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1、 TIA TELECOMMUNICATIONS SYSTEMS BULLETIN Polarization Dependent Loss: Measurement and Application Issues in Telecommunications TSB-141 July 2005 TELECOMMUNICATIONS INDUSTRY ASSOCIATION The Telecommunications Industry Association represents the communications sector of Copyright Telecommunications In
2、dustry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 23:42:28 MDTNo reproduction or networking permitted without license from IHS -,-,- NOTICE TIA Engineering Standards and Publications are designed to serve the publ
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6、d or Publication. This Standard does not purport to address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this Standard to establish appropriate safety and health practices and to determine the applicability of regulato
7、ry limitations before its use. (From Standards Proposal No. 3-0064-A, formulated under the cognizance of the TIA FO-4.5 Subcommittee on Fiber Optic Metrology.) Published by TELECOMMUNICATIONS INDUSTRY ASSOCIATION Standards and Technology Department 2500 Wilson Boulevard Arlington, VA 22201 U.S.A. PR
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21、S. Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 23:42:28 MDTNo reproduction or networking permitted without license from IHS -,-,- TIA-141 i TSB-141 Polarization Dependent Loss:
22、 Measurement and Application Issues in Telecommunications Contents 1. Introduction . 1 1.1 Purpose . 1 1.2 What is Polarization Dependent Loss? . 1 1.3 Where is PDL Typically Found? . 2 1.4 Visualizing the Polarization of Light and PDL . 2 2. PDL Measurement Methods . 4 2.1 Categories . 4 2.2 All-St
23、ates Techniques . 4 2.2.1 Deterministic All-States Method 4 2.2.2 Pseudo-random All-States Method . 6 2.3 Fixed-States Techniques . 7 2.3.1 Mueller-Matrix Method . 7 2.3.2 Jones-Matrix Method . 9 3. Important Issues . 11 3.1 Source Stability 11 3.2 Wavelength Dependence and Bandwidth . 11 3.3 Multip
24、le Reflection . 11 3.4 Measurements in Reflection . 11 3.5 Fixed-States Measurement Issues . 12 3.6 Optical Instrumentation and Metrology Topics in TIA . 13 4. Bibliography . 14 Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001,
25、 User=Wing, Bernie Not for Resale, 03/29/2007 23:42:28 MDTNo reproduction or networking permitted without license from IHS -,-,- TIA-141 ii This Page is Blank Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie
26、Not for Resale, 03/29/2007 23:42:28 MDTNo reproduction or networking permitted without license from IHS -,-,- TIA-141 iii _ Foreword _ This Standard was formulated under the cognizance of TIA Subcommittee FO-4.5. Key words: polarization dependent loss, PDL, single-mode fiber, SMF. Copyright Telecomm
27、unications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 23:42:28 MDTNo reproduction or networking permitted without license from IHS -,-,- TIA-141 iv This Page is Blank Copyright Telecommunications Industry
28、 Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 23:42:28 MDTNo reproduction or networking permitted without license from IHS -,-,- TSB-141 1 TSB-141 Polarization Dependent Loss: Measurement and Application Issues in T
29、elecommunications _ 1. Introduction _ 1.1 Purpose The purpose of this bulletin is to provide a brief introduction to measurement issues associated with polarization dependent loss in telecommunications systems. This bulletin is intended for both users and designers of telecommunications networks. Th
30、is version of the document is prepared on behalf of the TIA Subcommittee FO4.5, Fiber Optic Metrology. 1.2 What is Polarization Dependent Loss? With regard to polarization dependence, optical networks are generally based on four fundamental elements: a source laser that produces coherent, polarized
31、light; single-mode optical fiber (SMF); interconnecting components that preferentially pass and/or amplify certain signal polarizations; and a photodetector whose response depends, to some extent, on that polarization. The polarization of the source light is the key to understanding the problems tha
32、t arise from it. A high-degree of polarization implies a definite direction and phase relationship between the principal electric fields of a propagating wave, which is maintained over large distances by telecommunications grade SMF. By contrast, polarization effects are generally insignificant in m
33、ost multimode networks using broadband sources such as light-emitting diodes, as the phase relationship is not maintained over distances of more than a few decameters. Though SMF has no preferred axis that maintains a given launched state of polarization, phase maintenance allows the existence of ar
34、bitrary states. Consequently, the state is allowed to “wander“ and take on different values because of the effect of birefringence. Birefringence in SMF derives from the uneven distribution of refractive index in deployed cable induced by core non-circularity, stresses and bends. Polarization depend
35、ent loss (PDL) is the variation of transmitted power in SMF networks as the state of signal polarization takes on all values. PDL is defined as the peak-to-peak difference in transmission loss across all states of polarization. PDL can be determined as the ratio of maximum and minimum transmission a
36、s Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 23:42:28 MDTNo reproduction or networking permitted without license from IHS -,-,- TSB-141 2 10log(Tmax/Tmin) (dB) where T is the
37、optical transmittance (or power) taken over the entire polarization-state space. The impact of PDL on network performance is increased signal distortion, signal fading, and consequently, higher bit-error-rate (BER) because PDL elements in a network typically combine and cancel in a random way. 1.3 W
38、here is PDL Typically Found? Because PDL is generally negligible in optical fiber, it is primarily associated with localized interconnecting components and is due to several factors. These include: media-media interfaces such as glass-air angled with respect to incident power, oblique incidence refl
39、ections inside components, offset fiber cores at both connector and fusion junctions, fiber bending, and dichroic media within components. Table 1 provides representative PDL values as seen in network elements. PDL is usually characterized as a localized component effect as opposed to the distribute
40、d nature of polarization mode dispersion (PMD). Multiple PDL sources add as vectors due to the random coupling in SMF and interact with PMD in nonlinear ways to dramatically increase system BER (as discussed in Reference 3, Gisin and Huttner, Section 4). Complex components can have multiple sources
41、of PDL within them, but if they are fixed in space and minimal fiber between them, the aggregate acts as a single PDL element. Table 1. Commonly observed PDL values in components. This list is not exhaustive and values vary widely. Component PDL (dB) Notes Optical connector 0.005 - 0.02 Normal conta
42、ct “ 0.02 - 0.06 Angled contact (poorly aligned?) 50/50 “3 dB“ coupler 0.1 0.2 Single wavelength type “ 0.15 0.3 1300/1500 nm type 90/10 “10 dB“ coupler 0.02 Through path “ 0.1 -10 dB path Faraday isolator 0.05 0.3 Three port circulator 0.1 0.2 Any output port WDM (multiplexer) 0.05 0.1 Any output p
43、ort Table 1: Commonly observed PDL values in components. This list is not exhaustive and values vary widely. 1.4 Visualizing the Polarization of Light and PDL Though a further discussion of optical polarization is beyond the scope of this bulletin, the best way to visualize it is through a useful ai
44、d known as a Poincar sphere, cf. Figure 1. The Poincar sphere maps all states of fully polarized light to the surface of a sphere wherein the north and south “poles“ are mapped to right- hand circular (RCP) and left-hand circular polarization (LCP) states respectively. Copyright Telecommunications I
45、ndustry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 23:42:28 MDTNo reproduction or networking permitted without license from IHS -,-,- TSB-141 3 Similarly, the “equator“ is mapped to linear polarizations rotated th
46、rough 360. Refer to Reference 1 (Collett, Section 4) for more detail. We use the Poincar sphere to illustrate the differences between the various measurement methods. Figure 1. The Poincar sphere illustrated with key states and the progression of elliptical states. The effect of PDL can be illustrated with the example of a “random walk“ over the Poincar surface and the subsequent effect on signal amplitude through a device- under-test (DUT) as in Figure 2. In devices