Clamping-force induced birefringence in a single-mode fiber in commercial V-grooves investigated with distributed polarization analysis

Abstract

V-grooves are critical components for attaching fiber pigtails to photonics integrated circuits and for holding fibers in optical devices. Improper choice of V-groove angles and clamping method may cause large birefringence in the fibers and degrade polarization related performance of the devices. In this paper, we theoretically analyze the clamping-force induced birefringence of a single-mode (SM) fiber clamped in a V-groove by a flat-lid or by two identical V-grooves, respectively. We build a distributed polarization analyzer with complete Muller matrix analysis capability, which enables us to accurately measure local birefringence values in the fiber induced by clamped V-grooves of different angles. We find that for a SM fiber clamped in a commercial V-groove made with ZrO2 or SiO2 by a flat-lid, the zero-birefringence (ZB) angle is almost exactly 60°, suggesting that the friction coefficient in the V-groove can be safely ignored. In contrast, previous studies either indicated that the ZB V-groove angles clamped by a flat-lid never existed or significantly deviated from 60° due to the friction coefficient. More importantly, we also find, for the first time, both theoretically and experimentally, that a SM fiber clamped by two identical commercial V-grooves has a ZB when the V-groove angle is 90°. The methods and results reported in this paper shall prove beneficial for the fiber optic component industry to optimize polarization related performances of devices for sensing, communication, and instrumentation applications.