Measurement of direct frequency modulation characteristics of laser diodes by Michelson interferometry

This paper reports a modification of an interferometric technique [ H. Tsuchida , “ A Novel Technique for Measuring the Frequency Deviation of Semiconductor Lasers under Direct Modulation,” Jpn. J. Appl. Phys.22, L19– L21 ( 1983)] for measuring the frequency deviation and phase difference between the AM and FM modulation of semiconductor laser diodes. The frequency deviation can be determined by the fringe visibility of interference patterns provided the phase difference, AM index, and time delay in an unbalanced Michelson interferometer are given. It covers a wide range of modulation frequencies, i.e., 10 Hz to 10 MHz. This method has such advantages that a high speed photodetector is not necessary and the accuracy of the measurement is not reduced by the spectral linewidth of the lasers.