Polarization-Dependent Loss of Optical Connectors Measured with High Accuracy (<0.004 dB) after Cancelation of Polarimetric Errors

TL;DR

This paper presents a highly accurate method for measuring polarization-dependent loss in optical connectors, achieving errors below 0.004 dB by advanced calibration and polarization control techniques.

Contribution

It introduces a calibration approach that cancels polarimetric errors, enabling precise PDL measurements even with polarization drift and device variations.

Findings

Measured PDL with errors <0.004 dB

Demonstrated PDL >60 dB in a polarizer

Achieved rapid Mueller matrix sampling at 100 MHz

Abstract

State-of-the-art polarimeter calibration is reviewed. Producing many quasi-random polarization states and moving/bending a fiber without changing power allows finding a polarimeter calibration where the degree-of-polarization reaches unity and parasitic polarization-dependent loss is small. Using a polarization scrambler/transformer and a polarimeter a device-under-test can be characterized. Its Mueller matrix can be decomposed into a product of a nondepolarizing Mueller-Jones matrix times a purely depolarizing Mueller matrix. Test polarizations may drift over time. With help of an optical switch the reference device can be measured against an internal reference path. Later, with possibly different test polarizations, the actual device-under-test is measured against the internal reference. Polarization drift and need for repeated reference device measurement are thus overcome. When a patchcord is inserted, connector PDL can be measured, provided that errors are calibrated away, again by fiber moving/bending. Experimentally we have measured PDL with errors <0.004 dB. This easily suffices to measure connector PDL, which is demonstrated. PDL >60 dB was measured when the device under test was a good polarizer. A 20 Mrad/s polarization scrambler with LiNbO3 device generates the test polarizations. The polarimeter can sample at 100 MHz and can store 64M Stokes vectors. During laser frequency scans Mueller matrices can be measured in time intervals as short as 5 us.