Opt Express. 2023 Apr 10;31(8):13384-13392. doi: 10.1364/OE.485140.
We demonstrate ultralinear and ultrawideband frequency-modulated continuous-wave (FMCW) signal generation using an optical parametric wideband frequency modulation (OPWBFM) method. The OPWBFM method optically expands the bandwidths of FMCW signals beyond the electrical bandwidths of optical modulators via a cascaded four-wave mixing (FWM) process. Compared to the conventional direct modulation approach, the OPWBFM method simultaneously achieves high linearity and a short measurement time of the frequency sweep. On the other hand, it is also known that the OPWBFM method expands the phase noise of idlers as well as their bandwidths if an input conjugate pair has different phase noise. To avoid this phase noise expansion, it is crucial to synchronize the phase of an input complex conjugate pair of an FMCW signal using an optical frequency comb. For demonstration, we successfully generated an ultralinear 140-GHz FMCW signal by using the OPWBFM method. Moreover, we employ a frequency comb in the conjugate pair generation process, leading to the mitigation of phase noise expansion. By using a 140-GHz FMCW signal, we achieve a range resolution of ∼1 mm through fiber-based distance measurement. The results show the feasibility of an ultralinear and ultrawideband FMCW system with a sufficiently short measurement time.
我们展示了一种使用光学参量宽带频率调制（OPWBFM）方法的超线性和超宽带调频连续波（FMCW）信号产生。OPWBFM 方法通过级联四波混频（FWM）过程，将 FMCW 信号的带宽光学扩展到光调制器的电带宽之外。与传统的直接调制方法相比，OPWBFM 方法同时实现了高线性度和短的频率扫描测量时间。另一方面，如果输入共轭对具有不同的相位噪声，则众所周知，OPWBFM 方法会扩展闲频的相位噪声及其带宽。为了避免这种相位噪声扩展，使用光频梳同步 FMCW 信号的输入复共轭对的相位至关重要。为了演示，我们成功地使用 OPWBFM 方法生成了一个超线性的 140GHz FMCW 信号。此外，我们在共轭对生成过程中使用了一个频率梳，从而减轻了相位噪声扩展。通过使用 140GHz FMCW 信号，我们通过基于光纤的距离测量实现了约 1mm 的距离分辨率。结果表明，具有足够短的测量时间的超线性和超宽带 FMCW 系统是可行的。
