1、 TIA DOCUMENT FOTP-38 Measurement of Fiber Strain in Cables Under Tensile Load TIA-455-38 NOVEMBER 1995 TELECOMMUNICATIONS INDUSTRY ASSOCIATION The Telecommunications Industry Association represents the communications sector of NOTICE TIA Engineering Standards and Publications are designed to serve
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20、pyrighted by the TIA and may not be reproduced without prior permission of the Telecommunications Industry Association. For information consult our website at http:/www.tiaonline.org/about/faqDetail.cfm?id=18 Organizations may obtain permission to reproduce a limited number of copies through enterin
21、g into a license agreement. For information, contact: Global Engineering Documents 15 Inverness Way East Englewood, CO 80112-5704 U.S.A. or call U.S.A. and Canada 1-800-854-7179, International (303) 397-7956 EIA TIA-455-38 95 3234600 0567687 704 TIAEIA-455-38 FOTP-38 MEASUREMENT OF FIBER STRAIN IN C
22、ABLES UNDER TENSILE LOAD (From TIA Standards Proposal No. 3044, formulated under the cognizance of the TIA FO-6.7, Subcommittee on Fiber Optic Cables.) This FOTP is part of the series of test procedures included within Recommended Standard TIA-455. 1. 2. INTRODUCTION 1.1 1.2 Intent. The intent of th
23、is document is to provide an accurate method for measuring changes in the average longitudinal strain on a cabled optical fiber. It is not the purpose of this document to outline a method to statically measure absolute strain, but instead to actively measure changes in strain from one loading condit
24、ion to another. Background. The expected reliability of optical fiber (lifetime or failure rate) may be reduced by exposure to strain that may accompany deployment in cable structures. The fiber strain can be measured during cable tensile tests by a number of methods. One common method is the phase
25、shift technique and another is the time of flight technique. The basic principle of both measurement techniques is the determination of the change in fiber strain from a change in fiber length. The refractive index of glass changes with induced strain, which can impact the accuracy of optical fiber
26、length measurements. Therefore, a correction factor must be determined and utilized within this procedure. NOTE: This measurement procedure is typically performed in conjunction with the performance of FOTP-33, but such a relationship is not mandatory. APPLICABLE DOCUMENTS Test or inspection require
27、ments may include, but are not limited to, the following references: EIA-4920000-A Generic Specijcation for Optical Waveguide Fibers EIA TIA-455-38 95 m 3234600 0567690 426 W TIAEIA-455-38 EIAnIA-455-A FOTP-33 (EIA-455-33A) FOTP-60 (EIA-455-60) FOTP- 168 (EIA-455- 168A) FOTP- I 69 (EIA-455- I 69A) S
28、tandard Test Procedures jor Fiber Optic Fibers, Cables, Transctitcers, SeIisors, Connecting cind Terminating Devices, and other Fiber Optic Cornportents Fiber Optic Cable Tensile Loading and Bending Test Mensurement qf Fiber or Cable Length Using an OTDR Chi-onzatic Dispersion Measurement of Midtiin
29、ode Graded- index nrrd Single-Mode Optical Fibers bv Spectral Group Delay Measitrement in the Time Domain Chroinatic Dispersion Measurement of Single -Mode Optical Fibers by the Phase-Shift Method 3. APPARATUS 3.1 Test Fixture The test fixture of known gauge length shall be capable of applying and v
30、arying longitudinal stresses on the cable or fiber. Proper fixing of the ends of the specimen shall be observed in order to simulate a long, continuous cable sample or to prevent the fibers from slipping during loading. One example is the fixture suggested in FOTP-33 where the cable ends are wrapped
31、 and held around fixed mandrels (see Figure i). NOTES: I II III A test fixture other than the one described in FOTP-33 may be used if the accuracy and resolution have been demonstrated to be comparable to that stated in 3.3. A calibration test bench per 3.3.2 may be necessary. See also 5.1. Importan
32、t features of any test bench used include proper methods for (a) fixing and preventing fiber slippage at the test sample ends and (b) ensuring long enough test samples to reduce any end-effect errors. IV. Ensure that the diameters of all mandrels are equal and are greater than 30 times the cables ou
33、tside diameter. Verify that the mandrel diameters are also sufficiently large to prevent introduction of excessive bending strain to the cabled fiber. EIA TIA-455-38 75 3234600 0567671 362 TI AEIA-455-38 Figure 1. Cable Tensile and Bend Test Fixture. 3.2 Optical Test Equipment To measure fiber strai
34、n, use either Method A (equipment per 3.2.2) or Method B (equipment per 3.2.3), as preferred. The same test equipment will be used for both the stress optic correction factor determination and the actual test measurement. 3.2. I METHOD A. PHASE SHF TECHNIQUE. The phase shift technique may involve th
35、e use of a phase measurement system similar to the one used in FOTP-169. Unless otherwise specified in the Detail Specification, the test Set-up shall consist of the following minimal list of components. 3.2. I. I Light Source. Either a laser diode or a filtered light emitting diode may be used. The
36、 center wavelength and modulated output phase shall be stable over the measurement time period at the bias current, modulation frequency and diode temperature range encountered. Typically, a temperature-controlled, single longitudinal-mode laser diode with output power stabilization (e.g., PIN feedb
37、ack) or, a filtered edge-emitting LED, is sufficient. The central wavelength shall lie within 20 nm of the specified value, unless otherwise specified in the Detail Specification. The central wavelength(s) shall be 3 EIA TIA-455-38 95 3234600 0567692 2T9 TIAEIA-455-38 periodically verified using a s
38、uitable measuring instrument, such as an optical spectnim analyzer. The spectral width for the light source shall not exceed 30 nm at full width at half maximum. 3.2. I .2 Modulator The modulator shall amplitude-modulate the light sources to produce a waveform with a single dominant Fourier componen
39、t. For example, a sinusoidal, trapezoidal or square wave modulation shall be acceptable. The frequency stability shall be sufficient to achieve the resolution as stated in 3.3. It is essential to prevent ambiguities of 360n degrees, where tt is an integer, in measuring phase shift. This can be accom
40、plished by means such as tracking 360“ phase changes or by choosing a modulator frequency sufficiently low to limit the relative phase shifts to less than 360 degrees. However, the frequency of the modulator should be sufficiently high to ensure adequate measurement precision, as specified in sectio
41、n 3.3. The phase of the modulation at the light source may be adjustable to facilitate test set calibration, but should be stable for the duration of the test. 3.2. I .3 Launch Optics The output from the signal source(s) shall be coupled to the test fiber(s) or the stress optic correction factor det
42、ermination fiber such that the physical path length for each source is held constant during the test. Suitable devices may include multichannel single-mode optical switches or demountable optical connectors. When this test method is used for Class Ia and Ib multimode fiber, only the lowest order rno
43、de(s) should be transmitted and received. To ensure this, only single-mode launch and detector pigtails shall be used for testing multimode fibers. 3.2. I .4 Signal Detector and Signal Detection Electronics An optical detector that is sensitive and linear in response over the range of wavelengths to
44、 be measured shall be used in conjunction with a phase meter. An amplifier may be used to increase the detection system 4 EIA TIA-455-38 95 3234600 0567693 135 TIAEIA-455-38 sensitivity. A typical system might include a PIN photodiode, FET amplifier and a vector voltmeter. The detector-amplifier-pha
45、se meter system shall respond only to the fundamental Fourier component of the modulating signal and shall introduce a signal phase shift that is constant over the range of received optical powers encountered. The received power range may be controlled by a variable optical attenuator. 3.2.1.5 Refer
46、ence Signal A reference signal with the same dominant Fourier component as the modulating signal shall be provided to the phase meter against which to measure the phases of the signal sources. The reference signal should be phase-locked to the modulating signal and is typically derived from the modu
47、lating signal. Examples of Reference Signal Configurations a). Where the signal sources and detector are co-located, such as in a laboratory test, or during calibration, an electrical connection can be used between the signal generator and the reference port of the phase meter. b). An optical splitt
48、er, inserted before the test sample, and a detector may be used. 3.2.1.6 Computation Equipment A digital computer may be used for purposes of equipment control, data acquisition, and numerical evaluation of the data. 3.2.2 METHOD B. TIME-OF-FLIGHT TECHNIQUE. The time-of-flight technique may involve
49、the use of an OTDR, a fresnel reflection based OTDR, or other suitable pulse delay measurement system. FOTP-60 and FOTP-168 describe two possible systems. In the case of measurement systems that report length instead of a delay value, the effective group index, N, for the fiber under test must be properly set within the test equipment. Unless otherwise specified in the Detail Specification, the test Set-up shall consist of the following minimal list of components: 5 EIA TIA-455-38 95 W 3234600 0567694 071 TI APEIA-455 -3 8 3.2.2.1 Optical Transmitter This usual
