Incoherent Crosstalk Research Articles

Suppression of Crosstalk in Superconducting Qubits Using Dynamical Decoupling

Currently available superconducting quantum processors with interconnected transmon qubits are noisy and prone to various errors. The errors can be attributed to sources such as open quantum system effects and spurious inter-qubit couplings (crosstalk). The ZZ-coupling between qubits in fixed frequency transmon architectures is always present and contributes to both coherent and incoherent crosstalk errors. Its suppression is therefore a key step towards enhancing the fidelity of quantum computation using transmons. Here we propose the use of dynamical decoupling to suppress the crosstalk, and demonstrate the success of this scheme through experiments performed on several IBM quantum cloud processors. In particular, we demonstrate improvements in quantum memory as well as the performance of single-qubit and two-qubit gate operations. We perform open quantum system simulations of the multi-qubit processors and find good agreement with the experimental results. We analyze the performance of the protocol based on a simple analytical model and elucidate the importance of the qubit drive frequency in interpreting the results. In particular, we demonstrate that the XY4 dynamical decoupling sequence loses its universality if the drive frequency is not much larger than the system-bath coupling strength. Our work demonstrates that dynamical decoupling is an effective and practical way to suppress crosstalk and open system effects, thus paving the way towards higher-fidelity logic gates in transmon-based quantum computers.

Development of an OADM to reduce the incoherent crosstalk in WDM system

Performance of wavelength division multiplexing (WDM) system mostly depends on the components used in it. Optical add-drop multiplexer (OADM) is one of the most important and widely used components in WDM system used to add or drop the signals. Various types of crosstalk occurred due to the imperfections of OADM affect the WDM system performance. It is important to develop the low crosstalk or crosstalk free OADM to enhance the system performance. In this paper, we have developed an efficient OADM with low incoherent crosstalk based on coupler using isolators and Fiber Bragg Grating (FBG). We have also derived the analytical expressions for bit error rate (BER), relative intensity noise (RIN) and power penalty. It is also observed from the results that the proposed OADM has shown the better performance with lower BER and lower power penalty than the existing models while the performance of the WDM system can increase significantly.

Role of polarization-mode coupling in the crosstalk between cores of weakly-coupled multi-core fibers.

We develop a theory of crosstalk in weakly-coupled multi-core fibers that accounts for the effect of intra-core polarization-mode coupling. We show that random polarization-mode coupling plays a critical role, just like other polarization-independent effects such as fiber bending and twist, in explaining the observed incoherent crosstalk in weakly-coupled multi-core fibers.

Coherent and Incoherent Crosstalk Noise Analyses in Interchip/Intrachip Optical Interconnection Networks

Recently, interchip/intrachip optical interconnection networks have been proposed for ultrahigh-bandwidth and low-latency communications. These networks employ the microresonators (MRs) to modulate, direct, or detect the optical signal. However, utilized MRs suffer from intrinsic crosstalk noise and signal power loss, degrading the network efficiency via the signal-to-noise ratio (SNR). The amount of crosstalk noise and signal power loss may differ from network to network. Hence, there exists a need to systematically analyze the effect of the crosstalk noise and the power loss issues. In this paper, we have developed the analytical models considering both coherent and incoherent crosstalk for both the interchip and intrachip optical networks. The interchip/intrachip optical interconnection networks—the $\text{I}^{2}$ CON—are analyzed as a case study. The quantitative results on the individual networks have demonstrated that the architectural design determines the impact of crosstalk on the SNR. We have also demonstrated that the optical interconnection networks with interchip/intrachip interconnects result in better bit error rate (BER) compared with that of only intrachip interconnect. Our analyses of the worst case can be utilized as a platform to compare the realistic performance among different optical interconnection networks via the degradation of SNR/BER and data bandwidth.

Effects of Upstream Incoherent Crosstalk Caused by ASE Noise from Tx-Disabled ONUs in XG-PONs and TWDM-PONs

A large incoherent crosstalk (IC) caused by amplified spontaneous emission (ASE) noise power from Tx-disabled optical network units and a differential path loss has been shown to degrade upstream transmission performance in time-division multiplexing passive optical networks. This paper considers the IC-induced power penalty of an upstream signal both in an XG-PON and in a TWDM-PON. We investigate the degradation of the extinction ratio and relative intensity noise through a simulation and experiments. For the XG-PON case, we observe a 9.6 dB difference in the level of ASE noise power from Tx-disabled ONUs (hereafter known simply as ASE noise) between our result and the ITU-T XG-PON PMD recommendation. We propose an optical filtering method to mitigate an IC-induced power penalty. In the TWDM-PON case, the IC-induced power penalty is naturally negligible because the ASE noise is filtered by a wavelength multiplexer at the optical line terminal. The results provide design guidelines for the level of ASE noise in both XG-PONs and TWDM-PONs.

Performance Assessment of Single Stage and Multi-Stage L-WIXCs Considering Coherent and Incoherent Crosstalk

The statistical impact of Coherent and Incoherent Crosstalk Contributions on the performance of a proposed single stage and a multi-stage Share-per- Node L − WIXC configuration and a multi-stage Share-per-Wavelength L − WIXC configuration in terms of different Optical Propagation Delay Differences, Bit Duration etc., is compared both theoretically and analytically. Besides, considering Coherent and Incoherent Crosstalk contributions for each of those cases, analytical expressions of Electric Field, Leakage Crosstalk, Bit-Error-Rate (BER) and Power Penalty (pp) are being developed. Finally, the results obtained numerically, are thoroughly compared on the basis of Optimum Number of Wavelength Converters, Number of Inputs and Number of Wavelengths per Input Channel.

Evaluate the Performance of Optical Cross Connect Based on Fiber Bragg Grating Under Different Bit Rate

ABSTRACT In wavelength division multiplexed (WDM) optical networks, intraband and/or interband crosstalk plays a major role in limiting practical implementation of an OXC subsystem. Again FIBER BRAGG GRATINGS (FBGs), due to their properties, are emerging as very important elements for both the optical fiber communication and sensing fields. The crosstalk sources are related to the different individual components of the OXC’s. In this paper, an analytical model is established to evaluate the performance of an FBG-OC-based optical cross connect and proposed a novel scheme of transmission Fiber Bragg Grating for different wavelength separation and determine the BER and power penalty with optical wavelength division multiplexed cross-connect topologies at different bit rate. K EYWORDS Wavelength Division Multiplexing (WDM), Optical Cross Connect (OXC), Fiber Bragg Grating (FBG), Optical Circulator (OC). 1. I NTRODUCTION OPTICAL wavelength division multiplexing (WDM) networks are very promising due to their large bandwidth, their large flexibility and the possibility to upgrade the existing optical fiber networks to WDM networks [1-6]. WDM has already been introduced in commercial systems. Crosstalk analyses of OXCs presented so far are generally focused on conventional OXCs [7, 8]. All-optical cross connects (OXC), however, have not yet been used for the routing of the signals in any of these commercial systems. Several OXC topologies have been presented in the literature, but their use has so far been limited to field trials, usually with a small number of input–output fibers and/or wavelength channels. The fact, that in practical systems many signals and wavelength channels could influence each other and cause significant crosstalk in the optical cross connect, has probably prevented the use of OXC’s in commercial systems. The crosstalk levels in OXC configurations presented so far are generally so high that they give rise to a significant signal degradation and to an increased bit error probability. Because of the complexity of an OXC, different sources of crosstalk exist, which makes it difficult to optimize the component parameters for minimum total crosstalk. The crosstalk sources are related to the different individual components of the OXC’s. The crosstalk levels of the four topologies are compared in function of the number of cascaded OXC’s [9]. For evaluation of intra-band crosstalk in an FBG-OC-Based optical cross connect an analytical model is established to evaluate intra-band crosstalk performance and a novel scheme with improved intra-band crosstalk performance [10-11]. Incoherent crosstalk is defined as the case in which the beat term can be neglected (e.g., when the wavelengths are different). The case in which the beat term cannot be neglected is called coherent crosstalk. This crosstalk occurs in a WDM network

Theoretical Insights Into the Impact of Coherent and Incoherent Crosstalk on Optical DPSK Signals

This paper provides new theoretical insights into the properties of direct detection differential phase-shift keying (DPSK) signals impaired by coherent and incoherent crosstalk. Coherent crosstalk is due to multiple replicas originated while a data signal is routed through an optical network, whereas the source of incoherent crosstalk resides on the interference from other DPSK signals. A special emphasize has been put on modeling the multipath coherent crosstalk, with analytical expressions being derived and presented for both the moment generating function of the decision variable and the average error probability. A rigorous analysis, capable of dealing with arbitrary filtering, is also presented, which is used afterwards to assess the accuracy of the analytical formulas. A detailed comparison with incoherent crosstalk is also performed. Using also an exact treatment for this type of crosstalk it is shown that for low OSNR penalties the coherent crosstalk leads, in some circumstances, to slightly worse results than the incoherent one, but this situation is reversed when the total crosstalk level and the number of interferers increase.

A Contribution to Study the Effect of Multipath Coherent Crosstalk Due to Optical Network Nodes on DPSK Signals

Multipath coherent crosstalk, due to multiple replicas of the main signal in optical networks, is examined in terms of the potential impact on the performance of optical differential phase-shift keying signals. Analytical expressions are derived and presented for both the moment generating function of the decision variable and the average error probability. A detailed comparison with incoherent crosstalk is also performed. Using symbol-conditioned analysis for this crosstalk, it is shown that for low optical signal-to-noise ratio penalties, the coherent crosstalk is more damaging than the incoherent one.

Analysis and Development of Fixed and Variable Waveband MUX/DEMUX Utilizing AWG Routing Functions

We develop and analyze a new waveband multi/demultiplexer that exploits the routing functions of arrayed-waveguide gratings (AWG). The device can accommodate multiple input/output fibers simultaneously and be implemented monolithically using silica planar lightwave circuit (PLC) technology. We analyze AWG port usage for variants of the proposed multi/demultiplexers. The important characteristic of the device, its coherent and incoherent crosstalk performance is investigated. A technique to reduce the crosstalk is presented. We extend the capability of the device so that the waveband bandwidth can be changed by adding small switches. Experiments confirm the excellent performance of the proposed waveband multi/demultiplexer.

Analytical Analysis of Limited Power Penalty on Optical Cross Add and Drop Multiplexer (OXADM) – with OXC Comparison

This paper highlights the limited power penalty condition of OXADM that effect the number of maximum nodes that can be cascaded in optical network. If the limited power penalty condition is violated, the power penalty will become infinity. The condition for limited power penalty for OXADM occur when incoherent crosstalk multiply with the number of maximum nodes; (MN-1)L. Therefore the value must be less than 174, otherwise it will become infinity. It was found that as the number of ports and number of carriers increase, the number of maximum nodes decrease. When compared with conventional OXC device, it was found that the number of maximum nodes for OXC is larger than OXADM. This is due to large power penalty in OXADM. In addition, the accumulation function in OXADM reduces the scalability of this device. The objective of this paper is to study the limited power penalty condition of OXADM in order to avoid infinity. In addition, according to the limited power penalty con- dition, the relationship between number of maximum nodes against number of ports and number of carriers are also studied. Hence, the results are compared with conventional OXC device.

Experimental study of interband and intraband crosstalk in WDM networks

The impacts of interband and intraband crosstalk are studied and compared experimentally. Results show that interband crosstalk can be removed with narrow-band filters and has no influence on signal. Intraband crosstalk will result in signal eye diagram close and BER increasing. When the polarization states of signal and crosstalk align, intraband crosstalk seriously decreases signal quality. But when they misalign, it has little influence. Coherent and incoherent crosstalk are studied experimentally. Results show that coherent crosstalk is less harmful to system performance than incoherent crosstalk.

Incoherent in-band crosstalk induced power penalty in amplified WDM networks: a comparative study using Gaussian and chi-squared probability density functions

An analytical expression for power penalty (PP) from the formula for bit-error rate is derived by employing saddle point approximation in the chi-squared probability distribution function. This theory differs from the earlier ones in that it takes into account the dominant signal-amplified spontaneous emission beat noise applicable for optically pre-amplified systems. Imperfect extinction ratio accounting for higher power penalties is also considered in the analysis. Results have been compared with the available experimental results for a low number of crosstalk sources and an excellent agreement has been found. Although Gaussian probability density function (pdf) is simple to analyse, PP calculated from this pdf for a low number of crosstalk sources fails to match with the experimental results.

Modeling of Coherent and Incoherent Rayleigh Crosstalk in Conventional Optical Links

Performance of Rayleigh-dominated transmission is modeled using approximated and exact noise power spectral densities (PSDs) and results are compared to experimental measurements for nonreturn-to-zero, return-to-zero, and duobinary modulation formats. Both models accurately predict penalties associated with coherent Rayleigh crosstalk for all three formats with typical accuracy within 1 dB. For incoherent Rayleigh crosstalk, the numerical model using exact PSDs improves prediction accuracy by as much as 4 dB over the analytic model. The large, previously unexplained disagreement is attributed to the set of analytic approximations. Our results indicate that a rigorous description of the channel spectrum should be used when calculating impairments caused by incoherent Rayleigh crosstalk, particularly in very dense wavelength-division-multiplexed systems requiring a narrow optical filtering.

Optimization of Optical Add-Drop Multiplexers Based on Arrayed Waveguide Gratings with Fabrication Errors for Transparent Optical Networks

A transparent optical network (TON) composed by optical add-drop multiplexers based on arrayed waveguide grating (AWG) with fabrication errors is optimized for 10 Gbit/s per channel and channel spacing of 25 GHz. The optimization takes into account the effect of inter-symbol interference, amplified spontaneous emission noise accumulation, and coherent and incoherent homodyne crosstalk. Numerical results reveal that AWG fabrication errors can have a high influence on the TON performance; however, in all investigated situations, they do not affect the AWG parameters values corresponding to the optimum AWG frequency response. This surprising behavior is due to the fabrication errors affect mainly the AWG response outside the passband for the required AWG crosstalk level. It is shown that the optimum AWG frequency response is a flat-top response with a mean amplitude response outside the passband lower than −30 dB and the switch isolation should exceed 30 dB.

Wavelength-tunable dispersion-imbalanced loop mirror based on dispersion-flattened high-nonlinearity photonic crystal fiber and its application in suppression of the incoherent interferometric crosstalk

Wavelength-tunable nonlinear suppression of incoherent interferometric crosstalk has been experimentally demonstrated using the dispersion-imbalanced loop mirror based on a 64-m-long dispersion-flattened high-nonlinearity photonic crystal fiber. The signal quality improvement is achieved over a wavelength range of more than 25 nm (1545-1570 nm).

Evaluation of Transparent Optical Network Performance in Presence of Incoherent Homodyne Crosstalk

A simple method to evaluate the performance of transparent optical networks (TON) that takes into account the incoherent homodyne crosstalk, signal distortion, inter-symbol interference (ISI), amplified spontaneous emission (ASE) noise, and arbitrary optical and electrical filters is proposed. This method combines the effect of the incoherent homodyne crosstalk with an exhaustive Gaussian approximation for the influence of ASE noise, signal distortion, and ISI. It is shown that the incoherent homodyne crosstalk penalty depends on the ASE noise accumulated in the TON, ISI, and extinction ratio. The proposed method estimates are compared with experimental results published by other authors. Good agreement is observed for one, two, and four incoherent homodyne crosstalk signals, revealing that the proposed method provides accurate estimates even when the methods based on a Gaussian approximation for the incoherent homodyne crosstalk fail. The proposed method is used to assess the performance of a TON composed by optical add-drop multiplexers based on arrayed waveguide gratings. Results reveal that incoherent homodyne crosstalk, ASE noise, and ISI impair the TON performance and, therefore, none can be neglected in the TON design.

Calculation of bit-error rates and power penalties due to incoherent crosstalk in optical networks using Taylor series expansions

A new calculation method is presented for bit-error rates and power penalties due to incoherent crosstalk from up to eight interferers of different powers, based on a truncated Taylor series approximation of the crosstalk contribution to the noise probability density function. Formulae are provided for bit-error rates and power penalties in both thermal and ASE limited systems, with average-power and optimized decision thresholds, and include extinction ratio effects. The technique forms an excellent complement to the Gaussian approximation.

FBG-Based Bidirectional Optical Cross Connects for Bidirectional WDM Ring Networks

This paper proposes a new bidirectional optical cross connect (BOXC) using fiber Bragg gratings (FBGs) and optical circulators for bidirectional wavelength-division-multiplexing ring networks. Dynamic and independent wavelength routing is achieved by employing cascaded tunable FBGs. The proposed BOXC requires a small tuning range equal to wavelength channel spacing for tunable FBGs. Therefore, the wavelength count of the proposed BOXC could be increased easily without imposing constraint on the tuning range of FBGs. Coherent and incoherent crosstalk arising in the proposed BOXC and their impact on the power penalty are studied in detail. The Monte Carlo simulation is used to characterize the probability distribution of the power penalty due to both coherent and incoherent crosstalk under various conditions. The specification requirements are then obtained for the FBGs used in BOXC nodes with a different number of wavelengths. The study in this paper reveals that the requirement for the isolation of FBGs is more stringent than that for the reflectivity of FBGs at the Bragg wavelength. It is also shown that a large BOXC can be built based on the Benes network structure, and a method to reduce the complexity is also presented.

Noise Analysis of Photonic Packet Synchronizer

This paper investigates and analyzes the in-band crosstalk generated in the photonic packet synchronizer that consists of a sequence of optical fiber delay lines and 2 /spl times/ 2 optical switches. This paper shows that the second-order in-band crosstalk is dominant and its contribution is proportional to the square of the number of delay lines. It is found that coherent, partially coherent, and incoherent in-band crosstalk may coexist at the output of the synchronizer, causing the power penalty to vary with the delay time of the main signal. A close-form formula is derived for the mean and variance of the beating noise between the main signal and a crosstalk element. The power penalty caused by the in-band crosstalk is further numerically studied and a guideline for the requirement of the optical switches used in the synchronizer is provided.