Frequency-scanning nonlinearity suppression for FSI ranging based on a phenomenological modeling approach

Frequency-scanning nonlinearity fundamentally limits the ranging precision of frequency-scanning interferometry (FSI) systems based on external cavity diode lasers (ECDLs). To address this limitation, a frequency scanning nonlinearity suppression method based on a rate-dependent asymmetric Prandtl-Ishlinskii (RA-PI) model is proposed. By employing, for the first time, a phenomenological modeling approach, the rate-dependent and asymmetric nonlinear optical frequency response of the ECDL is accurately characterized. An inverse RA-PI model is derived and implemented as a feedforward compensator to linearize the frequency scanning. Experimental results show that the frequency-scanning linearity is improved by approximately one order of magnitude. Consequently, the maximum standard deviation of absolute distance measurements is reduced from 58.25 μm to 9.79 μm, and the maximum relative displacement deviation decreases from 42.97 μm to 11.56 μm. Furthermore, the velocity measurement precision for dynamic targets is improved by a factor of 2.61 to 5.75.