacent coded data bits occurs once the length of the decode signal (which is two times the code length) becomes longer than the reciprocal of the data rate.
  • This interference noise can significantly impact the system performance even under single user operation of the system.
  • Similar interference noise is also generated once there are simultaneous users of the system, transmitting either synchronously or asynchronously over the same fiber.
  • FIG. 7( a ) Our experimental setup for the 63 chip, 160 Gchip/s system experiments is shown in FIG. 7( a ) and is similar in principle to the 7-chip set-up.
  • the 2.5 ps pulse at 10 GHz were first gated down to a lower repetition frequency, and encoded with pseudorandom data at either 1.25, or 2.5 Gbit/s.
  • the data pulses were then split using a 3 dB coupler and fed onto two separate encoder gratings, denoted C 1 and C 2 respectively, before being recombined into a single fiber using a second 3 dB coupler.
  • the individual encoding SSFBG's contain phase-coding information within their refractive index profiles as defined by two ‘orthogonal’, 63-chip bipolar Gold codes. Once the data pulses are reflected from gratings C 1 and C 2 they generate two distinct data streams encoded with either one of these two distinct codes.
  • FIG. 7( b ) we plot both the distribution of the phase changes along the gratings as defined by the two Gold sequences selected, and their corresponding spectral responses. The spiky reflectivity spectrum observed results from the multiple phase jumps within the spectrum and is as theoretically expected.
  • the chip duration for these gratings is 6.4 ps, and the chip rate 160 Gchip/s.
  • the coded data bits have a total duration of ⁇ 400 ps as illustrated in FIGS. 8 ( a ) and 8 ( b ) in which we plot both the theoretically predicted, and experimentally observed, response of gratings C 1 and their corresponding conjugates C 1 * after excitation with 2.5 ps pulses. Although the response time of the detection system used to measure these pulses was insufficient to precisely resolve the individual chips, a clear correlation between theory and the experimental data is observed, confirming the high quality of the gratings.
  • the coded data stream was then either fed directly to decode grating C 1 *, or else transmitted over 25 km of standard single mode fiber whose dispersion was compensated over a 5 nm bandwidth using a suitably linearly chirped fiber Bragg grating and then fed to grating C 1 *.
  • Grating C 1 * was designed to provide a matched filter response to grating C 1 .
  • the decoded output from grating C 1 * was then either detected directly, or amplified in EDFA3 before being passed through the NOLM prior to detection.
  • the NOLM used in the 63-chip experiments was the same NOLM used in the previously described 7-chip experiments.
  • FIG. 9( a ) Disconnecting the fibers connected to grating C 2 in FIG. 7( a ) allowed us to make single user experiments using gratings C 1 and C 1 *.
  • FIG. 9( a ) we show the SHG autocorrelations of the central correlation spikes of the decoded pulseforms prior to the NOLM and directly after the decoder grating for bit-rates of both 1.25 and 2.5 Gbit/s. This particular data was taken with no intermediate transmission of the coded data bits.
  • the decoded pulseforms have a deconvolved temporal half-width of 6.4 ps at 2.5 Gbit/s, and 5.8 ps at 1.25 Gbit/s and exhibit an appreciable pedestal component which extends +/ ⁇ 400 ps from the central correlation spike as can be seen in the eye diagrams shown in FIG. 10( b ).
  • the presence of the pedestal component can still have a significant impact on the pattern recognition signal to noise ratio. This is particularly true at data rates above 1.25 Gbit/s for which the 800 ps long correlation pulses arising from individual data bits can have significant overlap in the pulse tails with decoded bits originating from neighboring bit slots. This overlap can result in significant amplitude noise associated with coherent interference between pedestals arising from adjacent/neighboring ‘1’ data bits. This increased noise level is apparent within FIG.
  • the power-penalty increased to 4.5 dB at 2.5 Gbit/s due to the intra-channel interference noise arising from decode signal overlap as previously discussed. Note that at both data rates there was no significant additional power penalty associated with transmitting the coded bits over the 25 km dispersion-compensated transmission line.
  • the measured BER plots are summarized in FIG. 14.
  • the residual power penalty of ⁇ 1.5 dB is comparable to that achieved previously for single channel operation without the NOLM.
  • the penalties in the two channel experiments to be due primarily to the contribution to the received average power made by imperfect suppression of the second (‘orthogonal’) channel.
  • the benefits of using the NOLM at the higher data rate of 2.5 Gbit/s are even more manifest. In this instance it was not possible to get error free operation without the use of the NOLM.
  • the power penalty relative to the back to back in this instance was 2.8 dB, and which again was similar to that previously obtained for conventional single channel operation at this data rate. Note that as previously discussed at a data rate of 2.5 Gbit/s the individual pattern recognition signatures overlap providing an additional element of intrachannel interference noise, and hence the slightly increased power penalty relative to the 1.25 Gbit/s case in which no such overlap occurs.
  • a header recognition signature can be used to effect onward processing, e.g. routing, of the optical data.
  • FIG. 15 shows as one example an optical switching node for IP data for use in a packet switched network.
  • An incoming data stream made up of a series of packets 506 is received at an input 508 of the routing node.
  • Each packet 506 comprises a header 502 , that defines the code address, and a subsequent data payload 504 , separated by a short (guard-) time from the header address.
  • the signal enters the routing node where it is split into two by a splitter 500 , for example a 3 dB fiber coupler.
  • the signal proceeds through an optical delay line 585 to an input of an optical switch (or router, filter or modulator) 570 .
  • the signal is supplied through an optical circulator 510 to one or more decoder gratings 520 of the kind described in relation to the previous embodiment.
  • the reflected signal is then routed onwards in the signal path by the circulator 510 .
  • multiple decoder gratings 520 may be arranged in series as shown or parallel.
  • Each decoder grating is designed to provide a matched filtered response to a particular optical header 502 . When correct matched filtering is obtained, (i.e.
  • a relatively intense autocorrelation signature is generated by the decoder grating which is then supplied to an optoelectronic converter 540 , e.g. a fast-response photodetector, through a non-linear element 530 for pulse shaping.
  • an optoelectronic converter 540 e.g. a fast-response photodetector
  • the non-linear element 530 may be a NOLM as in the previous embodiments, or some other non-linear element, for example a semiconductor optical amplifier (SOA).
  • SOA semiconductor optical amplifier
  • the optoelectronic converter 540 is connected to an electronic decision circuit 550 which has an electrical output line 560 connected to a control input of the optical switch 570 for triggering it.
  • the electrical control signal thereby gates the switch 570 for sufficient time to allow passage of the original data packet (and generally, but not necessarily, also the header) into the output line 590 .
  • the delay line 585 on the input arm 580 of the switch may be actively controlled (e.g. by stretching a fiber spool with a piezoelectric actuator) to ensure that the opening of the switch 570 occurs at the correct time relative to the incoming data signal (i.e. it can be used to accommodate the various time-lags within the system).
  • the optical packet switching system may operate with asynchronous transmitters, or a combination of synchronous and asynchronous transmitters and receivers.

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US20040136454A1 (en) * 2002-12-24 2004-07-15 General Electric Company System and method for digital transmission and modulation of conjugate pulse position
US20040234217A1 (en) * 2002-08-22 2004-11-25 Arie Shahar All optical phase insensitive code responsive and code separator devices apparatus and method
US20050047453A1 (en) * 2003-08-27 2005-03-03 Fujitsu Limited Multi-wavelength light source apparatus
US20070097854A1 (en) * 2005-10-27 2007-05-03 Chung Hwan S Apparatus and method for reducing signal noise and OCDMA receiver and method
WO2007053172A3 (en) * 2005-02-18 2007-12-13 Telcordia Tech Inc Phase chip frequency-bins optical code division multiple access
US20080240734A1 (en) * 2004-08-20 2008-10-02 Masaru Fuse Multimode Optical Transmission Device
US20110097079A1 (en) * 2008-07-03 2011-04-28 University Of Yamanashi Optical communication system, optical transmitter, optical receiver and methods, and correlators used therefor
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US6628864B2 (en) 2003-09-30
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