High-resolution measurement of the free spectral range of an etalon

High-resolution measurement of the free spectral range (FSR) for an etalon is becoming more important as greater amounts of information are multiplexed through a single fiber. A method to test the FSR of etalons or etalon based optical components used at telecommunication frequencies is discussed. Slope at a specific point of the etalon response curve is utilized as a means measurement of FSR. The theory that describes how slope, varying as a function of differing etalon signal peaks, can be utilized for the measurement of FSR is developed. This technique has been shown to measure FSR with a resolution of approximately one part in 2000.