1、 TIA-455-228 February 2002 (r 01/2012) FOTP-228 Relative Group Delay and Chromatic Dispersion Measurement of Single-Mode Components and Devices by the Phase Shift Method NOTICE TIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandings
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6、0023-A, formulated under the cognizance of the TIA TR-42 Telecommunications Cabling Systems, TR-42.13 Subcommittee on Passive Optical Devices and Fiber Optic Metrology). Published by TELECOMMUNICATIONS INDUSTRY ASSOCIATION Standards and Technology Department 2500 Wilson Boulevard Arlington, VA 22201
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22、OF THE CONTENTS HEREOF, AND THESE CONTENTS WOULD NOT BE PUBLISHED BY TIA WITHOUT SUCH LIMITATIONS. TIA-455-228 FOTP-228 RELATIVE GROUP DELAY AND CHROMATIC DISPERSION MEASUREMENT OF SINGLE-MODE COMPONENTS AND DEVICES BY THE PHASE SHIFT METHOD Contents Foreword iii 1 Introduction 1 2 Normative Referen
23、ces 6 3 Apparatus 7 4 Sampling And Specimens 15 5 Procedure 16 6 Calculations 18 7 Documentation 20 8 Specification Information 21 Annex A (Normative) 2 Annex B (Normative) 23 Annex C (Normative) 28 Annex D (Normative) 28 Annex E (Informative) 35 Annex F (Informative) 36 i TIA-455-228 This page left
24、 blank. ii TIA-455-228 FOTP-228 RELATIVE GROUP DELAY AND CHROMATIC DISPERSION MEASUREMENT OF SINGLE-MODE COMPONENTS AND DEVICES BY THE PHASE SHIFT METHOD Foreword (This Foreword is informative only and is not part of this Standard.) From TIA Project No.3-0023-A, formulated under the cognizance of TI
25、A FO-6.3.5, Subcommittee on Passive Fiber Optic Devices. This FOTP is part of the series of test procedures included within Recommended Standard EIA/TIA-455. There are six annexes, four of them Normative. Key words: Dispersion, Components, Isolators, Filters, Group Delay, WDM, DWDM, narrow-band comp
26、onent, filter, narrow-band. iii TIA-455-228 This page left blank iv TIA-455-228) 1 Introduction 1.1 Intent A procedure is described for the measurement of Relative Group delay (RGD) and chromatic dispersion (CD) of one or two port single-mode fiber components over the 1.0 to 1.7 micrometer wavelengt
27、h range. The RGD at each particular wavelength is determined from the phase shift of a modulated light source. The CD is then determined by suitably computing the wavelength derivative of the RGD data at given wavelengths. 1.2 Scope In this procedure, a modulated light source at a given wavelength i
28、s coupled into the component under test, and the phase shift of the modulated signal exiting the fiber at that wavelength is recorded with respect to the original modulation signal. The phase shift can be converted directly to RGD in the device. By collecting RGD data at various wavelengths, the chr
29、omatic dispersion of the component can be determined at these and other wavelengths from the derivative with respect to wavelength of the relative group delay. This FOTP does not apply to components that have in excess of 10 dB of polarization dependent loss (PDL). The main intent of this FOTP is to
30、 determine the average group delay and chromatic dispersion of the component and moreover to isolate the RGD from all polarization sensitivity in the device. Note that in the case of fiber pigtailed components, the pigtails may give a large absolute (standing) delay but also some relative delay, ove
31、r the component test wavelength range. In most cases of component measurements, only the relative group delay is of interest, so it is important to account for any RGD in the leads, and to ensure the standing delay is stable over the measurement time. Any changes in the standing delay and any RGD in
32、 the leads will be evident in the test results. 1.3 Background There already exist Test Procedures for group delay and chromatic dispersion measurement in fibers and fiber cables. Two of these methods use a phase shift approach to RGD measurement and rely on measuring the variation of phase shift wi
33、th wavelength to determine dispersion. These are the phase shift method (covered by FOTP-169) and differential phase shift method (covered by FOTP-175A). 1 TIA-455-228 The third Technique is the pulse delay method (covered by FOTP-168), a time-domain method, which generally lacks the resolution requ
34、ired for component RGD determination. Note- These three methods are shortly to be consolidated into one FOTP, FOTP-175B. A fundamental limitation of all the techniques cited above is that a finite (a few nm to 10s of nm) of wavelength range is required in order to perform the measurement of RGD and
35、subsequent determination of dispersion. Moreover, the test fiber delay is assumed to follow specific functional forms with wavelength, which are used to fit the delay/differential delay data to determine dispersion accordingly. In the present case of fiber optic components and devices, such function
36、al forms do not apply. The delay measurement technique described herein is adapted to use a comparatively small wavelength range, and in order to make the measurement of dispersion, one of two alternative generalized fitting methods is used, both of which have wide applicability to a variety of fibe
37、r components. The two alternatives are : a) “Linear fit” method; to measure the RGD over the pass-band and fit a linear delay equation to the data, from which a single chromatic dispersion value may be calculated. This has the advantage of requiring relatively few data points, but loses any and all
38、of the detail or structure within the RGD characteristic over the band. Such a method may be applicable to devices which are designed to have a single dispersion value (e.g. compensators), or which have negligible ripple structure compared to the dispersion (the overall slope of the delay curve). In
39、 addition, the few measurement points needed for this method allow for rapid measurement throughput in manufacturing situations. This method is therefore intended for screening and QA applications of “mature” products. b) “Local Derivative” method; to measure the RGD over the device pass-band and to
40、 locally calculate the wavelength derivative using the raw RGD data. This allows full detail of the delay characteristic to be examined but, in general, requires many data points to obtain the required resolution. This method applicable where the structure of delay is required, and where ripple is s
41、ignificant compared to the overall “slope” of delay with wavelength. This method is most applicable during process tuning and other development activities. Annex D (normative) provides a means for determining the chromatic dispersion from the RGD data. 2 TIA-455-228 This FOTP will find applications
42、in a variety of DWDM component testing applications. This is particularly true when using narrow band fixed or tunable laser sources. The fiber optic components to which this procedure applies often exhibit channel bandwidths smaller than 1 nm, filter response slopes greater than 100 dB/nm, and out-
43、of-band rejection extending over tens of nanometers. These features provide low loss in the pass channel and high rejection of signals belonging to other channels. Measurement of the associated dispersion and delay features requires high wavelength resolution and wavelength accuracy. Typically, dela
44、y and dispersion determination is limited to the pass-band(s) of the device. 1.4 Light Sources Typical optical sources suitable for this measurement include laser diodes or filtered light-emitting diodes. 1.5 Source Line-width, wavelength interval and Modulation Frequency The wavelength resolution i
45、s ultimately limited by the spectral width (line-width) of the tunable source and also by the modulation frequency, which imparts side-bands onto the source optical frequency. Hence both the inherent source line-width and the modulation used for RGD determination are contributions to the effective s
46、ource line-width. The effective source line-width limitation is most evident at narrow response features such as RGD peaks and notches, and on steep RGD slopes. To adequately resolve these details, the spectral width and modulation frequency should be less than or equal to the feature widths, as pre
47、scribed by Annex C. Note that in the “linear fit” method the spectral line-width requirement can be greatly relaxed because the desired resolution is very low. It is important to recall that the DUT may often exhibit insertion loss response slopes greater than 100 dB/nm. Measurement of the associate
48、d dispersion and delay features in these slope regions, requires high wavelength resolution and may be prone to error if the modulation frequency is significant in relation to the insertion loss slope 4. Therefore, the choice of modulation frequency is germane to measurement of RGD in the filter slo
49、pe regions. Typically however, RGD and dispersion determination is limited to the pass-band(s) of the device. Note that many tunable lasers exhibit a very narrow line-width (1 GHz. The modulation at frequency, f, will impart side-bands at +/-f Hz away from the center wavelength of the source, and in some very narrow band DUTs this might prove a limitation. To ensure accurate phase measurement, the total occupied bandwidth including the side-bands of the modulation and the source line-width itself must be less than or equal to the DUT bandwidth and any resolvable features in th
