Huawei Contribution

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					-1 Question(s): Source: Title: Contact: 6 Working Party: Meeting, date: Sunnyvale, 16 – 20 March 2009 2 Intended type of document (R-C-TD): WD6-13

Study Group: 15

Huawei Technologies Co., Ltd OSNR measurement description Stefano Beccia Huawei Technologies Co., Ltd. P.R.China Xixiang Li Huawei Technologies Co., Ltd. P.R.China Tel: +39 02 00628 819 Fax: +39 02 00628 838 Email: stefano.beccia@huawei.com Tel: +86-755-28977103 Fax: +86-755-28972935 Email: xxl@huawei.com

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1. Introduction In Geneva meeting on December 3, 2008, a breakout group met to discuss and draft some texts to WD6-01. The first part is titled “Framework for OSNR measurement with the noise shaping”. In this document, we propose a simple technique to determine the in-band OSNR by out-of-band OSNR measurement and noise shaping estimation. The proposed technique allows leveraging simple and cost effective measurement equipments. 2. Discussion The OSNR in-band measurements are critical for a WDM system that deploys the ROADM/PXC technology even when the bit rate is much lower than the channel spacing, due to the well known noise shaping effect brought by the filters cascading. Such WDM systems are used in the Metro, Regional and Backbone networks and they are designed to work under controlled temperature environment, limiting the effect of temperature variation on the devices with cooling techniques. Under this condition, we can assume that the transfer functions of the optical elements, along the light path, are stable enough to not cause the degradation of the system performance. Considering that, we can estimate the real-time transfer function of the optical element equal to the pre-determined one that could be tested before the product delivery and readily stored in the database of the network management system and retrieve as needed. Therefore, the noise shaping can be acquired by calculating the transfer function of optical filters which are cascaded along the transmission path as Formula-1. With this noise shaping estimation, the in-band OSNR can be measured by simply measuring the out-of-band OSNR at the end points as show in Figure-1 instead of measuring the filtered noise value before and after every ROADM. Nin = Nout +

 T F( f )
n 1 i

- N in : In-band Noise - N out : Out-of-band Noise Formula-1

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ROADM

ROADM OLA Pre-determined Transfer Function Input ports
Fibre span PA: Pre-amplifier BA: Boost-amplifier Dispersion compensator Measurement Point

ROADM OLA

ROADM

Output ports

Add ports

Drop ports

Figure-1 OSNR measurement points with pre-determined Transfer Function Similar with the scheme proposed in “Framework for OSNR measurement with the noise shaping”, as bit rates becomes comparable with channels spacing, the signal spectrum is completely overlapping with the noise floor. With this condition, some advanced techniques should be introduced for real in-band OSNR measurement, such as polarization nulling method [1], polarization splitting method [2], and polarization diversity method [3]. 3. Proposal It is proposed to consider this simple and effective OSNR measurement principle based on the transfer function of optical filters and measuring the out-of-band OSNR at the end point in WD601. 4. Reference [1] http://www.teralinkcom.com, OSMT-501 [2] http://www.jdsu.com, MTS/T-BERD 8000 [3] http://www.exfo.com, FTB-5240B


				
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