Xiaoen Chen, Long Wang, Jingbo Li, Jianping Chen, Guiling Wu
Opt Express. 2024 Apr 8;32(8):13864-13872. doi: 10.1364/OE.515039.
We proposed an ultra-broadband multi-tone frequency measurement (FM) approach based on frequency modulated continuous wave (FMCW). This work aims to achieve wide-range multi-tone FM without image interference, using electrical components with narrow bandwidth and low sampling rate, while maintaining high FM accuracy. The FM range is largely increased by extending the bandwidth of the optical FMCW through a recirculating frequency shift (RFS) loop, from 0.001 GHz-16 GHz to 0.001 GHz-437.5 GHz. The bandwidth-extended optical FMCW coherently beats with a continuous wave (CW) light modulated by the signal under test (SUT) at the balanced photodetector (BPD). The following low-pass filter (LPF) outputs pulses at the time when the frequencies of FMCW and SUT are equal, constructing frequency-to-time mapping (FTTM). Owing to the zero-intermediate-frequency (zero-IF) architecture, image interference is avoided. In addition, the up- and down-chirps of FMCW are used to achieve self-reference, avoiding the utilizing of reference signals, which realizes high FM accuracy. In the experiment, a FM within 0.1 GHz-43.5 GHz is demonstrated using an available microwave generator (MG) with a maximum output frequency of 43.5 GHz. The FM errors are kept within ±10 MHz for all frequencies with a mean and standard deviation of -0.3 MHz and 3.17 MHz, respectively. The multi-tone resolution is about 60 MHz at the FMCW chirp rate of 3.1998 / , which is consistent with the theoretical result. According to the theoretical derivation, the multi-tone resolution can be improved to 1 MHz by lowering the FMCW chirp rate.
我们提出了一种基于调频连续波（FMCW）的超宽带多音频率测量（FM）方法。这项工作旨在使用窄带宽和低采样率的电子元件，在不产生镜像干扰的情况下实现宽范围多音FM，同时保持高FM精度。通过循环频移（RFS）环路扩展光学FMCW的带宽，FM范围从0.001 GHz - 16 GHz大幅增加到0.001 GHz - 437.5 GHz。带宽扩展后的光学FMCW在平衡光电探测器（BPD）处与由被测信号（SUT）调制的连续波（CW）光相干拍频。随后的低通滤波器（LPF）在FMCW和SUT频率相等时输出脉冲，构建频率到时间映射（FTTM）。由于零中频（zero-IF）架构，避免了镜像干扰。此外，FMCW的上调频和下调频用于实现自参考，无需使用参考信号，从而实现了高FM精度。在实验中，使用最大输出频率为43.5 GHz的商用微波发生器（MG）展示了0.1 GHz - 43.5 GHz范围内的FM。所有频率的FM误差均保持在±10 MHz以内，均值和标准差分别为 -0.3 MHz和3.17 MHz。在FMCW啁啾率为3.1998 / 时，多音分辨率约为60 MHz，与理论结果一致。根据理论推导，通过降低FMCW啁啾率，多音分辨率可提高到1 MHz。
