The output of the wavelength-swept laser is sent to an external Michelson type interferometer module (INT-MSI-1300, Thorlabs, New Jersey) that splits the light into the sample and reference arms and also includes a 15-MHz balanced detector. An SMF-28 fiber is connected to the sample arm output of the interferometer module using an FC-APC connector and fusion-spliced at the other end to the DCF input of the DCFC (port A). The DCF output (port S) of the DCFC is then collimated with a 16-mm focal length fiber collimation lens (C2: FC260APC-C, Thorlabs, New Jersey). A dual-axis galvanometer is used to steer the beam (G: GVS002, Thorlabs, New Jersey). An uncoated, 50-mm focal length planoconvex lens (L: LA1131, Thorlabs, New Jersey), placed at one focal length of the galvanometer, is used to focus the beam on the sample for a telecentric scan. The light backscattered by the sample is collected by the fiber core and cladding, but only the signal collected in the core can travel back to the OCT interferometer. Light in the cladding is either transferred to the MM branch of the DCFC or lost at the splice between the DCF and the SMF-28 fiber. The reference arm is composed of an SMF-28 fiber that matches the sample arm dispersion. Since the double-clad and SMF-28 fibers have the same dispersion characteristics, the length of the SMF-28 fiber in the reference arm is simply the sum of all SMF-28 and DCF segments in the sample arm. No dispersion compensation method was used. The interference from the two arms is detected by a dual-balanced detector. The commercial OCT engine performs acquisition, processing, and display.