Fig. 1. The simulations with Zemax ray tracing software. (a) The spectrometer with one achromatic lens (EFL = 50 mm) used to replace the F-theta lens. (b) The spectrometer with a typical F-theta lens (EFL = 50 mm, SL50-2P2, Thorlabs, NJ, USA). (c) The spectrometer with the combined 4 achromatic lenses (EFL = 50 mm) used to replace the F-theta lens. The spot diagrams at the five representative wavelengths (0.75 µm, 0.8 µm, 0.85 µm, 0.9 µm, and 0.95 µm) on the line-array sensor plane are shown for comparison in (a)–(c). The RMS radii of the spot diagrams are shown in Table 1.

Fig. 2. The schematic of the home-built SDOCT system. PC1, PC2: polarization controllers; DP: dispersion compensation pair; L1–L4: achromatic lenses; CL: combination of four achromatic lenses. The CL is obtained by putting the four lenses together in one single-lens mounting tube.

Fig. 3. The results of the home-built SDOCT system. (a) The normalized power spectral density obtained by the customized spectrometer. (b) The reference data of the normalized power spectral density from the user manual of light source. (c) The point spread functions (PSFs) at different depths with an optical neutral density filter (OD = 2) inserted in the sample arm. (d) A healthy volunteer’s finger, and the marked position was scanned. (e) A 10 B-scans averaged structural image obtained by the proposed low-cost high-resolution spectrometer. The marked positions are blood vessels.