A Calorimetric Technique for the Measurement of Low Optical Absorption Losses in Bulk Glass and Optical Communication Fibres
In the bulk glass measurement, a pair of thin rod samples are rigidly mounted in a massive brass enclosure. As the rod ends are immersed in index matching liquid, no optical polishing is necessary. One sample is illuminated by a laser beam and the temperature rise due to the absorbed energy is measured by a thermocouple. For the fibre measurement, the solid rod is replaced by a fibre led through a silica tube filled with a low index liquid. A laser power of 100mW gives a sensitivity of 1dB/Km limited by thermocouple Johnson noise. Replacing the fibre by a fine resistance wire conducting a known current provides a calibration of the apparatus.
KeywordsSilica Tube Bulk Glass Fibre Absorption Direct Illumination Thermocouple Wire
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