PMD Effects on the Analogue Signal Transmission Abstract
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ALMA Memo # 506
PMD Effects on the Analogue Signal Transmission
P. Shen, N. J. Gomes, P. A. Davies (UKent), W. P. Shillue
(NRAO), P. G. Huggard (RAL)
2004-10-08
Keywords: PMD, Polarisation, phase drift, Photonic LO
We address the effects and problems of the polarisation mode dispersion (PMD) in the fibre transmission system for the Photonic LO. PMD is a random phenomenon, and varies from fibre to fibre, time to time and wavelength to wavelength. First, its value directly affects the efficiency of the LO generation. Then, the long term and short term stability of the PMD affect the long and short term phase stability of the delivered LO signal. It is suggested that ultra low PMD fibre should be used to preserve LO generation efficiency, to minimize system outage, and also maintain better phase stability (less phase drift). Measures to minimize the PMD effects are suggested. The polarisation mode noise at the receiver is also discussed. Any components in the receiver with large PMD, such as optical isolator, amplifier and photodetector will result in observable polarisation mode noise in the presence of large input polarisation fluctuation. A major contributor to this fluctuation is the antenna wrap, which has to be designed with care.
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