ASTM E1614-94(1999)
(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
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 1999)
Standard Guide for
Procedure for Measuring Ionizing Radiation-Induced
Attenuation in Silica-Based Optical Fibers and Cables for
Use inRemoteFiber-Optic Spectroscopyand
BroadbandSystems
This standard is issued under the fixed designation E 1614; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope EIA-455-78A-90 Spectral Attenuation Cutback Measure-
ment for Single-Mode Optical Fibers
1.1 This guide covers a method for measuring the real time,
in situ radiation-induced spectral attenuation of multimode,
3. Terminology
step index, silica optical fibers transmitting unpolarized light.
3.1 Definitions:
This procedure specifically addresses steady-state ionizing
3.1.1 Refer to MIL-STD-2196 for the definition of terms
radiation (that is, alpha, beta, gamma, protons, etc.) with
used in this guide.
appropriatechangesindosimetry,andshieldingconsiderations,
depending upon the irradiation source.
4. Significance and Use
1.2 This test procedure is not intended to test the balance of
4.1 Ionizing environments will affect the performance of
the optical and non-optical components of an optical fiber-
optical fibers/cables being used to transmit spectroscopic
based system, but may be modified to test other components in
information from a remote location. Determination of the type
a continuous irradiation environment.
and magnitude of the spectral attenuation or interferences, or
1.3 The values stated in SI units are to be regarded as
both, produced by the ionizing radiation in the fiber is
standard.
necessary for evaluating the performance of an optical fiber
1.4 This standard does not purport to address all of the
sensor system.
safety concerns, if any, associated with its use. It is the
4.2 The results of the test can be utilized as a selection
responsibility of the user of this standard to establish appro-
criteria for optical fibers used in optical fiber spectroscopic
priate safety and health practices and determine the applica-
sensor systems.
bility of regulatory limitations prior to use.
NOTE 1—The attenuation of optical fibers generally increases when
2. Referenced Documents
exposed to ionizing radiation. This is due primarily to the trapping of
radiolytic electrons and holes at defect sites in the optical materials, that
2.1 Test or inspection requirements include the following
is, the formation of color centers. The depopulation of these color centers
references:
by thermal and/or optical (photobleaching) processes, or both, causes
2.2 Military Standard:
recovery, usually resulting in a decrease in radiation-induced attenuation.
MIL-STD-2196-(SH) Glossary of Fiber Optic Terms
Recovery of the attenuation after irradiation depends on many variables,
2.3 EIA Standards:
including the temperature of the test sample, the composition of the
EIA-455-57 Optical Fiber End Preparation and Examina-
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
EIA-455-64 Procedure for Measuring Radiation-Induced
is never complete.
Attenuation in Optical Fibers and Cables
5. Apparatus
5.1 The test schematic is shown in Fig. 1.The following list
This guide is under the jurisdiction of ASTM Committee E-13 on Molecular
identifies the equipment necessary to accomplish this test
Spectroscopy and is the direct responsibility of Subcommittee E13.09 on Fiber
procedure.
Optics in Molecular Spectroscopy.
Current edition approved June 15, 1994. Published August 1994.
5.2 Light Source—Thelightsourceshouldbechosensothat
AvailablefromStandardizationDocumentsOrderDesk,Bldg.4SectionD,700
the spectral region of interest is provided. Lamps or globars, or
Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
3 both, may be used for analysis as long as they satisfy the
Available from Electronic Industry Association, 1990 M St. N.W., Suite 400,
Washington, DC 20036. power, stability, and system requirements defined. In general,
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1614
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
the silica fibers should be evaluated from '350 to '2100 nm, system so that multiple wavelengths can be simultaneously
therefore, more than one light source or multiple testing, or evaluated (that is, grating, prism, Acousto-optic tunable filter,
both, may be necessary. etc.).
5.3 Shutter—In order to determine the background stability, 5.10 Optical Detection—The optical detection system shall
the light will have to be blocked from entering the optical fiber be wavelength calibrated in accordance with the manufactur-
by a shutter. er’s recommended procedure utilizing standard spectral line
5.4 Focusing/Collection Optics—A number of optical ele- sources. The calibration and spectral response of the detection
ments may be needed for the launch and collection of light systems should be documented.
radiation into/from the test optical fiber and other instrumen- 5.10.1 Sample Detector—An optical detector that is linear
tation (light source, spectrometer, detector). The minimal and stable over the range of intensities that are encountered
requirement for these elements shall be that the numerical shall be used. The method employed must be able to evaluate
aperture of the adjacent components are matched for efficient a wide spectral range rapidly (that is, 500 ms). The primary
coupling. requirement of the detector is that the spectral detectivity
5.5 Mode Stripper—High-order cladding modes must be corresponds to the spectral transmission of the light source/
attenuated by mode stripping, and mode stripping should occur fiber system and that a spectral resolution of 610 nm is
prior to and after the radiation chamber, especially if the fiber attainable.
length is shorter than that specified in this guide. If it is found 5.10.2 Reference Detector—The reference detector is used
that the coating material effectively strips the cladding modes for light source stability measurements for the wavelength
from the optical fiber, then a mode stripper is not necessary. range of interest.The reference detection system should have a
5.6 Light Radiation Filtering—Filters may be necessary to similar response to the sample detection system. If an optical
restrict unwanted regions of the light spectrum. They may be fiber splitter is used for the reference arm of the detection
needed to avoid saturation or nonlinearities of the detector and scheme, then the detection system must be able to accept the
recording instrumentation by transient light sources (Cerenkov output from an optical fiber. If the detection scheme can
or other luminescence phenomena), or due to wide spectral monitor the output of two optical fibers (for example, a CCD
power variances with the output of the broadband sources. detector with an imaging spectrometer), it may be advanta-
5.7 Optical Splitter—An optical splitter or fiber optic cou- geous to package the reference fiber and sample fiber in the
pler shall divert some portion of the input light to a reference same termination so that a single detection system can simul-
detector for monitoring the stability of the light source. taneously monitor both outputs. This configuration is optional.
5.8 Optical Interconnections—The input and output ends of 5.11 Recorder System—A suitable data recording system,
the optical fiber shall have a stabilized optical interconnection, such as a computer data acquisition system, is recommended
such as a clamp, connector, splice, or weld. During an due to the large spectral data sets necessary.
attenuation measurement, the interconnection shall not be 5.12 Ambient Light Shielding—The irradiated fiber length
changed or adjusted. If possible, the optical interconnections shall be shielded from ambient light to prevent photobleaching
should not be within the irradiation region. by any external light sources and to avoid baseline shifts in the
5.9 Wavelength Demultiplexor—A means of separating the zero light level. An absorbing fiber coating or jacket can be
spectral information must be used at the detector end of the used as the light shield, provided that it has been demonstrated
E1614
to block ambient light and that its influence on the dose within 8. Radiation Calibration and Stability
the fiber core has been taken into consideration.
8.1 Calibration of Radiation Source—Calibration of the
5.13 Irradiation System—The irradiation system should
radiation source for dose uniformity and dose level shall be
have the following characteristics:
made at the location of the device under test (DUT) and at a
5.13.1 Dose Rate—A Co or other irradiation source shall
minimum of four locations, prior to introduction of fiber test
be used to deliver radiation at dose rates ranging from 10 to
samples. The variation in dose across the fiber reel volume
100 Gy(SiO )/min (see Note 3).
shall not exceed 610 %. If thermoluminescent detectors
5.13.2 Radiation Energy—The energy of the gamma rays
(TLDs) are used for the measurements, four TLDs shall be
emitted by the source should be greater than 500 KeV to avoid
used to sample dose distribution at each location. The readings
serious complications with the rapid variations in total dose as
from the multiple TLDs at each location shall be averaged to
a function of depth within the test sample.
minimize dose uncertainties. To maintain the highest possible
5.13.3 Radiation Dosimeter—Dosimetry traceable to na-
accuracy in dose measurements, the TLDs shall not be used
tional standards shall be used. Dose should be measured in the
more than once. TLDs should be used only in the dose region
same uniform geometry as the actual fiber core material to
where they maintain a linear response.
ensure that dose-build-up effects are comparable to the fiber
8.2 Thetotaldoseshallbemeasuredwithanirradiationtime
core and the dosimeter. The dose should be expressed in gray
equaltosubsequentfibermeasurements.Alternatively,thedose
calculated for the core material.
rate may be measured and the total dose calculated from the
5.14 Temperature-Controlled Container—Unless otherwise
product of the dose rate and irradiation time. Source transit
specified, the temperature-controlled container shall have the
time (from off-to-on and on-to-off positions) shall be less than
capability of maintaining the specified temperature to 23 6
5 % of the irradiation time.
2°C. The temperature of the sample/container should be
8.3 Stability of Radiation Source—The dose rate must be
monitored prior to and during the test.
constant for at least 95 % of the shortest irradiation time of
NOTE 2—Thewavelengthrangeindicatedin5.2isthelargestrangethat
interest. The dose variation provided across the fiber sample
should be tested if the equipment (that is, sources, detectors) is available.
shall not exceed 610 %.
Silica glass will transmit from '190 to '3300 nm, but this range is not
practical for optical fiber applications due to the high attenuations in the
9. Procedure
ultraviolet (UV) and near-infrared (NIR). The widest wavelength range
that can be tested that satisfies the requirements of the test procedure
9.1 Place the reel of fiber or cable in the attenuation test
should be evaluated if the equipment is available.
setup as shown in Fig. 1. Couple the light source into the end
NOTE 3—The average total dose should be expressed in Gray (Gy,
of the test fiber, and position the light exiting the fiber for
where 1 Gy 5 100 rads) to a precision of 65 %, traceable to national
collection by the spectrograph or other appropriate detection
standards. For typical silica core fibers, dose should be expressed in Gy
system.
calculated for SiO , that is, Gy(SiO ).
2 2
9.2 Temperature Stability—Stabilize the test sample in the
6. Hazards temperature chamber at 23 6 2°C prior to proceeding.
9.3 System Stability—Verify the stability of the total system
6.1 Carefully trained and qualified personnel must be used
under illumination conditions prior to any measurement for a
to perform this test procedure since radiation (both ionizing
time exceeding that required for determination of P (l) and P
and optical), as well as electrical, hazards will be present. b
(t,l ) (see 10.1) during the duration of the attenuation mea-
surement.
7. Test Specimens
9.4 For stability measurements, the system output need only
7.1 Sample Optical Fiber—The sample fiber shall be a
be evaluated in 50-nm increments over the useful range of the
previously unirradiated, silica-based, step-index, multimode
detection system. At each wavelength, convert the maximum
fiber.The fiber shall be long enough to allow coupling between
fluctuation in the observed system output during that time, into
the optical instrumentation outside the radiation chamber and
an apparent change in optical attenuation due to system noise,
the sample area, along with an irradiated test length of 50 6 5
Da (t, l), using Eq 1. Any subsequent measurement must be
n
m.
rejected if the observed DA (t, l) (defined in 10.1) does not
7.2 The test specimen may be an optical fiber cable assem-
exceed 103Da (t, l).
n
bly, as long as the cable contains the above specified fiber for
9.5 Baseline Stability—Also verify the baseline stability for
analysis as in 7.1.
a time comparable to the attenuation measurement with the
7.3 Test Reel—The test reel shall not act as a shield for the
light source blocked off. Record the baseline output power, P ,
radiation used in this test or, alternatively, the dose must be n
for the same wavelengths monitored for system stability. Any
measured in a geometry duplicating the effects of reel attenu-
subsequent measurement must be rejected if the transmitted
ation. The diameter of the test reel and the winding tension of
power out of the irradiated fiber is not greater than 10 3 P .
n
the fiber can influence the observed radiation performance,
9.6 Fig. 2 depicts the values described in 9.3-9.5.
therefore, the fiber should be loosely wound on a reel diameter
exceeding 10 cm.
9.7 If the initial attenuation spectrum of the fiber is known,
7.4 Fiber End Preparation—The test sample shall be pre- either from the fiber manufacturer or from prior testing, then
pared such that its end faces are smooth and perpen
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