Linearizing Optical Frequency Chirp of a Laser Diode for Accurate FMCW Optical Ranging

Optical frequency chirp of an external-cavity laser is linearized by optimizing the modulation waveform for long-range FMCW optical ranging system. The modulation signal of the laser is sampled with the interference signal of the auxiliary interferometer, and the sampled modulation signal is used as a new modulation signal. As a result, the optical frequency is linearly chirped. The linearization is realized at 50kHz modulation frequency and the measurement range of up to 66m optical fiber and up to 10m in free space. The linearity of the optical frequency chirp is evaluated by the ranging resolution and the ranging accuracy of the FMCW optical ranging system, and the ranging resolution is almost the theoretical limit, indicating that the optical frequency of the laser is highly linearly chirped.