Patent ID: 7800763

Claim:
A method for measuring the free spectral range of an etalon comprising the step of: generating a laser light from a laser source; generating a RF source signal; RF modulating the laser light with the RF source signal to produce an RF modulated laser signal; coupling the RF modulated laser signal through a circulator to the etalon; coupling a reflected RF signal from the etalon through the circulator to a detector; converting the reflected RF signal to an electrical signal at the photo detector; amplifying the electrical signal; mixing the amplified electrical signal with a RF delayed source signal; linearly scanning a frequency of the RF source signal; and monitoring a peak-to-peak mixer voltage V mixer during the linear scanning of the RF source signal frequency to detect a peak-to-peak minimum voltage when the RF modulation frequency is tuned approximately to a free spectral range of the etalon, the result having a precision greater than one part per 10 4 without the use of a high resolution optical spectrum analyzer or a tunable laser.