1、 TECHNICAL REPORT IECTR 62324Second edition 2007-01Single-mode optical fibres Raman gain efficiency measurement using continuous wave method Guidance Reference number IEC/TR 62324:2007(E) Publication numbering As from 1 January 1997 all IEC publications are issued with a designation in the 60000 ser
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7、further information. Customer Service Centre If you have any questions regarding this publication or need further assistance, please contact the Customer Service Centre: Email: custserviec.ch Tel: +41 22 919 02 11 Fax: +41 22 919 03 00 TECHNICAL REPORT IEC TR 62324Second edition 2007-01Single-mode o
8、ptical fibres Raman gain efficiency measurement using continuous wave method Guidance PRICE CODE IEC 2007 Copyright - all rights reserved No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without per
9、mission in writing from the publisher. International Electrotechnical Commission, 3, rue de Varemb, PO Box 131, CH-1211 Geneva 20, Switzerland Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmailiec.ch Web: www.iec.ch M For price, see current catalogue Commission Electrotechnique Int
10、ernationale International Electrotechnical Commission 2 TR 62324 IEC:2007(E) CONTENTS FOREWORD.3 1 Scope and object5 2 Normative references .5 3 Terms and definitions .5 4 Overview 6 5 Method.7 5.1 Description7 5.2 Laser safety 8 6 Apparatus.8 6.1 Optical pump source .8 6.2 Optical signal source.9 6
11、.3 Optical signal conditioning.10 6.4 Power meter10 6.5 Optical spectrum analyzer .10 6.6 Examples 10 7 Sampling and specimens10 7.1 Specimen endfaces .10 7.2 Specimen length10 7.3 Length selection10 7.4 Specimen attenuation coefficient.10 8 Procedure 11 9 Calculations and interpretation of results1
12、1 9.1 On/off gain 11 9.2 Raman gain efficiency .11 10 Documentation .11 10.1 Information to be reported with each measurement .11 10.2 Information that should be available upon request.11 Bibliography12 Figure 1 Typical test set-up for measuring the Raman gain efficiency of a fibre .7 Figure 2 Raman
13、 gain efficiency of depolarized light for a dispersion-unshifted fibre pumped at 1 486 nm 4 8 Table 1 Examples of parameters for measuring Raman efficiency10 TR 62324 IEC:2007(E) 3 INTERNATIONAL ELECTROTECHNICAL COMMISSION _ SINGLE-MODE OPTICAL FIBRES RAMAN GAIN EFFICIENCY MEASUREMENT USING CONTINUO
14、US WAVE METHOD GUIDANCE FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concernin
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23、 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent r
24、ights. IEC shall not be held responsible for identifying any or all such patent rights. The main task of IEC technical committees is to prepare International Standards. However, a technical committee may propose the publication of a technical report when it has collected data of a different kind fro
25、m that which is normally published as an International Standard, for example “state of the art“. IEC/TR 62324, which is a technical report, has been prepared by subcommittee 86A: Fibres and cables, of IEC technical committee 86: Fibre optics. This second edition cancels and replaces the first editio
26、n published in 2003. It constitutes a technical revision. This second edition differs from the first in that in the previous edition, in the paragraph before Figure 2, there was an approximation of the relationship between wavelength and optical frequency that led to some inconsistencies in interlab
27、oratory agreement. This approximation has been removed. 4 TR 62324 IEC:2007(E) The text of this technical report is based on the following documents: Enquiry draft Report on voting 86A/1058/DTR 86A/1072/RVC Full information on the voting for the approval of this technical report can be found in the
28、report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. The committee has decided that the contents of this publication will remain unchanged until the maintenance result date indicated on the IEC web site under “http:/webst
29、ore.iec.ch“ in the data related to the specific publication. At this date, the publication will be reconfirmed, withdrawn, replaced by a revised edition, or amended. A bilingual version of this publication may be issued at a later date. TR 62324 IEC:2007(E) 5 SINGLE-MODE OPTICAL FIBRES RAMAN GAIN EF
30、FICIENCY MEASUREMENT USING CONTINUOUS WAVE METHOD GUIDANCE 1 Scope and object This technical report is applicable to the Raman gain efficiency measurement of a single- mode transmission optical fibre. It is useful in assessing the fibres performance in Raman amplified transmission systems. This tech
31、nical report describes a method that uses two unmodulated continuous waves to measure the Raman gain efficiency of a single-mode transmission optical fibre. This parameter assesses the fibres efficiency at converting input pump power to information signal power. 2 Normative references The following
32、referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60793-1-22, Optical fibres Part 1-22: Measurement methods a
33、nd test procedures Length measurement IEC 60793-1-40, Optical fibres Part 1-40: Measurement methods and test procedures Attenuation IEC 60825-1, Safety of laser products Part 1: Equipment classification, requirements and users guide IEC 60825-2, Safety of laser products Part 2: Safety of optical fib
34、re communication systems 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 effective length L effthe fibres effective length accounts for decreasing nonlinear effects as light attenuates along a fibres length, and is defined as: 0,23 1 0,23 eff
35、 L e L = (1) where is the fibre attenuation coefficient in decibels per kilometre (dB/km),and L is the fibre length in kilometres (km). NOTE 1 When the in equation (1) is expressed in nepers per kilometre (Np/km), the two occurrences of 0,23 disappear, and the resultant equation is the form that typ
36、ically appears in the technical literature. 6 TR 62324 IEC:2007(E) NOTE 2 When 0,23L 1, equation (1) simplifies to give L eff 1/(0,23), which is the length at which the power in the fibre has decreased by a factor of 1/e. As an example, L eff = 17,4 km when = 0,25 dB/km. 3.2 depolarized light light
37、whose electric field vector, described in a plane perpendicular to the direction of propagation, is uniformly distributed in all radial directions NOTE 1 Rotation of a polarizer in a beam of depolarized light reduces its intensity by 50% regardless of the polarizers angular orientation. This test, h
38、owever, is not sufficient to assess whether the light is depolarized because circularly polarized light produces the same result. To guard against this possibility, a rotatable quarter wave retarder should be inserted before the polarizer. If the output intensity is constant over all independent rot
39、ations of the retarder and the polarizer, the input light can be considered depolarized. NOTE 2 Depolarized light is also termed unpolarized or randomly polarized. 4 Overview When a fibre carries high optical intensities, the optical power can be scattered because of interactions with mechanical vib
40、rations in the fibre. For low power levels, the scattered power is a small fraction of the incident power. However, as the incident power increases, the scattered power increases at a faster pace, and is said to be “stimulated”. There are two forms of nonlinear stimulated scatteringBrillouin and Ram
41、an. Stimulated Brillouin Scattering (SBS) arises because of an interaction between light and mechanical vibrations that occur in the form of a sound wave travelling along the length of the fibre (an “acoustic phonon”). SBS scatters light in the reverse direction. Stimulated Raman Scattering (SRS) is
42、 an interaction between light and the fibres molecular vibrations as adjacent atoms vibrate in opposite directions (an “optical phonon”). Some of the energy in an optical pump wave pis transferred to the molecules, thereby further increasing the amplitude of their vibrations. If the vibrational ampl
43、itudes become large, a threshold is reached at which the local index of refraction changes. These local changes then scatter light in all directionssimilar to Rayleigh scattering. However, unlike Rayleigh scattering, the wavelength of the Raman scattered light Ris shifted to longer wavelengths by an
44、 amount that corresponds to the vibrational frequencies of the molecules. The Raman scattered light amplifies information signals s . The magnitude or gain efficiency of this amplification depends on: pump wavelength p ; signal wavelength s ; fibre effective area A eff(the larger the area, the lower
45、 the power density); fibre material composition (vibration frequency and amplitude depend on material); fibre attenuation coefficient, and fibre length. The Raman gain efficiency of a fibre varies with signal wavelength when measured with a specific pump source. Consequently, Raman gain efficiency E
46、 R ( s ) is measured over a range of signal wavelengths. The peak Raman gain efficiency corresponds to a Stokes downshifted frequency of about 13 THz, which equates to an upshifted wavelength of 110 nm for a 1 450 nm pump, and 70 nm for a 1 240 nm pump. The Full Width Half Maximum (FWHM) of the gain
47、 profile is about 7 THz (55 nm) at 1 550 nm. NOTE The notation “C R ” is often used in the technical literature, and is variously referred to as the “Raman gain coefficient”1, the “Raman efficiency”2, and the “Raman gain.”3 1)_ 1)Figures in square brackets refer to the Bibliography. TR 62324 IEC:200
48、7(E) 7 5 Method 5.1 Description The method described in this technical report for measuring Raman gain efficiency uses unmodulated continuous waves generated by a signal source and a pump source. The signal source can be broadband (such as an LED or amplified spontaneous emission (ASE) or narrowband
49、 (such as one or more tunable lasers). If using a broadband signal source, a tunable filter might be needed at the sources output so that short signal wavelengths do not pump longer signal wavelengths. To minimize the influence of a noisy pump or one whose output power is not completely depolarized, the measurement is made by injecting light from the signal and pump
