Design and validation of a linear wavenumber spectrometer for SD-OCT using freeform optics

In spectral domain optical coherence tomography (SD-OCT), spectrometers traditionally use gratings to disperse light, producing spectral signals linearly related to wavelength. However, this induces nonlinearity in wavenumber (k) space, diminishing the sensitivity of SD-OCT systems. Conventionally, signals are interpolated and resampled to achieve linear interferometric spectral signals in wavenumber space. Our work presents a spectrometer that inherently produces linear wavenumber signals, obviating the need for post-interpolation and thus enhancing system sensitivity while reducing processing time. This advancement is achieved by employing a spectrometer equipped with a freeform surface lens that dramatically reduces wavenumber nonlinearity from 1.49% to 0.0043%. We have successfully manufactured this lens and experimentally validated the spectrometer’s wavenumber linearity.