An improved calorimetric technique is described for separating the absorption and scattering components of loss in optical fibers. Two long quartz tubes of small diameter are used. The surface of one is blackened to sense the heating effect of both the absorbed and scattered power; the surface of the other is ground to pass the scattered radiation and sense only the absorption loss. Experimental sensitivities are in excellent agreement with theoretical predictions and closely approach the radiation-limited sensitivity of the calorimeter. With minor modifications, losses as low as 0.1 dB/km should be conveniently measurable with 50 mW of laser power.
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