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.
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.
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