Single OTDR measurement for a plurality of fibers

Abstract

A first optical path and a second optical path have a common path branching point. An OTDR sampling optical signal is emitted into the first optical path and into the second optical path through the common path branching point. At least one predefined optical property of the OTDR sampling optical signal emitted into the second optical path is altered and/or of a reflection of the OTDR sampling optical signal received from the second optical path is altered. An OTDR reflected optical signal resulting from a reflection of the OTDR sampling optical signal on the first optical path and/or from a reflection on the second optical path is detected. The OTDR reflected optical signal is analyzed to determine, based on the at least one predefined optical property, whether the OTDR reflected optical signal resulted from a reflection on the first optical path and/or on the second optical path.

Claims

1. A method of performing an optical time domain reflectometry, OTDR, measurement in an optical transmission system comprising a first optical path and a second optical path, wherein the first optical path and the second optical path have a common path branching point, wherein the method comprises: emitting an OTDR sampling optical signal into the first optical path and into the second optical path through the common path branching point; altering at least one predefined optical property of the OTDR sampling optical signal emitted into the second optical path and/or of a reflection of the OTDR sampling optical signal received from the second optical path; detecting an OTDR reflected optical signal resulting from a reflection of the OTDR sampling optical signal on the first optical path and/or from said reflection of the OTDR sampling optical signal on the second optical path; and analyzing the OTDR reflected optical signal to determine, based on the at least one predefined optical property, whether the OTDR reflected optical signal resulted from a reflection on the first optical path and/or from a reflection on the second optical path.

2. The method of claim 1, wherein the first optical path is parallel to the first optical path.

3. The method of claim 1, wherein the at least one optical property comprises one or more of a pulse width, a pulse shape, a chromatic dispersion, and a polarization mode dispersion.

4. The method of claim 1, wherein the at least one optical property comprises a pulse width, and wherein altering the at least one optical property comprises broadening or narrowing the pulse width of the OTDR sampling optical signal emitted into the second optical path and/or of said reflection of the OTDR sampling optical signal received from the second optical path.

5. The method of claim 1, wherein the at least one predefined optical property is altered by means of a photonic crystal fiber and/or an optical filter.

6. The method of claim 1, wherein the at least one optical property is selectively altered within a predefined wavelength subrange of the OTDR sampling optical signal and/or of the OTDR reflected optical signal.

7. The method of claim 1, wherein analyzing the OTDR reflected optical signal comprises analyzing a superposition of a first OTDR reflected optical signal and a second OTDR reflected optical signal, wherein the first OTDR reflected optical signal results from a first reflection of the OTDR sampling optical signal on the first optical path and/or on the second optical path, and wherein the second OTDR reflected optical signal results from a second reflection of the OTDR sampling optical signal on the first optical path and/or on the second optical path.

8. The method of claim 1, wherein analyzing the OTDR reflected optical signal comprises detecting a number of local maxima in the OTDR reflected optical signal.

9. The method of claim 1, wherein analyzing the OTDR reflected optical signal comprises fitting one or more model functions to the OTDR reflected optical signal.

10. An optical system suitable for performing an optical time domain reflectometry (OTDR) measurement in an optical transmission system comprising a first optical path and a second optical path at least a portion of which is physically distinct from the first optical path, wherein the optical system comprises: an optical time domain reflectometer configured to provide an OTDR sampling optical signal; a common optical path configured to extend between the optical time domain reflectometer and each of the first optical path and second optical path, wherein the common optical path is further configured to communicate at least one of: to each of the first optical path and the second optical path, the OTDR sampling optical signal from the optical time domain reflectometer; to the optical time domain reflectometer, a respective reflection of the OTDR sampling optical signal communicated along at least one of the respective first optical path and second optical path; and wherein the second optical path is, at a portion of the second optical path that is physically distinct from the first optical path, configured to alter at least one predefined optical property of at least one of: the OTDR sampling optical signal communicated along the second optical path; the reflection of the OTDR sampling optical signal communicated along the second optical path; wherein the optical time domain reflectometer is configured to detect an OTDR reflected optical signal resulting from at least one of: the reflection of the OTDR sampling optical signal communicated along the first optical path; the reflection of the OTDR sampling optical signal communicated along the second optical path; and wherein the optical time domain reflectometer is further configured to analyze the OTDR reflected optical signal to determine, based on the at least one predefined optical property, whether the detected OTDR reflected optical signal resulted from a reflection of the OTDR sampling optical signal communicated along a given optical path among the first optical path and the second optical path.

11. The optical system of claim 10, wherein the at least one optical property comprises a pulse width, and wherein the second optical path is configured to one of: broaden the pulse width; narrow the pulse width.

12. The optical system of claim 10, wherein the second optical path is configured for selectively altering the predefined optical property within a predefined wavelength subrange.

13. The optical system of claim 10, further comprising an optical switch configured for selectively and optically coupling the optical time domain reflectometer with each of a plurality of paths that comprise at least each of the first optical path and the second optical path.

14. A method of performing an optical time domain reflectometry (OTDR) measurement in an optical transmission system comprising a first optical path and a second optical path at least a portion of which is physically distinct from the first optical path, wherein the method comprises: optically communicating an OTDR sampling optical signal along each of the first optical path and the second optical path; altering at least one predefined optical property of at least one of: the OTDR sampling optical signal communicated along the second optical path; a reflection of the OTDR sampling optical signal communicated along the second optical path; detecting an OTDR reflected optical signal resulting from at least one of: a reflection of the OTDR sampling optical signal communicated along the first optical path; the reflection of the OTDR sampling optical signal communicated along the second optical path; and analyzing the OTDR reflected optical signal to determine, based on the at least one predefined optical property, whether the detected OTDR reflected optical signal resulted from a reflection of the OTDR sampling optical signal communicated along a given optical path among the first optical path and the second optical path.

15. The method of claim 14, wherein the at least one optical property comprises at least one of: a pulse width; a pulse shape; a chromatic dispersion; a polarization mode dispersion.

16. The method of claim 14, wherein the at least one optical property comprises a pulse width, and wherein altering the at least one optical property comprises one of: broadening the pulse width; narrowing the pulse width.

17. The method of claim 14, wherein the at least one predefined optical property is altered by means of at least one of: a photonic crystal fiber; an optical filter.

18. The method of claim 14, wherein analyzing the OTDR reflected optical signal comprises analyzing a superposition of at least: a first OTDR reflected optical signal resulting from the reflection of the OTDR sampling optical signal communicated along the first optical path; and a second OTDR reflected optical signal resulting from the reflection of the OTDR sampling optical signal communicated along the second optical path.

19. The method of claim 14, wherein analyzing the OTDR reflected optical signal comprises at least one of: detecting a number of local maxima in the OTDR reflected optical signal; fitting at least one model function to the OTDR reflected optical signal.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1a is shows an optical system according to an embodiment of the invention.

(2) FIG. 1b shows an optical system according to another embodiment of the invention.

(3) FIG. 2 shows a flow diagram illustrating a method of performing an OTDR measurement according to an embodiment of the invention.

(4) FIG. 3 illustrates the analysis of a signal in a method according to an embodiment of the invention.

(5) FIG. 4 illustrates the analysis of a signal in a method according to another embodiment of the invention.

(6) FIG. 5 illustrates the analysis of a signal in a method according to another embodiment of the invention.

(7) FIG. 6 shows an optical system according to another embodiment of the invention.

(8) FIG. 7 shows an optical system according to another embodiment of the invention.

(9) FIG. 8 shows an optical time reflectometer according to an embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

(10) For the purposes of promoting an understanding of the principles of the invention, reference will now be made to a preferred embodiment illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated apparatus and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur now or in the future to one skilled in the art to which the invention relates.

(11) FIG. 1a shows an optical system 10 suitable for performing an OTDR measurement in an optical transmission system comprising a first optical path 52 and a second optical path 54 having a common path branching point according to an embodiment of the invention. The first optical path 52 and a second optical path 54 run optically in parallel implementing optical path protection. The optical system 10 comprises an OTDR optical connection port 18 that is suitable for being optically connected with an OTDR device that is not shown in the figure, an optical coupling device 20 configured for transmitting an optical signal from the OTDR optical connection port 18 to the first optical path 52 and to the second optical path 54 and for transmitting a first optical signal from the first optical path 52 and a second optical signal from the second optical path 54 to the OTDR connection port 18. The OTDR optical connection port 18 can be directly optically connected with the optical coupling device 20, which in the embodiment shown comprises the common path branching point.

(12) The optical system 10 further comprises a signal alteration device 30 optically coupled between the optical coupling device 20 and the second optical path 54. The signal alteration device 30 is configured for altering at least one predefined optical property of an optical signal transmitted from the OTDR optical connection port 18 to the second optical path 54 and/or of an optical signal transmitted from the second optical path 54 to the OTDR optical connection port 18. The optical system 10 further comprises an optical coupler 70 that is configured for optically connecting the OTDR optical connection port 18 with the first optical path 52 and the second optical path 54 through the optical coupling device 20.

(13) The optical system 10 can be implemented as an optical arrangement configured for being optically connected to an existing optical transmission system that comprises the first optical path 52 and the second optical path 54, wherein the second optical path 54 runs parallel to the first optical path 52, and for connecting an optical time domain reflectometer (not shown) to the OTDR optical connection port 18.

(14) FIG. 1b shows an optical system 10′ according to another embodiment of the invention suitable for performing an OTDR measurement in an optical transmission system comprising N optical paths 52-56 (of which only three are exemplarily represented in FIG. 16) having a common path branching point comprised in an optical splitter 20. Each of the N optical paths 52-56 optically connects the optical coupling device 20 with a respective ONT 60-64 of a PON. The optical system 10 further comprises an OTDR optical connection port 18 that is suitable for being optically connected with an OTDR device that is not shown in the figure. The optical coupling device 20, which in the embodiment shown comprises an optical splitter, is configured for transmitting an optical signal from the OTDR optical connection port 18 to each of the N optical paths 60-64 and for transmitting an optical signal from each of the N optical paths 60-64 to the OTDR connection port 18.

(15) The optical system 10′ shown in FIG. 1b further comprises N−1 signal alteration devices 30-34 (of which only two are exemplarily shown), wherein each of the signal alteration devices is optically coupled between the optical coupling device 20 and a respective one of the ONTs 62-64 through a respective one of the optical paths 54-56. The optical system 10 further comprises an optical coupler 70 that is configured for optically connecting the OTDR optical connection port 18 with each of the N optical paths 52-56 through the optical coupling device 20. An OLT 66 is optically connected to the optical coupling device 20, which in the embodiment shown comprises the common path branching point, through a main optical path 50. The optical coupler 70 is arranged between the OLT 66 and the optical coupling device 20.

(16) Each of the signal alteration devices 30-34 can be configured for altering the at least one predefined optical property of a respective optical signal transmitted through the respective optical path 54-56 in a different manner. For example, a first signal alteration device 30 can be configured for altering the at least one predefined optical property of an optical signal transmitted through the second optical path 54 and the (N−1).sup.th signal alteration device 34 can be configured for altering the at least one predefined optical property of an optical signal transmitted through the N.sup.th optical path 56, wherein the at least one predefined optical property is altered differently each time.

(17) Additionally or alternatively, each of the signal alteration devices 30-34 can be configured for altering a corresponding predefined optical property for a respective optical signal transmitted through the respective optical path 54-56.

(18) FIG. 2 shows a flow diagram illustrating a method 200 of performing an OTDR measurement in an optical transmission system comprising a first optical path 52 and a second optical path 54, wherein the first optical path 52 and the second optical path 54 have a common path branching point according to an embodiment of the invention. The method 200 illustrated in FIG. 2 may be better understood in connection with the optical system 10 shown in FIG. 1a, although the method 200 need not be applied to the particular exemplary embodiment shown in FIG. 1a.

(19) A method step 202 comprises emitting an OTDR sampling optical signal into the first optical path 52 and into the second optical path 54. The OTDR sampling optical signal may be fed into the OTDR optical connection port 18 and transmitted through the optical coupler 70 and the optical coupling device 20 for being emitted into the first optical path 52 and into the second optical path 54.

(20) A further method step comprises altering at least one predefined optical property of the OTDR sampling optical signal emitted into the second optical path 54 (step 204a) and/or of an OTDR reflected optical signal received from the second optical path 54 (step 204b). Method steps 204a and 204b may be carried out as alternatives or in combination, that is, the at least one predefined optical property may be altered before a reflection event occurs (step 204a), after a reflection event occurs (step 204b), or both.

(21) As a result of method steps 204a and/or 204b, although the OTDR sampling optical signal generated in method step 202 for being emitted into the first optical path 52 and into the second optical path 54 was one and the same, an OTDR reflected optical signal that is received from the first optical path 52 can be distinguished from an OTDR reflected optical signal that is received from the second optical path 54 with respect to the at least one predefined optical property.

(22) For example, if the at least one predefined optical property corresponds to a pulse width, the pulse width of an OTDR sampling optical signal and/or an OTDR reflected optical signal transmitted on the second optical path 54 may be broader or narrower than the pulse width of an OTDR sampling optical signal and/or an OTDR reflected optical signal transmitted on the first optical path 52 due to the effect of action of the signal alteration device 30. If the at least one predefined optical property corresponds to a pulse shape, the pulse shape of an OTDR sampling optical signal and/or an OTDR reflected optical signal transmitted on the second optical path 54 may be different from the pulse shape of an OTDR sampling optical signal and/or an OTDR reflected optical signal transmitted on the first optical path 52 due to the effect of action of the signal alteration device 30. Note that it is also possible to alter more than one predefined optical properties, for example both a pulse shape and a pulse width of the OTDR sampling optical signal and/or an OTDR reflected optical signal transmitted on the second optical path 54.

(23) A further method step 206 comprises detecting an OTDR reflected optical signal that results from a reflection of the OTDR sampling optical signal on the first optical path 52 and/or on the second optical path 54. If the OTDR sampling optical signal transmitted on the first optical path 52 encounters an irregularity that triggers a reflection event, an OTDR reflected optical signal is formed, that is reflected back on the first optical path 52 through the optical coupling device 20 and the coupler 70 to the OTDR optical connection port 18. Such an OTDR reflected optical signal resulting from a reflection on the first optical fiber 52 reaches the OTDR optical connection port 18 unaltered with respect to the at least one predefined optical property.

(24) If the OTDR sampling optical signal transmitted on the second optical path 54 encounters an irregularity and results in an OTDR reflected optical signal, this OTDR reflected optical signal is reflected back on the second optical path 54 through the signal alteration device 30, the optical coupling device 20 and the coupler 70 to the OTDR optical connection port 18 and reaches the OTDR optical connection port 18b being altered with respect to the at least one predefined optical property. This is a result of the signal alteration device 30 having altered the at least one predefined optical property of the OTDR sampling optical signal that was transmitted from the OTDR optical connection port 18 to the second optical path 54, of the OTDR reflected optical signal that was reflected back from the second optical path 54 to the OTDR optical connection port 18, or a combination of both.

(25) If, for example, both the OTDR sampling optical signal transmitted on the first optical path 52 and the OTDR sampling optical signal transmitted on the second optical path 54 encounter an irregularity and result in respective OTDR reflected optical signals that are reflected back to the OTDR optical connection port 18, the OTDR reflected optical signal that reaches the OTDR optical connection port 18 and is detected in method step 206 corresponds to a superposition of a first OTDR reflected optical signal resulting from the reflection on the first optical path 52 and a second OTDR reflected optical signal resulting from the reflection on the second optical path 54. For instance, there may be a first irregularity on the first optical path 52 and a second irregularity on the second optical path 54.

(26) A further method step 208 comprises analysing the OTDR reflected optical signal to determine, based on the at least one predefined optical property, whether the OTDR reflected optical signal resulted from a reflection on the first optical path 52 and/or from a reflection on the second optical path 54. The analysis may be performed according to any of the embodiments of the invention explained above, of which some examples will be now given with reference to FIG. 3 to 5.

(27) FIG. 3 illustrates a representation of an OTDR reflected optical signal resulting from a first reflection of the OTDR sampling optical signal at a distance of 200 m from the OTDR optical connection port 18, and from a second reflection of the OTDR sampling optical signal at a distance of 210 m from the OTDR optical connection port 18. The amplitude of the OTDR reflected optical signal is represented against time as a solid line. In the example illustrated in FIG. 3, analysing the OTDR reflected optical signal comprises analysing a superposition of a first OTDR reflected optical signal resulting from one of the reflections and a second OTDR reflected optical signal resulting from the other one of the reflections.

(28) A number of local maxima is detected in the OTDR reflected optical signal. In the example shown in FIG. 3, a peak picking algorithm is used that reveals that the OTDR reflected optical signal contains two local maxima. This is a consequence of the OTDR reflected optical signal comprising a first OTDR reflected optical signal and a second OTDR reflected optical signal. Accordingly, the analysis of the OTDR reflected optical signal is adapted to fit a superposition of a first model function and a second model function to the OTDR reflected optical signal.

(29) The first OTDR reflected optical signal and the second OTDR reflected optical signal are correlated in time as follows. The first and second model functions are represented as dashed lines in FIG. 3 to 5. In the considered example, each of the first and second model functions are Gauss functions g(x) of the form:

(30) $g_i\left(x\right)=a_i{e}^{-\frac{{\left(x-b_i\right)}^2}{2c_i^2}},i=1,2;$

(31) wherein i=1 refers to the first model function and i=2 refers to the second model function, x stands for the distance between the reflection event and the OTDR optical connection port 18 along the first optical path or the second optical path, a defines the amplitude, b defines the position of the center of the Gaussian peak, and c relates to the standard deviation and is hence related to the pulse width.

(32) If the detected OTDR reflected optical signal represented in FIGS. 3 to 5 by a solid line is denoted as f.sub.OTDR, a difference between the OTDR reflected optical signal f.sub.OTDR and the first and second model functions can be minimized by minimizing a least squares error function defined as:

(33) $s=\underset{j=1}{\overset{n}{.Math.}}{\left(a_1{e}^{-\frac{{\left(x_j-b_1\right)}^2}{2c_1^2}}+a_2{e}^{-\frac{{\left(x_j-b_2\right)}^2}{2c_2^2}}-f_{\mathrm{OTDRj}}\right)}^2,$

(34) wherein j stands for the jth acquired sample of f.sub.OTDR. A combination of parameters a, b, and c can hence be determined that minimizes the error function s. In the present case, the minimization yields:

(35) a.sub.1=6, b.sub.1=200, and c.sub.1=5 for the first model function; and

(36) a.sub.2=3, b.sub.2=210, c.sub.1=5 for the second model function.

(37) The first model function g.sub.1, as defined by a.sub.1, b.sub.1, and c.sub.1 and the second model function g.sub.2, as defined by a.sub.2, b.sub.2, and c.sub.2 can hence be individually compared with the OTDR sampling optical signal taking the reflection and diffraction characteristic of the first and second optical paths into account to determine which of the first and second model functions corresponds to each of the first and second OTDR reflection optical signal. If, for example, the at least one predefined optical property is altered by broadening the pulse width, and the first model function displays a pulse width that exceeds the pulse width that would be expected for a reflection of the OTDR sampling optical signal, it may be concluded that the first model function corresponds to a first OTDR reflected optical signal resulting from a reflection event on the second optical path 54 at a distance of 200 m from the OTDR optical connection port 18. If, instead, the first model function displays a pulse width that coincides with the pulse width that would be expected for a reflection of the OTDR sampling optical signal taking the reflection characteristic of the first optical path 52, it may be concluded that the first model function corresponds to a first OTDR reflected optical signal resulting from a reflection event on the first optical path 52 at a distance of 200 m from the OTDR optical connection port 18.

(38) The same analysis may be analogously performed for the second model function, so that after the analysis, it is possible to determine the location of each of the reflection events and whether they occurred on the first optical path 52 or on the second optical path 54.

(39) FIG. 4 and FIG. 5 respectively illustrate situations analogous to that explained with reference to FIG. 3. In FIG. 4, the irregularities are respectively located at distances from the OTDR optical connection port 18 of 200 m and 206 m.

(40) In FIG. 5 illustrates a situation in which a first reflection event occurs on the first optical path 52 and a second reflection event occurs on the second optical path 54, wherein the first and second reflection events occur at identical distances from the OTDR optical connection port 18, in this example at a distance of 200 m. Even in this extreme situation, the invention allows determining which one of the first OTDR reflected optical signal and the second OTDR reflected optical signal originated on which optical path.

(41) FIG. 6 shows an optical system 10 suitable for performing an OTDR measurement in an optical transmission system according to an embodiment of the invention. The optical system 10 of FIG. 6 has the same basic structure as the optical system 10 shown in FIG. 1a. The same reference signs are used for the same components, which are not described again. The optical system 10 comprises an optical time domain reflectometer 100 that is optically connected to the OTDR optical connection port 18 (not shown). The optical domain reflectometer 100 is configured for emitting an OTDR sampling optical signal into the first optical path 52 and into the second optical path 54 through the optical coupling device 20 and of detecting an OTDR reflected optical signal resulting from a reflection of the OTDR sampling optical signal on the first optical path 52 or on the second optical path 54 according to the method explained with reference to FIG. 2 or to any of the methods described above.

(42) The optical time domain reflectometer 100 further comprises a processing unit that is configured for analysing the OTDR reflected optical signal to determine, based on the at least one predefined optical property altered by the signal alteration device 30, whether an OTDR reflected optical signal detected in the optical time domain reflectometer 100 resulted from a reflection on the first optical path 52 and or from a reflection on the second optical path 54.

(43) FIG. 7 shows an optical system 10 according to a further embodiment of the invention. The optical system 10 is an optical arrangement configured for being integrated in an existing optical transmission system at a transmitting node so as to implement optical path protection via the first optical path 52 and the second optical path 54. The optical system 10 comprises a first optical connection port 14 suitable for being optically connected with the first optical path 52, a second optical connection port 16 suitable for being optically connected with the second optical path 54, and a third optical connection port 12 suitable for being optically connected with a main optical path 50. The optical system 10 is adapted to transmit optical data received from the main optical path 50 to the first optical path 52 and the second optical path 54 for protected transmission.

(44) The optical system 10 comprises an optical coupler 20 and a photonic crystal fiber 30 that respectively act as the optical coupling device 20 and as a pulse broadening device 30 as described above. The optical connection port 12 is optically connected with the optical coupling device 20 through an optical amplifier 40 that is configured for amplifying and optical data signal being transmitted between the main optical path 50 and the first optical path 52 and/or the second optical path 54.

(45) The photonic crystal fiber 30 is configured for broadening a pulse width of the OTDR sampling optical signal emitted into the second optical path 54 and of any OTDR reflected optical signal received from the second optical path 54 within a predefined wavelength subrange corresponding to the C-band, i.e., between 1530 nm and 1565 nm. This ensures that the action of the photonic crystal fiber does not interfere in the transmission of the optical data between the optical path 50 and the first optical path 52 and the second optical path 54, which may take place in a different wavelength subrange, which is sufficiently separated from the C-band.

(46) FIG. 8. shows an optical system 10 according to a further embodiment of the invention. The optical system 10 of FIG. 8 is an optical arrangement configured for being integrated in an existing optical transmission system at a transceiver node so as to implement optical path protection via two first optical paths 52 and 52′, and two second optical paths 54 and 54′. The optical system 10 comprises two first optical connection ports 14 and 14′ that are respectively suitable for being optically connected with a corresponding one of the first optical paths 52 and 52′, two second optical connection port 16 and 16′ that are respectively suitable for being optically connected with a corresponding one of the second optical paths 54 and 54′, and two third optical connection ports 12 that are suitable for being optically connected with a corresponding one of the main optical paths 50 and 50′. The optical system 10 is adapted to transmit optical data received from one of the main optical paths 50 to one of the first optical paths 52 and one of the second optical paths 54, and to transmit optical data received from the other one of the first optical paths 52′ and the other one of the second optical paths 54′ to the other one of the main optical paths 50′ for protected transmission. The same reference signs are used for components that have been previously described with respect to the foregoing figures, which are not described again.

(47) The optical system 10 shown in FIG. 8 further comprises a second optical coupling device 20 and a second signal alteration device 30 for implementing the principles of the invention on the second optical link that includes the optical paths 50′, 52′ and 54′, the first optical link including the optical paths 50, 52, and 54. In the optical system 10 shown in FIG. 8, the optical connection port 12′ is optically connected with the optical coupling device 20′ through an optical amplifier 40′ that is configured for amplifying and optical data signal being transmitted from the first optical path 52′ and/or the second optical path 54′ to the main optical path 50′.

(48) The OTDR optical connection port 18 is optically connected with one of the first optical paths 52 and one of the second optical paths 54 through the first optical coupling device 20 by means of a first optical coupler 70. Further, the OTDR optical connection port 18 is optically connected with the other one of the first optical path 52′ and the other one of the second optical path 54′ through the second optical coupling device 20 by means of a second optical coupler 70′. The first and second optical couplers 70 and 70′ comprise an optical filter configured for directing a part of an optical signal to the OTDR optical connection port corresponding to a wavelength range employed for OTDR measurements, for example the C-band.

(49) The optical system 10 further comprises an optical switch 32 optically connected between the OTDR optical connection port on one side and the first optical coupling device 20 and the second optical coupling device 20′ on the other side. The optical switch 32 is configured for selectively optically connecting the OTDR optical connection port 18 with one of the first optical path 52 and the corresponding one of the second optical path 54 through the first optical coupler 70 and through the first optical coupling device 20 or the other one of the first optical path 52′ and the corresponding other one of the second optical path 54′ through the second optical coupler 70′ and through the second optical coupling device 20′. The optical switch 32 hence allows selectively operating an optical time domain reflectometer 100 optically connected with the OTDR optical connection port 18 to perform OTDR measurements according to the principles of the invention on the first optical link, including the first optical path 52, the second optical path 54, and the main optical path 50, or on the second optical link, including the first optical path 52′, the second optical path 54′, and a main optical path 50′.

(50) Although preferred exemplary embodiments are shown and specified in detail in the drawings and the preceding specification, these should be viewed as purely exemplary and not as limiting the invention. It is noted in this regard that only the preferred exemplary embodiments are shown and specified, and all variations and modifications should be protected that presently or in the future lie within the scope of protection of the invention as defined in the claims.