Low-cost spectrometer design for ultra-high resolution spectral domain optical coherence tomography

In this Letter,we present a low-cost,high-resolution spectrometer design for ultra-high resolution optical coherence tomography(UHR-OCT),in which multiple standard achromatic lenses are combined to replace the expensive F-theta lens to achieve a comparable performance.For UHR-OCT,the spectrometer plays an important role in high-quality 3D image reconstruction.Typically,an F-theta lens is used in spectrometers as the Fourier lens to focus the dispersed light on the sensor array,and this F-theta lens is one of the most expensive components in spectrometers.The advantage of F-theta lens over the most widely used achromatic lens is that the aberrations(mainly spherical aberration,SA)are corrected,so the foci of the dispersed optical beams(at different wavelengths)with different incident angles could be placed on the sensor array simultaneously.For the achromatic lens,the foci of the center part of the spectrum are farther than those on the side in the longitudinal direction,causing degradations of the spectral resolution.Furthermore,in comparison with the achromatic lens with the same focal length,those with smaller diameters have stronger SA,but small lenses are what we need for making spectrometers compact and stable.In this work,we propose a simple method of using multiple long-focal-length achromatic lenses together to replace the F-theta lens,which is>8-fold cheaper based on the price of optical components from Thorlabs,US.Both simulations and in vivo experiments were implemented to demonstrate the performance of the proposed method.