Narrow-band measurement of differential group delay by a six-state RF phase-shift technique: 40 fs single-measurement uncertainty

• Published in: Journal of lightwave technology Vol. 22; no. 2; pp. 448 - 456
• Main Authors: Williams, P.A., Kofler, J.D.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.02.2004; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Confidence intervals; Delay; Exact sciences and technology; Frequency measurement; Group delay; Modulation; Narrowband; Optical fiber polarization; Optical fibers; Phase measurement; Phase modulation; Polarization; Radio frequencies; Radio frequency; Simulation; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Time measurement; Transmission and modulation (techniques and equipments); Uncertainty; Optical fiber communication; Phase shift; Measurement technique; Polarization mode dispersion; Group delay
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2003.822116

We describe in detail our implementation of a modulation phase shift (MPS) technique for narrow-bandwidth measurement of differential group delay (DGD) and the principal states of polarization (PSP) in optical fibers and components. Our MPS technique involves launching six orthogonal polarization states (as opposed to the four states typically launched) to achieve improved measurement stability. The measurement bandwidth is 4.92 GHz (twice the 2.46 GHz RF modulation frequency), the measurement time is 13 s per point, and the single-measurement uncertainty is better than 40 fs (/spl sim/95% confidence interval) for DGD values from 10 to 1000 fs. We demonstrate that this uncertainty can be greatly improved by averaging, yielding a 9.7 fs uncertainty (95% confidence interval) on a device with 315 fs of DGD. Sources of uncertainty are detailed, including a DGD contribution from the detector itself. Simulations illustrate the uncertainty contribution of multiple DGD elements in series.