Aspects of the present disclosure provide a method for wavelength calibration of a spectrometer. The method can include receiving a calibration light signal having first spectral components of different first wavelengths; separating and projecting the first spectral components onto pixels of a detector of the spectrometer; establishing a relation between the first wavelengths and pixel numbers of first pixels on which the first spectral components are projected; calculating first residual errors between the first wavelengths and estimated wavelengths that are associated by the relation to the pixel numbers of the first pixels; receiving an optical signal having a second spectral component of a second wavelength; projecting the optical signal onto a second pixel; and calibrating the second wavelength based on a second residual error calculated based on one of the first residual errors that corresponds to a pair of the first pixels between which the second pixel is located.