[asac] [almanews] ALMA Memo 506 Released

[Stacy Oliver]

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. 

View a pdf version of ALMA Memo #506. 

http://www.alma.nrao.edu/memos/html-memos/alma506/memo506.pdf

 

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