TIA/EIA-526-19:2000

$26.00

OFSTP-19 Optical Signal-to-Noise Ratio Measurement Procedures for Dense Wavelength-Division Multiplexed Systems

Published By	Publication Date	Number of Pages
TIA	2000	26

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Description

Introduction

Intent

At the optical interfaces within wavelength-division multiplexed
(WDM) networks, it is desirable to measure parameters that provide
information about the integrity of the physical plant. Such
parameters are necessary to monitor network performance as
an integral part of network management. They are also necessary to
assure proper system operation for installation and
maintenance of the network.

Ideally, such parameters would directly correspond to the bit
error ratio (BER) of each channel of a multichannel carrier at the
particular optical interface. Related parameters such as Q-factor
or those calculated from optical eye patterns would provide similar
information, that is, they would correlate to the channel BER.
However, it is difficult to obtain access to these parameters at a
multichannel interface point. It is necessary to demultiplex the
potentially large number of channels and make BER, Q-factor, or
eye-diagram measurements on a per-channel basis.

In contrast, useful information about the optical properties of
the multichannel carrier is readily obtained by measuring the
optical spectrum. Wavelength-resolved signal and noise levels
provide information on signal level, signal wavelength, and
amplified spontaneous emission (ASE) for each channel. Spectral
information, however, does not show signal degradation due to
waveshape impairments resulting from polarization-mode dispersion
(PMD), and chromatic dispersion. Also, intersymbol interface and
time jitter are not revealed from an OSNR measurement. In spite of
these limitations, OSNR is listed as an interface parameter in
ITU-T draft Recommendation G.692; "Optical interfaces for
multichannel systems with optical amplifiers." It is also proposed
that OSNR be listed in ITU-T draft recommendation G.959.1, "Optical
networking physical layer parameters."

This OFSTP provides a parameter definition and a test method for
obtaining optical signal-to-noise ratio (OSNR) using apparatus that
measures the optical spectrum at a multichannel interface. Three
implementations for an optical spectrum analyzer (OSA) are
discussed: a diffraction-grating-based OSA, a Michelson
interferometerbased OSA, and a Fabry-Perot-based OSA. Performance
characteristics of the OSA that affect OSNR measurement accuracy
are provided.

Additional information