Design of a linear-wavenumber spectrometer for ultrahigh-resolution spectral domain optical coherence tomography

In spectral-domain optical coherence tomography (SDOCT), traditional spectrometers with a grating and line-scan camera yield nonlinear wavenumber responses, affecting OCT signal sensitivity and resolution. This necessitates post-processing for spectral interferogram remapping, but it's limited in short-wavelength ranges due to uneven pixel frequency spacing. To overcome these challenges, we introduce a cost-effective, simple linear-wavenumber spectrometer using a dual-prism and reflector setup, significantly enhancing spectral dispersion linearity, vital for ultra-high resolution SDOCT. Our method employs iterative calculations with global stochastic gradient descent for higher-order dispersion linearization. This results in a substantial increase in wavenumber linearity, from 99.9714% to 99.9998% for 80 nm at 850 nm wavelength, and 99.6828% to 99.9861% for 260 nm bandwidth. Our design eliminates resampling needs for up to 260 nm bandwidth, with nonlinearity-induced wavenumber mismatch under one pixel. This innovation marks a significant advancement in SDOCT spectrometer design, enhancing performance and resolution beyond traditional system limitations.