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Theoretical and experimental research on the effect of coupler splitting ratio for fiber loop ring‐down spectroscopy technology

The Fiber Loop Ring‐down Spectroscopy (FLRDS) technique has become popular in recent years. However, as the ring‐down signal is a series of decaying pulses, very few pulses' peak intensities and their time delays could be found and fitted in an exponential equation. This paper analyzes the importance of splitting ratio of the couplers with respect to improving the accuracy of the fitted equation, makes mathematical models of the whole system, simulates the ring‐down signal under different splitting ratio of the couplers and establishes FLRDS experimental system. The experimental results are in good agreement with theory, which indicated that both of the two coupler splitting ratios of 10:90 are found to be the optimal solution with a ring‐down time of 24.5 µs in our system. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:99–103, 2014