2.2.1. OCT setup

In this study, we used a polarization sensitive OCT (PS-OCT) system, which has been described in Refs. [15,16]. However, we only used a single-polarization-channel OCT image (i.e., a conventional non-polarization sensitive OCT image) to demonstrate the MFA method. The light source was a sweeping laser source (AXP50124-8, Axsun Technologies, MA) with a central wavelength of 1.31-μm, a bandwidth of 106 nm, and a scanning rate of 50 kHz. The objective (LSM03, Thorlabs, NJ) had an effective focal length of 36 mm and gave a depth of focus (DOF) of 0.36 mm in air. The lateral and axial resolutions were measured to be respectively 18 μm and 14 μm in tissue. The influences from the focus tuning to the resolutions will be discussed in Section 4.3.4.

An electrical tunable lens (ETL, EL-10-30-CI-NIR-LD-MV, Optotune Switzerland AG, Switzerland) was set on the sample arm to modulate the focal position. It is noteworthy that the ETL can be easily aligned and applied to standard OCT systems.