We use a CP-SSOCT because it yields many benefits in a surgical setting.24 The ability to use a lensless fiber system yields small imaging probes, which are capable of being used in the restricted environment of the cochlear canal. Because probes must be sterile for each operation, a single-optical arm is beneficial. Furthermore, negating the additional alignment of a reference arm and the low cost of polished fiber allows the probes to be disposable between surgical procedures. Additionally, the single-arm setup of CP-SSOCT prevents the formation of complex-conjugate images of target tissue, allowing for simplified image processing. The main advantage of the common-path setup is that it allows accurate distal measurements relative to the probe tip, allowing highly accurate image registration. A schematic of our CP-SSOCT system is shown in Fig. 2. The system is built to have the ability to run in both standard and common-path configurations, though the latter is chosen for this work to allow for multiple experiments during a single session.25 The OCT engine is a 1310-nm swept-source laser (Axsun Technologies, Inc., Billerica, Massachusetts) operating at a 50-kHz A-scan rate with a 19-μm axial resolution. Return signal is collected using a single input on a balanced amplified photodetector (ThorLabs, Inc., PDB110C, Newton, New Jersey) and digitized (Alazar ATS9350, Pointe-Claire, Quebec, Canada). Output light is passed through an SC-connector rotary coupler (Princetel, Inc., Hamilton, New Jersey), which is rotated at 5 to 10 Hz. The distal fiber is SMF-28 (Gould Technology LLC, Millersville, Maryland) with a buffered diameter of 250 μm and a cladding diameter of 125 μm. In order to image “sideways,” perpendicular to the fiber axis, the fiber is polished to a 45-deg angle26 using an aluminum oxide fiber-optic polishing system (KrellTech, Morganville, New Jersey). Similar sideviewing schemes involving polishing, microprisms, and fused half-ball lenses have been previously used by many groups.27–31 In order to maintain a single-arm setup and to keep the probe simple for disposability, a bare-polished fiber is selected. Although this lensless system cannot focus light at the distal end of the probe, the reflected signal provides sufficient signal-to-noise ratio (SNR) for imaging. To confirm the imaging capability of the bare sideview probe, the SNR is calculated at various distances by translating a mirror from 0.5 to 3 mm. The overlaid A-scans are shown in Fig. 3. The SNR decays from 50 dB at 0.5 mm to 30 dB at 3 mm, a sufficient distance given the small diameter of the cochlear canal. The return interference signal from the OCT probe is passed through the circulator to an unbalanced detector, from where it is digitized and processed in custom C++ software.