Measurement and Nonlinear Correction of Instantaneous Relative Frequency of High-Speed FMCW Laser Signal Based on 3×3 Fiber Coupler
This study proposes a method for measuring the instantaneous relative frequency of a high-speed frequency-modulated continuous-wave(FMCW)laser signal based on a 3×3 fiber coupler.First,the operating principle of instantaneous relative frequency of the FMCW laser signal based on a 3×3 fiber coupler was theoretically analyzed.The study finds that the greater the delay difference between the two arms of the interferometer,the higher is the resolution of the measurement instantaneous relative frequency but the lower is the maximum sweep speed that can be measured.For example,when the delay between the two arms of the interferometer is 6.67×10‒8 s(20 m optical path difference),the lower is the measurement speed.The maximum scanning speed is 7.5×1015 Hz/s.Next,the study constructed a high-speed FMCW laser signal instantaneous relative frequency measurement system based on a 3×3 fiber coupler.The FMCW laser signal with a sweep period of 22 μs and frequency range of 820 MHz was measured experimentally,and nonlinear correction was performed using a pre-distortion nonlinear correction method.The correction results reveal a residual nonlinearity of the FMCW laser signal of 1-r2=2.6326×10‒5 and a root mean square frequency error of 1.23 MHz.The instantaneous frequency change measurement technology of the FMCW laser signal shows the advantages of high-speed and high-frequency resolution.
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