Full-set high-speed mode analysis in few-mode fibers by polarization-split segmented coherent detection method: Proposal and simulation of calculation error

Abstract

We propose a novel mode analysis method named the polarization-split segmented coherent detection (PSCD) method, which can obtain a full set of amplitudes, phases, and polarization states of guided modes including degenerate modes in few-mode fibers within the speed limit imposed by the response time of the electronics. The detailed calculation process of formulas for the complex amplitudes of the LP₀₁, LP₁₁^even, and LP₁₁^odd modes from the measured inter-frequency signals of the four elements of a quadrant photodetector is described. In addition, the calculation errors of the formulas for the LP modes as functions of the rotation of the quadrant photodetector and the offset of the beam from the local oscillator are evaluated by numerical simulation. From these error analyses, we derive formulas to compensate for the effect of the rotation of the quadrant photodetector and to reduce the error due to the offset of the beam from the local oscillator.