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1、 TIA DOCUMENT FOTP124 Polarization-Mode Dispersion Measurement for Single-Mode Optical Fibers by Interferometry TIA-455-124-A (Revision of TIA/EIA-455-124) FEBRUARY 2004 TELECOMMUNICATIONS INDUSTRY ASSOCIATION The Telecommunications Industry Association represents the communications sector of Copyri
2、ght Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 02:08:03 MDTNo reproduction or networking permitted without license from IHS -,-,- NOTICE TIA Engineering Standards and Publications are d
3、esigned to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for their particular need. The ex
4、istence of such Publications shall not in any respect preclude any member or non-member of TIA from manufacturing or selling products not conforming to such Publications. Neither shall the existence of such Documents preclude their voluntary use by non-TIA members, either domestically or internation
5、ally. TIA DOCUMENTS TIA Documents contain information deemed to be of technical value to the industry, and are published at the request of the originating Committee without necessarily following the rigorous public review and resolution of comments which is a procedural part of the development of a
6、American National Standard (ANS). Further details of the development process are available in the TIA Engineering Manual, located at http:/www.tiaonline.org/standards/sfg/engineering_manual.cfm TIA Documents shall be reviewed on a five year cycle by the formulating Committee and a decision made on w
7、hether to reaffirm, revise, withdraw, or proceed to develop an American National Standard on this subject. Suggestions for revision should be directed to: Standards FO-4.2, Subcommittee on Optical Fibers and Cables; and FO-4.6.1, Working Group on Single-mode Fibers and Standards Harmonization.) This
8、 is part of the series of test procedures included within Recommended Standard EIA/TIA-455. 1. Introduction Intent This test method describes a procedure for measuring the polarization-mode dispersion (PMD) of single-mode optical fibers and cable assemblies. It provides a single measurement value th
9、at represents the PMD defined as the root-mean squared (RMS) differential group delay (DGD) over the measurement wavelength range of the selected source in the 1310nm or/and the 1550nm region or any other region of interest. The method can be applied to any fiber length. Scope This procedure is rest
10、ricted to wavelengths greater than or equal to that at which the fiber is effectively single-mode. The cutoff wavelength cf of an uncabled fiber may be determined by FOTP-80, while the cutoff wavelength cc of a cabled fiber may be determined by FOTP-170. Background PMD causes an optical pulse to spr
11、ead in the time domain; this dispersion could impair the performance of a single-mode fiber-optic telecommunications system. The effect can be related to differential group velocities and corresponding arrival times of different polarization components of the signal. For a narrow band source, the ef
12、fect can be Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 02:08:03 MDTNo reproduction or networking permitted without license from IHS -,-,- TIA-455-124-A 7 related to the DGD be
13、tween pairs of orthogonal principal states of polarization (PSPs), in absence of polarization dependent loss and non-linear effects. In long fiber spans, PMD is a random effect since it depends on the details of the birefringence along the entire fiber length. It is also sensitive to time-dependent
14、temperature and mechanical perturbations on the fiber. For this reason, a useful way to characterize PMD in long fibers is in terms of the expected value of the mean DGD or the RMS DGD 1/2 when considering the DGD distribution as a function of wavelength. The two definitions (mean or RMS DGD) mathem
15、atically hold and are accepted. In principle, the expected value does not undergo large changes for a given fiber from day to day or from source to source, unlike the parameters or . In addition, or 1/2 is a useful predictor of lightwave system performance. When the DGD distribution as a function of
16、 wavelength can be approximated by a Maxwell distribution, then can be used as an easier predictor of system performance. In this case, can be easily correlated to 1/2; a maximum DGD can also be found for a defined value of the probability density function (frequency of occurrence of the DGD) from t
17、he Maxwell distribution. The term “PMD” is used in the general sense of the phenomenon of the two PSPs having different group velocities, and in the specific sense of the expected value or 1/2. The DGD or pulse broadening can be averaged over wavelength, yielding , or time, yielding t, or temperatur
18、e, yielding . For most purposes, it is not necessary to distinguish between these various options for obtaining . The coupling length h is the length of fiber or cable at which appreciable coupling (i.e. energy transfer) between the two PSPs begins to occur. Mode coupling is the physical phenomenon
19、by which energy is exchanged between PSPs. If the fiber length L satisfies the condition L /L or = 1/2/L ( 1 ) The fiber length satisfying the condition L h regime in which case the mode coupling is random. In this case or 1/2 scales with the square root of fiber length, and “long-length” PMD coeffi
20、cient = /L1/2 or = 1/2/L1/2 ( 2 ) Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 02:08:03 MDTNo reproduction or networking permitted without license from IHS -,-,- TIA-455-124-A 8
21、 Fiber lengths in the transition region L h (mixed mode coupling) cannot be described by either (1) or (2) and consequently PMD needs to be stated only by or 1/2. Typical units are ps for , and 1/2, km for L, ps/km for short-length PMD coefficient, and ps/km1/2 for long-length PMD coefficient. The p
22、rinciple of this interferometric method (INTY) is generically based on the measurement of the time broadening of the source field cross-correlation interferogram and then, PMD delay defined as the RMS DGD 1/2 is deduced from this time broadening. This will provide direct measurement of PMD. In the c
23、ase of an autocorrelation-type instrument, the resulting interferogram has a central coherence peak corresponding to the auto-correlation of the optical source. A cross-correlation-type interferometer has no central peak. A more general instrument has both autocorrelation and cross-correlation inter
24、ferograms. This INTY method is based on two different kinds of analysis: The traditional analysis (TINTY) using a set of specific operating conditions for its successful applications and a basic set-up 1-3; and A general analysis (GINTY) using no limiting operating conditions but using a modified se
25、t-up compared to TINTY 4. 2. Normative References Test or inspection requirements may include, but are not limited to, the following references: TIA/EIA-455-A, Standard test procedures for optic fibers, cables, transducers, sensors, connecting and terminating devices, and other fiber optic component
26、s TIA/EIA-455-57 (FOTP-57), Optical fiber end preparation and examination TIA/EIA-455-80 (FOTP-80), Cutoff wavelength of uncabled single-mode fiber by transmitted Power TIA/EIA-455-113 (FOTP-113), Polarization-Mode Dispersion Measurement for Single- Mode Fibers by Fixed Analyzer Copyright Telecommun
27、ications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 02:08:03 MDTNo reproduction or networking permitted without license from IHS -,-,- TIA-455-124-A 9 TIA/EIA-455-122A (FOTP-122A), Polarization-Mode Dispe
28、rsion Measurement for Single- Mode Optical Fibers by Stokes Parameter Evaluation TIA/EIA-455-170 (FOTP-170), Cable Cutoff Wavelength of Single-mode Fiber by Transmitted Power Users of this FOTP are encouraged to specify the most recent edition of the FOTPs referenced above. Caution: Do not make casu
29、ally the decision to require the most recent edition of a referenced FOTP. There have been instances when document revisions have completely changed intent, application, use etc. of a document such that the requirement to use an edition more recent than the one originally reviewed may be totally ina
30、ppropriate. 3. Apparatus Figure 1 shows the schematic diagram of a generic INTY measurement system. Broadband Source PolarizerInterferometer So( ) Ss()() sos( ) FUT J() SOP S( ) Analyzer sa Modulus of Sum Fourier Spectrum S()() So( ) Optical Frequency ()() Envelope E()() Delay ()() auto- correlation
31、 cross-correlation Fringes P( ) )(S s )( s 1 2 1 )(S oa += Broadband Source PolarizerInterferometer So( ) Ss()() sos( ) FUT J() SOP S( ) Analyzer sa Broadband Source Polarizer Broadband Source PolarizerPolarizerInterferometerInterferometer So( ) Ss()() sos( ) FUT J() SOPso s( ) FUT J() SOP S( ) Anal
32、yzer sa Analyzer sasasa Modulus of Sum Fourier Spectrum S()() So( ) Optical Frequency ()() Envelope E()() Delay ()() auto- correlation cross-correlation Fringes P( ) )(S s )( s 1 2 1 )(S oa += Modulus of Sum Fourier Spectrum S()() So( ) Optical Frequency ()() Envelope E()() Delay ()() auto- correlat
33、ion cross-correlation Fringes P( ) Modulus of Sum Fourier Modulus of Sum Fourier Modulus of Sum Fourier Spectrum S()() So( ) Optical Frequency ()() Spectrum S()() So( ) Optical Frequency ()() Envelope E()() Delay ()() auto- correlation cross-correlation Fringes P( ) Envelope E()() Delay ()() auto- c
34、orrelation cross-correlation Envelope E()() Delay ()() auto- correlation cross-correlation Fringes P( )Fringes P( )Fringes P( ) )(S s )( s 1 2 1 )(S oa +=)(S s )( s 1 2 1 )(S oa += Figure 1 Generic Interferometric Method (INTY) Measurement System The parameters used in Figure 1 and throughout the do
35、cument are: Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 02:08:03 MDTNo reproduction or networking permitted without license from IHS -,-,- TIA-455-124-A 10 optical frequency (
36、= c); difference of round-trip delay between the two arms of the interferometer; )(Ss optical spectrum, at fiber under test (FUT) input spectral density of )Es( r , the source spectrum; )(So optical spectrum, at FUT output (analyzer input); )(S optical spectrum, at analyzer output (interferometer in
37、put); )(Es r optical field complex amplitude at FUT input; )(Eo r optical field complex amplitude at FUT output (analyzer input); )(E r optical field complex amplitude at analyzer output (interferometer input); ),(Ed r optical field complex amplitude at interferometer output; 0 s input state of pola
38、rization (SOP) (at FUT input; a unit Stokes vector); )( s output SOP (at FUT output); a s analyzer transmission axis; x() )(s s a , the Stokes parameter giving the projection of )(s on the analyzer transmission axis. It is this parameter, x(), that contains the PMD information; )( J Jones matrix of
39、the FUT such that )(E )( J )(E so = rr ; )(P optical power at the interferometer output, as a function of delay ; )(P -dependent part of )(P (“a.c.“ part), or )(P minus the -independent part (“d.c.“ part); or in other words, the zero-mean oscillating fringes; Copyright Telecommunications Industry As
40、sociation Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 02:08:03 MDTNo reproduction or networking permitted without license from IHS -,-,- TIA-455-124-A 11 E() envelope of the interferogram: amplitude or RMS-value of the oscilla
41、ting fringes; AM-demodulation. The envelope may also be labelled “fringes visibility“; Ex() cross-correlation envelope. As illustrated in Figure 1 above, the analyzer transmission, )(S/ )(S 0 , consists of two parts: a constant part; and an SOP-dependent part. Therefore, the spectrum at the output o
42、f the analyzer, S(), also consists of two parts, and as a consequence, the interferogram, )(P , also consists of these two parts since it is the FT of the spectrum S(). In summary: The constant part gives: autocorrelation FT of spectrum )(S0 at input of analyzer. The SOP-dependent part: cross-correl
43、ation FT of )(S)( s s 0a . where )(s is the unit Stokes vector that represents the SOP at the output of the FUT (output-SOP) and a s is the unit Stokes vector that represents the analyzer axis. Figure 2a and Figure 2b show a schematic diagram of typical TINTY-based measurement systems. These systems
44、 may also be used with GINTY analysis. Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 02:08:03 MDTNo reproduction or networking permitted without license from IHS -,-,- TIA-455-12
45、4-A 12 Controller Fiber Connector or Splice Polarizer Mirror Coupler Moving Mirror Fringe envelope detection Optical source (A) Michelson Interferometer Polarizer Mirror Detection Optical source Fiber Connector or Splice Controller Moving arm /2 Beam Splitter Beam Splitter /2 Mirror Moveable Cube Co
46、rner (B) Mach-Zehnder Interferometer Figure 2 Basic Measurement Systems for the Interferometric Method Typically Using TINTY Analysis Figure 3 shows a schematic diagram of a typically modified GINTY-based measurement system using a polarization diversity detection system with a polarization beam spl
47、itter (PBS) in order to simultaneously and separately obtain both the autocorrelation and Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 02:08:03 MDTNo reproduction or networking permitted without license from IHS -,-,- TIA-455-124-A 13 cross-correlation envelopes. The input/output (I/O)-SOP scramblers may also be used with TINTY-based systems. Broadband Source Polarizer FUT Scramblers Fringes:
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