Linearizing optical frequency sweep of a laser diode by injection current modulation with a rectangular-signal-superimposed triangular signal for FMCW reflectometry

We have proposed and demonstrated a method of Linearizing the optical frequ ency sweep of a laser diode by superimposing a rectangular signal on the mo dulating triangular signal for high-resolution FMCW reflectometry. First, w e describe the principle of the proposed method. The waveform of the optica l frequency sweep is simulated by using a simplified model, in which only t he frequency modulation response is taken into account. The optimum amplitu de of the rectangular signal and the linearity of the optical frequency swe ep are discussed. Next, the proposed method is applied to FMCW reflectometr y to confirm the usefulness of the method. The spatial resolution is minimi zed when the amplitude of the rectangular signal normalized to the amplitud e of the triangular signal is between 0.5 and 0.7. It is difficult to linearize the optical frequency sweep perfectly by using the proposed method. However, the method is very effective because the lin earity of the optical frequency sweep can be significantly improved despite the simple configuration. (C) 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(10): 30-36, 1998.