Figure 1 Schematic view of the multiparameter monitoring technique, based on the polarization modulation of the optical WDM channels. Also shown in the inset of the calibration unit is the monitoring module. Those monitoring modules must be deployed at every monitoring point SIMPLIFIED APPROACH TO LOW-COST MULTIPARAMETER MONITORING BASED ON LOW FREQUENCY POLARIZATION MODULATION C. Floridia, 1 G. C. C. P. Simo ˜ es, 1 E. W. Bezerra, 1 M. M. Feres, 2 and M. A. Romero 2 1 CPqD, Rod. Campinas-Mogi Mirim, km 118.5, Campinas, SP, 13086-902, Brazil; Corresponding author: floridia@cpqd.com.br 2 Department of Electrical Engineering, University of Sa ˜ o Paulo, EESC-USP, Sa ˜ o Carlos, SP, Brazil1 Received 27 September 2011 ABSTRACT: We experimentally revisit a technique of low-cost multiparameter monitor for optical performance monitoring based on low frequency polarization modulation. A simplified calibration procedure, which significantly reduces the mathematical complexity and processing effort is proposed. Validation is achieved by carrying out relative optical power, wavelength, and differential group delay measurements. V C 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1820–1824, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26956 Key words: optical performance monitoring; polarization-mode dispersion; fiber optical communications; WDM networks 1. INTRODUCTION The need for high capacity communications has led to the devel- opment of optical communication systems of high performance. The use of dense wavelength division multiplexing (DWDM) as well as the increase in the transmission rate (10 Gb/s and beyond) are well-established technological milestones. Follow- ing those advances, optical networks are now becoming opti- cally reconfigurable, with optical paths and wavelengths dynami- cally allocated by user demand. In this context, the optical performance monitoring (OPM) [1] have been attracting great interest. In fact, OPM is essential to manage optical networks of increasing capacity and complexity. As no optical-to-electrical conversion takes place in these networks, it becomes impossible to guarantee QoS requirements without optical measurements along the transmission path. Among the parameters to be monitored, one can mention the optical signal-to-noise ratio, differential group delay (DGD) and polarization mode dispersion (PMD), optical power, and the Q factor [1], ideally measured on a channel-by-channel basis. A number of techniques have been proposed and implemented to monitor subsets of these parameters, including inband OSNR, monitored by polarization extinction [2–4], and PMD [5, 6]. Recently, a research group from Chalmers University of Technology, proposed a novel technique for multiparameter monitoring, on the basis of low frequency modulation of the polarization of the optical channels in transmission [7]. This technique enables low-cost monitor modules to be distributed in a great number of points of the optical networks, allowing fault identification and location. In this context, our particular implementation reports an improvement of the method proposed in Ref. 7, and its capacity of obtaining the equivalent of the polarization states of many channels in a DWDM system by means of an initial calibration. Specifically, we proposed and tested a simplified calibration pro- cedure, which reduces the mathematical complexity of the origi- nal technique, thereby limiting the possibility of errors and miti- gating processing effort. 2. POLARIZATION MODULATION MONITORING The multiparameter monitoring technique scheme proposed origi- nally in Ref. 7 is shown in Figure 1. Both the fundamental principles as well as the mathematical formulation are discussed in brief here, for the sake of completeness. In the technique, the optical WDM channels, each one with their own transmission rates and modulation formats, are additionally modulated in polarization, each channel with a specific frequency (f 1 , f 2 , f 3 ,…, f n ), of the order of few tens to few hundreds hertz, leaving the transmitted information unspoiled. At the desired monitoring point, the monitoring module is placed. This monitor consists of a polarizer, a detector and an A/D con- verter. Upon detection, the polarization modulation of each channel is converted into an amplitude variation and the corresponding fast 1820 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 8, August 2012 DOI 10.1002/mop