High-accuracy optical delay measurement based on linear frequency sweeping technology

A high-accuracy and wide-range optical delay measurement method based on linear frequency modulation (LFM) of a microwave source is proposed, which can measure the delay of each channel in a parallel multichannel interference structure. The light wave emitted by the light source is injected into the dual-parallel Mach-Zehnder modulator (DPMZM) as a carrier wave. The LFM microwave signal is loaded into the radio frequency ports of the DPMZM through a 90 degrees hybrid couple, and the bias voltages of the DPMZM are adjusted to make it work in carrier suppression single sideband (CS-SSB) modulation mode. The CS-SSB optical signal output by the modulator enters the test links, including a Mach-Zehnder interference loop composed of the reference arm and the device under test arm. Then, the output optical signal of the interference loop is input into a photodetector, and the intermediate frequency (IF) signals are obtained by the beat frequency. The frequency of the IF signal is obtained through data acquisition and fast Fourier transform calculation. Thus, the delay time is calculated. By increasing or decreasing the LFM signal scanning time, the delay measurement range can be extended, or the measurement accuracy over a short distance can be improved. The feasibility of this method is verified by experiments, and the delay of parallel multichannel measurement is carried out.