Recovery of the full wavelength modulation spectroscopy (WMS) signal in isolation from the residual amplitude modulation (RAM) due to nonlinear intensity modulation (IM) and distortion due to linear IM is demonstrated. The RAM is eliminated using a fiber delay line, while the linear IM-induced distortion is eliminated by a phasor decomposition approach. This generic and robust two-pronged strategy removes the need to separately measure the RAM in high-modulation-index calibration-free WMS. It is also important for widely tunable WMS using nontelecom diode lasers with highly nonlinear characteristics leading to high- RAM levels.
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