Polarization Scrambling Research Articles

Fast all-fiber polarization scrambling using re-entrant Lefèvre controller

We demonstrate a low-cost mechanical polarization scrambler capable of near 100 kHz scrambling speed using a single modified Lefèvre controller. By reusing the same controller, many sections can be implemented and the scalability promises higher scrambling rates. The design is wideband, polarization-independent and low-loss providing a degree of polarization of <5%.

Raman Crosstalk Suppression in CATV Overlay Passive Optical Network

In cable television (CATV) overlay passive optical networks (PONs), where a CATV signal copropagates with a downstream baseband signal, the crosstalk components mediated by stimulated Raman scattering (SRS) limit the performance of low-number CATV channels. In this letter, we propose and demonstrate a way of reducing the SRS-induced crosstalk in CATV overlay PONs. The proposed scheme utilizes a high-speed polarization scrambler in the transmitter to make the SRS-induced crosstalk independent of polarization evolution along the fiber and a subtractor module to compensate for the crosstalk. Our demonstration shows that crosstalk can be reduced by 9 dB

Dynamic Performance and Speed Requirement of Polarization Mode Dispersion Compensators

To study the dynamic performance of a polarizationmode-dispersion compensator (PMDC), a continuous PMD model and a dynamic PMDC model are presented. The continuous PMD model generates continuous PMD and state of polarization (SOP) variations. The statistics of the SOP variation generated by the continuous PMD model follows the Rayleigh distribution, and the SOP variation amplitude scales with the square root of sampling-time interval. The results are compared with those of a numerical and a commercial polarization scrambler, and the difference of the SOP variation characteristics between the PMD model and the polarization scramblers is explained. The continuous PMD model and the dynamic PMDC model are used to study the dynamic performance and speed requirement of a two-stage PMDC. The speed requirement of the PMDC is quantified in the SOP variation in one PMDC loop cycle. The authors found that when the SOP variation is within 3deg in one PMDC loop cycle, the dynamic PMD and SOP changes virtually does not cause any degradation in the PMDC performance

PMD Tolerance Testing of a Commercial Communication System Using a Spectral Polarimeter

A stress study methodology for polarization-mode dispersion (PMD) tolerance testing of commercial telecommunication systems is reported. By inserting additional PMD and using intralink polarization scrambling, multiple configurations of the fiber parameter space are sampled. By monitoring both the preforward-error-correction bit error rates and the spectrally resolved states of polarization or string lengths, the error rates are correlated with the PMD-induced system degradation, and it is shown that it is not correlated with power or optical signal-to-noise-ratio fluctuations. Configurations with the PMD uniformly distributed across the link and lumped at the transmitter or receiver ends are also compared

Narrow-bandwidth polarization-scrambling technique using delay-coupled binary phase pulse for carrier-distributed WDM networks

This paper proposes a novel polarization scrambler (PS) for the carrier-distributed wavelength-division multiplexing (WDM) networks based on the ring or the virtual single-star topology. In these networks, the WDM light source for an uplink transmission is located at the center node (CN) and the remote node (RN), or the optical-network unit (ONU) uses a modulator without any light sources. The PS is used to compensate the polarization dependence of the modulators. The proposed PS offers a narrow spectrum bandwidth, due to the use of delayed binary phase pulses coupled with an orthogonal polarization. The narrow bandwidth of the proposed PS is experimentally and analytically confirmed, in comparison to the conventional PS with an orthogonal phase modulation. An eye-pattern calculation for the proposed PS shows that the received eye diagram offers a sufficient margin to meet the transmitter eye-mask definition in IEEE 802.3. Its bit error rate (BER) performance shows that the received-power penalty at the BER of 10/sup -9/ is within 1 dB, even for the worst eye diagram. A transmission experiment is conducted, and the feasibility of the proposed PS is confirmed.

Experimental justification of a method for low-PMD measurements

When measuring very low differential group delay (DGD), standard techniques are affected by rather high uncertainties. This problem is usually solved by repeating many times the DGD measurements while randomly perturbing the fiber. Such an approach is founded on the basic assumption that polarization scrambling induces the DGD's decorrelation. Nevertheless, it has not been proved yet that the measured DGDs belong to an homogeneous statistical ensemble. We experimentally validate this approach by means of polarization-sensitive reflectometric measurements

Polarisation-scrambled Er-doped superfluorescent fibre source with improved mean-wavelength stability

A polarisation scrambling scheme is employed to reduce the pump-polarisation-dependent mean-wavelength change in the Er-doped superfluorescent fibre source for gyroscope application. A PZT-based fibre-optic polarisation modulation is used at the pump port for polarisation scrambling. Changes of mean wavelength owing to pump polarisation variation are suppressed below 1 ppm.

Statistical properties of the DGD in a long-haul optical fiber system with temporally drifting birefringence

Due to the temporal drift of the fiber birefringence in an optical fiber transmission system, the polarization mode dispersion (PMD) effects measured in a time window can be quite different for different time windows of the same duration. Every 10 s for 10 days, the accumulated differential group delay (DGD) was repeatedly measured at 5000 km in a 107-km recirculating loop with loop-synchronous polarization scrambling. In each DGD measurement, the polarization dispersion vector of the 107-km-long fiber was also measured. To model the measured temporal variation of the DGD, two different perturbation algorithms were used to construct random walks through the configuration space of birefringent fibers, where each fiber realization is determined by the standard coarse-step method. With these simulation models, the statistical properties of the spread of the DGD samples over a finite time period were reproduced.

System penalty owing to polarisation-mode-dispersion in presence of fast polarisation scrambling

Polarisation-mode-dispersion (PMD) induced penalty is investigated for an optical signal in a PMD medium under fast polarisation scrambling. A phenomenological model for the timing jitter penalty is proposed and is verified by computer modelling. The Q penalty from pulse distortion is complementary to the Q penalty from timing jitter.

Complete polarization controller based on magneto-optic crystals and fixed quarter wave plates

We propose and demonstrate a polarization controller, which is a concatenation of three Faraday rotators based on magneto-optic crystals separated by two fixed quarter wave plates. Comparing with former schemes, this polarization controller is fast, accurate and stable because it is completely driven by electric signals and has no mechanically moving parts.It is simple-structured and low-cost. Moreover, it is programmable to convert an arbitrary state of polarization (SOP) from the input to any designated SOP at the output. It can also be used as a polarization scrambler. It has potential applications in the research of the polarization dependence of optical communication systems or the compensation of polarization mode dispersion (PMD), etc.

Simple PMD-insensitive OSNR monitoring scheme assisted by transmitter-side polarization scrambling

Recently, degree of polarization (DOP) of light has been utilized as a parameter to monitor optical signal-to-noise-ratio (OSNR). However, in the presence of polarization-mode dispersion (PMD), when using DOP to determine OSNR, OSNR is always underestimated due to the depolarization effect induced by PMD. In this paper, we propose and experimentally demonstrate a simple PMD-insensitive OSNR monitoring technique based on DOP measurement. By the assistance of the transmitter-side polarization scrambling, the in-service OSNR parameter can be accurately derived from the measured maximum DOP value within the polarization scrambling period, which is immune to PMD effect. The monitoring performance is experimentally evaluated by statistical method at OSNR of 25 dB. Experimental results show that OSNR monitoring with about 1-dB standard deviation can be achieved in a 10-Gb/s NRZ-OOK system with DGD varying from 0 to 80 ps.

An improved optically based PD detection system for continuous on-line monitoring of HV cables

An optically-based remote sensing technique using a laser source, polarization scrambler, standard single mode fibers, fiber polarizer, electro-optic (EO) modulator and optical receiver, for continuous on-line monitoring of partial discharges (PD) in high voltage cable joints is proposed. Both the fiber polarizer and EO modulator, which are placed near cable joints, are passive without any power requirements. An EO modulator with no electrical bias, which operates close to the half-intensity point, was used and proved to have much better light transmission performance and higher measurement sensitivity than the bias modulator approach investigated earlier. Various multiplexing techniques including optical switches and a fused fiber coupler have been investigated in order to implement multi-channel monitoring so that one laser source can be used to provide light to several fibers. The revised PD optical remote sensing technique has been applied to practical PD measurements on both 132 kV cable joint at the University of Southampton in the UK and 400 kV cable joints at Sudkabel GmbH in Germany. Obtained results have verified the principle and demonstrated the effectiveness of the developed technique.

Simultaneous monitoring of both optical signal-to-noise ratio and polarization-mode dispersion using polarization scrambling and polarization beam splitting

This paper proposes a simple method to monitor both optical signal-to-noise ratio (OSNR) and polarization-mode dispersion (PMD) simultaneously using a polarization-scrambling module followed by polarization beam splitting. OSNR and PMD are obtained from interaction terms between two orthogonal polarization arms. Monitored OSNR and PMD are independent of each other. Experimental results are demonstrated in a 10-Gb/s nonreturn-to-zero (NRZ) system with OSNR from 18 to 36 dB and PMD from 0 to 70 ps.

Analysis of clusters and uniformity of distribution of states of polarization on the Poincaré sphere

An analysis of the clusters and the uniformity of distribution of states of polarization on the surface of a Poincaré sphere generated by rotating wave plates is given. The analysis of clusters of the states of polarization is based on a spherical radial distribution function. For uniform analysis of the distribution, two methods are proposed. The first method is based on calculation of the correlation coefficient; the second method is based on calculation of the angles between pairs of the states of polarization on the Poincaré sphere. For polarization scramblers consisting of eight or more rotating wave plates, nonclustered and near-uniform distribution of states of polarization is obtained.

Demonstration of broad-band PMD mitigation in the presence of PDL through distributed fast polarization scrambling and forward-error correction

We experimentally demonstrate broad-band mitigation of polarization-mode dispersion (PMD) in the presence of polarization-dependent loss (PDL) by using distributed fast polarization scramblers in systems adopting forward-error correction. The combined penalty of PMD and PDL is smaller than the sum of the individual penalties, which shows the robustness of the PMD mitigation scheme against PDL and the enhancement of PMD tolerance improvement in the presence of PDL. The desired number of scramblers and their distribution are also discussed.

Investigation of the state of polarization distribution generated by polarization scramblers on the Poincarè sphere

A new method for characterization of the distribution of the states of polarization on the Poincarè sphere is described. Analysis of the state of polarization distribution is based on spherical radial distribution function. Estimation of the degree of the clustering and the mean diameter of clusters on the Poincarè sphere is presented.

Polarization-dependent responsivity: a study of germanium and indium gallium arsenide photodetectors

It is well known that the response of semiconductor photodetectors depends on the state of polarization of the incident light. The magnitude of this effect is quantified as the logarithm of the ratio of the maximum and minimum values of the responsivity when the detector is illuminated with completely polarized radiation of different polarization states. It will be referred to as polarization-dependent responsivity (PDR) (defined in analogy to polarization-dependent loss).A first set-up was developed to measure the average PDR of several germanium (Ge) and indium gallium arsenide (InGaAs) photodetectors between 1510 nm and 1610 nm, using a polarization scrambler. It has been observed that Ge and InGaAs photodetectors are sensitive to polarization, and that the magnitude depends on wavelength. It is shown that the PDR increases dramatically at wavelengths beyond the responsivity peak: this effect is especially strong for Ge, which has its peak near 1550 nm at room temperature, whose PDR is ⩽ 0.005 dB at 1550 nm and 23 °C, while it increases to 0.05 dB at the same wavelength when the detector is cooled to −10 °C.A second set-up was developed to measure the response of photodetectors to four main states of polarization at a grid of points on the active area with a small collimated beam, which is moved over the detector's surface using a motorized translation stage. With the power measured at each polarization state, we propose an adaptation of the Mueller matrix that allows us to obtain the first row of this matrix, so as to calculate the polarization axis vector for each point measured on the photodetector. Results lead us to suspect the existence of a polarization axis in photodetectors.

Reduction of polarization-dependent gain due to signal-to-signal Raman interaction in fiber Raman amplifier

An excellent polarization-dependent gain (PDG) suppression technique using a polarization scrambler is proposed in this letter. Investigations on PDG due to signal-to-signal Raman interaction among 40 wavelength-division-multiplexer signal channels were carried out experimentally to evaluate the system performance after incorporating a polarization scrambler in the system. It was confirmed by experiment that the use of polarization scrambler is an effective way to reduce PDG caused by signal-to-signal Raman interaction.

Combinatorial polarization scramblers for many-segment PMD emulator

In this letter, we present a combinatorial approach to build polarization scramblers in a many-segment polarization-mode dispersion (PMD) emulator. This approach significantly reduces the required number of phase plates and their corresponding controls. It exploits the fact that rotation matrices are noncommutative which gives many different ways of building polarization scramblers out of just a few phase plates. Although these polarization scramblers are correlated, we show, numerically and experimentally, that there is sufficient polarization scrambling between segments to achieve the important key properties of a PMD emulator.

Automatic PMD compensator in a 160-Gb/s OTDM transmission over deployed fiber using RZ-DPSK modulation format

We report on a magneto- and electrooptically tuned dynamic polarization-mode dispersion (PMD) compensator that enabled error-free single-channel 160-Gb/s RZ-DPSK transmission over a 75-km SMF link with a mean differential group delay (DGD) of more than 30% of the bit period. Polarization scrambling and DOP measurements were utilized to automatically adapt the compensator. We present bit error rate (BER) measurements and describe the operation of the compensator in detail.