Classifications

• • 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
  • H04Q11/0003—Details
• • 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
  • H04Q2011/0007—Construction
• • 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
  • H04Q2011/0043—Fault tolerance
• • 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
  • H04Q2011/0049—Crosstalk reduction; Noise; Power budget
• • 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
  • H04Q11/0062—Network aspects
  • H04Q2011/0079—Operation or maintenance aspects
  • H04Q2011/0083—Testing; Monitoring

Definitions

• Optical circuit for obtaining a monitor signal Optical circuit for obtaining a monitor signal.
• the invention lies in the field of monitoring optical switching points in optical systems and networks. More in particular, it relates to an optical circuit for obtaining a monitor signal for monitoring an optical switch provided with two output gates.
• optical switches such as for protection purposes and for cross-connecting optical transmission channels, for example.
• switches with two outputs (1 x2 and 2x2 switches) are often applied.
• Such switches require driving and monitoring from a control system of such networks.
• the control system thereto requires information about a switch, such as, for example, about the switching state in which it is in. This information could be obtained by monitoring the (for example, electrical) control signals of the switch. It is preferable, however, to monitor the optical outputs of the switch, in order therewith not only to obtain more information about the functioning of the switch, but also about the optical signal itself.
• a possibility for obtaining said information is by taking off a relatively small fraction (for example 10%) of the optical output signal for monitoring purposes at each output by means of an optical signal tap, hereinafter referred to as signal tap for short.
• signal taps are known per se.
• Integrated versions hereof are known, for example, from references [1 ] and [2] (for more Bibliographical details with respect to the references, see below under C).
• Monitor signals obtained in this way are converted with separate o/e converters into electrical signals which are subsequently processed in the electrical domain.
• all relevant parameters required for proper control including the total optical power, can be determined in this way.
• optical switches are being increasingly applied in integrated form, often together with other optical signal-processing functions, it can further be advantageous to limit the number of conversions to the electrical domain as much as possible.
• a trivial solution for such a restriction consists of omitting one of the two detectors, including the related signal tap. This is done, however, at the expense of information whereby, for example, any occurring cross-talk of the switch and the total power can no longer be directly determined.
• St1 an optical signal applied to an input gate is switched via a first output gate
• St2 an optical signal applied to the input gate is switched via a second output gate
• St12 a signal-splitting state in which the optical signal applied is equally distributed across the two output gates according to power. Dependent upon the type of switch, this state can occur upon, for example electrical, failure of the driving action. Thus a digital optical switch (DOS) changes into a passive splitter when driving action fails. This state can also occur in a reconfigurable network having the possibility of signal distribution.
• StO a zero-state in which, for whatever reason whatsoever, for example by a failure of the optical path through the switch, an output signal is not present at either of the two output gates.
• the invention provides an optical circuit with which the said need can be met. It achieves this with an optical circuit in which, with means for coupling out, (power) fractions of any optical signals which may be present at the two output gates are obtained, which are subsequently combined by signal combination means into a combined optical signal to be detected which is led to one single detector for detection.
• Said combined optical signal which is to be detected hereinafter referred to as monitor signal, is such that the momentary state (that is to say, one of the switching states referred to above) of the switch can always be unambiguously determined therefrom.
• the optical circuit exhibits thereto either in the means for coupling out, or in the signal combination means, or in both, an unequality or an asymmetry in signal treatment, whereby in the monitor signal the optical signals that may be present at the two output gates are recognisable as specific power fractions.
• any interference that may occur in the monitor signal does not detract from an unambiguous determination of the momentary state of the switch.
• WDM optical wavelength channels
• the optical circuit is thereto characterised according to Claim 1.
• FIG. 1 shows a first embodiment of an optical circuit according to the invention
• FIG. 2 shows a second embodiment of an optical circuit according to the invention
• FIG. 3 shows a third embodiment of an optical circuit according to the invention.
• St1 an optical signal applied to an input gate is switched via a first output gate
• St2 an optical signal applied to an input gate is switched via a second output gate
• St12 a signal-splitting state in which the optical signal applied is distributed according to power across the two output gates
• StO a zero-state in which, for whatever reason whatsoever, an output signal is not present at either of the two output gates.
• the state St12 can occur upon failure of the, for example electrical, driving action.
• a digital optical switch (DOS) for example, changes upon failure of the driving action into a passive splitter.
• the state St12 can also occur in a reconfigurable network with the capability of signal distribution.
• the state StO occurs, for example, upon failure of the optical path through the switch, or upon failure of the input signal at the input gate.
• an optical signal tap is included, viz. signal tap 2 with output 2.1 and signal tap 3 with output 3.1 in the first embodiment of FIG. 1 , signal tap 6 with output 6.1 and signal tap 7 with output 7.1 in the second embodiment of FIG. 2, and signal tap 14 with output 14.1 and signal tap 15 with output 15.1 in the third embodiment of FIG. 3.
• the outputs of the signal taps are connected to input gates of an optical signal combiner 40, which is provided with an output gate 50 which is led to detection means.
• the optical signal combiner 40 is a Y-junction 4 with monomodai input gates 4.1 and 4.2, and a bimodal output gate 4.3, while the detection means are formed by a signal detector 5 with a bimodal input gate, hereinafter referred to as bimodal detector 5 for short.
• the optical signal taps 2 and 3 are signal taps with different coupling out fractions f 2 and f 3 respectively.
• bimodal designates that both zero-order and first-order modes may be present.
• the circuit according to the first embodiment operates as follows. Upon undisturbed operation of the switch, an optical signal I entering at an input gate 1 .3 of the switch 1 will exit either via output gate 1 .1 as output signal 0, or via output gate 1 .2 as output signal 0 2 .
• the power of either the output signal 0, or the output signal 0 2 is at any rate substantially equal to (or at any rate is in fixed proportion to) the power of the entering signal I.
• a partial signal d0 1 is coupled out by the signal tap 2.
• the partial signal d0 1 of the signal O is subsequently led to the detector 5 via the input gate 4.1 and the output gate 4.3 of the signal combiner 4 as monitor signal M, .
• a partial signal d0 2 from a possibly exiting signal 0 2 is coupled out in signal tap 3 and subsequently led to the detector 5 as monitor signal M,.
• the power of the partial signal dO, (d0 2 ) is a fraction f, (f 2 ) of the power of the signal O, (0 2 ). In principle, if f, and f 2 differ sufficiently from each other and from zero, an unambiguous distinction can be made by power measurement in the detector 5 between the switching states StO, St1 and St2 of the switch.
• the switching state St12 will also be unambiguously distinguishable from the other switching states.
• Suitable values for the two fractions are, for example, 5% and 10%.
• crosstalk can also be detected. If, for the suitable values mentioned for the fractions, a power for the monitor signal is measured, for example, of 5.1 % of the input power, then this implies a switching state in which the signal substantially exits at the output gate (for example 1 .1 ) in which the 5% signal tap (tap 2) is included, be it with a cross-talk of 20dB to the other output gate (1 .2).
• This first embodiment has two limitations. In the first place, the required bimodal detector is larger and therefore slower than a monomodal detector. This can give rise to problems if the optical signals must also be analysed at bit level, such as for BER measurements for example (BER: Bit Error Ratio). Further, an implementation with optical fibres is difficult, since bimodal optical fibres as a product are not current and the merging of two monomodal fibres gives rise to a coupling problem with the bimodal detector. Admittedly, a "fused" feeder of two monomodal fibres is indeed implementable in principle, and combination by projection on the detector is also possible. These are relatively expensive solutions, however.
• the second embodiment of the optical circuit which is diagrammatically shown in FIG. 2, meets these limitations.
• the optical signal combiner 40 consists of two Y-junctions 8 and 9 mutually coupled via their stem, while the detection means are formed by a signal detector 10 with a monomodal input gate, hereinafter referred to as monomodal detector 10 for short.
• the outputs 6.1 and 7.1 of the signal taps are connected respectively to input gates 8.1 and 8.2 of a first Y-junction 8.
• Output gate 8.3 of the first Y-junction 8 is connected directly to an input gate 9.1 of the second Y-junction 9.
• a first output gate 9.2 forms the output gate 50 of the signal combiner 40, which is led to the monomodal detector 10, while a second output gate 9.3 of it is not used.
• the first Y- junction 8 is a completely asymmetrical Y-junction which is provided with monomodal input gates 8.1. and 8.2, and a bimodal output gate 8.3, and which operates as a mode splitter or mode filter.
• the second Y-junction 9 is an incomplete asymmetrical Y-junction, which is provided with a bimodal input gate 9.1 and monomodal output gates, and which operates as a non-ideal mode splitter with a splitting ratio of ⁇ /(1 - ⁇ ), with 0 ⁇ 0.5.
• Such an incomplete asymmetrical Y-junction is known from reference [3], for example.
• the optical signal taps 6 and 7 are signal taps with coupling out fractions f 3 and f 4 respectively.
• the circuit according to the second embodiment operates as follows.
• an optical signal I entering at an input gate 1 .3 of the switch 1 will exit either via output gate 1 .1 as output signal 0,, or via output gate 1 .2 as output signal 0 2 .
• the power of either the output signal 0, or the output signal 0 2 is at any rate substantially equal to (or at any rate is in fixed proportion to) the power of the entering signal I.
• a partial signal dO is coupled out by the signal tap 6, said signal subsequently being led via the input gate 8.1 and the output gate 8.3 of the first Y-junction 8 to the input gate 9.1 of the second Y-junction 9.
• the power of partial signal dO is a fraction f 3 of the power of signal 0,.
• a partial signal d0 2 from a possibly exiting signal 0 2 at the output gate 1 .2 of the switch is uncoupled by the signal tap 7, and is led via the input gate 8.2 and the output gate 8.3 of the first Y-junction 8 to the input gate 9.1 of the second Y-junction 9.
• the power of partial signal d0 2 is a fraction f 4 of the power of signal 0 2 .
• one of the two partial signals dO, and d0 2 (for example partial signal dO, if the asymmetry of the first Y-junction 8 is such that the propagation constant of the input gate 8.1 is smaller than that of the input gate 8.2) propagates in the first order mode at the input gate 9.1 , while the other partial signal (partial signal d0 2 ) propagates in the zero-order mode.
• the optical signal combiner 40 is a Y-junction 17 with monomodal input gates 17.1 and 17.2, and a monomodal output gate 17.3, while the detection means are formed by a monomodal signal detector 18.
• the optical signal taps 14 and 15 are signal taps with coupling out fractions f 5 and f 6 respectively.
• the Y-junction 17 can also be an incomplete asymmetrical Y-junction in this embodiment, the most simple realisation is obtained if the Y-junction 17 is a symmetrical Y-junction and the coupling out fractions f 5 and f 6 are chosen sufficiently different from each other.
• cross-talk can also be established in the second and in the third embodiment by deviations of the percentages in the states St1 and St2, but this is restricted to an estimate of the order of magnitude, however, because of the occurring interferences.
• the total power through the switch is known. If this is not the case, however, it can be simply determined by putting the switch in the switching states St1 and St2 in succession. From the measured power levels in this regard the total power can be derived.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Optical Communication System (AREA)
• Electronic Switches (AREA)

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• 1998
  • 1998-02-05 NL NL1008206A patent/NL1008206C2/nl not_active IP Right Cessation
• 1999
  • 1999-01-21 AU AU27182/99A patent/AU745931B2/en not_active Ceased
  • 1999-01-21 WO PCT/EP1999/000386 patent/WO1999040738A1/en not_active Application Discontinuation
  • 1999-01-21 HU HU0100982A patent/HUP0100982A2/hu unknown
  • 1999-01-21 EP EP99907396A patent/EP1053647A1/de not_active Withdrawn
  • 1999-01-21 CA CA002320284A patent/CA2320284A1/en not_active Abandoned

Non-Patent Citations (1)

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