IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 17, NO. 11, NOVEMBER 2005 2451 Scalable Polarization-Mode Dispersion Emulator With Proper First- and Second-Order Statistics Yannick Keith Lizé, Student Member, IEEE, Leigh Palmer, Student Member, IEEE, Nicolas Godbout, Member, IEEE, Suzanne Lacroix, Member, IEEE, and Raman Kashyap, Member, IEEE Abstract—We present a novel polarization-mode dispersion em- ulator design that overcomes the scalability issue limiting conven- tional concatenated-section emulators by replacing the multiple mode coupling stages with a single modified Lefèvre polarization controller (PC). We demonstrate that undesirable correlation in the sections PC transfer functions can be mitigated through proper optimization of the free design parameters. Monte Carlo simula- tions and experimental results confirm that first- and second-order statistics for rare events are accurately emulated in a compact low- cost device. Index Terms—Differential group delay (DGD), emulator optical communications, polarization controller (PC), polarization-mode dispersion (PMD). I. INTRODUCTION P OLARIZATION-MODE dispersion (PMD) poses a se- rious impediment to the deployment of long-haul optical fiber links transmitting in excess of 10 Gb/s per channel [1]. To study the effect of PMD in systems, the impairment is syn- thesized artificially using a PMD emulator. This important tool is also essential for testing mitigation strategies. To reproduce PMD with the statistical distribution of a transmission link is cost effective and has the benefit of isolating the effect of PMD which is useful for many applications. Several emulator designs have been demonstrated in the literature, typically based on concatenating a number of fixed [2]–[5] or variable [6]–[10] differential group delay (DGD) elements. The mode coupling between stages is varied to generate the different PMD states. However, higher order PMD terms require an increasing number of emulator sections for their statistics to be accurately reproduced [1]. In this letter, we demonstrate a novel scalable PMD emu- lator design which uses a single customized Lefèvre polariza- tion controller (PC) [11] to implement dynamic mode coupling. We show through simulations and experimental data that the scalability of the design allows for the first- and second-order Manuscript received April 15, 2005; revised July 12, 2005. This work was supported by the Canadian Institute for Photonic Innovations (CIPI) and Adaptif Photonics. The work of R. Kashyap was supported by the Canadian Natural Science and Engineering Research Council’s Canada Research Chairs Program. Y. K. Lizé and R. Kashyap are with the Advanced Photonics Laboratory, École Polytechnique de Montréal, University of Montréal, Montréal, QC H3T 1J4, Canada (e-mail: yannick.lize@polymtl.ca). L. Palmer is with the Australian Photonics CRC, Photonics Research Labo- ratory, University of Melbourne, Melbourne 3010, Australia. N. Godbout and S. Lacroix are with the Optical Fiber Laboratory, École Poly- technique de Montréal, University of Montréal, Montréal, QC H3T 1J4, Canada. Digital Object Identifier 10.1109/LPT.2005.857600 Fig. 1. Single PC PMD emulator. PMD statistics to exceed those realizable with conventional con- catenated-section independently scrambled emulators. Through proper selection of design parameters, the theoretical PMD sta- tistics of a transmission link are replicated well into the tail of the probability density function (pdf) where system outages are likely to occur. II. SINGLE PC PMD EMULATOR An emulator employing a finite number of elements with fixed DGD has the disadvantage that the first-order and higher order pdfs of PMD are truncated. Nevertheless, if a large number of sections can be implemented practically, the disad- vantage can be mitigated. A new scalable class of multisection PMD emulators employing correlated polarization scrambling has recently been reported [12], [13]. The single PC emulator [13], shown schematically in Fig. 1, consists of a number of lengths of highly birefringent polarization-maintaining fiber (PMF) spliced to segments of standard single-mode fibers spooled independently on the paddles of a single customized Lefèvre PC [11]. The PC paddles are motorized and rotated continuously using generic electrical motors. The design of the paddles allows for multiple independent fibers to be spooled. III. ANALYSIS First- and second-order PMD vectors can be extracted from the frequency dependence of the transmission matrix using Jones matrix eigen-analysis [14]. An emulator is then described by the matrix (1) Here, is the rotation matrix, is the axes alignment for the th section, is the transfer matrix for the PC of the th section where are the angles of each of the 1041-1135/$20.00 © 2005 IEEE