1、Designation: E 1614 94 (Reapproved 2004)Standard Guide forProcedure for Measuring Ionizing Radiation-InducedAttenuation in Silica-Based Optical Fibers and Cables forUse in Remote Fiber-Optic Spectroscopy andBroadband Systems1This standard is issued under the fixed designation E 1614; the number imme
2、diately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 Thi
3、s guide covers a method for measuring the real time,in situ radiation-induced spectral attenuation of multimode,step index, silica optical fibers transmitting unpolarized light.This procedure specifically addresses steady-state ionizingradiation (that is, alpha, beta, gamma, protons, etc.) withappro
4、priate changes in dosimetry, and shielding considerations,depending upon the irradiation source.1.2 This test procedure is not intended to test the balance ofthe optical and non-optical components of an optical fiber-based system, but may be modified to test other components ina continuous irradiati
5、on environment.1.3 The values stated in SI units are to be regarded asstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and dete
6、rmine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 Test or inspection requirements include the followingreferences:2.2 Military Standard:MIL-STD-2196-(SH) Glossary of Fiber Optic Terms22.3 EIA Standards:EIA-455-57 Optical Fiber End Preparation and Examina-tion
7、3EIA-455-64 Procedure for Measuring Radiation-InducedAttenuation in Optical Fibers and Cables3EIA-455-78A-90 Spectral Attenuation Cutback Measure-ment for Single-Mode Optical Fibers33. Terminology3.1 Definitions:3.1.1 Refer to MIL-STD-2196 for the definition of termsused in this guide.4. Significanc
8、e and Use4.1 Ionizing environments will affect the performance ofoptical fibers/cables being used to transmit spectroscopicinformation from a remote location. Determination of the typeand magnitude of the spectral attenuation or interferences, orboth, produced by the ionizing radiation in the fiber
9、isnecessary for evaluating the performance of an optical fibersensor system.4.2 The results of the test can be utilized as a selectioncriteria for optical fibers used in optical fiber spectroscopicsensor systems.NOTE 1The attenuation of optical fibers generally increases whenexposed to ionizing radi
10、ation. This is due primarily to the trapping ofradiolytic electrons and holes at defect sites in the optical materials, thatis, the formation of color centers. The depopulation of these color centersby thermal and/or optical (photobleaching) processes, or both, causesrecovery, usually resulting in a
11、 decrease in radiation-induced attenuation.Recovery of the attenuation after irradiation depends on many variables,including the temperature of the test sample, the composition of thesample, the spectrum and type of radiation employed, the total doseapplied to the test sample, the light level used t
12、o measure the attenuation,and the operating spectrum. Under some continuous conditions, recoveryis never complete.5. Apparatus5.1 The test schematic is shown in Fig. 1. The following listidentifies the equipment necessary to accomplish this testprocedure.5.2 Light SourceThe light source should be ch
13、osen so thatthe spectral region of interest is provided. Lamps or globars, orboth, may be used for analysis as long as they satisfy thepower, stability, and system requirements defined. In general,the silica fibers should be evaluated from 350 to 2100 nm,1This guide is under the jurisdiction of ASTM
14、 Committee E-13 on MolecularSpectroscopy and is the direct responsibility of Subcommittee E13.09 on FiberOptics in Molecular Spectroscopy.Current edition approved Nov. 1, 2004. Published January 2005. Originallyapproved in 1994. Last previous edition approved in 1999 as E 161494 (1999).2Available fr
15、om Standardization Documents Order Desk, Bldg. 4 Section D, 700Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.3Available from Electronic Industry Association, 1990 M St. N.W., Suite 400,Washington, DC 20036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,
16、 PA 19428-2959, United States.therefore, more than one light source or multiple testing, orboth, may be necessary.5.3 ShutterIn order to determine the background stability,the light will have to be blocked from entering the optical fiberby a shutter.5.4 Focusing/Collection OpticsA number of optical
17、ele-ments may be needed for the launch and collection of lightradiation into/from the test optical fiber and other instrumen-tation (light source, spectrometer, detector). The minimalrequirement for these elements shall be that the numericalaperture of the adjacent components are matched for efficie
18、ntcoupling.5.5 Mode StripperHigh-order cladding modes must beattenuated by mode stripping, and mode stripping should occurprior to and after the radiation chamber, especially if the fiberlength is shorter than that specified in this guide. If it is foundthat the coating material effectively strips t
19、he cladding modesfrom the optical fiber, then a mode stripper is not necessary.5.6 Light Radiation FilteringFilters may be necessary torestrict unwanted regions of the light spectrum. They may beneeded to avoid saturation or nonlinearities of the detector andrecording instrumentation by transient li
20、ght sources (Cerenkovor other luminescence phenomena), or due to wide spectralpower variances with the output of the broadband sources.5.7 Optical SplitterAn optical splitter or fiber optic cou-pler shall divert some portion of the input light to a referencedetector for monitoring the stability of t
21、he light source.5.8 Optical InterconnectionsThe input and output ends ofthe optical fiber shall have a stabilized optical interconnection,such as a clamp, connector, splice, or weld. During anattenuation measurement, the interconnection shall not bechanged or adjusted. If possible, the optical inter
22、connectionsshould not be within the irradiation region.5.9 Wavelength DemultiplexorA means of separating thespectral information must be used at the detector end of thesystem so that multiple wavelengths can be simultaneouslyevaluated (that is, grating, prism, Acousto-optic tunable filter,etc.).5.10
23、 Optical DetectionThe optical detection system shallbe wavelength calibrated in accordance with the manufactur-ers recommended procedure utilizing standard spectral linesources. The calibration and spectral response of the detectionsystems should be documented.5.10.1 Sample DetectorAn optical detect
24、or that is linearand stable over the range of intensities that are encounteredshall be used. The method employed must be able to evaluatea wide spectral range rapidly (that is, 500 ms). The primaryrequirement of the detector is that the spectral detectivitycorresponds to the spectral transmission of
25、 the light source/fiber system and that a spectral resolution of 610 nm isattainable.5.10.2 Reference DetectorThe reference detector is usedfor light source stability measurements for the wavelengthrange of interest. The reference detection system should have asimilar response to the sample detectio
26、n system. If an opticalfiber splitter is used for the reference arm of the detectionscheme, then the detection system must be able to accept theoutput from an optical fiber. If the detection scheme canmonitor the output of two optical fibers (for example, a CCDdetector with an imaging spectrometer),
27、 it may be advanta-geous to package the reference fiber and sample fiber in thesame termination so that a single detection system can simul-taneously monitor both outputs. This configuration is optional.5.11 Recorder SystemA suitable data recording system,such as a computer data acquisition system,
28、is recommendeddue to the large spectral data sets necessary.5.12 Ambient Light ShieldingThe irradiated fiber lengthshall be shielded from ambient light to prevent photobleachingby any external light sources and to avoid baseline shifts in thezero light level. An absorbing fiber coating or jacket can
29、 beNOTE 1If a shuttered source is not used, the test engineer must account for the placement and extraction of the test sample in the irradiator.FIG. 1 Schematic Instrumentation DiagramE 1614 94 (2004)2used as the light shield, provided that it has been demonstratedto block ambient light and that it
30、s influence on the dose withinthe fiber core has been taken into consideration.5.13 Irradiation SystemThe irradiation system shouldhave the following characteristics:5.13.1 Dose RateA Co60or other irradiation source shallbe used to deliver radiation at dose rates ranging from 10 to100 Gy(SiO2)/min (
31、see Note 3).5.13.2 Radiation EnergyThe energy of the gamma raysemitted by the source should be greater than 500 KeV to avoidserious complications with the rapid variations in total dose asa function of depth within the test sample.5.13.3 Radiation DosimeterDosimetry traceable to na-tional standards
32、shall be used. Dose should be measured in thesame uniform geometry as the actual fiber core material toensure that dose-build-up effects are comparable to the fibercore and the dosimeter. The dose should be expressed in graycalculated for the core material.5.14 Temperature-Controlled ContainerUnless
33、 otherwisespecified, the temperature-controlled container shall have thecapability of maintaining the specified temperature to 23 62C. The temperature of the sample/container should bemonitored prior to and during the test.NOTE 2The wavelength range indicated in 5.2 is the largest range thatshould b
34、e tested if the equipment (that is, sources, detectors) is available.Silica glass will transmit from 190 to 3300 nm, but this range is notpractical for optical fiber applications due to the high attenuations in theultraviolet (UV) and near-infrared (NIR). The widest wavelength rangethat can be teste
35、d that satisfies the requirements of the test procedureshould be evaluated if the equipment is available.NOTE 3The average total dose should be expressed in Gray (Gy,where 1 Gy = 100 rads) to a precision of 65 %, traceable to nationalstandards. For typical silica core fibers, dose should be expresse
36、d in Gycalculated for SiO2, that is, Gy(SiO2).6. Hazards6.1 Carefully trained and qualified personnel must be usedto perform this test procedure since radiation (both ionizingand optical), as well as electrical, hazards will be present.7. Test Specimens7.1 Sample Optical FiberThe sample fiber shall
37、be apreviously unirradiated, silica-based, step-index, multimodefiber. The fiber shall be long enough to allow coupling betweenthe optical instrumentation outside the radiation chamber andthe sample area, along with an irradiated test length of 50 6 5m.7.2 The test specimen may be an optical fiber c
38、able assem-bly, as long as the cable contains the above specified fiber foranalysis as in 7.1.7.3 Test ReelThe test reel shall not act as a shield for theradiation used in this test or, alternatively, the dose must bemeasured in a geometry duplicating the effects of reel attenu-ation. The diameter o
39、f the test reel and the winding tension ofthe fiber can influence the observed radiation performance,therefore, the fiber should be loosely wound on a reel diameterexceeding 10 cm.7.4 Fiber End PreparationThe test sample shall be pre-pared such that its end faces are smooth and perpendicular tothe f
40、iber axis, in accordance with EIA-455-57.8. Radiation Calibration and Stability8.1 Calibration of Radiation SourceCalibration of theradiation source for dose uniformity and dose level shall bemade at the location of the device under test (DUT) and at aminimum of four locations, prior to introduction
41、 of fiber testsamples. The variation in dose across the fiber reel volumeshall not exceed 610 %. If thermoluminescent detectors(TLDs) are used for the measurements, four TLDs shall beused to sample dose distribution at each location. The readingsfrom the multiple TLDs at each location shall be avera
42、ged tominimize dose uncertainties. To maintain the highest possibleaccuracy in dose measurements, the TLDs shall not be usedmore than once. TLDs should be used only in the dose regionwhere they maintain a linear response.8.2 The total dose shall be measured with an irradiation timeequal to subsequen
43、t fiber measurements.Alternatively, the doserate may be measured and the total dose calculated from theproduct of the dose rate and irradiation time. Source transittime (from off-to-on and on-to-off positions) shall be less than5 % of the irradiation time.8.3 Stability of Radiation SourceThe dose ra
44、te must beconstant for at least 95 % of the shortest irradiation time ofinterest. The dose variation provided across the fiber sampleshall not exceed 610 %.9. Procedure9.1 Place the reel of fiber or cable in the attenuation testsetup as shown in Fig. 1. Couple the light source into the endof the tes
45、t fiber, and position the light exiting the fiber forcollection by the spectrograph or other appropriate detectionsystem.9.2 Temperature StabilityStabilize the test sample in thetemperature chamber at 23 6 2C prior to proceeding.9.3 System StabilityVerify the stability of the total systemunder illum
46、ination conditions prior to any measurement for atime exceeding that required for determination of Pb(l) and P(t,l ) (see 10.1) during the duration of the attenuation mea-surement.9.4 For stability measurements, the system output need onlybe evaluated in 50-nm increments over the useful range of the
47、detection system. At each wavelength, convert the maximumfluctuation in the observed system output during that time, intoan apparent change in optical attenuation due to system noise,Dan(t, l), using Eq 1. Any subsequent measurement must berejected if the observed DA (t, l) (defined in 10.1) does no
48、texceed 10 3Dan(t, l).9.5 Baseline StabilityAlso verify the baseline stability fora time comparable to the attenuation measurement with thelight source blocked off. Record the baseline output power, Pn,for the same wavelengths monitored for system stability. Anysubsequent measurement must be rejecte
49、d if the transmittedpower out of the irradiated fiber is not greater than 10 3 Pn.9.6 Fig. 2 depicts the values described in 9.3-9.5.9.7 If the initial attenuation spectrum of the fiber is known,either from the fiber manufacturer or from prior testing, thenthe test may proceed, otherwise, determine the initial attenua-tion by the cutback method described in EIA-455-64 orE 1614 94 (2004)3EIA-455-78A-90 with modifications made for multimode fiberand multiple wavelength analysis (see Note 4).9.8 Induced Attenuation MeasurementsPrior to irradia-tion,
