Fig. 1. Endoscopy imaging system. (a) Basic demonstration setup. (b) Reflections from different segments of the fiber can be studied to characterize the evolution of the beam wavefront passing through the MMF.

Fig. 2. Schematic design of the proposed experiment. Input beam polarization is known, and reflected ones are measured and deployed to estimate the output polarization. Any reflected pulse is from a specific segment of the channel, and the length of each segment is determined by the pulse width Δt.

Fig. 3. Demonstrated experiment and measurements. (a) Coherent measurement setup to capture the reflections from the test fiber including measured output on all four PDs denoting in-phase (I) and quadrature (Q) components of x and y polarization; PMF, polarization maintaining fiber; EOM, electro-optic modulator; AWG, arbitrary wave generator; PC, polarization controller; EDFA, erbium-doped fiber amplifier. (b) Zoomed-in period of the signal denoting different portions of the signal to be processed for the channel characterization. (c) Mirror, linear polarizer (LP), and quarter-wave plate (QWP) used as an object with known polarization characteristics, and (d) mirror, linear polarizer, and zero-order vortex half-wave plate (HWP) used as an object for polarization imaging experiment.

Fig. 4. Experiment results. (a) and (b) Statistical distribution of 100 measurement results for relative error in amplitude ratio and relative error in phase, respectively. Both distributions can fit to a normal random variable (dashed lines) to find the expected error and consequently precision of the experiments. (c) The expected degree of linear polarization (POL) is compared with the measured polarization using characterization setup of Fig. 3(c) as a function of the rotation angle of the QWP compared with the axis of the LP (θ). (d) Expected fast axis distribution for the zero-order vortex HWP reported by its spec sheet. (e) Measured fast axis angle distribution utilizing the polarization imaging setup of Fig. 3(d) found for eight slices of the circular wave plate.