AU678255B2

AU678255B2 - Asynchronous detection of a binary word transmitted serially in an optical signal

Info

Publication number: AU678255B2
Application number: AU68618/94A
Authority: AU
Inventors: Robert Osborne
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1993-07-21
Filing date: 1994-07-20
Publication date: 1997-05-22
Anticipated expiration: 2014-07-20
Also published as: DE59407518D1; AU6861894A; ATE175070T1; EP0635991B1; EP0635991A1

Abstract

An arrangement is specified in which a binary word is asynchronously transmitted in an optical signal and which is represented by high and low intensity levels is supplied to a plurality of optical inverting devices; the optical signals output by the inverting devices, which have mutually different wavelengths, are supplied as aggregate signal to a wave-length-selective delay device; when the desired binary word is present, the individual binary characters at the input of a detection device become superimposed to form an intensity level which is lower than a high intensity level caused by a single inverting device. Other embodiments relate to the changeability of the wavelength of the optical signals output by the inverting devices and the double inversion of the optical signal in individual signal branches. <IMAGE>

Description

I Asynchronous detection of a binary word transmitted serially in an optical signal Optical fibres are increasingly being used as the transmission medium for line-based message transmission in communication systems. The possible transmission rate is limited here less by the transmission links than by the signal processing. Optical signal processing offers advantages here with respect to the processing speed in comparison with signal processing which uses processing of signals converted into electrical signals.

The invention relates to an arrangement for evaluating binary words which are transmitted asynchronously and serially in an optical signal and which have a combination of binary elements represented by high and low intensity levels.

An optical evaluation means termed a correlator is known from IEEE LCS MAGAZINE, May 1990, pages 54 67, in which a serially transmitted optical signal is divided between a plurality of parallel delay lines having a different delay duration in each case. The optical power of the signals output by the delay lines is added and supplied to a threshold decision element. When a predetermined threshold value of its input signal is 25 exceeded, the threshold decision element outputs an nutput signal and thus indicates an autocorrelation peak of the optical input signal of the correlator. Said correlator requires a long code word length, relative to the number of code words that can be distinguished, in order to obtain an adequate amplitude spacing of the autocorrelation peak from the secondary maxima caused by cross correlation, and in addition a threshold switch with a high upper-limit frequency for detecting the autocorrelation peak.

The same also applies to an optical transmitting/receiving device known from Electronics Letters, November 1990, Vol. 26, No. 24, pages 1990 1992, in which the data to be transmitted pass in parallel through a plurality of delay lines having a different delay duration in each case at the transmitting end and are combined to form a sum signal at the receiving end after passing through delay lines that are identical to those at the transmitting end. The sum signal, to which a synchronization signal is added, is supplied to a photo-detector. The signal of the photodetector is supplied to a threshold decision element, which outputs an output signal when a threshold value of the supplied signal is exceeded.

In contrast to the previously mentioned correlator, this correlator is able to distinguish a larger number of code words given the same relatively long code word length, but only with the addition of the outlay for the synchronization.

An optical correlator has been disclosed in EP-91119564.2, in which a binary word transmitted in an optical signal is evaluated asynchronously, in that the optical signal is supplied to a plurality of delay lines having different delay durations from one another, the optical signals output by the delay lines are each converted into electrical signals in each case and the binary word is evaluated by logically gating the electrical signals. Said correlator requires a conversion means for each delay line and therefore for each binary element.

It is the object of the present invention to overcome or substantially ameliorate the above disadvantages.

20 There is disclosed herein an arrangement for evaluating binary words which are transmitted asynchronously and serially in an optical signal and which have a combination of binary elements represented by high and low intensity levels, said arrangement comprising; the optical signal is applied to a plurality of optical inversion means on the input side, the optical signals output by the optical inversion means on the output side :..have different wavelengths from one another, the optical signals output by the optical inversion means are supplied to a summing means, 30 the output of the summing means is connected to the input of a wavelengthselective delay line, the output of the delay line is connected to the input of a detection means, the detection means only outputs a significant output signal if the intensity level of the summed optical signals at its input is lower than the intensity level caused by a single inversion means.

The correlator according to this aspect combines the advantages that only one detection means is required with a considerably lower limit frequency than the limit frequency otherwise required for differentiating between autocorrelation peak and cross [n:\liblOO0987:MXL II I correlation, and that the detection means need not be synchronised with a binary word nor with any additional signal.

In a further refinement, the wavelength of the signals output by the inversion means is variable. This measure provides the capability for rapid adjustment to different binary words to be evaluated.

In a further refinement, an additional inversion means is inserted into the signal path of an inversion means. This measure makes it possible to evaluate optional combinations of binary words represented both by high and by low intensity levels, whereby on the one hand binary wvords associated with a non-redundant code can be 1o clearly distinguished and on the other hand immunity is provided from evaluation results caused by erroneous continuous signals at the input.

The invention will now be described in greater detail as an exemplary embodiment to an extent required for comprehension of the invention with reference to a figure, in which: Fig. 1 shows an arrangement for the asynchronous detection of a binary word transmitted serially in an optical signal, the binary elements of which are represented by high and low intensity levels. An optical input signal transmitted with a ooooo •go• o•: [n:\libeJOO987:MXL

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-4wavelength 10 is supplied with the aid of a branching means SP via fibre-optic lines to a plurality of tunable inversion means AINVI AINVm, the input signal being supplied to the tunable inversion means AINVI and AINV2 via an additional inversion means ZINV1,2 in each case.

The optical inversion means have the following features: If the optical inversion means is supplied on the input side with an optical signal having an intensity above a predetermined threshold, then it does not output an optical signal on the output side. If the optical inversion means is supplied with an optical signal having an intensity below the predetermined threshold, then it outputs an optical signal having a high intensity on the output side. The inversion means may be optical inverters described, for example, in B. Glance, J. Wiesenfeld "Optical Wavelength Shifter for Wavelength-Division- Multiplexed Networks", Optics and Photonics News, Dec.

page 31. In the present application, the fast switching speed, the high intensity of the optical signal output at the output and a relatively low intensity of the signal supplied on the input side which is required to exceed the predetermined threshold are advantageous.

The tunable inversion means have the further feature that the wavelength of the optical signal output by a respective tunable inversion means on the output side can be set via an address line AD. The optical signals having the wavelengths 11 Xn output by the tunable inversion means on the output side are combined to form an optical sum signal in a conventional n x 1 coupler KOP. The sum 30 signal is supplied via a conventional optical filter OW to a wavelength-selective delay line VL. The delay line results in different delay durations for optical signals having different wavelengths. In the exemplary embodiment, the delay line is formed by a waveguide, into which wavelength-selective reflection filters have been introduced at the points indicated by X1 Xn. Such delay lines are known, for example, from Application Physical Letters 32 15 May 1978, pages 647 649, "Photosensitivity in Optical Fibre Waveguides:

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5 Application to Reflection Filter Fabrication", or from Electronics Letters 18, March 1993, Vol. 29, No. 6, pages 566 568, "Production of In-Fibre-Gratings Using a Diffractive Optical Element". The delay of a signal with a given wavelength is calculated from the transit time from insertion into the waveguide to the respective reflection filter and back. The reflected optical signals exit the delay line via the optical filter and are supplied to the input of a detection means DET. According to the invention, the detection means only outputs a significant output signal if the intensity, that is to say the power of the summed optical signals, is lower than the intensity level caused by a single tunable inversion means instantaneously outputting a high intensity level on the output side. To satisfy this condition, the predetermined threshold of the detection means is set in such a way that it outputs a significant signal at its output only when given an optical signal on the input side which has a lower intensity than the intensity caused by a single tunable inversion means, for example only below an intensity corresponding to half of the high intensity of a single optical signal. The detection means may be formed, for example, by an inversion means described in more detail above with a downstream photodiode and evaluation means. Alternatively, the detection means may be formed by a photodiode and a downstream evaluation means with threshold characteristic.

The principle on which the invention is based 30 relates to the fact that the predetermined combination of serially transmitted bits is converted in any case into bits represented by a low intensity, and the converted bits are delayed in accordance with the order within the optical signal; only if the predetermined combination appears in the optical signal do the converted and correspondingly delayed bits become overlaid to form an optical signal having an intensity lower than the high intensity level output by a single tunable inversion means.. The characteristic bits of the predetermined

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-6combination of bits are therefore first of all converted into optical signals having a low intensity level. Bits of the input signal which have a high intensity level are handled further in each case only in a tunable inversion means, for example in the tunable inversion means AINVn-1, AINVn, whereas the bits of the input signal which have a low intensity level are handled in each case in a tunable inversion means and an additional inversion means, for example in the AINVI and ZINVl or in the AINV2 and ZINV2. The characteristic bits are then delayed in accordance with their chronological order in the input signal in such a way that they appear at the input of the detection means at the same time. To satisfy this condition, a bit of the combination that appears first is delayed correspondingly longer than a bit that appears later. The delay durations that can be achieved are predetermined by the arrangement of the reflection filters present in the delay line. The reflection filters are arranged in the delay line preferably spaced such that the difference in tho delay duration between two adjacent reflection filters is equal to the duration of one bit. After passing through an additional inversion means at the output of the following tunable inversion means, a characteristic bit of the combination having a low intensity level contained in the input signal is forwarded with the wavelength at which the bit, in accordance with its chronological order within the combination, arrives at the input of the detection means at the same time as all the other characteristic bits of 30 the combination. Analogously, after passing through only one tunable inversion means, a characteristic bit of the combination having a high intensity level contained in the input signal is forwarded with a wavelength at which the bit, in accordance with its chronological order within the combination, arrives at the input of the detection means at the same time as all the other characteristic bits of the combination. The required wavelength output at the output of a tunable inversion means is set via an address line AD connected to said tunable -7inversion means.

In the arrangement described, the number of characteristic bits of a combination that can be evaluated is determined by the number of tunable inversion means. If the number of bits that can be evaluated is less than the number of tunable inversion means, then any tunable inversion means not required can be switched to inactive via the address line. Inversion means that have been switched to inactive have a low intensity level at their output. The maximum time interval between the chronologically first and the chronologically last characteristic bit that can be evaluated with the arrangement described is determined by the difference between the shortest and the longest delay duration of the delay line.

In principle any combinations of bits, transmitted asynchronously, which are represented by high and eeeee low intensity levels can be evaluated with the arrangement described.

.ment described.

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Claims

1. An arrangement for evaluating binary words which are transmitted asynchronously and serially in an optical signal and which have a combination of binary elements represented by high and low intensity levels, said arrangement comprising: the optical signal is applied to a plurality of optical inversion means on the input side, the optical signals output by the optical inversion means on the output side have different wavelengths from one another, the optical signals output by the optical inversion means are supplied to a summing means, the output of the summing means is connected to the input of a wavelength- selective delay line, the output of the delay line is connected to the input of a detection means, the detection means only outputs a significant output signal if the intensity 8 15 level of the summed optical signals at its input is lower than the intensity level caused by a single inversion means.

2. An arrangement according to claim 1, wherein the wavelength of the signals output by the inversion means is variable.

3. An arrangement according to one of the preceding claims, wherein an additional inversion means is inserted into the signal path of an inversion means.

4. An arrangement for evaluating binary words, substantially as herein described with reference to the drawing. DATED this Third Day of March 1997 Siemens Aktiengesellschaft Patent Attorneys for the Applicant SPRUSON FERGUSON 1. (n:VIbeI00987:MXL I Asynchronous Detection of a Binary Word Transmitted Serially in an Optical Signal ABSTRACT An arrangement is disclosed in which a binary word which is transmitted asynchronously in an optical signal and which is represented by high and low intensity levels is supplied to a plurality of optical inversion means (AINV1 AINVm); the optical signals output by the inversion means (AINV1 AINVm), which signals have different wavelengths from one another, are supplied as sum signal to a wavelength-selective delay means when the desired binary word is present, the individual binary elements are overlaid at the input of a detection means (DET) to form an intensity level which is lower than a high intensity level caused by a single inversion means. Further refinements relate to the variability of the wavelength of the optical signals output by the inverstion means (AINV1 AINVm) and also to the double inversion (ZINV1, ZINV2) of the optical signal in single signal branches. Figure 1 e.. o oo 2565F/CMS t IM