Current modulation of a laser diode produces a change in the emission frequency. Hence, modulating the driving current with white noise, we can control the linewidth, that is, the coherence length of the source. Several commercial tunable laser products have a function of tuning the coherence length by this way. While, we have proposed and studied a method to control not only the coherence length but also the shape of the coherence function. We have called this technique as 'the synthesis of the optical coherence function.' In this paper, at first, the principle of the synthesis of the coherence function is explained. Next, as the application of this technique, a high resolution reflectometry, a distributed fiber-optic stress sensor, a multiplexed fiber-optic interferometric sensor, and optical parallel information processing are described.