ASTM E1614-94(2004)
(Guide)Standard Guide for Procedure for Measuring Ionizing Radiation-Induced Attenuation in Silica-Based Optical Fibers and Cables for Use in Remote Fiber-Optic Spectroscopy and Broadband Systems
Standard Guide for Procedure for Measuring Ionizing Radiation-Induced Attenuation in Silica-Based Optical Fibers and Cables for Use in Remote Fiber-Optic Spectroscopy and Broadband Systems
SIGNIFICANCE AND USE
Ionizing environments will affect the performance of optical fibers/cables being used to transmit spectroscopic information from a remote location. Determination of the type and magnitude of the spectral attenuation or interferences, or both, produced by the ionizing radiation in the fiber is necessary for evaluating the performance of an optical fiber sensor system.
The results of the test can be utilized as a selection criteria for optical fibers used in optical fiber spectroscopic sensor systems.
Note 1—The attenuation of optical fibers generally increases when exposed to ionizing radiation. This is due primarily to the trapping of radiolytic electrons and holes at defect sites in the optical materials, that is, the formation of color centers. The depopulation of these color centers by thermal and/or optical (photobleaching) processes, or both, causes recovery, usually resulting in a 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 the sample, the spectrum and type of radiation employed, the total dose applied to the test sample, the light level used to measure the attenuation, and the operating spectrum. Under some continuous conditions, recovery is never complete.
SCOPE
1.1 This 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 ionizing radiation (that is, alpha, beta, gamma, protons, etc.) with appropriate changes in dosimetry, and shielding considerations, depending upon the irradiation source.
1.2 This test procedure is not intended to test the balance of the optical and non-optical components of an optical fiber-based system, but may be modified to test other components in a continuous irradiation environment.
1.3 The values stated in SI units are to be regarded as standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E1614 − 94(Reapproved 2004)
Standard Guide for
Procedure for Measuring Ionizing Radiation-Induced
Attenuation in Silica-Based Optical Fibers and Cables for
Use in Remote Fiber-Optic Spectroscopy and
Broadband Systems
This standard is issued under the fixed designation E1614; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope EIA-455-64ProcedureforMeasuringRadiation-InducedAt-
tenuation in Optical Fibers and Cables
1.1 This guide covers a method for measuring the real time,
EIA-455-78A-90Spectral Attenuation Cutback Measure-
in situ radiation-induced spectral attenuation of multimode,
ment for Single-Mode Optical Fibers
step index, silica optical fibers transmitting unpolarized light.
This procedure specifically addresses steady-state ionizing
3. Terminology
radiation (that is, alpha, beta, gamma, protons, etc.) with
appropriatechangesindosimetry,andshieldingconsiderations, 3.1 Definitions:
depending upon the irradiation source. 3.1.1 Refer to MIL-STD-2196 for the definition of terms
used in this guide.
1.2 This test procedure is not intended to test the balance of
the optical and non-optical components of an optical fiber-
4. Significance and Use
basedsystem,butmaybemodifiedtotestothercomponentsin
a continuous irradiation environment. 4.1 Ionizing environments will affect the performance of
optical fibers/cables being used to transmit spectroscopic
1.3 The values stated in SI units are to be regarded as
information from a remote location. Determination of the type
standard.
and magnitude of the spectral attenuation or interferences, or
1.4 This standard does not purport to address all of the
both, produced by the ionizing radiation in the fiber is
safety concerns, if any, associated with its use. It is the
necessary for evaluating the performance of an optical fiber
responsibility of the user of this standard to establish appro-
sensor system.
priate safety and health practices and determine the applica-
4.2 The results of the test can be utilized as a selection
bility of regulatory limitations prior to use.
criteria for optical fibers used in optical fiber spectroscopic
sensor systems.
2. Referenced Documents
2.1 Test or inspection requirements include the following NOTE 1—The attenuation of optical fibers generally increases when
exposed to ionizing radiation. This is due primarily to the trapping of
references:
radiolytic electrons and holes at defect sites in the optical materials, that
is, the formation of color centers. The depopulation of these color centers
2.2 Military Standard:
by thermal and/or optical (photobleaching) processes, or both, causes
MIL-STD-2196-(SH)Glossary of Fiber Optic Terms
recovery, usually resulting in a decrease in radiation-induced attenuation.
2.3 EIA Standards:
Recovery of the attenuation after irradiation depends on many variables,
EIA-455-57Optical Fiber End Preparation and Examina- including the temperature of the test sample, the composition of the
sample, the spectrum and type of radiation employed, the total dose
tion
applied to the test sample, the light level used to measure the attenuation,
and the operating spectrum. Under some continuous conditions, recovery
is never complete.
This guide is under the jurisdiction of ASTM Committee E-13 on Molecular
Spectroscopy and is the direct responsibility of Subcommittee E13.09 on Fiber
5. Apparatus
Optics in Molecular Spectroscopy.
Current edition approved Nov. 1, 2004. Published January 2005. Originally
5.1 ThetestschematicisshowninFig.1.Thefollowinglist
approved in 1994. Last previous edition approved in 1999 as E1614–94 (1999).
identifies the equipment necessary to accomplish this test
DOI: 10.1520/E1614-94R04.
AvailablefromStandardizationDocumentsOrderDesk,Bldg.4SectionD,700 procedure.
Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
5.2 Light Source—Thelightsourceshouldbechosensothat
Available from Electronic Industry Association, 1990 M St. N.W., Suite 400,
Washington, DC 20036. thespectralregionofinterestisprovided.Lampsorglobars,or
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1614 − 94 (2004)
NOTE 1—If 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 Diagram
both, may be used for analysis as long as they satisfy the changed or adjusted. If possible, the optical interconnections
power, stability, and system requirements defined. In general, should not be within the irradiation region.
the silica fibers should be evaluated from ≈350 to ≈2100 nm,
5.9 Wavelength Demultiplexor—A means of separating the
therefore, more than one light source or multiple testing, or
spectral information must be used at the detector end of the
both, may be necessary.
system so that multiple wavelengths can be simultaneously
5.3 Shutter—In order to determine the background stability, evaluated (that is, grating, prism, Acousto-optic tunable filter,
thelightwillhavetobeblockedfromenteringtheopticalfiber etc.).
by a shutter.
5.10 Optical Detection—The optical detection system shall
5.4 Focusing/Collection Optics—A number of optical ele- be wavelength calibrated in accordance with the manufactur-
ments may be needed for the launch and collection of light er’s recommended procedure utilizing standard spectral line
radiation into/from the test optical fiber and other instrumen- sources. The calibration and spectral response of the detection
tation (light source, spectrometer, detector). The minimal systems should be documented.
requirement for these elements shall be that the numerical 5.10.1 Sample Detector—An optical detector that is linear
aperture of the adjacent components are matched for efficient and stable over the range of intensities that are encountered
coupling. shall be used. The method employed must be able to evaluate
a wide spectral range rapidly (that is, 500 ms). The primary
5.5 Mode Stripper—High-order cladding modes must be
requirement of the detector is that the spectral detectivity
attenuatedbymodestripping,andmodestrippingshouldoccur
corresponds to the spectral transmission of the light source/
prior to and after the radiation chamber, especially if the fiber
fiber system and that a spectral resolution of 610 nm is
length is shorter than that specified in this guide. If it is found
attainable.
that the coating material effectively strips the cladding modes
5.10.2 Reference Detector—The reference detector is used
from the optical fiber, then a mode stripper is not necessary.
for light source stability measurements for the wavelength
5.6 Light Radiation Filtering—Filters may be necessary to
rangeofinterest.Thereferencedetectionsystemshouldhavea
restrict unwanted regions of the light spectrum. They may be
similar response to the sample detection system. If an optical
needed to avoid saturation or nonlinearities of the detector and
fiber splitter is used for the reference arm of the detection
recording instrumentation by transient light sources (Cerenkov
scheme, then the detection system must be able to accept the
or other luminescence phenomena), or due to wide spectral
output from an optical fiber. If the detection scheme can
power variances with the output of the broadband sources.
monitor the output of two optical fibers (for example, a CCD
5.7 Optical Splitter—An optical splitter or fiber optic cou- detector with an imaging spectrometer), it may be advanta-
pler shall divert some portion of the input light to a reference geous to package the reference fiber and sample fiber in the
detector for monitoring the stability of the light source. same termination so that a single detection system can simul-
taneously monitor both outputs. This configuration is optional.
5.8 Optical Interconnections—The input and output ends of
the optical fiber shall have a stabilized optical interconnection, 5.11 Recorder System—A suitable data recording system,
such as a clamp, connector, splice, or weld. During an such as a computer data acquisition system, is recommended
attenuation measurement, the interconnection shall not be due to the large spectral data sets necessary.
E1614 − 94 (2004)
5.12 Ambient Light Shielding—The irradiated fiber length the fiber can influence the observed radiation performance,
shall be shielded from ambient light to prevent photobleaching therefore, the fiber should be loosely wound on a reel diameter
byanyexternallightsourcesandtoavoidbaselineshiftsinthe exceeding 10 cm.
zero light level. An absorbing fiber coating or jacket can be
7.4 Fiber End Preparation—The test sample shall be pre-
used as the light shield, provided that it has been demonstrated
pared such that its end faces are smooth and perpendicular to
to block ambient light and that its influence on the dose within
the fiber axis, in accordance with EIA-455-57.
the fiber core has been taken into consideration.
8. Radiation Calibration and Stability
5.13 Irradiation System—The irradiation system should
have the following characteristics:
8.1 Calibration of Radiation Source—Calibration of the
5.13.1 Dose Rate—ACo or other irradiation source shall
radiation source for dose uniformity and dose level shall be
be used to deliver radiation at dose rates ranging from 10 to
made at the location of the device under test (DUT) and at a
100 Gy(SiO )/min (see Note 3).
2 minimum of four locations, prior to introduction of fiber test
5.13.2 Radiation Energy—The energy of the gamma rays
samples. The variation in dose across the fiber reel volume
emitted by the source should be greater than 500 KeVto avoid
shall not exceed 610%. If thermoluminescent detectors
serious complications with the rapid variations in total dose as
(TLDs) are used for the measurements, four TLDs shall be
a function of depth within the test sample.
used to sample dose distribution at each location.The readings
5.13.3 Radiation Dosimeter—Dosimetry traceable to na-
from the multiple TLDs at each location shall be averaged to
tional standards shall be used. Dose should be measured in the
minimize dose uncertainties. To maintain the highest possible
same uniform geometry as the actual fiber core material to
accuracy in dose measurements, the TLDs shall not be used
ensure that dose-build-up effects are comparable to the fiber
more than once. TLDs should be used only in the dose region
core and the dosimeter. The dose should be expressed in gray
where they maintain a linear response.
calculated for the core material.
8.2 Thetotaldoseshallbemeasuredwithanirradiationtime
5.14 Temperature-Controlled Container—Unless otherwise
equaltosubsequentfibermeasurements.Alternatively,thedose
specified, the temperature-controlled container shall have the
rate may be measured and the total dose calculated from the
capability of maintaining the specified temperature to 23 6
product of the dose rate and irradiation time. Source transit
2°C. The temperature of the sample/container should be
time (from off-to-on and on-to-off positions) shall be less than
monitored prior to and during the test.
5% of the irradiation time.
NOTE2—Thewavelengthrangeindicatedin5.2isthelargestrangethat
8.3 Stability of Radiation Source—The dose rate must be
should be tested if the equipment (that is, sources, detectors) is available.
constant for at least 95% of the shortest irradiation time of
Silica glass will transmit from ≈190 to ≈3300 nm, but this range is not
interest. The dose variation provided across the fiber sample
practical for optical fiber applications due to the high attenuations in the
shall not exceed 610%.
ultraviolet (UV) and near-infrared (NIR). The widest wavelength range
that can be tested that satisfies the requirements of the test procedure
should be evaluated if the equipment is available. 9. Procedure
NOTE 3—The average total dose should be expressed in Gray (Gy,
9.1 Place the reel of fiber or cable in the attenuation test
where 1 Gy=100 rads) to a precision of 65%, traceable to national
setup as shown in Fig. 1. Couple the light source into the end
standards. For typical silica core fibers, dose should be expressed in Gy
calculated for SiO , that is, Gy(SiO ).
of the test fiber, and position the light exiting the fiber for
2 2
collection by the spectrograph or other appropriate detection
6. Hazards
system.
6.1 Carefully trained and qualified personnel must be used
9.2 Temperature Stability—Stabilize the test sample in the
to perform this test procedure since radiation (both ionizing temperature chamber at 23 6 2°C prior to proceeding.
and optical), as well as electrical, hazards will be present.
9.3 System Stability—Verify the stability of the total system
under illumination conditions prior to any measurement for a
7. Test Specimens
time exceeding that required for determination of P (λ) and
b
7.1 Sample Optical Fiber—The sample fiber shall be a P(t,λ ) (see 10.1) during the duration of the attenuation
previously unirradiated, silica-based, step-index, multimode measurement.
fiber.Thefibershallbelongenoughtoallowcouplingbetween
9.4 Forstabilitymeasurements,thesystemoutputneedonly
the optical instrumentation outside the radiation chamber and
be evaluated in 50-nm increments over the useful range of the
the sample area, along with an irradiated test length of 50 6 5
detection system. At each wavelength, convert the maximum
m.
fluctuationintheobservedsystemoutputduringthattime,into
7.2 The test specimen may be an optical fiber cable an apparent change in optical attenuation due to system noise,
assembly, as long as the cable contains the above specified ∆α (t, λ), using Eq 1. Any subsequent measurement must be
n
fiber for analysis as in 7.1. rejected if the observed ∆A(t, λ) (defined in 10.1) does not
exceed 10×∆α (t, λ).
n
7.3 Test Reel—The test reel shall not act as a shield for the
radiation used in this test or, alternatively, the dose must be 9.5 Baseline Stability—Also verify the baseline stability for
measured in a geometry duplicating the effects of reel attenu- a time comparable to the attenuation measurement with the
ation. The diameter of the test reel and the winding tension of light source blocked off. Record the baseline output power, P ,
n
E1614 − 94 (2004)
for the same wavelengths monitored for system stability. Any measurement time should be reduced. For this reason, it is
subsequent measurement must be rejected if the transmitted important to have the
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