Effect Of Polarization-dependent Loss Research Articles

Orthogonal vector based transmission method for security enhancement and PDL elimination in dual-polarized wireless communications

In this paper, we propose an orthogonal vector based transmission method to enhance the transmission security and eliminate the polarization dependent loss (PDL) effect in wireless communications. In the proposed method, the information is modulated into symbols with polarization state modulation technique. Then, two polarization signal vectors are reshaped into two matrices and each column of them is multiplied by an unique vector selected from an orthogonal matrix, which results into several matrices. After that, for each polarization, all matrices are added up into a mixed matrix and then, reshaped into a vector for transmission. To enhance the transmission security, the weighted fractional Fourier transform (WFRFT) technique is designed to process the mixed matrices before reshaping into vectors. For legitimate users, the received signals could be reshaped into matrices with right size and the inverse-WFRFT is operated to the matrices with right WFRFT orders. Moreover, the same orthogonal vectors are used to process the signal matrix in the right sequence to recover original signals. As orthogonal vectors are different for two polarizations, there is no mutual interferences in two recovered polarization signals, thus, the PDL effect is naturally eliminated. In addition, the signals are also difficult to crack. Finally, simulation results demonstrate the superior performance of the proposed method in enhancing the transmission security and eliminating the PDL effect.

Compensation of polarization-dependent loss using noiseless amplification and attenuation

Polarization dependent loss (PDL) is a serious problem that hinders the transfer of polarization qubits through quantum networks. Recently it has been shown that the detrimental effects of PDL on qubit fidelity can be compensated for with the introduction of an additional passive PDL element that rebalances the polarization modes of the transmitted qubit. This procedure works extremely well when the output of the system is postselected on photon detection. However, in cases where the qubit might be needed for further analysis this procedure introduces unwanted vacuum terms into the state. Here we present procedures for the compensation of the effects of PDL using noiseless amplification and attenuation. Each of these techniques introduces a heralding signal into the correction procedure that significantly reduces the vacuum terms in the final state. When detector inefficiency and dark counts are included in the analysis noiseless amplification remains superior, in terms of the fidelity of the final state, to both noiseless attenuation and passive PDL compensation for detector efficiencies greater than 40%.

Effect of Polarization Dependent Loss on the Quality of Transmitted Polarization Entanglement

Quantum networking brings together several diverse research areas, such as fiber-optic communication, quantum optics, and quantum information, to achieve capabilities in security, secret sharing, and authentication which are unavailable classically. The development of practical fiber-based quantum networks requires an understanding of the reach, rates, and quality of the entanglement of distributed quantum states. Here, we present a theoretical model describing how the magnitude and orientation of polarization dependent loss (PDL), a common impairment in fiber-optic networks, affects the entanglement quality of distributed quantum states. Furthermore, we theoretically characterize how PDL in one fiber channel can be optimally applied in order to nonlocally compensate for the PDL present in another channel. We present experimental results that verify our theoretical model.

Erbium-doped fiber ring laser with wavelength selective filter based on non-linear photonic crystal fiber Mach–Zehnder interferometer

A high output power, stable wavelength spacing and switchable multi-wavelength erbium-doped fiber laser has been demonstrated experimentally using a combination of non-linear photonic crystal fiber Mach–Zehnder (MZI) interferometer with polarization dependent loss effect. This MZI functions together with a polarization controller (PC) as a wave selecting filter (WSF). Adjusting the PC within the WSF part gives rise to three emissions as single, dual and triple wavelengths. Multi-wavelength laser with maximum spacing of 1.6 nm was achieved by controlling the polarization state in a ring cavity. Such stable wavelength spacing aroused interest in wavelength-division-multiplexer systems. Output power around −3 dB at 1550 nm wavelength, with small power fluctuation for each line, was recorded at room temperature. The measured 3-dB laser line-width was 0.03 nm, with a high side-mode suppression ratio of 48 dB.

Performance of Poly-Polarization Multiplexing in Narrow-Band Wireless Communication Aided by Pre-Compensation and Multi-Notch OPPFs

In this letter, a poly-polarization multiplexing system applying orthogonal dual polarized antennas is designed to enhance the spectrum efficiency for narrow-band wireless communication. In order to minimize the co-channel interference, we apply the multi-notch oblique projection polarization filters (OPPFs) to separate parallel streams at the same frequency at the receiver. Due to the polarization dependent loss effects of the narrow-band polarized channel, the pre-compensation method is proposed to mitigate the impairment of the signal-to-interference ratio in OPPFs. Whereas, the signal-to-noise of polarized channel would decrease after pre-compensation. Therefore, the optimal pre-compensation coefficient is calculated to obtain maximum capacity of the multiplexing system by signal to interference plus noise ratio. Simulation results demonstrate the performance of our design.

Combined Constellation Rotation With Weighted FRFT for Secure Transmission in Polarization Modulation Based Dual-Polarized Satellite Communications

In this paper, a novel transmission scheme based on constellation rotation and weighted fractional Fourier transform (WFRFT) is proposed to enhance the physical-layer security in polarization modulation (PM)-based dual-polarized satellite communications. Typically, by appropriately selecting the WFRFT order, the distribution of the signals processed by WFRFT can be close to Gaussian, which makes them difficult to be detected by eavesdroppers. However, once the signals are captured, it is possible for eavesdroppers to recover the information through the WFRFT order scanning method. To overcome this problem, in the proposed scheme, the constellation points are randomly rotated before the WFRFT operation, making it almost impossible to crack the WFRFT order. In this manner, the constellations are distorted, which is difficult for the eavesdropper to demodulate the signals accurately. Furthermore, a robust nonzero secrecy capacity is guaranteed. In addition, the impairment to the PM from the polarization-dependent loss effect is discussed, and a zero-forcing prefilter is applied at the receiver side to mitigate this adverse effect. Finally, the security performance of the proposed scheme is evaluated in terms of the average secrecy capacity and symbol error rate by numerical simulations in dual-polarized satellite communications.

Polarization Filtering Based Physical-Layer Secure Transmission Scheme for Dual-Polarized Satellite Communication

In this paper, we propose a polarization filtering-based transmission scheme to enhance the physical layer security in the dual-polarized satellite communication. To prevent eavesdropping, this paper first divides the information sequence into two parts and modulates them independently. Subsequently, a pair of dual polarization states (PSs) is selected to carry the two modulated signals based on the designed selection rule. Last but not least, two polarized signals are added up and transmitted by the orthogonally dual-polarized antenna. Based on the assumption that the selection rule of the dual polarization states is synchronous among the legitimate users, the legitimate users can separate the two polarized signals by polarization filtering (PF). After that, the polarization match is performed to the two polarized signals, respectively. Then according to the demodulation rule, the information can be recovered. However, the eavesdropper does not know the PS selection rule and could not separate the two signals. Therefore, it is impossible for the eavesdropper to recover any useful information so that the security can be enhanced. In addition, the PSs of the signals will be changed due to the polarization dependent loss effect of the satellite channel, which leads to the PF performance degradation. To tackle this problem, a zero-forcing pre-filter is utilized at the receiver side. Finally, the security performance is validated by the theoretical analysis and simulation results in the dual-polarized satellite systems.

A Power Amplifier Energy Efficient Polarization Modulation Scheme Based on the Optimal Pre-Compensation

To improve Power Amplifier (PA) energy efficiency, a Polarization Modulation (PM) scheme in wireless communication is proposed. The proposed scheme uses polarization state as the information-bearing parameter and can let the PA work in its nonlinear region without suffering distortion. Furthermore, to mitigate the impairment to the PM from the polarization dependent loss effect of the wireless channel, an optimal pre-compensation algorithm is also presented. Simulations under the same symbol error rate show the PM can improve the PA energy efficiency by 25% at most compared with the phase shifting keying.

Impact of nonlinear and polarization effects in coherent systems

Coherent detection with digital signal processing (DSP) significantly changes the ways impairments are managed in optical communication systems. In this paper, we review the recent advances in understanding the impact of fiber nonlinearities, polarization-mode dispersion (PMD), and polarization-dependent loss (PDL) in coherent optical communication systems. We first discuss nonlinear transmission performance of three coherent optical communication systems, homogeneous polarization-division-multiplexed (PDM) quadrature-phase-shift-keying (QPSK), hybrid PDM-QPSK and on/off keying (OOK), and PDM 16-ary quadrature-amplitude modulation (QAM) systems. We show that while the dominant nonlinear effects in coherent optical communication systems without optical dispersion compensators (ODCs) are intra-channel nonlinearities, the dominant nonlinear effects in dispersion-managed (DM) systems with inline dispersion compensation fiber (DCF) are different when different modulation formats are used. In DM coherent optical communication systems using modulation formats of constant amplitude, the dominant nonlinear effect is nonlinear polarization scattering induced by cross-polarization modulation (XPolM), whereas when modulation formats of non-constant amplitude are used, the impact of inter-channel cross-phase modulation (XPM) is much larger than XPolM. We then describe the effects of PMD and PDL in coherent systems. We show that although in principle PMD can be completely compensated in a coherent optical receiver, a real coherent receiver has limited tolerance to PMD due to hardware limitations. Two PDL models used to evaluate PDL impairments are discussed. We find that a simple lumped model significantly over-estimates PDL impairments and show that a distributed model has to be used in order to accurately evaluate PDL impairments. Finally, we apply system outage considerations to coherent systems, taking into account the statistics of polarization effects in fiber.

Limitation Imposed by Polarization-Dependent Loss on a Fiber Optic Communication System

Analytically the effect of polarization dependent loss on a high speed fiber optic communication link has been investigated. significant co-relation between them and their various combinations produces different effects on the system behavior which has been together to observe the attenuation effect induced by PDL in a link containing multiple PDL elements. It is found that in the presence of PDL the Q-factor and BER at the receiver undergoes fluctuation causing the system to be unstable and results show that it is mainly due to optical signal-to-parallel-noise ratio (OSNRpar) that these parameters fluctuate. Generally the Q-factor, BER deteriorates as the value of average PDL in the link increases except for depolarized light for which the system parameters improves when PDL increases.

Polarization division multiplexing system quality in the presence of polarization effects

In this paper the Polarization Division Multiplexing system testing method is presented. Presented method is based on simultaneous Polarization Mode Dispersion and Polarization Dependent Loss effects generation. These effects are generated by means of only one device that simulates the statistical nature of polarization effects of a real optical fiber link. The Polarization Division Multiplexing system is investigated by means of Polarization Mode Dispersion/Polarization Dependent Loss emulator.

Capacity limitations in fiber-optic communication systems as a result of polarization-dependent loss

We characterize the effect of polarization dependent loss (PDL) on the information capacity of fiber-optic channels. The reduction in the outage capacity owing to the PDL is quantified as well as the signal-to-noise ratio margin that needs to be allocated for the PDL in order to avoid loss of capacity.

PMD and PDL impairments in polarization division multiplexing signals with direct detection

We investigate polarization mode dispersion (PMD) and polarization dependent loss (PDL) impairments in polarization division multiplexing (PDM) signals with optical polarization demultiplexing and direct detection. We find that the time alignment between the bits in the two polarizations has a significant impact on the PMD impairments, and PMD impairments also depend on the bandwidth of PDM signals, whereas PDL impairments have little dependence on the relative time alignment between the two polarizations and the signal bandwidth. We show that with a proper configuration of the polarization demultiplexing, the PDL-induced crosstalk between the two polarizations can be completely eliminated. The combined effects of PMD and PDL are also studied, and we find that, in the presence of concatenated PMD and PDL, the impairment from one effect does not enhance that from the other.

Polarization mode dispersion measurement based on continuous polarization modulation

A novel technique is proposed for measurement of the group delay (GD) and the differential group delay (DGD) of optical material, components, and fiber. This new method is based on continuous polarization modulation of the stimulus optical field as opposed to sequential polarization state switching used in the traditional phase shift method. A new complete derivation of the phase shift method, based on the modified Jones calculus of elementary matrices, is presented. The derivation reveals that the phase shift measurement actually depends on all eight elementary parameters that represent DGD and optical frequency derivatives of polarization-dependent loss (PDL). Thus, the new expression for the phase shift includes the combined effect of PDL and DGD. The proposed method is evaluated by measuring a section of polarization-maintaining fiber and a 50 km length of single-mode fiber over a wavelength range from 1530 to 1610 nm. Measurements of DGD in a long single-mode fiber are shown to be highly insensitive to environmentally induced GD drift.

The effects of PMD and PDL on the performance of OOK and DPSK systems

Using multiple importance sampling (MIS) technique, the optical communication system performance affected by polarization-mode dispersion (PMD) and polarization-dependent loss (PDL) is simulated numerically. The power penalties and system outage probabilities are obtained for optical communication systems with on-off keying (OOK) or differential phase shift keying (DPSK) modulation. The simulation results show that DPSK always performs better than OOK. When the system has moderate PDL (about 1.5 dB), it is necessary to compensate effectively the fiber PMD in order to enhance the system tolerance to the PMD and PDL. However, the efficiency of PMD compensation will degrade rapidly when the PMD of the whole optical link drops into the low value.

Impact of dispersion, PMD, and PDL on the performance of spectrum-sliced incoherent light sources using gain-saturated semiconductor optical amplifiers

The effects of chromatic dispersion (CD), polarization-mode dispersion (PMD), and polarization-dependent loss (PDL) on the intensity noise suppression of spectrum-sliced incoherent light sources achieved by using gain-saturated (GS) semiconductor optical amplifiers (SOAs) are investigated. Passing the spectrum-sliced incoherent light through SOAs, the excess intensity noise (EIN) originating from beating of spontaneous emission against itself can be greatly reduced. However, since the noise suppression is achieved by an elaborate balancing between numerous frequency/polarization components of light, thus, forming a high correlation between them, it is vulnerable to frequency/polarization-dependent optical phenomena. Through Q-factor and bit error rate (BER) measurements, this paper shows that CD, PMD, or PDL deteriorates the SOA-based noise suppression technique by breaking the correlation. Spectral analysis is also performed to investigate the frequency dependency of these effects. It is shown that CD and PMD negate the noise suppression giving rise to intensity noise from high frequencies, whereas there is no frequency dependence for PDL effects. Therefore, CD-, PMD-, or PDL-induced penalties for incoherent light sources using the SOA-based noise suppression technique are considerably greater than those produced by pulse broadening or distortion alone.

Effect of polarization-dependent loss on optical signal-to-noise ratio monitoring technique based on polarization-nulling method

We analyzed the probability of errors in the measured optical signal-to-noise ratio (OSNR) by using the polarization-nulling method, when the amplified spontaneous emission noise (ASE) is partially polarized due to the polarization-dependent loss (PDL) in the transmission link.

Polarization-dependent loss as a waveform-distorting mechanism and its effect on fiber-optic systems

This paper presents a study on the effect of polarization-dependent loss (PDL) as a waveform-distorting mechanism in the presence of polarization-mode dispersion (PMD) and assesses its significance in fiber-optic communications links. A simple model is introduced that illustrates the joint effect of PDL and PMD on the transmitted waveforms within the first-order approximation in the transmitted bandwidth, and the nature of possible distortions is discussed. This paper analyzes the statistics of the PMD and PDL vectors and derives explicit formulas for their mean-square magnitudes. These formulas are used to show that, in systems with realistic parameters, the waveform-distorting effects of PDL are of very limited significance.

PDL Effects in PMD Emulators Made Out With HiBi Fibers: Building PMD/PDL Emulators

Nonnegligible polarization-dependent loss (PDL) arises when HiBi fiber-based polarization-mode dispersion (PMD) emulators are spooled in small diameters. PMD/PDL emulators with random fluctuating PDL can be made with loops along the polarization-maintaining fiber sections. Theoretical predictions for PDL statistics agree with the experimental results.

Change in PMD due to the combined effect of PMD and PDL for a chirped Gaussian pulse

The nature of how a chirped Gaussian pulse is affected in the system with both polarization mode dispersion (PMD) and polarization-dependent loss (PDL) is analyzed. We develop a mathematical description and verify the results through numerical simulation. The delay of a chirped Gaussian pulse depends not only on the group delay characteristic of the transmission system but also on the chirp of the pulse itself. The delay also depends on the magnitude profile of the frequency response of the system. Therefore, the effective PMD for a chirped Gaussian pulse is related to both the PMD and PDL in the transmission system. The results show that the effective PMD may deteriorate when a PDL exists.