Channel Crosstalk Research Articles

Reconfigurable photonic integrated mode (de)multiplexer for SDM fiber transmission.

Spatial division multiplexing in multi-mode fibers allows to largely enhance transmission capacity compared to single-mode links. Photonic integrated circuits can provide solutions for mode multiplexing at the transmitter and demultiplexing at the receiver but have to generally face high losses and inter-modal cross-talk issues. Here a photonic circuit for efficient mode multiplexing and demultiplexing in few-mode fibers is presented and demonstrated. Two 10 Gbit/s channels at the same wavelength and polarization are simultaneously transmitted over modes LP01 and LP11a of a few-mode fiber relying only on integrated mode MUX and DEMUX. The proposed Indium-Phosphide-based circuits have a good coupling efficiency with fiber modes and mode-dependant loss smaller than 1 dB. Measured mode excitation cross-talk is as low as -20 dB and a channel cross-talk after propagation and demultiplexing of -15 dB is achieved. An operational bandwidth of the full transmission system of at least 10 nm is demonstrated. Both mode MUX and DEMUX are fully reconfigurable and allow a dynamic switch of channel routing in the transmission system. These results enable fully-integrated fiber mode handling for high-bandwidth flexible optical networks.

Junctophilin 3 expresses in pancreatic beta cells and is required for glucose-stimulated insulin secretion.

It is well accepted that junctophilin (JPHs) isoforms act as a physical bridge linking plasma membrane and endoplasmic reticulum (ER) for channel crosstalk in excitable cells. Our purpose is to investigate whether JPHs are involved in the proper communication between Ca2+ influx and subsequent Ca2+ amplification in pancreatic beta cells, thereby participating in regulating insulin secretion. The expression of JPH isoforms was examined in human and mouse pancreatic tissues, and JPH3 expression was found in both the beta cells. In mice, knockdown of Jph3 (si-Jph3) in islets decreased glucose-stimulated insulin secretion (GSIS) accompanied by mitochondrial function impairment. Si-Jph3 lowered the insulin secretory response to Ca2+ signaling in the presence of glucose, and reduced [Ca2+]c transient amplitude triggered by caffeine. Si-Jph3 also attenuated mitofusin 2 expression, thereby disturbing the spatial organization of ER–mitochondria contact in islets. These results suggest that the regulation of GSIS by the KATP channel-independent pathways is partly impaired due to decrease of JPH3 expression in mouse islets. JPH3 also binds to type 2 ryanodine receptors (RyR2) in mouse and human pancreatic tissues, which might contribute to Ca2+ release amplification in GSIS. This study demonstrates some previously unrecognized findings in pancreatic tissues: (1) JPH3 expresses in mouse and human beta cells; (2) si-Jph3 in mouse primary islets impairs GSIS in vitro; (3) impairment in GSIS in si-Jph3 islets is due to changes in RyR2-[Ca2+]c transient amplitude and ER-mitochondria contact.

K+ channel signaling in irradiated tumor cells.

K+ channels crosstalk with biochemical signaling cascades and regulate virtually all cellular processes by adjusting the intracellular K+ concentration, generating the membrane potential, mediating cell volume changes, contributing to Ca2+ signaling, and directly interacting within molecular complexes with membrane receptors and downstream effectors. Tumor cells exhibit aberrant expression and activity patterns of K+ channels. The upregulation of highly "oncogenic" K+ channels such as the Ca2+-activated IK channel may drive the neoplastic transformation, malignant progression, metastasis, or therapy resistance of tumor cells. In particular, ionizing radiation in doses used for fractionated radiotherapy in the clinic has been shown to activate K+ channels. Radiogenic K+ channel activity, in turn, contributes to the DNA damage response and promotes survival of the irradiated tumor cells. Tumor-specific overexpression of certain K+ channel types together with the fact that pharmacological K+ channel modulators are already in clinical use or well tolerated in clinical trials suggests that K+ channel targeting alone or in combination with radiotherapy might become a promising new strategy of anti-cancer therapy. The present article aims to review our current knowledge on K+ channel signaling in irradiated tumor cells. Moreover, it provides new data on molecular mechanisms of radiogenic K+ channel activation and downstream signaling events.

Expression of a Diverse Array of Ca2+-Activated K+ Channels (SK1/3, IK1, BK) that Functionally Couple to the Mechanosensitive TRPV4 Channel in the Collecting Duct System of Kidney.

The voltage- and Ca2+-activated, large conductance K+ channel (BK, maxi-K) is expressed in the collecting duct system of kidney where it underlies flow- and Ca2+-dependent K+ excretion. To determine if other Ca2+-activated K+ channels (KCa) may participate in this process, mouse kidney and the K+-secreting mouse cortical collecting duct (CCD) cell line, mCCDcl1, were assessed for TRPV4 and KCa channel expression and cross-talk. qPCR mRNA analysis and immunocytochemical staining demonstrated TRPV4 and KCa expression in mCCDcl1 cells and kidney connecting tubule (CNT) and CCD. Three subfamilies of KCa channels were revealed: the high Ca2+-binding affinity small-conductance SK channels, SK1and SK3, the intermediate conductance channel, IK1, and the low Ca2+-binding affinity, BK channel (BKα subunit). Apparent expression levels varied in CNT/CCD where analysis of CCD principal cells (PC) and intercalated cells (IC) demonstrated differential staining: SK1:PC<IC, and SK3:PC>IC, IK1:PC>IC, BKα:PC = IC, and TRPV4:PC>IC. Patch clamp analysis and fluorescence Ca2+ imaging of mCCDcl1 cells demonstrated potent TRPV4-mediated Ca2+ entry and strong functional cross-talk between TRPV4 and KCa channels. TRPV4-mediated Ca2+ influx activated each KCa channel, as evidenced by selective inhibition of KCa channels, with each active KCa channel enhancing Ca2+ entry (due to membrane hyperpolarization). Transepithelial electrical resistance (TEER) analysis of confluent mCCDcl1 cells grown on permeable supports further demonstrated this cross-talk where TRPV4 activation induce a decrease in TEER which was partially restored upon selective inhibition of each KCa channel. It is concluded that SK1/SK3 and IK1 are highly expressed along with BKα in CNT and CCD and are closely coupled to TRPV4 activation as observed in mCCDcl1 cells. The data support a model in CNT/CCD segments where strong cross talk between TRPV4-mediated Ca2+ influx and each KCa channel leads to enhance Ca2+ entry which will support activation of the low Ca2+-binding affinity BK channel to promote BK-mediated K+ secretion.

Statistical Profile of Hermite–Gaussian Beam in the Presence of Residual Spatial Jitter in FSO Communications

In this letter, the statistics of the beam profile of a free-space optical (FSO) system is studied when the optical beam possesses a Hermite–Gaussian profile and the beam is subject to random pointing jitter. In particular, it is assumed that the received signal is impaired by the residual pointing error cause by the spatial tracking loop responsible for tracking the atmospheric beam wander and platform sway. The residual pointing jitter is assumed to have a Gaussian probability density function (pdf) with independent components in the two dimensions of the detector. The mean and variance of the beam profile along with the impact of spatial error on the signal-to-noise (SNR) loss and channel cross-talk are obtained assuming that the pointing jitter has a variance that is substantially smaller than the beam waist.

Information Limited Oligonucleotide Amplification Assay for Affinity-Based, Parallel Detection Studies.

Molecular communication systems encounter similar constraints as telecommunications. In either case, channel crosstalk at the receiver end will result in information loss that statistical analysis cannot compensate. This is because in any communication channel there is a physical limit to the amount of information that can be transmitted. We present a novel and simple modified end amplification (MEA) technique to generate reduced and defined amounts of specific information in form of short fragments from an oligonucleotide source that also contains unrelated and redundant information. Our method can be a valuable tool to investigate information overflow and channel capacity in biomolecular recognition systems.

Activity-Dependent Plasticity of Spike Pauses in Cerebellar Purkinje Cells.

The plasticity of intrinsic excitability has been described in several types of neurons, but the significance of non-synaptic mechanisms in brain plasticity and learning remains elusive. Cerebellar Purkinje cells are inhibitory neurons that spontaneously fire action potentials at high frequencies and regulate activity in their target cells in the cerebellar nuclei by generating a characteristic spike burst-pause sequence upon synaptic activation. Using patch-clamp recordings from mouse Purkinje cells, we find that depolarization-triggered intrinsic plasticity enhances spike firing and shortens the duration of spike pauses. Pause plasticity is absent from mice lacking SK2-type potassium channels (SK2(-/-) mice) and in occlusion experiments using the SK channel blocker apamin, while apamin wash-in mimics pause reduction. Our findings demonstrate that spike pauses can be regulated through an activity-dependent, exclusively non-synaptic, SK2 channel-dependent mechanism and suggest that pause plasticity-by altering the Purkinje cell output-may be crucial to cerebellar information storage and learning.

Demonstration of a 280 Gbit/s free-space space-division-multiplexing communications link utilizing plane-wave spatial multiplexing.

We demonstrate a 280 Gbit/s free-space space-division-multiplexing communications link incorporating a set of independent tilted truncated plane-waves, each generated by a single mode fiber placed at the back-focal plane of a spherical lens. Each of the seven tilted plane-wave channels are encoded with a 40 Gbit/s 16-QAM signal. Our approach comprises two identical linear fiber-arrays placed approximately 5 m apart. As each fiber array is placed at the back-focal-plane of a spherical lens, each fiber array is effectively placed in a conjugate image plane of the other. A channel crosstalk of less than 26 dB is shown, with a bit-error-rate below the FEC threshold of 3.8×10(-3).

Reconfigurable optical add-drop multiplexer based on thermally tunable micro-ring resonators

We report on an eight-channel reconfigurable optical add-drop multiplexer (ROADM) based on micro-ring resonators (MRRs). The effective footprint of the device is about 1000×760μm2. The free spectral range (FSR) is about 18nm. The adjacent channel crosstalk ranges from −19.02dB to −8.29dB. With the help of the multi-wire structure heaters, compact footprint and high tuning efficiency are achieved simultaneously. Therefore, the minimum average tuning efficiency is 2.723mW/nm.

Analysis of channel crosstalk in muliti-spectrum visible light communication system

In visible light communication, the wavelength division mutiplexing (WDM) technology can improve system data rate by increasing the number of channels. However, because the emission spectrum of the light emitting diode (LED) has a certain width, a phenomenon of spectral overlapping will occur when the number of channels increases and channel-spacing decreases, which results in channel crosstalk although optical filters are adopted. The channel crosstalk will restrict the capacity of WDM-VLC (visible light communication) system, which has great research significance. In this paper, the channel crosstalk based on LED spectra overapping is disscussed. The LED emission spectrum is modeled by combining the physical mechanism of LED emission with real shape of LED spectrum. According to the literature, the LED shape can be fitted greatly by Gauss function, and the full-width at half-maximum E is in a range from about 4.3kBTj to 6.8kBTj when the peak wavelengths of InGaN and AlInGaN LEDs are both less than 560 nm, E values range from 2.1kBTj to 3.3kBTj when the peak wavelength of InAlGaP LED is larger than 560 nm. In order to reduce the overall system complexity we use the following values: when the peak wavelength is less than 560 nm, E = 5.5kBTj; when the peak wavelength is larger than 560 nm, E = 3.0kBTj. Then, according to the overlapping spectra and VLC channel with considering optical filter transmittance and detector spectral response, the channel crosstalk formula is derived. Some quantities are given before simulation such as the semi-angle at half illuminance of an LED is 60; all LEDs are so closely arranged together to mix light in free space that spacing between LEDs can be ignored with respect to the propagating distance; the strongest signal situation is considered. The simulation result shows that although at the same channel spacing, different channels have different crosstalks because spectra are different. And the crosstalk from one adjacent channel will not exceed -13.6 dB when channel-spacing is larger than and equal to 28 nm, which means that when OOK modulation is used and the BER achieve 10-6, the channel-spacing should not be less than 28 nm. Finally, an experiment of channel crosstalk with using two-channel WDM VLC system and LEDs with different wavelengths is conducted and the correctness of the crosstalk analysis is verified. The colors of red (635 nm), red-orange (620 nm) and amber (596 nm) LEDs are used and two of them are used each time. Two sine signals with different frequencies are launched by AWGs (Agilent 33250A) and through amplifiers and Bias-Tees, drive two LEDs. The signal analyzer (Agilent N9020A) is used to observe the signal power. The experimental results of channle crosstalk are close to theoretical results. The analysis of channel crosstalk in muliti-channel WDM-VLC system will give some guidance in increasing the number of channels for optical communication in the future.

2D Silicon Magnetometer

A novel single-chip sensing device for measurement of two orthogonal magnetic-field components using one and the same transducer zone is presented. On a rectangular n-type silicon substrate, four n+- ohmic planar contacts are implemented – two of them are elongated and serves as power supply, and other two terminals positioned in the middle of the region between elongated ones, function as outputs only. A proper coupling arrangement is used for obtaining the information about vector components Bx (parallel to the supply contacts) and Bz (perpendicular to the substrate). The sensor operation is determined by the direction of individual parts of the curvilinear current trajectory and the Lorentz force action on them. The 2D magnetometer interface circuitry comprises three instrumentation amplifiers and a differential amplifier. Simple fabrication technology is applied. The effective spatial resolution is high consisting 90 x 60 x 40 μm3. The respective channel-magnetosensitivities without amplification reaches Sx ≈ 17 V/AT and Sz ≈ 23.3 V/AT, the channel cross-talk at induction B ≤ 1.0 T is no more than 3% and lowest detected induction Bmin for the two-axis device at a supply 3 mA over frequency range f ≤ 100 Hz is about 11 μT.

Frequency interleave in multicore fiber transmission systems for reducing influence of inter-core crosstalk

This paper describes a frequency interleaving scheme applied to WDM multicore fiber transmission systems. By shifting channel frequencies between neighboring cores, spectral overlap of inter-core crosstalk channels onto signal channels becomes small, and signal degradation due to the crosstalk is reduced. The effectiveness of the scheme is numerically demonstrated for QPSK and 16QAM signals in a conventional WDM system and duo-binary super-Nyquist WDM systems.

A highly reliable and super-speed optical fiber transmission for hyper-spectral SCMOS camera

In this paper, we propose a super-speed, high reliable and multi-channel optical fiber transmission system for hyper-spectral SCMOS camera with a large field of view. In our system, we use the super-speed serializer to connect parallel image side and serial optical module. A small form factor pluggable optical transceiver module is used as the electro-optic interface. 6-channels SCMOS images with parallel 96bit can be transmitted by only 3-channels serial optical fiber. The data rates reach 2.36Gbps. To improve the stability of optical fiber transmission, we propose a multi-channel merge transmission approach to avoid the channel to channel crosstalk. In order to improve the transmission bandwidth of digital image, the performance of fiber link, and the anti-interference ability of electromagnetic, we propose an error correction algorithm based on LCC approach. And the LCC implementation structure based on very large scale integration (VLSI) is proposed. Finally, the experiments were performed on the prototype in SCMOS camera. The results showed that the transmission system has a high reliability. The correcting algorithm has the characteristics of strong error detecting ability, less resource occupation and easier to be realized with hardware.

Optical fiber design with orbital angular momentum light purity higher than 99.9.

The purity of the synthesized orbital-angular-momentum (OAM) light in the fiber is inversely proportional to channel crosstalk level in the OAM optical fiber communication system. Here the relationship between the fiber structure and the purity is firstly demonstrated in theory. The graded-index optical fiber is proposed and designed for the OAM light propagation with the purity higher than 99.9%. 16 fiber modes (10 OAM modes) have been supported by a specific designed graded-index optical fiber with dispersion less than 35 ps/(km∙nm). Such fiber design has suppressed the intrinsic crosstalk to be lower than -30 dB, and can be potentially used for the long distance OAM optical communication system.

Mode division multiplexing using an orbital angular momentum mode sorter and MIMO-DSP over a graded-index few-mode optical fibre.

Mode division multiplexing (MDM)– using a multimode optical fiber’s N spatial modes as data channels to transmit N independent data streams – has received interest as it can potentially increase optical fiber data transmission capacity N-times with respect to single mode optical fibers. Two challenges of MDM are (1) designing mode (de)multiplexers with high mode selectivity (2) designing mode (de)multiplexers without cascaded beam splitting’s 1/N insertion loss. One spatial mode basis that has received interest is that of orbital angular momentum (OAM) modes. In this paper, using a device referred to as an OAM mode sorter, we show that OAM modes can be (de)multiplexed over a multimode optical fiber with higher than −15 dB mode selectivity and without cascaded beam splitting’s 1/N insertion loss. As a proof of concept, the OAM modes of the LP11 mode group (OAM−1,0 and OAM+1,0), each carrying 20-Gbit/s polarization division multiplexed and quadrature phase shift keyed data streams, are transmitted 5km over a graded-index, few-mode optical fibre. Channel crosstalk is mitigated using 4 × 4 multiple-input-multiple-output digital-signal-processing with <1.5 dB power penalties at a bit-error-rate of 2 × 10−3.

Comparative investigations of DWDM transmission system with PMD for different orthogonally modulated signals at 80 Gb/s

SummaryPolarization mode dispersion (PMD) has become one of the major limiting factors for high‐bit‐rate optical transmission systems. This paper evaluates the performance of dense wavelength division multiplexed (DWDM) system with PMD at 80 Gb/s in the presence of Kerr‐nonlinear effects. Orthogonally modulated signals have been investigated and compared for tolerance against PMD in a DWDM transmission system with direct detection receivers. The optimized combinations of orthogonal polarization (OP) with carrier‐suppressed return‐to‐zero (CSRZ) and CSRZ differential‐phase‐shift‐keying signals are shown to improve PMD tolerance over high bit rates and long transmission lengths. Improved performance greater than 4 dB is observed for CSRZ modulated signal with OP because of less channel cross talk and reduced power transfer between adjacent bits over different PMD values. The numerical results demonstrate that our proposed orthogonally modulated signals perform better with lesser complex direct detection receivers. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Long‐term drift induced by the electronic crosstalk in Terra MODIS Band 29

AbstractTerra MODerate Resolution Imaging Spectroradiometer (MODIS) is one of the key sensors in the NASA's Earth Observing System, which has successfully completed 15 years of on‐orbit operation. Terra MODIS continues to collect valuable information of the Earth's energy radiation from visible to thermal infrared wavelengths. The instrument has been well characterized over its lifetime using onboard calibrators whose calibration references are traceable to the National Institute of Standards and Technology standards. In this paper, we focus on the electronic crosstalk effect of Terra MODIS band 29, a thermal emissive band (TEB) whose center wavelength is 8.55 µm. Previous works have established the mechanism to describe the effect of the electronic crosstalk in the TEB channels of Terra MODIS. This work utilizes the established methodology to apply to band 29. The electronic crosstalk is identified and characterized using the regularly scheduled lunar observations. The moon being a near‐pulse‐like source allowed easy detection of extraneous signals around the actual Moon surface. First, the crosstalk‐transmitting bands are identified along with their amplitudes. The crosstalk effect then is characterized using a moving average mechanism that allows a high fidelity of the magnitude to be corrected. The lunar‐based analysis unambiguously shows that the crosstalk contamination is becoming more severe in recent years and should be corrected in order to maintain calibration quality for the affected spectral bands. Finally, two radiometrically well‐characterized sites, Pacific Ocean and Libya 1 desert, are used to assess the impact of crosstalk effect. It is shown that the crosstalk contamination induces a long‐term upward drift of 1.5 K in band 29 brightness temperature of MODIS Collection 6 L1B, which could significantly impact the science products. The crosstalk effect also induces strong detector‐to‐detector differences, which result in severe stripping in the Earth view images. With crosstalk correction applied, both the long‐term drift and detector differences are significantly reduced.

Adaptive Techniques for Joint Optimization of XTC and DFE Loop Gain in High-Speed I/O

High-speed I/O channels require adaptive techniques to optimize the settings for filter tap weights at decision feedback equalization (DFE) read channels to compensate for channel inter-symbol interference (ISI) and crosstalk from multiple adjacent channels. Both ISI and crosstalk tend to vary with channel length, process, and temperature variations. Individually optimizing parameters such as those just mentioned leads to suboptimal solutions. We propose a joint optimization technique for crosstalk cancellation (XTC) at DFE to compensate for both ISI and XTC in high-speed I/O channels. The technique is used to compensate for between 15.7 dB and 19.7 dB of channel loss combined with a variety of crosstalk strengths from to adaptively, where the transmit non-return-to-zero signal amplitude is a constant .

Orbital-angular-momentum crosstalk and temporal fading in a terrestrial laser link using single-mode fiber coupling.

Using a mobile experimental testbed, we perform a series of measurements on the detection of laser beams carrying orbital angular momentum (OAM) to evaluate turbulent channel distortions and crosstalk among receive states in an 84-m roofed optical link. We find that a receiver assembly using single-mode fiber coupling serves as a good signal selector in terms of crosstalk rejection. From the recorded temporal channel waveforms, we estimate average crosstalk profiles and propose an appropriate probability density function for the fluctuations of the detected OAM signal. Further measurements of OAM crosstalk are described for a horizontal 400-m link established over our campus.

Spectral demixing avoids registration errors and reduces noise in multicolor localization-based super-resolution microscopy

Multicolor single molecule localization-based super-resolution microscopy (SMLM) approaches are challenged by channel crosstalk and errors in multi-channel registration. We recently introduced a spectral demixing-based variant of direct stochastic optical reconstruction microscopy (SD-dSTORM) to perform multicolor SMLM with minimal color crosstalk. Here, we demonstrate that the spectral demixing procedure is inherently free of errors in multicolor registration and therefore does not require multicolor channel alignment. Furthermore, spectral demixing significantly reduces single molecule noise and is applicable to astigmatism-based 3D multicolor imaging achieving 25 nm lateral and 66 nm axial resolution on cellular nanostructures.