Abstract

An approach to measuring time delay with high speed and high precision is proposed based on using complementary frequency-swept light and frequency-shifted dechirping. The complementary frequency-swept light is generated by up-converting a linear frequency-modulated waveform into the optical domain, which sweeps linearly and fast. The frequency-shifted dechirping operation and a phase-noise-elimination algorithm are utilized to suppress the phase noise of the optical source, which enables high-precision time delay measurement without limitation of the coherence time on the measurement range. In the experiment, the bandwidth of the linear frequency-modulated waveform is set to be 4 GHz. The time delay of a spool of single-mode fiber with a length of 1 km is measured by using two different laser sources with linewidths of 1.9 MHz and 27 kHz. The standard deviations of the measured time delay are 0.42 ps and 0.52 ps, respectively, indicating that the optical phase noise has a negligible impact on the measurement results. Allan deviation is used to calculate the relative measurement errors, which are 1 × 10⁻⁷ and 4 × 10⁻⁹ within a measurement duration of 30 μs and 4.53 ms, respectively. Besides, the time delay change of an optical tunable delay line with a tuning step of 4 ps is clearly distinguished. Hence, this scheme can achieve ultrafast and high-precision time delay measurement within a large range.