Phase noise limited resolution of coherent lidar using widely tunable laser diodes

The spatial resolution of frequency modulated continuous wave (FMCW) LIDAR (light detection and ranging) using widely (> 500 GHz) tunable laser diodes is calculated, considering the effect of the laser phase noise. It is shown that the resolution Δ R at short distances (R ≤ 10 cm) is determined by the spontaneous emission phase noise. In this regime ΔR/R ≃ 10⁻⁴ … 10⁻³, which may be significantly smaller than estimated from the laser linewidth. At larger distances the phase noise caused by the carrier injection into the tuning region(s) usually dominates and the resolution can be deduced from the laser linewidth.