Determination of an optical signal to noise ratio of a dual-polarization optical signal

Abstract

A method is provided for determining an optical signal to noise ratio of a dual polarization optical signal. The method includes: detecting, in the dual polarization optical signal, a modulation signal which modulates, at at least one low amplitude level that is approximately zero and at a high amplitude level, the dual polarization optical signal, and determining the optical signal to noise ratio from a measurement of the power of the modulation signal.

Claims

1. A method for determining an optical signal-to-noise ratio (OSNR) of a dual-polarized optical signal, wherein the method comprises the following acts performed by a processor of a transmitter device, a receiver device or a device for determining OSNR: detecting, in said dual-polarized optical signal, a modulation signal modulating said dual-polarized optical signal, on at least one lower level of amplitude that is substantially zero and a higher level of amplitude, wherein said act of detecting comprises localizing a time slot dedicated to a modulation on said levels of amplitude of the optical signal by said modulation signal; and determining said optical signal-to-noise ratio on the basis of a measurement of power of said modulation signal, wherein the acts of detecting said modulation signal and determining the optical signal-to-noise ratio are implemented on a median time zone, called a second time zone, of said time slot.

2. The method according to claim 1, wherein the act of detecting comprises detecting a frequency of said modulation signal and said act of determining said optical signal-to-noise ratio comprises the following acts: generating a reference signal, having at least one lower level of amplitude that is substantially zero and a higher level of amplitude, the frequency of this reference signal being equal to said detected frequency, temporally shifting said reference signal relative to said modulation signal so that the higher level of amplitude of said reference signal is synchronized with the lower level of said modulation signal, delivering a lower reference signal, modulating said modulation signal by means of said lower reference signal, delivering a first superimposed signal associated with a lower level of said modulation signal, measuring the power of said superimposed first signal delivering a first power value, temporally shifting said reference signal relative to said modulation signal so that the higher level of amplitude of said reference signal is synchronized with the higher level of said modulation signal, delivering a higher reference signal, modulating said modulation signal by means of said higher reference signal, delivering a second superimposed signal associated with the higher level of said modulation signal, measuring the power of said second superimposed signal, delivering a second power value, obtaining said optical signal-to-noise ratio from said first and second power values.

3. The method according to claim 2, wherein said acts of modulation implement a modification of a duty cycle of said reference signal so that it is half as small as that of the modulation signal.

4. The method according to claim 2, wherein said detected frequency of the modulation signal is of the order of 1 MHz.

5. A method for transmitting a dual-polarized optical signal, wherein the method comprises: generating said dual-polarized optical signal, said optical signal comprising at least one time slot dedicated to a modulation by a modulation signal, of said optical signal on at least one lower level of amplitude that is substantially zero and a higher level of amplitude, wherein said at least one time slot comprises at least three successive and distinct time zones: a first time zone comprising a piece of information reporting the end of transmission of a part of payload data localized in said optical signal before said time slot, said first zone enabling a synchronization of a reception device on a synchronization mode internal to said reception device, a second time zone on which said optical signal is modulated by a modulation signal on said levels of amplitude, and a third time zone comprising a piece of learning information enabling a change in mode of synchronization of said reception device in order to pass from said internal synchronization mode towards a mode of synchronization associated with a part of payload data localized in said optical signal after said time slot, modulating, on said second time zone of said at least one time slot, said dual-polarized optical signal by said modulation signal, delivering a modified optical signal, and transmitting said modified optical signal in an optical transmission line.

6. A method for receiving a dual-polarized optical signal wherein the method comprises the following acts: receiving said dual-polarized optical signal, and localizing a time slot dedicated to a modulation, by a modulation signal, of said dual-polarized optical signal on at least one lower level of amplitude that is substantially zero and a higher level of amplitude of said optical signal, said time slot comprising at least three successive and distinct time zones, and wherein said method for receiving comprises the following successive steps, implemented by a reception device: on a first time zone of said time slot, first synchronization of said reception device on a mode of synchronization internal to said reception device, on a second time zone of said time slot, detecting, in said dual-polarized optical signal, said modulation signal modulating said dual-polarized optical signal, on said at least one lower level of amplitude that is substantially zero and said higher level of amplitude, and determining said optical signal-to-noise ratio on the basis of a measurement of power of said modulation signal, on a third time zone of said time slot, second synchronization of said reception device in using a mode of synchronization associated with a part of payload data localized in said optical signal received after said time slot.

7. A device for transmitting a dual-polarized optical signal, wherein the device comprises: a generator of said dual-polarized optical signal, said dual-polarized optical signal comprising at least one time slot dedicated to a modulation, by a modulation signal, of said dual-polarized optical signal on at least one lower level of amplitude that is substantially zero and a higher level of amplitude, said at least one time slot comprises at least three successive and distinct time zones: a first time zone comprising a piece of information reporting the end of transmission of a part of payload data localized in said optical signal before said time slot, said first zone enabling a synchronization of a reception device on a synchronization mode internal to said reception device, a second time zone on which said optical signal is modulated by a modulation signal on said levels of amplitude, a third time zone comprising a piece of learning information enabling a change in mode of synchronization of said reception device in order to pass from said internal synchronization mode towards a mode of synchronization associated with a part of payload data localized in said optical signal after said time slot, a modulator configured for modulating, during said second time zone of said time slot, said optical signal by said modulation signal, delivering a modified optical signal, a transmitter configured for transmitting said modified optical signal in an optical transmission line.

8. A device for receiving a dual-polarized optical signal, wherein the device comprises: a receiver configured for receiving said dual-polarized optical signal, a module, which is configured to determine an optical signal-to-noise ratio of said received dual-polarized optical signal and comprises: a module configured for localizing a time slot dedicated to a modulation, by a modulation signal, of said dual-polarized optical signal on at least one lower level of amplitude that is substantially zero and a higher level of amplitude of said optical signal, said time slot comprising at least three successive and distinct time zones, a module configured for performing a first synchronization of said reception device on a mode of synchronization internal to said reception device, on a first time zone of said time slot, a detector, configured for detecting, in said dual-polarized optical signal, said modulation signal modulating said dual-polarized optical signal, on said at least one lower level of amplitude that is substantially zero and said higher level of amplitude, on a second time zone of said time slot, and a unit, which is configured to determine, on said second time zone of said time slot, said optical signal-to-noise ratio on the basis of a measurement of power of said modulation signal, and a module configured for performing a second synchronization, on a third time zone of said time slot, of said reception device using a mode of synchronization associated with a part of payload data localized in said optical signal received after said time slot.

Description

4. LIST OF FIGURES

(1) Other features and advantages of the proposed technique shall appear more clearly from the following description of a preferred embodiment, given by way of a simple illustratory and non-exhaustive example and from the appended drawings, of which:

(2) FIG. 1 presents the main steps implemented by a method for determining an optical signal-to-noise ratio according to one embodiment of the invention;

(3) FIG. 2 presents the steps implemented by the steps for determining an optical signal-to-noise ratio according to alternative embodiments of the invention;

(4) FIG. 3 presents the main steps implemented by a method of transmission according to one embodiment of the invention;

(5) FIG. 4 illustrates the structure of an optical signal obtained in implementing the steps of FIG. 3;

(6) FIG. 5 presents the main steps implemented by a method of reception according to one embodiment of the invention;

(7) FIGS. 6 to 8 respectively illustrate the simplified structure of a module for determining an optical signal-to-noise ratio, the simplified structure of a transmission device and the simplified structure of a reception device according to one particular embodiment of the invention; and

(8) FIG. 9 represents an optical system comprising a module for determining an optical signal-to-noise ratio, a transmission device and a reception device according to one particular embodiment of the invention.

5. DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

(9) 5.1 General Principle

(10) The general principle of the invention relies on the implementing of a modulation signal, modulating an optical signal on at least one lower level of amplitude that is substantially zero and a higher level of amplitude. Such a modulation signal can be easily detected after transmission in an optical transmission line.

(11) After detection, it is possible to carry out a power measurement of low complexity using this modulation signal, this modulation signal being affected with the same noise introduced during transmission in a channel as the optical signal that it modulates.

(12) The technique according to the invention can be applied to the measurement of the optical signal-to-noise ratio in “in-band” mode. This averts the suspending of ongoing transmission on an optical channel, and averts the stopping of ongoing transmissions on channels that immediately neighbor the observed channel.

(13) The technique according to the invention can also be applied to the measurement of the optical signal-to-noise ratio in off-band mode, this mode conventionally entailing fewer constraints in its implementation.

(14) The invention can be applied especially in WDM optical transmission, especially for a dual-polarized WDM signals used in WDM transmission systems in service (which convey commercial data streams).

(15) It also performs particularly well in the measurement of the OSNR of new-generation systems of WDM transmission at 100 Gbps using quadrature phase shift keying modulation with dual polarization.

(16) However, the invention is not limited to dual-polarized optical signals and also offers an alternative to the techniques for measuring the optical signal-to-noise ratio of single-polarized signals.

(17) Thus, the technique according to the invention is compatible with different types of polarization of optical signals. The modules implementing the technique according to the invention are therefore extremely interesting because of their capacity to deliver OSNR for different types of optical signals. Such modules therefore avert the purchasing of two distinct modules, one dedicated to single-polarized optical signals and the other to dual-polarized optical signals.

(18) Here below, it must be noted that the details of implementation of the invention are presented with reference to an example based on a dual-polarized optical signal. However, the technique of the invention can be derived directly and without ambiguity for single-polarized optical signals or again any other type of multiple polarized optical signals.

(19) 5.2 Description of One Particular Embodiment of the Method for Determining an Optical Signal-to-Noise Ratio According to the Invention

(20) Here below, with reference to FIG. 1, are presented the main steps implemented by the method for determining an optical signal-to-noise ratio according to the invention.

(21) Such a method (1000) for determining an optical signal-to-noise ratio comprises a step (11) for detecting D_S.sub.mod (11) a modulation signal S.sub.mod in a dual-polarized optical signal S.sub.ob, the modulation signal S.sub.mod modulating the dual-polarized optical signal on at least two levels of amplitude (a lower level of amplitude that is substantially zero and a higher level of amplitude distinct from the lower level of amplitude), and a step (12) for determining the optical signal-to-noise ratio from a measurement of power of said modulation signal.

(22) The dual-polarized optical signal S.sub.ob is especially affected by optical transmission noise.

(23) More specifically, according to one particular embodiment, the step (11) for detecting comprises a step for localizing local_It (110) a time slot (It) dedicated to the modulation, by the modulation signal S.sub.mod, of the dual-polarized optical signal on least two levels of amplitude and a step (111) for detecting Det_F a frequency F of the modulation signal S.sub.mod.

(24) As illustrated in FIG. 2, the step 12 for determining the optical signal-to-noise ratio implements the following sub-steps: generating G_Ref (121) a reference signal S.sub.ref that has at least one lower level of amplitude that is substantially zero and a higher level of amplitude, and has a frequency equal to the frequency F detected, temporally shifting Dec.sub.0 (122) said reference signal relative to said modulation signal so that a higher level of amplitude of said reference signal is synchronized with a lower level of said modulation signal, delivering a lower reference signal, modulating Mod.sub.0 (123) said modulation signal by means of said lower reference signal, delivering a first superimposed signal S.sub.upO associated with the lower level of said modulation signal, measuring the power Mp.sub.0 (124) of said first superimposed signal S.sub.up0, delivering a first power value P.sub.0, temporally shifting Dec.sub.1 (125) said reference signal relative to said modulation signal so that a higher level of amplitude of said reference signal is synchronized with a higher level of said modulation signal, delivering a higher reference signal, modulating Mod.sub.1 (126) said modulation signal by means of said higher reference signal, delivering a second superimposed signal S.sub.up1 associated with the higher level of said modulation signal, measuring power Mp.sub.1 (127) of said second superimposed signal S.sub.up1, delivering a second power value P.sub.1, obtaining (128) said optical signal-to-noise ratio OSNR from said first and second power values P.sub.0 and P.sub.1.

(25) FIG. 9 illustrates an example of implementation of an optical system according to the invention.

(26) According to this example, the method for determining an optical signal-to-noise ratio OSNR is implemented by a module 91 for determining OSNR. According to this example of FIG. 9, the modulation signal S.sub.mod is an NRZ-OOK modulation signal that is perfectly periodic (01010101010 . . . ).

(27) The step Det_F for detecting a frequency of the modulation signal S.sub.mod corresponds for example to a clock signal retrieval/generation CDR 911, the clock signal being also called a reference signal S.sub.ref, the frequency of which is advantageously of the order of 1 MHz, the modulation signal having been selected so as to be robust with respect to the chromatic dispersion accumulated in the optical transmission line L.sub.TO (92). Such a module for detecting frequency and for generating clock signals CDR 911 inputs the optical signal S.sub.ob and outputs the clock signal also called S.sub.ref. This signal is a radiofrequency signal devoid of any optical component.

(28) The steps of temporal shifting Dec.sub.0 and Dec.sub.1 are carried out by a phase shifter 910 of the module for determining OSNR. Such a phase-shifter 910 is therefore positioned on the retrieved optical path.

(29) After it is amplified and shifted, this reference signal S.sub.ref corresponding to a clock signal will be fed into a Mach-Zehnder (MZM) type modulator M.sub.R or an acousto-optical modulator (AOM), the response of which does not depend on the polarization of the incoming signals.

(30) Through the phase-shifter 910, the periodic signal 01010101010 . . . retrieved at the receiver is successively synchronized with the “1s” and the “0s” of the NRZ-OOK signal S.sub.mod that have been generated at the emitter and that pass through the transmission line L.sub.TO (92).

(31) Through a measurement of power (Mp.sub.0, Mp.sub.1), the power values P.sub.1 and P.sub.0 contained respectively in the “1s” and the “0s” of the NRZ-OOK signal generated at the transmitter are determined successively after this signal has been propagated on the transmission line and has been affected by the ASE noise.

(32) The duty cycle R.sub.CY of the MZM/AOM modulator is optionally half as small as that used on the transmitter side.

(33) Thus, when the duty cycle R.sub.CY is ½ (there are many “1s” as there are “0s” in the periodic data sequence 01010101010 . . . ), it will be equal to ¼ for the modulator of the OSNR determining module so much so that the duration of the “0s” is twice as long as the duration of the “1s”.

(34) The measurement of power (Mp.sub.0, Mp.sub.1) made by means of the power measuring device 912 delivering an average power value of the first and second superimposed signals S.sub.up0 and S.sub.up1, is made, according to the example of FIG. 9, on an arm of an optical coupler C1 93 intended for monitoring the optical signal (localized after passage into the optical transmission line). This measurement is therefore non-destructive for the commercial data stream carried for example by a measured WDM channel. It must finally be noted that the channel to be measured is selected by means of an optical filter 913 embedded in the OSNR determining module.

(35) The power measured in the “1s” of the periodic sequence of the signal 01010101010 . . . integrates the power of the signal and that of the ASE noise while the power measured in the “0s” integrates only the power of the ASE noise accumulated in the transmission line L.sub.TO (92). Thus, once the power P.sub.1 measured in the “1s” and the power P.sub.0 measured in the “0s” have been obtained, the OSNR, for example in in-band mode, is obtained by the following relationship:

(36) $\mathrm{OSNR}=\frac{P_S}{P_{\mathrm{ASE}}}=\frac{P_1-P_0}{P_0}$

(37) 5.3 Description of One Particular Embodiment of the Method of Transmission According to the Invention

(38) Referring now to FIG. 3, we present the main steps implemented by the method of transmission according to the invention.

(39) Such a method for transmitting a dual-polarized optical signal comprises a step (31) for generating G_So (31) the dual-polarized optical signal, the dual-polarized optical signal comprising at least one time slot It dedicated to a modulation, by a modulation signal S.sub.mod, of the dual-polarized optical signal on at least one lower level of amplitude that is substantially zero and a higher level of amplitude.

(40) In other words, a slightly “excess bit rate” is applied to an optical signal S which is to be subsequently measured. For example, 1 ms or 500 μs are reserved to form a dedicated time slot and this is done for example every 5 or 15 minutes.

(41) Then, on the time slot It, a modulation (32) of the optical signal S by the modulation signal S.sub.mod, is done and delivers a modified optical signal S.sub.om, transmitted Tr (33) in the optical transmission line L.sub.TO (92).

(42) As can be seen in FIG. 9, illustrating an example of implementation of an optical system according to the invention, the modulation signal S.sub.mod used by the transmission device 90 according to the invention is an NRZ-OOK modulation signal. Such a modulation signal S.sub.mod modulates or “over modulates” a dual-polarized optical signal S, for example a QPSK optical signal at 100 Gbps.

(43) The modulator MOD.sub.T is for example of the Mach-Zehnder (MZM) type with a rate of extinction of 20 dB localized at the output of the emitter or preferably an acousto-optical modulator (AOM), the extinction rate of which can reach 100 dB.

(44) Such a MZM/AOM modulator is for example integrated into a 100 Gbps WDM interface of a WDM transmission apparatus.

(45) Preferably, this over modulation NRZ-OOK works at a very low frequency of the order of 1 MHz and is perfectly periodic (01010101010 . . . ).

(46) The choice of the frequency depends on the chromatic dispersion accumulated in the optical transmission line L.sub.TO (92). A low frequency enables the periodic sequence of the modulation signal S.sub.mod (01010101010 . . . ) to be unaffected by the accumulated chromatic dispersion accumulated in the optical link to be measured by the determination of corresponding OSNR. A frequency of 1 MHz for example provides immunity to the chromatic dispersion in most examples.

(47) 5.4 Description of One Particular Embodiment of the Method of Reception According to the Invention

(48) Here below, referring to FIG. 5, we present the main steps implemented by the method of reception according to the invention. Such a method of reception comprises a step (51) for receiving a dual-polarized optical signal S.sub.ob. This optical signal is especially affected by a noise from the optical transmission line used or from the optical channel of this optical transmission line.

(49) In addition, the method of reception according to the invention comprises a step (1000) for determining an optical signal-to-noise ratio of said dual-polarization optical signal received according to the method for determining OSNR described here above.

(50) More specifically, the method of reception according to the invention comprises a step for localizing a time slot It dedicated to a modulation, by a modulation signal, of said dual-polarized optical signal on at least one lower level having substantially zero amplitude and a higher level of amplitude.

(51) This localizing step (not shown) is for example common with the method for determining OSNR described here above or is distinct from it.

(52) In particular, as shown with reference to FIG. 4 illustrating the dual-polarized optical signal according to the invention, the time slot comprises at least three time zones (Z.sub.1, Z.sub.2, Z.sub.3) that are successive and distinct.

(53) With regard to these three distinct time zones, the method of reception comprises the following successive steps implemented by a reception device: on a first time zone (Z.sub.1) of the time slot, first synchronization (52) of the reception device on a synchronization mode internal to said reception device, on a second time zone (Z.sub.2) of the time slot, said steps for detecting and determining said optical signal-to-noise ratio, on a third time zone (Z.sub.3) of the time slot, second synchronization (53) of the reception device in using a mode of synchronization associated with a part of payload data localized in said optical signal received after said time slot.

(54) Referring to FIG. 9, illustrating an example of implementation of an optical system according to the invention, the reception device according to the invention therefore comprises a synchronization module 914 implementing the first and second steps of synchronization in order to temporally separate the determining of OSNR according to the invention from the processing P.sub.DATA 915 of the payload data.

(55) 5.5 Description of a Dual-Polarized Optical Signal According to the Invention

(56) FIG. 4 illustrates the structure of an optical signal obtained by implementing the steps of FIG. 3.

(57) More specifically, the dual-polarized optical signal comprises at least one time slot dedicated to a modulation, by a modulation signal, of said dual-polarized optical signal on at least one lower level having substantially zero amplitude and a higher level of amplitude.

(58) According to one particular embodiment illustrated by FIG. 4, the time slot It comprises at least three successive and distinct time zones: a first time zone Z.sub.1 (41) comprising a piece of information reporting the end of transmission of a part of payload data localized in said optical signal before said time slot, said first zone enabling a synchronization of a reception device on a mode of synchronization internal to said reception device, a second time zone Z.sub.2 (42) on which said dual-polarized optical signal is modulated by a modulation signal on at least one lower level having a substantially zero amplitude and a higher level of amplitude, a third time zone Z.sub.3 (43) comprising a piece of learning information used to change the mode of synchronization of said reception device in order to pass from said internal synchronization mode towards a mode of synchronization associated with a part of payload data located in said optical signal after said time slot.

(59) For example, in the case of an optical transmission of a DP-QPSK transmission slot for transmission towards a DP-QPSK reception device, the structure of the signal corresponds to a multi-frame structure as represented in FIG. 4 and comprising a long square-wave or time slot of payload data containing data DATA with a duration of 5 or even 15 minutes followed by a short time slot It of 1 ms or 500 μs for example during a part of which the AOM/MZM modulator works and so on and so forth.

(60) This short time slot consists of three zones: Zone 1 Z.sub.1: comprising a warning signal so that the DP-QPSK reception device gets ready to receive the loss of optical signal due to the “0s” of the signal periodic sequence 01010101010 mentioned here above, when the modulation signal S.sub.mod is an NRZ-OOK modulation signal that is perfectly periodic (01010101010 . . . ) and the reception device remains nevertheless synchronized in the mode known as the “hold-over” mode in using for example an internal synchronization present in the DP-QPSK reception device, Zone 2 Z.sub.2: comprising a modulation signal S.sub.mod used by the module for determining OSNR described here above, for example a pseudo-random binary sequence (PRBS) in the optical transport network (OTN) frames modulated in DP-QPSK and then over-modulated by the AOM/MZM modulator with the periodic sequence of the modulation signal S.sub.mod 01010101010 . . . , Zone 3 Z.sub.3: comprising a learning sequence in order to prepare the DP-QPSK reception device to get resynchronized on the next long time slot of payload bit rate and leave the “hold-over” synchronization mode towards the synchronization mode on a received signal.

(61) A synchronization device Synch 914 as shown in FIG. 9 notably drives the module 91 for determining OSNR according to the invention and especially the AOM/MZM modulator so that it activates its operation only during the Zone 2 of the time slot It.

(62) 5.6 Description of the Module for Determining an Optical Signal-to-Noise Ratio and Transmission and Reception Devices According to the Invention

(63) Finally, referring to FIGS. 6 to 8 respectively, we present the simplified structure of a module for determining an optical signal-to-noise ratio implementing a method for determining an optical signal-to-noise ratio, the structure of a transmission device implementing a technique of transmission of an optical signal and the structure of a reception device implementing a technique of reception according to one particular embodiment of the invention.

(64) As illustrated in FIG. 6, such a module for determining an optical signal-to-noise ratio M_OSNR for its part comprises a memory 61 comprising a buffer memory, a processing unit 62 equipped for example with a microprocessor μP, and driven by the computer program 63 implementing the method for determining an optical signal-to-noise ratio according to the invention.

(65) At initialization, the code instructions of the computer program 63 are for example loaded into a RAM and then executed by the processor of the processing unit 62. The processing unit 62 inputs the optical signal S.sub.ob. The microprocessor of the processing unit 62 implements the steps for determining an optical signal-to-noise ratio described here above according to the instructions of the computer program 63 to deliver the optical signal-to-noise ratio OSNR of the optical signal S.sub.ob. To this end, the rendering device furthermore comprises: a detector DETECT 64, detecting in the optical signal S.sub.ob, a modulation signal S.sub.mod modulating for example at least one lower level with a substantially zero amplitude and a higher level with amplitude, said optical signal, and a unit for determining U_OSNR 65 of the optical signal-to-noise ratio on the basis of a measurement of power of the modulation signal.

(66) These modules are driven by the microprocessor of the processing unit 62.

(67) As illustrated in FIG. 7, such a device for transmitting an optical signal comprises for its part a memory 71 comprising a buffer memory, a processing unit 72, equipped for example with a microprocessor μP, and driven by the computer program 73 implementing the method for transmitting an optical signal according to the invention.

(68) At initialization, the code instructions of the computer program 73 are for example loaded into a RAM and then executed by the processor of the processing unit 72. The processing unit 72 inputs data DATA to be transmitted. The microprocessor of the processing unit 72 implements the steps of the method of transmission described here above according to the instructions of the computer program 73 to transmit an optical signal and enable the determining of its optical signal-to-noise ratio. To this end, the transmission device furthermore comprises: a generator GEN 74 of the optical signal, the optical signal comprising at least one time slot It dedicated to a modulation, by a modulation signal S.sub.mod, of the optical signal on at least one lower level with substantially zero amplitude and a higher level with amplitude, a modulator MOD.sub.T 75 for modulating the optical signal by means of the modulation signal during said at least one time slot It and delivering a modified optical signal S.sub.om, a transmission unit U.sub.T 76 for transmitting the modified optical signal in an optical transmission line.

(69) These modules are driven by the microprocessor of the processing unit 72.

(70) As illustrated in FIG. 8, such a reception device comprises a memory 81 comprising a buffer memory, a processing unit 82 equipped for example with a microprocessor μP and driven by the computer program 83 implementing the method for determining an optical signal-to-noise ratio according to the invention.

(71) At initialization, the code instructions of the computer program 83 are for example loaded into a RAM and then executed by the processor of the processing unit 82. The processing unit 82 inputs data DATA to be transmitted. The microprocessor of the processing unit 72 implements the steps of the method of reception described here above according to the instructions of the computer program 83. To this end, the transmission device furthermore comprises: a reception unit U.sub.R 84 for receiving the optical signal S.sub.ob, a module for determining an optical signal-to-noise ratio M_OSNR as shown in FIG. 6.

(72) These modules are driven by the microprocessor of the processing unit 72.