Multi-Frequency Electric Field Measurement Method for Optical Under-Sampling System

This paper introduces an under-sampling E-field measurement system involving three femtosecond pulse lasers, which can be used to measure a multi-frequency electric field (E-field) in a wide frequency range. Optical under-sampling technology utilizes femtosecond laser pulses to sample the electrical signals and convert the high-frequency signal down to the first pulse repetition frequency (RPF) intervals for measurement, i.e., tens to hundreds of MHz. However, previous work rarely studied the measurement of multi-frequency signals. Therefore, in this work, we use three RPFs and propose the Remainder Matching (RM) method of three RPFs to eliminate false-alarm-triggered frequencies. Moreover, to solve the challenging problem of grouping the down-conversion components of each measured frequency, we suggest the Eigenvalue Matching of Remainder’s Difference (EMRD) method to obtain the correct group accurately. Hence, this work combines the RM and EMRD methods to improve the system’s measurement accuracy. To evaluate the suggested measurement technique, detailed theoretical analysis and simulation are performed to demonstrate the universality of our method that can effectively guide the design of E-field measuring systems using optical under-sampling technology. The proposed scheme manages an error rate less than 0.1% without any measurement error of the down-converted components when six frequencies exist simultaneously and is less than 5% when the measured frequency deviation is ±25kHz. Finally, the proposed system is challenged on noise perturbations, with the results demonstrating that the suggested combined RM and RDEM scheme attains an appealing performance.