CA2219286A1 - Measurement of polarization mode dispersion - Google Patents
Measurement of polarization mode dispersion Download PDFInfo
- Publication number
- CA2219286A1 CA2219286A1 CA002219286A CA2219286A CA2219286A1 CA 2219286 A1 CA2219286 A1 CA 2219286A1 CA 002219286 A CA002219286 A CA 002219286A CA 2219286 A CA2219286 A CA 2219286A CA 2219286 A1 CA2219286 A1 CA 2219286A1
- Authority
- CA
- Canada
- Prior art keywords
- mode dispersion
- polarization mode
- artefact
- fiber
- birefringent
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 239000006185 dispersion Substances 0.000 title claims abstract description 102
- 230000010287 polarization Effects 0.000 title claims abstract description 102
- 238000005259 measurement Methods 0.000 title claims abstract description 29
- 238000000034 method Methods 0.000 claims abstract description 42
- 239000000835 fiber Substances 0.000 claims abstract description 39
- 238000012360 testing method Methods 0.000 claims abstract description 18
- 238000005305 interferometry Methods 0.000 claims description 5
- 230000001419 dependent effect Effects 0.000 claims 4
- 239000013307 optical fiber Substances 0.000 description 11
- 230000003287 optical effect Effects 0.000 description 10
- 230000005540 biological transmission Effects 0.000 description 9
- 239000011159 matrix material Substances 0.000 description 8
- 238000004458 analytical method Methods 0.000 description 5
- 238000001228 spectrum Methods 0.000 description 5
- 230000010355 oscillation Effects 0.000 description 4
- 238000012545 processing Methods 0.000 description 4
- 230000006870 function Effects 0.000 description 3
- 238000003780 insertion Methods 0.000 description 3
- 230000037431 insertion Effects 0.000 description 3
- 238000013459 approach Methods 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000000670 limiting effect Effects 0.000 description 2
- 230000009268 pathologic speech processing Effects 0.000 description 2
- 208000032207 progressive 1 supranuclear palsy Diseases 0.000 description 2
- 230000002411 adverse Effects 0.000 description 1
- 238000005311 autocorrelation function Methods 0.000 description 1
- BJQHLKABXJIVAM-UHFFFAOYSA-N bis(2-ethylhexyl) phthalate Chemical compound CCCCC(CC)COC(=O)C1=CC=CC=C1C(=O)OCC(CC)CCCC BJQHLKABXJIVAM-UHFFFAOYSA-N 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 230000008520 organization Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J4/00—Measuring polarisation of light
- G01J4/04—Polarimeters using electric detection means
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/33—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face
- G01M11/336—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face by measuring polarization mode dispersion [PMD]
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/33—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face
- G01M11/331—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face by using interferometer
Abstract
A method is provided for high resolution measurement of Polarization Mode Dispersion (PMD) of an optic fiber (26), comprising the steps of: providing a Polarization Mode Dispersion measuring instrument with a light source (10);
providing a test fiber (26); arranging the artefact (28) having a stable known Polarization Mode Dispersion value in series with the test fiber (26);
transmitting light from the light source (10) through the artefact (28) and the test fiber (26); measuring a biased Polarization Mode Dispersion value with the Polarization Mode Dispersion measuring instrument biased away from a zero Polarization Mode Dispersion value; and determining the Polarization Mode Dispersion of the optic fiber from the biased measured Polarization Mode Dispersion value.
providing a test fiber (26); arranging the artefact (28) having a stable known Polarization Mode Dispersion value in series with the test fiber (26);
transmitting light from the light source (10) through the artefact (28) and the test fiber (26); measuring a biased Polarization Mode Dispersion value with the Polarization Mode Dispersion measuring instrument biased away from a zero Polarization Mode Dispersion value; and determining the Polarization Mode Dispersion of the optic fiber from the biased measured Polarization Mode Dispersion value.
Description
Measurement of Polarization Mode Dispersion This is a divisional of copending patent application serial no. 08t445,3Z0, filed May l9, 1995, hereby incorporated by reference.
FIELD OF INVENTION
The present invention relates to a method for testing optical fibers, and more particularly to a method for measuring at high resolution Polarization Mode Dispersion (PMD) values in single mode optical fibers.
BACKGROUND OF THE INVENTION
Single mode optical fibers are used to transmit large quantities of information over significant distances. In order to preserve the integrity of such transmissions, it is desirable to eliminate distortion. It is impossible, however, to remove all forms of distortion from transmissive media.
Therefore, it is necessary to measure the distortionj either to determine the suitability of a transmissive medium's ~;~um information capacity, or to determine the most satisfactory manner of handling the-distortion. For a fiber optic c~ ~ln;cations system, the bit-error rate is the most significant specification for determ;n;ng the information carrying capacity of the system. The bit-error rate is WO 96/36859 ~CT/US96/07197 increased by, among other factors, the pulse broadening caused by dispersion in a fiber. Use of a single mode fiber eliminates modal dispersion, but not chromatic dispersion or Polarization Mode Dispersion, which is a bandwidth limiting effect that is present to some degree in all single mode fibers that are suitable for optical transmissions. It is, therefore, a potential source of signal distortion in optical communications systems.
In general, Polarization Mode Dispersion measurement in~Lr; ~nts are known in the art, and particularly defined in draft standards of the Telecommunications Industries Association, headquartered in Arlington, Virginia. These st~n~ds include Fiber Optic Test Procedure FOTP-113 for Polarization-Mode Dispersion Measurement for Single-Mode Optical Fibers by Wavelength Scanning, FOTP-122 for Polarization Mode Dispersion Measurement for Single-Mode Optical Fibers by Jones Matrix Eigenanalysis, and FOTP-124 for Polarization-Mode Dispersion Measurement for Single-Mode Optical Fibers by Interferometric Method. The detailed operation and procedure of the Polarization Mode Dispersion measur t-- ~nt instrument is described in these standards.
Also, a particular prior art circuit means is described in U.S.- Patent No. 4,i50,833, -issued to R. Jones, hereby incorporated by referen~e. Polarization Mode Dispersion mea~u~ -nt instruments include cycle counting, time pulse methods, relative phase methods or Jones Matrix Eigenanalysis, as discussed in more detail below. For example, Jones describes a known method for measuring dispersion in optical fibers. In particular, Jones describes a relative-phase method and apparatus for measuring transmissive dispersion,-such as chromatic or polarization dispersion. A light source modulated at a first frequency is synchronously varied at a lower frequency back and forth to and from a first and a second value of a transmission parameter, e.g. source wavelength or polarization state. Relative phases of the first modulation signal and the light transmitted through the fiber under test are measured by a phase detector. A lock-in amplifier compares the phase detector output to the lower frequency signal to provide a direct current output indicative of dispersion.
Another method for measuring dispersion in optical fibers measures time differences. The Jones Matrix Eigenanalysis method measures DGDA~ as a function of wavelength, where DGD
is known as a differential group delay, and PMD is expressed as < Ar >~. The relative-phase method and apparatus described -in Jones proved to be superior in resolution than the method for measuring time differences.
Other known methods of measuring Polarization Mode Dispersion in optical fibers include Interferometry, Jones n Matrix Eigenanalysis, the Wavelength Sc~nn;ng (WS) cycle cou~ting metnod, and the WS Fourier method. Interferometry uses the time domain to employ a low-coherence light source and a Michelson or Mach-Zehnder Interferometer to observe output in the form of the autocorrelation function of the time WO 96136859 P~TIUS96/07197 distribution, and the Polarization Mode Dispersion of the fiber may be obtained from this data. Interferometry is limited at the low end by the coherence time, typically 0.15 picoseconds, of the broadband source used.
Jones Matrix Eigenanalysis uses a polarimetric - determination of the instantaneous polarization transmission behavior, in the form of a Jones matrix with two eigenstates called Principal States of Polarization (PSP). By measuring the wavelength variation of the Jones matrix and hence the PSPs, the different delays between PSPs may be determined.
The delay is averaged over~a specific wavelength scan to establish the fiber Polarization Mode Dispersion value. Jones Matrix Eigenanalysis is limited by polarimetric accuracy and resolution to 0.01 picoseconds.
The WS cycle counting and the WS Fourier methods both use a light power transmission through the fiber using a linearly polarized source and a polarization analyzer before the light detector. The fiber gives rise to an oscillation pattern whose oscillation frequency is related to Polarization Mode Dispersion. In the WS cycle counting method, the number of complete oscillations in a given wavelength interval is counted to determine Polarization-Mode Dispersion. The WS
cycle counting method is limited to a ;n;mum of three cycles in the wavelength scan, typically 0.09 picoseconds. In the WS
Fourier method, however, wavelength scanning Polarization Mode Dispersion is determined by a frequency analysis technique on the oscillation pattern based on a Fourier transform. The CA 022l9286 l997-ll-l7 Fourier method is limited to a minimum of one cycle in the wavelength scan used, typically 0.03 picoseconds.
One important disadvantage of the known prior art is that the determination of the Polarization Mode Dispersion value is adversely influenced by spurious responses that combine with measured results to distort the Polarization Mode Dispersion value.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method-for measuring with higher resolution Polarization Mode Dispersion values below 0.1 picoseconds, useful, e.g. with fibers used for transmission systems operating 5 Gigabits per second or above.
It is also an object of the present invention to provide a method for measuring Polarization Mode Dispersion values between 0.01 picoseconds and 0.1 picoseconds for use, e.g., with WS Fourier and Interferometry methods.
It is also an object of the present invention to use a birefringent or wavelength specific artefact to bias Polarization Mode Dispersion away from zero, resulting in a broadened Pol-arization Mode Dispersion peak of the artefact, in order to obtain improved detection and determination of very low Polarization Mode Dispersion levels in opt-ical fibers.
It is also an object of the present invention to determine the Polarization Mode Dispersion of an optical fiber W096/36859 PCT~S96/07197 by appropriate data processing of the broadened artefact peak.
It is also an object of the present invention to provide ,~
a method for calibrating wavelength scanning Polarization Mode Dispersion instruments using a birefringent or wavelength selective device.
In accordance with the present invention, a method is provided for improving the measurement of Polarization Mode Dispersion by incorporating an artefact with a stable known Polarization Mode Dispersion value in a Polarization Mode Dispersion measuring instrument, and having a light source transmit light serially through an optic fiber to be tested and the artefact. The artefact biases a total Polarization Mode Dispersion measured by the Polarization Mode Dispersion measuring instrument away from zero, thus removing the undesirable influence of any spurious (near-zero) Polarization Mode Dispersion response from the measurement. The Polarization Mode Dispersion of the optic fiber may then be accurately determined by appropriate data processing of the measured Polarization Mode Dispersion. The artefact may also be used to calibrate a wavelength sc~nn;ng Polarization Mode Dispersion instrument.
The invention enables a high resolution measurement of Polarization Mode Dispersion with at least one order of magnitude higher, and possibly two orders of magnitude higher, than that achievable with the prior art relative phase or time mqasurement system.
WO 9~/3~'i9 PCT/US96/07197 BRIEF DESCRIPTION OF THE DRAWINGS
The invention, both as to its organization and manner of operation, may be further understood by reference to a dra~ing (not drawn to scale) which includes Figures 1-4 taken in connection with the following description.
Figure 1 is a block diagrammatic representation of a Polarization Mode Dispersion measurement instrument in accordance with the present invention utilizing a Mach-Zehnder interferometer.
Figure 2 is a block diagrammatic representation of a Polarization Mode Dispersion measurement instrument in accordance with another embodiment of the present invention suitable for use with wavelength scanning Fourier analysis (WS
Fourier).
Figure 3a is a graph of time versus Polarization Mode Dispersion value for a prior art Polarization Mode Dispersion measurement instrument.
Figure 3b is a graph of time versus Polarization Mode Dispersion value for a Polarization Mode Dispersion measurement instrument of the present invention.
Figure 4 is a block diagram of an application of the present invention to calibrate a Polarization Mode Dispersion instrument.
WO 96/36859 P.CT/US96107197 DESCRIPTION OF THE BEST MODE OF THE INVENTION
Figures 1 and 2 are block diagrams of two Polarization Mode Dispersion measurement instruments for high resolution, polarization dispersion measurement, which are the subject of the present invention. Figure 1 shows one Polarization Mode Dispersion measurement instrument using an interferometric measurement technique, while Figure 2 shows another Polarization Mode Dispersion measurement instrument using a wavelength scanning Fourier analysis (WS Fourier) t~chn;que.
In Figure 1, the Polarization Mode Dispersion measurement i-nstrument has a light source 10 which may be either a light emitting diode (LED), as shown, or in an alternative embodiment, a superfluorescent light source (not shown). The Polarization Mode Dispersion measurement instrument has a polarizer 12 that responds to light coming from an output of the light source 10, for providing polarized light. A beam splitter 14 connected to the polarizer 12 divides the polarized light for transmission in a first path 16 and a second path 18. The second path 18 includes a delay line 20 for delaying the transmission of light. The delay line 20 can be adjusted to alter a relative optical delay between the first-and second paths 16 and 18. As shown, the delay line 20 is a Mach-Zehnder interferometer, which is known in the ~rt.
A beam splitter 22 receives light transmitted along the first and second paths 18 and 20 and delivers it to an artefact 28.
The artefact 28.is a device which produces a known, stable Polarization Mode Dispersion. The artefact 28 will WO 96t36859 P~T/US96/07197 assure that the Polarization Mode Dispersion measurement ~ instrument will have a known interference peak level at a particular time value T, as best shown in Figure 3b. In the embodiment shown in Figure 1, the artefact 28 is a birefringent device, which may be a birefringent waveplate, birefringent fiber or other birefringent device. The time T
is the time difference between the fast and slow polarization modes, or simply the Polarization Mode Dispersion of the artefact 28. In the present invention, the artefact 28 serves to bias the total Polarization Mode Dispersion measured by the instrument away from zero, removing the influence of any spurious (near-zero) Polarization Mode Dispersion response from the measurement, as shown in Figure 3b.
A test fiber 26 receives light from an output of the artefact 28. The connection between the artefact 28 and the test fiber 26 is known in the art, and may include a lens system, a butt splice to a single mode fiber pigtail or an index-matched coupling. However, the scope of the invention is not intended to be limited to any particular series arrangement between the artefact 28 and the test fiber 26.
For example, as shown, the artefact 28 is arranged before the test fiber 26 in Figure 1, while in Figure 2, the artefact 60 is arranged after the test fiber 56. Such a construction could also be incorporated in accordance with these teachings in a Michelson interferometer.
An output of the fiber 26 is delivered to an analyzer 30 that observes interferences between principal orthogonal _ g states of polarization, and provides an analyzed signal to a detector 32, that represents polarization states versus power.
The detector 32 converts an optical signal to an electrical.
signal. In an alternative approach, a polarimeter may be used. A lock-in amplifier 34 is a synchronized phase and volt meter which is used to demodulate chopped or modulated optical signals for signal processing. A computer 36 provides electronic signal processing and apparatus control functions.
The interference signature versus the setting of the delay line 20 is determined and stored using a standard computer 36.
Figure 2 shows an alternative embodiment of the present invention in which the Polarization Mode Dispersion measurement instrument has an artefact 60 coupled to an output of a test fiber 56. In Figure 2, a light source 50 delivers light to a polarizer 52 for coupling through a splice 54 to a fiber under test 56. A splice 58 couples an output of the test fiber 56 to the artefact 60. An analyzer 62 analyses the light polarization state, and an optical spectrum analyzer or monochromator 64 allows the polarization transmission versus optical wavelength to be measured. The computer 68 performs a Fourier analysis and apparatus control functions, and Polarization Mode Dispersion calculations.
The artefact 60 produces a known, stabie Polarization Mode Dispersion. It will assure that ~he Polarization Mode 26 Dispersion measurement output will have a known peak level at a particular time value T. In the embodiment in ~igure 2, the artefact 60 may be a birefringent device, which may be a CA 022l9286 l997-ll-l7 WO 96/36859 P~CT/US96/07197 birefringent waveplate, birefringent fiber or other birefringent device. The time T is the time difference between the fast and slow polarization modes, or simply the Polarization Mode Dispersion of the artefact 60. In alternative embodiments, the artefact 60 may also be a reflective or trAn~ ive device which provides a known stable sinusoidal response of power versus wavelength indicative of the insertion loss spectrum of the artefact. An example of either artefact 60 is a Fabry-Perot etalon, including an interferometer. The sinusoidal response of power versus wavelength will give an apparent Polarization Mode Dispersion peak at time T, corresponding to the known, stable insertion loss spectrum of the artefact.
A comparison of the results of the graphs in Figures 3a and 3b illustrates how the addition of the artefact 28 (Figure 1) or the artefact 60 (Figure 2) of the present invention greatly improves the resolution of Polarization Mode Dispersion measurement instruments shown in Figures 1 and 2.
In both Figures 3a and 3b, the abscissa is time, and the ordinate is Polarization Mode Dispersion value. As shown, spurious responses are illustrated in dotted lines, and measured results are illustrated in solid lines. As Polarization Mode Dispersion values approach zero, there are many effects that can produce a greater error than the value of the Polarization Mode Dispersion. Spurious responses are due to optical losses and other optical imperfections, or source coherence. Such responses provide results that combine WO 9~13c~s9 PCT/US96/07197 with a low level of Polarization Mode Dispersion and distort it. As shown in Figure 3a, in a prior art Polarization Mode Dispersion measurement instrument (not having the artefact.28 or 60), the width, e.g. Root Mean Square width, of the signature (solid line) is calculated to determine Polarization Mode Dispersion of the fiber under test. However, the spurious responses have combined with the measured results to distort the Polarization Mode Dispersion value.
In contrast, as shown in Figure 3b in the Polarization Mode Dispersion measurement instrument of the present invention, the basic Polarization Mode Dispersion signature is transposed by the artefact 28 or 60 from zero to time T. The spurious effects do not interact with the measured dispersion.
As shown in Figure 3b, the spurious responses do not affect measurement of Polarization Mode Dispersion during a calculation of the width, e.g. Root Mean Square width, of the measured peak.
Figure 4 shows a calibration of a Polarization Mode Dispersion in accordance with the present invention. A test fiber is not included in the light path. An artefact 106 is included, which receives light transmitted from a broadband source 100 through a polarizer 102 coupled to a splice 104. A
splice 108 couples the output of the artefact 106 to an analyzer 110 whose output is analyzed by a measuring means 112 comprising an optical spectrum analyzer or monochromator and ~uLation means 114 operating in-accordance with the principles described with respect to Figure 2. The artefact WO 961368S9 PCI~/US96/07197 104 will bias the measured Polarization Mode Dispersion away from zero. The measured Polarization Mode Dispersion is compared to the known Polarization Mode Dispersion value of the artefact 104. The result of this can be viewed in a number of ways. The system of Figure 4 is thus calibrated so that a particular electrical output corresponds to the known value of the artefact 104. Further, this operation provides an update to factory calibration or periodic field calibration. This method is applicable to a WS Fourier method and WS cycle counting measuring methods, discussed above.
Additionally, there are further calibration techniques available for wavelength scanning methods, which may use wavelength transmissive or reflective devices for an artefact.
In such a case, the Polarization Mode Dispersion apparatus lS produces a Polarization Mode ~ispersion signature at time T
equivalent to the known, stable insertion loss spectrum of the artefact in accordance with the principles described with respect to Figure 2. The above teachings will enable those skilled in the art to provide many different embodiments of high resolution measuring means which can employ wavelength transmissive devices for the artefact.
It will thus be seen that the objects set forth above, and those-made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall W096/36859 PCT~S96/07197 be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are r intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.
FIELD OF INVENTION
The present invention relates to a method for testing optical fibers, and more particularly to a method for measuring at high resolution Polarization Mode Dispersion (PMD) values in single mode optical fibers.
BACKGROUND OF THE INVENTION
Single mode optical fibers are used to transmit large quantities of information over significant distances. In order to preserve the integrity of such transmissions, it is desirable to eliminate distortion. It is impossible, however, to remove all forms of distortion from transmissive media.
Therefore, it is necessary to measure the distortionj either to determine the suitability of a transmissive medium's ~;~um information capacity, or to determine the most satisfactory manner of handling the-distortion. For a fiber optic c~ ~ln;cations system, the bit-error rate is the most significant specification for determ;n;ng the information carrying capacity of the system. The bit-error rate is WO 96/36859 ~CT/US96/07197 increased by, among other factors, the pulse broadening caused by dispersion in a fiber. Use of a single mode fiber eliminates modal dispersion, but not chromatic dispersion or Polarization Mode Dispersion, which is a bandwidth limiting effect that is present to some degree in all single mode fibers that are suitable for optical transmissions. It is, therefore, a potential source of signal distortion in optical communications systems.
In general, Polarization Mode Dispersion measurement in~Lr; ~nts are known in the art, and particularly defined in draft standards of the Telecommunications Industries Association, headquartered in Arlington, Virginia. These st~n~ds include Fiber Optic Test Procedure FOTP-113 for Polarization-Mode Dispersion Measurement for Single-Mode Optical Fibers by Wavelength Scanning, FOTP-122 for Polarization Mode Dispersion Measurement for Single-Mode Optical Fibers by Jones Matrix Eigenanalysis, and FOTP-124 for Polarization-Mode Dispersion Measurement for Single-Mode Optical Fibers by Interferometric Method. The detailed operation and procedure of the Polarization Mode Dispersion measur t-- ~nt instrument is described in these standards.
Also, a particular prior art circuit means is described in U.S.- Patent No. 4,i50,833, -issued to R. Jones, hereby incorporated by referen~e. Polarization Mode Dispersion mea~u~ -nt instruments include cycle counting, time pulse methods, relative phase methods or Jones Matrix Eigenanalysis, as discussed in more detail below. For example, Jones describes a known method for measuring dispersion in optical fibers. In particular, Jones describes a relative-phase method and apparatus for measuring transmissive dispersion,-such as chromatic or polarization dispersion. A light source modulated at a first frequency is synchronously varied at a lower frequency back and forth to and from a first and a second value of a transmission parameter, e.g. source wavelength or polarization state. Relative phases of the first modulation signal and the light transmitted through the fiber under test are measured by a phase detector. A lock-in amplifier compares the phase detector output to the lower frequency signal to provide a direct current output indicative of dispersion.
Another method for measuring dispersion in optical fibers measures time differences. The Jones Matrix Eigenanalysis method measures DGDA~ as a function of wavelength, where DGD
is known as a differential group delay, and PMD is expressed as < Ar >~. The relative-phase method and apparatus described -in Jones proved to be superior in resolution than the method for measuring time differences.
Other known methods of measuring Polarization Mode Dispersion in optical fibers include Interferometry, Jones n Matrix Eigenanalysis, the Wavelength Sc~nn;ng (WS) cycle cou~ting metnod, and the WS Fourier method. Interferometry uses the time domain to employ a low-coherence light source and a Michelson or Mach-Zehnder Interferometer to observe output in the form of the autocorrelation function of the time WO 96136859 P~TIUS96/07197 distribution, and the Polarization Mode Dispersion of the fiber may be obtained from this data. Interferometry is limited at the low end by the coherence time, typically 0.15 picoseconds, of the broadband source used.
Jones Matrix Eigenanalysis uses a polarimetric - determination of the instantaneous polarization transmission behavior, in the form of a Jones matrix with two eigenstates called Principal States of Polarization (PSP). By measuring the wavelength variation of the Jones matrix and hence the PSPs, the different delays between PSPs may be determined.
The delay is averaged over~a specific wavelength scan to establish the fiber Polarization Mode Dispersion value. Jones Matrix Eigenanalysis is limited by polarimetric accuracy and resolution to 0.01 picoseconds.
The WS cycle counting and the WS Fourier methods both use a light power transmission through the fiber using a linearly polarized source and a polarization analyzer before the light detector. The fiber gives rise to an oscillation pattern whose oscillation frequency is related to Polarization Mode Dispersion. In the WS cycle counting method, the number of complete oscillations in a given wavelength interval is counted to determine Polarization-Mode Dispersion. The WS
cycle counting method is limited to a ;n;mum of three cycles in the wavelength scan, typically 0.09 picoseconds. In the WS
Fourier method, however, wavelength scanning Polarization Mode Dispersion is determined by a frequency analysis technique on the oscillation pattern based on a Fourier transform. The CA 022l9286 l997-ll-l7 Fourier method is limited to a minimum of one cycle in the wavelength scan used, typically 0.03 picoseconds.
One important disadvantage of the known prior art is that the determination of the Polarization Mode Dispersion value is adversely influenced by spurious responses that combine with measured results to distort the Polarization Mode Dispersion value.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method-for measuring with higher resolution Polarization Mode Dispersion values below 0.1 picoseconds, useful, e.g. with fibers used for transmission systems operating 5 Gigabits per second or above.
It is also an object of the present invention to provide a method for measuring Polarization Mode Dispersion values between 0.01 picoseconds and 0.1 picoseconds for use, e.g., with WS Fourier and Interferometry methods.
It is also an object of the present invention to use a birefringent or wavelength specific artefact to bias Polarization Mode Dispersion away from zero, resulting in a broadened Pol-arization Mode Dispersion peak of the artefact, in order to obtain improved detection and determination of very low Polarization Mode Dispersion levels in opt-ical fibers.
It is also an object of the present invention to determine the Polarization Mode Dispersion of an optical fiber W096/36859 PCT~S96/07197 by appropriate data processing of the broadened artefact peak.
It is also an object of the present invention to provide ,~
a method for calibrating wavelength scanning Polarization Mode Dispersion instruments using a birefringent or wavelength selective device.
In accordance with the present invention, a method is provided for improving the measurement of Polarization Mode Dispersion by incorporating an artefact with a stable known Polarization Mode Dispersion value in a Polarization Mode Dispersion measuring instrument, and having a light source transmit light serially through an optic fiber to be tested and the artefact. The artefact biases a total Polarization Mode Dispersion measured by the Polarization Mode Dispersion measuring instrument away from zero, thus removing the undesirable influence of any spurious (near-zero) Polarization Mode Dispersion response from the measurement. The Polarization Mode Dispersion of the optic fiber may then be accurately determined by appropriate data processing of the measured Polarization Mode Dispersion. The artefact may also be used to calibrate a wavelength sc~nn;ng Polarization Mode Dispersion instrument.
The invention enables a high resolution measurement of Polarization Mode Dispersion with at least one order of magnitude higher, and possibly two orders of magnitude higher, than that achievable with the prior art relative phase or time mqasurement system.
WO 9~/3~'i9 PCT/US96/07197 BRIEF DESCRIPTION OF THE DRAWINGS
The invention, both as to its organization and manner of operation, may be further understood by reference to a dra~ing (not drawn to scale) which includes Figures 1-4 taken in connection with the following description.
Figure 1 is a block diagrammatic representation of a Polarization Mode Dispersion measurement instrument in accordance with the present invention utilizing a Mach-Zehnder interferometer.
Figure 2 is a block diagrammatic representation of a Polarization Mode Dispersion measurement instrument in accordance with another embodiment of the present invention suitable for use with wavelength scanning Fourier analysis (WS
Fourier).
Figure 3a is a graph of time versus Polarization Mode Dispersion value for a prior art Polarization Mode Dispersion measurement instrument.
Figure 3b is a graph of time versus Polarization Mode Dispersion value for a Polarization Mode Dispersion measurement instrument of the present invention.
Figure 4 is a block diagram of an application of the present invention to calibrate a Polarization Mode Dispersion instrument.
WO 96/36859 P.CT/US96107197 DESCRIPTION OF THE BEST MODE OF THE INVENTION
Figures 1 and 2 are block diagrams of two Polarization Mode Dispersion measurement instruments for high resolution, polarization dispersion measurement, which are the subject of the present invention. Figure 1 shows one Polarization Mode Dispersion measurement instrument using an interferometric measurement technique, while Figure 2 shows another Polarization Mode Dispersion measurement instrument using a wavelength scanning Fourier analysis (WS Fourier) t~chn;que.
In Figure 1, the Polarization Mode Dispersion measurement i-nstrument has a light source 10 which may be either a light emitting diode (LED), as shown, or in an alternative embodiment, a superfluorescent light source (not shown). The Polarization Mode Dispersion measurement instrument has a polarizer 12 that responds to light coming from an output of the light source 10, for providing polarized light. A beam splitter 14 connected to the polarizer 12 divides the polarized light for transmission in a first path 16 and a second path 18. The second path 18 includes a delay line 20 for delaying the transmission of light. The delay line 20 can be adjusted to alter a relative optical delay between the first-and second paths 16 and 18. As shown, the delay line 20 is a Mach-Zehnder interferometer, which is known in the ~rt.
A beam splitter 22 receives light transmitted along the first and second paths 18 and 20 and delivers it to an artefact 28.
The artefact 28.is a device which produces a known, stable Polarization Mode Dispersion. The artefact 28 will WO 96t36859 P~T/US96/07197 assure that the Polarization Mode Dispersion measurement ~ instrument will have a known interference peak level at a particular time value T, as best shown in Figure 3b. In the embodiment shown in Figure 1, the artefact 28 is a birefringent device, which may be a birefringent waveplate, birefringent fiber or other birefringent device. The time T
is the time difference between the fast and slow polarization modes, or simply the Polarization Mode Dispersion of the artefact 28. In the present invention, the artefact 28 serves to bias the total Polarization Mode Dispersion measured by the instrument away from zero, removing the influence of any spurious (near-zero) Polarization Mode Dispersion response from the measurement, as shown in Figure 3b.
A test fiber 26 receives light from an output of the artefact 28. The connection between the artefact 28 and the test fiber 26 is known in the art, and may include a lens system, a butt splice to a single mode fiber pigtail or an index-matched coupling. However, the scope of the invention is not intended to be limited to any particular series arrangement between the artefact 28 and the test fiber 26.
For example, as shown, the artefact 28 is arranged before the test fiber 26 in Figure 1, while in Figure 2, the artefact 60 is arranged after the test fiber 56. Such a construction could also be incorporated in accordance with these teachings in a Michelson interferometer.
An output of the fiber 26 is delivered to an analyzer 30 that observes interferences between principal orthogonal _ g states of polarization, and provides an analyzed signal to a detector 32, that represents polarization states versus power.
The detector 32 converts an optical signal to an electrical.
signal. In an alternative approach, a polarimeter may be used. A lock-in amplifier 34 is a synchronized phase and volt meter which is used to demodulate chopped or modulated optical signals for signal processing. A computer 36 provides electronic signal processing and apparatus control functions.
The interference signature versus the setting of the delay line 20 is determined and stored using a standard computer 36.
Figure 2 shows an alternative embodiment of the present invention in which the Polarization Mode Dispersion measurement instrument has an artefact 60 coupled to an output of a test fiber 56. In Figure 2, a light source 50 delivers light to a polarizer 52 for coupling through a splice 54 to a fiber under test 56. A splice 58 couples an output of the test fiber 56 to the artefact 60. An analyzer 62 analyses the light polarization state, and an optical spectrum analyzer or monochromator 64 allows the polarization transmission versus optical wavelength to be measured. The computer 68 performs a Fourier analysis and apparatus control functions, and Polarization Mode Dispersion calculations.
The artefact 60 produces a known, stabie Polarization Mode Dispersion. It will assure that ~he Polarization Mode 26 Dispersion measurement output will have a known peak level at a particular time value T. In the embodiment in ~igure 2, the artefact 60 may be a birefringent device, which may be a CA 022l9286 l997-ll-l7 WO 96/36859 P~CT/US96/07197 birefringent waveplate, birefringent fiber or other birefringent device. The time T is the time difference between the fast and slow polarization modes, or simply the Polarization Mode Dispersion of the artefact 60. In alternative embodiments, the artefact 60 may also be a reflective or trAn~ ive device which provides a known stable sinusoidal response of power versus wavelength indicative of the insertion loss spectrum of the artefact. An example of either artefact 60 is a Fabry-Perot etalon, including an interferometer. The sinusoidal response of power versus wavelength will give an apparent Polarization Mode Dispersion peak at time T, corresponding to the known, stable insertion loss spectrum of the artefact.
A comparison of the results of the graphs in Figures 3a and 3b illustrates how the addition of the artefact 28 (Figure 1) or the artefact 60 (Figure 2) of the present invention greatly improves the resolution of Polarization Mode Dispersion measurement instruments shown in Figures 1 and 2.
In both Figures 3a and 3b, the abscissa is time, and the ordinate is Polarization Mode Dispersion value. As shown, spurious responses are illustrated in dotted lines, and measured results are illustrated in solid lines. As Polarization Mode Dispersion values approach zero, there are many effects that can produce a greater error than the value of the Polarization Mode Dispersion. Spurious responses are due to optical losses and other optical imperfections, or source coherence. Such responses provide results that combine WO 9~13c~s9 PCT/US96/07197 with a low level of Polarization Mode Dispersion and distort it. As shown in Figure 3a, in a prior art Polarization Mode Dispersion measurement instrument (not having the artefact.28 or 60), the width, e.g. Root Mean Square width, of the signature (solid line) is calculated to determine Polarization Mode Dispersion of the fiber under test. However, the spurious responses have combined with the measured results to distort the Polarization Mode Dispersion value.
In contrast, as shown in Figure 3b in the Polarization Mode Dispersion measurement instrument of the present invention, the basic Polarization Mode Dispersion signature is transposed by the artefact 28 or 60 from zero to time T. The spurious effects do not interact with the measured dispersion.
As shown in Figure 3b, the spurious responses do not affect measurement of Polarization Mode Dispersion during a calculation of the width, e.g. Root Mean Square width, of the measured peak.
Figure 4 shows a calibration of a Polarization Mode Dispersion in accordance with the present invention. A test fiber is not included in the light path. An artefact 106 is included, which receives light transmitted from a broadband source 100 through a polarizer 102 coupled to a splice 104. A
splice 108 couples the output of the artefact 106 to an analyzer 110 whose output is analyzed by a measuring means 112 comprising an optical spectrum analyzer or monochromator and ~uLation means 114 operating in-accordance with the principles described with respect to Figure 2. The artefact WO 961368S9 PCI~/US96/07197 104 will bias the measured Polarization Mode Dispersion away from zero. The measured Polarization Mode Dispersion is compared to the known Polarization Mode Dispersion value of the artefact 104. The result of this can be viewed in a number of ways. The system of Figure 4 is thus calibrated so that a particular electrical output corresponds to the known value of the artefact 104. Further, this operation provides an update to factory calibration or periodic field calibration. This method is applicable to a WS Fourier method and WS cycle counting measuring methods, discussed above.
Additionally, there are further calibration techniques available for wavelength scanning methods, which may use wavelength transmissive or reflective devices for an artefact.
In such a case, the Polarization Mode Dispersion apparatus lS produces a Polarization Mode ~ispersion signature at time T
equivalent to the known, stable insertion loss spectrum of the artefact in accordance with the principles described with respect to Figure 2. The above teachings will enable those skilled in the art to provide many different embodiments of high resolution measuring means which can employ wavelength transmissive devices for the artefact.
It will thus be seen that the objects set forth above, and those-made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall W096/36859 PCT~S96/07197 be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are r intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.
Claims (10)
1. A method for high resolution measurement of a Polarization Mode Dispersion of an optic fiber, comprising the steps of:
providing a Polarization Mode Dispersion measuring instrument with a light source;
providing a test fiber;
arranging the artefact having a stable known Polarization Mode Dispersion value in series with the test fiber;
transmitting light from the light source through the artefact and the test fiber;
measuring a biased Polarization Mode Dispersion value with the Polarization Mode Dispersion measuring instrument biased away from a zero Polarization Mode Dispersion value;
and determining the Polarization Mode Dispersion of the optic fiber from the biased measured Polarization Mode Dispersion value.
providing a Polarization Mode Dispersion measuring instrument with a light source;
providing a test fiber;
arranging the artefact having a stable known Polarization Mode Dispersion value in series with the test fiber;
transmitting light from the light source through the artefact and the test fiber;
measuring a biased Polarization Mode Dispersion value with the Polarization Mode Dispersion measuring instrument biased away from a zero Polarization Mode Dispersion value;
and determining the Polarization Mode Dispersion of the optic fiber from the biased measured Polarization Mode Dispersion value.
2. The method according to claim 1, wherein the method includes providing the Polarization Mode Dispersion measuring instrument that utilizes interferometry.
3. The method according to claim 2, wherein the artefact is a birefringent device.
4. The method according to claim 3, wherein the birefringent device is a birefringent waveplate or birefringent fiber.
5. The method according to claim 1, wherein the Polarization Mode Dispersion measuring instrument utilizes a Wavelength Scanning Fourier method.
6. The method according to claim 5, wherein the artefact is a birefringent device.
7. The method according to claim 5, wherein the birefringent device is a birefringent waveplate or birefringent fiber.
8. The method according to claim 5, wherein the artefact is a wavelength-dependent transmissive device.
9. The method according to claim 5, wherein the artefact is a wavelength-dependent reflective device.
10. The method according to claim 1, wherein the step of providing an artefact further comprises the step of providing an artefact having either known wavelength-dependent transmissive characteristics or known wavelength-dependent reflective characteristics.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/445,320 | 1995-05-19 | ||
| US08/445,320 US5654793A (en) | 1995-05-19 | 1995-05-19 | Method and apparatus for high resolution measurement of very low levels of polarization mode dispersion (PMD) in single mode optical fibers and for calibration of PMD measuring instruments |
| US61733796A | 1996-03-18 | 1996-03-18 | |
| US08/617,337 | 1996-03-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2219286A1 true CA2219286A1 (en) | 1996-11-21 |
Family
ID=27034269
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002219286A Abandoned CA2219286A1 (en) | 1995-05-19 | 1996-05-17 | Measurement of polarization mode dispersion |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JP2000510573A (en) |
| KR (1) | KR19990014935A (en) |
| CN (1) | CN1196793A (en) |
| AU (1) | AU6022896A (en) |
| CA (1) | CA2219286A1 (en) |
| WO (1) | WO1996036859A1 (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2745082B1 (en) * | 1996-02-16 | 1998-04-30 | Univ Geneve | METHOD AND DEVICE FOR MEASURING THE POLARIZATION DISPERSION OF AN OPTICAL FIBER |
| US5949560A (en) * | 1997-02-05 | 1999-09-07 | Northern Telecom Limited | Optical transmission system |
| DE19724676A1 (en) * | 1997-06-11 | 1999-01-07 | Siemens Ag | Measuring apparatus for determining polarisation mode dispersion of optical elements e.g. glass fibre conductors |
| ITTO20020585A1 (en) * | 2002-07-05 | 2004-01-05 | Telecom Italia Lab Spa | SYSTEM METHOD AND DEVICE TO MEASURE THE POLARIZATION DISPERSION OF AN OPTICAL FIBER |
| FR2844354B1 (en) * | 2002-09-05 | 2005-09-30 | Cit Alcatel | POLARIZED OPTICAL WAVE REFLECTOMETRY METHOD (POTDR) |
| JP4781746B2 (en) * | 2005-04-14 | 2011-09-28 | 株式会社フジクラ | Optical fiber birefringence measuring method and measuring apparatus, and optical fiber polarization mode dispersion measuring method |
| CN101325454B (en) * | 2008-07-30 | 2012-05-02 | 烽火通信科技股份有限公司 | Method for reducing indeterminacy in chromatic dispersion test of optical fiber polarization film |
| CN102164003B (en) * | 2010-12-20 | 2014-04-09 | 武汉虹拓新技术有限责任公司 | Dispersion measurement device |
| CN102636337A (en) * | 2012-04-26 | 2012-08-15 | 江苏大学 | Method for measuring optical fiber dispersion |
| CN104006950B (en) * | 2014-06-12 | 2016-06-08 | 天津大学 | A kind of polarization maintaining optical fibre birefringence dispersion measuring method |
| CN105337969A (en) * | 2015-10-19 | 2016-02-17 | 朱建龙 | Safety communication method between two mobile terminals |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3445833A (en) * | 1965-11-01 | 1969-05-20 | Sperry Rand Corp | Signal responsive apparatus with a polar azimuth vibrator |
| US4241997A (en) * | 1978-12-11 | 1980-12-30 | General Motors Corporation | Laser spectrometer with frequency calibration |
| US4750833A (en) * | 1985-12-03 | 1988-06-14 | Princeton Applied Research Corp. | Fiber optic dispersion method and apparatus |
-
1996
- 1996-05-17 CN CN96194853A patent/CN1196793A/en active Pending
- 1996-05-17 JP JP08535104A patent/JP2000510573A/en active Pending
- 1996-05-17 WO PCT/US1996/007197 patent/WO1996036859A1/en not_active Application Discontinuation
- 1996-05-17 CA CA002219286A patent/CA2219286A1/en not_active Abandoned
- 1996-05-17 AU AU60228/96A patent/AU6022896A/en not_active Abandoned
- 1996-05-17 KR KR1019970708281A patent/KR19990014935A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| WO1996036859A1 (en) | 1996-11-21 |
| JP2000510573A (en) | 2000-08-15 |
| CN1196793A (en) | 1998-10-21 |
| KR19990014935A (en) | 1999-02-25 |
| AU6022896A (en) | 1996-11-29 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| EP1113250B1 (en) | Method and apparatus for determining the polarisation mode dispersion of an optical device | |
| US6204924B1 (en) | Method and apparatus for measuring polarization mode dispersion of optical devices | |
| US6724469B2 (en) | Polarization-OTDR for measuring characteristics of optical fibers | |
| JP4667728B2 (en) | Sweep wavelength meter and wavelength calibration method | |
| JP4722110B2 (en) | Wavelength calibration apparatus and method for swept laser | |
| US4750833A (en) | Fiber optic dispersion method and apparatus | |
| US7426021B2 (en) | Interferometric optical analyzer and method for measuring the linear response of an optical component | |
| US7009691B2 (en) | System and method for removing the relative phase uncertainty in device characterizations performed with a polarimeter | |
| EP1705471A1 (en) | Apparatus for measuring differential mode delay of multimode optical fiber | |
| US5654793A (en) | Method and apparatus for high resolution measurement of very low levels of polarization mode dispersion (PMD) in single mode optical fibers and for calibration of PMD measuring instruments | |
| US20090244522A1 (en) | Polarization Optical Time Domain Reflectometer and Method of Determining PMD | |
| Calvani et al. | Polarization measurements on single-mode fibers | |
| CN103900680A (en) | Device and detecting method for restraining polarization crosstalk measuring noise by the adoption of light source | |
| CA2219286A1 (en) | Measurement of polarization mode dispersion | |
| US7602499B2 (en) | Measuring polarization mode dispersion | |
| EP1207377A2 (en) | Method and apparatus for measuring optical properties by means of the Jones matrix | |
| US7061621B2 (en) | Interferometric-based device and method for determining chromatic dispersion of optical components using a polarimeter | |
| Oberson et al. | Interferometric polarization mode dispersion measurements with femtosecond sensitivity | |
| US7016023B2 (en) | Chromatic dispersion measurement | |
| CN115452015A (en) | Double-scale reference interference phase noise accurate correction optical frequency domain reflectometer | |
| Simova et al. | Characterization of chromatic dispersion and polarization sensitivity in fiber gratings | |
| JP3998460B2 (en) | Method for determining characteristics of optical device and inspection device | |
| CA2229219A1 (en) | Method and apparatus for measuring polarization mode dispersion of optical devices | |
| CA2236521A1 (en) | Method and apparatus for measuring polarization mode dispersion of optical devices | |
| Vifian | From microwaves to lightwaves: the new dimensions of lightwave measurements |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |