Schematic of the SD-OCT based on a linear k-domain spectrometer. (a) The sample arm to measure the system performance and obtain the skin tissue’s image. (b) The sample arm to get the image of the retina. SD-OCT, spectral domain optical coherence tomography; PC, polarization controller; CL, collimation lens; OL, objective lens; DCB, dispersion compensation block; RM, reference mirror; RC, reflective collimator; G, grating; DP, dispersive prism; PM, prism mirror; L1 to L4, lenses.|@|~(^,^)~|@|Resampled spectrum from the original spectrum with 10,001 sampling points, by means of the optical spectrum analyzer: (a) 2,048 sampling points, (b) 1,152 sampling points, and (c) 1,024 sampling points. (d) PSF of the coherence length for each spectrum, (a) to (c). PSF, point-spread function.|@|~(^,^)~|@|Graphs of three window functions and the frequency responses according to window functions. (a) Window functions, (b) the frequency response of the rectangular, (c) the frequency response of Hann, and (d) the frequency response of Gaussian window functions.|@|~(^,^)~|@|Examples of the super-Gaussian window function and frequency response of the super-Gaussian window function. (a) Graphs of the super-Gaussian window functions with [σ = 0.6, M = 2] and [σ = 0.7, M = 4], (b) frequency response of the super-Gaussian window function with [σ = 0.62, M = 2] compared to those of the rectangular and Gaussian window functions, and (c) frequency response of the super-Gaussian window function, according to changes in two parameters.|@|~(^,^)~|@|Images shown in (a), (b) are PSFs of the coherence length (or axial resolution) for the simulation, and (c), (d) are experiments using slide glass with a thickness of 1 mm. (a) and (c) are displayed with a linear scale. (b) and (d) are displayed with a log scale. PSF, point-spread function.|@|~(^,^)~|@|UHR FD/SD-OCT images of the skin on a human finger: (a) no window function, (b) Hann window function, (c) Gaussian window function, and (d) super-Gaussian window function applied. The image size is 576 pixels (depth) × 1,000 pixels (width). OCT, optical coherence tomography; UHR-OCT, ultrahighresolution OCT; FD-OCT, Fourier-domain OCT; SD-OCT, spectral domain OCT.|@|~(^,^)~|@|UHR FD/SD-OCT images of the human retina: (a) no window function, (b) Hann window function, (c) Gaussian window function, and (d) super-Gaussian window function applied. The image size is 576 pixels (depth) × 1,500 pixels (width). IS/OS, photoreceptor inner-segment/outer-segment junction; PR OS, photoreceptor outer segments; RPE, retinal pigment epithelium. OCT, optical coherence tomography; UHR-OCT, ultrahighresolution OCT; FD-OCT, Fourier-domain OCT; SD-OCT, spectral domain OCT.

Curr. Opt. Photon. 2023;7:73~82 https://doi.org/10.3807/COPP.2023.7.1.73