IEC 60793-1-54:2018 pdf download – Optical fibres – Part 1-54: Measurement methods and test procedures – Gamma irradiation.
4.8.3 Class B fibres (single-mode fibres) An optical lens system or fibre pigtail may be employed to excite the test fibre. The power coupled into the test sample shall be stable for the duration of the test. If an optical lens system is used, a method of making the positioning of the fibre less sensitive is to overfill the fibre end spatially and angularly. If a pigtail is used, it may be necessary to use index matching material to eliminate interference effects. A high order mode filter shall be employed to remove high order propagating modes in the wavelength range greater than or equal to the cut-off wavelength of the test fibre. The test condition specified in IEC 60793-1 -44, method C, satisfies this requirement. 4.9 Detector – Signal detection electronics An optical detector that is linear and stable over the range of intensities that are encountered shall be used. A typical system might include a photovoltaic mode photodiode amplified by a current input preamplifier, with synchronous detection by a lock-up amplifier. 4.1 0 Optical power meter A suitable optical power meter shall be used to determine that the power coupled from the optical source into the test sample is equal to 1 ,0 µW or the level specified in the detail specification. 4.1 1 Radiation dosimeter Thermo luminescent LiF or CaF crystal detectors (TLDs) or an ion chamber detector shall be used to measure the total radiation dose received by the specimen fibre. 4.1 2 Temperature-controlled container Unless otherwise specified, the temperature-controlled container shall have the capability of maintaining the specified temperatures to within ± 2 °C. 4.1 3 Test reel The test reel shall not act as a shield or sink for the radiation used in this test. Reels of wood, plastic or similar non-conducting materials would, in principle, act as transparent to the radiation. The additional absorption shall be taken into account for exact measurements. An appropriate dose build-up layer of similar material shall be used.
5.3 Test reel The test sample shall be spooled onto a reel with a drum diameter of more than or equal to 1 0 cm, or that as specified in the detail specification. Allowance shall be made for the unspooling of a measured length of the test sample from each end of the reel to allow for attachment to the optical measurement equipment. An alternative deployment method allows the fibre to be loosely wound in a coil of specified diameter. The minimum bending radius shall be considered. 5.4 Ambient light shielding The test sample shall be shielded from ambient light to prevent external photobleaching. 6 Procedure 6.1 General The radiation tests differ in exposure dose, dose rate, exposure time and temperature. The tests are an environmental background radiation test and an adverse nuclear radiation test. 6.2 Calibration of radiation source Calibration of the radiation source for dose uniformity and level shall be made prior to the test sample being set up in the chamber. Dose and dose rate measurements at four positions shall be made in the area of exposure where the test reel will be placed (four positions are used to get a representative average value). 6.3 Preparation and pre-conditioning The test sample shall be preconditioned in the temperature chamber at (25 ± 5) °C for 1 h prior to testing, or at the test temperature for a preconditioned time as specified in the detail specification. The input end of the short test length shall be placed in the positioning device and aligned in the test set to obtain maximum optical power as measured with a calibrated power meter. The power at the input end of the test sample shall be measured with a calibrated power meter. If necessary, the source power level shall be adjusted so that the power at the input end of the fibre is 1 ,0 µW or as specified in the detail specification. With the radiation source off, the input end of the test sample shall be positioned to obtain maximum optical power at the detector.